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Destruction of cyanide in gold mill effluents: Biological versus chemical treatments
Abstract
In gold mining, cyanide has been the preferred lixiviant worldwide since 1887. Although cyanide can be destroyed and recovered by several processes, it is still widely discussed and examined due to its potential toxicity and environmental impact. Biological treatment of cyanide is a well-established process and has been commercially used at gold mining operations in North America. Biological treatment processes facilitate growth of microorganisms that are essential for the treatment. The present review describes the advances in the use of biological treatment for the destruction of cyanide in gold mill effluents.
... Gold and silver recovery by cyanidation is widely used in mining operations. Other industrial applications of cyanide include metal processing, electroplating, steel hardening, photographic applications, and synthetic rubber production (Habashi, 1987;Mudder, 2001;Mudder et al., 2001a;Botz and Mudder, 2002;Akcil, 2003a). Although gold mining operations use dilute solutions of sodium cyanide (100-500 ppm), cyanide is used at nearly 90% of the gold mines in relatively high quantities and is potentially toxic. ...
... Several destruction or recovery processes are well proven and can produce treated solutions or slurries with low levels of cyanide and its related compounds (Botz et al., 1995;Botz, 2001;McNulty, 2001;Akcil, 2002Akcil, , 2003aBotz and Mudder, 2002;. Cyanide treatment processes may be classified as a destruction-based process versus the physical processes of cyanide recovery and activated carbon sorption. ...
... Through a considerable degree of testing conducted in the Homestake Toxicological Testing Facility in Lead, South Dakota utilizing the effluents from a pilot plant facility and a variety of test organisms, the hydrogen peroxide process was found to yield environmentally acceptable effluent (Mudder et al., 2001b). However, it is suggested that the use of hydrogen peroxide to treat slurries is limited due to the high consumption resulting from its reaction with solids in the slurry (Botz, 2001;Mudder et al., 2001a,b;Akcil, 2003a). Furthermore, high concentrations of heavy metals in slurries also may lead to excessive decomposition of hydrogen peroxide (FMC Corp., 2004). ...
The main objective of this work was to determine the effectiveness and kinetics of hydrogen peroxide in destroying cyanide in the tailings slurry from a gold mine with low sulphide and heavy metal content. The impacts of catalyst (Cu) and hydrogen peroxide concentrations, temperature and pH on the extent and rate of weak acid dissociable (WAD) cyanide destruction were investigated. Experiments were conducted using the variable-dose completely mixed batch reactor bottle-point method. Both the rate and extent of CNWAD destruction generally increased with increasing peroxide doses for either absence or presence of Cu catalyst. Catalyst addition was very effective in terms of not only enhancing the cyanide destruction rate but also significantly reducing the required peroxide dosages to achieve CNWAD concentrations of about 1 mg/l, independent of the temperatures tested (10, 20 and 30 °C). The initial cyanide destruction rates increased between 1.2 and 3 folds with the addition of 30 mg/l of Cu. Kinetic experiments showed that in most cases little CNWAD destruction occurred after a reaction time of 2–4 h. The impact of slurry pH on cyanide destruction varied depending upon the dosages of Cu catalyst. Relatively lower peroxide dose/CNWAD ratios required to achieve less than 1 mg/l of CNWAD may be due to lower heavy metals and sulphide content of the ore, resulting in lower peroxide requirement for metal bound cyanides. During cyanide destruction, nitrate was initially formed as a by-product and then possibly converted to other some volatile nitrogen-containing species, as supported by the mass balance calculations.
... De acuerdo con Abdoul-Raimi y col. (2013), Akcil (2003) y Akcil y col. (2003), la degradación biológica del cianuro se realiza en dos pasos, el primero de ellos es la oxidación del cianuro a amoniaco, carbonatos y sulfatos, mientras que en el segundo paso el amoniaco es convertido a nitrato y nitrito. ...
... En este caso, los microrganismos utilizan el oxígeno para transformar el cianuro en nitratos, bicarbonatos y sulfatos, este proceso microbiano es capaz de oxidar los complejos de cianuro metálicos, los iones metálicos de los complejos débiles y los subproductos intermedios de la oxidación de cianuro (Logsdon y col., 2001). De acuerdo con Akcil (2003) existen diversos mecanismos de degradación biológica del cianuro, estos incluyen discos biológicos rotativos, lechos empacados, filtros biológicos, reactores discontinuos de secuenciación, lagunas facultativas y sistemas de lodos activados. ...
... cidas, sintéticas, entre otras)(Dash y col., 2008). Adicionalmente, los humanos se encuentran expuestos a ciertos niveles de cianuro por el humo del tabaco (0.5 mg/ cigarro), escapes de automóviles (7-9 mg Km -1 ), pesticidas, plaguicidas, fertilizantes, uso de cosméticos (lápiz para ojos o lipstick) y algunas drogas farmacéuticas para el tratamiento de cáncer y presión arterial alta(Kuyucak y Akcil, 2013).La producción de cianuro de las industrias mencionadas anteriormente, se estima en más de 14 millones kg año-1 (Dash y col., 2008;), de lo cual un 90% procede de actividades mineras, siendo ésta la que mayores residuos de cianuro genera, causando problemas ambientales y siendo el enfoque de la presente investigación(Akcil, 2003; Kuyucak y Akcil, 2013). El cianuro es utilizado durante el proceso de extracción de oro y plata de los minerales, debido a su capacidad para disolverlos ya que éstos no pueden ser extraídos por procesos físicos como lo son la trituración y la separación por gravedad, este proceso es llamado hidrometalurgia(Logsdon y col., 2001; Abdoul-Raimi y col., 2013).Casos de estudio/desastresLos desastres dentro de la industria minera pueden ser ocasionados debido a las condiciones atmosféricas propias del lugar en el que se encuentran ubicadas (huracanes), por la falta o incorrecto estudio del impacto ambiental, por el fallo de las estructuras de almacenamiento de residuos (falla en la presa de jales y fugas diversas), la no aplicación de las mejores técnicas disponibles en las explotaciones mineras, errores en el diseño de las instalaciones, el no uso de las medidas de ...
... Although SCN − is almost seven times less toxic than CN − (Woffenden et al. 2008;Kuyucak and Akcil 2013), the greater chemical stability of SCN − compared to its parent compound (Akcil 2003) leads to its accumulation in mining waste streams (Woffenden et al. 2008), as well as its environmental persistence (Mediavilla et al. 2019). Therefore, although not explicitly addressed in regulatory guidelines for discharge of CN − -bearing mine effluents, SCN − is still considered by regulatory agencies to be a threat to aquatic wildlife (Bhunia et al. 2000;Gould et al. 2012). ...
... Comprehensive reviews have summarized current chemical and biological treatment methods for either CN − degradation (Gould et al. 2012) or concomitant degradation of CN − and SCN − (Akcil 2003;Botz et al. 2016;Mudder et al. 2001). Compared to physical or chemical approaches, bioremediation systems are considered to be more environmentally friendly, efficient (Akcil 2003), cost-effective (Akcil and Mudder 2003;Nelson et al. 1998), and substrate specific (Das and Dash 2014). ...
... Comprehensive reviews have summarized current chemical and biological treatment methods for either CN − degradation (Gould et al. 2012) or concomitant degradation of CN − and SCN − (Akcil 2003;Botz et al. 2016;Mudder et al. 2001). Compared to physical or chemical approaches, bioremediation systems are considered to be more environmentally friendly, efficient (Akcil 2003), cost-effective (Akcil and Mudder 2003;Nelson et al. 1998), and substrate specific (Das and Dash 2014). Accordingly, they constitute a preferred treatment approach in the mining industry, especially when cleaner effluents are targeted (Akcil 2003). ...
Bioremediation systems represent an environmentally sustainable approach to degrading industrially generated thiocyanate (SCN⁻), with low energy demand and operational costs and high efficiency and substrate specificity. However, heavy metals present in mine tailings effluent may hamper process efficiency by poisoning thiocyanate-degrading microbial consortia. Here, we experimentally tested the tolerance of an autotrophic SCN⁻-degrading bacterial consortium enriched from gold mine tailings for Zn, Cu, Ni, Cr, and As. All of the selected metals inhibited SCN⁻ biodegradation to different extents, depending on concentration. At pH of 7.8 and 30 °C, complete inhibition of SCN⁻ biodegradation by Zn, Cu, Ni, and Cr occurred at 20, 5, 10, and 6 mg L⁻¹, respectively. Lower concentrations of these metals decreased the rate of SCN⁻ biodegradation, with relatively long lag times. Interestingly, the microbial consortium tolerated As even at 500 mg L⁻¹, although both the rate and extent of SCN⁻ biodegradation were affected. Potentially, the observed As tolerance could be explained by the origin of our microbial consortium in tailings derived from As-enriched gold ore (arsenopyrite). This study highlights the importance of considering metal co-contamination in bioreactor design and operation for SCN⁻ bioremediation at mine sites.
Key points
• Both the efficiency and rate of SCN⁻biodegradation were inhibited by heavy metals, to different degrees depending on type and concentration of metal.
• The autotrophic microbial consortium was capable of tolerating high concentrations of As, potential having adapted to higher As levels derived from the tailings source.
... Furthermore, Hijosa-Valsero [8] examine plasma discharge technology for removal of cyanide from water having a concentration of 1 ppm. Akcil in 2003 examined the biodegradation of cyanide by a certain bacteria [9]. ...
... These microorganisms could proficiently convert cyanide into compounds that are less toxic, such as ammonia and carbonate [9]. Resting cells of Serratia marcescens was reported to biodegrade cyanide using shake flask as bioreactor [10,11]. ...
Cyanide is extremely toxic to living organisms. It is utilized in industries for gold and silver extraction, pharmaceuticals, plastic processing, electroplating, and agricultural chemistry. Cyanide can persevere for a long time in the soil and its bio-degradation is the best economical practice. A formerly isolated cyanide-degrading bacterium Azotobacter vinelandii exhibited substrate inhibition to degradation rate. Significant degradation inhibition constants were achieved reliably by means of non-linear regression modeling of the degradation rate profile utilizing models for substrate inhibition like Haldane, Teissier-Edward, Monod, Yano and Koga, Luong, Edward (Webb) Luong and Aiba models. Aiba model was selected as the top model established on statistical assessments like root mean square error, adjusted coefficient of determination, bias factor and accuracy factor. The calculated values for the Aiba constants qmax (the maximum specific substrate degradation rate (h−1), Ks (concentration of substrate at the half maximal degradation rate (mM) and Ki (inhibition constant (mM)) were 0.060 (95% CI, 0.024 to 0.096), 0.302 (95% CI, 0.381 to 0.222) and 0.953 (95% CI, 0.568 to 1.338), respectively. The novel constants gotten from the modeling application can be valuable for advanced secondary modeling implicating the influence of media conditions and some other dynamics on cyanide biodegradation by this bacterium.
... [16,20] Hence, before discarding CN À -bearing GCTs into the environment, toxic CN À and metal-cyanide complexes should be degraded to minimize their environmental impact. [20,21] To protect the environment from industrial CN À poisoning, environmental protection agencies worldwide have enacted strict regulations regarding the manufacturing, transportation, and utilization of CN À for industrial operations. For example, the American Conference of Governmental Industrial Hygienists set the threshold limit concentration of CN À in air at 4.7 mg/L, [22] and the Canadian water quality authorities allow a maximum CN À concentration of 0.2 mg/L in drinking water (Table 1). ...
... For example, pH, temperature, aeration, and nutrient availability are external factors that can affect the metabolic activity of microbes on GCTs. [21,77] Additionally, internal factors, such as poor growth caused by a low initial substrate concentration, can contribute to the ineffectiveness of microbes used for GCT biodegradation. [18] Nonetheless, under favorable conditions and using properly designed biological systems, these challenges can be overcome. ...
The initial cyanide (CN-) concentration and amount of co-contaminants in GCTs can inhibit bacterial growth and reduce the CN--degrading ability of bacteria. Several microorganisms can biotransform a wide range of organic and inorganic industrial contaminants into nontoxic compounds. However, active enzymatic CN- metabolism processes are mostly constrained by the physical and chemical characteristics of GCTs. High concentrations of toxic metal co-contaminants, such as, Pb, and Cr, and factors, such as pH, temperature, and oxygen concentration create oxidative stress and limit the CN--degrading potential of cyanotrophic strains. The effects of such external and internal factors on the CN--degrading ability of bacteria hinder the selection of suitable microorganisms for CN- biodegradation. Therefore, understanding the effects of the physicochemical properties of GCTs on cyanobacteria strains can help identify suitable microbes and favorable environmental conditions to promote microbial growth and can also help design efficient CN- biodegradation processes. In this review, we present a detailed analysis of the physicochemical properties of GCTs and their effects on microbial CN- degradation.
... In the case of adsorption, free cyanide is not treated, while membranes and biological processes remove all forms of cyanide. As for chemical oxidation, this involves removing mainly free cyanide and its weak bonds [12]. The decision about which is best will depend on factors such as the cost of the treatment, the available space to be used, the initial concentrations of the contaminant and the amount of waste to be treated, among others [13]. ...
Mexico is characterized as a mining country since it is the world’s main silver producer. During its extraction, wastewater (mining tailings) is generated which contains cyanide and heavy metals. The purpose of this research was to determine whether a bacterial consortium isolated from a tailings dam can use cyanide as a source of nitrogen and carbon to carry out its biodegradation. The study determined the effects of three physicochemical factors (pH, temperature and inoculum concentration) and three metals (copper, iron and nickel) on cyanide biodegradation. The results showed that the highest cyanide removals were obtained when working with a pH of 9.5, a temperature of 25 °C and 15% v/v of inoculum (88%), while the optimum values for copper, iron and nickel were 0, 7.7 and 0.46 mg·L−1, respectively, showing that copper causes an inhibitory effect (cyanide biodegradation of 68%) on the bacteria and consequently on the biological degradation of cyanide and that iron can promote the biodegradation of the pollutant by 91%.
... Apart from the sulfate anions produced by the oxidation process, the sulfur dioxide used for the destruction of cyanides in gold mining can also contribute to the formation of sulfate ions in tailings. 15 Consequently, a considerable amount of sulfate anions is produced and exists in the tailing materials. With the progression of cement hydration, the generated calcium hydroxide (CH) from tricalcium silicate (C 3 S) and dicalcium silicate (C 2 S) react with sulfate ions and generate the gypsum (CaSO 4 ⋅2H 2 O), which further reacts with tricalcium aluminate (C 3 A) to produce the expansive calcium sulfoaluminate hydrate (i.e., ettringite). ...
Tensile and shear fracture behaviors of fiber-reinforced cemented paste backfill (FRCPB) play critical roles in the safe and cost-effective engineering design of underground mine backfill structures. Sulfate pore solution is a key factor affecting the time-dependent evolution of fracture behavior and properties of FRCPB. However, no studies have been carried out to systematically investigate its effects on the fracture behavior and properties of mine backfill used in underground mines. The objective of this study is to discover the effect of sulfate concentration (0, 5000, 15,000, and 25,000 ppm) on FRCPB’s fracture behavior and properties at different curing times (3, 7, 28, and 90 days) and under pure mode-I, mode-II, and mode-III loadings. The results show that, except for the 3- day FRCPB, the increase in sulfate concentration can continuously improve pre-peak stiffness and peak fracture resistance force and significantly enhance the post-peak residual resistance, especially under mode-III loading. Moreover, fracture energy shows a higher sensitivity to the sulfate concentration with respect to fracture toughness and stiffness. Furthermore, sulfate concentration has a very limited effect on tensile crack trajectory under mode I loading, while a transition of shear cracks from a curved crack pattern to a sharp and straight one is detected under mode II and III loadings. In addition, the fracture toughness possesses a stronger correlation with material stiffness and thus is recommended for the design of FRCPB to offer a more effective immediate support to surrounding rock. The obtained results provide an in-depth insight into the sulfate-induced evolution of fracture behavior and properties of FRCPB under various loading conditions and thereby promote the safe implementation of mine backfill technology.
... In biological treatments, bacteria are used to naturally biodegrade both free and metallic cyanides into bicarbonate and ammonia. The metals released in the process are absorbed by the biofilm or precipitated into the solution [23]. In a European plant, tests were performed for the combined treatment of BF and coke oven gas washing water using activated carbon as oxidant agent. ...
The reduction of hazardous air pollutants and greenhouse gas emissions is increasingly required by steelworks. The purpose of this study is the definition of an additional blast furnace gas treatment when it is burned in hot blast stoves or in other users such as power plants. It was found that reducing cyanide in blast furnace gas through a spray-scrubber reduces NOx at the chimney, enabling the increase of hot blast temperature and consequently CO2 emission reduction. An H2O2-based gas washing water treatment was also investigated to reduce cyanide content before water recirculation/purge. Simulation tools, laboratory tests, and in-field measurement campaigns were used to prove process effectiveness in reducing cyanides both in blast furnace gas and in used washing water.
... Cyanide can be removed through physical, chemical and biological treatments [6][7][8], the most widely used of which are chemical methods including acidification [9], alkaline chloride oxidation [10], SO 2 -air oxidation [4], hydrogen peroxide oxidation [11] and ozone oxidation [12]. However, the above traditional treatments do not work satisfactorily for cyanide residues due to the high content of stable metal complex cyanides adsorbed on the ...
The toxic cyanides in gold cyanide residues produced in the cyanidation process of gold extraction threaten environmental safety and inhibit the recovery of valuable metals. In this study, the removal of cyanide through the persulfate-advanced oxidation process was investigated, and heat activation and ultrasonic activation were tested for cyanide removal. The results showed that cyanide in cyanide residue could be removed by 2.0 wt.% potassium persulfate at pH 10.0 after 60 min reaction with a removal efficiency of 53.47%. The removal efficiency increased to 62.18% at T = 60 °C for heat activation and 74.76% with an ultrasonic power of 100% for ultrasonic activation. The cyanide content in the toxic leaching solution of the residue after the ultrasonic-activated persulfate-advanced oxidation process (3.84 mg/L) reached the national standard of China. Two kinds of free radical scavengers, tert-butanol and methanol, were used to investigate the generation of free radicals. The results showed that both SO4•− and HO• were produced and accelerated the oxidation of cyanide, and HO• played a major role under alkaline conditions. According to XPS analysis, the oxidation of ultrasonic-activated persulfate focused on cyanide removal rather than pyrite in cyanide residue. More cyanides were transferred from the cyanide residue to the liquid phase, leading to the high efficiency of ultrasonic activation. The ultrasonic-activated persulfate-advanced oxidation process has potential application prospects for the treatment of gold cyanide residues.
... La contaminación del ambiente por cianuro se da por encima de 0.1 ppm (Mudder & Botz, 2004), su mitigación se consigue con el uso de tecnologías adecuadas para su tratamiento; a nivel industrial, esto es un problema por la gran cantidad de cianuro que se vierten en las plantas de procesamiento de oro (Shin et al., 2013). Sin embargo, en los últimos años este tipo de contaminación está siendo contrarrestado por la biorremediación con éxito en operaciones a gran escala, de manera fiable y económicamente viable (Akcil, 2003b;Murillo y Montañez, 2022). A pesar que el cianuro y sus derivados en las corrientes de aguas residuales están regulados, estas deben tratarse para reducir la concentración de cianuro total y cianuro libre por debajo de los límites reglamentados (Kuyucak & Akcil, 2013). ...
La biodegradación de compuestos cianurados, que se presentan en efluentes de plantas de lixiviación de minerales para la recuperación del oro, es un tratamiento biológico de actualidad que está permitiendo que no se continúe contaminando ecosistemas con vertidos cianurados, asimismo, permite que los ambientes que ya están contaminados se recuperen con la aplicación de microorganismos degradadores del cianuro. En este trabajo se tuvo como objetivo evaluar a Pseudomonas fluorescens nativo como degradador del cianuro presente en lixiviados en condiciones de laboratorio, para lo cual fue aislado de un lixiviado de mineral aurífero e inoculado en tres biorreactores aireados con lixiviado cianurado de mineral aurífero que tuvieron 250 ppm de cianuro libre, y un inóculo de 1.75x10⁸ cel/ml en un primer biorreactor, 8.75x10⁷ cel/ml en un segundo y 5.4x10⁶ cel/ml en un tercer biorreactor, que se incubaron a temperatura ambiente durante 168 horas. La evaluación del cianuro libre contenida en los biorreactores, cada 24 horas mediante el método titulométrico, permitió establecer que P. fluorescens con 1.75x10⁸ cel/ml degradó 246.25 ppm (98.5 %) del total de cianuro libre; con 8.75x10⁷ cel/ml, 240 ppm (96 %); y con 5.47x10⁶ cel/ml, 237.5 ppm (95 %). Estos resultados muestran que P. fluorescens tiene un gran potencial para seguir estudiándola con el propósito de emplearla en la biorremediación de ecosistemas contaminados con lixiviados cianurados o para el tratamiento de efluentes cianurados.
... synthesis of polymers) as well as biological importance (Arnold et al., 1957;Barton et al., 1991Barton et al., , 1999Bauer and Gnauck, 1987;Bauer et al., 1986Bauer et al., , 1998Bernsdorf and Köckerling, 2012;Britton and Dunitz, 1965a;Decius et al., 1965;Eyster and Gillette, 1940;Fang and Shimp, 1995;Grenier-Loustalot et al., 1996;Hamerton and Hay, 1998;Hendricks and Pauling, 1925;Kalmutzki et al., 2013;Kertes, 1979;Kotch et al., 1995;Decius, 1958, 1959;Marcos-Fernández et al., 1999;Moreno et al., 2013;Okubo and Ise, 1972;Osei Owusu et al., 1996;Rabalais et al., 1969aRabalais et al., , 1969bReghunadhan Nair et al., 2001;Schalke, 2006;Shorter, 1978). Especially the latter also applies to the thiocyanates (Aguirre et al., 2010;Akcil, 2003;Anderson, 1980;Anderson et al., 1990;Azizitorghabeh et al., 2021;Bahta et al., 1997;Banerjee, 1996;Betts et al., 1979;Bezsudnova et al., 2007;Bhunia et al., 2000;Castanheiro et al., 2016;Dash et al., 2009;Du Plessis et al., 2001;Ebbs, 2004;Happold et al., 1958;Jensen and Tuan, 1993;Kelly and Baker, 1990;Kim and Katayama, 2000;Kwon et al., 2002;McDonald et al., 1969;Mudder et al., 1991;Palatinszky et al., 2015;Ryu et al., 2015;Stafford and Callely, 1969;Staib and Lant, 2007;Stott et al., 2001;Stratford et al., 1994;Sorokin et al., 2001;Wald et al., 1939;Watts and Moreau, 2016;Wilson and Harris, 1961;Wijeyasinghe and Anthopoulos, 2015;Willemin and Lumen, 2017;Wilson et al., 1960;Youatt, 1954). However, these aspects are not examined in this review, nor are the many inorganic salts of cyanates and thiocyanates (Bahta et al., 1997;Bernsdorf and Köckerling, 2012;Britton and Dunitz, 1965a;Schalke, 2006;McDonald et al., 1969;Norbury et al., 1973;Schultz, 1996;Wilson and Harris, 1961;Wijeyasinghe and Anthopoulos, 2015). ...
Homoleptic cyanide compounds exist of almost all main group elements. While the alkali metals and alkaline earth metals form cyanide salts, the cyanides of the lighter main group elements occur mainly as covalent compounds. This review gives an overview of the status quo of main group element cyanides and cyanido complexes. Information about syntheses are included as well as applications, special substance properties, bond lengths, spectroscopic characteristics and computations. Cyanide chemistry is presented mainly from the field of inorganic chemistry, but aspects of chemical biology and astrophysics are also discussed in relation to cyano compounds.
... More sustainable mining practices require mitigation measures for existing tailings and improved processes and safety procedures for ongoing activities (Dudka and Adriano, 1997). Highly toxic chemicals, such as cyanide or mercury, should be replaced by less harmful extraction agents, such as halogens, or a zero-emission policy should be enforced (Akcil, 2003). Such technical measures should be supplemented by clear international regulations (Hamor, 2004) and corporate social responsibility in the mining industry, which is based on open information policies (Jenkins and Yakovleva, 2006). ...
Globalization is an inevitable and extremely complex phenomenon that involves transnational integration of culture, economy, environment, politics, and other social interest. Globally, we are witnessing multitude changes such as a rapid population growth, urbanization, international trade and commerce, agricultural intensification, and encroachment into the natural ecosystem. Further mismatching of food demand and supply, growth disparities, increasing food prices, and over utilization of natural resources are among the challenges to the economic status of a nation and its health sector. The health impacts of globalization can be both positive and negative; of course, its impacts vary based on factors such as geographical location, gender, age, literacy, and socioeconomic status. Globalization has played pivotal role in health improvements via dissemination of new medical knowledge, low-cost health technologies, fast transactions of medical supply and improvement of human rights. Thus it has shown potential positive impacts by minimizing the gaps in health inequalities between rich and poor people in the global South and North and improved the idea of healthcare for all. On the other hand, there are also shortcomings of globalization to global health, such as the spread of infectious diseases due to rapid mobility, which is emerging as the greatest threat to all. The interconnectedness of globalization and One Health is complex. Whereas, globalization is one of the main challenges to ensure global health security. One Health is a remedy to manage the negative health consequences of globalization, especially in least developed world. It is undeniable that the connection between humans, animals, and the environment calls for the attention of multi-sectorial institutes to collaborate to closely monitor and reduce the risks and consequences on health and wellbeing. One Health approach is increasingly recognized and streamlined into national and international plans and strategies for effective management of zoonotic diseases, food safety, antimicrobial resistance, and climate change. Human practices such as, changes in land use and how food is produced are driving ecological and evolutionary conditions that facilitate disease spillover events and contribute to antimicrobial resistance. These changes are occurring rapidly on a large scale, both locally and globally. The pursuit of understanding human, veterinary and environmental health issues separately leads to an incomplete understanding of disease dynamics and, therefore, missed synergy for a joint mitigation of the problems. One Health actions support the primary prevention of such problems, enabling more timely and effective containment and response to public health threats at the human-animal-environment interface. In short, systematic and sustained One Health approach becomes more important than ever in order to promote and ensure health security and avert the negative impacts of globalization. Therefore, there is a need to focus on the creation of socially and environmentally sustainable forms of globalization that provide the greatest benefits and least costs, shared more equitably than the status queue.
... Chemical treatment processes such as the SO2/air process, hydrogen peroxide process, Caro's Acid process, Acidification-Volatilization-Recovery (AVR) process, Alkaline Chlorination process, Dilution, natural attenuation, adsorption by activated carbon, reverse osmosis, electrowinning and hydrolysis/distillation have been successful but with some associated problems and limitations (Dwivedi et al., 2011). Biological treatment of cyanide waste is also yielding some good results although it is generally not used on a large scale (Akcil, 2003;Saarela and Kuokkanen, 2004). The fact that activated carbon can catalyse a lot of chemical reactions is known and established. ...
Cyanide, halides, thiosulphate, thiourea, and thiocyanate are some of the lixiviants used in the mining and metallurgical industries for gold and silver extraction from their ores. Cyanide remains the universal ligand for gold extraction because it is less costly as compared with the above-mentioned lixiviants. However, cyanide is toxic to plants, animals, aquatic life and humans, and hence, waste cyanide solutions need to be detoxified before disposal. Sawdust and waste charcoal pieces contribute immensely to waste disposal problems in Ghana, and there are efforts to remove them from the environment. This paper assesses the use of sawdust and charcoal pieces in the detoxification of cyanide wastewater in a bid to solve a twofold problem; waste and environmental problems. Different masses (0 g, 2 g, 5 g and 10 g) of as-received sawdust and charcoal pieces were contacted with different concentrations of standard cyanide solutions (50, 100, 200 ppm) for up to 24 hours. The control experiment, which had no carbonaceous material in 1 L of 100 ppm of cyanide solution, recorded 20% detoxification, ascribed to natural decomposition of cyanide. On the contrary, 90% and 82% detoxification of cyanide were achieved when 2 g of sawdust and charcoal pieces respectively were contacted with I L of 100 ppm cyanide solution for 24 hrs. In general, over the 24-hr contact time, the extent of detoxification was not influenced extensively by the mass of carbonaceous material used, and the rate of detoxification was higher with higher concentration of cyanide solution. Sawdust performed generally better than the charcoal pieces, and this was attributed to the finer particle sizes of the as-received sawdust (80%-150 µm) as against charcoal pieces (10%-150 µm), though the initial detoxification rate was higher with the charcoal poeces. The result opens avenues for further research in the twofold clean-up of liquid and solid waste from the environment.
... Sulfide minerals in gold-containing ores can generate thiocyanate with cyanide, which is formed faster under low alkalinity and inadequate aeration conditions (Kuyucak and Akcil 2013). There is a variety of chemical and biological treatments for the destruction and removal of cyanide (Akcil 2003) and thiocyanate (Gould et al. 2012) in industrial effluents. Microorganisms can degrade cyanide (Dash et al. 2009) and thiocyanate (Dwivedi et al. 2011) using the different biochemical pathway. ...
In nature, microorganisms developed at various places and adapted to the various weather and geological conditions. Microorganisms participate in geological transformations leading to the dissolution of some minerals and conversion to others. While some microorganisms with their metabolic activity increase the mobility of metals, others cause precipitation of metals and the formation of new minerals. These biogeochemical interactions found practical application in the recovery of metals. In the article, the proposals for improvement of existing engineering commercial processes for recovery of metals are given which can enable the formation of nanogold and nanogold compounds.
Key points
• Amino acids in pretreatment can increase the dissolution of the layer around the gold.• Amino acids in the complexing stage can increase gold leaching.• After the complexing stage, the bionanosynthesis of gold and its compounds is possible.Graphical abstract
... Nitriles are stable organic compounds with a -CN group. Traditional methods for the hydrolysis of nitriles require a strong alkali or acid (Akcil 2003) and thus are not suitable for feed applications. Bioconversion of nitriles by enzymes is, therefore, a much sought-after approach. ...
Nitriles derived from glucosinolates (GSLs) in rapeseed meal (RSM) can cause lesions on animal liver and kidneys. Nitrilase converts nitriles to carboxylic acids and NH3, eliminating their toxicity. Here we describe a nitrilase, BnNIT2, from Brassica napus (optimal temperature, 45 °C; pH, 7.0) that is stable at 40 °C and has a wide substrate specificity. Recombinant BnNIT2 converted the three main nitriles from GSLs (3-hydroxy-4-pentenenitrile, 3-butenenitrile, and 4-pentenenitrile), with the highest specific activity (58.6 U/mg) for 4-pentenenitrile. We used mutagenesis to improve the thermostability of BnNIT2; the resulting mutant BnNIT2-H90M had an ~ 14.5% increase in residual activity at 50 °C for 1 h. To verify the functionality of BnNIT2, GSLs were extracted from RSM and converted into nitriles at pH 5.0 in the presence of Fe²⁺. Then, BnNIT2 was used to degrade the nitriles from GSLs; ultimately, ~ 80% of nitriles were removed. Thus BnNIT2 is a potential enzyme for detoxification of RSM.
Key points
• Functional identification of the plant nitrilase BnNIT2.
• Identified a mutant, H90M, with improved thermostability.
• BnNIT2 was capable of degrading nitriles from transformed GSLs.
Graphical abstract
... However, these methods are expensive and hazardous chemicals are used as the reagents (chlorine and sodium hypochlorite) and some of them create additional toxic and biological persistent chemicals. Despite cyanide's toxicity to living organisms, biological treatments are feasible alternatives to chemical methods without creating or adding new toxic and biologically persistent chemicals (Akcil 2003, Dash et al. 2009Gurbuz et al. 2004) and thus considered as more efficient, eco-friendly and cost effective. Many authors have reported degradation of organic cyanide compounds by bacteria. ...
... For over a century, free cyanide (CN − ) has been considered as the preferred lixiviant in gold mining worldwide (Akcil, 2003). In addition, it is also an indispensable industrial chemical used in metal finishing and hardening, electroplating, steel, and printed circuit board manufacturing industries (Patil and Paknikar, 1999). ...
The role of β-cyanoalanine synthase (β-CAS) in cyanide (CN-) assimilation in rice plants has been confirmed, nevertheless, the contribution of sulfurtransferase (ST) in CN- assimilation in rice plants is still unclear. In this study, a microcosmic hydroponic system was used to investigate the contribution of β-cyanoalanine synthase (β-CAS) and sulfurtransferase (ST) in the CN- assimilation in rice seedlings under the exposure of potassium cyanide (KCN) in presence or absence of 1-amino-cyclopropane-1-carboxylic acid (ACC). Our results indicated that the measurable thiocyanate (SCN-) was detected in both rice roots and shoots under KCN exposure, and the abundances of ST-related transcripts were up-regulated significantly (p < 0.05), suggesting that the ST pathway is involved in CN- assimilation in the rice plants. The application of exogenous ACC significantly (p < 0.05) decreased the accumulation of CN- and SCN- in rice tissues after KCN exposures, and also up-regulated the expression of β-CAS- and ST genes and their enzymatic activities, suggesting a positive interaction between aminocyclopropane-1-carboxylate oxidase (ACO), β-CAS and ST in rice plants during the CN- assimilation. This is the first attempt to experimentally clarify the contribution of ST in CN- assimilation in rice plants.
... Hyphomonas are characterized as large negative marine bacteria; however, they have been found in shallow stagnant waters (Quintero et al. 2001). Pseudomonads have been the most widely reported as cyanide degraders; they are strictly aerobic and have a nonfermentative metabolism (Khamar et al. 2015;Akcil 2003& Huertas et al. 2010. Clostridium are gram positive and have been previously reported to grow in the presence of cyanide (Oswald et al. 2018). ...
Mexico is the top producer of silver and is on the eighth place from producing gold in the world. For instance, the hydrometallurgical extraction process produces wastewater (mining tailing) characterized by being composed with varying concentrations of cyanide and heavy metals. The purpose of this research was to study the biodegradation of cyanide contained in mining tailings by means of a bacterial consortium isolated from a tailings dam. For this purpose, three types of Eckendfelder reactors were used, one with suspended biomass (BS) and two moving bed biofilter reactors, one with biomass immobilized on Kaldnes (BK) supports, and the other on polyurethane cubes (BCP). Three experimental stages were worked; in each of them, the concentrations of total cyanide were varied. In the first one, it was 26 ± 2 mg·L⁻¹; in the second one 40 ± 4 mg·L⁻¹; and the third one 55 ± 4 mg·L⁻¹. During the whole operation, the pH and temperature were maintained at 9.5 units and 25 °C. After 141 days of operation, biodegradation of the total cyanide contained in the mining tailings was 69% (17 mg·L⁻¹) in the BS reactor, while in the BK reactor, it was 93% (3.9 mg·L⁻¹) and in the BCP reactor 95% (2.5 mg·L⁻¹). The predominant families in each of the reactors, as well as their respective relative abundances, were for the BS and for the BK of Cyclobacteriaceae (20.65% and 24.64%) and Rhizobiaceae (18.48% and 14.01%) and Halomonadaceae (46.97%) and Hyphomonadaceae (24.94%) in the BCP.
... Different treatment technologies such as alkaline chlorination, adsorption, biodegradation, and advanced oxidation processes (AOPs) have been investigated to remove cyanides and cyanocomplexes Akcil, 2003;Dash et al., 2009b;Novak et al., 2013). In general, these technologies have some common drawbacks such as poor treatment efficiency, high cost, and production of low-toxic intermediates (cyanate, CNO − ), which require further treatment to achieve deep mineralization of cyanides and cyanocomplexes. ...
Traditional methods of cyanides’ (CN⁻) mineralization cannot overcome the contradiction between the high alkalinity required for the inhibition of hydrogen cyanide evolution and the low alkalinity required for the efficient hydrolysis of cyanate (CNO⁻) intermediates. Thus, in this study, a novel Electro-Fenton system was constructed, in which the free cyanides released from ferricyanide photolysis can be efficiently mineralized by the synergy of •OH and •O2⁻. The complex bonds in ferricyanide (100 mL, 0.25 mM) were completely broken within 80 min under ultraviolet radiation, releasing free cyanides. Subsequently, in combination with the heterogeneous Electro-Fenton process, •OH and •O2⁻ were simultaneously generated and 92.9% of free cyanides were transformed into NO3⁻ within 120 min. No low-toxic CNO⁻ intermediates were accumulated during the Electro-Fenton process. A new conversion mechanism was proposed that CN⁻ was activated into electron-deficient cyanide radical (•CN) by •OH, and then the •CN intermediates reacted with •O2⁻ via nucleophilic addition to quickly form NO3⁻, preventing the formation of CNO⁻ and promoting the mineralization of cyanide. Furthermore, this new strategy was used to treat the actual cyanide residue eluent, achieving rapid recovery of irons and efficient mineralization of cyanides. In conclusion, this study proposes a new approach for the mineralization treatment of cyanide-containing wastewater.
... To date, several reports have described the ability of microorganisms to grow on cyanide compounds; bacterial communities such as Pseudomonas, capable of degrading cyanide 10 mg L -1 [10] and two isolates of this genus, immobilized on activated charcoal, degrading concentrations up to 340 mg L -1 [10,11] . Arthrobacter sp., Zoogloearamigera, Acidovorax sp., Achromobacter sp., Janthinobacterium sp., Klebsiella sp., Bacillus pumillus, Burkhoderia cepacia, Alcaligenes sp., Serratia marcescen and Rhodococcus sp., among others, have been reported as cyanide degrading organisms [6,[12][13][14][15][16][17][18][19]. Besides bacteria, species of the archaeal genus Methanosarcina (under anaerobic conditions), some fungi like Fusarium solani and Trichoderma polysporum at pH 4 [20] and some algae like Scenedesmus obliquus [21] have been reported to degrade cyanide. ...
Cyanide is the basic component of many industrial processes, among which is gold processing, being very toxic or even lethal. Treatment, with the help of microorganisms, can be used effectively to reduce the load of harmful chemicals into the environment. The combination of microbiological methods and molecular tools allowed inferring the presence of a dominant population and the composition varied both in the places of origin and in the method used. The dominant phylogenetic affiliations of the bacteria were determined by sequencing the 16S rRNA gene. The isolates identified, as Bacillus and Enterococcus were capable to degrade 41.9 and 27.5 mg CN- L-1 respectively. This study provides information about the presence of a diverse bacterial community associated with residual effluents from cyanidation processes in Colombia and suggests that their presence could play a role in the biological degradation of cyanide compounds, offering an alternative for mining wastewater treatment.
... Cyanide solutions are employed in almost all precious metals (Au, Ag) extraction plants worldwide (Akcil, 2003;Brüger et al., 2018;Gurbuz et al., 2009). This usually results in the generation of large flowrates of discharges to be dumped in tailings ponds and rivers in rainy seasons. ...
The main purpose of this research has been to evaluate and optimize the application of hydrodynamic cavitation (HC), combined with hydrogen peroxide, as a promising process for the effective degradation of cyanide in aqueous effluents. The experimental work was carried out using cavitation equipment with a venturi device connected to a tubular circuit which allowed a closed-cycle flow to run for 120 min, in which the effect of control parameters as inlet pressure, H2O2:CN─ ratio, pH, and temperature have been evaluated for the treatment of solutions with initial cyanide concentration in range 100 to 550 mg L─1.
The results showed that in optimal conditions cyanide degradation using only HC reached 70% and, using solely H2O2 as oxidizing agent it reached 63%. Efficiency of the combined treatment process was evaluated on the basis of their synergetic effect as it turned out to be more effective showing a 99.9 % cyanide degradation in less than 120 min. The optimum set of conditions that produced the highest degradation rate and efficiency was: inlet pressure 4 bar; pH 9.5; and H2O2:CN─ ratio = 1.5:1. The process was also evaluated on the basis of cavitational yield and in terms of energy and chemical treatment costs. The results have demonstrated that the combined treatment technology of HC + H2O2 can be effectively used as a fast and highly efficient treatment of wastewater containing cyanide.
... There are several treatment methods employed for the wastewater like reverse osmosis, adsorption, ion exchange, leaching, oxidization, precipitation, biodegradation, solvent extraction, etc. (Akcil 2003;Vedula et al. 2013). The above mentioned physicochemical processes for treatment had thoughtful limitations, so it has become essential to look for substitute and environment friendly treatment methods. ...
Water pollution is increasing due to urbanization and industrialization. Waste water pollution raised concern because of its influence on plants and humans. Water hyacinth ( Eichhornia crassipes ) is used for the removal of pollutants because of its phytoremediation efficiency. In this study, water hyacinth ( Eichhornia crassipes ) has been tested for simultaneous elimination of phenol and cyanide from mono and binary component aqueous solution in batch systems. The plant was grown at six concentrations of phenol and cyanide in the ratio of (10:1), i.e. 100:10, 200:20, 300:30, 500:50, 700:70 and 1000:100 mg/L in aqueous solution. The effect of process parameters such as initial concentration of phenol and cyanide and pH was evaluated. The plant was found capable of eliminating up to 96.42% of phenol (300 mg/L) and 92.66% of cyanide (30 mg/L) during the 13 days cultivation time at pH 8. The calculated K m of the root length elongation for phenol was 5.20 mm and the V max was 12.52 μg phenol/g root/h. However, the calculated K m of the root length elongation for cyanide was 0.39 mm and the V max was 14.99 μg cyanide/ g root/h. In the Eichhornia crassipes plant, the biochemical parameters such as chlorophyll, protein and sugar content have been indicated a decreasing trend due to uptake of phenol and cyanide throughout cultivation. Toxicity to 100–1000 mg/L of phenol and 10–100 mg/L of cyanide was measured by measuring the relative transpiration over 13 days. At 100 mg/L of phenol and 10 mg/L of cyanide, only a small reduction in transpiration but no morphological changes were noticed. Both pollutants are absorbed through the root of the Eichhornia crassipes plant by plasmalemma and become accumulated into the root cells and stem of a plant. Thus, this study will be beneficial for the decontamination of highly polluted waste water.
... Chemical oxidation (using SO 2 /air, hydrogen peroxide, alkaline chlorination, ozone), biodegradation and adsorption are the most commonly used methods for treatment of cyanide containing wastewaters (Mosher and Figueroa, 1996;Akcil 2003;Gurbuz et al 2009;Deveci et al. 2006;Dash et al. 2008). Despite high efficiency of oxidative treatment processes in removing the cyanide compounds, these methods are economically unjustifiable. ...
Cyanides are widely used as depressants in the selective flotation of sulphide minerals and as gold solvents in the gold cyanidation process. Despite widespread application of cyanide compounds in the mineral processing industry, they are highly toxic to humans and aquatic organisms. In this research study, two novel and efficient graphene-based magnetic nanocomposite adsorebnts namely magnetic chitosan graphene oxide (MCGO) and magnetic chitosan nitrogen-doped graphene oxide (MCNGO) were synthesized for cyanide removal from aqueous solutions. The prepared adsorbents were characterized by XRF (X-ray florescence), XRD (X-ray diffraction), SEM (scanning electron microscope), EDX (energy-dispersive X-ray spectroscopy), VSM (vibrating sample magnetometer) and FTIR (Fourier transform infrared spectroscopy) techniques. The adsorption experiments showed that at optimum conditions (adsorbent dosage: 1 mg/mL; cyanide concentration: 260 mg/L; pH = 9.5; contact time = 120 min) more than 93 and 98% of cyanide was removed by MCGO and MCNGO, respectively. The relationship between the process variables and the cyanide removal was modelled using the artificial neural networks (ANNs). The kinetic studies revealed that the cyanide adsorption process on the both adsorbents followed the pseudo-second-order kinetic model. The equilibrium data fitted best to the Langmuir model, confirming monolayer adsorption of cyanide on homogeneous surface of the adsorbents. The maximum adsorption capacities of MCGO and MCNGO were found to be 405.3 and 483.74 mg/g, respectively. The thermodynamic analysis indicated that the adsorption process was spontaneous (∆Go < 0), endothermic (∆HoMChGO = 13.04 kJ/mol; ∆HoMChNGO = 15 kJ/mol) and entropy-driven (∆SoMChGO = 51.48 k J/K.mol; ∆SoMChNGO = 58.50 kJ/K.mol). The adsorption experiments on the tailings of a gold cyanidation plant showed that the developed adsorbents were capable of removing more than 90% of cyanide from the real sample.
... More sustainable mining practices require mitigation measures for existing tailings and improved processes and safety procedures for ongoing activities (106). Highly toxic chemicals, such as cyanide or mercury, should be replaced by less harmful extraction agents, such as halogens or thiourea, or a zero-emission policy should be enforced (107). Such technical measures should be supplemented by clear international regulations (108) and corporate social responsibility in the mining industry, which is based on open information policies (109). ...
The global food system faces major risks and threats that can cause massive economic loss; dislocation of food supply chains; and welfare loss of producers, consumers, and other food system actors. The interrelated nature of the system has highlighted the complexity of risks. Climate change, extreme weather events, and degradation and depletion of natural resources, including water, arable, forestry, and pastural lands, loss of biodiversity, emerging diseases, trade chokepoints and disruptions, macroeconomic shocks, and conflicts, can each seriously disrupt the system. Coincidence of these risks can compound the effects on global food security and nutrition. Smallholder farmers, rural migrants, women, youth, children, low-income populations, and other disadvantaged groups are particularly vulnerable. The coronavirus disease 2019 (COVID-19) pandemic exemplifies a perfect storm of coincidental risks. This article reviews major risks that most significantly impact food systems and highlights the importance of prospects for coincidence of risks. We present pathways to de-risk food systems and a way forward to ensure healthy, sustainable, inclusive, and resilient food systems.
Expected final online publication date for the Annual Review of Environment and Resources, Volume 46 is October 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
... CN-22 from electroplating wastewater and Bacillus sp. isolated from cassava processing effluent are efficient in degrading pure KCN by 72, 75, 96.69 and 98%, respectively (Akcil 2003;Khamar et al. 2015;Nelson 2006;Sankaranarayanan and Gowthami 2015). A strain from Citrobacter sp. ...
Iron and steel industries are one of the seven major energy-extensive manufacturing industries strengthening any nation’s economic infrastructure. Processes involved in these industries generate a large number of contaminants, which cannot be directly released into the environment. Proper treatment methods for the wastewater are very necessary from ecological standpoint and economical concerns. Doing so naturally is also important to eliminate and reduce the amount of organic and inorganic wastes and heavy metal pollutants to their standard limits. Thus, a number of studies encompassing employment of different microorganisms, natural as well as genetically modified, and their on-site or off-site applications, either as pure microbial strains or as mixed microbial consortia have been conducted. This review aims to present the role of microorganisms that have been successfully investigated for the removal of toxicities from the wastewater generated by the processes of iron and steel industries.Graphical abstract
... Bioremediation associated with selection of suitable strain simplifies the process satisfying the ultimate requirement of separation and environmental control. The implementation of these processes is occurring on a large engineered scale owing to the favourable volumetric reaction rates and overall productivity of suspended cultures [25]. Several literature reports about the wide application of Pseudomonas sp., for degrading phenol and cyanide in batch and continuous mono substrate systems [26][27][28][29][30]. ...
Coke oven sector emanates phenol and cyanide as the eminent virulent compounds due to abrupt industrialization which is detrimental in aqueous state, and its severity is increased on simultaneous coexistence even at low concentrations that eventually causes extensive damage to the peripheral ecosystem. The efficacy of isolated mixed bacterial culture comprising of Alcaligenes faecalis JF339228 and Klebsiella oxytoca KF303807 in wastewater treatment was investigated following a batch study. The impact of initial concentration of phenol (100–1500 mg L⁻¹) and cyanide (10–150 mg L⁻¹) on the growth and treatment by the mixed microbial cultures were evaluated over a time period of 72 h. The biodegradation mechanism was explained by Monod, Haldane, Aiba and Edward kinetic models. The maximum specific growth rate was reported to be 0.096 h⁻¹ and 0.126 h⁻¹ for phenol and cyanide respectively. The substrate inhibitory effect became eminent after a concentration of 450 mg L⁻¹ for phenol and 45 mg L⁻¹ for cyanide. Based on the lower sum of squared error (SSE) values, Haldane model for phenol and Edward model for cyanide was found to be favourable for substrate inhibition kinetics. The fate of the secondary intermediates produced after microbial degradation was assessed by phytotoxicity studies using Vigna radiata. The interactive binding of the pernicious pollutants and resultant biodegraded compounds with the DNA (herring sperm DNA) was examined following spectrofluorometric and spectrophotometric anatomization. Toxicity studies revealed that biological treatment was viable for eco benign disposal and results also depicted that both the strains have potential in remediation of phenol and cyanide from coke oven wastewater.
... The major industries which use cyanide are electroplating and mining (extraction of gold, silver, etc.), nylon, pharmaceuticals (Harris and Knowels, 1983;Desai and Ramakrishna, 1998;Patil and Paknikar, 1999, 2000, Dursun and Aksu, 2002Akcil, 2003). Cyanides are very toxic and therefore effective clean-up requires their immobilisation to reduce or remove toxicity but current methods of soil remediation such as soil washing, mechanical separation, extraction and storage do not really solve the problem hence the need for cheaper and more efficient alternative methods to clean up heavily contaminated industrial areas (Finnegan et al, 1991;Meyers et al., 1991;Ezzi and Lynch, 2005;Otura et al., 2013). ...
Cyanide has wide and necessary applications in industry and over 1.1 million tonnes of the chemical was produced in 2017 for use in the electroplating, mining, nylon and pharmaceutical industries among others. Since the chemical is toxic, it has to be treated before cyanide containing wastewaters are released into the local environment. Current remediation techniques include ozonation, peroxide treatment and microbial degradation. Bioremediation has been promoted as very safe, economical and cheaper. Phytoremediation is a technology that uses plants to treat environmental pollution problems in an environmentally friendly and cost effective manner. This research investigated the use of the plant Alocasia macrorrhizos in biodegrading cyanide. The preliminary results indicate a reduction from 1000 ppm to 190 ppm and 2000 ppm to 530 after 72 h. 100% degradation was observed after 240 h. A macrorrhizos is therefore a promising plant for degrading cyanide.
... Although there are several chemical methods could be used for handling this kind of toxic waste [9,10], these methods are expensive and hazardous chemicals are used as the reagents and some of them create additional toxic and biological persistent chemicals. In general, biological treatments are eco-friendly, cost effective and sometimes more efficient and thus considered as a feasible alternative to the chemical methods [11,12,13]. ...
Nitriles are toxic organo-cyanide compounds, but extensively used in various industries as solvents, plastics, synthetic rubber, pharmaceuticals, herbicides, and starting materials for other industrially important chemicals. The wider use of these toxic compounds could lead to an environmental pollution, which have a negative impact on health. Some microbes are reported to be able to utilize both aliphatic and aromatic nitrile s as growth substrates and convert them into non-toxic compounds, some of which also have economic value as well. An indigenous bacterial isolate I-benzo, capable of growing on and utilizing of a high concentration of acetonitrile (CH 3 CN) and benzonitrile (C 6 H 5 CN), could be isolated from leather tanning waste by the enrichment-culture technique. Based on 16S rDNA sequence, the strain was identified as Rhodococcus pyridinivorans . These bacterium was shown to able to grow on acetonitrile (0.2-2.0 M) and on benzonitrile (5-25 mM), as a sole source of energy, carbon and nitrogen, respectively. The best growth of R. pyridinivorans strain I-benzo was on 500 mM acetonitrile and on 15 mM benzonitrile. During the degradation of both nitriles using whole cells of the bacterium, amide and carboxilic acid were detected in the reaction media, indicating that nitrile hydratase and amidase involved in the metabolism of the substrate. The involvement of both enzymes on the conversion of acetonitrile and benzonitrile was also proved by the ability of R. Pyridinivorans I-benzo to grow on their intermediate degradation products, acetamide (CH 3 CONH 2 ) and benzamide (C 6 H 5 ONH 2 ), respectively. Based on these results, R. pyridinivorans strain I-benzo could be expected as a potential candidate for biological treatment for nitriles-containing wastes, although further research is still needed before being applied on a field scale.
... 8 In the case of biological degradation, NH 4 + or NO 3 − is produced as a final product, which needs further nitrification and denitrification treatment steps. 9 Another common strategy for removing CN − is to oxidize it to cyanate (OCN − ) which is less toxic than CN − , using chemical oxidants (e.g., O 3 , H 2 O 2 , and S 2 O 8 2− ) with UV, 10,11 photocatalytic, 12 electrochemical 13−15 and photoelectrochemical (PEC) 16−19 methods: most investigations reported the transformation of CN − to OCN − that needs further treatment. As the initial pH of cyanide solution is usually adjusted above 9.2 for treatment to avoid the release of toxic HCN (pK a = 9.2) gas 20,21 and the hydrolysis of OCN − is much hindered under the alkaline condition, 22 OCN − generated from the oxidation of CN − persists under the alkaline condition. ...
Chemical treatments of toxic cyanide (CN–) typically involve its conversion to cyanate (OCN–), which is less toxic. An ideal treatment should be its conversion to N2 and CO2. This study proposed and demonstrated an engineered photoelectrochemical (PEC) system that converts CN– to N2. WO3 has been often used as a visible light active photoanode in the PEC system, but it is stable only in the acidic condition. Since cyanide is generally treated under the alkaline condition, it is necessary to develop a PEC system that is stable in the alkaline condition. To overcome this drawback, the TaON overlayer was electrodeposited on a WO3 film, which enhanced not only the stability of the WO3 electrode in the neutral/alkaline condition but also the interfacial charge transfer efficiency. The WO3/TaON electrode under visible light effectively generated reactive chlorine species (RCS) from Cl– oxidation along with concurrent production of H2O2 via O2 reduction on a graphite cathode. CN– was oxidized to OCN–, which subsequently reacted with RCS to produce NH3 and further to N2 as the final product. In particular, in situ generated H2O2 works synergically with RCS to enhance the CN– oxidation and the total nitrogen (TN) removal efficiency. This study demonstrated a new method that transforms CN– to N2 and CO2 as final products without using any toxic chemical reagents, which is environmentally friendly.
Cyanide tailings are the bulk solid waste generated by the production processes of gold mines. Since the highly toxicity of cyanide affects its disposal and comprehensive utilization, a decyanation treatment is needed. However, wide-ranging industrial uses of the current decyanation methods are restricted due to the treatment effects and costs. Based on the natural degradation method, the cyanide treatment effect was enhanced by raising the treatment temperature, increasing the ultraviolet (UV) irradiation and turning the pile periodically. Using the Arrhenius equation, the activation energies of the cyanide hydrolysis reactions were calculated as 52.22 kJ/mol and 34.59 kJ/mol for heating alone and for heating combined with UV irradiation, respectively. At 60 ℃, the cyanide tailings reached the discharge standard (leachate, total cyanide (CNt)< 5 mg/L) after 8 h of treatment. Moreover, after adding UV irradiation (with an intensity of 120 μW/cm2) and a hydrogen peroxide spray (spraying intensity, 2 mL/kg) to the above conditions and shortening the treatment time to 7 h, the cyanide tailings reached the standard for use in building materials (leachate, CNt <0.5 mg/L). Based on these results, UV irradiation, ventilation, spraying and pile-turning were integrated into the solar drying room to form an enhanced natural degradation system, which was applied in the semi-industrial scale treatment of the cyanide tailings. The results showed that the cyanide tailings consistently met the standards for discharge and use in building materials, successfully verified the conditions and effects of the laboratory treatment, and reduced the treatment cost by more than 50 %.
Modeling the assimilation of biodegradable contaminants by plants is a smart option to simulate the efficiency of phytoremediation in a field trial. The involvement of β-cyanoalanine synthase (β-CAS) and sulfurtransferase (ST) in cyanide (CN−) assimilation in plants was evident. However, the contribution of both enzymes to CN− assimilation by plants is not defined. In this study, a rice completely mixed reactor model (RCMRM) combined with boundary conditions is developed to mathematically examine the contribution of β-CAS and ST to CN− assimilation in rice plants. The modeling steps include: 1) estimation of CN− assimilation rates was based on the CN− in plant biomass and the solution; 2) inputs of the mass balance equations of CN− through either the β-CAS pathway or the ST pathway were calculated individually; 3) the boundary conditions refer to the condition, in which the expression levels of β-CAS and ST in the KCN treatments with application of exogenous 1-amino-cyclopropane-1-carboxylic acid (ACC) were higher than the KCN treatments without ACC addition. Results from the RCMRM suggested that CN− assimilation rates by rice seedlings followed an exponential kinetic (first order), which was linearly increased in the first 2 hour before more gradual until equilibrium was reached at about 12 hour. The catalytic efficiency of β-CAS on CN− assimilation was higher than that of ST, and the contribution of β-CAS and ST to CN− assimilation is time-dependent rather than dose-dependent. Overall, this is the first attempt to mathematically describe the contribution of β-CAS and ST to exogenous CN− assimilation in rice plants.
Because of the highly toxic cyanide in the gold cyanide residues, cyanide must be removed for environmental protection. The process mineralogy of residues was studied firstly, and then cyanide removal was carried out by three chemical methods. The results showed that the residue mainly contained Si, S and Fe. Pyrite was the main metallic mineral, and the iron-complex cyanides make cyanide removal difficult. The minerals in residues were in ultrafine particle size with high monomer dissociation degrees. In H2O2 oxidation process, the self-decomposition and side reactions resulted in high consumption of H2O2. In Na2S2O5-air oxidation process, the time for complete process was long because of the reactions between Na2S2O5 and O2. Na2SO3 oxidation method was found to be a new method for cyanide removal without air inflation device. The cyanide content was reduced to the national standard level in 90 min at pH 9.0 with optimum Na2SO3 dose of 2.0 g/L.
Cyanidation is considered the most employed process to recover precious metals such as silver and gold. However, cyanide containing wastes can be hazardous for the environment. Therefore, the soil electroremediation technique was systematically studied to eliminate/degrade the cyanide contained in mining tailing dams using an electrolytic cell with cationic separator and cheap-stable carbon electrodes. The extent and kinetics of cyanide degradation was firstly analyzed in synthetic solutions using the electrolytic cell at different current density, ionic conductivity, and cyanide concentration. The electrolytic system was also evaluated for the treatment of a sample obtained from a mining tailing dam containing cyanide. The results revealed that 100 % of cyanide can be degraded from synthetic solutions containing 200 ppm CN– at 60 A/m², 0.25 M NaOH and room temperature. It was also found that 100 % of cyanide can be degraded from the real samples obtained from a Mexican mining tailing dam. The kinetic analysis revealed that cyanide degradation can occur through two pathways: a) in the case of tests containing 500 and 800 ppm NaCN, the rate determining step of the cyanide degradation to cyanate species follows a first order reaction with respect to the cyanide ions, and b) when the tests are carried out with 200 ppm NaCN, the same first order reaction controls the process kinetics from 0 to 30 min, while at t > 60 min, the rate determining step for cyanide degradation is modified and limited by the occurrence of parasite reactions. The proposed mechanism for cyanide degradation is also consistent with the thermodynamic calculations. The results also revealed that complete cyanide electro-degradation can be achieved with a current efficiency of 100 %.
Cyanide compounds are hazardous compounds which are extremely toxic to living organisms, especially free cyanide in the form of hydrogen cyanide gas (HCN) and cyanide ion (CN−). These cyanide compounds are metabolic inhibitors since they can tightly bind to the metals of metalloenzymes. Anthropogenic sources contribute significantly to CN− contamination in the environment, more specifically to surface and underground waters. The treatment processes, such as chemical and physical treatment processes, have been implemented. However, these processes have drawbacks since they generate additional contaminants which further exacerbates the environmental pollution. The biological treatment techniques are mostly overlooked as an alternative to the conventional physical and chemical methods. However, the recent research has focused substantially on this method, with different reactor configurations that were proposed. However, minimal attention was given to the emerging technologies that sought to accelerate the treatment with a subsequent resource recovery from the process. Hence, this review focuses on the recent emerging tools that can be used to accelerate cyanide biodegradation. These tools include, amongst others, electro-bioremediation, anaerobic biodegradation and the use of microbial fuel cell technology. These processes were demonstrated to have the possibility of producing value-added products, such as biogas, co-factors of neurotransmitters and electricity from the treatment process.
Ammonia is a common contaminant in municipalities where human waste causes nitrification of local water bodies. In mining, ammonia contamination occurs as a byproduct of biological water treatment, from the use of ammonium nitrate fuel oil in explosives, and from the exposure of ammonia rich soils during the excavation process. In particular, gold mine effluent represents a significant source of ammonia and nitrogen-based contaminants. Current biological and abiotic treatment processes are difficult to employ at the scale required at mine sites due to the high operating costs, or are limited in effectiveness due to a lack of natural resources required to facilitate the treatment. This article evaluates the use of electrooxidation as a cost effective alternative to treating ammonia-laden wastewater in mining applications. Two mixed metal oxide electrodes are assessed in this article: IrO
$_{2}$
/Ti and RuO
$_{2}$
/Ti anodes. A Monte Carlo simulation is performed to determine a probabilistic range of capital and operating expenditure for a mining operation deploying an electrooxidation wastewater treatment system. The lowest capital cost of operating the electrochemical treatment occurs at a current density of 200 A/m
$^{2}$
, where the number of cells required for treatment is minimized.
Thiocyanate (SCN-) detection is highly significant because of the toxicity of SCN-. Herein, a portable and miniaturized lab-on-fiber (LOF) sensor is reported for the detection of SCN- through integrating a Fabry-Perot (F-P) optical resonance cavity based on anionic-responsive metal-insulator-metal (MIM) onto an optical fiber tip. The responsive MIM optical resonance cavity is constructed with an intermediate cationic polymer brush layer (poly[2-(methacryloyloxy)ethyl] trimethylammonium chloride, PMETAC) and two silver layers via a facile in situ "layer-by-layer" construction method. When the fabricated LOF sensor was immersed in SCN- solutions, an obvious reflection dip shift can be observed, which is feasible for the quantitative detection of SCN-. What's more, the fabricated LOF sensor exhibits outstanding selectivity and anti-interference against other interfering anions. Furthermore, the fabricated LOF sensor also displays other excellent advantages endowed by the polymer brush film, such as a fast response rate and outstanding reproducibility. Therefore, it is believed that the fabricated miniaturized LOF sensor would show great potential as a portable sensor in future applications, such as environmental monitoring and clinical diagnosis.
Cyanide is an important industrial chemical that is produced every year on a large scale during metallurgical operations such as gold mining and processes of chemical synthesis. A wide range of microorganisms and plants produce cyanide as part of their normal metabolism. The industrial and anthropological activities have resulted in contamination with toxic levels of cyanide in the environment which becomes a threat to animals and human beings. Biodegradation is the cheapest and the most effective method to clean-up cyanide from the environment via aerobically or anaerobically depending on the environmental conditions. Some microorganisms such as bacteria and fungi have been reported to degrade cyanide to corresponding nontoxic acids or amides. Some microbes have cyanide hydratase or dehydratase enzymes to convert cyanide to formamide or formic acid. In this chapter, we will discuss the causes and nature of cyanide pollution and the possible application of cyanide metabolizing species or immobilized enzymes in the biodegradation of contaminated habitats.
With the rapid development of society, wastewaters, such as cyanide-containing wastewaters (CBWs) have caused environmental problems. In the present work, an electrochemical approach using sacrificial Zn anode was investigated for the removal of cyanides from CBWs. The effects of operational parameters, such as current density, pH, initial cyanide concentration, and ionic strength, on the cyanides removal from synthetic solution were discussed in turn. Under the optimal conditions obtained, the treatment of industrial CBWs was considered. Subsequently, more attentions were paid to elucidate the removal mechanisms of cyanide ions and the corresponding metal-cyanide (copper and iron) complexes by a combination of cyclic voltammetry (CV), pHPZC, X-Ray diffractometer (XRD), scanning electron microscope with energy disperse spectroscopy (SEM/EDS) and X-ray photoelectron spectrometer (XPS) characterizations. Experimental results demonstrated that the removal efficiency of total cyanide (CNT), Cu, and Fe from industrial CBWs are 98%, 91%, and 96%, respectively, with an anode consumption of 1.78 kg/m³ and energy consumption of 2.50 kW·h/m³, of which 72% of Cu was collected on the cathode and almost all of Fe was in the precipitate. Removal mechanisms suggested that free cyanide (CN⁻) mainly presented as Zn(CN)2 into the electrolytic precipitate. The replacement of Zn²⁺ and electroreduction promoted 72% of Cu(I) to be reduced, while 57% of the remaining portion of Cu(I) was oxidized to Cu(II) and 43% of Cu(I) could form CuSCN into the precipitate by XPS analysis. With respect to Fe, it was mainly ascribed to the formation of Zn2Fe(CN)6 precipitate to be removed. From above, this work provided a method for enriching cyanides from wastewaters into the precipitate, while valuable metal Cu was deposited on the cathode, facilitating the separation and recovery of valuable resources.
The construction of a low-cost and green copper recovery method in gold plants is extremely important for treating CuSCN-containing refractory acidified sediments (ASs). In this work, an effective and environmentally-friendly hydrometallurgical process, consisting of thiosulfate leaching and protective electrodeposition, was proposed for selective copper recovering from ASs. The effects of leaching parameters on the leaching efficiency were systematically investigated. Subsequently, cyclic voltammetry, linear sweep voltammetry, and chronoamperometry were utilized to determine the predominant speciation and investigate the electrochemical behavior of the leachate. Eventually, the optimum electrolysis parameters for copper recovery were considered. The results demonstrated that the selective leaching efficiency of copper reached 99% under optimum leaching conditions, while no zinc and iron were leached, which coincides with the results of speciation calculations. Simultaneously, the kinetic analysis indicated that the leaching process exhibited a diffusion-controlled step with an apparent activation energy of 13.64 kJ/mol. Na2Zn3Fe(CN)6 as the main ingredient of the leaching residue was formed, which played a vital role in facilitating the copper leaching process. The electrochemical measurements indicated that the [Cu(S2O3)3]⁵⁻ complex was the dominant species in the pH range from 7.0 to 11.0, and the mass transfer diffusion was the main resistance element for the cathodic reduction of the [Cu(S2O3)3]⁵⁻ complex. Regarding the S2O3²⁻ stability, it decomposed more easily into S, S²⁻, S4O6²⁻, and SO4²⁻ in the presence of Cu²⁺. However, the presence of SO3²⁻ significantly alleviated thiosulfate decomposition. The electrodeposition experiments showed that metallic copper was obtained with a recovery efficiency of 95%, current efficiency of 50%, and energy consumption of 1.25 kW h/kg Cu. This research developed an approach for the efficiently recycling ASs, yielding great economic results and more favorable environmental performance.
The facile removal of cyanide anions from cyanide‐containing water was achieved using CO2 in conjunction with aldehydes which can be recycled from the process. The conversion of the cyanide ion into an insoluble cyanohydrin in water allowed the removal of cyanide and could be used as a method for treating cyanide contaminated wastewater and for recovering cyanide or cyanohydrins for further applications. Carbon dioxide promotes the formation of cyanohydrin in aqueous media and therefore, enabled to purify cyanide contaminated water without reactive oxidants and/or additional energy input. The method was tested in various conditions mimicking goldmine wastewater to elucidate the capacity of CO2‐mediated cyanide remedy process.
Fenton oxidation, coagulation/flocculation/sedimendation plus Fenton oxidation, and Fenton oxidation plus activated carbon adsorption were conducted to develop the effective processes for recycling a biologically treated coking plant effluent. Fenton oxidation enhanced adsorptive capacities of activated carbon for the residual organics and also made them more biodegradable. The Fenton oxidation followed by adsorption and biodegradation in a biological activated carbon (BAC) adsorber was the most cost-effective treatment process to recycle the final effluent for in-plant reuses while meeting the much more stringent discharge limits of the future. Batch experiments were also conducted to determine the effects of copper-loading and fixing methods on the capacity of granular activated carbon (GAC) for removing cyanide from KCN (pH = 11), K3Fe(CN)6 solutions and several Shanghai Coking Plant (SCP) effluent samples. KI-fixed carbon (Cu/KI-GAC) was the best GAC samples tested. Adsorption was the primary mechanism of cyanide removal; catalytic oxidation of the adsorbed cyanide on carbon surface contributed a minor amount of the observed removal. Four small adsorbers containing the base GAC and 0–100% of Cu/KI-GAC were employed for treating a Fenton-oxidized/precipitated SCP effluent sample. After the start-up period (<3 weeks) to establish the effective BAC function in the adsorbers, the effluents became stable and met the discharge limits (CODCr < 50 mg/L and TCN < 0.5 mg/L); with >30% Cu/KI-GAC in the adsorber, the effluent would meet the discharge limits during the start-up phase. The BAC function of the adsorber substantially reduced the carbon replacement cost, making the combined Fenton oxidation and BAC treatment process a cost-effective alternative for recycling the biotreated coking plant effluent.
Cyanide tailings(CT) are a typical hazardous waste, containing large amounts of heavy metals and highly toxic cyanide. As so far, it is difficult to solve this problem at the same time. In this study, a “two-step” process was proposed for the first time to treat CT, first using microorganisms to degrade cyanide and then using microbially induced carbonate precipitation (MICP) to solidify the CT. We isolated a bifunctional bacterium which exhibited cyanide degradation and high urease activity from CT, identified as Aneurinibacillus tyrosinisolvens strain (named JK-1). We used JK-1 bacteria to treat the CT in a “two-step” process. The results showed that the degradation of free cyanide (F–CN) and total cyanide (T-CN) in CT by JK-1 bacteria reached 94.54% and 88.13%. After the MICP treatment, the spindle-shaped CaCO3 solidified the CT into a block of calcite and sphalerite crystals, and the uncompressed compressive strength (UCS) reached 0.74 MPa; the morphology of heavy metals in the CT changed from the exchangeable state to the carbonate-bound state, and the mobility was significantly reduced. Compared with chemical treatment, the treatment of CT by the new process is highly efficient and green, which can realize the solidification of CT, degradation of cyanide and immobilization of heavy metals at the same time. Compared with chemical treatment, the new process is efficient and green, which can realize the solidification of CT, the degradation of cyanide and the immobilization of heavy metals at the same time; it is of great significance to the harmless treatment of CT and the sustainable development of gold smelting industry.
In this work, a highly sensitive colorimetric paper-based optode for the determination of thiocyanate in urine samples was developed for the first time. The cocktail solution of the optode was composed of 5,10,15,20-tetrakis(4-octyloxyphenyl)porphyrin cobalt(II) complex (L), tridodecylmethylammonium chloride (TDMACl), 2-nitrophenyl octyl ether, and polyvinyl chloride as an ionophore, an ion exchanger, a plasticizer, and a polymer, respectively. The paper-based optode responded to thiocyanate by increasing the blue component in the RGB index and a visible change, with the naked-eye, of the optode color from pink to green was observed. From the central composite design, the optimized conditions that yielded the highest sensitivity were 4.70 mmol/kg TDMACl and 13.75 mmol/kg L. The developed optode sensor was highly selective and responded to thiocyanate over other anions, with a working range of 0.001–5 mM and with a coefficient of determination (R²) of 0.9915. The limits of detection using naked-eye and camera were determined to be 50.0 μM and 1.26 μM, respectively. In addition, the LOD and LOQ estimated from the standard deviation of the blank were 0.65 and 1.87 μM, respectively. Furthermore, this sensor was successfully applied to the detection of thiocyanate in urine samples from non-smokers and smokers. The results were in good agreement with the standard ion chromatography (IC) technique. This developed paper-based optode sensor was simple, low-cost, portable, and easy to use as a sensing device without any complicated instrument.
Cyanide tailings are industrial hazardous solid wastes arising from gold mining industry. Hundreds of millions of tons of cyanide tailings that contain highly toxic cyanides and various valuable elements, such as gold, silver, iron, sulfur, copper, lead, and zinc are generated and discharged to tailing dams every year. Significant efforts have been undertaken to develop efficient detoxification and utilization technologies to reduce hazardous wastes and recover the valuable element in cyanide tailings. In this paper, the sources and characteristics of cyanide tailings are introduced. The technologies using various physical, chemical, and biological methods or a combination thereof to detoxify and utilize cyanide tailings are reviewed. However, the complexity of cyanide tailings and the high cost of treatment may seriously restrict their industrial application. It seems that thermal treatment with catalysts and autoclaved hydrolysis are certainly promising technologies for the detoxification of cyanide tailings with the removal rate of cyanides more than 99%, which can be good for the cleaner production of gold mining. The current research status and the obstacles in the recovery of cyanide, gold-silver, sulfur-iron, copper-lead-zinc, and “low-value content” from cyanide tailings are then reviewed in detail. These processes can be used independently or in conjunction with other treatment methods depending on the nature of cyanide tailings. The detoxification and comprehensive utilization of cyanide tailings would ultimately bring economic and environmental benefits.
Given that mining is considered to be an essential activity for Mexico’s industrial development, cyanide has been increasingly used to recover precious metals such as gold and silver. Along with that arises the need to develop new technologies to treat the wastes (mining tailings). In addition to their high cyanide content, metal and other contaminants that are found in tailings also present a problem. As a result, conventional (physicochemical) strategies have been developed to reduce contamination from tailings, nonetheless, these have high operating costs and generate unwanted by-products. For this reason, studies have begun to focus on non-conventional strategies to treat free cyanide and cyanide complexes such as fungi, bacterial consortia, and pure bacteria. These are important because of the mechanisms involved in degrading or modifying contaminants at neutral to high pH levels, which convert contaminants into non-hazardous products. The ability of microorganisms to grow at an alkaline pH prevents HCN volatilization. These studies have been performed at the laboratory level using two types of microbial binding: suspended biomass and immobilized biomass. They have used both natural (granite rock, citrus peels, cellulose, gravel) and synthetic (stainless steel, geotextiles, alginate, plastics) packing material, as well as reactors with different types of flow, namely, batch and continuous.
Natural oxidation of sulphide mineral wastes during their disposal and storage at the mining sites may result in generation of acid rock drainage (ARD) that may contain high acidity and high concentrations of dissolved metals and sulphates. Due to its chemical composition, ARD poses potential harm to the environment and significant challenges to many mining industries requiring development and application of effective ARD management plans to the mining sites during the operational and post-closure periods. If the generation of ARD cannot be prevented or controlled, it must be collected and treated to eliminate acidity and reduce the concentration of heavy metals and suspended solids before its release to the environment. As a group of microorganisms may contribute to the generation of ARD, different types of microorganisms may play a vital role in the development of microbiological prevention, control and treatment technologies. The role of microorganisms in the generation of ARD and their role in the methods used for prevention, control and treatment are discussed in this paper. Benefits, limitations and design criteria for passive biological processes are presented using examples of passive and biological treatment processes that have been developed recently and implemented to mine sites.
We compared the efficiency of transduction by an HIV-1-based lentiviral vector to that by a Moloney murine leukemia virus (MLV) retroviral vector, using stringent in vitro assays of primitive, quiescent human hematopoietic progenitor cells. Each construct contained the enhanced green fluorescent protein (GEP) as a reporter gene. The lentiviral vector, but not the MLV vector, expressed GFP in nondivided CD34+ cells (45.5% GFP+) and in CD34+CD38- cells in G0 (12.4% GFP+), 48 hr after transduction. However, GFP could also be detected short-term in CD34+ cells transduced with a lentiviral vector that contained a mutated integrase gene. The level of stable transduction from integrated vector was determined after extended long-term bone marrow culture. Both MLV vectors and lentiviral vectors efficiently transduced cytokine-stimulated CD34+ cells. The MLV vector did not transduce more primitive, quiescent CD34+CD38- cells (n = 8). In contrast, stable transduction of CD34+CD38- cells by the lentiviral vector was seen for over 15 weeks of extended long-term culture (9.2± 5.2%, n=7). GFP expression in clones from single CD34+CD38- cells confirmed efficient, stable lentiviral transduction in 29% of early and late-proliferating cells. In the absence of growth factors during transduction, only the lentiviral vector was able to transduce CD34+ and CD34+CD38- cells (13.5± 2.5%, n=11 and 12.2± 9.7%, n=4, respectively). The lentiviral vector is clearly superior to the MLV vector for transduction of quiescent, primitive human hematopoietic progenitor cells and may provide therapeutically useful levels of gene transfer into human hematopoietic stem cells.
To create mice expressing exclusively human sickle hemoglobin (HbS), transgenic mice expressing human α-, γ-, and βS-globin were generated and bred with knockout mice that had deletions of the murine α- and β-globin genes. These sickle cell
mice have the major features (irreversibly sickled red cells, anemia, multiorgan pathology) found in humans with sickle cell
disease and, as such, represent a useful in vivo system to accelerate the development of improved therapies for this common
genetic disease.
Applications of biotechnology are in use or have been proposed for almost all sectors of the mining and minerals industries for metal extraction, metal recovery, and environmental control. A recently completed study in Canada reviewed the status of biotechnological process development in different sectors of the industry and by commodity. This paper provides an overview of the findings of the study including a discussion of the sectors of the industry in which biotechnology enjoys commercial success and those for which future applications are indicated. Special emphasis is given to the commercial metal extraction processes and to applications for environmental control for which future technical and economic advantages are likely as environmental regulations become more stringent.
Cladosporium cladosporioides biomass was a highly efficient biosorbent of copper cyanide and nickel cyanide from aqueous solutions. A 32–38 fold concentration of initial 0.5mM metal cyanides could be achieved when biosorption process was carried out under standardised conditions. Residual, unrecoverable metal cyanide could be completely biodegraded in 5–6h. The solution treated with the combined biosorption-biodegradation process was fit for discharge in the environment.
Cyanide hydratase, which converts cyanide to formamide, was induced in mycelia of Stemphylium loti by growth in the presence of low concentrations of cyanide. Mycelia were immobilised by several methods. The most useful system was found to be treatment with flocculating agents. This technique is applicable to a wide range of easily isolated fungi that contain cyanide hydratase.
The detoxification of cyanide by algae was examined by exposing cultured suspensions of Arthrospira maxima, Chlorella sp. and Scenedesmus obliquus in growth media to varying concentrations in short-time batch tests. In each experiment, the pH was adjusted to 10.3. The effect of pH, initial concentration of algal cells, temperature and cyanide concentration on microbial detoxification were examined. Under the experimental conditions, initial microbial detoxification rates of 50 and 100 mg/L free cyanide were observed for 25 h. A. maxima did not survive due to its sensitivity to the higher cyanide concentrations in the solutions. S. obliquus removed the cyanide to a greater extent than did Chlorella sp. S. obliquus detoxified 99% of the cyanide, while Chlorella sp. removed about 86% in the same time period. For the raised cyanide concentrations between 100 and 400 mg/L, S. obliquus was the only microorganism tested for 67 h. Kinetic studies of cyanide detoxification showed that microbial removal was linearly correlated with concentration.
The effect of cyanide on the anaerobic treatment of synthetic wastewater, containing starch and volatile fatty acids, was evaluated. A laboratory-scale UASB reactor, operated at hydraulic retention time of 12 h, was successfully acclimatised to CN influent levels as high as 125 mg l−1. Evaluation of cyanide levels in the effluent demonstrated removal efficiencies of this compound of between 91 and 93% at volumetric CN loading rates of about 250 mg l d−1. First addition of CN at 5 mg l−1 and subsequent sudden increases in influent CN levels during the acclimatisation process resulted in temporary deterioration of reactor performance in terms of methane production and COD conversion, while CN levels in the effluent were temporarily increased. Recovery from CN inhibition was observed within 3–4 weeks, when effluent CN levels decreased again below about 10 mg l−1. Sludge activity measurements demonstrated an increased tolerance against CN, once sludge had been acclimatised to this toxic compound. The effect of CN inhibition on methanogenic activity was more pronounced for acetoclastic than for hydrogenotrophic methanogens. The findings of this study demonstrate the potential of anaerobic treatment for COD removal in CN contaminated waste waters. The results also suggest a potential application specifically for CN removal from waste streams.
A retrovirus belonging to the family of recently discovered human T-cell leukemia viruses (HTLV), but clearly distinct from
each previous isolate, has been isolated from a Caucasian patient with signs and symptoms that often precede the acquired
immune deficiency syndrome (AIDS). This virus is a typical type-C RNA tumor virus, buds from the cell membrane, prefers magnesium
for reverse transcriptase activity, and has an internal antigen (p25) similar to HTLV p24. Antibodies from serum of this patient
react with proteins from viruses of the HTLV-I subgroup, but type-specific antisera to HTLV-I do not precipitate proteins
of the new isolate. The virus from this patient has been transmitted into cord blood lymphocytes, and the virus produced by
these cells is similar to the original isolate. From these studies it is concluded that this virus as well as the previous
HTLV isolates belong to a general family of T-lymphotropic retroviruses that are horizontally transmitted in humans and may
be involved in several pathological syndromes, including AIDS.
A cyanide-metabolizing bacterium, strain DF3, isolated from soil was identified as Alcaligenes xylosoxidans subsp. denitrificans. Whole cells and cell extracts of strain DF3 catalyzed hydrolysis of cyanide to formate and ammonia (HCN + 2H2O----HCOOH + NH3) without forming formamide as a free intermediate. The cyanide-hydrolyzing activity was inducibly produced in cells during growth in cyanide-containing media. Cyanate (OCN-) and a wide range of aliphatic and aromatic nitriles were not hydrolyzed by intact cells of A. xylosoxidans subsp. denitrificans DF3. Strain DF3 hydrolyzed cyanide with great efficacy. Thus, by using resting induced cells at a concentration of 11.3 mg (dry weight) per ml, the cyanide concentration could be reduced from 0.97 M (approximately 25,220 ppm) to less than 77 nM (approximately 0.002 ppm) in 55 h. Enzyme purification established that cyanide hydrolysis by A. xylosoxidans subsp. denitrificans DF3 was due to a single intracellular enzyme. The soluble enzyme was purified approximately 160-fold, and the first 25 NH2-terminal amino acids were determined by automated Edman degradation. The molecular mass of the active enzyme (purity, greater than 97% as determined by amino acid sequencing) was estimated to be greater than 300,000 Da. The cyanide-hydrolyzing enzyme of A. xylosoxidans subsp. denitrificans DF3 was tentatively named cyanidase to distinguish it from known nitrilases (EC 3.5.5.1) which act on organic nitriles.
In order to obtain a transgenic mouse model of sickle cell disease, we have synthesized a novel human beta-globin gene, beta SAD, designed to increase the polymerization of the transgenic human hemoglobin S (Hb S) in vivo. beta SAD (beta S-Antilles-D Punjab) includes the beta 6Val substitution of the beta S chain, as well as two other mutations, Antilles (beta 23Ile) and D Punjab (beta 121Gln) each of which promotes the polymerization of Hb S in human. The beta SAD gene and the human alpha 2-globin gene, each linked to the beta-globin locus control region (LCR) were co-introduced into the mouse germ line. In one of the five transgenic lines obtained, SAD-1, red blood cells contained 19% human Hb SAD (alpha 2 human 1 beta 2SAD) and mouse-human hybrids in addition to mouse hemoglobin. Adult SAD-1 transgenic mice were not anemic but had some abnormal features of erythrocytes and slightly enlarged spleens. Their erythrocytes displayed sickling upon deoxygenation in vitro. SAD-1 neonates were anemic and many did not survive. In order to generate adult mice with a more severe sickle cell syndrome, crosses between the SAD progeny and homozygous for beta-thalassemic mice were performed. Hemoglobin SAD was increased to 26% in beta-thal/SAD-1 mice which exhibited: (i) abnormal erythrocytes with regard to shape and density; (ii) an enlarged spleen and a high reticulocyte count indicating an increased erythropoiesis; (iii) mortality upon hypoxia; (iv) polymerization of hemolysate similar to that obtained in human homozygous sickle cell disease; and (v) anemia and mortality during development.
We reviewed the results of transplantation of allogeneic marrow from HLA-identical donors in patients with beta-thalassemia who were less than 16 years old. Among the 222 consecutive patients who had received transplants since 1983, survival and event-free-survival curves leveled off about one year after transplantation, at 82 and 75 percent, respectively. Pretransplantation clinical characteristics were examined for their impact on survival, event-free survival, and the recurrence of thalassemia in the 116 consecutive patients who were treated with our current regimen, in use since June 1985. In a multivariate analysis, portal fibrosis and either the presence of hepatomegaly or a history of inadequate chelation therapy were significantly associated with reduced probabilities of survival and event-free survival. The patients were divided into three classes on the basis of the presence of hepatomegaly or portal fibrosis (class 1 had neither factor, class 2 had one, and class 3 had both). For class 1 patients the three-year probabilities of survival, event-free survival, and recurrence were 94, 94, and 0 percent, respectively. For class 2 patients the probabilities were 80, 77, and 9 percent, and for class 3 patients 61, 53, and 16 percent. We conclude that for patients under 16 years of age, transplantation of bone marrow from an HLA-identical donor offers a high probability of complication-free survival, particularly if they do not have hepatomegaly or portal fibrosis.
In activated sludge system, without mixed liquor suspended solids, in which CN served as only source of carbon and nitrogen, it was found that (1) more than 99% of CN was metabolized, (2) suspended solids were maintained, (3) approximately 98% of cyanide-carbon was converted to CO2, and (4) from 75% to 90% of cyanide-nitrogen was converted to ammonia and nitrite.
Cyanidation tailings disposed of in a surface impoundment experience a loss of cyanide due to natural attenuation, which frequently reduces the cyanide concentration to very low levels. Quantifying cyanide losses in terms of impoundment geometry, local weather conditions and feed-solution chemistry has been largely empirical in spite of the fact that, in many cases, mining operations rely on surface impoundments to reduce cyanide to below an internally regulated concentration or below an effluent limitation. To permit a quantitative evaluation of cyanide losses in an impoundment, a computer simulation was developed to estimate the losses of free, weak acid dissociable (WAD) and total cyanide due to dissociation, photolysis and volatilization. Results of the model are compared with data collected for a North American tailings impoundment in 1998.
Cydnidation tailings disposed of in a surface impoundment experience a loss of cyanide due to natural attenuation, which frequently reduces the cyanide concentration to very low levels. Quantifying cyanide losses in terms of impoundment geometry, local weather conditions and feed-solution chemistry has been largely empirical in spite of the fact that, in many cases, mining operations rely on surface impoundments to reduce cyanide to below an internally regulated concentration or below an effluent limitation. To permit a quantitative evaluation of cyanide losses in an impoundment, a computer simulation was developed to estimate the losses of free, weak acid dissociable (WAD) and total cyanide due to dissociation, photolysis and volatilization. Results of the model are compared with data collected for a North American tailings impoundment in 1998.
An attached growth aerobic biological treatment process has been developed at Homestake Mining Co. 's Homestake gold mine in Lead, SD, which not only oxidizes free and complexed cyanides, indlucing the stable iron complexed cyanides, but also thiocyanate, and the oxidation byproduct ammonia. Through the employment of a mutant strain of bacteria which has been gradually and specifically acclimated to the waste, these potential pollutants are mineralized to relatively harmless sulfates, carbonates, and nitrates. The resultant effluent, through toxicological testing, has been shown compatible with the receiving stream, which serves as a cold water marginal trout fishery.
The potential of sewage sludge for decomposition of cyanide has been investigated at different temperatures, ratio sewage sludge to cyanide, pH and also at prolonged and at four cycle repeated processes. Along with the kinetics of cyanide decomposition, the consumption of reagents necessary to maintain pH of the biosystem and the releasing of volatile cyanide have been examined. The positive effect of the activation of sewage sludge by means of aeration and its correlation to the kinetics of the bacterial growth have been also studied. Along with aeration, “carrier biology” has been employed to improve the characteristics of sewage sludge, using wood peels as a carrier material.
Former gasworks sites are sometimes be heavily contaminated with spent oxide which contains cyanide complexed to metals (especially iron). In this study, mixed fungal cultures have been isolated from acidic gasworks soil by their ability to utilize iron or nickel cyanide as the sole source of nitrogen at acidic or neutral pH, respectively. A mixed culture comprising Fusarium solani and Trichoderma polysporum was obtained by enrichment on tetracyanonickelate [K2Ni(CN)4] at pH 4. A second mixed culture consisting of Fusarium oxysporum, Scytalidium thermophilum, and Penicillium miczynski was isolated on hexacyanoferrate [K4Fe(CN)6] also at pH 4. Both consortia were able to grow on K4Fe(CN)6 as the sole source of nitrogen under acidic conditions. Growth was associated with progressive removal of cyanide from the culture supernatant. After the termination of growth, at least 50% of the total cyanide had been degraded. Growth of the fungi on K2Ni(14CN)4 as a source of nitrogen at pH 7 yielded 14C-labelled carbon dioxide. Growth of the Fusarium isolates on K2Ni(CN)4 at pH 7, associated with the removal of cyanide, required 5 days as compared to 28 days on K4Fe(CN)6 at pH 4. Cyanide uptake by the fungi on K4Fe(CN)6 at pH 4 occurred simultaneously with removal of iron from the biomass-free medium. Pure cultures of F. solani and F. oxysporum were grown on K2Ni(CN)4 or K4Fe(CN)6 in pure culture at pH 7 or 4, respectively.
Water-soluble iron cyanide compounds are widely used as anticaking agents in road salt, which creates potential contamination of surface and groundwater with these compounds when the salt dissolves and is washed off roads in runoff. This paper presents a summary of available information on iron cyanide use in road salt and its potential effects on water quality. Also, estimates of total cyanide concentrations in snow-melt runoff from roadways are presented as simple mass-balance calculations. Although available information does not indicate a widespread problem, it also is clear that the water-quality effects of cyanide in road salt have not been examined much. Considering the large, and increasing, volume of road salt used for deicing, studies are needed to determine levels of total and free cyanide in surface and groundwater adjacent to salt storage facilities and along roads with open drainage ditches. Results could be combined with current knowledge of the fate and transport of cyanide to assess water-quality effects of iron cyanide anticaking agents used in road salt.
Biological treatment of a synthetic leachate containing cyanide was accomplished in a sequencing batch biofilm reactor (SBBR). A mixed culture of organisms growing on silicone tubing were provided with cyanide as a sole carbon and nitrogen source. Organisms consumed cyanide (20 mg/liter CN−WAD) and produced ammonia in an approximate 1:1 molar yield. The SBBR was operated on a 24-h cycle. Over the course of each cycle, 20 mg/liter of cyanide was degraded to below 0.5 mg/liter. Results from four track studies are presented. It was demonstrated that, when supplied with glucose, the organisms would readily consume excess ammonia. For each mole of glucose added, 10 moles of NH3-N were removed from solution. The SBBR can be used as a mobile system for treatment of leachate from gold-mining operations. Large volumes of low concentration wastewater can be treated in the SBBR since it is not necessary to maintain a consortium of settling organisms. © 1998 Elsevier Science Ltd. All rights reserved
A retroviral vector system based on the human immunodeficiency virus (HIV) was developed that, in contrast to a murine leukemia
virus-based counterpart, transduced heterologous sequences into HeLa cells and rat fibroblasts blocked in the cell cycle,
as well as into human primary macrophages. Additionally, the HIV vector could mediate stable in vivo gene transfer into terminally
differentiated neurons. The ability of HIV-based viral vectors to deliver genes in vivo into nondividing cells could increase
the applicability of retroviral vectors in human gene therapy.
Tests were conducted at the Ryan Lode Mine near Fairbanks, Alaska, to determine the comparative costs of chemical and biological destruction of cyanide in mine wastewater. The main body of pond and rinse water was treated by the patented, INCO Air-SO2 process. A 250 ton test heap was built and inoculated with a cyanide-reducing bacterium Pseudomonas pseudoalcaligenes (UA7). The capital and operating costs for both processes were carefully recorded during the treatment. These costs were used as the basis for an analysis of the comparative costs of rinsing and detoxifying a hypothetical, two-million ton heap using each method. Four scenarios were analyzed. The biological method had a higher capital cost, but a significantly lower operating cost, so that the present-worth cost was significantly lower for the biological method.
The presence of cyanide in industrial effluent waste presents a major environmental and ecological hazard. Although chemical methods of treating this compound are known, bacterial detoxification of cyanide is of interest both in order to understand how cyanide may be dealt with in the environment and to evaluate the economic viability of bacterial systems for cyanide detoxification. The enzyme rhodanese, which catalyzes the formation of thiocyanate and sulfite from cyanide and thiosulfate, has been found in various organisms including Bacillus subtilis and E. coli. Thiobacillus denitrificans was shown to have the highest levels of this enzyme, but growth conditions in continuous culture on defined media have recently been developed for the production of equally high rhodanese levels in the thermophile Bacillus stearothermophilus. Purified rhodanese from this latter organism has already proved to be of value as an antidote in experimental cyanide poisoning in small mammals. This communication reports on the use of a culture of B. stearothermophilus in a small chemical reactor for the continuous removal of cyanide in the form of thiocyanate. The capacity of B. stearothermophilus to remove cyanide in the form of thiocyanate in the process described is high (5 to 8 g NaCN/l culture/hr at 27°C); furthermore, both the rate of cyanide removal and the half life of the process were unaffected by the presence of 5x10-5M Zn2+, Cu2+, Ni2+, or Al3+ over a 12 day period. By running the process at temperatures at which B. stearothermophilus is capable of growth in normal media (i.e. above 35°C) higher rates of cyanide detoxification are possible (14 to 25 g NaCN/l culture/hr at 50°C), although preliminary evidence indicates a reduction in half life at higher temperature.
Cyanide compounds are widely used in gold ore processing plants in order to facilitate the extraction and subsequent concentration of the precious metal. Owing to the high cyanide concentrations employed in gold processing, effluents generated have high contents of free cyanide as well as metallic cyanide complexes, which lend them a high degree of toxicity. The process under study, developed in laboratory scale with the use of a distillation apparatus, consists of highly decreasing the pH of the solution by adding sulfuric acid. Thus, the cyanide present in either free form or as a metallic complex is made volatile and the resulting cyanide gas is absorbed in an alkaline solution for reutilization. This work aims at recognizing the chemical relations between the cyanide and metals during distillation. The regeneration of cyanide from gold processing proved to be a viable procedure. Cyanide recoveries pointed to the fact that if a method for reutilization of cyanide contained in mining effluents is employed, the precious metal processing will become more efficient. Also, the environmental conditions in the area of the operation will be improved.
Accumulation of UO
22
+ by Scenedesmus obliquus 34 was rapid and energy-independent and the biosorption of UO
22
+ could be described by the Freundlich adsorption isotherm below the maximum adsorption capacity (75 mg g-1 dry wt). The optimum pH for uranium uptake was between 5.0_8.5.0.1_2.0 M NaCl enhanced uranyl, while Cu2+, Ni2+, Zn2+, Cd2+ and Mn2+ competed slightly with uranyl. Pretreatment had an unexpected effect on biosorption. After being killed by 0.1 M HCl, S. Obliquus 34 showed 45% of the uptake capacity of the control in which fresh cells were suspended directly in uranyl solution, while the pretreatment of cells by 0.1 M NaOH, 2.0 M NaCl, ethanol or heating decreased uptake slightly. Fresh S. obliquus 34 at 1.2_2.4 mg dry wt mL-1 was able to decrease U from 5.0 to 0.05 mg L-1 after 4_6 equilibrium stages with batch adsorption. Deposited U could be desorbed by pH 4.0 buffer. It is suggested that U was captured by effective groups or by capillary action in the cell wall in the form of [UO2OH]+.
A bacterial coculture capable of growing on thiocyanate has been isolated from thiocyanate adapted bacterial suspension of urban sewage treatment plant. The coculture is composed of two bacteria identified as species Acinetobacter johnsonii and Pseudomonas diminuta. The two end products of thiocyanate conversion are ammonia and sulfate. The thiosulfate has been identified as the sulfur intermediate product of the conversion of thiocyanate to sulfate.
The present study compared the efficiency of two unicellular green algae, Chlorella vulgaris (a commercial species from Carolina Biological Supplies Company) and WW1 (an indigenous species isolated from a local sewage treatment works, tentatively identified as Chlorella miniata) in removing Ni2+ from nickel solutions with concentration ranges similar to that in electroplating effluents. The Ni2+ removal efficiency of C. vulgaris (around 33–41%) was significantly lower than that of WW1 (more than 99%) in nickel solutions from 10 to 40 μg ml−1. The maximum Ni2+ uptake by C. vulgaris and WW1 under the present batch experiment was 641.76 and 1367.62 μg g−1, respectively. According to Langmuir adsorption isotherms the nickel adsorption capacity of WW1 (2985.07 μg g−1) was two times greater than that of C. vulgaris (1282.05 μg g−1). These results demonstrated that WW1 was a more powerful Ni2+ biosorbent than C. vulgaris. In both species, most Ni2+ in solution was sequestered by the algal cells within the first few minutes of treatment. The cellular Ni2+ concentration increased with the concentrations of nickel in solution. After treating Ni-containing wastewater for 24 h, both species were still capable of cell division, but the growth rate was reduced in proportion to the concentrations of nickel in the wastewaters.
Biological treatment is a proven process for the treatment of mining effluents such as tailings, wastewaters, acidic mine drainage etc. Several bacterial species (Pseudomonas sp.) can effectively degrade cyanide into less toxic products. During metabolism, they use cyanide as a nitrogen and carbon source converting it to ammonia and carbonate, if appropriate conditions are maintained. In this study, nine strains of Pseudomonas sp. were isolated and identified from a copper mine. Two (CM5 and CMN2) of the nine bacteria strains were used in a cyanide solution. Some important parameters in the biological treatment process were tested and controlled: pH, cell population and CN− concentration. Tests were conducted to determine the effect of the type of bacterial strains on the treatment of cyanide. Laboratory results indicated that biological treatment with Pseudomonas sp. might be competitive with other chemical treatment processes. This paper presents the results of an investigation of a biological treatment system for cyanide degradation in a laboratory batch process.
The removal of heavy metals by a dry biomass of a brown seaweed was evaluated. A continuous system was used, with an effluent from a Brazilian zinc producing industry, containing zinc (88.0 mg/L), cadmium (1.4 mg/L), and manganese (11. 7 mg/L), as well as high levels of calcium (444 mg/L), magnesium (100 mg/L) and sodium (37.0 mg/L). Preliminary results, in batch conditions, indicated fast uptake kinetics for the heavy metals, whose equilibria were reached in a maximum of 30 minutes. The continuous run was conducted in a laboratory acrylic column, lm high, containing several samplers, filled with the dry biomass. The system operated in upflow condition, at a flow rate of 25 mL/min, f or approximately 70 hours, with high operational stability. The results showed high efficiency in the biosorption of heavy metals. Sodium, calcium and magnesium were not incorporated by the biomass, probably as they are present in the structural polysaccharides of the biomass, thus preventing the establishment of an effective ion-exchange process. Analysis of the obtained results did not indicate selective uptake of the metals, probably due to their marked concentration differences in solution. The continuous laboratory system initially showed an efficiency close to 100% in the biosorption of all heavy metals, followed by a gradual decrease, as a function of the saturation of binding sites in the biomass. A mathematical adjustment of the curves obtained for the uptake of the different metals was used for estimating the amount of biosorbed metals, through mathematical computer integration.
In the history of Turkey the first use of cyanide for gold recovery has been at the Ovacik Gold Mine. During one-year test period, this mine has successfully been mining and processing after a complicated and extensive environmental impact procedure. In Turkey about 2500 ton of sodium cyanide are used with about 240 ton of sodium cyanide being used at this mine annually. During the test period, it has been shown that an effluent quality (CNWAD) between 0.06 ppm (min) and 1 ppm (max) was achievable after cyanide destruction with the Inco Process. It was also found that treated effluent values (CNWAD) of process water (decant) were between 0.04 ppm (min) and 0.59 ppm (max). This paper presents a review of the cyanidation and cyanide destruction processes at the Ovacik Gold Mine.
Biosorption is considered a potential instrument for the removal of metals from waste solutions and for precious metals recovery, an alternative to the conventional processes, such as those based on ion exchange, or adsorption on activated carbon. In this work the state of the art of biosorption investigation is presented and results found in literature are compared.
This paper discusses issues of cyanide management at the newly-constructed Ovacik gold–silver mine in Turkey. The mine, which has been using 120 ton/y of sodium cyanide (NaCN) since May 2001, was the first operation in the country to use cyanide to recover gold. Mine staff strives to continuously plan and provide detailed accounts of the management practices and initiatives being undertaken with regard to handling cyanide. It is believed that the programs and activities that have been implemented at Ovacik will facilitate improvement in this area.
Combined biodegradation and internal diffusion effects on the biodegradation rate of ferrous(II) cyanide complex (ferrocyanide) ions by Ca-alginate gel immobilized Pseudomonas fluorescens beads were investigated as a function of initial ferrocyanide concentration and particle size in a batch system. Assuming first-order biodegradation kinetics (ν=kC), first-order biodegradation rate constants for free and different sized immobilized particles were predicted and at 100 mg l−1 bulk ferrocyanide ion concentration experimental effectiveness factors (η) were determined for each particle size. Then using these data, the Thiele modulus (φ) was evaluated for each particle size. Finally effective diffusion coefficient (De) was calculated from the Thiele modulus equation, which is a function of particle size, effective diffusion coefficient and first-order biodegradation rate constant. The results showed that the intraparticle diffusion resistance has a significant effect on the observed biodegradation rate.
For over 100 years, cyanide has been the leach reagent of choice for the extraction of precious metals. Cyanide is used as a lixiviant in milling leach circuits, as well as in heap leach operations. Increasingly stringent environmental regulations have created much interest in a wide variety of methods to destroy residual cyanide. Traditional means of cyanide destruction include alkaline chlorination, hydrogen peroxide, and the INCOIS02 air process. Biological degradation of cyanide has often been offered as a potentially inexpensive, environmentally friendly alternative to conventional processes.In response to the costs of cyanide destruction, cyanide use has become increasingly efficient, and recovery and recycle processes are being employed in many operations. Because of this, and because the pilot studies necessary to develop a biological treatment process can be expensive and time consuming, biological treatment has not seen widespread use for the detoxification of cyanide. Recently, however, biological degradation of cyanide has received a great deal of consideration as a method for cyanide detoxification for heap leach closures.In the decommissioning of heap leaches, residual cyanide must be detoxified before the heap can be closed. Smaller heaps have been successfully decommissioned and larger heaps are in the process of decommissioning. During closure, residual concentrations in the heap must be reduced so that the leachate meets discharge requirements. This paper examines the various alternative methods of heap closure, and compares closing costs for 1.2 and 25 million ton heaps.
utilizes cyanide as the sole source of carbon and nitrogen. Agar, alginate, and carrageenan were screened as the encapsulating matrices for P. putida. Alginate-immobilized cells of P. putida degraded sodium cyanide (NaCN) more efficiently than non-immobilized cells or cells immobilized in agar or carrageenan. The end products of biodegradation of cyanide were identified as ammonia (NH3) and carbon dioxide (CO2). These products changed the medium pH. In bioreactors, the rate of cyanide degradation increased with an increase in the rate of aeration. Maximum utilization of cyanide was observed at 200 ml min−1 of aeration. Immobilized cells of P. putida degraded cyanides, cyanates and thiocyanates to NH3 and CO2. Use of Na[14C]-CN showed that 70% of carbon of Na[14C]-CN was converted into 14CO2 and only 10% was associated with the cell biomass. The substrate-dependent kinetics indicated that the K
m and V
max values of P. putida for the substrate, NaCN were 14 mM and 29 nmol of oxygen consumed mg protein−1 min−1 respectively.
Thesis (M.S.)--Pennsylvania State University.