ArticleLiterature Review

# Destruction of cyanide in gold mill effluents: Biological versus chemical treatments

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## 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.

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... 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). ...
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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.
... Since 1887, CN -is used in the hydrometallurgy industry, to extract gold and silver in alkaline conditions from the mineral ore containing them, as well as a reagent at low concentrations for the flotation of minerals such as lead, copper and zinc. The mining industry uses about 18% of the total CN -production [1] [2] [3] [4] [5] [6]. There are different processes to treat the effluents contaminated with CN -, such as biodegradation, alkaline chlorination, INCO process (SO2/air) (International Nickel Company), hydrogen peroxide, Caro's acid method (H2SO4/H2O2), ozonization, reverse osmosis, activated carbon, resins, among others [3] [6] [7] [8] [9] [10]. ...
... For the leaching of gold-containing ores using CN -, this may exist in three forms: total cyanide (CNT), weak acid dissociable cyanide or WAD and CNL [3][4][5][6][7][8][9][10][11]. The CNT includes the strong complexes such as iron cyanides ( . ...
... For the environmental regulations, the maximum permitted limits (LMP) for the emissions with a content of CNT are in the order of 1 mg/L and for the WAD CN in 0.2 mg/L [4]; the United States Environmental Protection Agency (USEPA, by the English acronym) has proposed a regulation for drinking water and aquatic water regarding CNT of 0.2 and 0.05 mg/L, respectively [6] [15] and in terms of CNL for the protection of aquatic life in fresh water is set in 0.022 and 0.0052 mg/L [3]. Peruvian regulations for water quality national standards; establishes the WAD CN in 0.1 mg/L and for CNL is established in 0.022 mg/L. ...
Article
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Cyanide ion (CN-) is widely used in different industrial operations, such as jewelry, steel manufacture, gold and silver extraction and electroplating. However, industrial emissions containing the CN- ion have to be treated to comply with environmental regulations. This research aimed to degrade free cyanide (CNL) present in the tailing of a metallurgical plant that processes gold-bearing ores and uses sodium cyanide (NaCN) as a leaching reagent. Sodium metabisulfite (Na2S2O5) and sodium metabisulfite with hydrogen peroxide (Na2S2O5 + H2O2) were used as oxidizing agents. To evaluate the effect of the factors, we used a factorial design with three independent variables: stirring time, reagent excess percentage, type of reagent and a dependent variable: CNL degradation (mg/L). According to the analysis of variance (ANPVA), the variables influenced significantly CNL degradation, being the most relevant the reagent excess percentage and according to the results, the maximum CNL degradation was 97.67% when 400% of Na2S2P5 was added with 4 hours of stirring.
... The cyanide ion (CN -) is a ligand, with strong complexing ability that allows it to bond with almost all heavy metals in abiotic and biotic systems. Cyanide is found in a wide variety of life forms, and has applications in several industries including cassava starch making, electroplating, steel tempering, nuclear processing, photography, pharmaceuticals, pesticides, fumigants, petrochemicals, resins production, refining, coal and metal mining, processing and finishing industries (Akcil, 2003;Potivichayanon and Kitleartpornpairoat, 2010;Luque-Almagro et al., 2016;Kumar et al., 2017). Though cyanide plays a valuable role in several industries, mineral extraction industries account for the highest volume, as it makes use of cyanide in the extraction of gold and silver from large reserves of low-grade ores (Huiatt, 1984;Akcil, 2003;Kuyucak and Akcil, 2013). ...
... Cyanide is found in a wide variety of life forms, and has applications in several industries including cassava starch making, electroplating, steel tempering, nuclear processing, photography, pharmaceuticals, pesticides, fumigants, petrochemicals, resins production, refining, coal and metal mining, processing and finishing industries (Akcil, 2003;Potivichayanon and Kitleartpornpairoat, 2010;Luque-Almagro et al., 2016;Kumar et al., 2017). Though cyanide plays a valuable role in several industries, mineral extraction industries account for the highest volume, as it makes use of cyanide in the extraction of gold and silver from large reserves of low-grade ores (Huiatt, 1984;Akcil, 2003;Kuyucak and Akcil, 2013). ...
... Conventional cyanide detoxification techniques predominantly involve separation or destruction, and may be grouped under physical, adsorption, complexation and/or oxidation methods, with the commonly used ones being the sulfur oxide/air, hydrogen peroxide and alkaline chlorination process (Akcil, 2003;Kitis et al., 2005;Kuyucak and Akcil, 2013). Degradation pathways are sensitive to the cyanide concentration and the physicochemical conditions such as oxygen concentration and pH of the media (Ebbs, 2004;Baxter and Cummings 2006;Kumar et al., 2017). ...
Article
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Cyanide, a carbon-nitrogen radical, is a major building block in many industries including pharmaceuticals, petrochemical and gold processing. In the gold extraction industry, cyanide has been the universal lixiviant for over a century due to better understood process chemistry, among others. Industries that discharge cyanide-laden effluents are mandated to keep concentrations below 0.2 mg/L to prevent death by cyanide-intoxification, which occurs when cyanide binds to key iron-containing enzymes and prevent them from supplying oxygen-containing blood to the tissues. Techniques used to attenuate cyanide in wastewater can broadly be grouped into chemical, physical and biological methods. In recent times, attention has been placed on biotechnological methods, which make use of cyanotrophic microorganisms to clean up cyanide-contaminated environments. This paper reports on studies set out to assess the ability of Phanerochaete chrysosporium to degrade cyanide under different conditions including changes in cyanide concentration, culture mass, time, closed system and open system. At the end of 24-hour contact in an open agitated system with initial pH of 11.5, a control experiment using 100 mg/L cyanide revealed a natural attenuation of 15% with pH decreasing to 9.88, while the best myco-detoxification of 85% was achieved by contacting 100 mg/L cyanide with 0.5 g culture mass, translating into degradation capacity of 17.2 mg/g (milligram of cyanide per gram of culture) with pH reducing to 8.4 in 24 hours. The degradation could be based on a number of mechanisms including hydrolysis to HCN, oxidation to cyanyl radical and cyanate due to natural attenuation through atmospheric contact, and secretion of organic acid, oxidative enzymes, and hydrogen peroxide by the fungus. Keywords: Cyanotrophic Organism, Myco-Detoxification, Cyanide-Laden Effluents, pH
... [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. ...
Article
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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.
... Although gold leaching can be performed using solutions with relatively low cyanide concentrations (100-500 mg L −1 ) [3,4], most mining companies use sodium cyanide in excess. The problem is that leaching is not a selective process and cyanide can react with different metals existing in the ores (e.g., mercury, zinc, copper, iron, and nickel) forming various complexes. ...
... According to the path for cyanide mineralization, cyanate formation and its subsequent decomposition is a consequence of a series of reactions, outlined in Eqs. (2)(3)(4)(5)(6)(7). One can see (Fig. 4) that the total cyanide concentration decreases with time, reaching X CN − of 0.999 (= 1 mg L −1 ) after 210 min of reaction. ...
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This study examines the electro-oxidation (EO) of cyanide originating from an industrial plant´s gold leaching effluent. Experiments were carried out in a laboratory-scale batch cell reactor. Monopolar configuration of electrodes consisting of graphite (anode) and aluminum (cathode) was employed, operating in galvanostatic mode. Response Surface Methodology (RSM), based on a Box–Behnken experimental Design (BBD), was used to optimize the EO operational conditions. Three independent process variables were considered: initial cyanide concentration ([CN⁻]0 = 1000–2000 mg L⁻¹), current density (J =7–107 mA cm⁻²), and stirring velocity (η = 250–750 rpm). The cyanide conversion XCN-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\left( {X_{{{\text{CN}}^{ - } }} } \right)$$\end{document}, Chemical Oxygen Demand (COD) removal percentage (%RCOD), and specific Energy Consumption per unit mass of removed cyanide (EC) were analyzed as response variables. Multi-objective optimization let to establish the most effective EO conditions ([CN⁻]0 = 1000 mg L⁻¹, J = 100 mA cm⁻² and η = 750 rpm). The experimental data (XCN-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$X_{{{\text{CN}}^{ - } }}$$\end{document}, %RCOD, and EC) were fitted to second-order polynomial models with adjusted correlation coefficients (Radj2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$R_{\text{adj}}^{2}$$\end{document}) of ca. 98, 99 and 87%, respectively. The kinetic analysis, performed at optimal EO operational conditions, allowed determination of time required to meet Colombian permissible discharge limits. The predictive capacity of kinetic expressions was verified against experimental data obtained for gold leaching effluent. Total cyanide removal and 96% of COD reduction were obtained, requiring EC of 71.33 kWh kg⁻¹ and 180 min. The BOD5 (biological oxygen demand)/COD ratio increased from 4.52 × 10⁻⁴ to 0.5573, confirming effluent biodegradability after EO treatment. Graphic Abstract The variation of cyanide (CN⁻), cyanate (CNO⁻) and ammonium (NH4⁺) ions concentrations vs. time at alkaline conditions. EO operational conditions: [CN⁻]0 = 1000 mg/L, J = 100 mA/cm² , η = 750 rpm, [NaCl] = 0.15 M and pH 11.1.
... Liquid waste containing cyanide and derivatives is generated at a large scale by different industrial activities, such as mining and metal processing, electroplating, coal coking, and nitrile polymer synthesis [5,8,[13][14][15][16][17]. These cyanide-containing wastes often present heavy metals and metalloids, increasing their toxicity and becoming hazardous effluents that are difficult to remove from the environment due to the very high stability of the metal-cyanide complexes. ...
... However, these methods are expensive, require special equipment and maintenance, and are usually inappropriate to degrade metal-cyanide complexes. Therefore, cyanide biodegradation may be an interesting alternative to these treatments [5,[13][14][15][16][17]19]. In this context, the strain P. pseudoalcaligenes CECT5344 was able to grow in a batch reactor at pH 9.5 in the presence of sodium cyanide as the sole nitrogen source, removing cyanide at an optimal rate of 2.3 mg/L × A 600 × h [10]. ...
Article
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The alkaliphilic bacterium Pseudomonas pseudoalcaligenes CECT5344 can grow with cyanate, cyanide, or cyanide-containing industrial residues as the sole nitrogen source, but the assimilation of cyanide and cyanate takes place through independent pathways. Therefore, cyanide degradation involves a chemical reaction between cyanide and oxaloacetate to form a nitrile that is hydrolyzed to ammonium by the nitrilase NitC, whereas cyanate assimilation requires a cyanase that catalyzes cyanate decomposition to ammonium and carbon dioxide. The P. pseudoalcaligenes CECT5344 cynFABDS gene cluster codes for the putative transcriptional regulator CynF, the ABC-type cyanate transporter CynABD, and the cyanase CynS. In this study, transcriptional analysis revealed that the structural cynABDS genes constitute a single transcriptional unit, which was induced by cyanate and repressed by ammonium. Mutational characterization of the cyn genes indicated that CynF was essential for cynABDS gene expression and that nitrate/nitrite transporters may be involved in cyanate uptake, in addition to the CynABD transport system. Biodegradation of hazardous jewelry wastewater containing high amounts of cyanide and metals was achieved in a batch reactor operating at an alkaline pH after chemical treatment with hydrogen peroxide to oxidize cyanide to cyanate.
... 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). ...
Article
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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.
... 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]. ...
Article
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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.
... Pseudomonas pseudoalcaligenes CECT 5344 was isolated from sludge of Guadalquivir River, and it is able to use cyanide as the only source of nitrogen [4]. Cyanide is an extremely toxic compound used in the synthesis of organic compounds such as nitriles, plastics, paints, adhesives, cosmetics, etc., while mining activities and the jewellery industry are the main source of cyanurated wastes [5][6][7][8]. This strain tolerates an unusually high concentration of cyanide (up to 30 mM) [4], but it requires a suitable carbon source for growing. ...
Article
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Pseudomonas pseudoalcaligenes CECT 5344 is a bacterium able to assimilate cyanide as a nitrogen source at alkaline pH. Genome sequencing of this strain allowed the detection of genes related to the utilization of furfurals as a carbon and energy source. Furfural and 5-(hydroxymethyl) furfural (HMF) are byproducts of sugars production during the hydrolysis of lignocellulosic biomass. Since they inhibit the yeast fermentation to obtain bioethanol from sugars, the biodegradation of these compounds has attracted certain scientific interest. P. pseudoalcaligenes was able to use furfuryl alcohol, furfural and furoic acid as carbon sources, but after a lag period of several days. Once adapted, the evolved strain (R1D) did not show any more prolonged lag phases. The transcriptomic analysis (RNA-seq) of R1D revealed a non-conservative punctual mutation (L261R) in BN5_2307, a member of the AraC family of activators, modifying the charge of the HTH region of the protein. The inactivation of the mutated gene in the evolved strain by double recombination reverted to the original phenotype. Although the bacterium did not assimilate HMF, it transformed it into value-added building blocks for the chemical industry. These results could be used to improve the production of cost-effective second-generation biofuels from agricultural wastes.
... Sulphate ions can be introduced into fresh CPB in various ways: (i) the oxidation of the sulphide minerals (e.g. pyrite) in the tailings; (ii) the use of sulfur dioxide/air for the removal of cyanides in some gold mines which generates sulphate ions (Akcil, 2003;Li and Fall, 2016); (iii) from cement (as gypsum or anhydrite are added to the clinker to deter the cement from flash setting); and (iv) from the mineral processing water (Wang et al., 2014). ...
Article
The rheological properties of cemented paste backfill (CPB) are important properties, which determine its flow ability or ease of transport in pipelines to fill underground voids. However, no research has been conducted to understand the effects of the sulphate content in CPB on its rheological properties, even though sulphate ions are usually found in CPB mixtures. Evaluating and understanding the effect of sulphate on the rheological properties of fresh CPB are important in carrying out backfilling with cemented paste. Therefore, the objective of this paper is to experimentally study the effects of the initial sulphate content on the rheological properties of CPB. Samples made with two different types of tailings (silica tailings and polymetallic tailings) with an initial sulphate content of 0, 5000, 15,000 and 25,000 ppm are prepared and cured at room temperature (20 °C). Their yield stress and apparent viscosity at different curing times of 0, 0.15, 1, 2, and 4 h are determined and then analyzed. Additional tests or measurements are carried out to further investigate the experimental results, which include monitoring through electrical conductivity (EC), measuring the pH and zeta potential as well as conducing thermal and XRD analyses. The results show that the initial sulphate concentration can significantly affect the rheological properties of CPB. The initial sulphate concentration can cause different microstructural or chemical changes in fresh CPB, such as inhibition of the cement hydration process or affecting the repulsive forces between particles. These changes significantly affect the yield stress and apparent viscosity of CPB. More specifically, the yield stress shows a trend of decline as the initial sulphate concentration is increased, while the apparent viscosity shows the opposite trend. The findings of this research demonstrate the significance of sulphate and its effects on the rheological behaviors or properties of CPB and can significantly contribute to the optimization of the transport of CPB through pipelines.
... 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. ...
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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
... The organs which are mainly affected by cyanide poisoning are the central nervous system and heart (8,9). Although conventional methods for treatments of cyanide wastewaters such as chemical and physical treatments efficiently can decrease the toxicity from cyanide, they involve high cost of construction and engineering, longterm storage, and require reagents that can be harmfulto the environment (10,11). Undertaking biological processes for cyanide degradation is the best alternatives and approaches to overcome these problems (12,13). ...
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Secretory production of recombinant proteins has many benefits such as solubility and ease of purification. The aim of this study was to find suitable signal peptides for secretory production of nitriles in Bacillus subtilis. The signal peptides were chosen from Signalpeptide web server. SignalP server was used to define probability of suitable signal peptides and their secretion pathways. Physico-chemical properties and solubility were predicted by ProtParam and Protein-sol, respectively. Bioinformatics analysis identified SUBF_BACSU, GUB_BACSU, SACB_BACAM and AMY_BACAM that linked to nitriles are appropriate signal peptides. Their fusion proteins could be stable, soluble and non-antigenic proteins that might have suitable secondary and tertiary structures. The recommended signal peptides by this study are appropriate for rational designing of secretory soluble nitriles. Thus, the results of present work can be useful for future experimental production of secretory and soluble nitriles.
... The organs which are mainly affected by cyanide poisoning are the central nervous system and heart (8,9). Although conventional methods for treatments of cyanide wastewaters such as chemical and physical treatments efficiently can decrease the toxicity from cyanide, they involve high cost of construction and engineering, longterm storage, and require reagents that can be harmfulto the environment (10,11). Undertaking biological processes for cyanide degradation is the best alternatives and approaches to overcome these problems (12,13). ...
Article
Secretory production of recombinant proteins has many benefits such as solubility and ease of purification. The aim of this study was to find suitable signal peptides for secretory production of nitriles in Bacillus subtilis. The signal peptides were chosen from Signalpeptide web server. SignalP server was used to define probability of suitable signal peptides and their secretion pathways. Physico-chemical properties and solubility were predicted by ProtParam and Protein-sol, respectively. Bioinformatics analysis identified SUBF_BACSU, GUB_BACSU, SACB_BACAM and AMY_BACAM that linked to nitriles are appropriate signal peptides. Their fusion proteins could be stable, soluble and non-antigenic proteins that might have suitable secondary and tertiary structures. The recommended signal peptides by this study are appropriate for rational designing of secretory soluble nitriles. Thus, the results of present work can be useful for future experimental production of secretory and soluble nitriles.
... This is due to the low light absorption coefficient of thiocyanates and its stability. A similar observation has been reported for various oxidizing agents (e.g., Inco SO 2 /air process [10] hydrogen peroxide [30]), typically leading to poor degradation efficiencies and/or kinetics of thiocyanates compared to cyanides (for which conversion proceeds faster though the hydrolysis to cyanates). ...
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We have explored the simultaneous degradation of cyanides and thiocyanate present in wastewaters from a cokemaking factory using photoassisted methods under varied illumination conditions (from simulated solar light to UV light). Overall, the photochemical degradation of cyanides was more efficient than that of thiocyanates, regardless of the illumination conditions, the effect being more pronounced in the absence of a photocatalyst. This is due to their different degradation mechanism that in the case of thiocyanates is dominated by fast recombination reactions and/or charge transfer reactions to electron scavengers. In all cases, cyanate, ammonia, nitrates, and nitrites were formed at different amounts depending on the illumination conditions. The conversion yield under simulated solar light was almost complete for cyanides and quite high for thiocyanates after 6 h of illumination. Regarding toxicity, photochemical oxidation at 254 nm and under simulated solar light decreased significantly the toxicity of the pristine wastewater, showing a correlation with the intensity of the irradiation source. This indicate that simulated light can be effectively used to reduce the toxicity of industrial effluents, opening an interesting perspective for optimizing cyanide detoxification systems based on natural light.
... This is similar to this study, the F-SBR system was operated and added with 10% (v/v) of buffer medium as nutrient sources in every 10 days under the optimal conditions which the cost was estimated at 3.15 TH Baht or 0.11 US Dollar per 1 m 3 of wastewater containing cyanide and organic matter with high initial concentration of 208.93 mg/L and 16,266.67 mg/L, respectively, whereas the traditional chemical treatments such as alkaline chlorination or hydrogen peroxide could be more expensive to operate due to high reagent usage and also undesirable toxic byproducts requiring further treatment (Akcil 2003;Parga et al. 2003;Dash et al. 2009aDash et al. , 2009bBotz et al. 2016;Pueyo et al. 2016); for example, if the usage of chlorine for alkaline chlorination process is in the range 3.0-8.0 g Cl 2 per gram of cyanide oxidized under pH 10.5, it will generate toxic byproduct compounds or excess chlorine in the effluent, and if that of hydrogen peroxide process is 50 mg/L H 2 O 2 for oxidizing 4.1 mg/L of initial cyanide under pH 10.9, the excess dosages of hydrogen peroxide are required for slurry treatment (Botz et al. 2016). ...
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The fixed-film sequencing batch reactor, or F-SBR, was developed to treat high organic compound levels and toxic cyanide concentrations in cassava wastewater. The performance of the F-SBR was compared with that of a conventional sequencing batch reactor, or SBR, that was operated with organic compound contents of 16,266.67–26,666 mg COD/L and 132.92–252.66 mg CN−/L. The cyanide and chemical oxygen demand removal efficiencies of the conventional SBR system were 42.61% and 36.83%, respectively, while those of the F-SBR were 77.95% and 74.43%, respectively; the cyanide removal efficiency reached 95.45% when the hydraulic retention time was increased to 5 days, and the F-SBR was very effective for the complete removal of cyanide when the hydraulic retention time was increased to 10 days. This effectiveness was similar to the effectiveness of chemical oxygen demand removal, which reached 40–78% efficiency with the F-SBR system. These results showed that the immobilization of cyanide-degrading bacteria such as Agrobacterium tumefaciens SUTS 1 and Pseudomonas monteilii SUTS 2 carried out with a polypropylene ring in a fixed-film aerobic system enhanced the performance of the reactor and can be successfully applied for cyanide and chemical oxygen demand removal from industrial wastewater with high cyanide and chemical oxygen demand concentrations. This study may provide a promising alternative technique that reduces economic operation costs in solving wastewater contamination problems.
... Due to the strong toxicity of to human and environmental health, the removal of thiocyanate from contaminated ecosystems is of great importance. There are various methods to treat thiocyanate-contaminated water, such as adsorption, ion exchange, solvent extraction, oxidation and biodegradation [16]. Chemical methods will, however, produce hazardous waste and create secondary pollution [17]. ...
Article
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Large-scale production of thiocyanate (SCN⁻) for industrial purposes has led to widespread environmental pollution by this compound. Thiocyanate (SCN⁻) is toxic for humans and recalcitrant to biological oxygenation and hydrolysis. Phytoremediation is an effective technique for disposal of SCN⁻ because thiocyanate (SCN⁻) can be assimilated by many plants from contaminated water and soil. In this study, we demonstrate that Thermosynechococcus elongatus BP-1 glutathione S-transferase (TeGST) is a good candidate gene for enhancing phytoremediation of thiocyanate (SCN⁻) in the plant. Our study demonstrated that Arabidopsis thaliana introduced with the glutathione S-transferase (GST) gene were able to germinate and grow in a medium containing 5 mmol L⁻¹ thiocyanate (SCN⁻), which was lethal for wild-type plants. Moreover, the GST can confer the capacity of plants to remove more thiocyanate in vivo. Our results suggest that grafting the T. elongatus BP-1 glutathione S-transferase (TeGST) gene into plants is a potentially effective strategy to enhance phytoremediation of environmental thiocyanates. To our knowledge, this is the first study on the degradation of guanidine isothiocyanate by transgenic plants.
... 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. ...
... Conventional chemical methods used to treat cyanide wastewater have drawbacks, such as high costs, the need for special infrastructure, and the use of chemical reagents that are themselves environmental hazards (Akcil, 2003). Considering these limitations, biological methods for cyanide degradation represent attractive alternatives (Dash et al., 2009;Gupta et al., 2010). ...
Article
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Despite its high toxicity, cyanide is used in several industrial processes, and as a result, large volumes of cyanide wastewater need to be treated prior to discharge. Enzymatic degradation of industrial cyanide wastewater by cyanide dihydratase, which is capable of converting cyanide to ammonia and formate, is an attractive alternative to conventional chemical methods of cyanide decontamination. However, the main impediment to the use of this enzyme for the biodegradation of cyanide is the intolerance to the alkaline pH at which cyanide waste is kept and its low thermoresistance. In the present study, the catalytic properties of whole E. coli cells overexpressing a cyanide dihydratase gene from B. pumilus were compared to those of the purified enzyme under conditions similar to those found in industrial cyanide wastewater. In addition, the capacity of whole cells to degrade free cyanide in contaminated wastewater resulting from the gold mining process was also determined. The characteristics of intracellular enzyme, relative to purified enzyme, included increased thermostability, as well as greater tolerance to heavy metals and to a lesser extent pH. On the other hand, significant enzymatic degradation (70%) of free cyanide in the industrial sample was achieved only after dilution. Nevertheless, the increased thermostability observed for intracellular CynD suggest that whole cells of E. coli overexpressing CynD are suited for process that operate at elevated temperatures, a limitation observed for the purified enzyme.
... 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. ...
Article
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.
... 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]. ...
Article
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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.
... 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. ...
Article
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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
... 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). ...
Conference Paper
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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.
... 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). ...
Article
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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.
... 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. ...
Article
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
... 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. ...
Article
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. ...
Article
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. ...
Article
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. ...
Article
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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 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. ...
Conference Paper
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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.
... 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). ...
Article
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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.
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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.
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Biological treatment of waste waters is a sustainable alternative for waste treatment to existing treatment methods. Microbial metabolism effects pH, BOD, COD, DO and concentration of suspended solids present in slaughter house waste water. Rhodobacter sp. GSKRLMBKU-02 from paper mill waste water was used in the present study to remediate slaughter house waste water. Treatment with this bacterium caused a significant decrease in some of the parameters tested for waste water. Remediation of slaughter house waste water of Warangal by Rhodobacter sp. GSKRLMBKU-02 showed a 28% decrease in DO, 52% decrease in BOD, 76% decrease in COD and organic matter decreased to the extent of 55%. Further a reduction in the levels of Chloride (68%), sulphates (69%) and bicarbonates (34%) were also noticed due to the growth of this bacterium.
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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.
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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.
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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.
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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.
Article
Cyanide is among the most toxic chemicals widely employed in the cyanidation process to leach precious minerals, such as gold and silver, by the minerals processing companies worldwide. This present article reviews the determination and detoxification of cyanide found in gold mine tailings. Most of the cyanide remains in the solution or the slurries after the cyanidation process. The cyanide species in the gold tailings are classified as free cyanide, weak acid dissociation, and metallocyanide complexes. Several methods, such as colorimetric, titrimetric, and electrochemical, have been developed to determine cyanide concentrations in gold mine effluents. Application of physical, natural, biological, and chemical methods to detoxify cyanide to a permissible limit (50 mg L ⁻¹ ) can be achieved when the chemical compositions of cyanide (type of species) present in the tailings are known. The levels of cyanide concentration determine the impact it will have on the environment.
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Biotechnology relevant to gold exploration, mining, recovery, and waste disposal is illustrated with respect to microbiological aspects of gold mineralization, Biooxidation of refractory sulfide ores and concentrates, cyanide-free gold dissolution, and biodegradation of cyanide containing effluents. Current industrial status of technological innovations in the bioreactor processing and heap bioleaching of refractory sulfide ores and concentrates are discussed. Biodetoxification and degradation of cyanides in waste tailings and waters are critically analyzed with examples from industrial practice. Prospects for direct biodissolution of gold are brought out. Recovery of gold from spent leach cyanide solutions and electronics wastes is examined. Bright future prospects for Biotechnology in gold exploration, mining, extraction, and waste disposal are emphasized.
Article
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.
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As one of the inorganic pollutants with the highest concentration in the waste water of gold tailings using biohydrometallurgy, thiocyanate (SCN⁻) was effectively degraded in this research adopting a two-stage activated sludge biological treatment, and the corresponding degradation pathway and microbial community characteristics in this process were also studied. The results showed that SCN⁻ at 1818.00 mg L⁻¹ in the influent decreased to 0.68 mg L⁻¹ after flowing through the two-stage activated sludge units. Raman spectroscopy was used to study the changes of relevant functional groups, finding that SCN⁻ was degraded in the COS pathway. Based on 16S rRNA high-throughput sequencing technology, the microbial diversity in this system was analyzed, and the results indicated that Thiobacillus played a major role in degrading SCN⁻, of which the abundance in these two activated sludge units was 32.05% and 20.37%, respectively. The results further revealed the biological removal mechanism of SCN⁻ in gold mine tailings wastewater.
Chapter
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.
Article
The ultraviolet light activation of persulfate (PS) was evaluated for the degradation of cobalt cyanocomplexes, which are considered as some of the most recalcitrant compounds present in mining wastewater. The influence of the solution pH (11 and 13), initial concentration of PS (0.1, 0.3, 0.5, 0.7 and 0.9 g/L), dissolved oxygen and initial concentration of contaminant were evaluated. Photolysis results showed that CoCN63- is photosensitive to UVC radiation, while the activation of PS by alkaline pH does not contribute to the degradation of the cyanocomplex. There was no presence of CN- at both solution pH values using UVC/PS. But at pH 13, the degradation of cobalt cyanocomplexes and the pseudo-first-order rate constant increased. This was attributed to the effective conversion of SO4•- to HO• and to the increase in the oxidative photolysis of PS at high pH. Additional tests demonstrated better performance of UVC/PS in the absence of oxygen which may be caused by the quenching effect of O2 to the higher energy excited state of the cyanocomplex that must be reached to initiate degradation reactions. Increasing the initial concentration of CoCN63- will increase the amount of Co removed but it represents the higher specific energy consumption.
Article
Cyanide is a known toxic chemical compound that has an adverse effect on living organisms. Nonetheless, it is one of the active reagents in industries such as mining, pharmaceutical, cosmetics, and food processing companies worldwide. The beneficiation of gold and other precious metals from ore generates great amount of cyanide-bearing contaminants, which is released into the environment. The abundance of cyanide contaminants from these industries have created public health concern since the inception of metal extraction from ore. There are strict regulations on the production, transportation, utilization, and disposal of cyanide-bearing contaminants worldwide. The conventional treatment of cyanide waste is either chemical or physical process. The use of these treatment processes has certain pitfalls like operational challenges, an increase in capital cost, and generation of secondary waste. A number of microorganisms have the potential to utilize cyanide as nitrogen and carbon source and transform it into ammonia and carbon dioxide. Biodetoxification might be efficiently, economically and environmentally safe to detoxify cyanide in contaminants and attractive alternative to conventional detoxification method like chemical or physical. This paper reviews the principles and methods of biodetoxification of cyanide contaminants found in the ecosystem.
Article
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.
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Development of receptors that can detect as well as treat cyanide in aqueous sample is an indispensable job for environmental protection. Herein, we present bulk-solvent free and instant green synthesis of a series of turn-on fluorimetric probes that can specifically detect the deadly poison cyanide among various anions and metal ions tested in water. Selective recognition of cyanide by the mechanosynthesized compounds is even observable by the naked eyes, which remained unaffected in presence of various challenging species. NMR spectroscopic investigation supports chemodosimetric sensing of cyanide by the receptors. Remarkable 55-83 fold fluorescence enhancement by the probes could reach limit of detection (LOD) in the range 8-26 ppb, well below the permissible limit of cyanide in drinking water. Being minuscule soluble in water, cyanide treatment studies with the ionophores showed greater than 99 % reduction in free cyanide concentration after three consecutive batches of operation. Furthermore, the compounds can be used as sensitive probes for the estimation of cyanide in human blood serum at physiological condition. Overall, results presented in this article would certainly find great use in the area of cyanide pollution with regard to simultaneous sensing and treatment of free cyanide, which is heretofore unprecedented.
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Based on the review of different research studies, we could assess that, due to their unique biological features, microbes, specifically bacteria, could be used to repair damaged soils with heavy metal and toxic compound contents. Furthermore, these microorganisms are metabolically capable to oxidize cyanide and its by-products to generate less-toxic compounds at the end of the process. This research proposal seeks to improve conventional mine closure designs, thus counteracting their negative short-term, medium-term, and long-term after-effects to the environment. The proposed technique as a solution, therefore, is microbial remediation, using pseudomonas fluorescens bacteria to oxidize this compound to non-toxic components. It will ensure operational continuity for the deposits and, in turn, the sustainability of the entire mining industry.
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Red Mud (RM) is a waste material of alumina industry. Herein, RM has been treated and its surface has been enhanced with acid activation, named as (RMA). The RM and RMA have been characterized using various techniques such as, wet chemical analysis, TGA-DTA, BET surface area, X-ray diffraction, SEM and particle size analysis. The enhanced surface area of RMA as compared to RM has been proved from various characterization techniques that is supported by using adsorption studies for sorption of Cyanide. Thus, the environmentally hazardous RM has been utilized for the removal of other high-risk persistent materials like Cyanide.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
Article
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.
Article
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.
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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.
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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.
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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.
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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.
Article
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
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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.
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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.
Article
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.
Article
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.
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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]+.
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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.
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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.
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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.
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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.
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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.
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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.
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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.
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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.