Article

First application of cyanidation process in Turkish gold mining and its environmental impacts

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Abstract

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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... Several destruction or recovery processes are well proven and can produce treated solutions or slurries with low levels of cyanide and its related compounds (Botz et al., 1995;Botz, 2001;McNulty, 2001;Akcil, 2002Akcil, , 2003aBotz and Mudder, 2002;. Cyanide treatment processes may be classified as a destruction-based process versus the physical processes of cyanide recovery and activated carbon sorption. ...
... The ore contains less than 0.02% S 2À in the form of pyrite and has high alkalinity value. As sulphide minerals are almost absent (less than 0.15%), there is no risk of acid mine drainage for the ore or waste material (Akcil, 2002(Akcil, , 2003b. Ovacik ore is significantly low in heavy metals contents compared with other typical ores. ...
... Table 1 shows the physicochemical characteristics of the tested tailings slurry samples. Average total cyanide and heavy metal concentrations measured during one-year testing period (June 2001-May 2002) were obtained from Akcil (2002). The gold-silver deposit consists of two economically mineable quartz veins epithermally formed in andesite. ...
Article
The main objective of this work was to determine the effectiveness and kinetics of hydrogen peroxide in destroying cyanide in the tailings slurry from a gold mine with low sulphide and heavy metal content. The impacts of catalyst (Cu) and hydrogen peroxide concentrations, temperature and pH on the extent and rate of weak acid dissociable (WAD) cyanide destruction were investigated. Experiments were conducted using the variable-dose completely mixed batch reactor bottle-point method. Both the rate and extent of CNWAD destruction generally increased with increasing peroxide doses for either absence or presence of Cu catalyst. Catalyst addition was very effective in terms of not only enhancing the cyanide destruction rate but also significantly reducing the required peroxide dosages to achieve CNWAD concentrations of about 1 mg/l, independent of the temperatures tested (10, 20 and 30 °C). The initial cyanide destruction rates increased between 1.2 and 3 folds with the addition of 30 mg/l of Cu. Kinetic experiments showed that in most cases little CNWAD destruction occurred after a reaction time of 2–4 h. The impact of slurry pH on cyanide destruction varied depending upon the dosages of Cu catalyst. Relatively lower peroxide dose/CNWAD ratios required to achieve less than 1 mg/l of CNWAD may be due to lower heavy metals and sulphide content of the ore, resulting in lower peroxide requirement for metal bound cyanides. During cyanide destruction, nitrate was initially formed as a by-product and then possibly converted to other some volatile nitrogen-containing species, as supported by the mass balance calculations.
... Although the use of cyanide is mostly perceived by the general public as being associated with the mining and metallurgical processes, only about 13% of world cyanide production is consumed by these industries with the remaining percentage being used elsewhere (WHO ECEH, 2000;Mudder and Botz, 2001;Mudder et al., 2001a,b;Akcil, 2002Akcil, , 2006Akcil, , 2010Mudder and Botz, 2004). Cyanide is an essential raw material in producing synthetic silk, synthetic rubber and nylon, paints, medical and pharmaceutical products, agricultural products, coloured photographic and television films, and cosmetics (Kirk-Othmer, 2002). ...
... While the allowable cyanide concentration in potable water is established at 0.2 mg/L by the United States and Canadian Environmental Protection Agencies (USA/Canada EPA), the World Health organisation (WHO) guidelines consider 0.07 mg/L CN safe for both acute and long-term exposure in drinking water. The European Union (EU) specifies 0.05 mg total CN per litre (Turkmen, 1998;WHO ECEH, 2000;Akcil, 2002). Usually, standards set for both fresh and marine aquatic life are lower than the standards set for the drinking water quality. ...
... ICMI promotes the adoption of the Code, evaluates its implementation, and manages the certification process. The participation to the Code that exclusively focuses on the safe management of cyanide at gold mines is voluntary (Akcil, 2002(Akcil, , 2010. Since the establishment of ICMI, the Cyanide Code has experienced dramatic growth. ...
... It is well known that this metal had also a religious and even mythical significance due to its remarkable stability. Ancients used gold to produce jewelry, sculptures, vessels, coinage as well as decoration for monuments and buildings, among others (Akcil 2002, Akcil 2003. Gold was used as commodity money during centuries and its accumulation was correlated to "social power" and even triggered wars. ...
... Cyanidation, which was developed in Scotland in 1887 (Habashi 1987), is widely used in the USA, Canada, Turkey as well as in several developing countries (Akcil 2002, Eisler and Wiemeyer 2004, Veiga et al. 2014. It consists in the dissolution of gold from the ore in an alkaline dilute cyanide solution. ...
Article
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Cyanidation is widely used by several gold mining companies worldwide. Since its wastewaters contain cyanide, appropriate treatments must be applied to remove this pollutant. Combinations of ozone (O3), hydrogen peroxide (H2O2) and activated carbon (AC) can be used for this purpose. In this work, synthetic cyanide solutions ([CN¯]o = 15.37 mM) were treated using O3 and the combinations O3/H2O2, O3/AC and O3/H2O2/AC under alkaline conditions. O3 was produced from dry oxygen at a rate of 2.51 g O3/h([O3] gas-phase = 6.9x10–2 g/L). The concentration of cyanide (CN¯) and O3 consumption were measured and the performance of the treatments evaluated. The highest cyanide removal was reached at pH 11.0 for all cases and with 10 mg H2O2/mg O3 upon adding H2O2. In contrast, the addition of AC did not improve the cyanide removal in comparison with O3 alone. The best cyanide removal was achieved with the combination O3/H2O2 followed by the combination O3/H2O2/AC. Moreover, cyanidation effluents were treated using the combination O3/H2O2. In this case, almost a total removal of free cyanide was achieved after 3 min of treatment.
... Of the approximately 1.4 million tons of hydrogen cyanide produced annually worldwide, about 13% is used to produce cyanide reagents for gold processing. The remaining 87% is used in other industrial applications which include the production of plastics, adhesives, fire retardants, cosmetics, pharmaceuticals, food processing, and as an anticaking additive for table and road salts (Akcil 2002(Akcil , 2003(Akcil , 2006Botz, Mudder, and Akcil 2005;ECIC 2003;Mudder andBotz 2001a, 2004;Mudder, Botz, and Smith 2001b;USEPA 1981USEPA , 1987USEPA , 1988USFWS 1991;www.cyanidecode.org 2009;www.cyantists.com ...
... Even if different environmental regulations and codes are in force in countries where cyanide is primarily used in mining, cyanide remains an indispensable chemical in these processes until there is a commercial, economical, and environmental alternative (Akcil 2002). ...
Article
The International Cyanide Management Code was developed to improve the management of cyanide at gold mines. Spills and other incidents involving cyanide solutions at gold mines such as the January 2000 incident at a Romanian gold mine (Baia Mare) demonstrated to the gold mining industry, governments, and the public that better management of cyanide was needed, particularly at operations with limited experience or in countries lacking adequate regulatory programs. In 2001, the Code was underwritten by a group of gold companies and cyanide producers from around the world. The Gold Institute was instrumental in organizing this financial and technical support and provided the administrative and logistical support necessary to successfully complete the project. This effort represents one of practical action that an industry has worked with mining companies and producers including UNEP, World Banks, and Environmental Groups to develop an international voluntary industry Code of Practice.The regional and national environmental management criteria of cyanide are different in various countries. Thus, a common language should be applied as a global perspective which is provided by the Cyanide Code Management. In this review article, a general and brief introduction on Cyanide Code Management is presented.
... Introduction Environmental legislation focusing on wastewater disposal has become increasingly stringent on industries that utilise cyanide and/or cyanide-related compounds. The International Cyanide Management Code (ICMC) of the International Cyanide Management Institute (ICMI) (www.cyanide-code.org) which is associated with the approval of process certification for industries that utilise cyanide has enforced such industries to develop alternative waste management practices (Gibbons, 2005, Akcil, 2002. The mineral processing, photo finishing, metal plating, coal processing, synthetic fibre production and extraction of precious metals, that is, gold and silver, contribute significantly to cyanide contamination in the environment through wastewater (Acheampong et al., 2013, Akcil, 2006, Akcil, 2003. ...
... Cu, Zn, Ni, etc.) and precious metals (e.g. Au, Ag, etc.), thus forming cyanide-metal complexes which are classified as weak-acid dissociable and strong-acid dissociable cyanides (Akcil, 2002, Mudder et al., 2001. The presence of these metallocyanides and thiocyanate adds to the complexity of the solution matrix. ...
Article
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A mesophilic alkali-tolerant bacterial consortium belonging to the Bacillus genus was evaluated for its ability to biodegrade high free cyanide (CN-) concentration (up to 500 mg CN-/L), subsequent to the oxidation of the formed ammonium and nitrates in a continuous bioreactor system solely supplemented with whey waste. Furthermore, an optimisation study for successful cyanide biodegradation by this consortium was evaluated in batch bioreactors (BB) using response surface methodology (RSM). The input variables, that is, pH, temperature and whey-waste concentration, were optimised using a numerical optimisation technique where the optimum conditions were found to be: pH 9.88, temperature 33.60 °C and whey-waste concentration of 14.27 g/L, under which 206.53 mg CN-/L in 96 h can be biodegraded by the microbial species from an initial cyanide concentration of 500 mg CN-/L. Furthermore, using the optimised data, cyanide biodegradation in a continuous mode was evaluated in a dual-stage packed-bed bioreactor (PBB) connected in series to a pneumatic bioreactor system (PBS) used for simultaneous nitrification, including aerobic denitrification. The whey-supported Bacillus sp. culture was not inhibited by the free cyanide concentration of up to 500 mg CN-/L, with an overall degradation efficiency of ≥99% with subsequent nitrification and aerobic denitrification of the formed ammonium and nitrates over a period of 80 days. This is the first study to report free cyanide biodegradation at concentrations of up to 500 mg CN-/L in a continuous system using whey waste as a microbial feedstock. The results showed that the process has the potential for the bioremediation of cyanide containing wastewaters. The final publication is available at Springer via http://dx.doi.org/10.1007/s11356-015-4221-4.
... In many countries there are effluent limits for the water discharged after chemical treatment prior to being discharged into the environment (Akcil, 2002;Akcil et al., 2002). According to the statistical data, periodical cyanide concentrations in the treated effluent at the Ovacik Gold Mine do not exceed those required by the national regulations (CN WAD = 1ppm). ...
Conference Paper
Full-text available
... This is due to the fact that it undergoes natural oxidation converting the cyanide to CO 2 and N 2 . Based on this process, there are currently a number of commercially available processes, both chemical and biological, to treat cyanide solution effluents and decontaminate concentrates from cyanide leaching operations (Akcil, 2002(Akcil, , 2003Barriga-Ordonez et al., 2006;Dash et al., 2009;Fatma et al., 2009;Gupta and Mukherjee, 1990;Kitis et al., 2005;Ozel et al., 2010;Parga et al., 2003;Patil and Paknikar, 2000;Yeddou et al., 2010). Aside from this, waste effluents can be treated using physical methods such as carbon sorption and the use of membrane technology (Deveci et al., 2006;Gonen et al., 2004;Lien, 2008). ...
Article
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This research proposes a new conceptual process to economically extract platinum group metals (PGMs), and as a secondary aim, base metals (BMs) from a low-grade concentrate originating from typical PGM concentrator plants. Slurry made from the concentrate was coated onto granite pebbles and packed into a column, in which it was bioleached with a mixed culture of thermophiles and mesophiles at 65 °C. After 30 days the extractions achieved were 52% copper, 95% nickel and 85% cobalt. The residual concentrate material was subsequently subjected to a cyanide leach also in a packed column operating at a room temperature of 23 °C. After 21 days 20.3% Pt, 87% Pd and 46% Rh were extracted. Using these results and projected extractions over longer operating times, a conceptual flowsheet was proposed for a possible process route to recover PGM values circumventing the problematic smelter route for this material.
... Turkey has epithermal type gold deposits and it is not economically feasible to operate this type of ores without using cyanide in today's conditions. Therefore, gold has been extracted by cyanide (cyanidation) [2] [3]. However, over the past decades, with the rising awareness of environmental consciousness and growing fear because of its extremely toxic character, cyanide has become a matter of considerable debates in Turkey. ...
... Bioremediation of cyanide tailings is becoming more important than conventional treatment technologies since plants, bacteria, and fungi can use the contaminant as a source of nitrogen for their metabolic activities [47,48]. Some bacteria can also use it as a source of carbon and nitrogen without needing additional external sources for their survival [49]. ...
Article
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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.
... Studies of the cyanidation of precious metals (Au and Ag) in the presence of sulfide minerals have shown that heavy metals such as Cu, iron (Fe) and Zn significantly increase the consumptions of both cyanide and oxygen and have a strong impact on leaching kinetics. The leaching behavior of gold in these situations depends greatly on both the solubility of the sulfides and the oxygen concentration in the solution (Fink and Putnam, 1950; Habashi, 1967; Hedley and Tabachnick, 1968; Akcil, 2002; Dai and Jeffrey, 2006). It is postulated that sulfide ions have detrimental effects on gold and silver cyanidation kinetics (Senanayake, 2008). ...
Article
Full-text available
In this study, cyanidation experiments on massive sulfide sample was investigated. The grade of precious metals (Au and Ag) in the ore are 4.2 g/t and 311.9 g/t. Also, the average grade of other elements are As-1751.6, Sb-619.7, Zn-781.4, Cu-454.6, Pb-101.8, Hg-324.3, and Bi-0.6 (all assays are in g/t). The first objective of test work focused on the determination of conditions for extracting gold from the ore ground to −75 μm. Different influential parameters such as cyanide concentration, particle size fraction, pH and leaching time have been comprehensively investigated. The optimum parameters were -25μm for size fraction, 2000 mg/L for cyanide concentration, pH=11 and 24hrs cyanidation time. The results showed that highest gold and silver leaching efficiencies were 76.88% and 59.63% in optimum condition. In addition, roasting as a pretreatment in temperature of 700oC in 2 hrs was evaluated. Cyanidation test on the roasted ore in optimized conditions decreased the gold and silver leaching efficiencies reached from 76.88% and 59.63% to 85.97% and 67.57%, respectively. In addition, the antimony extraction increased from 23.73% to 43.10%.
... The main sources of cyanide in water and wastewater are gold and silver mining, iron and steel production, and the organic chemical industries. Therefore, effective removal of cyanide from such aqueous solutions is necessary in the treatment of discharged from these industries [3]. The current research focuses on finding a plausible explanation to understand the adsorption mechanism of cyanide on activated and magnetic activated carbons. ...
Article
This study utilizes computational chemistry analysis (molecular dynamics and ab initio simulations) in order to understand the nature of adsorption of cyanide from aqueous solution by activated carbon and to compare the adsorption mechanism between activated and magnetic activated carbons. In addition, real adsorption mechanism of cyanide was investigated by laboratory adsorption tests using apricot plain (AAC) and magnetic activated (AMAC) carbon. The morphology, structure and property of AAC and AMAC were determined by BET, XRD, XRF and magnetometer, respectively. The simulation results reveal that the adsorption mechanism of cyanide on AAC and AMAC is nearly similar. Modifying the graphite surface with magnetite to mimic magnetic activated carbon does not have any significant influence on cyanide adsorption. The experimental results also support this fact to some extent as the maximum monolayer adsorption capacities of AAC and AMAC are very close with each other, 61.56 and 59.71 mg/g, respectively. Although iron impregnation does not significantly affect the removal of cyanide, considering the magnetic property of AMAC which can be removed easily by a magnetic separator, AMAC may be better sorbet than AAC and commercial activated carbon.
... Potential companies have taken a leading role in recognizing areas of extraordinary mineral potential: gold, silver, copper, zinc, cobalt, nickel, and other minerals throughout Turkey. The exploration of gold during the last 15 years in Turkey which includes the first production of gold, have entered a fast progress in recent years (Akcil, 2002). Especially, two gold mines (Kisladag and Cukurdere), with 245 t and 131 t of gold, respectively, which are discovered at the end of 1990s, are placed in the first ranks of the world literature. ...
Article
Bioleaching/biooxidation processes have been commercially applied for the recovery of copper, gold and uranium for two decades. Concerning these processes by mesophiles and thermophiles, academic and commercial applications have been extensively increasing in laboratory, pilot, full scale operations. Several bacterial species are used in many commercial operations in South America, Australia, South Africa, India, China. In near future Turkish copper and gold mines will probably use these processes as commercial applications due to the economical and environmental reasons. Therefore, the close relationship between biooxidation and cyani-dation with mineralogical composition is important for the commercial selection of these processes. In addition to lab tests, full-scale feasibility studies being performed to determine the impacts of climate and environmental factors for potential mining areas will also be completed in the near future. This paper presents an investigation of the potential bioleaching developments in Turkey.
... The Inco SO 2 /AIR process was selected for Ovacik because of its wide application for slurry treatment and advantages over other methods (Akcil, 2001(Akcil, , 2002(Akcil, , 2003cSmith and Mudder, 1991;Mudder, 2001;Mudder et al., 2001;Mudder, 1999;Botz, 2001). The process has predominantly been applied to the mining industry and mostly to the treatment of leach tailings slurries. ...
Article
The Ovacik Gold Mine is the first gold mine using the cyanide leaching method in Turkey and has been operating since early June, 2001. The process plant comprises a conventional carbon-in-pulp (CIP) process with a treatment capacity of 300,000tpy ore. Sodium cyanide consumption is approximately 0.5kg/t ore treated. Process tailings are treated in a three-stage chemical destruction circuit using the Inco SO 2 /AIR process before being discharged to a lined tailings pond in order to achieve the limits for cyanide and heavy metals set by the Turkish Ministry of Environment. The limit for cyanide in the chemical destruction effluent is 1mg/l, as weak acid dissociable (WAD) cyanide. The circuit was commissioned successfully, under the control of Inco experts, and has since been operating in compliance with all the regulatory environmental requirements.
... Recently, it has been established that approximately 13% of gold recovery is realized by physical and 87% by chemical and biological processes (29)(30)(31)(32)(33)(34). In most cases it is anticipated that auriferous ash would be treated by leaching in order to recover the contained gold at the very high extraction efficiencies i.e., greater than 99%. ...
Article
Considering the increasing environmental concerns and the potential for small gold deposits to be exploited in the future, the uses of environmentally friendly processes are essential. Recent developments point to the potential for greatly increased plant performance through a separation process that combines the cyanide and flotation processes. In addition, this kind of alternative treatment processes to the traditional gold recovery processes may reduce the environmental risks of present small‐scale gold mining. Gold recovery processes that applied to different types of gold bearing ore deposits show that the type of deposits plays an important role for the selection of mineral processing technologies in the production of gold and other precious metals. In the last 25 years, different alternative processes have been investigated on gold deposits located in areas where environmental issues are a great concern. In 1988, gold particles were first recovered by successful pilot trial of coal‐gold agglomeration (CGA) process in Australia. The current paper reviews the importance of CGA in the production of gold ore and identifies areas for further development work.
... Recently, it has been established that approximately 13% of gold recovery is realized by physical and 87% by chemical and biological processes (29)(30)(31)(32)(33)(34). In most cases it is anticipated that auriferous ash would be treated by leaching in order to recover the contained gold at the very high extraction efficiencies i.e., greater than 99%. ...
... It has been employed in full-scale facilities worldwide both in conventional cyanidation and heap leach applications. The microbial species can thrive in multiple environments allowing for uptake, treatment, sorption and/or precipitation of cyanide, its related compounds and metals (Adams and Gardener, 1994;Akcil, 2002;Arps et al., 1993;Babu et al., 1996;Chapatwala et al., 1998;Cellan et al., 1998;Finnegan, 1992;Finnegan et al., 1991a,b;Mosher and Figueroa, 1996;Nelson et al., 1998;Oudjehani et al., 2002;Trapp et al., 2003;White and Schnabel, 1998). However, it is known that the toxicity of cyanide can limit a microorganism's ability to use it as a substrate for growth. ...
Article
This study investigates the biooxidation of a refractory gold concentrate using a mixed culture of acidophilic mesophiles, moderate thermophiles and extreme thermophiles and their effect on the subsequent cyanidation and gold recovery. The experiments with high % solids using mixed mesophiles showed better oxidation potential compared to moderate thermophiles and extreme thermophiles. However, the extreme thermophiles performed better than mesophiles and moderate thermophiles during the biooxidation with
... The nearby Ovacik gold mine was partly discovered due to diligent archaeological research for the Roman Empire. Today, the town of Bergama is also famous for its cotton, carpets, and gold production (Akcil, 2002;Akcil and Koldas, 2004). ...
Article
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... deals with the proper management and approval of process certificates for cyanide-utilising industries. Additionally, the ICMC has enforced codes of practice that compel industries to implement alternative waste management practices in order to minimise environmental contamination by such industries (Gibbons, 2005;Akcil, 2002;Akcil, 2010). ...
Article
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The cyanidation process has been, and still remains, a profitable and highly efficient process for the recovery of precious metals from ores. However, this process has contributed to environmental deterioration and potable water reserve contamination due to the discharge of poorly treated, or untreated, cyanide containing wastewater. The process produces numerous cyanide complexes in addition to the gold cyanocomplex. Additionally, the discharge constituents also include hydrogen cyanide (HCN) – metallic complexes with iron, nickel, copper, zinc, cobalt and other metals; thiocyanate (SCN); and cyanate (CNO). The fate of these complexes in the environment dictates the degree to which these species pose a threat to living organisms. This paper reviews the impact that the cyanidation process has on the environment, the ecotoxicology of the cyanidation wastewater and the treatment methods that are currently utilised to treat cyanidation wastewater. Furthermore, this review proposes an integrated biological approach for the treatment of the cyanidation process wastewater using microbial consortia that is insensitive and able to degrade cyanide species, in all stages of the proposed process.
... All cyanide species are hazardous with free cyanide (CN -, HCN) being the most toxic form (Young and Jordan, 2005). Environmental regulations also enforce the reduction of concentration of cyanide to acceptable levels prior to discharge to the environment (Çelik et al., 1997; Akcil, 2002). Several remediation methods i.e. natural attenuation, chemical/biological oxidation, complexing/precipitation and recovery/recycling processes were suggested for the removal of cyanides from solutions/slurries (Mudder et al., 2001; Young and Jordan, 2005; Deveci et al., Destruction of cyanides using hydrogen peroxide (H 2 O 2 ), a strong oxidant (oxidation potential: 1.77 V) for free and weak acid dissociable (WAD) cyanides, is a widely utilised chemical oxidation process for the treatment of cyanide containing effluents (Mudder et al., handling-storage and non-toxic nature i.e. formation of no toxic by-products (2) during the oxidation process (US Peroxide, 2004). ...
Conference Paper
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In this study, the decomposition of H2O2 was studied. Effects of the initial concentration of H2O2 (131-800 mg/l), copper (10-40 mg/l CuSO4), solids (1-4% w/v), temperature (20-50°C) and pH (9.5-12) on the rate and extent of the decomposition of H2O2 were examined over a period of 3 hours. Statistical analysis of the results was also performed using Ergun’s test (essentially One-way Analysis of Variance (ANOVA) for gradients). The results have shown that concentration of copper and temperature was found to be the most significant parameters affecting the decomposition of H2O2. This was also confirmed by the statistical assessment of the results using Ergun’s test. Decomposition of H2O2 increased by 20-fold with the increase in temperature from 20°C to 50°C over 3 hours. At a copper sulphate concentration of 40 mg/l, ~76% of H2O2 was destructed. Solids up to 4% w/v and high pH adversely affected the stability of H2O2.
... copper, zinc and iron [4], [10]. Effluents generated in leach plants should be treated due to environmental concerns with regard to toxic effects of cyanide [3], [6], [17], [22]. Regulatory bodies force to reduce the cyanide level (CNWAD) down to <10 mg/L prior to discharge into tailings dam [23]. ...
Article
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Siyanür liçi işlemleri sonucu üretilen atık çözeltiler, siyanür içeriğinin yasal sınırlara indirilebilmesi için arıtma işlemine tabi tutulmaktadır. Siyanür geri kazanımı ekonomik ve çevresel nedenlerden dolayı, özellikle siyanür tüketimi yüksek cevherler için en çok tercih edilen seçenektir. Bu çalışmada, alkali çözeltilerde hidrojen siyanürün (HCN(g)) absorpsiyonu/geri kazanımı öncesinde siyanür çözeltilerinin asitleştirilmesi amacıyla karbon dioksit (CO2) kullanılmıştır. Yapılan kinetik testler, reaksiyon süresinin siyanür geri kazanımında önemli bir rol oynadığını göstermiştir (90 dk.’da %89,1 siyanür geri kazanımı). Siyanür konsantrasyonu (0,5-1,5 g/L NaCN), karbon dioksit akış debisi (0,38-1,15 L/dk. CO2) ve süre’nin (30-90 dk.) siyanür geri kazanımı (%) üzerindeki etkisi iki seviyeli tam faktöriyel deney tasarımı kullanılarak araştırılmıştır. Verilerin istatistiksel analizi karbon dioksit akış hızı ve süre’nin istatistiksel olarak anlamlı parametreler olduğunu göstermiştir. Siyanür konsantrasyonunun prosesin etkinliği üzerinde bir etkisinin olmadığı belirlenmiştir. Elde edilen sonuçlar, uygun koşullarda %93,1’e varan yüksek siyanür geri kazanımlarına ulaşılabileceğini göstermiştir. Karbon dioksit kaynağı olarak hava (1,15 L/dk.) kullanılmanın etkin olmadığı ve yüksek verimler için daha uzun süre gerektiği bulunmuştur (15 dk.’da kazanım sıfır iken 24 saatte %95,4 olmuştur). Gerçek bir yüklü liç çözeltisinden yapılan testte %49,7 verim elde edilmiştir. Elde edilen bulgular karbon dioksitin siyanürlü atık çözeltilerin asitleştirilmesinde ve siyanürün geri kazanımında kullanılabileceğini göstermiştir.
... After cyanidation, the solid and liquid fractions are separated and stored in storage ponds for the natural attenuation of cyanide and related complexes. The liquid fraction generated from the cyanidation process normally contains elevated concentrations of free cyanide (CN − ), thiocyanate (SCN − ) and metal-complexed cyanides in the form of weak acid dissociable (CN WAD ) and strong acid dissociable cyanides (CN SAD ) (Akcil 2002;Akcil and Mudder 2003). In most cases, SCN − and CN − are normally observed to be the major contaminants found in cyanidation wastewaters. ...
Article
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This study focused on the identification of free cyanide (CDO) and thiocyanate (TDO) degrading microbial communities using a culture-dependent and independent approach. Culturable microbial species were isolated from the CDOs (n = 13) and TDOs (n = 18). The CDOs were largely dominated by Bacillus sp. while the TDOs were dominated by Bacillus sp., Klebsiella oxytoca, Providencia sp. and Pseudomonas sp. However, 16S rRNA amplicon gene sequencing revealed the complexity and diversity of the microbial communities in contrast to the organisms that were detected using culture-dependent technique. Overall, the organisms were mainly dominated by Myroides odoratimimus and Proteus sp. at 37.82% and 30.5% for CDOs, and 35.26% and 17.58% for TDOs, respectively. The co-culturing of the CDOs and TDOs resulted in biochemical changes of key metabolic enzymes, and this resulted in the complete degradation of CN- and SCN- simultaneously; a phenomenon which has not been witnessed, especially under alkaline conditions. Current ongoing studies are focused on the application of these organisms for the biodegradation of CN- and SCN- in a continuous system, under changing operational parameters, to assess their effectiveness in the biodegradation of CN- and SCN-.
... This process has been successfully applied in the extraction of gold and silver from complex ore for the past 100 years. It is revealed from literature that cyanide and oxygen work as ligand and oxidant respectively and both play vital roles in the gold and silver extractions (Akcil , 2002 Habashi, 1992;Marsden, 1992). The presence of sulfides ore effect gold dissolution into different ways. ...
Article
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The gold cyanidation/leaching process is the most versatile processing technique used for extraction of gold utilizing different cyanidation parameters likes grinding time, pH, cyanidation time, sodium cyanide (NaCN) and lime CaO.. The efficiency of cyanidation process depends on dosage of each parameter. In present research work the extraction of gold and silver by cyanidation process from shoughur area of district Chitral, Khyber Pakhtunkhwa was carried out at laboratory scale. The three representative samples ground at time 25, 30 to 35 minutes and roasted at 650 oc for 1 hour were subjected to agitation cyanidation process at varying dosage of pH from 10 to 11.13 , CaO from 0.5 to 1.5 gm/kg, NaCN varies from 1 gram to 5.93 gram and cyanidation time varies from 0 to 39 hours. The maximum grade of 71.82 ppm with 99.03% extraction/recovery of gold and 34.34 ppm with 73.83% extraction of silver was obtained for 30 minutes ground sample at dosage of sodium cyanide (NaCN) of 5.33 gram, pH 10.40, CaO of 1.5 gram, and cyanidation time of 37 hours as compared to 25 and 35 minutes ground samples. The cyanidation process was also applied on un-roasted ground ore samples at 30 and 35 minutes, pH 10.40, lime of 1.5gm/kg and varying cyanidation time from 2 to 37 hours. The maximum grade of gold 11.95 ppm and silver 11.50 ppm was extracted. Based on the comparative analysis of result it is concluded that cyanidation process on roasted ore samples gives better results as compared to un-roasted ore samples.
... Siyanür, madencilik, naylon, akrilik plastik vb. kimyasal madde üretimi, sentetik fiber/kauçuk üretimi, elektrolitik kaplama, alüminyum elektrolizi, kömür koklaştırma/gazlaştırma ve endüstriyel gaz temizleme gibi birçok endüstri tarafından kullanılmasına rağmen yüksek toksik özelliğe sahip bir kimyasaldır (Akcil, 2014;Akcil, 2002;Jackson ve Logue, 2017;Zagury vd., 2004). Bununla birlikte, Dünya'da üretilen siyanürün %18'i madencilik sektöründe kullanılmaktadır (Yazıcı, 2005;Logsdon vd., 1999). ...
... Additionally, ozone must be manufactured where it is used which adds a high capital cost to this treatment process (Kurek, 1995). The commonly used techniques at mining operations are Degussa and INCO processes (Young, 2001, Akcil, 2002). The Degussa process uses hydrogen peroxide, which has little or no effect on thiocyanate (Young, 2001). ...
Article
A cyanide-laden effluent of the gold mining industry must be treated before it can be released to the aquatic environment. Current treatment methods such as natural degradation, sulfur based, hydrogen peroxide, ozonation, and alkaline chlorination are not adequate for meeting newer treatment standards. A new chemical oxidant that utilizes iron in the +6 oxidation state, ferrate [Fe(VI)] was studied to oxidize cyanides in gold mill wastewater. Reactions of cyanide and thiocyanate with Fe(VI) were analyzed to determine kinetic parameters, stoichiometry, and products. The complete removal of cyanide and thiocyanate can be achieved in seconds to minutes with the formation of less harmful products. Destruction of cyanide resulted in cyanate while sulfate and cyanate were the products of thiocyanate oxidation. Ferrate is therefore a suitable candidate as a new environmental friendly oxidant for gold mining wastewater.
... Many conventional processing methods, such as alkaline chlorination, hydrogen peroxide, ozonation, air condition, ion exchange, the basic technology of sulfur and biological processes, have been used in the treatment process of wastewater containing cyanide [16]. In some cases, cyanide contamination process solutions must be treated with strict standards and are released into the environment [17]. ...
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Abstract: In this study, the elimination of cyanide by the addition of hydrogen peroxide and calcium hypochlorite was investigated. This study was conducted to determine the optimum conditions of H2O2 and Ca(OCl)2: concentration, pH and contact time, and the combined ratio of concentration H2O2 with Ca(OCl)2 to remove cyanide in gold mining wastewater. Cyanide obtained by steam distillation of wastewater by steam distillation and Barnstead electromantel and assay using 0.02N silver nitrate. The results showed that the cyanide level was 50.22% w/v. The optimum conditions were obtained when the concentration of H2O2 at 500 ppm, pH 8 within 60 minutes contact time and Ca(OCl)2 concentration was at 500 ppm, pH 8 within 60 minutes contact time. The best cyanide removal was obtained at the concentration ratio of 5:5 amounting to 45.76% w/v. Keywords: Cyanide, Hydrogen Peroxide, Calcium Hypoclorite, Steam Distillation, Silver Nitrate
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Municipal Councils in the G20 Countries including Turkey
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Bacterial leaching of minerals is a simple, effective and environmental by benign technology in the treatment of sulphidic ores. This method has been successfully applied for the recovery of copper, gold and uranium in commercial scale for the past 25 years. Efficiency and cost-effectiveness of the bacterial leaching process depend mainly on the activity of bacteria and mineralogical and chemical composition of the ores. Bacterial leaching is based on the activity of mesophilic iron- and/or sulphur-oxidizing bacteria, notably Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans and Leptospirillum ferrooxidans. These bacteria oxidize metal compounds to water soluble metal sulphates by a series of biological and chemical oxidation reactions occurring in leaching medium. After the isolation of above bacteria from acidic mine drainage waters, two oxidation mechanisms (direct and indirect bacterial leaching) have been discussed as related to oxidation/leaching of sulphidic ores in leaching systems. Fully understanding the bacterial leaching mechanisms of sulphidic ores improves the design and operation of bacterial leaching plants. In this article, the importance of various leaching mechanisms employed for metal recovery and their application aspects are critically reviewed with emphasis on copper, lead, zinc and nickel minerals.
Conference Paper
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In this study, the decomposition of free cyanide by hydrogen peroxide was studied. The results have shown that the rate and extent of cyanide removal ([CN]0: 100 mg/l) improve with increasing the concentration of hydrogen peroxide, cyanide and copper as catalyst. At a fixed ratio of [H 2O2]0/[CN]0: 8 over 95% of CN - could be removed by maintaining a [CuSO4]0 level of ≥40 mg/l (i.e. [H2O2]0/[CuSO4]0 ≥20) over 180 min. Kinetics of cyanide removal was found to be consistent with the first-order kinetic model. The efficiency of the removal of cyanide by hydrogen peroxide was observed to deteriorate with increasing pH whilst the increase in temperature exerted a positive effect on the rate of cyanide destruction. The current findings suggest that hydrogen peroxide may be used more effectively for the treatment of the effluents containing high concentrations of cyanide since at low cyanide levels the decomposition of hydrogen peroxide by side reactions would probably become significant.
Article
Currently, low-grade and complex ores and mining wastes can be processed economically by using bacteria in heap and agitation leaching processes. Bacterial leaching tests are performed on the run-of-mine ore which is a mixture of two different massive and dissemine copper ores, fed to Küre Copper Plant. In this leaching process, using "Acidithiobacillus ferrooxidans" culture, bacteria count, pH, copper and iron recoveries are monitored during the 576 hours of test period. By increasing the solid ratio (1 %→5 %) the oxidation ability of bacteria decreases, thus the leaching rate. Therefore copper and iron recoveries decreased from 68 %, 35 % and 45 %, 20 %, respectively. As a result of laboratory tests, it is found that as the pulp density increased, the efficiency of copper recovery decreased using this bacterial culture.
Article
Four solid-phase reagents have been tested for indirect determination of cyanide using flow injection analysis-flame atomic absorption spectrometry (FIA-FAAS). The method is based on insertion of aqueous cyanide solutions into an on-line Ag2X (where X are SO32−, Cr2O72−, C2O42− and CO32−) packed column (25%, m/m suspended on silica gel beads) and re-distilled water or sodium hydroxide are used as the carrier stream. The eluent containing the analyte as silver cyanide complexes, produced from reaction between Ag2X and cyanide, measured by flame atomic absorption spectrometry. The method is simple, fast and selective than other published FIA procedures. A relative standard deviation (R.S.D.) better than 1.12% was obtained in a repeatability study. The method was applied to the determination of cyanide in industrial electrolytic baths.
Article
In this study, the removal of free cyanide from aqueous solutions by activated carbon was investigated. Effects of metal impregnation (Cu and Ag), aeration, and concentrations of adsorbent and cyanide on the rate and extent of the removal of cyanide were studied. The results have shown that the capacity of activated carbon for the removal of cyanide can be significantly improved (up to 6.3-fold) via impregnation of activated carbon with metals such as copper and silver. Silver-impregnated activated carbon was found to be the most effective at the reduction of cyanide level in solution. This appeared to be coupled with its comparatively high metal content after impregnation process where silver (5.07%) could be more readily loaded on activated carbon than copper (0.43%). Kinetics and equilibrium data for cyanide removal by plain and metal-impregnated activated carbons were determined to be consistent with the pseudo second-order kinetics and the Langmuir adsorption isotherms, respectively. Aeration (0.27 l/min) was found to exert a profound effect on the process leading to a 5.5–49.1% enhancement in the performances of plain and metal-impregnated activated carbons. This enhancement could be attributed to the increase in the availability of active sites on activated carbon for adsorption and the catalytic oxidising activity of activated carbon in the presence of oxygen. Practical limiting capacity of plain, copper-and silver-impregnated activated carbons for the removal of cyanide were experimentally determined to be 19.7, 22.4 and 29.6 mg/g, respectively.
Article
The leaching of zinc and copper from Nigerian bulk sulphide ore with sulphuric acid in the presence of hydrogen peroxide was studied. The aim of the study was to investigate the effectiveness of hydrogen peroxide as an oxidant for the sulphuric acid leaching of zinc and copper from a complex sulphide ore. Distribution of elementals within the various particle sizes was initially determined by ICP-OES and XRF to provide a basis for explaining the dissolution process. The effects of concentration of hydrogen peroxide, particle size, stirring speed, and leaching time at a constant temperature of 298K were studied. There were variations in elemental and mineralogical composition within the different sizes. The concentrations of zinc and copper reduced as particle size decreased while silica, sulphur, iron and lead contents increased. Dissolution results showed that the leaching rate of copper was lower than that of zinc. The highest recoveries of zinc and copper were obtained at a leaching time of 180 minutes, stirring speed of 160 rpm, particle size of 75 μn and a concentration of 1M H2SO4/1M H2O2. It was observed that the leaching rate of zinc and copper increased with increasing hydrogen peroxide concentration. Increased stirring speed had a negative leaching effect as it promotes hydrogen peroxide decomposition. © The Southern African Institute of Mining and Metallurgy, 2006.
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This study integrates observations from field and remote sensing data, along with geochemical and isotopic analyses, to assess the environmental impacts of cyanidation and mining activities in the Sukari gold mine (SGM), Eastern Desert, Egypt, in particular, and the orogenic gold deposits of the Arabian-Nubian Shield (ANS) in general. Our findings indicate: (1) groundwater flows south to north in the highly fractured basement aquifer related to the brittle deformation associated with the Najd Fault System; (2) massive gabbroic bodies separate the fractured basement aquifer into east and west conduits; (3) the tailings storage facility (TSF) pond and leach pad were constructed over the west conduit; and (4) cyanide-rich wastewater has leaked downward through tears and cuts in the lining of the TSF pond into the fractured aquifer and cyanide contaminants have migrated northward along the west conduit. Evidence for the latter includes: (1) toxic concentrations of cyanide (total: 0.018–9.4 mg/L; free weak-acid dissociable: 0.003–0.7 mg/L) were observed in groundwater samples north of the TSF pond; (2) similarities in electrical conductivity (EC) values and chloride/bromide (Cl⁻/Br⁻) ratios between groundwater north of the pond (EC: 88.8 mS/cm; Cl⁻/Br⁻: 346 to 363) and those of the TSF pond water (mean EC: 99 mS/cm; Cl⁻/Br⁻: 242 to 383) were observed; (3) the geochemical (e.g., sodium [Na⁺], Cl⁻) and isotopic compositions (δ¹⁸O and δ²H values) of groundwater are consistent with mixing of groundwater upgradient from the SGM with isotopically enriched pond water; and (4) cyanide contamination could not have resulted from an overflow of the TSF pond during flash flood events, given that rainfall is negligible and effective flood control systems are in place. Our findings show that the international codes/regulations do not fully address site-specific characteristics and highlight the importance of considering these parameters in mining of orogenic gold deposits in the ANS.
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This work investigates the removal of cyanide as a noxious pollutant in the gold processing effluent (Aq-Dara mine, Takab, Iran) using H2O2, H2O2+Fe(II) (Fenton), H2O2+Cu(II), NaClO and Ca(ClO)2 oxidants. Implementation of purification operation was carried out with the parameters change including pH, oxidant dosage, temperature and time of the reaction. The results show the oxidants have the highest efficacy at pH 10-12, while the Fenton process has the highest efficiency at pH 8. The results confirm that Ca(ClO)2 is the best oxidant due to less time, low reaction rate, high degradation of cyanide and low cost. The obtained results of response surface methodology optimization show that cyanide degradation has a direct relation with temperature, amount of oxidant, time and catalyst dosage parameters and has an inverse relation with pH. Also, the cyanide elimination efficiency is more than 99.5% and residual cyanide less than Environmental Protection Agency standards and 40% of the consumed water be compensated by the effluent treatment and its return to the factory's processing circuit.
Article
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Scientific objective of this work was elaboration of radiometric method for the development of hydrometallurgical process for recovery of Cu from the copper ore. A neutron activation analysis (NAA) was identified as a very convenient tool for the process investigation. The samples of copper ore were activated in a nuclear reactor. The parameters of the neutron activation were calculated. Radioisotope ⁶⁴Cu was selected as an optimal tracer, and it was used for the investigation of the leaching process. During the experiments, various processes applying leaching media such as sulphuric acid, nitric acid, and organic acids were investigated. The recovery of the metals using sulphuric acid was insufficient, around 10%. Investigated organic media also did not meet expectations. The best results were obtained in experiments with nitric acid. Up to 90% of Cu and other metals were extracted from the copper ore. Copper concentration calculations obtained by NAA were confirmed by inductively coupled plasma mass spectrometry (ICP-MS) technique. Both techniques gave comparable results, but the advantage of the NAA is a possibility for easy online measurements without shutting down or disturbing the system.
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Küresel ekonomideki dalgalanmaların en önemli tetikleyicilerinin başında, hammadde tedariğinden dolayı, madencilik sektörü gelmektedir. Bu durum, aynı zamanda, madencilik sektörünü kamuoyu gündeminde tartışmaların arttığı bir konuma oturtmaktadır. Ülkemizde olduğu gibi, küresel anlamda da madencilik sektörü içinde İş Sağlığı ve Güvenliği tedbirlerinin uygulanmasına en hassas olan Altın ve Gümüş madenciliğidir. Bunun ana sebebi; çok ince boyutta serbestleştirilmesi gereken cevher tipinden ve de çok düşük tenörlerin işlenmesinden dolayı bu değerli metallerin kazanımında siyanür kimyasalının kullanılmasından ileri gelmektedir. Bilindiği gibi, altın ve gümüş madenciliğinde siyanür kullanımı zorunluluğu bu konuda 120 yılı aşkın süren araştırma ve bilimsel gerekçelere dayanmaktadır. Siyanürün yerine kullanılabilecek başka kimyasallar üzerine 80’li yıllardan bu yana ciddi araştırmalar yürütülmektedir. Ancak siyanürün etkinliği, ekonomisi yanında, insan sağlığı ve çevre üzerinde bilinen risk ile birlikte kullanılabilirliğinden dolayı madencilik endüstrisinde kullanımı halen devam etmektedir. Dünya’da altın ve gümüş üretiminin % 90’ınında halen bu değerli metallerin kazanımı için etkin bir kimyasal olarak siyanür kullanılmaktadır. Şehir efsanelerinin aksine kanserojen etkisi olmayan bu kimyasalın küresel olarak yönetimi, 2000 yılındaki Baia Mare (Romanya) altın madenindeki kazadan sonra Birleşmiş Milletlerinde aralarında olduğu kuruluşlar tarafından ele alınmıştı ve 2002 yılından itibaren siyanür yönetiminin anayasası olarak bilinen “Uluslararası Siyanür Yönetim Kodu” (International Cyanide Management Code-ICMC) tüm dünyada yaygın olarak uygulanmaya başlandı. Dolayısı ile, siyanür kullanılan altın ve gümüş madenciliğinde 15 yıldır bu tür bir bağımsız dış denetleme aracının küresel düzeyde uygulanmasıyla iş sağlığı, güvenliği ve çevre konularında en üst seviyede yeni ama normal bir yaklaşım sergilenmektedir. Bu konuda dünyadaki en üst düzey denetleme şekli olmasına rağmen, bağımsız dış denetleme süreçlerine girmek istemeyen bazı şirketler ileri düzeyde yönetim uygulama kriterleri nedeniyle çekingen davranarak bu sürece girmemektedirler. Ülkemizde ise konuya uzak yakın birçok şirket için ilk örnek uygulama 2012 yılında başlamıştır (Kışladağ Altın Madeni, Uşak). Ülkemizde madencilik faaliyeti yapan birçok şirketlerinde önemli ölçüde Siyanür Koduna uyumlanma ve bağımsız dış denetleme sürecine katılmak için; eğitim, boşluk analizi ve ana denetleme (ICMI sertifikasyonu) çalışmaları yaklaşık 7 yıldır devam etmektedir.
Article
In the present paper, a review has been made for the recovery of copper from the ores using lixiviant sulphuric acid, the effects of the sulfuric acid concentration, leaching time, particle size and leaching temperature on the recovery of copper were examined. The results of leaching indicate that the recovery extraction of Cu increases with increasing acid concentration and temperature; while it decreases with particle size. The logical experimentation parameters for the extraction of copper were discovered. Later than 120 min of leaching treatment, the sulfuric acid concentration 2 mol/l⁻¹, leaching temperature 85 °C, smaller particle size 63 μm at low stirring rates (100 rpm) and solid-to-liquid ratio 1:10. The overall results of the dissolution studies indicated that the data fitted the shrinking core model for the controlled mechanism, with surface chemical reaction as the rate controlling step. The value of the activation energy Ea is calculated by multiplying the slope of the Arrhenius curve by the value of the universal gas constant 8.314 kJ/mol⁻¹.
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In this article, the sensing mechanism of cyanide anion chemosensor 2-((2-phenyl-2H-1,2,3-triazol-4-yl)methylene)malononitrile (M1) has been investigated through the density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods. The theoretical results demonstrate that the reaction barrier of 13.02 kcal/mol means a favorable response speed of the chemosensor M1 for cyanide anion. Cyanide anion attacks C=C double bond and hinders the ICT process from the malononitrile moiety to the fluorophore phenyl ring. The high viscosity of DMSO restrains the twisting of the group, inhibits the formation of the ICT state in the first excited state. Due to weak ICT character, the nucleophilic addition product shows the dramatic “off–on” fluorescence enhancement. Meanwhile, intramolecular charge transfer (ICT) mechanism accounts for how different solvents influence the fluorescence spectra. That is, more obvious ICT character of product in EtOH causes fluorescence quenching. The “reaction-based” recognition mode and large bond energy between M1 and cyanide anion minimize the interference by other anions, such as F⁻, AcO⁻. Thus, the chemosensor M1 has a high selectivity for cyanide.
Article
The leaching of iron (II) sulfate concentrate from Chaabet El Hamra, Algeria bulk sulphide ore with sphalerite concentrate in presence of sulfuric acid and hydrogen peroxide at low stirring rates (100 rpm). The influence of leaching temperature, leaching time, particle size and sulfuric acid concentration were studied. In this paper we focused our attention on the process of direct leaching of iron (II) sulfate concentrate with sulfuric acid. The results of leaching show that the combination of sulphuric acid and hydrogen peroxide enhances the dissolution of the bulk sulphide ore. The Leaching rate was studied as a function of the leaching temperature, the leaching time, the particle size and the sulfuric acid H2SO4 concentration. The optimal operational conditions were as follows: leaching temperature 100°C; leaching time 2 hours; sulfuric acid concentration 2 mol/L-1; the smaller particle size 63 µm and the solid-toliquid ratio 1:10. In these values the maximum extraction of iron (II) sulfates is 0.0416 mol/L-1.
Article
Thiosulphate leaching in gold recovery is an alternative chemical process with several advantages such as, lower cost and relatively harmless nature, faster leaching kinetics compared to cyanide effectiveness in gold recovery, and easy reaction with gold due to the presence of copper catalyst. It is economical and advantageous especially for ores with carbonate and copper content. However, the literature information, previous experiences and the problems encountered in existing applications should be well understood in order to employ this leaching process for other types of ores and full-scale applications. Therefore, in this study, thiosulphate chemistry, the ore types for which the thiosulphate leaching can be employed, economical aspects, environment impacts, advantages and disadvantages, the practical experiences are considered and critically evaluated.
Article
The mining industry has been using cyanide in their metal recovery processes for over 100 years. During this time, the mining industry has found several ways to destroy and recover the cyanide from their processes. However, due to cyanide's toxicity and potentially devastating environmental effects, it is still a major environmental concern. This paper examines both the chemical and biological treatment processes currently used by the mining industry to treat their cyanide wastes. Further, some discussion is made about the added water quality benefits of using a biological treatment process instead of a chemical process. The paper finishes by discussing the economic and environmental viability of a biological treatment process, as well as future applications of microorganisms, and even plants, in the biodegradation of cyanide.
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The use of cyanide (CN), which is characterized by volatility, toxicity and high odor, in gold mining is scarcely addressed in the literature and remain controversial. Environmentalists oppose CN usage as it potentially poses serious environmental threats, whereas economic and mining geologists are in favor of its usage for its extracting capacity and economic feasibility. The present study investigates the possible dispersion of CN into groundwater resources caused by a gold mine (ca. 15years old) located in the arid area of Yanqul, North Oman. The gold is hosted in gossan deposits associated with ophiolitic rocks and sulfide deposits. Sodium cyanide is mixed with 0.5m3 of water and then added to a tonne of crushed ore rock to extract 6g of gold mineral. The final residues are dumped in engineered, lined and uncovered tailing dams. Subsequent to rainfall water draining the mine plateau flows along the wadies and percolates into the shallow Quaternary alluvium aquifer. Hence, groundwater samples were collected from 16piezometers adjacent to and around the mine. The samples were analyzed for CN using the revised phenolphthalin method and they all show CN concentration below the detection limit (5ppb). The samples were also analyzed for heavy metals to investigate the potential of CN complexation. Most of heavy metals indicated very trace concentration. The absence of CN in groundwater is attributed to volatilization of CN (converted to HCN), lined dam structure, high evapotranspiration rate and deeper water table. This finding is consistent with the historical CN analysis in the groundwater and solid wastes. It can be pointed out that within few years of operation well engineered tailing dams can provide safe structure preventing CN-groundwater pollution in arid areas. Potential threats to the air and soil are not addressed in this article. KeywordsCyanide-Arid areas-Gold mining-Oman-Environmental pollution
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The year 1987 marks the centennial of the beginning of modern hydrometallurgy. On October 19, 1887, British Patent No. 14174 entitled Process of Obtaining Gold and Silver from Ores was issued. The discovery was made by John Steward MacArthur. This article describes the background to the discovery and modern developments since that time.
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Discusses 1996 as a year in which headline stories did the metals and minerals industry no favours. In particular it refers to the unauthorised dealings by the former chief copper trader of Sumitomo and to the collapse of Bre-X minerals after irregularities were found in its exploration data. On a more positive note the increase in exploration activity, particularly for gold, in Africa is highlighted. South African gold mines are under continuing economic pressure and the country produced its lowest output since 1956. However it still remains the world's biggest producer. Developments and trends in mineral exploration (including methods and instrumentation), surface and underground mining and mineral and coal processing are included as technical articles. Regional and national mining trends in 153 separate countries are covered in detail. Indexes include buyers, manufacturers, mines and companies.
Article
Chemical replacements for cyanide have been investigated for decades; however cyanide remains the exclusive lixiviant of choice in the mining industry due to a combination of its availability, effectiveness, economics and ability to use it with acceptable risk to humans and the environment. About 90% of the significant gold producing operations worldwide currently utilize cyanide for gold and silver extraction. Despite the number of cyanide-related mining operations, there have been no documented accounts during the previous three decades of the death of humans due to cyanide as a direct consequence of major mining-related environmental incidents. Major mining-related environmental incidents have not been concentrated in any geographic location, may occur regardless of the size of the company and do not occur more frequently with a specific type of mining activity. The main aspects of cyanide management that should be addressed at mining operations include transportation of cyanide to site, process solution conveyance, worker health and safety training, water management and treatment, emergency response and preparedness, workplace and environmental monitoring, and community relations. If these aspects of cyanide management are integrated into an overall cyanide management plan, dramatic reductions in risk and potential incidents at mine sites will be realized.
Article
Cyanidation tailings which are disposed in a surface impoundment experience a loss of cyanide due to natural attenuation, frequently reducing 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 though 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 more 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 against data collected for a North American tailings impoundment during 1998.
Article
The herbicide ·atrazine (2-chloro-4-ethylamino-6-isopropylamino-I,3,5- triazine) is the most heavily used agricultural pesticide in North America. In the United States alone, more than 50 million kg (110 million pounds) are applied annually to more than 25 million ha (62 million acres), primarily to control weeds in corn and sorghum. Residues have been detected at phytotoxic concentrations in groundwater, lakes, and streams as a result of runoff from treated fields. Atrazine degrades rapidly, usually by way of hydrolysis, nitrogen dealkylation, and splitting of the triazine ring to less toxic compounds not normally inhibitory to plants and animals. The half-time persistence of atrazine in soils is usually about 4 days, but may range up to 385 days in dry, sandy, alkaline soils, under conditions of low temperature and low microbial densities. Half-time persistence is about 3 days in freshwater, 30 days in marine waters, 35 days in marine sediments, and less than 72 hours in vertebrate animals. Sensitive species of aquatic plants experience temporary, but reversible, adverse effects at concentrations in the range of 1 to 5 ug atrazine/l. However, potentially harmful phytotoxic concentrations of atrazine, i.e., >10 ug/l for extended periods, have not been documented in the environment, and are probably unrealistic under current application and degradation rates. Aquatic fauna are indirectly affected at atrazine concentrations of 20 ug/l and higher, partly through reduction of the food supply of herbivores, and partly through loss of macrophyte habitat. Direct adverse effects to aquatic invertebrates and fishes were measured at 94 ug/l and higher. Bioaccumulation of atrazine. is limited, and food chain biomagnification is negligible in aquatic ecosystems. Birds are comparatively resistant to atrazine, having a low probability for uptake and retention. Known acute oral lD-50 values for birds are >2,000 mg/kg body weight, and dietary lD-50s are >5,000 mg/kg ration. However, indirect ecosystem effects of atrazine on seed- and insect-eating birds are unknown, and should be investigated. Data are lacking for atrazine toxicity to mammalian wildlife, but tests with domestic livestock and small laboratory animals indicate that this group is also comparatively resistant. Acute oral lD-50s for mammals are >1,750 mg/kg body weight; no adverse effects were measured at chronic dietary levels of 25 mg/kg (about 1.25 mg/kg body weight) and, for some species, 100 mg/kg diet. Proposed criteria for aquatic life protection include
Article
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
Microbial destruction of cyanide and its related compounds is one of the most important biotechnologies to emerge in the last two decades for treating process and tailings solutions at precious metals mining operations. Hundreds of plant and microbial species (bacteria, fungi and algae) can detoxify cyanide quickly to environmentally acceptable levels and into less harmful by-products. Full-scale bacterial processes have been used effectively for many years in commercial applications in North America. Several species of bacteria can convert cyanide under both aerobic and anaerobic conditions using it as a primary source of nitrogen and carbon. Other organisms are capable of oxidizing the cyanide related compounds of thiocyanate and ammonia under varying conditions of pH, temperature, nutrient levels, oxygen, and metal concentrations. This paper presents an overview of the destruction of cyanide in mining related solutions by microbial processes.
Technical Guide for Environmental Management of Cyanide in Mining. Mining Association of British Columbia
  • T W Higgs
Higgs, T.W. et al., 1995. Technical Guide for Environmental Management of Cyanide in Mining. Mining Association of British Columbia, Canada.
A case study: decomposition of cyanide and heavy metal stabilization in Ovacik Gold Plant
  • A Akcil
  • V Oygur
  • H Ciftci
Akcil, A., Oygur, V., Ciftci, H., 2002. A case study: decomposition of cyanide and heavy metal stabilization in Ovacik Gold Plant, in: International Conference on Mineral Processing Technology, Bangalore, India.
The cyanide guide Mining environmental management (special issue) The Mining Journal The cyanide compendium
  • T Mudder
Mudder, T. (Ed.), 2001. The cyanide guide. Mining environmental management (special issue), The Mining Journal, London, En-gland, p. 45. Mudder, T., Botz, M., Smith, A. (Eds.), 2001. The cyanide compendium, Mining Journal Books, London, England, 1000þ pages on CD.
The cyanide compendium
  • T Mudder
  • M Botz
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