Copper cyanide removal by precipitation with quaternary ammonium salts

Cyanide is widely used in the mining industry to extract gold from ores. Some of the minerals processed for precious metals extraction contain copper species which may react with cyanide to form cuprocyanide complexes. The presence of these copper species affects adversely the process and causes high cyanide consumption. In order to overcome these limitations this laboratory work explores the feasibility of removing the copper–cyanide complexes by precipitation with quaternary ammonium salts, allowing the remaining solution, free of copper and containing free cyanide, to be recycled to the cyanidation process. The first part of the experimental work was performed with synthetic copper–cyanide solution simulating a high copper–cyanide solution (2700 mg/L cyanide, 730 mg/L copper and pH adjusted to 12 with CaO) and three quaternary ammonium salts: hexadecyl trimethyl ammonium chloride (HTA), octadecyl trimethyl ammonium chloride (OTA) and dioctadecyl dimethyl ammonium chloride (DDA). The results showed that it is possible to remove up to 90% of the copper in the precipitate when adding 12.32 g OTA/g copper at pH 12. The free cyanide remains unreacted in the solution and could be recycled to the process. Results of tests performed at different pH values suggest that regardless the initial species distribution in the solution, the solid formed will contain mainly copper tricyanide and some of copper tetracyanide. The molar ratio CN/Cu in the solid is around 3 while the molar ratio OTA/Cu is around 2. This implies that some amount of copper tetracyanide is transformed into copper tricyanide while reacting with the amine and forming the precipitate. When zinc is also present in the cyanide solution, the ammonium salt will react first with the zinc–cyanide complexes before precipitating the copper cyanides. Tests performed with an industrial solution corroborated the results obtained with synthetic solutions: quaternary ammonium salts (e.g. OTA) react with copper and zinc cyanides (but not with free cyanide) to form a precipitated that can be separated from the solution by filtration. An analytic technique for measuring quaternary ammonium salts HTA and OTA in solution was developed.     

Recovery of copper cyanide from waste cyanide solution by LIX 7950

The use of the guanidine extractant, LIX 7950, to extract copper cyanide from waste cyanide solution has been investigated. Copper extraction is favorable at low pH while a high cyanide to copper molar ratio tends to suppress copper loading. The extractant also strongly extracted zinc and nickel from cyanide solution, but the extraction of iron was poor. The presence of thiocyanate ion significantly depressed copper extraction, but thiosulfate ion produced negligible impact on copper extraction. The preferential extraction of metal cyanide species to free cyanide has been noticed. The potential application of the recovery technique as a pre-concentration step for the treatment of cyanide effluent has been suggested, by which copper can be extracted and concentrated into a small volume of solution and the barren cyanide solution recycled to the cyanidation process.     

Cadmium removal from diluted aqueous solutions by electrowinning in a flow-by cell

Mineral processing and metal finishing industries produce large amounts of effluents containing a host of heavy metals - cadmium, lead, nickel and chromium - with cadmium as a heavy hazard, since, even in mild concentrations, it may give rise to serious environmental problems. Effluents from electroplating industries and from zinc ore hydrometallurgical processing may contain this metal in the range of 15 to 100 ppm. Cadmium harm to all living systems is aggravated by its strong cumulative effect, because of the long number of years required for its elimination. The electrolytic waste treatment has shown advantages over the classical chemical precipitations by alkalis or carbonates, because it does not produce bulky sludges, which require land for its accumulation, and which may have a retarded pollution effect, due to the redissolution by rain; a great advantage comes from the possibility of the metal recovery in a commercially pure form. In this paper, a laboratory scale electrolytic flow-by cell with a reticulated vitreous carbon (RVC) cathode, developed in our laboratory, is described, which permitted the purification of aqueous solutions containing cadmium ion on the usual order of concentration of metallurgical industries effluents; with this cell, operating in a mass transport regime, it has been possible to decrease cadmium concentration of solutions of 2 liters volume from 200 to 0.1 ppm, with current efficiencies up to 40%, in a matter of 85 minutes.     

Copper and nickel recovery from acidic polymetallic aqueous solutions

Acidic polymetallic wastewaters are generated during the pyrometallurgical treatment of chalcopyrite for the production of primary copper. The most important wastewater streams originate from the copper refining and the electrolyte regeneration stages, as well as the sulphuric acid and the precious metals plants. These wastewaters are characterized by medium to high concentration of residual sulphuric acid and heavy metals such Cu, Ni, Pb, Zn, Fe, As, Sb, Bi, etc. Taking into account that the outflows of these industrial streams are usually high, a large amount of valuable metals such as copper and nickel are potentially lost. Thus, it is of great importance to treat properly the wastewaters so that the contained valuable metals to be recovered. This paper is dealing with the treatment of synthetic solutions simulating industrial wastewaters from the copper pyrometallurgical plant in Bor, Serbia. The basic concept includes copper electrorecovery followed by nickel precipitation through neutralization. The feasibility of this treatment was proved theoretically with the thermodynamic analysis of electrochemical and precipitation reactions in this system, as well as experimentally under various conditions. The main conclusion is that copper can be recovered electrolytically followed by bismuth and the two metalloids arsenic and antimony that exhibits almost the same electronegativity with copper. The other high electropositive metals Ni, Pb, Zn, Fe remain, as it was expected, in the solution from which nickel can be recovered with neutralization, contaminated with Cu, Fe, Zn and traces of bismuth, arsenic and antimony. The proposed treatment technology has innovative character because it can mitigate environmental impacts and eliminate solid waste generation while at the same time can recover valuable metals.     

Solvent extraction of gold(I) from alkaline cyanide solutions by the cetylpyridinium bromide/tributylphosphate system

This paper explores the solvent extraction of KAu(CN)₂ from alkaline cyanide solutions using quaternary ammonium cetylpyridinium bromide (CPB) as an extractant with the addition of tributylphosphate (TBP) as a modifier. It also investigates the influence of several variables on gold extraction, including the molar ratio (β) of CPB to Au(I), the volume percentage of TBP (φ_TBP), NaCl concentration, phase ratio (AQ/ORG), and gold concentration in the aqueous phase. The results indicate that nearly all of the Au(I) (>98%) was transferred from the aqueous phase into the organic phase when β = 1 and φ_TBP = 30 vol%. We also carried out experiments for treating 20 L synthetic aurocyanide solution containing 10 mg/L Au(I) with column-shaped extraction equipment. The results demonstrated the recovery of more than 94.5% of Au(I) after two successive stages of extraction, and the Au(I) concentration in the raffinate was less than 0.5 mg/L. KSCN solution was used to strip the gold-loaded organic phase, and about 90% of Au(I) could be reverse extracted into the aqueous phase when the KSCN concentration reached 3.0 mol/L. The results obtained in this paper establish that the CPB/TBP extraction system has potential for practical application in the extraction and separation of gold from alkaline aurocyanide solutions.     

Extraction of hydrogen cyanide from waste solutions of cyaniding circuit for sulfide flotation concentrates

The process for extraction of hydrogen cyanide to decontaminate solutions produced at cyaniding of sulfide flotation concentrates is developed. The centrifugal-bubbling apparatus is employed as a reactor. The regularities of HCN formation in an acid medium are established in investigation into kinetics of SCN⁻ thiocyanate oxidation by hydrogen peroxide H₂O₂ in presence of Fe²⁺, Fe³⁺ and pH ≤ 3.5. In the process proposed the evolved HCN is adsorbed by NaOH solution and returned to the circuit of leaching of gold and silver as NaCN, and the waste cyaniding solution is discharged into a waste dump, where it is mixed with industrial water to be utilized to transport flotation tailings. __________ Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 1, pp. 98–105, January–February, 2009.     

Gold losses from cyanide solutions Part I: The influence of the silicate minerals

Shale material from Beatrix Gold Mine in South Africa has been found to be capable of adsorbing gold from cyanide solutions. Black shale bands occur in the reef zone at Beatrix Mine, but because of the mode of occurrence of the shale bands selective mining cannot be practised and ore delivered to the plant is contaminated by shale. Petrographical investigations and gold adsorption experiments were undertaken on samples of these shales, in an attempt to quantify their gold adsorption properties.Mineralogically the shales comprise muscovite, chlorite, pyrophyllite, and chloritoid which suggest that the shale is a low grade metamorphic rock. Gold adsorption experiments have shown that over time there is a drop in pH of the gold cyanide solutions. This is caused by decomposition of the phyllosilicates in the strongly alkaline solutions. Analysis of these solutions showed that high amounts of Si and Al are present. No Mg and Fe have been detected in the solutions which suggests that any dissolved Mg and Fe precipitate immediately on the surface of the solids so that gold can co-precipitate with colloidal Mg(OH)₂ and Fe(OH)₃. It was found that a tendency exists for high gold adsorption values to be preferentially related to high percentages of FeO (corrected for pyrite) + MgO + Al₂O₃ (corrected for muscovite) in the shales.     

The cyanide leaching of gold in solutions containing sulfide

A large proportion of the gold processed in the 21^st century will be recovered from sulfide ores. Since the sulfide minerals are to some extent soluble in cyanide solutions, there will always be some sulfur species present in the leach solution. It has been shown that soluble sulfide hinders the rate of gold leaching, forming a protective layer of the type Au/S_x. Electrochemical studies of the constituent half reactions: gold oxidation; and oxygen reduction, were consistent with this view. The effect of sulfide and cyanide concentrations on the leaching reaction were investigated, and it was shown that the sulfur formed is chemically attacked by cyanide, resulting in higher leach rates at higher cyanide concentrations. The effect of lead was also studied and is discussed in detail.     

Copper catalysed oxidation of thiosulfate by oxygen in gold leach solutions

The environmental and public concern over the continued use of cyanide in the recovery of gold has grown in recent times due to a number of recently publicised environmental incidents. Of the alternative lixiviants, thiosulfate appears to be the most promising, though the considerable amount of research conducted on thiosulfate leaching of gold over the last three decades has not resulted in its commercial introduction. Perhaps the largest contributing factor to this is the poor understanding of the thiosulfate leach solution chemistry, especially the oxidation of thiosulfate in the presence of copper(II) and oxygen. It has been shown in this research that the oxidation of thiosulfate in the presence of copper(II) and oxygen is very complex with the rates of copper(II) reduction and thiosulfate oxidation being significantly faster in the presence of oxygen. The higher initial rate of copper(II) reduction indicated that oxygen increases the rate of copper(II) reduction to copper(I) by thiosulfate, though the mechanism for this remains unclear. The rates of thiosulfate oxidation and copper(II) reduction were also shown to be affected differently by the presence of anions. This is consistent with thiosulfate oxidation occurring via two mechanisms, with one of these mechanisms involving the oxidation of thiosulfate by copper(II) and the other involving the oxidation of thiosulfate by the intermediate superoxide and hydroxide radicals formed as a result of copper(I) oxidation by oxygen. The effect of various parameters on the rate of thiosulfate oxidation and the copper(II) concentration are also shown.     

铜电解液电积脱铜制备高纯阴极铜

利用电积法制备高纯阴极铜, 研究了添加剂、电解液温度、电流密度以及Cu²⁺浓度对电积法脱铜制备高纯阴极铜质量的影响。当添加剂(骨胶: 明胶: 硫脲质量比为6∶4∶5)用量为40 mg/L, 电解液温度为55 ℃, 电流密度为200 A/m², 电解液中Cu²⁺浓度从48.78 g/L降至31.71 g/L时, 电积脱铜得到的阴极铜质量达到了高纯阴极铜标准(GB/T 467-1997); 其电流效率达到99.19%, 高纯阴极铜产率达到38.09%。电积脱铜制备高纯阴极铜不仅增加了阴极铜产量, 而且可大大减少电积时黑铜板和黑铜粉。     

Cyanide recovery in hydrometallurgical plants: use of synthetic solutions constituted by metallic cyanide complexes

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.     

铜冶炼渣浮选回收铜的研究现状

我国铜冶炼企业每年产生了大量的铜冶炼渣,其中含有大量的有价元素,如金、银、铜、钴、镍等,具有巨大的经济价值。如何经济环保地综合回收这部分有价元素不仅能为企业带来巨大的经济价值,更重要的是能解决铜渣大量堆存的问题。本文综述了目前铜冶炼渣浮选回收铜的研究进展,并在此基础上提出一些想法,为今后的铜渣综合回收提供了参考。     

Palladium(II) removal from chloride and chloride–nitrate solutions by chelating ion-exchangers containing N-donor atoms

The chelating ion-exchangers of functional iminodiacetate (Amberlite IRC-718), amidoxime (Duolite ES-346) and aminophosphonic (Duolite C-467) groups have been applied for Pd(II) removal from the model chloride (0.1–6.0 M HCl) and chloride–nitrate (0.1–0.9 M HCl and 0.9–0.1 M HNO₃ and 0.1–1.5 M HCl and 1.9–0.5 M HNO₃) solutions. The total ion-exchange capacities as well as recovery factors of Pd(II) were determined by the batch method. The influence of acid concentrations, phase contact time and macrocomponent addition (AlCl₃, CuCl₂, NiCl₂) was studied. The results show that the ion-exchangers of functional amidoxime and iminodiacetate groups can be widely recommended for Pd(II) ion removal from anodic slimes, and used up catalysts, as well as Pd(II) trace analysis due to their high selectivity.     

从炼铜水淬渣中浮选回收铜的试验研究

对湖北某铜冶炼厂的炼铜水淬渣(含铜1.06%)进行了浮选回收铜的试验研究。考察了磨矿粒度、矿浆浓度、pH值以及药剂用量等因素对炼铜水淬渣铜的浮选指标的影响。实验表明, 当磨矿粒度-0.074 mm占95%、矿浆浓度为30%、pH值为7.0、捕收剂(丁铵黑药与丁基黄药按1∶1配制)、活化剂(硫化钠)、分散剂(六偏磷酸钠)的用量分别为240 g/t、800 g/t、800 g/t时, 粗选铜的回收率为64.65%, 粗精矿铜的品位达到4.54%。     

湖北某铜尾矿再选回收铜硫试验

湖北某铜尾矿泥化严重,铜品位为0.13%、硫品位为2.89%,-200目占66.13%,主要铜矿物为黄铜矿。为综合利用该二次资源,进行了浮选试验。结果表明：试样采用1次浮选脱泥-磨矿-1粗3精浮铜-1粗3精1精扫浮硫流程处理,获得了铜品位为18.31%、回收率为60.71%的铜精矿和硫品位为53.70%、回收率为66.34%的硫精矿。     

混合铜冶炼渣浮选回收铜试验研究

粗选Ⅰ采用选择性强的捕收剂进行快速浮选,粗选Ⅱ采用捕收能力强的捕收剂进行分步浮选的工艺流程,对某冶炼混合炉渣进行了铜回收试验。结果表明,在磨矿细度为-45μm占85%给料下,以Z-200为粗选Ⅰ作业的捕收剂,快速浮选能直接获得含铜为27.57%、回收率为56.97%的铜精矿;以WP为粗选Ⅱ和扫选作业的捕收剂,并采用Na2S对矿浆进行硫化,调节p H为9.4,能获得含铜为17.32%、回收率为30.05%的铜精矿。混合后能获得含铜为22.89%,回收率为87.02%的最终铜精矿,同时渣选尾矿含铜降至0.23%。     

氰化尾渣熔融氯化提金银试验

以氰化尾渣原料,采用熔融氯化工艺提金,研究了氯化钙添加量、氯化时间、氯化钙的添加方式等因素对氯化提金的影响,并对如何降低熔融氯化温度进行了探索。结果表明,CaCl_2添加量为7%,分五次添加,熔融氯化时间为15min。氧化钙添加量为5%,熔融氯化温度为1 450℃。金挥发率为95.69%,渣含金为0.54g/t;银挥发率为77.06%,渣含银为4.20g/t。     

Gold losses from cyanide solutions part II: The influence of the carbonaceous materials present in the shale material

Gold was found to be mainly adsorbed onto the carbonaceous particles in the Beatrix shale material with possible minor loss of gold due to co-precipitation of gold with Mg(OH)₂ and Fe(OH)₃.Two types of carbonaceous material were present in low concentrations in the Beatrix shale and resembled kerogen. The one type can be described as filamentous particles and the other as roundish particles. Rank measurements done on the carbonaceous particles in the shales showed that they fall in the anthracite range. Adsorption of gold on carbonaceous material of similar rank showed that anthracite has the highest propensity to adsorb gold. This suggests that the carbonaceous particles would have similar gold adsorption properties as anthracite. The lack of an obvious correlation between the propensity of a shale to adsorb gold and its carbon content is probably due to the fact that not all the carbonaceous particles are liberated during milling so that they can be brought into contact with' the gold cyanide solution.     

Copper leaching from waste electric cables by biohydrometallurgy

This study examines the leaching of copper from waste electric cables by chemical leaching and leaching catalysed by Acidithiobacillus ferrooxidans in terms of leaching kinetics and reagents consumption. Operational parameters such as the nature of the oxidant (Fe³⁺, O₂), the initial ferric iron concentration (0–10 g/L) and the temperature (21–50 °C) were identified to have an important influence on the degree of copper solubilisation. At optimal process conditions, copper extraction above 90% was achieved in both leaching systems, with a leaching duration of 1 day. The bacterial leaching system slightly outperformed the chemical one but the positive effect of regeneration of Fe³⁺ was limited. It appears that the Fe²⁺ bio-oxidation is not sufficiently optimised. Best results in terms of copper solubilisation kinetics were obtained for the abiotic test at 50 °C and for the biotic test at 35 °C. Moreover, the study showed that in same operating conditions, a lower acid consumption was recorded for the biotic test than for the abiotic test.