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.     

预浮选-硫代硫酸钠浸金试验研究

通过对某矿原矿矿石性质的分析,采用预浮选—硫代硫酸盐法进行浸金工艺试验研究.浮选采用一粗一精浮选流程,药剂用量为硅酸钠1800g/t,硫化钠40g/t,丁基黄药80g/t,松油24g/t.浸出采用预浸(4h)-浸出(24h)-五次洗涤流程,常温常压、矿浆浓度33％、保护剂0.10kg/t、硫代硫酸钠10kg/t、助剂浓度0.76‰、氨水1.27％、石灰用量2kg/t,最终金浸出率达到86％以上.采用该法不仅毒性小,绿色环保,而且为金的中试回收提供了技术可行、经济合理的工艺流程和条件.     

焙烧温度对高岭石与硫代硫酸金相互作用的影响

因火法冶炼的高温活化作用,金可能与高岭石等硅酸盐类矿物相互作用,导致金的回收难度增大,探索焙烧温度对金与高岭石相互作用的影响具有意义。将室温高岭石及不同焙烧温度下的高岭石焙渣分别与硫代硫酸金充分混合进行搅拌试验,结合红外光谱和X射线衍射对高岭石与硫代硫酸金相互作用进行机理探讨。在矿浆浓度28.6%、初始金浓度85mg/L、搅拌转数500r/min及搅拌时间30min的条件下,得出高岭石与硫代硫酸金吸附能力强。与室温搅拌相比,焙烧活化了高岭石,增强了高岭石对硫代硫酸金的吸附效果。经700℃焙烧后的焙渣对硫代硫酸金的吸附量急剧增加,表明该温度下的焙渣对硫代硫酸金的吸附能力强。     

A kinetic and electrochemical study of the ammonia cyanide process for leaching gold in solutions containing copper

One of the biggest challenges for the gold industry in the 21st century is the presence of copper in gold containing ore bodies. This is because copper consumes large quantities of cyanide. In addition, copper cyanide species are more stable than free cyanide, and hence are problematic in events of tailings spillage. One of the methods which has been suggested for treating copper containing ores is to leach with an ammonia cyanide solution. The effect of copper and ammonia addition on gold leaching kinetics was studied in the present paper. It will be shown that when the solutions do not contain copper, the addition of ammonia decreases the rate of gold leaching. When copper is added to solution, the leach rate does decrease due to the formation of the copper cyanide complexes. However it will be shown that under conditions of zero free cyanide, gold does leach readily via the Cu(CN)₃²⁻ complex. It was found that the addition of ammonia had little effect on the leaching of gold by Cu(CN)₃²⁻, but did increase the leaching kinetics when the major cyanide species present is Cu(CN)₂⁻. Under these conditions, leaching in the absence of ammonia is very slow. The effect of copper(II) addition was also studied, and it was found that in the absence of free cyanide the presence of copper(II) increases the leach rate, provided there is enough ammonia to stabilise it against reaction with the copper(I) cyanide complexes.     

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.     

Thiosulfate leaching kinetics of gold in the presence of copper and ammonia

In recent years a significant amount of research has focused on thiosulfate as an alternative lixiviant for gold. However few fundamental studies have been undertaken due to the complexity of the solution chemistry. This study investigates the effect of various parameters on the gold leaching kinetics and the undesirable homogeneous copper(II) reduction by thiosulfate. The leach kinetics are measured at essentially constant solution conditions using a rotating electrochemical quartz crystal microbalance, which measures mass changes in real time and hence leach rates within minutes. The gold leaching kinetics were found to be chemically controlled and the rate was found to decrease with time as the copper(H) concentration decreased. This can be attributed to passivation of the gold surface by the products of the copper(II)-thiosulfate reaction. Optimum leach conditions derived from this study are 0.4M ammonia, 0.1M thiosulfate, pH > 11.4, and temperature at 30°C.     

硫代硫酸盐浸金体系中硫代硫酸钠电化学研究

循环伏安法(CV)研究了硫代硫酸盐以及模拟金浸出溶液中硫代硫酸钠电化学行为,计算了相关电化学参数;采用方波伏安(SWV)对硫代硫酸钠进行定量分析,可以发现硫代硫酸钠的浓度为0~0.15 mol/L呈现出良好的线性关系。     

难处理金矿热压氧化工艺研究

本试验以国内某超细微难处理金矿为研究对象,开展酸性热压氧化工艺研究;分析了温度因素对硫化矿物氧化、元素迁移和金氰化浸出等的影响。试验结果表明,通过温度变化可影响黄铁矿和砷黄铁矿氧化反应速率,进而对S、Fe和As元素的迁移状态产生影响。反应温度越高黄铁矿和砷黄铁矿氧化越彻底,有利于金的氰化浸出;完全氧化后金的浸出率约为94%。浮选金精矿中的黄铁矿、砷黄铁矿逐渐氧化转变为砷酸铁盐、铁砷硫硅等多元素共沉物质,未发现有碱式硫酸铁或铁矾物相,反应生成的各种沉淀产物对浸出率无显著影响。      

Leaching of gold from off-grade products

Kinetics of sulfide decomposition and gold dissolution during electrochemical extraction is described. The results are presented for the experiments on electrochemical extraction of gold from sulfide ores of the Kazakhstan deposits using sodium salt at the ABS Concern. The economically efficient parameters of applying leaching technology for rebellious sulfide ores are determined.Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 4, pp. 84–88, July–August, 2004.     

Ferrates performance in thiocyanates and ammonia degradation in gold mine effluents

Available technologies for cyanides (CN⁻) treatment in gold mine effluents marginally degrade the thiocyanates (SCN⁻). Commonly, they convert the CN⁻ into a less toxic compound, such as cyanates (OCN⁻), which afterwards are oxidized and generate ammonia nitrogen (NH₃-N). Thus, the pretreated effluents require additional steps for complete degradation of SCN⁻ and NH₃-N. Recent research shows that ferrates [Fe(VI)] might represent a sustainable option for the efficient treatment of gold mine effluents. In this context, the objective of the present study was to assess the performance of Fe(VI) in SCN⁻ and/or NH₃-N treatment, as well as in their by-products degradation. The performance of Fe(VI) was evaluated using three different synthetic effluents (solutions) and two gold mine effluents contaminated by SCN⁻ and/or NH₃-N. Results indicated that more than 97% of SCN⁻ were degraded with Fe(VI), while the NH₃-N increased up to 50%, after SCN⁻ oxidation of the presence of NH₃-N, within one hour of reaction time. Consequently, for effluents that contain SCN⁻ and NH₃-N, longer reaction time is required or complementary treatment technologies, such as nitrification – denitrification, should be evaluated for complete degradation of N-compounds.     

某金矿采矿活动对地下水的影响分析

采矿对地下水造成的影响主要是水位下降,以北方某金矿为例,探讨在《环境影响评价技术导则—地下水环境》指导下如何进行采矿区地下水环境影响评价工作。根据导则确定本次评价的等级为二级。通过水文地质条件合理概化,选用合理的公式,用解析法辅以数值法预测倾斜承压含水层中采矿对地下水的影响。结果表明,本区采矿活动对浅层地下水造成的影响不大,结果合理,可以为类似矿山的地下水环境影响评价提供参考。     

Dissolution of gold during pyrite oxidation reaction

Numerous papers discuss the mechanism of alkaline oxidation of pyrite but there is limited information available describing the actual kinetics of the pyrite sulphide to thiosulphate reaction. A previous investigation in this series determined the rate of sulphide sulphur oxidation and thiosulphate yield in the reaction of pyrite with sodium hydroxide under various testing conditions. The goal of the current study is to validate these rates using two different gold-containing pyrite concentrates. A further objective of the current work is to investigate the simultaneous dissolution of gold with in situ formed thiosulphate during pyrite oxidation.It was found that at 20 psi oxygen overpressure and a temperature of 80 °C, the initial rate of sulphide oxidation and thiosulphate yield were close to 0.08 mol/h and 0.0155 mol/h, respectively. These rates are in agreement with previously published data. However, a shift from linearity occurred when the pH decreased below 12. A rapid decay of thiosulphate was evidenced at pH 8.3–9.2 while E_H was in the range of 22–141 mV. Based on relevant thermodynamic analysis of metastable thiosalts system, such rapid decomposition is not expected at these pH and E_H values. It is believed that the presence of unreacted pyrite acting as a catalyst caused this behaviour. It appears that under mildly alkaline conditions, the rate of oxidation of sulphide to thiosulphate becomes slower than the rate of thiosulphate degradation, which causes a net loss of thiosulphate in the system. The maximum extraction of gold and silver (96% and 75% respectively) was achieved under conditions of pH < 12.     

黄金中游产品国际贸易网络演化特征研究

黄金是中国战略性矿产资源之一,黄金中游产品国际贸易能反映产业链上下游国际供给关系及供给安全,战略意义重大。为了研究黄金中游产品国际贸易网络演化特征,本文利用2008～2017年的黄金中游产品国际贸易数据,基于复杂网络理论,构建了有向加权复杂网络模型,从贸易网络的整体结构特征、幂律分布特征、贸易枢纽国、核心国家识别等方面进行研究。结果显示,其贸易参与规模不断扩大,但贸易份额向少数国家集聚程度增加;美国、德国的贸易控制能力较强,处于贸易枢纽地位。通过研究,建议黄金中游产品贸易国通过观测美国、德国的黄金贸易趋势调整贸易量;瑞士、南非、美国是相关国家的首选贸易伙伴;澳大利亚、巴西和南非是拥有精加工能力但资源不足的国家建立贸易关系的首选。     

次磷酸盐对煤氧化特性影响研究

用次磷酸钠、次磷酸铝、次磷酸镁三种磷化物对煤样进行阻化处理后,通过程序升温自燃氧化模拟实验,结合气相色谱分析仪全面分析了整个升温氧化过程中CO释放量,同时通过红外光谱实验分析了三种磷化物对煤表面官能团的影响。实验结果表明,添加次磷酸盐后,在升温过程中CO浓度均有不同程度的降低,次磷酸铝和次磷酸钠的阻化效果要好于次磷酸镁。三种磷化物对阻止煤分子中的C-O键断裂以及抑制甲基与亚甲基的氧化均起到一定作用。     

A gold content in brown coal and combustion products

The authors determine the forms of gold transfer under coal combustion by using the experimental data. It is found that the micron-sized and nano-sized gold particles are carried away with flue ash during combustion, and only the insignificant part of the gold, localized at underburnings, remains in the form of the free gold within a combustion chamber. The authors shows that applying the method of fumesteam mixing and its futher condensation provides the maximum volatile forms of gold, being the base for creating the geotechnology of unified production cycle of the efficient stock usage and the environmental safety provision.     

Initial loss of cyanide, thiocyanate, and thiosulfate adjuvants following amendment to an oxidic gold ore

Gold extraction and gold phytomining involve the use of adjuvants such as cyanide, thiocyanate, or thiosulfate to facilitate the dissolution of gold and its subsequent recovery. The adjuvants can be applied at high rates, in excess of 1 kg t⁻¹ for some ores. At these concentrations, concerns have been expressed about adjuvant persistence and associated detrimental repercussions for the environment. The incubation study here examined the initial disappearance of these adjuvants in the dark following their amendment at 1 g kg⁻¹ gold ore. Over a 24 d period, nearly 75% of the initial thiocyanate was lost within 24 d while >50% of thiosulfate and cyanide was lost over the same time frame. Cyanide and thiosulfate loss showed an exponential loss while thiocyanate was observed to follow a biphasic relationship. For the oxidic ore used, the adjuvants were not inherently persistent, suggesting that natural attenuation may rapidly promote adjuvant loss under specific conditions.     

难处理金矿热压氧化工艺研究.1.温度影响

本试验以国内某超细微难处理金矿为研究对象,开展酸性热压氧化工艺研究;分析了温度因素对硫化矿物氧化、元素迁移和金氰化浸出等的影响。试验结果表明,通过温度变化可影响黄铁矿和砷黄铁矿氧化反应速率,进而对S、Fe和As元素的迁移状态产生影响。反应温度越高黄铁矿和砷黄铁矿氧化越彻底,有利于金的氰化浸出;完全氧化后金的浸出率约为94%。浮选金精矿中的黄铁矿、砷黄铁矿逐渐氧化转变为砷酸铁盐、铁砷硫硅等多元素共沉物质,未发现有碱式硫酸铁或铁矾物相,反应生成的各种沉淀产物对浸出率无显著影响。     

内蒙古某金矿磨矿分级产物离心重选实验研究

针对内蒙古某金矿磨矿分级回路存在粗粒自由金的循环积聚,本文研究采用离心重选从磨矿分级产物中回收粗粒金.结果表明,离心重选对一段沉砂的分选效果较好,利用回归分析,建立一段沉砂离心重选中影响因素与选别指标的二元二次回归方程,并绘制响应曲面,确定较佳分选条件,即离心力场60 G左右、高反冲水压力＞70kPa.在较佳条件下,重选精矿金品位随批次给矿量增加而线性增大,当一次实验给矿量增加到15 kg时,精矿品位可达760g/t.研究成果为现场技术改造提供了重要参考依据.     

神华煤钌离子催化氧化解聚产物的FT-ICR MS分析研究

针对神华长焰煤初步开展了钌离子催化氧化法(RICO)的应用研究,对原煤进行降解反应并尝试运用高分辨电喷雾傅里叶质谱仪（ESI-FTMS）对氧化产物进行分析表征。结果表明,神华煤含有C-2～C-32烷基侧链和连接芳环之间的C-2～C-27亚甲基桥链,芳环缩合程度相对较低（主要以含有2～4个苯环的共轭结构为主）,有较多醚键连接的芳环结构及羟基（-OH）、羰基（CO）和甲氧基（-OCH-3）等含氧官能团存在。