Electro-recovery of gold and silver from a cyanide leaching solution using a three-dimensional reactor

The selective electro-recovery of gold and silver values from cyanide leaching solutions containing copper was accomplished in a three-dimensional (3D) electrochemical reactor. This case let to contrast three different points of view when dealing with a composed metallic solution: First, the thermodynamic predictions; second, the microelectrolysis approach and finally, the macroelectrolysis experiments. Standard electrode potentials for the study solution would indicate a tendency for gold to deposit first. However, microelectrolysis studies of the three-metallic solution indicated that gold and silver are co-deposited onto a Vitreous carbon (VC) electrode without copper interference in a narrow potential range. Mass balances during the macroelectrolysis experiments (batch model assuming mass transfer control) indicated a preferential deposition of silver during the first ten minutes, even if gold deposition also occurred. On the other hand, values of Stanton (St) for different linear flow velocity corroborated that metals concentration gradients may establish a limit to make profitable the fluid velocity increase in an electrochemical flow cell. Electrolysis experiments were carried out under potentiostatic (at −1400 mV versus SCE) and galvanostatic (at −3.9 Am⁻²) conditions in the FM-01 LC flow cell.     

Electrochemical studies of gold ore processing wastewater containing cyanide, copper, and sulfur compounds

The electrochemistry of real gold ore processing wastewater solutions from copper sulfide containing gold ore has been investigated. Analysis shows that the wastewater contains a range of sulfur compounds in various oxidation states from sulfide to sulfate. The electrochemical characteristics of the gold ore processing wastewater were evaluated using rotating disk, cyclic voltammetric, polarization and preparative electrolysis studies. The solutions show clear differences versus synthetic alkaline copper cyanide solutions. The copper cyanide/copper oxide catalysis normally seen in synthetic alkaline copper cyanide solutions is strongly inhibited. Two components of the wastewater solution identified as inhibiting the copper cyanide/copper oxide catalysis are copper sulfide complexes and thiocyanate. The inhibition of the copper cyanide/copper oxide catalysis appears to have an initiation time possibly related to the accumulation of copper-sulfur compounds at the electrode surface. The passivated surface is still able to oxidize cyanide, though at a maximum rate that corresponds to the limiting current for free cyanide assuming 1 electron per cyanide. The lack of the copper oxide coating that typically forms during oxidation of synthetic alkaline copper cyanide solutions, plus possibly the presence of various sulfur compounds, results in corrosion at higher anodic potentials when stainless steel is used as an electrode. However, stainless steel can be successfully used as an electrode material to treat the solutions if the potential is carefully controlled.     

Electrochemical treatment of dilute cyanide solutions containing zinc complexes by oxidation at carbon felt (Sigratherm)

The electrochemical oxidation of dilute solutions containing cyanide complexes of zinc using a carbon felt anode is described. The composition of the solution was determined using stability constants for particular complexes. The application of a GFA5 electrode enables the oxidation of cyanides (10 mmol dm^–3) in 99.2% at 0.7 V and 30 C (1.5 Q _t). Under these conditions, the electrical energy consumption is about 24 kWh (kg CN^–)^–1. Modification of the anode surface with copper oxides allows a cyanide conversion degree of 99.6% at 0.7 V and 17.5 C (0.875 Q _t with electrical energy consumption of 17.6 kWh (kg CN^–)^–1. However, modification of the anode resulted in 75% destruction.     

双脉冲DMS氰化光亮镀银工艺技术的应用

介绍了双脉冲氰化光亮镀银的工艺流程和工艺配方。讨论了脉冲电源参数、镀液中的硝酸银、氰化钾和DMS光亮剂的质量浓度以及镀液温度对镀层质量的影响。对镀层缺陷产生的原因进行了分析。实践证明,与直流电镀相比,在20～30℃的镀液中,采用双脉;中DMS氰化光亮镀银工艺,可以获得外观光亮的银镀层,且其抗变色性能增强．同时生产效率提高30％,每年可以节约银20％、铜刷72只、工时1240h。     

含硫浸出渣硫回收设计

介绍了从含硫浸出渣中回收硫磺的50kt／a硫回收装置的工艺流程及主要设备。在已有的硫回收设计经验及生产实践基础E,对硫回收工艺进行了优化。含硫浸出渣硫磺的回收率为80％～85％,硫化物滤饼中W（S）40％～45％,该滤饼可作为沸腾炉焙烧的原料。     

Recovery of copper from copper concentrator tailings by leaching

Tailings from a chalcopyrite beneficiation plant (concentrator) have been leached with dilute ferric chloride in a packed bed. The effect of leaching time and packed bed height on the conversion of cuprous sulphide (present in tailings) has been determined. For predicting the conversion, an expression based on the shrinking core model has been derived and compared with the experimental data. At low conversion, the agreement is good, but at intermediate and high conversion the deviation is considerable.     

从铜浸出渣中浮选回收元素硫的研究

考查了适合浸出渣中元素硫浮选回收的理想工艺参数,并利用旋流-静态微泡浮选柱取得了良好的分选指标,最终精矿的元素硫品位达到56.08%,为铜浸出渣的合理利用探求了一种工艺简单、成本节约的新方法.     

鼓氧氰化法生产高纯度氰化银钾的研究

以电解银粉为原料，采用鼓氧氰化法合成了氰化银钾，保持金属银过量投料，控制氰化银钾溶液浓缩水量是得到高纯度和高收率产品的关键，此方法具有原料简单，产吕纯度高，生产操作容易，生产成本低和环保要求低的优点，适合中小企业生产。     

Electrochemical removal of cadmium from dilute aqueous solutions using a rotating cylinder electrode of wedge wire screens

Rates of mass transfer at rotating cylinder electrodes of wedge wire screens were studied by measuring the limiting current for the cathodic reduction of ferricyanide as test reaction. The experimental data are well correlated by an empirical expression between the Sherwood number and the Reynolds number, both in terms of the internal slot opening as characteristic length, and including two additional dimensionless parameters in order to characterize the geometry of the screens. The performance of an undivided electrochemical batch reactor with a rotating cylinder cathode of wedge wire screens was tested analyzing the cadmium removal from dilute solutions. The effect of cathodic applied potential and size of the screen is studied. Taking into account the residual cadmium concentration the best results were obtained for a cathode potential of −1.1 V vs. SCE at 700 rpm, where the cadmium concentration decreased from 54 to 0.9 mg l⁻¹ after 30 min of electrolysis with a specific energy consumption of 10.7 kWh kg⁻¹ and a normalized space velocity of 3.54 h⁻¹.     

L-半胱氨酸电化学组装膜的研究

通过循环伏安法将L-半胱氨酸电化学组装到铜电极上,用交流阻抗法和循环伏安法研究了循环扫描周数以及组装时间与峰电流的关系,并研究了扫描速度对L-半胱氨酸膜的影响,结果表明L-半胱氨酸膜的氧化峰电流与扫描速度的平方根成正比,说明L-半胱氨酸在铜电极上的电化学组装过程受扩散控制。     

Anodic behaviour of alkaline solutions containing copper cyanide and sulfite on the graphite anode

Sulfite may be added to copper cyanide solutions to reduce cyanide oxidation at the anode during copper electrowinning. Anodic sulfite oxidation is enhanced in the presence of copper cyanide. Sulfite also suppresses the oxidation of copper cyanide. The effect of sulfite on the oxidation of copper cyanide decreases with increasing mole ratio of cyanide to copper. This is related to the shift in the discharged species from Cu(CN)₃ ^2– to Cu(CN)₄ ^3– with increasing mole ratio of cyanide to copper. Sulfite is oxidized to sulfate. At [Cu⁺] = around 1 M, CN:Cu = 3.0–3.2, [OH^–] = 0.05–0.25 M, [SO₃ ^2–] = 0.4–0.6 M and the temperature = 50–60 °C, the anodic current efficiency of sulfite reached 80–90%. With further increase in sulfite concentration beyond 0.6 M, the current efficiency of sulfite oxidation will not be increased significantly. Further increase in CN:Cu mole ratio will result in decrease in the anodic current efficiency.     

A spectroelectrochemical investigation of the influence of sodium diisobutyldithiophosphinate on silver dissolution in aqueous cyanide

Polarization studies have been carried out to determine the influence of diisobutyldithiophosphinate (DIBDTPI) on the dissolution of silver in cyanide solutions at pH 11. DIBDTPI was found to inhibit dissolution at concentrations similar to those used when this compound is applied as a flotation collector. The inhibition efficiency in 10^–2 mol dm^–3 CN^– was found to increase with increase in DIBDTPI concentration in the range 10^–6–10^–4 mol dm^–3, and with increase in time of exposure of the silver to the DIBDTPI solution. The inhibition efficiency found for 10^–4 mol dm^–3 DIBDTPI in quiescent 10^–2 mol dm^–3 CN^– solution at 23 °C was 64.6% and 95.0% for exposure times of 10 min and 2 h, respectively. These values are significantly less than those found previously for 2-mercaptobenzothiazole under the same conditions. Surface enhanced Raman spectroscopy showed that inhibition was associated with adsorption of DIBDTPI displacing cyanide from the silver surface. Voltammetry at 0.5 mV s^–1 indicated that adsorption of DIBDTPI involves charge transfer.     

Electrochemical process for metal recovery from iodized silver derivatives in liquid/solid mixture: Experimental and theoretical approaches

This work examines the electrochemical behavior of “iodized silver derivatives,” pure or adsorbed on solid industrial wastes, in order to devise an electrochemical process for metal recovery from matrices containing these species. Voltammetric, coulometric and adsorption measurements were used to determine the reduction mechanism of silver derivatives at the electrode and to propose a reaction rate law depending on operating conditions.Mass balances and electrical balances of electrolyses of aqueous suspensions of solid wastes led to a better understanding and to the optimization of the overall electrochemical process of silver recovery. Comparison of experimental and theoretical results indicates the feasibility of the process proposed.     

电化学法处理洗漱废水的试验研究

以家庭洗漱废水为研究对象,采用电化学法处理进行试验研究。考察在不同的槽电压、水力停留时间（HRT）下电化学反应器对废水中CODCr、氨氮、硝酸盐氮、亚硝酸盐氮的去除效果以及对溶解氧（DO）的增加率的影响。结果表明,电化学氧化对氨氮、硝酸盐氮、CODCr的去除有明显效果;对亚硝酸盐氮没有去除效果,反而使其浓度增加;对溶解氧（DO）的增加有显著效果。综合考虑各项水质指标,考虑能耗和经济效益,选择电压20V、停留时间5min处理效果较佳。     

An electrochemical investigation of the suppression of silver dissolution in aqueous cyanide by 2-mercaptobenzothiazole

Triangular potential sweep voltammetry, potentiokinetic generation of polarization curves, and coupon corrosion tests have been carried out to determine the influence of 2-mercaptobenzothiazole (MBT) on the dissolution of silver in cyanide solutions at pH 11. MBT has been shown to be an effective inhibitor for silver dissolution at concentrations similar to those used when MBT is applied as a flotation collector. The inhibition efficiency (i.e., [1 – the ratio of the corrosion rates in the presence and absence of MBT], expressed as a percentage) in 10^–2 and 10^–3 mol dm^–3 CN was found to increase with increase in MBT concentration in the range 10^–6 to 10^–4 mol dm^–3, and with increase in time of exposure of the silver to the MBT solution. The inhibition efficiency found for 10^–4 mol dm^–3 MBT in quiescent 10^–2 mol dm^–3 CN^– solution at 23 °C was 98.9%, 99.4% and 99.99% for exposure times of 10 min, 2 h and 5 days, respectively. Surface enhanced Raman spectroscopy showed that inhibition was associated with adsorption of MBT displacing cyanide from the silver surface.     

Corrosion of cyanide copper deposits on zinc diecastings in acid solutions

The corrosion potential and morphology of copper films deposited from a cyanide solution on zinc diecast were studied in acid solutions similar to those employed in industry for the deposition of a second copper layer. Open circuit potential measurements and gravimetric methods were employed to determine the influence of the copper electrodeposition variables on the corrosion potential. The influence of variables such as the presence or absence of additives, the current density and the copper or cyanide concentrations were studied. The corrosion potential decreased with increasing copper film thickness. Less protection was obtained when a thin copper layer was electrodeposited from a solution without additives. Higher protection for the same thickness was obtained from a solution with high cyanide content. This result is related to the strong interaction between cyanides and the metal surface during the electrodeposition. A smooth surface structure was observed by SEM under these conditions.     

水中氰化物测定方法改进及回收率提高探讨

水中总氰化物的测定是水质全分析中的一项毒性含量指标。它是衡量水体中生物生存、人类饮用用水、工业生产用水的重要参数。但其含量监测方法(GB7486-1997)步骤繁琐、费时。作者提出了在原方法基础上用蒸馏水分别代替氢氧化钠作为氰化氢吸收液和氰化钾稀释液的实验方法,通过对照试验分别采用不同浓度样品进行回收率测定。测得该法标准偏差为0．0004、检出限达到0．0026,监测效果较好,在一定程度上简化了试验操作的繁琐性。并讨论了使用改进后方法对于提高该法回收率测定的几点建议。     

电解铜箔钛阴极辊简轴电刷镀银工艺

电解法生产铜箔必须使用钛阴极辊筒，由于其工作电流高达35kA-40kA，为了提高钛阴极辊筒的导电性能，要求在其导电环内壁与之接触的轴表面电镀一层金属银，由于钛阴极辊筒体积庞大，无法在电镀槽内进行电镀，采用电刷镀方法镀银最合适，本文介绍电刷镀银的工艺过程及影响因素。     

Electrochemical reduction of dilute chromate solutions on carbon felt electrodes

Carbon felt is a potential material for electrochemical reduction of chromates. Very dilute solutions may be efficiently treated due to its large specific surface area and high porosity. In this work, the up-scaling of this technology is investigated using a new type of separated cell and once-through flow of industrial rinse water. A significant enhancement of the process is obtained due to copper deposition during long-term operation. The co-deposition and re-solution of copper occurs depending on the inlet chromate concentration. When previously deposited copper is present a current-free reduction of chromate takes place resulting in current efficiencies apparently above 100%. Very high space time yields are obtained even for effluents at low concentration and optimised conditions (high flow rates and pH 2). The economic feasibility of the technology is also considered. Continuous, single-pass operation results in lower energy requirements than batch processing. The economic potential of the process is also evaluated in comparison with chemical detoxification of chromate. The operating costs for the electrochemical treatment of very dilute effluents on a carbon felt electrode are 30% lower than for the chemical method.     

碳酸铜矿中钴的选择性浸出

对碳酸铜矿中铜、钴浸出过程的反应及行为进行了分析。在大量实验的基础上,结合理论分析,探讨了浸出条件对矿样中钴选择性浸出的影响,进而确定了钴选择性浸出的实验室最佳条件为:浸出时间3 h,浸出温度70℃以上,pH为5,液固体积比为5∶1,浸出液中添加质量浓度为27.11 g/L的硫酸铜溶液1.5 mL。实验结果表明,该条件下钴的浸出率可达到78.37%,铜的浸出率仅为0.04%,实现了钴与铜的有效分离,可以优先浸出钴,实现钴资源的充分利用。