DISSOLUTION THEORY OF GOLD IN ALKALINE THIOUREA SOLUTION(Ⅱ)——Electrochemical Study on Au-Fe Mix Anode in Alkaline Thiourea Solution Containing Na_2SO_3

１ＩＮＴＲＯＤＵＣＴＩＯＮＭａｎｙｓｔｕｄｉｅｓｏｎｔｈｅｅｘｔｒａｃｔｉｏｎｏｆｇｏｌｄｆｒｏｍｏｒｅｏｒｓｃｒａｐｗｉｔｈｔｈｉｏｕｒｅａｗｅｒｅｒｅｐｏｒｔｅｄ［１－３］，ｂｕｔａｌｔｈｏｓｅｗｅｒｅｌｉｍｉｔｅｄｏｎｌｙｉｎａｃｉｄｉｃｍｅｄ...     

Dissolution theory of gold in alkaline thiourea solution(Ⅲ) ——Thermodynamics on dissolution of gold in alkaline thiourea solution containing Na _2SO_3

１　ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｍｅｃｈａｎｉｓｍａｎｄｃｈｅｍｉｃａｌｐｒｏｃｅｓｓｆｏｒｄｉｓｓｏｌｖｉｎｇｇｏｌｄｉｎａｃｉｄｉｃｔｈｉｏｕｒｅａｓｏｌｕｔｉｏｎｗｅｒｅｓｔｕｄｉｅｄｂｙｍａｎｙｒｅｓｅａｒｃｈｅｒｓ［１～５］，ｗｈｏｇｅｎｅｒａｌｌｙｔｈｏｕｇｈｔｔｈａｔｔｈｉｏｕｒｅａａｓａｓｔｒｏｎｇｌｉｇａｎｄｃｏｍｐｌｅｘｅｓｓｅｌｅｃｔｉｖｅｌｙｗｉｔｈｇｏｌｄｉｏｎｔｏｆｏｒｍｓｔａｂｌｅｃｏｍｐｌｅｘｉｏｎＡｕ［ＣＳ（ＮＨ２）２］＋２，ａｎｄｓｏｍｅｏｘｉｄａｎｔｓ…     

DISSOLUTION THEORY OF GOLD IN ALKALINE THIOUREA SOLUTION(I) Anodic Behavior on Gold in Alkaline Thiourea Solution Containing Na2SO3

Anodic polarization behaviors of gold and its associated elements, e.g., silver, copper, nickel and iron, in the alkaline thiourea solution with and without Na2SO3 were examined. The results showed gold is hardly dissolved in the solution with Na2SO3 because of the passivation of elemental sulfur produced by irreversible decomposition of alkaline thiourea; however, the additive Na2SO3 improves the stability of thiourea in alkaline media, greatly increases anodic current of gold and accelerates the selective dissolution of gold in the alkaline thiourea solution, without changing the passivation states of the associated elements of gold. Also the factors affecting the polarization of gold anode were investigated in detail, and it was found that, the Na2SO3obviously decreases polarization potential of gold and the apparent activation energy of gold dissolution, and the controlling step of the dissolution of gold anode in the alkaline thiourea solution is changed from the anode dissolution reaction to the solute diffusion. The mechanism for accelerated dissolution of gold in the alkaline thiourea solution with Na2SO3 was considered as electrochemical reduction and catalysis, over the Na2SO3 concentration of 0.01 ～0.5 mol/L, at the potential of 0.34～0.44 V.     

Dissolution theory of gold in alkaline thiourea solution(

The oxidants of gold were investigated in an alkaline thiourea solution containing Na₂CO₃, in which Na₂S₂O₈ is a proper oxidant for dissolving gold because of in such homogeneous sulfur system coexisting complex agent, oxidant and stabilizing agent. The thermodynamic analyses were conducted on the dissolving of gold in the alkaline thiourea solution containing Na₂SO₃ by the oxidants oxygen or Na₂S₂O₈. The results show that the possibility of gold dissolution reduces with increasing pH value, while oxygen acts as oxidant; and when Na₂S₂O₈ acts as the oxidant of gold in the alkaline thiourea solution of pH 12.5, decomposition potential of thiourea decreases from the standard value 0.42 V to -0.32 V, also the dissolution trend of gold enhances with shifting the mix potential of the solution to the positive direction.     

亚硫酸钠在碱性硫脲溶金体系中的电化学行为

用电化学工作站测试金电极和铂电极的极化曲线和交流阻抗,研究亚硫酸钠对碱性硫脲溶解金的影响。结果表明,亚硫酸钠对金的腐蚀电位(E_(corr))为-0.776 V,远低于硫脲,腐蚀速率为0.014mm/a,是有效的溶金试剂;在铂电极上测试,硫脲在碱性条件下会发生不可逆氧化分解,但亚硫酸钠对硫脲的氧化分解没有明显抑制作用;当硫脲中添加亚硫酸钠后,E_(corr)降低,腐蚀速率增大,电化学阻抗弧值大大降低,协同促进金的溶解;0.15 mol/L硫脲+0.15 mol/L亚硫酸钠的溶液具有最佳溶金效果。     

Recovery of Precious and Base Metals from Waste Printed Circuit Boards Using a Sequential Leaching Procedure

This paper considers the issue of recycling of waste printed circuit boards (WPCBs) containing precious and base metals in appreciable amounts. High-pressure oxidative leaching (HPOL) with dilute sulfuric acid resulted in removal of a significant amount of base metals from a WPCB ash sample obtained by incineration at 800°C. The parameters investigated in the precious metal leaching from WPCB residue after HPOL included the sulfuric acid concentration, thiourea concentration, oxidant concentration, leaching temperature, and leaching time. Recovery of gold, silver, and palladium of 100%, 81%, and 13% from the WPCB residue sample was achieved by thiourea leaching under optimized conditions. The results show that the efficiency of precious metal dissolution from the WPCB sample using thiourea solution depended strongly on the concentration of both thiourea and oxidant.     

Dynamics of anodic process of gold electrode in thiourea solution in the presence of sulfur dioxide

1　INTRODUCTIONCyanidefreetechnologyofgoldextractionisanimportantissueinhydrometallurgy[1,2 ] .Thioureawasusedasanimportantmetallurgicalreagentduetoitsgoodselectivity ,low poisonousnessandhigheffi ciency[3,4 ] .Refs .[5 7]showedthatanodedissolv ingofgoldwillbeacceleratedifsulfurousacidorsul furdioxide (H2 SO3)isaddedintothioureasystem .Themechanismwasconsideredthatsulfurousacidwasinvolvedintotheelectrochemistryreactionofthesystem ,mainlyacceleratingdeoxidizationreactionofformamidinedisul…     

Separation of precious metals using selective mesoporous adsorbents

The mesoporous NH₂-MCM-41 adsorbent prepared by grafting aminopropyls on MCM-41 is selective towards gold and palladium adsorptions and can separate these precious metals from complex solutions containing other metal ions such as cobalt, nickel, copper and zinc. Adsorption is rapid and the adsorbent’s capacity for gold is better or comparable to most carbonaceous adsorbents including activated carbons. Furthermore, NH₂-MCM-41 can separate palladium from gold solution at pH1.0 with excellent selectivity and capacity. Thus, it is possible to design a two steps separation process for the separation of palladium and then gold from the complex solution. A simple acid wash was sufficient to recover the adsorbed palladium and gold as concentrated, high purity (i.e., > 95%) metal salt solutions and the regenerated adsorbent was reused without lost of performance.     

碱性硫脲浸金的研究现状与发展趋势

阐述了可能取代氰化浸金的高效、无毒碱性硫脲浸金的研究现状。相比酸性硫脲浸金,碱性硫脲浸金具有溶金选择性好,溶液的再生及净化工序相对容易等优点。阐明了碱性硫脲浸金原理及金在碱性硫脲溶液中的溶解机理,对碱性硫脲溶液中的稳定剂及氧化剂的选择做了详细探讨。最后,指明了碱性硫脲浸金所取得的成果及需要解决的问题,并展望了其发展趋势。     

Corrosion and corrosion inhibition of Cu-20%Fe alloy in sodium chloride solution

The electrochemical behavior of copper (Cu), iron (Fe) and Cu-20%Fe alloy was investigated in 1.0 M sodium chloride solution of pH 2. The effect of thiourea (TU) addition on the corrosion rate of the Cu-20%Fe electrode was also studied. Open-circuit potential measurements (OCP), polarization and electrochemical impedance spectroscopy (EIS) were used. The results showed that the corrosion rates of the three electrodes follow the sequence: Cu < Cu-20%Fe < Fe. Potentiostatic polarization of the Cu-20%Fe electrode in the range −0.70 V to −0.45 V (SCE), showed that iron dissolves selectively from the Cu-20%Fe electrode surface and the rate of the selective dissolution reaction depends on the applied potential. At anodic potential of −0.45 V, thiourea molecules adsorb at the alloy surface according to the Langmuir adsorption isotherm. Increasing thiourea concentration (up to 5 mM), decreases the selective dissolution reaction and the inhibition efficiency η reach 91%. At [TU] > 5 mM, the dissolution rate of the Cu-20%Fe electrode increases due to formation of soluble thiourea complexes. At cathodic (−0.6 V), the inhibition efficiency of thiourea decreases markedly owing to a decrease of the rate of the selective dissolution reaction and/or desorption of thiourea molecules. The results indicated that thiourea acts mainly as inhibitor of the selective dissolution reaction of the Cu-20%Fe electrode in chloride solution.     

改性活性炭吸附金的性能

为了改善活性炭的吸附性能,以硫脲和甲醛为主要原料对活性炭进行了改性,并对改性活性炭的吸附性能进行了研究.静态吸附实验表明:改性活性炭在酸性环境中比在碱性溶液中对Au3 的吸附能力要强;无论是对金的吸附容量还是在含有重金属离子(Cu2 、Ni2 和Zn2 )的混合溶液中吸附金的选择性,改性活性炭都比一般活性炭强得多;改性活性炭几乎可将混合溶液中Au3 完全吸附,而对重金属离子Ni2 和Cu2 的吸附率不到1/3.改性活性炭对金的吸附符合Langmuir单分子层吸附规律.     

合成亚砜MSO从碱性氰化液中萃取金的研究

合成亚砜MSO可以从碱性氰化液中萃取金,加入高碳醇P后能显著改善MSO对金的萃取性能。含45%(V/V)的P和1.3mol/LMSO的有机相能快速萃取金,其萃取率>94%;硫代硫酸钠能高效率地反萃金,40g/L的硫代硫酸钠溶液在相比A/O=1时一次反萃率>97%。     

LEACHING OF PRECIOUS METALS FROM COMPLEX SULPHIDE ORES——2.DIRECT LEACHING OF Cu SULFIDE CONCENTRATE BY ACIDIC THIOUREA SOLUTIONS

Recovery of gold and silver from a sulphide concentrate by thiourea leaching was investigat-ed.The effects of various parameters on the process,such as oxidants,the initial concentrationof thiourea and acidity in solutions as well as reaction temperature,were systematically exam-ined.From the results it was confirmed that(a)oxidants had no significant influence on the dis-solution of gold and silver at a fixed initial concentration of thiourea;(b)the initial concentra-tion of thiourea and acidity affected the dissolution rate only in the earliest period of leaching;(c)the rate of the process was controlled by reagent diffusion.The optimum operations wereworked out for the thiourea leaching process of the concentrate.     

碱性介质中铜镍合金及铜电极的光电化学研究

用动电位伏安法和光电化学方法对铜镍合金(7％Ni 93％Cu)和铜电极在碱性介质中的电化学行为进行了研究。铜镍合金电极的阳极氧化膜呈p型光电响应,光电响应来自电极表面的Cu_2O膜,其厚度大于纯铜电极的Cu_2O膜。铜电极在碱性Na_2SO_4溶液中电位正向扫描时的光响应呈p型,点蚀电位以后光响应从p型转为n型。     

Prevention of transpassive dissolution of austenitic stainless steel counter electrodes in nickel based electrolytic coloring solutions for anodized aluminum

In low nickel ion containing, weak acidic, electrolytic coloring solutions for anodized aluminium, austenitic stainless steel counter electrodes dissolve transpassively. The role of nickel and cobalt ions in preventing the transpassive dissolution of AISI Type 304 and 316 austenitic stainless steel counter electrodes was investigated. Potantiodynamic polarization method was used. The test solutions were a buffer (29.66 g/lt boric acid), a buffered supporting electrolyte (32.6 g/lt boric acid + 26.18 g/lt magnesium sulphate heptahydrate + 14,95 g/lt ammonium sulfate) and the coloring solutions (supporting electrolyte with different nickel (27.6–101 g/lt as heptahydrated sulfate) and cobalt (33–166 ppm) content). The oxidation of bivalent nickel ions starts 200 mV lower than the transpassive dissolution of stainless steel. However, even a small amount of cobaltous ions (165 ppm) in the solution produces a much steeper oxidation peak on the top of the nickel oxidation current. In order to transpassively dissolve a stainless steel electrode in cobalt containing nickel solutions, anodic current must be greater than the combined oxidation peak of nickel and cobalt ions, otherwise the working potential of the stainless steel electrode is always kept at the passive region hence the transpassive dissolution is prevented.     

Film Growth and Dissolution of Iron Ions at passive iron in neutral solutions containing chloride

The passivating oxide layer on iron grows by transfer of oxygen ions from the solution into the oxide. As expected theoretically, the dissolution rate of iron ions increases with the growth rate of the layer. In neutral solution the current efficiency for oxide growth is larger than in acid solutions. By addition of chloride to the solution the current efficiency is further enhanced, because chloride catalyzes the transfer of oxygen ions more strongly than the transfer of iron ions. Chloride in the solution does not change the ionic conductivity of the oxide to a measurable extent. During galvanostatic polarization in solutions containing chloride, fluctuations of the potential and of the dissolution rate of Fe(II) are observed. The frequency of the fluctuations increases with current density and chloride concentration.     

Electrocatalytic oxidation of glucose on gold–platinum nanocomposite electrodes and platinum-modified gold electrodes

Electrochemical oxidation of glucose on gold–platinum nanocomposite electrodes and platinum-modified gold electrodes was investigated with cyclic voltammetry. Gold–platinum nanoparticles were prepared by reducing aqueous solutions containing chlorauric acid and chloroplatinic acid, and the electrodes were obtained by depositing the gold–platinum nanoparticles from the colloidal solutions onto substrates. The gold–platinum nanocomposite electrodes display high electrocatalytic activity for the glucose oxidation in alkaline solution, showing 0.30–0.35 V negative shift in peak potential as compared with bare gold electrodes, and maintain stable catalytic activity in the reaction. The results of experiments indicate that both gold and platinum act as the dehydrogenation site and gold also functions to regenerate platinum from poisoned platinum. Surface modification of gold electrodes by platinum deposition also increases electrocatalytic activity of the electrodes for the glucose oxidation, showing about 0.10 V negative shift in peak potential, but a gradual decline in reactivity is observed.     

一种新的添加剂(Re-1)在硫脲浸金中的应用

报道了一种用于硫脲法浸金过程的新的Re－1型溶金添加剂,实验证实该添加剂可以改善硫脲浸金液状态,降低浸液硫脲浓度,提高金出率。可使含砷硫化原生矿的一次金浸出率达到89％以上。同时,测定了工艺的最佳条件并讨论了Re－1添加剂对浸金机理的影响。     

Anodic Behavior of a Titanium–Aluminum Hybrid Electrode: Formation of Hydroxide-Oxide Compounds

The electrochemical behavior of a titanium–aluminum hybrid electrode in aqueous solutions of electrolytes containing halide ions (F^– and Cl^–) was studied. The effects of current density, solution composition, and ratio of the working surface area of titanium and aluminum on the anodic dissolution rate of a Ti?Al hybrid electrode and its electrochemical characteristics were revealed. The joint anodic dissolution of aluminum and titanium in the aqueous media under study made it possible to obtain precursors of the highly disperse oxide system Al₂O₃–TiO₂. Data of X-ray and electron-microscopic analysis confirmed the results obtained.     

Co-Deposition of Sulphur from Acid Copper Solution Containing Thiourea

The co-deposition rate of thiourea, as far as sulphur is concerned, was measured on a rotating disc electrode in acid copper solution containing thiourea labelled with sulphur-35. For freshly made solutions at room temperature at higher current densities the co-deposition rate was controlled by diffusion, while mixed control of the co-deposition rate was found at lower current densities. In aged solutions as well as at higher temperatures the co-deposition rate decreased considerably and diffusion control was found to cease.