基于配位理论的碱性硫脲选择性溶金机理

采用电化学方法研究了金及常见伴生金属元素银、铜、镍、铁在高稳定性碱性溶液中阳极溶解的电化学行为,及碱性硫脲浸金的选择性.结果表明:在最佳溶金电势0.42 V时,金在碱性硫脲溶液的溶解电流密度分别是银、铜、镍和铁的3.4,5.2,27.3和42.6倍;而且碱性硫脲体系进行矿物浸出时金的伴生元素浸出率均小于0.1%,浸金具有显著的选择性.采用配合物的化学键理论、配位理论等分析了碱性硫脲选择性溶金的机理.碱性硫脲溶液中金、银、铜、镍和铁分别以Au(TU) 2,Ag(TU) 3,Cu(TU)2 4,Ni(TU)2 4和Fe(TU)2 6的形式存在,Au(TU) 2中反馈σ-π配键的形成显著增强了其稳定性.配合物Ni(TU)2 4和Fe(TU)2 6中,由于硫脲分子的特殊性,各配位体间硫原子和氮原子上电子云互相排斥,使其稳定性有所降低.而且碱性硫脲溶液中,Ag,Cu,Ni,Fe易于形成致密的硫化物钝化膜,在一定程度上也阻碍了金属的进一步溶解.     

亚硫酸在硫脲浸金中作用的电化学

采用循环伏安曲线和恒电流阶跃法进行了亚硫酸在硫脲浸金中的作用，亚硫酸存在下，硫脲的稳定性增大，溶液中硫脲的有效浓度增大，使金溶解活化能降低。溶解速度明显加快。亚硫酸具有电化学还原，催化硫脲浸金的作用。     

酸性硫脲法提金的研究进展

介绍了在酸性溶液中硫脲浸金的基本原理和主要影响因素,以及硫脲浸金的研究现状和技术改进.同时,对硫脲浸出液中金的提取方法进行了分类介绍,并展望了硫脲提金的发展前景.     

氧压渣非氰体系浸金及其机理

以氧压渣为原料,考察酸性硫脲体系和碱性多硫化物体系碳浸法浸金效果,对浸出过程矿相行为进行分析。结果表明:碱性多硫化物体系较酸性硫脲体系金浸出率高30%,碱性多硫化物体系包裹金得到释放和暴露,利于金的高效浸出。在碱性多硫化物体系下考察各因素对金浸出率的影响并确定最优浸出条件,在最优条件下,金的浸出率达85%以上。开展深度浸金研究,超声波强化金浸出率达89.77%,超细磨金浸出率达91.95%。     

增氧条件下的碱性硫脲浸金实验

碱性硫脲浸金需要用氧化剂来调节溶液的氧化电势,氧化剂的氧化电势既要大于金溶解形成Au[CS(NH2)2]2+的电势(0.38 V),由于电势太高硫脲易被氧化而失效,故氧化剂的氧化电热不能太高。在碱性溶液中,氧的标准电极电势为0.40 V,因此,理论上空气中氧是理想而经济的氧化剂。然而,水的饱和溶氧量小,自然溶氧速度慢,从而使氧用作氧化剂受到限制。通过在搅拌浸出槽底部接入螺旋空气管、微孔材料的方法改变发泡方式,进而在持续增氧(空气中氧作氧化剂)的条件下对碱性硫脲浸出低品位金矿石进行具体地研究。发泡方式的改变既增大空气中氧向水中传递的速率,又改善搅拌效果。结果表明:增氧条件下浸出体系的充氧能力越强,碱性硫脲浸金效果则越好。在相同充气量条件下,微孔材料发泡增氧的效果最好,浸出率最高。而且在一定范围内,金浸出率随着充气量的增加而增大,而充气量过大时则会降低金浸出率。     

硫脲在碱性介质中的电化学行为

为表征硫脲在碱性介质中的电化学行为并为碱性硫脲浸金提供理论依据，采用稳态极化法和循环伏安法等电化学测试技术，系统研究碱性介质中硫脲的氧化分解电势、硫脲分解与浓度的关系。结果表明：硫脲的阳极氧化分解为不可逆反应，其氧化分解峰电流对应的电势约为O．5V。硫脲浓度由0．05mol／L增加至0．15mol／L，其氧化分解的峰电流由1．559x10^-4A增大至9．068x10^-4A，峰电势由0．505V负移至0．430V，硫脲分解加剧。随pH值的升高，硫脲的氧化分解趋于严重，碱性介质中硫脲易于分解。     

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。     

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。     

硫脲-硫氰酸钠浸出难处理金矿及浸出剂的稳定性

采用高温焙烧、硫脲-硫氰酸钠浸出难处理金矿中的金,研究焙烧温度、硫氰酸钠浓度、硫脲(Tu)浓度、Fe3+浓度、pH值、浸出温度和时间对金浸出率的影响,得到混合体系浸金的最优条件,并研究浸出过程中硫氰酸钠和硫脲的稳定性。结果表明:金的浸出率达到93.1%,超过相同条件下单一体系中的浸出率之和,硫脲与硫氰酸钠摩尔比对金浸出率和金电极稳定电位影响较大;硫氰酸钠使硫脲的稳定性降低,而硫脲使硫氰酸钠的稳定性增强。     

氰化尾渣中金铁梯级提取及铁精粉中杂质形成机理

采用"磁化焙烧-硫脲浸金-磁选-碱浸除杂"的金铁梯级提取法从焙烧氰化尾渣中浸出金,并制取铁精粉,通过物相转化、焙烧过程热力学计算和颗粒群结构分析,揭示铁精粉中杂质形成机理。结果表明:氰化尾渣添加8%焦粉于700℃下磁化焙烧60 min,焙烧样以硫脲法浸金,金浸出率达65.87%;浸金渣经磨矿磁选得到TFe品位为55.01%的初级铁精粉,再于90℃的10%NaOH溶液中碱浸8 h,可得TFe品位为62.22%、回收率为69.80%的合格铁精粉。物相转化和热力学计算表明,磁化焙烧过程中含铁矿物与Si、Ca、Al及重金属等杂质反应,生成铁橄榄石、钙铝榴石和铁钙辉石等新物相,与磁铁矿紧密共生,混入铁精粉中;微细粒磁铁矿存在严重磁团聚,石英等杂质会机械夹杂在磁团聚中,降低铁精粉质量。     

Anodic dissolution of gold in alkaline solutions containing thiourea, thiosulfate and sulfite ions

Gld dissolves electrochemically in alkaline solutions containing ligands to form complex ions with gold ion.Therefore,selective leaching of noble metals is expected without dissolution of base metals such as steels,aluminum alloys in scrap treatment.Gold electrodes were investigated using linear sweep voltammetry,EQCM method and potentiostatic eclectrolysis in alkaline solutions containing thiourea,Na2SO3 and Na2S2O3.The solution composition,electrode potential affect gold dissolution rate and current efficiency.The gold dissolved from anode electrode forms complex ions,suspension particles as compound precipitates and deposits on cathode electrode as a metal.Anodic efficiency for gold dissolution is between 10% and 22%.This is caused by the oxidation decomposition of sulfite ions and thiourea.The statbility of the alkaline solution containing these elements was also estimated by capillary electrophoresis technique.     

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

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

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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.     

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.     

硫脲浸金电化学行为研究

采用循环伏安法(CV)、Tafel曲线和差分脉冲伏安法(DPV)等电化学方法对模拟硫脲浸金体系进行了研究.结果表明,硫脲浓度范围为0.005～0.04 mol/L,浓度增大有利于金的浸出;在Fe3+浓度为0.01～0.08 mol/L范围内,随着Fe3+浓度的增大,金腐蚀电位负移,腐蚀电流变大;适度升温可以提高金的腐蚀...     

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.