辉铜矿生物浸出电化学机制及动力学研究

采用Tafel法、交流阻抗法和恒电位阶极化法研究了辉铜矿生物浸出过程电化学行为,测定了腐蚀电化学动力学参数,确定了所发生的电化学反应。并结合第一性原理计算,分析了辉铜矿晶体结构性质变化,从电子结构和电化学角度揭示了细菌、 pH值和温度等因素对辉铜矿浸出的影响规律,查明了辉铜矿浸出过程主要影响因素及控制步骤。结果表明, pH值和温度对腐蚀电流和腐蚀电位影响显著,降低pH值和升高温度,降低了化学反应的吉布斯自由能,升高了阳极腐蚀电流密度,有利于辉铜矿电化学腐蚀反应的进行。辉铜矿溶解过程中生成了大量的Cu_nS多硫产物和S膜钝化层,导致电荷传递量较少,是阻碍辉铜矿氧化溶解的关键因素。细菌的存在,氧化Fe~(2+)增加了空穴浓度,提高了反应速率。同时,提高了溶液中的电位,阻抗弧变小,促进了多硫化物和S膜的氧化,从而加速了辉铜矿的氧化溶解。     

5083铝镁合金在不同浓度NaCl溶液中的腐蚀研究

采用扫描电化学显微镜（SECM）中的极化曲线法和交流阻抗图谱法研究5083铝镁合金在不同浓度NaCl溶液中的腐蚀行为,结果表明:合金在中性NaCl溶液中的腐蚀为钝化材料体系,随着盐度的增加,Cl-对合金基体的破坏加剧,腐蚀电位正移,点蚀电位减小,其电化学阻抗谱中仅有1个容抗弧且呈现收缩趋势.同时,阻抗减小,相位角增加,弥散指数降低,合金的耐腐蚀性能下降.溶液中存在强活化作用的Cl-,会损坏合金表面的氧化膜,逐渐取代腐蚀产物Al（OH）₃中的OH-,生成新的腐蚀产物AlCl₃.      

从铜浮选精矿中选择性溶解铀

从南澳大利亚Olympic Dam铜-铀-金矿床矿石中选出的铜浮选精矿含有与铜硫化物、脉石矿物共生的铀。对矿化为辉铜矿、斑铜矿类型的铜精矿的研究结果表明,在30—60℃、24h、不加氧化剂的情况下,用硫酸(>40g/1)能溶解出94—97％的铀。精矿中铜随铀一起被浸出。当反应是在氮气或氩气条件下(即在缺氧的情况下)进行时,在前15min内有5—7％的铜被溶解,而此后实际上不再有更多的铜溶解。在空气和氧气条件下,反应超过24h,铜还继续溶解。铜起初的快速溶解与低辉铜矿氧化成roxbyite和表面氧化物的溶解有关。在空气和氧气条件下,roxby-ite和斑铜矿氧化成靛青兰色烟灰状铜兰与铀的进一步氧化有关。矿浆的氧化还原电位通过铜硫化物反应来控制。对于在氮气条件下的反应来说,系统的氧化还原电位是225—250mV(用饱和甘汞电极作参比),而在空气或氧气条件下,随着铜硫化物的逐步氧化,氧化还原电位逐渐上升到350mV(用饱和甘汞电极作参比)。这些结果以及Olympic Dam冶金中间工厂的研究结果表明,从Olmpic Dam矿床矿石中得到的铜浮选精矿中的铀能够选择性的被去除.     

Acidithiobacillus ferrooxidans对软锰矿浸出的影响

利用循环伏安、交流阻抗谱和极化曲线研究了Acidithiobacillus ferrooxidans对软锰矿在模拟浸出溶液(9K基础培养基, A.ferrooxidans, Fe (Ⅲ), A.ferrooxidans+Fe (Ⅲ))中电化学腐蚀行为的影响; 利用模拟有菌/无菌浸出溶液中钝化膜的Mott-Schottky理论比较了有无细菌存在情况下形成的钝化膜的优劣性.结果表明, A.ferrooxidans促进MnO₂/Mn2+氧化还原转化, 催化MnO₂/Mn (OH)₂电极反应; 加速软锰矿/溶液界面电子交换, 无铁存在时A.ferrooxidans使电荷转移内阻降低34%, 比含Fe (Ⅲ)无菌体系低11%;引起软锰矿电极极化, 增强其氧化活性; 加速MnO₂向MnO·OH转化及其产物扩散.A.ferrooxidans与软锰矿作用更倾向于间接作用机理.在选取的各模拟电解液(pH值为2.0)中, 0.2~0.4 V区间内软锰矿形成耗尽层, 在模拟浸出溶液中形成的钝化膜都表现出p-n-p-n型半导体性能.在选取的0.2 V极化电位下, 无铁时引入A.ferrooxidans使膜中的施主/受主密度减少, 细菌含有多种基团参与半导体/溶液界面电子转移反应, 接受界面间自由电子或填充空穴, 促使软锰矿与溶液界面物质交换变频繁; 含铁溶液中加入A.ferrooxidans使得钝化膜受主/施主密度增大, A.ferrooxidans降低了膜的耐腐蚀性, 因而促进软锰矿浸出.      

Au-CN-H_2O和Ag-CN-H_2O系的多相平衡

一、前言 金、银在氰化物溶液中的溶解是一个电化学过程,可用下面(1)到(3)方程表述: Au+2CN~-=Au(CN)_2~-+e (1) Ag+2CN~-=Ag(CN)_2~-+e (2) O_2+4H~++4e=2H_2O (3) 一般金属在氰化物溶液中的溶解受多种因素的影响,诸如氰化物和金属浓度、pH值及电化学电位等。例如,根据现有的电化学研究,在低电位也即反应处在活化区时,金的阳极溶解速率随电位的增加而增大,而当电位达到某一值时,溶解速率明显减慢,即出现钝化。根据钝化理论,这种现象的出     

304不锈钢在模拟压水堆一回路水中高温电化学腐蚀行为

通过模拟压水堆一回路水环境,研究了氯离子浓度和溶解氧对304不锈钢高温电化学腐蚀行为的影响.动电位极化曲线结果表明,氯离子浓度主要影响高电位下的二次钝化效应,低电位下影响效果不明显,结合X射线光电子能谱对氧化膜元素成分的分析发现二次钝化效应与氧化膜中Fe/Cr元素含量比密切相关.电化学阻抗谱和扫描电镜结果表明,随着氯离子浓度增加,氧化膜阻抗逐渐降低,表面外层氧化物颗粒和间隙逐渐增大,耐腐蚀性能降低.随着溶解氧含量的升高,304自腐蚀电位逐渐升高,钝化电流密度降低,钝化区间缩小,表面氧化膜阻抗逐渐增加.      

镁离子对低品位硫化镍矿氧化浸出电化学行为的影响

低品位硫化镍矿中含镁硅酸矿物易被酸溶解出Mg^2+而影响其有价金属提取。采用不同氧化浸出体系研究了Mg^2+对硫化镍矿中Ni、Cu、Mg、Fe浸出的影响,利用循环伏安、动电位极化、交流阻抗等方法研究了Mg^2+影响硫化镍矿中硫化矿物氧化溶解电化学行为。结果表明,试验范围内,低品位硫化镍矿中硫化矿物氧化浸出受氧化产物扩散影响控制,含镁矿物被酸溶解释放出Mg^2+进入溶液,游离的Mg^2+受硫化矿物表面负电性离子吸引而吸附在矿石表面,降低矿物表面氧化溶解双电层电荷转移内阻,加速电荷转移过程;另一方面,由于Mg^2+吸附影响,使得硫化镍矿表面氧化产物膜致密生长而显著负影响硫化矿物浸出,致使硫化矿物自腐蚀速率随Mg^2+浓度增加而降低。Mg^2+对含S物种电对间转化不利,与Fe^3+协同影响硫化矿物氧化浸出效率,低Mg^2+浓度促进Fe^3+/Fe^2+循环,而高Mg^2+浓度引起硫化矿物腐蚀产物层致密生长而降低矿物被溶解的速率。硫化镍矿在不同体系氧化浸出时,初始含Mg^2+条件下,Ni、Cu、Fe浸出效率低于无Mg^2+体系。     

金纳米颗粒修饰钛电极的制备及其对葡萄糖氧化的电催化活性

利用恒电流电沉积法,制备出金纳米颗粒修饰钛电极（Au／Ti）。利用循环伏安、电位阶跃等电化学技术,研究了碱性溶液中Au／Ti电极对葡萄糖氧化的电催化活性。与多晶金电极相比,葡萄糖在Au／Ti电极上氧化的起始电位更低、电流密度明显增加。实验表明,A11／Ti电极对葡萄糖氧化具有很高的电催化活性。对葡萄糖在Au／Ti电极上的双电位阶跃分析表明,葡萄糖在0．1mol／LNaOH溶液中的电化学氧化反应速率常数为5．79×10^4cm^3／（mol·s）。     

电位对无捕收剂溶液中黄铜矿表面化学构成的影响

采用循环伏安法、X射线光电子能谱研究了黄铜矿在中性无捕收剂浮选介质中不同电位极化后其表面产物相的化学构成.结果显示黄铜矿在中性无捕收剂溶液中表面相中的S以具有黄铜矿晶体结构的亚稳相缺金属硫化物CuFe1-xS2,CuS2和稳定相多硫化物Sn-的形态存在.当电位提高到0.1 V/SCE,表面相中的Sn-消失,大量的So和少量高价态(+4/+6)硫相(S2O23-/SO24-)形成.当极化电位大于0.35 V/SCE,表面相中So的量急剧减小,氧化形成了大量的高价态(+4/+6)硫相(S2O23-/SO24-).表面相中的Cu以CuFe1-xS2的形式存在,高电位下出现少量的CuO相.Fe在低电位主要以FeOOH和Fe2O3的形式存在,高电位以Fe(OH)3相的形式沉淀在黄铜矿表面.     

铂电极上硫化钠溶液的电化学氧化研究

研究了硫化钠水溶液在Pt电极上的电化学氧化行为 ,探讨了电势扫描速率、Na2 S溶液浓度以及表面活性剂等条件对阳极液的循环伏安谱的影响。结果表明 ,硫化钠的阳极氧化是不可逆的电极过程。阳离子表面活性剂CTAB存在时 ,电势在 -0 .65～ 0 .2 5V(vs .SCE)范围内 ,由于CTAB在电极表面上的吸附 ,阻止了电活性物种向电极表面的迁移 ,从而出现阳极电流几乎为零的平台。硫化钠溶液浓度较大时 ,阳极钝化层在电势返程扫描时被硫化物溶解而除去 ,从而出现一阳极峰。恒电流电解过程中 ,若阳极电流较低 ,则在时间 电势曲线上出现电势变化缓慢的平台 ;而电流增加时则出现电势峰 ,表明电极过程存在自催化现象 ,由此可推算出自催化过程的反应速率常数     

Fluidised-bed anodic dissolution of chalcocite

The anodic dissolution of chalcocite (Cu₂S) has been investigated using a fluidised-bed anode technique. Results obtained for a variety of electrolytes and experimental conditions indicate that the fluidised-bed anodic dissolution of chalcocite occurs via the formation of an intermediate copper sulphide, viz., “blue-remaining” covellite, Cu_1.1S.In sulphuric acid electrolyte the dissolution of chalcocite is inhibited after about 50% copper extraction by the vigorous evolution of oxygen gas at the platinum feeder anode.In both sulphuric acid-sodium chloride and sulphuric acid-potasium bromide electrolytes, the dissolution of chalcocite occurs to 95% copper extraction in two stages. The first stage involves the formation of Cu_1.1S, as is the case for the sulphuric acid electrolyte, while the second stage is attributed to the reaction between chloride (or bromide) and Cu_1.1S.     

Leaching kinetics of copper from natural chalcocite in alkaline Na4EDTA solutions

The leaching behavior of copper from natural chalcocite (Cu₂S) particles in alkaline Na₄EDTA solutions containing oxygen was examined at atmospheric pressure. The EDTA leaching process took place with consecutive reactions, where the solid product of the first reaction, covellite (CuS), became the reactant for the second. The copper leached into the alkaline solutions was immediately consumed by the chelation of copper (II) with EDTA, and the mineral sulfur was completely oxidized to sulfate ion. The experimental data for the leaching rate of copper were analyzed with a familiar shrinking-particle model for reaction control. The conversion rate of chalcocite to covellite was found to be about 10 times as high as the dissolution rate of covellite. The time required for complete dissolution of covellite was directly proportional to the initial particle size and was inversely proportional to the square root of the product of the hydroxide ion concentration and the oxygen partial pressure, but it was independent of the Na4EDTA concentration in the presence of excess Na₄EDTA. The observed effects of the relevant operating variables on the dissolution rate were consistent with a kinetic model for electrochemical reaction control. The kinetic model was developed by applying the Butler-Volmer equation to the electrochemical process, in which the anodic reaction involves the oxidation of covellite to copper (II) ion and sulfate ion and the cathodic reaction involves the reduction of oxygen in alkaline solution. The rate equation allowed us to predict the time required for the complete leaching of copper from chalcocite in the alkaline Na4EDTA solutions.     

Fluidised-bed anodic dissolution of covellite

The anodic dissolution of synthetic covellite (CuS) has been investigated using a fluidisedbed anode technique. In sulphuric acid electrolyte the dissolution of CuS is accompanied by excessive oxygen evolution at the Pt feeder electrode unless the applied current is maintained at unrealistically low values. In mixed electrolytes, such as sulphuric acid-sodium chloride or sulphuric acid-potassium bromide, the anodic dissolution of CuS proceeds at acceptable values of applied current via a charge transfer mechanism provided by the $\text{Cl}{}^{\mathrm{?}}\text{-}\text{1}\text{2}\text{Cl}{}_2\text{or Br}{}^{\mathrm{?}}\text{-}\text{1}\text{2}\text{Br}{}_2$ redox couple. The results of the present study are compared with previous work on the fluidised-bed anodic dissolution of chalcocite (Cu₂S).     

Anodic dissolution of copper sulphides in sulphuric acid solution: II. The anodic decomposition of CuS

The anodic decomposition of CuS in sulphuric acid solutions was investigated by means of cyclic voltammetry. The pH of the electrolyte and the scan rate were varied. Our results are interpreted using the experience of semiconductor electrochemistry and of passivation of pure metals. At potentials E < E_np (E_np = potential of pitting nucleation), the current/voltage curves were interpreted by the formation of metastable nonstoichiometric copper oxide or hydroxide. After the dissolution of these layers at the potential E_np, total decomposition of CuS starts. These results were confirmed by rest potential measurements and by scanning electron microscopy.     

New observations on the anodic oxidation of copper in hot acidified copper sulfate solutions

The anodic oxidation of copper in acidified copper sulfate solution has been investigated by potentiostatic and voltammetric techniques. The morphology and composition of the films were determined by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The passive layer is mainly composed of CuSO₄. The presence of a Cu₂O phase becomes detectable after multiple sweeps and thorough rinsing of the electrode with water at the end of the experiment. The effects of electrolyte composition and temperature on the phenomenon of passivation are also discussed. The initial steps of the copper dissolution were found to obey Tafel kinetics, and the maximum dissolution current, as well as the limiting transpassive current, was controlled by the rate of diffusion of cupric ions. The phenomenon of current oscillations occurs at potentials near the peak current upon scan reversal, suggesting that oscillations only occur with the formation of a sufficiently thick film. Oscillatory behavior disappears when conditions favor salt film stability. Formerly with the Departement de Mines et Métallurgie, Université Laval. MAGDY GIRGIS, formerly with the Department of Chemistry, Carleton University.     

Pressure leaching of copper minerals in perchloric acid solutions

The leaching of covellite (CuS), chalcocite (Cu₂S), bornite (Cu₅FeS₄), and chalcopyrite (CuFeS₂) was carried out in a small, shaking autoclave in perchloric acid solutions using moderate pressures of oxygen. The temperature range of investigation was 105° to 140°C. It was found that covellite, chalcocite, and bornite leach at approximately similar rates, with chalcopyrite being an order of magnitude slower. It was found that chalcocite leaching can be divided into two stages; first, the rapid transformation to covellite with an activation energy of 1.8 kcal/mole, followed by a slower oxidation stage identified as covelite dissolution with an activation energy of 11.4 kcal/mole. These two stages of leaching were also observed in bornite with chalcocite (or digenite) and covellite appearing as an intermediate step. No such transformations were observed in covellite or chalcopyrite. Two separate reactions were recognized as occurring simultaneously for all four minerals during the oxidation process; an electrochemical reaction yielding elemental sulfur and probably accounting for pits produced on the mineral surface, and a chemical reaction producing sulfate. The first reaction dominates in strongly acidic conditions, being responsible for about 85 pct of the sulfur released from the mineral, but the ratio of sulfate to elemental sulfur formed increases with decreasing acidity. Above 120°C the general oxidation process appears to be inhibited by molten sulfur coating the mineral particles; the sulfate producing reaction, however, is not noticeably affected above this temperature. For chalcopyrite, activation energies were determined separately for the oxygen consumption reaction and for the production of sulfate, with values of 11.3 and 16.0 kcal/mole respectively. This paper is based upon a thesis submitted by F. LOEWEN in partial fulfillment of the requirements of the degree of M.A. Sc. in Metallurgical Engineering at The University of British Columbia.     

Raman characterization of secondary minerals formed during chalcopyrite leaching with Acidithiobacillus ferrooxidans

Chalcopyrite passivation greatly reduces the yields from leaching and bioleaching but the problem has not been successfully resolved. Passivation involves the formation of a layer of secondary minerals on chalcopyrite surface, which becomes a diffusion barrier to fluxes of reactants and products. This study aims to identify secondary minerals formed during chalcopyrite passivation in the presence of iron- and sulfur-oxidizing bacteria (Acidithiobacillus ferrooxidans) in mineral salts solution. The minerals were characterized with X-ray diffraction, Fourier transform-infrared spectroscopy, and Raman spectroscopy. Potassium jarosite was the initial product covering chalcopyrite grains, followed by the formation of ammonio-jarosite. Covellite and elemental sulfur were also detected in the passivation layer. The results suggest that passivation may be reduced by controlling jarosite precipitation and prior acclimatization of bacteria to oxidize CuS and elemental S in the presence of ferrous and ferric iron.     

Heterogeneous phase equilibria as a basis for crevice corrosion modelling

The presented crevice corrosion model is intended to provide basic understanding of formation and dissolution of passivating layers during time dependent metal dissolution in an already deoxygenated crevice. It operates along a constant cathodic polarization curve in subsequent time steps with time dependent anodic polarization curves and corrosion currents. The anodic polarization curves are determined by dissoluted ionic chromium and respective Nernst potentials as well as by the mass of precipitated passivating chromiumhydroxide layers. All chemical reactions including diffusion of chloride into the model crevice configuration are assumed to be at equilibrium during the respective time steps. The amounts of passivating chromiumhydroxide masses are determined by lever-rule application at increasing chromium and chloride contents in aquaeous solution of the quaternary water-chromium-hydrogen-chloride phase diagram at various Nernst potentials. For this purpose, the established water–chromium Pourbaix diagram had to be redrawn in terms of ternary water-chromium-hydrogen phase diagrams for constant potentials. It was tentatively extended to the quaternary chloride including diagram based on literature results. This included solubility of chromiumchloride in hydrochloric acid and most probable effects of chloride ions on chromiumhydroxide solubility at saturation with chromium metal. The results of the interactive corrosion process are based on a crevice geometry drawn from previous publications and given initial solution concentrations as well as assumed polarization curves for time steps of one second. It is shown, how the process starts with concentration changes of chromium, chloride and hydrogen in the crevice, the subsequent formation of the passive layer and the corresponding decrease in the corrosion current and increase in the mixed potentials. In the presence of the chromiumhydroxide phase, however, chromium and hydrogen remain at low levels in the equilibrium aqaeous solution while chloride is increasing. The saturated solution reaches the four phase equilibrium concentration including saturation by chromium, chromiumhydroxide and chromiumchloride at corresponding Nernst potentials. The further increase in total chromium and chloride concentrations of the crevice then leads to initiation and propagation of crevice corrosion by formation of non-passivating chromiumchloride at the expence and finally, the total dissolution of passivating chromiumhydroxide, at decreasing mixed potentials and increasing currents. Due to the low solubility of chromiumchloride in hydrochloric acid, the latter is finally formed with the result of the well-known increase in crevice acidity. Thus, it is demonstrated that the acidification itself is not a requirement for crevice corrosion but rather a consequence of it.     

Study of the mechanism of anodic dissolution of Cu2S

The anodic dissolution of Cu₂S in sulfuric acid solutions was studied under galvanostatic and potentiostatic conditions. The anodic products were studied by mineralogical and X-ray diffraction methods. In every case, the formation of a digenite Cu_1-8S layer is observed at the surface of Cu₂S according to 5Cu₂S → 5Cu_1.8S + Cu⁺⁺ + 2e A copper concentration gradient appears through the digenite layer whose thickness remains constant as soon as a Cu_1.1S layer appears at its own surface according to 3Cu_1.8S → 4Cu_1.1S + Cu++ + 2e If the electrolysis conditions are such that the anodic potential remains low, the next reaction to occur is 10Cu_1.1S → HCu⁺⁺ + 10S + 22e But if under galvanostatic conditions, the current density is high enough at a given temperature to reach the sharp rise in anodic potential, or if under potentiostatic conditions the potential is kept high, two other reactions are possible: 10Cu_1.1S → 10CuS + Cu⁺⁺ + 2e followed by CuS → Cu⁺⁺ + S + 2e Moreover, at high anodic potential, the following reaction occurs also to some extent CuS + 4H₂O ? Cu⁺⁺ + SO₄ ⁼ + 8H⁺ +8e resulting in a decrease in anodic current efficiency for the copper dissolution. From a more practical point of view, it was shown that it is possible to deplete virtually completely the copper content of the anode (residue at less than 0.5 pct Cu)keepingthe electrode potential at a low value (less than +650 mV/ENH). Providing the temperature is high enough (75°C at least), the mean current density remains near to 2 A/dm², a suitable value to obtain good cathodic deposits.