重金属强化含金矿石的氰化浸出

通过分析铊、铋、汞和铅等重金属强化金氰化溶解的电化学原理,对含金氧化物矿石和难浸硫化物金精矿进行了重金属强化浸金研究.结果表明:重金属对金氰化溶解的阳极过程有显著的强化作用,但在常规供氧条件下,金的溶解速率并未显著提高;只有同时采用阴极强化措施,才能使重金属起到显著提高金溶解速率的作用;对于含金氧化物矿石,单独采用重金属强化即可明显提高浸金速率,如果在过氧化氢助浸的基础上添加重金属,金的浸出速率会有更大幅度的提高;对硫化物金精矿而言,单独采用重金属无明显强化效果,只有在添加过氧化氢作为辅助氧化剂的基础上,重金属对金的浸出才能起到强化的作用,该体系中过氧化氢起到了强化阴极过程和氧化硫化物的双重作用.     

Applications of mixed potential model in leaching of gold

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高岭石对氰化浸金的影响及助浸研究

采用电化学实验研究了在氰化浸金过程中常见矿物高岭石对金溶解速率及对溶液中金的吸附效果的影响。结果表明,高岭石的存在会使金的溶解速率加快,随着高岭石粒度逐渐降低金的溶解速率提高,且高岭石对溶液中金的吸附率增加。氰化浸出实验结果表明,高岭石存在时金的浸出率由93.21%降低到91.76%,采用柠檬酸三钠、过氧化镁和十二烷基硫酸钠助浸时,金浸出率升高至94.42%。能谱分析(EDS)发现浸出物中高岭石表面有金元素存在,表明高岭石会吸附溶液中的金。红外光谱分析和密度泛函理论计算表明,高岭石与金发生化学吸附作用,氢原子为高岭石的活性位点,C6H5O7^3-会优先吸附于高岭石(001)表面,加入助浸剂可降低高岭石与金的吸附强度,提高金的浸出率。     

Electrochemical behavior of nickel in HNO<Subscript>3</Subscript> and the effect of chloride ions

The electrochemical behavior of nickel in HNO₃ solutions of varying concentrations was examined using the cyclic voltammetry and potentiodynamic anodic polarization techniques. The anodic branch of the cyclic voltammogram is characterized by one anodic dissolution peak and a passivation region before oxygen evolution. The cathodic branch shows only one cathodic reduction peak corresponding to the reduction of HNO₃. Analysis of the anodic polarization data shows features of both reversible and irreversible reactions pointing to the complexity of the system. CT⁻ ions enhance the active dissolution of nickel in HNO₃ due to the adsorption on the bare metal surface and cause destruction of the passive film and initiation of pitting corrosion.     

铜-氨-硫代硫酸盐体系金溶出影响因素的电化学研究

铜-氨-硫代硫酸盐浸金体系中，金的溶出本质上是电化学过程。采用交流阻抗和Tafel曲线分析硫代硫酸盐、铜离子、氨浓度对金的溶出影响。结果表明:在金的溶出过程中，硫代硫酸盐和铜离子可能会导致钝化，尤其使铜离子浓度增大会导致钝化加剧，这种钝化会交替出现；氨水不会导致钝化；对金溶出速率的影响，硫代硫酸盐最大，铜离子最为复杂，氨影响相对最小。     

Mechanism and rate-controlling factors in the dissolution of gold in cyanide solution

The factors which control the rate of dissolution of pure gold in cyanide solution were studied both directly and through measurement of the current-potential curves for the anodic and cathodic portions of the reaction. The mechanism of dissolution is probably electrochemical in nature, and the rate is determined by the rate of diffusion of dissolved oxygen or cyanide to the gold surface, depending on their relative concentrations. The significance of the results and the effects of impurities are considered.     

Electrochemical behaviour of nickel anode in H2SO4 solutions and the effect of halide ions

The electrochemical behaviour of pure nickel in H₂SO₄ solutions has been potentiodynamically investigated. The effects of the following factors on the anodic dissolution and passivation of the metal are discussed: potential scan rate, successive cyclic voltammetry and progressive additions of Cl^?, Br^? and I^? ions. Increasing the potential scan rate increases the critical current density i_cc, denoting that the active dissolution of nickel in H₂SO₄ is a diffusion controlled process. Cyclic voltammetry shows that the reverse excursion does not restore the anode to its active state. On successive cycling, the height of i_cc decreases; this could be attributed to the decrease in the reduction efficiency of passivating oxide film during the cathodic half cycles. The presence of the halogen ions below a certain concentration specific to each anion inhibits the anodic dissolution both in the active and passive states. The inhibitive action of these additives decreases in the order I^?, Br^?, Cl^?. Beyond the specific concentrations, the halogen ions accelerate the anodic dissolution and shift the active passive transition to more positive values. The aggressiveness of these anions decreases in the sequence Cl^?, Br^?, I^?, Further increase in the halogen ion concentrations can lead to breakdown of the passive film and initiate pitting. The susceptibility of nickel to pitting attack enhances with increasing H₂SO₄ concentration.     

The Effect of Oxygen on Copper Dissolution during Cathodic Polarization

The effect of oxygen on the anomalous dissolution of copper in acidic chloride media is studied. An increase in the copper corrosion rate during cathodic polarization in the potential range from –0.4 to –0.7 V is attributed to stirring of the near-electrode layer by evolving hydrogen bubbles. An addition of surface-active tetrabutylammonium iodide shifts the overpotential of hydrogen evolution and eliminates this effect. The copper dissolution rate during cathodic polarization is shown to be directly proportional to the reduction rate of dissolved oxygen. It is shown experimentally that H₂O₂ does not affect the dissolution rate of copper during cathodic polarization. The latter fact makes it possible to assume that oxygen reduction stages, which involve hydrogen peroxide, do not affect the anomalous dissolution of copper.     

Effect of halide ions on the dissolution of copper single crystal planes in dilute sulphuric acid

The rates of dissolution of copper single crystal planes in dilute sulphuric acid containing various concentrations (10⁻⁸ to 10⁻²M) of Cl⁻, Br⁻ and I⁻ are determined at 30°C. The dissolution rates, which are controlled by transport process in solution, are a function of the temperature, stirring rate, oxygen solubility, crystallographic orientation and the concentration of halide ions. Halide ions acted as anodic inhibitor at low concentrations and cathodic inhibitor at high concentrations. The changes in the dissolution rates have been attributed to specific adsorption of halide ions or precipitation of cuprous halides on the surface of the crystal planes.     

Determination of electrochemical parameters and corrosion rate for carbon steel in un-buffered sodium chloride solutions using a superposition model

Corrosion of carbon steel in un-buffered NaCl solutions was studied applying linear potential sweep technique to a rotating disk electrode. Current-potential curves were obtained from linear potential sweep at a rate of 1 mV s⁻¹ in solution with concentrations in the range 0.02-1 M NaCl and rotation rates in the range 170-370 rad s⁻¹, at 22 °C. Potential sweeps, which were conducted in the potential range −700 to −100 mV/SHE, were started from the cathodic limit in order to approach the measurement of corrosion under rust-free conditions. Polarization curves were analyzed with a superimposition model developed ad hoc and implemented in a computer program, which enabled determining the corrosion rate and kinetics parameters of the underlying anodic and cathodic sub-processes. The anodic sub-process, dissolution of iron, was well described in terms of a pure charge transfer controlled reaction, while the cathodic sub-process, oxygen reduction on iron, was well described in terms of mixed mass transfer and charge transfer control. Increase of electrode rotation rate increases the limiting current of oxygen reduction, which results in an enhanced corrosion rate of carbon steel. Increase of NaCl concentration has a dual effect: the limiting current of oxygen reduction decreases as a result of the influence of NaCl concentration on solution viscosity and the anodic dissolution of iron increases due to the influence of NaCl on pitting formation. However, this last mechanism predominates and a net increase in carbon steel corrosion rate is observed in this case.     

Potentiodynamic behaviour of the nickel electrode in acid media

The electrochemical behaviour of nickel has been investigated in H₂SO₄ and HCl solutions of various concentrations by means of the potentiodynamic method. In very dilute solutions, the low anodic current is controlled by the presence of pre-existing film. At higher concentrations the film is removed and dissolution occurs. In H₂SO₄ solutions, pseudopassivity, primary passivity, transpassivity and secondary passivity are observed prior to oxygen evolution. In all these regions, the rate of dissolution increases with acid concentration. In HCl solutions, the anodic polarization curves exhibit a current peak followed by a passivation region; the latter may not involve complete passivity. In the active region, the uniform dissolution is controlled by diffusion processes. In the passive region, local attack in the form of pitting occurs. In both acid solutions, the cathodic and anodic polarization curves satisfy Tafel's relation.     

Zur Redoxwertigkeit des Sauerstoffs an Nickelproben in 1 n Salz-und Schwefelsäure

Redox valence of oxygen on nickel specimens in 1 n hydrochloric and sulfuric acids The ratio of dissolved nickel to oxygen consumption was studied for the corrosion of nickel in oxigen containing acid. In air saturated 1 N H₂SO₄ 4 electrons are accepted per molecule of oxygen (reduction to water). In air-saturated 1 N HCL only 2 electrons are reacting per molecule of oxygen (reduction to hydrogenperoxide) at the beginning of the reaction, in the course of the reaction (times greater than 2 hours) this value rises to 3 electrons per molecule of oxygen, according to a stationary hydrogenperoxide concentration of 7 · 10^?4 moles/l in both acid, however, the oxygen reduction leads to hydrogen peroxide as an intermediate product which in the presence of chloride ions is desorbed faster from the metal surface than it is reduced. with increasing chlorid concentration the corrosion rate decreases from H₂SO₄ to HCL solutions.It is proposed that this effect is due to different mechanisms for the anodic dissolution of the nickel.     

Co-intensification of gold leaching with heavy metals and hydrogen peroxide

Co-intensification was researched to accelerate gold leaching with regards to its electrochemical nature by using anodic intensifiers of heavy metal ions (Pb2+, Bi3+, Tl+, Hg2+ and Ag+) on the basis of hydrogen peroxide assistant leaching on three different types of materials which were classified as a refractory sulphide gold concentrate, an easily leachable sulphide gold concentrate, and a low grade oxide gold ore according to their leaching characteristics. The results showed that, favorable co-intensification effects on the three materials were obtained and leaching time of gold was effectively shortened to no longer than 12 h from 16 to 24 h for hydrogen peroxide assistant leaching. For the five tested heavy metal ions, Bi3+and Tl+ presented co-intensifying effect on all the three materials, and Hg2+ caused co-intensifying effect on both refractory and easily leachable sulphide gold concentrates, and Pb2+ and Ag+ only had co-intensifying effect on the easily leachable sulphide gold concentrate.     

Anodic dissolution of nickel in acidic chloride solutions

The anodic dissolution of nickel was studied galvanostatically in hydrochloric acid solutions of various concentrations. The reaction orders of chloride ion and hydrogen ion concentrations were found to be 0.5 and 1.0, respectively. An anodic Tafel slope equal to 120 ± 10 mV · decade⁻¹ was obtained. The dissolution rate of nickel at constant acid concentration was increased with stirring of the solution and increasing temperature. The activation energy, ΔH, for the anodic dissolution process was found to be 12 kcal · mol⁻¹. The presence of oxygen in solutions assisted the passivation process. The effect of addition of aniline and some of its derivatives (o-, m-, and p-anisidine) as inhibitors on the dissolution kinetics of Ni in 1 M HCl was also investigated. These compounds inhibited the anodic dissolution of nickel without affecting the Tafel slope, indicating that the adsorption of such inhibitors could not interfere with the mechanism of metal dissolution.     

Inhibiting the corrosion of stainless steel in phosphoric acid

The effect of Cu²⁺ and NO ₃ ⁻ ions on the stability of the passive state of a X18H10T type steel in phosphoric acid is investigated by constructing true curves of the anodic and cathodic processes. In a 3 M H₃PO₄ at 100°C, the steel is found to be in an unstable passive state. Copper(II)- and nitrate-ions transfer it into a steady passive state. Adding copper (II) ions to phosphoric acid accelerates the cathodic process and impedes the anodic dissolution in the active potential range. The steel passivation potential decreases under their action.     

Electrochemical polarization studies of BS 4360 50D steel in 3.5% NaCl

Anodic and cathodic polarization studies have been carried out on the steel BS 4360 50D in de-aerated 3.5% NaCl (0.6 M) in the pH range 2–10 and 2–13 respectively. A stepwise potentiostatic method was employed and the current was allowed to attain a steady value at each potential. The free corrosion potential was observed to be independent of pH in the range 5–10.5 but to change to more positive potentials for pH values < 5 and to more negative potentials for pH values > 10.5. The rate of anodic dissolution and cathodic reduction of hydrogen ions and water also showed a complex dependence on pH. At pH 4 varying the chloride-ion concentration in the range 0.1–1.5 M had little effect on the polarization curves but in 4 M solution a decrease in the anodic current density was observed.     

Inhibition of the anodic dissolution of iron in alkaline solution by metal complex ions

The possible inhibiting effects of GaO₃^3?, GeO₃^2?, CrO₃^2?, and MoO₄^2? ions on anodic and cathodic reactions on iron in 5 M KOH were studied. It was shown that a concentration of these ions of 10^?3 M inhibits the anodic iron dissolution reaction 2–3 times, while no effect on the hydrogen evolution reaction was observed. The effect was explained by the underpotential deposition of adatoms of the metal complexing ions on the iron electrode.     

The Dissolution of a Copper Cathode in Acidic Chloride Solutions

The dissolution of cathodically polarized copper under various conditions is definitely measured. The process is most substantially affected by the concentration of dissolved oxygen, while the effect of hydrogen ions is small. Stirring the solution produces a noticeable effect at high cathodic potentials. On the surface of a copper electrode, two opposite processes proceed, namely, the ionization of copper and the deposition of copper ions. A technique for estimating the true rate of the anomalous copper dissolution when the deposition of the dissolution products is minimal is proposed. These dissolution rates of copper substantially exceed the values evaluated from the analysis of the working solution. The integral dissolution of copper is considered in terms of the chemical conjugation of the copper ionization and oxygen reduction. The hydrogen evolution is thought of as also probable.     

The electrochemical reduction of oxygen on copper in dilute sulphuric acid solutions

The electrolytic reduction of O₂ on Cu was studied in dilute H₂SO₄ at 25°C by steady-state and transient electrochemical techniques. A distinctive hump (i.e. a current maximum) is observed in the steady-state potentiostatic polarization curve approximately 50 mV negative to the open-circuit corrosion potential. Results of transient studies, of varying the solution agitation, and varying the concentrations of oxygen, sulphuric acid, and sulphate ions indicate that the hump is due to cathodic film formation which inhibits the rate of oxygen reduction. The inhibiting film appears to be composed of intermediates from the O₂ reduction process and also may contain adsorbed sulphate ions. The film is removed under corrosion conditions by rapid dissolution of the substrate copper. Extrapolation of the cathodic Tafel curve to the corrosion potential yields corrosion rates lower than those measured because of the cathodic passivation.     

焙烧氰化尾渣提金工艺研究现状

焙烧氧化过程中铁物相出现熔融或再结晶,对金造成二次包裹,使焙砂中部分金仍难以浸出,导致焙烧氰化尾渣金品位较高。破坏尾渣中铁氧化物对金的包裹可提高金的浸出率。综述了焙烧氰化尾渣主要提金工艺,包括直接酸溶法、还原焙烧法、氯化法、炼铁-电解法、硫酸熟化法和硫脲法等。直接酸溶工艺简单,金浸出效果较差;还原焙烧法金浸出率高,但工艺复杂、能耗大;氯化焙烧法对矿石适应性强,可综合回收有价金属,但基建及维护费用高;炼铁-电解法在富集金的同时可获得纯铁产品,对矿石有较高的要求;硫酸熟化法显著提高金银浸出率,与直接酸溶法相比,所需更高的温度与酸度;硫脲法反应速率快、选择性好,但生产成本较高。 关健词:有色金属冶金;氰化尾渣;铁氧化物;包裹金;提金