Leaching Kinetics of Willemite in Ammonia-Ammonium Chloride Solution

The leaching kinetics of willemite in ammonia-ammonium chloride solution was investigated. The effects of the ammonia-ammonium ratio, particle size, temperature, and total ammonia concentration on the leaching rate of willemite were determined. The results show that the optimum ammonia-ammonium ratio is 1:2 over the studied range. The zinc extraction increases with the reduction of particle size and with the increase of temperature and the total ammonia concentration. Leaching kinetics indicate that the grain pore model could be adopted to describe the leaching process, and diffusion is the main rate-controlling step. The apparent activation energy was determined to be 54.47 ± 6.39 kJ/mol and a reaction order with respect to NH₃(aq) was 3.16 ± 0.40, both of which are likely a result of the parallel nature of the chemical reaction and diffusion in porous solids, even if the chemical reaction is not the rate-controlling step.     

Leaching kinetics of malachite in ammonium carbonate solutions

Leaching of malachite was conducted with ammonium carbonate as lixiviant and with temperature, lixiviant concentration, and particle size as variables. Two stages of reaction were found. In Stage I, the initial dissolution of malachite proceeds rapidly, but after about 10 pct reaction the rate is reduced by surface blockage due to the presence of a needle-structured intermediate, presumably Cu(OH)₂. Subsequently, malachite and the intermediate dissolve concurrently. In Stage II, after 90 pct reaction, essentially all of the malachite has dissolved and only the intermediate remains. It dissolves in Stage II. The activation energy is 64 kJ/mole (15.3 kcal/mole) for Stage I and 75 kJ/mole (18 kcal/mole) for Stage II. The rate of reaction in Stage I is proportional to the reciprocal of particle size and is 0.8 order with respect to the concentration of ammonium carbonate. The structures of leaching residues were studied using a scanning electron microscope. The kinetic data (activation energy and entropy), particle size and concentration dependence, residue morphology, and general leaching behavior evident from microscopic monitoring during leaching were used to develop the geometric equation for leaching in Stage I. The equation, based on a heterogeneous reaction with geometric rate control, is: 1 − (1 − α^1/3 = K₀₁/r₀/[(NH₄)₂C0₃]^0.8 exp(-64,000/RT)t. It was deduced that initial steps in reaction were: (1) release of Cu²⁺ from malachite; (2) initial complexing with ammonia to form Cu(NH₃)²⁺; and (3) subsequent complexing to produce Cu(NH₃) ₄ ²⁺ which is stable in solution at pH 8.8, the buffered pH of reaction. Stage II appears to be a similar reaction except that the reaction obeys cylindrical geometry instead of spherical geometry as in Stage I.     

高碱性氧化锌矿氨性浸出研究

以NH3—NH4C1体系浸出某高碱性氧化锌矿,考察了氨浓度、液固比、时间和温度等因素对锌浸出率的影响,并分析了相应的浸出过程,得到的最佳实验条件为:NH3:NH4Cl摩尔浓度比为1∶1、氨浓度5 mol/L、液固比为3∶1、浸出时间为2 h、浸出温度40℃,此时锌浸出率为89.3%。     

Leaching of lead sulphate in sodium carbonate solution

The recovery of lead from scrap lead acid batteries by pyrometallurgical processes is generally accompanied by emissions of sulphur dioxide and lead-containing particulates into the atmosphere. The latter two products are undesirable as they lead to serious environmental problems. In an effort to overcome these difficulties, a sodium carbonate leaching process was investigated. In the present contribution, the leaching reactions of pure lead sulphate in sodium carbonate solutions are discussed from both a thermodynamic and kinetic aspect based on the experimental results obtained on leaching rates, stoichiometry of the reaction and X-ray diffraction analysis of the reaction products. A mass transfer model based on the diffusion of CO₃^2? ions through a solution boundary layer is proposed to account for the leaching rates.     

Leaching of zinc sulfide in alkaline solution via chemical conversion with lead carbonate

A novel hydrometallurgical process for recovering Zn from ZnS in alkaline solution via chemical conversion with PbCO₃ was developed in this work. The S originally present in ZnS can be converted into PbS, while the Zn can be converted into Na₂Zn(OH)₄ in the alkaline solution in the presence of PbCO₃. And then, the Pb in PbS deposited in the leach residues can be converted into PbCO₃ again in the Na₂CO₃ solution. It was found that over 90% of Zn can be extracted from ZnS when the leaching process is operated in 6 mol/L NaOH solution at 90 °C with PbCO₃ as additive, and over 95% of PbS in the leach residues can be converted into PbCO₃ by stirring the leach residues in Na₂CO₃ solution with air bubble at a temperature of 80 °C. The leaching solution can be used to produce metallic zinc powder by electrowinning after chemical separation of impurities.     

Leaching of a limonitic laterite in ammoniacal solutions with metallic iron

The leaching of a limonitic laterite (containing approximately 1% Ni, 0.1% Co and 50% Fe) was studied in ammoniacal solution. The laterite was leached in the presence of metallic iron which acted as a reductant. The kinetic parameters studied included the effect of temperature, metallic iron concentration, total ammonia concentration and ammonium sulphate to ammonium hydroxide ratios. Tests were performed in a batch cell with temperature ranging from 50 to 80 °C at atmospheric pressure. The kinetic behavior for nickel and cobalt extraction was observed to be different. Cobalt extraction was initially faster than nickel and it showed good extractions at lower temperatures, however, after reaching a maximum value of approximately 80%, extraction decayed by as much as 50%. This was likely due to cobalt co-precipitation and/or adsorption into iron and/or manganese oxides and hydroxides which could form during the process. Cobalt losses tended to increase with temperature, total ammonia concentration, ammonium hydroxide to ammonium sulphate ratio and metallic iron concentration. Nickel extraction was increased by higher temperature, total ammonia concentration and metallic iron concentration up to a maximum of roughly 70% after 48 h at 80 °C.Through feed and solid residue analysis, by X-ray diffraction and SEM, it was possible to characterize and understand how the feed mineral reduction occurred. The main phases present in the feed and residue were goethite and magnetite, respectively. Results suggest that the reduction occurs through two main reactions. First, the reaction between goethite and metallic iron produced Fe(II) ammines. The Fe(II) ammines are capable of reducing goethite and producing magnetite. The Fe(II) ammines play an important role because they accelerate the reduction and favor the extraction kinetics of nickel. The main advantage of using metallic iron as a reducing agent is the possibility of generating an autocatalytic system.     

Catalytic-Oxidative Leaching of Low-Grade Complex Zinc Ore by Cu (II) Ions Produced from Copper Ore in Ammonia-Ammonium Sulfate Solution

The catalytic-oxidative leaching of a mixed ore, which consists of low-grade oxide copper ore and oxide zinc ore containing ZnS, was investigated in ammonia-ammonium sulfate solution. The effect of the main parameters, such as mass ratio of copper ore to zinc ore, liquid-to-solid ratio, concentration of lixivant, leaching time, and temperature, was studied. The optimal leaching conditions with a maximum extraction of Cu 92.6?pct and Zn 85.5?pct were determined as follows: the mass ratio of copper ore to zinc ore 4/10?g/g, temperature 323.15?K (50?°C), leaching time 6?hours, stirring speed 500?r/min, liquid-to-solid ratio 3.6/1?cm³/g, concentration of lixivant including ammonia 2.0?mol/dm³, ammonium sulfate 1.0?mol/dm³, and ammonium persulfate 0.3?mol/dm³. It was found that ZnS in the oxide zinc ore could be extracted with Cu(II) ion, which was produced from copper ore and was used as the catalyst in the presence of ammonium persulfate.     

Leaching kinetics of colemanite by aqueous EDTA solutions

The dissolution kinetics of colemanite, a boron-containing mineral, in aqueous disodium EDTA solutions were studied. The effects of concentration and pH of the solution, particle size, and temperature were examined. A decrease in pH and particle size increased the dissolution rate, while an increase in the concentration of the solution and temperature increased the rate. The activation energy and pre-exponential factor were calculated as 50.6 kJ mol^-1 and 5.14 x 10⁷ m s^-1, respectively. Mahir Alkan, Assistant Professor, formerly with Atatürk University, Kazim Karabekir Faculty of Education     

Mechanism of the interaction of slimes of alumina production with carbonate solutions

In the course of laboratory investigations, it is established that slimes of desiliconization of alumina production possess selective properties with respect to alkali metals during interaction with carbonate solutions. By the magnitude of sorption by slimes, cations of alkali metals are arranged in the series Li > K > Rb > Cs. In general, selectivity of slimes is determined both by the ion-exchange properties and by the formation of binary and ternary carbonates of alkali metals and calcium.     

Leaching kinetics of natural cobalt triarsenide in chlorine solutions

The influence of stirring speed, particle size, chlorine and hydrochloric acid concentrations, and temperature on the kinetics of chlorine leaching of skutterudite particles in a stirred vessel has been investigated. The reaction rate is limited by transport in the aqueous phase with significant resistance of the chemical reaction at temperatures below 20 °C. This is supported by (a) the rate constant increases with decrease in particle size, (b) the first-order dependence of the leaching rate with the total chlorine concentration and the insignificant effect of the hydrochloric acid concentration, (c) an apparent activation energy of 18 kJ/mole for transport control and an approximate value of 85 kJ/mole for the chemical reaction, and (d) the agreement of the experimental transport constants with the expected values for mass transfer coefficients. The reaction kinetics were analyzed by a shrinking core model in which [(Sh) _p − 2] (D/d) was considered virtually independent of particle size, which is consistent with the experimental data.     

Kinetics of pyrite oxidation in sodium carbonate solutions

The kinetics of pyrite oxidation in sodium carbonate solutions were investigated in a stirred vessel, under temperatures ranging from 50 °C to 85 °C, oxygen partial pressures from 0 to 1 atm, particle size fractions from −150 + 106 to −38 + 10 μm (−100 + 150 Mesh to −400 Mesh + 10 μm) and pH values of up to 12.5. The rate of the oxidation reaction is described by the following expression:−dN/dt = SbkpO ₂ ^0.5 [OH₋]^0.1 whereN represents moles of pyrite,S is the surface area of the solid particles,b is a stoichiometric factor,k is an apparent rate constant, pO```2`` is the oxygen partial pressure, and [OH⁻] is the hydroxyl ion concentration. The experimental data were fitted by a stochastic model for chemically controlled reactions, represented by the following fractional conversion(X) vs time (t) equation: (1−X)^−2/3−1 =k _STt The assumption behind this model,i.e., surface heterogeneity leading to preferential dissolution, is supported by the micrographs of reacted pyrite particles, showing pits created by localized dissolution beneath an oxide layer. In addition to the surface texture, the magnitude of the activation energy (60.9 kJ/mol or 14.6 ± 2.7 kcal/mol), the independence of rate on the stirring speed, the inverse relationship between the rate constant and the initial particle diameter, and the fractional reaction orders are also in agreement with a mechanism controlled by chemical reaction.     

A simple kinetic model for sulfuric acid leaching of copper from chrysocolla

Experimental results obtained in room temperature laboratory leaching studies of lowgrade chrysocolla are interpreted by a kinetic equation of the form 1?(1?R)^1/3=(1/αKr _c) ln (αkKC ₀t+1) derived on the basis of a special form of the shrinking-core model and assuming chemical-reaction control. The experimental program encompasses a large range of particle sizes and reaction times and significantly extends previous experimental data on similar ore systems. The kinetic model, shown to be consistent with the experimental data, assumes the ore-particle structure to be characterized by pores and channelized regions which extend from the outer surface through a reacted zone into the unreacted core. Scanning electron microscope observations of unreacted particle surfaces as well as reacted particle surface structures lend support to this concept of leaching. The reaction rate is observed to vary inversely with initial mean particle radius, and diffusion in any form appears to be negligible by comparison with surface reaction phenomena.     

烧结烟气氨法脱硫技术在柳钢的应用

柳钢烧结厂烟气脱硫工程采用了氨-硫铵法脱硫技术,本文对氨法脱硫中的几个技术要点,以及真空蒸发结晶技术进行了简要介绍,并对系统参数的选择作了相应分析.该系统至今已连续稳定运行一年多,为钢铁行业减排SO2提供了很好的经验.     

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.     

Leaching of Chalcopyrite with Sodium Hypochlorite

A laboratory study was conducted on the leaching of chalcopyrite with NaOCl (sodium hypochlorite). Experiments were carried out in the following two stages: (1) Chalcopyrite was converted to CuO (cupric oxide) with a sodium hypochlorite solution, and (2) cupric oxide was dissolved to cupric ions with 1 normal sulfuric acid at room temperature. In the first-stage leaching, the initial pH varied from 12.5 to 13.7, the temperature from 35 °C to 75 °C, the sodium hypochlorite concentration from 0.2 to 0.85 molar, and the chalcopyrite dosage from 1 to 10 g/500 ml. The leaching conversion showed a maximum (68.3 pct) around a pH of 13.2 at 0.5 molar OCl^– (hypochlorite) concentration and at 65 °C in 1 hour. The reagent consumption ratio—defined as the number of moles of hypochlorite consumed to leach 1 mole of chalcopyrite—was much higher than its stoichiometric ratio of 8.5. It reached 57.6 when the solid dosage was 1 g/500 ml and decreased to 12.9 when the solid dosage was increased to 10 g/500 ml. The leaching rate of chalcopyrite in the first stage was controlled by a chemical reaction with the activation energy of 50.2 kJ/mol (12.0 kcal/mol). A leaching scheme was identified in which 98 pct of the chalcopyrite was leached by adding hypochlorite stock solution stepwise in less than 3 hours.     

Leaching of pyrrhotite with hydrochloric acid

Abstract

When nonstoichiometric pyrrhotite is leached under nonoxidizing conditions in warm aqueous solutions containing HCl, both hydrogen sulphide and elemental sulphur are formed. The amount of sulphur is proportional to the nonstoichiometry of the pyrrhotite. The leaching reaction is rapid (only seconds required to completion) but, when minimum conditions of acidity and/or temperature are not met, the sulphur coating becomes protective and the reaction ceases. When the reaction is begun rapidly, all of the acid or all of the pyrrhotite will be consumed, depending upon which is in excess. In hydrochloric acid, pentlandite dissolves more slowly than pyrrhotite but chalcopyrite is almost insoluble.

Résumé

A des températures au-dessous de 100°C quand les pyrrhotines de composition non stoichiométriques sont lixiviées par des solutions d'acide chlorhydrique en milieu non-oxydant, les produits de la réaction sont l'hydrogéne sulfuré et le soufre. La quantité de soufre produit est proportionnelle au degré de non stoichiométrie de la pyrrhotine. La réaction est rap ide (question de secondes seulement) mais au-dessous d'un minimum d'acide et de température, la couche de soufre recouvre la surface et la réaction s'arrête. Par contre, si la réaction débute rapidement elle se continuera jusqu’è l'épuisement du réactif minoritaire (HCl ou pyrrhotine). En milieu chlorhydrique la pentlandite se dissout plus lentement que la pyrrhotine, mais la chalcopyrite est très peu soluble.     

Separation of cobalt from nickel in ammonia-ammonium carbonate solutions using pressurized ion exchange

High resolution pressurized ion exchange has been used successfully to study and separate the various cobalt and nickel complexes present in commercial ammonia-ammonium carbonate solutions produced by the Caron process. Using chromatographic elution from Dowex 50W-X8 (15–25 micron) resin with ammonium carbonate solutions, three cobalt species, identified as the purple carbonato tetrammine complex, [Co(NH₃)₄CO₃]⁺, the red carbonato pentammine complex, [Co(NH₃)₅CO₃]⁺, and the yellow hexammine complex [Co(NH₃)₆]³⁺, were separated from a single nickel species. Nickel sorption was found to be a strong function of pH, whereas sorption of the cobalt complexes was essentially independent of pH over a rather wide range, extending from ～pH 7.8 to 10. Distribution ratios for all species increased significantly with decreasing ammonium carbonate concentration. With ammonium carbonate solution at pH 9.5, the complexes were eluted in the following order: [Co(NH₃)₄CO₃]⁺, [Co(NH₃)₅CO₃]⁺, [Ni(NH₃)_6-x(H₂O)_x]²⁺, and [Co(NH₃)₆]³⁺. From 4 M (NH₄)₂CO₃, distribution ratios were 5.0, 7.5, 18, and 75 for the respective complexes identified in the order above. This study points out some of the difficulties and opportunities in developing a viable ion exchange process for the recovery and separation of these metal ions.     

锌的氧压浸出与常压浸出的比较及与常规流程的结合

从工艺技术、设备、投资、元素分布等方面对锌业上的氧压浸出、常压浸出进行了系统的比较,并结合国内现有的锌业常规流程的实际,指出了利用国外技术提升、改造国内湿法炼锌的途径,以便进一步提升中国锌冶炼行业的竞争力。     

盐酸氧化酸浸-亚硫酸钠浸出法处理银精矿氧化焙砂的研究

湿法炼锌过程中产出的铅银渣经硫化浮选得到的银精矿 ,通过氧化焙烧产出含银达± 1 .0 %的富银焙砂。研究了采用盐酸氧化酸浸预处理该富银焙砂以分离锌、铜等 ,同时使银转化为氯化银 ,再用亚硫酸钠碱性络合浸出转化渣回收银的工艺。考查了盐酸氧化酸浸过程中银的分散情况 ,结果表明 ,该过程中银的浸出率平均为 2 .7% ;采用了单因素条件试验研究方法 ,在试验的最佳条件下 ,富银焙砂经盐酸氧化酸浸后亚硫酸钠络合浸银 ,银的浸出率达 90 %以上 ,浸银液未经净化 ,直接用水合肼还原可得含量为 96 %以上的银粉。