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.     

化工原料碳酸铵中氨和二氧化碳的测定

测定铵盐中的氨,通常采用甲醛解蔽法直接测定。而测定碳酸铵中氨时,由于溶液中存在弱酸状态的二氧化碳,无法用盐酸进行测定。当测定碳酸铵中二氧化碳时,铵盐也有严重干扰,必须分离铵盐而单独测定,这样操作既繁杂又费时。本试验采用一次称样,加入氢氧化钠和氯化钡,使     

Dissolution of malachite in aqueous ethylenediaminetetraacetate solution

The kinetics of malachite dissolution in aqueous ethylenediaminetetraacetate (EDTA) solution has been investigated in the temperature range of 298 to 318 K. The dissolution rate of malachite determined under the present set of experimental conditions was found to be independent of agitation speed. The dissolution rate increased with increasing EDTA concentration, but leveled off at higher concentrations. At constant EDTA concentration, an increase in dissolution rate was detected at higher temperatures. A dissolution mechanism involving Langmuir-type EDTA adsorption was proposed, in which the dissolution rate of malachite is controlled by the removal of Cu(II)-EDTA complex from the malachite lattice. The proposed mechanism can explain the dependency of the dissolution rate on EDTA concentration. The activation energies determined at pHs 5, 7.5, and 10 were found to be 51.4, 50.2, and 57.5 kJ mol⁻¹, respectively. The calculated enthalpy changes of EDTA adsorption equilibrium were −43.2, −35.2, and −45.0 kJ mol⁻¹ for pHs 5, 7.5, and 10, respectively. These values are in agreement with the proposed mechanism. Formerly Graduate Student, Department of Metallurgy, Kyoto University, is Formerly Professor, is Professor Emeritus, Department of Metallurgy, Kyoto University.     

Reduction roasting/ammonia leaching of nickeliferous laterites

A well characterized ore sample from Sukinda (India) consisting of nickeliferous limonite has been used to study the extractibility of nickel by the reduction roast/ammonia leach process. Techniques such as X-ray diffraction, surface area measurement and electron spectroscopy for chemical analysis (ESCA) have been used to investigate the ore after various treatments. It has been observed that the process is very sensitive to the roasting conditions, particularly subsequent cooling. Reoxidation during cooling occurs unless special precautions are taken to prevent it and is often limited to surface regions, where it is not detected by X-ray diffraction. ESCA has been used to identify constituents in surface regions of the ore particles. It is shown that careful control of the reduction process is a prerequisite for high recovery of nickel. Under the experimental conditions it was observed that for high Ni recovery it is necessary for iron to be present in a soluble state. It is not necessary to reduce the iron constituent to the metallic state as wustite d dissolves rapidly.     

Dissolution kinetics of argentian plumbojarosite from old tailings of sulfatizing roasting pyrites by Hcl-CaCl2 leaching

The nature of argentian plumbojarosite contained in old tailings of sulfatizing roasting pyrites has been studied. HCl-CaCl₂ leaching has been investigated over a temperature range of 60 to 90 °C with 0.175 to 1 M HC1 and 0 to 200 g/1 CaCl₂ as a means of selective leaching. The analysis of experimental data, independent of the stirring speed and cinder particle size, shows that the chemical reaction on the surface of the plumbojarosite crystals is the rate limiting step. This is supported by an activation energy of 96 kJ/mole. A first-order dependence with respect to the hydrochloric acid activity was found with or without the addition of calcium chloride. A micrograin model was applied to explain the leaching behavior, which is in satisfactory agreement with the experimental data.     

The leaching kinetics of chalcopyrite (CuFeS2) in ammonium lodide solutions with iodine

The leaching kinetics of chalcopyrite (CuFeS₂) in ammonium iodide solutions with iodine has been studied using the rotating disc method. The variables studied include the concentrations of lixiviants, rotation speed, pH of the solution, reaction temperature, and reaction product layer. The leaching rate was found to be independent of the disc rotating speed. The apparent activation energy was measured to be about 50 kJ/mole from 16 °C to 35 °C, and 30.3 kJ/mole from 35 °C to 60 °C. The experimental findings were described by an electrochemical reaction-controlled kinetic model: rate =k [NH₃]^0.69[OH⁻]^0.42[I ₃ ⁻ ]^0.5.     

硫氧混合铅锌矿中锌的氧化氨浸动力学

常压低温条件下在NH₃-（NH₄）₂SO₄体系中使用过硫酸铵作为氧化剂对硫氧混合铅锌矿中的锌进行浸出实验,系统研究了搅拌速度、浸出剂浓度、氧化剂浓度与温度对于锌浸出率的影响.结果表明,在最优条件下锌的浸出率可达93.2%,且浸出过程中几乎没有其他离子进入溶液,实现了锌的选择性高效浸出,从而简化了后续的浸出液净化与材料制备过程.动力学研究表明,硫氧混合铅锌矿中锌的氧化氨浸过程遵循固体产物层扩散控制的未反应核收缩模型,浸出反应的表观活化能为17.89 kJ·mol^-1.     

Dissolution kinetics of argentian plumbojarosite from old tailings of sulfatizing roasting pyrites by Hcl-CaCl2 leaching

The nature of argentian plumbojarosite contained in old tailings of sulfatizing roasting pyrites has been studied. HCl-CaCl₂ leaching has been investigated over a temperature range of 60 to 90 °C with 0.175 to 1 M HC1 and 0 to 200 g/1 CaCl₂ as a means of selective leaching. The analysis of experimental data, independent of the stirring speed and cinder particle size, shows that the chemical reaction on the surface of the plumbojarosite crystals is the rate limiting step. This is supported by an activation energy of 96 kJ/mole. A first-order dependence with respect to the hydrochloric acid activity was found with or without the addition of calcium chloride. A micrograin model was applied to explain the leaching behavior, which is in satisfactory agreement with the experimental data.     

Dissolution kinetics of phenylbutazone

This study investigated the possible effects of simultaneous, noninstantaneous, reversible chemical ionization of carbon acids on the dissolution of a typical pharmaceutical carbon acid, phenylbutazone, and its deutero analog. The dissolution rate versus pH profile for phenylbutazone was consistent with phenylbutazone acting as if it were an acid where the ionization can be considered instantaneous. In view of the dissolution behavior of phenylbutazone under various conditions, it is unlikely that the noninstantaneous ionization kinetics demonstrated for this compound play a major role in determining the dissolution rate, either in vitro or in vivo, since the average residence time in a typical aqueous diffusion layer for phenylbutazone dissolution is longer than the reaction time for its ionization. Slowing the reaction time with a primary isotope effect by deuterium substitution for the ionizable proton caused significant deviation from classical behavior for d-phenylbutazone.     

Solubility of ammonium paratungstate in aqueous diammonium phosphate and ammonia solution and its implications for a scheelite leaching process

Scheelite could be digested with an aqueous diammonium phosphate and ammonia solution in an autoclave. However, unexpected ammonium paratungstate (APT) crystallisation and tungstophosphoric acid formation occasionally occurred. In order to provide a theoretical basis for the scheelite leaching process, the solubility of APT in solution was determined by the isothermal solution equilibrium method. The effects of initial ammonia and diammonium phosphate concentration as well as temperature on APT solubility and tungstophosphoric acid formation were investigated. Results showed that APT solubility increased with increasing ammonia concentration, diammonium phosphate concentration and temperature, while tungstophosphoric acid concentration in the leaching solution increased with decreasing ammonia concentration and increasing diammonium phosphate concentration. In order to verify the effects of these factors on the leaching of scheelite, scheelite digestion experiments using diammonium phosphate and ammonia solution were also carried out.     

Treatment of a Nigerian covellite ore. Part I: Dissolution kinetics study by ammonia solution

In the present work, the leaching kinetics of covellite ore in ammonia solution was studied and the following variables, the solution concentration, reaction temperature and particle size were considered. A kinetics model representing the effects of these variables on the leaching rate was developed and it was ascertained that the leaching rate increases with increasing solution concentration, reaction temperature and decreasing particle size. At optimal conditions, 75.1% of covellite ore was reacted within 120 min and the leaching reaction was diffusion controlled by surface chemical mechanism. The calculated activation energy of 56.98 kJ/mol supported the proposed dissolution process.     

Dissolution kinetics of particulate graphite injected into iron/carbon melts

An experimental investigation was undertaken to study the kinetics of graphite dissolution in gasstirred iron/carbon melts. Laboratory apparatus was developed to allow the injection of closely sized graphite into the bottom of a 1 kg scale reactor with nitrogen as a carrier gas. The effects of gas flow, particle loading, particle size, bath sulfur, and temperature on the rate of dissolution were assessed. It was found under the experimental conditions used that the graphite dissolution rate kept pace with the injection rate up to approximately 85 pct of carbon saturation, except when sulfur is present in the bath, in which case the dissolution rate is retarded. Modeling the rate of graphite particle dissolution supports the experimental results in that particle dissolution occurs quickly and under mass transport limitations. Computer generated gas-stirred flow field diagrams for the experimental reactor indicate that conditions exist for particle entrainment in the bath, and hence complete contact with the melt at all times during dissolution. formerly Experimental Scientist, CSIRO, Division of Mineral Engineering     

Dissolution kinetics of particulate graphite injected into iron/carbon melts

An experimental investigation was undertaken to study the kinetics of graphite dissolution in gasstirred iron/carbon melts. Laboratory apparatus was developed to allow the injection of closely sized graphite into the bottom of a 1 kg scale reactor with nitrogen as a carrier gas. The effects of gas flow, particle loading, particle size, bath sulfur, and temperature on the rate of dissolution were assessed. It was found under the experimental conditions used that the graphite dissolution rate kept pace with the injection rate up to approximately 85 pct of carbon saturation, except when sulfur is present in the bath, in which case the dissolution rate is retarded. Modeling the rate of graphite particle dissolution supports the experimental results in that particle dissolution occurs quickly and under mass transport limitations. Computer generated gas-stirred flow field diagrams for the experimental reactor indicate that conditions exist for particle entrainment in the bath, and hence complete contact with the melt at all times during dissolution. formerly Experimental Scientist, CSIRO, Division of Mineral Engineering     

Production of lead via ammoniacal ammonium sulfate leaching

Laboratory-scale investigations of a novel hydrometallurgical process for lead production are described. The process is based upon the solubility of certain oxidized lead compounds in aqueous ammoniacal ammonium sulfate (AAS) solutions. There are, essentially, five steps in the process, viz: pretreatment to convert lead in the raw material to a suitable oxidized form; dissolution of the lead compounds in an AAS solution at ambient temperatures and pressures; recovery of the lead from solution by electrolysis or precipitation; conversion of the products of the preceding stage to saleable products; treatment of solutions to make them suitable for recycling. This new process avoids many of the difficulties of existing hydrometallurgical processes for lead.     

Dissolution kinetics of copper sulphide anodes

Constant current and voltammetric experiments were carried out with synthetic and natural chalcocite and synthetic digenite anodes in a variety of electrolytes. Rapid dissolution of copper occurred at low potentials until limited by the rate at which copper could be transported from the reaction zone by diffusion through electrolyte held within the porous product layer. At this point, the potential rose sharply (galvanostatic) or the current began to fall (voltammetric) corresponding to the formation of elemental sulphur. Quantitative support for this mechanism was obtained using a simplified model of the pore diffusion process. The complexity of the solid-state reactions occurring in the anode product was revealed by a novel technique which enabled direct observation of the product profile during electrolysis.     

CuO-CO_2-NH_3-H_2O体系孔雀石浸出的热力学分析

针对氨浸出孔雀石的问题,对CuO-CO2-NH3-H2O体系进行了热力学分析,获得了一系列平衡关系图.结果表明,随着pH值升高,OH-取代CO32-参与形成沉淀,使稳定存在的固体按蓝铜矿、孔雀石、氢氧化铜的顺序转变.pH值对铜的溶解起决定性作用.pH值较低时,H+和Cu2+竞争与NH3的结合,溶液中铜氨配合物浓度低;pH值较高时,OH-和NH3竞争与Cu2+的结合,使铜转化为氢氧化铜沉淀;pH值8~11时,H+和OH-的竞争作用较弱,大部分NH3与Cu2+形成配合物,其中Cu(NH3)2+4为优势物种.氨浸出孔雀石的理论最佳pH值在9.3~9.4之间,该条件时总铜和总氮平衡浓度大体呈直线关系.     

CuO-CO2-NH3-H2O体系孔雀石浸出的热力学分析

针对氨浸出孔雀石的问题,对CuO-CO2-NH3-H2O体系进行了热力学分析,获得了一系列平衡关系图.结果表明,随着pH值升高,OH^-取代CO3^2-参与形成沉淀,使稳定存在的固体按蓝铜矿、孔雀石、氢氧化铜的顺序转变.pH值对铜的溶解起决定性作用.pH值较低时,H^＋和Cu^2＋竞争与NH3的结合,溶液中铜氨配合物浓度低;pH值较高时,OH-和NH3竞争与Cu^2＋的结合,使铜转化为氢氧化铜沉淀;pH值8-11时,H^＋和OH^-的竞争作用较弱,大部分NH3与Cu^2＋形成配合物,其中Cu（NH3）2＋4为优势物种.氨浸出孔雀石的理论最佳pH值在9.3-9.4之间,该条件时总铜和总氮平衡浓度大体呈直线关系.