Kinetics of copper dissolution during pressure oxidative leaching of lead-containing copper matte

The kinetics of pressure oxidative leaching of lead-containing copper matte with sulfuric acid was investigated. The effects of particle size, leaching temperature, oxygen partial pressure and sulfuric acid concentration on the kinetics and mechanism of copper extraction were studied. It was found that the reaction kinetic model follows the shrinking core model of chemical reaction control and the apparent activation energy was determined as 39.1 kJ/mol. The order of the reaction with respect to total pressure was found to be 0.64. The kinetic equations for the effect of particle size, leaching temperature, total pressure and sulfuric acid concentration were obtained and a mathematical model of copper extraction from lead-containing copper matte was developed as:

This equation estimates the extraction of copper with very good agreement (r = 0.99) between the experimental and calculated values.     

锌精矿常压浸出与加压浸出工艺比较

比较了常压浸出与加压浸出两种工艺的机理、流程、技术经济指标、投资以及存在的问题。试验和生产数据表明,加压浸出在技术上和工艺上都更具有吸引力。     

锌精矿常压浸出与加压浸出工艺比较

比较了常压浸出与加压浸出两种工艺的机理、流程、技术经济指标、投资以及存在的问题。试验和生产数据表明,加压浸出在技术上和工艺上都更具有吸引力。     

A kinetic study on the pressure leaching of sphalerite

The dissolution of sphalerite (ZnS) in sulfuric acid solution under oxygen pressure was investigated. Effects of temperature, percent solids, agitation, sample size, oxygen partial pressure and foreign ions were evaluated. The effect of hydrogen pretreatment on sphalerite leaching rate was also examined. Leaching of sphalerite at 90°C and 150 psi oxygen pressure was found to occur at a constant rate. This rate was determined from the experimental data observed under the different leaching conditions mentioned above. The constant leaching rate was attributed to the chemical reaction occurring on the surface of the flat-plate type sphalerite sample. The rate-controlling step of the reaction was determined to be the oxidation of hydrogen sulfide to elemental sulfur. Oxidation of hydrogen sulfide was studied through the addition of iron and through the observation of the change in iron concentration during leaching. The oxidation was concluded to be by reaction with ferric ion rather than by direct oxygen oxidation. Leaching tests run with samples pretreated with hydrogen do not show any increase in the rate of zinc extraction. M. T. HEPWORTH, formerly with University of Denver.     

Kinetics and mechanisms of the non-oxidative dissolution of sphalerite (zinc sulphide)

The kinetics of the non-oxidative dissolution of four samples of sphalerite (ZnS) of different origin were studied. It was concluded that the dissolution is independent of the stirrer speed and is first order in [H⁺], and that the activation energies for the removal and deposition reactions are not sensitive to the impurity content of the solid. The rate of reaction is described by an ionic charge transfer mechanism. A large addition of Zn²⁺ retards the initial rate because equilibrium conditions are established, whereas the addition of H₂S to the reaction system lowers the final extent of reaction. The addition of Fe (III) retards the initial rate of reaction due to an anodic shift in the potential difference at the surface-solution interface, but increases the final extent of reaction as a result of the consumption of H₂S by Fe (III) to form elemental sulphur and Fe (II). The observed inhibition of the initial rate for the impure samples is explained in terms of an electron-transfer theory similar to that proposed for non-stoichiometric metal sulphides.     

富锗硫化锌精矿的氧压酸浸研究

对云南某地富锗硫化锌精矿进行了氧压酸浸回收锗的试验研究。通过正交试验,研究了浸出温度、浸出时间、氧分压、精矿粒度、酸锌摩尔比和搅拌速度对锗浸出率的影响。结果表明,浸出温度和氧分压是影响锗浸出率的主要因素,在试验选定的条件下,锌和锗的浸出率能达到99%和90%以上。     

锌氧压浸出工艺现状及技术进展

本文在广泛收集整理国内外有关锌精矿氧压浸出研究成果的基础上,对锌冶炼氧压浸出工艺的生产现状及技术进展进行了详细介绍。     

Kinetics of vanadium dissolution from black shale in pressure acid leaching

The leaching kinetics of vanadium from black shale in the sulphuric acid-oxygen system is presented. The effects of agitation speed, leaching temperature in the range of 110-150 °C, sulphuric acid concentration, oxygen partial pressure and particle size on the rate of vanadium leaching were determined. The results indicate that the rate is nearly independent of agitation above 200 rpm and increases with increasing temperature, sulphuric acid concentration and oxygen partial pressure. As leaching occurs, there is a progressive dissolution of a vanadium-bearing alumino-silicate phase, while the inert quartz phase assembles onto the mineral surface and remains as an “ash” layer. The leaching kinetics was analyzed by using a new variant of the shrinking core model (SCM) in which both the interfacial transfer and diffusion across the product layer affect the leaching rate. The determined activation energy was found to be 40.14 kJ/mol and the reaction orders with respect to sulphuric acid concentration and oxygen partial pressure were 0.61 and 1.67, respectively. A semi-empirical rate equation was derived to describe the process.     

The dissolution of sphalerite in ferric sulfate media

The dissolution of sphalerite, (Zn,Fe)S, in ferric sulfate media was investigated using closely sized fractions of crushed sphalerite crystals. Linear kinetics were observed, and the rate increased in proportion to the surface area, as the average particle size of the sphalerite decreased. The predominant reaction products are ZnSO₄, FeSO₄, and elemental sulfur. The leaching rate increases with increasing temperature, and the apparent activation energy is 44 kJ/mol. The relatively high apparent activation energy suggests that the rate is chemically controlled, a conclusion supported by the insensitivity of the rate of the rotation speed that was observed in complementary rotating disk experiments. The rate increases as the 0.3 to 0.4 power of the Fe(SO₄)_1.5 concentration, and is nearly independent of the pulp density, in the presence of a stoichiometric excess of ferric sulfate. In 0.3 M Fe(SO₄)_1.5 media, the rate increases with increasing acid concentrations >0.1 M H₂SO₄, but is insensitive to more dilute acid concentrations. In the absence of ferric ions, the rate increases rapidly with increasing H₂SO₄ concentrations, and relatively rapid rates are observed in solutions containing >0.5 M H₂SO₄. The rate decreases with increasing initial concentrations of ZnSO₄, MgSO₄, or FeSO₄ in the ferric sulfate leaching solution, and this emphasizes the importance of maintaining the dissolved iron in a fully oxidized state in a commercial leaching operation.     

Reaction mechanism for the ferric chloride leaching of sphalerite

Reaction mechanisms for the ferric chloride leaching of sphalerite are proposed based on data obtained in leaching and dual cell experiments presented in this work and in a previous study. The results from the leaching experiments show that at low concentrations the rate is proportional to [Fe³⁺]_T ^0.5 and [Cl^-]_T ^0.43 but at higher concentrations the reaction order with respect to both [Fe³⁺]_T and [Cl^-]_T decreases. Using dual cell experiments which allow the half cell reactions to be separated, increased rates are observed when NaCl is added to the anolyte and to the catholyte. The increase in rate is attributed to a direct, anodic electrochemical reaction of Cl^- with the mineral. When NaCl is added only to the catholyte, a decrease in the rate is observed due to a decrease in theE ⁰ of the cathode which is attributed to the formation of ferric-chloro complexes. Several possible electrochemical mechanisms and mathematical models based on the Butler-Volmer relation are delineated, and of these, one model is selected which accounts for the experimentally observed changes in reaction order for both Fe³⁺ and Cl^-. This analysis incorporates a charge transfer process for each ion and an adsorption step for ferric and chloride ions. The inhibiting effect of Fe²⁺ noted by previous investigators is also accounted for through a similar model which includes back reaction kinetics for Fe²⁺. The proposed models successfully provide a theoretical basis for describing the role of Cl^-, Fe³⁺, and Fe²⁺ as well as their interrelationship in zinc sulfide leaching reactions. Possible applications of these results to chloride leaching systems involving other sulfides or complex sulfides are considered.     

The kinetics of dissolution of sphalerite in ferric chloride solution

The dissolution of sphalerite in acidic ferric chloride solution was investigated in the temperature range 320 to 360 K. Both sized particles from three sources and polished flat surfaces were used as samples. The effect of stirring rate, temperature, ferric and ferrous ion concentration, purity, and particle size on the dissolution rate were determined. During the initial stages of the process chemical reaction at the mineral surface is rate controlling while during the later stages diffusion through the product sulfur layer is rate controlling. Overall the process follows the mixed-control model embodying both chemical reaction and diffusion. The activation energy for the dissolution of sphalerite particles was found to be 46.9 kJ/mol.     

A Microscopic study of the transformation of sphalerite particles during the roasting of zinc concentrate

The formation of zinc ferrite (ZnFe₂O₄) during the roasting of iron-bearing zinc concentrates requires substantial additional processing to recover the zinc from this compound by leaching and to eliminate the iron from the leachate. The phase changes that occur in the particles of a typical industrial zinc sulfide concentrate during roasting in a fluidized bed at 1223 K were investigated by the use of light microscopy, electron microprobe analysis, and SEM with EDS. The processes which the iron undergoes during its eventual transformation into ferrite have been clarified by examination of the phases and the morphology of partially roasted marmatitic sphalerite particles (Zn, Fe)S, and by reference to the known phase equilibria involved in the Zn-Fe-S-0 system. The oxidation of ironbearing sphalerite occurs in three stages. The first involves the selective diffusion of most of the iron to the particle surface resulting in the formation of an iron oxide shell enclosing a largely unreacted zinc sulfide kernel. In the second stage, this kernel is oxidized to form a solid solution of zinc oxide and iron oxide. The iron is initially present in the ferrous state but, with the disappearance of the sulfide kernel, is oxidized to ferric iron. In the final stage, this dissolved iron oxide and the iron oxide shell react with the surrounding zinc oxide to form the refractory spinel zinc ferrite.     

Effect of aging conditions on the leaching of mechanically activated pyrite and sphalerite

The leaching of mechanically activated pyrite and sphalerite exposed to nitrogen (99.999 vol pct) or air at ambient temperature or 573 K was investigated. The results indicate that at the same leaching time, the iron-leaching ratio of mechanically activated pyrite or sphalerite aged in nitrogen at both ambient temperature and 573 K decreases slightly with increasing aging time and remains constant after a certain aging period. The iron-leaching ratio of mechanically activated pyrite exposed to ambient air varies with the exposure period. But, at the same leaching time, the zinc-leaching ratio of mechanically activated sphalerite aged at ambient temperature does not change with the aging atmosphere. The structures of mechanically activated pyrite and sphalerite after being aged were determined. The specific granulometric surface area of mechanically activated pyrite and sphalerite decreases with increasing aging time, but keeps constant after a certain aging period. The X-ray diffraction patterns of mechanically activated pyrites aged in nitrogen do not change with aging time; neither do the X-ray diffraction patterns of mechanically activated sphalerites aged either in air or in nitrogen. For mechanically activated pyrite exposed to ambient air for 3 and 6 months, new phases were found. The lattice distortion and the elemental sulfur content of pyrite and sphalerite mechanically activated in nitrogen were also investigated. The results indicate that the elemental sulfur content of mechanically activated pyrite rises noticeably, and its lattice distortion (ε) rises slightly, with increasing grinding time. The elemental sulfur content of mechanically activated sphalerite remains constant at 0.5 mg elemental sulfur per gram of sphalerite, and its lattice-distortion ratio increases apparently with increasing grinding time. These observations provide further evidence for our opinion that the formation of dangling bonds on the surface of mechanically activated pyrites and the lattice distortion on the surface of mechanically activated sphalerites may mainly result in the enhancement of hydrometallurgical process for corresponding sulfide minerals.     

新型尾气洗涤系统在锌精矿氧压浸出工艺的应用

压力浸出工艺的排气会夹带固体颗粒和酸性液滴,利用新型尾气洗涤系统对排气进行洗涤,保证外排气体达标。新型尾气洗涤系统包括排气冷凝器、文丘里、分离器和排气筒。     

Reaction kinetics of the ferric chloride leaching of sphalerite—an experimental study

Chloride leaching processes have significant potential for treating complex sulfides. One advantage of chloride leaching is fast dissolution rates for most sulfide minerals. This experimental study is concerned with ferric chloride leaching of sphalerite, a common component of many complex concentrates. The effects of stirring, temperature, ferric ion concentration, and particle size have been examined. In addition, reaction residues at various levels of zinc extraction were examined by SEM, and the products of reaction were identified by energy dispersive X-ray analysis and X-ray diffraction. These observations indicated that the dissolution reaction is topochemical. Moreover, the leaching results fit a surface reaction control model. The activation energy was calculated to be 58.4 kJ/mole which is reasonable for a rate limiting surface reaction. The order of the reaction was 0.5 with respect to Fe³⁺ at low concentrations and zero at high concentrations. The change in reaction order occurred at similar Fe³⁺ concentrations for various particle sizes. This is believed to be indicative of an electrochemical reaction mechanism at low Fe³⁺ and an adsorption mechanism at higher Fe³⁺. A kinetic model for the ferric chloride leaching of sphalerite was also obtained for the lower Fe³⁺ concentrations and is given by: (ie5-01) This model is in excellent agreement with the experimental results for fractions of zinc extracted up to 0.95.     

Measurements of dielectric properties for particulate sphalerite samples and zinc concentrates

Little is known about the electronic nature of pulverized sphalerite which is used for pressure leaching. In order to clarify the relationship between the oxidation rate in suspension and the electronic nature, the dielectric properties of particulate samples of six sphalerites (screen size: 250 to 88 and -88 μm), prepared by crushing and sieving, and four zinc flotation concentrates were measured using a packed bed condenser. A glass plate, particulate samples of it, and pure ZnS powder were used as references. From the capacitance and porosity of the bed, the specific dielectric constant for the dense substance was calculated using B?ttcher’s empirical equation. The values obtained at 120 Hz were generally larger than those at 1 kHz, suggesting that dielectric dispersion and absorption occurred. The specific dielectric constant for very low frequency (ε _L ^* ), the maximum value of dielectric loss tangent (tan δ_max), the frequency for the dielectric absorption peak (f_max), and the relaxation time (τ) were calculated according to Debye’s theory, assuming that the specific dielectric constant for very high frequency was constant. The results revealed that ε _L ^* , tan δ_max, and f_max increased with the Fe content of the samples (0.7 to 13.4 wt pct), whereas τ decreased. Particle size (5 to 710 μm) had a slight effect on the dielectric properties. There was an apparent correlation between the dielectric loss tangent measured for the packed bed and that calculated for the dense substance. formerly with National Research Institute for Metals