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     

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.     

The kinetics of the dissolution of chalcocite in alkaline cyanide solution

A kinetic study of the dissolution of chalcocite in an alkaline cyanide solution indicates that the reaction is first order with respect to surface area and free cyanide ion concentration, and inversely proportional to the sulfide ion concentration to approximately the 0.1 power. The experimental rate constant is approximately 7.5 × 10⁻⁵ (mole Cu¹⁺/ min) ([S⁻²]^0.1/[CN¹⁻]/cm²/l at 25°C. The activation energy of 2.5 kcal/mole indicates rate control by diffusion through a limiting boundary layer. The concentrations of the important ions in the cyanide solutions are obtained by solving the ionic equilibria and mass balance equations for the system.     

Kinetics of the dissolution of scheelite in aqueous Na4EDTA solutions

The reaction kinetics of the dissolution of pure scheelite (CaWO₄) particles in aqueous Na₄EDTA solutions were studied at atmospheric pressure. As expected, the dissolution rate increased with decreasing initial particle size and with increasing temperature and Na₄EDTA concentration. Further, the dissolution rate decreased as the initial solid-liquid ratio and the ionic strength of the solution were increased. The experimental results do not support the conventional shrinking-core model for a single irreversible reaction. A new shrinking-core model for multiple reactions, composed of a noninstantaneous reversible reaction (scheelite dissociation into the ions Ca²⁺ and WO ₄ ²⁻ ) and an instantaneous irreversible reaction (formation of Ca-EDTA complex), was presented. The observed dependency of the dissolution rate on the relevant operating variables was the same a the theoretical predictions based on the present shrinking-core model. The activation energy was 49800 J mol⁻¹. These findings justify the validity of the assumed kinetic model with the multiple reactions as the rate-controlling step. The dissolution rate expression was obtained as a function of the initial particle size, initial solid-liquid ratio, Na₄EDTA concentration, temperature, and ionic strength of the solution.     

Viscosity of copper slags from chalcocite concentrate smelting

The viscosity of smelting slags from the Glogow copper plant in Poland was measured using a concentric cylinder viscometer. These slags contain typically 45 pct SiO₂, 16 pct CaO, 8 pct MgO, 11 pct Al₂O₃, and only 5 to 7 pct total iron. The viscosity was measured as a function of the CaO, MgO, SiO₂, Cu₂O, Cr₂O₃, and Fe₃O₄ contents in the temperature range from 1473 to 1623 K. Silica and chromium oxide additions increased the viscosity, while small additions of the other oxides decreased the viscosity. However, at large additions of CaO or MgO, cooling resulted in a rapid increase in the viscosity upon reaching the transition temperature. This critical transition temperature increased with increasing additions of CaO and MgO. This was explained by the precipitation of solid particles upon reaching the saturation limit. Depending on the slag composition, the activation energy for viscous flow was found to be in the range from 200 to 370 kJ/mol.     

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.     

Recovery of copper from chalcocite by means of the pyridine and chloride ion donor systems

Recovery of copper from natural chalcocite by means of pyridine—hydrochloric acid mixtures and pyridine solutions of pyridine hydrochloride is described. The systems were found to be effective media for leaching of chalcocite. Total copper recovery is reached after 15 minutes at 60°C.     

Leaching kinetics of the magnetic fraction of converter matte in sulfuric acid and hydrochloric acid solutions

The kinetic peculiarities of the dissolution of the magnetic fraction of converter matte in H₂SO₄ (150 g/l) and HCl (200 g/l) solutions are studied in the temperature range of 30–90°C. Under comparable conditions, the dissolution rate of the magnetic fraction of converter matte in HCl solutions is shown to be substantially higher than that in H₂SO₄ solutions. The kinetic parameters of the processes under study are calculated. It is found that the dissolution of the magnetic fraction of converter matte in a sulfuric acid solution occurs within a diffusion range (E _a ∼ 6.5 kcal/mol), whereas the dissolution in a hydrochloric acid solution corresponds to a kinetic range (E _a ∼ 15 kcal/mol). Possible mechanisms of the dissolution of the magnetic fraction of converter matte in mineral acid solutions are considered.     

Leaching of copper and zinc from oxidised ores by fungi

Various types of fungi have been isolated from Indian mine water samples and the leaching of oxidised copper and lead—zinc ores by these species investigated. Metal dissolution characteristics with respect to one specific type of fungi, viz. Aspergillus niger, are illustrated. The effects of pH, pulp density and carbon source on the fungal activity are also reported.     

分子识别技术(MRT)在铜精炼中的应用—从铜电解液中除铋

在世界经济中,高纯电解铜是一种重要的商品,主要用来生产铜线。全球冶炼厂处理来自不同产地的矿石,生产出高纯电解铜。这些铜精矿通常含有0.1%的铋。如果最终产品中的铋含量超过2×10^-6,会导致产品出现脆性,使得铜产品不适合用于拉丝生产。IBC先进技术有限公司开发出一种有效的除铋系统,用于分离铜电解液中溶解的铋,使铋含量达到一个理想的水平。该系统与铜生产系统一体化,可实现连续作业。IBC采用一种分子识别技术（MRT）工艺来进行分离作业。在该工艺中,专门设计的螯和剂或配位体与固体骨架（例如硅胶）进行化学结合,产生一种称为SuperLig^的固相系统。这套除铋系统已经用于几家电解厂的铜精炼生产中。本文介绍了从铜电解液中分离和回收铋的工艺步骤,这些工艺步骤包括:吸收、一段洗涤、预解吸、主要解吸、后解吸、二段洗涤、铋沉淀,给出了每个步骤控制和监测的项目。本文讨论了采用其它技术控制铋的局限性。作者还介绍了MRT系统为铜电解厂带来的经济效益,这些铜电解厂都存在铋的问题。     

人造金红石制备过程的浸出动力学

研究了钛渣杂质浸出过程的动力学,利用未反应核收缩模型描述了反应过程.实验结果表明:杂质的浸出过程属于化学反应控制,浸出过程的表观活化能为43.52 kJ/mol.通过X射线衍射和扫描电镜分析了渣样的物相组成和显微形貌,改性渣中只含有金红石相和玻璃相,相比较改性前更加简单,有利于分离过程.     

Tungsten recovery from alkaline leach solutions as synthetic scheelite

The recovery of tungsten from alkaline leach solutions has been studied examining the effect of temperature, pH, Ca/WO₃ molar ratio and nature of the precipitated calcium tungstate. The precipitation kinetics of calcium tungstate, upon the addition of aqueous sodium tungstate to calcium solutions, was followed by potentiometric measurements using a calcium ion-selective electrode. Two models, a crystal growth model and a second-order reaction opposed by zero-order reaction, have been used to test the experimental data. Both models show that the apparent activation energy of CaWO₄ precipitation falls in the range 58 to 67 kJ mol^− 1.The kinetic data shows that the maximum recovery of precipitated calcium tungstate occurs at pH ≥ 8.5 with a 10% excess of CaCl₂ at 50 °C over a period of 20 min using sodium tungstate solutions of 100 g L^− 1 and 150 g L^− 1 WO₃.     

Coarsening kinetics of silica in copper

Coarsening experiments have been conducted in the copper-silica system to study the aging behavior of compound precipitates in metallic systems under various conditions of temperature and atmosphere. Most of the experiments were conducted in a two-zone heating furnace, wherein a copper-cuprous oxide mixture was heated in one zone and the copper-silica sample was heated in the other zone, all enclosed in a quartz capsule. The temperature of the former zone determined the oxygen partial pressure in the system and the temperature of the latter zone determined the coarsening temperature. The silica particles from the coarsened samples were extraction-replicated and photographed in an electron microscope. The average radii obtained from these photographs were used to determine coarsening rate constants and activation energies. Isothermal coarsening kinetics followed the γ^-3 vs t law, indicating volume diffusion control. Activation energies were obtained for four different sets of experimental conditions. In each case the activation plot was linear. For coarsening under variable oxygen pressure the experimental activation energy of 530 kJ (127 Kcal) agrees fairly well with the predicted value of 514 kJ (123 Kcal) which takes into consideration the heats of solution and dissolution, as well as the activation energy for diffusion. For coarsening under constant oxygen pressures the experimental activation energies do not compare well with the predicted values, calculated on the basis of complete equilibration of oxygen between the gaseous phase and the sample. However, the experimental activation energies of 524 kJ (125 Kcal) and 447 kJ (107 Kcal) lie in the predicted range calculated on the basis of fixed amounts of oxygen in solution in copper. In no case is the activation energy for coarsening equal to that for diffusion of either species in the matrix as is sometimes assumed. Formerly DSR Staff Member.     

Coarsening kinetics of silica in copper

Coarsening experiments have been conducted in the copper-silica system to study the aging behavior of compound precipitates in metallic systems under various conditions of temperature and atmosphere. Most of the experiments were conducted in a two-zone heating furnace, wherein a copper-cuprous oxide mixture was heated in one zone and the copper-silica sample was heated in the other zone, all enclosed in a quartz capsule. The temperature of the former zone determined the oxygen partial pressure in the system and the temperature of the latter zone determined the coarsening temperature. The silica particles from the coarsened samples were extraction-replicated and photographed in an electron microscope. The average radii obtained from these photographs were used to determine coarsening rate constants and activation energies. Isothermal coarsening kinetics followed the γ^-3 vs t law, indicating volume diffusion control. Activation energies were obtained for four different sets of experimental conditions. In each case the activation plot was linear. For coarsening under variable oxygen pressure the experimental activation energy of 530 kJ (127 Kcal) agrees fairly well with the predicted value of 514 kJ (123 Kcal) which takes into consideration the heats of solution and dissolution, as well as the activation energy for diffusion. For coarsening under constant oxygen pressures the experimental activation energies do not compare well with the predicted values, calculated on the basis of complete equilibration of oxygen between the gaseous phase and the sample. However, the experimental activation energies of 524 kJ (125 Kcal) and 447 kJ (107 Kcal) lie in the predicted range calculated on the basis of fixed amounts of oxygen in solution in copper. In no case is the activation energy for coarsening equal to that for diffusion of either species in the matrix as is sometimes assumed.     

Leaching reaction and kinetics of zinc from indium-bearing zinc ferrite under microwave heating

Leaching of zinc from indium-bearing zinc ferrite (IBZF) under microwave heating (MH) has been investigated. The result showed microwave intensified the leaching reaction of IBZF in the MH process. Microwave had a great nonthermal effect on the leaching reaction. The effective collision and the H₂SO₄ activation under the action of microwave belonged to the nonthermal microwave effect. Particle size of IBZF in the range from 45 to 150 μm almost had no effect on the zinc leaching in the MH process. Leaching temperature and leaching time had important effects on the zinc leaching. Zinc leaching in the MH process obeyed the unreacted shrinking core model very well, and the activation energy was 73.747 kJ/mol. The kinetic equation was \(1 - (1 - x)^{1/3} = 8.82 \times 10^8 e^{ - 73.747 \times 10^3 /RT} t\). The ratio of frequency factor of K_0(In)/K_0(Zn) was up to 4.69, indicating the effect of microwave intensification on the indium leaching was greater than that on the zinc leaching.     

EDTA分光光度法测定铜金粉中的高含量铜

目前,常用的高含量铜的测定方法仍为古老的碘量法,其碘化钾的用量大、成本高、耗时多,而新近开发的光度法又因铜显色剂的问题不宜于高含量铜的测定,故有必要研究、开发新的显色剂。该文作者试用醋酸-醋酸钠缓冲溶液控制pH值,用乙二胺四乙酸二钠盐（EDTA）作显色剂,测定铜金粉中的高含量铜,同时利用EDTA掩蔽锌、铝等元素以消除其干扰。Cu^2＋与EDTA生成摩尔比1：1的蓝色络合物,该络合物最大吸收波长为2=730nm,摩尔吸光系数为ε=88．9,铜离子含量在12-24mg／50mL范围内呈良好的线性关系,线性回归方程为A=0．0354＋0．02317c,线性相关系数R=0．9995。采用EDTA分光光度法测定铜金粉中的高含量铜,所得结果令人满意,有开发应用前景,尤其适用于设备比较简陋的中、小型企业实验室。     

Leaching of chrysocolla with Ammonia-Ammonium carbonate solutions

Chrysocolla was leached in solutions of ammonium hydroxide and ammonium carbonate as a function of the variables: temperature (25 to 55 ‡C), ammonia-ammonium ratio (0.0:1.0 to 1.0:0.0), total ammonia concentration (0.25 to 6.0 M), and particle size (100 to 400 mesh). A model of the leaching behavior was deduced based on: (1) the activation energy of 60.75 kJ/mole (14.51 kcal/mole) for 3 M total NH₃ which was dependent on both total ammonia concentration and temperature; (2) first-order dependence of rate on [(NH₄)₂CO₃]; (3) dependence of initial reaction rate on reciprocal of particle diameter; and (4) morphological evidence from SEM and ED AX measurements of diffusion and leaching occurring primarily in surface microcracks and not in the submicroscopic pores. In addition to the importance of diffusion through microcracks in rate control chemical reaction at active surface sites to produce the species, CuNH ₃ ^{2 +}, is also important. Only a fraction of the Cu atoms react that are exposed to lixiviant. Higher ammonia-ammonium ion concentrations, higher temperatures, or much longer times are required for more refractory Cu atoms to dissolve. Formerly Graduate Student, Department of Metallurgy and Metallurgical Engineering, University of Utah     

Arsenic removal from copper ores and concentrates through alkaline leaching in NaHS media

Removal of arsenic impurity in ores and concentrates containing copper (Cu) through alkaline leaching in NaHS media was investigated in this work. Samples containing Cu from 10 to 40 wt.% and arsenic from 0.8 to 14 wt.% with enargite (Cu₃AsS₄) as main arsenic bearing mineral were used as starting materials and all leaching tests were conducted at 80 °C under normal atmospheric pressure. Solution and/or slurry potential and pH were maintained consistently below − 500 mV (SHE) and above 12.5 respectively with the addition of NaHS and NaOH, creating a reducing environment for arsenic dissolution and conversion of Cu₃AsS₄ to Cu₂S. Pulp density ranged from 100 to 1000 g/L, NaHS and NaOH reagents were added at 50–200 g/L each and leaching time varied from 10 min to 10 h.Characterization of solid samples (original and leach residue) by XRD and XRF analyses and chemical analysis of both solid and solution samples by ICP analysis showed that Cu₃AsS₄ in the starting material was completely decomposed or transformed to Cu₂S and arsenic released into solution as As (III)/As³⁺ ions (Na₃AsS₃). Over 90% of arsenic in the starting materials was removed within 1–3 h for materials with arsenic content from 1 to 4 wt.% and within 3–6 h for materials with arsenic content over 4–10 wt.%. Dissolution and analysis of leach residues obtained after leaching by ICP indicated that arsenic in the starting materials has been reduced in all cases to below 0.5 wt.%. In all test conditions dissolution of Cu and Fe into solution was not detected, indicating selective leaching of arsenic. NaHS application for removal of arsenic in Cu-ores and/or concentrates was demonstrated in this work and further research is in progress to develop a process to include treatment of arsenic leached into solution.