Fluidised-bed anodic dissolution of chalcocite

The anodic dissolution of chalcocite (Cu₂S) has been investigated using a fluidised-bed anode technique. Results obtained for a variety of electrolytes and experimental conditions indicate that the fluidised-bed anodic dissolution of chalcocite occurs via the formation of an intermediate copper sulphide, viz., “blue-remaining” covellite, Cu_1.1S.In sulphuric acid electrolyte the dissolution of chalcocite is inhibited after about 50% copper extraction by the vigorous evolution of oxygen gas at the platinum feeder anode.In both sulphuric acid-sodium chloride and sulphuric acid-potasium bromide electrolytes, the dissolution of chalcocite occurs to 95% copper extraction in two stages. The first stage involves the formation of Cu_1.1S, as is the case for the sulphuric acid electrolyte, while the second stage is attributed to the reaction between chloride (or bromide) and Cu_1.1S.     

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.     

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.     

Optimization and dissolution kinetics of vanadium recovery from LD converter slag in alkaline media

Alkaline roasting-alkaline leaching process was used to recover vanadium from LD (Linz Donawitz) converter slag. The independent leaching parameters investigated were liquid to solid ratio (L/S) (10–20 mL/g), temperature (40–60°C), NaOH concentration (1.0–3.0 M), and time (60–120 minutes). Response surface methodology (RSM) was utilized to optimize the leaching parameters and as a result, the most influencing parameter was found to be liquid to solid ratio. Based on the results, the optimum recovery condition (approx. 99%) was obtained with L/S ratio of 20, temperature of 40°C, NaOH concentration of 3.0M, and leaching time of 100 minutes, respectively. Furthermore, the kinetics of alkaline leaching process was investigated using shrinking core model (SCM) equations. It was found that the rate of vanadium leaching is controlled by a mixed controlling mechanism which is comprised of chemical reaction and diffusion through the solid product layer.     

Kinetics of dissolution of synthetic scheelite by an alkaline EDTA leach solution

The dissolution rate of synthetic scheelite in an alkaline EDTA leach solution under atmospheric pressure has been determined by use of a rotating disc method. The effects of disc rotation speed, temperature, reagent concentration and pH of leach solution have been investigated. The dissolution rate was proportional to the square root of the disc rotation speed. The apparent activation energy of dissolution of synthetic scheelite was 22 kJ mol⁻¹ within the experimental temperature region of 24 to 99°C. A first order dependence of dissolution rate on EDTA concentration was observed. It has been shown from the experimental results that the dissolution reaction was controlled by the mass transfer in the aqueous solution.     

Synthesis of new phosphonate ester resins for adsorption of gold from alkaline cyanide solution

Resin ion-exchange technology is a possible alternative to well-established gold recovery processes of carbon adsorption and zinc-dust cementation. The search for a suitable resin for gold recovery from alkaline cyanide solution continues at several research centers. Recent discoveries involving alkyl phosphorus esters for selective gold solvent extraction from alkaline cyanide solution suggest that similar chemistry on a resin substrate might likewise be effective. In this regard, polystyrene-supported phosphonate ester-based resins were synthesized from the poly(styrene/divinylbenzene) copolymers. Gold adsorption/desorption characteristics were established for these resins with respect to functional group chemistry, pH, ionic strength, and temperature. Gold loading was found to be promoted at increased ionic strength with fair selectivity over various cyanoanions. Stripping was possible at higher temperatures and/or low ionic strength of the strip solution. Solvation extraction of an alkali cation/aurocyanide anion ion pair seems to explain the adsorption/desorption phenomena which are discussed in terms of the variables studied.     

Electrochemical behavior of the dissolution of gold-silver alloys in cyanide solutions

The dissolution behavior of gold and silver from Au/Ag alloys in aerated cyanide solutions has been investigated using rotating disc electrodes. The variables studied included concentration of cyanide, oxygen partial pressure, and rotating speed of the disc. The dissolution potential and the rate of dissolution were obtained in view of the anodic and cathodic current-potential relationships. The results were discussed in terms of the mixed potential theory. The results showed that the dissolution rate of gold and silver from the alloys was partially controlled by chemical reaction but largely controlled by transport of either oxygen or cyanide, depending on their relative concentrations under the experimental conditions employed in this study. The diffusion coefficient of free cyanide, D_cn ^?, was found to be (1.25 ± 0.05) X 10^?5 cm²/s. The diffusion coefficient of oxygen, $D_{O_2 } $ , was calculated to be (1.29 ± 0.02) X 10^?5 cm²/s.     

Ternary dissolution kinetics in the Fe-Ni-P system

The dissolution of (FeNi)₃P in the ternary Fe-Ni-P system has been studied by optical and electron microprobe techniques. Precipitates of (FeNi)₃P, initially in equilibrium with their ternary matrix (a at 750°C, y at 875°C), were examined after being partially dissolved by heating at 975°C. In addition, diffusion couples with starting compositions similar to the equilibrated ternary alloys were examined after also being heat treated at 975°C. Phosphide, (FeNi)₃P, dissolution in the α or γ phase is diffusion controlled at 975°C. The ternary dissolution paths observed in each of the diffusion couples are unique and the same as those observed in the comparable alloys. The dissolution rate of (FeNi)₃P is controlled by the diffusion rate of P in the α or y phases. The Ni interface compositions in (FeNi)₃P and α or γ and the dissolution path through the ternary are determined by the rate of dissolution and the major Ni ternary diffusion coefficients. It is possible to calculate both the dissolution path and rate for (FeNi)₃P by using the binary dissolution equations in combination with the Fe-Ni-P diagram and the major (ternary) diffusion coefficients. In addition, numerical solutions can be correctly calculated for diffusion controlled dissolution where impingement of overlapping gradients occurs. Formerly Graduate Assistant, Department of Metallurgy and Materials Science, Lehigh University, Bethlehem, Pennsylvania     

Ternary dissolution kinetics in the Fe-Ni-P system

The dissolution of (FeNi)₃P in the ternary Fe-Ni-P system has been studied by optical and electron microprobe techniques. Precipitates of (FeNi)₃P, initially in equilibrium with their ternary matrix (a at 750°C, y at 875°C), were examined after being partially dissolved by heating at 975°C. In addition, diffusion couples with starting compositions similar to the equilibrated ternary alloys were examined after also being heat treated at 975°C. Phosphide, (FeNi)₃P, dissolution in the α or γ phase is diffusion controlled at 975°C. The ternary dissolution paths observed in each of the diffusion couples are unique and the same as those observed in the comparable alloys. The dissolution rate of (FeNi)₃P is controlled by the diffusion rate of P in the α or y phases. The Ni interface compositions in (FeNi)₃P and α or γ and the dissolution path through the ternary are determined by the rate of dissolution and the major Ni ternary diffusion coefficients. It is possible to calculate both the dissolution path and rate for (FeNi)₃P by using the binary dissolution equations in combination with the Fe-Ni-P diagram and the major (ternary) diffusion coefficients. In addition, numerical solutions can be correctly calculated for diffusion controlled dissolution where impingement of overlapping gradients occurs.     

The kinetics of gold cyanide adsorption on activated charcoal

Adsorption rates of gold cyanide on activated carbon were determined as a function of temperature, free cyanide concentration and charcoal concentration. The experimental rate data is explained by use of a diffusion controlled model developed by Crank. The adsorption rates were determined to be controlled by pore diffusion with the effective diffusion coefficient having an activation energy of 3.3 kcal/mol. Good agreement between experimental rate data and predicted rate curves by the diffusion model was obtained. Formerly with the Department of Metallurgy,University of Utah.     

The kinetics of dissolution of chalcopyrite in ferric ion media

The kinetics of dissolution of chalcopyrite (CuFeS₂) in ferric chloride-hydrochloric acid and in ferric sulfate-sulfuric acid solutions have been investigated using the rotating disk technique. Over the temperature range 50 to 100‡C, linear kinetics were observed in the chloride media while nonlinear kinetics were noted in the sulfate system. The apparent activation energy in the chloride system was about 11 kcal/mole. The rate increased with increasing ferric chloride concentrations but was insensitive to the concentrations of hydrochloric acid, the ferrous chloride reaction product and “inert≓ magnesium or lithium chlorides. Cupric chloride substantially accelerated the rate. Small amounts of sulfate in an otherwise all chloride system greatly reduce the chalcopyrite leaching rate; still larger amounts of sulfate make the system behave essentially like the slower-reacting ferric sulfate medium.     

The kinetics of dissolution of chalcopyrite in ferric ion media

The kinetics of dissolution of chalcopyrite (CuFeS₂) in ferric chloride-hydrochloric acid and in ferric sulfate-sulfuric acid solutions have been investigated using the rotating disk technique. Over the temperature range 50 to 100?C, linear kinetics were observed in the chloride media while nonlinear kinetics were noted in the sulfate system. The apparent activation energy in the chloride system was about 11 kcal/mole. The rate increased with increasing ferric chloride concentrations but was insensitive to the concentrations of hydrochloric acid, the ferrous chloride reaction product and “inert? magnesium or lithium chlorides. Cupric chloride substantially accelerated the rate. Small amounts of sulfate in an otherwise all chloride system greatly reduce the chalcopyrite leaching rate; still larger amounts of sulfate make the system behave essentially like the slower-reacting ferric sulfate medium.     

The kinetics of magnesium vapour dissolution into pig iron

Abstract

Magnesium injections are used extensively in the iron and steel industry for the production of ductile iron, and for the desulphurization of blast furnace pig iron. However, little is currently known about the kinetic mechanisms involved in either of these two cases. In the present work, a magnesium vaporizer was used to inject pure magnesium vapour into 60-kg pig iron melts (1250°C) at rates of between 0.7 and 12 gm/min for bubbling periods of 20 to 60 minutes. The efficiency of magnesium dissolution ranged between 20 and 80%. A mass transfer model, based on single bubbles, was used, to interpret the results. In addition, residual magnesium concentrations following holding times of up to 60 minutes after bubbling compared reasonably well with those predicted on the basis of theoretical evaporation rates.

Résumé

L'injection de magnésium est utilisée intensivement dans l'industrie siderurgique pour la production de fonte ductile et pour la désulfuration de la fonte en gueuse provenant du haut-fourneau. Cependant, il y a présentement peu dapos;informations sur les mécanismes de réactions impliqués dans l'un ou l'autre des deux cas. Dans ce présent travail, un va porisateur de magnésium a été utilise afin d'introduire la vapeur de magnésium pur dans un bain de 60 kg de fonte liquide à 1250°C, a des taux variant entre 0.7 et 12 gn/min pour des durées d'injection variant de 20 à 60 minutes. L'efficacité de la dissolution du magnésium dans la fonte liquide était comprise entre 20 et 80%.

Un modele de transfert de masse a été utilisé pour interpréter les résultats. Il est à noter que les concentrations résiduelles de magnésium correspondant à des temps de bouillonnement allant jusqu'à 60 minutes se comparent raisonnablement bien avec les valeurs prédites théoriquement à partir des taux d' évaporation du Mg.     

氰化浸出体系中金的溶剂萃取

本文评述了金的碱性氰化溶液溶剂萃取研究与开发工作的最新进展。包括改性胺，季铵盐，磷氧化物及胍类萃取剂等。     

The kinetics of dissolution of covellite in acidified ferric sulphate solutions

Abstract

Pure synthetic CuS disks and high-grade natural covellite were dissolved in acidified ferric sulphate solutions in the temperature range 25 to 95°C. For both materials, the rates were relatively slow and increased during the initial stages of the dissolution, eventually becoming nearly linear. The activation energy, as determined from the initial dissolution rates of the synthetic covellite, was 17.8 ± 2.0 kcal/mole. Microscopic examination of both the natural and the synthetic sulphide revealed that the attack occurred preferentially in certain areas. It was felt that the progressive development of such pits was responsible for the gradual rate increase observed during the initial leaching stage. From 0 to 6° of the leached sulphur reported in the sulphate form. The rate of copper dissolution decreased sharply with increasing ferrous sulphate concentrations in the leaching medium. The rate varied directly with the ferric concentration for initial concentrations below 0.005 M Fe³⁺ but was insensitive to higher ferric strengths. Natural covellite dissolved at approximately the same rate and with essentially the same temperature dependence as the synthetic material. The rate controlling step for the dissolution of CuS was felt to be a chemical reaction occurring on the surface of the sulphide.

Résumé

Des disques de CuS synthétique pur et de la covelline naturelle de haute qualité ont été dissous dans des solutions acidifiées de sulfate ferrique entre 25 et 95°C. Pour les deux matériaux, les vitesses étaient relativement lentes et augmentaient durant la période initiale de dissolution, pour finalement devenir presque linéaires. L'énergie d'activation, déterminée à partir de la vitesse de dissolution initiale de la covelline synthétique était de 17.8 ± 2.0 kcal/mole. L'examen microscopique des sulfures naturel et synthétique a révélé que l'attaque se produit de préférence dans certaines régions. On pense que le développement progressif de telles piqûres etait responsable de l'accroissement graduel observé durant le lavage initial. Zéro à 6% du soufre dissous l' était sous forme de sulfate. La vitesse de dissolution du cuivre diminuait rapidement avec l'accroissement de concentration en sulfate ferreux dans la solution. La vitesse variait directement avec la concentration ferrique pour des concentrations initiales inférieures à 0.005 M Fe³⁺, et était insensible aux plus fortes concentrations ferriques. La covelline naturelle se dissolvait avec approximativement la même vitesse, et avec la meme dépendance de la température que le matériau synthétique. On pense que l' étape contrôlant la vitesse de dissolution du CuS est une réaction chimique se produisant à la surface du sulfure.     

The kinetics of dissolution of enargite in acidified ferric sulphate solutions

Abstract

Over the temperature range 60° to 95°C, sintered discs of synthetic enargite (Cu₃AsS₄) were dissolved slowly in acidified ferric sulphate solutions, yielding both elemental and sulphate sulphur, together with soluble copper and arsenic. The dissolution kinetics were linear and this was interpreted as indicating rate control by a reaction occurring on the surface of this sulphosalt. The activation energy associated with this reaction was 13.3 kcal/mole. The rate of copper extraction increased according to the 0.55 power of the ferric sulphate concentration and the 0.20 power of the sulphuric acid concentration. The rate decreased in a complex manner with increasing strengths of the ferrous sulphate reaction product. Natural enargite dissolves like the synthetic sulphosalt and at approximately the same rate.

Résumé

A des températures variant entre 60°C et 95°C, des disques frittés d'énargite synthétique (Cu₃AsS₄) ont été dissous lentement dans des solutions acides de sulfate ferrique, pour produire du soufre élémentaire et sous forme de sulfate, ainsi que du cuivre et de l'arsenic soluble. Les cinétiques de dissolution suivent une loi linéaire, due à la réaction qui a lieu en surface de ce sulfosel et qui, semble-t-il, contrôlerait la dissolution. L'énergie d'activation associée à la réaction est de 13.3 kcal/mole. Le taux d'extraction du cuivre croît comme la puissance 0.55 de la concentration en sulfate ferrique et la puissance 0.20 de la concentration en acide sulfurique. La vitesse décroît de façon complexe lorsque augmente la concentration du produit de la réaction du sulfate ferreux. L'énargite naturelle se dissout de la même manière que le sulfosel synthétique, et à sensiblement la même vitesse.     

The kinetics of dissolution of bornite in acidified ferric sulfate solutions

Sintered disks of synthetic bornite were dissolved in acidified ferric sulfate solutions at temperatures ranging from 5δ to 94δC. The dissolution occurs in two stages; in the first a nonstoichiometric bornite with up to 25 pct deficiency of copper is formed. In the second, the nonstoichiometric bornite is converted to chalcopyrite and elemental sulfur, which accumulates on the disk surface. At temperatures below 35°C, the reaction follows parabolic kinetics and stops at the nonstoichiometric bornite stage. At higher temperatures it continues through to chalcopyrite and follows linear kinetics. Both the parabolic and linear processes have activation energies of 5 to 6 kcal per mole. At higher temperatures the sensitivity of the reaction rate to changes in stirring velocity indicates control by diffusion through the liquid boundary layer. Natural and synthetic bornite dissolve by the same process and at essentially the same rate.