Representation of the Kinetics of Leaching of Galena by Ferric Chloride in Concentrated Sodium Chloride Solutions by a M
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INTRODUCTION
THEkinetics of leaching galena by ferric chloride solutions has recently been studied by several authors: Murray 1 (1972) had a disk of galena leached by a 0.5 tool/1 solution of ferric chloride. He found that the diffusion of the ferric ion through the sulfur layer is the limiting step of the kinetics. Vygoda ~ (1976) established that the kinetics of dissolution of galena particles in solutions containing 75 to 175 g/dm 3 of ferric ions is first order with respect to the ferric concentration. Kametani 3 (1977) kept a constant ferric chloride concentration and therefore at a constant solution potential by addition of a solution of potassium permanganate during the leaching experiments. The kinetics were controlled, according to the mode of operation, by a chemical reaction or diffusion through an aqueous film. Palmer (see Wadsworth (1982)) carried out the leaching of galena particles of 35 x 45 mesh in a 4 M sodium chloride solution in a range of ferric chloride concentration 0.025 to 2 M and found that the diffusion of ferric ions through the sulfur layer controlled the kinetics. These results were obtained at experimental condittons which are different from those of our own work since there was not always an excess of chloride ions and the potential of solution was not controlled except in Kametani's work. High concentration of chloride ions is used in order to increase the concentration of plumbous complexes and PbCI2 solubility. The regulation of the potential of the solution reproduces the conditions of one of the leaching steps of the Minemet Recherche process (Demarthe and Georgeaux 4 (1980)). In this process a galena concentrate is dissolved in two steps: leaching of flotation concentrate is carried out first at a low ferric concentration and low potential of solution, then the dissolution is completed at high ferric concentration. This kinetics study is concerned with the second step only. D MORIN. formerly with the School of Mines, Paris, France, is Engineer, BRGM, Orldans. France A GAUNAND, Assistant, and H. RENON, Professor, are with the School of Mines, 60, boulevard Saint-Michel, 75006 Paris, France Manuscript submitted October 14. 1983 METALLURGICAL TRANSACTIONS B
EXPERIMENTAL
Leaching was carried o u t in a double jacket reactor. A 1.4 liter ferric and ferrous solution containing 4 mol/dm 3 of NaC1 at pH 2.4 was first introduced. Then 2.5 g of ore of a prepared narrow granulometric fraction of ore was fed as a pulp. The ore composition is shown in Table I. A significant variation in lead content with the particle diameter was observed as shown in Table II. The lead content was determined by PbSO~ gravimetry after dissolution by aqua regia. The solution temperature was maintained constant within 0.25 ~ The stirring speed was high enough to be without any influence on the kinetics (750 rpm). Most experiments were carried out at a solution potential kept constant either by adding to the leaching solution a concentrated ferric chloride solution, or by adding a concentrated solut
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