Kinetics of nonoxidative leaching of galena in perchloric, hydrobromic, and hydrochloric acid solutions
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I.
INTRODUCTION
THE abundance
of galena, the relative ease with which secondary lead is recycled, the low cost of this metal, and the current pyrometallurgical process-roasting (DwightLLoyd) and high-speed coal reduction (Water-Jacket), mean that it is very unlikely that there will be any major change in the procedures used for obtaining lead in the near future. However, increasing environmental pressures and the large number of operations in progressive dry refining to obtain sufficiently pure lead by pyrometallurgical processes have stimulated the examination and study of possible alternative hydrometallurgical procedures for leaching galena. The selective dissolution of lead sulfide from complex minerals or low grade concentrates is another focus of interest, tl'21 The need to obtain sufficiently soluble salts from which the metal can be easily electroplated suggests the desirability of converting galena into lead chloride, which can be done by leaching with hydrochloric acid. Although other acids may come to mind, they are unstable, expensive, or exhibit poor kinetics for dissolving natural galena. Up to the present time several techniques have been developed for obtaining lead using electrolytic methods, t3j The Norwegian Institute of Technology [4] and the U. S. B.M.[5] have developed processes using baths of molten salts. Minemet Recherche (IMETAL) has also developed similar processes with the cooperation of Peflarroya. I61 Reacting galena with a hydrochloric acid solution produces H2S, which can be converted into elemental sulfur via the Claus process. HCI leaching in the presence of oxidizing agents can be used to prevent H2S formation. If strong oxidizing agents are used, sulfur may form and coat the galena, which could slow down the reaction. If more gentle or dilute oxidizing agents are used, the sulfur which forms may not coat the galena. Depending on the concentrations of the acid and the oxidizing agent, either sulfur or H2S will be obtained, tvl There are still doubts remaining specifically with regard to the individual order of activity of each of the ions present and the mean ionic activity of the hydrochloric acid. For example, Awakura, Kamei, and Majima 181conclude that
there is a first-order dependence between the galena dissolution rate and the hydrogen ion activity in HCI solutions-alone or with NaC1 added--although they admit that, above concentrations that are not very high (2M HC1), the order must be greater than one. They compare these results with the leaching behavior of an acid like HC104, whose anion has no complex-forming effect on the lead ion. Finally, to complete the study of the effect of the complexforming power of the acid anion on the kinetic parameters of galena leaching, we studied the dissolution kinetics in HBr. II.
MATERIALS AND PROCEDURE
For this study we used blocks of galena from the Cia. Minera de Catalufia concession in the town of Martorell, province of Barcelona, Spain, with a composition of 85.9 pct Pb and 13.3 pct S. Spectrographic analysis showed the prese
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