Lixiviacao de tetraedrites.

Abstract

This work describes the study of the chloride leaching of three samples of tetrahedrite with special reference to the acid leaching of the purified samples (tetrahedrite >90%) with a ferric chloride solution at atmospheric pressure. Some pressure leaching tests were also carried out with one of the samples using a FeC1_3 or CuC1_2 solution in a NaC1 or NH_4C1 medium. The tetrahedrite studied have different copper, silver, zinc, mercury and iron content and so it was possible to analyse the influence of solid composition on the leaching rate. The results show that the leaching of tetrahedrite involves the breakdown of the sulphide structure and that this mineral is very refractory to chloride leaching. In fact, after 8 hours of leaching with a solution 1M in FeC1_3, 0.5M in HC1 and 3M in NaC1, only 50% of the solid is leached. The increase in iron content in the solid increases the rate of reaction. Speciation in the leaching solution is very sensible to changes in chloride concentration. The shrinking core model can describe the ferric chloride leaching of tetrahedrite. The rate of the leaching is controlled by the surface reaction with an activation energy of 65 #+-#6 KJ/mol between 70-104 deg C, and an order of reaction of 0.35 #+-# 0.03 regarding the initial ferric concentration. The leaching results are also described by an electrochemical model with the introduction of the redox potential of the leaching solution as a model parameter.Available from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1249-074 Lisboa, Portugal / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga