Hydrothermal precipitation from aqueous solutions containing iron(III), arsenate and sulphate

Abstract

Hydrometallurgical processing of sulphide concentrates is an attractive method for the selective extraction of valuable metals. The dissolution of minerals in a leaching process involves several electrochemical parameters that need to be investigated· to ensure the development and growth of the base metal industry in South Africa. A study has been carried out to elucidate the leaching mechanism of a nickel-coppercobalt sulphide concentrate in an oxidative pressure-acid medium. The sulphide concentrate studied in this research, comprises mainly of the minerals pyrrhotite, (Fe1_xS) with x = 0 to 0.2, pentlandite, (Ni,Fe)9S8 and chalcopyrite, (CuFeS2). The leaching behaviour of these minerals was successfully studied by means of Atomic Absorption (AA) measurements, Scanning '·Electron Microscopy (SEM) and Moss bauer spectroscopy, after leaching took place in an oxidative pressure-acid medium. The dissolution of the valuable metals was achieved effectively with recoveries of well over 90% for nickel, copper and cobalt under the specific conditions studied. Mechanical activation by means of ultra fine milling improved metal extraction with an average of approximately 40%, after a leaching period of 150 minutes. The most suitable conditions for the oxidative pressure-acid leaching of the mechanically treated nickel-copper-cobalt sulphide concentrate in a dilute sulphuric acid medium were found to be: particle size 80% - 10J.Lm; temperature l10°C; oxygen partial pressure 10 bar; sulphuric acid concentration 30 kg/ton; solids content 15% by mass and an impeller agitation rate of 800 r/min. The values of the apparent activation energies of nickel, copper and cobalt, extracted from the sulphide concentrate, were found to be 20.6 (± 4.4) kJ/mol K, 33.6 (± 4.2) kJ/mol K and 17.4 (± 3.5) kJ/mol K respectively.