Study of the dissolution of chalcopyrite in solutions of different ammonium salts

Moyo, Thandazile; Petersen, Jochen

Study of the dissolution of chalcopyrite in solutions of different ammonium salts

Conference Paper

2017-09-11

Publisher

SAIMM

Publisher

University of Cape Town

Department

Centre for Bioprocess Engineering Research

Faculty

Faculty of Engineering and the Built Environment

Series

Copper Cobalt Africa Conference in association with the 8th Southern African Base Metals Conference

Abstract

The oxidative leaching of chalcopyrite in ammoniacal solutions has been evaluated using electro-analytical techniques. The anodic dissolution process has been established to be a seven-electron transfer process under nitrogen in ammonia–ammonium sulphate solutions and ammonia–ammonium carbonate solutions. The number of electrons transferred in the carbonate and sulphate salts suggests that the sulphur is oxidised to a thiosulphate intermediate and the copper and iron released as Cu+ and Fe2+. The Cu+ and Fe2+ is subsequently oxidised in solution in non-Faradaic reactions. The deportment of Fe2+ and S2O32- is affected by choice of the ammonium salt used in the leaching process. In the perchlorate salt, only five electrons are transferred, however observations made on the mineral surface after leaching do not support the formation of elemental sulphur. Scanning electron microscopy and energy-dispersive spectroscopy analysis of the mineral surface suggest presence of an iron–sulphur surface layer completely free of copper under the ammonia–ammonium sulphate conditions, an iron-rich surface layer under ammonia–ammonium perchlorate solutions and absence of surface layer build up under ammonia–ammonium carbonate solutions.

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