The interaction of ethyl xanthate with copper(II)-activated zinc sulphide: Kinetic effects

Abstract

Kinetic studies of ethyl xanthate adsorption onto copper(II)-activated zinc sulphide surfaces were performed by ultraviolet and Fourier transform infrared spectroscopy under flotation related conditions. Copper(II) activation is a prerequisite for ethyl xanthate adsorption on to zinc sulphide. Both the rate of adsorption and the form of the adsorbed ethyl xanthate species are controlled by the activation time and the concentration of copper(II) used. At low copper(II) additions, where copper(II) adsorption shows high affinity behaviour, copper(I) ethyl xanthate is the predominant surface species and the rate and extent of ethyl xanthate adsorption are decreased by extended copper(II) conditioning periods. At high copper(II) additions, where copper(II) is in excess, both diethyl dixanthogen and copper(I) ethyl xanthate can be detected on the zinc sulphide surface. However, their formation is by precipitation from solution rather than via a surface reaction. It is proposed that the penetration of copper ions into the zinc sulphide lattice and the subsequent diffusion back to the solid—aqueous solution interface may be responsible for the time dependence of ethyl xanthate adsorption. X-ray photoelectron spectroscopy depth-profiling by argon ion etching has confirmed that copper ions can penetrate considerable depths into the zinc sulphide lattice and gives credence to the proposed mechanism for the time-dependent adsorption behaviour of ethyl xanthate.