The differential depression of an oxidized starch on the flotation of chalcopyrite and graphite

Abstract

It is difficult to achieve a clean separation during flotation when unwanted graphitic material exists in association with valuable copper sulphides such as chalcopyrite. Attempts to improve the separation has been driven by green and innocuous reagents such as starch or its derivatives to ensure environmental sustainability. In this study, the depressive action of an oxidized wheat starch in comparison to the normally used native counterpart during flotation of chalcopyrite and graphite was investigated. Starch oxidation, depending on the degree, yields an uncommon phenomenon of concurrent depolymerisation of the large supramolecular assembly of starch chains as well as generation of CO (carbonyl) and (COO) carboxyl moieties on the starch matrix. Adsorption and AFM imaging measurements were performed and correlated with flotation recovery to probe into the influence of the structural and functional changes due to starch oxidation. The base material (native wheat starch – NWS) exhibited a similar adsorption response on chalcopyrite and graphite with increasing polymer concentration, which corresponded to their similar depression during flotation. However, the oxidized starch (Ox 5/120) produced in the laboratory resulted in significant depression of graphite with a modest effect on chalcopyrite flotation. Ox 5/120 also showed marked differences in adsorption behaviour between graphite and chalcopyrite in consonance with the flotation results. It is clear that starch oxidation has an intriguing effect on the underlying binding mechanisms and conformations at mineral surface governing the separation efficiency.