The Influencing Mechanisms of Sodium Hexametaphosphate on Chalcopyrite Flotation in the Presence of MgCl2 and CaCl2

Sea water has been used in flotation plants, showing a promising way to save fresh water usage. Previous studies indicated that divalent salts in sea water played negative roles in chalcopyrite flotation, but not much work have been conducted to understand the eliminating mechanisms. This study systematically investigated the effects of divalent cations of Ca2+ and Mg2+ on natural flotability of chalcopyrite in the absence of collectors and frothers. The reduced recovery was mainly due to the adsorption of Mg and Ca hydroxyl complexes and precipitation on chalcopyrite surfaces, giving rise to a less hydrophobic surface. The addition of sodium hexametaphosphate (SHMP), however, significantly improved chalcopyrite recovery. Species calculation, contact angle, zeta potential, FTIR and XPS analyses were conducted to understand the influencing mechanisms of divalent ions and the beneficial effects of SHMP on chalcopyrite recovery. The primary mechanism was that SHMP prevented the adsorption of positively charged Mg and Ca compounds or precipitation with hydrophilic properties such as Mg(OH)(2) on chalcopyrite surfaces, confirmed by the Derjguin-Landau-Verwey-Overbeek (DLVO) theory. Secondly, SHMP reacted with Mg2+ and Ca2+ to form dissolvable complexes, thereby declining the formation of insoluble Mg2+ and Ca2+ compounds or precipitation.