The modification of bubble characteristics and chalcopyrite surface hydrophobicity in water containing NaCl

Abstract

Recycled water has been utilized in various industries as a response to global water scarcity, despite the accumulation of salts in process water and the subsequent alteration of water structures and interfacial properties caused by salts. This study investigated the effect of NaCl, a dominant salt in process water in mineral flotation plants, on chalcopyrite flotation, a major source of copper. For the first time, this study decoupled the effects of surface hydrophobicity and bubble characteristics modified by NaCl on chalcopyrite flotation and also considered the effect of NaCl on the true floatability by removing the effect of collectors and the recovery caused by mechanical entrainment. Cyclic voltammetry (CV) and Cryogenic x-ray photoelectron spectroscopy (Cryo-XPS) were combined to understand chalcopyrite surface oxidation and the formation of hydrophobic products, while bubble size distributions were measured to understand bubble characteristics. It was demonstrated that the addition of NaCl improved the true flotation of chalcopyrite slightly from de-ionised water to 0.1 M NaCl solution, but significantly from 0.1 M NaCl solution to 0.7 M and 1.2 M NaCl solutions. This trend was consistent with the extent of oxidation on the chalcopyrite surface, but inconsistent with the atomic concentration of hydrophobic oxidation products formed. It was identified that the atomic concentration of hydrophobic oxidation products on the chalcopyrite surface was optimised in 0.1 M NaCl solution, suggesting that the surface hydrophobization by NaCl was not a primary factor in chalcopyrite flotation. In contrast to the reduced amount of hydrophobic oxidation products on the chalcopyrite surface in 0.7 M and 1.2 M NaCl solutions, the bubble size was reduced significantly, suggesting that bubble size played a significant role in chalcopyrite flotation in saltwater containing NaCl.