Selective depression of millerite (β-NiS) by polysaccharides in alkaline solutions in Cu-Ni sulphides flotation separation

Abstract The presence of a nickel sulphide mineral – millerite (β-NiS) has a significant impact on the Cu/Ni flotation separation efficiency in the plant operations. In this study, the feasibility of using corn dextrin as a representative of polysaccharides to depress millerite (β-NiS) in the differential Cu-Ni sulphides flotation at pH 9 and pH 12 was examined. Micro-flotation tests showed that dextrin can depress xanthate-treated millerite without deteriorating chalcopyrite (CuFeS2) recovery when using potassium ethyl xanthate (KEX) as a collector, resulting in efficient Cu/Ni separation at both pH 9 and pH 12. X-ray photoelectron spectroscopy (XPS) analysis revealed that dextrin adsorption on millerite at alkaline pH was identified as a chemisorption process. Dextrin’s hydroxyl functional group can interact with the metal hydroxide on the mineral surface. At pH 12, dextrin can adsorb on xanthate-treated millerite while negligible adsorption was observed on xanthate-treated chalcopyrite. Mineral dissolution tests and ethylenediaminetetraacetic acid (EDTA) extraction tests suggested the preferential adsorption of dextrin on millerite over chalcopyrite might be associated with the predominant passivation layer of nickel hydroxide formed on the millerite surface at alkaline pH due to the extensive nickel dissolution. Atomic force microscopy (AFM) imaging was used to visually investigate the adsorption of dextrin on millerite and xanthate-treated chalcopyrite at pH 12. Overall, this study provided a feasible depression strategy for millerite in the copper concentrate using a cost-effective and environmental-friendly reagent.