An Investigation of Millerite (beta-NiS) Flotation Behaviour in Alkaline Solutions in Cu-Ni Sulphide Mineral Flotation Separation

  • Author / Creator
    Wang, Han
  • In the Sudbury Basin nickel deposit, the presence of a less common nickel sulphide mineral – millerite (beta-NiS) has a substantial impact on the Cu/Ni flotation separation efficiency. In this study, the flotation chemistry of millerite in alkaline solutions was investigated with pure minerals using potassium ethyl xanthate (KEX) as the collector. From the perspectives of surface and colloidal chemistry, the selective depression of millerite by natural polysaccharide in Cu-Ni sulphides flotation separation and the activation of millerite flotation by copper (II) ions were fundamentally studied.
    Polysaccharides have been applied widely in the sulphide mineral flotation as depressants. In this study, the feasibility of using corn dextrin as a representative of polysaccharides to depress millerite in the differential Cu-Ni flotation at an alkaline environment was examined. Micro-flotation tests showed that adding corn dextrin after KEX can depress xanthate-treated millerite without deteriorating chalcopyrite (CuFeS2) recovery, resulting in an efficient Cu/Ni flotation separation at both pH 9 and pH 12. The underlying interaction mechanism was investigated by static contact angle measurement, X-ray photoelectron spectroscopy (XPS) analysis, mineral dissolution and ethylenediaminetetraacetic acid (EDTA) extraction tests, atomic force microscopy (AFM) imaging, bulk adsorption tests, electrokinetic study and quartz crystal microbalance with dissipation (QCM-D). In the presence of xanthate, dextrin can lower the surface hydrophobicity of millerite but not chalcopyrite. Dextrin adsorption on millerite at alkaline pH was a chemisorption process, for which dextrin’s hydroxyl functional group interacted with the nickel hydroxide on millerite surface. Dextrin adsorbed less on xanthate-treated millerite surface, indicating dextrin and xanthate adsorbed through different surface sites. As pH was increased, the nickel hydroxide passivation layer gradually inhibited xanthate adsorption on millerite, which favoured dextrin adsorption. Comparing with chalcopyrite, dextrin displayed a higher affinity toward millerite accompanied with a higher free energy of adsorption. At pH 12, dextrin can adsorb on xanthate-treated millerite while negligible adsorption was observed on xanthate-treated chalcopyrite. The preferential adsorption of dextrin on millerite over chalcopyrite might be associated with the predominant passivation layer of nickel hydroxide on millerite surface at alkaline pH even in the presence of xanthate, while chalcopyrite was less prone to surface oxidation.
    Furthermore, the effect of copper (II) ions on the millerite flotation was studied. Millerite flotation can be activated by conditioning with copper ions prior to KEX at both pH 9 and pH 12. The surface chemistry of millerite in the presence of Cu was studied by mineral dissolution and EDTA extraction tests as well as XPS analysis. At alkaline pH, the main copper species on millerite surface was Cu (I) sulphide with minor Cu (II) sulphide and Cu (II) oxide/hydroxide. The Cu (I) sulphide arose from the adsorption and reduction of Cu (II) species. In the meantime, sulphur oxidation was affected upon the reduction of Cu (II) to Cu (I). Monosulphide species (S2-)) at the surface was oxidized into disulphide species (S22-), resulting in less sulphoxy species (SxOy2-). There was no remarkable increase in nickel dissolution and growth in nickel hydroxide passivation layer upon the adsorption of Cu. In essence, copper ion activated millerite flotation under alkaline pH through affecting millerite surface oxidation.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
  • Degree
    Master of Science
  • DOI
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