The effect of calcium, magnesium, and sulphate ions on the surface properties of copper activated sphalerite

• Hydrophobicity of Cu2+ activated sphalerite in solutions of Ca2+, Mg2+ and SO42− was studied.
• CuS (Cu+1 and S−1) layer formed on copper activated sphalerite at mildly acidic pH.
• Electrostatic adsorption occurred between sphalerite and Ca2+/Mg2+ at mildly acidic pH.
• Ca2+ and Mg2+ decreased Cu2+ uptake and hydrophobicity of sphalerite.

Hydrophobicity and many other surface properties of copper (Cu) activated sphalerite can be changed by calcium, magnesium and sulphate ions in solutions, but have not been quantitatively investigated previously. Here, the effect of Ca(NO3)2, Mg(NO3)2, MgSO4 and CaSO4 on the surface properties of Cu-activated sphalerite was studied using contact angle (CA) measurements, X-ray photoelectron spectroscopy (XPS), and zeta potential measurements. The CA measurements show that the hydrophobicity of sphalerite developed after copper activation, but the presence of 30 mM Ca(NO3)2 or Mg(NO3)2 or MgSO4 decreased its hydrophobicity: CA reduced from 67° to 48°. The presence of 30 mM of Ca2+ and SO42− ions in solutions reduced CA further to 42°. This CA change could be due to the simultaneous presence of ionic calcium species and calcium sulphates that precipitated as gypsum. The XPS data show Cu presence on the sphalerite surface after copper activation in the salt solutions was in the Cu(I) state. The effect of Ca(NO3)2, Mg(NO3)2, MgSO4 and CaSO4 on the copper activated sphalerite surface appeared to be the same, namely a decrease in Cu(I) adsorption and polysulphide formation. Neither Ca2+ nor CaSO4 were detected by surface analysis, but some Mg ions were found on the surface. Zeta potential measurements confirmed the presence of calcium and magnesium ions on the sphalerite surface. The role of calcium and magnesium ions in copper activation of sphalerite appears to be that of moderators which act to reduce the amount of Zn replaced by Cu on the sphalerite surface, whether SO4 is present or not.