Use of ZnSO4 and SDD mixture as sphalerite depressant in copper flotation

The depression performance and mechanism of the zinc sulfate (ZnSO4) and sodium dimethyl dithiocarbamate (SDD) combined depressant with butyl xanthate (BX) as collector in a mixed Cu-Zn sulfide floation system were fully investigated using micro-flotation experiments, zeta-potential determination, and local electrochemical impedance spectroscopy (LEIS) analysis. The micro-flotation experimental results indicated that the combined depressant has a significant selective depression effect on sphalerite but has slight effect on chalcopyrite. The depression performance of the combined depressant strictly depends on the dosage of ZnSO4 + SDD and flotation pH. However, excessive SDD is detrimental to chalcopyrite flotation. The optimum conditions for flotation separation of chalcopyrite from the Cu-Zn sulfide were as follows: combined depressant dosage of 10−4 mol/L (ZnSO4: SDD = 3:1), BX dosage of 10−5 mol/L, and flotation pH of 10. Under such conditions, a copper concentrate assaying 30.21% Cu with 86.79% recovery was achieved from the Cu-Zn sulfide flotation system, and this concentrate had a very low Zn grade of 4.20% with 5.48% recovery. Both the zeta-potential and LEIS results confirmed that the presence of the combined depressant can significantly prevent the adsorption of BX onto the sphalerite surface, especially for an alkaline pH range of 9-12; however, the adsorption of BX onto the chalcopyrite surface is not affected. The LEIS provides a powerful tool for observing the adsorption of flotation reagents on mineral surface.