Electrochemical aspects in the flotation of lead-zinc sulfides in Brazilian silicate ore: Use of Na₂S as modulator

Sodium sulfide plays a multifunctional role in sulfide minerals flotation. The restorative action of minerals surface is its main function. As pH regulator, it reacts on surface and provides the conditions for interactions between minerals-collectors. However, changes in pulp composition can affect the electrochemical conditions desirable for flotation. Thus, the purpose this study was the evaluation of electrochemical state established in flotation, involving a willemite ore bearing zinc and lead sulfide minerals, when Na₂S was used as pH regulator. So, the electrochemical potential established in the pulp, the recoveries and contents of Zn, Pb, and Ag were considered as criteria for assessing the process. The pH equal to 9 yielded the best results for recovery (95.33% Zn; 61.24% Pb; 79.01% Ag) and content (12.96% Zn; 1.54% Pb; 307.33 ppm Ag), due to the smaller interference that occurred in the electrochemical conditions of systems when compared to pH 11, also included in the evaluations. However, larger dosages of Na₂S were counterproductive due to depressant action. Decrease in the potential can be related to the excessive amount of HS- , impairing the sulfides flotation. (author)