Zinc sulphate addition point (Pb/Zn flotation) Froth
I think you should increase the dosage, it seems low. For example, if the head grade reports 1% Pb and 3% Zn, the addition of ZnSO4 could be 700 g/t in grinding, 100 g/t in rougher flotation. In this case, activated sphalerite is not a problem. NaCN should be added in the grinding circuit (e.g. 2030 g/t).