Abstract

The depression of pyrite by lime is attributed to the surface formation of Ca(OH) 2, CaSO 4 and Fe(OH) 3 as determined by XPS analysis. Xanthate flotation tests show that oxalic acid and other organic acids, as well as sulphuric acid and other inorganic acids and their salts can restore xanthate flotation of pyrite after depression by lime. In terms of XPS analysis, solution chemistry calculations and electrochemical measurements, it is evident that these chemicals act as activators to reduce pulp pH, prevent further oxidation of pyrite, and dissolve surface calcium or iron species to create a fresh surface. Activation efficiency was quantitatively discussed based on an activation index related to the polar group functionality of the activators. The results for activation flotation of pyrite are very well explained using the activation index. Oxalic acid which exhibited the greatest activation index can be substituted for sulfuric acid, which may solve potential environmental and maintenance problems associated with calcification/scaling reaction expected with sulfuric acid.