KINETICS OF SULFIDIZATION OF MALACHITE IN HYDROSULFIDE AND TETRASULFIDE SOLUTIONS

The kinetics of sulfidization of malachite in sodium hydrosulfide and tetrasulfide as the sulfidizing agents was investigated in this study. The sulfidization reaction occurred in two stages. The first stage in volved the formation of a primary sulfidized layer and the second invo lved two types of secondary reactions. One was the precipitation of co pper ions which diffused through the primary layer, and the other was the oxidation of the sulfidizing agent to oxysulfide species. The infl uence of the type and concentration of the sulfidizing reagent and sol ution pH was determined. A significant difference in the surface morph ology was observed for malachite treated with these two reagents. With sodium tetrasulfide, a uniform sulfidized layer formed on the particl e surface, whereas for sodium hydrosulfide, the malachite surface was coated with loosely adherent precipitates, which might peel-off upon a gitation. The results indicate that the extent of the reaction in the second stage was smaller in sodium tetrasulfide than in sodium sulfide .