R. Zhou et S. Chander, KINETICS OF SULFIDIZATION OF MALACHITE IN HYDROSULFIDE AND TETRASULFIDE SOLUTIONS, International journal of mineral processing, 37(3-4), 1993, pp. 257-272
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
.