Depressant Action of Ca and Mg on Flotation of Cu Activated Sphalerite

Abstract

Calcium and magnesium are commonly present in flotation process waters in the order of 500 and 50 ppm, respectively. The effect of Ca (500 ppm) and Mg (50 ppm) ions on the uptake of copper and xanthate on sphalerite and flotation of Cu-activated sphalerite was investigated as a function of pH. Copper and xanthate uptake showed no change due to the presence of Ca and Mg. Flotation recovery was significantly reduced when pH exceeded that for the formation of the corresponding hydroxide precipitate. The recovery decrease was more pronounced for Mg, reflecting the lower pH for the onset of hydroxide precipitation (≈pH 9) than for Ca (≈pH 12). Imaging by X-ray photoelectron spectroscopy and scanning electron spectroscopy indicated that coverage by Mg(OH)2(s) was general. Attachment of Mg(OH)2(s) is probably a heterocoagulation process. The coating appears to be porous to Cu and xanthate. The depressant mechanism is attributed to competition by hydrophilic hydroxide sites with hydrophobic (xanthate) sites.