Abstract:Ultra fine grinding of the plant tailings of a refractory silver ore was studied using a laboratory type vertical stirred media mill. Preliminary tests confirmed that ultra fine grinding substantially improves the extraction of silver from the tailings in cyanide leaching (i.e. 36% Ag extraction rate from the as-received tailings with d₈₀ of 100 μm, c.f. 84% extraction rate after ultra fine grinding of the tailings with d₈₀ of 1.2 μm). In the ultra fine grinding tests, the effects of ball diameter (2-4.5 mm), stirring speed (200-800 r/min) and ball charge ratio (50%-80%) on the fineness of grind (d₈₀, mm) were investigated through a Box-Behnken design. Increasing stirrer speed and ball charge ratio decreased fineness of grind while larger balls resulted in the coarser products. The tests demonstrated that a fineness of grind less than 5 mm can be achieved under suitable conditions. Analysis of stress intensity indicated an optimum range of stress intensity of (0.8-2)×10^-3 N·m for all power inputs.

Key words: refractory ore tailings; stirred media mill; ultra fine grinding; experimental design; Box-Behnken design; stress intensity