Electrolysis of Gold from Filtration Waste by Means of Mechanical Activation
The intensification of the gold thiourea leaching from a filtration waste (Kosice, Slovakia) using mechanical activation as the pretreatment step has been studied. The leaching of “as-received“ sample in an acid thiourea solution resulted in 65 % Au dissolution. However, after mechanical activation in a planetary mill 99 % of the gold was leached. The optimum redox potential for electrolysis is in the range 500-523 mV for the gold extraction 99.79 % from the mechanically activated sample. The mechanical activation resulted in an increase of the specific surface area of the waste from 0.7 m 2 g -1 to a maximum value of 13.5 m 2 g -1 . The physicochemical changes in the filtration waste as a consequence of mechanical activation had a pronounced influence on the subsequent gold extraction.
Thiourea leaching of silver from mechanically activated tetrahedrite
Abstract The thiourea leaching of silver from a tetrahedrite concentrate mechanically activated in a planetary mill or an attritor was studied. It was found that the two types of equipment gave rise to different rates of new surface formation and of crystal structure disordering. The rate of thiourea leaching of silver from tetrahedrite (Cu,Ag)10(Zn,Fe)2(Sb,As)4S13 is a structure-sensitive quantity, while the dependence of the rate constant of leaching on the empirical coefficient S A (1 − R) (SA = specific surface, R = disordering of tetrahedrite structure) exhibits a linear character with equal slope for both types of mills. The results are also of prognostic character because they enable us to propose suitable equipment for intensive grinding depending on the demand for fineness or reactivity of the solid substances.
Differences between the dissolution and the decomposition kinetics of mechanically activated magnesium hydroxide
Decomposition and dissolution kinetics of vibro-milled Mg(OH)2 were studied to elucidate the determining factors for each reaction. The BET specific surface area, SB, and the exterior surface area, Sp, both of which were measured by air permeability, were found to have decreased after vibro-milling, indicating the formation of compact agglomerates. The rate constant of decomposition, kp, increased with increased grinding time. In contrast, the rate constant of dissolution, kd, decreased on grinding. The exterior surface area, Sp, of aggregated particles, was revealed to be determining for kd. On the other hand, the hypothetical boundary surface of the crystallite plays a more important role for kp. Each rate constant, when divided by the appropriate boundary specific to the particular reaction showed a steep increase with either a rapid leveling off or a slow decrease with increasing time of activation, similar to the change in the X-ray amorphous portion, 1 - If.