Gold Cementation Kinetic Features Using Dendritic Zinc Powders

Gold cementation kinetic features from cyanide solutions using zinc powders of various origins were studied. The first powder was obtained by distillation and is currently used in the vast majority of industries (traditional powder). The second powder was obtained by electrochemical reduction from alkaline solution (electrolytic powder). The main distinguishing feature of these powders is specific surface area. This indicator for the electrolytic powder is 2.6 times higher than for the traditional one (3.02 and 1.16 m2/g, respectively), which is associated with dendritic form of electrolytic powder. For cementation studies, a solution with a gold content of 50.8 μmol/dm3 and 0.04 mol/dm3 sodium cyanide (NaCN) was taken. Studies have shown the presence of a depassivation period associated with oxide film dissolution on the powder surface and overcoming diffusion difficulties. The depassivation period of a traditional powder (10–15 seconds) exceeds the depassivation period of an electrolytic powder (5–8 seconds). Values of cementation reaction experimental rate constants are determined for the process using traditional and electrolytic powders at different ratios of zinc and gold masses in solution. Experimental reaction rate constants for electrolytic powder under the studied conditions are 1.3–1.6 times higher than the experimental rate constants for traditional powder. Zinc oxidation rates are compared under these conditions for various ratios m(Zn)/m(Au). Powder dissolution rates referred to specific surface area (taken in initial period) practically do not differ. The electrolytic powder’s absolute dissolution rate at the initial time is almost two times greater. As powder reacts with an alkaline solution, absolute dissolution rates of electrolytic and traditional powders are equalized.