Study of the patterns of adsorption of cyanide complexes Au, Ag, Hg, Cu, Ni by carbonaceous products and the use of Ag additives to suppress preg-robbing

The aim is to study the patterns of adsorption of Au, Ag, Hg, Cu, Ni by carbonaceous products and to search for the effects of suppression of preg-robbing to increase gold recovery. The studies were carried out on the cyanidation tails of three preg-robbing products bearing from 0.34 to 0.60% of organic carbon. The isotherms of metal adsorption were determined by the method of variable metal concentrations at NaCN concentrations varied from 0.7 to 2.0 g/dm³ and temperature from 20 to 80 °C. An alternative approach to reduce the preg-robbing activity, which involves the use of cyanide complexes of Ag, Cu, Ni, is considered. It has been established that the highest constant K of the Freundlich isotherms is achieved by Au (1.70–1.82), followed by Hg (0.47–1.81) and Ag (0.37–0.55) in the range of selectivity. It has been shown that Cu and Ni are adsorbed an order of magnitude worse (K at the level of 0.022–0.067). The study revealed that the adsorption of Au and Ni is practically independent of the NaCN concentration; for Ag, Hg, and Cu, a decrease in adsorption is observed with an increase in the reagent concentration. The adsorption of Au, Ag, Hg, Cu, Ni by the carbonaceous product decreases 5–12 times with increasing temperature; the differential isosteric heats of metal adsorption were 14–22 kJ/mol, which is characteristic of physical adsorption. It has been established that the studied patterns of metal adsorption by the carbonaceous product completely coincide with those for activated carbons. It has been shown that, among the studied metals, silver can be successfully applied to suppress the preg-robbing activity of the material under study, as it is well adsorbed by natural carbonaceous matter and does not require special waste detoxification technology. In the conducted bottle cyanidation tests, with the amount of adsorbed Ag being 0.08–0.10 g/t of ore, the amount of additionally recovered Au amounted to 0.06–0.11 g/t, resulting in an increase in gold recovery by 2.5–8.0%. The discovered effect of preg-robbing suppression can be applied at gold plants during cyanidation of preg-robbing ores.

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