A Comparative Study of Cyanide and Thiosulfate for Silver Leaching from Tailings: A Kinetics Approach

The mining process has always generated residues that often still contain valuable metals. This work focuses on the re-processing of these residues by evaluating and comparing two reagents that can extract valuable silver from tailings. A preliminary kinetic study of silver leaching was conducted in both cyanide and thiosulfate media, and a comparative analysis was performed to determine the optimal leaching conditions. The mining residue was found to contain 83 g/ton of Ag and 0.28 g/ton of Au. This study, carried out for both cyanide and thiosulfate, involved determining the effects of the reagent concentration, temperature, and pH. For the reagent concentration, apparent reaction orders of n = 0.0531 and n = 0.41 were determined for cyanide and thiosulfate, respectively. The apparent activation energies were Ea = 21.7 kJ/mol for cyanide and Ea = 23.13 kJ/mol for thiosulfate, indicating mixed-control kinetics in both systems. Under the conditions studied, maximum silver recoveries of 92% and 93% were achieved using cyanide at 323 K and thiosulfate at 328 K, respectively. Notably, pH had no significant effect on the cyanide system, whereas for thiosulfate, the reaction order was n = 3.27. The results show similar behavior in both systems, but the thiosulfate system is more attractive due to its non-toxic nature and lower cost.