Sequential biodegradation and sodium percarbonate oxidation for the removal of free cyanide from the liquid phase of gold plant tailings

Abstract

Hydrometallurgical gold processing generates cyanide-bearing solutions that have to be treated to low residual levels at a moderate reagent demand. This work evaluated the sequential use of biological degradation and chemical post-oxidation for the liquid phase of a gold plant tailings storage facility containing 443.2 mg/dm³ of free cyanide. The biological stage was carried out with an indigenous cyanide-degrading strain isolated from the same solution and identified by 16S rRNA gene sequencing as Janibacter hoylei C4; sodium percarbonate was used as the oxidant. Operating parameters were established for each stage, after which both stages were combined in a single reactor without intermediate separation of the biomass. When the optimized biological treatment was applied to the actual industrial tailings solution, the free cyanide concentration decreased from 443.2 to 101.9 mg/dm³, corresponding to a detoxification degree of 77%.. Addition of 1.35 g/dm³ of sodium percarbonate reduced the residual content to 0.04 mg/dm³ at an overall detoxification degree of 99.99 %. The chemical treatment applied on its own reached 87.33 % at a dosage of 3.5 g/dm³. The biological stage removed the bulk of the cyanide load and the chemical stage brought the solution to the discharge limit, so the sequential scheme consumed 2.6 times less oxidant than the single-stage chemical route.