Abstract

Mining operations use cyanide for gold extraction from low-grade ores through the conversion to a water-soluble coordination complex. Accordingly, cyanide-containing tailings have to be treated. In addition to chemical and physical processes, detoxification by microorganisms has allowed the development of biotechnologies to degrade cyanide compounds in industrial wastes. This study aimed to obtain cyanide-degrading microorganisms and investigate their capacity of removing cyanide in solid mining tailings from a gold extraction process and to design the process configuration and the inoculation strategy. Cultures were enriched from industrial solutions and tailings. The 16S rRNA gene sequences of the cultures revealed the predominance of members of the genus Halomonas. To evaluate the microbial degradation of free cyanide present in the tailings, column tests and a 4-level semi-industrial heap was run, using samples from the Minera Guanaco gold extraction plant, in order to simulate the conditions of the large-scale tailings. Samples at different stack levels were taken to assess colonization and cyanide degradation. Results showed 30% cyanide degradation at 50 days of operation, and greater than 95% after 350 days. Furthermore, efficient colonization was observed at different depths of the heap. Those results were compared with the cyanide attenuation treatment, in intentionally designed surface tailings impoundment, currently running at Minera Guanaco plant.