INTEGRATED BIOLOGICAL PROCESS FOR THE TREATMENT OF A CHILEAN COMPLEX GOLD ORE

A process for gold recovery from a complex Chilean ore from Burladora (IV Region) which integrates concentration by flotation, bacterial lea ching and cyanidation was studied at a laboratory scale. The chemical composition of the ore is 8.2% Fe, 0.78% Cu, 0.88% As and 3.5 g/t Au, with pyrite, hematite, covelite, arsenopyrite and chalcopyrite as the main metal-bearing minerals. The initial gold recovery by conventional cyanidation on a crushed ore sample was only 54%. The ore was ground and concentrated by flotation with a gold recovery of only 56%. The go ld content of the concentrate is 17 g/t Au. Concentrate samples were l eached in 1.5 1 stirred reactors at 10% pulp density in 1000 ml of aci d medium (pH 1.8). Some experiments were inoculated with harvested bac teria previously isolated from mining solutions. Dissolved metals, pH and bacteria concentration in the leaching solutions were periodically determined. In the presence of bacteria, oxidation of the ferrous ion produced by acid dissolution of the concentrate was observed, and aft er 4 days of leaching 100% of the dissolved iron was present as ferric ion. Gold recovery by cyanidation increased from 13% for the initial concentrate to 34% after 10 days of chemical acid leaching and 97% aft er 10 days of bacterial leaching, To increase the total gold recovery, the flotation tailings were submitted to cyanidation. A complete flow sheet of the process and a first economical evaluation are proposed. A s a possible alternative process, heap bacterial leaching and further cyanidation of the ore are suggested.