Biooxidation and Cyanidation for Gold and Silver recovery from Acid Mine Drainage generating Tailings (Ticapampa, Peru)

摘要

The acid mine drainage (AMD) generating sulfidic tailings have a total mass of 1,639,130 t containing 1.65 g/t Au, 34.5 g/t Ag, 7.74 percent Fe, 5.91 percent S, 3.2 percent As, 0.75 percent Zn and 0.05 percent Cu. The precious metals Au and Ag are enriched in the fine fractions. Approximately 35 percent of the material is below 25 mu m in size and 53 percent below 63 mu m. Electron microprobe analysis of a sulfide concentrate of the tailings, produced by gravity separation, proved the occurrence of pyrite and arsenopyrite with appreciable sphalerite and galena. Refractory gold (up to 316 g/t) is hosted in As-rich zones of some arsenopyrites. Approximately 200 g of the sulfide concentrate of the tailings was biooxidized in laboratory shake flasks using an adapted mixed culture of Acidithiobacillus ferrooxidans (Ram 6F), Acidithiobacillus thiooxidans (Ram 8T) and Leptospirillum ferrooxidans (R3). During biooxidation, arsenopyrite was preferentially dissolved and the secondary mineral tooeleite (Fe_8(AsO_4)_6(OH)_5 centre dot H_2O) precipitated. The following cyanidation of the biooxidized sulfide concentrate showed a recovery of 97 percent and 50 percent for Au and Ag, respectively. The values were 56 percent and 18 percent for the untreated concentrate. The recovery of Au and Ag from the tailings significantly reduces the costs for the tailings remediation to mitigate AMD release.