Pretreatment of a low grade refractory gold sulfide ore (Andacollo, Neuquen-Argentina) using an airlift reactor

摘要

Biooxidation of refractory gold ore from Andacollo in the northwest of Province of Neuquen (Argentina) was studied using an airlift reactor. Its main sulfide constituents were sphalerite, galena, argentite, pyrite, arsenopyrite and chalcopyrite. Gold inclusions (10 g per ton) are encapsulated into those three last sulfides. Other metals contained in the mineral were copper (238 ppm), zinc (2975 ppm), iron (4.57%) and manganese (0.30%). Previous experiments in shaken flasks showed an adequate growth cell and a solubilization of iron, copper and zinc using a mixed culture of Acidithiobacillus thiooxidans(DSM 11478) and Acidithiobacillus ferrooxidans (DSM 11477). Experiments in the airlift reactor were carried out at 30 +- 0.5 ℃ using the mineral at a particle size under than 200 mesh. The redox potential and the pH were measured throughout the experiment. Samples of suspension were periodically taken for chemical analysis. Copper, zinc, total soluble iron and manganese were determined by absorption atomic spectrophotometry. Iron (II) concentration was determined titrimetrically. After bioleaching high recoveries of copper and zinc were obtained. Solid residues were recovered by centrifugation and analyzed by X-ray diffraction. Original and biooxidized samples were leached by cyanide for gold recovery showing an increase of gold recovery after biooxidation process.