Basic research on flash roasting of pyrite

Evolution Assessment of Soils Contaminated by Roasted Pyrite Wastes

Since its 1995 closure and the subsequent 1998 accident, the Aznalcóllar mine pit has been used as a disposal site for diverse metal-rich materials, such as the polluted soils removed during the cleaning of areas along the Guadiamar River, waste rock, pyrite sludge, and ashes deriving from pyrite roasting. At present, the mining pit is partly flooded and contains a highly acidic (pH 2.7) pit lake with approximately 6 Mm3 of metal and sulphate-rich water. Recent detailed research performed in the area has proven that the reaction of the lake water with both the dumping mining wastes and the inflow of acid mine waters are strongly modifying the water quality of the pit lake. A major change was identified in the water quality that resulted from the dumping of 1.4 Mm3 of pyritic wastes during 2005 and 2006. The oxidative dissolution of this mineral has resulted in: (1) a total consumption of dissolved oxygen, (2) a notable increase of electric conductivity (from 8.6 to 12 mS/cm) and (3) a strong acidification (pH from 4.2 to 2.7) and an important heating that was observed as a result of the exothermic character of pyrite oxidation. Despite the total lack of oxidizing agents-such as 02 and Fe(III) (Fe[III] < 5% total Fe)-in the pit lake, pyrite is being oxidized with a continuous increase of the SO(4)2- and Fe concentrations.

Pyrite roasting in modified fluidized bed: Experimental and modeling analysis

The experiment focused on the bioleaching and desulfurization of pyrite roasting residues by the bacteria for the recovery of Cu, Zn and the magnetic materials. First of all, the study systematically performed XRD, which provided scientific and technique basis for extraction of valuable metals. Subsequently, the effect of the pH, the temperature and the bacterial inoculum volume ratio on the bioleaching was investigated. The data revealed that the condition under the pH of 1.2, the temperature of 45°C and bacterial inoculum volume ratio of 10% had the most significant effect on the bioleaching and the recovery rates of Cu, Zn and SO42- reached up to 80%, 99% and 80%, respectively. Finally, multi-elements analysis before and after the bioleaching experiments was performed to further explore the ability of the NB bacteria to oxidize the Deerni pyrite roasting residues. The study demonstrated that the total Fe and sulfur contents of the bioleaching residues accounted for 68.47% and 0.28%, respectively. The content of Cu and Zn in the leaching residue were only 0.09% and 0.01%. The desulfurization effects are evident and bioleaching residues meet the requirements as magnetic materials in steel making industry.