Copper biodissolution from a low grade chalcopyrite ore by unadapted/adapted acidithiobacillus ferrooxidans

The depletion of high-grade deposit of copper around the world has drawn attention for the utilisation
of low-grade reserves . Malanjkhand Copper Project (MCP) in India is a low-grade ore containing
-0.3% Cu in which copper metal is found to be present as chalcopyrite associated with pyrite in
quartz veins and granitic rocks. In order to extract copper from this material , an alternate processing
option such as bioleaching has been followed. Bench scale bioleaching experiments were carried out
using Acidithiobacillus ferrooxidans (Ac. Ti) isolated from mine water. On using unadapted Ac. Tf
isolate directly at pH 2.0 and 35°C, the optimum leaching conditions in shake flask were found to be
5% pulp density (PD), 2.OpH , 35°C temperature for <50p .m particles , yielding 72% Cu biorecovery in
35days. The Tf isolate when adapted to the ore and employed for the bioleaching of the ore at 5% PD
(w/v), 2.OpH and 25 °C with three particle sizes viz.150 -76μm, 76-5011m and <50μm, resulted in
recovery of 38 .31%, 29.68% and 47.5% Cu respectively with a rise in Eh from 530 to 654 mV in 35
days. Under similar conditions , the unadapted strain gave maximum recovery of 44.0 % for <50pm
ore size with rise in Eh from 525 to 650mV . Copper biorecovery increased to 75.3% with the adapted
isolates at 35°C for the finer particles of <50gm at 2.OpH with a rise in cell count from lx l 07 cells/mL
to 1.13x109 cells/mL in 35 days. The biodissolution of copper from chalcopyrite with the involvement
of adapted Ac. Tf species resulted in the improvement of iron oxidation rate (Fe2+ to Fe'`) and
consequently higher redox potential.