Banshi Dhar Pandey

Biochemical leaching of sea nodules using Bacillus circulans was carried in an external circulation-loop airlift bioreactor. In contrast to the slightly high recovery (92% Cu, 73% Ni, 72% Co, 38% Mn, and 17% Fe) with fine particles (−1. The use of air flow assisted in retaining good metal recoveries with reduced grinding costs in the air lift reactor. Computational Fluid Dynamics (CFD) with a multiphase mixture model was used to describe the mass transfer and hydrodynamics vis-à-vis its role in improved leaching efficacy. The leach liquor was treated to eliminate iron, followed by selective extraction of copper by 10% Acorga M5640. The remaining leach liquor with Mn, Co and Ni were separated as respective salts by sulfide/carbonate precipitation.

Bio-leaching of copper (0.3%) from a low grade Indian chalcopyrite ore of Malanjkhand copper mines, using a native mesophilic isolate predominantly Acidithiobacillus ferrooxidans (A.ferrooxidans), is reported. A bio-recovery of 72% Cu was recorded in the presence of this culture (not adapted), which increased to 75% with an ore adapted culture after 35 days at 35ºC and pH 2.0 with <50fim particles. The kinetic data showed best fit for the diffusion-controlled shrinking core model, exhibiting linear plots for [1- 2/3X-(1-X)2/3] vs time (X-fraction leached). Apparently, the role of the bacteria is to convert the ferrous ion to the ferric state, which oxidizes the chalcopyrite in order to dissolve copper, while maintaining a high redox potential. The activation energy value (E) was calculated to be 96 and 108 kJ/mol for the un-adapted culture and the ore adapted culture respectively in the temperature range 25-35ºC. This leaching mechanism was corroborated by XRD phase identification and SEM studies of the leach residue.