Sandeep K. Panda

Extraction of nickel by microbial reduction of lateritic chromite overburden of Sukinda, India.

Microbial extraction of nickel from lateritic chromite overburden (COB), Sukinda by Acidithiobacillus ferrooxidans has been investigated in this work. In anoxic environment, A. ferrooxidans reduced the ferric iron in goethite [Fe(O)OH] mineral of COB by using elemental sulphur as electron donor. Nickel embedded in the complex goethite matrix of COB was successfully recovered by cumulative action of sulphuric acid, generated by oxidation of elemental sulphur and reduction of ferric iron in goethite matrix by A. ferrooxidans. Forty one percent of the nickel present in COB was extracted in a 3 L scale bioreactor (pH of 1.8 ± 0.05, temperature of 28 ± 2°C) maintained in anoxic environment. In contrast, only 11% of the nickel present in COB was extracted with continuous supply of air to the bioreactor keeping all the parameters unchanged. Kinetics study of anoxic microbial processing of COB revealed that the chemical reaction rate control model fits to the rate of nickel dissolution (R(2)=0.975).

Bioleaching of copper from pre and post thermally activated low grade chalcopyrite contained ball mill spillage

Bioleaching of a low grade chalcopyrite (ball mill spillage material) was tested for copper recovery in shake flasks. The original samples (as received) were thermally activated (600°C, 30 min) to notice the change in physico-chemical and mineralogical characteristics of the host rock and subsequently its effect on copper recovery. A mixed culture of acidophilic chemolithotrophic bacterial consortium predominantly entailing Acidithiobacillus ferrooxidans strain was used for bioleaching studies and optimization of process parameters of both original and thermally activated samples. Mineralogical characterization studies indicated the presence of chalcopyrite, pyrite in the silicate matrix of the granitic rock. Field emission scanning electron microscopy coupled with Energy dispersive spectroscopy (FESEM-EDS) and X-ray Fluorescence (XRF) analysis indicated mostly SiO2. With pH 2, pulp density 10% w/v, inoculum 10% v/v, temperature 30°C, 150 r·min−1, 49% copper could be recovered in 30 days from the finest particle size (−1 + 0.75 mm) of the original spillage sample. Under similar conditions 95% copper could be recovered from the thermally activated sample with the same size fraction in 10 days. The study revealed that thermal activation leads to volume expansion in the rock with the development of cracks, micro and macro pores on its surface, thereby enabling bacterial solution to penetrate more easily into the body, facilitating enhanced copper dissolution.