Debabrata Pradhan

Bioleaching kinetics and multivariate analysis of spent petroleum catalyst dissolution using two acidophiles

Bioleaching studies were conducted to evaluate the recovery of metal values from waste petroleum catalyst using two different acidophilic microorganisms, Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans. Various leaching parameters such as contact time, pH, oxidant concentration, pulp densities, particle size, and temperature were studied in detail. Activation energy was evaluated from Arrhenius equation and values for Ni, V and Mo were calculated in case of both the acidophiles. In both cases, the dissolution kinetics of Mo was lower than those of V and Ni. The lower dissolution kinetics may have been due to the formation of a sulfur product layer, refractoriness of MoS(2) or both. Multivariate statistical data were presented to interpret the leaching data in the present case. The significance of the leaching parameters was derived through principle component analysis and multi linear regression analyses for both iron and sulfur oxidizing bacteria.

Bioleaching of low-grade uranium ore using Acidithiobacillus ferrooxidans

Bioleaching of uranium was carried out with Turamdih ore sample procured from Uranium Corporation of India Limited, Jaduguda. The bacterial strain that was used in the leaching experiments was isolated from the Jaduguda mine water sample. Efficiency of bioleaching was studied by varying parameters like pulp density and initial ferrous concentration as source of energy. It is observed that the efficiency of bioleaching was 49% at 10% pulp density (w/v) and initial pH 2.0. Addition of external has no effect on efficiency of bioleaching showing domination of direct leaching mechanism over indirect.

Bio-dissolution of Ni, V and Mo from spent petroleum catalyst using iron oxidizing bacteria

Bioleaching studies of spent petroleum catalyst containing Ni, V and Mo were carried out using iron oxidizing bacteria. Various leaching parameters such as Fe(II) concentration, pulp density, pH, temperature and particle size were studied to evaluate their effects on the leaching efficiency as well as the kinetics of dissolution. The percentage of leaching of Ni and V were higher than Mo. The leaching process followed a diffusion controlled model and the product layer was observed to be impervious due to formation of ammonium jarosite (NH4)Fe3(SO4)2(OH)6. Apart from this, the lower leaching efficiency of Mo was due to a hydrophobic coating of elemental sulfur over Mo matrix in the spent catalyst. The diffusivities of the attacking species for Ni, V and Mo were also calculated.

A comparative study of biosorption of Cu using Aspergillus niger and Aspergillus flavus

In the present work a comparative study has been made to adsorb Cu ion from solution using pre-treated biomass of two fungal strains, Aspergillus niger and Aspergillus flavus . Several parameters such as pH, adsorbate and adsorbent concentration and fraction size of the fungal biomass were studied to observe their effect on the percentage of metal uptake by the treated biomass. Although both the fungal strains proved to be potential biosorbents, but novel observation was, under similar experimental conditions Aspergillus flavus showed better biosorption properties than Aspergillus niger . Overall experimental data fitted well to both Freundlich and Langmuir adsorption isotherm models.

Evaluation of iron oxidation rate of Acidithiobacillus ferrooxidans in presence of heavy metal ions

Abstract The present study deals with the determination of the iron oxidation rate (IOR) of Acidithiobacillus ferrooxidans in the presence of various heavy metal ions. Initially, the IOR of this particular strain was enhanced to 718 mg L–1 h–1 by several sets of subculturing of the whole biomass in fresh medium. In the process, the bacterial regeneration time was determined to be 3˙7 h. The effect of various heavy metal ions (Hg, Ag and Pb) on IOR of this active strain was studied and the reaction kinetics in the presence of various concentrations of heavy metal ions in the solution has been determined. The tolerance index of the active culture to various heavy metals has also been established. The tolerance index in the presence of 700 mg L–1 Pb, 50 mg L–1 Ag and 0˙1 mg L–1 Hg was 5˙1, 5˙1 and 11˙9 respectively. Therefore, it was concluded that Hg ion rendered maximum toxicity to the bacterial strains followed by Ag and Pb. By statistical interpretation of the observed data, it was possible to formulate a very significant correlation between all the sets of experiments that were conducted in the presence and absence of metal ions.