nan Abhilash

Microbially Assisted Leaching of Uranium—A Review

Due to depletion of high-grade deposits of uranium and generation of large quantities of tailings produced by mining and metallurgical activities, there is a need to find an economical way to recover uranium from low-grade deposits and secondary resources. Bioleaching of uranium from the ores, minerals, and wastes in heap and dumps, besides in-situ biodissolution processes, is rapidly expanding globally, and its economic values may exceed that of the underground mining. The biodissolution of uranium is a consequence of hydrometallurgical treatment of ore with microbial intervention. Uranium bioleaching is mainly driven by the combined action of Fe(III) and the protons that are produced by the activity of chemolithotrophic micro-organisms which use either iron or sulfur as their energy source for their growth. In this review, an attempt has been made to understand the process of bioleaching of uranium while deliberating on mechanism as to whether the reactions are direct or indirect and the role of micro-organisms, besides the types and effectiveness of processes by which uranium is extracted from its ores on bench/industrial/large scale. The processes developed or in vogue for bioleaching of uranium are described in some detail, along with recent initiatives.

Column Bioleaching of a Low-Grade Silicate Ore of Uranium

The bioleaching of a low-grade Indian uraninite ore (triuranium octoxide, U3O8: 0.024%), containing ferro-silicate and magnetite as the major phases, and hematite and pyrite in minor amounts, has been reported. Experiments were carried out in laboratory scale column reactors inoculated with enriched culture of Acidithiobacillus ferrooxidans isolated from the source mine water. The pH effect on uranium recovery was examined with the same amounts of ores in different columns. With the presence of 10.64% Fe in the ore as ferro-silicate, the higher uranium biorecovery of 58.9% was observed with increase in cell count from 6.4 × 107 to 9.7 × 108 cells/mL at pH 1.7 in 40 days as compared to the uranium recovery of 56.8% at pH 1.9 with a corresponding value of 9.4 × 108 cells/mL for 2.5-kg ore in the column. The dissolution of uranium under chemical leaching conditions, however, recorded a lower value of 47.9% in 40 days at room temperature. Recoveries were similar with 6-kg ore when column leaching was carried out at pH 1.7. The bioleaching of uranium from the low-grade ore of Turamdih may be correlated with the iron(II) and iron(III) concentrations, and redox potential values.

Extraction of Ce and Th from Monazite Using REE Tolerant Aspergillus niger

ABSTRACT In the present study, bioleaching of monazite, one of oldest and most water-resistant mineral to microbial attack, was tested for its amenability toward extraction of Ce, Th, and U using heterotrophic fungal species, Aspergillus niger. Shake flask experiments were carried out using Bromfield, sucrose, synthetic, and standard media containing 2%(w/v) of monazite for 60 days. Several parameters such as media pH, redox potential, siderophore production, biomass, and metal oxidation were analyzed at different intervals during the process of bioleaching. The maximum concentration of Ce obtained was 0.701, 0.229, 0.132, and 0.052 mg/L in Bromfield, synthetic, sucrose, and standard media(s), respectively. Thorium was identified only in synthetic (0.026 mg/L) and sucrose (0.0175 mg/L) media, whereas uranium was not observed in any of the media attempted. The results were corroborated with analysis by SEM characterization of the head and residues.

Bacterial leaching kinetics for copper dissolution from a lowgrade Indian chalcopyrite ore

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.