Abstract:

The accelerated global demand for battery metals has emphasized on the extraction of critical metals like nickel (Ni) and cobalt (Co). Due to the depletion of high grade sulphide resources, the focus has been shifted towards laterite ores as the major resource for Ni and Co. However, processing of the laterite ore is challenging due to its complex mineralogy, dominated by goethite (FeO(OH)) and hematite (Fe₂O₃), which strongly encapsulate Ni and Co within the iron matrix.

Conventional pyrometallurgical and hydrometallurgical approaches can achieve >90 % nickel recovery. But these technologies are associated with high energy consumption, intensive acid usage and significant environmental footprints. In contrast, bioleaching has attracted increasing attention as a low-energy and environmental benign alternative, capable of selectively destabilising metal-bearing mineral phases through microbially mediated redox reactions. Despite these advantages, however, bioleaching of laterite ores is often limited by slow reaction kinetics and incomplete metal liberation.

In order to address these limitations, this work investigates an integrated bio-hydrometallurgical approach wherein the ore is primarily treated with Shewanella oneidensis MR-1 for the metal reduction, followed by atmospheric nitric acid leaching for the complete metal recovery. The major metal constituents of the ore were found to be Fe: 45.3%, Ni: 1.35 %, Co: 0.33% and Cr: 2.44% through XRF elemental analysis, while X-ray diffraction indicated goethite laterite profile. Though the bacteria has the ability to reduce the goethite matrix yet the rate of reaction is quite slow. To enhance the bio-reduction kinetics, humic acid was supplemented as an external electron transfer aid to accelerate the bacterial iron reduction. Further experimental results and mechanistic insights will be presented and discussed in detail at the conference.

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Dr. Aishvarya V