The Microbiology of Lateritic Co-Ni-Bearing Manganese Oxides.

Abstract

Cobalt is a metal with a high-supply risk with >50% sourced from the DRC in 2018. Oxide-type laterites represent an alternative source of Co with >7500Mt of ore at Co and Ni grades of 0.1-0.2% and 1-1.6%, respectively. Both Co and Ni are often hosted in Mn(III/IV)-oxides, e.g. lithiophorite (Li,Al]Mn3O6[OH]6). Microbial consortia present in such environments play a critical role in the cycling of redox active metals such as Mn and through metabolic functions influence the uptake or release of metals either into or from mineral phases via direct interaction, e.g. metal reduction or metal oxidation, or indirect interaction, e.g by generating, through fermentation of organic matter, organic acids that complex with metals. Microbial influence on the mineralogy of laterites has implications for ore processing while additionally representing biochemical processes which could be developed into low-energy bioprocessing routes for lateritic ore. In this study, the geochemistry and mineralogy of Co- and Ni-bearing Mn(III/IV)-oxides and microbiological interactions with these phases have been studied. Lateritic ore from Nkamouna, S.E. Cameroon, was characterised by XRD and XRF. A synthetic analogue for lateritic ore phases was synthesised (Co-Ni asbolane) and characterised with XRD, SAED, ICP-AES and EDS. Ore samples were incubated with glucose to stimulate the indigenous microbial consortia while the asbolane was incubated with a pure culture of Geobacter sulfurreducens and acetate. Synchrotron-based XAS was used to determine features of crystal chemistry of Co, Ni and Mn in both natural and synthetic samples before and after microbiological activity. Soluble fractions of the lateritic ore incubations were analysed for Co and Mn speciation. The data suggests that in fresh ore, compared to Co(III), which primarily associates with Mn(III/IV) in minerals, Ni(II) crystal chemistry is more varied being either incorporated into aluminous fractions of lithiophorite or adsorped at Mn-oxide edges. To what degree these occur is indicative of redox conditions and microbial influence at different heights in the laterite. Within the incubated ore the microbial consortia fermented glucose to VFAs and deconstructed Mn(III/IV)- thereby releasing Co, Ni and Ba into solution. Mn(III/IV) and Co(III) were both reduced to divalent forms in solid and soluble fractions while solid fractions contained Ni in a highly disordered phase. G. sulfurreducens was shown to effectively break down synthetic asbolane and release Co and Ni into solution. Subsequent precipitation of Mn, Co and Ni into carbonate phases represents a method of forming products often used as intermediates in numerous industrial processes. The results of this study highlight the importance of microbes in ore lateritic deposit evolution and their potential applications as ore bioprocessors.

Date of Award	4 Sept 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Jonathan Lloyd (Co Supervisor) & Victoria Coker (Main Supervisor)