Sulfur-enhanced reductive bioprocessing of cobalt-bearing materials for base metals recovery

Abstract

The abundance of limonitic laterite ores in tropical and sub-tropical areas represents a large, and mostly unexploited, cobalt resource. Bioprocessing oxidised ores, and also waste materials such as tailings and processing residues, using acidophilic microorganisms to catalyse the reductive dissolution of iron and manganese minerals, is an environmentally benign alternative approach of extracting valuable base metals associated with these deposits. This work describes results from laboratory-scale experiments in which five cobaltbearing materials, three primary limonitic laterite ores and two processing residues (filter dust and slag), all sourced from mines and a processing plant in Greece, were bioleached under reducing conditions by a consortium of acidophilic bacteria (using elemental sulfur as electron donor) in stirred tank bioreactors at pH 1.5 and 35ºC. Whilst the target metal, cobalt, was successfully bioleached from all five materials (40 -50% within 30 days) the extraction of some other metals was more variable (e.g. between 2 and 48% of iron). Concentrations of soluble cobalt were highly correlated, in most cases, with those of manganese, correlating with the finding that cobalt was primarily deported in manganese (IV) minerals. Acid consumption also differed greatly between mineral samples, ranging between 3 and 67 moles H 2 SO 4 g -1 cobalt extracted. Comprehensive mineralogical analysis of the three limonitic samples before and after bioprocessing revealed significant variations between the ores, and demonstrated that elemental and mineralogical variabilities can greatly impact their amenability for reductive bioleaching.

Bioleaching of Transition Metals From Limonitic Laterite Deposits and Reassessment of the Multiple Roles of Sulfur-Oxidizing Acidophiles in the Process

“…have at least four potential roles in the reductive bioleaching of limonite: (i) generating (sulfuric) acid, by coupling the oxidation of ZVS to the reduction of oxygen (all species) or soluble ferric iron (iron-oxidizing/reducing species only); (ii) generating and maintaining low redox potentials in oxygen-free mineral suspensions (iron-oxidizing/reducing species only); (iii) latent reduction of ferric iron in aerated mineral suspensions (all species); (iv) generating a more reactive form of sulfur, by combined “wetting” and potential formation of sulfane derivatives. Limonite deposits, even from within a single geographical area, can display considerable variations in how amenable they are to bio-processing ( Santos et al, 2020 ) and testing and fine-tuning of the main operational parameters (pH, E H and temperature) is required to identify optimum conditions for bioleaching and to determine which of the specific microbial roles in this (e.g., acid production or iron reduction) should be prioritized, and how operational protocols (e.g., pH, temperature, and aeration status) should be engineered to optimize these.…”

Chromium (VI) Inhibition of Low pH Bioleaching of Limonitic Nickel-Cobalt Ore

“…Reductive mineral dissolution is favoured by anoxic conditions, though aerobic pure cultures of some sulphur-oxidising acidophiles can also promote the reduction of ferric iron (Marrero et al, 2015;Johnson et al, 2021). Limonitic laterite samples from diverse global locations have been found to be amenable to reductive bio-processing, though most reported laboratory tests have been carried out in stirred bioreactors at relatively low (2.5-5% w/v) solids density (e.g., Hallberg et al, 2011;Ñancucheo et al, 2014;Smith et al, 2017;Santos et al, 2020). In the current study, NC1 limonite added en bloc at 10% (w/v) completely inhibited the microbial reduction of iron, allowing only acid dissolution to occur (Figure 2).…”

Ferric Iron Reduction in Extreme Acidophiles

“…According to the diverse composition of laterites, different base metals have already been the target of reductive bioleaching, such as nickel ( Hallberg et al, 2011a ), copper ( Nancucheo et al, 2014 ), and cobalt ( Smith et al, 2017 ), reaching up to 100% yield. It also became apparent, that the geographical origin of the ore and its mineralogical composition had a major impact on their biohydrometallurgical application ( Santos et al, 2020 ). Initially, the applicability of reductive bioleaching was examined by using pure cultures of Acidithiobacillus ferrooxidans operating under anoxic conditions ( Hallberg et al, 2011a ; Johnson et al, 2013 ; Nancucheo et al, 2014 ).…”

“…Initially, the applicability of reductive bioleaching was examined by using pure cultures of Acidithiobacillus ferrooxidans operating under anoxic conditions ( Hallberg et al, 2011a ; Johnson et al, 2013 ; Nancucheo et al, 2014 ). Afterward, other acidophiles and consortia as well as different aeration setups (AeRD, Ae-AnRD and AnRD) were investigated for this reductive extraction approach ( Marrero et al, 2015 ; Santos et al, 2020 ; Johnson et al, 2021 ). In some processes, also thermotolerant strains were used ( Smith et al, 2017 ; Johnson et al, 2021 ) which enable higher operation temperatures and thereby enhanced reaction kinetics.…”

“…In some processes, also thermotolerant strains were used ( Smith et al, 2017 ; Johnson et al, 2021 ) which enable higher operation temperatures and thereby enhanced reaction kinetics. However, the use of consortia also showed that the diversity of the microbial community decreases during the reductive bioleaching process, which could sometimes be due to a lack of adaptation of the acidophiles to the mineral, resulting in the predominance of a few strains ( Smith et al, 2017 ; Santos et al, 2020 ). Monitoring of cell numbers by qPCR also showed a constant number of active bacteria during the AeRD process and a decrease after 3 days in the case of AnRD and Ae-AnRD ( Marrero et al, 2015 ).…”