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

Abstract

Limonitic layers of the regolith, which are often stockpiled as waste materials at laterite mines, commonly contain significant concentrations of valuable base metals, such as nickel, cobalt, and manganese. There is currently considerable demand for these transition metals, and this is projected to continue to increase (alongside their commodity values) during the next few decades, due in the most part to their use in battery and renewable technologies. Limonite bioprocessing is an emerging technology that often uses acidophilic prokaryotes to catalyse the oxidation of zero-valent sulphur coupled to the reduction of Fe (III) and Mn (IV) minerals, resulting in the release of target metals. Chromium-bearing minerals, such as chromite, where the metal is present as Cr (III), are widespread in laterite deposits. However, there are also reports that the more oxidised and more biotoxic form of this metal [Cr (VI)] may be present in some limonites, formed by the oxidation of Cr (III) by manganese (IV) oxides. Bioleaching experiments carried out in laboratory-scale reactors using limonites from a laterite mine in New Caledonia found that solid densities of ∼10% w/v resulted in complete inhibition of iron reduction by acidophiles, which is a critical reaction in the reductive dissolution process. Further investigations found this to be due to the release of Cr (VI) in the acidic liquors. X-ray absorption near edge structure (XANES) spectroscopy analysis of the limonites used found that between 3.1 and 8.0% of the total chromium in the three limonite samples used in experiments was present in the raw materials as Cr (VI). Microbial inhibition due to Cr (VI) could be eliminated either by adding limonite incrementally or by the addition of ferrous iron, which reduces Cr (VI) to less toxic Cr (III), resulting in rates of extraction of cobalt (the main target metal in the experiments) of >90%.

Unveiling the bioleaching versatility of Acidithiobacillus ferrooxidans

“…Subsequently, released Cr can be efficiently removed. Cr is naturally occurring in minerals such as the Cr-bearing phase of goethite Fe 3+ O(OH), or in limonite deposits (Santos et al, 2022). The liberation of Cr from sludge or rocks is contingent upon redox processes.…”

Immobilisation of chromium in magnesium carbonate minerals

“…The extent of water–rock interactions during the weathering of ultramafic rocks and serpentinites affects the concentration of Cr in the surrounding waters and soils, with the oxidation state dependent on the degree of redox reaction with other electron donors and acceptors present (McClain and Maher, 2016). For example, the occurrence of Cr 6+ (~3–8% of the total chromium) in the lateritic regolith developed on ultramafic rocks in New Caledonia has been associated strongly with the presence of Mn 3+ or Mn 4+ (Fandeur et al , 2009; Santos et al , 2022). Notable amounts of Cr 6+ found in natural systems have a direct anthropogenic origin, related to the sediment drainage from open pit mining (Gunkel-Grillon et al , 2014) or pyro- and hydrometallurgical processing of ultramafic rocks and Ni laterites (PT Vale Indonesia Tbk, 2017).…”

Fe(III) bioreduction kinetics in anaerobic batch and continuous stirred tank reactors with acidophilic bacteria relevant for bioleaching of limonitic laterites

“…The concept of reductive bioleaching was first introduced by Hallberg et al (2011) . Since then, several studies dealing with the proof of concept of reductive bioleaching have been released ( Johnson and du Plessis, 2015 ; Marrero et al, 2015 ; Santos et al, 2020 , 2022 ; Johnson and Pakostova, 2021 ; Stankovic et al, 2022 ). These studies are mainly dedicated to the study of microorganisms, with a microbiological approach.…”