Bioreductive Dissolution as a Pretreatment for Recalcitrant Rare-Earth Phosphate Minerals Associated with Lateritic Ores

Abstract

Recent research has demonstrated the applicability of a biotechnological approach for extracting base metals using acidophilic bacteria that catalyze the reductive dissolution of ferric iron oxides from oxidized ores, using elemental sulfur as an electron donor. In Brazil, lateritic deposits are frequently associated with phosphate minerals such as monazite, which is one of the most abundant rare-earth phosphate minerals. Given the fact that monazite is highly refractory, rare earth elements (REE) extraction is very difficult to achieve and conventionally involves digesting with concentrated sodium hydroxide and/or sulfuric acid at high temperatures; therefore, it has not been considered as a potential resource. This study aimed to determine the effect of the bioreductive dissolution of ferric iron minerals associated with monazite using Acidithiobacillus (A.) species in pH- and temperature-controlled stirred reactors. Under aerobic conditions, using A. thiooxidans at extremely low pH greatly enhanced the solubilization of iron from ferric iron minerals, as well that of phosphate (about 35%), which can be used as an indicator of the dissolution of monazite. The results from this study have demonstrated the potential of using bioreductive mineral dissolution, which can be applied as pretreatment to remove coverings of ferric iron minerals in a process analogous to the bio-oxidation of refractory golds and expand the range of minerals that could be processed using this approach.

The Materials Science behind Sustainable Metals and Alloys

“…270,454,534 Examples of efficient bio-leaching with sulfur addition in bioreactors with organisms of the sulfur-oxidizing genus Acidithiobacillus in the laboratory resulted in high metal yields for various industrial residues. 540,546 Examples are metal recovery from electroplating sludges by using Acidithiobacillus thiooxidans where 100% chromium, 95% copper, and 85% zinc were recovered.…”

Ferric Iron Reduction in Extreme Acidophiles

“…The bio-reductive processes would be especially suitable to recycle scrap electronics or bioremediate metal-contaminated soil ( Johnson et al, 2013 ). Another approach aimed at the pretreatment of laterite-associated monazite, a rare earth elements-containing phosphate mineral, by ferric iron reduction to improve the monazite exposure for further acid dissolution ( Nancucheo et al, 2019 ). However, due to the innovation of this method, further research is required before it is ready for application.…”

Comparison of Three Approaches for Bioleaching of Rare Earth Elements from Bauxite

“…Oxidative bioleaching was marginally better than reductive bioleaching, so oxidative leaching will be the more likely method to use for bioleaching of REE from bauxite. Further investigation into reductive bioleaching should be explored using other microorganisms, as leaching of La was enhanced in the presence of A. thiooxidans but not A. ferrooxidans [30].…”

“…Leaching of the REE fluorcarbonate mineral bastnäsite was less successful, with only up to 0.08% detectable in the leaching solution [29]. One study has considered bioreductive dissolution for leaching REE from monazite [30], leaching up to 8% La with A. thiooxidans. The red mud tailings from the processing of bauxite have been a target for the bioleaching of REE, focusing on organic acid bioleaching with heterotrophic bacteria and fungi [23,[31][32][33], and one recent study demonstrates the ability of microalgae to accumulate REE (plus Y and Sc) in quantities of up to 54.5 mg•kg −1 of dry biomass from red mud [34].…”