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

Ivan Nancucheo,Manoel Lopes,David Johnson,Guilherme Oliveira

doi:10.3390/min9030136

Ivan Nancucheo, Manoel Lopes + Show 2 more

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https://doi.org/10.3390/min9030136

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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.

Highlights

The main supplier of rare earth elements (REE) to the world market is China, which accounted for 86% of total world production in 2014 and hosts the largest (~42%) proportion of the total global reserves, estimated to be ca. 110 million tons [1,2]
The reductive dissolution of ferric iron minerals was greater in the bioreactor that was conditions and fixed pH (1.8)
The reductive dissolution of ferric iron minerals was greater in the bioreactor that was both reactors, virtually allvirtually the soluble iron was present as present ferrous as iron, concentrations of which of which both reactors, all the soluble iron was ferrous iron, concentrations continuously sparged with the oxygen-free nitrogen (OFN)/CO2 gas mix than that which was sparged only with OFN

Summary

Introduction

The main supplier of REE to the world market is China, which accounted for 86% of total world production in 2014 and hosts the largest (~42%) proportion of the total global reserves, estimated to be ca. 110 million tons [1,2]. The three main rare-earth-bearing minerals are monazite, bastnaesite, and xenotime; these are highly refractory minerals and are not solubilized by conventional chemical treatment, requiring digestion with sulfuric acid and/or concentrated sodium hydroxide at high temperatures [5,6]. Biomining is well established as an important applied biotechnology in the metal mining sector; it is often perceived as a technology that is less energy consuming and has been promoted as being a more “environmentally friendly” approach to processing minerals ores and concentrates than conventional practices such as smelting. Biomining operations use far lower temperatures and pressures than conventional extraction processes, require less energy, and produce lower CO2 emissions, though extraction of metals from primary ores and wastes tend to be far more protracted [7]

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