Abstract
Rare earth elements (REE) are essential in high-technology and environmental applications, where their importance and demand have grown enormously over the past decades. Many lanthanide and actinide minerals in nature are phosphates. Minerals like monazite occur in small concentrations in common rocks that resist weathering. Turquoise is a hydrous phosphate of copper and aluminum scarcely studied as copper ore. Phosphate-solubilizing microorganisms are able to transform insoluble phosphate into a more soluble form which directly and/or indirectly contributes to their metabolism. In this study, bioleaching of heavy metals from phosphate minerals by using the fungus Aspergillus niger was investigated. Bioleaching experiments were examined in batch cultures with different mineral phosphates: aluminum phosphate (commercial), turquoise, and monazite (natural minerals). The experiments were performed at 1% pulp density and the phosphorous leaching yield was aluminum phosphate > turquoise > monazite. Bioleaching experiments with turquoise showed that A. niger was able to reach 8.81 mg/l of copper in the aqueous phase. Furthermore, the fungus dissolved the aluminum cerium phosphate hydroxide in monazite, reaching up to 1.37 mg/L of REE when the fungus was grown with the mineral as the sole phosphorous source. Furthermore, A. niger is involved in the formation of secondary minerals, such as copper and REE oxalates.
Highlights
Rare Earth Elements (REE) attract enormous interest because of their importance to current and high technological manufacturing industries and the expectation of an increase in requirements throughout the world on a monopolistic market of REE due to geopolitical controls [1]
This work has shown that valuable metals from mineral phosphates were mobilized using A. niger
A. niger leached REE from monazite, obtaining the best results when the fungus was cultivated on minimal medium with the mineral as the sole phosphorous source
Summary
Rare Earth Elements (REE) attract enormous interest because of their importance to current and high technological manufacturing industries and the expectation of an increase in requirements throughout the world on a monopolistic market of REE due to geopolitical controls [1]. The distribution of rare earths by their end use is estimated as follows: catalysts, 60%; ceramics and glass, 15%; metallurgical applications and alloys, 10%; polishing, 10%; others, 5% [2]. The production of rare earths increased with renewed mining activities in the United States of America as well as new and or increased production in Australia, Burma (Myanmar), and Burundi. Mine production in China increased 14% in 2018 compared with the quota in 2017. The European Commission carries out a critical assessment on non-energy and non-agricultural raw materials that, in 2017, included heavy rare earth elements, light rare earth elements, and platinum group metals [4]
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