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

Megan J Barnett,Eimear A Deady,Barbara Palumbo-Roe,Simon P Gregory

doi:10.3390/min10080649

Abstract

Approximately 300 million tonnes of bauxite are processed annually, primarily to extract alumina, and can contain moderate rare earth element (REE) concentrations, which are critical to a green energy future. Three bioleaching techniques (organic acid, reductive and oxidative) were tested on three karst bauxites using either Aspergillus sp. (organic acid bioleaching) or Acidithiobacillus ferrooxidans (reductive and oxidative bioleaching). Recovery was highest in relation to middle REE (generally Nd to Gd), with maximum recovery of individual REE between 26.2% and 62.8%, depending on the bauxite sample. REE recovery occurred at low pH (generally < 3), as a result of organic acids produced by Aspergillus sp. or sulphuric acid present in A. ferrooxidans growth media. Acid production was seen when A. ferrooxidans was present. However, a clear increase in REE recovery in the presence of A. ferrooxidans (compared to the control) was only seen with one bauxite sample (clay-rich) and only under oxidative conditions. The complex and varied nature of REE-bearing minerals in bauxite provides multiple targets for bioleaching, and although the majority of recoverable REE can be leached by organic and inorganic acids, there is potential for enhanced recovery by bioleaching.

Highlights

The rare earth elements (REE) are widely used in a range of modern technologies, which is driving a steady increase in demand, for the most critical REE, such as neodymium (Nd) and praseodymium (Pr) [1]
The three samples selected for this study are referred to as low-Ca, high-Ca and clay-rich bauxite; these can be distinguished by bulk chemistry (Table 4 and Figure 2) and mineralogy
Due to the variety of REE-bearing minerals present in bauxite material, and the variety of targets for bioprocessing, enhanced REE recovery might be expected in all bioleaching processes tested here

Summary

Introduction

The rare earth elements (REE) are widely used in a range of modern technologies, which is driving a steady increase in demand, for the most critical REE, such as neodymium (Nd) and praseodymium (Pr) [1]. There has been significant interest in developing alternative REE resources, and one area of research has focused on the recovery of the REE from bauxite [4]. Bauxites are subdivided into three types [5]: (1) lateritic bauxite deposits, derived from in situ weathering of aluminosilicate rocks;. (2) Tikhvin-type deposits, deposited on aluminosilicate rocks of no genetic relation, and (3) karst bauxite deposits. Karst bauxite deposits occur in the karst topography of limestone and dolomite and comprise aluminosilicate residues transported from either proximal or distal locations, undergoing lateritic weathering [5]. Of the karst bauxite types, the “Mediterranean type” is of interest in this study due to its REE content.

Methods

Discussion

Conclusion