Rare Earth Element Phases in Bauxite Residue

Johannes Vind,Alan Tkaczyk,Vicky Vassiliadou,Annelies Malfliet,Petros Tsakiridis,Dimitrios Panias,Bart Blanpain

doi:10.3390/min8020077

Johannes Vind, Alan Tkaczyk + Show 5 more

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https://doi.org/10.3390/min8020077

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Abstract

The purpose of present work was to provide mineralogical insight into the rare earth element (REE) phases in bauxite residue to improve REE recovering technologies. Experimental work was performed by electron probe microanalysis with energy dispersive as well as wavelength dispersive spectroscopy and transmission electron microscopy. REEs are found as discrete mineral particles in bauxite residue. Their sizes range from <1 μm to about 40 μm. In bauxite residue, the most abundant REE bearing phases are light REE (LREE) ferrotitanates that form a solid solution between the phases with major compositions (REE,Ca,Na)(Ti,Fe)O3 and (Ca,Na)(Ti,Fe)O3. These are secondary phases formed during the Bayer process by an in-situ transformation of the precursor bauxite LREE phases. Compared to natural systems, the indicated solid solution resembles loparite-perovskite series. LREE particles often have a calcium ferrotitanate shell surrounding them that probably hinders their solubility. Minor amount of LREE carbonate and phosphate minerals as well as manganese-associated LREE phases are also present in bauxite residue. Heavy REEs occur in the same form as in bauxites, namely as yttrium phosphates. These results show that the Bayer process has an impact on the initial REE mineralogy contained in bauxite. Bauxite residue as well as selected bauxites are potentially good sources of REEs.

Highlights

It can be argued that humankind is mostly heading on a collision path with the ecosystems of theEarth [1]
Bauxite samples were studied to expand existing knowledge about the precursor rare earth element (REE) phases entering to the Bayer process
Calcium oxide is present in the Greek karstic bauxite sample and not in the Ghanaian lateritic bauxite

Summary

Introduction

It can be argued that humankind is mostly heading on a collision path with the ecosystems of theEarth [1]. One of the sectors bearing responsibility for the damaging actions is the minerals industry. The world’s largest rare earth element (REE) mine Bayan Obo has a large footprint which can have a major ecological impact while providing the largest proportion of worldwide REE supplies [2]. The future of critical metals industry as well as any other industry must increasingly follow the practices of concepts in responsible sourcing [3]. REEs are defined as lanthanides, found in the periodic table from atomic numbers 57–71, with the first one of them being lanthanum. Due to the chemical similarities, yttrium is categorised as a REE. The LREEs are elements from lanthanum to europium, HREEs are yttrium and gadolinium to lutetium, this division is ambiguous [4]. Scandium is not considered as part of the REEs group in the present

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