Characterisation of a ferruginous rare earth bearing lateritic ore and implications for rare earth mineral processing

Abstract

Detailed characterisation of a lateritic rare earth ore formed from the weathering of a primary carbonatite was carried out to determine the mode of occurrence and distribution of rare earths and gangue species in the ore. The ore was characterised by a number of techniques including chemical analysis, quantitative X-ray diffraction, screen analysis, QEMSCAN and SEM/EDX. The primary rare earth bearing mineral identified was monazite in its various forms; florencite the other rare earth mineral identified is of secondary importance. The main gangue species was goethite with lesser amounts of dolomite and apatite. As a result of the weathering process, the ore was enriched in rare earth oxides with the head grade being 7.65 wt%. Screen analysis of the crushed ore shows that it consists predominantly of fine and ultra-fine particles below 38 μm with the rare earths and iron distributing in the finer size fractions. Microstructural characterisation of the rare earth minerals in crushed ore showed that the rare earth minerals were of very fine grain size and occurred as polycrystalline aggregates and fine disseminations in gangue. Compositionally, monazite was cerium dominant and contained calcium and strontium as impurities whilst florencite was either cerium or lanthanum dominant and was enriched in strontium. The rare earth content in monazite was much higher relative to florencite, making it an important source of rare earths in the ore. Concentrate grades are likely to be impacted by the presence of structural impurities (Ca, Sr, Al) associated with monazite and florencite. In light of these findings, potential processing options such as magnetic separation and froth flotation for recovering rare earths from this ore are discussed which are also potentially applicable to the beneficiation of other ferruginous rare earth bearing ores of similar mineralogy.