Abstract
Rare earth elements (REE) are critical to a wide range of technologies ranging from mobile phones to wind turbines. Processing and extraction of REE minerals from ore bodies is, however, both challenging and relatively poorly understood, as the majority of deposits contain only limited enrichment of REEs. An improved understanding of the surface properties of the minerals is important in informing and optimising their processing, in particular for separation by froth flotation. The measurement of zeta potential can be used to extract information regarding the electrical double layer, and hence surface properties of these minerals.There are over 34 REE fluorcarbonate minerals currently identified, however bastnäsite, synchysite and parisite are of most economic importance. Bastnäsite–(Ce), the most common REE fluorcarbonate, supplies over 50% of the world's REE. Previous studies of bastnäsite have showed a wide range of surface behaviour, with the iso-electric point (IEP), being measured between pH values of 4.6 and 9.3. In contrast, no values of IEP have been reported for parisite or synchysite.In this work, we review previous studies of the zeta potentials of bastnäsite to investigate the effects of different methodologies and sample preparation. In addition, measurements of zeta potentials of parisite under water, collector and supernatant conditions were conducted, the first to be reported. These results showed an iso-electric point for parisite of 5.6 under water, with a shift to a more negative zeta potential with both collector (hydroxamic and fatty acids) and supernatant conditions. The IEP with collectors and supernatant was <3.5. As zeta potential measurements in the presence of reagents and supernatants are the most rigorous way of determining the efficiency of a flotation reagent, the agreement between parisite zeta potentials obtained here and previous work on bastnäsite suggests that parisite may be processed using similar reagent schemes to bastnäsite. This is important for future processing of REE deposits, comprising of more complex REE mineralogy.
Highlights
IntroductionRare earth elements (REE) are often utilised in magnets due to their high remanence and coercivity, which is a result of the relatively large number of unpaired electrons in their atomic structure, in particular neodymium is a constituent of neodymium iron boron magnets [3]
Surface behaviour describes a wide range of phenomena ranging from kinetic to electrochemistry, as this review focuses on zeta potential measurements, the electrical double layer is described in detail
Most surfaces are positively charged at acidic pH and negatively charged at base pH [62], the magnitude and gradient of the zeta potential results agrees with those of bastnäsite [71,81].The sign and magnitude of the charge indicate the uptake of different species in the solution
Summary
REE are often utilised in magnets due to their high remanence and coercivity, which is a result of the relatively large number of unpaired electrons in their atomic structure, in particular neodymium is a constituent of neodymium iron boron magnets [3]. Rare earth elements are contained within over 200 minerals and ore deposits located over seven continents [4,5,6,7], the concentrations of REE within the ores are low and such they are difficult to process [2]. There is a broad range of interest in rare earth bearing minerals, with the European Commission identifying them as one of the twenty seven critical raw materials, the processing of them is still relatively poorly understood [8,9,10].
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