Twenty-first century technological advances have dramatically accelerated the global demand for rare earth element (REE) resources. Although ore grades and reserves of many REE deposits worldwide are known, the dominant producer remains as just one country, China. In recent years, dramatic price fluctuations have intensified attention on the security of supply of REE resources, and although such geopolitical factors are important, other issues have been also been recognized. These include ore deposit locations, the complexity and diversity of geological occurrences, understanding geochemical mobilities, mineralogical constraints (intergrowths, refractory phases, associated radionuclides), processing challenges (element separation), and all the concomitant economic and environmental risks connected with extraction and mineral processing. Some of these problems and several much wider science questions can be addressed with zeolite mineralogy and REE geochemistry (mineral-fluid interactions). Here, we present new data from our recent NERC project within the mineral resources theme “SoS” (Security of Supply of Mineral Resources), based on these issues.
Rare earth element behaviours in alkaline fluid-mineral-rock systems can be examined by observational and experimental methods, but several analytical challenges exist in dealing with Si-undersaturated and hydrated phases (peralkaline glasses and zeolites). We have developed new protocols for the analysis of zeolites by electron microprobe and by LA-ICPMS and are now beginning to be able to align major and trace element natural compositions with advanced understandings of zeolite stabilities (constrained by pH, temperature and ion activities). Ultimately, these studies will lead to predictive understanding of REE mobilities in low temperature fluids. Such fundamental patterns, some of which might be aligned with those of the actinides, have potential value and impacts in mineral exploration, mineral processing, waste management, and earth system cycles. Zeolite reaction path modelling can further provide access to deeper Earth histories.
Supporting the findings from natural mineral compositions, studies of ion exchange characteristics are also being undertaken in bench-top experiments to determine mineral-fluid distribution coefficients for individual rare earths (Nd3+ and Dy3+). Our preliminary set of experimental residues (industrial clinoptilolite), will soon be taken to the Diamond Light Source for determination of the crystallographic binding sites of both of these rare earths, in the open cavities of the clinoptilolite structure.
Collaborations and Acknowledgements: D. Polya, A. Dyer, J. Charnock, N. Pearce, S. Chenery, A. Langella, F. Stoppa, G. Giordano, S. Conticelli, J. Readman, C. M. B. Henderson, K. Brodie, G. Droop, R. Pattrick, NERC, Erasmus, STFC, Pratley Analytical, INZA, MIRO.