Lanthanide structural state in Ion Adsorption Deposits

The rare earth elements (REE) are critical metals underpinning the decarbonisation of energy and transport. Weathered rock deposits provide over 90% of world heavy REE supply, and host these elements adsorbed to clay minerals. Previous measurements of REE co-ordination and bonding in these important deposits have focussed on the use of the Y K-edge as an analogue for the REE because of limitations on the k-range possible using the L3-edge. Lanthanide K-edge XANES and XAFS have not been measured in this context. We propose to utilise the XMaS BM28 beamline to measure Ce-Sm K-edge XANES and XAFS to directly determine the structural site of the REE in these critical deposits. The results will constrain changes in adsorption mechanism under different natural conditions and provide information on Ce redox state, thus informing genetic models and the design of extraction processes.