Diffusion-Desorption Study of Rare Earth Elements from Ion Adsorption Clays

摘要

The extraction of rare earth elements (REEs) from ion adsorption clays (IACs) provides for around 30 % of the World's REE supply and many deposits of such clays exist outside of China. The REEs are extracted through conventional ion-exchange lixiviants such as (NH4)2SO4 and NaCl (through artificial sea water) in percolation type processes. Due to the significant environmental impact experienced through artisanal mining of such deposits, technically more rigorous approaches are sought. An in-situ leaching approach envisages injecting leach solutions into clay deposits and draining solution from REE deposits through a series of narrowly spaced wells.The present study investigates the desorption-diffusion and transport behaviour of REE removal likely to be experienced in this process. Ion-exchange reagent selection is tested through batch leach and diffusion tests using clay beds as well as column leach studies. The results of this study shows that if sufficient channels for solution percolation through the clay bed can be created, significant but slow extraction of REE from the deposit is possible. A mixture of sea water with (NH4)2SO4 appears to facilitate the preferential leaching of the heavy REEs due to complex ion-exchange and pore transport interactions.