Recovery of technologically critical lanthanides from ion adsorption soils

Abstract

Rare earth elements (REEs) are in increasing demand due to rapidly rising use in consumer technology, the automotive industry and in renewable energy generation systems, amongst other technology sectors. Ion-adsorption type REE ore deposits are currently being exploited in China’s southern provinces and there is increasing interest in identifying potential reserves globally. Here we investigated the extraction of REEs from an ion-adsorption clay sampled at a surficial deposit in Madagascar. Using a 1 M NH4Cl lixiviant salt solution, chosen based on experimental evidence to maximise REE extraction, minimises undesirable dissolved Al in eluate. Lower Al concentration in solution reduces its interference with NH4+ in oxalate precipitation of REEs in the extraction process. We show that NH4Cl solutions can be used to efficiently extract REE with relatively low lixivient volumes in a through-flow column system. We show that when extraction with a pulse of lixiviant is followed by a rinsing step, there are several identifiable stages during the extraction process, including a marked increase in total lanthanides extracted, which is correlated with the breakthrough of ammonium ions, and where the eluted dissolved Al concentration decreases from its peak concentration.