BCR leaching procedure to evaluate the mobilization behaviour of ion adsorption type REE deposit in I-type granite weathering profiles

Abstract

Rare earth elements (REE) with specific application value have become the relatively important strategic resource for all countries. These so called 'technology minerals' are in increasing demand due to rapidly rising use in consumer technology, renewable energy generation systems, automotive industry, and other high technology sectors. In order to provide information on the chemical processes in mobilization behaviour of ion-adsorption type REE, this study investigated the extraction of REE from ion-adsorption clay deposit samples from weathering I-type granite profiles (saprolite horizon) at Maran, Pahang and Mersing, Johor (Eastern Belt of Peninsular Malaysia). Using a 0.5 M ammonium sulfate solution (adjusted at pH = 4), samples were leached in 1 hour through a Bureau of Certified Reference (BCR) leaching using BCR-701 standard, chosen based on experimental evidence to optimize the leachable REE. The Al2O3 concentration (27-31 wt.%) in saprolite horizon indicates depleted (change <0%) in mobile major (alkali and alkaline earth) elements, most conspicuously in the upper parts of the weathering profiles. The total REE concentrations in saprolite samples is between 438 - 453 ppm and experimental results revealed 70% of σREE was leached as ion-adsorption fraction. Saprolite horizon is strongly depleted in Fe and Ti and this depletion in Fe and Ti suggests that REE-bearing minerals containing these elements were broken down and were mobilized in this horizon. Therefore, BCR leaching was proven to be the potential leaching process and could be useful to assess ion-adsorption type REE deposit with low-grade geological resources, especially granite weathering profiles with similar geological settings.