Step-Leaching and Pre-Enrichment of Light and Heavy REEs from Kaolinite and Montmorillonite

Abstract

Kaolinite (Kao) and montmorillonite (Mt) are the primary minerals present in ion-adsorption rare earth ores. Better understanding the adsorption/desorption characteristic for light and heavy rare earth elements (REEs) of Kao and Mt will be beneficial for the step-leaching and pre-enrichment of light and heavy REEs from ion-adsorption REE ores. The experiments show that the more negative ζ potential and the larger specific surface area of Mt contribute to the higher adsorption capacity of REEs. The stability of REEs onto Kao and Mt increases with the increase in adsorption pH. There are obvious differences in the desorption characteristic among Nd3+, Eu3+, and Lu3+ due to the different adsorption mechanisms. Lu3+ almost adsorbed on Kao through electrostatic force, and its recovery is 88% when the desorption pH was higher than 4; however, the recoveries were only 50% for Nd3+ and 56% for Eu3+, which interact with the Kao surface dominated by coordination bonds. However, the opposite desorption characteristic occurred on Mt. Based on these different desorption characteristics of light and heavy REEs, step-desorption and pre-enrichment for Nd3+ and Lu3+ from Kao and Mt were feasible. In the first lixivium of Kao, the percentage of Lu3+ is high, up to 68.4%, and Nd3+ is enriched in the second lixivium, with a percentage of 73.9%. As for Mt, Lu3+ is difficult to be desorbed and enriched in the second lixivium with a percentage of 87.7%.