Leaching of Rare Earth Elements from Gibbsite-bearing Shale of Southwestern Sinai, Egypt using Ammonium Sulfate via Ion Exchange Mechanism

Gibbsite-bearing shale ore, South Western Sinai, Egypt has been identified as containing physically adsorbed rare earth elements (REEs). The investigated material mainly contains an average rare earth elements (REEs) concentration of 6350 ppm. In spite of low grade compared to other rare earth elements (REEs) sources, the low mining cost and the ease of exploitation make it a promising source of rare earth elements (REEs). In this study, experiments were conducted to investigate desorption of rare earth elements (REEs) via ion-exchange mechanism using monovalent electrolyte solution of ammonium sulfate. All laboratory experiments were conducted at ambient temperature by using a batch leaching technique. The impact process factors that affect the leaching of rare earth elements (REEs) such as the ionic strength of (NH4)2SO4, the solution's pH, liquid/solid (L/S) ratio and the reaction contact time have been optimized. Rare earth elements (REEs) maximum leaching efficiency of 93.8% was achieved with combination of 0.5 M (NH4)2SO4, 30 minutes contact time, L/S ratio of 3:1 at pH 5. The selectivity of REEs has been enhanced and improved as a result of the fast-leaching rate and the ease of the ion exchange process. The simplicity with which REEs can be desorbed from gibbsite surface by ion exchange is due to that the rare earth cations are more hydrated than NH4+ monovalent cation which results in attachment of NH4+ to gibbsite surface and desorption of rare earth cations to the liquid phase.