Efficient recovery of rare Earth elements and cadmium from El-Missikat Fluorite-bearing Granite, Eastern Desert, Egypt

Abstract

This study presents an optimized hydrometallurgical process for recovering Rare Earth Elements (REEs) and Cadmium (Cd) from El-Missikat fluorite-bearing granite ore (0.68% REEs, 0.045% Cd). The extraction process involved two consecutive thermal treatment stages designed to maximize recovery of REEs and Cd from El-Missikat fluorite-bearing ore. In the initial fluorine deactivation stage, finely ground ore (-150 mesh) was thermally treated with MgO under controlled conditions, with systematic investigation of critical parameters including mixing ratio, roasting temperature, and reaction duration. This was followed by a secondary sulfation roasting stage where the deactivated matrix was mixed with (NH₄)₂SO₄ and roasted, with careful optimization of salt ratio, temperature profile, and residence time. Subsequent leaching of the optimally roasted product with hot distilled water (80–90 °C, solid-to-liquid ratio 1:2) demonstrated excellent retention of valuable elements, recovering approximately 92% of initial REEs content and 95% of original Cd content in the aqueous sulfate solution. The recovery process achieved exceptional separation efficiency, with no less than 98% of REEs precipitated as oxalates using 2 g/L oxalic acid, while quantitative recovery (100%) of Cd was obtained as sulfide using 10 g/L Na₂S through precise pH adjustment. Comprehensive characterization of the final products by EDS analysis confirmed both the phase purity of the REE oxalate precipitate and the composition of the CdS product, validating the effectiveness of the sequential thermal and precipitation processes for element recovery.