Selective recovery of high-grade rare earth, Al, and Co-Mn from acid mine drainage treatment sludge material

Rare earth elements (REEs) and critical elements (CEs) have been in the spotlight recently due to their vital role in high-tech applications and green energy initiatives. Due to the scarcity of mineral resources for the majority of these elements, there has been significant interest in the recovery of these elements from secondary resources. Among the secondary resources, acid mine drainage (AMD) and associated sludge materials have been found to be viable sources of multiple critical elements, including REEs, Al, Co, and Mn. AMD and sludge samples from 3 AMD treatment sites in Pennsylvania were characterized for elemental content and contained value evaluation. A novel purification process based on a previously developed 3-stage AMD treatment process was designed to recover high-grade Al, REE, Co, and Mn products from the sludge materials through aqueous processing with multiple cleaner steps and precise control of the process parameters. The final products of the three stages of this purification process are boehmite and dawsonite in Stage I, adamsite-(REE) in Stage II, and cobalt oxide and ramsdellite in Stage III. Recoveries of > 99 % for the target elements were achieved with the design of a recycling load. Through the proposed purification process, 92.8 % aluminum minerals in Stage I, 88.5 % mixed-REE-carbonate in Stage II, 68 % ramsdellite, and 6.9 % cobalt oxide in Stage III were produced.