Recovery Of Rare Earth Elements (Rees) From Coal Mine Drainage Sludge Leachate

Acid mine drainage (AMD) is the primary cause of aquatic habitat loss in the Appalachian Coal Basin and many other mining districts across the U.S. and the world. The objective of this work is to develop a cost-effective and environmentally benign process to treat and recover Rare Earth Elements (REEs) from AMD. Solvent extraction (SX) is one effective way to turn AMD into a commercially viable feedstock for rare earth production. In this work, SX experiments were conducted on Y-Ca-Mg-Al-HDEHP-n-heptane-HNO3-H2O system to simulate AMD treatment for Yttrium recovery by changing four parameters: pH values, concentration ratio of Yttrium (Y) over total major metal ions (Ca, Mg and Al) (Y:CMA ratio), extractant HDEHP concentration in organic solvent n-heptane (C(HDEHP)), volume ratio of organic phase to aqueous phase (O:A ratio). Extraction efficiencies of major metal ions and Y were compared under different conditions. Separation factors of Y over total major metal ions were also analyzed. The most desirable SX conditions for this system were found by numerical optimization. Using waste water with low REE concentrations as feedstock, the separation factor can reach about 3000 under the following conditions: 1) solution pH 2.4, 2) extracting with HDEHP at a concentration of 15 g/L in 3) in n-heptane solvent at 4) O:A ratio of 1.5. Besides work on synthetic solution, bench-scale REEs recovery from different kinds of sludge leachate with different pH values, mid-scale and multi-step SX experiments were performed. The whole process mainly includes solvent extraction, scrub and stripping steps. The estimated TREE percentage in solid phase obtained in one mid-scale experiment (1.25 kg wet sludge from DLM site; solvent extraction: 20 L filtered leachate (pH 3.2) with 30 L organic solution; obtained 2.5 g concentrate solid sample) increased from initial 0.77% in leachate to final 4.63% in the solid. To determine how many steps required for sufficient recovery of REEs and high selectivity of REEs over major metal ions, bench-scale exploratory tests of solvent extraction, scrub and stripping process were conducted to provide a purposeful starting point for the scale-up lab SX system testing. Results of this program were provided as McCabe Thiele diagrams. Optimum parameters and steps needed were obtained for different kinds of leachate in this work. Continuous work following whole flowsheet with optimum parameters was conducted on RS leachate for REEs recovery and separation of heavy and light REEs