Assessment of Stabilization/Solidification for Residue and Water Treatment Sludge from Extraction Process of Rare Earth Elements

Abstract

For residue and water treatment sludge from extraction process of rare earth elements in China, addition of stabilizing/solidifying agents was evaluated by Toxicity Characteristic Leaching Procedure (TCLP). Coal mine drainage sludge mixed at 10% ratio removed 76% and 67% of As and Se, respectively, from the sludge. Ferrous sulfate mixed at 2% ratio removed 99% of Ba. Bone char mixed at 10% ratio removed 82%, 86% and 92% of Be, Ba and Pb, respectively, possibly because of its micro-structure. Be, Pb, and Th were reduced to <0.08 mg/L at a cement amendment ratio of 10%. As and Se decreased by 98.0~99.9% and 54.7~98.6%, respectively, after amendment of cement at mixing ratios of ≥20%, suggesting formation of Ca-As and Ca-Se complex. However, Se increased at pH>10.5, indicating increase of mobility.