Abstract:Physicochemical and mineralogical characteristics of an alkali leaching residue of wolframite were studied by XRD, SEM-EDS, chemical phase analysis, mineral liberation analyzer (MLA), and TG-DSC methods. Batch leaching tests, toxicity characteristic leaching procedure (TCLP) tests and Chinese standard leaching tests (CSLT) were conducted to determine the environmental mobility of toxic elements. The results show that, due to the high contents of W, Fe, Mn, Sn, and Nb, the residue is with high resource value, but the content of a toxic element, As, is also high. The existing minerals of the investigated elements mainly occur as monomer particles, but it is difficult to extract these valuable metals by conventional acid leaching due to their mineral properties. The release of As increases over time in acidic environment. The leaching concentration of all investigated harmful elements through TCLP is within the limiting value, while the leaching concentration of As through CSLT exceeds the limiting value by more than 4 times, so the residue is classified as hazardous solid waste based on the Chinese standard. A process for valuable metals recovery from this residue was proposed. Preliminary experimental results indicated that the main valuable metals could be extracted effectively.

Key words: alkali leaching residue; physicochemical characteristics; environmental characteristics; valuable metals recovery