A novel process for recovery of scandium, rare earth and niobium from Bayan Obo tailings: NaCl-Ca(OH)2-coal roasting and acid leaching

Abstract

Bayan Obo tailings from Baotou Steel were discharged into tailings pond. The advantages of symbiotic resources have not been fully played. A large number of accumulated tailings also have a great impact on the surrounding environment. Comprehensive utilization of valuable elements in tailings becomes key measure to solve the above problems. Extraction of valuable elements, such as scandium, rare earth and niobium could be achieved by roasting Bayan Obo tailings in NaCl-Ca(OH)2-coal, followed by hydrochloric acid and sulfuric acid leaching. The phase transitions of main minerals were investigated. In the roasting process, niobium minerals were converted to CaTiO3-type compounds. The original rare earth minerals turned into rare earth oxide or rare earth silicate. Iron in Sc-Fe-bearing silicate migrated to CaFeSiO4, FeSiO3 and Fe3O4. Meanwhile, the structure of silicate was destroyed completely, which facilitated for leaching scandium. In the acid leaching process, newly generated niobium minerals were dissolved in sulfuric acid as niobium sulfate or niobic acid. For Bayan Obo tailings, under the optimal roasting and leaching conditions determined in this research, 97.6% Sc2O3, 97.18% REO and 40.1% Nb2O5 entered hydrochloric acid. 51.67% Nb2O5 was leached by concentrated sulfuric acid. Sc2O3 and REO were enriched in hydrochloric acid.