Enrichment of Niobium and Titanium from Kaolin Using an Acid–Alkali Leaching Process

Niobium is a strategic resource because it is useful in a wide number of applications and its global distribution is uneven. It has been reported that kaolin clay from the bottom of the Xuanwei Formation, the Late Permian sequences in southwest China, contains Nb. In this paper, the major, trace, and mineral compositions of kaolin clay were characterized using XRF, ICP-MS, and XRD. The results show that it is mainly composed of kaolinite, anatase, and rutile, with a chemical composition of Al₂O₃ 34.38 pct, SiO₂ 39.97 pct, TiO₂ 8.79 pct, Fe₂O₃ 3.24 pct, and Nb 491 μg/g. A process including calcination treatment and acid–alkali leaching with HCl and NaOH was employed to separate Al, Fe, and Si in a leaching solution and to enrich Nb and Ti in the residue. The experimental results indicated that the reaction temperature played a vital role for Al and Fe extractions from acid leaching, while the concentration of alkali was the key factor for Si extraction. Under the optimal conditions, the contents of Nb and Ti in the final product were 4280 μg/g and 80.5 pct, respectively.