The extraction of Ta, Nb and rare earths from fergusonite by using KOH sub-molten salt leaching

Abstract

It is very important to efficiently extract Ta, Nb and rare earths from polymetallic ore such as fergusonite. A new method combining an alkaline leaching of sub-molten salt (SMS) and an acid leaching is recommended for extracting Ta, Nb and rare earths from fergusonite concentrate using an environmentally friendly process.The leaching yields of Ta and Nb from the concentrate reached to 98% and 99%, respectively under the most suitable KOH SMS leaching conditions, KOH concentration 80 wt%, leaching temperature 300C, KOH to concentrate mass ratio 3, stirring speed 800 rpm, leaching time 1 h. The overall recovery of Ta and Nb were 96% and 97%, respectively, and the total content of Ta and Nb in the crude Ta-Nb product was 98.6% (45.1%-Ta2O5, 53.5%-Nb2O5) when the solid to liquid mass ratio in the diluting stage was 1:2 and KOH concentration in the evaporating concentration stage was 30 wt%. The recovery yield of rare earths (96.5%-RE2O3) reached to 92% when the KOH SMS leach residue was leached with 15 wt% HCl solution.