Sustainable extraction of tungsten from the acid digestion product of tungsten concentrate by leaching-solvent extraction together with raffinate recycling

Abstract

Acid digestion of tungsten concentrates has attracted more and more attention in recent years, sustainable extraction of tungsten from acid digestion product of tungsten concentrates to obtain (NH4)2WO4 solution with low impurity content is the key for ammonium paratungstate production. In this work, a process of extracting tungsten from acid digestion product by leaching-solvent extraction together with raffinate circulation was introduced. The acid digestion product was firstly leached by Na2CO3, and the leaching efficiency was 99.47% with circulation of Na2CO3 solution converted from the raffinate of solvent extraction. The tungsten in pure Na2WO4 solution with 121.26 g/L WO3 could be almost completely extracted by solvents containing 15% N235 or 15% Alamine 308 in one stage. The extraction mechanism of N235 and Alamine 308 was the same, while Alamine 308 showed better performance and higher saturated loading capacities for tungsten extraction. The loaded tungsten was stripped from organic phases using NH3·H2O with stripping efficiency of 99.98%, obtaining (NH4)2WO4 solutions with WO3 concentration above 260 g/L and low impurity content. The raffinate containing high Na2SO4 concentration was converted to Na2CO3 solution by adding BaCO3 and recycled for the leaching of digestion product, which could significantly reduce the discharge of sodium salt wastewater. The presented work provides a cleaner production route for preparing pure (NH4)2WO4 solution from acid digestion product of tungsten concentrates.