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

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 (NH 4 ) 2 WO 4 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 Na 2 CO 3 , and the leaching efficiency was 99.47% with circulation of Na 2 CO 3 solution converted from the raffinate of solvent extraction. The tungsten in pure Na 2 WO 4 solution with 121.26 g/L WO 3 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 NH 3 ·H 2 O with stripping efficiency of 99.98%, obtaining (NH 4 ) 2 WO 4 solutions with WO 3 concentration above 260 g/L and low impurity content. The raffinate containing high Na 2 SO 4 concentration was converted to Na 2 CO 3 solution by adding BaCO 3 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 (NH 4 ) 2 WO 4 solution from acid digestion product of tungsten concentrates. • Tungsten was extracted from crude tungstic acid by leaching-extraction with raffinate recycling. • The leaching efficiency of tungsten from crude tungstic acid with Na 2 CO 3 was 99.6%. • The tungsten in Na 2 WO 4 solution could be almost completely extracted in one stage. • The saturated loading capacity for WO 3 of Alamine 308 was higher than that of N235. • The raffinate was converted to Na 2 CO 3 solution and recycled for the leaching process.