Sustainable extraction of tungsten from the acid digestion product of tungsten concentrate by leaching-solvent extraction together with raffinate recycling
2022
Chen, Yuanlin | Huo, Guangsheng | Guo, Xueyi | Wang, Qinmeng
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.
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