Sustainable Extraction and Complete Separation of Tungsten from Ammonium Molybdate Solution by Primary Amine N1923

• Published in: ACS sustainable chemistry & engineering 2020-05, Vol.8 (18), p.6914-6923
• Main Authors: Li, Zhihua, Lu, Jin, Wu, Shengxi, Zhang, Guiqing, Guan, Wenjuan, Zeng, Li, Li, Qinggang, Cao, Zuoying
• Format: Article
• Language: English
• ISSN: 2168-0485; 2168-0485
• DOI: 10.1021/acssuschemeng.9b06383

Complete separation of tungsten from molybdenum has long been a technical bottleneck in the metallurgy of molybdenum because no theoretical basis exists for the complexation and extraction mechanism of tungsten and molybdenum from aqueous solution. To completely separate tungsten from ammonium molybdate, the speciation and equilibria of compounds in H+–WO4 2–, H+–MoO4 2–, and H+–MoO4 2––WO4 2– aqueous systems were systematically investigated. With decreasing pH, the stability of polymerized tungsten species in H+–MoO4 2––WO4 2– decreased in the following order: MoW6O24 6– > Mo2W5O24 6– > Mo3W4O24 6– > Mo4W3O24 6– > Mo5W2O24 6– > Mo6WO24 6–, and as the W­(VI) concentration decreased, low-molecular-weight species increasingly dominated the W­(VI) and Mo­(VI) polymerization products. The extraction characteristics of tungsten and molybdenum with primary N1923 were consistent with their polymerization behaviors. Methods based on the thermodynamic theory and the aforementioned extraction mechanism were used to completely separate W­(VI) from ammonium molybdate solution containing different grades of W­(VI) (trace to macro). Ammonium molybdate solution with a 2.25 × 10–7 W/Mo mass ratio met the purity requirement for ultra-high-purity ammonium molybdate (99.999%, 5N) and further molybdenum products. During extraction, the equilibrium pH was controlled by extractant acidification using inexpensive mineral acids. The proposed process is cheap and sustainable and has a broad spectrum and high efficiency; these advantages are expected to provide economic and environmental benefits.