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Towards zero-consumption of acid and alkali recycling rare earths from scraps: A precipitation-stripping-saponification extraction strategy using CYANEX®572
- Li, Fujian, Wang, Yanliang, Su, Xiang, Sun, Xiaoqi
- Journal of cleaner production 2019 v.228 pp. 692-702
- acidity, ammonium, chemical precipitation, environmental impact, fluorides, industry, powders, rare earth elements, recycling, risk, saponification, thermodynamics, waste treatment, wastewater
- Recycling schemes from rare-earth-containing scraps have been developed rapidly due to the increasing supply risk for rare-earth elements (REEs). This article aimed to reduce the ecological impact and reagent costs for separating and recycling REEs from scraps, i.e., spent ceria-based polishing powders and lutetium-based crystal waste. A simultaneous process was proposed using an industrial extractant Cyanex®572, which allowed efficient recycling of REEs from the wastes with less acid and alkali consumption than traditional hydrometallurgy process. Based on thermodynamic and kinetic analyses, common acid scrubbing was avoided by employing REEs scrubbing. Additionally, the alkali saponification, acid stripping and oxalic acid precipitation were substituted by one step of precipitation-stripping-saponification with ammonium fluoride which contained abundant F− in the solution with weak acidity. F− was easy to complex with REEs on the extractant as precipitate while NH4+ bonded with anion of the extractant. Using this technique, the vast consumption of chemicals and million tons of wastewater in REEs industry may be avoided. Totally, the chemical consumption could be reduced over 80% and the wastewater was decreased more than 90%. REEs recovery yield also increased considerably using the novel process. Moreover, the ammonium fluoride was designed in containment system and was reused with no emission to the environment. This article provides a sustainable and efficient alternative process to REEs waste treatment industry.