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<p>Direct discharge of treated fluorine-containing wastewater not only escalates costs but also wastes valuable fluorine resources. This study addresses these challenges by synthesizing cryolite (Na₃AlF₆)—a high-value-added material—from alkaline fluoride wastewater generated during low-temperature molten salt treatment of rare earth electrolytic slag. Thermodynamic analysis revealed AlF₆<sup>3</sup>⁻ as the dominant species at pH 5–9, with saturation index (SI) calculations guiding optimal precipitation conditions. Key parameters were optimized as follows: Al/F molar ratio of 1:6, endpoint pH 7, temperature 30&#xa0;℃, stirring time 20 min, and stirring speed 200 rpm. Under these conditions, fluorine and aluminum recovery efficiencies reached 98.82% and 99.62%, respectively. The cryolite product exhibited a uniform morphology with a median particle size of 4.32 μm and complied with the Chinese national standard for common cryolite (GB/T 4291–2017). This approach enables efficient resource utilization of fluorine-rich wastewater while mitigating pressure on fluorite reserves.</p> Graphical Abstract <p></p>

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Synthesis of Cryolite from Alkaline Fluorine-Containing Wastewater Generated from Treated Rare Earth Electrolytic Slag

  • 期刊论文

  • 发表日期：

    2025年10月22日

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  • Delong Yang,
  • Jie Wang,
  • Mingming Yu,
  • Yusufujiang Mubula,
  • Heyue Niu,
  • Lei Wang,
  • Guangjun Mei

摘要

Direct discharge of treated fluorine-containing wastewater not only escalates costs but also wastes valuable fluorine resources. This study addresses these challenges by synthesizing cryolite (Na₃AlF₆)—a high-value-added material—from alkaline fluoride wastewater generated during low-temperature molten salt treatment of rare earth electrolytic slag. Thermodynamic analysis revealed AlF₆3⁻ as the dominant species at pH 5–9, with saturation index (SI) calculations guiding optimal precipitation conditions. Key parameters were optimized as follows: Al/F molar ratio of 1:6, endpoint pH 7, temperature 30 ℃, stirring time 20 min, and stirring speed 200 rpm. Under these conditions, fluorine and aluminum recovery efficiencies reached 98.82% and 99.62%, respectively. The cryolite product exhibited a uniform morphology with a median particle size of 4.32 μm and complied with the Chinese national standard for common cryolite (GB/T 4291–2017). This approach enables efficient resource utilization of fluorine-rich wastewater while mitigating pressure on fluorite reserves.

Graphical Abstract