Unraveling Fluorapatite Dissolution in Molten CaCl2 for Sustainable Phosphorus Extraction

High-purity white phosphorus can be produced by dissolving phosphate rock in molten CaCl 2 and subsequently electrolyzing phosphate ions in the melt. This method is anticipated to address the technical challenges associated with the conventional carbothermal process, including high energy consumption, significant pollution, and low product purity. This paper systematically investigated the dissolution mechanism of fluorapatite [Ca 5 (PO 4 ) 3 F, the principal phase in phosphate rock] in molten CaCl 2 , as well as the influence of fluorine ions on the dissolution and electrolysis processes. The findings revealed that the solubility of Ca 5 (PO 4 ) 3 F in molten CaCl 2 increased with temperature, and the dissolution process was endothermic, with a standard dissolution enthalpy of 73755.9   J   mol⁻¹ K⁻¹ over a temperature range of 1073   K to 1273   K. The diffusion of phosphate ions in the melt significantly influenced the dissolution rate, which can be enhanced through improved mass transfer. During the dissolution process, Ca 5 (PO 4 ) 3 F initially dissociated into Ca 5 (PO 4 ) 3 Cl and CaF 2 , followed by the transformation of Ca 5 (PO 4 ) 3 Cl into Ca 2 PO 4 Cl. The presence of CaF 2 increased the solubility of phosphorus, slightly reduced the dissolution rate, and had minimal impact on the electrochemical reduction of phosphate ions. High-purity white phosphorus was successfully prepared through electrolysis in a molten CaCl 2 -CaF 2 dissolving phosphate rock, demonstrating superior quality compared to industrial-grade phosphorus products. These results provide a comprehensive understanding of the electrochemical preparation of white phosphorus and highlight its potential for promoting the green and sustainable development of the phosphorus chemical industry.