A New Concept for Producing White Phosphorus: Electrolysis of Dissolved Phosphate in Molten Chloride

• Published in: ACS sustainable chemistry & engineering Vol. 8; no. 36; pp. 13784 - 13792
• Main Authors: Yang, Xiao, Nohira, Toshiyuki
• Format: Journal Article
• Language: English
• Published: American Chemical Society 14.09.2020
• Subjects: Phosphorus; Calcium phosphate; Electrolysis; Clean production; Calcium chloride
• ISSN: 2168-0485; 2168-0485
• DOI: 10.1021/acssuschemeng.0c04796

Producing white phosphorus exclusively by carbothermic reduction of phosphate rock is extremely energy-intensive and environmentally unfriendly. As for now, the phosphorus-making industry worldwide is thus disappearing, while the market demand for white phosphorus, spurred by fine chemicals and high-tech devices, is increasing. Technical defects have posed challenges to the downstream sectors relying on phosphorus-derived chemicals. This work presents a new concept for producing white phosphorus by electrolysis. Phosphate dissolved in a solvent can be electrochemically converted to elemental phosphorus. The concept was demonstrated by conducting experiments in the molten salt system of CaCl2-Ca3(PO4)2. Ca3(PO4)2 dissolves in molten CaCl2 to form a solution containing diffusible and electrochemically reducible phosphate ions. Electrolyzing the molten bath of CaCl2-Ca3(PO4)2 (2 mass %) at a constant potential of −2.48 V (vs Cl2/Cl–) at 850 °C results in continuous evolution of gaseous phosphorus on the cathode. Producing white phosphorus by electrolysis shows substantial advantages over the conventional carbothermic reduction technology in simplicity, energy efficiency, and cleanness. This work may lead to an upgrading of the phosphorus-making industry toward a cleaner and more sustainable production.