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

Abstract

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.

Electrolytic Synthesis of White Phosphorus is Promoted in Oxide-Deficient Molten Salts

“…We note that this gas leakage is attributed to the poor thermal stability of the perfluoroelastomer O-ring seals em-ployed in our laboratory-scale electrochemical setup; incumbent electrochemical devices (such as solid-oxide electrolyzers) utilize metal, ceramic, and/or glass based seals that are stable to higher temperatures and pressures than those demanded in this process, 33 and thus, we envision that increased gas collection efficiency can be realized with improved engineering of a larger scale reactor. In contrast to legacy and contemporaneous studies of phosphate electrolysis that omit quantitative product analysis, [14][15][16][17][18][19][20][21][22][23][24] our spectroscopic and faradaic efficiency data provide the first numerical evidence that P4 is the predominant cathodic product of metaphosphate electrolysis.…”

“…Modulating the Lux acidity of alternative fluxes such as CaCl2 could additionally serve to promote P4 electrosynthesis across a wide range of reaction media. 24,35 Insights into the mechanism of PRR may be gleaned by analyzing the steady-state current-overpotential (Tafel) behavior of the system. In anhydride-rich pure trimetaphosphate melts (Fig.…”

“…The fundamental insights presented here about the role of Lux acidity in phosphate electroreduction suggest that phosphoryl anhydride moieties may serve to promote phosphate reduction across a wide array of electrolyte compositions. 21,22,24,35,47 Complementarily, the full decarbonization of P4 electrosynthesis (like many industrial electrolyses, including the Hall process) requires the development of stable and efficient oxygen-evolving anodes. Analogous to the promotion of oxygen evolution in alkaline aqueous electrolytes, 48,49 oxygen evolution in molten salts may be promoted by modulating the Lux basicity of the electrolyte, 23 providing a powerful handle for balancing anode and cathode efficiency, selectivity, and durability.…”

Temporal Dynamics and Performance Association of theTetrasphaera-Enriched Microbiome for Enhanced Biological Phosphorus Removal

“…In comparison, the Tetrasphaera -enriched sludge ash showed white color and compact morphology, which resulted from the designed operation process and influent compositions (e.g., MgSO 4 and CaCl 2 ). Theoretically, the Tetrasphaera -enriched sludge ash is attractive to be further used for the white P recovery and promise to replace the depleting phosphate rock, in which Ca 3 (PO 4 ) 2 is the main component 30 . Therefore, three essential conditions to promote the P recovery from wastewater are achieved: i) high P removal efficiency, ii) microbiome with enhanced P storage ability, and iii) P-rich ashes and compounds for further value-added P recovery.…”

“…The pH and DO concentration were monitored using the portable multi-parameter analyzer (HQ40d, Hach, USA). Seven samples were taken at three time points of anaerobic phase (13,45 and 135 min) and four time points of the aerobic phase (30,90,210 and 320 min). The sludge samples were centrifuged at 3000 rpm for 3 mins then the supernatant was collected for further physicochemical analysis.…”