Extracting White Phosphorus from AlPO4 through Molten Salt Processing

The authors focus on the development of a molten salt processing technology for extracting white phosphorus (P4) from sewage sludge ash, which is recognized as a potential secondary P source due to its composition of various metal phosphates. This work offers insights into the interaction between solid AlPO4 and molten CaCl2. The results show that solid AlPO4 exhibits favorable solubility in molten CaCl2, although at a slower rate compared to solid Ca3(PO4)2 due to the presence of stable Al–O bonds. The study also demonstrates the feasibility of extracting high-purity P4 from the molten mixture through electrolysis. The purity of the obtained electrolyzed P4 from AlPO4 is comparable to the commercially available high-purity-grade product. These findings underscore the potential of sewage sludge ash containing AlPO4 as a viable source for extracting high-purity P4. This research contributes to the advancement of sustainable P utilization technologies from secondary sources.