Unveiling the hidden culprit: salinity inhibition on phosphorus recovery from high-salt wastewater via vivianite crystallization.

Food pickling wastewater, a representative high-salinity effluent from the food processing industry, is rich in phosphorus and therefore represents a promising resource for phosphorus recovery. However, elevated salinity substantially reduces both the efficiency of phosphorus recovery and the quality of the recovered product, while the underlying mechanisms remain poorly understood. In this study, the effects of salinity on phosphorus recovery via vivianite crystallization were systematically investigated. Phosphorus recovery efficiency decreased significantly with increasing salinity, from 95.66 % at 0 % salinity to 79.97 % at 12 % salinity. Higher salinity also progressively inhibited vivianite crystal growth, leading to smaller crystals and poorer product quality. Mechanistic analysis revealed that this inhibition is governed by two primary factors: (i) the formation of an ionic atmosphere, which reduces the effective activity and mobility of crystal-forming ions, and (ii) the development of a Na+ blocking layer, where competitive adsorption of Na+ onto surface PO43- groups sterically hinders the incorporation of PO43- and Fe2+ into the growing crystal lattice. Theoretical calculations further supported these mechanisms. These findings provide new insights into salinity-induced constraints on vivianite crystallization and offer a scientific basis for optimizing phosphorus recovery from high-salinity wastewaters.