Removal of organic pollutants and recovery of crystalline salt from ammonium sulfate waste salt by antisolvent crystallization process

The main challenge of industrial waste ammonium salt recycling is the efficient removal of organic pollutants. Conventional pyrolysis process cannot be used due to ammonium salts readily decompose at temperatures well below typical pyrolysis ranges, resulting in nitrogen loss and product alteration. To address this, an efficient antisolvent crystallization (ASC) method is developed for simultaneous organic pollutant removal and salt recovery. The results show that ethanol, as an efficient antisolvent, can achieve a total organic carbon (TOC) removal rate of approximately 96.44 % and a salt recovery rate of 85.07 % when used in a 2:1 vol ratio with the waste salt solution. The optimal operating conditions are a temperature range of 0–30 °C, a pH range of 2–8, and a reaction time of 60 min. Ethanol can be effectively recycled and reused for over seven times while maintaining approximately 93.99 % TOC removal efficiency. Elemental mapping of the waste salt after treatment shows a carbon content as low as 0.3 %, indicating efficient removal of organic pollutants. Compared to the maximum TOC removal rates achieved by pyrolysis(87.43 %) and advanced oxidation(86.17 %) processes, the ASC process demonstrates superior performance with a removal efficiency exceeding 95 % under ambient temperature conditions. Mechanism analysis reveals that adding ethanol to the saturated waste salt solution can induce salt ion recrystallization and release organic pollutants into the solution, thereby achieving efficient separation of salt and organic pollutants. This study provides an environmentally and economically feasible solution for the treatment of ammonium sulfate waste salt.