Recovering element sulfur from sulfur-containing waste through a pressure induced melting-crystallization method: Optimization using response surface methodology

Metallurgical sulfur-containing wastes (MSCWs) is an important secondary resource for recovering element sulfur in chemical and metallurgical industries. However, it is challenging to simultaneously achieve high recovery rate and sulfur purity, due to the multiple impurities combining with sulfur in these wastes. In this paper, we developed a novel method of pressure induced melting-crystallization to efficiently recover sulfur from MSCWs. The effects of condition parameters on the sulfur recovery rate and purity were optimized through response surface methodology. The single objective optimization results showed that the interaction between melting temperature and slurry concentration had a great influence on sulfur purity. The slurry concentration and pressure had great influence on sulfur recovery rate. The results of multi-objective optimization showed that under the conditions of pressure 1.2 MPa, slurry concentration 14.9% and melting temperature 140.9℃, the highest sulfur purity and recovery rate could reach 93.0% and 89.1% respectively. Mechanism investigation revealed that the high efficiency of sulfur recovery was ascribed to recrystallization of molten sulfur under the combined action of pressure and water, forming dense sulfur blocks and separating hydrophilic impurities. This work provides a new way to recover sulfur resources from MSCWs with sulfur content higher than 50%.