A novel method for the sequential removal and separation of multiple heavy metals from wastewater.

A novel method was developed and applied for the treatment of simulated wastewater containing multiple heavy metals. A sorbent of ZnS nanocrystals (NCs) was synthesized and showed extraordinary performance for the removal of Hg2+, Cu2+, Pb2+ and Cd2+. The removal efficiencies of Hg2+, Cu2+, Pb2+ and Cd2+ were 99.9%, 99.9%, 90.8% and 66.3%, respectively. Meanwhile, it was determined that solubility product (Ksp) of heavy metal sulfides was closely related to adsorption selectivity of various heavy metals on the sorbent. The removal efficiency of Hg2+ was higher than that of Cd2+, while the Ksp of HgS was lower than that of CdS. It indicated that preferential adsorption of heavy metals occurred when the Ksp of the heavy metal sulfide was lower. In addition, the differences in the Ksp of heavy metal sulfides allowed for the exchange of heavy metals, indicating the potential application for the sequential removal and separation of heavy metals from wastewater. According to the cumulative adsorption experimental results, multiple heavy metals were sequentially adsorbed and separated from the simulated wastewater in the order of the Ksp of their sulfides. This method holds the promise of sequentially removing and separating multiple heavy metals from wastewater.