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 (K_sp) 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 K_sp of HgS was lower than that of CdS. It indicated that preferential adsorption of heavy metals occurred when the K_sp of the heavy metal sulfide was lower. In addition, the differences in the K_sp 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 K_sp of their sulfides. This method holds the promise of sequentially removing and separating multiple heavy metals from wastewater.