Highly efficient and irreversible removal of cadmium through the formation of a solid solution

Abstract

Sulfur-containing materials are very attractive for the efficient decontamination of some heavy metals. However, the effective and irreversible removal of Cd²⁺, coupled with a high uptake efficiency, remains a great challenge due to the relatively low bond dissociation energy of CdS. Herein, we propose a new strategy to overcome this challenge, by the incorporation of Cd²⁺ into a stable Zn_xCd_1-xS solid solution, rather than into CdS. This can be realised through the adsorption of Cd²⁺ by ZnS nanoparticles, which have exhibited a Cd²⁺ uptake capacity of approximate 400 mg g^-1. Through this adsorption mechanism, the Cd²⁺ concentration in a contaminated solution could effectively be reduced from 50 ppb to <3 ppb, a WHO limit acceptable for drinking water. In addition, ZnS continued to exhibit this noteworthy uptake capacity even in the presence of Cu²⁺, Pb²⁺, and Hg²⁺. ZnS displayed high chemical stability. Particles aged in air for 3 months still retained a> 80% uptake capacity for Cd²⁺, compared with only 9% uptake capacity for similarly-aged FeS particles. This work reveals a new mechanism for Cd²⁺ removal with ZnS and establishes a valuable starting point for further studies into the formation of solid solutions for hazardous heavy metal removal applications.

Keywords: Environmental remediation; Heavy metal; Metal sulfides; Solid solution.