Improvement of zeolites on solidification/stabilization of mercury-contaminated wastes in chemically bonded phosphate ceramics: Stabilization effect and mechanism study

Abstract

In this study, two kinds of zeolites materials [natural zeolite (NZ) and thiol-functionalized zeolite] were added to the chemically bonded phosphate ceramics (CBPCs) processes for the stabilization/solidification (S/S) of mercury-contaminated hazardous wastes. The stabilization effect of the process and the stabilization mechanism are investigated in detail. Strong promotion effects of zeolites on the stability of mercury in the hazardous wastes were obtained, and the technology showed great advantages toward traditional Portland cement process. Not only high stabilization efficiency is obtained but also lower dosage of solidification and stabilization agents were used compared with Portland cement process. Treated by thiol-functionalized zeolite (TFZ) and CBPC under optimum parameters, the waste containing 1500 mg Hg/kg could successfully pass the Toxicity Characteristic Leaching Procedure (TCLP) test. The S/S technology using NZ and CBPC could effectively reduce the mercury waste containing 625 mg Hg/kg pass the TCLP limit. The functions of NZ for reinforcing S/S of Hg-containing CBPC matrixes could be assumed as physical filling by fine zeolites particles and microencapsulation by cementing gel formed by zeolites and phosphate; while for CBPC and TFZ processes, the reaction of SH with Hg to form HgS may play a major role in the stabilization of mercury.