Synthesis and toxic metals (Cd, Pb, and Zn) immobilization properties of drinking water treatment residuals and metakaolin-based geopolymers

Using aluminum/iron-based drinking water treatment residuals (DWTR) to replace metakaolin (MK) in geopolymerization can improve resource utilization from solid waste and reduce the cost of geopolymer preparation. This study researched the preparation feasibility of geopolymer with DWTR and MK and investigated its immobilization performance on toxic heavy metals. Results indicated that a composite geopolymer with higher mechanical strength was successfully prepared with DWTR and MK. The characterization results showed that the microstructure of the geopolymer was more stable with curing time, and the geopolymeric process with suitable proportion can be completed in a shorter time. According to the leaching properties results, the immobilization efficiency of heavy metals was between 97.79 and 99.72%. The immobilization efficiency of Cd was significantly higher than Pb and Zn, and the immobilization mechanism of Cd was different from those of Pb and Zn. This study indicated that the DWTR could be used as a substitute material for MK in geopolymer preparation, which provides a cost-effective method for strength enhancement of geopolymers.