Geopolymers produced from drinking water treatment residue and bottom ash for the immobilization of heavy metals.

Drinking water treatment residue (DWTR) and municipal waste incineration bottom ash (BA) have been traditionally considered as solid waste. With the development of urbanization, their subsequent treatment and resource regeneration need to be further researched. In this work, a composite geopolymer with BA and DWTR was successfully synthesized and applied in the immobilization of Cd, Pb and Zn. The analysis of the geopolymers with different ratios of BA and DWTR, curing times and heavy metals was performed through chemical analysis, SEM, FTIR, XRD, XPS, ICP-AES and compressive strength tests. The results show that the geopolymer samples based on BA and DWTR (BWG) presented higher compressive strength than the samples with single BA material. The sample with 20% DWTR and 80% BA (BWG20) possesses the highest compressive strength (24.10 MPa) among the materials ratios. Furthermore, the microstructure and characterization results indicate that the geopolymer matrix was successfully formed in BWG and was significantly changed by the ratio, curing time and addition of heavy metals. The immobilization efficiency for different categories and dosages of heavy metals by BWG20 were all higher than 99.43%. Moreover, the XPS results demonstrate that the heavy metals were immobilized in geopolymer mainly by divalent state forms.