Stabilization/solidification of heavy metals in kaolin/zeolite based geopolymers

Abstract The present work investigated the efficiency and mechanism of immobilization of Pb(II), Cu(II), Cd(II) and Cr(III) metal solutions in kaolin/zeolite based geopolymers. Leaching of heavy metals from the geopolymeric matrix into different aggressive solutions was studied by measuring the amount of metal, pH and conductivity of leachates. The effect of heavy metal concentrations, pressing pressure that employed through preparing geopolymer, and aging time on the geopolymer resistance toward leaching was also studied. The mechanical strength, XRD, XRF and SEM of geopolymers containing heavy metals were investigated. The results indicated that heavy metals could be effectively immobilized in kaolin/zeolite based geopolymers with a release of safe metal ions like Na⁺ and K⁺. The immobilization of heavy metals in geopolymer may be due to participation of heavy metal cations in the balance of the negative charge of Al in the frameworks of unreacted zeolite, kaolin and geopolymer phases. Immobilization using kaolin-based geopolymers has lower cost than metakaolin-based geopolymers. The kaoline-based geopolymerization process is of much lower energy cost than metakaolin-based one.