Detoxification and solidification of heavy metal of chromium using fly ash-based geopolymer with chemical agents

Geopolymers are new cementitious materials that with 3 dimensional networks, which can effectively solidify/stabilize heavy metals. Utilization of fly ash as precursor to prepare geopolymers, and influences of dosages and chemical valences of chromium reagents on geopolymers, as well as detoxification effectiveness of chemical agents for geopolymers were studied. The results showed that compressive strength of geopolymers could be improved when dosage of Cr(NO3)3 is small. Reinhardbraunsite (Ca5(SiO4)2(OH)2) was generated in geopolymers with Cr(NO3)3 or CrO3 due to 'ions exchange'. Respectively dosing Cr2O3, Cr and CrO3 could make total pore volume of geopolymers smaller and make geopolymers more compact. Chemical bonding and physical encapsulation both existed in geopolymers. Chemical bonding played main role in geopolymers with Cr(NO3)3, and physical encapsulation played main role in geopolymers with Cr2O3, Cr and CrO3, respectively. Chemical agent DTCR could effectively improve compressive strength and capture Cr3+ of geopolymers, enhancing their abilities of anti-erosion.