Efficiency of stabilization/solidification of heavy metals contained in hydroxide sludge waste into metakaolin based geopolymers

In this work, the S/S of heavy metals contained in hydroxide sludge waste was used into geopolymers. Metakaolin, sludge waste, hydroxide, and sodium silicate were mixed. Amount of waste added varied between 10% and 40% in the synthesis of geopolymers. Geopolymers were cured at 40 degrees C for 24 h. After 7 and 28 days of aging, strength of the geopolymers specimen were studied. Mineralogical phases, morphology and FTIR analysis were used to characterize raw materials and geopolymers. TCLP test was used to determine amount of heavy metals released from S/S materials. Amount of heavy metals released are lower than quantities released from raw waste. Heavy metals were identified, by XRD analysis, within mineralogical phases. Results obtained shows that geopolymers can immobilize heavy metals and reduce their release to the environment. Mechanical strengths of all samples are higher than the lower required for the S/S processes. Best mechanical strength was of 9.29 and 10.02 MPa at 7 and 28 days, respectively. A decrease of mechanical strengths recorded is due to increasing amount of waste added that causes structural discontinuity within the gel during geopolymerization. (c) 2018 American Institute of Chemical Engineers Environ Prog, 38:e13137, 2019