Property and Mechanism of Immobilization of Cd(II) in Fly Ash Based Geopolymers
Due to their special three-dimensional structure, geopolymers have a good effect in immobilizing heavy metal ions. At present, there is very little research that heavy metal ion[Cd(II)] are immobilized by fly ash geopolymers. Therefore, in this study, with the addition amounts of Cd(II) 1, 1.5, 2, 3, 4 and 5 wt%, respectively added into fly ash geopolymers, the immobilization effect of Cd(II) was tested and the immobilization mechanism was analyzed. The immobilization results were explained by XRD, SEM-EDS, compressive strength and leaching. It was found that fly ash geopolymers were effective for immobilizing Cd(II). Cd(II) (1 wt%) is beneficial to improve the compressive strength of geopolymers, reached 38.55 MPa at 7d. But the compressive strength of samples after more than 1 wt% [Cd(II)] is reduced. According to results of XRD, SEM-EDS and leaching, Cd(II) is considered to balance the negative charge of tetrahedral[AlO4] in geopolymer frameworks. The more Cd(II) immobilized in the geopolymers, the more exchangeable ions (Na or Ca) is replaced during this work. The leaching shows that the Cd(II) is highly immobilized, and the immobilize rate of Cd(II) can reach 99%.
KeywordsFly ash Geopolymers Immobilization Cd(II)
Thanks to the support of the National International Science and Technology Cooperation Base (2015D01016) and China EU International Cooperation Project (SQ2013ZOG300003).
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