Simultaneous Reduction and Immobilization of Cr2O72- in Metakaolinite-Based Geopolymer Complexed Reductant

Reduction and immobilization of Cr (VI) as Cr2O72- is investigated by using metakaolinite-based geopolymer complexed reductant. Without reductants, the leached Cr concentration from metakaolinite-based geopolymer containing Cr (VI) is very high. Adding reductants as FeCl2·4H2O, FeSO4·7H2O, and Na2S·9H2O respectively during geopolymerization, the leached Cr concentration is below 5 mg L-1 with high Cr immobilization rate above 99 %. By comparison with the immobilization of Cr (III), the added reductants reduced Cr (VI) to Cr (III) which can be locked successfully in the amorphous structure of geopolymer. Meanwhile, Cr (VI) initial concentration is lower than 0.7 wt. % in metakaolinite-based geopolymer, the above reductants can all meet the requirements. While for Cr (VI) initial concentration larger than 0.7 wt. %, Na2S·9H2O is more appropriate. Such a simultaneous reduction and immoboilization process enables the feasibility of using metakaolinite-based geopolymer complexed reductant to implement a one-step procedure for chromite ore processing residue cleanup.