Immobilization of Hexavalent Chromium in Aqueous Solution through the Formation of 3CaO ・ (Al,Fe)_2O_3・ Ca(OH)_2/ xH_2O Phase, Ettringite and C-S-H Gel

概要

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The immobilization of hexavalent chromium in aqueous solution is found to occur through the formationof Cr6+ -bearing AFm phase, ettringite and C–S–H gel, which are formed by calcium aluminate or ferrite, a mixture of lime and Al2(SO4)3 or Fe2(SO4)3, and calcium silicate, respectively. In the case of AFm phase, which is most effective one to the immobilization of Cr6+, the Cr6+ concentration in aqueous solution decreases from initial 50 ppm to below 0.05 ppm. The Cr6+ -containing AFm phases identified are 3CaO·Al2O3·Ca[(OH)2, CrO4]·18H2O, 3CaO·(Al, Fe)2O3·Ca[(OH)2, CrO4]·18H2O, 3CaO·Fe2O3·Ca(CO3, CrO4)·12H2O and 3CaO·Al2O3·CaCrO4·12H2O. The immobilization occurs through the OH- or CO32− site substitution with CrO42−. No significant amount of Cr6+ is identified in either ettringite phase or C–S–H gel, indicating that these two phases do not play an important role for the immobilization of Cr6+ in cement-based solidification/stabilization process. The immobilization takes place by the substitution of SO42− site in the case of ettringite, while in the case of C–S–H gel the sorption mechanism is more possible.
社団法人日本鉄鋼協会の論文
2002-02-15