EXAFS Study of Sn(IV) Immobilization by Hardened Cement Paste and Calcium Silicate Hydrates
journal contributionposted on 12.04.2003, 00:00 by Isabelle Bonhoure, Erich Wieland, André M. Scheidegger, Michael Ochs, Dominik Kunz
In this study, the immobilization mechanisms of Sn(IV) onto calcium silicate hydrates (C−S−H) and hardened cement paste (HCP) have been investigated by combining wet chemistry experiments with X-ray absorption spectroscopy (XAS). Evidence is presented which demonstrates the formation of a Sn(IV) inner-sphere surface complex on C−S−H with a CaO/SiO2 weight ratio of 0.7. Two possible structural models, implying a corner sharing between the Sn octahedra and Q1 or Q2b Si tetrahedra, have been developed based on the experimentally determined structural parameters. In HCP, the formation of a different type of Sn(IV) inner-sphere complex has been observed, indicating that C−S−H may not be the uptake-controlling phase for Sn(IV) in the cement matrix. An alternative structural model for Sn(IV) binding in HCP has been developed, assuming that ettringite is the uptake-controlling phase. At high Sn(IV) concentrations, Sn(IV) immobilization in HCP occurs due to the formation of CaSn(OH)6.