title: EXAFS study of Sn(IV) immobilization by hardened cement paste and calcium silicate hydrates.
abstract: 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.
authors.affiliation: Waste Management Laboratory and Swiss Light Source, Paul Scherrer Institute, 5232 Villigen, Switzerland. isabelle.bonhoure@psi.ch
authors.forename: Isabelle
authors.initials: I
authors.lastname: Bonhoure
authors.forename: Erich
authors.initials: E
authors.lastname: Wieland
authors.forename: André M
authors.initials: AM
authors.lastname: Scheidegger
authors.forename: Michael
authors.initials: M
authors.lastname: Ochs
authors.forename: Dominik
authors.initials: D
authors.lastname: Kunz
mesh_terms: D017610:Calcium Compounds / Q000737:chemistry*; D003252:Construction Materials; D008958:Models, Molecular; D011850:Radioactive Waste / Q000517:prevention & control*; D017640:Silicates / Q000737:chemistry*; D017971:Tin Compounds / Q000737:chemistry*
chemical_list: D017610:Calcium Compounds; D011850:Radioactive Waste; D017640:Silicates; D017971:Tin Compounds; C041694:stannic chloride; C031293:calcium silicate