EXAFS study of Sn(IV) immobilization by hardened cement paste and calcium silicate hydrates.
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.
Bonhoure
Isabelle
I
Waste Management Laboratory and Swiss Light Source, Paul Scherrer Institute, 5232 Villigen, Switzerland. isabelle.bonhoure@psi.ch
Wieland
Erich
E
Scheidegger
André M
AM
Ochs
Michael
M
Kunz
Dominik
D
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*
D017610:Calcium Compounds; D011850:Radioactive Waste; D017640:Silicates; D017971:Tin Compounds; C041694:stannic chloride; C031293:calcium silicate