title: Strontium binding by calcium silicate hydrates.
abstract: In the present study the binding of strontium with pure calcium silicate hydrates (C-S-H) has been investigated using batch-type experiments. Synthetic C-S-H phases with varying CaO:SiO(2) (C:S) mol ratios, relevant to non-degraded and degraded hardened cement paste, were prepared in the absence of alkalis (Na(I), K(I)) and in an alkali-rich artificial cement pore water (ACW). Two types of experimental approaches have been employed, investigating sorption and co-precipitation processes, respectively. The Sr(II) sorption kinetics were determined as well as sorption isotherms, the effect of the solid to liquid ratio and the composition (C:S ratio) of the C-S-H phases. In addition, the reversibility of the Sr(II) sorption was tested. It was shown that both the sorption and co-precipitation tests resulted in Sr(II) distribution ratios which were similar in value, indicating that the same sites are involved in Sr(II) binding. In alkali-free solutions, the Sr(II) uptake by C-S-H phases was described in terms of a Sr(2+)-Ca(2+) ion exchange model. The selectivity coefficient for the Sr(2+)-Ca(2+) exchange was determined to be 1.2+/-0.3.
authors.affiliation: Laboratory for Waste Management, Nuclear Energy and Safety Research Department, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland. jan.tits@psi.ch
authors.forename: J
authors.initials: J
authors.lastname: Tits
authors.forename: E
authors.initials: E
authors.lastname: Wieland
authors.forename: C J
authors.initials: CJ
authors.lastname: Müller
authors.forename: C
authors.initials: C
authors.lastname: Landesman
authors.forename: M H
authors.initials: MH
authors.lastname: Bradbury
mesh_terms: D017610:Calcium Compounds / Q000737:chemistry*; D052918:Environmental Restoration and Remediation / Q000379:methods*; D011848:Radioactive Pollutants / Q000737:chemistry / Q000302:isolation & purification; D017640:Silicates / Q000737:chemistry*; D013324:Strontium / Q000737:chemistry / Q000302:isolation & purification*; D013326:Strontium Radioisotopes / Q000737:chemistry / Q000302:isolation & purification*
chemical_list: D017610:Calcium Compounds; D011848:Radioactive Pollutants; D017640:Silicates; D013326:Strontium Radioisotopes; C031293:calcium silicate; D013324:Strontium