Contribution to Understanding Iodine Sorption Mechanism onto Mixed Solid Alumina Cement and Calcium Compounds.

Abstract

An experimental study on the iodine sorption mechanism onto mixed solid alumina cement and calcium compounds was carried out. The solids were prepared by mixing the alumina cement with Ca(OH) 2 and/or CaSO 4 •2H 2 O. Batch experiments were performed for iodine sorption onto the solid and iodine desorption from the solid that was obtained after a sorption experiment. In order to clarify the hydrates in the solids, X-ray diffraction measurement and scanning electron microscopic observation were adopted. The iodine sorption onto the solid proceeded to replace the OH − in 4CaO•Al 2 O 3 •13H 2 O by I − in solution to form the new hydrate, 3CaO•Al 2 O 3 •CaI 2 •12H 2 O. The results of sorption and desorption experiments showed that the iodine sorption proceeded reversibly and was independent of concentration of iodine up to 1×10 −2 mole/dm 3 in solution.

Reactions in cement encapsulated nuclear wastes: need for toolbox of different cement types

“…One advantage of the matrix is the reduced pH of any pore solution. Toyohara et al 38 showed that CACs could incorporate iodide into the hexagonal hydrate structure forming C 3 A.CaI 2 .12H 2 O. The reaction was reversible and dependent on I 2 concentration, but this does emphasise the potential for anion retention.…”

Immobilization of iodine into a hydroxyapatite structure prepared by cementation

“…Among them, calcium silicate hydrate (C-S-H) seems to exhibit the highest capacity towards iodide or iodate retention, 4,5 but the question of the chemical durability of a Portland cement-based matrix with respect to the half-life of iodine-129 is still considered as an issue. 6 This is why some low melting temperature glass matrices, 7,8 calcium (sulfo)aluminate phases, [9][10][11][12] and also some ceramic matrices like iodine-bearing sodalite (Na 8 (AlSiO 4 ) 6 I 2 ) 13,14 and iodine-bearing apatite [15][16][17][18][19][20] have been studied in order to incorporate iodine into the core of the materials. More recently, glass-bonded mordenite composites 21 and MOFs (Metal Organic Frameworks) [22][23][24] have also been proposed as possible matrices.…”

Immobilization of radioactive waste in cement: Iodine binding by cementitious materials under highly alkaline conditions

“…In our experiment portlandite is responsible for the alkalinity of HCP suspension. We suppose that incorporation of iodine to cement may occur because of replacing the OHby Iand formation of a new hydrate [16]. Based on these observations the mechanisms of sorption of iodine by cement under oxidizing highly alkaline conditions remain ambiguous, therefore, further comprehensive structural and chemical analysis is necessary to obtain the knowledge of iodine sorption mechanisms.…”

“…A number of studies on the mechanism of the iodine uptake in cementitious materials have been conducted [12][13][14][15][16]. Most of the studies have focused on the investigations of the potential of individual cement minerals to immobilize iodine and elucidation of a molecular-scale mechanism for the I -/IO 3 interaction with HCP and CSH.…”