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SnI4 is Iron carbide structured and crystallizes in the cubic P-43m space group. The structure is zero-dimensional and consists of one stannic iodide molecule. Sn4+ is bonded in a tetrahedral geometry to four equivalent I1- atoms. All Sn–I bond lengths are 2.71 Å. I1- is bonded in a single-bond geometry to one Sn4+ atom.
The capture of radioiodine from nuclear processes and the mitigation of environmental release are important topic areas of research. Some of the more commonly employed chemisorption-type iodine scavengers reported in the literature are based on metal-exchanged porous sorbents such as Ag-zeolites or metal-functionalized aerogels and xerogels. However, another option is to use zero-valent metals directly that have known high affinities for iodine gas [i.e., I2(g)]. In this study, fine metal particles of Ag0, Bi0, Cu0, and Sn0 were embedded in porous polyacrylonitrile (PAN) substrates at 75 mass% metal loadings within the form of ellipsoidal beads with maximum diameters of ~2–3 mm. These composite beads showed extremely high iodine loadings that are directly related to the metal particle loadings. The X-ray diffraction (XRD) analyses of Ag0, Bi0, Cu0, and Sn0 particles as well as metal-PAN composite beads reacted with iodine gas at 120 ± 1 °C showed phases of AgI, BiI3, CuI, and SnI4, respectively. For the Ag-PAN, Cu-PAN, and Sn-PAN beads, no other crystalline peaks were observed in XRD for unreacted metal or oxidized metals after 48 h in saturated I2(g) at 120 ± 1 °C, whereas unreacted metallic Bi0 was observed within the Bi-PAN composites. However, after a 72 h exposure at 120 ± 1 °C, both the Bi0 particles and the Bi-PAN composites showed full conversion from Bi0 to BiI3 with XRD. Comparisons between mass uptake data and X-ray absorption spectroscopy were used to better understand the phase distribution of the Bi phases present in the Bi-PAN+I composites. The iodine loadings (mg iodine per g sorbent, or qe) for these materials were 1120 (Ag-Particle), 1382 (Bi-Particle-72h), 1033 (Cu-Particle), 3000 (Sn-Particle), 753 (Ag-PAN), 1012 (Bi-PAN-72h), 1457 (Cu-PAN), and 1669 (Sn-PAN). It is possible that inexpensive sorbents such as these could be deployed to help limit or prevent release of radioiodine to the environment.
Ni3S4 is Hausmannite structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. there are two inequivalent Ni+2.67+ sites. In the first Ni+2.67+ site, Ni+2.67+ is bonded to four equivalent S2- atoms to form corner-sharing NiS4 tetrahedra. The corner-sharing octahedral tilt angles are 58°. All Ni–S bond lengths are 2.17 Å. In the second Ni+2.67+ site, Ni+2.67+ is bonded to six equivalent S2- atoms to form NiS6 octahedra that share corners with six equivalent NiS4 tetrahedra and edges with six equivalent NiS6 octahedra. All Ni–S bond lengths are 2.28 Å. S2- is bonded to four Ni+2.67+ atoms to form a mixture of distorted edge and corner-sharing SNi4 trigonal pyramids.
NiS2 is Fluorite structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. Ni4+ is bonded in a body-centered cubic geometry to eight equivalent S2- atoms. All Ni–S bond lengths are 2.47 Å. S2- is bonded to four equivalent Ni4+ atoms to form a mixture of edge and corner-sharing SNi4 tetrahedra.
Ni3S2 crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are three inequivalent Ni+1.33+ sites. In the first Ni+1.33+ site, Ni+1.33+ is bonded in a 3-coordinate geometry to three equivalent S2- atoms. All Ni–S bond lengths are 2.28 Å. In the second Ni+1.33+ site, Ni+1.33+ is bonded to four S2- atoms to form distorted corner-sharing NiS4 trigonal pyramids. There are one shorter (2.15 Å) and three longer (2.30 Å) Ni–S bond lengths. In the third Ni+1.33+ site, Ni+1.33+ is bonded in a distorted trigonal non-coplanar geometry to four S2- atoms. There are three shorter (2.16 Å) and one longer (2.65 Å) Ni–S bond lengths. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded in a 6-coordinate geometry to seven Ni+1.33+ atoms. In the second S2- site, S2- is bonded to four Ni+1.33+ atoms to form corner-sharing SNi4 tetrahedra.
CoNi5S8 is Spinel-like structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Co4+ is bonded to four equivalent S2- atoms to form CoS4 tetrahedra that share corners with twelve equivalent NiS6 octahedra. The corner-sharing octahedral tilt angles are 57°. All Co–S bond lengths are 2.15 Å. There are two inequivalent Ni+2.40+ sites. In the first Ni+2.40+ site, Ni+2.40+ is bonded to six S2- atoms to form NiS6 octahedra that share corners with three equivalent CoS4 tetrahedra, corners with three equivalent NiS4 tetrahedra, and edges with six equivalent NiS6 octahedra. There are three shorter (2.28 Å) and three longer (2.29 Å) Ni–S bond lengths. In the second Ni+2.40+ site, Ni+2.40+ is bonded to four equivalent S2- atoms to form corner-sharing NiS4 tetrahedra. The corner-sharing octahedral tilt angles are 58°. All Ni–S bond lengths are 2.17 Å. There are two inequivalent S2- sites. In the first S2- site, S2- is bonded to four Ni+2.40+ atoms to form a mixture of distorted edge and corner-sharing SNi4 trigonal pyramids. In the second S2- site, S2- is bonded in a distorted rectangular see-saw-like geometry to one Co4+ and three equivalent Ni+2.40+ atoms.
Four promising iodine “getter” materials (Ag, Cu, Bi, and Sn) for radioiodine capture were assessed in their pure metal-iodide (MI x ) pelletized forms to compare relative chemical durabilities. To study chemical durability, commercial MI x compounds of AgI, BiI 3 , BiOI, CuI, and SnI 4 were converted to dense monolithic pellets using spark plasma sintering. Semidynamic leach testing in the form of modified ASTM C1308 tests was then performed on the pellets in two different forms including unmounted (as-pressed) specimens (i.e., “U”) and epoxy-mounted specimens (i.e., “M”) with polished surfaces. The chemical durability results and sample characterizations showed that three of the five MI x compounds tested (i.e., AgI, CuI, and BiOI) displayed moderate to high leach resistances. Further, the remaining two MI x compounds (i.e., BiI 3 and SnI 4 ), which are both desirable iodine waste forms due to their high iodine loading capacities, readily decomposed during leach testing, indicated by crystallographic changes in the specimens as well as large amounts of iodine detected in the leachate solutions. The instabilities of BiI 3 and SnI 4 raise uncertainties for using the base metals/cations (i.e., Bi 0 /Bi 3+ and Sn 0 /Sn 4+ , respectively) as viable getters for radioiodine capture due to likely poor waste form chemical durabilities after capture and consolidation into waste forms.