Radioiodide sorption to sediment minerals
Laboratory studies were conducted to quantify and understand the processes by which iodide (I{sup {minus}}) sorbs to minerals found in subsurface arid sediments. Little or no I{sup {minus}} sorbed to montmorillonite (K{sub d} = {minus}0.42 {+-} 0.08 mL/g), quartz (K{sub d} = 0.04 {+-} 0.02 mL/g), vermiculite (K{sub d} = 0.56 {+-} 0.21 mL/g), calcite (K{sub d} = 0.04 {+-} 0.01 mL/g), goethite (K{sub d} = 0.10 {+-} 0.03 mL/g), or chlorite (K{sub d} = {minus}0.22 {+-} 0.06 mL/g). A significant amount of I{sup {minus}} sorbed to illite (K{sub d} = 15.14 {+-} 2.84 mL/g). Upon treating the iodide-laden illite with dissolved F{sup {minus}}, Cl{sup {minus}}, Br{sup {minus}}, or {sup 127}I{sup {minus}}, desorption (or isotopic exchange in the case of {sup 127}I) removed, respectively, 43 {+-} 3%, 45 {+-} 0%, 52 {+-} 3, and 83 {+-} 1% of the I{sup {minus}} originally adsorbed to the illite. The fact that such large amounts of I{sup {minus}} could be desorbed suggests that the I{sup {minus}} was weakly adsorbed, and not chemically bonded to a soft metal, such as mercury or silver, that may have existed in the illite structure as trace impurities. Finally, I{sup {minus}} sorption to illite was strongly pH-dependent; the K{sub d} values decreased from 46 to 22 mL/g as the pH values increased from 3.6 to 9.4. Importantly, I{sup {minus}} sorbed to illite even under alkaline conditions. Together, these experiments suggest that illite removed I{sup {minus}} from the aqueous phase predominantly by reversible physical adsorption to the pH-dependent edge sites. Illites may constitute a substantial proportion of the clay-size fraction of many arid sediments and therefore may play an important role in retarding I{sup {minus}} movement in these sediments.
- Research Organization:
- Westinghouse Savannah River Co., Aiken, SC (US)
- Sponsoring Organization:
- US Department of Energy
- DOE Contract Number:
- AC09-89SR18035; AC06-76RL01830
- OSTI ID:
- 20015864
- Country of Publication:
- United States
- Language:
- English
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Iodide sorption to subsurface sediments and illitic minerals
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