Iodide sorption to subsurface sediments and illitic minerals
Laboratory studies were conducted to quantify and identify the key processes by which iodide (I{sup {minus}}) sorbs to subsurface arid sediments. A surprisingly large amount of I{sup {minus}} sorbed to three alkaline subsurface sediments that were low in organic matter content; distribution coefficients (K{sub d}'s) ranged from 1 to 10 mL/g and averaged 3.3 mL/g. Experiments with pure mineral isolates, similar to the minerals identified in the clay fraction of the sediments, showed that there was little or no I{sup {minus}} sorption to calcite (K{sub d} = 0.04 {+-} 0.01 mL/g), chlorite (K{sub d} = {minus}0.22 {+-} 0.06 mL/g), goethite (K{sub d} = 0.10 {+-} 0.03 mL/g), montmorillonite (K{sub d} = {minus}0.42 {+-} 0.08 mL/g), quartz (K{sub d} = 0.04 {+-} 0.02 mL/g), or vermiculite (K{sub d} = 0.56 {+-} 0.21 mL/g). Conversely, a significant amount of I{sup {minus}} sorbed to illite (K{sub d} = 15.14 {+-} 2.84 mL/g). Treating the {sup 125}I{sup {minus}}-laden illite mixtures with dissolved F{sup {minus}}, Cl{sup {minus}}, Br{sup {minus}}, or {sup 127}I{sup {minus}}, caused 43 {+-} 3%, 45 {+-} 0%, 52 {+-} 3%, and 83 {+-} 1%, respectively, of the adsorbed I{sup {minus}} to desorb. 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. An appreciable amount of I{sup {minus}} sorbed to illite even under alkaline conditions. 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:
- 20026679
- Journal Information:
- Environmental Science and Technology, Journal Name: Environmental Science and Technology Journal Issue: 3 Vol. 34; ISSN ESTHAG; ISSN 0013-936X
- Country of Publication:
- United States
- Language:
- English
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