Factors affecting the soil sorption of iodine

✍ Scribed by Marsha I. Sheppard; D. H. Thibault; Jude McMurry; P. A. Smith

• Publisher: Springer Netherlands
• Year: 1995
• Tongue: English
• Weight: 951 KB
• Volume: 83
• Category: Article
• ISSN: 0049-6979
• DOI: 10.1007/bf00482593

✦ Synopsis

Iodine-129 is an important radionuclide released from nuclear facilities because of its long radioactive half-life and its environmental mobility. Its retention in surface soils has been linked to pH, organic matter, and Fe and A1 oxides. Its inorganic solution chemistry indicates I will most likely exist as an anion. Three investigations were carried out to provide information on the role of the inorganic and organic chemistry during sorption of I by soil.

Anion competition using C1-showed that anion exchange plays a role in I sorption in both mineral and organic soils. The presence of C1 decreased the loss of I-from solution by 30 and 50% for an organic and a carbonated sandy soil respectively. The I remaining in solution was associated primarily with dissolved organic carbon (DOC). The loss rate from solution appears to depend on two reactions of I with the soil solids (both mineral and organic) creating both a release to and a loss from solution, and the reaction of I with the DOC (from very low to high molecular weight). Composition analyses of the pore water and the geochemical modelling indicate that I sorption affects the double-charged anion species in solution the most, particularly SO4--. Iodide introduced to natural bog groundwater at three concentrations (10 -3, 10 -1 and 10 meq L -1) remained as I-and was not lost from solution quickly, indicating that the association of I with DOC is slow and does not depend on the DOC or I concentration. If sorption of I to soil solids or DOC is not sensitive to concentration, then stable I studies, which by necessity must be carried out at high environmental concentrations, can be linearly extrapolated to radioactive I at much lower molar concentrations.