Factors affecting the soil sorption of iodine |
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| Authors: | Marsha I Sheppard D H Thibault Jude McMurry P A Smith |
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| Institution: | 1. Whiteshell Laboratories, AECL Research, ROE 1L0, Pinawa, MB, Canada
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| Abstract: | 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 Al 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 Cl? showed that anion exchange plays a role in I sorption in both mineral and organic soils. The presence of Cl 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. |
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