Iodide Sorption to Subsurface Sediments and Illitic Minerals

Environmental Science & Technology1999Vol. 34(3), pp. 399–405

Citations Over TimeTop 14% of 1999 papers

Daniel I. Kaplan, R. Jeff Serne, Kent E. Parker, Igor V. Kutnyakov

Abstract

Laboratory studies were conducted to quantify and identify the key processes by which iodide (I-) sorbs to subsurface arid sediments. A surprisingly large amount of I- sorbed to three alkaline subsurface sediments that were low in organic matter content; distribution coefficients (Kd'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- sorption to calcite (Kd = 0.04 ± 0.01 mL/g), chlorite (Kd = −0.22 ± 0.06 mL/g), goethite (Kd = 0.10 ± 0.03 mL/g), montmorillonite (Kd = −0.42 ± 0.08 mL/g), quartz (Kd = 0.04 ± 0.02 mL/g), or vermiculite (Kd = 0.56 ± 0.21 mL/g). Conversely, a significant amount of I- sorbed to illite (Kd = 15.14 ± 2.84 mL/g). Treating the 125I--laden illite mixtures with dissolved F-, Cl-, Br-, or 127I-, caused 43 ± 3%, 45 ± 0%, 52 ± 3%, and 83 ± 1%, respectively, of the adsorbed I- to desorb. Finally, I- sorption to illite was strongly pH-dependent; the Kd values decreased from 46 to 22 mL/g as the pH values increased from 3.6 to 9.4. An appreciable amount of I- sorbed to illite even under alkaline conditions. These experiments suggest that illite removed I- 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- movement in these sediments.

Citations Over TimeTop 14% of 1999 papers

Abstract

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