Sorption of iodine on minerals investigated by X-ray absorption near edge structure (XANES) and 125I tracer sorption experiments

The sorption of I on a set of selected minerals was examined by: X-ray absorption near edge structure (XANES) and high concentration chemical sorption experiments, as well as very low concentration tracer (using 125I) sorption experiments. A XANES method was used to determine I2, I(V) and I (-I) in supernatant solutions and slurries of minerals. This is, we believe, the first reported use of XANES to investigate the redox state of I that is sorbed on minerals. With this technique, it was determined that pyrite, biotite and magnetite sorb I from solutions containing 1000 μg ml−1 I. In the pyrite/water system, IO3− was reduced to what appeared to be I2 in the XANES scans and sorbed on the minerals surface. Magnetite sorbed I− from solution but not IO3−. In contrast, biotite sorbed IO3− from solution but did not take up any I−. No changes in I redox state were observed in the magnetite and biotite experiments. Based on this association the presence of Fe(II) in the sorbing phase appears to be related to uptake, but not necessarily to a change in I redox.