Time-dependent iodate and iodide adsorption to Fe oxides
Aqueous iodine removal via adsorption to Fe oxides could provide an efficient remedial pathway for vadose zone and groundwater contamination. We conducted a series of macroscopic batch experiments to determine the extent of the time-dependent iodate (IO3-) and iodide (I-) adsorption to four Fe oxides (i.e., ferrihydrite, goethite, magnetite and hematite) at different pH values and solution ionic strengths (IS). The results showed that IO3- adsorption extent [in terms of the average distribution coefficient (Kd) after 2 days of reacting time] followed the order: ferrihydrite (927.5 mL/g) > goethite (84.9 mL/g) > magnetite (23.8 mL/g) > hematite (9.5 mL/g). However, the range of specific surface area (SSA) normalized Kd values was narrow (2 - 4.6 mL/m2), suggesting SSA control over the adsorption extent. The adsorption extent correlated negatively with both pH and IS, implying IO3- outer-sphere adsorption. The adsorption extent increased with time (~27-48%) after 200 days, likely because of interparticle diffusion within aggregates. I- adsorption was insignificant for all Fe oxides. Because of its large SSA, ferrihydrite could be efficient at removing aqueous iodate, potentially decreasing the time of groundwater plume spreading.
Revised: May 19, 2020 |
Published: November 21, 2019
Wang G., N. Qafoku, J.E. Szecsody, C.E. Strickland, C.F. Brown, and V.L. Freedman. 2019.Time-dependent iodate and iodide adsorption to Fe oxides.ACS Earth and Space Chemistry 3, no. 11:2415-2420.PNNL-SA-142955.doi:10.1021/acsearthspacechem.9b00145