Iodine release front silver iodide under reducing condition with iron-bearing minerals

Iodine release from silver iodide (AgI) to water was evaluated under reducing conditions in the presence of iron-bearing minerals, goethite (FeOOH), magnetite (Fe3O4) and Wustite (FeO). The release tests were pcrformed in a glove box purged with gas mixture (Ar+5%H-2,), and the concentrations of dissolved iodine, silver and on were measurred. The apparent equilibrium concentration of dissolved iodone was 4.0 x10(-8), 4.3 x 10(-8) mol/l for the tests with FeOOII and Fe3O4, respectively. The values were almost the same as in the test without minerals. For the test with FeO, the concentration of dissolved iodine was 5.4 x 10(-3) mol/l, which is five orders of magnitude higher than for the other tests. Solid phase analyses by using XRD and SEM/EDS indicated that metallic silver precipitated on the surface of the original AgI for the test with FeO and on the surface of Fe3O4 for the test with Fe3O4, but not for that with FeOOH. These results showed that only FcO could reduce AgI effectively to increase iodine release. The amount of dissolved Fc(II) was a key factor affecting AgI reduction instead of redox potential of solution. Kinetic processes may also play an important role in AgI reduction andassociated iodine release under reducing condition.