Speciation of Iodide and Iodate Anions in Geochemical Environments: A Theory Driven Experimental Study

Speciation of heavy metal ions in geochemical environment is utmost importance due to its environmental relevance. Iodine exists as iodide and iodate anions and are heavier anions, and they can be more labile in the absence of humic environments. This study particularly focusses on iodine speciation in Humic Acid (HA) environments. First, we have carried out extensive quantum chemical calculations to understand the structure-function relationship of iodide and iodate binding in humic acids. We predict that iodide anion binds through hydrogen bonding and are thus weak in acidic conditions. Iodate anion binds at the macrocyclic pocket of the humic acid, and is somewhat pH independent. Computed structure of the complex and binding energies explain the binding affinities of iodide and iodate with HA and quantum theory of atoms and molecules QTAIM analysis reveal the nature of forces involved in each case. To justify our computational claim, sorption experimental studies are carried out on the uptake of iodine species with humic acid. The studies are quite encouraging and there is a close agreement between the theoretical and experimental results.