Adsorption of iodine from aqueous solutions by aminosilane-grafted mesoporous alumina

Abstract

Adsorptive removal of iodine from aqueous waste streams is an efficient way of minimizing the environmental footprints associated with radioactive species, however, developing highly efficient, durable, adsorbents is key to this technique’s success. Here, we investigated the iodine adsorption performance of aminosilane-grafted mesoporous alumina using various aminosilanes, including 3-Aminopropyl-triethoxysilane (APS), N-methylaminopropyl-trimethoxysilane (MAPS), and 3-N,N-dimethylaminopropyl-trimeth-oxysilane (DMAPS). The successful incorporation of amine moieties within the mesopores of alumina was confirmed by FTIR and elemental analysis. From the iodine adsorption tests, Al-APS, Al-MAPS and Al-DMAPS exhibited capture capacities of 124, 223 and 241 mg/g, respectively, while the bare alumina had a capacity of 107 mg/g. Assessing the iodine adsorption front on the Al-DMAPS sample revealed sharp adsorption kinetics from 0 to 4 h followed by a gradual increase from 4 to 24 h, indicating that the aminated Al2O3 had high affinity towards the contaminate. Increasing the Al-DMAPS loading from 30 to 50 wt% revealed only a 4% enhancement in iodine adsorption capacity, implying that the lower aminosilane concentration was optimal. The equilibrium uptake and kinetics of iodine adsorption over aminosilane-grafted mesoporous alumina were represented by Langmuir and pseudo-second-order models, respectively. Meanwhile, the leach test results revealed that amine grafting moderately enhanced the material’s ability to permanently trap iodine for safe geological disposal, however, further waste consolidation is required to improve the iodine retention in these adsorbents.