Anion exchange on hydrous zirconium oxide materials: application for selective iodate removal.

The radioactive 129I is a top-priority radionuclide due to its the long half-life (1.57 × 107 years) and high mobility. Because of the planned and accidental releases to the environment, specific separation technologies are required to limit the potential radiation dose to human beings. Zirconium oxides are known for their adsorption capability and selectivity to oxyanions and here the applicability to selective IO3 - removal has been investigated regarding the uptake mechanism, regeneration and competition caused by other anions, like environmentally relevant SO4 2-. Granular aggregates of hydrous zirconium oxides with and without Sb doping showed high potential for the selective IO3 - removal in the presence of competing anions, like the forementioned SO4 2- (apparent capacity between 0.1-0.4 meq g-1 depending on SO4 2- concentration). The main uptake mechanism was found to be outer-sphere complexation (ion-exchange) to the protonated hydroxyl groups of hydrous zirconium oxides, but also minor mechanisms were identified including inner-sphere complexation and reduction to I-. The materials were observed to be easily and successively regenerated using dilute acid. Hydrous zirconium oxides showed high potential for IO3 - removal from waste solutions regarding technical (high selectivity and apparent capacity) and ecological/economic (feasible regeneration) aspects.

Submicron fibers as a morphological improvement of amorphous zirconium oxide particles and their utilization in antimonate (Sb(v)) removal.

Mesoporous and large surface area zirconium oxide aggregate granules with good adsorption properties were synthesized using a simple precipitation method. Since utilization of these small and fragile particles is considered rather difficult in larger scale column operation, the product was formed into a fibrous form to improve its usability. The submicron fibers were obtained from an optimized electroblowing synthesis that resulted in elastic and uniform fibers with a tetragonal structure and high length-to-diameter ratio. In antimonate (Sb(v)) adsorption experiments, the higher calcination temperature (350 °C) of the fibers did not seem to decrease the Sb(v) adsorption capacity excessively since the high theoretical adsorption capacities were 113 mg g-1 and 58 mg g-1 for the aggregate and fibers, respectively. Both materials had fast kinetics, fibers being faster in the beginning of the reaction. Moreover, both materials offered efficient Sb(v) removal in the studied pH range from 1 to 11 by reaching over 99.9% adsorption in the optimal pH range. X-ray absorption near edge spectroscopy (XANES) revealed that Sb(v) stays as pentavalent antimony after being adsorbed by these materials and based on the isoelectric point shifts in the zeta potential measurement, adsorption occurs mainly by an inner-sphere complexation reaction. Finally, our study showed that pressure buildup in a flow-through column packed with zirconium oxide fibers was significantly lower than in a column packed with aggregates. Thus, zirconium oxide aggregates can be formed into submicron fibers with enhanced column operation properties without a too large compromise in the adsorption properties.

Removal of Cd2+, Ni2+ and PO43- from aqueous solution by hydroxyapatite-bentonite clay-nanocellulose composite.

A novel hydroxyapatite-bentonite clay-nanocellulose (CHA-BENT-NCC) composite material was successfully prepared as adsorbent for the removal of Ni2+, Cd2+ and PO43- from aqueous solutions. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive analysis of X-rays (EDAX), X-ray diffraction analysis (XRD) and Fourier-transform infrared spectroscopy (FTIR) were used for characterization of the adsorbent. The effect of pH, contact time, temperature, and initial adsorbate concentration were studied for optimization purpose. The adsorption behavior of the investigated ions were well described by the Freundlich adsorption model, and the maximum adsorption capacity for Ni2+, Cd2+ and PO43- was estimated to be 29.46 mmol/g, 10.34 mmol/g and 4.90 mmol/g, respectively. Desorption efficiency was achieved by treatment with 0.01 M HNO3 for metals and 0.10 M NaOH for PO43-. Five adsorption-desorption cycles were performed without significant decrease in adsorption capacities. The CHA-BENT-NCC material proved to be a very effective adsorption material for the treatment of mining water also from a copper mine in Finland.