Valtteri Suorsa

Hydrous ZrO₂ materials showed high potential for the selective adsorption of IO₃⁻ in the presence of competing anions. The main adsorption mechanism was found to be ion-exchange and efficient regeneration was demonstrated with dilute acid.

The effect of phosphonate groups on selective lanthanide sorption for a series of inorganic–organic hybrid materials was investigated. Four functional ligands with an increasing number of aminomethylenephosphonate groups were attached to the porous zirconia matrix via the post-synthetic grafting method. Successful surface grafting was confirmed by FTIR and ³¹P MAS-NMR spectroscopies. All the synthesized hybrids showed a lanthanide uptake of about 100 μmol g⁻¹ at pH 3. The sorption studies revealed that the hybrids of ligands with a larger number of phosphonate groups possess higher selectivity, as one with the largest number showed a separation factor of over 80 for La³⁺ and Lu³⁺. Fixed-bed column experiments also demonstrated the materials’ favored uptake of Lu³⁺ over La³⁺ at pH 3, in addition to the reusability and applicability to the actual separation settings. These results propose strategies for the selection of organic ligands for hybrid sorbent synthesis.

Radioactive ¹²⁹I with a long half-life (1.57 × 10⁷ y) and high mobility is a serious radiohazard and one of the top risk radionuclides associated with its accidental and planned releases to nature. The complex speciation chemistry of iodine makes its removal a complicated task, and usually a single method is not able to remove all iodine species. Especially its oxidized form iodate (IO₃⁻) lacks a selective and effective removal method. Here, the granular aggregates of hydrous zirconium oxides with and without antimony doping were tested for IO₃⁻ removal and the effects of contact time, competing anions in different concentrations and pH were examined. The materials showed high selectivity for IO₃⁻ (K_d over up to 50,000 ml/g) in the presence of competing ions and relatively fast uptake kinetics (eq. < 1 h). However, B(OH)₄⁻ and SO₄²⁻, as competing ions, lowered the iodate uptake significantly in basic and acidic solution, respectively. The suitability of the materials for practical applications was tested in a series of column experiments where the materials showed remarkably high apparent capacity for the IO₃⁻ uptake (3.2–3.5 mmol/g). Graphic abstract

Submicron ZrO₂ fibers with three different Sb-doping levels (5, 10 and 15 cation%) were produced with an electroblowing synthesis for removal of ⁹⁹TcO₄^–. The Sb-doped ZrO₂ fibers showed high selectivity toward ⁹⁹TcO₄^–, which was not interfered by ClO₄^–, NO₃^– or Cl^– ions and showed no selectivity toward ReO₄^–. The optimal pH range for the ⁹⁹Tc separation was 2–6 but the Sb-doped fibers maintained very high uptake level throughout the studied pH range of 1–10. According to the uptake experiments, Sb(III) is assumed to reduce Tc(VII) to Tc(IV) that is then adsorbed by the zirconia surface.

The speciation of iodine in environment must be known in order to properly assess its geological fate and to study potential remediation materials for the decontamination of water containing radioactive iodine. In this study, the utilization of silver-impregnated granular activated carbon for separation between two iodine species, iodate and iodide, from each other was studied in different solution matrices with batch and column experiments. A high separation of the iodine species was achieved in the high concentrations of interfering ions, e.g. chloride, and in both μM and trace iodine concentrations. The method is suitable for both radioactive and non-radioactive iodine.

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.