New Materials for Immobilization of Cs and the Design of Unique Inorganic Ion Exchangers for Separation of Li Isotopes

ChEMS Seminar

Featuring, Yong-Hong Zhang, Ph.D.
Assistant Professor, Department of Chemistry
Sophia University, Tokyo, Japan

Location:  Engineering Tower, Room 331

Abstract:
This presentation deals with the processing of potential new materials for the immobilization of Cs. In particular, the results on the incorporation mechanism of Cs ions from CsNO3 into NH4Zr2(PO4)3 will be presented. By powder X-ray diffraction analysis and by monitoring off-gases released from the mixture upon heating with a thermogravimetry analyzer connected to an infrared spectrometer, it was found that with increasing temperature, the decomposition of CsNO3 was followed by the conversion of NH4Zr2(PO4)3 to HZr2(PO4)3 with the release of NH3. At around 500°C, the CsZr2(PO4)3 phase started to appear as a result of the H+/Cs+ ion exchange. No Cs ion loss was observed at thermal treatment temperatures of 900°C and lower. Guided by those results, a Cs incorporated powder material CsZP was thus synthesized by wet blending of NH4Zr2(PO4)3 and CsNO3 (mole ratio: 1.0:0.4), followed by heating at 600°C for 10 hours. This thermally treated product (designated as 0.4CsZP) was then mixed with nitrates of Na, K, Ca, Sr and chloride of Mg, respectively, followed by heating at 600°C for 10 hours, in order to substitute the H part of synthesized 0.4CsZP for incorporating these cations into CsZP. All the resultant powder materials were applied to the MCC-1 Test by immersion into the simulated Na, K solutions and their mixed one to test and discuss the short term chemical durability through the estimation of their leaching amounts as well as the powder XRD analysis and the SEM microscopy before and after leaching. Incorporating the group 2 metal ions, in particular Ca ions, into 0.4CsZP was found reducing the Cs leaching thus improving the immobilization of Cs with NZP type ceramics.

The presentation will also discuss our processing and studies of another new material: semicrystalline titanium phosphate, Ti2O3(H2PO4)2.2H2O (TiOP), synthesized mainly in the interior pores of porous silica beads. The ion exchange properties of TiOP-loaded silica beads (TiOP-SiO2) and their thermally treated products at 500°C (TiOP-SiO2-500) were investigated.  The average degree of TiOP loading was 16.5%. As a whole, TiOP-SiO2 and TiOP-SiO2-500 retained the ion exchange properties including very high ion exchange rates. Li isotopes were chromatographically fractionated in a breakthrough manner with the above-stated novel ion exchangers, TiOP-SiO2 and TiOP-SiO2-500. From the profiles of Li contents, pH and Li isotopic ratios of the effluent, this novel exchanger was found to exhibit the Li-6 specific property with a high ion exchange rate. Its Li isotopic fractionation ability was dependent on the pH of influent. The thermal treatment of the exchanger substantially improved the Li-isotope separation performance.

About the Speaker:
Yong-Hong Zhang, Ph.D., assistant professor of chemistry at Sophia University, Tokyo, Japan, received his bachelor’s degree in radiochemistry from Lanzhou University, Lanzhou, China, and his Ph.D. degree in nuclear engineering, Tokyo Institute of Technology, Tokyo, Japan.  Zhang’s research interests include isotope effects and their applications; immobilization of Cs/Sr with NZP; synthesis of Li isotope specific inorganic materials; and, separation of Li isotopes by chromatography.