Preparation of Ammonium Tungstophosphate-Calcium Alginate Composite Adsorbent and its Adsorption Properties of Rubidium

A spherical composite adsorbent AWP-CaALG was prepared by the calcium alginate(CaALG) and ammonium tungstophosphate(AWP). The composite adsorbent was characterized by XRD, FT-IR and TG-DTG-DTA, it proves that the crystal structure of AWP isn’t destroyed and the adsorption ability of the composite adsorbent can be retained up to 120°C. Effects of adsorbent dosage, adsorption time, pH, temperature, concentration of Rb and K were investigated. The results show that the adsorption capacity of composite adsorbent to rubidium is 20.64mg/g.The adsorption equilibrium is gained after 24h. When the concentration ratio of K to Rb is 16, the adsorption rate of Rb can still be up to 94.1% and the Rb/K separation coefficient is 86.

Selective Separation and Recovery of Cesium by Ammonium Tungstophosphate-Alginate Microcapsules

A fine crystalline ammonium tungstophosphate (AWP) exchanger with high selectivity toward Cs+ was encapsulated in biopolymer matrices (calcium alginate, CaALG). The characterization of the AWP-CaALG microcapsule was examined using SEM/WDS, IR and DTA/TG analyses, and the selective separation and recovery of 137Cs were examined by the batch and column methods using simulated and real high-level liquid waste (HLLW). The free energy (ΔG0) of the ion exchange (NH4+ ↔ Cs+) for fine AWP crystals was determined at −13.2 kJ/mol, indicating the high selectivity of AWP towards Cs+. Spherical and elastic AWP-CaALG microcapsules (∼700 μm in diameter) were obtained and fine AWP crystals were uniformly immobilized in alginate matrices. Relatively large Kd values of Cs+ above 105 cm3/g were obtained in the presence of 10−3∼1 M Ca(NO3)2, resulting in a separation factor of Cs/Rb exceeding 102. The irradiated samples (60Co, 17.6 kGy) also exhibited large Kd values exceeding 105 cm3/g in the presence of 2.5 M HNO3. The Kd values in the presence of 0.1–9 M HNO3 for 67 elements were determined and the order of Kd value was Cs+ ≫ Rb+ > Ag+. The breakthrough curve of Cs+ had an S-shaped profile, and the breakpoint increased with decreasing flow rate; the breakpoint and breakthrough capacity at a flow rate of 0.35 cm3/min for the column (0.7 g AWP-CaALG) were estimated at 25.2 cm3 and 0.068 mmol/g, respectively. Good breakthrough and elution properties were retained even after thrice-repeated runs. The uptake (%) of Cs+ in simulated HLLW (28 metal components-1.92 M HNO3, SW-11, JAEA) was estimated at 97%, and the distribution of Cs+ and Zr/Ru into the AWP and alginate phases, respectively, were observed by WDS analysis. Further, the selective uptake of 137Cs exceeding 99% was confirmed by using real HLLW (FBR “JOYO”, JAEA). The AWP-CaALG microcapsules are thus effective for the selective separation and recovery of Cs+ from HLLWs.