Bauxite residue (BR) is an inevitable industrial waste generated through the classic Bayer extraction of alumina from bauxite minerals. It contains relatively significant amount of valuable rare earth elements, including scandium, and therefore we explored the suitability of trace scandium recovery from BR acid leachate by titanium phosphate (TiP) ion exchangers. Three kinds of TiP materials (amorphous TiP, α-TiP and γ-TiP) were synthesized through fluorine-free precursors and characterized by chemical analysis, XRD, FE-SEM, FTIR, UV/Vis diffuse reflectance spectrometry, 31 P MAS NMR, TGA and potentiometric titration. The Sc 3+ exchange capacities were determined as 1.74, 0.55 and 0.22 meq g -1 for amorphous, α-and γ-TiP, respectively. Competition of major elements (Fe, Al, Ca) in BR leachate with Sc uptake was studied in batch experiments using binary equimolar mixtures, and the separation factors of Sc/Fe 2+ , Sc/Al and Sc/Ca reach the magnitudes of 10 to 1000 on amorphous TiP. 2 The high Sc 3+ selectivity by amorphous TiP was suspected to be the matching of Ti 4+ lattice radius with Sc 3+ ionic radius (both 0.745 Å). Finally, the separation of trace scandium from the simulated BR leachate solution was demonstrated on an amorphous TiP column. The interference of Fe 3+ has been partially resolved by on-column reduction using sodium sulphite. The optimized final eluate contained only Sc, Fe and Al. The concentration ratio of Sc/Fe can be increased by a factor of 8.8 and Sc/Al by 265 through a single cycle of chromatographic separation with a Sc recovery rate of 91.1%. KEY WORDSTitanium phosphate; scandium recovery; ion exchange; bauxite residue.

This paper describes the processes used at the Fukushima Daiichi plant, Japan, to purify the waste effluents generated in the cooling of damaged reactors. These include primary cesium removal with the Kurion zeolite system and the SARRY system utilizing silicotitanate to remove radiocesium from water recirculated to reactors for cooling. Another process is the ALPS system to purify the retentates of the reverse osmosis plant to further purify the water from radionuclides after primary cesium separation. In ALPS, a major role is played by the transition metal hexacyanoferrate product CsTreat and sodium titanate SrTreat in the removal of radiocesium and radiostrontium, respectively. The performance of these four exchangers (zeolite, silicotitanate, hexacyanoferrate, and sodium titanate) are critically analysed with respect to processing capacities and the decontamination factor obtained in the processes. Furthermore, general information on preparation, structure, and ion exchange of these ion-exchanger categories are given with additional information on their use in nuclear waste effluent treatment processes. Finally, the importance of selectivity and associated factors are discussed.

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