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The aluminum Keggin polycation (Al13) has been identified as an effective specie for neutralization and coagulation of anionic contaminants in water. In this study, we compare efficacy of the aluminum Keggin-ion to the analogues containing a single Ga-atom or single Ge-atom (GaAl12 and GeAl12, respectively) substituted into the center of the polycation in water-treatment studies. We investigated removal of bacteriophage (model viruses), Cryptosporidium, dissolved organic carbon (DOC), and turbidity. In every study, the order of contaminant removal efficacy trends GaAl12 > Al13 > GeAl12. By ESI MS (electrospray ionization mass spectrometry), we noted the GaAl12 deprotonates least of the three aluminum polycations, and thus probably carries the highest charge, and also optimal contaminant-neutralization ability. The ESI MS studies of the aluminum polycation solutions, as well as solid-state characterization of their resulting precipitates both reveal some conversion of Al13 to larger polycations, Al30 for instance. The GaAl12 does not show any evidence for this alteration that is responsible for poor shelf life of commercial prehydrolyzed aluminum coagulants such as polyaluminum chloride. Based on these studies, we conclude that substitution of a single Ga-atom in the center of the aluminum Keggin polycation produces an optimal water-treatment product due to enhanced shelf life and efficacy in neutralization of anionic contaminants.

A new hydrous crystalline silicotitanate, labeled TAM-5 or CST, was developed for removing radioactive Cs+ from aqueous nuclear waste. This material is stable to radiation, highly selective for cesium relative to sodium, potassium, rubidium, and protons, and performs well in acidic, neutral, and basic solutions. Various experiments were conducted to determine the ion exchange properties of TAM-5. Two kinds of ion exchange sites exist in the solid, and cation exchange in one site affects the ion exchange properties of the other site. These two types of sites have different thermal effects: with increasing temperature the pH of one increases and the pH of the other one decreases. The total ion exchange capacity is 4.6 mequiv/g, but the cesium ion exchange capacity was less, which shows that not all of the ion exchange sites are available for cesium exchange. Step changes were observed in the ion exchange isotherms. The solid phase behaved ideally prior to the step changes. The apparent capacities within the ideal solid region were 0.57 mequiv/g for Cs+, 1.18 mequiv/g for Rb+, and 1.2 mequiv/g for K+. Both direct competition by rubidium and protons and indirect competition by protons and potassium were observed. The rational selectivities, which were measured from binary ion exchange data, can be used in different solutions including the multicomponent ion exchange systems, because they are constant for an ideal solid. Binary ion exchange isotherms were also developed using the rational selectivity as the parameter for the isotherms of cesium, rubidinium, and potassium.