ION-EXCHANGE OF GROUP-I METALS BY HYDROUS CRYSTALLINE SILICOTITANATES

A new hydrous crystalline silicotitanate, labeled TAM-5 or CST, was de veloped 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 acid ic, neutral, and basic solutions. Various experiments were conducted t o determine the ion exchange properties of TAM-5. Two kinds of ion exc hange sites exist in the solid, and cation exchange in one site affect s the ion exchange properties of the other site. These two types of si tes 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 capaci ty was less, which shows that not all of the ion exchange sites are av ailable for cesium exchange. Step changes were observed in the ion exc hange isotherms. The solid phase behaved ideally prior to the step cha nges. 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 b y protons and potassium were observed. The rational selectivities, whi ch were measured from binary ion exchange data, can be used in differe nt solutions including the multicomponent ion exchange systems, becaus e they are constant for an ideal solid. Binary ion exchange isotherms were also developed using the rational selectivity as the parameter fo r the isotherms of cesium, rubidinium, and potassium.