Cation exchange reactions of a sedimentary phillipsite

Abstract

Exchange isotherms of alkali-metal and alkaline earth-metal ions have been measured at 25 °C and for 0·1N solutions in a sedimentary phillipsite from Pine Valley, Nevada, having an initial oxide composition (Na_1·42K_0·38Ca_0·03)-O,Al₂O₃,5·6SiO₂,5·7H₂O. Reversible isotherms were obtained for the pairs Na ⇌ Li, Na ⇌ K, Na ⇌ Rb, Na ⇌ Cs, 2Na ⇌ Ca, and 2Na ⇌ Sr. The isotherm for 2Na ⇌ Ba was however irreversible with apparent fixation of Ba. The crystals were very selective for K, Rb, and Cs as compared with Na and for Na as compared with Li. A synthetic near-phillipsite showed an even stronger preference for K over Na. From the 0·1N solutions there was little preference for Ca or Sr over Na, but a very strong selectivity was observed for Ba, which allowed its quantitative removal from admixture with Na. Thermodynamic equilibrium constants were evaluated for all reversible exchanges, and activity coefficients of each ion in the exchanger as functions of exchanger composition