Ion exchange in amorphous alkali-activated aluminosilicates: Potassium based geopolymers

Abstract

Ion exchange properties of pure potassium-based geopolymer (pure K-GP) formulated with Si/Al=2.1 and K/Al=1.0±0.02 atomic ratios have been studied. For pure K-GP, the maximum ion-exchange level of K+ with respect to Na+ and Cs+ is 77 and 61%, respectively, as determined by exhausted exchange with 1M solutions of appropriate nitrates at 22±2°C. The geopolymer shows a slight preference for K+ over Cs+ as indicated by the normalized Cs/K-GP isotherm obtained under noncompetitive exchange. Parent geopolymer yields a pure geopolymer when it is extensively washed with deionized water until neutral pH is obtained and equilibrated with aqueous solution of KNO3 resulting in changing in composition and textural properties. As calculated from N2 sorption–desorption isotherms, surface specific area and cumulative pore volume for parent K-GP are 5.5m2g−1 and 0.01cm3g−1, respectively, whereas for pure K-GP surface specific area and cumulative pore volume are 270m2g−1 and 0.4cm3g−1, respectively.