Here, we report the rapid synthesis of Al-substituted tobermorites from zeolites under microwave-hydrothermal (M-H) conditions. The synthesized phases were characterized by powdered XRD analysis, SEM and selective Cs exchange determination. Zeolites served as aluminosilicate sources and M-H conditions yielded highly crystalline Al-substituted tobermorites in 2 h at 180degreesC and they showed high selectivity for Cs. For example, an Al-substituted tobermorite synthesized from phillipsite showed Cs exchange K-d of 2161 +/- 465 and 118,589 +/- 44,928 from 0.02N NaCl and 0.02N CaCl2 solutions (both contained 0.0002N CsCl), respectively. Al-substituted tobermorites are expected to be useful for the selective separation of radioactive Cs and tobermorites can be incorporated in cement and/or concrete matrix for Cs immobilization. (C) 2002 Elsevier Science Ltd. All rights reserved.