Al-substituted 11 angstrom-tobermorite was formed by alkaline hydrothermal treatment of blast furnace slag with sodium silicate added at 180 degrees C for 2-48 h. Effects of the hydrothermal treatment time were characterized by XRD, SEM, and isothermal adsorption of N-2. Sorption characteristics of the obtained samples were examined for Cs+ and Sr2+. The sample obtained by hydrothermal treatment for 48 h (HT-48 h) consisted of calcium silicate hydrate (C-S-H), and Al-substituted 11 angstrom-tobermorite. The HT-48 h showed the highest performance for Cs+ and Sr2+ selectivity in the presence of Na+. The interlayer Na+ of Al-substituted 11 angstrom-tobermorite and surface Ca2+ played an important role in selective Cs+ and Sr2+. (C) 2014 Elsevier B.V. All rights reserved.