The effect of soluble silicate on the sorption of U(VI) to gamma-Al2O3 was investigated by batch experiments and extended X-ray absorption fine structure (EXAFS) method. The presence of silicate enhanced the sorption of U(VI) on gamma-Al2O3 surface and the sorption was attributed to inner-sphere surface complexation. The structure of the adsorbed U(VI) and silicate on gamma-Al2O3 was investigated in the analysis of EXAFS spectra. The fitting of the experimental EXAFS data was obtained by including two uranium coordination shells with 2 axial (O-ax) and 5 equatorial (O-eq) oxygen atoms at 1.79 +/- 0.02 and 2.43 +/- 0.02 A, respectively, and the third coordination shells with Al atom at similar to 3.35 angstrom. Silicate contributed to the formation of ternary inner-sphere surface complexes, acting as "bridge" between U(VI) and gamma-Al2O3 and enhanced the sorption of U(VI). The observations suggested that the interactions between U(VI) and silicate were important in controlling U(VI) retention. (C) 2015 Elsevier B.V. All rights reserved.