Incorporation of humic acid in the FDU-1 mesoporous silica improved Hg(II) adsorption and did not destroy the ordered network, providing surface area of 500 m(2) g(-1), pore volume of 0.9 cm(3) g(-1), and mean pore diameter of 10 nm. Carboxylic and phenolic groups increased the affinity by forming surface complexes with Hg(II). Isotherms (25.0 +/- 0.1 degrees C) were fitted to the Freundlich equation, exhibiting K-f values that increased with pH and 1/n that decreased to values < 1 with the heterogeneity of sites. Hg(II) desorption in 0.10 mol L-1 acetic acid was lower than 10%, suggesting that chemisorption processes govern the Hg(II) removal.