The association of Eu(III) and Am-243(111) with humic acid-bound gamma-Al2O3 (HA-Al2O3) was investigated using batch technique and the kinetic dissociation properties were studied using chelating resin. The results indicated that Eu(III) and Am-243(111) had very similar sorption properties. The kinetics of desorption of (243)(III) from HA-Al2O3 hybrids were studied at three different pH values (pH 4.0, 5.0 and 6.0) after aging time for 2 h, 4 days, and 1 month by adding chelating resin to remove the desorbed free Am-243 (III) ions from the HA-Al2O3 hybrids. The fraction of Am-243(III) on the irreversible binding sites of the HA-Al2O3 hybrids increased as the pH increased. Two different Am-243(III)-HA-Al2O3 species (i.e., "fast" and "slow" dissociation kinetics, which represented the "weak" and "strong" species on reversible sites) were required to fit the kinetic dissociation results. Although Am-243(III) was initially a "fast" dissociating species, it became a "slow" dissociating species as the aging time increased and at low HA concentrations. When the HA concentration was high, the "fast" and "slow" dissociating species of Am-243(III) bound to HA-Al2O3 particles were not influenced by the aging time. These results describe the physicochemical behavior of trivalent lanthanides and actinides in the natural environment, which is important to understand the potential pollution of long-lived radionuclides. (C) 2015 Elsevier B.V. All rights reserved.