A chemically-modified coal fly ash was prepared by immobilization of mercaptoethanol or mercaptoacetic acid to develop a low-cost and effective solid phase retention system for low levels of lead from aqueous solutions. The organically-functionalized coal fly ash-based retention system experienced high thermal and chemical stability. The batch extraction procedure was used to explore the equilibrium, kinetic and thermodynamic characteristics of the retention of lead by the functionalized sorbent at various temperatures. Several equilibrium models were compared to evaluate the lead retention process with a better fitting using the Langmuir model. Kinetic studies were also carried out to fit the experimental data. The pseudo-second-order and Elovich models provided the highest coefficients of determination, but the function Z and the McLintock method confirmed better applicability of the Elovichian model. Lead was retained up to about 45 mu g g (1) at pH 5.0, with similar results for the two ligands, mercaptoethanol and mercaptoacetic acid. Thermodynamic studies provided negative free energy changes, indicating spontaneity of the retention process. Positive values for both enthalpy and entropy indicated an endothermic retention with high affinity lead-sorbent. (C) 2012 Elsevier Ltd. All rights reserved.