The characteristics of lead removal by crab shell particles were investigated. The removal efficiency of lead was dependent on contact time, initial solution pH, crab shell dose, ionic strength, co-ion concentration and settling time. Approximately 99% of the lead was removed within 2 h after contact with crab shell particles. The removal efficiency was slightly affected by initial solution pH over 3.0. In addition, when the crab shell dose increased from 0.5 to 1.5 g/litre, 84% removal efficiency improved to 99.8% at initial pH 2.0. Maximum uptake of lead was 870 mg Pb/g crab shell at initial pH 3.0. Removal efficiency was not affected by ionic strength up to 1.0 M of NaNO3. Co-ions such as Cd2+, Cu2+, Fe2+, and Zn2+ did not decrease the removal efficiency significantly. All the solids formed in 'crab shell-free' solutions were difficult to settle. In contrast, in 'crab shell' solutions, the solids quickly settled which might be as a result of the adsorption of lead precipitates on the surface of the crab shell particles. (C) 1998 Elsevier Science Ltd. All rights reserved.