In order to investigate the process of Pb2+ removal by crab shell, the effects of pretreatment of crab shell with acid and alkali on Pb2+ removal by crab shell were examined. In acid treatment of crab shell with HCl for the demineralization of crab shell, Ca2+ and Mg2+ in crab shell were largely extracted during the acid treatment and the Pb2+ removal by acid treated crab shell was very low. The total released Ca2+ and Mg2+ amounts in the alkali treated crab shell during Pb2+ removal were not greatly different from those in the untreated crab shell. However, the times to reach an equilibrium state were quite shortened by alkali treatment and the reason was explained by transmission electron microscope. (C) 2003 Elsevier Ltd. All rights reserved.