Effects on the removal of Pb 2+ from aqueous solution by crab shell

The effects of temperature, pH, chitin and chitosan on Pb 2+ removal by crab shell were investigated. Pb 2+ removal by crab shell was greater than that of chitin and chitosan, indicating that chitin did not contribute to Pb 2+ removal by crab shell. The quantity and rate of Pb 2+ removal increased as the pH value increased. The rate of Pb 2+ removal increased with increased temperature, but the maximum amount of Pb 2+ removal was constant irrespective of temperature. Metal ions (K + , Na + , Mg 2+ , Ca 2+ ) were released from crab shell concomitant with Pb 2+ removal by ion exchange. The amount of Ca 2+ released was greater than any for other metal ions in both Pb 2+ and Pb 2+ ‐free solutions. The amount of Ca 2+ released in Pb 2+ solution was greater than that in Pb 2+ ‐free solution, whereas CO 3 2− release in Pb 2+ solution was less than in Pb 2+ ‐free solution. Pb 2+ removal was mainly a consequence of dissolution of CaCO 3(s) with consequence precipitation of Pb 3 (CO 3 ) 2 (OH) 2(s) and PbCO 3(s) . Pb 2+ accelerated the dissolution of CaCO 3(s) by ion exchange and the precipitation occurred both at the surface and in the inner part of the crab shell. © 2001 Society of Chemical Industry