Effects on the removal of Pb<SUP>2+</SUP> from aqueous solution by crab shell

The effects of temperature, pH, chitin and chitosan on Pb²⁺ removal by crab shell were investigated. Pb²⁺ removal by crab shell was greater than that of chitin and chitosan, indicating that chitin did not contribute to Pb²⁺ removal by crab shell. The quantity and rate of Pb²⁺ removal increased as the pH value increased. The rate of Pb²⁺ removal increased with increased temperature, but the maximum amount of Pb²⁺ removal was constant irrespective of temperature. Metal ions (K⁺, Na⁺, Mg²⁺, Ca²⁺) were released from crab shell concomitant with Pb²⁺ removal by ion exchange. The amount of Ca²⁺ released was greater than any for other metal ions in both Pb²⁺ and Pb²⁺-free solutions. The amount of Ca²⁺ released in Pb²⁺ solution was greater than that in Pb²⁺-free solution, whereas CO₃^2- release in Pb²⁺ solution was less than in Pb²⁺-free solution. Pb²⁺ removal was mainly a consequence of dissolution of CaCO_3(s) with consequence precipitation of Pb₃(CO₃)₂(OH)_2(s) and PbCO_3(s). Pb²⁺ 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