Abstract
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+^βfree solutions. The amount of Ca^2+^ released in Pb^2+^ solution was greater than that in Pb^2+^βfree solution, whereas CO~3~^2β^ release in Pb^2+^ solution was less than in Pb^2+^βfree 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.
Β© 2001 Society of Chemical Industry