Three different carbonaceous adsorbents consisting of (i) commercially available lignin (L); (ii) carbon
soot produced by arc evaporation of graphite rods (AC); and (iii) commercially available carbon (RC)
were employed for the removal of hexavalent and trivalent chromium, and the cations of lead and zinc.
AC carbon was found to selectively adsorb only the hexavalent form of chromium which exists as a
number of anionic species in the water. Insignificant metal cation adsorption was observed with AC.
However, lignin is found to adsorb all the metal ions employed in the study. RC used in this investigation
adsorbs only the metal cations and does not remove the hexavalent form of chromium used. Equilibrium
as well as kinetic data obtained are analyzed in light of a mathematical model developed which assumes
that the overall metal removal rate is controlled by the rate of mass transport of solute from bulk to the
surface of the adsorbent.