REMOVAL OF Pb(II) FROM AQUEOUS SOLUTION BY NATURAL AND SYNTHETIC CALCITES

A comparative evaluation of the adsorption capacity and kinetics of Pb(II) uptake by both synthetic and natural calcites has been undertaken using batch equilibration technique. The originality of the calcite materials was confirmed by XRD and elemental composition by XRF. The point of zero charge values of 9.57 and 8.20 were obtained by mass titration method for synthetic and natural calcite, respectively. The maximum adsorption capacities of 200 mg/g and 150 mg/g Pb(II) of synthetic calcite and natural calcite were obtained at initial lead loading of 1200 mg/L at 25 +/- 2 degrees C, respectively. The study showed a very slight dependence of sorption capacity on the ionic strength and pH, but a strong dependence on the particle size and contact time. The sorption data results fitted better the Langmuir than the Freundlich isotherms. The kinetic data fitted well to pseudo-first order sorption kinetic model with a regression coefficient value of 0.96 and 0.94 for synthetic and natural calcites, respectively. Desorption of Pb(II) from calcite surface was achieved with efficiency of 95% using 4 M HNO3. The extent of reversibility of sorption reaction was a function of the equilibrium pH of calcite-Pb(II) solution suspension.