Abstract
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 °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 HNO 3 . The extent of reversibility of sorption reaction was a function of the equilibrium pH of calcite-Pb(II) solution suspension. KEY WORDS : Pb(II), Calcite, Sorption, Kinetics, Desorption, Aqueous solution Bull. Chem. Soc. Ethiop. 2012 , 26(2), 195-210. DOI: http://dx.doi.org/10.4314/bcse.v26i2.4
Highlights
Heavy metals are widely spread in the environment and they could be of anthropogenic or natural origin
The higher percentage of impurities in natural calcite could account for its lower point of zero charge (PZC) value compared to synthetic calcite
The results show that ionic strength has very little or no effect on the sorption of lead by calcite
Summary
Heavy metals are widely spread in the environment and they could be of anthropogenic or natural origin. Several industrial operations release some of these heavy metals in their effluents, which eventually find their way into water sources such as lakes, rivers and streams [1]. The non-biodegradability of Pb results in its bioaccumulation in living organisms causing serious health disorders [3]. This is as a result of its long residence time in the environment. Several methods have been documented in the literature viz-a-viz the removal of heavy metals and especially Pb(II) from aqueous solutions These methods include electro-deposition, cementation, reverse osmosis, membrane process, solvent extraction and adsorption [7]. Most of these methods present the inconvenience of high cost, large organic solvent consumption, requiring high level of expertise
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