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Water Air Soil Pollut (2009) 199:343351 DOI 10.1007/s11270-008-9883-9
Adsorption of Lead and Cadmium from Aqueous Solution by Using Almond Shells
Mohammad Reza Mehrasbi &
Zohreh Farahmandkia & Bahareh Taghibeigloo &
Azra Taromi
Received: 9 June 2008 /Accepted: 27 September 2008 /Published online: 5 November 2008 # Springer Science + Business Media B.V. 2008
Abstract The potential of almond shells was assessed for adsorption of heavy metal ions such as Pb2+ and
Cd2+ from aqueous solution. Almond shells were pre-treated separately with 0.4 mol/L NaOH, 0.4 mol/L HNO3, and distilled water and their adsorption abilities were compared. Batch adsorption experiments were carried out as a function of the initial ion concentration, pH, and adsorbent dosage. Adsorption isotherms of metal ions on adsorbents were determined and correlated with common isotherm equations such as Langmuir, Freundlich, and BET models. The alkali-modified almond shells had adsorption capacities for Pb2+ from 2 to 9 mg/g and for Cd2+ from 2 to 7 mg/g, which was much higher than acid-and water-pretreated adsorbents. Experimental results showed that the best pH for adsorption was 56 and the adsorption values decreased with lowering pH. Isotherm models indicated the best fit for Langmuir model for alkali-modified almond shells. In comparing the parameters of the models, it was observed that the affinity of almond shells for adsorption of lead is stronger than affinity for adsorption of cadmium.
Keywords Adsorption . Heavy metal .
Low-cost adsorbent . Almond shell . Plant waste
Nomenclatureq amount of metal ion adsorbed per specific amount of adsorbent (milligrams per gram) C residual metal ion concentration
(milligrams per liter)
C0 initial metal ion concentration
(milligrams per liter)qm amount of metal ions required to form a monolayer (milligrams per gram)n Freundlich equilibrium constant indicative of bond energies between metal ion and adsorbent KL Langmuir equilibrium constant related to the energy of adsorption (liters per milligram)
KB BET constantKF Freundlich equilibrium constant related to bond strength (milligrams per gram)
Cs solute concentration at the saturation of all layers (milligrams per liter)
m adsorbent massR2 correlation coefficients
1 Introduction
Heavy metals have been widely used in industrial processes such as metal plating, mining activities, smelting, battery manufactures, dying, etc. They are
M. R. Mehrasbi (*) : Z. Farahmandkia : B. Taghibeigloo :
A. TaromiDepartment of...