Lead sorption to selected Portuguese soils |
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| Authors: | M A Trancoso M M Correiados Santos & M L S Gonçalves |
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| Institution: | Instituto Nacional de Engenharia, Tecnologia e Inovação –LAACQ, Estrada do Paço do Lumiar, 1649–038 Lisboa; , and Centro de Química Estrutural, Instituto Superior Técnico, Avenida Rovisco Pais, 1049–001 Lisboa, Portugal |
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| Abstract: | We studied the interaction of lead with seven Portuguese soils with different physical and chemical properties in order to elucidate more fully the behaviour of Pb in soil. We studied these adsorption phenomena by voltammetric titrations with differential pulse polarography (DPP) at different pH (6.0–7.2) and ionic strengths, I (0.010–0.50 m ) in order to clarify some of the factors that might control soil sorption capacity for Pb. From the voltammetric data, average formation constants,  , and binding capacity, Cc, have been estimated according to a surface complexation model based on Scatchard and van den Berg–R?zic methods. Linear Scatchard and van den Berg–R?zic plots (r≥ 0.99) indicated that the results can be interpreted according to the existence of just one predominant active site for Pb(II) adsorption. The  values from both procedures ( ) agreed in all cases (r= 0.938, n= 66, P < 0.001). The same happened with Cc values that were statistically equivalent (r= 0.9998; n= 66; P < 0.001). The Cc values were found to depend on the pH and I, as well as on the soil properties. Either Langmuir or Freundlich isotherms fitted the experimental data well (r > 0.90, P < 0.05). The lead binding capacities were strongly and significantly correlated (P < 0.05) with pH, cation exchange capacity, organic carbon, loss‐on‐ignition, total Al2O3 content, extractable forms of Al and pyrophosphate extractable Fe, Fep]. From a forward, stepwise regression model we concluded that Al2O3], Pb′] (concentration of labile lead in solution), Fep], pH and I are able to explain more than 99.7% of the variation in lead sorption in our soils. The soils’ surface groups with special affinity to Pb(II) are in the inorganic fraction associated with aluminium. |
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