Adsorção individual e competitiva de Cd, Cu, Ni e Zn em solos em função da variação de pH / Individual and competitive adsorption of Cd, Cu, Ni and Zn in soils as a function of pH variation

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

The disposal of solid waste or the application of pesticides and fertilizers may increase the concentration of potentially toxic elements, especially heavy metals, in soil and in groundwater. As the soil has been considered a potential deposit for the provision of such wastes, it is important to know the mechanisms of retention and transport of these elements to minimize their impact to the environment. The behavior of a metal in soil may be evaluated through adsorption studies. The effect of pH variation on the adsorption of heavy metals was evaluated, under individual and competitive systems, in samples from the surface layer (0-0.2 m) of 30 representative soils of the State of São Paulo. Adsorption isotherms were prepared after addition of 10 to 200 mg L-1 of Cd, Cu, Ni and Zn in the form of nitrate, and the background electrolyte was a 0.01 mol L-1 NaNO3 solution. The pH effect on metals adsorption was evaluated after adding 20 ml of 0.01 mol L-1 NaNO3 solution with 0.1 mol L-1 of each metal. The adjustment of pH was made or with HNO3 or with NaOH, in order to achieve pH values among 4 to 7. After shaking the samples and subsequent centrifugation, metal concentration was determined in the equilibrium solution. The amount of adsorbed metal was calculated by the difference between the added and the remaining concentration in the equilibrium solution. Adsorption parameters estimated by Langmuir and Freundlich models were obtained with the experimental data and were related with physical, chemical and mineralogical soil attributes. Langmuir and Freundlich models fitted well the adsorption results for the four metals, with high correlation coefficients for the majority of the data. For all soils, adsorbed amounts of Cd, Cu, Ni and Zn were directly correlated to the added doses. Cu had the highest values of adsorption parameters estimated by both Langmuir and Freundlich models. The maximum adsorption from Langmuir model and the adsorption capacity from Freundlich model were positively correlated with soil pH. In The adsorption increased as a result of pH increase until a plateau was achieved. Under high pH values, a decrease in the adsorption of some metals was observed in some soils. The sequence of adsorption found for the majority of the soil pH 4.5 and 5.5 was Cu >Cd >Zn >Ni. For the pH 6.5 the sequence found in most soils was Cd >Zn >Cu >Ni.

ASSUNTO(S)

zinc. cadmium níquel ph do solo zinco. heavy metal nickel soil ph cádmio metal pesado no solo copper cobre

ACESSO AO ARTIGO

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