Adsorção e dessorção de cobre em solos sob aplicação de lodo de esgoto e calda bordalesa / Adsorption and desorption of copper in soils under sewage-sludge and bordeaux mixture application

AUTOR(ES)
DATA DE PUBLICAÇÃO

2005

RESUMO

The introduction of heavy metals in soil could be effectuated in differents ways, being the applications of sewage-sludge and industrial residues the most studied of them. However, traditional agricultural practices can contribute to take metals to the soil as well, through the use of mineral fertilizers, pesticides and also organic manure.The objectives of this research were to consider the relationship between copper concentrations in soil solution and in its solid phase on soils of orchards in Louveira region of São Paulo State, Brazil, which had been previously contaminated by copper due the application of the Bordeaux mixture; and also another two soils contaminated by copper due to the application of sewage-sludge. This study included the determination of the adsorption and desorption capacity of these soils through adsorption isotherms; the values of free energy (∆Go) and the distribution coefficient Kd. The Langmuir and Freundlich models were fitted to experimental data. Soil samples were stirred during 24 hours in duplicate with 20 mL of 0.01 mol L-1 Ca(NO3)2 solution (relation 1:10) containing: 0; 2; 5; 10; 15; 30; 50; 75 and 100 mg L-1 Cu. The metal concentrations in the equilibrium solution were determined by atomic absorption spectrophotometry. The adsorbed metal amounts were calculated with basis on the difference between the initial amount and the metal remaining content at the end of the reaction period. To determine the desorbed metal amount, the soil samples previously submitted to the adsorption trial were stirred for 2 hours, three consecutive times, with 20 ml of solution of Ca(NO3)2 0.01 mol L-1 in duplicate. The cumulative desorbed copper amount was calculated by the sum of the copper extracted in each step. The Freundlich and Langmuir isotherms presented themselves as equally capable of describing the Cu adsorption in all the studied soils. Generally, soils containing the greater organic matter content and pH, adsorbed higher amounts of copper, and presented greater distribution coefficients (Kd). In the soils submitted to sludge application copper desorption was very low. For all the studied soils samples the hysteresis phenomenon was expressive. In all soils the copper adsorption reaction was thermodynamically exothermic and spontaneous. Despite the high copper content in soils treated with sludge and the Bordeaux mixture application, a great adsorption capacity of the added copper was detected. Such results strengthen the importance of the organic matter in the correct soil management of copper contaminated soils due to the addition of sewage-sludge and Bordeaux mixture.

ASSUNTO(S)

cobre copper solos metal pesado do solo lodo de esgoto adsorption bordeaux mixture desorption adsorção calda bordalesa dessorção sewage-sludge

ACESSO AO ARTIGO

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