Adsorption and displacement of heavy metals (Cr, Pb, and Cd) in some soils of São Paulo State

Em solos de uma área nunca cultivada do litoral paulista no Vale do Ribeira com Podzólico Vermelho Amarelo-orto e Glei Húmico do município de Juquiá - SP e Terra Roxa estruturada do município de Piracicaba - SP estudou-se a adsorção e deslocamento de alguns metais pesados, Cr, Pb e Cd. No estudo da adsorção adotou-se a metodologia de JOHN (1972) aplicando-se as isotermas de Langmuir e Freundlich. A adsorção foi verificada ao nível de a 1.000 ppm para os três metais. A seletividade da adsorção dos três metais e solos observou-se da seguinte forma: - em relação a massa, mg/1009 solo Pb > Cd ≥ Cr TE ≥ PV-orto > GH; - em relação a meq, meq/100g solo Cr > Cd ≥ Pb TE ≥ PV-orto > GH. Os deslocamentos dos metais pesados foram estudados em colunas de solos, aplicando-se um pulso de metais em solução de sais provenientes de nitrato e cloretos. Após a inoculação, foram efetuados percolações com água destilada em 5, 10 e 20 vezes o volume de poros. As amostras foram retiradas a cada Δx = 5 cm da coluna de solo imediatamente após haver percolado o volume de poros. Os resultados mostraram que o deslocamento dos metais através das colunas estão correlacionados com as características físicas e químicas dos solos. Verificou-se ainda, que no deslocamento dos metais pesados, o pH mostrou-se fundamental no seu mecanismo de equilíbrio químico assim como a CTC do solo, tendo a TE maior capacidade de retenção dos metais pesados em relação a PV-orto e GH.The purpose of this study was to evaluate adsorption and displacement of chromium, lead, and cadmium in an Ultisol (Podzolico Vermelho Amarelo-orto), an Alfisol (Terra Roxa Estruturada), and a Humic Glei soil (Glei Húmico) of São Paulo State. Soil samples were collected from the A horizon, air-dried, and crushed to pass a 2 mm sieve. The adsorption of heavy metals was determined by the method of John (1972). The soil samples were equilibrated with solutions containing the heavy metal, concentration of which varied from 1 to 1,000 μg/ml. The equilibrium solution was analyzed and the amount of the heavy metal adsorbed was calculated by the difference of the solution concentration before and after the equilibrium. The Freundlich and the Langmuir equations were used to evaluate the chromium lead, and cadmium adsorption in the soils. At the same equilibrium concentration (μg/ml), the adsorption of heavy metals in terms of mass (mg/100g soil) decreased in the following order: Pb > Cd ≥ Cr, and in terms of chemical equivalence (meq/100g soil): Cr > Cd ≥ Pb. Among the three soils, the magnitude of adsorption was related to their effective cation exchange capacity and decreased in the following order: Alfisol ≥ Ultisol > Humic Glei soil. The displacement of heavy metals in soil columns was studied by applying solution containing CrCl2, Pb(NO3)2, or CdCl2 on the top of soil column, and 5, 10 or 20 pore-volumes of water. Immediately after the percolation of water, soil samples were collected from the column at the interval of 5 cm and analyzed. The results showed that the displacement of heavy metals in the soils is correlated to the physical and chemical characteristics of the soils. The main factors which influenced the displacement of these elements were the soil reaction and the effective cation exchange capacity. The Alfisol had a greater capacity to retain the heavy metals than the Ultisol and the Humic Glei soil