Remediação de um argissolo contaminado por zinco e cobre com o uso da bentonita.

Abstract

The contamination of soil by heavy metais has been a growing problem to the environment and to the people's health in function of their toxicity, that has induced the science to search alternatives to prevent, or at least, minimize the pollutant effects of those metais or still, remediate the already polluted environment. Thus, several studies using sorbent materiais are conducted aiming to reduce the pollution problems produced by the excess of heavy metais. It is important to know the process of adsorption of heavy metais by clay minerais, because these are capable to immobilize such metais. The present study was carried out aiming, through three experiments, to evaluate the ability of the bentonite clay on the remediation of soils contaminated with zinc and copper. The fírst experiment consisted in studying the adsorption of these metais by bentonite at pH 4; 5 and 6, using the mathematical models of Langmuir and Freundlich. Adsorption isotherms were elaborated from batch adsorption assays, with increasing zinc and copper concentrations (5; 10; 20; 30; 50; 100; 150 and 200 mg L"1); the second experiment consisted in studying the zinc and copper mobility through leaching columns, prepared with soil and increasing bentonite leveis (0; 30 and 601 ha"1). The transport parameters were calculated using the computer model DISP. Finally, a greenhouse experiment was conducted to evaluate the effects of zinc and copper (50; 250 and 450mg kg"1) and bentonite (0; 30 and 60 t ha"1) added to the soil, on the phytomass production and mineral composition of a bean plant (Vigna unguiculata.h). At the end of the experiment (65 days) the phytomass and the content of zinc and copper in the aerial part, in the roots and in the soil were determined. It was observed that the adsorption of the elements increased with the bentonite application being dependent of the pH of the solution; the two studied models are appropriate to describe the zinc and copper adsorption for the bentonite; the granulometric size of the bentonite does not influence the metais adsorption and that the application of bentonite to the soil contributed to the decrease the concentration and accumulation of the heavy metais in the bean plant.