Equilíbrio e cinética da adsorção de cobre e zinco em solos tropicais

Abstract

The expansion resulted in the use of several classes of soil for cultivation and the use of fertilizers made essential. However, the physical-hydraulic and chemical properties of soils are determinants of their greater or lesser susceptibility to leaching and contamination of groundwater by metal ions present in agrochemicals, such as copper and zinc. These metals are essential to the life cycle of plants and their availability in the soil is related to the type and content of clay, organic matter and iron and aluminum oxides present. Thus, the objective of this paper was to quantify the adsorption of copper and zinc in mono and multicomponent systems in a Red Latosol (LV), Haplic Cambisol (CX) and Quartzarenic Neosol (RQ) using adsorption isotherms and kinetics, by Batch method. The Langmuir, Freundlich, Langmuir multocomponent and Freundlich multicomponent equilibrium models were fitted to the observed data, for initial concentrations of the evaluated and companion ion of 10, 15, 30, 40 and 50 mg L-1, determining the Gibbs free energy and the separation factor. For the kinetics test, the contact times of 2, 5, 10, 20, 60, 120, 180, 240 and 1440 minutes were evaluated, adjusting the models of pseudo-first order, pseudo-second order and Elovich. To evaluate the average adsorption for the equilibrium and adsorption kinetics, it was used a completely randomized design in a factorial scheme with three replications. Copper was the ion most adsorbed in the mono and multicomponent systems for equilibrium and adsorption kinetics because its greater electronegativity. Among the soils, CX was the one with the greatest ion retention capacity due to the presence of 2:1 and 1:1 clay minerals. The RQ, on the other hand, was the one that least adsorbed the ions and, despite the higher energy of the binding sites, it is a soil more conducive to the leaching of copper and zinc. The LV, although it has the highest clay content among the studied soils, did not show a high capacity for adsorption by the type of clay present. The Freündlich and Langmuir multicomponent isotherm model obtained good adjustments to the observed data. For kinetics, the pseudo-first order model fits both mono and multicomponent systems. Gibbs' free energy showed that the adsorption process was spontaneous and there was a predominance of physisorption.