Atributos fisicoquímicos e adsorção de fósforo na fração argila de latossolos vermelhos em presença de ácido fúlvico

Abstract

This study was conducted in the Dipartimento di Valorizzazione e Protezione delle Risorse Agroforestalle, located at the Facoltà Agrária of University of Torino, Italy, aiming to quantify the adsorption of P and evaluate the influence of the presence of fulvic acid on clay fractions extracted from Rhodic Ferrasol (LVDf) and Rhodic Hapludox (LVD) of the State of Mato Grosso do Sul, natural kaolinite few cristalinized (KGa2) and goethite (Gt) and hematite (Hm) synthetic. First the materials were characterized to the knowledge of their specific surface areas (SBET) and pore through adsorption isotherms of N2. The results for SBET and porosity of the particles were connected with adsorption maximum of P (P - Xmax) as determined by Langmuir model. To help the discussion of the data analysis was performed of the potential of electrostatic surface during the adsorption of P. The SBET of the clay fractions from LVDf and LVD were close together and higher when compared to Gt, Hm and KGa2. The class of predominant pores in the clay fractions of LVDf e and LVD was mesoporous. The fractions extracted clay soil and natural kaolinite were able to adsorve similar amounts of phosphorus (P) per unit area. This indicates that the mechanisms for such materials adsorption P were similar. The difference of values of P adsorption between the clay fractions extracted from soil and clay compared to the values observed for the synthetic oxides was attributed, possibly, to the quantities and types of distributions of OH groups on the surface of the constituents of these fractions, which command the electrochemical processes, and the grooves or imperfections such areas. The kaolinite, although the greater filossilicate on representation in clay fractions of LVDf and LVD, had lower participation on the phenomenon of adsorption of P. The P – Xmax in the presence of fulvic acid (AF) presents different dynamics in low and high concentration of P. The model adjusted to the Langmuir adsorption isotherms of P in the presence of AF was appropriate for the region of low concentration of P. Under high concentrations of P, the model doesn`t fit the Langmuir isotherms due to the fact that in this condition the P and AF have promoted dispersion and/or dissolution of the materials, and precipitation with iron and aluminum. Overall, the AF was able to reduce t the P adsorption on the materials. In low concentrations of P, the P – Xmax on the clay extracted from LVDf doesn`t depended of order incubation of P with AF, but the presence of AF. For the clay extracted from LVD, the orders of incubation with P and AF influenced the P – Xmax. In high concentrations of P, there was no influence of the orders of incubation for P and AF on the P adsorption of extracted clay from LVDf, and the P adsorption on the extracted clay from LVD depended of their order of incubation with the AF, as occurred in low concentrations of P.