Caracterização de bentonita sódica e seu comportamento coloidal na presença de polifosfato

Abstract

Suspensions of clay with polymers have been the subject of many research activities due to obtaining new materials with unique physicochemical properties, arousing interest for various productive sectors. In the agricultural sector the search for obtaining controlled release fertilizers (CRFs) is a new alternative that seeks to minimize the environmental impact. A CRF in the form of a hydrogel constituted by clays connected to polyphosphate chains has a great chance of meeting this requirement, as well as releasing phosphorus which is an essential nutrient for the plant, at the end of the process, the clay itself remains as a residue that is a natural constituent from soil. The present work aims to study the physicochemistry of the clay-polyphosphate (PP) interactions in the search for a CRF-type material. Colloidal dispersions involving the Industrialized Sodium Bentonite (BSI) and PP chains were studied. At first, the clay was characterized, showing a polycationic clay, with Na^+ and Ca^2+, cations, with an average swelling value of 8 mL/g. The XRD analysis of pure clay indicated characteristic planes of smectite groups, however, with traces of impurities such as quartz. For the analysis of colloidal stability, the technique of photosedimentometry measurements was applied in order to address the sedimentation velocity of the particles and to relate the diameter of the particles based on the Stokes' Law. The factors that were investigated to verify the influence on the sedimentation were: concentration of particles, concentration of the polymer and variation of ionic strength. The results showed that, for the concentration of clay, the best condition for the analysis using Stokes' law, is a system that contains low solid content (0,1% m / v) in order to minimize interactions between particles during the analysis. With respect to the polymer the concentration of 0,01 M PP was the one that allowed a more consistent association between the polymer chains and the clay particles, forming strongly bonded aggregates. Finally, a low ionic strength, in the value of 0,001 allowed the minimization of the electric double layer of the lamellae, making the edges accessible for the adsorption of the polymer chains. These conditions reflected in a viscous, flow resistant system. This system described that presented the best conditions increases the expectations for obtaining a future CRF, making it necessary to deepen this study through rheological measurements of the systems besides the introduction of other essential elements to the plants, as is the case of nitrogen and potassium.