Síntese de adsorventes magnéticos utilizando casca de soja e sua aplicação na adsorção de ácido cafeico

Abstract

Wastewater management has gained increasingly space on the world stage, with significant advances in both the environmental and financial spheres. Phenolic compounds are present in wastewater of various processes, such as in petrochemical plants, paper, wood, metallurgy, agroindustrial processes, coffee industry, olive mills and others. Among the phenolic compounds present in industrial waste, caffeic acid has an important space, due to its positive biological effects, such as the inhibition of carcinogenesis, antioxidant, antiviral, anti-inflammatory and antirheumatic properties. Despite the many studies on the oxidation of caffeic acid, little has been done about its recovery by adsorption. In the adsorption process, biomass residues can be used as precursors in the synthesis of adsorbents, being a source of low cost for adsorption processes. However, although these materials are inexpensive and available in large quantities, difficulties can be encountered in the separation at the end of the adsorption process. In this way, the objective of this project was to develop magnetic adsorbents with different concentrations of Fe, for adsorption and desorption in batch of caffeic acid for recovery. The magnetic characteristic of the material being studied is a key factor for separating the adsorbent from the liquid phase when it becomes saturated. In the synthesis of the adsorbents, an iron-containing polymer was first obtained by the modified Pechini method. This polymer was mixed with the soybean hull and this mixture was charred and activated in a pyrolysis reactor with CO2 flow under different temperatures. For the characterization of the material, specific surface area, Zeta potential, X-ray diffractometry (XRD), Infrared spectroscopy (FTIR), magnetization analysis using vibration sample magnetometry (VSM) and thermogravimetric (TG) analysis were performed. In the batch adsorption study, the effect of the pH on the adsorption and its relation with zeta potential of the adsorbent were evaluated. The pseudo-first and pseudo-second order models were fitted to the adsorption kinetic data. The equilibrium isotherms were analyzed at different temperatures to verify their influence on the adsorption process, and to determine the thermodynamic process quantities and isosteric heat values. In the desorption study, solutions with different concentrations of NaOH, methanol, ethanol and water at 80 ºC were used. The magnetic adsorbents synthesized and activated at 800 ºC presented high adsorptive capacities, and coal containing 1.3% Iron (418 mg g -1) showed the best result, followed by coal containing 12% Fe (316 mg g- 1). In addition to favoring adsorption, the presence of iron led to the formation of an adsorbent with properties magnetic fields. The coal containing 1.3% Fe also showed a faster adsorption kinetics with better magnetic properties. With regard to desorption, it was possible to desorb about 55% caffeic acid using methanol. The adsorption of phenolic compounds present in a real effluent presented a maximum capacity of 52 mg g-1.