Adsorção de fósforo em carvão ativado impregnado com óxidos de ferro

Abstract

The presence of nutrients, such as phosphorus (P), in water bodies represents a global issue for water quality. Among all the pollution problems, the eutrophication has been considered a serious environmental problem. Tertiary treatment technologies are available for the control of soluble phosphorous, and adsorption has been investigated as a relatively simple process facilitating the recycling of the nutrient. The increase of the adsorption capacity has been investigated, as the impregnation of the adsorbent by iron oxides. The objective of this work was to evaluate the phosphorus adsorption by commercial granular active carbon impregnated with iron oxides (GAC-Fe). For this, a preliminary study was carried out to define the impregnation method that obtains the better capacity of adsorption of phosphorus. The adsorbent developed must be stock in an inert environment after the process. Physical and chemical characterization of GAC-Fe was performed including Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS), Thermogravimetric analysis (TGA) and zero point charge (pH ZPC ) analyzes. A new adsorption isotherm was development considering the presence of two activated sites in the adsorbent surface. This model was showed as be best isotherm model to describe the system equilibrium. The results indicated high dependence of the adsorption with pH solution, showing best adsorption capacity in pH 3.0 ( = 2.874 mg g -1 ). An analysis of the zero charge point of the adsorbent indicated a positive charge at pH less than 3.5, explaining the higher affinity to phosphate. The process was spontaneous and favorable at the temperatures studied (25, 35 and 45°C). The thermodynamic results suggest two types of adsorption mechanisms at the surface, related to chemisorption. The best kinetic model of adsorption considers the internal mass transfer as the rate-limiting step. The temperature and initial concentration not shows influence on effective diffusion coefficient. Hence, the study shows an alternatively material for phosphorus adsorption and contributes know the mechanism involved in the process and equilibrium of the system.