Avaliação de tortas de oleaginosas com potencial para produção de biodiesel na obtenção de materiais adsorventes para remoção de metais em meio aquoso

Abstract

In this work, different adsorbent materials were obtained from six kinds of oilseed cakes with potential for biodiesel production, such as jatropha (Jatropha curcas L.), radish (Raphanus sativus L.), castor beans (Ricinus communis L.), sunflower (Helianthus annuus L.), pequis (Caryocar brasiliense L.) and lupine (Lupinus albus L.). The adsorbents were evaluated in nature, after chemical modification and in the form of activated carbon. The chemical modification was carried out by treating the radish cakes with citric acid, NaOH, or by the combination of NaOH and citric acid. The activated carbon was obtained by physical activation with CO2 (g) and functionalization with HNO3 (CAT). All adsorbents were characterized by surface analysis, thermogravimetric analysis, fluorescence spectrometry Xray, elemental analysis, infrared spectroscopy (FTIR), scanning electron microscopy, point of zero charge and potentiometric titration (PT). From the characterization, some materials were selected for studies of adsorption of Cd2+ and Pb2+ from aqueous solutions in batch or in batch experiments?. The effects of the different factors such as pH, concentration of adsorbent, agitation time, particle size and chemical modification were evaluated in the adsorption studies. After optimization of the conditions for adsorption, studies were performed to determine the maximum adsorption capacity of these materials. The experimental data were fitted to the Langmuir and Freundlich isotherm linear models. Results indicated that the chemically modified materials showed high adsorption capacity Cd2+ and Pb2+ from aqueous medium, being the highest obtained with radish press cake (TNF). The maximum adsorption capacities obtained from the adsorbents derived TNF, according to the Langmuir isotherm were 58.5 mg Cd g-1 (0.52 mmol Cd g-1) and 357.1 mg Pb g-1 (1.72 mmol Pb g-1) for material modified with citric acid 0.6 mol L-1 (NC0.6 ); 64.1 mg Cd g-1 (0.57 mmol Cd g-1) and 270.3 mg Pb g-1 (1.30 mmol Pb g-1) for modified with NaOH and citric acid (NHC), and 166.7 mg Cd g-1 (1.48 mmol Cd g-1) and 500.0 mg Pb g-1 (2.41 mmol Pb g-1) for functionalized activated carbon (CAT). These materials showed higher adsorptive capacity than some commercial activated carbons such as Norit C. Adsorption-desorption studies showed that these materials can be used for several consecutive cycles, indicating that the adsorbent-metal interaction is reversible and complete desorption was achieved using HNO3 solution of 0.1 mol L- 1. The results obtained in this study indicate the feasibility of using these byproducts of biodiesel production for the production of adsorbents of metal ions, since they are an abundant agricultural waste product, therefore low cost, obtained by a simple process, and that showed high adsorptive capacity, representing a excellent alternative for the removal of Cd2+ and Pb2+ in industrial effluents. Therefore, they can contribute to sustainable development of biodiesel production.