Among the potentially toxic metals, chromium (Cr) stands out due to its wide range of applications in various industrial processes. Although trivalent chromium, Cr(III), is an essential trace element for the proper functioning of living organisms, hexavalent chromium, Cr(VI), is toxic to biological systems. The treatment of wastewater containing potentially toxic elements is a broad field of research, especially with regard to studies about the use of agroindustrial waste as biosorbents for inorganic or organic contaminants. There are no reports in the literature of studies with sugarcane straw as a biosorbent for Cr(VI). Sugarcane straw, an abundant waste of the Brazilian agroindustry and the crops, is a potential low cost biosorbent which contain macromolecules with functional groups for the formation of complexes with metal ions. It should be emphasized that most studies published in the field of biosorption relegate to the background or do not address studies on the recovery and reuse of biosorbents. In view of the above, the general objective of this research proposal is to study the potential of sugarcane straw for the removal of Cr(VI) from synthetic solutions containing Cr(VI) in the form of K2Cr2O7. Considering that the initial pH of the Cr(VI) solution, the contact time, the initial concentration of Cr(VI) in solution and the biosrbent concentration are among the main factors that can affect the biosorption process, the effect of them on the removal of Cr(VI) by sugarcane straw will be studied, adopting the Rotational Central Compound Design for the biosorption tests, aiming to optimize these factors. In addition, the possibility of sugarcane straw reuse will be evaluated by performing six successive biosorption-desorption cycles. To reach the proposed objectives, the identification of the functional groups and possible binding sites present in the sugarcane straw and related to Cr(VI) sorption will be performed by infrared molecular spectroscopy. Surface analysis and elemental microanalysis of sugarcane straw samples will be performed by scanning electron microscopy coupled to dispersive energy spectroscopy. The biosorption assays, as well as desorption assays, will be in batchwise at 30 oC and constant agitation (150 rpm). The concentrations of the remaining chromium in solution will be determined by atomic absorption spectroscopy and by molecular spectroscopy in the visible region. The biosorption capacity of the sugarcane straw and the percentage of chromium removal will be calculated and the Langmuir and Freundlich adsorption isotherm models applied to the results.
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