Adsorção de Cu II em lignina e celulose obtidos a partir de resíduos agrícolas

Abstract

The use of heavy metals in agroindustrial process, it has generated environmental negatives impacts and this way calling attention to this problem, once the heavy metals are toxics and can contaminate soil, underground, water tables, contaminate the food chain as well. Adsorption is a process in which a substance (adsorbate) is physically or chemically attached to the surface of the adsorbent component and currently this process may be an alternative method to remove toxic metals from water bodies and contaminated effluents. Inside this context, this study aims the adsorption of copper II (Cu II) from lignin a modified natural polymer obtained from agricultural waste, in this case, from corn stover. The study was divided into two parts: the first corresponding to the obtaining and characterization of crosslinked adsorbent lignin Formica (LFRT) and adsorbate (heavy metal), and the second part consists in the adsorption between heavy metal and LFRT. It was used the methodology proposed by Browning (1967) to extract lignin from lignocellulosic material, where it was isolated by pulping with formic acid (CH2O2) at 80% concentration, obtaining lignin Formica (LFOR). LFOR already been crosslinked with hydrochloric acid (HCl) 37% to give the polymer adsorbent used in this study crosslinked lignin Formica (LFT). The LFRT passed by ultraviolet spectroscopy (UV-vis) for the solubility test, and was characterized by infrared spectroscopy (IR). Adsorption tests were performed with different times of contact between adsorbent and the solution of 10 mg L-1 copper II, and the final concentration of the solution was measured by atomic absorption spectrophotometry (AAS), this way becoming possible to analyze the saturation of the adsorptive system and the adsorption efficiency. The solubility test of the polymer through the absorbance of ultraviolet light at a wavelength of 280 nanometers (nm) showed that the LFRT is less soluble compared to the LFOR. This low solubility was observed in the polymer characterization by infrared spectroscopy, where it was possible to see the addition of methyl groups (−CH4) on the crosslinking reaction of lignin. The results obtained after analyzes of kinetic study shows off that the interaction of adsorption, in this case, is a chemically process, given by the Ho’s equation of pseudo-second order. About the efficacy of adsorption system, there was obtained a removal of 72,36% of the metal in solution by the LFRT adsorbent, on the other hand, the corn stover adsorbent shows increased efficiency with respect to removal of heavy metal reaching an average of 88,26%. However, this study can be characterized as effective when compared to the 2.914/2011 order of the Ministry of Health about water potability, this parameter being achieve.