Potencialidade de remoção de Cr(VI) de soluções aquosas por biossorção usando resíduos da agroindústria

Abstract

In this study, Cr(VI) removal from agricultural residues via biosorption was investigated. In order to obtain biosorbents, sugarcane bagasse (Saccharum L.), cassava peel (Manihot esculenta) and dried coconut mesocarp (Cocos nucifera L.) were used. Biosorbent efficiencies were compared in natura and in heat treatment conditions. Subsequently, biosorbents were crushed and sorted by grain size. Cr(VI) determination was made by UV-visible spectrophotometer through complexation with 1,5-diphenylcarbazide, and absorbance was measured at 540 nm wavelength. Experiments were performed at 25 ± 1 °C, pH 2, with biosorbent mass of 0.1g and Cr(VI) concentration ranging from 1 to 8 mg L-1 . The effect of pH in the initial Cr(VI) solution, biosorbent mass, Cr(VI) initial concentration and equilibrium time were assessed. In the kinetic study, in natura dried coconut mesocarp and sugarcane bagasse had equilibrium time of 25 minutes, while other biosorbents had equilibrium time of over 100 minutes. The pseudo first-order model was the one that better represented in natura cassava peel, and the other biosorbents were better represented by the pseudo second-order model. In the equilibrium data, the Langmuir model was the best fit for in natura and heat-treated cassava peel experimental data. Freundlich model was more suitable to describe dried coconut mesocarp and sugarcane bagasse Cr(VI) biosorption, both in natura and in heat-treated conditions. Maximum biosorption capacity (Qmax) for sugarcane bagasse in heat treatment was of 0.1229 mmol g-1 , while cassava peel Qmax was of 0.1407 and 0.1315 mmol g-1 in natura and heat-treated, respectively. Thus, through the results, the studied biosorbents proved to have great potential for the treatment of wastewater containing Cr(VI). Biosorbents were characterized by organic matter and ash levels determination. The pH was also determined in the point of zero charge, and infrared region absorption (FTIR), Xray fluorescence (XRF) and scanning electron microscopy (SEM) were analyzed. XRF revealed chromium absence in the biosorbents composition before biosorption, and chromium appearance after biosorption, which confirmed the of biosorption occurrence on the surface of the biosorbents under study.