Lignina extraída do sabugo de milho modificada como adsorvente de poluentes em efluentes industriais

Abstract

The population growth and increased consumption have intensified industrial production. This rise has generated more pollutants that, when improperly disposed of, impact human health and ecosystems. Significant environmental issues include produced water from oil extraction, which is rich in salts, heavy metals, and organic compounds, and effluents from the textile industry, contaminated by chemical dyes. To mitigate these issues, recent research highlights lignin as a promising adsorbent material due to its abundance in nature and its chemical properties, such as a high binding capacity with contaminants. Brazil, a major corn producer, generates significant volumes of corncob, which contains approximately 15% lignin, emphasizing its potential for such applications. This study aims to investigate the use of modified lignin extracted from corncob as an adsorbent material for pollutants in contaminated effluents. An alkaline pretreatment was applied to the corncob biomass to extract lignin. The extracted lignin was modified with reagents such as choline chloride and hydrogen peroxide to enhance its ability to interact with contaminants. Characterization techniques (Zeta potential, TG, FTIR, and SEM) were performed to understand the physical, chemical, structural, and functional properties of the adsorbent materials. Using UV-Vis spectroscopy, bench tests were conducted to evaluate the efficiency of the material as an adsorbent for pollutant removal, considering parameters such as initial pollutant concentration and contact time. The adsorption kinetics of oil removal were studied using lignin and sodium alginate spheres. The lignin spheres exhibited superior performance compared to pure alginate spheres. The lignin sphere modified with choline chloride (ELMC) achieved the best result, reaching 90% oil removal from water, followed by the lignin sphere oxidized with hydrogen peroxide (ELOX), with 88.23% removal. The pseudo-first-order model provided the best fit for the experimental data. The maximum adsorption capacities were 172.7 mg/g for ELMC and ELOX, 161.18 mg/g for the unmodified lignin sphere (ELNM), and 84.43 mg/g for the pure sodium alginate sphere (EALG). For Congo red dye, the adsorption kinetics fitted better to the pseudo-second-order model. The PSO model demonstrated high accuracy in R² values and successfully predicted the adsorption capacity (qe). For unmodified lignin (LNM), the qe values were 35.54, 66.58, and 155.24 mg/g for concentrations of 50, 100, and 250 mg/L, respectively; for lignin modified with choline chloride (LMC), the values were 33.89, 65.95, and 165.79 mg/g. The Langmuir and Freundlich isotherm models did not fit the experimental values well, with R² values deviating from the ideal. Therefore, the adsorption study using modified lignin extracted from corncob proved to be an efficient and sustainable alternative for wastewater treatment, outperforming conventional materials such as activated carbon. This material is capable of removing contaminants found in produced water from oil extraction as well as Congo red dye, frequently present in textile industry effluents. The modified lignin exhibited high adsorption capacity, standing out as a promising solution for mitigating environmental impacts.