Preparation Of Magnetic Lignin-based Adsorbent And Its Application In Wastewater Treatment

Lignin is the only aromatic polymer that can be obtained from nature,however,it causes a huge waste of biomass resources,as a by-product in pulp and paper making.In this paper,a lignin-based magnetic adsorbent（OA@Lignin@Fe₃O₄）was prepared from industrial alkali lignin,with abundant functional groups,by chemical modification.And its removal efficiency,recyclability and adsorption mechanism in oil and dye treatment were studied,broadening the application of lignin as a green adsorbent in industrial wastewater treatment.Preparation and characterization of a lignin-based magnetic adsorbent OA@Lignin@Fe₃O₄were carried out.The preparation includes two steps.The first step is to synthesize magnetic lignin（Lignin@Fe₃O₄）by using a reversed suspension method to graft polyethyleneimine onto lignin and coat Fe₃O₄ nanoparticles with modified lignin.The second step is surface modification of 40 m L 1.5 g/L Lignin@Fe₃O₄,which was best carried out with 1 m L oleic acid for 20 min under 85℃.The characterization results showed that OA@Lignin@Fe₃O₄was in a micro-spherical shape with stable structure,perfect magnetism and hydrophobicity,with water contact angle of over 134°.Oil adsorption and adsorption mechanism study of OA@Lignin@Fe₃O₄ were carried out.The adsorbent had good adsorption capacity of pump oil,soybean oil,dimethicone and kerosene,and difference between them is related to the oil properties such as density,viscosity,surface tension and polarity,etc.OA@Lignin@Fe₃O₄ showed perfect recyclability under ethanol and the surfactant sodium dodecyl benzene sulfonate（SDBS）desorption.After 5times of regeneration with ethanol,its morphology had no obvious change,and oil adsorption capacity remained 87.53%.After 6 times of desorption,its mass loss was 11.37%±2.22%.The oil adsorption is a physical adsorption,mainly due to the hydrophobic interaction between surface alkyl chain and oil molecules,surface adsorption and the squeeze in gap.Cationic dye methylene blue（MB）adsorption of OA@Lignin@Fe₃O₄ was carried out.Static adsorption showed that OA@Lignin@Fe₃O₄ had a better adsorption property in alkaline system（p H=10.0）.The adsorption equilibrium reached at 120 min,while the MB removal efficiency was up to 91.36%,and remained 85.7%after 5 cycles,showing good recycling potential.Langmuir and Freundlich isotherms showed that adsorption process involved chemical monolayer and physical multilayer adsorption,and the Langmuir saturated adsorption capacity was 173.61 mg/g.Kinetics and characterization showed that the adsorption process was mainly controlled by external diffusion and surface adsorption（including electrostatic attraction and hydrogen bond interaction,etc.）.The adsorption performance at room temperature was better than at high temperature.In this study,OA@Lignin@Fe₃O₄ showed perfect adsorption performance and recyclabilityin oil and dye treatment,describing the good application prospect and providing theoretical data and technical support for the high-value utilization of biomass.