Adsorption and Removal of Phosphate from Wastewater Using Lignin-Based Adsorbent Modified with Lanthanide: Characterization, Performance, and Mechanisms

Water eutrophication due to the discharge of wastewater containing phosphate has aroused considerable concern around the world, and adsorption has been identified as one of the viable solutions to solve the problem. It is crucial to develop an eco-friendly and cost-effective adsorbent for preventing eutrophication of water bodies. In this study, we developed a simple coprecipitation approach to prepare a lanthanum-based modified calcium lignosulfonate (La-CL) for treating phosphate wastewater. La-CL exhibited excellent adsorption ability for phosphate due to its high loading of lanthanum (59.29%) and large specific surface area (175.3 m2 g-1). In a wide range of pH values (2-11), the adsorption capacity of phosphate onto La-CL remained stable, and the removal rate was above 90%. The maximum adsorption capacity could reach 107 mg g-1 for phosphate at optimum pH = 7, and the adsorption reached equilibrium within 240 min. After seven consecutive regeneration adsorption experiments, La-CL could still maintain a desorption rate of more than 75%, indicating that La-CL exhibited a certain degree of regenerative performance. Moreover, the adsorption behaviors of phosphate onto the La-CL adsorbents were fitted to the Freundlich isotherm and pseudo-second-order model, suggesting chemical adsorption and a heterogeneous adsorption process. The mechanistic studies revealed that ligand exchange played a significant role in the adsorption of phosphate. This study would provide a strategy of "treating waste with waste" for removing phosphate from wastewater at low concentrations based on La-CL.