Interfacial Solid-Phase Chemical Modification with Mannich Reaction and Fe(III) Chelation for Designing Lignin-Based Spherical Nanoparticle Adsorbents for Highly Efficient Removal of Low Concentration Phosphate from Water

Advanced adsorption of low concentration phosphate by low cost lignin-based adsorbents from water or wastewater is an economic and effective way to prevent the occurrence of eutrophication. In this work, lignin, a waste material recovered from black liquor, was treated with a simple interfacial solid-phase chemical modification method to design a high efficiency phosphate adsorbent. First, the lignin was modified by triethylenetetramine (TETA) with the Mannich reaction, and then Fe(III) was chelated onto the aminated lignin. An efficient low concentration phosphate adsorption was observed by the kinetics experiments, which followed pseudo-second-order kinetically. The adsorption isotherms and thermodynamics were examined. This adsorbent was characterized by FTIR, SEM, particle size analysis, zeta potential analysis, and XPS. FTIR and XPS analyses indicated that iron atom was the binding site for phosphate adsorption. SEM pictures suggested that the adsorbent was uniformly ball-shaped and the particle size was about 450 nm. Both the adsorption experiments and characterization demonstrated that the phosphate adsorption mechanism of Fe(III)-complexed lignin (Fe-CL) followed the complexation mechanism between iron and phosphate on Fe-CL. This study implied that biomass-based lignin could be used as a potential adsorbent for efficient removal of low concentration phosphate from water or wastewater.