Analysis on approximate site energy distribution and adsorption behaviors unveils reasons for highly efficient phosphorus removal by a novel sludge-based magnetic gel bead

Abstract

• Energy and active site-oriented analysis is a powerful method to reveal adsorption mechanisms. • Good performance in real water proves its practicability. • Good recyclability and separability make it a promising adsorbent. Revelation of phosphate adsorption mechanisms by adsorbent commonly concerns characterization-based analysis. Yet the combination of energy and adsorption site-oriented and characterization-based analysis for mechanisms’ revelation remains deficient. Herein, we originally used this macro–micro hybrid method to disclose the P adsorption mechanisms by a novel sludge-based magnetic gel bead. The synthesized gel bead exhibited highly efficient phosphate uptake of 87.79 mg/g when the system operated at 293 K with initial P addition of 100 mg/L. Deliberating over the similarities and disparities in adsorption energy and energy frequency distribution between this gel bead and its feedstocks (Biochar, Chitosan and Fe 3 O 4 ), we concluded that 2 factors contributed to desirable P uptake — higher distribution frequency of valid adsorption site and higher solution temperature. Furthermore, the diffusion behavior was demonstrated neither film diffusion nor intra-particle diffusion dominated the adsorption process thoroughly through, and temperature exerted greatly on diffusion pathway. Characterization-based analysis proposed several probable adsorption mechanisms, including porous filling, electrostatic effect, chelating, etc. While considering the ASED analysis we concluded that surface precipitation and Fe-O-P bonding as the foremost adsorption mechanisms by this gel bead. Additionally, the good performance of this gel bead in natural water, in recycle experiments and in column trials made it economically competent and possible for large-scale application.