Simultaneous preparation of humic acid and mesoporous silica from municipal sludge and their adsorption properties for U(VI)

In this study, humic acid (HA) rich in various highly active functional groups was first synthesized by hydrothermal method using silica- and organic-rich municipal sludge, followed by mesoporous SiO2 with high specific surface area (SSA) by roasting. The prepared HA and mesoporous SiO2 were then used to adsorb uranium from an aqueous solution. The adsorption behaviors of two adsorbents were investigated using batch experiments, adsorption kinetic and isotherm models, and the adsorption mechanisms were analyzed by Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray Photoelectron Spectroscopy (XPS). Under the present experimental conditions, the maximum adsorption capacity of HA was 220.26 mg/g. The adsorption process of HA was well described by the pseudo-second-order model and the adsorption isotherm was consistent with the Langmuir model. For mesoporous SiO2, the pseudo-second-order model and the Freundlich model better represent its adsorption behavior. Mechanism analysis showed that various functional groups such as amide, phenol, ether or alcohol on HA provide active sites for uranium adsorption, and mesoporous SiO2 has a porous structure and a large SSA, all of which play an important role in the uranium adsorption performance. By preparing two adsorbent materials from municipal sludge, not only the high-value utilization of sludge is fully realized, but also the environmental benefit is achieved through effective adsorption of uranium.