Sol–gel synthesis of a humic acid-silica gel composite material as low-cost adsorbent for thorium and uranium removal

A new humic acid-silica gel composite (HASi) to serve as an adsorbent was synthesized via a single-pot method, and its formation via the sol–gel process was confirmed by FTIR and SEM-EDS characterization. The adsorbent effectively removed Th and U at low pH (2.5–3), and the Langmuir model yielded a maximum sorption capacity of 32.3 and 33.2 mg/g for Th and U, respectively. The removal process was rapid (85 % removal within 5 min) and followed a pseudo-second-order model. The salinity of the solution had little effect on the removal efficiency, which continued throughout the adsorbent’s repeated use up to nine times.