The search for new adsorbents to decontaminate large bodies of water is a top priority for the scientific community. The presence of radionuclides like uranium and thorium in the ecosystem has negative impacts in living organisms. Inexpensive biological waste such as spent green tea (GT), powdered yellow corn cob (YC), powdered chitosan (CH) and brown algae (AL) were evaluated as adsorbents of thorium and uranium ions from aqueous solutions. Equilibrium studies show that maximum adsorption capacities of 177 and 182 mg/g are achieved for thorium ions at pH 4 for GT and YC, respectively. Uranium ions are adsorbed at a maximum adsorption capacity of 68, 317 and 76 mg/g at pH 4 by GT, CH and AL, respectively. Salt effect demonstrated that the mechanism of adsorption is mainly driven by electrostatic and polar interactions for each radionuclide/adsorbent system. Desorption was optimized by using diluted HCl as eluting solvent. Time-dependent tests indicate that adsorption is complete in less than 10 minutes for thorium ions and less than 40 minutes for uranium ions. Scanning electron micrographs of the adsorbents display heterogeneous surfaces in agreement with their high adsorptive properties. Further studies are needed to scale up the process using these eco-friendly adsorbents for the decontamination of larger volumes of solution in column studies.
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