Remobilization of ZnO–TA nanoadsorbent for U(vi) and Th(iv) extraction: adsorption optimization through the Box–Behnken design model†

The rapid expansion of nuclear technology has led to increasing volumes of radioactive wastewater, threatening the environment and necessitating the removal of contaminants in order to protect the surroundings. This report presents the sequestration of U(VI) and Th(IV) ions through an adsorption technique using a highly efficient ZnO–TA nanoadsorbent, driven by ionic interactions with the surface-active functional groups of the adsorbent. This nanoadsorbent was successfully synthesized using a hydrothermal process and structurally analyzed through various analytical techniques. Batch experiments were performed to study different parameters such as the influence of pH, amount of sorbent, time, initial concentration of sorbate, and interference of other ions. Adsorption study parameters were optimized via the response surface methodology and systematic batch studies. The highest removal efficiencies of 99.98% (U(VI)) and 98.80% (Th(IV)) ions were obtained at pH =4, using 10 mL of 50 mg L⁻¹ adsorbate concentration with 3 mg and 4 mg of adsorbent within 15 min, respectively. Moreover, the maximum adsorption capacities under optimum conditions were evaluated to be 909.09 mg g⁻¹ and 380.62 mg g⁻¹ for U(VI) and Th(IV) ions, respectively. These results were derived using the Langmuir isotherm model adhering to pseudo-second-order kinetics. The dominant adsorption mechanism of U(VI) and Th(IV) onto the ZnO–TA nanoadsorbent is explained through the interplay of electrostatic interactions and hydrogen bonding between the functional group active binding sites. Therefore, the results stated that the synthesized adsorbent, with its excellent recyclability, is effective in uranium and thorium uptake.