Study on the Adsorption Mechanisms and Process Optimization of Different Forms of Iron Hydroxide for Low-Level Uranium-Containing Wastewater

Uranium mining and the processing of nuclear materials generate significant quantities of low-level radioactive wastewater, which, if untreated, pose environmental and health risks. This study addresses the challenge of removing uranium from such wastewater by comparing the uranium ion removal performance and mechanisms of iron hydroxide colloids and powders. Iron hydroxide colloids were synthesized under alkaline conditions via an environmentally friendly oxidation process using ferrous sulfate and hydrogen peroxide. The colloids and powders were characterized using scanning electron microscopy (SEM), particle size analysis, and zeta potential measurements. The results showed that the colloid's average particle size (17.61 nm) was significantly smaller than that of the powder (164.18 nm), resulting in a higher specific surface area, more uniform particle distribution, and increased adsorption site density. Zeta potential analysis indicated that the colloid reduced the solution potential from -22.13 mV to -15.46 mV, promoting uranium flocculation through double-layer compression, whereas the powder maintained a potential of -23.43 mV, preventing effective flocculation. Response surface methodology (RSM) was employed to optimize process parameters, identifying the optimal conditions as a pH of 8.82, a dosing concentration of 424.80 mg/L, and a settling time of 2.2 h. Under these conditions, the uranium removal rate achieved 98.38%, closely aligning with the predicted rate of 98.81%. This method outperforms conventional ferric salt flocculation by avoiding the introduction of additional impurity ions, with the only by-products being oxygen and water. Moreover, this study demonstrates for the first time how the adjustment of iron hydroxide colloids can enhance uranium removal efficiency, offering a promising and eco-friendly approach to treating radioactive wastewater.