Thereafter, we evaluated the PEC U extraction performance at different initial U concentrations ranging from 0.025 mM to 0.20 mM (Figure and Figure ). The high initial U concentrations, i.e., 0.10 mM and 0.20 mM, enabled faster kinetics in the first 30 min. As for the low initial U concentrations, i.e., 0.025 mM and 0.05 mM, the accumulation of U precipitates on the Ti cathode, which was beneficial for the extraction of aqueous U, was more difficult , so slower initial rates were obtained. But once some U precipitates were deposited, the extraction was accelerated and resulted in similar kinetics with high initial U concentrations in the later phase. In the case of the 0.20 mM U experiment, the extraction rate in the later phase declined and became the slowest, which might be due to the saturation of the active sites .