Design and economic comparison of uranium-contaminated soil cleaning system based on ultrasonic technology

This investigation focused on a comprehensive design for decontamination of actual uranium (U)-contaminated soil/gravel from economical and practical perspectives. The primary objective of this study was to evaluate the effectiveness of an ultrasonic process in decontaminating U-contaminated soil/gravel. Several decontamination experiments were carried out to investigate the total U concentration in U-contaminated soil/gravel, consisting of (i) soluble U under a neutral pH condition, (ii) insoluble U fine particles at the surface of soil/gravel, and (iii) strongly (or chemically) bound U in soil/gravel. Subsequently, we adopted an ultrasonic process for decontamination of crushed U-contaminated gravel to meet the guideline for the clearance level of U (<1 Bq·g⁻¹) suggested by the International Atomic Energy Agency. Normalized decontamination performance tended to increase with increasing ultrasonic frequency, and the U concentration in a relatively low concentration sample met the required clearance level of U after decontamination by relatively high ultrasonic frequency under a neutral pH condition. In addition, the OH· concentration in solution during ultrasonication was attributed to the removal of strongly (or chemically) bound U in gravel. Finally, on the basis of an economic analysis comparing the present study with our previous study and permanent disposal of all of the U-contaminated soil/gravel without any decontamination, the suggested comprehensive zero liquid discharge system is expected to be a feasible and viable strategy.