Decontamination of Uranium-Contaminated Soil by Acid Washing with Uranium Recovery

Abstract

Optimal soil-washing conditions for efficient decontamination of U-contaminated soil generated during the dismantling of a uranium conversion facility were determined. A size fraction of 0.2–0.5 mm after dry sieving was used for evaluating the decontamination efficiency. Uranium in the soil was leached by an acidic washing method, and among various acidic washing agents, including H2SO4, HNO3, HCl, and citric acid, H2SO4 was selected as an appropriate washing agent considering economic feasibility and decontamination efficiency. In a multi-step washing process using 0.5 M H2SO4, the uranium concentration in the soil was reduced to less than the clearance level by a two-step acid washing with rinsing, regardless of temperature. A solid–liquid ratio of 1:4 or higher is recommended in soil washing to ensure decontamination efficiency by sufficient mixing between the soil and the washing agent. Soil washing using various concentrations of 0.3 to 1.0 M H2SO4 can reduce the uranium concentration in the soil to less than 1.0 Bq/g through multi-step washing regardless of the concentration. The applicability of neutralization and distillation treatments was evaluated to purify the soil-washing effluent. The distillation treatment method is considered more efficient than the neutralization treatment. These results provide that the multi-step washing of soil and uranium recovery by neutralization or distillation method can be applied as an appropriate treatment process for decontamination of U-contaminated soil.