A device for uranium series leaching from glass fiber in HEPA filter

Abstract

For the disposal of a high efficiency particulate air (HEPA) glass filter into the environment, the glass fiber should be leached to lower its radioactive concentration to the clearance level. To derive an optimum method for the removal of uranium series from a HEPA glass fiber, five methods were applied in this study. That is, chemical leaching by a 4.0 M HNO₃–0.1 M Ce(IV) solution, chemical leaching by a 5 wt% NaOH solution, chemical leaching by a 0.5 M H₂O₂–1.0 M Na₂CO₃ solution, chemical consecutive chemical leaching by a 4.0 M HNO₃ solution, and repeated chemical leaching by a 4.0 M HNO₃ solution were used to remove the uranium series. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after leaching for 5 h by the 4.0 M HNO₃–0.1 M Ce(IV) solution were 2.1, 0.3, 1.1, and 1.2 Bq/g. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after leaching for 36 h by 4.0 M HNO₃–0.1 M Ce(IV) solution were 76.9, 3.4, 63.7, and 71.9 Bq/g. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after leaching for 8 h by a 0.5 M H₂O₂–1.0 M Na₂CO₃ solution were 8.9, 0.0, 1.91, and 6.4 Bq/g. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after consecutive leaching for 8 h by the 4.0 M HNO₃ solution were 2.08, 0.12, 1.55, and 2.0 Bq/g. The residual radioactivity concentrations of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th in glass after three repetitions of leaching for 3 h by the 4.0 M HNO₃ solution were 0.02, 0.02, 0.29, and 0.26 Bq/g. Meanwhile, the removal efficiencies of ²³⁸U, ²³⁵U, ²²⁶Ra, and ²³⁴Th from the waste solution after its precipitation–filtration treatment with NaOH and alum for reuse of the 4.0 M HNO₃ waste solution were 100, 100, 93.3, and 100%.