Removal of Heat-Generating Nuclides from High-Level Liquid Wastes through Mixed Zeolite Columns

Abstract

The simultaneous removal of heat-generating nuclides Cs and Sr from high-level liquid wastes was achieved through columns packed with mixed zeolites of ferrierite (F) and zeolite A (A). A simulated waste solution was efficiently denitrated with formic acid up to pH 6.5 8.3 in the region of the initial molar ratio of [HCOOH^-]/[HNO₃] from 2.3 to 2.7. Large portions of multivalent nuclides including lanthanoids and actinoids were filtered off as precipitates in this pH region. Both Cs and Sr remaining in the filtrate were then completely removed by passing through the column packed with mixed zeolites. Break points for a column with an appropriate mixing ratio of A:F-=2:3 were found to be 12.6 bed volumes (BV) for Cs and 11.0 BV for Sr; the amounts of Cs and Sr adsorbed were estimated to be 0.28 and 0.12 mmol/g, respectively. The mixed zeolites adsorbing Cs and Sr were readily converted into a solid form by calcination at 1, 200°C.