Integrated AMP–PAN, TRUEX, and SREX testing. I. Extended flowsheet testing for separation of surrogate radionuclides from simulated acidic tank waste

Abstract

Three unit operations for the removal of selected fission products, actinides, and Resource Conservation and Recovery Act metals (mercury and lead) were integrated successfully and tested at the Idaho National Engineering and Environmental Laboratory (INEEL) for extended run times with simulated acidic tank waste. The unit operations were ion exchange (IX) for Cs removal, followed by transuranic extraction (TRUEX) for Eu (actinide surrogate), Hg, and Re (Tc surrogate) removal, and subsequent strontium extraction (SREX) for Sr and Pb removal. Approximately 45 L of simulated acidic tank waste were processed through three IX columns, packed with composite ammonium molybdophosphate–polyacrylonitrile (AMP–PAN) sorbent for Cs removal. The IX system was operated continuously for ∼34 hr at 22 bed volumes (BV) per hour through the first two columns, each sized at 60 cm3 BV and operated to 100% breakthrough. The experimental breakthrough data were in excellent agreement with modeling predictions based on data obtained with much smaller (1.5 cm3) columns. The third column (220 cm3 BV) was used for polishing and Cs removal after breakthrough of the upstream columns. Cesium removal was >99.83% in the IX system and interference from other species was not observed. The IX effluent was processed through a TRUEX solvent extraction flowsheet to remove Eu (Am surrogate), Hg, and Re (Tc surrogate) from the simulated waste. The TRUEX flowsheet test was performed using 23 stages of 3.3 cm centrifugal contactors, operated a total of 71.3 hr, and processed ∼41 L of the IX effluent using 1.5 L of TRUEX solvent with constant solvent recycle. The TRUEX solvent was recycled through the flowsheet an estimated 17 times. Greater than 99.999% of the Eu, 96.3% of the Hg, and 56% of the Re were extracted from the simulated feed and recovered in the strip and wash streams. Over the course of the test, there was no detectable build-up of any components in the TRUEX solvent. The raffinate from the TRUEX test was processed subsequently through a SREX solvent extraction flowsheet to remove Sr, Pb, and Re (Tc surrogate) from the simulated waste. The SREX flowsheet test was performed using the same centrifugal contactors used in the TRUEX test after reconfiguration and the addition of three stages. Approximately 51 L of TRUEX raffinate was processed through the system during 77.9 hr of continuous operation with 1.5 L of SREX solvent and continuous solvent recycle. The SREX solvent was recycled through the system an estimated 45 times without measurable build-up of any components in the solvent. Approximately 99.9% of the Sr, >99.89% of the Pb, and >96.4% of the Re were extracted from the aqueous feed to the SREX flowsheet and recovered in the strip and wash sections.