PNNL

Abstract

Approximately 9 liters of supernatant from Hanford waste tank 241-AP-105 was delivered by Washington River Protection Solutions to the Radiochemical Processing Laboratory (RPL) at Pacific Northwest National Laboratory. The as-received AP-105 waste was diluted with process water (Columbia River water) from approximately 8.7 M sodium (nominal tank concentration) and partitioned into a batch of 7 M sodium and a batch of 5.5 M sodium. Dilution increased the combined volume of the two batches to approximately 7.8 liters of 7 M Na feed and 4.4 liters of 5.5 M Na feed. These two batches of 241-AP-105 supernatant were chilled to 16 °C for 1 week prior to testing. Filtration testing was then conducted using a backpulse dead-end filter (BDEF) system equipped with a feed vessel and a Mott inline filter Model 6610 (Media Grade 5) in the hot cells of the RPL. This was done to assess the performance of the anticipated third feed to the Tank Side Cesium Removal (TSCR) system. Similar to samples from tanks 241-AP-101 and 241-AP-107, no visible solids were observed in the as-received or diluted samples. The feed was filtered through the BDEF system at a targeted flux of 0.065 gpm/ft2 to match the prototypic operation of the TSCR system. During filtration of the 5.5 M sodium batch, the differential pressure required to effect filtration at 0.065 gpm/ft2 increased steadily over the filtration campaign. Once the bottoms of the bottles were added to the slurry, reservoir pressure rise increased and required two backpulses as the transmembrane pressure (TMP) reached 2 psid (the TSCR action limit). In contrast, the 7 M sodium batch did not require a backpulse for the feed volume tested. This indicates that the higher dilution of the feed resulted in more solids precipitating and these solids do settle over time. The prototypic filter cleaning process effectively restored filter performance. Solids concentrated from the backpulse solutions displayed sodium nitrate, sodium carbonate, calcium sulfate, iron oxide, steel particles, titanium oxide particles, and aluminum oxides. Electron diffraction was used to determine the types of phases that were present in the solids. The possible identifications of gibbsite, natrite, nitrite, gypsum, anatase, allophane, and cancrinite were made during this investigation. Most of the phases found were only weakly crystalline, possibly owing to their rapid precipitation during the process water treatment. The identifications of the phases therefore are tentative.