Characterization, Washing, Leaching, and Filtration of C-104 Sludge

Brooks, KP ; Bredt, PR ; Golcar, GR ; Hartley, SA ; Jagoda, LK ; Rappe, KG ; Urie, MW

Pacific Northwest National Laboratory (U.S.)

关键词: Leaching;    Sludges;    Radioactive Waste Processing;    Dissolution;    Alkaline Hydrolysis;   

DOI  :  10.2172/756361
RP-ID  :  PNWD-3024
RP-ID  :  AC06-76RL01830
RP-ID  :  756361

美国|英语

来源: UNT Digital Library

【 摘 要 】

Approximately 1,400 g of wet Hanford Tank C-104 Sludge was evaluated by Battelle for the high-level waste (HLW) pretreatment processes of ultrafiltration, dilute caustic washing, and elevated-temperature caustic leaching. The filterability of diluted C-104 sludge was measured with a 0.1-{micro}m sintered metal Mott filter using a 24-inch-long, single-element, crossflow filtration system (cells unit filter [CUF]). While the filtrate was being recirculated prior to washing and leaching, a 6.9 wt% solids slurry was evaluated with a matrix of seven 1-hour conditions of varying trans-membrane pressure (30 to 70 psid) and axial velocity (9 to 15 ft/s). The filtrate flux and backpulse efficiency were determined for each condition. The slurry was concentrated to 23 wt% solids, a second matrix of six 1-hour conditions was performed, and data analogous to that recorded in the first matrix were obtained. The low-solids-concentration matrix produced filtrate flux rates that ranged from 0.038 to 0.083 gpm/ft{sup 2}. The high-solids-concentration matrix produced filtrate flux rates that ranged from 0.0095 to 0.0172 gpm/ft{sup 2}. In both cases, the optimum filtrate flux was at the highest axial velocity (15 ft/s) and transmembrane pressure had little effect. Nearly all of the measured filtrate fluxes were more than an order of magnitude greater than the required plant flux for C-104 of 0.00126 gpm/ft{sup 2}. In both matrices, the filtrate flux appeared to be proportional to axial velocity, and the permeability appeared to be inversely proportional to the trans-membrane pressure. The first test condition was repeated as the last test condition for each matrix. In both cases, there was a significant decrease in filtrate flux, indicating some filter fouling during the test matrix that could not be removed by backpulsing alone, although the backpulse number and duration were not optimized. Following testing of these two matrices, the material was washed within the CUF by continuously adding approximately 5 L of 0.01-M NaOH and then removing it through the filter as permeate. The purpose of this washing step with 0.01-MNaOH was to remove water-soluble components that might inhibit dissolution of salts during caustic leaching, while avoiding peptization of the solids that occurs at a pH below 12. After washing the sludge with dilute caustic, it was combined with 3-M caustic, and the slurry was leached in a stainless steel vessel at 85 C for 8 hours. This leaching was followed by two 0.01-M caustic washes, each conducted in a stainless steel vessel to dilute remaining analytes from the interstitial liquids. Each rinse was performed at 85 C for 8 hours. Permeate from each of these process steps was removed using the crossflow filter system. Samples of the permeate from each slurry-washing activity and all intermediate process steps were taken and analyzed for chemical and radiochemical constituents. The fraction of each component removed was calculated. Key results are presented in Table S.1.