Washing and Caustic Leaching of Hanford Tank Sludge: Results of FY 1998 Studies

Abstract

DISCLAIMERPortions of this document may be illegible in electronic image products. Images are produced from the best available original document. AbstractSludge washing and parametric caustic leaching tests were performed on sludge samples fiom five Hadord tanks: B-101, . These studies examined the effects of both dilute hydroxide washing and caustic leaching on the composition of the residual sludge solids.the P, and 63 to 99% of the Na from the H d o r d tank sludge samples examined. The partial removal of these elements was likely due to the presence of water-soluble sodium salts of aluminate, chromate, hydroxide, nitrate, nitrite, and phosphate, either in the interstitial liquid or as dried salts.The response of Al to caustic leaching was v~a b l e .When leached with 3 M NaOH for one week at 95 to 100°C, the cumulative Al removals were 62,99,61,95, and 89% for the B-101, BX-110, BX-112, (2-102, and S-101 samples, respectively. For the B-101 and the BX-110 samples, Al dissolution was rapid, with the AI concentrations reaching >SO% of their final values within the first 5 h of leaching.Interestingly, for the BX-112 sample, A I removal decreased with increasing leaching time and temperature-a trend contrary to what was expected. We hypothesize that this is due to the formation of aluminosilicate minerals. For the C-102 sludge, there was clearly a benefit in increasing the NaOH concentration from 1 M to 3 M. Leaching with 1 M NaOH removed -20 to 30% of the Al from the dilute hydroxide-washed solids while 3 M NaOH removed -95% of the Al. Aluminum dissolved slowly from the S-101 sample, which is consistent with boehmite being the predominant Al-containing phase.all the sludge samples examined, Cr removal during caustic leaching was highly time-dependent, but the Cr dissolution did not fit simple zero-, first-, or second-order kinetic models. Consistent trends in the effects of temperature and hydroxide concentration on Cr removal were difficult to discern. P from the sludge samples examined. Except for the Tank C-102 sample, cumulative P removals,were 285%. For C-102, the cumulative P removals were only -60%. Increasing temperature or hydroxide concentration generally did not result in large improvements in P removal; that is, relatively mild conditions tended to be adequate to remove P. 'The projected 137Cs content for the low-level waste (LLW) resulting fiom immobilizing the sludge washinglleaching solutions would range fiom -50 to -540 CVm3 for the samples examined. Although these concentrations are below the U.S. Nuclear Regulatory Commission Class C LLW limit of 4,600 Cum3, they are well above the proposed guideline of 3 Cum3 for the immobilized LLW product fiom the proposed private-processing facilities. Thu, it is likely that I3'Cs will need to be removed fiom the washing and leaching solutions. On the other hand, transuranic and Sr removal would likely not be required for the washing and leaching solutions fiom processing the sludges examined here. An estimate of high-level waste (HLW) glass produced in im...

Review of Alternative Enhanced Chemical Cleaning Options for SRS Waste Tanks

“…A caustic aluminum dissolution process has been used at SRS and tested at other DOE sites in the past. [80][81][82] Recently, a low temperature aluminum dissolution (LTAD) process was used to remove aluminum from sludge at SRS. Both a laboratory scale demonstration and the full scale process removed 40-60% of the aluminum at 55 -65 °C over a 3-5 week contact period.…”

Modeling of Boehmite Leaching from Actual Hanford High‐Level Waste Samples

“…Combining Equations (5), (8), (11), and (12) produces an equation describing the dissolution of boehmite based on a model system of a distribution of various length shrinking platelets.…”

“…To better understand the mechanisms governing the leaching performance, a second series of dissolution tests, reported in Ref. (7,11), were performed with samples from Hanford tanks S-110 and S-101. These tests involved periodically measuring the dissolution over longer durations with a broader range of hydroxide concentrations.…”

PEP Support Laboratory Leaching and Permeate Stability Tests

“…In this respect, caustic leaching was meant to remove the large amount of aluminum from the waste, thus reducing the nitric acid demand and simplifying the solvent extraction feed. Subsequently, caustic leaching (sometimes referred to as "Enhanced Sludge Washing) was chosen as the baseline method for Hanford tank sludge pretreatment (Lumetta et al 1998). Following this decision, caustic-leaching tests were performed under a standard set of conditions at Pacific Northwest National Laboratory (PNNL) and Los Alamos National Laboratory from FY 1994 through FY 1997 (Lumetta et al 1996(Lumetta et al , 1997Rapko et al 1995;Willingham 1994;Temer and Villarreal 1995.…”

“…Following this decision, caustic-leaching tests were performed under a standard set of conditions at Pacific Northwest National Laboratory (PNNL) and Los Alamos National Laboratory from FY 1994 through FY 1997 (Lumetta et al 1996(Lumetta et al , 1997Rapko et al 1995;Willingham 1994;Temer and Villarreal 1995. In subsequent years, a limited number of parametric caustic-leaching experiments were performed at PNNL and also at Oak Ridge National Laboratory (Lumetta et al 1998;Palmer et al 2000;Lumetta et al 2001;Brooks et al 1998). After establishing the Hanford WTP project, a limited number of laboratory-scale caustic-leaching experiments were performed using a standard testing protocol (Brooks et al 2000a(Brooks et al , 2000bPoirier et al 2003;Russell et al 2009), but these were generally focused on processing double-shell tank wastes rather than the single-shell tanks where the bulk of the sludge is stored.…”