No 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...

No abstract

Because of the expected high cost of vitrifying and disposing of high-level waste at the U.S. Department of Energy's Hanford Site, pretreatment processes are being developed to reduce the anticipated volume of borosilicate glass. Sludge washing and caustic leaching, the baseline sludge pretreatment process, is expected to leach out a substantial portion of the 137C.9, possibly other radionuclides, and a significant portion of such major nonradionuclides as A I or P. The decontaminated solution will be routed to the low-level waste stream, where it will be immobilized in a glass matrix. The leached solids, which will contain the transuranic elements and W r , will be handled as high-level waste. Previous studies indicate that poor removal of chromium in the +3 oxidation state [Cr(III)] occurs during baseline pretreatment. Because the concentration of Cr allowed in high level waste glass is low, a relatively small amount of Cr in the sludge can have a relatively large impact on the volume of high level waste glass produced. For this reason, additional leach steps to remove Cr would be desirable, and oxidative alkaline leaching has been proposed as a simple addition to the baseline sludge pretreatment. This report describes small-scale screening tests on the oxidative alkaline leaching of Cr performed with actual Hanford tank sludges. from Tanks B-1 1 1 and SY-103 was evaluated. Two types of oxidants, KMnO4 and 0 3 , were investigated as a function of time, temperature, and (for permanganate) Mn to Cr ratio. Reaction times were rapid with both oxidants, and very little additional Cr dissolved upon further heating of the solution to 80°C. Analysis of the reaction of sludge with either 1:l or excess permanganate to Cr indicates that insoluble MnO2 will be produced under any practical processing conditions. The oxidation of Cr(II1) to soluble CrO42-allows for good dissolution of Cr during oxidative alkaline leaching with high Cr(II1) sludges. Calcium is the only other element that dissolves significantly, probably due to changes in the supernatant pH rather than any direct oxidant-Ca reaction. Under the test conditions, less than a third of the available Cr dissolved with B-1 1 1 sludge, but 90% dissolved with SY-103 sludge. Heating the dried sludges in air at 80°C for several hours oxidized some Cr(II1) to Cr(V1) and may have oxidized a small portion of PU. Some enhanced dissolution of Pu was observed when ozone was contacted with SY-103 sludge, although the concentrations should not prohibit the formation of low-level-waste glass if the oxidative leaching supernatant is combined with the caustic leach supernatant. For B-1 1 1, oxidative alkaline leaching did not reduce the amount of high-level glass required because no further dissolution of the glasslimiting component, P, was observed. For SY-103, however, it reduced the amount of high-level glass required by 90%. Either permanganate or ozone appears to be about equally effective. However, the nature of the glass-limiting component can change. If ozone is used Cr re...

Laboratory -Engineering development and testing of the SRT~K solvent extraction process are discussed in this paper. This process provides a way to carry out alkaline-side removal and recovery of technetium in the form of pertechnetate anion from nuclear waste tanks within the DOE complex. The SRTALK extractant consists of a crown ether, bis-4,4'(5')[(tert-butyl)cyclohexano] -18-crown-6, in a modifier, tributyl phosphate, and a diluent, Isopar%. The SRTALK flowsheet given here separates technetium ilom the waste and concentrates it by a factor often to minimize the load on the downstream evaporator for the ., technetium effluent. In this work, we initially generated and correlated the technetium extraction data, measured the dispersion number for various processing conditions, and determined hydraulic performance in a single-stage 2-cm centrifugal contactor. Then we used extraction-factor analysis, single-stage contactor tests, and stage-to-stage process calculations to develop a SRTALK flowsheet. Key features of the, flowsheet are (1) a low O%afic-to-aqueous