Sulfur Partitioning During Vitrification of INEEL Sodium Bearing Waste: Status Report

Abstract

The loading of Idaho National Engineering and Environmental Laboratory sodium bearing waste (SBW) in glass will be limited by the allowable concentration of sulfate in the feed which is defined by the highest concentration that can be vitrified into glass at an acceptable rate without the accumulation of molten salt on the melt surface. This allowable concentration of sulfate in the feed is determined by many chemical (e.g., waste composition, chemistry of glass forming additives, waste loading, acid or reductant addition) and physical (e.g., melter-feed rate, plenum temperature, heat-transfer rate to the cold cap) parameters. This report documents the status of an ongoing study to determine the impacts of key processing parameters on the partitioning of sulfur species between the glass, a molten salt phase, and the off gas. As this study is continuing, the nature of these results is preliminary and incomplete. However, this report does give an indication of the relative importance of many parameters and the range of expected sulfur-partition coefficients during SBW vitrification. A series of tests was conducted to measure the partitioning of sulfur species between glass, the off gas, and a molten salt. In crucible tests, between 79 and 100% of the total sulfur was found to remain in the glass, and molten salts were not formed until the target concentration of sulfur in the glass exceeded roughly 1 mass% on an SO 3 basis. The use of high gas purge rates (e.g., 2300 ccm) in crucible tests decreased the fraction of sulfur in the glass to roughly 23% of that targeted. The influence of sugar concentration, heating rate, and starting feed pH were found to be minimal on the partitioning of sulfur species in these tests. Glass-forming additive composition was found to influence the formation of a salt layer. Details of the crucible tests are reported by Peeler et al. (2001). Three melter tests were performed with simulated SBW feed. The first test (EV-16-1999-1) was performed using the pilot-scale Envitco EV-16 melter at Clemson University in April 1999. The asbatched glass composition for this test contained 1.07 mass% of SO 3. The measured concentration of sulfur in the glass produced was roughly 0.58 mass% based on SO 3. No salt layer was observed during or after the test, suggesting that the remaining sulfur was driven to the off gas. However, power excursions occurred during the test, which occasionally brought the melt temperature to 1350°C. These excursions may have had a strong influence on the partitioning of sulfur during the test. Results of this test have yet to be published; highlights are described in Section 3.1. The second melter test (RSM-01-1) with simulated SBW feed was performed using the Research-Scale Melter (RSM) at Pacific Northwest National Laboratory in January 2001. This test was conducted in eight segments. The waste loading (30 to 35 mass% on a dry, non-volatile oxide basis), sulfur concentration (1.07 to 1.75 mass% based on SO 3), and sugar concentration (135 to 197 g/L of waste simulant) w...

Iron Phosphate Glass as an Alternative Waste-Form for Hanford LAW

“…One observation from the present CSM tests was that the glass that formed at the bottom of the crucible contained some clusters of unreacted materials while most of the feed was converted to glass. This may be attributed to the relatively high feed rate used in the present tests at 2.4 mL/min compared to the typical rate of 1.3 mL/min used in most tests with borosilicate glasses for INEEL SBW (Darab et al 2001). This high feed rate was used based on the visual observation indicating that the feed was melting at a much faster rate than typical borosilicate glass feeds.…”

“…The glass-forming chemicals were added to the LAW simulant to prepare the LAW glass slurry feed. The CSM was developed to better simulate those processes that are important to determining the behavior of sulfur in a slurry-fed melter system with batch heating from the glass melt below the batch cold cap (Darab et al 2001) and was used extensively in the glass (borosilicate) development for the Idaho National Engineering and Environmental Laboratory (INEEL) sodium-bearing waste (SBW) (Vienna et al 2002a). The CSM consists of a main vessel of 1-in.-diameter fused silica tubing as shown in Figure 3.2.…”

“…The CSM set-up can also be used to estimate the off-gas released during melting (see Darab et al [2001]) for a detailed description of various setups for the off-gas treatment/analyses. However, the present study LAW phosphate glass feed was aimed at monitoring any indication of salt formation during slurry-fed melting.…”

“…This high feed rate was used based on the visual observation indicating that the feed was melting at a much faster rate than typical borosilicate glass feeds. However, the conclusion on the salt-phase formation will not be affected by the fact that a high feed rate was used because it was found from the past CSM tests with borosilicate glass feeds that the higher feed rate generated significantly more separated salt phases (Darab et al 2001). It is also possible that the incomplete melting was caused by improper selection of raw materials for glass-forming additives as we learned the importance of raw materials on the crucible melting discussed Section 4.8.…”

Effects Influencing Plutonium-Absorber Interactions and Distributions in Routine and Upset Waste Treatment Plant Operations

“…The nominal concentration of sugar added to both LAW and HLW (0.75 moles of TOC per mole of NO x ) will result in an iron redox ratio of less than 6% Fe(II), divalent iron, to total Fe. Studies show that increased sugar dosage to the LAW melter feed linearly increases the redox ratio (Fe(II)/total Fe) in the product glass (Section 3.1.3.5.6 of Jenkins et al (2013); see also Darab et al (2001)and Goles et al (2001)). Although the dependence of the extent of Fe(III) reduction on sugar dosage seems less distinct in HLW glass (Section 4.1.3.4.9 of Jenkins et al (2013)), this is not generally true.…”