The effect of chemical composition on the PCT durability of mixed waste glasses from wastewater treatment sludges

An experimental program has been designed to examine the chemical durability of glass compositions derived from the vitrification of simulated wastewater treatment sludges. These sludges represent the majority of low-level mixed wastes currently in need of treatment by the US DOE. The major oxides in these model glasses included SiO{sub 2}, Al{sub 2}O{sub 3}, B{sub 2}O{sub 3}, Na{sub 2}O, CaO and Fe{sub 2}O{sub 3}. In addition, three minor oxides, BaO, NiO, and PbO, were added as hazardous metals. The major oxides were each varied at two levels resulting in 32 experimental glasses. The chemical durability was measured by the 7-Day Product Consistency Test (PCT). The normalized sodium release rates (NRR{sub Na}) of these glasses ranged from 0.01 to 4.99 g/m{sup 2}. The molar ratio of the glass-former to glass-modifier (F/M) was found to have the greatest effect on PCT durability. Glass-formers included SiO{sub 2}, Al{sub 2}O{sub 3}, and B{sub 2}O{sub 3}, while Na{sub 2}O, CaO, BaO, NiO, and PbO were glass-modifiers. As this ratio increased from 0.75 to 2.0, NRR{sub Na} was found to decrease between one and two orders of magnitude. Another important effect on NRR{sub Na} was the Na{sub 2}O/CaO ratio. As this ratio increased from 0.5 to 2.0, NRR{sub Na} increased up to two orders of magnitude for the glasses with the low F/M ratio but almost no effect was observed for the glasses with the high F/M ratio. Increasing the iron oxide content from 2 to 18 mole% was found to decrease NRR{sub Na} one order of magnitude for the glasses with low F/M but iron had little effect on the glasses with the high F/M ratio. The durability also increased when 10 mole percent Al{sub 2}O{sub 3} was included in low iron oxide glasses but no effect was observed with the high iron glasses. The addition of B{sub 2}O{sub 3} had little effect on durability. The effects of other composition parameters on durability are discussed as well

Mechanistic modeling of pollutant removal, temperature, and evaporation in chemical air scrubbers

Chemical air scrubbers reduce the concentration of water-soluble components such as ammonia from the outgoing ventilation air through absorption in water, followed by chemical conversions and removal of the end products. A mechanistic model for a countercurrent air scrubber was set up. Mass balances for ammonia, hydrogen sulfide, nitrous oxide, and methane were implemented, as well as the water mass balance and heat balances. The model was validated against experimental data from a conventional fattening pig housing facility. The effect of influent characteristics, design parameters, and control handles on the removal efficiency, the temperature profile, and the water evaporation rate were investigated through simulation. The model was able to describe the behavior of a countercurrent chemical air scrubber

Vitrification Demonstration with Argentine Ion Exchange Material in the Stir- Melter (U)

SUMMARY The Savannah River Technology Center (SRTC) is investigating the viability of vitrification treatment of Argentine ion exchange material as part of a Department of Energy (DOE) -Office of Science and Technology Development Task Plan. Bench-scale studies were performed by the SRTC to define the necessary vitrification process for this material. However, the process had to be demonstrated in a melter system before vitrification could be considered a viable treatment option. A vitrification demonstration with resin representative of the Argentine ion exchange material was performed at the Clemson Environmental Technologies Laboratory (CETL) under a South Carolina Universities Research and Education Foundation (SCUREF) contract. The demonstration was performed in the 1/4 square foot Stir-Melter using the iron-enriched borosilicate glass composition developed at the SRTC. The glass produced from the demonstration was determined to be homogeneous and durable. The vitrification process utilized represented a 59.5% volume reduction. The radioactive material retention was 100% for Cs and Sr and ~43% for Co, which was based on glass retention calculations and demonstrated with surrogate chemical compounds. It is expected that the Co retention would be higher with actual spent resin because the Co would be bound on the resin matrix instead of loosely adsorbed as was the case with this test. Offgas characterization did not include the surrogates used for the radioactive isotopes. Iron represented the most prominent particulate element characterized in the offgas system, while sodium was the most volatile element. Organic compounds emitted were not positively identified or quantified, but were believed to be high molecular 2 WSRC-TR-98-00112, Rev.1 weight cyclic and heterocylclic nitrates and cynates and organosilicates. The nitrates and cynates were expected with amine resins, whereas the silicates were not. Changes to the offgas and melter system design would be necessary to help break-down these organic compounds into harmless species. In the identified form, the compounds would form tars in the offgas system and may be carcinogenic