Investigation of foaming during nuclear defense-waste solidification by electric melting

Blair, H.T.; Lukacs, J.M.

doi:10.2172/6948154

Cited by 5 publications

(10 citation statements)

References 3 publications

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“…Although this conclusion may (or may not) be correct, the prior work does not constitute adequate proof that it is correct. Some of this work was based on the maximum height of expansion produced when glass feed batches (calcined simulated waste plus frit) were heated in 16-or 25-g batches in laboratory crucibles in air (Blair and Lukacs 1980). In some of these experiments, FeO and/or MnO was substituted for F%03 and/or Mn$, and in others various carbonaceous or other reducing agents were added.…”

Section: Reducing Agents Present In or Added To Melter Feedmentioning

confidence: 99%

“…Also, laboratory experiments were conducted using small crucibles of glass batches (Blair and Lukacs 1980). The observation that foaming was supposedly lessened by slightly more than the demonstrated experimental scatter by th addition of all the Fe and Mn as FeO and MnO instead of as Fe(II1) and MnO, does not prove that hi ier oxidation state Fe and Mn species produce the foaming observed in the liquid-fed melters.…”

Section: Introductionmentioning

confidence: 97%

“…Foaming has been proposed to result from oxygen release caused by the decrease in higher oxidation state stability of various multivalent elements (Blair and Lukacs 1980;Goldman, Brite, and Richey 1986;Lucktong and Hrma 1988;Goldman 1986). Such a conclusion is certainly logical because of the significant amount of evidence for foaming produced by such mechanisms in commercial glasses.…”

Section: Introductionmentioning

confidence: 99%

“…Because decomposition of some higher-valent oxides to release oxygen can produce foaming in molten glass, it was logical to study and use reducing agents to avoid these higher oxidation state species during waste glass production (Blair and Lukacs 1980;Goldman, Brite, and Richey 1986;Lucktong and Hrma 1988;Goldman 1986). The use of reducing agents (carbon, organic compounds, aluminum, silicon, etc.)…”

Section: Introductionmentioning

confidence: 99%

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Redox reaction and foaming in nuclear waste glass melting

Ryan¹

1995

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SummaryFoaming has often been observed in experimental continuous liquid-fed, joule-heated, ceramic melters that produce simulated nuclear waste-containing borosilicate glass. Such foaming, which results in significantly decreased melter throughput rates, has been attributed to the release of 9 gas resulting from the decomposition of higher valency metal oxides to lower valency oxides. It has been claimed that this foaming can best be controlled by adding reducing agents to the melter feed. In particular, the use of formic acid has been proposed to 1) acidify the aqueous waste stream, thereby dissolving some of the hydrous oxides and improving feed rheology, and 2) act as a reducing agent to control foaming. This document, prepared at Pacific Northwest Laboratory, reviews studies of nuclear waste glass foaming and the effects of reducing agents, particularly formic acid, on such foaming. It reviews the redox chemistry of many of the potential oxidizing and reducing species in or added to the glass-melter feed with the objective of predicting some of the chemistry that occurs in the cold cap and the glass melt as they might affect the foaming phenomenon. The review is not exhaustive since the literature search was limited by the complexity of the subject, and unknown effects on the chemistry, including various unknown catalytic effects, will certainly be important in such complex mixtures.Based on this review, little is actually known about the causes of or best remedies for foaming in the nuclear waste glass melters. The actual temperature regime (cold cap(a) plus melt) in the melter that is most important to the actual melter foaming is unknown. Workers have made widely different implicit assumptions in this regard. No evidence was found that adequate testing of proposed foaming remedies with well designed control experiments has been conducted in the glass melters.There is significant evidence based on run experience that, in the absence of added reductants, acidic feeds do not foam nearly as badly as alkaline feeds. Although alkaline feeds promote formation of higher oxidation state metal species in the cold cap, it is far from clear that easier formation of higher oxidation state metals causes the apparent greater foaming with alkaline feeds. The problem is that no run data were found in which only acidity or alkalinity were the significant variables.Based on the results of this review, there is strong question whether the varying degree of melter foaming is caused by different extents of decomposition of higher oxidation state metal oxides releasing O,, and whether this foaming can, therefore, be best controlled by adding reductants. This concept, while somewhat reasonable, must be proven with carefully designed experiments having virtually identical feeds with and without reductants in adequate quantity. These experiments must also compare other factors such as feed acidity-alkalinity with other variables held constant. Available laboratory data on the effect of reductants do not, for one reason or another...

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Section: Reducing Agents Present In or Added To Melter Feedmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Redox reaction and foaming in nuclear waste glass melting

Ryan¹

1995

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“…Thus, the total quantity of evolved gas will be increaskd rather than decreased. Blair and Lukacs (1980) perhmed several crucible tests to study the effect of a variety of reductants (sugar; cornstarch; coal; Si, Al, and Fe metal; graphite; e&). They condud@ that these agents lessened the fiam height in the crucible.…”

Section: 1: Iron Redox and Foaming In Simulated Nuclear Waste Glassmentioning

confidence: 99%

NCAW feed chemistry: Effect of starting chemistry on melter offgas and iron redox

Smith¹,

Vienna²,

Merz³

1995

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@ f i e document was printed on recycled paper. SummaryThe Pacific Northwest Laboratory(*) (PNL) Vitrification Technology Development (PVTD) program has been established to develop technology to support immobilization of selected Hanford wastes.The effort of the PVTD program is directed by the U.S. Department of Energy (DOE). This report is. part of the effort and focuses on the effect of feed preparation process chemistry on the vitrification process, The objective of the investigation w q the evaluation of the effect of starting chemistry on the cold cap behavior in the vitrification of simulated neutralized current acid waste (NCAW. The investigation included the measurement of iron oxidation state, the reaction sequence during gIass melting, and laboratory batch expansion measurements of the melter M. Low temperature reduction oftransition metals during cold cap reactions reduces the generation of O2 gas. The production of 0, gas by transition metals is thought to be Correlated with foaming in large-scale waste vitrification. Highvolume exparisions of the batch material in the laboratory sugest poor heat transfer in the cold .--cap and possible reductions in large-scale melting rate.The term "starting chemistry" refers to the oxidants (such as nitric acid) and reductants (such as sugar and formic acid) present in'the waste prior to vitrification. The starting chemistry of simulated NCAW includes untreked (unfbrmated) waste, kimic acid, nitric acid, and sugar. The formic acid, nitric acid, abd sugqr Samples were produced by addition of these materials to the untreated waste. These (un)treated wktes were combined with frit to produce melter W. Offgas measurements of the formic acidcontaining melter €ked show@ that formic acid/krmate decomposed at temperatures too low for participation in a glass redox reaction. Sugar clearly pyrolized and produced CO and H2 at temperatures exceeding 665°C. For the sugar9ntaining samples, the gIass quenched.from 1200°C produced an Fk?*EFe of 0.79. The measured iron redox ratios of the glasses made from untreated waste, formic acid-, and nitric acidcontaining wastes were essentially indistinguishable. The use of krmic acid as a reductant did not alter the iron redox state and, therefore, was decidedly ineffective in these laboratory experiments. This result hplies that formic acid will be less than 100'5% efficient as a reductant in large-scale vitrification. Volume expansion measurements of the batch material showed a more than sewenfbld @crease in volume for the sugar-containing sample below 200°C. Volume expansions fbr the fo'rmic acid (-6.5 times original volume, VJ, nitric acid (-1.5 VJ, and untreated (-2.5 VJ samples were observed in the 720" to 890°C range. Unfbrtunately, data is not amiIabIe from large-scale testing that wodd afford a relative comparison of the volume expansion data.

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