Geomelting

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GeoMelt is a process by which dangerous, contaminated material (such as radioactive waste [1] and heavy metals [2] ) is mixed with clean soil, a blend of industrial minerals, and/or glass frit and melted to create an extremely hard and leach-resistant glass product. [3] Vitrification immobilizes nearly all of the inorganic contaminants (i.e., radionuclides and heavy metals) present in the initial mixture by incorporation into the glass matrix. [4] Organic wastes in the melt are destroyed by pyrolysis, and gaseous contaminants released during the melting process are treated separately. [5]

Contents

Developed in 1980 by the U.S. Department of Energy's Pacific Northwest National Laboratory [6] (PNNL), the GeoMelt process is deployed in one of two ways: in-situ (in-place) treatment of buried radioactive and hazardous wastes, and In-Container Vitrification (ICV), which is ex-situ treatment where radioactive and hazardous wastes are vitrified in a refractory-lined steel container. [3]

Process

Vitrification

Geomelting is based on the principle of vitrification, the process by which a glass is formed. To effectively vitrify any mixture of materials, substances that contribute to glass formation (called glass formers) must be present. [1] These glass formers usually contain silicon and oxygen and are present in most soils.

Much of the efficiency of this process has to do with how much waste material can be mixed with glass formers. Industrial-scale melts have shown that a stable glass compound is formed even when the original melt mixture is up to 33-40% waste material by weight, [1] [3] [5] depending on the type of waste.

Melting

First, waste is mixed with soil containing glass formers in a large container installed with electrodes (electrical conductors) suitable for heating the mixture. The container used is either underground [7] (subsurface planar vitrification, or SPV) or above ground (in-container vitrification, or ICV). [7] In both cases, the waste/soil mixture is loaded into the container and the heating processes begins when the electrodes are turned on. Due to spatial restrictions, the entire mixture cannot melt at the same time. The materials closest to the electrodes are melted first, and convection currents (movements of substances in a fluid) within the molten mixture continue to add more solid material into the molten material. After about 36-58 [8] hours, all of the mixture is molten and the convection currents create homogeneity (equal distribution of components) within the resultant mixture. [9]

Subsurface Planar Vitrification (SPV)

In subsurface planar vitrification, all melting operations are performed at the site of contamination. A very tall (around 6 meters deep), [9] narrow cavern is dug into the contaminated soil, which serves as the melting container. Very large electrodes are positioned within the cavern to optimize melting times. [5] The hazardous waste is then mixed with soil inside the cavern and the melt is initiated. After the glass product has been formed, it is either left in the ground [10] or transferred to a disposal facility.

Advantages

SPV melts do not require much capital investment, because the only construction necessary is the cavern that must be dug and the retrieval of the vitrified mass after the melt. [11] SPV melts cost roughly $355–461 per ton [12] of processed waste. When compared to the disposal cost of $555 per kilogram [13] (or $500,000 per ton) of nuclear waste, SPV is very cost-effective. There is also very little risk of worker injury on the job because the melting process happens underground and away from the workers at the site. [10] Finally, the melt caverns have no size restrictions, [5] so SPV can handle very large volumes of waste at once.

Disadvantages

SPV does not come without its drawbacks. In order to perform an SPV melt, all materials and personnel must be moved to the melting site, [9] so the costs of transportation for both must be taken into consideration. Once all contaminants have been removed or destroyed at the site, the project must relocate to continue operations. Melts cannot begin immediately after a treatment team arrives because it takes a few hours to dig the caverns and position the electrodes inside. [5]

In-Container Vitrification (ICV)

In-container vitrification melts are carried out above ground in a container made of heat-resistant metal coated with a protective layer of sand. [14] The sand separates the container walls from the molten mixture and shapes the glass product after it has cooled. [15] Melts are carried out in quick succession; once one melt has cooled, another waste container is loaded with electrodes and the process begins again. The vitrified glass is then sent to a disposal facility. [1]

Advantages

Because these melts are carried out at a treatment facility, all melts are efficient and centralized to that location. [16] Waste/soil mixtures are systematically loaded and processed in the facility. Since the mixtures are melted above ground, machines do not have to dig up the glass product like in SPV melts. The melt containers are also the containers used to transport the glass, [3] so there are fewer transfers involved in the glass's disposal.

Disadvantages

ICV melts have their downsides as well. The most immediate concern of ICV melts is the cost. ICV requires a treatment facility, meaning either a new facility must be built or an existing facility must be renovated to accommodate the new process. Both methods require considerable capital investment. Even after the facility is prepared for the process, ICV melts cost about $1,585 per ton [12] of processed waste (3-4 times the cost of an SPV melt). This extra cost is due to the necessary safety precautions in the facility. For example, the melting process occurs at very high (1200 to 2000 °C) temperatures, [17] and some of this heat is dispersed throughout the facility; so adequate cooling and ventilation are needed for areas where workers are present. [18]

Off-Gas Treatment

While the contaminated mixture is melting, gases (called off-gases) are released, [19] which are hazardous substances themselves. These gases are captured by a steel fume hood [20] and sent through a treatment system [1] that then removes about 99.9999% of the contaminants. [1] [21] Standard treatment procedures span from filtration [1] to wet scrubbing [20] [22] (using liquid to remove gaseous contaminants), though the exact procedures depend on the gases being treated.

Applications

Hazardous materials are often very difficult to remove and treat. [23] The contaminants might be seeped into the soil, [24] contained within a sludge, [25] or present within spent nuclear reactor cores. [26] No matter where a hazard exists, each requires a different method of treatment and disposal using standard waste management processes. With geomelting, however, the treatment (melting) process is essentially the same [27] for each batch, as is the glass produced, regardless of the contaminants in the mixture. Due to this versatility, geomelting is employed in many hazard-control operations. [3]

Organics

GeoMelt is used to treat a variety of organic wastes including oils, pesticides [28] and herbicides, solvents [29] and persistent organic pollutants including polychlorinated biphenyls (PCBs), dioxins, and furans (GeoMelt is permitted by the U.S. Environmental Protection Agency (EPA) as an approved thermal treatment method for PCBs throughout the U.S. [30] These wastes are carcinogens [31] (cancer-causing substances) and often impair critical bodily functions (e.g. breathing) over time. The melting process destroys organic compounds because no organic materials are able to survive the high temperatures of the melt process. [1]

Inorganics

Inorganic contaminants like heavy metals (toxic metals including mercury, cadmium, and lead [32] ) are released into the environment via industrial leaks and automobile waste. [33] If left unattended, these inorganic hazards can deteriorate ecosystems [34] and cause mental/physical illnesses [32] in humans. Regardless of the mixture of metals, geomelting isolates these heavy metals in a glass matrix and prevents them from entering the environment, [6] eliminating the threat posed to the surroundings.

Radioactive Materials

Since the advent of nuclear power plants, nuclear pollution (the dispersal of radioactive materials) has become a problem for the environment. The amount of radiation in radioactive materials may not be safe for living organisms, [35] so it is important for all nuclear pollution to be removed. Nuclear waste naturally remains hazardous for hundreds of years, [36] but when processed with geomelting, radioactive materials are immobilized. [37]

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<span class="mw-page-title-main">Radioactive waste</span> Unusable radioactive materials

Radioactive waste is a type of hazardous waste that contains radioactive material. Radioactive waste is a result of many activities, including nuclear medicine, nuclear research, nuclear power generation, nuclear decommissioning, rare-earth mining, and nuclear weapons reprocessing. The storage and disposal of radioactive waste is regulated by government agencies in order to protect human health and the environment.

<span class="mw-page-title-main">Welding</span> Fabrication or sculptural process for joining materials

Welding is a fabrication process that joins materials, usually metals or thermoplastics, by using high heat to melt the parts together and allowing them to cool, causing fusion. Welding is distinct from lower temperature techniques such as brazing and soldering, which do not melt the base metal.

<span class="mw-page-title-main">Vitrification</span> Transformation of a substance into a glass

Vitrification is the full or partial transformation of a substance into a glass, that is to say, a non-crystalline amorphous solid. Glasses differ from liquids structurally and glasses possess a higher degree of connectivity with the same Hausdorff dimensionality of bonds as crystals: dimH = 3. In the production of ceramics, vitrification is responsible for their impermeability to water.

<span class="mw-page-title-main">Materials recovery facility</span> Plant to process recyclates

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<span class="mw-page-title-main">Glass recycling</span> Processing of waste glass into usable products

Glass recycling is the processing of waste glass into usable products. Glass that is crushed or imploded and ready to be remelted is called cullet. There are two types of cullet: internal and external. Internal cullet is composed of defective products detected and rejected by a quality control process during the industrial process of glass manufacturing, transition phases of product changes and production offcuts. External cullet is waste glass that has been collected or reprocessed with the purpose of recycling. External cullet is classified as waste. The word "cullet", when used in the context of end-of-waste, will always refer to external cullet.

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Aluminium recycling is the process in which secondary aluminium is created from scrap or other forms of end-of-life or otherwise unusable aluminium. It involves re-melting the metal, which is cheaper and more energy-efficient than the production of aluminum from raw bauxite via electrolysis of aluminum oxide (Al2O3) during the Hall–Héroult and Bayer processes.

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<span class="mw-page-title-main">Waste</span> Unwanted or unusable materials

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Vitrified sand is sand that has been heated to a high enough temperature to undergo vitrification, which is the melting of the silicon dioxide or quartz that compose common sand. Vitrified sand is a type of natural glass, contrasted with manufactured glass in which soda ash or potash are added to lower the melting point. Pure quartz melts at 1,650 °C (3,002 °F). There are several natural processes that produce more or less melted sand and one man-made form:

<span class="mw-page-title-main">FLiBe</span> Chemical compound

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Solid waste policy in the United States is aimed at developing and implementing proper mechanisms to effectively manage solid waste. For solid waste policy to be effective, inputs should come from stakeholders, including citizens, businesses, community-based organizations, non-governmental organizations, government agencies, universities, and other research organizations. These inputs form the basis of policy frameworks that influence solid waste management decisions. In the United States, the Environmental Protection Agency (EPA) regulates household, industrial, manufacturing, and commercial solid and hazardous wastes under the 1976 Resource Conservation and Recovery Act (RCRA). Effective solid waste management is a cooperative effort involving federal, state, regional, and local entities. Thus, the RCRA's Solid Waste program section D encourages the environmental departments of each state to develop comprehensive plans to manage nonhazardous industrial and municipal solid waste.

<span class="mw-page-title-main">Hanford Tank Waste Treatment and Immobilization Plant</span>

The Hanford Tank Waste Treatment and Immobilization Plant, known as the Vit Plant, will process the nuclear waste at the Hanford Site in Washington into a solid glass form using vitrification. A proven technology that has been used at the Savannah River Site and West Valley Demonstration Project, vitrification involves mixing the waste with glass-forming chemicals, heating it to 2,100 degrees Fahrenheit, and pouring it into stainless steel containers to solidify.

References

  1. 1 2 3 4 5 6 7 8 K.G. Finucane; L.E. Thompson; T. Abuku; H. Nakauchi (24–28 February 2008). "Treatment of Asbestos Waste Using the GeoMeltⓇ Vitrification Process" (PDF). Waste Management 2008 Conference: 3. Retrieved October 11, 2013.
  2. ↑ John Vijgen; Ron McDowall. "GeoMelt Technology Specification and Data Sheet" (PDF). Retrieved October 22, 2013.
  3. 1 2 3 4 5 Kurion, Inc. "GeoMelt". Archived from the original on 2013-10-13. Retrieved October 11, 2013.
  4. ↑ Fraser, Don; Leo Thompson. GeoMelt Process: An alternative for pesticides waste and soil treatment (PDF). 6th International HCH and Pesticides Forum. p. 553.
  5. 1 2 3 4 5 Morse, M.K.; B.R. Nowack; L.E. Thompson (Feb 26 – Mar 2, 2006). "Subsurface Planar Vitrification Treatment of Problematic TRU Wastes: Status of a Technology Demonstration Program" (PDF). WM '06 Conference: 2.
  6. 1 2 Kurion, Inc. "Kurion Acquires GeoMelt® to Expand Vitrification Solutions" . Retrieved October 22, 2013.
  7. 1 2 Thompson, L.E. (27 February 2002). Mixed Waste Treatment Cost Analysis for a Range of GeoMelt Vitrification Process Configurations. Waste Management 2002 Symposium, Tucson, AZ (US), 02/24/2002--02/28/2002. OSTI   828961.
  8. ↑ K.G. Finucane; L.E. Thompson; T. Abuku; H. Nakauchi (24–28 February 2008). "Treatment of Asbestos Waste Using the GeoMeltⓇ Vitrification Process" (PDF). Waste Management 2008 Conference: 6. Retrieved October 11, 2013.
  9. 1 2 3 Morse, M.K.; B.R. Nowack; L.E. Thompson (Feb 26 – Mar 2, 2006). "Subsurface Planar Vitrification Treatment of Problematic TRU Wastes: Status of a Technology Demonstration Program" (PDF). WM '06 Conference: 7.
  10. 1 2 Morse, M.K.; B.R. Nowack; L.E. Thompson (Feb 26 – Mar 2, 2006). "Subsurface Planar Vitrification Treatment of Problematic TRU Wastes: Status of a Technology Demonstration Program" (PDF). WM '06 Conference: 3.
  11. ↑ Thompson, L.E. (24–28 February 2002). Mixed Waste Treatment Cost Analyses for a Range of Geomelt Vitrification Process Configurations (PDF). Waste Management 2002 Symposium. p. 7.
  12. 1 2 Thompson, L.E. (24–28 February 2002). Mixed Waste Treatment Cost Analayses for a Range of Geomelt Vitrification Process Configurations (PDF). Waste Management 2002 Symposium. p. 1.
  13. ↑ Orszag, Peter R. (14 November 2007). "Costs of Reprocessing Versus Directly Disposing of Spent Nuclear Fuel" (PDF). Congressional Budget Office. p. 9.
  14. ↑ Hrma, P.R.; D.-S. Kim; J. D. Vienna; J. Matyáš; D. E. Smith; M. J. Schweiger; J. D. Yeager (March 2005). "Testing of Large-Scale ICV Glasses with Hanford LAW Simulant" (PDF). Pacific Northwest National Laboratory. p. 20.
  15. ↑ Hrma, P.R.; D.-S. Kim; J. D. Vienna; J. Matyáš; D. E. Smith; M. J. Schweiger; J. D. Yeager (March 2005). "Testing of Large-Scale ICV Glasses with Hanford LAW Simulant" (PDF). Pacific Northwest National Laboratory. p. 3.19.
  16. ↑ Thompson, L.E. (24–28 February 2002). Mixed Waste Treatment Cost Analyses for a Range of Geomelt Vitrification Process Configurations (PDF). Waste Management 2002 Symposium. p. 4.
  17. ↑ "GeoMelt Vitrification of ILW (Pre-Conceptual stage) Summary of Assessment Report" (PDF). Nuclear Decommissioning Authority. 30 May 2008. p. 1.
  18. ↑ US Department of Labor. "Occupational Heat Exposure".
  19. ↑ Aquadecks Group. "Geo-Melt Thermal Treatment Process" . Retrieved Oct 30, 2013.
  20. 1 2 Thompson, L.E. (24–28 February 2002). Mixed Waste Treatment Cost Analyses for a Range of Geomelt Vitrification Process Configurations (PDF). Waste Management 2002 Symposium. p. 3.
  21. ↑ Thompson, L.E. (24–28 February 2002). Mixed Waste Treatment Cost Analyses for a Range of Geomelt Vitrification Process Configurations (PDF). Waste Management 2002 Symposium. p. 2.
  22. ↑ Thompson, Leo E.; Nicholas Megalos; David Osborne (Feb 27 – Mar 2, 2000). Hexachlorobenzene Destruction With the Geomelt Process (PDF). Waste Management 2000 Symposium. p. 5.
  23. ↑ US Department of Labor. "Decontamination".
  24. ↑ US EPA. "Soil Contamination".
  25. ↑ UN Environment Programme. "Sludge Treatment, Reuse and Disposal".
  26. ↑ Frogatt, Anthonhy (2 Nov 2005). "Nuclear Reactor Hazards". Nuclear Power: Myth and Reality: 23.
  27. ↑ K.G. Finucane; L.E. Thompson; T. Abuku; H. Nakauchi (24–28 February 2008). "Treatment of Asbestos Waste Using the GeoMeltⓇ Vitrification Process" (PDF). Waste Management 2008 Conference: 5. Retrieved October 11, 2013.
  28. ↑ Department of Environmental Protection, Florida. "Synthetic Organic Contaminants and their Standards".
  29. ↑ National Institute for Occupational Safety (3 December 2020). "Organic Solvents".
  30. ↑ U.S. Environmental Protection Agency (January 25, 2017). "Approval issued pursuant to Section 6(e)(1) of the Toxic Substances Control Act of 1976 (TSCA), Public Law No. 94-469, and the Federal Polychlorinated Biphenyls (PCB) Regulation, 40 CFR 761.60" (PDF). epa.gov. Retrieved May 30, 2017.
  31. ↑ "Organic Solvent Neurotoxicity". Current Intelligence Bulletin. No. 48. Centers for Disease Control and Prevention. March 1987. doi: 10.26616/NIOSHPUB87104 .
  32. 1 2 US Department of Labor. "Toxic Metals".
  33. ↑ Fairfax County VA. "Heavy Metal Pollution Is More Common Than You Think".
  34. ↑ Singh, Reena; Neeta Gautam; Anurag Mishra; Rajiv Gupta (2011). "Heavy metals and living systems: An overview". Indian Journal of Pharmacology. 43 (3): 246–253. doi: 10.4103/0253-7613.81505 . PMC   3113373 . PMID   21713085.
  35. ↑ NRC. "Radiation Protection".
  36. ↑ World Nuclear Association. "Waste management: Overview".
  37. ↑ K.G. Finucane; L.E. Thompson; T. Abuku; H. Nakauchi (24–28 February 2008). "Treatment of Asbestos Waste Using the GeoMeltⓇ Vitrification Process" (PDF). Waste Management 2008 Conference: 1. Retrieved October 11, 2013.
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