The International Information Center for Geotechnical Engineers

Vitrification

Advantages

The Environmental Protection Agency has declared vitrification to be the “best demonstrated available technology” for heavy metals and high-level radioactive waste (Meegoda and Ezeldin, 2003). It’s a good option especially for disposal of fly ashes containing heavy metals, highly toxic materials, nuclear and radioactive wastes, etc. The advantages of vitrification could be recognized by several aspects, regarding to its durability, high applicability to lots of kinds of soils and contaminants, volume saving, and cost effectiveness.

1.1 Stability and Durability

Vitrification technology enables contaminated waste to be stabilized in a glass-like form, for which durability issue is of great importance. Waste glass products always have stable chemical and physical properties and excellent weathering properties. Ewing and Haaker’s (1979) tested the long-term stability of vitrified glass products, using naturally occurring analogues for comparison. Durability tests have also been conducted by Pacific Northwestern National Lab, (PNNL, 2005). The durability of vitrified glass products was predicted to be as high as obsidian. According to the results, vitrification can lock dangerous contaminants, especially radioactive waste in glass forms for thousands of years (PNNL, 2005). Considering vitrifying MSW ashes, if left untreated, landfilled MSW ashes can leach unacceptable levels of As, Br, Cd, Cl, Cr, Cu, F, K, Mo, Na, Pb, S, Sb, Zn, chlorinated dioxins and benzofurans. Sewage sludge can also leach As, Cr and Se (Bingham and Hand, 2006). Leaching from vitrified wastes is generally much lower than from comparable untreated wastes. In the leaching test, the heavy metal releases tended to be lower than required by regulations, with durability in alkali and acidic solutions remaining constant as well (Scarinci and Brusatin, 2000).

1.2 Volume Reduction

A major attractive aspect of vitrification is that it can bond a wide variety of toxic species into glass matrix at atomic level and usually with a significant reduction of waste volume. Generally, vitrification leads to significant volume reduction by 25~50% for most natural soils (USEPA, 1997e). Research indicated that volume reduction factor (VRF) was at low level for vitrification, e.g. it was only around 1.2-2.4 according to vitrification method for non-combustible wastes (Park and Moon, 2007). Generally, it’s desirable to exclude the bulky cavities from a volume reduction and waste form quality perspective. Research indicated that there are few bulky cavities in glassy waste forms, which resulted in a high volume reduction.

When dealing with incinerator ashes wastes, comparisons of overall volume reduction compared to other stabilization strategies shows that vitrification reduces the stabilized volume by 96% (Jantzin and Pickett, 1993).

1.3 Cost Effectiveness

Vitrification technology is a cost-effective method for difficult sites with mixed contaminants or stringent cleanup standards. The major costs of vitrification operation are electrical power, labor, and consumable materials. The cost of vitrification can at first be slightly higher than other conventional waste disposal technologies. However, the high expenses at first stage will be offset by the savings from storage costs resulting from long-term durability and in volume reduction (up to a 97% reduction in volume compared to the most commonly used alternative) (Meegoda and Ezeldin, 2003).

1.4 Other Advantages

  • Ability to process a variety of waste types
  • Potential reuse of the waste glass
  • Good acceptance of ISV, which requires no excavation, transport, or reburial of contaminated soil, improving worker safety and reducing costs
 

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