11:32 am - Monday May 28, 2012

Asbestos Recycling

Asbestos RecyclingThe current disposal of asbestos containing materials (ACM) in the private sector consists of sealing asbestos wetted with water in plastic for safe transportation and burial in regulated land fills. This disposal methodology requires large disposal volumes especially for asbestos covered pipe and asbestos/fiberglass adhering to metal framework, e.g. filters. This “wrap and bury” technology precludes recycle of the asbestos, the pipe and/or the metal frameworks. Safe disposal of ACM at U.S. Department of Energy (DOE) sites, likewise, requires large disposal volumes in landfills for non-radioactive ACM and large disposal volumes in radioactive burial grounds for radioactive and suspect contaminated ACM. The availability of regulated disposal sites is rapidly diminishing causing recycle to be a more attractive option. Asbestos adhering to metal (e.g., pipes) can be recycled by safely removing the asbestos from the metal in a patented hot caustic bath which prevents airborne contamination/inhalation of asbestos fibers. The dissolution residue (caustic and asbestos) can be wet slurry fed to a melter and vitrified into a glass or glass-ceramic. Palex glasses, which are commercially manufactured, are shown to be preferred over conventional borosilicate glasses. The Palex glasses are alkali magnesium silicate glasses derived by substituting MgO for B2O3 in borosilicate type glasses. Palex glasses are very tolerant of the high MgO and high CaO content of the fillers used in forming asbestos coverings for pipes and found in boiler lashing, e.g. hydromagnesite (3MgCO3•Mg(OH)2•3H2O) and plaster of paris, gypsum (CaSO4). The high temperate of the vitrification process destroys the asbestos fibers and renders the asbestos non-hazardous, e.g. a glass or glass-ceramic. In this manner the glass or glass-ceramic produced can be recycled, e.g., glassphalt or glasscrete, as can the clean metal pipe or metal framework.

There are many places you may find asbestos in your life, including:

  • Adhesives
  •  Artificial ashes and embers in gas-fired fireplaces
  • Cement pipes
  • Door gaskets
  • Electrical equipment
  • Floor tiles
  • Heat-resistant fabrics
  • Insulating boards
  • Paper products
  • Pipe insulation
  • Roof shingles
  • Sound proofing material
  • Talc products
  • Textured wall surfaces
  • Transmission and brake parts for automobiles
  • Vermiculite products

Safe Asbestos Handling

If you’re concerned that there are asbestos-containing products in your home, there are things you can do to protect you and your family.

  • Identify Asbestos : Follow the US Environmental Protection Agency’s (EPA) steps to identify asbestos.
  • Do not handle yourself : Damaged or loose asbestos can be easily inhaled or come into contact with your skin and so should be avoided if at all possible. Follow these safe handling methods to ensure that you do not expose yourself to this material unnecessarily.
  • Hire a Pro : In many cases, an asbestos professional will need to be called in to inspect and handle disposal of potential materials. In the US, the EPA manages a list of Accredited Asbestos Professionals, but you may be able to find a professional in your area to remove asbestos by looking online or in the yellow pages.

Caustic Dissolution Of Asbestos

A caustic-acid-caustic dissolution methodology was developed for dissolution of contaminated fiberglass HEME/HEPA filters from the SRS High Level Waste glass melter off-gas system. These filters are housed in metal filter frames. The fiberglass was found to convert to silica gel after the first dissolution step in 5 wt% NaOH at 90°C for 48 hours. After the NaOH dissolution, the HEME/HEPA filter frames were found to be clean. Air sparging of the tank accelerated the reaction and was necessary to ensure the total conversion. The dissolution solutions (NaOH) and the dissolution residues (silica gel) are glass forming elements that are sent back to the DWPF melter and vitrified. A patent was applied for and granted that umbrellas the use of the DWPF dissolution methodology on all fibrous high silica containing materials, including asbestos.

Since asbestos covered pipe is the largest volume of ACM and the most difficult to deal with at the SRS, the one step NaOH dissolution methodology was tested on a 7″ section of an asbestos covered pipe without separating the asphalt cover or the metal wires that tightly hold the asphalt around the ACM and the pipe (Figure 1). The hot 5 wt% NaOH solution was not sparged, not bubbled, not stirred, and 2000mL of solution was used on a 7″ long segment of pipe.

The 48 hour dissolution in hot 5%NaOH did nothing to the asphaltic material covering the pipe. This was confirmed by a second x-ray diffraction analysis, e.g. the same phases were present in the asphaltic material before and after the 48 hour treatment. Although the tar paper contains ~40% organics it can be vitrified along with the ACM since the tar paper comprises only a small amount (by weight or volume) of the overall material being processed.

The white ACM material was partially converted after the 48 hour dissolution. All of the hydromagnesite had been converted and the amosite asbestos had been partially converted. X-ray diffraction of the converted ACM indicated that magnesium hydroxide (Mg(OH)2) sodium carbonate (Na2CO3) were present as decomposition products of the non-asbestos phase, hydromagnesite. X-ray diffraction of the amosite asbestos were broad instead of sharp indicating that the crystalline structure of this phase had been partially destroyed, e.g. became amorphous. The NaOH solution was analyzed and found to contain high concentrations of Al and Si indicating that the silicate based asbestos minerals were indeed dissolving. The NaOH plus dissolved ACM was the consistency of “lumpy oatmeal” and could easily be fed to a melter for vitrification. The final vitrification completes the conversion of the ACM to an NCS.

If the asphaltic material covering the pipe is loosened, pierced, or removed to allow better reaction between the ACM and the solution, and/or if the tank is agitated slightly the ACM will convert more completely in the dissolution tank before being pumped to a melter. If the pipe is not sufficiently clean, a rinse in HNO3 can sufficiently decontaminate the iron pipe as the surface of the pipe reacts with the acid to form various iron oxides and hydroxides. The iron oxides and hydroxides spall off releasing the adhering ACM so that the pipe can be recycled. These smaller amounts of ACM and iron oxides/hydroxides can be admixed with the converted ACM from the caustic only process during the vitrification process.

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