Electric lamp and discharge devices – Having vapor generating material – Mercury vapor material
Reexamination Certificate
1998-11-27
2001-05-08
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
Having vapor generating material
Mercury vapor material
C313S318010, C313S490000, C445S002000
Reexamination Certificate
active
06229260
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention is directed broadly to mercury vapor arc discharge lamps and more particularly to methods for avoidance of soluble mercury pollution of landfills and groundwater upon disposal of such lamps and during TCLP testing for leaching of soluble mercury materials from such lamps. Compositions of matter useful in preventing the formation of leachable mercury in disposal and testing procedures form a part of the invention.
Low pressure mercury arc discharge lamps are standard lighting means which include electrodes sealed in a glass envelope, the interior of which may be coated with a phosphor. The lamp also contains a small amount of mercury and an inert gas at low pressure, of about 1 to 5 torr. The term lamp, as used herein, means the complete unit including the glass envelope and the end pieces and plugs for mounting in a lamp fixture, and wires which connect the internal components of the envelope with the end pieces.
During manufacture of fluorescent or low pressure mercury arc lamps an amount of elemental mercury (Hg
0
) is sealed in the lamp envelope. Most of the mercury adheres to the phosphor coating, a small amount being in the vapor phase.
During operation, alkali metal carbonates from the electrodes decompose and form free oxygen in the lamp. The oxygen may react with a portion of the mercury to form soluble mercury oxide (HgO). Soluble mercury oxide is leachable from land fills and other disposal facilities. Soluble mercury oxides or other oxidized forms of mercury formed in the course of the test are detrimental to the accuracy and reliability of the standard test for determination of the leachability of toxic materials from lamp waste. This test is generally referred to as the Toxicity Leaching Characteristic Procedure or TLCP test.
There is concern about the environmental impact of soluble mercury compounds which can leach into ground water sources, rivers, streams, and the like. The lamps provided by this invention are characterized by low levels of leachable mercury when the lamp is pulverized for testing or upon disposal in a landfill.
In the prior art, certain oxidants and reductants are placed in a lamp to alter the form of mercury in the course of the TCLP test. These agents function to remove leachable mercury from the TCLP solution. The method of the instant invention prevents formation of leachable mercury and also reduce any leached or soluble mercury to insoluble elemental mercury. The dehydroascorbic acid antioxidant of this invention prevents oxidation of iron and copper, thereby preventing formation of leachable mercury, and also reduces oxidized or soluble mercury. This later capability lessens mercury contamination within a landfill. Reduction of soluble mercury to insoluble elemental mercury also provides a method for recovery of mercury from contaminated soil and water.
SUMMARY OF THE INVENTION
Ferric and cuprous ions form soluble compounds which are capable of oxidizing elemental mercury to the monovalent, mercurous, form which is soluble in an acidic aqueous environment and therefore leachable. The formation of ferric and cuprous compounds depend on exposure to and reaction with oxygen. Dehydroascorbic acid incorporated in the lamp prevents formation of ferric and cuprous compounds, in the presence of water or moisture, by oxidation of iron and copper from lamp components, thereby greatly reducing or substantially preventing the formation of leachable mercurous and mercuric compounds by oxidation of elemental mercury.
In the course of performing the Toxicity Leaching Characteristic Procedure, TCLP, upon manually dosed (10 mg of elemental Hg added to an undosed lamp) T12 fluorescent lamps it was found that leachable mercury was generated. The metal components of the lamp, specifically the iron lead wires, copper coated leads, and brass pins generate Fe
+3
and Cu
+1
are both capable of oxidizing elemental Hg to Hg
+1
in the TCLP extractant solution.
If one performs the TCLP extraction upon the rest of the lamp once the metal components have been removed the leachable mercury values are significantly decreased. The dissolution of Fe
+3
and Cu
+1
in the TCLP extraction depend upon the presence of oxygen for the corrosion process to occur. By addition of antioxidants within the test, the amount of soluble Fe
+3
and Cu
+1
is decreased and, concomitantly, the amount of mercury that leaches from the extraction is also significantly reduced. Metal reductants have been employed that prevent the dissolution of Fe
+3
and Cu
+1
so that the oxidation of Hg
0
is greatly diminished. The antioxidants also are capable of removing leachable mercury from solution so that benefit is obtained to pass the TCLP test and to the environment if lamps are disposed within a landfill. The antioxidant that has proven to be effective and capable of manufacture within the lamp design is ascorbic acid. It has been found that ascorbic acid can oxidize to dehydroascorbic acid under lamp manufacturing conditions. Dehydroascorbic acid and some of its degradation products are effective as an anti-oxidants in TCLP testing of fluorescent lamps. Some of the degradation products included are the following: 2,3-dioxo-L-gulonic acid, oxalic acid, L-threoic acid, ([R-(R*,S*)]-2,3,4-trihydroxybutanoic acid), tartaric acid, furfural, 2-furoic acid, ethylglyoxal, furoin, and 2-methyl-3,8-hydroxychroman.
The invention provides a mercury vapor discharge lamp comprising an envelope of light transmitting glass which contains, an inert gas and an amount of elemental mercury, a pair of electrodes for establishing an arc discharge, and an effective amount of an antioxidant.
Fluorescent lamps generally include at least one base or end cap which defines a cavity having an inner surface. The cap is secured to the glass lamp envelope by a basing cement. The dehydroascorbic acid reagent can be conveniently admixed with the basing cement and incorporated into the lamp accordingly. Generally, fluorescent lamps of the tube type have a pair of end caps.
The dehydroascorbic acid is admixed with the basing cement used to secure the end caps in place on the glass envelope or can be placed in the end cap as an adhesive composition which does not function as a cement for the caps.
The invention, accordingly, includes dehydroascorbic acid admixed with an inert water soluble adhesive binder composition which can be included in the lamp structure for the purpose of controlling oxidation of iron and copper in order to minimize or prevent formation of soluble mercury compounds. The composition functions by reducing or preventing formation of water soluble leachable mercury compounds in landfills or TLCP test samples.
REFERENCES:
patent: 5229686 (1993-07-01), Fowler et al.
patent: 5229687 (1993-07-01), Fowler et al.
patent: 5754002 (1998-05-01), Haitko et al.
patent: 5898265 (1999-04-01), Woodward et al.
Dietrich David Key
Foust Donald Franklin
Haitko Deborah Ann
Henkes Ora Marie
Bennett Bernadette M.
General Electric Company
Guharay Karabi
Johnson Noreen C.
Patel Ashok
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