Hazardous or toxic waste destruction or containment – Containment – Solidification – vitrification – or cementation
Reexamination Certificate
2001-05-04
2004-01-20
Sandy, Robert J. (Department: 3677)
Hazardous or toxic waste destruction or containment
Containment
Solidification, vitrification, or cementation
C588S252000, C588S257000, C106S710000, C106S763000, C501S155000
Reexamination Certificate
active
06679823
ABSTRACT:
FIELD OF THE INVENTION
The present invention pertains to the stabilization of electric arc furnace dust (EAFD) and, more specifically, the reduction of leaching of heavy metals from EAFD in both acidic and alkaline environments.
BACKGROUND OF THE INVENTION
The electric arc furnace process is a common steel making practice in use for many years. In a typical electric arc furnace process, solid charge ingredients including raw scrap, lime, burnt lime, iron ore and ferro-alloy additives are placed in a top-charge furnace unit.
A conventional furnace unit is equipped with (1) a roof lift and swing arrangement which permits the roof to swing aside when cold scrap is charged into the furnace, (2) a rocker and rail tilting type arrangement which permits the furnace to tilt forward for tapping and backward for slagging, (3) a system for additions through the furnace roof, and (4) evacuation systems for the removal of dust generated during the steel making cycle.
In an electric arc furnace, electrodes are supported by electrode arms and clamps and project from overhead down through the furnace roof. An electric arc surging between the electrodes and through the furnace charge, typically comprising largely scrap metal, produces heat which melts the charge and refines the steel. The molten steel is tapped, typically at about 3000° F., into a ladle and cast into blooms or poured into ingot molds.
In such a process, particulate emissions are generated during (1) the charging of scrap, (2) the tapping of furnaces, (3) the pneumatic injection of additives, (4) oxygen blowing, and (5) meltdown/refining periods. This particulate, which is individually and collectively referred to as electric arc furnace dust (hereinafter EAFD), is typically collected either as a dry waste in baghouses but can also be collected wet, as a sludge.
In its emitted form, EAFD readily leaches heavy metals when wet, producing heavy metals concentrations in a leachate which exceed certain limits as set forth by the United States Environmental Protection Agency (EPA). In fact, EAFD is designated hazardous by the EPA and carries the designation of “KO61” as a hazardous material because of the presence of relatively high amounts of leachable heavy metals, such as lead, chromium, cadmium, and thallium. The disposal, transportation, and handling of hazardous materials are more expensive than the disposal, transportation, and handling of non-hazardous materials. EAFD is generally considered one of the more difficult EPA-listed wastes to treat.
The current state of the art for the treatment and disposal of EAFD is either high temperature processing or chemical stabilization/fixation. For technical and economic reasons, the chemical stabilization/fixation treatment is growing rapidly in use and was performed on over one-third of the approximately 875,000 tons of EAFD generated in 1999 in the United States.
There are two sets of standards currently in use by the EPA for land disposal of EAFD; one standard is for placement in secure landfills (land disposal regulations (LDR)), and the second set is for converting the EAFD to a non-hazardous material for placement in a conventional municipal landfill (“delisting”). The current (1998) limits established as LDR are based on the EPA's SW846 Method 1311, the well-known Toxicity Characteristic Leaching Procedure (TCLP). This protocol involves exposing the material to be tested to an acetic acid solution (at a pH of 2.88) for eighteen (plus or minus two) hours. Recent discussions have indicated that the EPA may be considering additional leaching tests at other pH levels, including higher pH levels.
Delisting protocol for many years required testing by TCLP followed by the Multiple Extraction Procedure (MEP). This procedure is a nine cycle sequence of leaching in a pH 3.00 sulfuric and nitric acid fluid of the solids filtered from the TCLP. This test has been deemed equivalent to exposure to 1,000 years of acid rainfall. For many years, the EPA his discussed the technical weakness of this protocol, emphasizing the unrealistic pH levels used. Very recent petitions for delisting treated hazardous wastes, at the federal level and in U.S. EPA Regions V and VI, have been required to provide testing data for TCLP and MEP tests carried out at leaching fluid pH levels of from 2.88 to as alkaline as pH 12.
In response to each petition filed with the EPA for delisting, the EPA sets limits of heavy metals concentration specific to that petition. The particular limits vary from petition to petition depending on a number of factors. For example, for a delisting petition filed by a company related to the assignee, the EPA granted the petition and set forth the limits shown on Table 1 as generic delisting limits (GDL).
As mentioned above, an EAFD sample undergoing the TCLP must yield a result which is less than the concentration limit specified by the EPA as its Land Disposal Regulations (LDR) in order for the material to be disposed of in a secure landfill. As can be seen in Table 1, the LDRs include thirteen metals. In order to “delist” or reclassify EAFD as non-hazardous according to this granted petition, the sequential testing on a treated waste is the TCLP followed by the nine MEP cycles all on a single sample. Delisting under the above-mentioned granted petition requires that the metals concentrations of fourteen various metals (i.e., the thirteen in the LDR plus vanadium) in a leachate be below specified generic delisting limits (GDLs), as set forth in Table 1. It should be pointed out that there is some benefit or usefulness event for any reduction in heavy metals concentration, even if one or more of the metals concentration exceeds these specific limits.
TABLE 1
GDL
LDR
Antimony
0.06 mg/L
1.15 mg/L
Arsenic
0.50 mg/L
5 mg/L
Barium
7.6 mg/L
21 mg/L
Beryllium
0.010 mg/L
1.22 mg/L
Cadmium
0.050 mg/L
0.11 mg/L
Chromium
0.33 mg/L
0.6 mg/L
Lead
0.15 mg/L
0.75 mg/L
Mercury
0.009 mg/L
0.025 mg/L
Nickel
1 mg/L
11 mg/L
Selenium
0.16 mg/L
5.7 mg/L
Silver
0.30 mg/L
0.14 mg/L
Thallium
0.020 mg/L
0.2 mg/L
Vanadium
2 mg/L
Zinc
70 mg/L
4.3 mg/L
Both of the tests described above are primarily directed to testing EAFD exposure under acid conditions for the purpose of simulating acid rain conditions. As mentioned above, the EPA has recently begun open discussions directed to the utilization of extraction fluids having a pH above 3.0 for the purpose of heavy metal testing and has recently proposed to grant a delisting petition using other levels, including pH values of approximately neutral and strongly alkaline. The Synthetic Precipitation Leaching Procedure (SPLP) protocol has a fluid pH of 4.2 which is obtained by the addition of sulfuric and nitric acids to water. Moreover, government agencies in Europe and Canada, as well as the American Society for Testing of Materials and the State of California, have developed aqueous leaching tests which are directed to the testing of materials at neutral pH conditions.
Several methods of chemically stabilizing EAFD have been disclosed. For example, U.S. Pat. Nos. 4,840,671 and 4,911,757, entitled PROCESS FOR CHEMICAL STABILIZATION OF HEAVY METAL BEARING DUSTS AND SLUDGES and issued to Lynn et al., disclose methods and mixtures for stabilizing EAFD and similar dusts with fly ash, lime, and water, among other ingredients. These methods partially rely on the pozzolanic characteristics of fly ash to physically entrap the hazardous constituents of EAFD within a cementitiously hardened product.
U.S. Pat. No. 5,245,122, entitled METHOD AND MIXTURE FOR TREATING ELECTRIC ARC FURNACE DUST, discloses a method for chemically stabilizing a hazardous waste composition containing EAFD by utilizing the pozzolanic characteristics of EAFD. This method involves forming a mixture of EAFD with water and lime and, optionally, ferrous sulfate. The freshly blended product has acceptable leachate concentrations when tested by the TCLP protocol. The method disclosed in the '122 patent minimizes the concentration of certain heavy metals in the leachate from the freshly blended produc
Envirosafe Services of Ohio, Inc.
Mitchell Katherine
RatnerPrestia
Sandy Robert J.
LandOfFree
Treatment of electric arc furnace dust to resist acid and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Treatment of electric arc furnace dust to resist acid and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Treatment of electric arc furnace dust to resist acid and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3192952