Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF NONHAZARDOUS REMOVAL
OF PAINT CONTAINING HEAVY METALS AND
COATING PREPARATION FOR PERFORMING THE SAME
Background of the Invention
Elimination of hazardous material is gaining more
attention due to the new Environmental Protection Agency
(EPA) laws imposed because of the extreme toxicity of many of
these waste products. Wastes from lead paint removal are often
hazardous due to the high lead content as well as zinc, cadmium,
copper, nickel, barium and other heavy metals present.
Handling and disposal of these hazardous wastes is far more
complicated and expensive than if they were nonhazardous.
Thus, it could be extremely beneficial if the lead paint could be
rendered nonhazardous prior to its removal from the surface it is
on. This would eliminate the production of hazardous wastes
thereby avoiding the requirement of adhering to strict EPA
regulations since no hazardous wastes are ever produced. This
would reduce costs greatly and simplify the methods of handling
and disposal of the resulting nonhazardous waste.
A method of rendering the lead paint nonhazardous is via
a treatment process which introduces an additive that renders
metals to a nonhazardous form to a coating preparation formula.
This coating preparation could then be applied over the existing
lead paint before the lead paint is removed from the surface.
The lead paint is thereby rendered nonhazardous before it is
removed from its surface and becomes a waste material.
This process has numerous advantages. First, the
additive is in intimate contact with the lead-bearing (or other
heavy metal-bearing) paint, since they are removed together, and
there will be no question of achieving sufficient mixing between
the paint waste and the additives.
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Second, since the paint is treated before it is removed
from the surface, the generation of a hazardous waste is
eliminated. The treated waste will need to be disposed in
accordance with local, state, and federal regulations regarding
solid waste disposal, but it will not need to be handled as a
hazardous waste. Tkius, this treatment process reduces the
amount of United States EPA regulation and reduces time consuming EPA
filing requirements and similar filing requirements to meet environmental
regulations in other countries, such as Canada.
Third, since the additive is introduced on top of the
existing paint surface, the underlying surface after removal
should be unaffected by the treatment process. In other words,
the waste treatment will not effect the underlying surface with
regards to future painting.
Yet another advantage is since this technique eliminates
the generation of hazardous waste it will reduce both the short-
term cost and long-term liability for anyone with lead painted
items and, or course, it provides intangible benefit of the
manifesting requirements of a hazardous waste generator.
Another advantage is that the application procedure to
the lead painted surface is extremely simple and thereby
reduces the potential for human error.
Description of the Invention
The present invention involves a method of removing
paint containing heavy metal from a surface without the
production of hazardous wastes. Specifically, this method
involves applying a coating preparation to the paint containing
heavy metal prior to its removal, as illustrated in Table 2. The
coating primarily contains any number of forms of phosphate as
the key lead-reactive (heavy-metal reactive) material. The
preferred containing preparation may also contain other
additives such as buffers, binders, solvents, and pigments in
addition to the phosphate. The invention also involves the
coating preparation in combination with the additive itself.
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Examples of phosphate compounds within the scope of
this invention include triple super phosphate (TSP). Other
forms of phosphate in addition to TSP are effective for treating
the waste, such as a group of phosphorus containing chemicals
such as calcium phosphate, single super phosphate, trisodium
phosphate, or phosphoric acid. The lead reactive chemicals may
also include metal sulfides such as barium sulfide, zinc sulfide
and organic sulfide such as sodium dithiocarbamate. These
chemicals react with the heavy metals rendering them
nonhazardous.
Phosphate, alone or in combination, with buffers such as
magnesium oxide or magnesium hydroxide, separately or in
combination, is introduced to lead (or other heavy metal)
containing paint prior to paint removal thereby rendering waste
created from the process nonhazardous.
The preferred method of treatment is to introduce the
additives in a liquid or gel form that is applied to the surface of
the paint. The additives could be introduced to the paint by any
type of preparation which acts as a carrier. Introduction of the
additives could be accomplished by utilizing a preparation which
is in a liquid, gel or slurry form that will allow a thin layer of
these additives to be placed over and remain on the surface of
the lead paint. The preparation should preferably be
inexpensive, quick drying and strongly adhere to paint surface.
Generally, the preparation could be any type of paint
stripping solution. The coating preparation containing the
additives could also be any type of paint, a paint matrix, a paint
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stripper, or simply a quick drying slurry. The inventors have
found that the treatment additives can even be added to a
standard commercial water-based paint.
Specifically, the coating preparation may contain a
mixture of the additives including a lead reactive chemical, a
binder, a solvent, (or combination of solvents), pigments, and
buffering compounds such that the mixture is sprayable or
blowable with commercially available spraying equipment and
blow coating equipment. The combination of the
aforementioned additives will dependent upon the site-specific
conditions of application and the economic combination of the
same. The lead reactive chemical can be a phosphate in the
form of TSP, calcium phosphate, single superphsophate, etc. as
outlined above. Additionally, the lead reactive material may also
include the aforementioned metal sulfides or organic sulfides.
The concentration of the lead reactive chemicals would range
from 5% by weight to 50% by weight.
The binders, which may be used alone or in combination,
may include a wide variety of polymers such as acrylic resins,
polyester resins, epoxy resins, polyether resins, alkylide resins,
urethane and polyurethane resins.
The solvents include water, alcohols, glycol ethers,
glycols and also xylene, toluene, acetone, methyl-ethyl ketone,
methyl-150-butyl based ketone, and mineral spirits. Again,
these may be used alone or in combination.
Pigments (utilized alone or as a mixture) may be any
commercial paint pigment such as titanium dioxide, calcium
carbonate, silica, or aluminum oxide, the purpose of which is to
show coverage and to regulate the elasticity of the coating.
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The buffering compounds may consist of magnesium
oxide, magnesium hydroxide, ammonia, organic amines, such as
triethylamine, and triethanoyamin utilized alone or as a buffering
mixture. The concentration of buffer selected may range from
5%-30% by weight. The primary purpose of the magnesium
oxide or magnesium hydroxide is to buffer the pH of the treated
waste in the region of minimum solubility of lead phosphate (i.e.
pH 8-10). Even if the dosage of magnesium oxide/hydroxide is
too low to reach a pH in the 8-10 range, any amount of buffer
will raise the pH somewhat, which will decrease the solubility of
the lead.
Typically, commercial binders may be augmented with
the lead reactive chemicals and buffering compounds to
formulate a coating which meets the above requirements. For
example, a commercial available latex binder and solvent would
be augmented with the lead reactive chemicals and a buffer.
After application, the lead paint and coating preparation
are then removed from the surface using standard paint removal
techniques. Techniques for removing the paint can involve
surface cleaning methods ranging from the mechanical abrasion,
such as scraping lead paint from an item by hand or subjecting
items to the ball mill techniques, to the use of strong chemicals.
More delicate surfaces may require careful chemical removal to
prevent damage or destruction of the substrate.
Hard, durable surfaces such as heavy steel plating can be
cleaned or stripped by relatively fast abrasive methods, such as
sand blasting.
Composite materials such a plastics or epoxy, which often
contain fiber such as glass strands, graphite, Kevlar* or the like
for reinforcement, may require applying a granular media
* trade-mark
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substantially composed of particles of a material which has a
Mohs scale hardness lower than 3.5 to remove the paint, which
is outlined in U.S. Patent No. 4,731,125.
The granular media is accelerated using media
propelling means to produce a substantially and continuous
media flow on to the paint surface in order to remove the paint.
As one can see, there is a myriad of different methods for
removing the lead paint (with the coating preparation) and all
are contemplated as being within the scope of this invention.
This coating preparation can be applied to any surface
coated with lead paint. Specifically, it can be used for outdoor
surfaces of building, bridges, industrial machinery, petroleum
tanks and the like. Additionally, it can be used on indoor
surfaces such as walls, floors and ceilings of homes or business.
The chemistry behind this invention is based on the
reaction between the lead in the paint with phosphate in the
additive. Lead phosphates are among the least soluble and most
stable forms of lead in the natural environment. This means that
the lead, once stabilized, will remain in the phosphate form
unless subjected to highly acidic (pH < 4) or basic (pH > 11)
conditions, which are extremely uncommon in the natural
environment. Since the treatment process occurs through a
chemical reaction involving the lead, rather than through pH
control, the regulatory agencies find it acceptable.
Detailed Description of the Preferred Embodiment
EXAMPLE I
A Toxicity Characteristic Leaching Procedure (TCLP) test
was utilized to determine the toxicity of the resultant waste
material. The EPA standard to determine whether a waste is
nonhazardous material is 5 mg per liter (ppm) lead in the
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material as measured by the TCLP. Specifically, this test utilizes
a buffered acetic acid leach solution, which is mixed with the
waste for about 18 hours. The filtrate is then analyzed for lead.
If the lead level in the filtrate is >5.0 mg/1, the waste is
hazardous by the characteristic of lead toxicity.
The Example 1 analysis consisted of sandblasted paint
waste samples that were collected off of a sandblasted bridge.
Testing of leaded paint mixed with the treated paint has shown
treatment effectiveness, even with relatively low dosages of the
preparation (see Table 1). Dust from paint removal from a
bridge was found to be hazardous for lead (29.4 mg/L in a TCLP
test versus the criteria of 5 mg/L). In some states (such as
Michigan) this waste is also hazardous to zinc. Addition of 5%,
10% TSP or 5% TSP and 5% MgO reduced lead in a TCLP test
leachate to below the regulatory criterion of 5 mg/L and zinc
concentrations were also reduced to below the state regulated
criteria of 500 mg/L.
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TABLE 1
BRIDGE BLASTING PAINT WASTE
TREATMENT TEST RESULTS
Sample Screening TCLP Test Results
Cadmium Lead Zinc
pHl mg/L mg/L mg/L
Untreated 5.0 <0.3 29.4 1980
+ 5% TSP 5.2 <0.15 2.7 246
+ 10% TSP 5.1 <0.15 0.6 69
+ 5% MgO & 5% TSP 7.1 <0.15 <0.6 <0.15
+ 10% MgO & 10% TSP 9.6 <0.15 <0.6 <0.15
TSP - Triple super phosphate
MgO - Magnesium Oxide
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TABLE 2
USE OF INVENTION TO RENDER
PAINT REMOVAL WASTE NONI=[AZARDOUS
PAINTED SURFACE
Paint containing heavy metals
that render untreated
paint waste hazardous
Additives introduced in
surface layer on paint
PAINT AND ADDITIVE REMOVAL
USING CONVENTIONAL REMOVAL TECHNIQUES
NONHAZARDOUS PAINT WASTES
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TABLE 3
SCREENING TCLP TEST RESULTS
Extraction TCLP Lead,
Product Mixture Final pH Fluid mg/l
Untreated Paint Waste Residue 5.0 #1 12.5
+0.2% Dry Coating Preparation 5.0 #1 4.4
Solids
+0.4% Dry Coating Preparation 5.0 #1 2.1
Solids
+0.6% Dry Coating Preparation 5.1 # 1 1.0
Solids
+0.8% Dry Coating Preparation 5.2 # 1 0.41
Solids
+1.0% Dry Coating Preparation 5.2 #1 0.48
Solids
NOTE: The screening TCLP test is modified, scaled-down TCLP
leaching test that gives results that are similar to those of
a standard TCLP test on the waste material. The
screening test is not suitable for regulatory submittals.
The treatability results demonstrate the effect of the
treatment on the samples tested. Extrapolation of the
results to waste streams or contaminated sites depends
on the representativeness of the samples collected.
EXAMPLE 2
Another analysis seen in Example 2 was conducted of
sandblasted waste samples that were collected at the Blatnik
bridge in Superior, Wisconsin. The results of TCLP tests
(performed as outlined in Example 1) and compositional analysis
performed on the samples was collected during the field trial
test at the Blatnik bridge are listed in Table 3. Samples of
untreated sandblasted waste products from the bridge site were
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treated with a dry material which contained approximately 30%
binder and approximately a 70% magnesium oxide/TSP
combination at dosages ranging from .2% to 1.0% by weight.
The magnesium oxide/TSP combination were present in a
50%/50% ratio relative to each other.
