Note: Descriptions are shown in the official language in which they were submitted.
WO 90/15642 - 1 - ~~~~t~t~x~~' PCT/US90/03333
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IMPROVED METHOD AND PRODUCTS FOR TREATING ASBESTOS
Backcrround of the Invention
The invention relates to a method for treating
asbestos so as to render it harmless, and to a solution
effective for use in such treatment.
Asbestos is a commercial term applied to a group of
silicate minerals which occur in fibrous form. There -
are six principal asbestos minerals. Of these six
minerals, only one, chrysotile asbestos, belongs to the
group classified as serpentine asbestos, that is,
minerals characterized by long fibers that are
serpentine in shape. The chemical composition of
chrysotile asbestos may be represented as:
Mgg(Si205)(OH)4 or 3Mg0.2Si02.H20. The crystalline
structure of chrysotile asbestos consists of alternating
layers of silica and magnesium oxide/ hydroxide bound to
each other through covalently shared oxygen. These
layers are transverse to the fiber axis.
The other varieties of asbestos are silicates of
magnesium, iron, calcium, and sodium. These varieties
of asbestos belong to the amphibole (straight fiber)
group of minerals. About 95% of world production is the
chrysotile form of asbestos.
Due to the unique properties of the asbestos
minerals, many different kinds of products were
' developed during the 1940~s through the early 1970~s
that incorporated asbestos fibers for fire resistance,
moisture control, and thermal insulation. Many building
WO 90/15642 ~~~ k PCT/US90/03333
2
products, for example, friable thermal insulation,
asbestos-cement pipe, asbestos-cement sheet, floor and
roof shingles, transite tiles, acoustical plaster,
insulation and fire-retardant paper products, and high-
s temperature insulation, include asbestos fibers. In the
overwhelming majority of cases, these products contain
the chrysotile form of asbestos.
For a number of years now it has been recognized
that many chronic diseases are associated with the
inhalation of airborne asbestos fibers. These diseases
include lung cancer, chronic fibrosis of the lung
lining, and mesothelioma (a rare but fatal cancer of the
lungs). Although not completely understood, it is
believed that when an asbestos fiber comes into contact
with a living cell, the asbestos fiber irritates the
cell lining and leads to its eventual weakening. After
such weakening, it is believed the asbestos fiber enters
the cell. Once inside the living cell, the asbestos
fiber appears to set in motion a collagen synthesis
ultimately resulting in chronic fibrosis and a potential
for developing carcinoma.
Due to its hazardous nature, there has been a
concerted effort by governmental agencies to ban the use
and encourage the removal of materials containing
asbestos fibers. The U.S. Environmental Protection
Agency has set an upper limit of 1% for the allowable
asbestos fiber content in building materials.
Furthermore, local governmental agencies in many cities,
for example, New York City, require the removal of
WO 90/15642 - 3 - ~ ~ ~ ~ ~ ~ (1,f ~. 'P.~'/US90/03333
t~ . ~ y,
asbestos materials from buildings before they will issue
permits for building renovation or demolition. Many
. safeguards must be employed to prevent inhalation of
airborne asbestos fibers by workers and others in the
vicinity of the work area. Respirators must be worn by
workers handling the asbestos. Any area in a building
in which asbestos material is exposed or is being
removed must be isolated by partitions from the
remainder of~the building. Also, the work area must be
kept at a negative pressure with respect to the
atmosphere to prevent airborne fibers from leaving the
area. Needless to say, these measures are both
cumbersome and costly. Additionally, disposal of
asbestos products removed from the building also remains
a problem.
A number of methods have been proposed for '
rendering asbestos less harmful but without
substantially affecting its significant physical and
chemical properties. In U.S. Patent No. 4,401,636
(Flowers) a method is described for treating silicate
minerals with an aqueous metal salt solution to form a
metal-micelle silicate. The method purports to render
the resulting silicate less harmful to living cells
while the treated silicate retains most of its asbestos-
like properties. However, the method proposed therein
is not totally satisfactory since it does not destroy
the fibrous nature of the asbestos. According to the
. , method described in U.S. Patent No. 4,401,636, a metal
WO 90/15 "~~ ~ ~ ~ y ~ S j~: ~~ ~ PCT/US90/03333
4 -
is added to the crystal structure of the asbestos,
thereby forming a~metal-micelle which masks the iron-
binding sites in the asbestos. According to that
patent, the metal-micelle asbestos, when introduced into
a living cell, does not react with cellular iron.
Therefore, it is asserted, the reaction that is believed
to initiate fibrosis should be blocked and biological
hazards associated with exposure of living organisms to
asbestos should be reduced.
Accordingly, it is an object of the present
invention to provide a process for rendering asbestos
harmless by destroying its crystalline structure and
fibrous nature.
It is another object of the present invention to
provide an in situ process for rendering harmless
asbestos-containing building materials which are already
in use, thereby obviating the need to remove these
materials from buildings.
It is yet another object of the present invention
to provide such a process which is simple and much less
expensive than present methods of removing asbestos-
containing building materials from buildings.
Summary of the Invention
In accordance with the present invention, a simple
method for treating asbestos to render it harmless is
provided. The method, in its broadest embodiment,
comprises applying a dilute aqueous weak acid solution
WO 90/15642 PCT/US90/03333
n
to asbestos-containing materials. For chrysotile
asbestos the acid solution hydrolyzes the magnesium
oxide (Mg0) units in the crystal structure, thereby
destroying the crystal structure and the fibrous nature
5 of the chrysotile asbestos. The aqueous solution should
have an acid concentration of about 1-25% by weight,
preferably about 5-15% by weight.
The term "weak acid" is used herein in its
generally understood sense, i.e., an acid is defined as
being "weak" if its protolysis reaction with water does
not go essentially to completion unless the solution is
extremely dilute.
In accordance with one embodiment of the invention,
the method may be used in situ by spraying asbestos-
containing materials which are in place, for instance,
in a building, with the weak acid solution. Depending
on what acid is used, one is able to achieve 90% and
preferably greater conversion of the asbestos such that
what remains is a non-asbestos material which, however,
retains fire retardant properties. When 90% or more of
asbestos is converted in-accordance with the method of
the present invention, the remaining material no longer
has the characteristic asbestos fibrous nature and so is
essentially no longer asbestos.
When the method of the invention is performed in
situ, the asbestos-containing materials preferably
receive more than one, e.g., two to six or more, spray
applications of an aqueous solution of a weak organic
WO 90/15642 PCi'/US90/03333
-
acid, such as trifluoroacetic acid, to achieve a 98% or
more conversion of the asbestos. Advantageously, in
accordance with this embodiment of the invention,
depending on the initial condition of the asbestos-
containing material, the types of binders and other
materials combined with the asbestos and its adherence
to the underlying substrate, the converted material can
be left in place and still retain good insulating and
tire retardant properties. In such case, a stabilizing
agent, which may preferably comprise a resin in
combination with a sodium silicate material, is applied
to the converted material. The stabilizing agent binds
the converted material together and to the substrate and
prevents them from becoming airborne.
In accordance with another preferred embodiment of
the invention, the asbestos-containing materials are
sprayed in situ With an aqueous solution containing a
weak acid and a source of fluoride ions, such as
ammonium fluoride (NH4F) or sodium fluoride (NaF).
Desirably, the aqueous solution should comprise about
1-25%, preferably about 5-15%, by weight of a weak
organic acid, and about 1-10%, preferably about 2-8%, by
weight of the fluoride ion source. The concentration of
the acid in the solution should be higher than that of
the fluoride ion source such that their molar ratio is
maintained at greater than one during use. A solution
containing both a dilute weak acid and a source of
>j
WO 90/15642 ~ PCT/US90/03333
'°L..
- ' - 2060~~Of~ K'
fluoride ions attacks asbestos in two ways. As
mentioned above, the acid attacks the Mg0 layers
in the crystal structure of chrysotile asbestos.
Simultaneously, the fluoride ions attack the silica
layers, converting them into fluorosilicate. Adding
fluoride ions to the treatment solution greatly speeds
up the rate of conversion of asbestos. It is believed
that the fluoride ion increases the rate at which the
weak acid diffuses into the magnesia layers. It also
makes the solution much more effective in converting
forms of asbestos other than chrysotile, such as
amosite, which are not attacked very strongly by the
weak acid solution alone.
In accordance with a further embodiment of the
invention, the treatment of the asbestos-containing
material may be performed by immersing asbestos-
containing material which has been removed from a
substrate, such as, for example, building structural
members or pipes, in a solution of the kind described
above, preferably with heating and agitation of the
solution. Most preferably the asbestos-containing
material is first wet in situ with the solution one or
more times, for instance, by spraying, and then removed
while still wet and soaked in the solution, e.g., by
immersion, preferably with heating and agitation, until
the conversion is complete. Thereafter, the residue may
be neutralized and disposed of as a non-hazardous
material. Preferably, the asbestos-containing material
WO 90/15642 ~~.. ~ PCT/US90/03333
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x ~i r v
should be permitted to dry between successive in situ
wettings by the treatment solutions.
In accordance with a still further aspect of the
invention in cases where the asbestos-containing
material is a solid which cannot easily be penetrated
with the solution by spraying or immersion, the material
can be ground, preferably while immersed in the
solution, to expose the asbestos to the solution.
The solution of the invention useful for converting
asbestos to a non-crystalline material comprises an
aqueous solution of between about 1-25%, preferably
about 5-15%, by weight of a weak organic acid and about
1-10%, preferably about 2-8% by weight of a fluoride ion
source.
Brief Description of the Drawings
FIGs 1-3 are photomicrographs of untreated
chrysotile asbestos fibers at magnifications of 1000X,
5000X, and 10,000X respectively.
FIGS 4-6 are photomicrographs.of chrysotile
asbestos after treatment in accordance with the process
of the present invention at magnifications of 1000X,
5000X, and 10,000X respectively.
Detailed Description of Preferred Embodiments
While the present invention is primarily intended
for the conversion of the chrysotile form of asbestos to
a non-asbestos material, it is also effective,
WO 90/15642 f',ø /~ ~,~ PCT/US90/03333
- 9 - 20fi0~'p'~°<.'~~~.~.
particularly when a source of fluoride ions is included,
for the conversion of other forms of asbestos, such as
amosite. Referring to FIGS 1-3, untreated chrysotile
asbestos is shown at magnifications ranging from 100oX
to 10,000X. The serpentine fibers characteristic of
chrysotile asbestos are clearly evident in these
photomicrographs. The harmful effects of these fibers
is well documented at this time.
In accordance with the present invention, asbestos
l0 such as is shown in FIGS 1-3 is treated, for example by
spraying or immersion, with a dilute aqueous solution of
a weak acid having a concentration of about 1 to 25%,
and preferably 5 to l5%, by weight of the weak acid.
Preferably, the solution also contains about 1 to 10%,
most preferably about 2 to 8%, by weight of a source of
fluoride ions. Higher concentrations of weak acid and '
fluoride ion source may be used but increase expense and
materials handling problems, without having been found
to provide significant increased benefits. The
concentrations of the fluoride ion source is further
limited by its solubility. Preferably, the weak acid is
a weak organic acid having a pH in the range of about 2
to 6. Among the weak organic acids which have been used
successfully in accordance with this invention are
acetic acid, p-cyanobenzoic acid, trifluoroacetic acid,
lactic acid, benzoic acid, and formic acid. Of these,
trifluoroacetic, lactic, formic and acetic acids are
preferred, with trifluoroacetic acid being most
,.. .
- to -
. ~ 2060500
preferred. Acetic acid is substantially slower
',".:
acting than the others, so that it is less preferred.
' Weak acids having lower pH's are normally preferred
over ones having higher pH's. In principle, any
water soluble weak acid may be used, particularly any
organic weak acid. The reaction rates and other
characteristics of particular acids may make them
undesirable, however. Dilute solutions of organic
weak acids are preferred because, in accordance with
the invention, they have been found to wet the
asbestos-containing materials extremely well, and
obviate the need for any separate wetting agent.
The above weak acids have the following pKa's:
Acid p~C,
Acetic 4.76
Benzoi~r 4.21
Lactic 3.86
Formic 3.75
p-cyanobenzoic 3.55
Trifluoroacetic 0.25
All forms of asbestos are crystalline minerals. The
conversion process of the invention converts the
asbestos to a noncrystalline material, such as a
glass, or at least to a material which no longer has
more than trace amounts of asbestos crystallinity
when measured by currently accepted methods, such as
polarizing light microscopy, TEM or X-ray
diffraction. Preferably, all traces of asbestos
- l0a -
' ~ 2060500
crystallinity are destroyed by the process of the
invention. When reductions in crystallinity are
referred to herein, it is referring to the reduction or
substantial elimination of asbestos crystallinity.
Similarly, when the process of the invention is
referred to as converting the asbestos-containing
material to a non-fibrous material, it refers to the
elimination of asbestos fibers. Other types of
~I_.a w
WO 90/15642 - 11 - ~ ~ ~ ~~~~P ''CT/US90/03333
fibers, such as fine glass fibers, may remain,
particularly if the process is performed completely
in situ.
The crystalline structure of chrysotile asbestos
consists of a polymeric silica backbone interspersed
with Mg0 units. When chrysotile asbestos is wet or
immersed by or in a dilute solution containing a weak
acid in accordance with the invention, it is believed
that the MgO~units are hydrolyzed to Mg(OH)2, which is
leached out of the structure by the solution while
leaving the silica backbone intact. This destroys the
original crystalline structure of the chrysotile
asbestos. Depending on the type of treatment, the
resulting material may comprise fine glass fibers, a
particulate or a combination of both. A substantial
portion of the asbestos dissolves completely and is
believed to form compounds such as fluorosilicic acid.
The resulting materials retains good fire-retardant and
thermal insulation properties. FIGs 4-6 show chrysotile
asbestos at magnifications ranging from 1000X to 10,000X
after being immersed in a 5% aqueous solution of
trifluoroacetic acid in accordance with the method of
the present invention.
FIGs 4-6 show the dramatic differences resulting
from treatment of chrysotile asbestos with a dilute weak
acid solution in accordance with the method of the
present invention. The fibrous nature of asbestos is
destroyed and only non-fibrous silica particles remain.
W090/15642 ;~.~~ PCT/US90/03333
~c .r~ ~ ;:.:
12
Depending on the weak acid that is chosen and its
concentration, it is possible to achieve more than 90%
reduction of the crystallinity of asbestos by means of
the present invention. All that is necessary is to wet
the chrysotile fibers with the weak acid solution, for
instance, either by spraying or immersing the asbestos
material with or in the solution. In the case of
asbestos-containing building materials such as
fireproofing materials on girders and decking, this can
be done in situ by spraying the weak acid solution
directly onto the asbestos-containing materials. In the
case of such asbestos-containing building materials it
is usually necessary to open up the building structures
in order to expose the fibers. So long as the weak acid
solution can penetrate into the asbestos-containing
materials so as to wet the fibers, a significant
reduction in crystallinity can be achieved and with
repeated applications the asbestos is converted to a
non-fibrous, non-hazardous material. In order to
improve the wetting process, it is desirable in some
cases to add a wetting agent to the weak acid solution
being sprayed on the asbestos-containing material. For
example, an anionic surfactant, such as sodium dodecyl
sulfate or a non-ionic surfactant such as Surfynol 465,
a product sold by the Air Products Company, can be added
to the weak acid solution in conventional amounts (e. g.,
in amounts of about 1% by weight) to increase wetting of
the asbestos fibers. Excellent wetting has been
WO 90/15642 PCT/US90/03333
- 13 - 2060~~00
r.~:; ,,
achieved in most instances, however, with.the '~''."°'~
application of a weak organic acid solution alone,
without an additional wetting agent.
If the asbestos-containing material is to be
removed from the building component or other substrate
to which it is applied, or if loose asbestos-containing
material is to be treated in accordance with the
invention, it is frequently preferable to immerse the
asbestos-containing material in the weak acid solution
to insure complete wetting. In such case, the solution
is preferably agitated, for instance with the use of a
propeller-type mixer such as is commonly used in
industrial settings, which significantly speeds the
conversion of the asbestos. The conversion can be
further speeded, if desired, by heating the solution.
Heating the solution usually has less effect on the
conversion rate in spraying operations because the mass
and thermal inertia of the material being treated is
normally much greater than that of the solution being
applied.
Table 1 sets forth a number of weak organic acids
that have been used in accordance with the present
invention without the presence of fluoride ions to
reduce the crystallinity of chrysotile asbestos. Table
1 also sets forth the degree of reduction in
crystallinity of chrysotile fibers which were immersed
in the aqueous solution as measured by X-ray
diffraction.
WO 90/15642 PCT/US90/03333
. ;. .-, #; <.: - 14 -
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Table 1
Concentration Reduction of
Acid jin wt.%y Crystallinity
p-Trifluoromethyl.
benzoic acid 0.6% <10%
Acetic acid 5% 30-90%
p-Cyanobenzoic acid 1% 90%
Trifluoroacetic acid 5% >98%
Lactic acid 5% 95%
The conversions shown in Table 1 take place in
periods ranging from 2 days to 4 weeks. In large
measure, these long periods of time are required by the
slow nature of the reaction, particularly the slow rate
at which the weak acids diffuse through the silica
layers. Some acids, such as trifluoroacetic acid,
react much faster than others and are preferred. In
some cases, the slow reaction is due to the difficulty
in actually wetting the asbestos fibers contained
therein. For example, it is much easier to wet the
exposed asbestos fibers in pipe insulation than it is to
wet asbestos fibers which are tightly bound to a binder
such as, for example, transite board or floor tile.
In order to ensure that as much conversion as
possible takes place in in situ conversion treatments,
the asbestos fibers are preferably subjected to
successive sprayings with the weak acid solution. Thus,
after wetting the asbestos-containing materials a first
time with the solution and allowing the hydrolysis
reaction to proceed, for instance, for 24 hours, the
WO 90/15642 PCT/US90/03333
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- 15 - ~ ~ ~ ~ ~~ ~-4 a
;,
materials can be wet a second and successive times',
preferably with about 12 to 24 hours between each
application, until the destruction of the asbestos
fibers is achieved. The number of wettings or sprayings
required for complete destruction of the asbestos fiber
depends on a variety of factors, such as the amount and
porosity of the binder with which the asbestos fibers
are mixed, the particular weak acid employed, whether a
fluoride ion source is included in the solution, and the
type of asbestos fibers being treated. It has been
found, in accordance with the invention, that the
effectiveness of the individual sprayings is
substantially increased if the material being treated
is permitted to dry between each successive spray
application. It is believed that the reason for this is
that degradation products produced by the reaction
become hydrated and~impede transport of fresh treatment
solution to the asbestos fibers during subsequent
applications. Drying the asbestos-containing material
between applications obviates this problem.
If the asbestos-containing material is converted in
situ in accordance with the invention, the resulting
non-fibrous material may be left in place to perform the
fireproofing or other function for which the asbestos
was originally installed provided it has retained its
physical integrity and adheres adequately to the
underlying substrate. In such event, the resulting
material is preferably sprayed or washed with a mild
WO 90/t5642 PCT/US90/03333
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~~~:~~.. ~ .. :k a ~ ,~t
alkaline solution, such as of sodium bicarbonate, in
order to neutralize any remaining acid in the material.
The material is fully neutralized when the pH of a
sample placed in water is at 7.
After being neutralized, the material may be
stabilized by applying a stabilizing or fixing agent to
the material to bind it together. The stabilizing agent
should contain a resin-like material, such as a latex
resin, as a binder. Desirably, the stabilizing agent
also contains a sodium silicate material which helps to
bind and harden the material. The stabilizing_agent may
also include an alkaline neutralizing material, in which
case the neutralizing and stabilizing steps may be
combined, so that the need for a separate neutralizing
step is obviated.
One suitable stabilizing agent comprises about 25%
by volume N-sodium silicate, 25% by volume acrylic latex
(Rohm and Haas), 5% by volume latex (BF Goodrich), 10%
by volume alkaline cleaner (Du Bois), 5% by volume water
softener (Calgon), 5% by volume wetting and dispersing
additive (Byk), and 25% by volume water. Other
. stabilizing agents may include styrene-butadiene or
polyvinyl chloride resins. Such resins may be used with
or without sodium silicate. Yet another stabilizing
agent includes a urethane resin and no sodium silicate.
The stabilizing agent is applied, preferably by
spraying, after the asbestos-containing material has
been treated sufficiently to effectively destroy the
WO 90/15642 PCT/US90/03333
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fibrous asbestos. Preferably it should be applied while
the material is somewhat damp, in two coats applied at a
90° angle with one another. The stabilizing agent
typically requires about 4 to 8 hours to cure, depending
on the atmospheric humidity. If necessary, for
additional fire-retardant characteristics, a layer of
non-asbestos-containing fireproofing material can be
sprayed over the stabilized material.
As pointed out above, the use of the weak acid
alone in the treatment solution has drawbacks. The rate
of conversion of the asbestos by the weak acid is slow
and the solution is effective only for the treatment of
chrysotile asbestos. While applicants do not wish or
intend to be bound by any particular theory or the
manner in which the reactions in the method of the
invention proceed, it is believed that the Mg0 layers of
chrysotile asbestos attacked by the weak acid are
interleaved with silica layers and that the rate of
conversion depends, to a great extent, on the rate at
which the weak acid diffuses through the silica layers.
Applicants have found, in accordance with a preferred
embodiment of the invention, the addition of a source of
fluoride ions to the treatment solution both
dramatically speeds the rate of conversion of the
asbestos to a non-fibrous material and makes the process
of the invention effective for the conversion of other
types of asbestos, such as amosite, to a non-fibrous
material. In the case of amosite, it is believed that
WO 90/15642 PCT/US90/03333
s,) ~,~ ~~ 18 -
t~ i. l:. i.
the treatment solution of the invention converts the
asbestos to a noncrystalline product by the fluoride
ions attacking the silica content of the asbestos. To
do this it is necessary that the fluoride ions-be in an
acid environment.
Suitable fluoride ion sources include, for example,
ammonium fluoride (NH4F), alkali metal fluorides (LiF,
NaF, KF, CsF), and hydrofluoric acid (HF) and mixtures
of the above. The fluoride ion, especially in weak acid
solution, is believed to attack the silica layers and
greatly enhances the rate at which the weak acid attacks
the Mg0 units in chrysotile asbestos. An HF solution
may be used alone both as the acid and the fluoride ion
source but extreme care must be exercised in handling it
and it is not preferred. An important advantage of the
preferred treatment solutions of the invention is that
they can be handled with only reasonable precautions.
For example, in laboratory tests, it has been found
that samples of chrysotile asbestos which are not
completely converted in 24 hours when immersed in a 10%
trifluoroacetic acid solution due to the slow nature of
the reaction, are completely dissolved in only 2 hours
in an aqueous solution containing 10% trifluoroacetic
acid and 5% ammonium fluoride.
It has further been found that the rate of reaction
is also significantly increased if the asbestos material
immersed in the treating solution is stirred or agitated
while the treatment continues. Heating the treatment
WO 90/15642 PCT/US90/03333
-19-
solution to a temperature of, e.g., about 50-85°C,
further increases the rate of reaction.
In accordance with another and often preferred
embodiment of the invention, the asbestos-containing
material is removed from the substrate to which it has
been applied, preferably while still wet from one or
more initial spray applications of the treatment
solution of the invention, and digested by immersion in
the solution,~preferably with heat and agitation, until
the asbestos is destroyed.
It has been found that about 2 parts to 10 parts by
weight of the treatment solution per part of asbestos
should be used for the digestion step, with about 5
parts by weight of the acid solution to 1 part of
asbestos material normally being adequate to effect
conversion in a reasonable amount of time.
The process of the invention, as applied to the
abatement of asbestos in buildings, may typically
include the steps of removing any obstructions, such as
interior partitions, ceilings and column covers to
expose the suspected asbestos-containing materials,
sampling and testing the suspected asbestos-containing
materials in accordance with applicable standards to
determine its composition and other relevant
characteristics, determining an optimum formulation for
a treatment solution depending on such composition and
characteristics, including the need for a separate
wetting agent and suitable types and concentrations of
WO 90/15642 PCT/US90/03333
y
weak acids and fluoride ion sources, providing a
sufficient amount of such treatment solution, repeatedly
spraying the asbestos-containing material in situ with
such solution, or removing the asbestos-containing
5 material from the substrate to which it is applied,
preferably while it is still wet from an initial spray
application of the solution, and immersing the removed
material in a container of such treatment solution, in
either case until the fibrous nature of the asbestos is
10 effectively destroyed. Thereafter the surfaces that
were coated with such asbestos-containing material are
refireproofed by either neutralizing and stabilizing the
converted material in situ, or by applying a non-
asbestos-containing fireproofing material on such
15 surfaces from which the asbestos has been removed. In
the latter case a final light spray application or
misting of the treatment solution to the surfaces is
desirable to convert any remaining asbestos fibers which
have been missed by the removal process. For the
20 reasons indicated above it is preferred that the surface
be dry before the misting. The surfaces are also
preferably neutralized by spraying with mild alkaline
solutions. Optionally, an additional layer of
fireproofing material can be applied over the stabilized
material. The asbestos abatement process may also be
carried out by spraying the asbestos-containing material
one or more times with the treatment solution, removing
the asbestos-containing material while still wet and
WO 90/15642 PCT/US90/03333
- 21 - ~p
6 0 ~ p p ~~ r~ ?,
disposing of it in a conventional manner. The
underlying substrate can then be misted with the
treatment solution (after drying, if desired),
neutralized, and then refireproofed as described above.
The particular composition of the solution used for the
various spray applications, or for an initial spray
application and immersion, may be varied if desired, but
are referred to herein collectively as a singular
solution. For instance, the concentration of the
solution used for the digestion step might preferably be
higher than that used for the spray application steps
for safety reasons.
During the removal of asbestos-containing
materials, it frequently occurs that substantial amounts
of asbestos-containing dust is generated which coats
building surfaces such as floors and walls. All traces
of this dust must be carefully collected and removed.
This is an expensive and time-consuming project because
the dust is itself hazardous and must be handled with
extreme care. In accordance with the invention, this
dust may be dealt with easily and much less expensively
by spraying it in situ with the solution of the
invention, repeatedly if necessary, in order to convert
any asbestos in the dust to a non-fibrous, non-hazardous
material. Thereafter the dust may be collected and
removed by inexpensive, conventional means, since it no
longer contains asbestos.
WO 90/15642 PCf/US90/03333
The initial generation of the dust during the
removal of asbestos-containing material from the
underlying substrate is preferably minimized in
accordance with the invention by wetting the material
with the treatment solution of the invention before
removal and by keeping such material wet with such
solution while it is removed from the substrate.
In cases where the asbestos-containing materials
are collected and digested by immersion in a vat
containing the treatment solution preferably with
stirring or agitation, it is also often desirable to
grind up the asbestos-containing material either before
or during immersion: This is particularly in the case
when the asbestos-containing material is non-porous and
not attacked by the treatment solution. Typical
examples of such materials are transite board or pipe
and asbestos-containing tiles: In such situations it is
necessary to grind up the material to enable the
treatment solution to contact the asbestos fibers. In
accordance with the invention, this grinding is
preferably performed while the material is immersed in
or being wet down by the treatment solution in order to
prevent the generation of asbestos-containing dust.
Often, in such situations, a substantial portion of the
material dissolves in the treatment solution, thus
reducing the volume of material to be disposed of in a
landfill site.
WO 90/15642 ~~ b" ,~A ,_.~ r .PCT/US90/03333
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In view of the fact that conditions are more
controlled during the digestion step than during
spraying in situ it is possible, in accordance with the
invention to use a dilute solution of a strong acid
rather than a weak acid for digesting the asbestos-
containing material after it has been sprayed in situ
with the weak acid solution and removed from the
substrate. Examples of suitable acids include
hydrochloric, hydrofluoric, sulfuric and nitric acids.
In all cases except hydrofluoric acid it is preferred to
include a fluoride ion source in the solution for the
purposes described above. The strong acids have the
advantage of being faster acting, but have the
disadvantage of requiring much more careful handling and
a higher potential for causing serious injury or damage
if they are mishandled.
After the asbestos in the material has been
digested, it is necessary to dispose of the resulting
solid and liquid matter in an environmentally safe
manner. It is preferred that the solution be
neutralized and the fluoride ions be tied up in
compounds having low solubility in water. One way of
dealing with the fluoride ions is to merely add sand to
the used solution to exhaust the fluoride ions and form
fluorosilicates upon neutralization having low
solubility in water. Neutralization can be accomplished
by adding any alkaline species to the used solution.
For instance, sodium hydroxide, sodium bicarbonate or
WO 90/15642 ~ PCf/US90/03333
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calcium hydroxide could be used, with calcium hydroxide
having the advantage that it will tend to form calcium
fluoride with any remaining fluoride ions, that is very
insoluble in water.
In some situations it is desirable for the
treatment solution to contain about 20 to 50% by weight
of ethanol in order to increase the rate of evaporation.
It should be kept in mind, however, that a treatment
solution containing fluoride ion should not be allowed
to come into contact with any glass surfaces which would
be etched by the fluoride ions.
The invention will now be described by reference to
the following examples:
Example 1
A 5% by weight aqueous solution of trifluoroacetic
acid was applied to various different kinds of
chrysotile-containing building materials. Different
asbestos-containing materials required different
reaction times depending on factors such as binder,
asbestos fiber length, asbestos fiber content and other
fibers present. When thermal insulation, such as used
for insulating pipe runs and boilers, was washed a first
time with the acid solution, allowed to penetrate for 24
hours, and then washed a second time with the solution,
a reduction in crystallinity of 98% or greater was
achieved in periods ranging from 2 to 4 days.
WO 90/15642 ~ , ; , ~ , PCT/US90/03333
25 -
..,
20~0~00
Example 2
Thermal insulation was washed five times with a 5%
solution of acetic acid with a three to four day wait
between successive applications. The material did not
dry completely between applications. The treatment
resulted in a 90% reduction in crystallinity of the
chrysotile asbestos. However, the time required for
such conversion was approximately 3 to 4 weeks.
Example 3
A 5% solution of lactic acid was used to wash
chrysotile asbestos-containing thermal insulation.
Six successive washings spaced from one another by
approximately 24 hours resulted in a 95% reduction of
the chrysotile crystalline structure.
Example 4
44 milligrams of chrysotile asbestos were immersed
in 550 ml of a 1% aqueous solution of p-cyanobenzoic
acid and heated to reflux for 15 hours. Thereafter the
material was filtered through a Nuclepore 0.2 micron
filter while still hot and the filter cake dried.
Examination by differential X-ray analysis showed
approximately 90% reduction in the crystallinity of the
chrysotile asbestos.
W4 90/15 ~r PCT/US90/03333
26
Example 5
Chrysotile asbestos was removed from an asbestos
rock with tweezers, resulting in fiber bundles of
various sizes ranging in size up to a few mils in
diameter. 0.5 grams of the asbestos fiber bundles was
soaked in a solution of 2.5 g of trifluoroacetic acid in
47.5 g water for about 48 hours without agitation. A
small sample was collected and examined by X-ray
analysis and showed a reduction of about 75$ in
l0 crystallinity. Further examination of the remaining
soaking material over the following 2 weeks showed
little further reduction.
Example 6
A 0.595g sample of fairly short fiber chrysotile
asbestos in mineral wool (ca. 50$ asbestos) was stirred
in a beaker on a magnetic stirring hotplate with 118 ml
of a solution consisting of five volume percent
trifluoroacetic acid in water. Heat was applied, and
the slurry allowed to stir at 55-60.°C for 2.5 hours.
The reaction had proceeded to only a small degree (as
judged by visual inspection), so an additional 4.0 ml of
concentrated trifluoroacetic acid was added. Heating
was continued for an additional 11 hours. The remaining
solid was collected by filtering over a Nuclepore 0.2
micron polyester filter. Qualitative examination with a
transmission electron microscope (TEM) showed the sample
in various stages of degradation, but many of the fibers
WO 90/15642 PCT/US90/03333
27 2U~U~~'U ~ ,
(ca. 30-40%) still exhibited selected area electron
diffraction (SAED) patterns characteristic of chrysotile
asbestos.
Example 7
1.437g of the chrysotile/mineral wool sample of
Example 6 was stirred magnetically in 90 ml of an
aqueous solution of ten volume percent trifluoroacetic
acid and five~weight percent ammonium fluoride. The
temperature was raised to 55-60°C and maintained. After
to one hour, most of the material had visibly dissolved. A
portion was removed and the insoluble matter collected
on a 0.2 micron filter. TEM analysis of this residue
revealed very few remaining fibers (estimated at less
than one percent), most of the material being in the
form of particulate matter. '
Example 8
0.365g of the chrysotile/mineral wool sample was
magnetically stirred in 20m1 of the solution used in
Example 7: no heat was applied. The bulk of the
material had obviously dissolved after one hour, but the
reaction was continued for three hours. A small amount
of solid residue was collected on a 0.2 micron filter;
TEM analysis showed no fibers remaining.
WO 90/15642 PCT/US90/03333
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Example 9
0.265g o.f the chrysotile/mineral wool sample was
magnetically stirred in an aqueous solution of ten
volume percent formic acid (a weaker acid than
trifluoroacetic) and five weight percent ammonium
fluoride. Stirring at room temperature was continued
for three hours, at which time undissolved material was
collected on a 0.2 micron filter. TEM analysis of the
residue showed a low percentage of fibers which appeared
under TEM examination not to be asbestos remaining
(estimated at ca. 1-2%).
Example 10
0.470g of the chrysotile/mineral wool sample was
stirred at room temperature for ten hours in 30m1 of an
aqueous solution of ten volume percent acetic acid (a
weaker acid than formic acid) and five weight percent
ammonium fluoride. TEM analysis of the collected
residue showed very low fiber content which appeared
under TEM not to be asbestos, as in Examples 7-9.
Example 11
0.370g of the chrysotile/mineral wool sample was
stirred at room temperature in 20m1 of an aqueous
solution of ten volume percent trifluoroacetic acid and
five weight percent sodium fluoride for three hours.
TEM analysis of the small amount of collected residue
WO 90/15642 _ 29 - ~ ~ ~ ~ ~t~ ~ ,e ' PCT/US90/03333
i~
showed only a trace level of fibrous material which
appeared not to be asbestos.
Example 12
A 0.253g sample of 7 to 8% chrysotile in amatrix
consisting of gypsum and other unidentified components
was stirred at room temperature in 15 ml,of the
solution used in Example 7 for 16 hours, at which time
dissolution of the majority of the material Was obvious.
Example 13
0.300g of a sample of pure long fiber amosite
asbestos was stirred at room temperature for 15 hours in
20m1 of the solution used in Example 7. Most of the
material was dissolved; the small amount of remaining
insoluble material was not fibrous in nature.
Example 14
0.479g of the chrysotile/mineral wool sample was
situated on the raised area of a plastic 4 ounce
specimen cup such that any drainage could be removed.
The sample was treated dropwise with 3.6 ml of the
solution used in Example 7 over a period of three
minutes. Approximately 1.5 ml of drainage was removed.
The sample was then allowed to dry at ambient
temperature. The treatment cycle was then repeated as
described a total of ten times, with a minimum of 12
hours between treatments. Since the total amount of
WO 90/15642 PCT/US90/03333
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residue declined during the treatments, the amount of
solution added per cycle was gradually lowered to a
final value of 2.0 ml.
After two treatment cycles, the TEM micrographs
show that the appearance of the treated fibers differs
from untreated fibers, although many of the fibers
continued to exhibit chrysotile asbestos SAED patterns.
After six treatments, the appearance of the fibers is
significantly altered. None of the fibers exhibited
SAED patterns. Further treatments continued to lower
the total residue remaining, but some fibrous material
was still present at ten treatments.
While the invention has been described by reference
to specific embodiments, this was for purposes of
illustration only and should not construed to limit the
spirit or the scope of the invention. Those skilled in
the art will recognize that numerous alternative
embodiments are within the scope of the invention.
