U.S. patent application number 10/972068 was filed with the patent office on 2006-01-12 for in-container mineralization.
Invention is credited to John Bradley Mason, Thomas W. Oliver.
Application Number | 20060009671 10/972068 |
Document ID | / |
Family ID | 35840698 |
Filed Date | 2006-01-12 |
United States Patent
Application |
20060009671 |
Kind Code |
A9 |
Mason; John Bradley ; et
al. |
January 12, 2006 |
In-container mineralization
Abstract
A method of waste stabilization by mineralization of waste
material in situ in a treatment container suitable or treatment,
transit, storage and disposal. The waste material may be mixed with
mineralizing additives and, optionally, reducing additives, in the
treatment container or in a separate mixing vessel. The mixture is
then subjected to heat in the treatment container to heat-activate
mineralization of the mixture and form a stable, mineralized,
monolithic solid. This stabilized mass may then be transported in
the same treatment container for storage and disposal.
Inventors: |
Mason; John Bradley; (Pasco,
WA) ; Oliver; Thomas W.; (Marietta, GA) |
Correspondence
Address: |
NEXSEN PRUET ADAMS KLEEMEIER, LLC
PO BOX 2426
COLUMBIA
SC
29202
US
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20050096495 A1 |
May 5, 2005 |
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|
Family ID: |
35840698 |
Appl. No.: |
10/972068 |
Filed: |
October 22, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10209090 |
Jul 31, 2002 |
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10972068 |
Oct 22, 2004 |
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10374293 |
Feb 26, 2003 |
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10972068 |
Oct 22, 2004 |
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10246266 |
Sep 18, 2002 |
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10374293 |
Feb 26, 2003 |
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10185616 |
Jun 28, 2002 |
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10246266 |
Sep 18, 2002 |
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10111148 |
Apr 19, 2002 |
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10185616 |
Jun 28, 2002 |
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PCT/US00/41323 |
Oct 19, 2000 |
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10185616 |
Jun 28, 2002 |
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09421612 |
Oct 20, 1999 |
6280694 |
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PCT/US00/41323 |
Oct 19, 2000 |
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Current U.S.
Class: |
588/252 ;
588/254; 588/256 |
Current CPC
Class: |
F23G 2201/301 20130101;
C04B 28/008 20130101; B01D 53/75 20130101; G21F 9/304 20130101;
C02F 11/008 20130101; F23G 2900/50205 20130101; F23G 2900/54401
20130101; G21F 9/302 20130101; B01D 53/8625 20130101; G21F 9/301
20130101; A62D 2101/20 20130101; A62D 2101/45 20130101; A62D
2203/04 20130101; B09B 3/0066 20130101; Y02P 40/10 20151101; Y02P
40/165 20151101; A62D 2101/41 20130101; F23G 5/0276 20130101; C02F
1/70 20130101; C10B 47/46 20130101; F23J 2219/60 20130101; B01D
53/56 20130101; F23G 2209/18 20130101; A62D 2101/43 20130101; B09B
3/0025 20130101; A62D 2101/47 20130101; A62D 3/33 20130101; F23J
2219/10 20130101; B01D 53/565 20130101; A62D 3/36 20130101; C02F
2101/16 20130101; C02F 1/725 20130101; Y02W 30/91 20150501; F23G
5/006 20130101; A62D 3/40 20130101; A62D 2101/49 20130101; B09B
3/00 20130101; B09B 3/0083 20130101; A62D 2101/22 20130101; F23J
2217/10 20130101; C04B 28/008 20130101; C04B 14/022 20130101; C04B
14/10 20130101; C04B 14/36 20130101; C04B 14/405 20130101; C04B
18/0463 20130101; C04B 22/062 20130101; C04B 22/085 20130101; C04B
24/00 20130101; C04B 24/02 20130101; C04B 24/04 20130101; C04B
24/10 20130101; C04B 40/0263 20130101 |
Class at
Publication: |
588/252 ;
588/254; 588/256 |
International
Class: |
B09B 3/00 20060101
B09B003/00; C03B 5/00 20060101 C03B005/00; C03B 5/027 20060101
C03B005/027; C02F 11/00 20060101 C02F011/00; A62D 3/00 20060101
A62D003/00; C04B 18/02 20060101 C04B018/02 |
Claims
1. A process for stabilizing a material, said process comprising
steps of mixing the material and a mineralizing additive to form a
heat-activated, mineralizable mixture; and applying sufficient heat
to said mixture in a treatment container to cause at least a
portion of said mixture to mineralize and form a monolithic
mineralized solid.
2. The process of claim 1, wherein a majority of said mixture is
mineralized and forms a monolithic, mineralized solid.
3. The process of claim 1, wherein substantially all of said
mixture is mineralized and forms a monolithic, mineralized
solid.
4. The process of claim 1, wherein said mineralizing additive
comprises a calcium containing compound, a phosphorus containing
compound, a magnesium containing compound, a silicon containing
compound, an aluminum containing compound, an aluminosilicate
compound, an alkali metal compound, an iron containing compound, a
titanium containing compound, or a combination of two or more
thereof.
5. The process of claim 4, wherein said waste comprises asbestos
and said alkali metal compound is sodium hydroxide.
6. The process of claim 1, wherein said material and said
mineralizing additive are mixed in said treatment container.
7. The process of claim 1, wherein said material contains water and
said heat applying step heats said mixture to a temperature
sufficient to evaporate substantially all of said water, but below
a temperature at which a majority of said mixture melts.
8. The process of claim 1, wherein said material contains water and
volatile organic compounds, and wherein said heat applying step
heats said mixture to a temperature sufficient to evaporate
substantially all of said water and to volatize substantially all
of said volatile organic compounds, but below a temperature at
which a majority of said mixture melts.
9. The process of claim 1, wherein said heat applying step heats
said mixture to a temperature above 400.degree. C., but below a
temperature at which a majority of said mixture melts.
10. The process of claim 1, wherein said material contains water
and semi-volatile organic compounds, and wherein said heat applying
step heats said mixture to a temperature sufficient to evaporate
substantially all of said water and to volatize substantially all
of said semi-volatile organic compounds, but below a temperature at
which a majority of said mixture melts.
11. The process of claim 1, wherein said heat applying step heats
said mixture to a temperature in the range of 600.degree. C. to
850.degree. C.
12. The process of claim 1, further comprising a step of adding a
reducing agent to said mixture.
13. The process of claim 12, wherein said reducing agent comprises
carbon or an organic material.
14. The process of claim 13, wherein said organic reducing agent
comprises sugar, glycol, glycerol, ethylene carbonate, formic acid,
alcohols, other carbonaceous compounds, or a combination of two or
more thereof.
15. The process of claim 14, wherein said mineralizing additive
comprises a calcium containing compound, a phosphorus containing
compound, a magnesium containing compound, a silicon containing
compound, an aluminum containing compound, an aluminosilicate
compound, an alkali metal compound, an iron containing compound, a
titanium containing compound, or a combination of two or more
thereof.
16. The process of claim 12, wherein said reducing agent comprises
a gaseous compound.
17. The process of claim 12, wherein said reducing agent comprises
sodium sulfide, potassium sulfide, calcium sulfide, iron sulfate,
hydrazine, formic acid, sulfuric acid, stannous chloride, other
metal reducing agents, or a combination of two or more thereof.
18. The process of claim 1, wherein said material comprises
heavy-metal containing waste, sulfur compound containing waste,
halogen containing waste, radionuclide containing waste, asbestos
containing waste, alkali metal containing waste, or a combination
of two or more thereof.
19. The process of claim 1, wherein said mineralizing additive is
selected to produce a monolithic solid containing feldspathoid
minerals, silicate-rich minerals or a combination thereof.
20. The process of claim 1, wherein said mineralizing additive is
selected to produce a monolithic solid containing calcium-rich
minerals, phosphate-rich minerals, titanium-rich minerals,
magnesium-rich minerals, iron-rich minerals, silica-rich minerals,
aluminum-rich minerals, or a combination of two or more
thereof.
21. A process for stabilizing a waste material, said process
comprising steps of mixing the waste material and a mineralizing
additive in a disposal container to form a heat-activated,
mineralizable mixture; and applying sufficient heat to said mixture
in said disposal container to cause at least a portion of said
mixture to mineralize and form a monolithic mineralized solid.
22. A process for stabilizing a nitrate-containing material, said
process comprising steps of mixing the nitrate-containing material
and a mineralizing additive to form a heat-activated, mineralizable
mixture; and applying sufficient heat to said mixture in a disposal
container to cause at least a portion of said mixture to mineralize
and form a monolithic mineralized solid.
23. The process of claim 22, wherein said nitrate-containing
material is heavy-metal containing waste, sulfur compound
containing waste, halogen containing waste, radionuclide containing
waste, organic compound containing waste, alkali containing waste,
or a combinations of two or more thereof.
24. The process of claim 22, wherein said heat applying step heats
said nitrate-containing waste to a temperature sufficient to
convert at least 50% of the nitrates to nitrogen containing
gas.
25. The process of claim 22, wherein said mineralizing additive
comprises a calcium containing compound, a phosphorus containing
compound, a magnesium containing compound, a silicon containing
compound, an aluminum containing compound, an aluminosilicate
compound, an alkali metal compound, an iron containing compound, a
titanium containing compound, or a combination of two or more
thereof.
26. The process of claim 22, wherein said mixing step takes place
in said disposal container.
27. The process of claim 22, further comprising a step of adding a
reducing agent to said mixture.
28. A process for stabilizing a material containing fibers of
asbestos, said process comprising steps of mixing the
asbestos-containing material and a caustic solution containing an
alkali metal compound as a mineralizing additive to form a
heat-activated, mineralizable mixture; allowing said caustic
solution at least partially dissolve said asbestos; and applying
sufficient heat to said mixture in a disposal container to cause at
least a portion of said mixture to mineralize and form a
non-fibrous mineralized solid having a monolithic form.
29. The process of claim 28, wherein said mixture contains a
residue from partial dissolution of asbestos and said process
further comprises a step of contacting said residue with an acidic
solution to at least partially dissolve said residue prior to said
heating step.
30. The process of claim 29, wherein prior to said contacting step
said residue is separated from said mixture and said separated
residue is contacted with said acidic solution to dissolve at least
a portion thereof and form an acidic residue solution, and then
said acidic residue solution is added to said mixture before said
heating step.
31. The process of claim 28, further comprising a step of adding a
second mineralizing additive to said mixture, said second
mineralizing additive being selected to facilitate formation of
said monolithic solid.
32. The process of claim 31, wherein said second mineralizing
additive comprises a clay, a calcium containing compound, a
phosphorus containing compound, a magnesium containing compound, a
silicon containing compound, an aluminum containing compound, an
aluminosilicate compound, an alkali metal compound, an iron
containing compound, a titanium containing compound, or a
combination of two or more thereof.
33. A process for stabilizing a material containing asbestos, said
process comprising dissolving a first portion of said material in a
caustic solution containing an alkali metal compound as a
mineralizing additive, dissolving a second portion of said material
in an acidic solution, combining said solutions containing portions
of said material to form a heat-activated, mineralizable mixture,
and applying sufficient heat to said mixture in a disposal
container to cause at least a portion of said mixture to mineralize
and form a mineralized solid having a monolithic form.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 10/209,090 filed Jul. 31, 2002, and also is a
continuation-in-part of U.S. patent application Ser. No. 10/246,266
filed Sep. 18, 2002, which is a continuation-in-part of U.S. patent
application Ser. No. 10/185,616 filed Jun. 28, 2002, which is a
continuation-in-part of U.S. patent application Ser. No. 10/111,148
filed Apr. 19, 2000, and also a continuation-in-part of
PCT/US00/41323, filed Oct. 19, 2000, which is a continuation of
U.S. Pat. No. 6,280,694, issued on application Ser. No. 09/421,612
filed Oct. 20, 1999. The entire contents of each of these prior
applications and patents are expressly incorporated herein by
reference.
TECHNICAL FIELD OF INVENTION
[0002] The present invention relates generally to a process for
promoting a chemical change of waste materials into a monolithic
solid through the application of heat. In particular, this
invention applies to the stabilization of hazardous wastes that
require treatment prior to shipment, storage, and/or disposal.
BACKGROUND OF THE INVENTION
[0003] Hazardous waste handling, transportation and disposal are
heavily regulated activities. In particular, hazardous waste must
be processed for disposal prior to shipment to the disposal site.
Therefore, there is a need for processing methods to enable waste
to meet disposal requirements prior to shipment.
[0004] There are currently many types of treatment processes for
stabilizing hazardous waste including micro-encapsulation,
macro-encapsulation, and heat-activation processes. In addition to
the effectiveness of the stabilization processes, handling
requirements and costs also have an impact on the type of treatment
process selected by the waste generator. As requirements and costs
increase, generators demand more effective and cost efficient means
of waste treatment.
[0005] Hazardous wastes may be in the form of sludge, debris,
wastes with high organic content, wastes with high nitrate or
nitrogen containing content, wastes with high heavy metal content,
radioactive wastes, asbestos, liquid solutions and slurries or
solids.
[0006] One means by which hazardous waste is presently stabilized
is through the use of cement. Cement and waste are mixed at ambient
temperatures. Hydration and crystallization reactions occur upon
the addition of water. These reactions lead to the formation of a
monolithic solid in which the waste is chemically bound or
encapsulated in the resulting matrix.
[0007] Still another treatment process is encapsulation. In
encapsulation, polymeric reagents and waste are mixed. Heat is then
applied to the mixture to melt the polymer reagent. As the mixture
cools, thermosetting polymer reagents such as siloxane, sol-gel,
and polyester form long-chain polymers that encapsulate waste in a
monolithic solid. Alternatively, thermoplastic reagents such as
polyethylene, paraffin, and bitumen may be used.
[0008] Heat activated vitrification, another stabilization process,
uses glass to form a matrix for encapsulating the wastes. Glass
frit or glass forming chemicals are combined with waste and melted
to form a fluid mixture that solidifies upon cooling into an
amorphous solid. The solidified, stabilized matrix is suitable for
transportation and disposal.
[0009] Hydroceramic cement stabilization is yet another
stabilization process, commonly used on hazardous nitrate waste.
This process combines calcine compounds with reagents such as clay,
sodium hydroxide, and vermiculite to form a hydroceramnic mixture.
The hydroceramic mixture is then mixed with nitrate-containing
wastes to form a waste mixture. The waste mixture is heated to
activate it. However, this process is limited in the proportion of
nitrates that can be input. For example, the maximum nitrate level
that can be efficiently immobilized is about 25% of the amount of
the alkali metals present. If the amount of nitrates exceeds this
alkali metal ratio, some of the nitrate will not be immobilized and
can be readily leached from the solid matrix. Furthermore, heat
activation temperatures must be kept below about 150.degree. C. to
prevent decomposition of nitrates present in the waste.
[0010] Yet another heat activation treatment method involves
premixing waste materials with additives. The resulting mixture is
dried and sintered to achieve the final monolithic waste form.
Sintering involves heating the waste and additives to a high enough
temperature to partially melt or fuse the waste and additives into
a monolithic solid. This method uses three separate operations in
three separate process containers.
[0011] There is a need for a process for stabilizing hazardous
wastes that is more effective and efficient for stabilizing wastes
prior to transport, storage and disposal.
SUMMARY OF THE INVENTION
[0012] Mineralization of waste in a suitable treatment container
achieves the stabilization of waste materials in a single
operation, namely heat treatment, and the product of this process
is a stable monolithic final waste form. Furthermore, the treatment
container is suitable for storage or direct disposal.
[0013] According to its major aspects, waste materials are heated
in a treatment container. The heat induces a chemical change that
causes the waste to form a solid monolithic mass. This mass may
then be properly transported in the treatment container for
disposal or storage. This single step process has significant
advantages for hazardous waste treatment and handling.
[0014] Some hazardous wastes have high nitrate content. Another
waste is magnesium hydroxide (magnox) rich sludges from
reprocessing of spent nuclear fuel. This magnox sludge contains
heavy metals, organics, and radioactive constituents that are
treated to remove water and organics, to stabilize the heavy metals
and radionuclides, and to form a qualified monolithic final waste
form suitable for disposal. Another waste is asbestos that
comprises magnesium and iron rich silicates. This waste is heat
treated to stabilize asbestos so as to destroy the fibers and leave
the asbestos residues immobilized in a stable solid matrix, thus
eliminating the hazardous characteristics of asbestos fibers.
[0015] In the first embodiment of the present invention, waste
material is transferred into a treatment container and mineralizing
additives are added. The waste material and mineralizing additives
are mixed, heated, and disposed of in the same treatment container
after being allowed to cool. In the second embodiment of this
invention, waste material and additives (including both
mineralizing and reducing additives) are mixed in a separate
vessel. After mixing, the mixture is placed in the treatment
container for heat treatment. The treatment container is also used
for transportation, disposal, and storage.
[0016] Generally the waste material/mineralizing additive mixture
is heated to an activation temperature of at least 150.degree. C.
but less than the fusion or melting temperature of a majority
(50%), preferably substantially all, of the constituents of the
mixture. Although the activation temperature is kept relatively
low, stabilized minerals form. There is thus no need for heating to
temperatures that will cause a majority of the mixture to vitrify,
or melt thermosetting or thermoplastic materials. The heat
treatment is used in part to vaporize any water in the waste.
Heating the material to temperatures of at least 200.degree. C.
will also result in the vaporization of most, preferably a majority
(50%), more preferably substantially all, of the volatile organic
compounds within the material. At temperatures greater than
400.degree. C., most, preferably a majority (50%), more preferably
substantially all, of the volatile and semi-volatile organic
compounds will have vaporized, and at temperatures greater than
600.degree. C., most, preferably at least a majority (50%), more
preferably substantially all, of the nitrates will have vaporized.
The heat source for the heat treatment of the mixture may be
internal or external to the treatment container.
[0017] Importantly, because the additives are mineralizing agents
that form a heat activatable mixture with the waste material, they
cause this mixture in the treatment container to form stable,
insoluble mineral crystals or phases when heated to their
mineralization temperature range. Thus, the mineralization
reactions of the present invention produce at least one crystalline
mineral substance, and a final product in which preferably a
majority, more preferably substantially all, of the mixture has
been converted to a monolithic form.
[0018] Several types of mineralized product compounds may be formed
in this process. Product compounds include sodium aluminosilicate,
sodium silicate, sodium aluminate, sodium carbonate, sodium calcium
silicate, calcium sulfate, calcium chloride, calcium fluoride,
calcium phosphate, magnesium phosphate, sodium magnesium/iron
silicates, sodium magnesium/iron silicate phosphates, and still
others, such as compounds where sodium is substituted by potassium
or other alkali metals. The type of product compounds resulting
from the process depends on the mineralizing additives used and the
composition of the waste.
[0019] The preferred mineralizing additives include
aluminosilicates such as clays, zeolite, silica gel, silica,
silicates, phosphate compounds, calcium compounds, magnesium
compounds, titanium compounds, iron compounds, and aluminum
compounds. These additives combine with alkali metals in the waste
to form nepheline, nosean, sodalite, fairchildite,
natrofairchildite, dawsonite, elitelite, shortite, parantisite,
maricite, buchwaldite, bradleyite, combeite, and numerous other
similar mineral variations of these compound components. Certain
wastes can be pretreated with an additive to facilitate
mineralization. For example, asbestos can be at least partially
dissolved in a caustic or acidic solution with the resultant
partially dissolved slurry or solution being optionally mixed with
other additives, and then the final mixture can be heat treated to
form a non-hazardous, non-asbestos, non-fibrous mineralized
monolith--all without melting the waste.
[0020] Generally water soluble alkali metal compounds in waste
require further stabilization prior to disposal to prevent water
dissolution, an undesirable characteristic because free water could
lead to leaching and migration of waste material after the product
is buried. Therefore, the production of water insoluble alkali
metal compounds, such as Nosean and Nepheline, is preferred.
[0021] Reducing additives may also be mixed with the waste along
with mineralizing additives to remove oxygen. Oxygen is present in
the waste materials containing nitrates, nitrites, and other
nitrogen oxides. Suitable reductants may include sugar, glycol,
glycerol, ethylene carbonate, formic acid, alcohols, carbon, and a
wide variety of other carbonaceous or organic compound reducing
agents. Gas phase reductants may also be added to the mixture for
reduction of nitrates and other unwanted waste material oxides.
Additional metal reducing additives may also be mixed with the
waste along with mineralizing additives to reduce certain waste
constituents (mainly metals) to a lower, less water-soluble form.
For example, mercury can be reduced to mercury sulfide by addition
of a reducing agent such as sodium sulfide, potassium sulfide,
calcium sulfide, iron sulfate, hydrazine, formic acid, sulfuric
acid, stannous chloride, and other similar reducing agents. In like
manner, water-soluble chromium in a +6 oxidation state can be
reduced to insoluble chromium in a +3 oxidation state by means of
the metal reducing agents.
[0022] In a third embodiment of the invention, the waste material
is pretreated by addition of a reducing agent or by dissolution in
a mineralizing additive prior to optional mixing with other such
additives. For example, asbestos can be partially dissolved by
placing the asbestos in a hot caustic solution so that the asbestos
fibers are destroyed by being at least partially dissolved prior to
further treatment according to the first and second embodiment
processes described above. The destructive of asbestos fibers can
be performed in one or two steps. In the first step, the asbestos
fibers are destroyed by at least partially dissolving them in a
caustic solution, preferably a sodium hydroxide solution. The
asbestos that is not completely dissolved in this step forms a
non-fibrous, gelatinous residue and the asbestos solution
containing this residue can then be mixed with additives, such as
clay, and heated in a treatment container. Alternatively, the
resulting residue can be treated with an acid solution, either
separately or in the asbestos solution, to further dissolve the
residue. The asbestos solution and the residue solution may then be
mixed with additives and heat treated, either together in the same
container or separately in different containers. For the second
step, i.e., dissolution of the residue with an acid, the preferred
acids include sulfuric acid, formic acid, oxalic acid, and
phosphoric acid. Other organic and mineral acids also may be used.
However, it is preferred that hydrofluoric, nitric and hydrochloric
acids not be used for the second acid dissolution step as they
contribute fluorides, nitrates and chlorides, respectively, to the
waste material, which could adversely impact the quality of the
stabilized product from the treatment process and the off-gas
emissions from the treatment process.
[0023] Another embodiment of heat-activated stabilization may be
achieved by mixing the waste with additives that will partially
react at ambient temperature to produce a mixture having a modified
chemical composition and properties. The partially reacted mixture
is then exposed to thermal treatment in a fluidized bed to form a
granular product, such as an inorganic grit as described in U.S.
Pat. No. 6,084,147, the entire contents of which are expressly
incorporated herein by reference. This granular product is
subsequently solidified into a monolithic waste form in a treatment
container in accordance with the present invention. This type of
process therefore uses two separate stages or operations and two
separate process containers, i.e., the fluidized bed vessel and the
subsequent heat treatment container. Mixing of the waste with
additives for forming the granular product is not deemed to be one
of these operations.
[0024] These embodiments and their advantages will be apparent to
those skilled in the art of hazardous waste treatment from a
careful reading of the Detailed Description of Preferred
Embodiments as presented below.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0025] The present invention is a process for converting waste into
a monolithic solid suitable for transportation and disposal by
mixing the waste with mineralizing additives and, optionally,
reducing additives, to form a mixture, and then by heating the
mixture to a temperature within a mineralization range. The present
disclosure is described with respect to radioactive waste and
asbestos waste but any nitrogen-containing, magnesium-containing,
silicate-containing, calcium-containing, aluminum containing waste,
alkali-containing wastes, chloride-containing waste,
fluoride-containing waste, phosphorous- or phosphate-containing
waste, and sulfur- or sulfate-containing waste, or output stream
containing one or more of the foregoing wastes, can be processed
using the methods and apparatuses described herein.
[0026] The terms "disposal container" and/or "treatment container"
both refer generally to a relatively small container, holding
preferably 1 to 50 cubic feet, more preferably 7 to 30 cubic feet,
which is made for the purposes of containerizing wastes for
disposal by shallow land burial (as opposed to a separate reaction
or mixing vessel). The treatment and disposal container also is not
designed for higher temperatures, say 1000.degree. C. or higher,
but can withstand environments in which their temperature rises to
600.degree. C. to 750.degree. C., or perhaps somewhat higher,
without loss of structural integrity or geometry.
[0027] A preferred embodiment of the invention involves a single
treatment and disposal container in which the waste material can be
mixed with additives, heat treated and disposed of. Another
preferred embodiment involves the use of a first container or
vessel for mixing waste materials with additives, and a second
container for heat treatment of this mixture. This heat treatment
container is also intended for use as a storage and/or disposal
container, in which the waste materials and additives, once heated,
will form a mineralized monolithic solid. The reduced handling, and
in particular, the reduced transferring of the waste from one
container to another, is an important feature of the present
invention.
[0028] The monolithic solid that is formed after heat treatment is
a solid, sufficiently stable form for transportation and disposal
without further treatment. The mineralized solid typically includes
sodium aluminosilicates, sodium aluminosilicates with substituted
chlorine, fluorine, phosphorus, sulfate, radionuclides, and heavy
metals in the crystalline structure, sodium calcium silicate,
calcium sulfate, calcium fluoride, calcium phosphate, magnesium
phosphate, magnesium silicate, magnesium silicate phosphates,
magnesium/iron silicate, magnesium/iron phosphates, and similar
water-insoluble compounds, including alkali metals substituted for
the sodium in the above list.
[0029] Stabilization as used in the present process is the
conversion of waste materials into a substantially mineralized,
substantially solidified and substantially monolithic form that has
the following properties and/or characteristics: [0030] The
solidified waste form satisfies treatment standards for heavy metal
leach resistance. [0031] Radionuclides and other toxic and
hazardous materials present in the waste are substantially
immobilized in the solid monolithic waste form so that they satisfy
disposal facility performance requirements. [0032] The solid
monolithic waste form has structural and compositional
characteristics that meet requirements of applicable regulatory
agencies, including requirements related to: compressive strength,
porosity, permeability, leach resistance, oxidation resistance,
friability, fungal and bacterial resistance, hydration resistance,
integrity after thermal cycling, and dryness or lack of free
liquids.
[0033] Stabilization as defined for this invention does not include
production of a monolith by typical cement or other methods of
encapsulation, incorporation, bonding or binding where the monolith
is formed by non-heat-activated means. For example, typical cement
solidification processes turn the waste/cement mixture into
monoliths by the growth of hydration bonds and/or crystallization
at or near ambient temperatures. These chemical reactions may be
slightly exothermic which may increase the temperature of the
materials, but the reactions initiate at ambient temperatures, and
temperatures significantly above ambient are not required to
initiate the reactions.
[0034] Heat-activated as defined for this invention means that heat
is applied to the mixture to initiate a mineralization reaction
that will result in formation of a monolithic solid waste form.
Although some mineralization reactions can partially occur at
ambient temperature, i.e. without heat application that increases
the material temperature, the extent of reaction is limited and
would not produce a stabilized monolith. Heat-activation applies to
methods of stabilizing waste mixtures where ambient temperature
reactions are not sufficient to cause these mixtures to
stabilize.
[0035] In addition, the heat-activation temperature is less than
the melting point of most, preferably a majority, more preferably
substantially all, of the waste materials and additives. This means
that stabilized minerals can be formed without melting a majority
of the wastes and additives, in contrast to the processes of
vitrification, sintering, and thermosetting and thermoplastic
encapsulation. Therefore, the present process takes place at less
than the temperature of waste vitrification (melter) processes and
sintering processes which operate at temperatures greater than
900.degree. C., such that substantially all or at least a majority
of the materials melt and/or fuse into a final waste form that
becomes a monolithic solid upon cooling.
[0036] For example, if one were to mix magnesium hydroxide sludge
with Portland cement and water in the right proportions at ambient
temperature, one could achieve a monolithic solid of magnesium
hydroxide and calcium carbonates and silicates. However, according
to the invention, if magnesium hydroxide and Portland cement are
mixed and heated to a temperature above approximately 600.degree.
C., the mineral magnesium-calcium-silicate would be formed, which
has superior leach resistance and stability compared to a solid
achieved by mixing magnesium hydroxide sludge with Portland cement
at ambient temperature. Additionally, the Mg--Ca--Si mineral would
occupy a smaller volume, as water and organics would have been
eliminated in the higher temperature heat-activated stabilization.
The reduced volume translates into greater savings in disposal
costs and perhaps lower transportation costs as well.
[0037] Another example of the invention would be the denitration
and mineralization of sodium nitrate containing wastes. If the
sodium nitrate wastes are mixed with a reductant and one or more
mineralization additives, but not heat activated, some denitration
reactions and even some mineralization reactions may occur, but
only very slowly, over a period of hours and days. In fact,
monolithic stabilization will likely never be achieved without the
introduction of sufficient heat. However, when heat is applied to
the same mixture, at temperatures over 200.degree. C., preferably
over 400.degree. C., the water in the waste is quickly evaporated,
the majority, preferably substantially all, of the nitrates are
converted to nitrogen gas, and the majority, preferably
substantially all, of the inorganic components and alkali metals in
the wastes are converted into crystalline mineral products in a
monolithic waste form in a matter of seconds to hours depending
upon the temperature used. Thus the present process makes rapid
monolithic mineralization feasible, with corresponding increases in
productivity.
[0038] A purpose of the present invention is to stabilize waste
materials in a single operation in a single container, wherein
following mixing of waste and additives in the container, the
solidification, stabilization, and production of a monolithic final
waste form are accomplished in the same container by the
introduction of heat.
[0039] The inorganic constituents in the waste material, as well as
any radionuclides, non-volatile heavy metals, Cl, F, S, and P
compounds present in the waste, will be converted into stable
minerals by the present process. The predominant mineralized
products that are produced are listed below. These minerals are
generally not water soluble. The relative amount of each product
compound is dependent upon the type of additives used and the
inorganic composition of the waste, where the more complex
compounds are shown with abbreviated chemical formulas for
simplicity: [0040] Sodium-aluminosilicate (Na2O--Al2O3-2SiO2,
Na--Al--Si), including substituted NO3, Cl, F, P, S compounds,
metals, and heavy metals in the crystalline structure [0041] Sodium
silicate (Na2O-2SiO2) [0042] Sodium aluminate (Na2O-2Al2O3) [0043]
Sodium calcium silicate (Na--Ca--Si) [0044] Calcium sulfate (CaSO4)
[0045] Calcium fluoride (CaF2) [0046] Calcium phosphate
(Ca3(PO.sub.4).sub.2) [0047] Magnesium phosphate (MgKPO4) [0048]
Magnesium calcium silicate (Mg--Ca--SiO2) [0049] Magnesium silicate
phosphate (Mg--SiO2-PO4 [0050] Magnesium calcium silicate phosphate
(Mg--Ca--SiO2-PO.sub.4) [0051] Magnesium iron silicate
(Mg--Fe--SiO2) [0052] Magnesium silicate (Mg--SiO2)
[0053] The preferred mineralizing additives include
aluminosilicates (clays), silica gel, silica, silicates,
phosphates, Ca, Mg, Ti, Fe, aluminum gel, and Al compounds that
combine with alkali metals to form synthetic and naturally
occurring minerals as listed above and below (Note: Only the main
elemental constituents are listed for simplicity). In the event the
waste material is deficient in alkali metal content, alkali metals
compounds and hydroxides can also be added to provide for
substantially complete mineralization of the waste: [0054]
Nepheline, Na--Al--Si [0055] Nosean, Na--Al--Si--SO4 [0056]
Carnegieite, Na--Al--Si [0057] Sodalite, Na--Al--Si, and
substituted species with NaCl, NaNO3, and NaF [0058] Fairchildite,
K--Ca--CO.sub.3 [0059] Natrofairchildite, Na--Ca--CO.sub.3 [0060]
Dawsonite, Na--Al--CO.sub.3 [0061] Eitelite, Na--Mg--CO.sub.3
[0062] Shortite, Na--Ca--CO.sub.3 [0063] Parantisite, Na--Ti--Si
[0064] Maricite, Na--Fe--PO4 [0065] Buchwaldite, Na--Ca--PO4 [0066]
Bradleyite, Na--Mg--PO4--CO3 [0067] Combeite, Na--Ca--Si [0068]
Na--PO4, Na2CO3, Na--Al, Mg--PO4, Na--Al--PO4, Na--Mg--PO4, Ca--Si,
and Na--(Ca,Fe,Mg)--Si
[0069] The most environmentally stable minerals have been shown to
be feldspathoids, Nepheline, Nosean, Sodalite, Carnegieite and
related aluminosilicates, and these are thus most preferred.
[0070] The generation of water-insoluble
sodium/potassium/aluminum/calcium/magnesium/phosphate/sulfide
products is preferred. Thus, the generation of water-insoluble
alkali metal products is very desirable. For this reason, the most
preferred products are the water-insoluble species such as Nosean
and Nepheline. The Nosean and related sodium aluminosilicate
compounds form a crystalline, cage-like structure that has the
ability to substitute and bind large atoms (such as cesium,
technetium, and other radionuclides and heavy metals) within the
crystalline structure to produce a highly leach-resistant product.
The sodium aluminosilicate compounds have demonstrated that they
have leach-resistance that is substantially better than the Land
Disposal Restrictions (LDR) Universal Treatment Standard (UTS)
limits for heavy metals. The Cl, F, P, and sulfates in wastes are
also incorporated into the crystalline structure of the sodium
aluminosilicate compounds. The present process can thereby
effectively stabilize potential acid gases as well as inorganic
materials.
[0071] In order to generate the alkaline earth mineralized
compounds mentioned above, the following mineralizing additives can
be used, each mineralizing additive would be added to the waste
materials in the proportions needed to generate the desired higher
melting point and water-insoluble compounds. In the following
examples, sodium is used but the same is true of other alkaline
metals such as potassium, cesium, etc. Other combinations of the
mineralizing additives and waste constituents are anticipated as
there are literally hundreds of variations of mineral forms with
substituted mineral structures that all use the same elements:
[0072] Addition of lime (CaO) or other Ca compounds such as calcium
carbonate, calcium silicate or nitrate could provide conversion of
alkaline earths to Ca rich final product, e.g. Natrofairchildite.
[0073] Addition of magnesia (MgO) would produce minerals rich in
magnesia, e.g. Eitelite. [0074] Addition of clays (aluminosilicates
such as kaolin, bentonite, troy, etc) or zeolites or precursors to
produce a Nepheline, Nosean or other related sodium
aluminosilicates. [0075] Addition of only Al compounds including;
aluminum nitrate, Al(NO3)3, aluminum hydroxide or tri-hydrate
Al(OH)3; aluminum gel, aluminum metal particles, etc. will produce
a sodium-aluminate product compound. For wastes with a high silica
content the product would be sodium aluminosilicates. In this case
the aluminum additive and the silica in the waste form a synthetic
clay that can then form alkali aluminosilicates with the alkali
metals in the waste. [0076] Addition of alkali metal hydroxides
will produce alkali-rich minerals that will tend to more easily
form monolithic solids from wastes that are deficient in alkali
metals. For example, addition of sodium hydroxide to asbestos
(Mg/Fe-Silicates) will partially dissolve the asbestos fibers and
then convert the Mg/Fe-Silicates into a monolithic, non-fibrous
solid that is free of asbestos fibers. [0077] Addition of phosphate
compounds produces bonded ceramic minerals such as Maricite,
Buchwaldite, Bradleyite or other PO.sub.4 containing compounds. For
waste feeds containing phosphate compounds, such as tri-butyl
phosphate, the final solid product would be an inorganic phosphate
as listed above. To bond with phosphate in the waste, it is
preferred that a clay, silica, iron, or calcium additive be used to
make a water-insoluble product. [0078] Addition of silica gel,
silica, and/or sodium-silicate compounds produces a sodium
silicate, magnesium silicate, sodium magnesium silicate product, or
for wastes with a high aluminum content, the product would be
sodium aluminosilicates. In this case the silica additive and the
aluminum in the waste form a synthetic clay that can then form
alkali aluminosilicates with the alkali metals
[0079] Table 1, below, provides typical simplified reaction
equations for formation of some of the mineralized products of the
present invention. Generally, the minerals form larger structures
with much large numbers of atoms than shown in Table 1, which is
shown only as an example of the types of reactions that can occur.
TABLE-US-00001 TABLE 1 Mineralization Chemistry For Converting
Sodium, Potassium, Aluminum, Sulfates, Chlorides and Radionuclides
into Sodium AluminoSilicates Na + Al2O3--2SiO2 (Clay) =
Na2O--Al2O3--2Si02 Na + K + Al2O3--2SiO2 (Clay) =
NaKO--Al2O3--2SiO2 Na + SO4 + Al2O3--2SiO2 (Clay) =
Na2SO4--Al2O3--2SiO2 Na + Cl + Al2O3--2SiO2 (Clay) =
NaCl--Al2O3--2SiO2 Na + F + Al2O3--2SiO2 (Clay) = NaF--Al2O3--2SiO2
Na + Al2O3 + SiO2 (Silica) = Na2O--Al2O3--2SiO2
[0080] Reductants may also be mixed with the waste in the treatment
container to assist in the removal of unwanted oxidized compounds.
Oxygen is often present in the waste materials in the form of
nitrogen oxides, such as nitrates and nitrites, as well the oxides
of other elements. Reducing additives (or "reductants") that can be
added to the waste materials can be essentially any solid or liquid
that can remove oxygen from the waste materials or change oxidation
state of certain metals. Reductants can include: carbon and
carbonaceous materials such as sugar, glycol, glycerol, ethylene
carbonate, formic acid, alcohols, and a wide variety of other
liquid or solid carbonaceous reductants, i.e. essentially any
organic material. Reductants to be mixed with the waste materials
can be miscible with the waste materials, soluble in water or other
liquid, or solid and any combination of the above.
[0081] In addition to solid and liquid reductants that can be added
to the waste material, gas-phase reductants such as carbon
monoxide, methane, hydrogen or other gaseous carbonaceous materials
can be injected or pumped into the treatment container to provide
reduction of nitrates and other unwanted waste material oxides.
Additional metal reducing additives may also be mixed with the
waste along with mineralizing additives to reduce certain waste
constituents (mainly metals) to a lower, less water-soluble form.
For example, mercury can be reduced to mercury sulfide by addition
of a reducing agent such as sodium monosulfide, potassium
monosulfide, calcium sulfide, iron sulfate, hydrazine, formic acid,
sulfuric acid, stannous chloride, and other similar reducing
agents. In like manner, water-soluble chromium in a +6 oxidation
state can be reduced to insoluble chromium in a +3 oxidation state
by means of the metal reducing agents.
[0082] Wastes containing nitrogen oxides require processing to
remove these oxides, to stabilize heavy metals and radionuclides,
if present, and to remove organics in order to stabilize these
wastes. For this type of waste, it is possible to mix the nitrogen
oxide waste with a reductant and one or more mineralizing additives
in a separate vessel. The mixture is then placed in a treatment
container and heated. Alternatively, the mixing and heating can be
accomplished in a single container.
[0083] The application of heat to the contents of the treatment
container will cause any water to evaporate, thus drying the waste
material. Continued heating will cause organics to volatize and/or
pyrolyze, and nitrates and nitrites to decompose. The reductant
will serve to convert the nitrates and nitrites in the waste
material to nitrogen gas with only relatively small amounts of
gaseous nitrogen oxides being generated. The heat will also cause
the waste materials and mineralizing additives to crystallize and
bond into a solid monolithic final form. A specific example of this
is the stabilization of a sodium nitrate solution that contains
nitrate-containing materials, such as nitric acid, sodium nitrate,
other nitrates, nitrites, organics, heavy metals, sulfur, halogens,
and radioactive materials. To stabilize this waste, it is mixed
with a reductant and a mineralization additive in a separate mixing
container or vessel. Samples can be taken to verify the uniformity
of the mixture and that the mixture contains the desired
proportions of additive and waste material.
[0084] The mixture is then placed into a treatment container for
heat-activation. The mixture is heated in this container by means
of an internal or external heat source to initiate the chemical
reactions. As the waste mixture is heated to its mineralization
temperature, the water is evaporated and volatile organics vaporize
first. As additional heat is applied, the semi-volatile organic
compounds are thermally distilled through pyrolysis reactions,
which break the long-hydrocarbon polymers and chains into more
volatile gas-phase organics. The application of heat causes
evaporation of nitric acid and thermal decomposition of nitrates
and nitrites to form gaseous nitrogen oxides. The reductant(s) will
react with the solid, liquid and gas-phase nitrogen oxide (NOx) and
carbon components to form mainly nitrogen gas, carbon oxides
(mainly carbon dioxide and some carbon monoxide) and water from the
oxygen in the NOx components.
[0085] The application of heat further provides the energy needed
for the inorganic components of the waste materials and additives
to form mineral compounds that will effectively solidify a
majority, preferably substantially all, of the waste into a final
mineralized monolithic waste form. The specific minerals that form
depend on the inorganic composition of the waste material and the
choice and amount of the additive or additives used. For example,
if clay were added as the mineralizing additive, a sodium
aluminosilicate and other feldspathoid related minerals would be
formed as the monolithic solid. If a silicate were used as the
mineralizing additive, a sodium silicate mineral would be formed as
the monolithic solid. If the waste had a high magnesium content and
silica were added as the additive, a magnesium silicate would be
formed as the monolithic solid. The sulfur and halogens, such as
chlorine and fluorine, would also be mineralized to form Na2SO4,
NaCl and/or NaF substituted sodium aluminosilicates or similar
minerals. The heavy metals and radioactive components are also
incorporated into the structure of the minerals of the monolith. It
will be appreciated that heavy metals, halogens, sulfur,
radionuclides and other undesirable constituents in the wastes can
be mineralized into a stable monolithic waste form according to the
teachings of the present invention.
[0086] The invention may be further understood by the following
description of a test run that demonstrates its feasibility. A
waste surrogate was prepared by mixing 1358 grams (g) of water, 270
g of NaOH and 303 g of NaNO3 in a plastic mixing vessel, and then
adding to this surrogate waste in the mixing vessel 889 g of clay
as a Al--Si mineralizing additive and 152 g of sucrose as a
reducing additive (reductant). These five components were then
mixed together in the mixing vessel with two drops of a non-silicon
defoamer, which was organic-based and also served as a second
reductant. This mixture of waste materials, mineralizing additive
and reducing additives was then poured into a 500 ml steel can,
which served as the treatment container.
[0087] The treatment container and its contents were placed into a
furnace and heated up to 750.degree. C. at a rate of 10.degree.
C./minute, and then were held at 750.degree. C. for a two hour
period, after which the container was removed from the furnace and
allowed to cool. The final solid monolithic waste form resulting
from this process was white in color and was hard to the touch.
Mechanical action was required to break this monolith into pieces.
A volume reduction by a factor of approximately two was observed
from the initial waste and additive mixture volume to the volume of
the final monolithic form. There were minimal nitrogen oxides (NOx)
noticed in the off-gases generated during heating, thereby
demonstrating the desired reduction of nitrates to nitrogen gas.
The off-gases were vented to a hood and released to the
atmosphere.
[0088] The following narrative describes a full-scale application
of the invention wherein waste materials and mineralizing additives
are combined into the desired mixture composition in a mixing tank
or vessel stirred with an internal mixer. The fluid solutions are
first placed into the mixing vessel and the solid materials are
then metered into this vessel while mixing the fluid solutions to
form a slurry. The fluids and solids may include mineralizing
and/or reducing additives. The slurry of combined waste and
additives is mixed until sufficiently homogeneous and then the
contents of the mixing vessel are transferred to a metal treatment
container. It is also feasible to perform the foregoing mixing step
in this same metal treatment container so that only a single
container is used for mixing, heat treatment and disposal. The
treatment container is then heated to the desired mineralization
temperature by means of external or internal heaters, which are
preferably electrical although combustion-fired, microwave,
induction heating or other suitable heating means are also
suitable.
[0089] The treatment container heat-up time is controlled by
adjusting the heat input from the heat source. The water is first
evaporated from the waste/additive mixture. As the waste/additive
mixture continues to heat-up, volatile organics are evaporated and
then semi-volatile organics are pyrolyzed such that semi-volatile
hydrocarbon molecules are thermally broken down into smaller sized
fractions which are then volatized from the mixture. Once the water
and volatiles are removed, the mixture generally becomes a solid
monolith.
[0090] As heating is continued, the non-volatile waste constituents
and the mineralizing additives react and combine into new,
generally crystalline mineral structures that provide the strength
in the monolith. The amount of crystal growth and bonding between
the waste and additives largely determines the strength and
ultimate properties of the final post treatment monolithic waste
form. The temperature of the heat treatment is dependent upon the
waste constituents, the selection of mineralizing and reducing
additives, and the desired final monolithic mineral form. The time
of heat treatment is dependent upon the size of the treatment
container and the cure time for the minerals to fully form. These
times can vary from 1 hour to several days for a large monolith to
fully mineralize.
[0091] The composition of each waste stream and additive mixture
will need to tested to verify the time and temperature that provide
for desired level of mineralization and conversion to the desired
monolithic mineral form. The adequacy of the stabilization is
determined by sampling the monolith and performing analytical tests
to confirm that the properties of the monolith meet the
requirements for disposal or storage. The treatment container is
sealed after the desired monolith form has been achieved and cooled
to near ambient temperature. The sealing device can be a simple
snap-on lid or a more complex lid, such as seal welding a metal lid
for certain more restrictive applications.
[0092] Off-gases from the treatment container are directed through
an off-gas treatment system that is designed to remove trace
particulates and residual acid gases and other volatiles of
concern. If mercury has not been stabilized, it can volatize and
will also need to be removed from the off-gas stream through
adsorption or other approved process. Water vapors and volatile
organics can be condensed and treated separately if desired. Purge
gases are not required in the treatment container but can be used
to help control the environment, such as using nitrogen or other
inert gas to prevent accumulation of organic vapors in the
container. An example of the hardware for heating the treatment
container and handling the off-gases is that shown and described in
U.S. patent application Ser. No. 10/209,090 filed Jul. 31, 2002,
and published as Pub. No. US 2004/0024279 A1 on Feb. 5, 2004, the
entire contents of which are expressly incorporated herein by
reference.
[0093] Another typical waste material is Magnox (magnesium
hydroxide) rich sludge from reprocessing of spent nuclear fuel. The
Magnox sludge contains heavy metal, organic and radioactive
constituents that must be treated to remove the water and organics,
stabilize the heavy metals and radionuclides and form a monolithic
final waste form that is qualified and suitable for disposal. With
Magnox wastes, there are usually minimal nitrates so a reductant is
not normally used. One or more mineralizing additives, such as
clay, phosphate, silica or sodium silicate compounds, are added to
these wastes to form a monolithic structure during heat treatment.
For example, the clay would bind the heavy metals and radionuclides
and the silica, phosphate, and/or sodium-silicate compounds would
mineralize the magnesium and form the base structure of the
monolithic final waste form. In this case it may be necessary to
add caustic (sodium hydroxide) to provide full mineralization of
the heavy metals and radionuclides with the clay via formation of
sodium aluminosilicate.
[0094] In an additional embodiment of the invention, waste asbestos
is made non-hazardous without vitrification. The treatment of
asbestos can be performed in two or three steps. First, asbestos
can be partially dissolved by placing the asbestos in a hot caustic
(sodium hydroxide) solution so that the silica in the asbestos
fibers is partially to substantially dissolved. Although partial
dissolution destroys the fibers, it leaves a gelatinous residue.
The optional second step involves dissolution of this residue by
contacting it with an acidic solution. This second step may be
necessary if temperatures less than 200.degree. C. are used when
heating the treatment container. The partially dissolved asbestos
solution from the caustic step and/or the substantially completely
dissolved asbestos solution from the optional acid step may then be
mixed with another mineralizing additive, such as iron oxide,
phosphate or calcium oxide, although in some instances the caustic
and/or acid used may alone serve as the mineralizing additive. The
dissolved asbestos and mineralizing additives are then treated by
heating the treatment container to preferably about 400.degree. C.
to 600.degree. C. until a majority, preferably substantially all,
of the mixture, is converted into a Na--Mg--Fe--Ca-Silicate mineral
solid if calcium and/or iron additives are used, or if there is
sufficient calcium and/or iron already present in the asbestos
waste.
[0095] It will be apparent to one of ordinary skill in the art of
waste treatment that many modifications and substitutions can be
made to the preferred embodiments described above without departing
from the spirit and scope of the present invention as defined by
the following claims.
* * * * *