CA1266573A

CA1266573A - Soil and industrial waste decontamination

Info

Publication number: CA1266573A
Application number: CA000498093A
Authority: CA
Inventors: Hosep Torossian; Michael M. Avedesian; Abe Limonchik
Original assignee: Domtar Inc
Current assignee: Domtar Inc
Priority date: 1985-12-19
Filing date: 1985-12-19
Publication date: 1990-03-13
Anticipated expiration: 2007-03-13

Abstract

ABSTRACT
SOIL REVITALIZATION
A process and an apparatus for the decontamination of industrial waste and the revitalization of soil containing industrial waste, having dioxins and/or polychlorinated aromatic compounds, without depletion of the valuable nutrient contained in said soil. The process comprises contacting a soil or industrial waste with supercritical carbon dioxide, an ecologically acceptable fluid, bringing the carbon dioxide to temperature and pressure to maintain said fluid in its supercritical state to dissolve the dioxins and/or polychlorinated aromatic compounds, while producing an insoluble and a soluble fraction. The soluble fraction is then separated from the insoluble fraction. The insoluble fraction contains the decontaminated industrial waste and/or soil and trace amount of an ecologically compatible fluid. The pressure-temperature conditions of the soluble fraction are then modified to cause the carbon dioxide in supercritical fluid to vaporize and separate from the soluble dioxins and/or polychlorinated aromatic com-pounds. An apparauts is also disclosed, as well as means to recycle industrial waste. The process is unique in that it would permit the revitalization of soils around various industrial sites such as chemical plants, oil exploration and production fields, beaches contaminated by oil spills, and the recovery and recycling of industrial waste.

Description

FIELD OF TXE INVENTION
This invention relates to a method and an apparatus for the decontamination of industrial wast~, to the art of revitalizing soil and in particular to a process for the decontamination of soil containing industrial waste while aiming at minimizing the depletion of soil ingredients, such as valuable soil nutrients which are generally present in the soil. In particular this invention relates to se~ective decontamination of soil having industrial waste containing dioxins and polychlorinated aromatic componds, thereafter collectively and individually referred to as contaminants. This invention also relates to the recycling of industrial waste.
BACKGROUND OF I~ INYENTION
The methods that are known for the decontamination of industrial waste, water or soil, generally imply either burning, that is destruction of all the ingredients present, or the use of solvent extraction, generally organic solvents and aqueous organic solvents. It involves tedious and costly extraction processes and purification steps while leaving behind at least trace amounts of these solvents used for the decontamination steps. These costly solvents remove valuable soil ingredients.
The other method used for the disposal of industrial waste is landfill burial which involves trucking costs.
They are also ecologically risky, water could always form a leachate of the waste products.
The use of the substances described in the above references cause the extraction of materials such as salts 5~3 of calcium, potassium, magnesium and other similar salts, phosphorous containing compounds and others, which are valuable soil consti.tuents, and at high temperatures using solvents which are not part of the eco-system.
Problems arise however, since soil is often rendered steri.le following the removal of a portion of its constituents.
In a pref~rred embodiment, applicant wishes to provide a soil decontamination, industrial waste decontamination and contamination recycling facility which could either be fixed or mobile, depending upon the local requirement.
Furthermore, the use of some ~hemical solvents increase the risk of residual contamination, thereby requiring elaborate residual removal techniques in such extraction processes.
Applicant aims at tru'y decontaminating the industrial waste and preferably the soil so as to "revitalize it", that is to provide a process for revitalizing soil by selectively sxtracting the contaminants from the industrial waste while unaffecting the natural constituents of the soil.
Applicant wishe~ to be able to extract from soils that fraction which is the contaminants of the industrial waste, without stripping off the soil and the other ingredients which are ecologically useful, and doing away with the problems enunciated above.
The present invention provides a process for revitalizing soil utilizing a compatible supercritical fluid, in order to eliminate subsequent residual contamination generally e~count~red wh~n solvent extraction is used.
The process is unique in that it permits the decontamination of soils and thereby of indust.rial waste, around various industrial sites such as chemical plants, oil explora~ion and production fields, beaches contaminat-ed by oil spills, and of waste wood preservatives in wood preservative plants from wood shavings, sludges, soils, all thereabove individually and collecti~ely referred to in said application by the expression "industrial waste".
The process also enables the recovery and recycling o~ industrial waste, for instance waste wood preservatives.
BRIEF DESCRIPTION OF THE INVENTION
Broadly stated, the invention is directed to a process for the decontamination of industrial waste and soil, containing at least one contaminant selected from the group consisting of dioxins and polychlorinated aromatic compounds, comprising:
a) contacting with carbon dioxide, (also known as CO2) a substrate comprising at least one member of the group consisting of industrial waste and soil containing said at least one contaminant, b) increasing the pressure and temperature o~ said carbon dioxide above the critical temperature and pressure of carbon dioxide, to maintain said carbon dioxide fluid in supercritical state, as to dissolve into said carbon dioxide in supercritical state said at least one contaminant, while keeping said substrate substantially insoluble to said carbon dioxide in supercritical state 5~3 fluid thereby producing a supercritical fluid fraction containing said at least one contaminant and an insoluble fraction, c) separating under said supercritical state said supercritical fluid containing said at least one contaminant, from said insoluble fraction, d) reducing the pressure of said insoluble fraction to subcritical pressure to obtain a decontaminated substrate and trace amounts of an ecologically compatible carbon dioxide, e) reducing the pressure of said supercritical carbon dioxide containing said at least one contaminant to subcritical pressure, to cause said at least one contaminant to precipitate out and to separate from said carbon dioxide.

This invention alsc relates to an apparatus for the decontamination of industrial waste and soil containing at least one contaminant selected from the group consisting of dioxins and polychlorinated aromatic compounds, comprising: a staged pressurized extractor, means of feeding to said staged pressurized extractor at least one member selected from the group consisting of industrial waste and soil, said member being contaminated with at least one contaminant selected from the group consisting of dioxins and polychlorinated aromatic compounds, means of feeding into said extractor carbon dioxide, heating and pressure means for maintaining in said staged pressurized extractor said carbon dioxide with said member under super-critical state, and agitation means for contacting said at leas~ one member wit~ said carbon dioxide in supercritical . ~;
state to obtain therfrom said supercritical fluid containing said contamlnant, means of filtering the resulting supercritical fluid to obtain said filtered fluid containing said contaminant, pressure releasing means for flashing out to separate said filtered fluid, and means of removing the unfilterable fraction, said unfilterable fraction being said member decontaminated.
BRIEF DESCRIPTION OF T~E DRAWING5 Further features, objects and advantages will be evident from a detailed description of a preferred embodiment taken in con~unction with the accompanying drawing.
Figure l is a schematic flow diagram of a version of a soil decontamination apparatus for carrying out the invention.
Referring to Figure l, we shall deal first with the charging operation.
CHARGING
The contaminated soils are charged to a feeder 10 at atmosphere i.e. pressure which is sealed from the autoclave by means of at least one of the valves 12 or 14. The feed hopper i5 then closed by valve 12, and then the valve 14 opened to deliver the soils into the extractor 16.
MULTIST~GE PRESSURE EXTRACTOR
The pressurized extractor 16 consists of multi-stages separated by baffles 18 and provided with heating means such as a heating mantle not shown for sake of clarity.
The charged soil(s) moves from stage to stage as a solid-fluid slurry by gravi~y and by turbulence such as ~ 7 obtained by mechanical stirrers 20 (schematically shown) with the soil contaminants being reduced at each stage after being extracted with supercritical C02. After khe last stage of the extraction, the decontaminated soil moves to a pressure filter 30 via line 28 and valve 29.
I'urbulence by other stirring means, such as sonic vihrations, or other pulsating means may be used, if desired.
PRESSURE FILTRATION
The high pressure filter 30, operating at the process crtical pressure separates the fluid solvent and soluble contaminants from soils. Fluid solvent and soluble contaminents are carried via line 32 through a pressure let-down valve 34 to a product separating rec~iver or flash vessel 36. Because of the decrease in pressure and hence density of the solvent, the contaminants separate and are collected via lines 38 while the carbon dioxide escapes via line 40. If pressure in line 32 is lower than in vessel 16, a compressor, also referred to as "booster"
37 is us~d to raise the pressure to the same level as in extractor 16.
Instead of having a flash vessel, one may elect as shown, fractional separation by zones divided by walls as shown in 36a, b, c and d, each zone leading to the other by pressure let-down valves 34a, b, c and d. Each zone having valves 38a, b, c and d, and lines 39a, b, c and d for receiving the respective fractions. For instance, to recuperate or recover by fractionation and recycle the various waste wood preservatives. In order to limit energy and time losses, preferably several pressure filters are operating in parallel, one only being schematically shown at 30a for sake of clarity: Thus, one filter operates under process pressure while the decontaminated soil is being removed via lines 52, after prior removal of the CO2 fluid via line. 32. These lines 52 are provided with a pressure let-down valves 54. A
third similar filter not shown may be (for sake of clarity) available on standby.
The supercritical fluid contained in a pressurized re~evoir 60 is fed into the extracter 16 via line 62 and a divider provided with nozzles 66. This divider shown out-side may also be located inside. These nozzles 66 may be arranged to effectuate pulsating distribution of the fluid by valve diagramatically shown at 68. Once the gas leaves the flash vessel 36, the supercritical fluid is now in a gas phase and may be recycled via lines 40 and 70 by means of a compressor 72 leading to line 62 after which the gas becoming superciritcal fluid.
If desired, heating means 35 and 63 may be used to preheat the supercritical fluid to operating temperature and at 35 also to prevent freezing of the line.
In using carbon ~ioxide, one must bear in mind the critical pressure of 1070.4 psi (73.8 ~ar) (1 bar = .987 ATMOSPHERE) and critical temperature of 31C, the extraction is generally carried out within pressures ranging from 3,000 to 5,000 psi and temperatures ranging from 41 to 130C, preferably between 50 to 120C, the best result being in the vicinity of 81C. It is ecologically safe. It represents no health hazards, it is non-flammable, noncorrosive, inexpensive, and readily i73 g available in high purity and its critical temperature, slightly above ambient, permits easy handling and removal from products.
The pariod of contact of said substrate with C02 in step b) for extraction varies according to the nature of the soil or of other industrial waste. In some cases 2-30 minutes has been found satisfactory and sometimes even better than a 60 minute extraction peri~d. For some soil a 70% industrial waste extraction has been obtained within lO minutes.

Although the present invention is particularly suited to the extraction of contaminants such as dioxins, and polychlorinated aromatic compounds (such as pentachloro-phenol and tetrachlorophenol, and the like), it may also be used with other industrial waste such as petroleum oils, coal tar based creosotes etc.
Although the revitalization could be done in a non-continuous manner, it is desirable to have a continuous flow of carbon dioxide in order to provide a higher con-centration gradient between the soil and the carbondioxide.
As can be seen, the process is uni~ue in that it permits the decontamination of soils and industrial waste around various industrial sites such as chemical plants, oil exploration and production fields, beaches contaminated by oil spills, and the recovery and recycling o~ waste preservative raw materials in plants from sludges. As stated on page 3 above, this apparatus could either be fixed or mobile.

The process combines an ability to improve the ~6~73 environmental aspect by rehabilitating soils in proximity to industrial plants that use or have used polychlorinated aromatic hydrocarbons, petroleum oils or coal tar oils such as wood preservation plants that use polychlorinated aromatic compounds such as penta-, tetra and tri-chlorophenols, creosote oils and petroleum oil and coal tar distillation plants that use coal tar, with an economic aspect that restores the value of the rehabilitated land surface and recycles useful waste material if required.
The process permits the substitution of a low cost, non-toxic solvent such as CO2 for more expensive organic solvents that may present actual or future environmental problems.
The main application of the invention is the decon-tamination of soils around industrial plants and appreciation of the land values.
The main economic advantage offered by the invention is the possibility of providing a soil decontamination and waste recycling facility and process which could be either fixed or mobile depending upon the local requirement. The process includes both the specially selected and designed equipment integrated with the technology package required.
The following examples will serve to illustrate particular embodiments of the invention, but should not be construed however, to limit the invention.

A soil contaminated with ~9,OOO ppm of oils, including 400 ppm of pentachlorophenol, 3~ ppm tetachloro-phenols was revitalized by using CO2 as the super-~6~S~3 critical fluid. The extractor was operated at 60C and 4100 psi. It was found that over 90% and generally between 92 and 96% were thus removed.
EX~PLE 2 The same was conducted as in Example 1 within temp~rature ranging from 60-120C and pressures from 3100-4100 psi. Under these conditions, some revitaliz-ation was obtained but generally not bette~ than that obtained in Example 1.

Using a tubular extractor to extract contaminants from contaminated sandy soil using supercritical C02.
At 4000 psi and 81C at a CO2 flow rate of 10 L/min at STP the oil content of the soil was reduced from 29,000 ppm to 1390 ppm (95.2% extraction) in 60 minutes. Under the same conditions but at a lower C02 flow rate of 7.5 L/min the extraction dropped to 91.8%.
Sup~rcritical CO2 was thus used to effectively extract oil and pentachlorophenol and tetrachlorophenol from contaminated soil.

Eurther optimization experiments were carried out on a sample containing tetrachlorophenol as one of the main industrial waste at an extraction temperature of 120C
and at a pressure of 4000-4100 psi. The results show that no improvement can be achieved by increasing the extraction temperature from 80 to 120C. Also, the results indicate that between 85 to 90% of contaminating oils can be removed in the initial 30 minutes of C02 extraction. Th~ tetrachlorophenol extraction in the soil was between 88.~ and 94%. The concentration of tetra-chlorophenol was reduced from 3~ ppm to 2 ppm.
~AMPLES 5 to :L5 The present process for soil decontamination was carried out on eleven homogeneous examples of contaminated soil. Each of the examples contained concentrations of penta- and tetrachlorophenol of 400 ppm and 34 ppm respectively. The physical characteristics of the sample of fluid in superciritical condition ranged in temperature from 61C to 120C and in pressure from 3100-4100 psi.
As can be seen in Table 1, pentachlorophenol extrac-tion ranged from 52.5% to 97.5~ while tetrachlorophenol removal ranged from 55.9% to 99.1%.

Having described the invention, modifications will be evident to those skilled in the art without departing from the spirt of the invention, as defined in the appended claimsO

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Claims

1. A process for the decontamination of industrial waste and soil, containing at least one contaminant selected from the group consisting of dioxins and polychlorinated aromatic compounds, comprising:
a) contacting with carbon dioxide a substrate comprising at least one member of the group consisting of industrial waste and soil, contaminated with at least one contaminant selected from the group consisting of dioxins and poly-chlorinated aromatic compounds, b) increasing the pressure and temperature of said carbon dioxide above the critical temperature and pressure of carbon dioxide, to maintain said carbon dioxide fluid in supercritical state, as to dissolve into said carbon dioxide in supercritical state said at least one contamin-ant, while keeping said substrate substantially insoluble to said carbon dioxide in supercritical state fluid thereby producing a supercritical carbon dioxide fluid fraction containing said at least one contaminant and an insoluble fraction, c) separating under said supercritical state said supercritical fluid fraction containing said at least one contaminant, from said insoluble substrate forming an insoluble fraction, d) reducing the pressure in said insoluble fraction to subcritical pressure to obtain a decontaminated substrate and trace amounts of the ecologically compatible carbon dioxide, e) reducing the pressure of said supercritical fluid carbon dioxide containing said at least one contaminant to subcritical pressure, to cause said at least one contaminant to precipitate out and separate from said carbon dioxide.

2. A process according to claim 1, wherein the step e) is carried out by a gradual decrease in pressure in order to obtain fractional separation of the components forming said at least one contaminant.

3. The process as defined in claim 1 wherein in step b), said temperature ranges between 41 and 130°C and said pressure between 3000 and 5000 psi.

4. The process as defined in claim 3 wherein the temperature is between 50 and 120°C.

5. A process as defined in claim 1 wherein said at least one contaminant comprises tetrachlorophenol and pentachlorophenol.

6. The process as defined in claim 5 wherein the contact with said soil under supercritical conditions is conducted at a temperature ranging between 60°C and 120°C and a pressure ranging from 3100 to 4100 psi.

7. The process as defined in claim 1,3 or 5 wherein said substrate is soil.

8. The process as defined in claim 1,3 or 5 wherein said substrate is wood shavings.

9. The process as defined in claim 1,3 or 5 wherein said substrate is sludges.

10. The process as defined in claim 1,3 or 5 wherein said substrate is waste preservative.

11. The process as defined in claim 1,3 or 5 to remove oil and polychlorinated aromatic compounds from soil.

12. The process as defined in claim 1 or 5 wherein the temperature is about 81°C.

13. The process as defined in claim 1,3 or 4 wherein said contact of said substrate with said carbon dioxide in step b) is 2 to 30 minutes.

14. The process as defined in claim 1,3 or 4 wherein said contact of said substrate with said carbon dioxide in step b) is between 10 minutes and an hour.

15. The process as defined in claim 1,3 or 5 wherein turbulence is created in step b) to mix the carbon dioxide in supercritical state to the substrate.

16. The process as defined in claim 5 wherein said contact of said substrate with said carbon dioxide is for a period of about an hour, and wherein between 85 to 95%
of said tetrachlorophenol and said pentachlorophenol are removed.

17. The method as defined in claim 1 wherein said step e) is conducted under gradual reduced pressure to obtain contaminant by fractions.

18. A process for the decontamination of industrial waste and soil containing at least one contaminant selected from the group consisting of dioxins and polychlorinated aromatic compounds, comprising: feeding to a staged pressurized extractor at least one member selected from the group consisting of industrial waste and soil contaminated with at least one contaminant selected from the group consisting of dioxins and polychlorinated aromatic compounds, feeding into said extractor carbon dioxide, maintaining said carbon dioxide with said member, in said extractor at temperature between 60 and 120°C
under a pressure from 3100 to 4100 psi under supercritical state, and agitation for a period of between 20 and 60 minutes, filtering the resulting supercritical fluid, flashing out said filtered fluid to obtain there from said supercritical fluid containing said contaminant, and collecting as the unfilterable fraction said at least one member decontaminated.

19. The process as defined in claim 18 wherein said at least one contaminant comprises tetrachlorophenol and pentachlorophenol.

20. The process as defined in claim 18 wherein said at least contaminant comprises at least one of the members selected from the class consisting of tetrachlorophenol and pentachlorophenols, and wherein between 85 to 95% of said tetrachlorophenol and pentachlorophenol are removed.

21. The process as defined in claim 18 wherein said member selected from the group consisting of industrial waste and soil, comprises soil containing contaminants and waste products and the process yield a decontaminated earth without substantial depletion of valuable nutrients contained in said soil.

22. The process as defined in claims 1,18 and 21 wherein said member comprises sludges.

23. The process as defined in claims 1,18 and 21 which further includes at least one member selected from the group consisting of petroleum oils and coal tar based creosotes in said member selected from the group consisting of industrial waste and soil.

24. The process as defined in claims 1, 18 and 21 wherein a continuous flow of carbon dioxide is provided for a higher concentration gradient between the carbon dioxide and said member selected from the group consisting of industrial waste and soil.

25. The process as defined in claims 1,18 and 21 which includes waste wood preservatives in said member selected from the group consisting of industrial waste and soil.

26. An apparatus for the decontamination of industrial waste and soil containing at least one contaminant selected from the group consisting of dioxins and polychlorinated aromatic compounds, comprising: a staged pressurized extractor, means of feeding to said staged pressurized extractor at least one member selected from the group consisting of industrial waste and soil, said member being contaminated with at least one contaminant selected from the group consisting of dioxins and polychlorinated aromatic compounds, means of feeding into said extractor carbon dioxide, heating and pressure means for maintaining in said staged pressurized extractor said carbon dioxide with said member under supercritical state, and agitation means for contacting said at least one member with said carbon dioxide in supercritical state to obtain therefrom said supercritical fluid containing said contaminant, means of filtering the resulting super-critical fluid to obtain said filtered fluid containing said contaminant, pressure releasing means for flashing out to separate said filtered fluid from said contaminant, and means of removing the unfilterable fraction, said unfilterable fraction being said member decontaminated.

27. The apparatus as defined in claim 26 wherein said pressure releasing means consists in a plurality of gradually decreasing pressure zones mounted in series, said zones being provided with means for delivering liquid collected in said zones as to fractionally recuperate the various waste products.