DE4208591C2 - Process for cleaning contaminated soil - Google Patents

Description

The invention relates to a method for cleaning with or ganic contaminants contaminated soil at fortlau fender revolution and water vapor exposure to the earth rich.

In the present case, the term "earth" is used together slope other than soil and soil in the narrower sense granular solids or sludges, such as residues from others Floor washing systems, adsorbents and the like, understood, the, e.g. B. for reasons of environmental protection. Hydraulic and. Are available for decontamination of contaminated sites pneumatic measures, chemical / physical and biolo gische procedures as well as the thermal treatment available supply.  

Thermal cleaning processes are common to all organic as well as for volatile inorganic impurities and have the highest efficiency. In contrast to time-consuming biological processes, the renovation success is short to be reached on time and relatively easy to control. Of the Advantage over floor washing systems on chemical / physical agents The complete basis also lies in the listic basis of the pollutants that adsorbs into the fine and very fine grain are. In contrast, floor washing processes have a principle mandatory application limit for silt portions of the soil of greater than about 20%. The highly contaminated fine grain fraction cannot be decontaminated by washing the floor, but is to be disposed of elsewhere as a residue.

A thermal process for cleaning with hydro contaminated soil is described in DE 36 04 761 A1 specified. The cleaning is achieved by the Er heating of the soil to the boiling temperature of the contained therein NEN pollutants at about atmospheric pressure. The required Liche heat is supplied indirectly. To remove the An inert carrier gas is used for pollutant gases. The end inert carrier gas, water vapor and hydrocarbons best The resulting mixture can then be fractionally distilled the. With this method, the soil is heated to around 400 ° C heated.

DE 37 06 684 A1 describes a method for thermal ab separate volatile pollutants from contaminated soil described. Here, the soil together with its  Water content in a rotary kiln with the help of superheated steam gradually heated to 200 to 700 ° C so that the volatile Evaporate pollutants. The resulting things Gases containing steam and pollutants are then added eats condensation, and the main part of what serdampfes is condensed out of the system and withdrawn and be wet chemical or physical from the pollutants free. Only pollutants can be removed using this process separate that cursed at the specified temperatures are active.

Non-volatile contaminants can be classified according to the state technology only at the high temperatures of pyrolysis and Combustion process - in the range from 350 to 1200 ° C - split off; these temperatures do not only effect the Decomposition of anthropogenic impurities (pollutants), but also the destruction of the natural organic Soil constituents (useful substances), that means above all the Hu minerals. Soils pretreated in this way are therefore only after additional processing can be used as a plant substrate.

Furthermore, the contamina transferred into the gas phase tion in thermal processes usually directly or in separate units burned. The downstream flue gas cleaning exceeds in terms of plant technology and knockout most clearly the corresponding values of the primary step, that is, the actual cleaning process. Cost-intensive measures for dust separation, for che mix laundry, for denitrification and for the adsorption of  Heavy metals and ultra poison from the exhaust gas flow lead to Cleaning costs of 500, - DM / t contaminated soil and more. Finally, the thermal cleaning process because of the emission of Ul tragacs (ecotoxicological organic substances) over the Exhaust gas flow from large parts of the population is not acceptable animals.

In the unpublished DE 40 30 416 A1 a Ver drive to decontaminate contaminated soils wrote the floor in a first treatment stage dried with a hot gas and then in a second treatment stage with a desorption medium, e.g. B. heated steam is flushed out. Furthermore, in the Document spoken of strip gases by desorption or the strip gases can impurities from the respective be washed out to the floor. But driving out requires an evaporation of the respective contamination at their normal boiling point. The necessary in many cases temperatures lead to the destruction of natural organic soil components.  

From US 41 79 462 is a method for cleaning the drill small of oil drilling in a non-oxidizing atmosphere sphere known. In this process, organically dead people are killed Materials cleaned; a consideration of any organization There is apparently no question of any useful materials.

Furthermore, from US 36 54 705 a method for drying egg nes known material in the contained in the material Vaporizing substances by applying heat and using a Gas flow are discharged. In the known drying process The substances to be evaporated must therefore conform to their norm le boiling temperature to be heated.

The invention has for its object a thermal To create cleaning process, which has the advantages of a high efficiency, a wide field of application and short has renovation periods without the often high boiling points temperatures of the organic pollutants to be expelled would be put.

The solution according to the invention is specified in claim 1 ben. The invention decouples the Dampfver need for cleaning the soil on the one hand and the Fluidization, on the other hand, is achieved so that less Steam consumption (only the one actually needed for the extraction steam) is required.  

According to the organic pollutants after Principle of steam distillation with the help of a continuously ver in the sense of an increase in surface area swirled soil continuously conducted water vapor flow driven out of the ground and separated. The earth is mechanically "swirled" so that it is the water vapor flow offers the largest possible surface. The more careful that  Soil is swirled, the faster the orga can niche pollutants except for the prescribed rest be extracted. A in the sense of the procedure according to the invention sufficient swirling is achieved in a reactor, whose internals work sufficiently quickly. So it's enough not a simple circulation like in a rotary kiln, rather, such a spatial distribution of the individual Particles of the soil desirable - especially in the back efficiency and economy - that of the kitchen Mixing mechanism of steam distillation practically in the entire volume of the reactor and practically at the same time on all particles to be cleaned can take place.

The extraction of organically contaminated gusts according to the invention the or residues with the help of water vapor conventional thermal cleaning methods common that a Transfer of pollutants from the liquid or adsorbed Condition in the vapor or gas phase. However works the water vapor extraction used according to the invention in space mean already satisfactory at temperatures considerably below 200 ° C, at most with very low volatile contamina tions, e.g. B. with tar residues, higher operating temperatures temperatures up to about 300 ° C in question. On the oxidative - and limited also with known pyrolytic working thermal process necessary high temperature level - in DE 37 06 684 A1 mentioned are still 200 to 700 ° C. preferred - can therefore be dispensed with. The invention low be preferably between 100 and 200 ° C. drive temperatures lead to significantly lower changes  of the physical and chemical soil structure and lower operating costs of the cleaning process.

In the method according to the invention, the ver vortexed water vapor flow preferentially held at a pressure of (0.1 to 7) 10⁵ Pa. The amount of Depending on the type of contamination, pressure is in the sense of a faster reaction, especially H₂O addition, or in Adjusted to lower the boiling point. In practice tical operation, the pressure is generally close to the Nor painting pressure of 10⁵ Pa. Pressures are preferred from (1 to 1.5) 10⁵ Pa. If, especially at normally very high-boiling contaminations, an additional boil point lowering is desired, it can be according to further Er be favorable, the operating pressure in the reactor, that is Operating pressure of water vapor, down to 10 Werte Lower Pa. As such, one would think that in the present Does this relate to one another through steam distillation lowering of the boiling point and that caused by negative pressure just add justified boiling point depression, over  It has been surprising when testing the method shows that lowering the pressure below 10⁵ Pa also a Improving the efficiency of steam distillation itself results. In this sense, it can be in many ways be favorable, the water vapor pressure in one generally preferred range from (0.1 to 1.5) 10⁵ Pa despite the additional effort for sealing in one area lower more or less below 10⁵ Pa. At all for various reasons it is operating pressures according to another inven  advantageous if the water vapor used is not sown is done. In particular, saturated steam should not normally superheated steam is preferred.

The use of steam is one at all, if not that essential feature of the invention. The steam serves according to the invention not primarily for heating the in poss Smallest particles swirling cleaning substance, son to seemingly lower the boiling point of this substance put. According to the invention, it is therefore not one more or more less liquid, possibly like in a rotary kiln slowly circulating swamp heated with the help of steam, such that contamination present in the liquid sump evaporate due to the higher bottom temperature, but they become those in the whirled up particles of the earth contained contamination molecules or the like by Um shell with H₂O molecules driven out of the particles and transported away with the steam.

Basis of the method for floor cleaning according to the invention with water vapor is the application of one in large chemical set steam distillation. This is the most important special case of so-called carrier steam stillation with which high-boiling, hydrophobic substances often have it separated at 100 ° C. Because of their egg Such substances normally show a very high boiling point sometimes by itself a correspondingly low one Vapor pressure, which is common with the water vapor pressure added to the total pressure (cf. Dalton's law of  Partial pressures). With steam distillation, however, occurs a solvation and consequently a considerable boiling point lowering the point of organic pollutants. The mole coolers of the substance to be distilled are namely through Water molecules enveloped, making their real chemical Character is masked. These "quasi-water atoms" can distill off at relatively low temperatures.

In chemical engineering, steam distillation takes place neither in mixtures with water or by blowing what Steam into the bubble sump (still). The water Steam distillation is carried out in the laboratory, e.g. B. in the nitrogen mood according to Kjeldahl, or in the representation of quinone puts. In technology it is used for fatty acids refining and in the production of essential oils and Essences.

When using the steam treatment according to the invention for soil remediation it was found that not only - how expected - volatile, but surprisingly difficult volatile organic pollutants according to the relevant State of the art of separation by distillation from earth rich - at the temperatures used - not at all should be accessible, must be separated without residue and that the treated soil is practically unchanged in its physical properties, e.g. B. regarding grain sizes distribution, remains. Another advantage is - as I said - still surprisingly, the useful substances are essentially remain. This unforeseen effect does that  Steam cleaning of the type according to the invention is particularly worthwhile full, because it contains the humine embedded in the soil matrix gentle on fabrics.

Another essential advantage of the inventive Rei cleaning process results when separating the organic Water vapor pollutants following extraction from the ground. A complex multi-stage gas scrubbing is namely not required in the water vapor process according to the invention derlich if the in the aforementioned first procedure step separated or removed with the steam gan pollutants according to another invention in one two th process step in the presence of water vapor Use of temperatures up to about 500 ° C and pressures of cracked up to 7 10⁵ Pa, i.e. chemically split and / or being transformed. The water vapor as a carrier component thus free again and can return to water in the cycle steam distillation can be used. Alternatively, the vapors laden with pollutants already separated from the ground by the way, even in the first process step alone -  without the second process step, cracking, kon densify.

The pollutants already separated from the soil can un The supply of oxygen or air largely in simpler, essentially harmless substances converted or added will split. The pollutants can also go directly to H₂O, CO₂, NH₃ or sulfur-containing or halogenated orga African substances implemented in the corresponding mineral acids become.

Those with the water vapor at the low temperatures organic soil expelled from the contaminated soil Pollutants are preferably in a single apparatus or in a single container with a colder zone up to to about 200 ° C and a hot zone up to about 500 ° C the temperature intended for the cracking and Brought pressure values. Accordingly, the organic Steam splitting pollutants - additional if necessary too simple under oxidative reaction conditions - not or less toxic molecules such as alcohols, ammonia, Decomposes carbon dioxide and / or water. Alcohols are created halogenated by hydrolysis, for example Hydrocarbons. Organic nitriles can with water higher temperatures to corresponding carboxylic acid amines or Carboxylic acids are saponified.  

The inventive method for extracting the orga niche pollutants can in the same reaction vessel as that downstream process for splitting or converting the organic pollutants occur when the respective reak a correspondingly colder zone and a suitable one hotter zone. Basically, e.g. B. if difference liche pressures are desired, it is also possible to use the two Process steps in two consecutive react execution units. Then in the first unit the contaminated soil is brought in and under constant Circulation by steam distillation from the organic Free pollutants. The opening takes place in the second unit cleavage and / or conversion of the mitge with the water vapor resulted in organic pollutants.

During the first process step for possible humine substances and the like in essentially harmless tempera tures can be carried out in the second step much higher temperatures are used because it is here only about the conversion or decomposition of the organic Pollutants go and no longer adversely affect useful materials can be flowed. To save energy and if necessary however, it can be beneficial to improve efficiency be adhering to the process of the invention final conversion step a catalyst or a Use reaction mass.  

When using the extraction process, the grain size of the materials to be cleaned in a range of 0.001 to 20 mm include. With these granular values it is sufficient accordingly short diffusion paths for water vapor on the one hand and the organic pollutants to be separated on the other hand ge guarantee.  

Based on exemplary embodiments and drawings tere details of the invention explained. Show it:

Figure 1 is a plant for water vapor extraction organically contaminated soils and the like.

Figure 2 is an ion current chromatogram showing the contamination of a soil sample prior to treatment.

Fig. 3 is an ion current chromatogram of the bottom of Fig. 2 after treatment (T = 100 ° C, p = 1 bar);

Fig. 4 is an ion current chromatogram of the condensate of Fig. 3 during the first thirty minutes;

Fig. 5 is an ionic flow chromatogram of the condensate of Fig. 3 during the half hour following the first 30 minutes after the start of the extraction;

Fig. 6 is an ionic flow chromatogram of the condensate of Fig. 3 from sixty to one hundred and twenty minutes after the start of extraction;

Fig. 7 is an ion current chromatogram showing the contamination of a water sample prepared in the laboratory before the steam distillation to be carried out for detoxification;

Fig. 8 is a Ionenstromchromatogramm by steam distillation over silica glass at T = 500 ° C ei nes condensate obtained from the water sample shown in FIG. 7;

FIG. 9 shows an ion flow chromatogram after water vapor distillation over copper at T = 500 ° C. from the condensate obtained from the water sample according to FIG. 7; and

Fig. 10 is an ion current chromatogram, which represents the residual contamination of the distillation bottoms of the water sample of Fig. 7.

The water vapor extraction according to the invention of an organically contaminated soil is described below in a first example ( FIGS. 2 to 6). In a second example ( FIGS. 7 to 10) results of the detoxification of organic contaminations of a water vapor stream are given.

Fig. 1 shows a test facility for water vapor extraction of organically contaminated soils or residues. With the aid of a steam generator 1 , steam 2 is passed via a valve 3 into a (heated) reaction mixer 4 . In the reaction mixer 4 5 contaminated solid material 6 , z. B. contaminated soil, worn in the direction of the arrow. On the output side 7 , the cleaned solid material 8 is discharged in the direction of the arrow. Within the mixer 4 , the introduced solid 6 is constantly swirled with the help of blades 9 , so that new surfaces of the granular solid matter are continuously formed. At the same time, the water vapor 2 is continuously passed directly through the swirled solid. The reac tion mixer 4 of FIG. 1 has a heating mantle with a passage 11 and outlet 12 for a heating medium, for example. B. steam.

The reaction used in Fig. 1 for treating soil mixer 4 may be charged with a conventional steam generator 1 with preferably Bulb temperature steam system. After flowing through the solid in the reac tion mixer 4 , the vapors laden with the contamination can be passed via a line 13 - possibly with a valve 14 - into a condenser 15 , where they are deposited and subjected to a phase separation in a parallel plate separator (not shown). The condensate 16 can leave the condenser 15 via an output 17 . The valve 14 , like the valve 3 , serves to set or maintain a specific vapor state in the reaction mixer 4 .

example 1 Water vapor extraction from an organically contaminated soil (first stage of the process)

The investigations were based on a system according to FIG. 1. Contaminated soil from an old deposit site was used as the feed material (solid). Before the treatment, the floor had a dark brown to black appearance and consisted mainly of medium sand with gritty and slightly silty secondary components. Table 1 shows the chemical parameters of the sample used on the contaminated site.

Table 1

Chemical parameters of the sample used

In addition, the soil was treated with a phenol mix (tracer) artificially contaminated. It is a mixture cher mass fractions of 2-chlorophenol, 2,4-dichlorophenol, m -Cresol, 2,4,6-trichlorophenol with boiling points between 180 and 230 ° C. The soil was acidified to pH 3 with H₃PO₄.

The Figs. 2 to 6 show Ionenstromchromatogramme of the extracts of the soil before and after treatment, as well as the densatproben Various NEN during the experimental period continuously drawn kon. The abscissa represents the retention time (time steps) of the sample constituents. The intensity value noted on the right ordinate is used to compare different chromatograms. Identical or similar numerical values allow a direct comparison of the peak heights and thus also a first approximation of the concentration. The detected relative ion current (RIC) is plotted on the left ordinate. The highest recorded peak is automatically assigned the value 100%.

In addition to specifying the total chemical parameters of the contaminated soil in Table 1, the chromatogram of FIG. 2 (soil before treatment) allows the contamination spectrum to be characterized. In Figs. 2 to 6 denote:
1 o-cresol
2 2-chlorophenol
3 2,4-dichlorophenol
4 2,4,6-trichlorophenol
5 C₁₂H₂₆
6 C₁₃H₂₈
7 C₁₄H₃₀
8 C₁₅H₃₂
9 C₁₆H₃₄
10 C₁₇H₃₆
11 tributyl phosphate
12 hexaclorobenzene (HCB)
DCB dichlorobenzene isomers

Before the steam treatment, various alkanes are C₁₂ to  C₁₇, hexachlorobenzene (original contamination) and tributyl phosphate (plasticizer) detected. The shares of the at un treated soil added phenol mix (0.4 g / kg) approximately recovered using GD / EDC analysis (GD / EDC = Gas Chromatography / Electron Detecture Capture).

The relevant process parameters are summarized below:
Weight: 90 kg soil sample
Contamination: approx.8.5 g / kg KW (KW = hydrocarbon). Additional doping with 0.4 g / kg phenol mix.
Reactor pressure / temperature: p in 10⁵ Pa, T = 100 ° C.
Steam throughput: mp = 65 kg / h
Test duration: 120 minutes
Soil sampling: before / after trial
Sampling condensate: mixed samples 0-30 ′, 30-60 ′, 60-120 ′.

The analysis of the soil sample after the steam treatment at T = 100 ° C and p = 10⁵ Pa shows a completely different picture than the starting material according to Fig. 3 (soil after treatment).

The alkanes found before treatment are as well as the "Mountain" of alkane degradation products, except for the slightest residue C₁₄ and C₁₅ disappeared. This also applies to hexachlor benzene too. The tracer substances (phenol mix) are up to below depleted the detection limit. Only the plasticizer opposes water vapor extraction.

The analyzes of the condensates obtained reflect the depletion of the soil with regard to contamination. A majority of the alkanes, their biodegradation products ("mountain"), are found in the condensate mixed sample (0-30 min; Fig. 4, T = 100 ° C, p = 10⁵ Pa) from the first thirty minutes Hexachlorobenzene (boiling point 322 ° C) as well as the tracer substances. Furthermore, 9-ethylcarbazole can be identified as a nitrogen-containing compound. Dichlorobenzene, which has also been detected, can be attributed to residues from other test series.

This contamination spectrum continues to weaken in the extracts of the further condensate samples (T = 100 ° C, p = 10⁵ Pa) ( Fig. 5 and 6; condensate from the period 30'- 60 'or 60'-120' after the start extraction).

Tributyl phosphate was not driven out of the soil ( Fig. 2 and 3), nor is it found in the condensate or water samples ( Fig. 4 to 6).

The condensate of the first half hour (0-30 ′) is rough contain approximately 90% of the contamination. Between thirty and sixty minutes (30'3-60 ') after the start of the Wasserdampfbe action will be 5-8%, in the following sixty to hun Twenty minutes (60'-120 ') only 2 to 5% of the Contamination found.

Example 1 shows that when using steam with  100 ° C the entire existing contamination spectrum from the Soil could be removed. Even existing curses term substances were released to below the detection limit drove. For example, all hydrocarbons and Hexachlorobenzene as an example of less volatile impurities after two hours of treatment over 98% removed. Be Already at a steam temperature of 100 ° C the as Tracer used chlorinated phenols completely expelled.

Example 2 Detoxification of organic contaminants in the water vapor stream (second stage of the process)

In laboratory tests, water was mixed with contaminants, here halogen-organic compounds ( FIG. 7, contamination of the water sample before steam distillation). A laboratory apparatus was loaded with this mixture. The following substances are identified in FIGS. 7 to 10:
1 hexachlorobutadiene
2 tetrachlorobenzene
3 hexachlorocycloheptadiene
4 tetrachlorobenzene
5 bromotrichlorobenzene
6 pentachlorobenzene
7 hexachlorobenzene
8 octachlorophthalene
X₁-X₁₀ other halogenated substances present
X _N newly formed halogenated substance,
p phthalate

In the equipment loaded with the prepared mixture was steam at a temperature of 100 ° C under Nor painting started. The emerging, with contamination loaded steam then entered a quartz U-tube (Length 80 cm, diameter 1.8 cm) and was at 500 ° C heated (tube furnace). The superheated steam was then condensed in a cooler, the condensate was on Brought to room temperature.

Two different variants were tested in the tests:

• a) Steam distillation over quartz at 500 ° C
• b) Ditto, but over copper granulate (⌀ around 1 mm)

FIG. 8 shows the spectrum of substances found in the condensed vapors after flowing through the quartz glass tube (condensate after steam distillation over quartz glass at T = 500 ° C.).

The condensates were worked up by stirring with a mixture of hexane and acetone (9: 1). After drying over Na₂SO₄ the extracts were turned into a volume of 1 ml tight. The analysis was carried out using GC / MS (Gas Chromatography / Mass Spectrometry). The volume of the same treated Reference solution (contamination without water vapor treatment) be  carried 0.5 ml, which means the solution was twice as concentrated like that of the extracts.

The presence of alkylated aromatics as well as the occurrence of polyaromatic compounds, such as. B. naphthalene, in Condensate from the distillation experiment over quartz glass means that carbon-halogen bonds broken in the molecules were. The mean residence time of the steam in the hot Quartz U-tube was around 1 second.

Even if the contamination occurs in the test described reasonable, as due to the short exposure time of the high tem expected temperature, have hardly decreased, let this result agree that if the Steam in the hot zone of the apparatus an increasing number break of carbon-halogen bonds and thus the ver bonds to less toxic substances are broken down can.

When using a catalytically active element, such as copper (variant b), the decrease in quantity relative to the originally present contamination levels is evident ( Fig. 9: condensate after steam distillation over copper at T = 500 ° C). Thus, compounds such as hexachlorobutane, the highly chlorinated compound octachloronaphthalene and the halogenated compound X₉ ( FIG. 7) are completely absent. A comparison with the ingredients (residual contamination) of the distillation sump ( Fig. 10) excludes that this could be the result of an apparent degradation caused by incomplete steam distillation. Substances with comparable retention times and mass spectra are identified in the same way in all chromatograms.

The Al. Found during the distillation over quartz glass alkyl compounds can no longer be detected. That means for further destruction or dechlorination of the ent speaking molecules both through the catalytic effect of copper as well as due to the longer dwell time the lower permeability of the related copper granules there. The mean stay was around 2 to 3 Seconds. Here too, the result is longer Exposure time an even higher efficiency.

All in all, the tests with Konta typical of contaminated sites showed minations that the process is simple, not optimized version for the targeted detoxification of water steam flow of expelled pollutants is advantageous. The experiments prove that the detoxification halo genomic compounds in certain reaction conditions gene by the appearance of carbon-halogen bond bridges Chen can be carried out successfully.

Claims (8)

1. Process for cleaning with organic pollutants contaminated soil where the soil is heated in a th and discontinuously operated reaction mixer with Help from shovels mechanically to distribution on the entire volume of the reaction mixer is fluidized and the organic pollutants with the help of a such swirled soil continuously conducted water steam flow are expelled and separated. 2. The method according to claim 1, characterized, that unsaturated water vapor is used. 3. The method according to claim 1 or 2, characterized, that a water vapor flow of 100 to 200 ° C through the tangle belte soil is conducted. 4. The method according to any one of claims 1 to 3, characterized,  that the water vapor flow with (0.1 to 7) 10⁵ Pa, in particular with (0.1 to 1.5) 10⁵ Pa through the swirled earth is leading. 5. The method according to any one of claims 1 to 4, characterized, that the separated in a first step and organic pollutants removed with water vapor a second process step in the presence of the steam fes and at temperatures up to about 500 ° C and pressures up to chemically split and / or converted to about 7 10⁵ Pa become. 6. The method according to claim 5, characterized, that the second process step with the addition of oxygen or air is running. 7. The method according to any one of claims 5 or 6, characterized, that the splitting or conversion of the organic pollutants in the second process step using a catalyst or a reaction mass is executed. 8. The method according to any one of claims 1 to 7, characterized,  that each part of the water vapor is circulated and another part of the water vapor is condensed.