WO2006122537A1

WO2006122537A1 - Method for decontaminating cyanide-containing soils/aquifers and groundwaters

Info

Publication number: WO2006122537A1
Application number: PCT/DE2006/000861
Authority: WO
Inventors: Peter Harborth; Martin Kucklick; Helmut Hanert; Matthias Thieme
Original assignee: Technische Universität Braunschweig
Priority date: 2005-05-18
Filing date: 2006-05-18
Publication date: 2006-11-23
Also published as: DE112006002039A5; DE102005023598A1; EP1883608A1

Abstract

The invention relates to a method for decontaminating cyanide-containing media, particularly soils, aquifers and groundwaters, comprising the step of dosing in nitrate. The invention particularly relates to a method during which, in addition to the nitrate, agents for aerobic oxidation are dosed into the cyanide-containing media.

Description

PROCESS FOR DECONTAMINATING CYANIDE-CONTAINING FLOORS / AQUIFERES AND GREEN WATERS

description

The present invention relates to methods for the decontamination of cyanide-containing media, such as soils, aquifers and / or groundwaters, in particular of cyanide-containing soils. The methods of the invention include the step of nitrating the contaminated areas of both contaminated water and contaminated soil. Preferably, the method for decontamination of cyanide-containing media, such as soils, aquifers and groundwaters, comprises the simultaneous metering of nitrate and peroxides, such as hydrogen peroxide, to the area to be decontaminated.

State of the art

Numerous industrial processes, such as electroplating processes, plastics production, coking plants, pig iron production, etc., employ cyanides, i. Hydrocyanic acid and its salts, free. These cyanides then get into the ground due to improper handling or direct deposition of residues on the premises and thus contaminate the soil area of these sites. The cyanides can be present both in free and in complexed form. A typical example of contaminated areas are former gasworks sites as well as coking plants, e.g. through used gas cleaner masses. Frequently, these cyanide concentrations occur in compounds with other impurities, such as organic, in particular polycyclic and halogenated hydrocarbons.

Many areas of contamination are located in an area of dense development, so that, for example, excavated soil or processes that shift pollutants from the soil into aquifers, sewage or the atmosphere, are not suitable. Especially in large areas contaminated areas excavation is not possible, or it is due to the depth of the decontaminated area consuming measures, such as the watertight confinement, to prevent ingress of groundwater necessary.

From wastewater treatment, it is known that some complexed cyanides are particularly stable. It is described in the literature that the iron complex of cyanides is virtually unaffected by H ₂ O ₂ . The iron-cyanide complexes are among the most stable cyanide compounds, which, however, regularly prevail in the iron-rich soils and especially in former gas works (gas purification by means of iron ore filters). In contrast, the cyanide pollution in old sites is usually toxicologically unproblematic, since from a toxicological point of view primarily the free hydrogen cyanide is of particular importance. However, the cyanide levels are extremely persistent due to complexation and its inherent stability. By changing the environmental conditions, eg by photooxidation, influence of acidic or basic liquids, etc., a later release of hydrogen cyanide from these complexes can not be excluded. Although these contaminations are not an acute hazard, these soils pose a high risk potential and must therefore be decontaminated.

For the treatment of cyanide-containing industrial wastewater, i. There are basically 6 options for cyanide detoxification:

1. Chemical oxidation (e.g., sodium hypochlorite)

This process has the disadvantage of producing chlorinated compounds which now also contaminate soils, aquifers or groundwaters. In addition, very severe oxidative conditions for cyanide destruction are necessary. Producing these conditions in an open area is costly and risky and involves the above-mentioned disadvantages of chlorinated compound contamination. 2. Electrochemical oxidation

This method is straight in situ in open terrain can not be used and expensive.

3. Photochemical oxidation

Also, this method is not applicable on a large scale in open terrain and costly.

4. detoxification by precipitation

Cyanide precipitation can be an effective technique for purifying groundwater. However, it leaves most of the cyanides in precipitated form in the decontaminated area, so that there is still the risk of a later remobilization.

5. Thermal decomposition

The thermal decomposition comes only for smaller amounts of soil, e.g. ausgekoffertem material, used. For large-scale applications in open terrain, in particular the in situ application, this method is not suitable.

6. deposition by means of ion exchanger

The cyanide deposition by means of ion exchangers is occasionally carried out on site, but is extremely expensive because the anion exchangers nonspecifically absorb all anions of the terrain and therefore have only a low absorption capacity. The use of nitrate in the decontamination of organic compounds, for example BTEX, MKW and especially solvent contaminants, is known in the art. For example, nitrate is added to the water to be purified to serve as an electron acceptor for the microbial anoxic degradation of aliphatic and aromatic hydrocarbons. In this degradation of aliphatic and aromatic hydrocarbons, the nitrate also serves as a source of nitrogen for the microorganisms. Nitrate is particularly preferably used because it is easily introduced in large quantities and very inexpensive. However, the use of nitrate has the disadvantage that the reaction produces intermediately toxic nitrite. This nitrite can again be a problem substance in the soil, aquifer or groundwater. Therefore, the use of nitrate for denitrification is limited. Incidentally, denitrification is also referred to as anoxic bioremediation. A use of nitrate is therefore hitherto only for the treatment of organic compounds, such as halogenated or nitrated hydrocarbons in treated soils, such as soil rental or in on site processes, eg DE 4117513, for example in a slurry reactor called. However, the process described there requires a chemical-physical pretreatment of the soil. The process described in DE 4117513 furthermore requires the addition of appropriate cultures which serve for denitrification. Such a method, as described in DE 4117513, is therefore not applicable in situ. However, the use of nitrate for decontamination of cyanides in loaded masses has not been described in any way so far.

The present invention is therefore based on the problem to provide a method for the decontamination of cyanide-containing media or substrates, such as soils, aquifers and / or groundwaters, which allows the degradation of free and complexed cyanides. In particular, this process should enable in situ decontamination of cyanide-containing soils, aquifers and / or groundwaters. Furthermore, the cyanide-contaminated terrain should be decontaminated cost-effective and sustainable so far that even with later changed environmental conditions, such as after a Erdaushub, no toxic compounds can be set free. In the following, only the term "medium or media" will be used for the various forms of media and substrates. Furthermore, the inventive method for decomposing cyanides must be designed so that the method can be integrated into existing rehabilitation concepts without much additional effort, since the cyanides are usually part of complex mixed contaminants. These mixed contaminants include aliphatic and aromatic hydrocarbons, eg tar products. The process should destroy as much as possible the free and easily releasable cyanides as well as the complexed cyanides without contamination by other substances.

Based on this problem, the inventive method is characterized in that for the decontamination of cyanide-containing media, such as soils, aquifers and / or groundwater nitrate in the cyanide-containing media, such as soils, aquifers and / or groundwater is metered. Surprisingly, it has been found that free and readily releasable cyanides are broken down by metering in nitrate. This was particularly surprising since it was assumed that the nitrogen from the cyanides serves as an N source in the case of microbial degradation and therefore that the nitrate, which usually also serves as a nitrogen source in bioremediation, would not be usable here. The use of nitrate still has considerable economic advantages over the previously known methods.

By combining this chemical oxidation by peroxide with anoxic bioremediation (denitrification) by dosed nitrate, it is possible to destroy both free cyanides and complexed cyanides.

In a preferred embodiment, peroxides are thus further metered into the cyanide-containing media. Examples include peroxides, such as perborates, percarbonates, organic peroxy compounds, such as peracetic acid, and particularly preferably hydrogen peroxide (H2O ₂ ) called.

Particularly advantageous is a simultaneous dosing of nitrate and peroxide, in particular hydrogen peroxide, in the cyanide-containing media, such as soils, aquifers and / or groundwaters. In a further embodiment of the method according to the invention, the metered addition of the nitrate can take place in a first step alone, especially to destroy free and easily releasable cyanides. In a second step, then nitrate and peroxide such as H2O _2, metered simultaneously, so that complexed cyanide also released and then immediately destroyed.

The use of the chemical oxidant peroxide, such as H ₂ O ₂ , allows the destruction of free cyanides as well as a part of the complexed cyanides. However, the disadvantage of peroxide use is a strong mobilizing effect on, inter alia, the complexed cyanides from the solid portions of the samples to be treated. Such a possibility of mobilization of complexed cyanides is not yet known. By simultaneous dosing of nitrate for denitrification, this strong mobilizing effect of peroxides, such as H ₂ O ₂ can be compensated for the cyanides, so that no free cyanide is released, for example, in the aquifers or effluents.

The simultaneous dosage of peroxides, such as H ₂ O ₂ , and nitrate has proven to be particularly advantageous, although these two processes are physiologically in competition. The use of peroxides such as H ₂ O ₂ results in aerobic oxidation while the use of nitrates causes anoxic denitrification. The simultaneous dosing of eg H ₂ O ₂ / nitrate leads for the first time to a complete decontamination of the groundwater of free and complexed cyanides and at the same time to a cleaning of the soil below the required limits. The two components peroxide, such as H ₂ O ₂ , and nitrate complement each other in an ideal manner, so that there is neither cyanide mobilization and release nor precipitation. Instead, the chemically mobilized cyanides are degraded immediately and completely under anoxic conditions. It turned out surprisingly that the denitrification takes place even in the presence of peroxides, such as H ₂ O ₂ .

The process according to the invention can be designed such that nitrate is metered in in a first step and, in a subsequent step, the nitrate is metered in simultaneously with the peroxide, such as H ₂ O ₂ . In a further embodiment, the metered addition of nitrate and peroxide can be carried out simultaneously, without the sole addition of nitrate in a preceding step. The The inventive method is suitable for in-situ decontamination as well as for on-site decontamination, such as in regeneration rents. In this case, in situ decontamination is particularly preferred.

The previously known methods for decontamination of cyanide-containing media, such as soils, aquifers and / or groundwaters were not suitable for use in situ, but usually required a Auskoffern or excavation of the contaminated areas to this excavation then z. to treat on site. The contaminated areas are subjected to on-site chemical-physical pretreatment, which is not possible in an in situ process. According to the invention, such a chemical-physical pretreatment is not necessary. In a preferred embodiment, no chemical-physical pretreatment of the contaminated media takes place.

The inventive method is particularly suitable for the treatment of contaminated soils, aquifers and groundwater in situ. But also wastewater, the e.g. incurred in industrial production processes can be treated by the method according to the invention. However, the process according to the invention is particularly preferably used for in situ decontamination of cyanide-containing soil.

It is known that the stability of iron cyanocomplexes depends very much on the redox potential and pH. Advantageously, therefore, by addition of a carbon source, such as glucose, fructose or mannitol and their subsequent fermentative reaction, the redox conditions in the reductive region and the pH can be deliberately discontinued by the fermentation products formed in an acidic range. Likewise, other fermented products can be dosed as C source, as a technical by-product while molasses is particularly economical. Alternatively, without the microbial conversions, the fermentation products, in the present case, for example, butyric acid, butanol, optionally hydrogen, and the like, can be added directly to the redox / pH-controlled complex destruction. The successful complex destruction can be detected by the increase of free CN ^" , which in turn can be oxidatively removed with nitrate.

The incorporation of nitrate causes in particular a degradation of easily releasable and free cyanides in the cyanide-containing media, such as soils, aquifers and / or groundwaters. By simultaneously using nitrate and hydrogen peroxide, it is possible to degrade both free and readily releasable cyanide and complexed cyanide. The effect of cyanide mobilization, which is observed when hydrogen peroxide is used alone as an example of a peroxide, is avoided and cyanide release after insufficient hbOa dosage or premature discontinuation of the dosage is prevented by the presence of nitrate. The highly complexed cyanide-destroying effect of H ₂ O _{2 is} not diminished. Another advantage of using peroxide, such as hydrogen peroxide, in combination with the nitrate is that the microbial bizoenosis is not damaged. That is, the bioremediation, which is caused by the use of nitrate, is not affected by the administration of peroxide, such as hydrogen peroxide.

Other electron acceptors for the oxidative step than peroxide can also be used in the process according to the invention. By way of example, elemental oxygen and ozone can be mentioned as further agents for aerobic oxidation. However, other means are well known to those skilled in the art.

The dosing of nitrate and peroxide, such as hydrogen peroxide can be done by known methods. By way of example, mention may be made of the dissolution of the nitrate salt, such as potassium nitrate, sodium nitrate and ammonium nitrate, and hydrogen peroxide in water to be introduced. The entry may be made by a one-shot method or a multi-well method e.g. with infiltration and delivery wells.

The invention will be explained in more detail with reference to the accompanying drawings and the embodiments, but is not limited to these. Show it:

Figure 1 - a schematic representation of the incorporation of nitrate and

Hydrogen peroxide via a Einbrunnenverfahren.

FIG. 2 shows the degradation of total cyanide comprising free and complexed cyanide after nitrate treatment according to Example 1

FIG. 3 shows the degradation of free cyanides after nitrate dosing according to Example 1

FIG. 4 shows the mobilization of total cyanide under denitrifying conditions according to Example 2

FIG. 5 - Degradation of free cyanide in the water of denitrifying experimental arrangements according to Example 2

FIG. 6 shows the course of the total cyanide concentration under anoxic conditions

Conditions in the body of water according to example 2

Figure 7 - degradation of the free cyanide under denitrifying conditions in the water body according to Example 2

FIG. 8 - total cyanide content with H ₂ O ₂ dosing in the water body according to the example with strong mobilization effect on the cyanides

Figure 9 - free cyanide in the water body in H ₂ θ ₂ dosage of Example 2

Figure 10 - total cyanide in the water body with H ₂ O ₂ dosage and one-time Nitratzudosierung in the body of water according to Example 2 below

Avoidance of mobilization effects Figure 11 - free cyanide in the body of water according to Example 2 with dosage of H ₂ O ₂ and nitrate

Figure 12 - Cyanide degradation in the soil body in the presence of hydrogen peroxide / nitrate

Figure 13 - Total Cyanidabbau in water body at glucose dosage

Figure 14 - Free cyanide in the water body with glucose dosage

Figure 15 - (A) Change of pH in the body of water at glucose dosage;

(B) Change in the redox potential in the water body with glucose dosage

FIG. 16 - Analysis of the fermentation products in the case of glucose dosage (A) alcohols, (B) organic acids

FIG. 1 shows a one-well process with the three phases: a) oxidative charging, b) contact time and c) reductive discharge, which represent a treatment cycle. In Zumischbehälter 1 is hydrogen peroxide or nitrate in the form of his

Salt admixed with the groundwater to enriched with H ₂ O ₂ or nitrate

To get water. This is metered via the supply line 2 in the well 4.

The regions 5 and 6 indicate the oxidation zone for H ₂ O ₂ addition 5 or nitrate addition 6. Groundwater containing either no H ₂ O ₂ or nitrate or

H ₂ O ₂ or nitrate depleted water is removed from the well and returned via the supply line 3 to the mixing tank, in this mixing tank 1 can then again by adding appropriate substances enrichment of the

Water with H ₂ O ₂ or nitrate done.

However, according to the invention, the method can also be carried out by a multi-well method. Here, the H ₂ O ₂ or nitrate-enriched water is introduced via an infiltration well in situ in the soil zone and a Förderbrunnen, the fluids, such as the groundwater, taken from the soil zone and fed to the mixing tank. This also improves the fluid flow within the bottom zone. Corresponding processes are described, for example, in DE 196 06 379 and WO 98/55241. Further processes are mentioned in DE 393 75 93 and EP 988118.

With the help of the following examples, the invention is explained in more detail, but it is not limited thereto.

Example 1 in situ bioremediation experiment on a gas plant site in Berlin

As a test arrangement, the Einbrunnenverfahren shown in Figure 1 was used. In the experiment, water recirculation was omitted to minimize mixing and dilution effects in aquifers. Instead, about 10 to 30 m ^{3 of} water were pumped from a single well and re-filtered after enrichment with the respective electron acceptors. As nitrate, KNO ₃ with a concentration of 300 mg / l was added to the infiltrated groundwater. At the end of the field trial, H ₂ O _{2 was} infiltrated 3 times with about 1200 mg / l each time. The measurement of total cyanides and free cyanides is as follows: a. Water samples: "Free cyanide" with the cyanide test Spectroquant (Merck No. 9701), analogous to DIN 38405 D 13, total cyanide according to DIN 38405 D 13 b soil samples: Extraction according to ISO 11262, cyanide analyzes of the extracts see "Water samples" ,

FIG. 2 shows the course of the total amount of cyanide in the infiltration water. With the beginning of the first nitrate additions, the cyanide concentration dropped rapidly in the first 10 days and then slowed down over the entire investigation period of about 195 days. In the end, nitrate dosing alone was able to reduce total cyanides by 57%. The times of nitrate dosing are shown in the figure with arrows. At the end of the treatment, finally, H ₂ O _{2 was} added. This led to a further rapid degradation of the total cyanides. Since both nitrate and H ₂ O _{2 were present} in the field at that time, The conditions of degradation corresponded to simultaneous administration of H ₂ O ₂ and nitrate. In this experiment, no mobilization effects due to H ₂ O _{2 were} observed.

FIG. 3 shows the degradation of the free cyanides after nitrate dosing. Already after 60 days, a very strong degradation of the free cyanides is recognizable only by Nitratzugabe.

Example 2 Attempts to eliminate cyanide under in situ similar conditions in closed test columns

Various column tests were carried out to eliminate cyanides with approx. 10 kg of soil material each. The column systems with hydraulic recirculation are completely closed, saturated with water and flow through in a defined direction (vertically from top to bottom). To exclude photolytic decomposition of hexacyanoferrates, the columns are completely darkened. The columns contain cyanide-contaminated soil and have sampling points for soil at different heights of the column, via a mixing vessel and feed vessel, the dosage of substances is regulated. Furthermore, the system has a pump to ensure a defined direction of flow. The determination of total cyanide and free cyanide both in the water body of the columns and in the bottom body was carried out according to the procedures described in Example 1. Nitrate was added once at the beginning in an amount of 300 mg / l. The H ₂ θ ₂ dosage was carried out continuously for at least 80 days with 100-200 mg H ₂ O ₂ /! (Low-dose phase) and later over 37 days with 1000-1500 mg H ₂ O ₂ /! (High-dose phase, see Figures 8 to 11). The glucose was added punctiform 7 times in the mixing vessel with a concentration of 800 mg / l in the circulating water. The individual dosing points are marked in Fig. 13.

The pH was determined potentiometrically with a combination electrode. The redox potential was also measured potentiometrically against an Ag / AgCl reference electrode and converted to a standard hydrogen electrode. FIG. 4 shows that nitrate treatment does not mobilize total cyanide under denitrifying conditions. Figure 5 shows, however, that in the body of denitrifying test columns a 94% tiger degradation of free cyanide is observed.

In another column experiment, the development of the total cyanides in the water body (circulating water) was observed with the addition of nitrate as the terminal electron acceptor for 90 days.

In this case, the circulating water was first mixed with about 300 mg / l nitrate. 83% cyanide decrease was observed within 30 days. This course is identical to the untreated control column. However, the administration of nitrate caused a significant decrease of free cyanide in the body of water. This becomes clear from the figure 7. While free cyanide is present in the control at unchanged levels, the addition of nitrate showed 97% degradation of the free cyanides.

FIG. 8 shows the results when using hydrogen peroxide initially in a low dosage of 100 to 200 mg / l H ₂ O ₂ and later in a high-dose phase with 1000 to 1500 mg / l H ₂ O ₂ . The total cyanide content in the body of water increased after dosing briefly, and then decrease again. However, the mobilizing effect of H ₂ O ₂ after completion of the high load phase becomes clear, see the course of the curve after day 120. Free cyanide is rapidly degraded by metering in hydrogen peroxide in the water body. The mobilized cyanide, which resulted in an increase in the total cyanide content in the body of water, comes from the bottom body of the column. That is, on the one hand a sole H ₂ θ ₂ treatment leads to the desired effect of leaching cyanides from the bottom body; These cyanides are predominantly complexed cyanides. On the other hand, there is a side effect of the problem of increased mobilization of total cyanide in the water body (see Figure 8).

With simultaneous dosage of hydrogen peroxide and nitrate this problem could be overcome. As said, a difficulty is the H ₂ θ ₂ dosage the low stability of the compound, ie after discontinuation of dosing and during transport over long distances, H ₂ O ₂ decomposes relatively quickly and is therefore no longer available to a full extent for later degradation. This can lead to an increase in the total cyanide concentration in the water body. This problem can be surprisingly solved by simultaneous administration of nitrate and H ₂ O ₂ , as can be seen clearly in FIG. In the experimental setup, the nitrate was once added at 300 mg / l at the start of the experiment. The dosage of H ₂ O ₂ is as described above, ie within the first 80 days, a low dose and then a high-dose phase.

Figure 10 clearly shows that there is no undesirable increase in total cyanide in the body of water. Free cyanide is also degraded rapidly by the existing electron acceptors, see Figure 11. Thus, both substances complement each other ideally in the treatment of cyanide-contaminated soils. While the hydrogen peroxide can liberate both free cyanide and complexed cyanide, the addition of nitrate allows the total cyanide level to remain low, and it is believed that the main task of the hydrogen peroxide is to destroy the complexed cyanide compounds, while nitrate for degradation the free cyanide provides. The surprising effect of the combined use of H ₂ O ₂ and nitrate can also be seen in FIG. Figure 12 shows the cyanide degradation in the soil body in the presence of hydrogen peroxide and nitrate. As can be clearly seen, concomitant administration allows degradation of the total cyanide content in the body below the allowable limit.

Furthermore, it turned out that the H ₂ O _{2 has} no negative effect on the biocoenosis of the soil and thus the necessary for denitrification microflora is not damaged by the oxidative conditions of the hydrogen peroxide. Furthermore, the nitrite content could be kept low with simultaneous administration of hydrogen peroxide and nitrate. The formation of nitrite from nitrate usually presents a problem with the use of nitrate. In FIGS. 13 and 14 the influence of the metering in of a carbon source, in the present case glucose, is shown. It should be noted that the experiments already preceded by a phase of aerobic oxidation. As can be clearly seen, the dosage of glucose under aerobic conditions allows a strong elimination of total cyanides in the body of water. Further, as can be seen in Figure 14, an increase in the free cyanides is evident as evidence of the destruction of the cyano complexes. FIGS. 15A and 15B show the pH values and redox potentials in the water body determined for the experiment shown in FIGS. 13 and 14. As can be clearly seen, in the course of treatment with a carbon source, such as glucose, the pH decreases over time. The redox potential also shifts to more negative values. It can be clearly seen from these figures that on the one hand a reduction in the pH value on the other hand a shift in the redox potential has a positive effect on the elimination of the total cyanides.

Figures 16 A and 16 B show the analysis of the resulting fermentation products after dosing of glucose under anaerobic conditions (see above, corresponding

Figures 13 and 14). As one clearly recognizes, large quantities are created

Butyric acid. It concerns as the so-called butyric acid fermentation. These

Acidification leads to a lowering of the pH. Therefore, too

Fermentation products, such as the fermentation products shown in Figure 16, are metered to allow the inventive method for the degradation of cyanides.

Claims

claims

1. A method for the decontamination of cyanide-containing media, characterized in that it comprises the step of metering nitrate into the cyanide-containing media for degrading the cyanides.

2. The method according to claim 1, characterized in that the cyanide-containing media soils, aquifers and / or groundwaters are.

3. The method according to claim 1 or 2, characterized in that it further comprises the step of metering in peroxides, in particular hydrogen peroxide (H ₂ O ₂ ) for degrading the cyanides.

4. The method according to any one of claims 1 to 3, wherein the nitrate and the peroxide are metered in at the same time.

5. The method according to any one of claims 1 to 4, characterized in that metered in a first step, nitrate and in a subsequent step, the nitrate is metered in simultaneously with the peroxide.

6. The method according to any one of claims 1 to 5, characterized in that the method is carried out in situ.

7. The method according to any one of claims 1 to 5, characterized in that the method takes place on site.

8. The method according to any one of the preceding claims, characterized in that it further comprises the step of dosing a carbon source.

9. The method according to any one of the preceding claims, characterized in that it further comprises a dosing of Fermentation products of microorganisms from carbon sources.

10. The method according to any one of the preceding claims, characterized in that means for regulating the redox potential of the media to be decontaminated is metered.

11. The method according to any one of the preceding claims, characterized in that it comprises a dosing of means for regulating the pH of the media to be decontaminated.

12. The method according to any one of the preceding claims, characterized in that the cyanide-containing media free / readily releasable and / or complexed cyanides.

13. The method according to any one of the preceding claims, wherein the method is carried out in Einbrunnenverfahren.

14. Use of nitrate for the bioremediation of cyanide-containing media, in particular soils, aquifers and / or groundwaters.