DE19536882B4 - Process for reducing harmful impurities - Google Patents

Abstract

Process for the electrochemical oxidation and / or reduction of pollutants dissolved and / or sorbed in substrates or media in the at least temporary presence of an artificial electric potential field, comprising the following steps:
The substrates or media are rinsed artificially (a) with an aqueous solution of an iron and / or manganese compound and / or (b) with an aqueous humate solution,
Thereafter, the present in the solution of iron and / or manganese and / or humic substance are brought by chemical or electrochemical means in the substrate or medium to precipitate, and
Subsequently, the oxidation and / or reduction of the pollutants takes place in the presence of the at least temporarily existing artificial electric potential field.

Description

The The invention relates to a process for electrochemical oxidation and / or reduction of dissolved in substrates or media and / or sorbed pollutants in the at least temporary presence an artificial one electric potential field.

A method for the electrochemical oxidation and / or reduction of dissolved and / or sorbed in substrates or media pollutants is in the previously filed, but later published DE 195 28 635 A1 described.

One such method is also described in WO 95/01232 A1. Therefore becomes a treatment zone in a soil to be decontaminated from in individually counted Substances exposed to an electric field.

The Invention is based on the object to improve this method.

Therefore, the method according to the invention provides the following steps:
The substrates or media are rinsed artificially (a) with an aqueous solution of an iron and / or manganese compound and / or (b) with an aqueous humate solution,
Thereafter, the present in the solution of iron and / or manganese and / or humic substance are brought by chemical or electrochemical means in the substrate or medium to precipitate, and
Subsequently, the oxidation and / or reduction of the pollutants takes place in the presence of the at least temporarily existing artificial electric potential field.

It are other methods of electrochemical material conversion in the Presence of aqueous electrolytes become known, which one or more of the following Underlying principles of action:

1. Method under use electron-conductive catalyst particles in the presence of natural electrical Potential differences:

• – Halogenmineralisation von Halogen-Kohlenstoffverbindungen an mit Edelmetallen oder Graphit dotierten Unedelmetallen. Dabei fungieren: Halogen-Kohlenstoffverbindung als Elektronenakzeptorreaktant, Unedelmetall als Elektronendonorreaktant, Edelmetall oder Graphit als Elektrodenpartikel.
• – Schwefelwasserstoffoxidation an Aktivkohle. Dabei fungieren: Sauerstoff als Elektronenakzeptorreaktant, Schwefelwasserstoff als Elektronendonorreaktant, Aktivkohle als Elektrodenpartikel.
• – Zementation. Dabei fungieren: KupferII-Kationen als Elektronenakzeptorreaktant, Eisen als Elektronendonorreaktant, Kupfer als Elektrodenpartikel.
• – Photographischer Entwicklungsprozeß. Dabei fungieren: Silberkation als Elektronenakzeptorreaktant, Thiosulfatanion als Elektronendonorreaktant, Silberkeim als Elektrodenpartikel.

Reactions under the influence of natural electric fields, the potential of which is determined by the difference between the electron donor potential and the electron acceptor potential of the reactants, can take place on such catalyst (= electrode) particles which, in addition to their electron conductivity, have receptor functions for electron transfer (anodically active functions) and electron transfer ( cathodically active functions) from the electron donor reactant or to the electron acceptor reactants. The catalyst particles thus contain cathodic and anodic functions. Examples of these methods are:

• - Halogen mineralization of halogen-carbon compounds on precious metals or graphite-doped base metals. In this case function: halogen-carbon compound as Elektronenakzeptorreaktant, base metal as Elektronendonorreaktant, precious metal or graphite as electrode particles.
• - Hydrogen sulfide oxidation on activated carbon. Oxygen acts as an electron acceptor reactant, hydrogen sulfide as an electron donor reactant, activated carbon as an electrode particle.
• - cementation. The following functions are used: copper II cations as electron acceptor reactants, iron as electron donor reactants, copper as electrode particles.
• - Photographic development process. In this case act: silver cation as Elektronenakzeptorreaktant, Thiosulfatanion as Elektronendonorreaktant, silver seed as electrode particles.

2. Method using Electron-conductive electrodes (particles) in the presence of artificial electrical Potential differences:

• – Chlor-Alkali-Elektrolyse. Dabei fungieren: Natriumkationen als Elektronenakzeptorreaktant, Chloridanionen als Elektronendonorreaktant, Quecksilber als Rezeptor für den Elektronenakzeptorreaktant (Kathode), Graphit als Rezeptor für den Elektronendonorreaktant (Anode).
• – Wasserelektrolyse. Dabei fungieren: Natriumkationen als Elektronenakzeptorreaktant, Hydroxylanionen als Elektronendonorreaktant, Eisen als Rezeptor für den Elektronenakzeptorreaktant (Kathode), Nickel als Rezeptor für den Elektronendonorreaktant (Anode).
• – Elektrolytische Verzinnung. Dabei fungieren: Zinn-II-Kationen als Elektronenakzeptorreaktant, Zinn als Elektronendonorreaktant, Stahlblech als Rezeptor für den Elektronenakzeptorreaktant (Kathode = zu verzinnender Gegenstand), Zinn als Rezeptor für den Elektronendonorreaktant (Anode = "Opferanode").

Reactions under the influence of artificial electric fields, the potential of which can be arbitrarily set according to requirements, can take place on such electrodes (= catalysts) which, in addition to their electron conductivity, have receptor functions for electron acceptance (at the anode) and electron transfer (at the cathode) from the electron donor reactant Examples of these methods are

• - Chlor-alkali electrolysis. In this function: sodium cations as Elektronenakzeptorreaktant, chloride anions as electron donor reactant, mercury as a receptor for the Elektronenakzeptorreaktant (cathode), graphite as a receptor for the electron donor reactant (anode).
• - Water electrolysis. Here: sodium cations act as an electron acceptor reactant, hydroxyl anions as an electron donor reactant, iron as a receptor for the electron acceptor reactant (cathode), nickel as a receptor for the electron donor reactant (anode).
• - electrolytic tinning. Act as: Tin II cations as Elektronenakzeptorreaktant, tin as Elektronendonorreaktant, steel sheet as a receptor for the Elektronenakzeptorreaktant (cathode = object to be tinned), tin as a receptor for the electron donor reactant (anode = "sacrificial anode").

3. Method under use of electron-semiconductor catalyst particles in the presence artificial electrical potential differences:

• – Abbau organischer Schadstoffe mit Sauerstoff Dabei fungieren Sauerstoff als Elektronenakzeptorreaktant, Organischer Schadstoff als Elektronendonorreaktant, Titandioxid als Elektrodenpartikel.

Electron semiconductors are under the influence of sufficiently high-energy electrical field components, as they also contains the short-wave light radiation, electron-conductive. These include substances such as titanium dioxide, zirconium dioxide, heavy metal oxides, dyes, and humic substances. Short wavelength photons can be used to produce mobile reactive charge separation states in these materials, these serving as receptor functions for electron donor reactants (the anodically active functions are the positively charged functions) and the electron acceptor reactants (the cathodic functions are negatively charged functions). These semiconductor catalysts which are effective in the irradiated state can be used for decomposition of water into hydrogen and oxygen and also for reductive or oxidative pollutant removal. It has recently been published that the irradiated semiconductors, when additionally exposed to the effect of an artificial potential difference, are far more effective catalysts. An example of this method with additionally impressed electric potential difference is the

• - Degradation of organic pollutants with oxygen Here, oxygen act as an electron acceptor reactant, organic pollutant as an electron donor reactant, titanium dioxide as an electrode particle.

The Process of so-called geo-oxidation, carried out by P + P Geotechnik, Stuttgart is perhaps a combination of the aforementioned principles of action: For the removal of pollutants in the soil thereby metal electrodes introduced into the soil, between which a DC field is built. At a Minimum potential gradient from approx. 1.2 V / m to 2 V / m electrode distance, the soil water or groundwater electrolysis. The optimum operating level is 3 A / m2 Electrode surface. The pollutant degradation in the soil takes place oxidatively and reductively mainly in the area between the electrodes and not, as at first the expectation of electrically insulating so non-conductive mineral particles as quartz would have been expected at the electrodes. As explanation therefor the bipolar polarization of each soil particle is postulated and suspected the cause in the heavy metal content of the soil particles (Company publication of P + P GmbH).

• 1. Der Prozeß 3 an den durch das künstliche elektrische Feld aktivierten Halbleiter-Partikelelektroden, – falls eine Aktivierung auch ohne zusätzliche Photonenaktivierung möglich ist, was bis jetzt nach dem Stand von Wissenschaft und Technik bis jetzt unbewiesen ist.
• 2. Die Prozesse 1 und 2 an den durch die an den Halbleiterkathoden sich als Folge von Reduktionsreaktionen sich abscheidenden, in Spuren ubiquitär vorhandenen Elemente, mit gehobenem Elektronenakzeptorpotential, wie zB. Nickel oder Kupfer.

On the assumption of a semiconductor content in or on particle surfaces, the following hypothesis can be developed:
By the electrochemical reduction processes (at the cathodic particle pole) and oxidation processes (at the anodic particle pole) which are possible in bipolar fashion in the artificial electric potential field, then in principle all three of the mentioned active principles could take place on the single particle of the soil treated in this way in the pollutant degradation:

• 1. The process 3 to the activated by the artificial electric field semiconductor particle electrodes, - if activation is possible without additional photon activation, which is still unproven until now according to the state of science and technology.
• 2. The processes 1 and 2 at the by the on the semiconductor cathodes are deposited as a result of reduction reactions, in ubiquitously present in tracks elements, with elevated electron acceptor potential, such as. Nickel or copper.

With the method according to the invention, with which the so-called geooxidation process is designed substantially more effectively, this working hypothesis could be surprisingly confirmed:
It has surprisingly been found that by artificial enrichment of electrolyte-containing and aqueous fluids with solid semiconductors, which are referred to as active substances, the so-called geo-oxidation process can be carried out many times more effectively and thus also on the wide field of water treatment, sediment and sludge treatment can be extended.

Either The so-called geo-oxidation process itself can also according to the invention be used to bring about the enrichment with active ingredients as also the already known processes for the enrichment of the soil, the mud or the water with active ingredients such as inorganic and / or organic Semiconductors.

The electrochemical enrichment according to the invention with active substances using the so-called. Geooxidationsverfahrens done in such a way that the penetrated by the artificial electric field potential substrate, such as. Soil, sludge or filter gravel is rinsed with an aqueous solution of heavy metal compounds. Solvent and electrolyte can eg. be the natural groundwater stream, natural leachate or artificial irrigation water, sewage or groundwater to be treated enriched with the active substance precursors or already included.

By the electrochemical effect within the electric potential field the active substances are precipitated brought to the bipolar polarized active particles or the active substance-enriched particle surfaces of the cathodically active Areas are like the active substances as low-value compounds like eg. Magnetite. In the anodically active areas, the heavy metal active substances in contrast, as higher active substances like such as. Ferric hydroxide, manganese, and possibly higher valency Iron and manganese oxygen compounds.

Heavy metals, like copper and nickel belong not to the preferred artificial applied active precursors; However, they are usually in the least amount in natural Substrates and / or media already present and can be cathodic elementary precipitated become. Among the preferably used heavy metal active substance precursors, which are preferably precipitated electrochemically for Aktivstoffanreicherung counting the soluble compounds of iron and / or widespread in nature Manganese.

To another variant of the active agent enrichment according to the invention can be proceeded so that the Soil is chemically enriched with the active ingredients and preferably with ocher, an oxide / hydroxide mixture of 3-valent iron and / or an oxide / hydroxide mixture of 4-valent Manganese. This happens preferably in the way, as in the German Published patent application 42 42 682.0, filing date 17.12.92 becomes. additionally to the suggestions given there for oxygen-induced precipitation by gas input from above, can the oxygen also by electrolytic means at appropriate Anode arrangement are brought into the ground. The enrichment from ocher in other substrates and media such as. Gravel filters for water purification, in flocculators for wastewater treatment or the resulting whitewash is well known. But also the enrichment of lower valued ones iron-containing activators such as magnetite or iron sulfides in digested sludge facilities or the resulting sludge is well known.

to Enrichment of soil with active ingredients from the class of predominantly In particular, organic semiconductors, namely humic matter, can be after in German Patent Application P 44 43 828.1 with priority date of 19.04.94 and published in German Patent Application P 195 05 200.5 Proceed procedure. This happens in such a way that the of the artificial one electrical potential field penetrated or yet to be treated Soil is rinsed with an aqueous Huminatlösung. As a solvent can do it eg. the natural one Groundwater flow, natural Leachate or artificial Irrigation water can be applied, which enriched with the huminates For this, the groundwater or leachate or artificial Applied water added with humate, then through the soil rinsed becomes. By precipitation humic acid from humate by acid and / or polyvalent metal cations in the soil, the enrichment is achieved. The accumulation of humic substances after their precipitation for flocculation or heavy metal precipitation in gravel filters or sludges of water treatment is also well known. Likewise, the accumulation of Humic substances in water or wastewater treatment facilities known.

Of the so in the aquifer or in the unsaturated soil zone above of the groundwater level with active substances in the form of so-called ocher barriers or humic barrier-enriched soil or the said active agent-enriched filter, sludge or even in the water suspended particles containing active can then be used for purification a potential field according to the so-called. Geooxidation be electrochemically cleaned. that the electrochemical cleaning of the particle phase, of course, too associated with the purification of the water or electrolyte phase, because the particle phase in the sorption-dependent mass transfer with the Water phase is. Therefore, the inventive method is not on the Purification of the particle phase is limited, but also applies on the fluid phase.

The Pollutant removal from the inventively prepared media with the method of Geochemical oxidation can then be done in a manner known per se This is achieved by increased reaction rates both oxidation processes and reduction processes within a material, eg. up to 1/10 shortened time span. In order to there is also the possibility eg. such, originally Barriers set for groundwater protection, quickly adsorbed by the or chemically bound organic pollutants by electrochemical To cleanse degradation and thereby regenerate.

In the case of the media enriched with the active material iron ocher or magnetite or iron sulfides, the following changes in the active chemical composition take place after the electrical potential field has been built up: the bipolarization of the active Fuel Particles; Reduction of cathodic districts to low-grade heavy metal compounds; It may be in older or contaminated with the corresponding heavy metals Ocher such as. in the ocher barriers in the soil or in gravel filters or sludges, which are already enriched with larger corresponding amounts of pollutants, for the metallic excretion of metals with higher electron acceptor potential such as. Copper or nickel come from the sorbed pollutant inventory; Oxidation of the anodic particle districts to III, IV and possibly higher-value heavy metal oxide compounds. Thus, the originally relatively homogeneous Aktivstoffausscheidung is decomposed into a fractal micromosaic structure of reduced and oxidized particulate compartments, which remains active even after a long time after removal of the artificial potential field with respect to their Schadstoffmineralisations effectiveness.

By the anodically precipitated Metallic heavy metals will generally reduce pollutants. reaction significantly accelerated. It may therefore be advantageous additionally to enrich the semiconductor enrichment with these heavy metals.

In the case of the media enriched with the predominantly organic active substance humic substance, the following changes in the active chemical composition take place after the electrical potential field has been built up, due to the electrochemical reaction:
Bipolarization of the humic substance particles; Reduction of cathodic districts to electron-donor functions such as. hydroquinone-like functions, amine, ether, mercaptan, low to zero valent heavy metal complexes; It may be in older Huminstoffbarrieren, which are already enriched with larger amounts of pollutants, or if the humic substances by heavy metal compounds, such as. those of the iron, with which they have precipitated, come to significantly higher concentrations of heavy metal functions; Therefore, the cathodic deposition of metallic phases is also possible in this case; Oxidation of the anodic particle districts to electron acceptor functions such as. quinoid functions, ammonium, oxonium, disulfide, higher-value heavy metal complexes. Thus, the originally relatively homogeneous Huminstoffausscheidung is decomposed into a fractal micro mosaic structure of reduced and oxidized particulate compartments, which also remains active for a longer time after removal of the potential field with respect to their Schadstoffmineralisations effectiveness.

In organic semiconductor active enriched electrochemically treated media compete for the electrochemical degradation processes of the organic Pollutant substance with those of the organic active substance. Nevertheless, the active ingredient humic substance is much more resistant to Degradation as most organic pollutants such as. polycyclic aromatic hydrocarbons and aliphatics.

The Method of electrochemical pollutant removal method of geooxidation artificial in the present With one or more active ingredients enriched particles can be So easily on the purification of waters, sediments, sewage sludge or Residues from the floor washing expand, with the same parameters in terms of potential difference, current, etc. can be applied. Unlike the in situ process, this material can be used for improved pollutant mineralization are additionally moved through.

Especially suitable for the inventive method are Aktivstoffprecursorhaltige waters containing these precursors as Huminate, iron or manganese compounds precipitation the activator or activators from their precursors in the conventional Manner performed and thus achieves the Aktivatoranreicherung invention. As a rule, the raw water is additionally mixed with precursor. The then present as a fixed or agitated Aktivatorbett Aktivatoranreicherung can then for electrochemical pollutant degradation in the mentioned Fashion with an artificial one be treated electric potential field.

Becomes the natural, by simple acid extraction mobilizable iron- / manganese-containing active substance content of a soil or sediment raised from about 0.5 g / kg to 1.5 g / kg, the electrochemical pollutant degradation rate already around the Factor 10 will be raised. Will be the natural, extractable by alkali Humic acid actives content of the soil of 0.01 g / kg raised to 1 g / kg, the electrochemical Pollutant degradation rate increased by a factor greater than 10 become.

Claims (4)

Process for the electrochemical oxidation and / or reduction of pollutants dissolved and / or sorbed in substrates or media in the at least temporary presence of an artificial electric potential field, comprising the following steps: The substrates or media are produced artificially (a) with an aqueous solution of an iron and / or manganese compound and / or (b) is rinsed with an aqueous humate solution, then the An parts of iron and / or manganese and / or humic substance by chemical or electrochemical means in the substrate or medium to precipitate and then carried out the oxidation and / or reduction of the pollutants in the presence of at least temporarily existing artificial electric potential field. Method according to claim 1, characterized in that that the substrates or media are in their natural state Location left soils, bodies of water or Sediments is. Method according to claim 1, characterized in that that the substrates or media are soil, sewage sludge, sediments, sewage, groundwaters for remediation or for use, drinking water, bath water or sewage. Method according to claim 1, characterized in that that the substrates or media are procedural Facilities such as gravel filters or process stages such as flocculators, Sedimentation, sludge thickening or sludge digestion.