DE19703927A1 - Fixing or mobilisation of contaminants or useful materials from soil onto solid matrices - Google Patents

Abstract

Parent Patent DE19528635.9 relates to the removal of contaminants or elution of useful materials from soil by insertion of electrodes such that micro-conductors in the soil induce reactions. In this Patent of Addition solid matrices containing contaminants and/or useful materials are also added to the soil, the matrices being of soil-containing stones, waste or dumped materials, slurries or residues and the contaminants being immobilised on the micro-conductors by redox reactions and contaminants and useful materials being mobilised for elution.

Description

The invention relates to a method for fixing pollutants or eluting pollutants or Recyclable materials from a solid matrix according to the preamble of claim 1, such as Soils, ore-containing rocks, compacted waste materials, landfill material, sludges or Residues by means of targeted electrochemical influencing of this solid matrix microconductor-induced redox reactions according to DE 195 28 635.9.

The current state of the art is characterized in that one is relatively good water-soluble pollutants in soil water are removed from this medium by using pumped out of the groundwater and mostly in conventional installed above ground Water purification systems ex-situ by e.g. B. precipitation, flocculation, biological treatment, Ozonation and the like be eliminated.

For example, with regard to the elimination of soluble uranium complexes from the aqueous phase so that the uranyl compounds by surface adsorption aluminum or iron hydroxides formed by flocculation are bound. This polluted solids are filtered or by sedimentation from the aqueous Phase separated and deposited in hazardous waste landfills. With this disposal you can However, do not rule out that uranium or other radionuclides are caused by precipitation or Groundwater can be remobilized and returned to the water cycle.

The accumulation of harmful or valuable substances from solid matrices is currently taking place mostly in that the solid containing harmful substances or valuable substances is leached out or leached out, in mostly above ground systems and transported by means of suitable processing (e.g. Extraction or similar) is eliminated from the solid matrix.

Using electrochemical techniques, it is known to utilize the migration of electrically charged particles in the field and to transport mobile pollutants through the solid matrix using electrokinetic processes (electromigration, electroosmosis, electrophoresis). The pollutants are collected near the electrodes and removed in an ex-situ process using standard methods. Such techniques are described, for example, in US 5,074,986, in Pamukcu, S., Wittle, JK ( 1992 ) Electrokinetics for Removal of Low-Level Radioactivity from Soil. Proc. of the 14th Annual DOE Low-Level Radioactive Waste Management. Conference, Phoenix, Arizona, November, 18-20, Conf-921 137-Proc, 256-278 or in Probstein, RF, Hicks, RE (1993). Removal of Contaminants from Soils by Electric Fields. Science, V.260, 498-503.

The use of electrochemically induced material conversions in the solid matrix is becoming widespread less sought.

DE-OS 43 01 270 describes a method for removing pollutants from soils known. According to the characterizing part, the object is achieved in that electrical voltage an electrical field is built up that is so large that not electrokinetically transportable pollutants are destroyed on site. The practical one Experience shows that it is extraordinary with the specified voltages or currents it is difficult to destroy pollutants on site. EP 0 729 796 A1 therefore attempts to to circumvent the physical problems in that under the influence of an electrical Field of each soil particle is polarized and even water electrolysis is possible on them should be. Triggering electrochemical reactions e.g. B. is on sand or clay particles already theoretically impossible and consequently never been observed before.

From DE 195 28 635.9 it is known that electrochemical on so-called micro-conductors induced reactions can occur.

The object of the invention is now compared to DE 195 28 635.9 in pollutants Solids such as waste, landfill material, sludge or residues and in soils to immobilize electrochemically without removing the pollutants from these materials to transport complex procedures or pollutants or recyclables in a relatively simple manner Way out and prepare by known methods.

According to the invention, the object is achieved by a method having the features of claim 1 solved. Advantageous variants of the method result from subclaims 2 to 6.

In a variant of the method, the problem is solved in that electrochemically active micro-conductors mobile pollutants through redox processes in immobile pollutants are transferred. Generalized run on the micro-conductors the following reactions:  

• a) adsorption of the pollutant on the micro-conductor;
• b) formation of a pollutant micro-conductor complex;
• c) Transfer of one or more electrons from the micro conductor to the pollutant Pollutant reduction, transfer of one or more electrons from the pollutant the micro-conductor in the case of pollutant oxidation;
• d) decay of the pollutant microconductor complex;
• e) desorption of the pollutant from the micro conductor;
• f) optionally further reaction of the reduced / oxidized pollutant in the aqueous phase e.g. B. by hydrolysis and precipitation or by reaction with solid components;
• g) deposition of the product formed in the pore structure of the solid matrix.

In a second variant, the object is achieved by converting immobile pollutants or valuable substances on electrochemically active micro-conductors into mobile substances by redox reactions, which are then transported with the aqueous phase and processed in suitable plants. The following processes take place:

• a) Contact of the immobile pollutant or valuable substance with the micro-conductors (if Microconductors are not available or are not available in sufficient numbers Micro-conductor washed in or generated);
• b) transfer of one or more electrons from the micro conductor to the harmful or Recyclable or from the pollutant or recyclable to the micro conductor;
• c) desorption of the harmful or valuable substance from the micro conductor;
• d) if necessary, further reaction of the reduced / oxidized pollutant or valuable substance z. B. by Complex formation;
• e) transport of the pollutant or valuable substance in the aqueous phase;
• f) version, possibly concentration, working up of the aqueous solution with suitable Process depending on the type and concentration of the harmful or valuable substance.

The advantage of the method according to the invention is that according to variant 1 the Water pollutants are no longer captured, transported and in as usual in the mobile phase separate, mostly above-ground systems using complex processes from the aqueous phase must be eliminated, but is immobilized in the solid matrix. According to variant 2, an immobile pollutant or valuable substance can be carried out in a simple manner targeted redox reactions are mobilized on the microconductor. Elaborate steps of the  Suitcases, transport and separation of the harmful or valuable substance from the solid matrix can be omitted if necessary.

The process control described by the invention allows pollutants to be added directly in situ immobilize or mobilize pollutants or recyclables without expensive transport, Drafting and preparation procedures must take place.

The invention is explained in more detail below on the basis of exemplary embodiments. In the only Fig. 1, a diagram is shown with the representation of the pollutant concentration as a function of time.

Example according to variant 1

Sand was mixed with electronically conductive particles (carbon particles) dilute solution of uranyl acetate passed.

In Fig. 1, the change of the Uranylkonzentration is shown as a function of the duration of the experiment.

In the currentless phase, the uranyl ions are first adsorbed on the solid matrix up to an equilibrium value. When the current is switched on, the uranyl ions on the micro-conductors are reduced according to the following gross equation:

UO ₂ ²⁺ + 4 H⁺ + 2e ↔ U ⁴⁺ + 2 H ₂ O.

In subsequent reactions, the volatile reaction products are immobilized depending on the environmental conditions. B. the following reaction is possible:

U ⁴⁺ + SiO ₂ + 2 H ₂ O ↔ USiO ₄ (coffinite) + 4 H⁺.

Analyzes of the soil material showed that there were deposits on the surface of the grains of sand immobile uranium compounds with a uranium content of up to 12 atom percent.

The originally used amount of soluble uranium could under these comparison conditions can be reduced by a factor of 10.

The unloaded comparison sample showed none within the analytical error limit Change in uranium concentration.

Example according to variant 2

A gold-containing solid matrix is filled with a cyanide-containing micro-conductor Solution pumped. The microconductor particles come into intimate contact with the gold-bearing minerals of the rock. By applying a voltage and thus building one electrical field, electrons are transferred from the gold to the microconductor. The gold is oxidized and bound in a cyanide complex. The resulting gold cyano complexes are mobile and can in the aqueous phase without significant interaction with the Solid matrix can be transported to the location and processed. The presence of Oxygen favors the process. There is enough metallic gold in the solid matrix available, then the addition of micro-conductors can be omitted, since the metallic gold itself Function of the micro conductor takes over.

Claims (6)

1.Procedure for the removal of pollutants or elution of valuable materials from soils, electrodes being introduced into the soil, an electric field being built up by an electrical voltage, and the removal of the pollutants being carried out at a ratio of ionic to electronic conductivity of the soil in which according to DE 195 28 635.9, characterized in that in addition to the floors also other solid matrices interspersed with pollutants and / or valuable substances, which consist of materials such as ore-containing Rocks, waste materials, landfill material, sludge or residues etc. are formed, used and the pollutants are immobilized by redox reactions on the micro-conductors for fixation and the pollutants or valuable materials are mobilized for elution. 2. The method according to claim 1, characterized in that by targeted infiltration one or more components generated by the solid matrix microconductor or in the Solid matrix are introduced, which are then available as such for redox reactions stand. 3. The method according to claim 1, characterized in that at the at the Solid matrix existing or added into the solid matrix through the triggered redox reactions immobilize mobile pollutants. 4. The method according to claim 1, characterized in that at the at the Solid matrix existing or added into the solid matrix through the triggered redox reactions can mobilize immobile pollutants or valuable materials. 5. The method according to any one of claims 1 to 4, characterized in that a optimal pH in the mobile phase is adjusted to a largely complete To ensure adsorption of the pollutant on the micro conductor and thus optimal To achieve conditions for electron transitions.   6. The method according to any one of claims 1 to 5, characterized in that the at the reaction of the pollutants or valuable substances on the solid matrix or short-lived reaction products through follow-up actions with solid components mobile or immobile species are formed.