The electrokinetic method of cleaning soil from radioactive and toxic substances

 

The invention relates to the field of environmental protection, in particular to the purification of natural and man-made materials, and most can be effectively used when cleaning clay soils containing radioactive and toxic substances. Technical result: improved productivity, efficiency, speed cleanup of the soil and the reduction of energy consumption. The method includes creating at sites of cleared ground of the two cathode cavity and located between the anode cavity, placing the electrolyte in these cavities and wrap them positive and negative potentials of the DC voltage, the output of the electrolyte from the anode cavity and flow into the cathode cavity, the output of the electrolyte and the gas phase from the cathode cavities and purification of the electrolyte. Before summarizing the electrolyte anode and cathode cavities of positive and negative voltage potentials of the constant current in the soil between the anode and cathode cavities serves the electrolyte in an amount of 0.1-0.5 volume on the volume of treated soil through perforated pipes. Tubes are installed in the soil at the depth of contamination and at the same distance from each other. When this exercise constant contraria voltage drop on them and by submission on sites with low conductivity of the electrolyte in the amount ensuring alignment of the conductivity plots of ground. table 1.

The invention relates to the field of environmental protection, in particular to the purification of natural and man-made materials, and most can be effectively used when cleaning clay soils containing radioactive and toxic substances.

A known method of cleaning soil from contaminating their substances (1) with the use of electroosmosis, including installation into the soil to a predetermined depth of one or more porous electrode serving as a cathode, and one or more electrodes that serve as the anode, leading to the electrodes, the electrical potential difference between the cathodes and the anodes, the supply in the soil in the location of one of the electrodes, anode or cathode, clean washing liquid such as water, excretion of electrolyte from the near-cathode area and clear it.

The disadvantage of this method is the impossibility of cleaning soils from tightly bound with them elements of pollutants, for desorption which requires high concentration reagent more than 0.1 N, such as electroosmosis almost absent.

The known method electrokinetic cleaning of soils from zaraznaya distance from each other areas of cleared ground, the anode and cathode compartments, the initial filling of the anode and cathode cavities electrolytes, creating a pressure difference between anode and cathode cavities, leading to electrolyte anode and cathode cavities of positive and negative voltage potentials of the constant current, constant during the whole process of removing electrolyte from the anode and cathode compartments, the selection of the selected electrolytes polluting the soil of nutrients and the supply of treated electrolyte in the anode and cathode cavity. The disadvantage of this method is limited scope due to the possibility of its use only for cleaning vodokanalnyh soils with good permeability.

The known method electrokinetic cleaning of soil from contaminating its substances (3), based on the principle of electrolysis and including the creation located at a distance from each other areas of cleared ground of the two cathode cavity and located between the anode cavity, placing electrolytes with working concentrations desorbers ions and acidity in the anode and cathode cavities and wrap them positive and negative voltage potentials postoannogo substances, polluting the soil, adjusting the acidity of electrolyte withdrawn from the cathode cavities to pH 3 and the flow of electrolytes with adjusted acidity in the cathode cavity.

The disadvantages of this method are: low productivity, due to a decrease in the process of implementing a number extracted from the cleaned soil polluting its substances; reduced profitability; as well as the formation of secondary liquid waste associated with the need for periodic replacement of the spent electrolyte anode cavity on a new electrolyte; limited scope, due to the fact that the known method is not applicable in cases when it is necessary to preserve the integrity of the structure being cleaned of soils; reduced emission rates of pollutants soil substances, because the selection is carried out only from the electrolyte of the cathode cavities.

The closest to the technical nature of the claimed method is a method electrokinetic cleaning of soil from radioactive and toxic substances (4), including the establishment located at a distance from each other areas of cleared ground of the two cathode cavity and located between the anode cavity, accommodation summary to them of the positive and negative voltage potentials of the constant current, removing electrolyte from the cathode cavities, cleaning withdrawn from the cathode cavities electrolytes from polluting the soil radioactive and toxic substances and the subsequent adjustment of the pH of treated electrolytes to their working concentration simultaneously with the creation of the electrolyte anode and cathode cavities of positive and negative voltage potentials of the constant current from the anode cavity deduce the electrolyte and the gas phase and serves them in the cathode cavity, the electrolyte from the cathode cavities bring together gas phases cathode cavities, and filed in the cathode cavity electrolyte and gas phase in the anode cavity, and in the anode cavity is injected electrolyte with working concentrations desorbers ions and acidity, then before cleaning shall mixture withdrawn from the cathode cavities of electrolytes and the mixture withdrawn from the cathode cavities of the gas phase, their separation from each other and removing the separated mixture of the gas phase, cleanup withdrawn from the cathode cavities electrolytes from polluting the soil radioactive and toxic substances and the subsequent adjustment of the acidification is carried out in a mixture with the electrolyte supplied to the cathode polcou acidity of treated electrolytes are adjusted concentrations, contained in them desorbers ions to the business units that comprise 0.01 to 5.0 mol/l, instead of the electrolyte with the working concentrations desorbers ions and acidity in the anode cavity serves purified mixture of electrolytes corrected with acidity and concentration desorbers ions, after which the above-mentioned circulation of the mixture of the electrolyte is carried out in a continuous mode to achieve the necessary degree of purification of the ground, the pressure in the anode and cathode cavities are kept lower than atmospheric, and as an electrolyte placed in the anode and cathode cavities, use the same electrolyte. The disadvantages of this method are: increased duration, especially early in the process, due to the low rate of reagent from the anode cavity in the treated soil by electromigration and electroosmosis, and also due to re-adsorption on soil desorbed ion-pollutant during its motion in the field of a permanent electric current; and areas that have not yet reached deformirujuschij reagent, have low electrical conductivity, which is not possible in the initial period of the treatment process to achieve the required densities the system is s ground when the cathode and anode cavity is set at a sufficiently large distance from each other; reduced efficiency due to energy consumption in the initial stage of the process, lasting several tens of days, when the movement of the reagent front along the electric field without emissions in the electrode cavity; the possibility of local overheating of individual sections of the soil because of their low conductivity associated with different composition and porosity of the soil and, consequently, its dehydration by evaporation and the decrease in the density of electric current, resulting in decrease of speed cleaning; reduced resistance of structural materials of the electrode device, due to possible increase of temperature, above the permissible because of overheating adjacent parcels of ground in the process.

The technical result of the proposed method is to reduce the duration of the process, increase efficiency, reduce energy costs and increase the service life of structural materials.

The achievement of the technical result is ensured by the fact that the proposed method includes: creating located in the ne of the cavity, accommodation electrolytes with working concentrations desorbers ions and acidity in the anode and cathode cavities and wrap them positive and negative potentials of the DC voltage, the output of the electrolyte from the anode cavity and flow into the cathode cavity, the output of the electrolyte and the gas phase from the cathode cavities, cleaning bred electrolytes from polluting the soil radioactive and toxic substances and the subsequent adjustment of the pH of treated electrolytes to the working parameters, the components of the pH<3 and the adjustment of the concentrations contained in them desorbers ion to the business units that comprise 0.01 to 5.0 mol/l, the flow of purified electrolyte with adjusted acidity and concentration desorbers ions in the anode cavity, the circulation of a mixture of electrolytes in continuous mode to achieve the necessary degree of purification of the ground, the pressure in the anode and cathode cavities are kept lower than atmospheric, and as an electrolyte placed in the anode and cathode cavities, use the same electrolyte, in this case, before the announcement of electrolyte anode and cathode cavities of positive and negative voltage potentials of the constant is on the ground through perforated tube, installed in the soil at the depth of contamination and at the same distance from each other, and continuously monitoring the conductivity of all parts of the ground along the line connecting the anode and cathode cavity by measuring the voltage drop on them and on sites with low conductivity serves the electrolyte, in an amount to provide alignment of the conductivity plots of ground.

Distinctive features of the proposed method is that: before the announcement of electrolyte anode and cathode cavities of positive and negative voltage potentials of the constant current in the soil between the anode and cathode cavities serves the electrolyte in an amount of 0.1-0.5 volume on the volume of treated soil through perforated pipes installed in the ground to the depth of contamination and at the same distance from each other, and continuously monitoring the conductivity of all parts of the ground along the line connecting the anode and cathode cavity, by measuring the voltage drop on them and on sites with low conductivity serves the electrolyte in the amount ensuring alignment of the conductivity plots of ground.

The introduction of the original process is through the tube, evenly placed all around the cleaned area, allows you to immediately start the process of desorption of the contaminant in the entire volume of treated soil, which is especially important when cleaning objects from tightly bound contaminant slow desorption kinetics. At the same time it prevents the re-sorption of contaminant ions as they move to the cathode and increases the conductivity of the soil, and accordingly, the current density and speed of treatment. In turn, this leads to a sharp reduction in the length of inefficient initial stage of the process and increase the speed of cleaning and reduce energy consumption.

Specify the interval entered in the soil of the original electrolyte solution in an amount of 0.1-0.5 volume on the volume of treated soil is determined by the value of its total porosity, which has a maximum value of 0.45 for sandstones and 0.5 for clay soils. Therefore, when submitting it to the tube more than 0.5 volume on the volume of treated soil on its surface is formed a mirror solution that will result in the case of soils with a low infiltration capacity, such as clay, to the spreading of the solution beyond the cleared area and increase the area of contamination. Upon the filing of restaurantbali desorbers ions in the pore solution, resulting due to dilution of the pore water.

The flow of electrolyte solution in the perforated tube is determined by the necessity of soil treatment on the depth of the contamination of the cleaned area, which is especially important when the treatment of the soil with low filterability.

Continuous monitoring of electrical conductivity of all plots and maintaining it at the required level by feeding additional quantities of the electrolyte in the tube leads to higher current density and, consequently, speed cleaning, as well as to increase the service life of the equipment due to prevent local overheating of individual sections of the ground.

An example of the proposed method.

The actual soil moisture content 20%, contaminated with Cs-137, with a specific activity of 120 kBq/kg, 50 kg, was placed in a container with a volume of 40 liters, made of polypropylene in the form of a parallelepiped with a length of 2 m and a cross section 0,15x0,15 M. the ends of the tanks were equipped with a cathode cavities with a volume of 1.5 liters each, separated from the soil by the membranes. In which were placed the electrodes in the form of stainless steel plates of size 0,1x0,1x0,005 m

In the center of the vessel was equipped with anode cavity with a volume of 1.5 l, separated on both sides from the ground membranes. the blow cavity introduced in 1.3 l of electrolyte 0.5 M HNO3+1M NH4NO3.

On each side between the anode and cathode cavities in the ground post on the same 0.2 m distance from each other 8 perforated tubes, which serves the electrolyte solution in an amount of 0.2 volume on the volume of treated soil (8 l). The feed solution is performed in such a way as to prevent the formation of mirror solution on the surface of the soil. Then to the electrolyte of the anode cavity down positive and electrolyte cathode cavities negative potential of the DC voltage (U=70 B). Continuously monitoring the conductivity of various parcels of ground of equal length between the anode and cathode cavities along the line connecting these cavities by measuring the voltage drop across them, and the results of measurement serves the additional amount of the electrolyte solution in the tube to an area with lower conductivity in an amount to provide alignment of the conductivity plots of ground.

For example, the results of one of the voltage measurements on the plots of the soil between the anode and cathode were 10-10-11-11-20 Century After the filing of the tube to an area with a voltage drop of 20 In electrolyte volume of 0.1 l voltage drop, iraniana it all the way, which ensures early in the cleanup process required technological parameters - current density and, consequently, the speed of treatment. As a result of exposure to soil desorbers ions included in the composition of the electrolyte, there is a transition of radionuclides and toxic substances from the soil particles in the pore solution and their movement under the influence of an electric field in the electrolyte cathode cavities.

Simultaneously with the announcement of the electrolyte of the anode cavity positive and electrolyte cathode cavities negative potential of the DC voltage, using a vacuum pump (through the cathode cavity) discharge of the electrolyte and the gas phase of the anode cavity, the flow in the cathode cavity, the output of the electrolyte and the gas phase cathode cavities and filed them in the electrolyte and the gas phase of the anode cavity. The result is the neutralization of the excess formed in the cathode cavity in the electrolysis of water, hydroxyl ions, which prevents the formation of cathode cavities of insoluble hydroxides rock-forming elements, which are transferred together with contaminant ions.

Derived from the cathode cavities electrolytes and Gazovye and so p. ) present in it from radioactive and toxic elements.

After separation from the electrolyte solution Cs-137 it is directed to the correction of electrolyte composition to the initial values. Then the purified electrolyte solution with adjusted composition is introduced into the anode cavity, followed by circulation of the electrolyte solution in a continuous mode to achieve the necessary degree of purification of the soil.

For comparison, an experiment was different from the above that the flow of electrolyte in the soil did not.

The test results of the prototype and the proposed method for cleaning the actual soil contaminated with Cs-137 showed that the latter has higher productivity, efficiency, speed cleanup of soil and low energy consumption. As seen in the table of results, preliminary submission of the Stripping solution of the reagent in contaminated soil reduced the duration of treatment (for example, up to 40%) more than in 2 times, increase the average speed of cleaning, from 0.23 to 0.5%/day, respectively, to reduce energy consumption in ~2 times.

Tests have demonstrated the efficiency of the proposed method in the pilot the LITERATURE 1. Avca Germany 4307719, MKI 5: G 21 F 9/28, op. 15.09.94.

2. U.S. patent 5074986, MKI 5: 25 1/22, op. 24.12.91.

3. International application WO 95/11095, MCI: 09 WITH 1/00, A 62 D 3/00, op. 27.04.95.

4. RF patent 2172531 C1, G 21 F 9/28 At 09 With 1/08, bull. 23, op. 20.08.2001.

Claims

The electrokinetic method of cleaning soil from radioactive and toxic substances, including the creation of areas of cleared ground of the two cathode cavity and located between the anode cavity, placing electrolytes with working concentrations desorbers ions and acidity in the anode and cathode cavities and wrap them positive and negative potentials of the DC voltage, the output of the electrolyte from the anode cavity and flow into the cathode cavity, the output of the electrolyte and the gas phase from the cathode cavities, cleaning bred electrolytes from polluting the soil radioactive and toxic substances and the subsequent adjustment of the pH of treated electrolytes to the working parameters, the components of the pH < 3, and the adjustment of the concentrations contained in them desorbers ion to the business units that comprise 0.01 to 5.0 mol/l, the flow of purified electrolyte with adjusted acidity and concentration desorbers the penalties purification of soil, moreover, the pressure in the anode and cathode cavities are kept lower than atmospheric, and as an electrolyte placed in the anode and cathode cavities, use the same electrolyte, characterized in that before the announcement of electrolyte anode and cathode cavities of positive and negative voltage potentials of the constant current into the ground on each side between the anode and cathode cavities serves the electrolyte in an amount of 0.1-0.5 volume on the volume of treated soil through perforated pipes installed in the ground to the depth of contamination and at the same distance from each other, and continuously monitoring the conductivity of all parts of the ground along the line, connecting the anode and cathode cavity, by measuring the voltage drop on them and on sites with low conductivity serves the electrolyte in an amount to provide alignment of the conductivity plots of ground.

 

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FIELD: environment protection.

SUBSTANCE: method involves introducing into soil contaminated with oil or oil products ameliorant, such as complex of aluminosilicate mineral and nitrogen-phosphate fertilizer; plowing soil to depth of at least 25-30 cm.

EFFECT: reduced soil recultivation time and decreased consumption nitrogen-phosphate additives.

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