RU2508954C1 - Method of removal hydrocarbons, radioactive nuclides and heavy metals from soil and device to this end - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to environmental protection, particularly, to reclamation of soils contaminated with hydrocarbons (oil products), radioactive nuclides and heavy metals with the help of electric osmosis. Proposed method consists in inducing nonuniform electric field between central and peripheral electrodes and applying magnetic field perpendicular to cleaning zone. Proposed device comprises central electrode. Said electrode is composed of a rod with cross-section of polygonal shape with concave sides. System of peripheral electrodes is composed by separate rods. The latter are interconnected by plates arranged in zigzag line so that its recess or ledge is aligned with those of central electrode surface. Besides, proposed device comprises two extra solenoids arranged one above the other. First solenoid is plunged in submerged zone soil while second electrode is fixed by crossbar at the post extending through central electrode axis.

EFFECT: higher quality of cleaning.

4 cl, 4 dwg

Description

The invention relates to the protection of the environment, namely the reclamation of lands contaminated with hydrocarbons (oil products), neutralizing the soil from radionuclides and heavy metals when using the phenomenon of electroosmosis.

A known method of cleaning a capillary-porous medium contaminated with oil and oil products by introducing a solution of oil-oxidizing microorganisms into the cleaning zone, introducing an electrically conductive liquid, passing electric current to create electroosmosis (RU 96115094 A, IPC V09C 1/10, publ. 11/27/1998, )

A known method of in situ restoration of contaminated (heterogeneous) soils of various composition and properties, including introducing material for cleaning pollutants into a heterogeneous soil region, passing a constant electric current within a contaminated heterogeneous soil between electrodes, applying a hydraulic gradient across the pollution region (RU 2143954 C1, IPC B09C 1/08, publ. 10.01.2000).

The disadvantage of the above analogues is the complexity of their use and the insufficient degree of purification of the soil from pollution.

The closest analogue of the method adopted as a prototype is a method of cleaning the soil from hydrocarbons, including the creation of an electric field gradient between the central and peripheral electrodes in the zone of cleaning, supplying a cleaning carrier fluid to the cleaning area, moving the carrier fluid under the action of the electroosmotic effect of the central the electrode to the peripheral, displacement from the soil by the carrier liquid of hydrocarbons and their removal from the peripheral electrodes (RU 2132757 C1, IPC 6 V09C 1/02, B01D 61/56 1/18, publ. 10.07.1999).

The disadvantage of the prototype is the insufficient degree of purification of the soil from hydrocarbons, as well as ineffective cleaning from radionuclides and heavy metals, since cleaning using electroosmosis is carried out in a uniform electric field.

A device is known for applying a method for cleaning contaminants of a capillary-porous medium, including a chamber for accommodating a medium to be cleaned with electrodes connected to a direct current source, a container with a liquid to be cleaned and a container for waste liquid (RU 2106432 C1, IPC 6 C25C 1/22, publ. March 10, 1998).

A known line for cleaning oil-contaminated soils, soils and oil sludge containing a hopper, screw conveyor, oil overflow tank, vibrating screen, loading grate, washing unit (RU 2244686 C1, IPC C02F 1/40, publ. 20.01.2005).

The disadvantage of the above analog devices is also the insufficient degree of soil purification from contamination.

Closest to the proposed device for implementing the method adopted for the prototype, is a device that consists of immersed in the soil on the cleaned area of the central and peripheral electrodes, nozzles for supplying water, a pump used to remove water with hydrocarbons from the peripheral electrodes, a separator serving for separating water and hydrocarbons, tanks with a venturi nozzle and a heater, a pump for pumping water into nozzles and a venturi nozzle. The separator and the tank are connected by a water pipe to a non-return valve, the tank is additionally connected to the nozzle by a high-pressure water supply pipe (RU 2132757 C1, IPC 6 V09C 1/02, B01D 61/56 1/18, publ. 10.07.1999).

The disadvantage of the prototype is the inefficient cleaning of the soil from hydrocarbons (oil products) and insufficient cleaning of the soil from heavy metals and radionuclides.

The objective of the proposed method and device for its implementation is to increase the efficiency of soil cleaning from hydrocarbons (petroleum products), as well as from heavy metals and radionuclides.

The technical result is achieved due to the fact that the method of cleaning the soil from hydrocarbons, radionuclides and heavy metals involves immersing in the soil on the cleaned area of the central and peripheral electrodes, creating a voltage gradient between the central and peripheral electrodes, supplying a non-polluting liquid to the region adjacent to the central electrode -carrier, the movement of the carrier fluid under the action of the electroosmotic effect from the central electrode to the peripheral electrode, displacement from the soil by the carrier fluid hydrocarbons and their removal from the peripheral electrodes, but in contrast to the prototype, to increase the degree of soil purification from hydrocarbons, radionuclides and heavy metals between the central and peripheral electrodes create an uneven electric field, and perpendicular to the surface of the cleaned area is additionally exposed to a magnetic field. In addition, the surface of the soil to be cleaned is affected by a magnetic field of reverse polarity.

The technical result of the application of the device for implementing the method is achieved due to the fact that it contains a central electrode and a system of peripheral electrodes immersed in the soil of the cleaning zone, nozzles for supplying carrier fluid, pumps for injecting liquid into the nozzles and removing liquid containing contaminants from the cleaning zone, but unlike the prototype, to increase the degree of soil purification, the central electrode is made in the form of a rod, the cross section of which is a polygon with concave sides, and the system of peripheral electrodes made of separate rods interconnected by plates located along a broken line in such a way that opposite the protrusion or depression on the surface of the central electrode there is a depression or protrusion of the broken line of the plates, the device further comprises two solenoids placed one above the other, the first of which it is immersed in the soil of the cleaning zone, the second is fixedly mounted with the help of a traverse on a stand passing through the axis of the central electrode.

In addition, the surface of the central electrode is made of mesh with seals, and in the middle of each plate parabolic or needle spikes are rigidly fixed, and plate spikes are located opposite the seals of the central electrode.

In the claimed invention, an inhomogeneous electric field is created due to the passage of a constant electric current between the protrusions or depressions (peak) of the central electrode and the depressions or protrusions formed by the connecting plates of the peripheral electrodes, or when the direct current flows between the seals on the surface of the mesh central electrode and rigidly fixed parabolic or needle spiked plates.

It is known that radionuclides and heavy metals adsorbed by soils form complexes on the surface of clay particles, while the pH of the pH decreases at the anode to pH = 2, and at the cathode increases to pH = 12 depending on the current strength (Soil pollution and the latest technologies for their restoration. Stupin D.Yu. St. Petersburg. - Because of the Doe. - 2009. - P.363). The transfer of substances in soils under the influence of an electric field occurs in the following directions: diffusion, electromigration, electroosmosis. They are influenced by: the mineral composition of the soil, the composition of the conductive medium with the carrier fluid, the conductivity of the carrier fluid, the electrochemical composition of the soil and its porosity. Electromigration is the main mechanism of transport of substances in an electric field. Cations of radionuclides and heavy metals are attracted and adsorbed on negative charges of clay particles. Moreover, the sorption mechanism includes the formation of components on their surface (adsorption) or ion exchange. The help in desorption (removal) of cations of radionuclides and heavy metals from the soil is provided by the formation of hydrogen ions H ⁺ on the anode during electrolysis of water and their transfer to the soil by diffusion, electromigration, electroosmosis. In this case, heavy metals and radionuclides form complexes on the surface of clay particles, which is expressed by the reaction:

$$n{H}^{+}-Me{e}^{n+}{\left[P\mathrm{about}h\mathrm{at}\mathrm{but}\right]}^{n-}=H_n{}^{n+}{\left[P\mathrm{about}h\mathrm{at}\mathrm{but}\right]}^{n+}+M{e}^{n+}\left(\mathrm{one}\right)$$

where Me ⁺ is the cation of heavy metals or radionuclides, n is the number of complexes formed.

Heavy metals and radionuclides have various sorbing characteristics, which depend on the type of adsorbents, i.e. sorbents that absorb surface layer pollution. The main difficulty in removing cations of heavy metals and radionuclides from the clay surface is their desorption from finely granulated clay sediments with a large cationic capacity. Help in the desorption of these cations is provided by H ⁺ ions formed on the anode during electrolysis of water (carrier fluid) and their movement in the soil under the influence of electroosmosis.

In the proposed method, cations of radionuclides and heavy metals of contaminated soil, adsorbed by clay particles, are polarized in an inhomogeneous electric field under the influence of a moment of force, tend to rotate axis along the direction of field action. An inhomogeneous electric field created by the electrodes causes the migration of clay cations with sorbed radionuclides and heavy metals from the system of peripheral electrodes to the central electrode.

Under the action of a magnetic field perpendicular to the contaminated soil, created by the upper and lower solenoids, a Lorentz force arises. Under the influence of this force, clay cations with sorbed radionuclides and heavy metals will begin to deviate from their straight path from the anode to the cathode and will entrain a carrier fluid in which a circular flow arises around the central electrode.

The circular motion of the carrier fluid around the central electrode increases the cleaning path when the carrier fluid flows from the cathode to the anode, intensifies the cleaning process — electromigration and electroosmosis of clay cations with radionuclides and heavy metals absorbed on them, which increases the efficiency of soil cleaning from contamination.

Figure 1 shows a diagram of a device for implementing the method of cleaning the soil from hydrocarbons, radionuclides, heavy metals;

figure 2 is a diagram of a soil treatment zone with a central and peripheral electrodes connected by plates along a broken line, top view;

figure 3 - diagram of the cleaning zone with solenoids;

figure 4 - diagram of the cleaning zone with peripheral electrodes in the form of plates with parabolic or needle spikes, top view.

The diagram (figure 1) of the device shows: a cleaning zone 1, a central electrode (anode) 2 immersed in the soil of the cleaning zone 2, a system of peripheral electrodes (cathode) 3, a nozzle 4 for supplying a carrier fluid, a pump 5 for removing liquid from the peripheral electrodes containing oil products, radionuclides, heavy metals, a pump 6 for injecting the carrier fluid into the nozzle 4, protrusions and depressions of the surface of the central electrode with a cross section in the form of a polygon with concave sides 7 (figure 2), protrusions and depressions 8 formed by connecting the edges of the system of peripheral electrodes located along the broken line, the upper solenoid 9 (figure 3), the lower solenoid 10, stand 11, the beam 12, the perforated pipe 13 (figure 1), pump 14 for pumping contaminants containing heavy metals and radionuclides, parabolic or needle spikes 15 (figure 4), the mesh central electrode 16.

The proposed method of soil cleaning is carried out using the device as follows.

The carrier fluid by the pump 6 is fed through the nozzle 4 to the area adjacent to the Central electrode 2 (figure 1). Since the cross section of the central electrode has protrusions and depressions 7, and the connecting plates of the peripheral electrode system are located along a broken line with depressions and protrusions 8 directed towards each other, when the direct current is turned on, an uneven electric field is created between them (Fig. 2). An uneven electric field is also created between the seals of the mesh central electrode 16 and the spikes 15 mounted on the plates of the peripheral electrode system (Fig. 4).

The carrier fluid under the action of the electroosmotic effect flows from the central electrode 2 to the system of peripheral electrodes 3 (figure 1). The carrier fluid when the soil is contaminated with oil products forms an emulsion, which enters the peripheral electrodes 3, from where it is removed by the pump 5.

As a result of electrolysis of water, hydrogen ions H ⁺ are formed on a negatively charged electrode - cathode, and hydrogen gas is also released. When cleaning the soil from radionuclides and heavy metals, H ⁺ hydrogen ions cut the cations of radionuclides and heavy metals sorbed on clay particles. In this case, cathode precipitates of radionuclides and heavy metals, which are removed through the perforated tube 13 by the pump 14 (Fig. 1).

Between the upper 9 (figure 3) solenoid mounted on the rack 11 and the traverse 12, and the lower 10 solenoid creates a magnetic field. Under the action of a perpendicularly directed magnetic field, the Lorentz force arises. Under the action of this force, clay cations with sorbed radionuclides and heavy metals will begin to deviate from their straight path from the anode to the cathode and will entrain a carrier fluid in which a circular flow will occur (Fig. 3). The circular motion of the liquid intensifies the electromigration and electroosmosis of clay cations with sorbed radionuclides and heavy metals and ensures their removal from the soil, which increases the cleaning efficiency. If during a certain period of time the current direction is reversed in the upper 9 and lower 10 solenoids, then the direction of the magnetic field is cyclically reversed, and then the direction of the circular motion of the carrier fluid changes. This leads to more intensive cleaning of the contaminated soil from radionuclides and heavy metals.

Example 1. The treatment was subjected to a contaminated soil with dimensions: 3 × 5 m, a depth of 11 m from heavy sandy loam containing heavy metal ions Cu, Zn, Pb, Cd as a pollutant.

Six graphite rods and one graphite rod for the anode with a diameter of 220 mm are used as cathode electrodes. The rods are wrapped with a shell filled with iron filings and graphite in a proportion of 1/1. The device consists of six cathode graphite rods located along the perimeter of the cleaning zone at a distance of 1-1.2 m from each other and fastened with 40-50 mm wide plates, and an anode graphite rod located in the center of the soil cleaning zone. The distance between the cathode rod system and the anode rod is 2.2 m. The voltage between the cathode rod system and the anode was maintained at 100-150 V, the current density was 1 mA / cm ² , and the voltage gradient was 0.25 V / cm. Processing time: 20, 30, 50, 70, 225, 450 hours. The magnetic field strength is 250-370 Oe. During the processing of a contaminated soil, the velocity of the carrier fluid during electroosmosis is 0.3-0.45 cm / day.

After soil cleaning and excavation of the samples, they were cut into several parts, then processed by several extracts to remove forms of heavy metals in a mobile and absorption state. The concentration of heavy metal ions in the aqueous solution was determined by the absorption method using Zeiss AAS-3 equipment. The concentration of heavy metal ions in the solid phase was determined by x-ray spectral method. To separate the solid and liquid phases of the soil, the method of successive ammonium acetate extracts was used. These forms along with the water-soluble form characterize the potential mobility of heavy metals. The change in the concentration of heavy metal ions in samples of polymineral loam before and after exposure to an uneven electric field is presented in tables 1 and 2.

Table 1 The concentration of heavy metal ions in samples of polymineral loam before exposure to an uneven electric field Heavy metal ions Humidity The concentration of ions in the exchange complex The concentration of ions in aqueous solution % mEq mg / l Cu ⁺² 29th 38.16 2830 Zn ⁺² 29th 73.57 6450 Pb ⁺² 29th 139.99 10370

table 2 The concentration of heavy metal ions in samples of polymineral loams after exposure to an uneven electric field Heavy metal ions Humidity Zone The concentration of ions in the exchange complex The concentration of ions in the pore soil solution The concentration of ions in the pore soil solution % mEq mg / l mEq Cu ⁺² 32 Anode 0.018 0.04 0.009 Cu ⁺² 28 Cathode 0,068 0.96 0.267 Zn ⁺² 32 Anode 0.016 0.01 0.003 Zn ⁺² 28 Cathode 0.187 0.73 0.162 Pb ⁺² 32 Anode 0.012 0,07 0.017 Pb ⁺² 28 Cathode 0.847 3.89 0.944

The results are shown in table 1, show that a significant part of the ions of Pb ^{+2 is} contained in absorbed form.

Under the influence of an uneven electric field, the concentration of adsorbed Cu ^{+ 2} ions changes from 38.16 mEq to 0.018 mEq in the anode zone, Zn ⁺² changes from 73.57 mEq to 0.016 mEq in the anode zone, Pb ^{+ 2} varies from 139.99 mEq to 0.07 mEq in the anode zone (Tables 1 and 2). This is due to the influence of the pH of the pH, because an acidic medium pH = 3-5 is formed in the anode zone. Under such conditions, the solubility of lead compounds with hydrated OH ^{+ I} ions and bicarbonate ions increases sharply. Under the influence of an uneven electric field and an acidic medium, part of the adsorbed ions is redistributed from the solid phase of the soil to the liquid phase. The above studies showed that the main part of heavy metals under the influence of an uneven electric field forms complexes with the anions of the pore soil solution, which are removed using electroosmosis.

Cleaning the contaminated soil from radionuclides (cesium (CS 137), strontium (Sr 90), uranium, barium, as well as organophosphorus and organofluorine compounds) is similar to cleaning the soil from heavy metals (copper, lead, manganese, mercury, cobalt, cadmium, chromium nickel). The degree of soil cleaning using an uneven electric field from heavy metals was 99%.

Example 2. In the study of the purification of soil loams from hydrocarbons using an uneven electric field, a technique similar to that described in Example 1 was adopted. The content of liquid hydrocarbons in the soil was determined by thermal methods, as well as by chemical extraction of oil and machine oil from samples with chloroform.

As a result of the research, the following results were obtained.

Petroleum products and engine oil are removed from both the cathode and anode zones.

50% is removed from samples with an initial oil content of 5%, 40% is removed with an initial oil content of 10%.

Similarly, 60% is removed from samples with an initial engine oil content of 5%, 50% is removed with an initial engine oil content of 10%.

Cleaning the contaminated soil from heavy metals (lead, manganese, mercury, cobalt, cadmium, chromium, nickel) is similar to cleaning the soil from radionuclides (cesium (CS 137), strontium (Sr 90), uranium, barium, and also organophosphorus and organofluorine compounds )

When processing a contaminated soil using the inventive device, the soil cleaning from radionuclides (cesium (CS 137), strontium (Sr 90), uranium, barium, as well as organophosphorus and organofluorine compounds) is significantly increased.

In addition, when processing a contaminated soil using the inventive device, the content of heavy metals in the soil decreases: for lead - up to 99%, for manganese - 95%, for mercury - up to 64%, for cobalt - up to 97%, for cadmium - up 96%, for chromium - up to 92%, for iron - up to 99%, for nickel - up to 90%.

Claims (4)

1. A method of cleaning the soil from hydrocarbons, radionuclides and heavy metals, including immersion in the soil on the cleaned area of the central and peripheral electrodes, creating a voltage gradient between the central and peripheral electrodes, supplying to the region adjacent to the central electrode a non-contaminating carrier fluid, moving the fluid -carrier under the action of an electroosmotic effect from the central electrode to the peripheral, displacement of hydrocarbons from the soil by the carrier fluid and their removal from the peripheral ele ctrod, characterized in that between the central and peripheral electrodes create an uneven electric field, and perpendicular to the surface of the cleaned area is additionally affected by a magnetic field. 2. The method according to claim 1, characterized in that the surface of the soil to be cleaned is exposed to a magnetic field of reverse polarity. 3. A device for implementing the method of cleaning the soil from hydrocarbons, radionuclides and heavy metals according to claims 1, 2, comprising a central electrode and a system of peripheral electrodes immersed in the soil of the cleaning zone, nozzles for supplying a carrier fluid, pumps for pumping liquid into the nozzles and removal liquid containing contamination from the cleaning zone, characterized in that the central electrode is made in the form of a rod, the cross section of which is a polygon with concave sides, and a system of peripheral electro the cores are made of separate rods interconnected by plates placed along a broken line so that opposite the protrusion or depression on the surface of the central electrode there is a depression or protrusion of the broken line of the plates, the device further comprises two solenoids placed one above the other, the first of which is immersed into the soil of the cleaning zone, the second is fixedly mounted with the help of a traverse on a stand passing through the axis of the central electrode. 4. The device according to claim 3, characterized in that the surface of the central electrode is made of mesh with seals, and parabolic or needle spikes are rigidly fixed in the middle of each plate, and plate spikes are located opposite the seals of the central electrode.

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