Plasma electrolytic corrosion reactor and method of use thereof

Abstract

The proposed invention relates to the field of liquid industrial waste treatment, in particular to a plasma electrochemical reactor for the comprehensive treatment of industrial wastewater and stormwater, as well as treated water from nuclear power plants, for the purpose of inactivating and purifying them, in particular the removal of cesium-137( 137 Cs), Strontium 90 ( 90 Sr), Americium ( 241 Am), Cobalt 60 ( 60 This document relates to a plasma electrochemical reactor for the removal of radioactive nuclides of Co, chromium (Cr), copper (Cu), zinc (Zn), nickel (Ni), tin (Sn), lead (Pb) and heavy metals such as cadmium (Cd), and to methods of use thereof, including the treatment of liquid waste from nuclear power plants (NPPs).

Description

[Technical field]

[0001] The proposed invention relates to the field of liquid industrial waste treatment, in particular to a plasma electrochemical reactor for the comprehensive treatment of industrial wastewater and stormwater, as well as treated water from nuclear power plants, for the purpose of inactivating and purifying them, in particular the removal of cesium-137( 137 Cs), Strontium 90 ( 90 Sr), Americium ( 241 Am), Cobalt 60 ( 60 This document relates to a plasma electrochemical reactor for the removal of radioactive nuclides of Co, chromium (Cr), copper (Cu), zinc (Zn), nickel (Ni), tin (Sn), lead (Pb) and heavy metals such as cadmium (Cd), and to methods of use thereof, including the treatment of liquid waste from nuclear power plants (NPPs). [Background technology]

[0002] Those skilled in the art know that one of the methods for inactivation and treatment of contaminated liquids to remove radionuclides and heavy metals is a coagulation process using inorganic coagulants based on iron and aluminum compounds, which in an alkaline environment are able to form hydroxides of aluminum and iron, thus precipitating the abovementioned contaminants. The main drawback of this technique is that it requires the use of additional reagents to create the required pH environment, which makes the application of this process complicated and more expensive.

[0003] Also, the prior art [see, for example, Shakhova NB, Yurmazova TAA model of the physical and chemical processes that occur during the dispersion of metals by pulsed electric discharges in water and dilute salt solutions (Model fiziko-khimicheskikh protsessov, protekayushchikh pri dispergirovanii metallov impulsnymi elektricheskimi razryadami vode i razbavlennykh rastvorakh soley)] teaches a method of inactivation and treatment of contaminated liquids using a coagulation process to remove radionuclides and heavy metals, when a coagulant is obtained during the electrochemical dispersion (evaporation and condensation) of metallic aluminum or iron granules with the formation of a mixture of short-lived aluminum and iron ions, these ions being cesium-137( 137 Cs), Americium 241( 241 Am), Strontium 90 ( 90 Sr), Cobalt 60 ( 60 During the presence of Со) ions, they interact very actively with them, subsequently forming their oxides and hydroxides, the latter of which solidify to form complex compounds that are insoluble in water. For example, during the galvanic dispersion of metallic aluminum granules in aqueous solutions of NPP liquid waste, aluminates are formed, which are insoluble salts of orthoaluminate (HAlO2) and metaaluminate (MAl2O4), where M is Cs, Sr, Am, Z, Zn, Pb, etc. A distinctive property of aluminates is their isomorphism, i.e. the ability of chemical elements with similar chemical properties to form mixed crystals or to substitute for one another in the molecular composition of simple or complex substances. Strontium ions ( 90 Sr) and cesium ions ( 137The highly selective sorption and coagulation of ionic and polyvalent complexes of oxides and hydroxides of aluminum for cesium (Cs) is explained by the fact that strontium and cesium belong to the highly active alkali and alkaline earth metals which easily form complexes with each other. At the same time, cesium has a high dissociation capacity (Cs + It is notable that cesium is a metal that breaks down very easily into ions. Generally, isotopes of cesium are ionic. Cesium hydroxide is extremely reactive and extremely hygroscopic, and when it interacts with the bound water in Al(OH)3, it forms very strong aluminates that precipitate and can be easily separated from the liquid and purified.

[0004] The destructive effect of ozone and OH radicals on complexones is also known from the prior art, since ozone destroys almost all organic compounds very rapidly. The products of complexone destruction do not deteriorate the parameters of further processes. At the same time, the toxicity level of the products formed during the oxidation of complexones with ozone and OH radicals is much lower than that of the original compounds. In addition, the direct synthesis of ozone and OH radicals during solution treatment does not require separate actions and costs for obtaining and storing large quantities of solution treatment reagents. Thus, as a result of complexone destruction, the ions of radioactive metals are easily transferred to sorbed and solidified forms. At the same time, this forms solid phases of the corresponding hydroxides and oxides of transition metals (Fe, Ni, Cr, etc.), which are usually present in the initial solution to be purified. Radioactive nuclides such as cobalt (Co), zinc (Zn), lead (Pb), etc. are sorbed on these hydroxides and oxides. At the same time, the depth of oxidation of the organic complexes greatly influences the extent of removal of these and other radionuclides.

[0005] Water treatment by removing heavy metals and radionuclides using iron hydroxides has been carried out for a long time, mainly by the ferritization method [see, for example, patents RU2220110 and UA95723]. The disadvantage of this method is the high energy consumption, since it is usually carried out at temperatures above 75°C.

[0006] By exposing the reaction mixture to electromagnetic pulse discharges of different powers at room temperature, instead of high temperature activation, it is possible to increase the energy efficiency of the ferritization process [see, for example, patents SU1787950, SU861332, UA56454]. Water treatment methods in electrolytic cell chambers using both constant and alternating voltages are also known [see, for example, patents UA11271, UA2180, UA902, UA124]. The general disadvantage of the named technologies is not only their relatively low efficiency, but also the possibility of passivation and therefore destruction of the electrodes by organic substances present in the effluent.

[0007] A solution close to the claimed invention is a reactor using electric discharge technology, in which the coagulation process is carried out with the aid of metal particles, in particular aluminum, added to the reactor, which allows a significant increase and acceleration of the coagulation process compared to the treatment of wastewater in electrolytic cells [Zubenko AA, Yuschishena ANStudying the properties of electric-discharge aluminum hydroxide (Issledovaniye svoystv elektrorazryadnogo gidroksida alyuminiya) / / Elektronnaya obrabotka materialov, 2001. No. 6, pp. 60-65]. The disadvantage of these methods is the inability to treat complex compounds containing organic substances and radionuclides.

[0008] Another solution close to the claimed invention is the technical solution according to WO2020180277, in which the water to be purified is fed to a reactor containing metal granules. Under the influence of electric pulses applied to the electrodes, a process of galvanic corrosion of the granules occurs, and an air-oxygen mixture is additionally fed, causing the particles to coagulate the heavy metal ions. A disadvantage of this solution is the intermittent nature of the process, which allows only limited amounts of water to be purified. Another disadvantage of this technical solution is the use of unipolar pulses, which significantly reduces the efficiency of the reactor.

[0009] Another solution close to the claimed invention is the technical solution according to patent UA124651, which provides a discharge chamber made of a dielectric material with an internal electrode and a lower partition in which aluminum granules are present, which under the influence of an electric pulse interact with each other and cause a process of electroerosion with the formation of aluminum hydroxide, as well as orthoaluminates and metalloaluminates, which become coagulants with a high purification rate for liquid waste from nuclear power plants. The main drawback of the above technical solution is its low efficiency in terms of coagulation of radioactive elements, which are usually present in the liquid waste in the form of compounds with organic complexes. In addition, liquid radioactive waste usually contains organic substances that significantly complicate the treatment process, and the use of unipolar pulses leads to passivation of the reactor electrodes, reducing their efficiency.

[0010] The closest prior art to the claimed invention is the technical solution disclosed in the utility model patent of Ukraine No. 76821, which was selected as the prototype. In this technical solution, a reactor with electrodes embedded inside the chamber is used for the purification of polluted water. A unipolar pulse with a duty ratio of 75-85 microseconds and a voltage amplitude of 300-800 V is applied to the electrodes. The reactor chamber is filled with the water to be purified through an intake pipe. Inside the chamber there are spherical granules made of iron and aluminum alloys, which occupy about 20-25% of the chamber volume, which interact with each other under the influence of water pressure and electric pulses applied to the electrodes of the reactor, generating electric sparks at the contact points, which causes electrolytic corrosion of the granules, which generates metal ions accompanied by the generation of ozone, local temperature increase and cavitation, and then the coagulant iron and aluminum hydroxides are obtained, which interact with heavy metals and radioactive elements to form complexes and precipitate. Within the chamber there are upper and lower partitions that prevent the removal of granules from the working volume, while at the top of the reactor there is a nozzle that ejects the purified water. Summary of the Invention [Problem to be solved by the invention]

[0011] The specified technical solution has several drawbacks, namely: - The simultaneous use of iron and aluminum metal granules with Fe-Fe, Al-Fe, Al-Al granules will result in different discharge powers, reducing the efficiency of electrolytic corrosion. At the same time, aluminum granules will be consumed faster than iron granules, which will lead to the loss of iron-aluminum mass ratio, non-uniformity of the discharge medium, and reduced efficiency of the solidification process; - high concentrations of coagulants cause preferential interaction of iron ions with organic matter dissolved in the water to be purified, but not with heavy metals and radioactive elements, thus reducing the purification of contaminated water from radioactive elements and heavy metals; - passivation of electrodes by organic matter when using unipolar voltage pulses; - The amount of ozone produced is not sufficient to oxidize the organic matter present in the pollutants.

[0012] The goal of the claimed invention is to create a highly efficient plasma electrochemical reactor and method of its use for treating liquid industrial waste, especially those containing pollutants of organic origin, to remove radioactive elements and heavy metals. [Means for solving the problem]

[0013] This problem is solved by creating a plasma electrolytic reactor for treating liquid waste, which includes an intake pipe located at the bottom of the reactor and feeding the liquid waste; a cylindrical or other curved discharge chamber filled with metal granules (balls) and made of a dielectric material, which ensures a stable passage of the liquid and the absence of "dead" areas, where at the top and bottom of the reactor there are dielectric grids that limit the removal of the granules by the liquid from the chamber; at the top of the reactor there is an extraction pipe that removes the solidified suspension; on the inner surface of the reactor there are metal electrodes, in particular made of steel, to which a source of rectangular pulses with a control unit is connected.

[0014] According to the claimed invention, the reactor also comprises a second discharge chamber filled with metal granules (balls) and connected to the first chamber by a connecting pipe, and the solidified suspension is fed from the first chamber to the second chamber, where one chamber is filled with iron granules and the other chamber is filled with aluminum granules. An intake pipe feeding the liquid waste is connected to the first chamber and an outlet pipe removing the solidified suspension is connected to the second chamber.

[0015] According to the claimed invention, the size of the granules (balls) is correlated with the inner diameter of the discharge chamber, and this correlation is as follows: 0,001D≦d≦0,15D where d is the diameter of the ball (granule), mm, and D is the inner diameter of the chamber, mm.

[0016] According to the invention now claimed, the reactor further comprises a source of ozone-air mixture and a mixer connected in series to the intake pipe which supplies the liquid waste to the reactor.

[0017] The problem is also solved by creating a method for treating liquid waste using a plasma electrolytic reactor, where the liquid waste is continuously fed under pressure through an intake pipe to the reactor. A source of rectangular pulses with a voltage amplitude having a value ranging from 300V to 800V depending on the type of pollutant is activated with a control unit to feed rectangular pulses to the discharge electrodes to generate volumetric discharges between the packed granules (balls) and volumetric microplasma, respectively, which ionize the liquid and form nanoparticles of the metals from which the granules are made. At the same time, a process of coagulation and separation of organic and / or inorganic pollutants, in particular heavy metals and / or radioisotopes, from the solution takes place in the reactor with the help of a coagulant, which is a hydroxide of the metal from which the granules are made, formed during the plasma chemical reaction, and which consequently transfers the pollutants from a soluble to an insoluble state. The suspension formed during the purification process is then removed from the reactor through an intake pipe. The suspension may then be fed, for example, to a membrane filter to separate it into a solid fraction and water.

[0018] Now, according to the claimed invention, liquid waste is fed under pressure through an intake pipe to a first discharge chamber filled with metal granules made from one type of material, iron or aluminum; after completion of the solidification process in the first chamber, the suspension is fed through a connecting pipe to a second discharge chamber filled with metal granules made from the other type of material, aluminum or iron; after completion of the solidification process in the second chamber, the resulting suspension is fed to an extraction pipe.

[0019] According to the claimed invention, the liquid waste is premixed with the sorbent.

[0020] According to the claimed invention, the liquid waste is pre-saturated with an ozone-air mixture in a mixer connected to the intake pipe of the reactor.

[0021] Here, according to the claimed invention, the rectangular pulses applied to the electrodes are bipolar, i.e. each subsequent pulse changes polarity to the opposite and has a frequency of 50-200 Hz. Effect of the Invention

[0022] The technical results of the claimed invention are as follows: - this process is implemented using two discharge chambers, one filled with granules (balls) made of iron and the other filled with granules (balls) made of aluminum, in which the contaminated liquid is successively solidified with hydroxides of iron and aluminum, while bipolar rectangular pulses with a voltage amplitude of more than 300-800 V and a frequency of 50-200 Hz are supplied to the electrodes of the device, making it possible to significantly intensify the coagulation process and the degree of liquid waste treatment, respectively; - The stated dependence between the inner diameter of the discharge chamber and the diameter of the filled balls (granules) allows to increase the efficiency of the device and the degree of liquid waste treatment, respectively. In case of a relatively small size of the balls, the energy of the discharge generated by the reactor electrodes is divided into a large number of micro-discharges, as a result of which the power of each micro-discharge is low, which is not sufficient to obtain nanoparticles. Instead, ultraviolet radiation is generated and the liquid is partially heated. In case of a large size of the balls, the number of micro-discharges is small and the power of each discharge is high, which leads to an aggregation (sticking) process between the balls. At the same time, the number of nanoparticles formed is insufficient for an effective realization of the solidification process. - the stated electrical parameters of the pulse are also related to the generation of the optimum energy in one micro-discharge that effectively realizes the process. Under conditions of low pulse power, the discharge is unstable and almost no nanoparticles are generated. Under conditions of high pulse power, the ball melts, the discharge acquires the properties of arc welding and almost no nanoparticles are generated; - pre-saturating the removed contaminated liquid with an ozone-air mixture before feeding it into the first discharge chamber makes it possible to obtain iron(III) hydroxide, which has significantly stronger coagulation properties than the iron(II) hydroxide formed in the discharge chamber during operation of the device, which makes it possible to remove organic impurities, heavy metals and, in part, radioactive elements with high strength and purification; - premixing the liquid waste with a sorbent makes it possible to increase the degree of purification of the liquid waste from radioactive isotopes when using the claimed device; [Brief description of the drawings]

[0023] [Figure 1] The proposed invention is illustrated by a figure in which the components bear the following references: intake pipe (1) supplying the liquid waste, reactor body (2), electrodes (3); first discharge chamber (4), metal granules in the first discharge chamber (5), dielectric grid (6), connecting pipe (7), second discharge chamber (8), metal granules in the second discharge chamber (9), extraction pipe (10) removing the solidified suspension, rectangular pulse source with control unit (11), source of ozone-air mixture (12), and mixing device (13). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The proposed invention is illustrated by the following use example: Liquid waste generated during the operation of an NPP reactor is used for treatment. This liquid waste contains heavy metals such as cadmium, chromium, copper, zinc, tin, nickel, lead, radioactive elements such as cesium, strontium, americium, cobalt, as well as organic compounds, in the concentrations given in table 2. The specified waste is premixed with a sorbent. The liquid waste is fed under pressure to a mixer (13), to which an ozone-air mixture is simultaneously fed from a source (12). From the mixer (13), the liquid is fed through an intake pipe (1) of a reactor (2) to a first discharge chamber (4) filled with iron granules (balls) (5) forming a quasi-liquefied mixture. A source (11) of rectangular pulses is activated by means of a control unit. The resulting suspension is fed through a dielectric grid (6) at the top of the first chamber and through a connecting pipe (7) to a second discharge chamber (8) with aluminum granules (9), where a coagulation process similar to that in the first discharge chamber (4) occurs. The resulting suspension is fed through a dielectric grid (6) at the top of the second discharge chamber (8) and through an extraction pipe (10) to the outside of the reactor (2). The coagulated precipitate is then separated from the clarified liquid using a press filter or other equipment.

[0025] As illustrated by this example of treating a model liquid, Tables 1 and 2 show the concentrations of contaminants before and after passing through the claimed apparatus, as well as the optimal operating mode of the claimed apparatus. [Table 1] [Table 2]

Claims

1. 1. A plasma electrolytic reactor for treating liquid waste comprising: an intake pipe located at the bottom of the reactor for supplying liquid waste; a cylindrical or other curved discharge chamber made of dielectric material and filled with metal granules (balls), with dielectric grids at the bottom and top of the chamber; an outlet pipe located at the top of the reactor for removing the solidified suspension; and a metal electrode on the inner surface of the reactor, connected to a source of rectangular pulses with a control unit.

2. A plasma electrolytic reactor for treating liquid waste comprising: an intake pipe located at the bottom of the reactor for supplying liquid waste; a cylindrical or other curved discharge chamber made of dielectric material and filled with metal granules (balls), with dielectric grids at the bottom and top of the chamber; an outlet pipe located at the top of the reactor for removing the solidified suspension; and a metal electrode on the inner surface of the reactor, connected to a source of rectangular pulses with a control unit.

3. A plasma electrolytic reactor for treating liquid waste comprising:

2. 2. The plasma electrolytic reactor for treating liquid waste according to claim 1, characterized in that the size of the granules (balls) is correlated with the inner diameter of the discharge chamber in the following manner: 0.001 D ≦ d ≦ 0.15 D, where d is the diameter of the balls (granules) in mm and D is the inner diameter of the chamber in mm.

3. 3. A plasma electrochemical reactor for treating liquid waste according to claims 1 and 2, further comprising a source of ozone-air mixture and a mixer connected in series to an intake pipe for supplying liquid waste to the reactor.

4. Liquid waste is continuously fed under pressure through an intake pipe to the reactor, a source of rectangular pulses with a voltage amplitude having a value ranging from 300V to 800V is activated by means of a control unit to feed the discharge electrodes with the rectangular pulses, respectively generating a volumetric discharge between the packed granules (balls) and a volumetric microplasma, whereby the liquid is ionized to form nanoparticles of the metals from which the granules are made, and a process of coagulation and separation of organic and / or inorganic pollutants, in particular heavy metals and / or radioisotopes, from the solution takes place in the reactor with the aid of the coagulant, which is a hydroxide of the metals from which the granules are made, formed during the plasma chemical reaction, so that the pollutants are dissolved in a soluble state.

4. A method of using a plasma electrolytic reactor for treating liquid waste according to claims 1 to 3, characterized in that the liquid waste is fed under pressure through the intake pipe to the first discharge chamber filled with metal granules made of one of the types of material, iron or aluminum, and after the end of the solidification process in the first chamber, the suspension is fed through the connecting pipe to the second discharge chamber filled with metal granules made of the other type of material, aluminum or iron, and after the end of the solidification process in the second chamber, the obtained suspension is fed to the withdrawal pipe.

5. 5. The method of using a plasma electrolytic reactor to treat liquid waste as claimed in claim 4, characterized in that the liquid waste is premixed with a sorbent prior to feeding the plasma electrolytic reactor into the intake pipe.

6. A method of using a plasma electrolytic reactor for treating liquid waste according to claims 4 and 5, characterized in that the liquid waste is additionally pre-saturated with an ozone-air mixture in the mixing device connected to the intake pipe of the reactor.

7. A method of using a plasma electrolytic reactor for treating liquid waste according to claims 4 to 6, characterized in that the rectangular pulses applied to the electrodes are bipolar, i.e. each successive pulse changes its polarity to the opposite one, and have a frequency of 50 to 200 Hz.

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