RU2357309C2 - Method of decontamination of exposed water reservoirs, water drains - Google Patents

Abstract

FIELD: water-supply.

SUBSTANCE: invention relates to the methods of decontaminating exposed water reservoirs and water drains contaminated with radioactive nuclides, as well as for decontamination of neutral or alkaline process solutions used in radio-chemical production. The proposed method comprises water preparation, electrochemical treatment in electrolyser (electro-coagulator) with soluble electrodes made in manganese steels at pH of 8.5 to 9.5, the treated water being saturated with air oxygen to concentration of 10 to 12 mg/l. It includes also separating coagulated products by settling, clarifying, filtering through coarse and fine filters, correcting the water hydrogen index to pH 8.5 to 9.0 and filtering through sorbents from alkaline and earth metals that feature radioactive nuclides selectivity. Finally, water is treated by electrodialysis and decontamination reagents are regenerated.

EFFECT: higher degree of decontamination, minimised volumes of radioactive slimes, reduced operating costs.

1 cl, 4 dwg, 2 ex

Description

The invention relates to the field of ecology, and in particular to methods for decontamination of open water bodies, water effluents contaminated with radionuclides, as well as for the decontamination of neutral or alkaline technological solutions of radiochemical plants.

Contamination of natural waters with radioactive materials is a common problem. It can occur during the extraction of uranium, the operation of nuclear devices, the processing of nuclear fuel, and the disposal of radioactive waste without proper environmental control measures.

The economic task of environmental cleaning is the complete effective cleaning of objects contaminated with radionuclides with a minimum amount of secondary waste.

There is a method of purifying liquid waste by the method of reagent coagulation with iron (III) hydroxides with various collectors (co-precipitators) that facilitate the removal of heavy metals, radionuclides, colloidal and organic impurities from a solution (K.M. Abdulaev, I.A. Malakhov, L.N. .Poletaev, A.S. Sobol “Water treatment at the CHPP using urban wastewater”. M: Energoatomizdat, 1988, p. 103).

A method is described for treating liquid radioactive waste with reagent coagulation together with collectors by soda-lime softening of liquid waste with further separation of the pulp into sludge and water (A. S. Nikiforov, V. V. Kulichenko, M. I. Zhikharev. “Neutralization of liquid radioactive waste. "M., 1985, p.35).

Reagent coagulants in this method are iron (III) and aluminum hydroxides, and collectors are hydroxides of magnesium, manganese and other metals introduced into the water to be treated as additional purification reagents.

The disadvantage of these reagent methods is a low cleaning coefficient, the formation of large volumes of radioactive sludge that require further processing, and an increased salt content of the solutions.

A known method of treating water with oxidizing agents such as chlorine and ozone, which allows to reduce the concentration of organic impurities, including complexing agents (K.M. Abdulaev, I.A. Malakhov, L.N. Poletaev, A.S. Sobol. "Water treatment at the CHPP when using municipal wastewater. ”M .:“ Energoatomizdat ”, 1988, p. 130). The disadvantage of this method is its low efficiency in removing radioactive metal salts from water.

Methods for the electrochemical treatment of liquid radioactive waste (LRW) and water from heavy metals and their radioactive isotopes are described.

One of them includes electrochemical treatment of LRW by oxidation of complex compounds of heavy metals and their isotopes on electrodes using an insoluble electrode as an anode, and a gas diffusion electrode as a cathode, followed by deposition of heavy isotopes on coagulants and collectors. Coagulant - iron (III) hydroxide is obtained in another electrolyzer using a soluble anode and a gas diffusion cathode. Nickel and cobalt hydroxides are used as collectors (Patent RU No. 2127459, G21F 9/06, 1999). The method provides an increase in the degree of purification of LRW from heavy metals and their isotopes and minimum volumes of radioactive sludge.

The disadvantage of this method is that it does not purify LRW from radionuclides, alkaline and alkaline earth metals, such as cesium-137 and strontium-90, whose activity in standard LRW is up to 80% of the total activity, and their nature is such that they are very difficult extracted from solutions without the use of special selective sorbents.

A known method of electrochemical water purification from heavy and radioactive metals and organic impurities in an electrolytic cell with soluble iron electrodes (Yu.V. Kuznetsov, V.N. Schechetkovsky, A.G. Trusov. "Basics of water purification from radioactive contamination." M: Atomizdat, 1974, p. 183).

In this method, adopted by the totality of features as a prototype, including water treatment, water treatment is carried out in an electrolyzer (electrocoagulator) with soluble iron electrodes. The essence of the method consists in the deposition of salts of oxo ions of actinides (IV) on a coagulant-iron hydroxide (III). The coagulant is formed in the electrolyzer during the oxidation of iron at the anode, and the actinide (IV) oxo ions - by the reduction of oxo-ion (III) salts at the cathode.

The disadvantages of the method is the low efficiency of water purification from radionuclides.

The objective of the invention is to increase the degree of decontamination of natural waters and wastewater, minimizing the volume of radioactive sludge, reducing operating costs for decontamination.

The problem is solved in that in the method of decontamination of water of open reservoirs, water drains, including water treatment, electrochemical treatment in an electrolyzer (electrocoagulator) with soluble electrodes, according to the invention, the electrochemical treatment of water is carried out in an electrolyzer (electrocoagulator) with soluble electrodes of manganese steel at pH 8 , 5-9.5 when the treated water is saturated with atmospheric oxygen to a concentration of 10-12 mg / l, followed by separation of the coagulated products by sedimentation, clarification, f by filtration through coarse and fine filters, correction of the pH of water to pH 8.5-9.0, and filtration through sorbents selective for radionuclides of alkali and alkaline-earth metals with further purification of water by electrodialysis and regeneration of deactivation reagents.

The inventive method of decontamination of water of open reservoirs, water effluent, in which they carry out water treatment, electrochemical treatment in an electrolyzer with soluble electrodes (electrocoagulator), has the following distinguishing features from the known method adopted for the prototype, signs:

- the first is the use in the electrolyzer of soluble electrodes of manganese steels when the electrolyte is saturated with oxygen. When using manganese steels as electrodes, along with the formation on the anode of the electrolyzer - iron (III) hydroxide and the reduction of actinide (VI) oxo ions into the cathode of actinides (IV) oxides, conditions are created for the formation of a collector (co-precipitator, known for its effectiveness) in the electrolyzer ) of heavy metal radionuclides - manganese (IV) oxide MnO ₂ .

The formation of the collector flows in the working zone of the electrolyzer through the stages of electrochemical oxidation of metallic manganese, which is part of the electrodes of manganese steels, to the cation of manganese (II), the formation of manganese (II) hydroxide and the oxidative destruction of the latter by atmospheric oxygen to manganese (IV) oxide according to the equations:

+6Н₂O→[Mn(H₂О₆)]²⁺,Mn ⁰ -2

+ 6H ₂ O → [Mn (H ₂ O ₆ )] ²⁺ ,

[Mn (H ₂ O) ₆ ] ²⁺ + 2OH ^- → Mn (OH) ₂ + 6H ₂ O,

2Mn (OH) ₂ + O ₂ → 2MnO ₂ ↓ + 2H ₂ O.

The formation of an additional co-precipitator (collector) in the working zone of the electrolyzer — manganese (IV) oxide, naturally, will increase the degree of decontamination of the treated water from heavy metal radionuclides;

- the second is the use of atmospheric oxygen in decontamination technology.

The oxygen saturation of the electrolyte in the electrolysis chamber creates favorable conditions for both the formation of the collector, MnO ₂ , and for the oxidation of organic pollutants. In parallel with the electrochemical oxidation of organic compounds, oxygen activated by the electric discharge of the interelectrode space additionally oxidizes alcohols, aldehydes, ketones, unsaturated compounds to the corresponding acids, which with heavy metals, for example, with iron (III) ions, give slightly soluble salts that precipitate in sediment. It should be added that activated oxygen accelerates the oxidation of iron (II) ions into iron (III) ions, thereby increasing the amount of coagulant in the water being treated;

- the third is the use of selective sorbents based on transition metal ferrocyanides.

The addition of the line for the decontamination of aqueous solutions with filters for selective sorption purification of ions of radioactive alkali and alkaline earth metals ensures a decrease in the concentration of the latter in the purified water stream;

- fourth - the use of electrodialysis at the final stage of decontamination allows you to bring the treated water to the MPC standards for salt loads and regenerate cleaning reagents from concentrated solutions of anolytes and catholytes.

Using the proposed method of decontamination of natural waters and effluents in comparison with the prototype allows more efficiently remove from the treated waters radionuclides of heavy, alkaline-earth and alkali metals, organic pollutants, minimize the amount of radioactive sludge, reduce operating costs for decontamination.

Thus, the claimed method of decontamination of water of open reservoirs, water drains, in which water is prepared, electrochemical treatment in an electrolyzer with soluble electrodes differs from the well-known accepted as a prototype in that electrochemical water treatment is carried out in an electrolyzer (electrocoagulator) with soluble electrodes from manganese steels at pH 8.5-9.5 when saturated water is saturated with atmospheric oxygen to a concentration of 10-12 mg / l, followed by separation of coagulated products by sediment, Bleaching filtration through coarse and fine filters, water adjusted pH value to pH 8.5-9.0 and filtered through a selective to radionuclides alkali and alkaline earth metal sorbents with further water purification and electrodialysis regeneration of decontamination reagents.

From the patent and scientific literature there is no known method in which the electrochemical treatment of water is carried out in an electrolyzer with dissolved electrodes of manganese steels at pH 8.5-9.5 when the solution is saturated with atmospheric oxygen to a concentration of 10-12 mg / l, followed by removal coagulated products by sedimentation, clarification, filtration through coarse and fine filters, correction of water pH to 8.5-9.0 and filtration through sorbents selective for radionuclides of alkali and alkaline earth metals with further purification of water by electrodialysis and regeneration of deactivation reagents, which allows to achieve the effect described above.

The claimed technical solution can be used in the field of ecology for the decontamination of natural waters, drains, alkaline and neutral technological solutions of radio engineering industries.

The inventive method of decontamination is carried out using a device, a diagram of which is shown in the drawing.

The device includes four nodes A, B, C, D, shown in figures 1-4.

Figure 1 - node A - node water treatment - includes a storage tank - sump 2, clarifier 3, reactor-mixer 5, grate 1, sludge collector 4, measuring tank of alkaline solution 6, measuring tank for salt solution 7.

Figure 2 - node B - node electrocoagulation - includes an electrolyzer (electrocoagulator) 8, sump 10, clarifier 11, block filter 12, air compressor 9, sludge collector 13.

Figure 3 - node B - sorption block - includes a reactor-mixer 14, a filter with selective sorbent 16, an acid meter 15.

Figure 4 - node G - block electrodialysis - includes an electrodialysis unit 17, storage tanks: alkali 18, acid 19, salt 20.

The method of decontamination of water of open reservoirs and water flows is carried out as follows and is illustrated by examples.

Example 1. Decontamination of open water

Water from the reservoir is fed through the inlet collector through a mechanical grill 1 with a gap between collecting plates 3 mm wide into a storage tank - sump 2 (Node A, Fig. 1).

The storage tank-settler 2 is provided for the separation of large suspended particles and sand in order to equalize the supply of decontaminated water to the treatment system.

A pump from a settling tank 2 supplies water to a continuous clarifier 3 to separate fine suspended particles. The settled sludge from the apparatuses 2 and 3 is discharged as it accumulates into the sludge collector 4. After washing with water and measuring the level of radioactivity, the sludge is discharged to the ground or to a decontamination tank.

From the clarifier 3, the water flow is sent to the mixer reactor 5, which is a chan type apparatus with a stirrer, for mixing purified water with reagents in order to impart the necessary electrical conductivity and pH to the water. The supply of reagents - 20% alkali solution (measurer 6) and 10% sodium chloride solution (measurer 7) - is regulated so that the pH of the treated water is maintained within pH 8.5-9.5, and the concentration of sodium chloride is 1.9 -2.3 g / l.

From the reactor-mixer 5, the alkaline solution is fed into the electrolyzer (electrocoagulator) 8 with soluble electrodes (node B, figure 2). The electrochemical treatment of the solution is carried out when the electrolyte is saturated with air oxygen by compressor 9 to a concentration of 10-12 mg / l at a current density on the electrodes of 50-150 A / dm ² , the interelectrode distance of 10-40 mm, the processing time of the solution is 5-15 minutes.

The electrodes are made of manganese steels.

The pulp with a suspension of coagulated products from the electrolyzer (electrocoagulator) 8 is pumped into a sump 10, then to a clarifier 11 and a coarse and fine filter block 12. As filter materials in block 12 polystyrene foam, expanded clay or zeolite, activated carbon or carbon fibers are used specified sequence.

Radioactive sludge from the sump 10, clarifier 11, as they accumulate, is dumped into the sludge collector 13, dried, pressed, and disposed of in special storage facilities. Wash water from the block filter 12 is returned to the sump 10.

From the block filter 12, the water flow is directed to the mixer reactor 14 (assembly B, FIG. 3), where the pH of the water is adjusted to pH 8.5-9.0 with a solution of 10% hydrochloric acid from the measuring device 15 and passed through the filter 16, filled with selective sorption material based on transition metal ferrocyanides.

The final purification of water is carried out by electrodialysis in the block of electrodialyzers 17 (node G, figure 4).

The main stream of purified water (90%) with a total content of β-active radionuclides of less than 10 ^-9 ki / l is discharged into open water bodies. Decontamination reagents - alkalis, acids, chlorides - are regenerated from anolytes and catholytes by electrodialysis concentration and collected in storage tanks 18, 19, 20, respectively. Excess concentrated salts are recycled.

Example 2. Decontamination of technological effluents of radiochemical plants

Decontamination of neutral and alkaline technological solutions is carried out similarly with the correction of the hydrogen index for alkaline solutions with acid, and neutral solutions with alkali in a mixing reactor 5.

Claims (1)

A method for decontamination of open reservoir waters, water effluents contaminated with radionuclides, including water treatment, electrochemical treatment in an electrolyzer (electrocoagulator) with soluble electrodes, characterized in that the electrochemical treatment of water is carried out in an electrolyzer (electrocoagulator) with soluble electrodes from manganese steels at pH 8.5 -9.5, at saturation of the treated water with atmospheric oxygen to a concentration of 10-12 mg / l, followed by separation of the coagulated products by sedimentation, clarification, filtration Erez filters coarse and fine cleaning, hydrogen water adjusted to pH 8.5-9.0 index, filtration through selective to radionuclides alkali and alkaline earth metal sorbents with further water purification and electrodialysis regeneration decontamination reagents.

Images