RU2394659C1 - Method of decontaminating toxic industrial wastes - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to methods of processing (decontaminating) waste mineralised water of atomic power stations, which contain environmentally hazardous toxic substances, particularly ethanolamine, and wastes (phosphogypsum) from industries which produce phosphorous fertiliser and phosphoric acid. The dehydrated salt product which contains toxic ethanoamine, obtained after distillation of liquid toxic wastes and evaporation to maximum salt concentration of the stillage residue, is mixed with phosphogypsum and the obtained mixture undergoes two-step thermal treatment while stirring continuously at 120-200°C to obtain a granular product (step for evaporation to maximum salt concentration). The product is then roasted in a roasting furnace at 900-1200°C (reducing roasting step) until complete combustion of ethanolamine and completion of the process of thermochemical decomposition of mineral salts and phosphogypsum to lime, magnesium oxide and sulphur dioxide.

EFFECT: decontamination of waste mineralised water of atomic power stations, which contain toxic ethanolamine; recycling environmentally hazardous wastes (phosphogypsum) from industries which produce phosphorus fertiliser and phosphoric acid.

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Description

The invention relates to the field of environmental protection, and more specifically to a technology for the neutralization (processing) of industrial waste containing toxic and environmentally hazardous substances.

At present, at the domestic and foreign nuclear power plants (NPPs) with VVER-type reactors (RU), the water-chemical regime (VCR) is widely used using an anti-corrosion correction additive (corrosion inhibitor) to the coolant ethanolamine (ETA) ) This regime, in particular, is provided for at the second stage of the Leningrad NPP with VVER under construction.

Despite the obvious advantages of the ethanolamine water chemistry of the secondary circuit of the reactor facility in comparison with the ammonia-hydrazine one, such as reducing the corrosion of structural materials, reducing the amount of operating deposits formed on the surfaces of the equipment and pipelines of the secondary circuit, and, accordingly, extending the service life of the main equipment of the reactor plant, using ETA as additives to the heat carrier create environmental problems. The stringent requirements to limit the content of ETA in water discharges, associated with its high toxicity, necessitate the disposal (neutralization) of liquid waste from nuclear power plants (high salt water from regeneration of ion exchange filters of a condensate treatment system and regeneration effluents of a steam generator purge water treatment system) [US Patent, No. 7081194, dated July 25, 2006].

In the list of wastes from various industries that create an additional environmental burden on the environment, in the Leningrad region one can also identify wastes from the processing of natural phosphorites or apatites used in the production of phosphoric acid and phosphoric fertilizers at Phosphorite LLC in Kingisepp, namely phosphogypsum.

Reducing emissions of harmful chemicals throughout the world is achieved through the purification and processing of discharges by various physicochemical methods, concentration of harmful substances with their subsequent storage in the allocated areas. To more effectively solve urgent problems of protecting the planet’s biosphere from exposure to toxic compounds, it is necessary not only to tighten the requirements for the composition and quantity of industrial waste (gaseous, liquid or solid) discharged into the natural environment, but also to ensure safe conditions for long-term storage of the final products of processing toxic waste . It is believed that the best solution to environmental problems associated with the production activities of enterprises is closed technologies (waste-free production), which allow not only to safely dispose of the resulting environmentally hazardous waste in the production process of the main products (electricity, phosphoric acid and phosphoric fertilizers, etc.) but also to ensure the possibility of using products of their processing in the production cycle of enterprises or in the national economy. At the same time, important factors in the effectiveness of such technologies are their energy intensity, cost and availability of energy carriers, reagents and materials used in the neutralization cycle.

In the practice of utilization of highly mineralized liquid wastes of nuclear power plants containing toxic ETA or other harmful organic substances, the methods of their processing using chemical (oxidation and decomposition of organic impurities by sodium hypochlorite, bleach, etc.) and physical (electrolytic decomposition of organic substances) and biological (biological destruction of organic substances by active microorganisms) methods. Due to the fact that ETA is very difficult to destroy to carbon dioxide and nitrogen, it is believed that combined technologies for its neutralization involving the use of chemical, physical and biological methods are most effective [US Patent No. 7081194, July 25, 2006].

Each of the above methods of neutralizing ETA has its own specific disadvantages.

The chemical method requires:

- at least three-fold excess of the oxidizing agent in relation to its theoretically necessary amount, which significantly increases the total salt content of the neutralized waste;

- neutralization of excess oxidizing agent used;

- the use of large-sized equipment (mixing reactors, precipitators, storage pools of final highly saline waters, etc.).

The electrolytic method provides for the effective pretreatment of wastes from suspended matter and dissolved metals, which is carried out using large-sized equipment (mixers, sedimentation tanks, settling tanks, mechanical filters, etc.). The electrolyzers themselves are bulky (length - 17.5 m, width - 7 m and height - 3 m, the number of cathode-anode electrode pairs - 1040), and the electrodes used in them are expensive, since they are made of stainless steel and titanium coated with noble metals [US Patent No. 7081194, July 25, 2006].

The biological method is ineffective (a long exposure time of the neutralized water in the system is necessary). The cleaning system cannot work in the winter in the northern regions. Large areas are required for the ponds, and after the biological ponds stopped working, the territory on which they were located is almost lost [A.A. Khonikevich. Treatment of radioactive contaminated water. Atomizdat, Moscow, 1974, p. 75]. Biological ponds themselves represent a known environmental hazard to the surrounding area, associated with the possibility of unauthorized release of toxic waste (gaseous, dusty, aerosol and liquid) into the biosphere of the region where industrial enterprises are located [Yu.V. Kuznetsov, V.N. Schechetkovsky, A.G. Cowards. Basics of water decontamination. Atomizdat, Moscow, 1968, p. 190].

A common disadvantage of the considered methods is the urgent problem of environmentally safe storage of final processed products, which are high salt solutions and / or dry salts. It is known that the issue of dry salts is quite complex and still unresolved in the energy system. Salts formed during the treatment of wastewater from chemical water purification and other technological systems of power plants are soluble in water and, therefore, they cannot be stored in the open air, filling them with gullies and quarries [Yu.M. Kostrikin et al. On creating drainless thermal electric stations. Water treatment, water regime and chemical control on steam-powered plants. Sat articles, issue 6, Moscow, Energy, 1978, p.163].

Phosphogypsum (FG) formed from the processing of natural phosphorites or apatites is mainly two-water gypsum (CaSO ₄ · 2H ₂ O) with a mechanical water-soluble admixture of phosphorus pentoxide (P ₂ O ₅ ) and a certain amount of silica and sesquioxides of metals [ A.S. USSR No. 1805626, publ. Bull. No. 20, 07/20/96]. According to estimates, in the production of extraction phosphoric acid, the waste of phosphogypsum per 1 ton of P ₂ O ₅ is 4-6 tons, which is associated with the problems of storage of phosphogypsum and environmental protection [as. USSR No. 1413070, publ. Bull. No. 28, 07/30/08]. Currently, the bulk of phosphogypsum is stored in open dumps (technological maps of dry storage of phosphogypsum).

Almost all known methods of phosphogypsum utilization are carried out by thermal decomposition (burning) at temperatures of 900-1200 ° С using carbon materials (graphite dust, coal, petroleum coke, lignite-bauxite, etc., as well as gases) as a reducing agent and fuel obtained by the conversion of natural gas with water vapor) [US patent, No. 4102989, CL 423-541, 1978; A.S. USSR No. 1413070, publ. Bull. No. 28, 07/30/08; A.S. USSR No. 1030310, publ. Bull. No. 27, 07/23/83; A.S. USSR No. 1805626, publ. Bull. No. 20, 07/20/96]. At the same time, in the firing zone, the necessary reducing potential of the medium (ratio - CO / CO ₂ ) is maintained, which is usually determined experimentally.

Often, in practice, the neutralization of phosphogypsum and the production of building mixed cements on its basis as additives to phosphogypsum, in addition to carbon materials, use natural mineral substances (dolomite, apatite, phosphorite, etc.) [A. with. USSR No. 1413070, publ. Bull. No. 28, 07/30/08; A.S. USSR.№1030310, publ. Bull. No. 27, 07/23/83].

Closest to the claimed is a thermal method for the neutralization of regeneration wastewater from chemical treatment of TPPs and nuclear power plants, including their evaporation to dry salts with their subsequent removal to special landfills of industrial waste [SM. Gurvich, Yu.M. Kostrikin. Water treatment operator. M., Energy, 1974, p. 188], [SM. Gurvich, Yu.M. Kostrikin. Water treatment operator. M., Energy Publishing House, 1981, pp. 194-195].

The objective of the present invention is to provide a method for the disposal of highly mineralized wastewater from nuclear plants containing toxic ethanolamine and environmentally hazardous mineral waste from the production of phosphate fertilizers and phosphoric acid (phosphogypsum), which allows:

- neutralize waste mineralized water of nuclear power plants containing toxic ethanolamine;

- Dispose of industrial environmentally hazardous waste (phosphogypsum) enterprises for the production of phosphate fertilizers and phosphoric acid;

- use the final products of neutralization of phosphogypsum and toxic toxic wastes in the technological cycle of nuclear power plants as: mineral sorption additives to cement during the final stage of neutralization of liquid radioactive waste (curing stage); mineral raw materials additives for cement in composite compositions used in the construction and road-building industries; a neutralizing agent for acidic wastewater instead of sodium hydroxide.

To solve the problem and achieve the technical result in a method of processing environmentally hazardous liquid waste from nuclear and thermal power plants, including their preliminary distillation to produce condensate and bottoms and concentration of the bottoms by deep evaporation to a dry product with subsequent evacuation of the dry product to special industrial landfills waste, it is proposed obtained after deep evaporation of waste dehydrated salt product containing current egg ethanolamine, mix with phosphogypsum and subject the resulting mixture to two-stage heat treatment with constant stirring at a temperature of 120-200 ° C until a granular product is obtained (stage of deep dehydration), after which the product is fired in a kiln at a temperature of 900-1200 ° C (stage of reduction roasting) until ethanolamine is completely burned and the process of thermochemical transformation (decomposition) of mineral salts and phosphogypsum to lime, magnesium oxide and sulfur dioxide is completed.

It is also proposed that the gases formed at the stages of deep evaporation and deep dehydration be sent to the kiln.

In addition, it is proposed that the final product obtained after firing be used as a mineral-sorption additive for cement during the stage of curing of liquid radioactive waste concentrates in nuclear power plants or as a mineral raw material additive for cement in composite compositions used in the construction and road-building industries, and oxidize the resulting sulfur dioxide to sulfuric anhydride. The resulting sulfuric acid (contact method for producing sulfuric acid) [B.V. Nekrasov. Fundamentals of General Chemistry, v.1. Chemistry. M. 1965, p. 338] to use in the technological cycle of nuclear power plants, for example, in the regeneration of H-cation exchange filters of the condensate treatment system.

The essence of the proposed method lies in the fact that it incorporates the principle of "toxic is disposed of with toxic." It is proposed, for example, that neutralization of non-radioactive mineralized wastewater from NPPs containing toxic ETA be carried out together with environmentally hazardous industrial waste (phosphogypsum) to produce products suitable for use at NPPs and in the national economy at the final stage of their neutralization. organize non-waste environmentally safe production at the NPP (closed production cycle).

The cationic composition of high-salt wastewater under construction in the area of Sosnovy Bor NPP with VVER is mainly determined by the composition of the source of natural water, which after chemical water treatment is used in the NPP technological cycle. The composition of the source of natural water and mineralized effluent from a nuclear power plant under construction (Sosnovy Bor, Leningrad Region) is characterized by an average content of the following main impurities:

Waste water from H-cation exchange filters of the condensate purification system of the second circuit (main stream).
Sulfates of Ca, Mg, Na.
Total salinity up to 5 g / kg.
Ethanolamine up to 1 g / kg. Source natural water (purified water of the Sista River). Sulfates and carbonates of Ca, Mg, Na Ca ⁺² - 66, Mg ⁺² -31, Na ⁺¹ - 3 wt.%
Total salinity up to 0.3 g / kg.

In the process of using the source of natural water in the technological cycle of a nuclear power plant, water is freed from carbonates. Therefore, the waste water in mineral composition can be attributed to the products of the destruction of natural minerals - gypsum (CaSO ₄ · 2H ₂ O) and kieserite (MgSO ₄ · H ₂ O) [B.V. Nekrasov. Fundamentals of General Chemistry, v.2. Chemistry. M. 1965, p. 275, 314].

It is known that when calcining gypsum and kieserite in the presence of organic carbon-containing additives or products of their thermal decomposition, which have reducing properties, mineral building materials for various purposes and sulfuric acid are obtained in industry. For example, when firing gypsum (900-1200 ° C), you can get the so-called hydraulic gypsum (xCaSO ₄ · yCaO), which when mixed with water gives a hardening, mechanically strong, water-resistant mass (product). Natural kizerite can serve as a good material for producing magnesium oxide MgO, which is used in a mixture with MgCl ₂ as magnesia cement [B.V. Nekrasov. Fundamentals of General Chemistry, v.2. Chemistry. M. 1965, p. 330, 275, 271].

It is also known that in the production of a raw material mixture (mineral additive to Portland cement), natural lignite-bauxite containing up to 10% (by weight of rock) carbon is used as a carbon-containing additive to phosphogypsum and dolomite [a.s. SU 1413070, publ. Bull. No. 28, 07/30/08]. From the same source it follows (see the claims) that for 1 ton of the processed mixture of phosphogypsum and dolomite, 0.33 tons of lignite-bauxite containing about 0.033 tons of organic substances in terms of carbon are needed.

Ethanolamine (NH ₂ CH ₂ CH ₂ OH) is also a combustible carbon-containing organic substance with reducing properties [A.A. Petrov et al. Organic chemistry. Graduate School. M, 1973, p. 215]. The boiling point of ETA is -171 ° C. ETA mixes with water in every way. ETA itself and its aqueous solutions are highly toxic. The maximum permissible concentration of ETA in waste water is not more than 0.01 mg / l. The elemental composition of ETA: C - 40, H - 11, O - 26 and N - 23 wt.%, Respectively. In terms of elemental composition and percentage of chemical elements in ETA, it is close to such combustibles as dry wood, peat, moss, lignite, ethyl alcohol [V.I. Perelman. Quick reference chemist. M., 1955, p. 295], whose calorific value is from 4500 to 6500 kcal / kg of fuel. It is also known that with the complete combustion of organic substances in the presence of atmospheric oxygen, their carbon and hydrogen are completely converted to carbon dioxide and water, and nitrogen is usually released in a free state. This is the basis for the quantitative analysis of organic substances [L.N. Glinka. General chemistry. Chemistry. M., 1976, p. 488]. Thus, the final products of ETA combustion are environmentally friendly exhaust hot gas discharges containing CO ₂ , N ₂ and H ₂ O.

In the case of processing liquid waste of nuclear power plants containing ethanolamine, in accordance with the proposed method, 1 ton of product (salt concentrate with ETA) obtained before firing will contain about 0.167 tons of ethanolamine, which in terms of carbon is at least 0.07 tons. Thus, the proposed method allows for the processing of 1 ton of waste of nuclear power plants containing ETA, at the stage of their roasting, simultaneously neutralize up to 1 ton of phosphogypsum (in terms of dry products) and obtain at the final stage of processing mineral raw materials suitable for use at nuclear power plants and in national the farm.

Fundamentally, the proposed method allows for the simultaneous neutralization of other non-radioactive wastewater mineralized waters of nuclear power plants that do not contain toxic ethanolamine (water of chemical flushing of steam generators, reverse osmosis and ultrafiltration plants, etc.), and you can use natural raw materials instead of phosphogypsum as mineral additives ( gypsum, dolomite, chalk) or mineral waste from other industrial enterprises in the region.

It was experimentally established that during the stages of distillation and deep evaporation of the bottom residue at temperatures of 100-120 ° C and deep dehydration of the product at temperatures of 120-200 ° C, low-boiling gaseous fractions of the thermal decomposition of ETA (ammonia, possibly methylamine, etc.) fly together with water vapor .). Therefore, it is advisable that the non-condensable harmful gases generated at these stages be sent to the kiln, where they are burned together with ethanolamine to form water, nitrogen and carbon dioxide, and the condensate obtained should be used at nuclear power plants as additional water in the condensate-feed path of the reactor plant.

It is advisable to complete the stage of deep dehydration of the product after stopping the emission of gases from it and the formation in the apparatus of a free-flowing dehydrated powder, which is a crystalline mixture of mineral and organic salts saturated with ethanolamine and high-boiling products of its partial thermal decomposition.

The optimum temperature and firing time of bulk powder obtained at the stage of deep dehydration according to the proposed method is determined experimentally, since they depend on the salt composition of the processed waste, the design of the kiln used, the heating method, etc.

The proposed method of neutralizing toxic industrial waste is implemented in laboratory conditions as follows.

In the experiments used:

- an artificial mixture of crystalline hydrates of sulfate salts of Ca, Mg and Na with ethanolamine. In quantitative and qualitative composition, the mixture corresponded to the composition of waste water from the regeneration of N-cation exchange filters of the NPP condensate purification system in terms of anhydrous components;

- phosphogypsum, selected from conveyor No. 5 of LLC “Phosphorite” of the tract for its disposal into dumps (dry storage cards).

The artificial mixture was mixed in a quartz crucible with phosphogypsum in a weight ratio of 1: 1 in terms of dry components, after which it was moistened and subjected to periodic heat treatment at 100-120 ° C until a quasi-homogeneous product was formed in the crucible (stage simulating the deep evaporation of bottoms balance). Then the temperature of the product in the crucible was increased and in the range of 120-200 ° C, with periodic stirring, the stage of deep dehydration of the product was carried out. The criterion for the completion of the process was the cessation of vapor and gas evolution and the formation of a dry powder product. After cooling to room temperature, the crucible with the product was placed in a laboratory electric furnace and calcined at a temperature of 1000 ± 100 ° C for 15-20 minutes. After firing, the resulting product was cooled to room temperature and used in strength experiments as an additive to cement.

The results of these experiments showed that the strength of the products (cylindrical samples of the same geometric shape) made from Portland cement (M-500) and Portland cement containing from 10 to 50% volume additives, after 28 days of hardening, is almost the same.

The proposed method allows the entire cycle of neutralization of non-radioactive waste water of nuclear power plants in its territory using well-known domestic and foreign technologies and standard industrial equipment (possibly after their partial structural refinement) used in the practice of thermal processing of liquid and solid industrial wastes.

In this case, it is possible to use a combined version of the technology for processing waste. For example, an intermediate product obtained at the stage of deep dehydration can be processed (rendered harmless, used) at cement, lime and sulfuric acid production plants operating in the region where the NPP is located, as a raw material additive, reducing agent, and fuel. The sulfuric acid produced can be used in the regeneration of H-cation exchange filters of the condensate purification system of the secondary circuit of nuclear power plants. Ultimately, all of the above can reduce the financial costs of nuclear power plants for the purchase of chemicals and cement. The determining factors are economic and environmental calculations and estimates.

In general, the use of the invention will reduce the anthropogenic impact of harmful substances on the environment of the regions and improve the ecological situation, which is one of the priority areas for the development of science, technology and technology in domestic and foreign practice of handling radioactive, toxic and environmentally hazardous waste from nuclear power plants and industrial plants, ensure conservation and restoration of natural ecosystems in the environmental sphere, stabilize and improve the quality of the environment.

Claims (1)

The method of neutralizing environmentally hazardous liquid waste from nuclear and thermal power plants, including their preliminary distillation to obtain condensate and bottoms and concentration of the bottoms by deep evaporation to a dry product and subsequent evacuation to special industrial waste landfills, characterized in that the dehydrated obtained after deep evaporation of waste the salt product containing toxic ethanolamine is mixed with phosphogypsum and the resulting mixture is subjected to a two-stage t heat treatment with constant stirring and a temperature of 120-200 ° C until a granular product is obtained, after which the product is calcined in a kiln at a temperature of 900-1200 ° C until ethanolamine is completely burned and the process of thermochemical decomposition of mineral salts and phosphogypsum into lime, magnesium oxide and sulfur dioxide, while the gases formed at the stages of deep evaporation and deep dehydration of waste containing ethanolamine are sent to the kiln.