A method for treating uranium-containing high-salt wastewater in a nitric acid system

Abstract

The present invention belongs to the technical field of uranium purification, and specifically relates to a method for treating uranium-containing high-salt waste liquid in a nitric acid system. The waste liquid after filtering out impurities is transported to a waste liquid incinerator via a diaphragm metering pump and evenly sprayed into the combustion chamber of the waste liquid incinerator through a feed nozzle. The flue gas after the combustion of natural gas and air is used as a heat source to completely gasify the waste liquid. At the same time, the organic phase and interface contaminants contained in the waste liquid can be fully burned and oxidized into carbon dioxide, nitrogen oxides, sulfur dioxide and water vapor by excess air; the nitrate in the waste liquid is partially decomposed into metal oxides and nitrogen oxide gases by heat, and the uranium contained is also decomposed into uranium oxides and nitrogen oxide gases. The salts, metal oxides and uranium oxides remaining in the waste liquid are discharged from the lower outlet of the waste liquid incinerator in the form of powder for temporary storage. The present invention combines waste liquid incineration technology with nitric acid distillation technology, which can not only achieve standard discharge of waste liquid but also realize the recycling and utilization of nitric acid resources therein.

Description

Technical Field

[0001] The invention belongs to the technical field of uranium purification, and particularly relates to a method for treating uranium-containing high-salt waste liquid in a nitric acid system. Background Art

[0002] Domestic natural uranium purification utilizes a "wet-process" uranium purification and extraction process. During the extraction, tail gas treatment, and extract residue distillation and concentration steps, a large amount of high-metal uranium-containing wastewater containing nitric acid is generated. This wastewater has a complex composition, typically containing a significant amount of residual uranium after extraction, other metal salt impurities, nitric acid-insoluble matter, extractant entrained in the aqueous phase, and other organic interface contaminants. The nitric acid concentration can reach over 10 mol / L, making this wastewater highly corrosive, flammable, and highly toxic. With the expansion of domestic uranium purification and conversion production capacity and increasingly stringent environmental protection requirements, the pressure on wastewater treatment generated in the uranium purification production sector is increasing. This high-metal uranium-containing wastewater must undergo uranium removal and other treatment processes to reduce the uranium content of the discharged wastewater to within the national requirement of 0.05 mg / L. The levels of other impurities must also meet relevant national requirements to ensure the harmless treatment of wastewater from uranium purification production lines.

[0003] The current treatment process for high-metal uranium-containing wastewater generated by uranium purification production in China involves alkali neutralization, precipitation, filtration, and then ion exchange to remove uranium from the clear liquid. This process is only suitable for treating wastewater that does not contain organic phases, interface contaminants, or other impurities that could impact the ion exchange system. Using an ion exchange system to treat high-metal nitric acid-containing and uranium-containing wastewater generated by uranium purification production requires the installation of a pretreatment system to remove organic matter and other degradable impurities from the wastewater through methods such as supercritical oxidation before treatment using an ion exchange uranium removal system. This process system suffers from high investment, high maintenance costs for the ion exchange system, high operating expenses, and limited wastewater treatment capacity. Furthermore, the nitric acid in the wastewater cannot be recycled.

[0004] Therefore, it is necessary to develop a treatment method for treating uranium-containing high-salt wastewater in the nitric acid system, which can not only achieve the discharge of the wastewater in compliance with the standards but also realize the recycling and utilization of the nitric acid resources therein. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for treating uranium-containing high-salt waste liquid in a nitric acid system. By combining waste liquid incineration technology with nitric acid distillation technology, it is possible to achieve both standard discharge of waste liquid and recovery of nitric acid resources therein.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for treating uranium-containing high-salt wastewater in a nitric acid system,

[0008] Step 1: The waste liquid is filtered to remove insoluble solid particles and other easily separable impurities;

[0009] Step 2: The waste liquid after filtration and impurity removal is transported to the waste liquid incinerator via a diaphragm metering pump and evenly sprayed into the combustion chamber of the waste liquid incinerator through a feed nozzle. The flue gas after the combustion of natural gas and air is used as a heat source to completely gasify the waste liquid. At the same time, the organic phase and interface pollutants contained in the waste liquid can be fully burned and oxidized into carbon dioxide, nitrogen oxides, sulfur dioxide and water vapor by excess air; the nitrate in the waste liquid is partially decomposed into metal oxides and nitrogen oxide gases by heat, and the uranium contained is also decomposed into uranium oxides and nitrogen oxide gases. The remaining salts, metal oxides and uranium oxides in the waste liquid are discharged from the lower outlet of the waste liquid incinerator in the form of powder and temporarily stored;

[0010] Step 3: The exhaust gas from the waste liquid incinerator is removed by the primary dust collector and the secondary dust collector before entering the condenser;

[0011] Step 4: The tail gas from the condenser is further absorbed and purified by the leaching tower. The acidity of the nitric acid solution absorbed by the leaching tower reaches 5-8 mol / L. The tail gas at the outlet of the leaching tower enters the alkaline washing tower for neutralization and absorption before being discharged;

[0012] Step 5: The acid mixture recovered by the condenser and the elution tower enters the distillation tower. The condensed water taken from the top of the distillation tower is returned to the elution tower for elution and recovery of nitric acid. The concentrated nitric acid taken from the bottom of the tower is returned to the main uranium purification process for recycling.

[0013] The filter is a centrifugal filter.

[0014] The second step: using the flue gas after combustion of natural gas and air as the heat source, wherein the air is in excess of 20%.

[0015] The second step is to control the temperature of the combustion zone of the waste liquid incinerator to 1200° C. so that the waste liquid can be completely gasified.

[0016] The temperature of the first-stage dust collector is 350-450°C.

[0017] The temperature of the secondary dust collector is 250-350°C.

[0018] The first-stage dust collector adopts a high-precision nickel tube filter.

[0019] The secondary dust collector adopts an electrostatic dust collector.

[0020] The third step: the condensate collected by the condenser has a nitric acid concentration of 6 to 10 mol / L.

[0021] The distillation tower is in the form of a packed tower, has a theoretical plate number of 10, a reflux ratio of less than 0.3, and performs atmospheric distillation.

[0022] The beneficial effects achieved by the present invention are:

[0023] The incinerator and other key process equipment used in the present invention's method for treating uranium-containing, high-salt wastewater from a nitric acid system boasts advantages such as simple structure, low cost, easy processing, simple operation, and convenient maintenance. This process oxidizes and decomposes organic matter and other substances in the wastewater through combustion, avoiding the need for oxidation treatment in a pretreatment process. It also purifies and recovers nitric acid from the wastewater, concentrating it to a concentration of 10 mol / L for return to the main process. The discharged alkaline wash neutralization solution has a uranium content of less than 0.05 mg / L, meeting national emission standards. The device can also be applied to other high-salt, acidic wastewater treatment applications, achieving both wastewater treatment and acid recovery. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a process flow chart for treating uranium-containing high-salt wastewater in the nitric acid system;

[0025] In the figure: 1—filter; 2—waste liquid incinerator; 3—primary dust collector; 4—secondary dust collector; 5—condenser; 6—elution tower; 7—distillation tower; 8—alkali washing tower. DETAILED DESCRIPTION

[0026] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] Utilizing waste liquid incineration technology, with natural gas as a fuel source, the waste liquid is gasified upon encountering high-temperature flue gas. Most of the salts and other insoluble impurities in the waste liquid are granulated and precipitated before being discharged through the bottom of the incinerator. Some nitrates are decomposed into oxides and nitrogen oxide gases. Uranium in the waste liquid forms uranium oxides at high temperatures and is discharged along with the salts for temporary storage. The organic phase, interfacial contaminants, and other impurities in the waste liquid are oxidized and incinerated by the high-temperature flue gas (900-1200°C) to form gases such as carbon dioxide, nitrogen oxides, sulfur dioxide, and water vapor. The exhaust gas from the waste liquid incinerator is filtered through high-precision stainless steel nickel tubes and deep-filtered with an electrostatic precipitator to remove uranium and dust particles. The exhaust gas is then condensed and washed to recover water vapor and nitrogen oxide gases, resulting in a relatively pure nitric acid solution.

[0028] Using nitric acid distillation and concentration technology, the nitric acid recovered through condensation and elution is concentrated to above 10 mol / L. The overhead condensate (pH > 4) is returned to the elution tower for elution and nitric acid recovery, while the concentrated nitric acid in the bottom of the tower is transported to the main process of the uranium purification production line for recycling. This process, combining waste liquid incineration with nitric acid distillation, achieves the harmless treatment of high-metal, nitric acid, and uranium-containing waste liquids, while also enabling the recycling of nitric acid resources.

[0029] The invention provides a method for treating uranium-containing high-salt waste liquid in a nitric acid system. After insoluble solid particles are removed from the waste liquid through a filter, the waste liquid enters a waste liquid incinerator through a nozzle and is incinerated and gasified by hot flue gas in the waste liquid incinerator. Remaining residue is discharged from the bottom of the waste liquid incinerator. Tail gas at the outlet of the waste liquid incinerator passes through a primary dust collector and a secondary dust collector and then enters a condenser. The tail gas of the condenser is further absorbed and purified in a washing tower and then sent to an alkali washing tower for neutralization and discharge. The acid liquid recovered by the condenser and the washing tower enters a distillation tower for concentration to 10 mol / L and then returns to the main process for recycling.

[0030] The specific implementation is as follows:

[0031] Step 1: The waste liquid passes through filter 1 to remove insoluble solid particles and other easily separable impurities, wherein the filter is a centrifugal filter.

[0032] Step 2: The filtered and impurity-removed waste liquid is transported to the waste liquid incinerator 2 via a diaphragm metering pump. It is evenly sprayed into the combustion chamber of the waste liquid incinerator 2 through a feed nozzle. The flue gas from the combustion of natural gas and air (with a 20% excess air) is used as the heat source. The temperature in the combustion zone of the waste liquid incinerator 2 is controlled at approximately 1200°C to completely vaporize the waste liquid. Simultaneously, the organic phase and interfacial contaminants contained in the waste liquid are fully burned and oxidized by the excess air into carbon dioxide, nitrogen oxides, sulfur dioxide, and water vapor. Nitrates in the waste liquid are partially decomposed by heat into metal oxides and nitrogen oxide gases. Uranium contained in the waste liquid is also decomposed into uranium oxides and nitrogen oxide gases. The remaining salts, metal oxides, and uranium oxides in the waste liquid are discharged from the lower outlet of the waste liquid in powder form and temporarily stored.

[0033] Step 3: Exhaust gas from the waste liquid incinerator 2 passes through a primary dust collector 3 (350-450°C) and a secondary dust collector 4 (250-350°C) for two-stage dust removal before entering a condenser 5. The primary dust collector 3 utilizes a high-precision nickel tube filter (≤10μm), while the secondary dust collector 4 utilizes an electrostatic precipitator (dust removal efficiency >99.9%). The condensate collected in the condenser 5 has a nitric acid concentration of 6-10 mol / L.

[0034] Step 4: The tail gas from the condenser 5 is further absorbed and purified by the elution tower 6. The acidity of the nitric acid solution absorbed by the elution tower 6 can reach 5-8 mol / L. The tail gas from the outlet of the elution tower 6 enters the alkaline washing tower 8 for neutralization and absorption before being discharged. The tail gas emission standard meets the requirements of the "Integrated Emission Standard of Air Pollutants" (GB16297-1996) for NO X The emission limit is 240mg / m 3 .

[0035] Step 5: The acid mixture is recovered from condenser 5 and elution tower 6 and fed to distillation tower 7. Condensed water (pH > 4, [U] ≤ 0.02 mg / L) is removed from the top of distillation tower 7 and returned to elution tower 6 for elution and recovery of nitric acid. Concentrated nitric acid (nitric acid concentration > 10 mol / L) is removed from the bottom of the tower and returned to the main uranium purification process for recycling. Distillation tower 7 is a packed tower with 10 theoretical plates, a reflux ratio < 0.3, and atmospheric distillation.

[0036] The above shows and describes the main process, main equipment, main features and advantages of the present invention, etc. Any improvements or equivalent changes based on the solution of the present invention are not excluded from the scope of protection of the present invention.

Claims

1. A method for treating uranium-containing high-salt wastewater in a nitric acid system, characterized by: Step 1: The waste liquid is filtered to remove insoluble solid particles and other easily separable impurities; Step 2: The waste liquid after filtration and impurity removal is transported to the waste liquid incinerator via a diaphragm metering pump and evenly sprayed into the combustion chamber of the waste liquid incinerator through a feed nozzle. The flue gas after the combustion of natural gas and air is used as a heat source to completely gasify the waste liquid. At the same time, the organic phase and interface pollutants contained in the waste liquid can be fully burned and oxidized into carbon dioxide, nitrogen oxides, sulfur dioxide and water vapor by excess air; the nitrate in the waste liquid is partially decomposed into metal oxides and nitrogen oxide gases by heat, and the uranium contained is also decomposed into uranium oxides and nitrogen oxide gases. The remaining salts, metal oxides and uranium oxides in the waste liquid are discharged from the lower outlet of the waste liquid incinerator in the form of powder and temporarily stored; Step 3: The exhaust gas from the waste liquid incinerator is removed by the primary dust collector and the secondary dust collector before entering the condenser; Step 4: The tail gas from the condenser is further absorbed and purified by the leaching tower. The acidity of the nitric acid solution absorbed by the leaching tower reaches 5-8 mol / L. The tail gas at the outlet of the leaching tower enters the alkaline washing tower for neutralization and absorption before being discharged; Step 5: The acid mixture recovered by the condenser and the elution tower enters the distillation tower. The condensed water taken from the top of the distillation tower is returned to the elution tower for elution and recovery of nitric acid. The concentrated nitric acid taken from the bottom of the tower is returned to the main uranium purification process for recycling.

2. The method for treating uranium-containing high-salt wastewater in a nitric acid system according to claim 1, wherein: The filter is a centrifugal filter.

3. The method for treating uranium-containing high-salt wastewater in a nitric acid system according to claim 1, wherein: The second step: using the flue gas after combustion of natural gas and air as the heat source, wherein the air is in excess of 20%.

4. The method for treating uranium-containing high-salt wastewater in a nitric acid system according to claim 1, wherein: The second step is to control the temperature of the combustion zone of the waste liquid incinerator to 1200° C. so that the waste liquid can be completely gasified.

5. The method for treating uranium-containing high-salt wastewater in a nitric acid system according to claim 1, wherein: The temperature of the first-stage dust collector is 350-450°C.

6. The method for treating uranium-containing high-salt wastewater in a nitric acid system according to claim 1, wherein: The temperature of the secondary dust collector is 250-350°C.

7. The method for treating uranium-containing high-salt wastewater in a nitric acid system according to claim 1, wherein: The first-stage dust collector adopts a high-precision nickel tube filter.

8. The method for treating uranium-containing high-salt wastewater in a nitric acid system according to claim 1, wherein: The secondary dust collector adopts an electrostatic dust collector.

9. The method for treating uranium-containing high-salt wastewater in a nitric acid system according to claim 1, wherein: The third step: the condensate collected by the condenser has a nitric acid concentration of 6 to 10 mol / L.

10. The method for treating uranium-containing high-salt wastewater in a nitric acid system according to claim 1, wherein: The distillation tower is in the form of a packed tower, has a theoretical plate number of 10, a reflux ratio of less than 0.3, and performs atmospheric distillation.

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