Comprehensive treatment method for uranium mine tail water

Abstract

The invention discloses a uranium mine tail water comprehensive treatment method, and relates to the field of radiation-containing wastewater comprehensive treatment, and the uranium mine tail water comprehensive treatment method comprises the following treatment steps: (1) pretreatment: filtering large particle impurities in uranium mine wastewater, and adjusting the pH value of the wastewater to 5-7; (2) concentration treatment: performing NF treatment on the pretreated wastewater to obtain first-stage concentrated water and first-stage produced water, and performing RO treatment on the first-stage produced water to obtain second-stage concentrated water and second-stage produced water; and (3) adsorption and precipitation treatment: collecting the primary concentrated water in the reaction tank, mixing the primary concentrated water with the secondary concentrated water to obtain high-concentration uranium-containing wastewater, adding modified biochar which is loaded with Ca3 (PO4) 2 into the reaction tank, and fully reacting and adsorbing. The uranium content removal rate of the produced water after two-stage membrane concentration can reach about 98%, the COD removal rate is almost 100%, and the hardness removal rate can reach about 96%; after full adsorption and precipitation of the modified biochar, the uranium content removal rate of effluent in the reaction tank can reach about 92%, the COD removal rate can reach about 90%, and the hardness removal rate can reach about 87%.

Description

Technical Field

[0001] The invention relates to uranium-containing wastewater generated in the process of uranium mining and processing, and specifically to a method for comprehensive treatment of uranium tail water, in particular to comprehensive treatment of low-concentration uranium tail water. Background Art

[0002] A large amount of uranium-containing wastewater is produced during uranium mining, nuclear fuel cycle and spent fuel reprocessing. The World Health Organization stipulates that the uranium content in mineral water and drinking water must be less than 20μg / L and 9μg / L, respectively. However, the concentration of wastewater produced during uranium mining and processing can be as high as several to several hundred mg / L. -1 If these uranium-containing wastewaters are not effectively treated, the chemical toxicity and radioactive radiation produced by uranium will pose a huge potential threat to the earth's organisms and the human environment.

[0003] Usually, uranium mine tail water is low-concentration uranium-containing wastewater with a uranium content of 5-30 mg / L. The uranium in the uranium wastewater usually exists in hexavalent form. The uranium mine tail water in the present invention refers to production wastewater containing low-concentration hexavalent uranium and its compounds. In addition, in addition to heavy metal pollutants, uranium mine tail water also contains a certain amount of salt and relatively high COD.

[0004] In recent years, the main treatment methods for uranium-containing wastewater include chemical precipitation, ion exchange, membrane separation, adsorption, reduction, etc. These methods are mostly aimed at removing heavy metals in wastewater, but have poor effects on removing salt and COD in wastewater. Therefore, it is necessary to propose a method for the simultaneous removal of multiple pollutants in uranium mine tailings. Summary of the invention

[0005] The purpose of the present invention is to provide a method for comprehensive treatment of uranium mine tailings water in view of the above-mentioned problems, which can treat various pollutants in the tailings water.

[0006] The technical solution of the present invention is achieved as follows: a method for comprehensive treatment of uranium mine tailings, characterized in that it includes the following treatment steps:

[0007] (1) Pretreatment: filtering large particles of impurities in uranium mine wastewater and adjusting the pH of the wastewater to 5-7;

[0008] (2) Concentration treatment: the pretreated wastewater is first treated by NF to obtain primary concentrated water and primary product water. The primary product water is then treated by RO to obtain secondary concentrated water and secondary product water. The secondary product water can be reused for cleaning NF membranes and RO membranes or for other industrial water purposes.

[0009] (3) Adsorption and precipitation treatment, collecting the primary concentrated water and the secondary concentrated water in the reaction tank and mixing them to obtain high-concentration uranium-containing wastewater, adding modified biochar to the reaction tank, wherein the modified biochar is loaded with Ca3(PO4)2, and after sufficient reaction and adsorption, the wastewater can be returned to step (2) for concentration treatment together with the pretreated wastewater or industrial water for other purposes.

[0010] Wherein, the modified biochar preparation steps in step (3) are:

[0011] a. Take the biomass and air-dry it, crush it and then sieve it, and then carbonize the sieved biomass under an inert atmosphere to obtain biochar;

[0012] b. Dissolve Ca3(PO4)2 powder in nitric acid and stir thoroughly until dissolved to prepare tricalcium phosphate solution;

[0013] c. The biochar was crushed to a particle size of 2-4 mm and then immersed in a tricalcium phosphate solution, followed by low-speed stirring, standing and drying to obtain modified biochar;

[0014] Wherein, in step a, the biomass is cow dung, the inert atmosphere is nitrogen, the carbonization temperature is 400-600° C., and the carbonization time is 4-6 hours;

[0015] In step b, the amount of Ca3(PO4)2 added is adjusted according to the actual situation so that the solution is a saturated solution of Ca3(PO4)2;

[0016] In step c, the stirring time is 1-2 hours, the standing time is 4-8 hours, the drying time is 1-2 hours, and the drying temperature is 150-200°C.

[0017] In addition to U(VI), the uranium mine tailings also contain Na + ,cl - , Ca 2+ 、CO3 2- As well as organic matter and other pollutants, uranium ore is usually extracted by alkaline leaching. The uranium ore tailings are alkaline. If the concentration treatment is directly carried out, the membrane corrosion resistance is required to be high. Using dilute hydrochloric acid to adjust the wastewater pH to 5-7 (weakly acidic) is not only conducive to the subsequent membrane treatment, but also can remove some CO3 2- Converted to HCO3 - or CO2, reducing the risk of subsequent scaling. In addition, when the pH of the wastewater is between 5 and 7, the uranyl in the wastewater is mainly in the form of (UO2)3(OH)5 + 、(UO2)4(OH)7 +The contact surface of Ca3(PO4)2 in the wastewater is negatively charged, and the electrostatic attraction between the two helps to generate stable calcium uranium mica (Ca(UO2)2(PO4)2·xH2O); when the pH is too low (pH < 5), uranyl in the wastewater is mainly in the form of UO2 2+ 、(UO2)2(OH)2 2+ In this case, the contact surface of Ca3(PO4)2 in the wastewater is positively charged, and there is electrostatic repulsion between it and uranyl, which makes it difficult to form stable calcium uranium mica. When the pH is too high (pH>7), uranyl in the wastewater is mainly in the form of (UO2)3(OH)7 - 、UO2(OH)3 - At this time, the contact surface of Ca3(PO4)2 in the wastewater is still negatively charged, and electrostatic repulsion will gradually occur between it and Ca3(PO4)2, affecting the formation of stable calcium uranium mica.

[0018] If low-concentration uranium-containing wastewater is directly treated for its pollutants, its treatment efficiency is low. In the present invention, the pretreated wastewater is first concentrated, and the concentrated concentrated water is efficiently treated. The present invention comprehensively considers the concentration cost and water production efficiency, first uses NF membrane for concentration treatment, and its water production rate can reach about 60%. Then the primary produced water is concentrated by RO membrane, and its water production rate can reach 90-95%. After two-stage filtration, its uranium content removal rate can reach about 98%, COD removal rate is almost 100%, and hardness removal can reach about 96%.

[0019] Using cow dung rich in C and P as biochar raw material can effectively utilize waste biomass. Cow dung biochar has rich organic carbon and π bonds as well as rich pore structures and surface functional groups. It can remove pollutants in uranium-containing wastewater through distribution and adsorption. At the same time, more P elements are introduced into biochar, which is helpful for the formation of subsequent precipitation. The saturated tricalcium phosphate-nitric acid solution can dissolve more tricalcium phosphate and load it on biochar. On the other hand, nitric acid etching can increase the specific surface area of ​​biochar and increase the adsorption points. Nitric acid also has a strong ability to generate oxygen-containing functional groups. It can act as an oxidant to oxidize and modify the surface of biochar, improve the hydrophilicity of surface functional groups, and enhance the complex adsorption capacity of pollutants. It has been observed through practical applications that the modified biochar has a certain degradation ability for COD in wastewater, which may be caused by the oxygen-containing functional groups on the surface of the modified biochar. The pore size of the modified biochar is 20-100nm, and the BET specific surface area can reach up to 1043m 2 / g, after sufficient adsorption and precipitation of modified biochar, the uranium content removal rate in the effluent of the reaction pool can reach about 91%, the COD removal rate can reach about 85%, and the hardness removal rate can reach about 89%.

[0020] The remarkable effects of the present invention are:

[0021] (1) The present invention first concentrates the uranium mine tailings, thereby improving the pollutant treatment efficiency. After two-stage membrane concentration, the uranium content removal rate in the produced water can reach about 98%, the COD removal rate is almost 100%, and the hardness removal rate can reach about 96%;

[0022] (2) During pretreatment, the uranium mine tailings are adjusted to a preset pH value, which not only reduces the membrane treatment pressure but also ensures the subsequent uranyl removal effect;

[0023] (3) The modified biochar prepared according to the method of the present invention has a strong adsorption and precipitation effect on pollutants. After sufficient adsorption and precipitation of the modified biochar, the uranium content removal rate in the effluent of the reaction tank can reach about 92%, the COD removal rate can reach about 90%, and the hardness removal rate can reach about 87%. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a flow chart of the comprehensive treatment method of uranium mine tailings of the present invention. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail in conjunction with the embodiments and comparative examples. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0026] Example 1

[0027] The water quality of the uranium mine tail water treated in this example was measured as follows: U(VI) 24 mg / L, COD 893 mg / L -1 , total nitrogen 10mg / L, total hardness 957mg / L, conductivity 83ms / cm.

[0028] (1) Pretreatment: Use a security filter to filter out larger impurities in the wastewater, and automatically add hydrochloric acid to adjust the pH of the wastewater to 7;

[0029] (2) Concentration treatment: the pretreated wastewater is first treated by NF to obtain primary concentrated water and primary product water. The primary product water is then treated by RO to obtain secondary concentrated water and secondary product water. The U(VI) in the secondary product water is 0.4 mg / L and the COD is 5.4 mg / L. -1 , total nitrogen 0.2mg / L, total hardness 17.3mg / L, conductivity 0.3ms / cm;

[0030] (3) Adsorption precipitation treatment: the first concentrated water is collected in the reaction pool and mixed with the second concentrated water to obtain high-concentration uranium-containing wastewater. At this time, the water quality in the reaction pool is measured as: U(VI) 108 mg / L, COD 3351 mg / L -1, total nitrogen 32mg / L, total hardness 3985mg / L, conductivity 253ms / cm, modified biochar loaded with Ca3(PO4)2 was added to the reaction tank, and after sufficient reaction and adsorption, U(VI) 8.6mg / L and COD 336.8mg / L were found in the effluent of the reaction tank. -1 , total nitrogen 3.1 mg / L, total hardness 516.9 mg / L, conductivity 45.5 ms / cm.

[0031] Wherein, the modified biochar preparation steps in step (3) are:

[0032] a. Take the discarded cow dung and air-dry it, crush it and sieve it, then place the sieved biomass in a nitrogen atmosphere and carbonize it at 500°C for 4 hours to obtain biochar;

[0033] b. Dissolve Ca3(PO4)2 powder in nitric acid and stir until dissolved to prepare a saturated solution of tricalcium phosphate;

[0034] c. The biochar was crushed to a particle size of 3 mm and then immersed in a tricalcium phosphate solution, followed by low-speed stirring for 1.5 h, standing for 6 h, and drying at 150 ° C for 2 h to obtain modified biochar;

[0035] Example 2

[0036] The water quality of the uranium mine tail water treated in this example was measured as follows: U(VI) 24 mg / L, COD 893 mg / L -1 , total nitrogen 10mg / L, total hardness 957mg / L, conductivity 83ms / cm.

[0037] (1) Pretreatment: Use a security filter to filter out larger impurities in the wastewater, and automatically add hydrochloric acid to adjust the pH of the wastewater to 5.5;

[0038] (2) Concentration treatment: The pretreated wastewater is first treated with NF to obtain primary concentrated water and primary product water. The primary product water is then treated with RO to obtain secondary concentrated water and secondary product water. The U(VI) in the secondary product water is 0.3 mg / L and the COD is 6.1 mg / L. -1 , total nitrogen 0.2mg / L, total hardness 15.8mg / L, conductivity 0.3ms / cm;

[0039] (3) Adsorption precipitation treatment: the first concentrated water is collected in the reaction pool and mixed with the second concentrated water to obtain high-concentration uranium-containing wastewater. At this time, the water quality in the reaction pool is measured as: U(VI) 113 mg / L, COD 3307 mg / L -1, total nitrogen 34mg / L, total hardness 3895mg / L, conductivity 248ms / cm, modified biochar loaded with Ca3(PO4)2 was added to the reaction tank, and after sufficient reaction and adsorption, U(VI) 9.0mg / L and COD 317.2mg / L were found in the effluent of the reaction tank. -1 , total nitrogen 2.9 mg / L, total hardness 504.7 mg / L, conductivity 44.1 ms / cm.

[0040] Wherein, the modified biochar preparation steps in step (3) are:

[0041] a. Take the discarded cow dung and air-dry it, crush it and sieve it, then place the sieved biomass in a nitrogen atmosphere and carbonize it at 600℃ for 6h to obtain biochar;

[0042] b. Dissolve Ca3(PO4)2 powder in nitric acid and stir until dissolved to prepare a saturated solution of tricalcium phosphate;

[0043] c. The biochar was crushed to a particle size of 2 mm and then immersed in a tricalcium phosphate solution, followed by low-speed stirring for 2 h, standing for 8 h, and drying at 150 ° C for 2 h to obtain modified biochar;

[0044] Comparative Example 1

[0045] The primary concentrated water and secondary concentrated water obtained in Example 2 were mixed, the pH was adjusted to 3.0, and the modified biochar prepared in step (3) of Example 2 was added. After sufficient reaction and adsorption treatment, U(VI) in the effluent was 30.7 mg / L and COD was 319.7 mg / L. -1 , total nitrogen 2.6 mg / L, total hardness 513.8 mg / L, conductivity 44.7 ms / cm.

[0046] Comparative Example 2

[0047] The primary concentrated water and secondary concentrated water obtained in Example 2 were mixed, the pH was adjusted to 9.0, and the modified biochar prepared in step (3) of Example 2 was added. After sufficient reaction and adsorption treatment, U(VI) in the effluent was 19.4 mg / L and COD was 323.9 mg / L. -1 , total nitrogen 3.1 mg / L, total hardness 498.2 mg / L, conductivity 42.5 ms / cm.

[0048] Comparative Example 3

[0049] The primary concentrated water and secondary concentrated water obtained in Example 2 were mixed, the pH was adjusted to 5.5, and modified biochar was added. After sufficient reaction and adsorption treatment, U(VI) in the effluent was 14.3 mg / L and COD was 413.8 mg / L. -1 , total nitrogen 3.9 mg / L, total hardness 603.7 mg / L, conductivity 50.1 ms / cm.

[0050] Wherein, the modified biochar preparation method is as follows:

[0051] a. Take the forest waste and air-dry it, crush it and sieve it, then place the sieved biomass in a nitrogen atmosphere and carbonize it at 600℃ for 6h to obtain biochar;

[0052] b. Dissolve Ca3(PO4)2 powder in nitric acid and stir until dissolved to prepare a saturated solution of tricalcium phosphate;

[0053] c. The biochar was crushed to a particle size of 2 mm and then immersed in a tricalcium phosphate solution, followed by low-speed stirring for 2 h, standing for 8 h, and drying at 150 ° C for 2 h to obtain modified biochar;

[0054] It can be seen that the pH value of wastewater plays an important role in the uranium removal results during the process of modified biochar removing uranium from wastewater, and different biomass substrates will also affect the removal of pollutants in wastewater by modified biochar. The present invention selects cow dung with high phosphorus content as the biomass substrate. Compared with other common biochar substrates, more phosphorus elements can be introduced. From the results, it can be seen that the introduction of more phosphorus elements plays a positive role in removing pollutants.

[0055] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0056] The above is only a preferred embodiment of the present invention. Based on the above concept of the present invention, those skilled in the art can also make various modifications and changes. For example, adjust the pH of the wastewater, change the carbonization time and carbonization temperature, change the standing time, etc. However, such changes and modifications belong to the essence of the present invention.

Claims

1. A method for comprehensive treatment of uranium mine tailings, characterized in that: The processing steps include: (1) Pretreatment: filtering large particles of impurities in uranium mine wastewater and adjusting the pH of the wastewater to 5-7; (2) Concentration treatment: the pretreated wastewater is first treated by NF to obtain primary concentrated water and primary product water. The primary product water is then treated by RO to obtain secondary concentrated water and secondary product water. The secondary product water can be reused for cleaning NF membranes and RO membranes or for other industrial water purposes. (3) Adsorption and precipitation treatment, collecting the primary concentrated water and the secondary concentrated water in the reaction tank and mixing them to obtain high-concentration uranium-containing wastewater, adding modified biochar to the reaction tank, wherein the modified biochar is loaded with Ca3(PO4)2, and after sufficient reaction and adsorption, the wastewater can be returned to step (2) for concentration treatment together with the pretreated wastewater or industrial water for other purposes.

2. The method for comprehensive treatment of uranium mine tailings according to claim 1, characterized in that: The steps for preparing modified biochar in step (3) are as follows: a. Take the biomass and air-dry it, crush it and then sieve it, and then carbonize the sieved biomass under an inert atmosphere to obtain biochar; b. Dissolve Ca3(PO4)2 powder in nitric acid and stir thoroughly until dissolved to prepare tricalcium phosphate solution; c. The biochar is crushed into a particle size of 2-4 mm and then immersed in a tricalcium phosphate solution, followed by low-speed stirring, standing and drying to obtain modified biochar.

3. The method for comprehensive treatment of uranium mine tailings according to claim 2, characterized in that: In step a, the biomass is cow dung, and the inert atmosphere is nitrogen.

4. The method for comprehensive treatment of uranium mine tailings according to claim 2, characterized in that: In step a, the carbonization temperature is 400-600° C. and the carbonization time is 4-6 hours.

5. The method for comprehensive treatment of uranium mine tailings according to claim 2, characterized in that: In step b, the amount of Ca3(PO4)2 added is adjusted according to actual conditions so that the prepared solution is a saturated solution of Ca3(PO4)2.

6. The method for comprehensive treatment of uranium mine tailings according to claim 2, characterized in that: In step c, the stirring time is 1-2 hours, the standing time is 4-8 hours, the drying time is 1-2 hours, and the drying temperature is 150-200°C.

7. The method for comprehensive treatment of uranium mine tailings according to claim 1, characterized in that: After two-stage concentration and filtration, the uranium content removal rate in the produced water can reach about 98%, the COD removal rate is almost 100%, and the hardness removal rate can reach about 96%.

8. The method for comprehensive treatment of uranium mine tailings according to claim 2, characterized in that: After the modified biochar is fully reacted and adsorbed, the uranium content removal rate in the effluent from the reaction pool can reach about 91%, the COD removal rate can reach about 85%, and the hardness removal rate can reach about 89%.

9. A modified biochar, characterized in that: The production steps include: a. Take the discarded cow dung and air-dry it, crush it and sieve it, then place the sieved biomass in a nitrogen atmosphere and carbonize it at 400-600℃ for 4-6h to obtain biochar; b. Dissolve Ca3(PO4)2 powder in nitric acid, stir thoroughly until dissolved, stir at low speed for 1-2h, let stand for 4-8h, and dry at 150-200°C for 1-2h to obtain a saturated solution of tricalcium phosphate; c. The biochar is crushed into a particle size of 2-4 mm and then immersed in a tricalcium phosphate solution to modify the biochar.

10. A use of preparing modified biochar according to claim 9, characterized in that: The modified biochar can be used to treat uranium mine tailings.

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