CN108439633B

CN108439633B - Method for treating high-alkalinity fluorine-containing uranium-containing wastewater and recycling uranium

Info

Publication number: CN108439633B
Application number: CN201810101432.XA
Authority: CN
Inventors: 陈宗元; 高超; 郭治军
Original assignee: Lanzhou University
Current assignee: Lanzhou University
Priority date: 2018-02-01
Filing date: 2018-02-01
Publication date: 2022-09-27
Anticipated expiration: 2038-02-01
Also published as: CN108439633A

Abstract

The invention provides a method for treating high-alkalinity fluorine-containing uranium-containing wastewater and recycling uranium. Firstly, adding nano zero-valent iron into alkaline fluorine-containing uranium waste liquid, fully mixing under the condition of isolating oxygen, then carrying out solid-liquid separation, transferring the solid phase loaded with uranium to a liquid containing CO ₃ ^2‑ Introducing oxygen into the solution, fully mixing gas, liquid and solid phases, and utilizing O ₂ And CO ₃ ^2‑ The uranium is separated from the solid phase and returns to the liquid phase under the synergistic effect of the two components, so that the recycling of the uranium is realized. The method is carried out under the alkaline condition, and pretreatment such as acidification and the like on alkaline wastewater is not needed, so that the process flow is shortened, and the treatment cost is saved; compared with the acidic condition, the corrosion consumption of zero-valent iron is reduced, and the content of iron impurities in the recycled uranium solution is reduced; when uranium-bearing waste water removes the uranium purification, realized the recovery of uranium, this wastewater treatment scheme is complete, both includes water treatment, includes the uranium recovery again.

Description

Method for treating high-alkalinity fluorine-containing uranium-containing wastewater and recycling uranium

Technical Field

The invention belongs to the field of wastewater treatment, and particularly relates to a method for treating high-alkalinity fluorine-containing uranium-containing wastewater and recycling uranium.

Background

Uranium enrichment is an important link in the nuclear fuel manufacturing process. The container cleaning and other links of the uranium concentration plant can generate a large amount of high alkalinity (containing CO) ₃ ^2- The concentration is as high as 0.3mol/L, the pH value can be as high as 11), and the fluorine content is 1-5000mg/L, wherein a large amount of alkali and fluorine contained in the uranium waste liquid cause great interference to the recycling of uranium.

For the treatment of uranium-containing waste water, there are many methods such as adsorption method, extraction method, ion exchange method, membrane separation method, etc., but these methods are generally limited by the chemical group of waste liquidLarge influence, high cost and the like. For example, due to uranium and CO ₃ ^2- By strong coordination, conventional adsorption processes in the presence of large amounts of CO ₃ ^2- Especially also containing F ^- The alkaline wastewater is difficult to play a role; solvent extraction and ion exchange processes, except by CO ₃ ^2- And F ^- Besides the interference, the method also has other obvious defects of high price of the extracting agent and the ion exchange resin, complex operation, complex treatment process, low efficiency, troublesome treatment of a large amount of raffinate, easy secondary pollution caused by residual extracting agent and the like; the membrane separation method also has the disadvantages of high price, low efficiency and the like. For CO ₃ ^2- The above-mentioned wastewater treatment method requires that a large amount of concentrated sulfuric acid (H) is previously added to the wastewater ₂ SO ₄ ) Acidifying to remove CO ₃ ^2- The purpose of reducing the alkalinity of the acidized solution is achieved, a large amount of acid is consumed in the process, new impurities can be introduced while the treatment cost is increased, and the subsequent recycling and purification of uranium are not facilitated.

In recent years, research on the utilization of nano zero-valent iron to treat uranium-containing wastewater has been reported. This is a hexavalent UO in which uranium is readily soluble in water by utilizing the reducibility of iron ₂ ²⁺ Morphological reduction to UO which is easily removed from the liquid phase ₂ The solid state is enriched to the surface of zero-valent iron, thereby achieving the aim of removing uranium in the liquid phase. However, the current method for treating uranium-containing wastewater by using nano zero-valent iron still focuses on the treatment of wastewater under an acidic condition, and acid is required to be added to adjust the pH value of the wastewater to an acidic range before the nano zero-valent iron is added, so that the method has many disadvantages: consumption of large amounts of acid will produce large amounts of CO ₂ Gas generates larger pressure on equipment, and is easy to cause acid pollution and equipment corrosion; meanwhile, the consumption of zero-valent iron in an acidic environment is remarkably increased, so that the treatment cost is increased, a large amount of corrosion products are generated, a large amount of iron impurities are introduced into the solution, and the separation of uranium and iron in the subsequent uranium recovery process is not favorable. It is therefore necessary to develop a process which operates directly in the alkaline range.

In addition, the existing method only focuses on removing uranium in uranium-containing wastewater, and does not consider the problem of recycling uranium after removing uranium by using zero-valent iron. In consideration of the fact that the uranium resources in China are precious and limited, the uranium is not recycled, and huge waste is caused. Therefore, the method for treating the high-alkali fluorine-containing uranium-containing wastewater and simultaneously recovering the uranium has important practical value and practical significance.

Disclosure of Invention

Aiming at the technical problems and solving the defects in the prior art, the invention provides a method for treating high-alkalinity fluorine-containing uranium-containing wastewater and recycling uranium. The whole process of the method is operated under an alkaline condition, and wastewater does not need to be acidified; the recycling of uranium in the wastewater is realized while the uranium-containing wastewater is treated.

The method specifically comprises the following steps:

(1) adding nano zero-valent iron into high-alkalinity fluorine-containing uranium wastewater under the condition of isolating oxygen, and fully mixing to enrich uranium by the nano zero-valent iron, wherein the solid-to-liquid ratio of the nano zero-valent iron is 0.042g/L-1.5 g/L;

(2) solid-liquid separation, and solid phase is reserved; if the liquid phase reaches the discharge standard (<50 mug/L) of uranium, directly discharging or further processing other harmful components, and returning to the step (1) if the liquid phase does not reach the discharge standard;

(3) putting the solid phase separated in the step (2) into CO ₃ ^2- In the solution with the concentration of 0.01-0.1mol/L, the solid-liquid ratio is 1.5-150 g/L, and oxygen is introduced to fully mix the gas phase, the liquid phase and the solid phase;

(4) and (4) carrying out solid-liquid separation, and reserving a liquid phase to obtain a recycled uranium-containing liquid phase.

Further, the pH value of the wastewater is 10.0-11.0.

Furthermore, the concentration range of the fluorine ions in the wastewater is 0-3.8 g/L.

Furthermore, the uranium concentration of the wastewater is 1-6000 mg/L.

Furthermore, nano zero-valent iron is added in the step (1) to ensure that the solid-to-liquid ratio is 1.5 g/L.

Further, in the step (1), the method for fully mixing the solid and the liquid comprises one or more of the following methods: a, introducing inert gas for bubbling; and B, mechanically stirring, vibrating, overturning and rolling under the condition of isolating oxygen.

Further, the enrichment time in the step (1) is 12 hours.

Further, the solid-liquid separation in the step (2) and the step (4) is centrifugal separation.

Further, CO in the step (3) ₃ ^2- The concentration was 0.1 mol/L.

Further, the solid-to-liquid ratio in the step (3) is 1.5 g/L.

Further, in the step (3), the gas phase, the liquid phase and the solid phase are fully mixed, and the method for ensuring the full mixing is one or the combination of the following two methods: a, introducing oxygen into a system, bubbling and mixing; and B, under the condition of keeping the oxygen in the container sufficient, carrying out mechanical stirring or shaking or overturning or rolling.

Further, the oxygen in the step (3) may be replaced with air.

The invention has the beneficial effects that:

the method utilizes the nano zero-valent iron to directly treat the alkaline fluorine-containing uranium-containing wastewater, does not need to carry out pretreatment such as acidification on the wastewater, saves the production cost and the treatment time, and avoids CO generated in the acid treatment process ₂ The problem of (2);

(2) the method of the invention recovers uranium while treating the high-alkali fluorine-containing uranium-containing wastewater;

(3) the invention utilizes the nanometer zero-valent iron and O ₂ And CO ₃ ^2- The uranium is recycled, the operation is simple and convenient, the energy consumption is low, and the price and the efficiency are low;

(4) the whole process flow is carried out under an alkaline condition, so that a large amount of iron is effectively prevented from being dissolved under an acidic condition, a large amount of iron impurities cannot be introduced into the recycled uranium solution, and the purity of uranium is improved;

(5) the method can realize the concentration of uranium while recycling uranium, and has practical application value for recycling uranium in the high-alkali fluorine-containing wastewater.

Drawings

FIG. 1 Effect of enrichment of uranium under air, argon and intermittent air contact conditions

FIG. 2 Effect of nano-zero-valent iron dosage on uranium enrichment

FIG. 3 synergistic effect of oxygen and carbonate on uranium recovery process

FIG. 4 influence of carbonate concentration on recovery Process

FIG. 5 Effect of oxygen concentration on recovery Process

FIG. 6 Effect of mixing conditions on recovery Process

FIG. 7 is a process flow diagram

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the drawings in the specification, and it is obvious that the described embodiments are only a part of the present invention, and not all of the invention. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.

Example 1 enrichment recovery of uranium from uranium-containing waste water of a plant of a uranium concentration plant

The processing method and the steps are as follows:

(1) enrichment of uranium in high-alkali fluorine-containing wastewater

(1.1) determination of enrichment time

100mL of typical high-alkali uranium-containing wastewater in a certain workshop of a uranium concentrating plant is taken, and the main components are as follows: the uranium concentration is 200mg/L and the fluorine ion concentration is 400mg/L, CO ₃ ² The concentration is 1000mg/L, pH ═ 10.8, nano zero-valent iron powder 0.15g is added according to the solid-to-liquid ratio of 1.5g/L, argon is used as protective gas to isolate oxygen, the mixture is fully mixed, and the liquid phase uranium concentration is detected at intervals until the uranium concentration does not decrease any more, which indicates that the reaction has reached equilibrium.

From the experimental results and fig. 1, it can be known that the uranium enrichment rate can reach 96.5% in 2h, 99.0% in 4h and 99.8% in 10h, and the actual production process should balance the production efficiency and the uranium enrichment rate to determine the enrichment response time.

(1.2) selection of the amount of solid to be added, i.e., the solid-to-liquid ratio

The amount of nano iron to be added, namely the solid-liquid ratio (unit g/L) is used for expressing the solid-liquid ratio, the solid-liquid ratio is larger, the reaction is more rapid and complete, however, the solid-liquid ratio is too large, the waste of the solid phase and the cost are increased, and the proper solid-liquid ratio can be determined according to a series of simple experiments for different waste water in the actual production process.

The experimental method comprises the following steps: taking four parts of wastewater, respectively adding different amounts of solid, fully mixing, and detecting the liquid phase uranium concentration at intervals. In the embodiment, four parts of the wastewater in the step (1) are taken, 9.5mL of each part is added with 0.4mg (solid-liquid ratio of 0.042g/L), 2.1mg (solid-liquid ratio of 0.221g/L), 7.6mg (solid-liquid ratio of 0.8g/L) and 14.25mg (solid-liquid ratio of 1.5g/L) of nano iron respectively, and the four parts are fully mixed under the protection of argon gas, and the liquid phase uranium concentration is detected at intervals.

From the experimental results and fig. 2, it can be seen that for the typical uranium-containing wastewater treated, the addition of 0.8g/L of nano-iron can enrich 99% of uranium in 12 hours, and in this experiment, in order to ensure that sufficient nano-iron can rapidly and completely enrich uranium in the liquid phase, the addition of 1.5g/L is selected.

(1.3) Effect of oxygen on enrichment Process

The uranium is reduced by iron in the process of enriching uranium by nano zero-valent iron, so that the uranium enrichment process is not facilitated by the presence of oxygen, and as can be seen from figure 1, the uranium removal rate can finally reach 100% in an argon environment (the oxygen content is less than 5 ppm); the uranium can hardly be enriched under the condition that the container opening is open, namely the solution is fully contacted with the air; whereas, under conditions where the vessel is intermittently opened so that the solution is in contact with oxygen but not sufficiently, the enrichment rate shows a tendency to rise first to the highest point (4 hours in fig. 1) and then to fall over time.

The above results can be fully explained: oxygen has a significant impact on the reductive enrichment process and therefore the amount of oxygen must be severely limited during the enrichment phase.

Theoretically, the smaller the oxygen content is, the more beneficial the rapidity and completeness of the enrichment process is, however, the strict oxygen control operation will inevitably increase the production cost of equipment and the like, lengthen the time of the whole treatment process, and simultaneously, the operation procedure will be more complicated. Experiments show that in actual production, the strategy that the container is filled with liquid as much as possible, air residue at the top is reduced, and the reaction container is quickly sealed after the nano zero-valent iron is added is used as oxygen control operation, so that the enrichment purpose can be achieved.

(2) Solid-liquid separation

Performing solid-liquid separation on the system which finishes the uranium enrichment in the step (1) by adopting a centrifugal method (the speed is 4000rpm/min, the time is 10min), if the uranium concentration in the liquid phase does not reach the discharge standard of uranium, entering the step (1) again, and if the uranium concentration reaches the standard, sending the system to other workshops to process other components; and (4) retaining the solid phase to enter a uranium recovery flow.

(3) Uranium recovery

(3.1) synergistic Effect of oxygen and carbonate in uranium recovery Process

The solid phase is put into CO according to the solid-liquid ratio of 1.5g/L (the same as the solid-liquid ratio in the enrichment process) ₃ ^2- In the solution with the concentration of 0.1mol/L, the volume of the solution is 100mL, and simultaneously sufficient O is introduced ₂ Bubbling or fully oscillating ensures the sufficient contact of gas, liquid and solid phases, detects the concentration change of uranium in the liquid phase, and realizes the recycling of uranium enriched on the surface of the nano zero-valent iron.

The experimental results are shown in fig. 3, and it can be seen that: o is ₂ +CO ₃ ^2- In the system, the recovery rate of uranium recovered to a liquid phase reaches 81% in 30 minutes, 91% in 1.5 hours, 98% in 4 hours and 100% in 8 hours. And as O of a control group ₂ +H ₂ O system, Ar + CO ₃ ^2- The system recovery was consistently less than 1.5%.

The results fully illustrate the synergistic effect of oxygen and carbonate in the recycling process of uranium on the surface of nano iron.

(3.2) influence of carbonate concentration during uranium recovery

FIG. 4 is a graph showing the effect of carbonate concentration on O retention during recovery ₂ Sufficient and same concentration, fully shaking, comparing 0.01mol/L CO with 0.1mol/L CO under the same condition ₃ ^2- The system can find that the recovery was 62% and 81% at 30 minutes, 91% and 98% at 4 hours, respectively, and remained essentially unchanged thereafter.

It can be confirmed that CO ₃ ^2- Rate of recovery of uranium by concentration and finalThe recovery rate is influenced, and the high concentration is selected to ensure that sufficient CO exists in the system in consideration of the rapid and full recovery of uranium ₃ ^2- 。

(3.3) influence of oxygen concentration in uranium recovery Process

FIG. 5 shows the effect of oxygen concentration on CO maintenance during recovery ₃ ^2- The concentration is 0.1mol/L, the mixture is fully shaken, and air (O) is compared under the same condition ₂ Content 20%) and pure O ₂ The system can find that the recovery rate is 51 percent and 81 percent respectively at 30 minutes, 98 percent can be achieved at 4 hours, and the subsequent recovery rate is kept unchanged.

It is stated that the oxygen concentration has a large influence on the uranium recovery rate, but has no significant influence on the final uranium recovery rate, so that, in view of reducing the production cost, as a preferred scheme: air may be selected to replace pure oxygen for uranium recovery.

(3.4) influence of mixing conditions in uranium recovery Process

Fig. 6 is the influence of the mixing condition in the recycling process, and the change of the uranium concentration in the liquid phase under the two conditions of full oscillation and standing without oscillation is compared under the same condition, so that it can be seen that: the uranium recovery under standing conditions (about 10%) is much lower than the well-mixed conditions (98%).

Therefore, the gas-liquid-solid three-phase intensive mixing is crucial to the recycling of uranium, oxygen bubbling is conducted in a system in actual production, or mechanical stirring or oscillation or overturning or rolling is conducted under the condition that oxygen in a container is sufficient, and the gas-liquid-solid three-phase intensive mixing is guaranteed.

(4) And centrifuging again (the speed is 4000rpm/min, the time is 10min) and retaining the liquid phase to obtain the recycled uranium solution.

Example 2 enrichment recovery of uranium by 10 times in uranium-containing wastewater from a plant of a uranium enrichment plant

The same procedure as described in steps (1) - (4) of example 1, except that in step (3.1), a volume of virgin spent liquor 1/10 (i.e., 10mL) containing CO was added ₃ ^2- The uranium is recycled by the solution, so that the purpose of concentrating the original uranium solution by 10 times can be achieved.

Example 3 enrichment recovery of uranium by 100 times in uranium-containing wastewater from a plant of a uranium enrichment plant

The same procedure as described in (1) - (4) except that in step (3.1), a volume of raw spent liquor 1/100 (i.e., 1mL) containing CO was added ₃ ^2- The solution recovers the uranium, so that the purpose of concentrating the original uranium solution by 100 times can be achieved.

To summarize the description of examples 1-3, as shown in the overall process flow diagram of FIG. 7, this example utilizes O in the overall process flow under thorough mixing ₂ +0.1mol/L CO ₃ ^2- The system recovers uranium loaded on the surface of the nano iron, the total recovery rate can reach 98%, and the recovery rate under the condition of 10 times concentration can reach 92%; the concentration of the recycled uranium solution is improved, and impurities such as fluorine and the like are not contained, so that a uranium concentrated solution with less impurities is obtained, and a foundation is laid for subsequent purification and reutilization of uranium; and meanwhile, uranium in the wastewater is removed, so that the wastewater is purified, and the wastewater can be directly discharged or sent to other workshops to treat other impurities such as fluorine and the like after meeting the uranium discharge standard.

This example fully demonstrates "oxygen", "CO" in the process of the invention ₃ ^2- The important functions of 'full mixing' in the whole process fully disclose the selection principle and method of the operation condition, fully prove the effectiveness of the method in three aspects of enrichment (wastewater uranium removal), recovery and concentration of uranium after enrichment of uranium in high-alkali fluorine-containing uranium-containing wastewater, wherein the enrichment process can be independently used for removing uranium in high-alkali fluorine-containing uranium-containing wastewater in the water treatment field, and the recovery process of uranium can be independently used for recovering uranium on the surface of nano iron and the recovery can achieve the effects of concentration and purification.

Claims

1. A method for treating high-alkalinity fluorine-containing uranium-containing wastewater and recycling uranium is characterized in that,

the high-alkalinity fluorine-containing uranium-containing wastewater comprises the following main components: the uranium concentration is 200mg/L and the fluorine ion concentration is 400mg/L, CO ₃ ^2- The concentration is 1000mg/L, pH-10.8;

the method comprises the following steps:

(1) the wastewater does not need to be subjected to acidification pretreatment, the nano zero-valent iron is added into the high-alkalinity fluorine-containing uranium wastewater under the condition of oxygen isolation, and the nano zero-valent iron is fully mixed to enrich uranium by the nano zero-valent iron, wherein the solid-to-liquid ratio of the nano zero-valent iron is 0.042g/L-1.5 g/L;

(2) solid-liquid separation, and solid phase is reserved; if the liquid phase reaches the discharge standard of uranium, directly discharging or further treating other harmful components, and if the liquid phase does not reach the discharge standard of uranium, returning to the step (1);

(3) putting the solid phase separated in the step (2) into CO ₃ ^2- In the solution with the concentration of 0.01-0.1mol/L, the solid-liquid ratio is 1.5-150 g/L, sufficient oxygen is introduced for bubbling or sufficient oscillation, and the gas phase, the liquid phase and the solid phase are fully mixed;

(4) performing solid-liquid separation, and reserving a liquid phase to obtain a recycled uranium-containing liquid phase;

in the step (1), the method for fully mixing the solid and the liquid comprises one or more of the following methods: introducing inert gas for bubbling; b, mechanically stirring, vibrating, overturning and rolling under the condition of isolating oxygen;

in the step (3), the gas phase, the liquid phase and the solid phase are fully mixed, and the method for ensuring the full mixing is one or the combination of the following two methods: a, introducing oxygen into a system, bubbling and mixing; and B, under the condition of keeping the oxygen in the container sufficient, carrying out mechanical stirring or shaking or overturning or rolling.

2. The method for treating the fluorine-containing high-alkalinity wastewater and recycling the uranium as claimed in claim 1, wherein the solid-to-liquid ratio of the nanoscale zero-valent iron in the step (1) is 1.5 g/L.

3. The method for treating the high-alkalinity fluorine-containing wastewater and recycling the uranium according to claim 1, wherein the enrichment time in the step (1) is 12 hours.

4. The method for treating the fluorine-containing high-alkalinity waste water and recycling the uranium according to claim 1, wherein solid-liquid separation in the step (2) and the step (4) is centrifugal separation.

5. The method for treating high-alkalinity fluorine-containing wastewater and recycling uranium according to claim 1, wherein in the step (3), CO is used for treating high-alkalinity fluorine-containing wastewater and recycling uranium ₃ ^2- The concentration was 0.1 mol/L.

6. The method for treating the high-alkalinity fluorine-containing wastewater and recycling the uranium according to claim 1, wherein the solid-to-liquid ratio in the step (3) is 1.5 g/L.

7. The method for treating high-alkalinity fluorine-containing wastewater and recycling uranium as set forth in claim 1, wherein the oxygen in the step (3) is replaced by air.