CN114988601B - Method for strengthening uranium and arsenic mineralization and improving mineral stability - Google Patents

Abstract

The invention discloses a method for strengthening uranium and arsenic mineralization and improving mineral stability. The method comprises the following steps: and (3) continuously introducing inert gas into the solution containing uranium and arsenic, and then slowly and sequentially adding a certain amount of ferrous salt and phosphate for reaction. The method can strengthen the mineralization of uranium, arsenic and iron in the solution, and can improve the conversion rate of uranium and arsenic from a liquid phase to a solid phase, and the conversion rate can be improved by 78% to the maximum. But also can cause the mineral phase component of the mineral to change from single-component mineral (uranolite ferriferous) to double-component mineral (uranolite ferriferous and uranite). In addition, the addition of the phosphate improves the stability of the ore, reduces the leaching rate of uranium and arsenic in the ore, reduces the leaching rate of uranium by 99 percent at most, and reduces the mobility of uranium and arsenic at the same time.

Description

A method to enhance uranium-arsenic mineralization and improve mineral stability

technical field

The invention relates to the technical field of various heavy metal wastewater treatment, in particular to a method for strengthening uranium and arsenic mineralization and improving mineral stability, which can be used for enhanced treatment of heavy metal wastewater containing uranium and arsenic.

Background technique

The mining of uranium mines, the enrichment of uranium, the manufacture of nuclear components, and the decommissioning of nuclear facilities will produce a large amount of wastewater containing uranium and arsenic. At present, the treatment of radioactive wastewater mainly includes physical, chemical and biological methods. The physical method is mainly based on adsorption. The uranium and arsenic in the solution are transferred to the material by using an adsorbent, and then the adsorbed material is separated from the solution by filtration and precipitation. The adsorption method requires the preparation of adsorbents with excellent performance, and the adsorbed materials need to be treated again to prevent secondary pollution caused by the re-desorption of pollutants, which is limited. The biological method is to use specific organisms (microorganisms, plants, protozoa) to remove uranium and arsenic in the water body through absorption, enrichment, transfer, etc. The biological method has strict requirements on the treatment environment, and generally only meets the specific conditions for biological survival. It has a processing effect and cannot be applied on a large scale. The chemical method mainly produces precipitation through the reaction of chemical reagents with uranium and arsenic, thereby removing it from the solution. Chemical treatment of uranium and arsenic heavy metals has the advantages of convenient operation, simple process flow, low processing cost, and no interference from the external environment. However, there are also shortcomings, such as low efficiency in acidic environment, unstable precipitate, loose structure, and easy secondary dissolution. Therefore, it is particularly important to find a method that can not only promote the mineralization of uranium and arsenic, but also improve the stability of minerals.

Phosphate is used for the modification of heavy metal adsorption materials, which can enhance the active sites of materials; it can also be used as a passivator for soil heavy metal treatment for soil remediation, etc. Phosphate combines with heavy metals through chelation to reduce the activity of heavy metals and reduce the migration of heavy metal ions. For example, hydroxyapatite minerals are used to treat lead-contaminated wastewater and soil, and Pb can replace Ca in apatite and Phosphate groups combine to form hydroxyphosphenite, which fixes the lead in the mineral. Therefore, phosphate plays a very important role in the removal of heavy metal ions, which can not only chelate heavy metals, but also affect the crystal structure of iron-containing minerals.

Contents of the invention

The primary purpose of the present invention is to provide an economical and efficient method that can strengthen the mineralization of uranium and arsenic in acidic solution. The method can enhance the ore-forming efficiency of uranium and arsenic in the solution, has low treatment cost and simple operation, and provides a unique treatment method for improving the ore-forming efficiency of uranium and arsenic.

A method for strengthening uranium-arsenic mineralization and improving mineral stability. The implementation steps of the method include: passing an inert gas into a solution containing uranium-arsenic to exclude dissolved oxygen, and then adding ferrous salt and phosphate for reaction.

In the method, at least one of hydrochloric acid, sulfuric acid, acetic acid, sodium hydroxide, potassium hydroxide and ammonia water is used to adjust the solution containing uranium and arsenic to pH=2-7; more preferably, the solution is pH=2-5.

For wastewater containing uranium and arsenic, when the pH value of the solution is weakly acidic, the uranium and arsenic elements respectively meet the easily ore-forming forms. When the pH value of the solution is greater than 7, although the uranium and arsenic elements in the solution exist in the form of ore-forming elements, too high OH ^- will combine with Fe ²⁺ ions, causing the Fe ²⁺ ions to be consumed, thereby affecting the mineralization. Formation.

In the method, the inert gas includes at least one of nitrogen, argon, and helium.

A certain amount of inert gas is passed into the solution containing uranium and arsenic pollutants to eliminate the dissolved oxygen in the solution, so that the whole system is in an anaerobic state, so as to ensure that Fe ²⁺ ions will not be oxidized.

In the method, the ferrous salt includes at least one of ferrous chloride, ferrous sulfate and ferrous acetate, preferably ferrous chloride.

A further preferred solution is that the initial molar concentration of Fe ²⁺ is 0.4mM-3mM; a further preferred initial molar concentration of Fe ²⁺ is 0.9mM-2.7mM; the most preferred initial molar concentration of Fe ²⁺ is 1.8mM.

Control the concentration of Fe ²⁺ , the concentration of Fe will affect the content of iron in uranium arsenide iron ore, thus affecting the consumption of phosphate.

A further preferred solution is to select a syringe to control the adding rate of the ferrous salt, and the adding rate of the ferrous salt is 1mL/min～5mL/min; more preferably, the adding rate of the ferrous salt is 2mL/min～4mL/min; most preferably The adding rate of ferrous salt was 3mL/min.

The addition rate of ferrous salt should be controlled within a certain range. If the addition rate is too fast, the local distribution of Fe ²⁺ will be uneven, and the local ionic strength in the solution will be too high instantaneously, which will eventually lead to uneven crystal grains; if the addition rate is too slow, it will affect the grain size. nucleation rate, and it is not advisable to expose Fe ²⁺ to air for a long time.

In the method, the phosphate includes at least one of sodium phosphate, sodium hydrogen phosphate, and sodium dihydrogen phosphate, preferably sodium phosphate.

Phosphate, as an inorganic salt chelating agent, can interact with Fe, promote more Fe ²⁺ in solution to enter into minerals, increase the content of Fe in minerals, and thus help to improve the stability of minerals. Phosphate can also dissolve some iron-containing minerals, thereby affecting the existence of Fe in minerals, indicating that phosphate can affect the lattice energy of minerals and destroy the coordination bonds between Fe and ligands, which is conducive to the reorganization of mineral structures. reorganization.

In a further preferred solution, the initial molar concentration of phosphate is 0.3mM-2mM; further preferred, the initial molar concentration of phosphate is 0.6mM-1.6mM; the most preferred initial molar concentration of phosphate is 0.9mM.

The concentration of phosphate is controlled. Different phosphate concentrations have different strengthening effects on uranium-arsenic mineralization, which is mainly related to the consumption of iron. In an environment without dissolved oxygen, when there is no phosphate in the system, uranium and arsenic in the solution will form a relatively stable single mineral of ferrouranium mica through co-precipitation with ferrous iron, which is a tetragonal crystal system; when there is In the case of phosphate, the addition of phosphate can consume H ⁺ and change the oxidation-reduction potential of the solution, so that uranium and arsenic in the solution will co-precipitate with ferrous iron to form a two-component composite mineral of metamorphic uranium mica and uranite , improve the ore-forming efficiency of uranium and arsenic in strong acid solution.

There are two main ways of phosphate consumption: on the one hand, Fe ₃ (PO ₄ ) ₂ is formed on the mineral surface and Fe ²⁺ ; on the other hand, it is adsorbed on the mineral surface or in the pores through adsorption.

A further preferred solution is to select a syringe to control the addition rate of phosphate, and the addition rate of phosphate is 1mL/min～5mL/min; more preferably, the addition rate of phosphate is 2mL/min～4mL/min; most preferably the addition rate of phosphate The addition rate was 3 mL/min.

Control the addition rate of phosphate. If the addition rate is too fast, the local ionic strength will be too high, and the concentration of Fe ²⁺ ions will also increase, which will affect the formation and uniformity of minerals; if the addition rate is too low, the ore-forming efficiency will be affected.

In the described method, the ratio of n(P):n(Fe):n(U):n(As) in the solution is (0.5～2):(0.5～3):1:1; preferably (0.75～ 1.75):(1～2):1:1, most preferably 1:2:1:1.

The ratio of n(P):n(Fe):n(U):n(As) in the solution should be kept within a certain range, and the theoretical stoichiometric ratio of ferrouranium mica minerals is 1:2:2, so in order to To maximize the ore-forming efficiency of uranium and arsenic in the solution, the ratio of Fe to uranium and arsenic must be greater than the theoretical value. In addition, considering the hydrolysis of Fe ²⁺ and the consumption of phosphate, the minimum content of iron element should be 2 times the theoretical value. Secondly, phosphate radical and ferrous iron can form ferrous phosphate. When the Fe content is high, adding phosphate can promote the further mineralization of iron arsenic and uranium. This is mainly because when the Fe content is low, adding phosphate will consume a part of Fe. content, thereby inhibiting the mineralization of uranium and arsenic; when the Fe content is high, phosphate will promote more Fe to enter the mineral, and promote the formation of minerals, which may be related to the transformation of mineral components.

The solution containing uranium and arsenic in the present invention is derived from acidic waste water or groundwater containing uranium and arsenic.

Compared with the prior art, the beneficial technical effects brought by the technical solution of the application of the present invention:

1. A method of strengthening uranium-arsenic mineralization and improving mineral stability according to the present invention has simple process, low cost, strong controllability and large-scale application.

2. Compared with the method without adding phosphate, the method of the present invention can increase the ore-forming efficiency of uranium and arsenic by up to 78%, and the leaching rate of the formed mineral uranium can be reduced by up to 99%.

3. In the method of the present invention, by adding phosphate, the ore phase composition of the mineral is changed, from a single-component mineral to a two-component composite mineral.

4. The method of the present invention strengthens the further mineralization of uranium and arsenic, improves the stability of minerals, and provides a treatment idea and method for the treatment of strongly acidic uranium and arsenic wastewater.

Description of drawings

Fig. 1 is the comparative figure that has or does not have phosphate to the removal rate influence of uranium arsenic in embodiment 1;

Fig. 2 is the removal rate figure of uranium and arsenic under different phosphate concentrations in embodiment 2;

Fig. 3 is the removal rate figure of uranium and arsenic under different phosphate concentrations in embodiment 3;

Fig. 4 is the removal rate figure of uranium ^and arsenic under different Fe in embodiment 4;

Fig. 5 is the removal rate figure of uranium and arsenic under different pH values in embodiment 5;

Fig. 6 is in embodiment 5 with or without phosphate on Fe ²⁺ impact contrast figure of reducing amount;

Fig. 7 is the XRD collection of illustrative plates of the mineral that embodiment 5 generates;

Fig. 8 is the XRD collection of illustrative plates of the mineral that embodiment 5 generates;

Fig. 9 is the leaching concentration comparison chart (without phosphate (left) and phosphate (right)) of the mineral uranium generated in Example 1;

Fig. 10 is a SEM comparison image of minerals generated in Example 1 (without phosphate (left) and with phosphate (right)).

Detailed ways

The technical solutions of the present invention will be further elaborated below through specific examples, rather than limiting the protection scope of the claims of the present invention.

Example 1

Two groups of experiments were carried out respectively. The first group of experiments: Take 10mL, 1g/L uranyl acetate solution in a 200mL wide-mouth conical flask, then add 5mL, 1g/L sodium arsenate solution, and then add 78mL deionized Water, adjust the pH value of the above mixed solution with 0.1moL/L hydrochloric acid and ammonia solution, so that pH=3, then add 5mL, 1000mg/L ferrous sulfate heptahydrate solution at a rate of 2.5mL/min under nitrogen atmosphere. The second group of comparative experiments: on the basis of the first group of experiments, use a syringe to add 2 mL dropwise at 1 mL/min, 1000 mg/L of sodium phosphate solution (the molar concentration of phosphorus is 0.65 mM), stop feeding nitrogen, and place React in a constant temperature shaker at 25°C for 24 hours, then centrifuge, wash with pure water three times, and vacuum freeze-dry to obtain solid minerals. The removal rates of uranium and arsenic in the first and second groups are shown in Figure 1. It can be seen from the figure that when pH=3, the addition of phosphate has a great influence on the mineralization of uranium and arsenic. The removal rates of uranium were 20.6% and 98.6%, respectively, and the efficiency increased by 78%. The arsenic removal rates of the first group and the second group were 10.22% and 90.43%, respectively, and the efficiency increased by 80.21%. It shows that under strong acid conditions, adding phosphate can promote the mineralization of uranium and arsenic, and improve the ore-forming efficiency of uranium and arsenic. Under strongly acidic conditions, the easy ore-forming forms of uranium and arsenic in the solution are limited, and the H ⁺ in the solution is consumed after adding phosphate, so that the uranium and arsenic are converted to the easy ore-forming forms respectively, thereby improving the ore-forming efficiency .

Example 2

Take 10mL, 1g/L uranyl sulfate solution in a 200mL wide-mouth Erlenmeyer flask, then add 5mL, 1g/L sodium arsenate solution, then add 70mL deionized water, and use 0.1moL/L hydrochloric acid and ammonia solution Regulate the pH value of above-mentioned mixed solution, make pH=5, pass into solution then the dissolved oxygen in the nitrogen removal solution, then add 2.5mL with 2mL/min speed, the ferrous sulfate heptahydrate solution of 1000mg/L ( ^Fe2 The molar concentration of ⁺ is 0.45mM), and then use a syringe to add 1, 1.5, 3, 4, 5mL dropwise at 1mL/min, sodium phosphate solution of 1000mg/L (the initial molar concentration of phosphorus is 0.32, 0.48, 0.96 , 1.29, 1.61mM), then add a small amount of deionized water to make the total volume 100mL, then place it in a constant temperature shaker at 25°C for 24h, then centrifuge, wash with pure water three times, and vacuum freeze-dry to obtain solid minerals . The removal rate of uranium and arsenic is shown in Figure 2. It can be seen from the figure that as the initial concentration of sodium phosphate increases, the removal rate of uranium and arsenic decreases gradually. It shows that when the concentration of iron is low, the concentration of phosphate will inhibit the mineralization of uranium and arsenic, which is mainly because when the concentration of ferrous iron is low, a large amount of phosphate will consume Fe ²⁺ , thereby reducing the mineralization efficiency. The highest removal rate of uranium is 83.6%, and the highest removal rate of arsenic is 97.12%.

This embodiment can know:

The concentration of P is 0.32-1.61mM, and the removal rate of As is over 80%;

The concentration of P is 0.32-0.96mM, and the removal rate of U is over 78%;

The concentration of P is 0.32-0.96mM, and the removal rate of As and U is above 78%.

Example 3

Take 7.5mL, 1g/L uranyl acetate solution in a 200mL wide-mouth conical flask, then add 2.5mL, 1g/L sodium arsenate solution, then add 70mL deionized water, and use 0.1moL/L hydrochloric acid and Ammonia solution was used to adjust the pH value of the above mixed solution so that pH=3, and then 15 mL, 1000 mg/L of ferrous acetate solution was added at a rate of 5 mL/min under a nitrogen atmosphere, and then 1 , 1.5, 3, 4, 5mL, 1000mg/L sodium phosphate solution (the molar concentration of phosphorus is 0.32, 0.48, 0.96, 1.29, 1.61mM respectively), then add a small amount of deionized water to make the total volume 100mL, set React in a constant temperature shaker at 25°C for 24 hours, then centrifuge, wash with pure water three times, and vacuum freeze-dry to obtain solid minerals. The removal rate of uranium is shown in Figure 3. It can be seen from the figure that the removal rate of uranium does not change much with the increase of phosphorus content, indicating that when the initial concentration of iron is high, the presence of phosphate has an effect on the mineralization of uranium and arsenic. The highest removal rate of uranium is 98.2%, and the lowest removal rate is 93.3%; the highest removal rate of arsenic is 98.07%, and the lowest removal rate is 95.27%. This result further shows that when the Fe content is high, the addition of phosphate can promote the further mineralization of FeAs-U, which is mainly because when the Fe content is low, the addition of phosphate will consume part of the Fe content, thereby inhibiting the mineralization of UAs ; When the content of Fe is high, phosphate will promote more Fe into the minerals, and promote the formation of minerals, which may be related to the transformation of mineral components.

This embodiment can know:

The concentration of P is 0.32-1.61mM, and the removal rate of U is over 92%;

The concentration of P is 0.32-1.61mM, and the removal rate of As is over 94%;

The concentration of P is 0.32-1.61mM, and the removal rate of U and As is over 92%.

Example 4

Take 10mL, 1g/L uranyl nitrate solution in a 200mL wide-mouth conical flask, then add 5mL, 1g/L sodium arsenate solution, then add 65mL deionized water, and use 0.1moL/L hydrochloric acid and ammonia solution Regulate the pH value of above-mentioned mixed solution, make pH=3, then add 5,7.5,10,12.5,15mL with 3mL/min speed under nitrogen atmosphere, the ferrous chloride solution of 1000mg/L, (Fe ²⁺ ion The molar concentrations are 0.89, 1.24, 1.44, 1.49, 1.59mM), and then use a syringe to add 2mL dropwise at a rate of 1mL/min, 1000mg/L sodium phosphate solution (the molar concentration of phosphorus is 0.65mM), and then add A small amount of deionized water, so that the total volume is 100mL, placed in a constant temperature shaker at 25°C for 24 hours, then centrifuged, washed with pure water three times, and vacuum freeze-dried to obtain solid minerals. The removal rate of uranium is shown in Figure 4. It can be seen from the figure that with the increase of the initial concentration of ferrous chloride, the removal rate of uranium and arsenic does not change much, indicating that when the initial concentration of phosphorus is constant and low, ^Fe2 The concentration change of ⁺ has little effect on the mineralization of uranium and arsenic, and the removal efficiency of uranium is improved compared with that without phosphate. The highest removal rate of uranium is 98%, and the lowest removal rate is 96.2%; the highest removal rate of arsenic is 98.33%, and the lowest removal rate is 95.29%.

This embodiment can know:

The concentration of ferrous ions is 0.89-1.59mM, and the U removal rate is over 95%;

The concentration of ferrous ions is 0.89-1.59mM, and the removal rate of As is over 94%;

The concentration of ferrous ions is 0.89-1.59mM, and the removal rate of U and As is over 94%.

Example 5

Take 5mL, 1g/L uranyl nitrate solution in a 200mL wide-mouth Erlenmeyer flask, then add 2.5mL, 1g/L sodium arsenate solution, then add 80mL deionized water, add 0.1mol/L sulfuric acid and hydrogen Sodium oxide solution adjusts the pH value of above-mentioned mixed solution, makes pH=3,4,5,6,7, then adds 2.5mL with 1mL/min speed under nitrogen atmosphere, the ferrous sulfate heptahydrate solution of 1000mg/L (Fe The molar concentration of ²⁺ ions is 0.45mM), and then utilizes a syringe to add 2mL dropwise at a rate of 1mL/min, 1000mg/L of sodium hydrogen phosphate solution (the molar concentration of phosphorus is 0.65mM), then add a small amount of deionized water, The total volume was made 100 mL, and placed in a constant temperature shaker at 25° C. for 24 h. The removal rate of uranium and arsenic is shown in Figure 5. It can be seen from the figure that the removal rates of uranium and arsenic are different under different pH conditions. As the pH increases, the removal rate of uranium first decreases and then increases, and the removal rate of arsenic gradually decreases raised. When the initial pH value was 7, the removal rate of uranium was the highest, which was 95.3%. The highest removal rate of arsenic is 96.3%.

This embodiment can know:

pH=3-4 or 6-7, the removal rate of U is over 80%;

pH=4-7, the removal rate of As is over 85%;

pH=4 or 6-7, the removal rate of U and As is above 80%.

Example 6

This example is the reduction of Fe ²⁺ with or without phosphate when the initial pH value of the solution in Example 5 is 4 (as shown in Figure 6). It can be seen from the figure that when no sodium phosphate is added to the system, the reduction of Fe ²⁺ ions is 0.07mM, and when sodium phosphate is added to the system, the reduction of Fe ²⁺ ions is 0.38mM. It shows that the introduction of phosphate causes more Fe ²⁺ ions in the solution to enter the minerals, which is mainly due to the consumption of more Fe ²⁺ ions in the process of mineral formation, not because the existence of phosphate radicals consumes Fe ^{2 +} , because the ferrous phosphate phase was not detected in the generated minerals.

Example 7

This embodiment is the XRD spectrum of the minerals generated after the reaction in Example 5 (as shown in Figure 7). It can be seen from the figure that two kinds of minerals were formed after adding sodium phosphate at different pH values, namely uranite [Fe ²⁺ (UO ₂ ) ₂ (AsO ₄ ) ₂ ·8H ₂ O] and uranite [Fe (UO ₂ ) ₂ (AsO ₄ ) ₂ ·12H ₂ O], indicating that after the introduction of phosphate, the ore phase of the mineral has changed, from a single ore phase to a composite ore phase, and the crystallinity of the mineral has increased. In addition, after the addition of sodium phosphate, the system did not generate uranyl phosphate minerals or replace arsenate with phosphate, and there was no phase of ferrous phosphate. Combining the above experimental results, it further proved that the introduction of sodium phosphate promoted the UO ₂ ² The further mineralization of ⁺ -Fe ²⁺ -AsO ₄ ^3- promotes the entry of Fe ²⁺ ions into minerals. At the same time, the XRD characterization results also show that the presence of phosphate does not compete with arsenate for mineralization.

Example 8

This embodiment is the XRD spectrum of the minerals generated after the reaction in Example 5 (as shown in Figure 8). It can be seen from the figure that when the pH of the system is 4, the XRD patterns of minerals generated by adding different amounts of sodium phosphate are different. With the increase of phosphate content, the relative intensity of the characteristic peak at 2θ=24.8° in the XRD pattern gradually decreases, and the relative intensity of 25.3° A new characteristic peak appeared at , which is the characteristic peak of uranite. When the P content increased from 0 to 15 mg/L, the characteristic peak at 2θ at 24.8° disappeared gradually, and the relative intensity of the characteristic peak at 25.3° gradually increased; when the P content was greater than 15 mg/L, the characteristic peak at 24.8° appeared , the relative intensity of the characteristic peak at 25.3° increases gradually. This phenomenon further proves that the introduction of phosphate will lead to the transformation of mineral phase in UO ₂ ²⁺ -Fe ²⁺ -AsO ₄ ^3- system.

Example 9

This embodiment is the stability assessment of the minerals generated after the reaction in Example 1. The same amount of metamorphic uranium mica single mineral, metamorphic uranium mica and uranite composite minerals were respectively placed in sulfuric acid rain with different pH values, and the leaching of uranium in the minerals was evaluated (as shown in Figure 9, the left picture is variable The single mineral of iron uranium mica, the picture on the right is the composite mineral of iron uranium mica and yellow arsenic uranite). It can be seen from the figure that the stability of a single mineral composed of metamorphic uranium mica is general in acid rain environment, and the stability is different in different environments. With the increase of pH, the leaching concentration of U gradually decreases, and the leaching amount of U is the highest. It is 2.8mg/L, and the lowest is 1mg/L. The stability of the composite mineral composed of uranite and uranite is higher than that of the single mineral of uranite. When the pH value is 5 and 5.5, the leaching concentration of U is lower than the detection line of the instrument, and the leaching of U The highest content is 0.095mg/L, and the lowest is 0.068mg/L. This shows that the introduction of phosphate will increase the stability of minerals.

Example 10

This example is a solid material obtained after vacuum freeze-drying the minerals obtained in Example 1, and the morphology of the minerals is characterized and analyzed by SEM (as shown in FIG. 10 ). The results show that when phosphate exists in the system, the morphology of the formed composite minerals changes dramatically. When no phosphate is added, the mineral formed is a single-component mineral of metamorphic uranium mica, which is formed by stacking flake particles with a loose overall structure; when phosphate is added, the minerals generated are metamorphic uranium mica and yellow As a two-component mineral of arsenite, the composite mineral contains both flaky particles and rock-like particles with uniform voids, and the overall structure of the composite mineral is relatively dense, which is consistent with the stability results.

Claims (15)

1. A method for strengthening uranium and arsenic mineralization and improving mineral stability is characterized by comprising the following steps: introducing inert gas into the uranium and arsenic-containing solution to remove dissolved oxygen, and then adding ferrous salt and phosphate to react;

the uranium and arsenic containing solution is a solution with pH = 2-7;

the ratio of n (P) to n (Fe) to n (U) to n (As) between phosphorus, iron, uranium and arsenic in the solution is (0.5-2) to (0.5-3) to 1:1;

the initial molarity of the added ferrous salt solution is 0.4 mM-3 mM;

the rate of adding the ferrous salt solution is 1mL/min to 5mL/min;

the initial molarity of the added phosphate solution is 0.3 mM-2 mM;

the rate of adding phosphate solution is 1mL/min to 5mL/min.

2. The method of claim 1, wherein: the uranium arsenic-containing solution is a solution having a pH =2 to 5.

3. The method of claim 1, wherein: the ferrous salt comprises at least one of ferrous chloride, ferrous sulfate and ferrous acetate; the phosphate comprises at least one of sodium phosphate, sodium hydrogen phosphate and sodium dihydrogen phosphate.

4. The method of claim 3, wherein: the ferrous salt is ferrous chloride; the phosphate is sodium phosphate.

5. The method of claim 1 or 2 or 3 or 4, wherein: the ratio of n (P) to n (Fe) to n (U) to n (As) between phosphorus, iron, uranium and arsenic in the solution is (0.75-1.75): (1-2): 1:1.

6. The method of claim 1 or 2 or 3 or 4, wherein: the initial molarity of the added ferrous salt solution was 0.9mM to 2.7mM.

7. The method of claim 6, wherein: the initial molarity of the added ferrite solution was 1.8mM.

8. The method of claim 1 or 2 or 3 or 4, wherein: the rate of adding the ferrite solution is 2mL/min to 4mL/min.

9. The method of claim 8, wherein: the rate of addition of the ferrite solution was 3mL/min.

10. The method of claim 1 or 2 or 3 or 4, wherein: the initial molarity of the added phosphate solution was 0.6mM to 1.6mM.

11. The method of claim 10, wherein: the initial molarity of the added phosphate solution was 0.9mM.

12. The method of claim 1 or 2 or 3 or 4, wherein: the rate of adding phosphate solution is 2mL/min to 4mL/min.

13. The method of claim 12, wherein: the phosphate solution was added at a rate of 3mL/min.

14. The method of claim 1 or 2 or 3 or 4, wherein: the inert gas comprises at least one of nitrogen, argon and helium.

15. The method of claim 1 or 2 or 3 or 4, wherein: the uranium and arsenic containing solution is derived from acidic uranium and arsenic containing wastewater or underground water.

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