Method for treating raffinate water-phase distillation raffinate

Abstract

The invention relates to the technical field of nuclear fuel circulation uranium conversion, in particular to a method for treating raffinate water-phase distillation raffinate. The treatment method comprises the following steps: adjusting the pH value of the distillation residual liquid to be greater than 5 by using sodium hydroxide, precipitating impurities and uranium together, and then filtering and separating to obtain filtrate and a filter cake; adding a mixed solution of sodium bicarbonate and sodium carbonate into the filtrate to obtain a leaching agent; a leaching agent is added into the filter cake, uranium in the filter cake is leached out, solid-liquid separation is conducted, and leaching residues and leaching liquid are obtained; mixing the leachate with acid and hydrogen peroxide, controlling the acidity pH of the final solution to be 1.5-4.0, and carrying out solid-liquid separation to obtain uranium peroxide solid and uranium peroxide precipitation mother liquor; the uranium peroxide solid is dissolved by nitric acid and then enters the extraction and purification process again. According to the method, the adverse effect of sodium nitrate in the raffinate water phase on the distillation and concentration process is avoided, and the recovery rate of the whole uranium purification and extraction process is increased to 99.99% or above.

Description

Technical Field

[0001] The invention relates to the technical field of nuclear fuel cycle uranium conversion, in particular to a method for treating raffinate water phase distillation residue. Background Art

[0002] The raw materials for wet purification at home and abroad are divided into diuranate and uranium oxide in chemical form, and the processing of the two raw materials is still different. In the purification line using uranium oxide as raw material, the raffinate water phase obtained after extraction and purification mainly contains nitric acid, as well as a small amount of metal impurity elements and uranium nitrate. Afterwards, the nitric acid and water can be recovered by evaporation and concentration to finally obtain the distillation residue. This will not only recover the remaining nitric acid in the raffinate water phase, but also greatly reduce the discharge volume of radioactive wastewater; when non-uranium oxide is used as the purification raw material, the raffinate water phase obtained after purification contains nitric acid, a small amount of metal impurity elements and uranium nitrate, but also a large amount of nitrates, such as sodium nitrate, ammonium nitrate, etc. It is difficult to recover the nitric acid by evaporation and concentration, and reduce the volume of the raffinate water phase. The volume of radioactive wastewater to be treated is large, which is a process with a greater impact on the environment.

[0003] In the process of treating the residual water phase by evaporation concentration technology, in order to prevent the residual uranium and impurity elements in the solution from precipitating, the volume of the solution can only be concentrated to a certain limit to obtain a distillation residue. In this distillation residue, uranium, nitric acid and impurity elements are highly enriched. At this time, the uranium concentration in the distillation residue is about 20g / L, the nitric acid concentration is about 10mol / L, and a large amount of impurity elements such as silicon, iron, aluminum, and molybdenum. Figure 1 As shown, the current process for treating distillation residue is to add sodium hydroxide to the residue to gradually reduce the acidity of the residue, precipitate uranium and some impurity elements together, filter and separate, and then discharge the filtrate after deep purification. The slurry filter cake is stored in barrels, and the uranium content of the dry residue is about 5%.

[0004] The uranium in the current precipitation slurry exists in the form of sodium diuranate. In addition to the sodium element combined with uranium, the slurry also contains a large amount of metal element impurities, which cannot be re-extracted and purified as a purification raw material. Otherwise, sodium and impurity elements will continue to accumulate in the system, affecting the evaporation and concentration of the residual water phase. Therefore, in order to avoid this bad result, the precipitation slurry can only be stored in a pile, which not only causes the loss of uranium but also increases the cost of environmental disposal. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for treating residual liquid from distillation of raffinate aqueous phase, recover uranium in the residual liquid from distillation in the form of oxides and return it to the extraction and purification process, thereby reducing waste stacking and wastewater discharge.

[0006] A method for treating a residual aqueous phase distillation residue, comprising the following steps:

[0007] Step 1: Adjust the distillation residue to pH>5 with sodium hydroxide to precipitate the impurities together with uranium, and then filter and separate to obtain a filtrate and a filter cake;

[0008] Step 2: adding a mixed solution of sodium bicarbonate and sodium carbonate to the filtrate to obtain a leaching agent;

[0009] Step 3: adding the leaching agent into the filter cake to leach the uranium therein, separating the solid and the liquid to obtain leaching residue and leaching liquid;

[0010] Step 4: the leaching solution is mixed with acid and hydrogen peroxide, the acidity of the final solution is controlled to be pH 1.5-4.0, and the solid-liquid is separated to obtain uranium peroxide solid and uranium peroxide precipitation mother liquor;

[0011] Step 5: After the uranium peroxide solid is dissolved by nitric acid, it re-enters the extraction and purification process.

[0012] Preferably, the step 1 further includes:

[0013] washing the filter cake with water, and combining the washing water and the filtrate to obtain a first solution;

[0014] The first solution is used in step 2 to prepare a leaching agent.

[0015] Preferably, the concentration of sodium bicarbonate is from 0.1 mol / L to saturation concentration, and the concentration of sodium carbonate is from 0 to 1 mol / L.

[0016] Preferably, the uranium concentration of the uranium peroxide precipitation mother liquor is controlled to be below 5 mg / L and is discharged after deep purification.

[0017] Preferably, in step three, the leaching liquid-to-solid ratio L / S>1.5.

[0018] Preferably, in step three, the leaching temperature is 10-60° C., the reaction time is greater than 10 min, and the final pH is controlled to be less than 12.

[0019] Preferably, in step three, the leached residue is washed with water or a dilute sodium bicarbonate solution, and the obtained washing liquid is combined with the leachate for subsequent steps.

[0020] Preferably, in step 4, the acid is nitric acid, hydrochloric acid or sulfuric acid.

[0021] Compared with the prior art, the method for treating the residual liquid of the raffinate aqueous phase of the present invention has the following beneficial effects:

[0022] (1) The purification process for evaporating and reusing the residual water phase solves the uranium recovery problem

[0023] In order to avoid the discharge of the raffinate water phase, the evaporation concentration technology is required to reduce its volume, so the raw materials for uranium purification are limited to not contain cations other than uranium. Therefore, the raw materials dissolved by nitric acid can only be uranium oxides. The present invention converts the precipitate of diuranate into UO4, which can be smoothly returned to the extraction process.

[0024] (2) Alkaline leaching is used to effectively separate uranium and impurity elements

[0025] Utilizing UO2 2+ Can be used with CO3 2- Formation of stable complex anion UO2(CO3)3 4- The characteristics of sodium bicarbonate are used as a leaching agent to dissolve uranium into the solution, completing the separation of uranium and metal impurities.

[0026] (3) Effectively avoids the reflux of impurity elements

[0027] The invention sets two precipitation conditions, alkaline and acidic, and fully utilizes the characteristics that uranium can be dissolved in a sodium bicarbonate and sodium carbonate buffer system to remove metal impurities. The characteristics that uranium peroxide is insoluble in dilute acid, non-metallic impurities and amphoteric metals are removed, and an outlet is set for the impurity elements in the purification process, thereby avoiding the accumulation of impurity elements in the system due to the return, thereby affecting the normal progress of the purification process.

[0028] (4) The specific radioactivity of solid waste is reduced, saving storage costs

[0029] Through the alkaline leaching process, the uranium content in the precipitated slag can be reduced from about 5% to 0.02%, which is equivalent to the uranium content in the slag discharged from uranium hydrometallurgical mines, expanding the storage space and reducing storage costs.

[0030] (5) Maximize the reuse of process water

[0031] The residual neutralization wastewater in the original process is directly discharged for treatment. The present invention uses it for the preparation of the leaching agent. Except for the water used for washing uranium peroxide, the water content of hydrogen peroxide, and the concentrated nitric acid consumed for alkali neutralization, no other process water is added in this process. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 A flow chart showing the existing method for disposing the residual liquid from the distillation of the raffinate water phase;

[0033] Figure 2 The flow chart of the method for treating the residual liquid from the distillation of the raffinate aqueous phase is shown. DETAILED DESCRIPTION

[0034] In order to further understand the present invention, the embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the present invention.

[0035] The embodiment of the present invention discloses a method for treating a residual aqueous phase distillation residue, such as Figure 2 As shown, the following steps are included:

[0036] Step 1: adjusting the distillation residue to a pH value greater than 5 with sodium hydroxide to precipitate the impurities together with the uranium, and then filtering and separating them to obtain a filtrate and a filter cake;

[0037] Step 2: adding a mixed solution of sodium bicarbonate and sodium carbonate to the filtrate to obtain a leaching agent;

[0038] Step 3: adding the leaching solution into the filter cake to leach the uranium therein, separating the solid and the liquid to obtain leaching residue and leaching solution;

[0039] Step 4: the leaching solution is mixed with acid and hydrogen peroxide, the acidity of the final solution is controlled to be pH 1.5-4.0, and the solid-liquid is separated to obtain uranium peroxide solid and uranium peroxide precipitation mother liquor;

[0040] Step 5: After the uranium peroxide solid is dissolved by nitric acid, it re-enters the extraction and purification process.

[0041] The following steps are specifically described in detail:

[0042] Step 1, adjusting the distillation residue to a pH value greater than 5 with sodium hydroxide to precipitate the impurities together with the uranium, and then filtering and separating them to obtain a filtrate and a filter cake;

[0043] The purpose of this step is to neutralize the precipitated uranium and impurities.

[0044] HNO3+NaOH====NaNO3+H2O

[0045] 2UO2(NO3)2+6NaOH===4NaNO3+Na2U2O7↓+3H2O

[0046] When the uranium content in the distillation residue is higher than 5 mg / L, the filter cake needs to be washed after precipitation. Specifically:

[0047] washing the filter cake with water, and combining the washing water and the filtrate to obtain a first solution;

[0048] The first solution is used in step 2 to prepare a leaching agent.

[0049] When the uranium content in the distillation residue is less than 5 mg / L, there is no need to wash the filter cake after precipitation, and the process can be directly carried out into step 2.

[0050] Step 2: adding a mixed solution of sodium bicarbonate and sodium carbonate to the filtrate to obtain a leaching agent;

[0051] Alternatively, in step 1, when there is washing water, the washing water and the filtrate are combined, and a mixture of sodium bicarbonate and sodium carbonate is added.

[0052] The sodium bicarbonate concentration is from 0.1 mol / L to saturation concentration, and the sodium carbonate concentration is from 0 to 1 mol / L.

[0053] Na2U2O7+6NaHCO3===2Na4UO2(CO3)3+3H2O

[0054] Na2U2O7+6Na2CO3+3H2O===2Na4UO2(CO3)3+6NaOH

[0055] Step 3: adding the leaching agent into the filter cake to leach the uranium therein, separating the solid and the liquid to obtain leaching residue and leaching liquid;

[0056] This step is used to alkalinely leach uranium from the filter cake.

[0057] The leachate-solid ratio L / S>1.5.

[0058] The leaching temperature is 10-60°C, the reaction time is greater than 10 minutes, and the final pH is controlled to be less than 12.

[0059] The obtained leaching residue is washed or not according to the actual situation.

[0060] When the uranium content of the leached residue is higher than 5 mg / kg, the leached residue is washed with water or a dilute sodium bicarbonate solution, and the obtained washing solution is combined with the leaching solution for subsequent steps.

[0061] Step 4: the leaching solution is mixed with acid and hydrogen peroxide, the acidity of the final solution is controlled to be pH 1.5-4.0, and the solid-liquid is separated to obtain uranium peroxide solid and uranium peroxide precipitation mother liquor;

[0062] This step is used to precipitate uranium peroxide.

[0063] Na4UO2(CO3)3+6HNO3===4Na NO3+UO2 NO3+3H2O+CO2↑

[0064] UO2NO3+H2O2==UO4↓+2HNO3

[0065] The uranium concentration of the uranium peroxide precipitation mother liquor obtained by solid-liquid separation is controlled below 5 mg / L, and enters the external wastewater treatment process and is discharged after deep purification.

[0066] Step 5: After the uranium peroxide solid is dissolved by nitric acid, it re-enters the extraction and purification process.

[0067] The acid is used to dissolve uranium peroxide and may be nitric acid, hydrochloric acid or sulfuric acid.

[0068] The uranium peroxide solid is used in the same manner as U3O8 in the nitric acid dissolution process.

[0069] The present invention adopts the method of co-precipitating uranium and impurity elements, and then utilizing the property that uranyl ions and carbonate ions form stable complex ions to separate them from the metal impurity elements; and then utilizing the property that uranium and hydrogen peroxide can form uranium peroxide to prepare uranium oxide at room temperature, and returning the uranium oxide to the U3O8 dissolution process in the form of non-diuranate, and smoothly docking with the uranium purification extraction line, thereby avoiding the adverse effect of sodium nitrate in the raffinate water phase on the distillation and concentration process, and improving the recovery rate of the entire uranium purification and extraction process to above 99.99%.

[0070] In order to further understand the present invention, the method for treating the residual liquid of the raffinate aqueous phase provided by the present invention is described in detail below in conjunction with the embodiments. The protection scope of the present invention is not limited by the following embodiments.

[0071] Example 1

[0072] Take 100ml of distillation residue, uranium 5g / L, and obtain a total uranium of 0.5g, then add sodium hydroxide solution to adjust the acidity, control pH = 7.35, then filter, wash with 1.5 times the volume of the filter cake with distilled water, and obtain a filtrate and a filter cake or slurry. The first solution obtained by combining the washing liquid and the filtrate is used for the preparation of the leaching solution; the obtained filter cake is used as the raw material for leaching uranium in the next step.

[0073] A mixed solution of sodium bicarbonate and sodium carbonate is added to the first solution to obtain a leaching agent; the concentration of the sodium bicarbonate is a saturated concentration, and the concentration of the sodium carbonate is 1 mol / L.

[0074] The leaching solution is added to the filter cake to leach the uranium therein, the leaching liquid-solid ratio L / S>1.5, the leaching temperature is 60°C, a small amount of sodium carbonate can be mixed into the leaching agent sodium bicarbonate, the reaction time is 20 minutes, and the final pH is controlled to be 11.5. Filter and separate, wash the filter cake with water or a dilute sodium bicarbonate solution, combine the washing liquid and the filtrate, the obtained solution is a uranyl ammonium tricarbonate solution, the filter cake is stored as a leaching waste residue tail, the water content is 24%, and the dry basis uranium content is 0.015%.

[0075] Uranyl ammonium tricarbonate solution, hydrogen peroxide and sulfuric acid are directly added to the same reactor, and the end point pH is controlled to be 3.4. After the reaction is completed, the solid and liquid are separated, and the solid is uranium peroxide, which is returned to nitric acid for dissolution. The uranium concentration of the filtrate is less than 10 mg / L, and it is discharged after deep purification.

[0076] Example 2

[0077] Take 500 ml of distillation residue, the uranium concentration is 69 mg / L, and the total amount of uranium is 34.5 mg. Then add sodium hydroxide solution to adjust the acidity and control the pH to 6.75, so that the impurities are precipitated together with the uranium, and then filter and separate to obtain filtrate and filter cake;

[0078] The filter cake is washed with distilled water, and the washing water and the filtrate are combined to obtain a first solution. The obtained first solution is used to prepare the leaching solution; the obtained filter cake is used as the raw material for leaching uranium in the next step.

[0079] A mixed solution of sodium bicarbonate and sodium carbonate is added to the first solution to obtain a leaching agent; the concentration of the sodium bicarbonate is 0.1 mol / L to a saturated concentration, and the concentration of the sodium carbonate is 1 mol / L.

[0080] The leaching solution is added to the filter cake to leach the uranium therein, the leaching liquid-solid ratio L / S>1.5, the leaching temperature is 50°C, a small amount of sodium carbonate can be mixed into the leaching agent sodium bicarbonate, the reaction time is 15 minutes, and the final pH is controlled to be 10.6. Filter and separate, wash the filter cake with water or a dilute sodium bicarbonate solution, combine the washing liquid and the filtrate, the obtained solution is a uranyl ammonium tricarbonate solution, the filter cake is stored as a leaching waste residue tail, the moisture content is less than 30%, and the dry basis uranium content is less than 0.02%.

[0081] Add uranyl ammonium tricarbonate solution, hydrogen peroxide and nitric acid directly into the same reactor, control the end point pH = 2.45, separate the solid and liquid after the reaction is completed, the solid is uranium peroxide, return to nitric acid to dissolve, the filtrate uranium concentration is less than 10 mg / L, and is discharged after deep purification.

[0082] The above embodiments are only used to help understand the method and core idea of ​​the present invention. It should be noted that, for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0083] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for treating residual aqueous phase distillation residue, characterized in that: The following steps are involved: Step 1: Adjust the distillation residue to pH>5 with sodium hydroxide to precipitate the impurities together with uranium, and then filter and separate to obtain a filtrate and a filter cake; Step 2: adding a mixed solution of sodium bicarbonate and sodium carbonate to the filtrate to obtain a leaching agent; Step 3: adding the leaching agent into the filter cake to leach the uranium therein, separating the solid and the liquid to obtain leaching residue and leaching liquid; Step 4: the leaching solution is mixed with acid and hydrogen peroxide, the acidity of the final solution is controlled to be pH 1.5-4.0, and the solid-liquid is separated to obtain uranium peroxide solid and uranium peroxide precipitation mother liquor; Step 5: After the uranium peroxide solid is dissolved by nitric acid, it re-enters the extraction and purification process.

2. The method for treating the raffinate aqueous phase distillation residue according to claim 1, characterized in that: The step 1 also includes: washing the filter cake with water, and combining the washing water and the filtrate to obtain a first solution; The first solution is used in step 2 to prepare a leaching agent.

3. The method for treating the raffinate aqueous phase distillation residue according to claim 1, characterized in that: The sodium bicarbonate concentration is from 0.1 mol / L to saturation concentration, and the sodium carbonate concentration is from 0 to 1 mol / L.

4. The method for treating the raffinate aqueous phase distillation residue according to claim 1, characterized in that: The uranium peroxide precipitation mother liquor controls the uranium concentration to be below 5 mg / L and is discharged after deep purification.

5. The method for treating the raffinate aqueous phase distillation residue according to claim 1, characterized in that: In the step 3, the leaching liquid-to-solid ratio L / S>1.

5.

6. The method for treating the raffinate aqueous phase distillation residue according to claim 1, characterized in that: In the step 3, the leaching temperature is 10-60° C., the reaction time is greater than 10 min, and the final pH is controlled to be less than 12.

7. The method for treating the raffinate aqueous phase distillation residue according to claim 1, characterized in that: In the step three, the leached residue is washed with water or a dilute sodium bicarbonate solution, and the obtained washing liquid is combined with the leaching liquid for subsequent steps.

8. The method for treating the raffinate aqueous phase distillation residue according to claim 1, characterized in that: In the step 4, the acid is nitric acid, hydrochloric acid or sulfuric acid.

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