RU2521606C2 - Method of recycling waste solutions in production of uranium tetrafluoride - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to hydrometallurgy of uranium and can be used to recycle mother solutions formed when producing uranium tetrafluoride from nitrate solutions via extraction, re-extraction and heat treatment of uranium compounds obtained from re-extracts to obtain uranium dioxide and further treatment thereof with chloride and fluoride solutions. The method of recycling mother solutions from production of uranium tetrafluoride involves mixing said solutions at pH 4.0-5.2 by bubbling air until pH stabilises and treating with sodium hydroxide at pH 10.5-11.0, separating the uranium-containing residues from the solutions and return thereof to the step of leaching raw products, settling the waste solutions in a tailing pond and pumping the remaining part of the solutions into the ground.

EFFECT: low consumption of nitric acid, sodium hydroxide and lime, reduced discharge of liquid wastes in the tailing pond.

3 cl, 6 tbl

Description

The invention relates to uranium hydrometallurgy and can be used to dispose of waste solutions in the preparation of uranium tetrafluoride (TFU) from nitric acid solutions of leaching of concentrates using the processes of extraction, re-extraction and heat treatment of uranium compounds obtained from re-extracts to obtain uranium dioxide and its further treatment with fluoride chloride solutions.

In the scheme for the production of TFU (with extraction refining of nitric acid leaching solutions with tributyl phosphate (TBP) and subsequent solid-phase reextraction with a solution of ammonium carbonate), uranium is precipitated from solutions in the form of crystals of ammonium tricarbonaturanylate (AUTC). The resulting precipitate is calcined to obtain UO ₂ , which is sent to obtain TFA by treating it with a solution of a mixture of hydrochloric and hydrofluoric acids.

In this scheme, three types of effluent solutions containing uranium and requiring special processing are formed:

- raffinates - nitric acid solutions with a concentration of nitric acid from 50 to 100 g / dm ³ for HNO ₃ and uranium up to 100 mg / dm ³ ;

- fluoride-chloride mother liquors (PCM) after receiving TFA with a concentration of HF up to 5 g / dm ³ , HCl up to 50 g / dm ³ and uranium up to 8 g / dm ³ ;

- carbonate mother liquors (KM) resulting from solid-phase reextraction of uranium from saturated TBP and separation of AUTC crystals containing ammonium carbonate up to 60 g / dm ³ , uranium up to 8 g / dm ³ and excess ammonia up to 20 g / dm ³ .

Known methods for the disposal of mother liquors of uranium production by neutralizing alkaline reagents, followed by separation of the sediment and dumping the clarified part to the tailings.

The closest analogue to the claimed technical solution is a known method of disposing of uranium production recycled solutions, including treatment with alkali or lime “milk”, separation of uranium-containing sediments from solutions and returning them to the leaching stage of the starting products, clarification of waste solutions at the tailing dump [O. Sabrekova, Syrtsov S.Yu. Methods of preparing circulating solutions for the production of uranium tetrafluoride for discharge. Materials of the industry scientific and technical conference dedicated to the 50th anniversary of the Seversk State Technological Academy, May 18-22, 2009 “Technology and Automation of Nuclear Energy and Industry TAAEP-2009”, Seversk, 2009. P.26].

By a known method:

- raffinates (nitric acid solutions) are neutralized with lime “milk” and dumped into a tailing dump;

- CM is subjected to heating to destroy ammonium carbonate and distillation of ammonia and carbon dioxide, the bottom residue is treated with lime “milk” to precipitate uranium and filtered, after which the precipitation is returned to the production cycle, and the clarified part is dumped into the tailing dump;

- The PCM is neutralized with lime “milk” or a sodium hydroxide solution and filtered, then the precipitates are returned to the production cycle, the clarified part is discharged to the tailing dump.

This processing method allows to prevent the ingestion of spent solutions into surface water bodies and to transfer most toxic and radioactive polyvalent metals from the liquid phase to the solid phase. After filling the tailings, the formed sediments will be reliably isolated from contact with the environment.

The main disadvantages of this method are as follows:

- each type of mother liquor is processed separately, which leads to an unreasonable increase in the number of units of equipment, including reactors, sumps, filters, etc .;

- significant consumption of reagents, in particular lime, sodium hydroxide and flocculants, electricity, steam;

- high residual uranium content after processing KM (more than 100 mg / l);

- increased discharge of liquid waste to the tailings due to dilution of the mother liquors with lime “milk”;

- a large number of impurities returned to the process cycle with precipitates (including calcium carbonate supplied with lime “milk”), which leads to a significant increase in the consumption of nitric acid during their dissolution and a decrease in the quality of TFU.

The objective of the invention is to reduce the costs of nitric acid, lime and sodium hydroxide, reduce energy costs for processing solutions, reduce the amount of pulp discharged to the tailings.

The technical result is achieved by recycling the mother liquors for the production of uranium tetrafluoride, including the operation of precipitating uranium from solutions by neutralizing them, characterized in that the acid chloride-fluoride mother liquors from the production of uranium tetrafluoride and / or raffinates formed during the extraction of uranium from nitric acid solutions with organophosphorus compounds, jointly treated with carbonate mother liquors formed during the reextraction of uranium and precipitation of ammonium tricarbonaturanilate, with a purge nd solutions air doosazhdeniem uranium and sodium hydroxide at a value pH 8,0-12,0.

When neutralizing PCM and / or raffinates at the first stage of processing to a pH of 4.0-5.2, the largest amount of neutralizing agent is consumed from the total amount necessary for complete neutralization, so the process is carried out to the indicated pH limits. At lower pH values, the consumption of pH sharply decreases, while an increase in pH values above these values leads to incomplete precipitation of uranium from solutions. The same is observed when neutralizing acidic solutions with a carbonate mother liquor to pH values below 4.0. Air purging is necessary for the destruction of carbonate and bicarbonate ions and their removal from solutions in the form of CO ₂ . If the solution is not blown with air, uranium bound to the carbonate complex will not precipitate. In the second stage of neutralization, the solutions (pulps) are neutralized with sodium hydroxide solution to a pH of 8.0-12.0. The use of sodium hydroxide instead of lime “milk” is due to the fact that the introduction of NaOH does not precipitate fluoride (in the form of fluorite) together with uranium. Almost all fluorine (90-95%) remains in solution. Therefore, the return of the obtained uranium-containing sediments to leaching will not lead to an increase in the concentration of fluorine in the solution and to a deterioration in the extraction performance. When the pH value is maintained at the second stage below 8.0, the degree of uranium deposition decreases, above 12.0, an unreasonable alkali consumption occurs. When neutralized with sodium hydroxide, the pulp is not blown with air, since in this case the effect of increasing the degree of deposition of uranium is not observed.

In the patent and scientific literature there is no information about the joint treatment of waste solutions produced by TFU. Therefore, the proposed technical solution is characterized by novelty and has significant differences.

Thus, the analysis of the proposed technical solution shows that between the distinguishing features of the proposed method and the result achieved there is a new causal relationship: the presence of these signs in the claimed method provides a positive effect, and the absence of these signs does not give the effect set by the purpose of the invention .

A comparison of the effectiveness of the proposed and previously known method (prototype) is given in the examples.

Example 1. In this example, results are presented showing the range of pH values at which the most complete precipitation of uranium from the mother liquors occurs during their joint processing and justifies the need to purge acidic solutions with air after neutralizing CM.

Jointly processed:

- raffinates and KM;

- FKhM and KM;

- a mixture of raffinates with FHM and KM.

In order to study the dependence of the residual uranium concentration on the pH value (table 1), a series of experiments were carried out in which the raffinates were neutralized with a solution of ammonium carbonate (imitate of a carbonate mother liquor) to a certain pH value (pH _ref ), after which air was bubbled through the solution until stabilization pH values (pH _K0H ). In the solution separated from the precipitate, the residual uranium concentration was determined.

Table 1 Dependence residual uranium concentration (C _u) in treated solutions of pH values during neutralization _ref raffinates KM followed by purging with air No. p / p Deposition parameters pH _ref pH _K0H The amount of uranium in the sediment, g C _and in solution, mg / dm ³ one 3,50 3.62 no 1940 2 3.6 3.74 no 1900 3 3.80 3.91 no 1856 four 3.90 4.06 no 1778 5 4.00 4.72 0.140 22.8 6 4.10 4.74 0.142 22.6 7 4.20 4.75 0.144 22.4 8 4.30 5.22 0.140 22.4 9 4.40 5.31 0.138 20,2 10 4,50 5.42 0.136 21.3 eleven 4.60 5.63 0.133 18.6 12 4.70 5.85 0.130 18.6 13 4.80 6.26 0.136 8.3 fourteen 4.90 6.83 0.138 2,5 fifteen 5.00 7.13 0.138 1.9 16 5.10 7.48 0.137 3.2 17 5.20 7.65 0.135 13.9 eighteen 5.30 7.72 0.128 40,2 19 5.40 7.84 0.115 232,2 twenty 5.50 7.89 0.104 382.0

For the experiment, 100 ml of a solution was taken with a content of nitric acid of 70 g / dm ³ and uranium 2 g / dm ³ , which was poured into 200 ml glasses. A bubbler was placed in a glass with a solution. A solution of ammonium carbonate was introduced into the beaker from the burette and air was simultaneously introduced. Mixing the solution was carried out using a magnetic stirrer.

The results showed that most fully uranium from raffinates deposited in pH values _outgoing from 4.0 to 5.2. The imbalance in the amount of precipitated uranium and its residual concentration in the solution is associated with dilution due to the introduction of a solution of ammonium carbonate.

It should be noted that without purging neutralized solutions with air, uranium practically does not precipitate, and only in the pH range of 5 a small suspension appears with the transition of uranium to the precipitate from the solution within 15% of its total amount. Further neutralization to pH 11.5 with sodium hydroxide does not lead to further precipitation of uranium.

To increase the degree of uranium extraction from the solution into the precipitate, the use of combined precipitation is proposed: first, after neutralization of the KM raffinate and air sparging until the pH stabilizes (pH ₁ ) (the bulk of the uranium goes into the precipitate), the remaining uranium is precipitated with further neutralization of the solution with alkali (20% NaOH solution) to pH ₂ (table 2).

table 2 Dependence residual uranium concentration (C _u) in treated solutions of pH values during neutralization _ref raffinates CM with air blowing and by treatment with sodium hydroxide solution No. p / p pH _ref pH _K0H C ₀ in a mixture of mg / DM ³ The concentration of uranium in solution (mg / DM ³ ) after treatment with sodium hydroxide to pH ₂ pH 8 pH 9 pH 10 pH 11 pH 11.5 5. 4.00 4.72 22.8 20,4 16.1 6.6 6.5 6.5 6. 4.30 5.22 22.4 18.0 16,0 6.3 6.0 6.0 7. 4.40 5.31 20,2 16.1 14.1 6.0 5.9 5.9 8. 4,50 5.42 21.3 14.3 12,2 10.0 5,0 5,0 9. 4.60 5.63 18.6 14.6 10,2 9.8 5.2 5.2 10. 4.70 5.85 18.6 12.6 10.1 9.5 5,0 5,0 eleven. 4.80 6.26 8.3 5.5 4.3 3,1 3,1 2,5 12. 4.90 6.83 2,5 1,2 0.9 0.8 0.6 0.6 13. 5.00 7.13 1.9 0.8 0.7 0.7 0.6 0.6 fourteen. 5.10 7.48 3.2 2.0 1,5 1.3 1,0 0.9 fifteen. 5.20 7.65 13.9 3.3 3,1 2,5 1.4 1,1 16. 5.30 7.72 43.3 40,0 40.1 40,2 40.1 40.1 17. 5.40 7.84 232,2 104 77 63 51 42 eighteen. 5.50 7.89 382.0 320 289 177 150 156

The results of the experiments show that raffinates neutralized by CM to pH 4.0-5.2 with air sparging after additional treatment with sodium hydroxide contain significantly less uranium than without alkali treatment.

When neutralizing PCM using CM and further passing air through the solution, the precipitate does not precipitate, which is associated with the formation of stable uranyl fluoride and chloride complexes. At low pH values, these complexes prevent the transition of uranium to precipitate. Therefore, the precipitation of uranium requires neutralization with alkali to higher pH values than in the case of raffinates. The initial PCM (pH 1.81) was neutralized by the KM value to pH _ref , then air was passed through the solution until the pH value stabilized (pH ₁ ), after which alkali (20% NaOH solution) was added to pH ₂ . After filtration, the solution was analyzed for uranium content. The results of the experiments are presented in table 3.

Table 3 Dependence residual uranium concentration (C _u) from the pH value in the neutralization _ref FHM pH 3,51 4.02 4.60 4.80 4.90 5.00 5.10 5.20 5,4 pH ₁ 4.1 4.4 4.62 4.84 4.94 5.03 5.13 5.40 6.0 pH ₂ 11.60 11.58 11.63 11.65 11.60 11.56 11.59 11.55 11.6 C _u in solution, mg / dm ³ 213.5 17.6 15.3 1.71 1.22 0.98 0.98 0.98 42.5

The results of the experiments show that using this method, it is possible to achieve a fairly complete deposition of uranium by neutralizing the PCM KM in the pH range 4.0-5.2.

The following is an example of the deposition of uranium from a mixture of all three types of mother liquors. For this, mixtures of PCM raffinate nitrate were prepared in volume ratios 1: 1 and 1: 2, which were then neutralized by CM.

In experiments with such mixtures, the deposition of uranium by simple passing of air could not be achieved. As in the case of PCM, an alkali solution had to be used for precipitation. The experiments were carried out in the same way as with FKM alone. The results are presented in tables 4 and 5.

Table 4 Dependence residual uranium concentration (C _u) of the values of pH in the neutralization _ref raffinates and FHM mixture in the ratio 1: 1 CM pH 3,50 4.02 4.80 4.90 5.00 5.10 5.20 5.50 pH ₁ 3.77 4.25 4.87 4.98 5.09 5.18 5.28 6.1 pH ₂ 11.7 11.62 11.66 11.58 11.59 11.6 11.5 11.44 C _u in solution, mg / dm ³ 64.6 5.52 2.20 1.96 1J1 1.47 1.71 48.6

Table 5 Dependence residual uranium concentration (C _u) of the values of pH in the neutralization _ref raffinates and FHM mixture in the ratio 1: 2 CM pH _ref 3,50 4.00 4.80 4.90 5.00 5.10 5.20 5.45 pH ₁ 3.80 4.22 4.85 4.96 5.05 5.18 5.30 5.55 pH ₂ 11.66 11.60 11.61 11.60 11.60 11.58 11.55 11.60 C _u in solution, mg / dm ³ 55.7 3.43 1.96 1.96 1.22 1.22 2.44 44.35

Example 2. In a 1 liter beaker, a stirrer and pH meter electrodes were placed. Three liters of each were filled with 0.5 L of a production solution of the raffinate composition according to the main components: nitric acid 60 g / dm ³ , ammonium nitrate about 100 g / dm ² , uranium 0.11 g / dm ² , iron 10 g / dm ² . The other four glasses were injected with the same volume of PCM composition: 40 g / dm ^{3 of} hydrochloric acid, 2 g / dm ^{2 of} hydrofluoric acid and 6 g / dm ^{2 of} uranium. For the next experiment, a mixture of PCM and raffinate in a ratio of 1: 1 and 2: 1 was used. Each of these mixtures was also poured into three glasses.

All of the listed batches of solutions were processed according to the following schemes:

1. Neutralization with 10% lime “milk”.

2. Neutralization of KM to a pH value of 5.0, followed by neutralization with a 20% sodium hydroxide solution to a pH value of 10.5.

3. Neutralization of CM to a pH value of 5.0, followed by purging with air for 20-30 minutes until the pH value is stabilized at about 7 and neutralized with a 20% sodium hydroxide solution to a pH value of 10.5.

4. In addition to the listed methods of neutralizing PCMs, they were treated only with a 20% sodium hydroxide solution to a pH of 11.5.

CM had the following composition: ammonium carbonate 79 g / dm ³ , uranium - 3.2 g / dm ³ .

As can be seen from the presented results (table 6), with the joint processing of the mother liquors, the residual concentration of uranium is slightly higher than when treated with lime or sodium hydroxide.

Table 6 The results of the treatment of waste solutions by various methods. Recyclable solution Solution composition Solution Processing Scheme The specific consumption of the reagent, ml / DM ³ The residual content of uranium, mg / DM ³ The volume of solution after neutralization, ml Raffinate HNO ₃ - 60 g / dm ³ , NH ₄ NO ₃ 95 g / dm ³ , U (VI) 0.11 g / dm ³ , Fe (III) 10 g / dm ³ 1 circuit 380 3 690 2 circuit 368 CMR to pH 4.95 + 6.6 NaOH 1960 874.6 3 circuit 368 CMR - up to pH 4.9 air purge to pH 6.9 + 4.2 ml 20% NaOH to pH 11 9.7 872.2 FHM HCl - 40 g / dm ³ , HF - 2 g / dm ³ , U (VI) - 6 g / dm ³ 1 circuit 410 About 1 705 2 circuit 385 CMR to pH 4.9 + 6.8 NaOH 4150 585 3 circuit 385 CMR - up to pH 4.85; air purge to pH 6.85 + 4.5 ml 20% NaOH to pH 11 5,4 589.5 4 circuit 20% NaOH solution About 1 530 A mixture of PCM and raffinate in a ratio of 1: 1 HNO ₃ - 30 g / dm ³ , NH ₄ NO ₃ 47.5 g / dm ³ , HCl - 20 g / dm ³ , HF - 1 g / dm ³ , Fe (III) 5 g / dm ³ , U (VI ) - 3.05 g / dm ³ 1 circuit 400 10 700 2 circuit 394 CMR to pH 4.95 + 7.2 NaOH 2910 901.2 3 circuit 372 CMR to pH 4.9 air purge to pH 7.0 + 4.6 ml 20% NaOH to pH 11 8.5 876.6 A mixture of fluoride chloride mother liquor and raffinate in a ratio of 2: 1 HNO ₃ - 20 g / dm ³ , NH ₄ NO ₃ 31.7 g / dm ³ , HCl - 26.6 g / dm, HF - 1.3 g / dm ³ , Fe (III) 3.3 g / dm ³ , U (VI) - 4.03 g / dm ³ 1 circuit 406 4,5 703 2 circuit 394 CMR to pH 4.95 + 7.2 NaOH 3000 3 circuit 372 CMR to pH 4.9 air purge to pH 7.0 + 4.6 ml 20% NaOH to pH 11 8.1

However, it should be borne in mind that CM after distillation of ammonia at elevated temperature and subsequent processing with lime of the bottom residue contain 60-80 mg / dm ^{3 of} uranium. When all mother liquors are mixed after neutralization, the average uranium content in the effluent solution pax is substantially less than 30-40 mg / dm ³ .

According to the proposed method, in addition to reducing the residual concentration of uranium, the total volume of wastewater is reduced by about 1.5 times due to the fact that they do not introduce lime “milk”, and KM is mainly used for neutralization.

Thus, with a decrease in the volume of effluent solutions and the concentration of uranium in them, there is a significant decrease in the total amount of uranium sent to the tailing dump.

Claims (3)

1. The method of disposal of waste solutions for the production of uranium tetrafluoride, including the operation of precipitating uranium from solutions by neutralizing them, characterized in that the acid chloride-fluoride mother liquors from the production of uranium tetrafluoride and / or raffinates formed during the extraction of uranium from nitric acid solutions with organophosphorus compounds, together are treated with carbonate mother liquors formed during the reextraction of uranium and precipitation of ammonium tricarbonaturanylate with the simultaneous purging of neutralized races thieves air to stabilize the pH value, followed by treatment with sodium hydroxide the pulp produced without blowing air. 2. The method according to claim 1, characterized in that the joint processing of chloride-fluoride mother liquors and / or raffinates is carried out by carbonate mother liquors to a pH of 4.0-5.2. 3. The method according to claim 2, characterized in that the resulting solution is further treated with sodium hydroxide to a pH of 8.0-12.0.