Recycling of nuclear liquid waste with boron control

Abstract

The invention relates to the complex processing of a nuclear power plant's NPP's liquid, boron-containing waste with a complex composition, being generated during the operation of NPPs, including of ones VVER-type, and can be used to isolate boric and nitric acids and hydroxides of sodium and potassium for their reuse in the NPP process cycle. The invention allows to obtain crystalline boric acid and highly concentrated solutions of nitric acid and hydroxides of sodium and potassium, suitable for reuse in the NPP process cycle and for general industrial use. Conducting electrodialysis at low values of current and voltage provides a reduction of the method's energy intensity. The involvement of all major components of waste mother liquors into the processing reduces the amount of stored and disposed hazardous waste.

Claims

1. A method of liquid waste processing for a nuclear power plant (NPP) with boron control, wherein a waste comprises sodium and potassium salts, the method including: a) introduction of calcium nitrate into a borate solution to provide a resulting composition, precipitation of calcium borate, and separation of the calcium borate from a mother liquor of the separated calcium borate; b) obtaining solutions of boric acid and sodium and potassium hydroxides; and c) electrodialysis with the use of an electrodialysis device with cation-exchange and anion-exchange membranes; wherein in step a) the borate solution, as sodium and potassium salts, comprises nitrates and sulphates of both sodium and potassium, wherein the introduction of calcium nitrate into the borate solution causes a co-precipitation of the calcium borate and calcium sulphate; wherein in step b) the obtaining the solution of boric acid is achieved by treating the co-precipitated calcium borate and calcium sulphate with a solution of nitric acid and separating the calcium sulfate precipitate from a solution of calcium borate, which is followed by treating the solution of calcium borate with nitric acid to cause formation of a precipitate of boric acid and a solution of calcium nitrate, and separating and drying the precipitate of boric acid; and wherein step c) comprises directly subjecting the mother liquor to electrodialysis to obtain solutions of nitric acid and sodium and potassium hydroxides.

2. The method according to claim 1, wherein the calcium nitrate is introduced into the borate solution at a pH of 9.3-11.0.

3. The method according to claim 1, wherein the co-precipitated calcium borate and calcium sulphate are treated with the nitric acid solution until a pH of 5-7 is provided.

4. The method according to claim 1, wherein the calcium borate solution is treated with the nitric acid at a temperature of 10-20 C. until a pH of 1-3 is provided.

5. The method according to claim 1, wherein, after separation of the precipitate of boric acid, the solution of calcium nitrate is added to the borate solution.

6. The method according to claim 1, wherein the electrodialysis of the mother liquor is conducted in a three-chamber electrodialysis device at the ratio of the mother liquor volume V.sub.ml in the middle chamber of the electrodialysis device to the volumes of the anolyte V.sub.a and the catholyte V.sub.c in the anodic and cathodic chambers, respectively, equal to V.sub.ml:V.sub.a=1:0.5-1.0 and V.sub.ml:V.sub.c=1:0.4-0.6, thereby obtaining the solution of nitric acid in the anodic chamber, and the solution of sodium and potassium hydroxides in the cathodic chamber.

7. The method according to claim 1, wherein the electrodialysis is executed at a current value of 1-3 A and a voltage of 4-10 V.

8. The method according to claim 1, wherein the boric acid precipitate is washed with a nitrate solution of pH 2-3, comprising 30-35 g/l of boric acid.

9. The method according to claim 1, wherein the boric acid precipitate is dried at a temperature not exceeding 60 C.

Description

EXAMPLE 1

(1) We take 1,000 ml of initial borate solution which contains, g/l: 104 Na.sup.+, 50.8 K.sup.+, 263 NO.sub.3.sup., 24 SO.sub.4.sup.2, 5.3 Cl.sup., 42 H.sub.3BO.sub.3, pH (borate solution)=8.7. pH of initial solution is upgraded to reach the value of 11 by adding 69 ml of NaOH solution (8.5 mole/l) After that 149 ml of Ca(NO.sub.3).sub.2 solution (5.5 mole/l) are added to borate solution As a result a co-precipitation of calcium borate and sulfate is generated. After the generated co-precipitation is separated from the solution using the method of filtration, 1.168 ml of mother liquor are electrodialysed, and co-precipitated calcium borate and sulfate are used for producing boric acid.

(2) Co-precipitated calcium borate and sulfate are treated with the solution which contains nitric acid (48.4 ml with concentration=12.2 mole/l) and 120 ml of water to reach the value of pH=5 with further conversion of calcium borate into a solution and separation of calcium sulfate precipitation (34 g) which, in terms of the equivalent amount of anhydrous salt, is 6.95% of overall salt content in the mother liquor. After that the sodium borate solution is treated with nitric acid solution (48.4 ml, concentration=12.2 mole/l) at a temperature of 20 C. to reach the value of pH=1. The generated boric acid co-precipitation is separated from calcium nitrate solution, then washed with nitrate solution (pH=2) which contains boric acid (concentration=35 g/l) and dried at a temperature of 55 C. As a result 32.4 g of boric acid are generated. The calcium nitrate solution is added to the initial borate solution after separation of boric acid precipitation.

(3) The mother liquor is electrodialysed in a 3-chamber electrodialysis device with cathion- and anion-exchange membranes. 1,168 ml of mother liquor are exposed to electrodialysis, the solution contains, g/l: 319 NO.sub.3.sup., 0.8 SO.sub.4.sup.2, 4.6 Cl.sup., 102 Na.sup.+, 44 K.sup.+ and 4.8 H.sub.3BO.sub.3, with I=2 A, V=6 V and following the proportion: V.sub.Mp:V.sub.a=1:0.5 and V.sub.Mp:V.sub.K=1:0.5 to have as a result 584 ml of nitric acid solution generated in the anode chamber, this solution contains, g/l: 648.3 HNO.sub.3, 1.63 H.sub.2SO.sub.4, 9.5 HCl, in cathode chamber there are 584 ml of sodium and potassium hydroxide solution, which contains, g/l: 354.8 NaOH, 181.4 KOH, and in the middle chamber there are 1.168 ml of demineralized mother liquor which contains 1.6 g/l of the following ions: NO.sub.3.sup., SO.sub.4.sup.2, Cl.sup., Na.sup.+, K.sup.+ and 4.8 g/l of H.sub.3BO.sub.3. Ion extraction from the mother liquor is 99.5%. The current yield of electrodialysed products is 60%.

EXAMPLE 2

(4) We take 1,000 ml of initial borate solution which contains, g/l: 111.3 Na.sup.+, 31.5 K.sup.+, 244.3 NO.sub.3.sup., 35.5 SO.sub.4.sup.2, 10.2 Cl.sup., 34.6 H.sub.3BO.sub.3, solution pH=8.5. pH of initial solution is upgraded to reach the value of 9.3 by adding 54 ml of NaOH solution (8.5 mole/l) After that 132 ml of Ca(NO.sub.3).sub.2 solution (5.5 mole/l) are added to borate solution As a result a co-precipitation of calcium borate and sulfate is generated. After the generated co-precipitation is separated from the solution using the method of filtration, 1150 ml of mother liquor are electrodialysed, and co-precipitated calcium borate and sulfate are used for producing boric acid.

(5) Co-precipitated calcium borate and sulfate are treated with the solution which contains nitric acid (41 ml with concentration=12.2 mole/l) and 150 ml of water to reach the value of pH=7 with further conversion of calcium borate into a solution and separation of calcium sulfate precipitation (50.3 g) which, in terms of the equivalent amount of anhydrous salt, is 10.8% of overall salt content in the mother liquor. After that the sodium borate solution is treated with nitric acid solution (41 ml, concentration=12.2 mole/1) at a temperature of 10 C. to reach the value of pH=3. The generated boric acid co-precipitation is separated from calcium nitrate solution, then washed with nitrate solution (pH=3) which contains boric acid (concentration=30 g/l) and dried at a temperature of 60 C. As a result 27.5 g of boric acid are generated. The calcium nitrate solution is added to the initial borate solution after separation of boric acid precipitation.

(6) The mother liquor is electrodialysed in a 3-chamber electrodialysis device with cathion- and anion-exchange membranes. 1.150 ml of mother liquor are exposed to electrodialysis, the solution contains, g/l: 291.4 NO.sub.3.sup., 1.2 SO.sub.4.sup.2, 8.9 Cl.sup., 106.7 Na.sup.+, 27.4 K.sup.+ and 3.1 H.sub.3BO.sub.3, with I=2 A, V=6.2 V and following the proportion: V.sub.Mp:V.sub.a=1:0.5 and V.sub.Mp:V.sub.K=1:0.4 to have as a result 575 ml of nitirc acid solution generated in the anode chamber, this solution contains, g/l: 592.2 HNO.sub.3, 2.45 H.sub.2SO.sub.4, 18.3 HCl, in cathode chamber there are 460 ml of sodium and potassium hydroxide solution, which contains, g/l: 463.9 NaOH, 56.2 KOH, and in the middle chamber there are 1.150 ml of demineralized mother liquor which contains 1.17 g/l of the following ions: NO.sub.3.sup., SO.sub.4.sup.2, Cl.sup., Na.sup.+, K.sup.+ and 3.1 g/l of H.sub.3BO.sub.3. Ion extraction from the mother liquor is 99.6%. The current yield of electrodialysed products is 60%.

EXAMPLE 3

(7) We take 1,000 ml of initial borate solution which contains, g/l: 101.9 Na.sup.+, 19 K.sup.+, 141.1 NO.sub.3.sup., 4.8 SO.sub.4.sup.2, 15.1 Cl.sup., 80.3 H.sub.3BO.sub.3, solution pH=8.2. pH of initial solution is upgraded to reach the value of 10.1 by adding 82 ml of NaOH solution (8.5 mole/l) After that 236 ml of Ca(NO.sub.3).sub.2 solution (5.5 mole/l) are added to borate solution As a result a co-precipitation of calcium borate and sulfate is generated. After the generated co-precipitation is separated from the solution using the method of filtration, 1.250 ml of mother liquor are electrodialysed, and co-precipitated calcium borate and sulfate are used for producing boric acid.

(8) Co-precipitated calcium borate and sulfate are treated with the solution which contains nitric acid (103 ml with concentration=12.2 mole/l) and 200 ml of water to reach the value of pH=6.6 with further conversion of calcium borate into a solution and separation of calcium sulfate precipitation (6.8 g) which, in terms of the equivalent amount of anhydrous salt, is 1.9% of overall salt content in the mother liquor. After that the sodium borate solution is treated with nitric acid solution (103 ml, concentration=12.2 mole/l) at a temperature of 18 C. to reach the value of pH=2. The generated boric acid co-precipitation is separated from calcium nitrate solution, then washed with nitrate solution (pH=2) which contains boric acid (concentration=33 g/l) and dried at a temperature of 40 C. As a result 69.3 g of boric acid are generated. The calcium nitrate solution is added to the initial borate solution after separation of boric acid precipitation.

(9) The mother liquor is electrodialysed in a 3-chamber electrodialysis device with cathion- and anion-exchange membranes. 1.250 ml of mother liquor are exposed to electrodialysis, the solution contains, g/l: 241.8 NO.sub.3.sup., 1.4 SO.sub.4.sup.2, 12.1 Cl.sup., 94.3 Na.sup.+, 15.2 K.sup.+ and 1.9 H.sub.3BO.sub.3, with I=1 A, V=4 V and following the proportion: V.sub.Mp:V.sub.a=1:0.6 and V.sub.Mp:V.sub.K=1:0.6 to have as a result 750 ml of nitirc acid solution generated in the anode chamber, this solution contains, g/l: 409.5 HNO.sub.3, 2.38 H.sub.2SO.sub.4, 27.7 HCl, in cathode chamber there are 750 ml of sodium and potassium hydroxide solution, which contains, g/l: 273.3 NaOH, 36.4 KOH, and in the middle chamber there are 1,250 ml of demineralized mother liquor which contains 2.42 g/l of the following ions: NO.sub.3.sup., SO.sub.4.sup.2, Cl.sup., Na.sup.+, K.sup.+ and 1.9 g/l of H.sub.3BO.sub.3. Ion extraction from the mother liquor is 99%. The current yield of electrodialysed products is 70%.

EXAMPLE 4

(10) We take 1,000 ml of initial borate solution which contains, g/l: 155.8 Na.sup.+, 11.2 K.sup.+, 227 NO.sub.3.sup., 6 SO.sub.4.sup.2, 3.8 Cl.sup., 18 H.sub.3BO.sub.3, solution pH=12. pH of initial solution is upgraded to reach the value of 10.6 by adding 130 ml of HNO.sub.3 solution (4 mole/l) After that 62 ml of Ca(NO.sub.3).sub.2 solution (5.5 mole/l) are added to borate solution As a result a co-precipitation of calcium borate and sulfate is generated. After the generated co-precipitation is separated from the solution using the method of filtration, 1.190 ml of mother liquor are electrodialysed, and co-precipitated calcium borate and sulfate are used for producing boric acid.

(11) Co-precipitated calcium borate and sulfate are treated with the solution which contains nitric acid (23 ml with concentration=12.2 mole/l) and 150 ml of water to reach the value of pH=6.2 with further conversion of calcium borate into a solution and separation of calcium sulfate precipitation (8.5 g) which, in terms of the equivalent amount of anhydrous salt, is 2% of overall salt content in the mother liquor. After that the sodium borate solution is treated with nitric acid solution (23 ml, concentration=12.2 mole/l) at a temperature of 16 C. to reach the value of pH=2.3. The generated boric acid co-precipitation is separated from calcium nitrate solution, then washed with nitrate solution (pH=2.3) which contains boric acid (concentration=33 g/l) and dried at a temperature of 57 C. As a result 15.6 g of boric acid are generated. The calcium nitrate solution is added to the initial borate solution after separation of boric acid precipitation.

(12) The mother liquor is electrodialysed in a 3-chamber electrodialysis device with cathion- and anion-exchange membranes. 1,190 ml of mother liquor are exposed to electrodialysis, the solution contains, g/l: 346 NO.sub.3.sup., 0.8 SO.sub.4.sup.2, 3.2 Cl.sup., 130.9 Na.sup.+, 9.44 K.sup.+ and 0.6 H.sub.3BO.sub.3, with I=3 A, V=10 V and following the proportion: V.sub.Mp:V.sub.a=1:1 and V.sub.M:V.sub.K=1:0.5 to have as a result 1.190 ml of nitirc acid solution generated in the anode chamber, this solution contains, g/l: 352 HNO.sub.3, 0.81 H.sub.2SO.sub.4, 3.3 HCl, in cathode chamber there are 595 ml of sodium and potassium hydroxide solution, which contains, g/l: 455.3 NaOH, 27.0 KOH, and in the middle chamber there are 1190 ml of demineralized mother liquor which contains 1.04 g/l of the following ions: NO.sub.3.sup., SO.sub.4.sup.2, Cl.sup., Na.sup.+, K.sup.+ and 0.6 g/l of H.sub.3BO.sub.3. Ion extraction from the mother liquor is 99.7%. The current yield of electrodialysed products is 50%.

EXAMPLE 5

(13) We take 1,000 ml of initial borate solution which contains, g/l: 89.2 Na.sup.+, 22.4 K.sup.+, 132.7 NO.sub.3.sup., 17.3 SO.sub.4.sup.2, 11.7 Cl.sup., 37 H.sub.3BO.sub.3, solution pH=10.7. After that 336 ml of Ca(NO.sub.3).sub.2 solution (4 mole/l) are added to borate solution As a result a co-precipitation of calcium borate and sulfate is generated. After the generated co-precipitation is separated from the solution using the method of filtration, 1,220 ml of mother liquor are electrodialysed, and co-precipitated calcium borate and sulfate are used for producing boric acid.

(14) Co-precipitated calcium borate and sulfate are treated with the solution which contains nitric acid (53 ml with concentration=12.2 mole/l) and 150 ml of water to reach the value of pH=6 with further conversion of calcium borate into a solution and separation of calcium sulfate precipitation (24.5 g) which, in terms of the equivalent amount of anhydrous salt, is 7.9% of overall salt content in the mother liquor. After that the sodium borate solution is treated with nitric acid solution (53 ml, concentration=12.2 mole/l) at a temperature of 20 C. to reach the value of pH=2. The generated boric acid co-precipitation is separated from calcium nitrate solution, then washed with nitrate solution (pH=2) which contains boric acid (concentration=35 g/l) and dried at a temperature of 60 C. As a result 36.1 g of boric acid are generated. The calcium nitrate solution is added to the initial borate solution after separation of boric acid precipitation.

(15) The mother liquor is electrodialysed in a 3-chamber electrodialysis device with cathion- and anion-exchange membranes. 1.220 ml of mother liquor are exposed to electrodialysis, the solution contains, g/l: 198.4 NO.sub.3.sup., 0.9 SO.sub.4.sup.2, 9.6 Cl.sup., 79.1 Na.sup.+, 18.4 K.sup.+ and 2.5 H.sub.3BO.sub.3, with I=1 A, V=5 V and following the proportion: V.sub.Mp:V.sub.a=1:0.6 and V.sub.Mp:V.sub.K=1:0.5 to have as a result 732 ml of nitirc acid solution generated in the anode chamber, this solution contains, g/l: 336 HNO.sub.3, 1.53 H.sub.2SO.sub.4, 16.4 HCl, in cathode chamber there are 610 ml of sodium and potassium hydroxide solution, which contains, g/l: 275.1 NaOH, 53.1 KOH, and in the middle chamber there are 1220 ml of demineralized mother liquor which contains 1.98 g/l of the following ions: NO.sub.3.sup., SO.sub.4.sup.2, Cl.sup., Na.sup.+, K.sup.+ and 2.5 g/l of H.sub.3BO.sub.3. Ion extraction from the mother liquor is 99%. The current yield of electrodialysed products is 70%.

(16) From the above description and Examples 1-5 it is clear that the proposed method of liquid nuclear waste recycling, as compared with the prototype method, allows for production of marketable boric acid (in crystallized form) and highly concentrated solutions of boric acid (up to 648.3 g/l) and sodium hydroxide (up to 463.9 g/l) and potassium hydroxide (up to 181.4 g/l) which are suitable for re-use in NPP process cycle and for general industrial needs. Electrodialysis carried out at lower values of current intensity and voltage ensures lower energy consumption. The fact that all major components of waste mother liquors are involved in the process of recycling means less hazardous waste to be further buried and stored. Mostly standard chemical equipment is used for this embodiment.