RU2250521C2 - Method for decontaminating liquid radioactive wastes - Google Patents

Abstract

FIELD: decontaminating liquid radioactive wastes.

SUBSTANCE: proposed method includes mixing of permanganate and oxalic acid solutions, recovery of potassium permanganate in oxalic acid medium, and formation of manganese dioxide while neutralizing mentioned solution. Then neutralized solution is corrected to pH = 10 - 11 and nickel ferrocyanide is introduced in solution. Sediment formed in the process that includes radionuclides sorbed therein is separated for next solidification by case-hardening. Solution is treated with powdered nickel ferrocyanide dried out at 100 - 200 °C.

EFFECT: reduced amount of radioactive wastes subject to solidification.

1 cl 1 tbl, 2 ex

Description

The invention relates to the field of purification of liquid radioactive waste (LRW) containing potassium permanganate and oxalic acid.

To deactivate the equipment of nuclear power plants, the “two-bath” method is used, in which the treatment is carried out sequentially with an alkaline solution of permanganate and a solution of oxalic acid / 1 /.

A known method of purification of LRW by restoring permanganate in them with oxalic acid to create an acidic medium with subsequent neutralization to form manganese dioxide, introducing nickel ferrocyanide and separating the precipitate formed with radionuclides sorbed on it for subsequent curing / 2 /. This method in its essence and the achieved effect is the closest to the claimed and selected as a prototype.

Nickel ferrocyanide obtained by mixing solutions of potassium ferrocyanide and nickel salts (with a mass ratio of ferrocyanide and nickel of about 1: 1) is the best sorbent for radiocaesium, with the highest sorption activity of freshly prepared nickel ferrocyanide. The combined use of manganese dioxide and nickel ferrocyanide increases the purification not only of cesium, but also of the rest of the mixture of radionuclides, however, this requires their introduction in an alkaline medium (pH 10-11) .When the precipitate is separated, the manganese dioxide precipitate - nickel ferrocyanide - leaching of radionuclides of cement blocks is reduced by more than 10 times.

The disadvantage of this method is the relatively large volume of radioactive fallout, which increases the cost of their curing and disposal.

The problem solved by this invention is to reduce the volume of radioactive fallout to be cured and buried without reducing the coefficient of LRW purification from radionuclides.

The essence of the invention lies in the fact that in the method of purification of LRW containing potassium permanganate and oxalic acid, comprising mixing permanganate and oxalic acid solutions, reducing potassium permanganate in an oxalic medium with the formation of manganese dioxide during neutralization of the averaged solution, introducing nickel ferrocyanide and separating the precipitate formed it with radionuclides for its subsequent curing by cementing, after the displacement of permanganate and oxalic solutions, an adjustment is made the averaged solution to a pH of 10-11, and nickel ferrocyanide is pre-dried at 100-200 ° C, crushed and introduced into the treated solution in powder form.

The drying of the prepared nickel ferrocyanide in the temperature range of 100-200 ° C is due to the fact that completely hydrated water is not removed at a temperature of less than 100 ° C, and decomposition of nickel ferrocyanide begins at a temperature of more than 200 ° C.

The method is as follows.

Nickel ferrocyanide prepared by mixing potassium ferrocyanide solutions and nickel salts is isolated from the solution, dried at a temperature of 100-200 ° C and ground. The crushed nickel ferrocyanide is introduced into the mixture of permanganate and oxalic acid solutions after reduction of potassium permanganate in an oxalic acid medium and formation of manganese dioxide with a pH adjustment of 10-11. Radionuclides from the solution are coprecipitated with a precipitate of manganese dioxide - nickel ferrocyanide, which is separated and sent for curing, for example, by cementing and subsequent disposal.

Compared with the known method for cleaning LRW from radionuclides on manganese dioxide and nickel ferrocyanide, this method reduces the amount of radioactive fallout to be disposed of by 7 times, which does not follow explicitly from the prior art, i.e. meets the criteria of inventive step.

Examples of specific performance.

Example 1 (prototype). The spent deactivating oxalic acid solution containing 3.4 g / l H ₂ C ₂ O ₄ , 1.7 g / l H ₃ PO ₄ , 3.4 g / l H ₂ O ₂ was neutralized and mixed in a weight ratio of 3: 2 with spent deactivating permanganate solution containing 3.4 g / l KOH and 0.8 g / l KmnO ₄ . After thorough mixing, potassium permanganate was reduced in an oxalic acid medium (pH <2) of an averaged solution. Nickel ferrocyanide was prepared by mixing solutions of potassium ferrocyanide and nickel nitrate in a ratio of 1: 1, which was introduced into the averaged solution after neutralization. The resulting precipitate of manganese dioxide - nickel ferrocyanide was separated by settling. The process parameters are given in the table.

Example 2. It differs from example 1 in that the prepared nickel ferrocyanide was dried at 150 ° C and ground before introduction into an averaged solution, previously adjusted to pH 10-11.

Table.
Characterization of the cleaning process. Example
No. The amount of the preparation of nickel ferrocyand, g / per 1 liter of solution The content in the preparation of dry nickel ferrocyanide,% wt. The purification coefficient of ¹³⁷ Cs after decantate filtration The volume of sediment in% of the volume of solution through. 1 hour 4 hours 24 hours 1 5 twenty 400-500 twenty thirteen 10 2 5 100 400-500 2,8 1,6 1.3

From the data given in the table, it is seen that in order to achieve the same cleaning coefficients, the consumption of nickel ferrocyanide after heat treatment increases by 5 times, however, due to an increase in the volumetric sorption capacity of the precipitate, the volume of precipitated decontamination solutions obtained during processing is reduced by 7 times.

The proposed method can be carried out using the same reagents and on the same equipment as the prototype. A decrease in the volume of radioactive fallout reduces the amount of solidified and landfill waste by 7 times, which is of great environmental importance. In addition, the rapid sedimentation of the sediment in the proposed method can significantly improve the performance of equipment for the separation of radioactive fallout.

Information sources.

1. Boguslavsky VB, Gruzdev N.I., Sklyarov V.P. - In the book: Radiation safety and protection of nuclear power plants. - M., 1977, issue 3., Pp. 27-34.

2. French patent No. 2451617, IPC G 21 F 9/16, publ. 10/10/1980.

Claims (1)

A method for purifying liquid radioactive waste containing potassium permanganate and oxalic acid, including mixing permanganate and oxalic acid solutions, reducing potassium permanganate in an oxalic acid medium and the formation of manganese dioxide during neutralization of the averaged solution, adjusting the averaged solution, introducing nickel ferrocyanide into the precipitate formed and separating it radionuclides for subsequent curing by cementing, characterized in that after mixing permanganate and sorrel left solutions carry out the adjustment of the averaged solution to pH 10-11, and Nickel ferrocyanide is pre-dried at 100-200 ° C, crushed and introduced into the treated solution in powder form.