RU2152650C1 - Method for decontaminating ground polluted with cesium radionuclides - Google Patents

Abstract

FIELD: environment control. SUBSTANCE: method involves treatment of contaminated ground with aqueous solution of oxalic acid of minimum 0.5 M concentration mixed up with water-soluble ammonium, potassium, or sodium salt of hydrofluoric and/or hydrofluoric silicate acid; concentration of each salt is minimum 0.1 M in case they are used separately and total numeric concentrations of each salt, minimum 0.1 M in case of their joint use. EFFECT: enlarged functional capabilities, reduced time, improved safety.

Description

 The inventive method relates to the field of environmental protection, and more specifically to the field of processing of solid radioactive waste (SRW). The most effectively claimed method can be used for the decontamination of soils contaminated with cesium radionuclides.

 A known method of soil decontamination by mechanical removal of the upper, contaminated with radionuclides, soil layer [1].

 The disadvantages of this method are: the danger of secondary contamination of the area with radionuclides, (for example, due to dust generation), as well as the increased volume of generated radioactive waste due to the presence of radioactive soil in them, almost always captured together with radioactive during its mechanical removal.

 There is also known a method of treating soil contaminated with radioactive substances, including treating soil contaminated with radionuclides with an aqueous solution containing carbonated water, a conditioning agent and a complexing agent containing a carboxylic acid anion with 2 to 6 carbon atoms [2].

 The disadvantages of this method are: a low degree and speed of deactivation of cesium radionuclides.

 Closest to the technical nature of the claimed method is the "Method of decontamination of cesium-137 soils", which includes treating the soil with an aqueous solution of a mixture of mineral acid (nitric or hydrochloric) with a water-soluble salt of hydrofluoric and / or hydrofluoric acid (fluorides and / or silicofluorides of ammonium, potassium or sodium), moreover, the concentration of mineral acid in the aqueous solution is not less than 1 M, the concentration of the water-soluble salt of hydrofluoric or hydrofluoric acid, if any individual use - not less than 0.1 M, and in case of their joint use, the sum of the numerical values of the concentrations of each of the salts, expressed in moles, is not less than 0.1 [3].

 Despite the fact that the above method is intended for decontamination of soil from cesium-137 radionuclide, it is quite acceptable for decontamination of soil and from other cesium radionuclides, for example, from cesium-134, due to the identity of their chemical properties.

 The disadvantages of this method are the reduced degree and speed of deactivation of cesium radionuclides, the increased danger of the method (due to the release of toxic fumes of nitric or hydrochloric acids into the gas phase), as well as the limited applicability of the method due to its unsuitability for processing soils intended for subsequent use in industry and agriculture.

 The advantages of the proposed method are: increasing the degree and speed of deactivation of cesium radionuclides, increasing the safety of the method, as well as expanding the scope of its application.

 These advantages are achieved due to the fact that the soil contaminated with cesium radionuclides is treated with an aqueous solution of a mixture of oxalic acid with a water-soluble salt of hydrofluoric and / or hydrofluoric acid (fluorides and / or silicofluorides of ammonium, potassium or sodium), and the concentration of oxalic acid in the aqueous solution is not less than 0.5 M, the concentration of the water-soluble salt of hydrofluoric or hydrofluoric acid in the case of their separate use is not less than 0.1 M, and in case of their sharing the sum of the numerical values of the concentrations of each of the salts, expressed in moles, is not less than 0.1.

 At concentrations of the mentioned components of the decontamination solution below the above limits, the effects of increasing the degree and speed of decontamination are not achieved.

 The upper concentration limits are limited by the maximum natural water solubility of oxalic acid and the water-soluble salt of hydrofluoric and / or hydrofluoric acid, and an increase in the degree and rate of deactivation is observed with increasing concentrations from lower to upper limits.

 The method is implemented as follows.

 Loamy soil contaminated with cesium radionuclides with a specific activity of up to 88 Bq / g is treated with an aqueous solution of oxalic acid with a concentration of 0.5 M in the presence of ammonium, potassium or sodium fluoride fluoride or a concentration of 0.5 M in the presence of ammonium fluoride or silicofluoride, potassium or sodium with a concentration of 1 M in case of their separate use or with a concentration of 0.5 M for each of the salts in the case of using a mixture of fluoride and silicofluoride of ammonium, potassium or sodium (the most severe conditions).

 The consumption of the decontamination solution (in ml) in relation to the decontaminated soil (in g) is 5: 1, the decontamination time is 3 days, and the loamy soil was chosen as the most difficult decontamination medium.

 As a result of the experiments, it was found that the degree of deactivation of loamy soil with cesium radionuclides for possible combinations between oxalic acid and fluoride and / or ammonium, potassium or sodium silicofluoride is 64–68% (versus 60% in the prototype method), and the average decontamination rate 22 - 24% per day (against 20% in the prototype method).

 In the process of implementing the method, the absence of toxic fumes in the gas phase was also established, as well as the possibility of using decontaminated soil in industry and agriculture.

 Thus, the replacement of toxic nitric or hydrochloric acid with oxalic acid with the specified concentration provides an extension of the scope of the proposed method, and also increases the degree, speed and safety of its implementation.

Sources of information
1. Zimon A.D. and other Decontamination, M., published, 1994, S. 256-257.

 2. Application EP 0533494, CL G 21 F 9/28, 1993.

 3. RF patent N 2094867, cl. G 21 F 9/28, 1997.

Claims (1)

 A method for decontamination of soils from cesium radionuclides, comprising treating the soil with an aqueous solution of a mixture of acid and a water-soluble ammonium, potassium or sodium salt of hydrofluoric and / or hydrofluoric acid with a concentration of each salt of at least 0.1 M in case of their separate use and the sum of numerical values the concentration values of each of the salts is not less than 0.1 M in case of their joint use, characterized in that oxalic acid with a concentration of at least 0.5 M is used as the acid.