RU2303074C2 - Method of processing the uranium- and fluorine-containing wastes - Google Patents

Abstract

FIELD: technology of processing uranium-and fluorine-containing wastes.

SUBSTANCE: proposed method includes preparation of solutions from wastes, concentration of solutions by sedimentation of uranium followed by dissolving of sediments in nitric acid, extraction conversion of concentrated solutions with the use of tributyl phosphate in hydrocarbon thinner and sedimentation of ammonium polyuranates from re-extracts thus obtained. Sedimentation of uranium at stage of concentration is performed with the use of sodium hydroxide at pH= 9-10 and temperature of 60-90C. Proposed method enhances purification of uranium from fluorine due to enhanced sedimentation and filtration properties of sediments at concentration stage. Content of admixtures in triuranium octa-oxide powders obtained from re-extracts by sedimentation of ammonium polyuranates and subsequent calcination does not exceed specified norms.

EFFECT: enhanced efficiency.

1 dwg, 2 tbl, 1 ex

Description

The invention relates to a technology for processing uranium-fluorine-containing wastes of uranium production.

A known method of processing uranium-containing waste (spills, solutions from equipment decontamination, substandard stock solutions, solid waste), including dissolving solid waste in nitric acid solutions, mixing the resulting solutions with liquid waste, filtering the solutions, concentrating the uranium-poor solutions, extraction extraction uranium and its purification from impurities using tributyl phosphate in a hydrocarbon diluent as an extractant (Mayorov A.A., Braverman I.B. Powder production technology in ceramic uranium dioxide -. M .: Energoatomisdat 1985 s.115-122).

In the aforementioned method, the concentration of the "poor" in uranium solutions is carried out by evaporation.

When processing waste containing fluorine, the latter corrodes equipment made of steel X18N10T, because possesses high corrosion activity. During evaporation, fluorine is not purified from solutions, and the direction of fluorine-contaminated solutions to the extraction redistribution complicates the extraction redistribution. In order to bind fluorine, iron nitrate is introduced into solutions directed to the extraction stage, forming strong complex compounds with fluorine. (Ritchie G.M., Ashbrook A.V. Extraction. Principles and application in metallurgy. - M.: Metallurgy, 1983, p. 285).

A known method of processing uranium fluorine-containing wastes (RF Patent No. 2200992, IPC G21A 9/04, 9/30, publ. March 20, 2003), adopted as a prototype, including obtaining solutions from waste, the stage of concentration of solutions by precipitation of uranium and subsequent dissolution of the precipitate in nitrogen acid, extraction of uranium from concentrated solutions using tributyl phosphate in a hydrocarbon diluent, re-extraction and precipitation of ammonium polyuranates from the obtained re-extracts.

The concentration of solutions in the prototype method, including the precipitation of uranium with ammonium hydroxide in the form of ammonium polyuranates and their subsequent dissolution in nitric acid, leads to the purification of uranium from fluorine. However, the cleaning is insufficient, because when precipitated with ammonium hydroxide, fine precipitates are formed with low sedimentation and filtration properties, which “capture” fluorine from the mother liquors.

The objective of the invention is to increase the degree of purification of uranium from fluorine by improving the sedimentation and filtration properties of sediments obtained by precipitation from solutions in the concentration operation.

The solution to the problem is achieved in that in a method for processing uranium-fluorine-containing wastes, including obtaining solutions from them, the stage of concentration of the solutions by precipitation of uranium and subsequent dissolution of the precipitate in nitric acid, extraction of uranium from concentrated solutions using tributyl phosphate in a hydrocarbon diluent, reextraction and precipitation of ammonium polyuranates from obtained strips, the precipitation of uranium at the concentration stage is carried out with sodium hydroxide at a pH of 9-10 and a temperature of 60-90 ° C.

Example

Uranium nitrate solutions to be processed were obtained by mixing solutions from dissolving cinder with the fluorination of triuran octoxide and pastes from stripping equipment with floor drain solutions and irrigation solutions of the gas treatment system. As a result of mixing, an initial solution of the composition was obtained: 0.06 mol / L of uranium, 0.3 mol / L of nitric acid, 1.05 mol / L of fluoride ion, which was sent to the concentration stage.

Uranium was precipitated at the concentration stage. The initial uranium-fluorine-containing solution and a 40% sodium hydroxide solution were fed into the precipitation reactor at predetermined costs with constant stirring. In the precipitation reaction zone, a pH of 9-10 and a temperature of 60-90 ° C were maintained

The sedimentation and filtration properties of the obtained sediments were evaluated by the filtration coefficient, sedimentation speed and time, and other characteristics shown in the drawing and table 1.

The drawing shows the dependence of the sedimentation rate of precipitation formed during deposition at the concentration stage, V, mm / min, on the sedimentation time t, min, for the proposed method (deposition with sodium hydroxide) and the prototype method (deposition with ammonium hydroxide).

Table 1 presents the characteristics of precipitation formed during deposition at the concentration stage in the proposed method (lines 4-7) and the prototype method (lines 1-3).

Table 1 Precipitator The deposition temperature, ° C The ratio of the volume of the initial solution to the volume of reagent precipitator The relative volume of sediment, vol.% Filtration coefficient, 10 ^-6 cm / sec The moisture content of the sediment, wt.% Specific surface, m ² / g Pycnometric density, g / cm ³ The density of the filling, g / cm ³ The content of components in the sediment, wt.% The content of components in the mother liquor, g / l in 20 minutes after 24 hours Uranus fluorine Uranus fluorine NH ₄ OH twenty 0.5 68 36 1,1 75 39 3.44 0.6 60,2 0.78 0.015 5.1 NH ₄ OH 60 0.5 51 26 3,1 62 37 3.48 0.7 60.5 0.73 0.015 5,4 NH ₄ OH 80 0.35 38 23 5.1 fifty 31 3,55 0.95 59.5 0.53 0.015 7.6 NaOH 60 10 32 twenty 10.0 55 31 3.52 1,0 60.1 0.25 0.014 10.8 NaOH 70 9.8 8.8 6.6 6.5 32,4 26.3 3.66 1.01 60.3 0.13 0.015 10.8 NaOH 80 9.1 7.2 6.4 5.7 31.9 25,2 3.62 1,07 58.0 0.13 0.012 10.8 NaOH 90 8.8 6.4 5,6 5.5 31,4 15.4 3.66 1.44 61.7 0.2 0.013 10.8

From the data presented in table 1 and in the drawing, it can be seen that the use of sodium hydroxide for the deposition of uranium in the concentration operation allows to increase the filtration coefficient of the formed sediments, the rate of sedimentation, bulk and pycnometric density, to reduce the moisture content in the sediments, the specific surface and the volume of sediment occupied by him after decantation. This increases the degree of purification of uranium from fluorine: the fluorine content in uranium precipitates is reduced by 3-5 times compared with the prototype, and the uranium content in the mother liquor remains at the same level as in the prototype method.

The use of sodium hydroxide in the operation of concentrating uranium from uranium-fluorine-containing solutions also significantly reduces the volume of the resulting mother liquors, which facilitates their disposal.

The resulting precipitates were dissolved in nitric acid solutions of a given concentration and sent to the extraction redistribution using tributyl phosphate in a hydrocarbon diluent and, further, to the ammonia precipitation of ammonium polyuranates from uranium reextracts.

Due to the improved purification of precipitates from fluorine at the concentration stage, solutions with a significantly lower fluorine content are sent to the extraction redistribution than in the prototype, which facilitates the extraction redistribution (less iron nitrate is required for fluorine binding).

The use of sodium hydroxide in waste concentration operations does not adversely affect the results of the extraction redistribution. On the extraction redistribution of concentrated uranium solutions with a flow ratio of extraction operations O: B = 1: 3, the technological indicators were obtained, which are presented in table 2 (line 1 - prototype method, line 2 - proposed method).

table 2 No. p / p The content in a concentrated solution, g / l Uranium content, g / l Uranium purification factor for extraction operations from HNO ₃ U F Fe water-tail solution circulating extractant F Fe one 44 309 12.6 6.3 0.003 0.005 250 680 2 42 300 3,1 1,6 0.0025 0.005 260 680

The content of impurities in triuran octaoxide powders obtained from reextracts by precipitation of ammonium polyuranates from them and their subsequent calcination did not exceed the established norms.

Claims (1)

A method of processing uranium-fluorine-containing wastes, including obtaining solutions from them, the stage of concentration of solutions by precipitation of uranium and subsequent dissolution of the precipitate in nitric acid, extraction of uranium from concentrated solutions using tributyl phosphate in a hydrocarbon diluent, reextraction and precipitation of ammonium polyuranates from the obtained strips, characterized in that uranium precipitation at the concentration stage is carried out with sodium hydroxide at a pH of 9-10 and a temperature of 60-90 ° C.