Method of processing chemical concentrate of natural uranium

FIELD: chemistry.

SUBSTANCE: method involves leaching the concentrate with aqueous nitric acid solution at high temperature to obtain a pulp consisting a solid and an aqueous phase. The aqueous phase is then separated by filtration from the solid phase in form of uranium nitrate solution. Uranium is then extracted from the nitrate solution using tributyl phosphate in a hydrocarbon solvent. The extract is washed and uranium is re-extracted. Leaching is carried out by adding nitric acid and water in an amount which enables to obtain a nitrate solution in the aqueous phase of the pulp, said nitrate solution containing dissolved silicon in concentration of 2.5-3.7 g/l. The solid phase, which consists of insoluble concentrate residues, is separated by filtration from the solution which contains dissolved silicon, uranium in concentration of 170-250 g/l and nitric acid in concentration of 80-120 g/l. Filtration is carried out not more than 24 hours after leaching, preferably not more than 5 hours after leaching.

EFFECT: obtaining clean nuclear materials, suitable for producing uranium hexafluoride for enrichment.

2 tbl, 2 ex

The invention relates to methods for processing chemical concentrates, natural uranium (NUC) and can be used in the technology of extraction processing NUC with a high content of silicon in order to obtain nuclear-friendly materials, suitable for the production of uranium hexafluoride for enrichment.

During processing NUC leached with solutions of nitric acid, obtained by the nitric acid solution of uranyl nitrate is cleaned from impurities by extraction with 30%TBP in the organic diluent. In the leaching solutions of nitric acid concentrates with a high content of silicon are formed suspension (slurry)containing, in addition to the insoluble residue formed mainly by hydrated iron and aluminum oxides, the gels of silicic acid, which is a product of polymerization of silicic acid.

Known methods of processing NUC, in which the extraction of uranium by tributyl phosphate in a hydrocarbon diluent direct or slurry consisting of water and solid phases, or solutions of uranium obtained by separating the pulp.

For example, known methods of processing NUC with the extraction of uranium from the pulp:

- A method of processing NUC (Cherrington, Arule. Production technology of uranium. - M.: gosatomizdat, 1961, s-162). Leaching NUC spend 60%-but the nitric acid for 3 hours. In the processing of concentrates with a high content of silicates contents of the reactor are heated to 82°C with the aim of coagulation silicate; this reduces, but does not completely exclude the emulsification and the allocation of precipitation at the following stages of the process (extraction). Leachate receive the pulp with a uranium content of 200±10 g/l of nitric acid 3,0±0,2 mol/l, which is sent on the extraction. The disadvantage of this method is the formation of jellyfish and the allocation of precipitation on the extraction operation;

- A method of processing NUC (Cherrington, Arule. Production technology of uranium. - M.: gosatomizdat, 1961, s-182). Leaching is carried out 40%nitric acid at a temperature 93-104°C for 4 hours. In the finished pulp uranium contains 350-450 g/l, free of nitric acid of 0.8 to 1.8 mol/L. the Slurry is directed to the extraction of 30%tributyl phosphate in an organic diluent. I have problems associated with high emulsification in the extraction process (persistent, nerastraivaisya emulsion), when the raw material contains a lot of silicates.

Apparently, the extraction of uranium from the pulp particles of insoluble residues concentrate in the presence of gels of silicic acid contribute to the stabilization of emulsions, which are formed by the interaction of the extractant with uranyl nitrate solution, it leads to the cessation is the separation of emulsions, the formation of so-called jellyfish, violation of the extraction process.

Known, for example, the processing methods NUC with carrying out the extraction of uranium from solution:

- Method (Patent RF №2360988, IPC SW 60/02, 3/38 (2006.01), publ. 10.07.2009), including the leaching of the concentrate solution of nitric acid with obtaining pulp, from which after separation of the insoluble residue receive a solution of uranium. A solution of uranium containing 400-500 g/l of uranium and 0.5-0.8 mol/l of nitric acid, is directed to the extraction of 30%tributyl phosphate in a hydrocarbon diluent. From the washed extracts are reextraction uranium. The concentrates do not contain large amounts of silicon, therefore, the separation of the insoluble residue from the solution did not cause difficulties.

- A method of processing NUC (RF Patent No. 2315716, IPC 01G 43/01, publ. 27.01.2008). The method chosen for the prototype. Way to recycle the concentrate with silicon content of 1.0-3.6 wt.%, leaching of the concentrate conduct of 1.0-1.5 M nitric acid while maintaining the leaching solution to the excessive content of nitric acid of from 0.3 to 1.0 M After leaching under these conditions, the pulp defend 4-6 hours, during which formed a dense precipitate in the form of silica gel, which contains insoluble residues concentrate, precipitate is filtered off. After filtration get the solution the concentration of uranium 130-150 g/l, nitric acid 33-63 g/l, silicon, 0.1-0.2 g/l, which is correct in uranium content up to 100 g/l of nitric acid to 1.5-1.8 M and is directed to the extraction. Thus, the direct extraction solution containing a small amount of silicon, not more than 0.2 g/L. Disadvantage of this method is that the gels hinder sucks and filtering the insoluble residues concentrate, increase the volume of the filtered precipitation capture when filtering aqueous solution of uranyl nitrate, increase loss of uranium precipitation.

The separation of the insoluble residue from a solution of uranyl nitrate interfere with gels of silicic acid.

It should be noted that in the manufacture of pulp is first cooled (several hours), the slurry may some time be in containers-drive, if there is a need to unite the pulp from several operations, leaching, etc. All from the end of the leaching until the precipitate may take from several hours to several days.

The objective of the invention is the reduction of losses of uranium by separating the aqueous phase of the slurry, obtained by leaching NUC, from insoluble residues concentrate.

The set task is solved by the fact that in the method of chemical processing of natural uranium concentrate with a high content of silicon, comprising leaching the concentrate water R is a target of nitric acid at elevated temperature to obtain the pulp, consisting of solid and aqueous phases, the separation by filtration of the aqueous phase in the form of a nitrate solution of uranium from solid phase extraction of uranium from nitric acid solution of tributyl phosphate in a hydrocarbon diluent, washing of the extract and reextraction uranium leaching lead by adding nitric acid and water in an amount to provide a receipt in the aqueous phase of the pulp nitric acid solution containing the dissolved silicon concentration of 2.5-3.7 g/l, the solid phase comprising insoluble residues concentrate is separated by filtration from the solution containing the dissolved silicon, uranium concentrations 170-250 g/l and nitric acid in a concentration of 80-120 g/l, while the filtering is made not later than 24 hours from the end of leaching, mainly no later than 5 hours after leaching.

Recycle concentrate containing uranium from 36 to 42 wt.%, silicon from 0.47 to 0.71 wt.%.

The direct extraction solution containing uranium 170-250 g/l, silicon 2,2-4,2 g/l of nitric acid 80-120 g/l

The method is as follows.

Processed NUC "yellowcake" (ammoniyuraniltrikarbonata). Yellowcake contains 36-42 wt.% U and other elements such as silicon, iron and aluminum. The content in the yellow cake ballast impurities is:

- (wt.%): Si (0,47-0,71); SiO₂- (1,0-1,52); Fe - (0,58-1,0);Al - (0,54-1,0);

- (wt.% to U): Si (1.3 to 1.7); SiO₂- (2,8-3,6); Fe - (1,6-2,4); Al - (1,5-2,4).

Example 1.

Refined yellowcake, containing, wt.%: U - 40,0; Si - 0,60; Fe - 0,79; Al - 0,70. In terms of wt.% to U: Si - 1,49; Fe - 1,98; Al - 1,74.

The leaching is carried out at bubble mixing of the concentrate in an aqueous solution of nitric acid air at elevated temperatures. Use a solution of nitric acid of a concentration of 5.0÷16 mol/L. of Water and nitric acid is taken from the calculation dissolve all soluble components of the concentrate, the insoluble residues are hydrated compounds of iron and aluminum. Nitric acid and water is added in an amount to provide leaching to produce in the aqueous phase of the pulp concentration of uranium 170-250 g/l and residual concentrations of nitric acid of from 80 to 120 g/L.

As it turned out, the indicated concentration of uranium and nitric acid in the leaching contribute to the presence of silicic acid in dissolved form (without curing) during leaching and for several hours after leaching, then begins appreciable formation of silica gel.

About the end of the leaching judged by cessation of gas evolution. After leaching, the slurry was cooled and the aqueous phase is analyzed for the content of U, Si, NGO₃. Receive the slurry from the concentration of the th in the aqueous phase of the pulp uranyl nitrate in terms of uranium 170-250 g/l, silicic acid, calculated on the silicon 2.5 to 3.7 g/l of nitric acid 80-120 g/l Pulp contains insoluble residue, the number ≈0,5%, consisting mainly of hydrated compounds of iron and aluminum, but not containing silica gel.

Silica gel starts to form from dissolved when the claimed parameters leaching of silicon in appreciable quantities, those that interfere with the separation of the insoluble residue from the solution by 24 hours after the end of the leaching operation. After 5, 10 and 24 hours, the slurry was separated by filtration on water and solid phase. The separation of the solid phase after 5 and 10 hours was carried out quickly enough (with satisfactory speed fillratio). Difficulties arose when filtering through the 24 hours, because by this time already formed a considerable amount of silica gel, the filtration rate of the slurry was visibly declining, the volume of filtered sludge increased, causing increasing loss of uranyl nitrate solution with the precipitate. The results of the experiments are shown in table 1.

*In experiments 5 and 6 (dissolution "yellowcake" conducted on the prototype) almost all of the silicon from concentrate 4-6 hours after leaching forms a gel of silicic acid, which forms a dense precipitate (solid phase), in addition to containing gel of silicic acid insoluble residues of hydrated oxides of iron and aluminum in the aqueous phase are traces of silicon <0.2 g/l Gel of silicic acid during the filtration of sediment captures the uranyl nitrate solution, increasing loss of uranium in the sediment.

In experiments 1-4 claimed method almost all of the silicon from concentrate first is in the aqueous phase. Loss of uranium in the sediment when the duration of exposure of the pulp to 5 hours is negligible. As exposure of the pulp up to 10 hours of continuing education gels of silicic acid and increasing the losses of uranium filtered precipitation. When the duration of exposure of the pulp, is equal to 24 hours after leaching, loss of uranium from the filtered precipitation increase to 2.0-2.8 wt.%,but it is less than in experiments 5, 6, in which the leaching is carried out on the prototype.

Almost in the absence of gels of silicic acid or a small number of them (experiments 1-4, 5-10 hours after leaching yellowcake) is possible with minimal loss of uranium to separate from the aqueous phase insoluble residues filtering.

As can be seen from the table, the loss of uranium precipitation is much less than in experiments 1-4 than in experiments 5, 6.

Uranium, partially gone with precipitation, it is necessary to wash the acid, the resulting solution is directed to the leaching of a new portion of the concentrate. Together with uranium washed and silicon. The more silica in the sediment, the more it is washed out from the uranium and sent to the leaching of a new portion of concentrate, increasing the already high silicon content in the pulp.

Example 2.

Solutions of uranyl nitrate from experiments 1-4 of example 1 (obtained from filtration of the pulp, seasoned after leaching for 5 hours), free from insoluble residue was subjected to extraction with tributyl phosphate in a hydrocarbon diluent. The solutions used for extraction, had the composition: uranium 170-249 g/l, silicon 2.5 to 3.7 g/l of nitric acid 80-120 g/l

Silicon extraction remained in the aqueous phase and do not contaminate the uranium from the washed extract was carried out by reextraction uranium, reextract sent to the denitration of uranyl nitrate. Reach the tracts were analyzed for impurities. The composition reextractors are shown in table 2.

(The content of elements that are dashes in the second column, in the yellow cake little, they are not defined).

As can be seen from table 2, the inventive method provides the necessary cleanup of uranium from impurities, including silicon, iron, aluminum, as one stripped off reextractors meet the requirements of technical conditions With ASTM 788-03 on a solution or crystals of uranyl nitrate nuclear purity.

Silicon-on operation of the extraction of redistribution in the absence of solid particles of undissolved residues were removed by filtration) does not interfere with carrying out the extraction and re-extraction, including not stabilize the emulsion of the extractant with an aqueous solution, does not form a jellyfish does not contaminate the final product is uranium.

The method of chemical processing of natural uranium concentrate with a high content of silicon, comprising leaching the concentrate with an aqueous solution of nitric acid at elevated temperature to obtain slurry consisting of solid and aqueous phases, the separation by filtration of the aqueous phase in the form of a nitrate solution of uranium from solid phase extraction of uranium from nitric acid solution Tr is butylphosphate in a hydrocarbon diluent, washing of the extract and reextraction uranium, characterized in that the leaching of lead by adding nitric acid and water in an amount to provide a receipt in the aqueous phase of the pulp nitric acid solution containing the dissolved silicon concentration of 2.5-3.7 g/l, the solid phase comprising insoluble residues concentrate is separated by filtration from the solution containing the dissolved silicon, uranium concentrations 170-250 g/l and nitric acid in a concentration of 80-120 g/l, while the filtering is made not later than 24 hours from the end of leaching, mainly within 5 h after leaching.