RU2444576C1 - Method of processing chemical concentrate of natural uranium - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves leaching in order to dissolve uranium when the concentrate reacts with nitric acid solution to obtain pulp from the concentrate. Uranium is then extracted from the pulp using tributyl phosphate in a hydrocarbon solvent. The extract is washed and uranium is re-extracted. Extraction is carried out from freshly prepared pulp which is obtained through direct-flow reaction at temperature 20-65°C of a stream of a suspension of the concentrate in water which is prepared beforehand and a stream of nitric acid solution with flow rate ratio which ensures nitric acid concentration in the pulp of 25-120 g/l. The period from the beginning of leaching to the beginning of extraction is not more than 10 minutes.

EFFECT: protection of extraction from formation of non-demixing emulsions, providing given purity of uranium from ballast impurities and obtaining raffinates which can be removed into underground collector sand layers.

2 tbl, 1 ex

Description

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

Known methods for processing HKPUs in which uranium is leached with solutions of nitric acid, and pulp containing an insoluble residue of hydrated iron oxides and other impurities in a solution of uranyl nitrate is directed to the extraction of uranium with tributyl phosphate in a hydrocarbon diluent. Extraction from the pulp is carried out, for example, by the method (C. Harrington, A. Ruele. Uranium production technology. - M .: Gosatomizdat, 1961, p. 157-162 [1]) or by the method (C. Harrington, A. Ruele Uranium Production Technology. - Moscow: Gosatomizdat, 1961, p. 179-182 [2]).

A positive point of extraction from pulp is the exclusion of the time-consuming operation of separating the suspension (solid and liquid phases) in order to obtain a solution of uranyl nitrate.

During processing of HKPU with a high silicon content, the pulp contains, in addition to undissolved residues of the concentrate (mainly in the form of hydrated compounds of iron and some other metals), silicic acid, which is prone to polymerization and forms gels. The drawback of extraction from pulp, which contains both insoluble residues and silicon in the form of silicic acid, is that particles of insoluble residues of the concentrate, especially in the presence of silicic acid gels, help to stabilize emulsions that are formed when the extractant interacts with uranyl nitrate solution, this leads to the termination of delamination emulsions, the formation of so-called jellyfish, violation of the extraction process.

This disadvantage is inherent in both of the above methods. In addition, raffinates containing silicic acid gels are obtained, which makes it impossible for them to be buried underground in sand reservoirs due to low filtration rates and the resulting mudding of reservoir reservoirs.

In both methods, the pulp obtained as a result of several hours of interaction of the acid and the concentrate is sent for extraction.

In the method [1], leaching of HKPU is carried out with 60% nitric acid for 3 hours at a temperature of 82 ° C, the result is a pulp with a content of uranium 200 ± 10 g / l and nitric acid 3.0 ± 0.2 mol / l which is directed to extraction.

In the method [2] during the processing of HKPU with a high silicon content, leaching is carried out with 40% nitric acid at a temperature of 93-104 ° C for 4 hours. The finished uranium pulp contains 350-450 g / l, free nitric acid 0.8-1.8 mol / l. The pulp is sent for extraction with 30% tributyl phosphate in an organic diluent. The method selected for the prototype.

The objective of the invention is the processing of pulp HKPU with a high content of silicon without the formation of non-stratified aqueous-organic emulsions on the extraction of uranium, with the receipt of raffinates that can be buried in underground sand reservoirs, ensuring a given degree of purification of uranium from impurities.

The problem is solved in that in a method for processing a chemical concentrate of natural uranium with a high silicon content, including dissolving uranium by leaching the concentrate with a solution of nitric acid to obtain pulp from a concentrate, extracting uranium from the pulp with tributyl phosphate in a hydrocarbon diluent, washing the extract and reextracting uranium, extraction is carried out from freshly prepared pulp, which is obtained by direct-flow interaction at a temperature of 20 ÷ 65 ° C the flow rate of the suspension of the concentrate in water and the flow of the solution of nitric acid at a ratio of flow rates ensuring the concentration of nitric acid in the pulp 25 ÷ 120 g / l, while the time from the beginning of leaching to the start of extraction does not exceed 10 minutes.

The essence of the method is to extract from a freshly prepared pulp, that is, such a pulp, which, after receipt, is immediately sent to the extractor.

The method is as follows.

The method processes silicon-containing concentrates of natural uranium, including ammonium uranyl tricarbonate, uranium peroxide, octoxide triuran, and uranium trioxide.

Recycled HKPU "yellow cake". "Yellow cake" is a salt - ammonium uranyltricarbonate. "Yellow cake" contains 36 ÷ 42 wt.% U and other elements such as silicon, iron and aluminum. The content in the "yellow cake" of ballast impurities is:

(wt.%): Si - (0.47 ÷ 0.71); SiO ₂ - (1.0 ÷ 1.52); Fe - (0.58 ÷ 1.0); Al - (0.54 ÷ 1.0);

(wt.% to U): Si - (1.3 ÷ 1.7); SiO ₂ - (2.8 ÷ 3.6); Fe - (1.6 ÷ 2.4); Al - (1.5 ÷ 2.4).

Example.

In the experiments of series 1, 2 and 3, the "yellow cake" was processed, containing, wt.%: U - 40.0; Si 0.60; Fe - 0.79; Al is 0.70. In terms of wt.% To U: Si - 1.49; Fe - 1.98; Al - 1.74.

In experiments of series 1 and 2, a suspension of yellow cake in water was first prepared, for this, the crushed concentrate was mixed with a given amount of water at a ratio of T: W of the concentrate mass to the water volume (t / m ³ ) 1: (0.54 ÷ 0, 60). The conversion of yellow cake to an aqueous suspension significantly accelerates the subsequent process of dissolution of the concentrate in acid.

Then, the suspension flow was introduced into the interaction with the flow of a 40% solution of nitric acid (7.9 mol / L) by feeding the flows into a direct-flow reactor thermostatically controlled at a given temperature (from the interval 20–65 ° C). The flow rate ratios were selected so that after dissolution of uranium, the residual concentration of nitric acid in the pulp at the outlet of the reactor (or, which is the same, at the inlet of the extractor) would be equal to 25 ÷ 120 g / l, and the concentration of uranyl nitrate in the pulp would be converted to uranium would be equal to 200 ÷ 300 g / l. The pulp contained insoluble residues of hydrated metal compounds. The duration of the dissolution of uranium at 65 ° C did not exceed 5 minutes, at 20 ° C - 10 minutes (the end of the dissolution of uranium was indicated by the cessation of gas evolution).

From a once-through reactor, a stream of the reaction mixture in the form of freshly prepared pulp moved to an extractor of the first extraction stage. From the start of leaching to the start of extraction, no more than 10 minutes passed.

In experiments of series 3, the "yellow cake" (not a suspension, but in solid ground form, as in the prototype) was mixed with a solution of nitric acid. Leaching to obtain a solution of uranyl nitrate and insoluble residues was carried out at a temperature of 65 ° C, it was completed in 15-20 minutes. The pulp 3 hours after the start of leaching of the concentrate was fed for extraction. Extraction was performed on the same cascade and under the same conditions as in the experiments of series 1 and 2.

Table 1 shows the conditions for the dissolution of the "yellow cake" and the composition of the pulps obtained in experiments of series 1-3.

In all experiments of series 1-3, the extraction cascade consisted of four blocks of settling mixers: extraction (from 5 steps), washing (from 2 steps), reextraction (from 6 steps) and regeneration of the reverse extractant (from 2 steps). Uranium was extracted with 30% tributyl phosphate in a hydrocarbon diluent. At the same time, [U] = 100 ÷ 105 g / L was maintained in the extract, and raffinates with [U] <0.1 g / L were obtained. Then, uranium was reextracted.

During the extraction processing, the accumulation of interfacial formations at the phase boundaries in the extraction unit was monitored and the content of impurities in the uranium reextracts was analyzed.

In experiments of series 1 and 2 at the phase boundaries in the settling chambers of the mixer-settlers, the accumulation of interphase formations (“jellyfish”) did not occur. The extract was clear with no visible residue of sediment. Particles of insoluble residues, being in the aqueous phase, were already enlarged at the first extraction stage, as occurs in the presence of a coagulant, and followed with the aqueous phase.

In addition, there was no formation of silicic acid gels in the aqueous phase of all stages of extraction; the filtration rate of raffinates clarified by sedimentation (separation from insoluble residues was carried out by decantation) through a sand filter layer did not change for one month from the moment of their receipt and was comparable to the water filtration rate. This makes possible the underground burial of clarified raffinates into sand reservoirs.

In series 3 experiments, at the phase boundaries in the settling chambers of the mixer-sumps of the extraction unit, immediately after the pulp was fed for extraction, the accumulation of interfacial formations (“jellyfish”) began, which led, after a tenfold exchange of solutions in the extraction unit, to stop delamination of the emulsions and stop the cascade. The extract obtained before the cascade stopped was cloudy with traces of sediment.

The silicic acid gel contained in the raffinate, after clarification of the raffinate with sedimentation followed by decantation, clogged the sand filter, which made underground raffinate burial impossible.

Table 1 shows the following. In experiments 1.1, 1.2, 2.1, 2.2, the silicon content in the aqueous phases of the pulps sent for extraction corresponds to the percentage of silicon to uranium in HKPU equal to 1.49%. In experiments 2.3 ÷ 2.5, the silicon content in the aqueous phase of the pulp decreases compared with the percentage of silicon to uranium, equal to 1.49% in HKPU, with a decrease in the consumption of nitric acid and the residual concentration of nitric acid in the pulps. This is accompanied, as shown by the analysis of precipitates isolated from raffinates, by the appearance of silicon in precipitates in experiments 2.3–2.5. The amount of precipitated sediment in the raffinates increased from 1.2% in experiment 2.3 s [HNO ₃ ] in the pulp 47.0 g / l to 11.3% in experiment 2.5 s [HNO ₃ ] in the pulp 25.1 g / l The revealed regularity - an increase in the amount of solid waste with a decrease in the consumption of nitric acid - allows you to choose the economically optimal consumption of expensive nitric acid (subject to the declared interval of residual nitric acid in the pulp supplied for extraction) and the amount of solid waste obtained in this process that must be disposed of.

Thus, neither undissolved residues nor silicon interfere with the extraction process from freshly prepared pulp; this eliminates the time-consuming operation of the separation of solid and liquid phases.

Uranium reextracts in experiments of series 1 and 2 had the same composition; in experiments of series 3, reextracts differed in the content of individual impurities. The content of impurities in the strips is shown in table 2.

As can be seen from table 2, the inventive method (experiments of series 1 and 2) provides the necessary purification of uranium from impurities, namely the quality of the stripped strips meets the requirements of ASTM C 788-03 specifications for a solution or crystals of uranyl nitrate of nuclear purity. In experiments 3, a uranium reextract was obtained with an impurity content exceeding the normalized values established by ASTM C 788-03 (exceeding the sum of impurity elements that do not form volatile fluorides and silicon).

Thus, the inventive method allows extraction from pulp obtained from concentrates with a high silicon content, without the inherent drawbacks of extraction from such pulps, that is, to protect the extraction from the formation of immiscible emulsions, to ensure the specified purification of uranium from impurities and to obtain raffinates that can be removed in underground sand reservoirs.

Claims (1)

A method of processing a chemical concentrate of natural uranium with a high content of silicon, including leaching to dissolve uranium by reacting the concentrate with a solution of nitric acid to obtain pulp from a concentrate, extracting uranium from the pulp with tributyl phosphate in a hydrocarbon diluent, washing the extract and reextracting uranium, characterized in that the extraction is carried out from freshly prepared pulp, which is obtained by direct-flow interaction at a temperature of 20 ÷ 65 ° C pre-cooked stream suspension concentrate in water and the flow of nitric acid solution at a ratio of flow rates to ensure the concentration of nitric acid in the pulp 25-120 g / l, with no more than 10 minutes from the start of the leach prior to extraction.