JPS641535B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for separating molybdenum in acidic solutions containing uranium by selective precipitation. As is well known to those skilled in the art, in wet smelting of uranium, the concentrate obtained by ore impregnation is treated with nitric acid. After separation of insoluble matter, the resulting solution is brought into contact with an organic solvent to extract uranyl nitrate. This salt is re-extracted from the solvent by the aqueous phase,
Then they are processed differently to obtain UF ₆ or the metal itself. Derived from the raw ore, uranium concentrate contains some molybdenum. Furthermore, molybdenum dissolves at the same time as uranium in acidic solutions, and also partially dissolves during purification treatment with organic solvents. The result is uranyl nitrate contaminated with molybdenum. The nuclear technology industry requires molybdenum in uranium to be on the order of 1 ppm, and those skilled in the art are faced with the problem of separating this element from uranium-containing solutions, especially uranyl nitrate. Indeed, a number of solutions have already been proposed. For example, US Pat. No. 3,156,524 describes a method for treating an amino solvent containing molybdenum and uranyl nitrate with an oxidizing agent prior to re-extraction.
However, this method is applied to mineral solutions, in particular to avoid the formation of slag, and although it actually reduces the molybdenum content, it does not make it possible to obtain the required purity. Recognizing the insufficiency of the known solutions, the applicant has found a method by which molybdenum in acidic solutions containing uranium, in particular in the form of uranyl nitrate, can be separated by precipitation. This process can be carried out before or after conventional refining operations by liquid-liquid extraction of uranium-containing concentrates. This process is characterized in that a product belonging to the class of hydroxamic acids which is soluble in a solvent miscible with the solution is used as a precipitant. A suitable precipitating agent should be one that completely precipitates the molybdenum without introducing uranium into the precipitate formed. The applicant has the following general formula; [wherein R and R′ are alkyl, ethoxyalkyl, aryl, and benzylalkyl] molecules of hydroxamic acids having the formula are soluble in a solvent that is miscible with the aqueous phase to be treated and do not interfere with uranium. It has now been found that it is a highly selective precipitation reactant for molybdenum and thus fully meets the objectives pursued. Particularly representative of this class are: - N-benzoylphenylhydrokylamine, commonly referred to as NBPH; -decanehydroxamic acid, -Dodecanehydroxamic acid, is particularly effective. Hydroxamic acid is an ion in the medium to be treated.
It is a chelator of MoO ₂ ²⁺ and produces an insoluble material. For example, the reaction in the case of N-benzoylphenylhydroxylamine is shown below. Hydroxamic acid or a mixture of these acids is therefore added to an acidic solution of uranium containing molybdenum as a solution in a solvent miscible with the acidic solution containing uranium to cause precipitation and then, for example, by decantation. The precipitate may be recovered by known methods such as filtration, centrifugation, filtration, or a combination thereof. Furthermore, the applicant has discovered that R and R of hydroxamic acid
If the conjugate of R' exhibits some hydrophobicity, for example in the case of N-benzoylphenylhydroxylamine, the precipitate formed between the molecule and molybdenum can be recovered by flotation. I also discovered something. The process is generally carried out by passing an upward flow of bubbles of inert gas (air or nitrogen) into the reaction medium through the middle of the medium. The hydrophobic nature of the precipitate allows it to be absorbed by the gas bubbles and rise to the surface, where it can be recovered from the bubbles formed without flowing out. The starting acidic solution contains at least one of the acids group consisting of nitric acid, sulfuric acid, hydrochloric acid and mixtures thereof, preferably nitric acid. Particularly effective results are obtained with the process according to the invention when the uranium-containing acidic solution contains from 0.05 to 2 equivalents of acid per liter. 500 dl/, preferably 200 dl/in such medium
dl/ of uranium and a molybdenum content of 100 mg/, preferably 50 mg/, especially 1 mg/
For solutions on the order of 60℃, preferably 40℃
At temperatures not exceeding , precipitation with hydroxamic acid is practically completed within 15 minutes without interference of uranium. The amount φ of the precipitant, also called a scavenger, is between 2 and 1 mole of molybdenum contained in the starting acidic solution.
On the order of 5000 moles, this results in an extremely low molybdenum residual rate, i.e., less than 0.1 mg/mole, which corresponds to the purity required in the nuclear technology industry ((M0/U ratio less than 1 ppm). The amount used depends on the initial molybdenum content, and φ increases the lower this initial molybdenum concentration. Other features and advantages of the invention are detailed below with reference to the accompanying drawings. In Figure 1, the solid lines show the various stages of the uranium smelting cycle from concentrate to UF ₆ or uranium itself, and the dotted lines show the stages of the molybdenum removal process according to the invention. In the figure, A indicates a reactor producing suspension L2 by impregnation of concentrate S1 with nitric acid L1;
The suspension L2 is separated at B into a liquid L3 containing uranyl nitrate and soluble impurities, such as molybdenum, and waste rock S2. The liquid L3 is purified by extraction of uranium with an organic solvent in C to become liquid L4, and D
The uranium in the aqueous phase L5 is re-extracted from the liquid. This is intended for special treatment in E to obtain the final product S5. S5 is UF ₆
Or uranium itself. In the present invention, in order to obtain uranyl nitrate containing less molybdenum, the aqueous phase L
5 is sent to the F reactor and hydroxamic acid S3 is introduced therein to precipitate the molybdenum. The resulting suspension L6 then passes through G, where it is separated into a molybdenum-containing solid S4 and a purified liquid L7. Liquid L7 is reintroduced at E into the normal processing circuit. The invention is illustrated by the following examples. Example 1 Uranium 135 dl/, Mo 0.28 mg/i.e.
An industrial uranyl nitrate solution containing 2.9×10 ^-6 mol/liter and having an acidity of 0.1N was treated with N-benzoylphenylhydroxylamine previously dissolved in ethanol or 1N NaOH. In the latter case,
The acidity was brought to 0.1N by adding nitric acid. A fully congealed product is obtained and after a precipitation time of 15 minutes, the amount of N-benzoylphenylhydroxylamine used is defined as φ, i.e. as a function of the ratio of the molar amount to the amount of molybdenum in the nitrate. The residual rate of Mo in nitrate and the recovery rate of molybdenum are shown below.

[Table] In the case of ethanol, a nitrate solution of nuclear industrial purity can be obtained, but as φ increases, it is confirmed that the separation rate decreases. Conversely, in the case of NaOH, the value of φ must be much higher to obtain nuclear industrial purity. In the case of a uranyl nitrate solution with a uranium content of 135 dl/, if φ is 4000 (residual Mo is 0.08 mg/), the consumption of N-benzoylphenylhydroxylamine is only about 18 g per 1 kg of uranium. Example 2 A uranium-containing acidic solution containing the following was used. Uranium in the form of uranyl nitrate () 150g molybdenum 10mg/0.1N nitric acid The precipitant was dissolved in ethanol and different amounts of φ
(ratio of moles of precipitant to moles of Mo present) was used. The precipitated molybdenum obtained was recovered by flotation after air blowing. The following table shows the residual amount of Mo obtained as a function of the amount φ of precipitant used.

[Table] 3 〓0.01

[Table] 5 〓0.01
10 〓0.01
It has been found that the invention is particularly suitable for use in obtaining uranyl nitrate of nuclear grade purity.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the steps of uranium refining including the method of the present invention.

Claims (1)

[Scope of Claims] 1. A method for separating molybdenum from an acidic solution containing uranium by precipitation with a reagent belonging to the hydroxamic acids that can be dissolved in a solvent miscible with the acidic solution, the reagent being N-benzoyl phenyl. The above method, characterized in that it is selected from the group consisting of hydroxyamine, decanehydroxamic acid and dodecanehydroxamic acid. 2. The method according to claim 1, characterized in that the precipitate is recovered by flotation. 3 The precipitate is decanted, centrifuged,
2. The method according to claim 1, wherein the method is performed by an operation belonging to a group consisting of a combination of these two methods. 4. Claim 1, wherein the acidic solution contains at least one type of acid from the group consisting of nitric acid, sulfuric acid, hydrochloric acid, and mixtures thereof.
The method described in section. 5 Acidic solution containing uranium per liter
The method according to claim 1, characterized in that it contains 0.05 to 2 equivalents of acid. 6. Process according to claim 1, characterized in that the precipitant is used in an amount of 2 to 5000 mol per mol of molybdenum contained in the acidic solution.