JPS6035286B2 - How to recover uranium from wet phosphoric acid - Google Patents

Description

[Detailed Description of the Invention] The present invention involves recovering a certain amount of uranium contained in wet phosphoric acid obtained by decomposing phosphate rock with mineral acids such as sulfuric acid and phosphoric acid, using gypsum as a medium. It is about the method.

Natural phosphate rock generally contains 100 to 20 ypm of uranium, and in the so-called wet phosphoric acid production process, which is wet decomposed with a mixed acid of phosphoric acid and sulfuric acid, most of the uranium is dissolved in a phosphoric acid solution. to move to.

Although the concentration of uranium in the phosphoric acid solution is not very high,
Since the absolute amount of phosphoric acid solution produced is very large, attempts have been made to recover uranium from wet phosphoric acid. As industrial methods for recovering uranium from wet phosphoric acid, solvent extraction methods, ion exchange methods, precipitation methods, adsorption methods, etc. are known.

Although the solvent extraction method is currently being industrialized worldwide, it requires purification of phosphoric acid as a pretreatment to prevent the formation of sludge during the extraction process, and the equipment costs are high. However, since the extraction solvent is expensive, complicated operations are required to avoid its loss. In addition to the need for pretreatment of phosphoric acid in the ion exchange method, there are other issues such as the need to operate in a region where the concentration of the phosphoric acid solution supplied to the ion exchange column is usually lower than the concentration of the wet phosphoric acid produced. There are problems, and it has not been widely put into practical use. Precipitation and adsorption methods require further improvement because the uranium recovery agent is expensive and its loss is a problem. 0 On the other hand, the present inventors have already developed a method for producing wet phosphoric acid in which phosphate rock is decomposed with sulfuric acid.
A method for producing wet phosphoric acid with a high uranium content (Japanese Patent Application No. 102409/1983), characterized in that an oxidizing agent is present in the reaction step for producing ishigae to make the uranium in the solution hexavalent;
In the evening, a hemihydrate sludge and/or a compound that generates hemihydrate gypsum is added to the wet phosphoric acid to convert all of the hemihydrate gypsum to hemihydrate gypsum.
It is characterized by separating the wet phosphoric acid and hemihydrate tube, hydrating the separated gypsum hemihydrate, then separating the hydrated gypsum, and adding a precipitant to the separated liquid to recover uranium as an insoluble precipitate.
Method of recovering uranium from wet phosphoric acid (Samurai Warawa 56-2
No. 4242) was proposed.

The present invention relates to improvement of the process of the latter prior invention,
This work has been completed by achieving an industrial method for recovering uranium from wet phosphoric acid and easing the conditions for the transformation to gypsum hemihydrate. In addition, Japanese Patent Application Publication No. 55-144
Publication No. 41y discloses a method for solvent extraction and recovery of uranium that is incorporated into the wet phosphoric acid production process using the hemihydrate method, taking advantage of the fact that tetravalent uranium is easily incorporated into hemihydrate pipes. The method was a combination of a uranium recovery method and a phosphoric acid production method, and was applicable only to the phosphoric acid production process of the hemihydrate-dihydromethod.

Therefore, it cannot be applied to other wet phosphoric acid production methods such as the dihydrous method, anhydrous method, hemihydrous method, dihydric and hemihydrous method, and the uranium-containing liquid, which is special for processing using stone as a medium, still requires a large amount of phosphoric acid. P24
In order to prevent the loss of P205 when extracting uranium from the liquid, it is necessary to use a limited method and conditions of solvent extraction, and the extraction solvent used in this solvent extraction method is expensive and the equipment cost is low. However, it had drawbacks such as being expensive. The present invention eliminates the drawbacks of these conventional uranium recovery methods from phosphoric acid solutions, and uses phosphoric acid obtained by various wet phosphoric acid production methods (hereinafter referred to as wet phosphoric acid) or wet phosphoric acid with Si02 Phosphoric acid with low fluorine content, which is obtained by adding three sources of alkali and alkali to remove the fluorine in wet phosphoric acid as an alkali fluorosilicate (hereinafter referred to as defluorinated phosphoric acid)
After adding sulfuric acid to the resulting mixed acid and adding hydrated gypsum to form hemihydrate gypsum, preferably at least an equivalent amount of triphosphate rock to the sulfuric acid is added, and green decomposition is performed to completely dissolve the hemihydrate. After making hydrogypsum, the hemihydrate gypsum is separated, the separated hemihydrate gypsum is hydrated, the hydrated gypsum is separated, a precipitant is added to the separated liquid, and uranium is recovered as an insoluble precipitate. This invention relates to an industrial method for recovering uranium from wet phosphoric acid or defluorinated tetraphosphoric acid.

In this way, the method of the present invention separates the uranium recovery process and the phosphoric acid production process as completely separate processes, so it can be applied to wet phosphoric acid produced by any method, and it can be applied to wet phosphoric acid produced by any method, using gypsum as an extractant. , the uranium recovery solution back-extracted with water is P
Since uranium does not contain components such as 205 and S04 and exists in a concentrated state, uranium can be easily recovered by precipitation, the precipitant is inexpensive, and the operation is much easier than solvent extraction. It's easy to do.

On the other hand, in the method described in JP-A-55-14441, when this precipitation method is applied, it has a negative effect on the phosphoric acid production process, and it is impossible to recover uranium by precipitation. The present invention will be explained in more detail below.

In carrying out the present invention, in a wet phosphoric acid production method in which phosphate rock is decomposed with sulfuric acid and phosphoric acid, an oxidizing agent is coexisted in the reaction step to produce gypsum to make the uranium in the solution hexavalent, and then the produced gypsum is It is preferable to use, as a raw material, wet phosphoric acid from which phosphoric acid is separated, or defluorinated phosphoric acid obtained by further reducing the fluorine content in wet phosphoric acid. Oxidizing agents include KC SoQ, NaC So03, Hi202, KM Yama04, HN03,
Examples include hydrochloric acid, 02, and air. The reason why defluorinated phosphoric acid is particularly preferred as a raw material is due to the fact that the fluorine content in phosphoric acid affects the uranium yield, and the uranium yield is higher when phosphoric acid with a lower fluorine content is used as a raw material. . If necessary, even better results can be obtained by further adding an Si02 source and an alkali source to the defluorophosphoric acid to fix fluorine ions as silicic acid ions. The reason for this correlation between fluorine content and uranium yield is not clear, but it is thought that the presence of a large amount of fluorine ions may inhibit the substitution reaction between uranium and calcium to some extent. As described above, it has been experimentally revealed that the smaller the amount of fluorine ions in phosphoric acid, the more effective it is for recovering uranium, and that a high recovery rate can be achieved as long as the limit is approximately 0.5% or less. In addition, when gypsum is applied to the raw material phosphoric acid, since tetravalent uranium is more easily incorporated into hemihydrate gypsum than hexavalent uranium, it is necessary to add a reducing agent such as metallic iron, electrolytic reduction, etc. It is desirable to reduce valent uranium to tetravalent uranium (see attached drawing). In the attached drawings, A: raw material phosphoric acid, B: Fe powder, C: Si02, D: 2S04, E, E': dihydrate gypsum (E is circulation), F: phosphate rock, G: water, H: NaOH, 1: Phosphoric acid (return), J: Dihydrate gypsum (product), K: In-system recovery, L: U cake (product), 1: Reduction process, 2: Hemihydration process, 3: DeH2S04 process , 4: Hemiwater separation step, 5: Dihydration step, 6: Dihydrate separation step, 7: Neutralization step, 8: U furnace passing step, which is the U recovery step using gypsum hemihydrate according to the present invention. It is a flow diagram showing an outline.

Next, sulfuric acid is added to the raw material phosphoric acid to form a moated acid composition. The reason for using a mixed acid composition is to achieve relaxation of the conditions for transformation into a hemihydrate tube (lower heat treatment temperature), and to make the present invention more industrially advantageous. The amount of sulfuric acid to be added is such that the amount of 2S04 in muddy acid is 25% by weight or less, preferably 5 to 5% by weight.
15 weight percent. If the specific amount of S04 is small, the effect will be poor, and if it exceeds 25% by weight, the amount of phosphate rock added in the subsequent process will increase, resulting in an increase in the amount of gypsum to be processed and an increase in the equipment capacity, which is not preferable. Next, hydrated stone (dihydrate) is added to the moating acid.

Gypsum dihydrate acts as a scavenger for uranium in the hemihydration process. It is preferable to recycle and use a part of the generated dihydrate gypsum produced in the subsequent hydration process for the dihydrate pipe, but dihydrate gypsum from other processes is also effective. The amount added varies depending on the composition of the mixed acid, but it is generally added so that the slurry concentration in the hemihydration step is 5 to 40% by weight. In the next hemihydration step, the slurry of mixed acid and hydrated gypsum is maintained at a temperature at which dihydrate transitions to hemihydrate tubes.

The transition temperature is phosphoric acid concentration P20 in a system consisting of wet phosphoric acid containing a large amount of impurities and a stone pipe. = 30%, generally 9
Although it may be higher than 0, and sometimes higher than 10,000, the transition conditions are relaxed because it is a system consisting of a mixed acid and gypsum, and about 85 to 90 qo is sufficient. The produced gypsum hemihydrate contains 1 PM to 500 m of uranium, but the mother liquor has a falconic acid composition containing 25% or less of sulfuric acid, and simply separating the gypsum hemihydrate does not produce the product phosphoric acid. Therefore, in the next step, phosphate rock is added to the slurry containing the mixed acid and gypsum hemihydrate, and at the same time it is reacted with excess sulfuric acid by a wet decomposition reaction, the uranium in the phosphate rock is also captured in the gypsum hemihydrate. The amount of phosphate rock added is the ratio S0 in the mixed acid.
4.Add enough amount to match the concentration and adjust so that the mother liquor after reaction has the composition of the product phosphoric acid. As with the hemihydration step, a reaction temperature of about 85 to 90 q○ is sufficient. The added dihydrate and all gypsum hemihydrate derived from the IJ ore are separated from the phosphoric acid and then sent to the next uranium stripping step. The process after the uranium stripping process is the same as that of the previous invention (Samurai Sho No. 56-24242). That is, the gypsum hemihydrate that has captured uranium is dispersed and hydrated in water, and in the process of transferring the gypsum hemihydrate to gypsum dihydrate, uranium is expelled from the solid phase to the liquid phase. This operation is characteristic of the present invention, and the advantage of using gypsum as a uranium recovery medium is that the process of extracting uranium from gypsum hemihydrate can be performed by a simple hydration operation. . A trace amount of sulfuric acid, a hydration accelerator, or an oxidizing agent may be added to the hydration reaction to accelerate the reaction.
The reaction can be carried out at room temperature. The dihydrate tube produced by hydration contains almost no uranium, and is mechanically separated and removed from the hydration mother liquor (hereinafter referred to as "recovered liquid") from which uranium has been eluted. Operationally, the slurry concentration is preferably in the range of 5 to 40% by weight. The amount of water supplied to gypsum hemihydrate should be determined in consideration of uranium yield, post-treatment method, etc., so as to provide the optimum uranium concentration. The amount is (supply water/
A practical weight ratio of gypsum hemihydrate) is in the range of 0.1 to 20. Alternatively, the recovered liquid may be circulated to the hydration step to increase the uranium concentration in the recovered liquid. Through the above steps, uranium is separated from phosphoric acid, and finally, a recovered liquid substantially free of phosphoric acid is obtained in a solution state.

The recovered liquid usually contains tens of ppm to several thousand ppm of U, and uranium can be easily and economically recovered by applying a precipitation method from the recovered liquid. Caustic soda, ammonium compounds, etc. are commonly used as precipitants, but divalent iron salts, organic chelating reagents, etc. are also used. Since phosphoric acid liquid, which is the raw material for recovered uranium, is the main product, we cannot add additives that would reduce the value of the product, but the recovered liquid is now completely separated from the phosphoric acid manufacturing process. In addition to the above-mentioned precipitating agent, the liquid properties can be adjusted as desired by adding additives such as a flocculant, an adsorbent, a full coating agent, a surfactant, and a pH regulator, so that uranium can be recovered effectively. On the other hand, it goes without saying that the recovered liquid, which does not contain harmful substances even if mixed with phosphoric acid, may be recycled to the phosphoric acid manufacturing process. In addition, a part of the separated hydrated gypsum can be recycled for use in the hemihydration process, and the rest can be discharged as is and used for cement, so it can be said to be an extremely advantageous process industrially.

Example 1 Wet phosphoric acid (P) obtained by decomposing Florida phosphate rock with sulfuric acid
205 concentration = 30%, F concentration = 1.9% U concentration 100
300 ppm) 98% sulfuric acid (30 ppm) was added to a polypropylene container with a stirrer, and the mixture was immersed in an oil bath to give a concentration of 870 ppm.

In order to reduce the uranium in the mixed acid to tetravalent, 0.2 liters of iron powder was added with stirring as a pretreatment. 40 g of hydrated gypsum (U concentration 2 ppm) was added to the pretreated mixed acid, the slurry temperature was adjusted to 870° C., and the mixture was allowed to react for 1 hour. After confirming that the entire amount of hydrated gypsum has been transferred to hemihydrate gypsum, phosphate rock (BPL75 from Florida, P2Q 34.4%, U concentration 100 ppm) is added for 32 hours, and the slurry temperature is raised to 870.
The decomposition reaction was carried out for 2 hours. After confirming that the phosphate rock has reacted to become hemihydrate gypsum, filter it to obtain P20530.
．． 3% of phosphoric acid containing 5 ppm of U was obtained. The hemihydrate gypsum cake was washed first with hot water and then with acetone and air dried. The weight of the gypsum hemihydrate was 74 mm, and the uranium content was 426 ppm as U. The ratio of the amount of uranium in the gypsum hemihydrate to the total amount of uranium derived from the phosphoric acid solution and the IJ ore was 95%. Subsequently, 60 parts of the gypsum hemihydrate were dispersed and hydrated with 70 parts of water, and then filtered, and the washing liquid and mother liquor were combined to obtain a recovered liquid 72. The uranium concentration in the recovered liquid was 348 ppm, and therefore the uranium yield in the hydration operation was 98%. Furthermore, the recovered liquid of pll≠1 was
Uranium was neutralized to pH=5.5 with OH aqueous solution to 15.0%.
A precipitate of 0.167 ta of sodium diuranate containing 0% (as U) was obtained. The uranium yield of this operation is 99.9%
Met. Therefore, the overall uranium yield is 93% (0.95
×0.98×0.999). Example B So-called defluorinated phosphoric acid obtained by defluorinating wet phosphoric acid (P2Q concentration = 30%
, F concentration = 0.5%, U concentration 10 pm) 300 saw 9
The same operation as in Example 1 was carried out using a mixed acid to which 30% of 8% sulfuric acid was added.

Pour into a polypropylene container with a stirrer and add 0.
Reduction treatment was carried out by adding 2 nights. Add hydrated gypsum to the moat acid for 40 minutes (
U concentration 2 ppm) was added thereto, and the mixture was reacted at 8700 for 1 hour while stirring. After confirming that the entire amount of hydrated stone pipe had been transferred to hemihydrate pipe, we confirmed that phosphate rock (BPL75 from Florida)
, P20534.4%, U concentration 100 ppm) was added for 32 hours, and the decomposition reaction was carried out at 8700 for 2 hours. After confirming that it was all hemihydrate gypsum, it was filtered and P2430.5%, U
330 ml of phosphoric acid containing 3 ppm was obtained.

The hemihydrate gypsum cake was washed first with hot water and then with acetone and air dried. The weight of the gypsum hemihydrate was 75 mm, and the uranium content was 429 ppm as U. Therefore, the uranium yield in the hemihydration operation was 97%. Subsequently, 60 ounces of the gypsum hemihydrate was dispersed and hydrated with 70 ounces of water, and then filtered.
A recovered solution 72' was obtained by combining the washing solution and the mother liquor. The uranium concentration in the recovered liquid was U=35 PM, and therefore the uranium yield in the hydration operation was 98%. Furthermore, when the recovered liquid with a pH of 1 is neutralized with aqueous ammonia to pH 6, uranium is reduced to 1
0.136 ta of ammonium uranate precipitate containing 8.5% (as U) was obtained. The uranium yield of this operation was 99.
It was 9%. Therefore, the overall uranium yield is 95% (0.
97×0.98×0.999).

[Brief explanation of the drawing]

The accompanying drawings are flow diagrams outlining the uranium recovery process according to the mountain embodiment of the present invention.

Claims (1)

[Claims] 1 H_2SO obtained by adding sulfuric acid to wet phosphoric acid
＿4 Add dihydrate gypsum to a mixed acid containing 25% or less, hold it above the hemihydrate transition temperature and transform it into hemihydrate gypsum, then add phosphate rock and perform wet decomposition to produce the hemihydrate gypsum. Recovery of uranium from wet phosphoric acid, characterized by separating and hydrating the separated gypsum hemihydrate to separate gypsum dihydrate, and adding a precipitant to the separated liquid to recover uranium as an insoluble precipitate. how to. 2. The method according to claim 1, in which defluorinated phosphoric acid with a concentration of 0.5% or less is used as the wet phosphoric acid. 3. The method according to claim 1, wherein a part of the separated dihydrate gypsum is recycled as a uranium recovery agent by returning it to the mixed acid.