NL7900581A - Recovering a uranium-contg. concentrate and purified phosphoric acid - from wet process acid, using an inorganic fluorine contg. pptn. agent and an organic partition agent - Google Patents

Abstract

In a process for recovering a U-contg. concentrate and purified H3PO4 from wet process H3PO4, crude acid is treated with an inorganic F cpd. (I) as precipitating agent in the presence of an organic partition agent (II). Resulting ppte. is then sepd. from teh residual mixt. of (II) and H3PO4. Pref. (I) is NH4F, alkali(ne earth) metal fluorides or HF. The (IIe is e.g. acetone. Pref. 120-900 wt.% (IIe and 7-0.15 wt.% (I) are used w.r.t. P2O5 in the phosphoric acid. Uranium and other metals can be pptd. almost quantitatively without noticeable losses of H3PO4. Smaller amts. of solvent can be used thanin prior art processes, and less H3PO4 is converted into ammonium phosphate.

Description

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> STAMICARBON B.V.

Inventors: Cornells A.M. WETERINGS in Stein Johannes A. JANSSEN in Schinveld 1 3053

METHOD FOR EXTRACTING A URANIUM-CONTAINING CONCENTRATE

AND PURIFIED PHOSPHORIC ACID

The invention relates to a method for recovering a uranium-containing concentrate and purified phosphoric acid from wet-process phosphoric acid by treating wet-process phosphoric acid with a precipitant in the presence of an organic dispersant, separating the precipitate formed and from the residual mixture of phosphoric acid and dispersant to recover the phosphoric acid.

Such a method is known from US Defensive Publication T970.007. In the process described therein, a uranium-containing precipitate from wet-process phosphoric acid is obtained by treating it with ammonia and / or ammonium salts in the presence of a reducing agent and a water-miscible organic solvent, especially methanol. The uranium is then recovered from the precipitate formed in a known manner via treatment with sulfuric acid, oxidation and extraction with an organophosphorus compound. The solvent is recovered and recycled via distillation and rectification.

A drawback of this known method is that very large amounts of ammonia and / or ammonium salts are required to effect a satisfactory precipitation of uranium from the phosphoric acid. As a result, a relatively large part of the phosphoric acid is bound as ammonium phosphate, which is moreover contaminated in such a way that it is practically only suitable for use as fertilizer.

Moreover, this phosphate deposit with the uranium therein is quite large, so that the reprocessing of this precipitate is also a fairly expensive matter.

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Another drawback of this known method is that large amounts of organic solvent are required. These must then be recovered from the phosphoric acid by distillation and rectification, which in addition to a large amount of energy required is associated with loss of solvent.

The invention now provides a method in which it is possible to separate the uranium and other metals present quantitatively from wet process phosphoric acid, without substantial losses of phosphoric acid due to ammonium phosphate formation, and wherein a smaller amount of solvent is sufficient. turn into.

According to the invention, this is achieved by using an inorganic fluorine compound as the precipitant.

As inorganic fluorine compounds, use can be made, inter alia, of ammonium fluoride, alkali metal fluorides, alkaline earth metal fluorides, hydrogen fluoride and mixtures thereof. Silicofluorides, hydrofluorosilicic acid, mixed fluorides, e.g. cryolite, and acidic fluorides such as ammonium bifluoride can be used. It has been found that ammonium fluoride as the precipitant by far is preferred because it requires a smaller amount to precipitate a certain amount of uranium. The fluorine compound can be added to the phosphoric acid in various ways, for example in solid form, in liquid form or as a solution.

The amount of fluorine compound required can vary within wide limits, partly depending on the amount of organic dispersant used.

To achieve a precipitation efficiency of the uranium of. above 90%, for an amount of dispersant of 120 to 900 wt.%, calculated on the PgOg, a k ° amount of fluorine compound of 7 to 0.15 is 30 wt.% calculated as fluorine relative to the weight amount of PO of the phosphoric acid , required.

Preferably, an amount of fluorine compound of 0.5 to 5% by weight is calculated as fluorine relative to the PO, and an amount of

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partial agent of 450 to 160 wt.%, calculated relative to the PO, used.

2 5 35 A larger amount of fluorine compound can be used without any objections. · 7900581 4 3, but does not bring any additional advantages. When a smaller amount of fluorine compound is used, it appears that part of the uranium present in the phosphoric acid does not precipitate, unless a very large amount of dispersant is used.

As an organic dispersant, water-miscible alcohols, ketones, ethers, carboxylic acids, carbonitriles, or mixtures thereof can be used, inter alia. Examples of suitable dispersants are methanol, ethanol, isopropanol, acetone, methyl ethyl ketoa, dimethyl ether, dioxane, acetic acid and acetonitrile.

It has been found that when using the method according to the invention the use of aliphatic ketones, in particular acetone, as a dispersant is particularly favorable, because it is sufficient to achieve a certain uranium precipitation efficiency with a smaller amount of dispersant and precipitant. The amount of dispersant is selected depending on the amount of fluorine compound used. When using acetone as a dispersing agent and ammonium fluoride as a precipitant, an amount of acetone of 200 to 450 wt.% And an amount of ammonium fluoride of 3 to 0.5 wt.% Is preferably calculated as fluorine, relative to 20 wt. phosphoric acid.

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Preferably, the fluorine compound is first added to the phosphoric acid and then the mixture is treated with the organic dispersant. Any small amount of precipitate which may form after the addition of the fluorine compound can, if desired, be removed before further treatment of the phosphoric acid, for example by filtration.

The method according to the invention can in principle be applied to any kind of wet process phosphoric acid. Both the so-called green wet-process phosphoric acid (obtained from calcined raw phosphate) and the so-called black wet-process phosphoric acid (which contains an amount of organic impurities) can be treated by means of the method without further pretreatment. The method can also be readily applied both to dilute phosphoric acid (the so-called filter acid) and to concentrated phosphoric acid, and even to so-called superphosphoric acids.

7900581 J *. 4 f.

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It may be an advantage to start from phosphoric acid with a low sulphate content, because it has been found that an even smaller amount of precipitant and / or dispersant will suffice. To this end, the crude phosphoric acid can be treated with a sulfate precipitation agent, for example calcium or barium compounds.

In contrast to the method according to US Def. Publ. T970.007, no longer necessary to pre-reduce the uranium contained in the phosphoric acid from the hexavalent to the tetravalent state to effect a practically quantitative precipitation of the uranium. It has been found, however, that when such a reduction is used, a smaller amount of fluorine compound and / or organic dispersant may suffice to achieve a certain uranium precipitation efficiency. Preferably, therefore, a reducing agent is added to the phosphoric acid during the treatment. It is of particular advantage to add the reducing agent after the precipitating agent, since a smaller amount of precipitate is then formed, in which the uranium is nevertheless almost quantitatively present. The reducing agents which can be used include powdered metallic iron, zinc or aluminum. Optionally, an electrolytic reduction can also be applied. Powdered metallic iron is preferably used as the reducing agent.

The amount of reducing agent is not critical, but is preferably selected to reduce all uranium to the tetravalent state.

In addition to uranium, the precipitate formed in the process contains most of the metals present in the wet-process phosphoric acid, for example magnesium, aluminum, cobalt, vanadium, yttrium, strontium, lead and rare earth metals, such as l'anthan and cerium.

This precipitate can be separated from the phosphoric acid dispersant mixture in a known manner, for example by filtration or centrifugation. If desired, the separated uranium-containing concentrate can be further worked up in various ways known per se.

The mixture of phosphoric acid and organic dispersant resulting from the separation of the uranium-containing precipitate (and 7900581 ♦ 5

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water) can be separated in various ways, for example by distilling, decanting or extracting, after which the separated distributing agent can be recycled back to the precipitation step, optionally after further treatment, such as rectification.

5 The residual phosphoric acid, which is practically free from all metal impurities, can be used for various purposes, for example as a raw material for the preparation of high-quality fertilizers, technical phosphates and animal feed phosphate.

The invention is further illustrated in the following examples.

Example 1

100 grams of wet process phosphoric acid, with the composition shown in the table below, were placed in a beaker. Then, 4 grams of iron wire was added and the mixture was stirred for 30 minutes, after which the iron was removed from the liquid using a magnet. 500 mg of solid ammonium fluoride was added to the remaining liquid and the mixture was stirred for about 1 minute.

186 grams of acetone were then added with stirring to form a precipitate. After a settling time of 1 hour, the precipitate was filtered to yield 6 grams of solid.

The filtrate was distilled under vacuum to obtain acetone as top product and a phosphoric acid solution as bottom product.

The composition of this phosphoric acid was determined and is also summarized in the table below.

7900581 ¥ 6 original phosphoric acid phosphoric acid after filtration P „05 29.1% 29.7% 2 5

Si02 0.72% 0.14%

Al 0.23% 0.01% S04 1.5% 0.9% K 0.04% <0.01%

Approx 0.62% 0.09%

Fe 0.25% 0.20% F 1.6% 0.22% V. 135 ppm 20 ppm

Cd 10 ppm <4 ppm

Ti 29 ppm 7 ppm U 120 ppm 16 ppm

The analysis results clearly show that the resulting phosphoric acid contained a much lower impurity content than the original wet process phosphoric acid.

The uranium content was reduced from 120 to 16 ppm. This means a uranium precipitation efficiency of> 87%.

Example 2

Example 1 was repeated with the proviso that first the treatment with ammonium fluoride and then the addition of the iron took place.

When the precipitate was filtered, an amount of 4 grams of solid was now obtained.

The other results were the same as in Example 1.

Example 3 100 grams of wet-process phosphoric acid of the same composition as in Example 1 was treated with 500 mg of ammonium fluoride and 269 grams of acetone, without the addition of iron.

The uranium precipitation yield was 91%, 7900581 7

Example 4

Example 3 was repeated using 3000 mg of ammonium fluoride and 134 grams of methyl ethyl ketone (= MEK). The uranium precipitation efficiency was over 90%.

5 Example 5-14

In the same manner as in Example 1, 100 g of wet-process phosphoric acid of the same composition as in Example 1 were treated with 4 g of iron, varying amounts of ammonium fluoride and different dispersants. The results are summarized in the table below.

. | test NHF in NHF in dispersant dispersant uranium precipitation No. mg / 100 g wt% in g / 100 g wt% / P 0; tattooed-. H PO F / P_0_ [H PO 5; ment in% r 3 4 2 5: 3 4 5! 4000 mg 6.8%; 48 g acetone 160 95% -98% 6 3100 mg 5.2%; 85 g acetone 280 95-98% 7 860 mg j 1.5% \ 186 g acetone 613 95-98% 8 100 mg | 0.17% 1 272 g acetone 897 95-98% i 9 9 j 2400 mg 4%: 120 g methanol 396 97% 10 {1200 mg 2%! 120 g of methanol 396 56% 11 2400 mg 4%; 130 g ether 429 95-98% 12 y 2500 mg 4.2% 120 g dioxane 396; 95-98% 13 | 1200 mg 2% 125 g isopro- 412 j 95-98% panol j - 14 i 1200 mg 2% 120 g MEK 396 I 95-98%

Example 15

In the same manner as in Example 1, 100 g of wet-process phosphoric acid, with the same composition as in Example 1, was treated with 4 g of iron, 2500 mg of potassium fluoride (2.8 wt.% F / PoO) and 160 g of acetone ( 528 wt% / P O).

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The uranium precipitation yield was 90%.

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Example 16-20

In the same manner as in Example 1, 100 g of wet process phosphoric acid, which had a P 2 O 2 content of 52%, was treated with 4 grams of iron, varying amounts of ammonium fluoride and organic dispersant.

The results are summarized in the table below, test NH F in NH ^ F in dispersant dispersant Juris precipitation mg / 100 g wt% F in g / 100 g in wt% Iteration yield versus PO H PO versus PO : ment in% 0¾ 25o4 254,400 mg 4.3% 112 g acetone 215%> 90% 17 3,100 mg 3.0% 143 g MEK 275%> 90% 18 1,000 mg 1.0% -216 g acetone 1415%> 90% 19 1000 mg 1.0% 218 g iso 419%> 90% propanol 20 400 mg 0.4% 247 g acetone 475%> 90% 7900581

Claims (11)

4 * f. 9 3053 * 1. Process for recovering a uranium-containing concentrate and purified phosphoric acid from wet-process phosphoric acid by treating it with a precipitant in the presence of an organic dispersant, separating the precipitate formed thereby and from the residual mixture of phosphoric acid and dispersant recover the phosphoric acid, characterized in that an inorganic fluorine compound is used as the precipitating agent. 2. Process according to claim 1, characterized in that the inorganic fluorine compound used is ammonium fluoride, an alkali metal fluoride, an alkaline earth metal fluoride and / or hydrogen fluoride. Process according to either of Claims 1 and 2, characterized in that when using 120 to 900% by weight of organic dispersant 7 to 0.15% by weight of fluorine compound, calculated as fluorine, relative to the weight amount of PO of the phosphoric acid. 2 5 Process according to any one of claims 1 to 3, characterized in that when using 160 to 450% by weight of organic dispersant 5 to 0.5% by weight of fluorine compound, calculated as fluorine, relative to the weight amount of PO of the phosphoric acid. 2 5 5. Process according to any one of claims 1-4, characterized in that, using 200 to 450 wt.% Acetone as dispersant, 3 to 0.5 wt.% Ammonium fluoride, calculated as fluorine, relative to the amount by weight of P0_ of the phosphoric acid. 2 0 6. Process according to any one of claims 1-5, characterized in that a reducing agent is added to the phosphoric acid. Process according to claim 6, characterized in that the reducing agent / 000531 is added to the phosphoric acid after the addition of the precipitating agent. Process according to either of Claims 6 and 7, characterized in that powdered metallic iron is used as the reducing agent. Method according to claim 1, as substantially described and further elucidated in the examples. 10. Uranium-containing concentrate obtained by using the method as claimed in any of the claims 1-9. 11. Purified wet-process phosphoric acid obtained using the method according to any one of claims 1-9. 7900531