FR2485509A2 - Extraction of uranium, thorium, yttrium and rare earths from acid soln - using a di-(alkylphenyl)phosphoric acid and hydrocarbon solvent - Google Patents

Abstract

The continuous process comprises contacting the soln. with a homogeneous organic phase comprising a di-(alkylphenyl) phosphoric acid substantially free of mono(alkylphenyl) phosphoric acid and an organic solvent selected from aliphatic and aromatic hydrocarbons or mixtures of these such that after sepn. of the phases the aq. phase is substantially exhausted. The extracting compsn. is novel when the alkyl in the alkylphenyl is 4-12C.. The process is used to recover metal values from acidic solns. (e.g. solns. obtd. from leaching phosphate rocks or used nuclear fuels). It enables total recovery with its extractant being stable and suitable for recycling over long periods.

Description

PROCESS FOR THE GLOBAL RECOVERY OF URANIUM,
RARE EARTHS, THORIUM AND YTTRIUM
APPLIED TO THE TREATMENT OF SOLUTIONS REMOVED
PHOSPHORIC ACID
The present invention relates to the application to the treatment of spent phosphoric acid solutions resulting from the solvent extraction of a crude wet phosphoric acid from the process for the overall recovery of uranium, rare earths, thorium and yttrium according to the main patent.

 In the main patent application No. 79.23517, there is described a process for the overall recovery of the aforementioned species contained in an acid solution having, in its most general aspect, the treatment of the acidic aqueous solution by means of a homogeneous organic phase, insoluble in water comprising a di- (alkylphenyl) phosphoric acid free of the mono- (alkylphenyl) phosphoric derivative and an inert organic solvent selected from aliphatic or aromatic hydrocarbons, used alone or as a mixture, whereby after separation of the phases, a substantially depleted aqueous phase and an organic phase loaded with desired species are collected. Where appropriate, the organic phase contains a solvating or modifying derivative.

 Then, in a preferred variant, the preceding organic phase is subjected to a contact reextraction by means of an aqueous phase comprising hydrofluoric acid dissolved in a strong mineral acid such as phosphoric acid, whereby collects in the aqueous phase a precipitate containing uranium, thorium, rare earths and yttrium, in the form of salts which are separated, the spent organic phase is recycled to the extraction. Depending on the valence state of the uranium contained in the starting solution, the reextraction can be carried out in the presence, in the aqueous reextraction phase, of a uranium (IV) reducing agent for uranium (IV).

 The above process is particularly applicable to the non-selective recovery of the above-mentioned species contained in a crude wet phosphoric acid originating from the attack of phosphatic rocks by a strong mineral acid such as sulfuric acid and after having separated the slurry. etching into a solution and a phosphogypsum residue.

 On the other hand, there is a growing commercial demand for purified phosphoric acid which is generally used in the food and feed industry and as a starting material for polyphosphates for laundry compositions.

As a result, an increasing fraction of wet crude phosphoric acid is generally purified by known liquid-liquid extraction processes using insoluble or poorly water-soluble organic solvents such as sodium phosphates. alkyl, such as, for example, tributyl phosphate, or aliphatic alcohols, for example butanol or isobutanol.

Such purification processes are described in the previous patents in the name of the Applicant FR 1,531,487 1,553,095 and 2,259,787 by way of non-limiting examples. According to these methods, the crude wet phosphoric acid solution resulting from the attack of a phosphocalcic rock by a strong acid such as
H2SO4 and after filtration is subjected to extraction using the above-mentioned solvents, whereby a significant fraction of the phosphoric acid is extracted into the organic phase. After separation of the phases, the extraction battery is collected at the outlet of the reactor. organic phase rich in P205 and a depleted aqueous solution (or raffinate) of a low P205 concentration and containing most of the catlonic impurities present in the aqueous starting solution. In addition, if necessary, during said extraction, concentrated sulfuric acid is added to promote the extraction of phosphatic species; as a result, a significant fraction of the added sulfuric acid is found in the aqueous raffinate. Consequently, a large fraction, if not all, of uranium, rare earths, yttrium and thorium are found in the said raffinate from which it is worthwhile to recover it.

 The present invention thus relates to a continuous process for recovering uranium, rare earths, yttrium and thorium in an acidic aqueous phase according to any one of claims 1 to 18 of the main patent, characterized in that said acidic aqueous phase is obtained as an aqueous raffinate from the extraction with insoluble or poorly water-soluble solvents of a crude phosphoric acid such as a crude wet phosphoric acid.

The aqueous raffinate used in the present invention and resulting from the liquid-liquid extraction contains, inter alia, phosphoric acid at a concentration by weight expressed as
P205 in general less than 20%, preferably around 10%, of the sulfuric acid resulting from the excess of reagent introduced to attack the phosphate rock at a weight content in general of the order of 1 to 3 %, according to the excess present at the beginning, other anions such as fluoride ions etc ..., and cations such as those of iron, aluminum, magnesium, alkali, uranium, rare earths, yttrium and thorium, these four the last being generally in the state of traces. Of course if the extraction process has included the addition of sulfuric acid, its concentration in the raffinate is higher and can be up to about 15% by weight, while conversely the weight content of P205 can be as low. than 2% (see the above-mentioned patents).

 The foregoing aqueous raffinate is particularly suitable as a starting means used in the liquid-liquid extraction process by a homogeneous organic phase containing a monosubstituted dl- (alkylphenyl) phosphoric acid and a suitable organic solvent according to the patent. main. After separation of the phases, the desired species are obtained from the organic phase loaded by treatment with an aqueous solution of hydrofluoric acid dissolved in a strong mineral acid, if appropriate, in the presence of a reducing agent of the uranium (VI) in uranium (IV) such as iron (II) ions. In doing so, it is possible to recover industrially up to at least 90% of the uranium, rare earths, thorium and yttrium present in the raffinate.

 The invention will be better understood by reference to the following illustrative examples, the parts being in pold unless otherwise indicated.

EXAMPLE 1
An aqueous raffinate from the extraction with tributyl phosphate of a crude wet phosphoric acid obtained by sulfuric attack of an apatite from Togo with the introduction of sulfuric acid into the extraction battery according to the invention is available. teaching and the operating method of the example of French Patent No. 1,531,487. Its weight composition is as follows
P2O5 ................... 3,5%
H2SO4 .................. 12.2%
Fe203 ................. 15.9 g / liter
Al2O3 .................. 20.4 g / liter
MgO ................... 10.6 g / liter
Na2O ........ 16.8 g / liter
U (VI) ............... 203 mg / liter
TR203 ......... 74 mg / liter
Y203 ........ 88 mg / liter
Th02 ........... approximately 0.5 mg / liter
The preceding raffinate is extracted by an organic phase whose weight composition follows
Di (octylphenyl) phosphoric acid ......... 23% Trioctylphosphine oxide ................. 5 z
Kerosene ................................. 36%
Solvesso 150 (hydrocarbon mixture
aromatic) trademark of the
Company EXXON) .............................. 36% at 30 C. by means of a single-stage extractor. The following table gives the extraction yields of uranium (VI) and yttrium.

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Extraction <SEP> of <SEP>: <SEP> Extraction <SEP> of
<tb>: <SEP> A / O <SEP>: <SEP> uranium <SEP> (%) <SEP>: <SEP> yttrium <SEP><SEP> (%) <SEP>
<tb><SEP> 1 <SEP> 98 <SEP> 95
<tb><SEP> 2 <SEP> 2 <SEP>: <SEP> 95 <SEP>: <SEP><SEP> 89
<tb><SEP> 5 <SEP> 87 <SEP> 78
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EXAMPLE 2
The aqueous raffinate of Example 1 is available. The solvent is extracted from Example 1 against the current of the phases in a battery of theoretical four-stage mixer-settlers maintained at 400 ° C. in a phase flow ratio. organic / aqueous phase of 1.2. It comes out of the battery a depleted aqueous phase containing less than 10 mg / liter of uranium, rare earths, yttrium and thorium.The enriched organic phase contains
U (VI) ................ 165 mg / l
TR2O3 ................ 57 mg / l
Y203 9 73 mg / l
ThO2 ................. 0.4 mg / l
Then the organic phase is brought into contact with an aqueous solution containing P2O5: 56%; HF: 6.5% and
Fe: 1.5 g / liter in a mixer-settler at 40 ° C. in an organic phase / aqueous phase flow ratio of 5. A green precipitate is formed which is entrained by the aqueous phase and then separated by centrifugation. The depleted organic phase contains less than 10 mg / liter of uranium, rare earths, yttrium and thorium.By liter of solvent is recovered 0.35 g of dry precipitate of uranium fluoride (IV), rare earths, yttrium and thorium which corresponds to an overall 95% raffinate recovery yield of uranium, rare earths, yttrium and thorium.

EXAMPLE 3
An aqueous raffinate is obtained from the extraction with tributyl phosphate of a crude wet phosphoric acid obtained by sulfuric attack of a TOGO apatite without introducing additional sulfuric acid into the extraction battery. .

Its composition is as follows
P205., 15%
H2S04 ................. 4%
Fe203 ................. 16 g / l
A1203 ................. 20 g / l
MgO .................. 11 g / l
Na20 ................. 17 g / l
U (VI) ............... 215 mg / l
TR203 ..... 75 mg / l
Y203 .................. 90 mg / l
The preceding raffinate is extracted by the organic phase of Example 1, against the current of the phases in a battery of theoretical four-stage mixer-settlers, maintained at 400C in an organic phase / aqueous phase flow ratio equal to 1.

 It leaves the extractor an exhausted aqueous phase containing less than 20 mg / l of uranium, rare earths, yttrium and thorium and a charged organic phase containing: U = 210 mg / l; TR203 70 mg / l and Y203 = 87 mg / l, ie an average extraction rate greater than 90%. This organic phase is reextracted as in Example 2 with a solution containing P2O5 = 56%; HF = 6.5% and Fe = 1.5 g / l.

EXAMPLE 4
The aqueous raffinate of Example 3 is considered. Its preliminary reduction is carried out on a bed of iron shot so as to reduce both iron (III) to iron (II) and uranium (VI) to uranium ( IV).

The extraction is then carried out in a phase report
O / A = 1/5 over five stages with the solvent of Example 1. An organic phase containing U = 1.07 g / l is obtained; TR203 = 0.37 g / l and Y203 = 0.45 g / l which is re-extracted in a phase ratio A / O equal to 1/5 with a solution containing P2O5 = 50% and HF = 7 X to obtain after centrifugation, a precipitate of fluorides of the abovementioned species and an organic phase containing less than 10 mg / l of each of the elements, which corresponds to a recovery rate greater than 98% for uranium and 96% for yttrium. and 95% for rare earths.

Claims (3)

 1. Process for the global recovery of uranium, rare earths, yttrium and thorium contained in an acidic aqueous phase according to any one of claims 1 to 18 of the main patent, characterized in that said acidic aqueous phase is obtained as an aqueous raffinate from extraction with insoluble or poorly water-soluble solvents of a crude wet phosphoric acid.  2. A process according to claim 1, characterized in that the aqueous raffinate is derived from the extraction of wet phosphoric acid by means of an aryl phosphate or an aliphatic alcohol substantially insoluble in water.  3. Method according to claim 1 or 2, characterized in that the aqueous raffinate has a P205 content of between 1 and 20, preferably close to 10% and an H2SO4 content of between 1 and 15%.