FR2461681A1 - Extn. of uranium from wet process phosphoric acid - washes organic uranium phase with aq. sulphuric acid to give uranium with a low iron content - Google Patents

Abstract

Extn. of uranium (VI) from impure phosphoric acid comprises: (a) a first cycle to extract impure acid with an organic phase contg. a dialkylphosphoric acid and trialkylphosphine oxide in inert dilute diluent followed by phase sepn.; treating U-charged organic phase with an aq. soln. of phosphoric acid contg. Fe (II) ions; to extract the uranium (IV) into aq. phase, followed by phase sepn. of the phases; (c) recycling of exhausted organic phase to extract the impure acid and (d) in a second cycle oxidn. of aq. phase; (e) extn. of this oxidised aq. phase with a second extn. medium contg. inert diluent, a dialkylphosphoric acid and opt. synergistic extn. agent, chosen from trialkylphosphine oxides, dibutyl-butyl- phosphonate and trialkylphosphates, followed by phase sepn. to give aq. phase exhausted of uranium and U-charged organic phase, (f) washing the organic phase with water, recovery of the uranium and recycling of organic extractive phase. An improvement is that prior to the washing of the second uranium contg. extractive phase with water in (f), it is treated with aq. sulphuric acid soln, which is free of iron; this solution is obtd. by diluting iron-free concd. sulphuric acid with the aq. soln. obtd. from the water washing-stage (f) to give a 25-60%, pref. about 45% sulphuric acid soln.. After treatment with the sulphuric acid solution uranium is recovered with a Fe/U wt. ratio of less than 0.5%, pref. less than 0.2%.

Description

PERIECTION TO THE PROCESS OF RECOVERING URANIUM FROM A
ACID 1 SPIIOR1QUE IMPUR.

 The present invention relates to an improved process for recovering uranium contained in a phosphoric acid and more particularly relates to the recovery of uranium from a phosphoric acid obtained by the wet process by means of liquid-liquid extractions.

 It is known to recover the uranium from aqueous solutions containing it at low concentrations, by separating it from the other species (where appropriate recoverable) constituting the treated ores, by means of a set of liquid-liquid extractions and treatments. Chemicals for the purpose of isolating uranium and recovering it in the form of U308 oxide of high purity, usable as a source of nuclear fuel. These methods apply to recovery. ores such as pllosphated rocks, otherwise supplying phosphoric acid or ores of various origins with a higher or lower uranium content, most often present in the form of oxides.The process generally comprises the treatment of the ore with using a strong and concentrated acid such as sulfuric, phosphoric, hydrochloric, nitric acids, to provide an aqueous solution containing uranyl ions in a very dilute state together with other contaminating ions, hence the we recover the uranium.

A typical example of a method for recovering uranium contained in wet phosphoric acids is described in US Patent 3,711,591.
This process is broken down into two successive extraction cycles.

In the first cycle of this process, uranium at valence 6 contained in impure phosphoric acid is extracted by means of a first extractive organic phase comprising an inert diluent, a primary extractant - di (2-ethylhexyl) acid. ) phosphoric acid - and a synergistic extractant - trioctylphosphine oxide, at selected concentrations in the diluent. After separation of the phases, the impure acid depleted in uranium is returned to the unit of phosphoric concentration, while the organic phase loaded with uranium (VI) is treated with an aqueous solution of phosphoric acid at a moderate flow rate. containing a reducing agent based on.

metal iron or iron (II) salt, whereby the uraIii'lm (1V) is selectively re-extracted into the aqueous phase.

 In the second cycle of this process, the aqueous solution of phosphoric acid rich in uranium and iron obtained above, after reoxidation of uranium at the G level, is treated continuously by means of a second organic phase extractive from same nature as the first one, by which we obtain an organic phase loaded with uranium (VI) and an exhausted aqueous phase which is recycled to the reextraction of the first cycle or which is sent to the unit. The preceding organic phase is washed with water and then treated to recover the uranium by precipitation in the form of mixed carbonate of uranium and ammonium (AUT). The resulting organic phase, depleted in uranium is recycled.

 The industrial exploitation of this process implies that, in order to effectively extract the uranium from the first extractive phase, the concentration of iron in the aqueous phosphoric acid solution is relatively high, of the order of 15 to 30 g / liter of aqueous solution. Under these conditions, and despite very little extraction of iron by the organic phase of the second cycle, the uranium obtained contains imported quantities of iron up to 4 to 5% by weight. There is therefore a need for an improved process for obtaining sub-iron-free uranium under economically viable conditions.

 The object of the present invention is to provide an improved process for recovering the uranium contained in an impure phosphoric acid comprising in a first cycle the treatment of the impure acid by means of a first extractive organic phase comprising a dialkylphosphoric acid, a trialkylphosphine oxide and an inert diluent, followed by phase separation; the treatment of the preceding organic phase loaded with uranium by means of an aqueous solution of phosphoric acid containing iron (II) ions, whereby uranium (IV) is extracted in said aqueous phase, and then the separation phases and recycling of the spent organic phase to the extraction of the impure acid; in a second cycle, the treatment of the preceding aqueous phase after oxidation by means of a second extractive organic phase comprising an inert diluent, a dialkylphosphoric acid and, where appropriate, a synergistic extraction agent chosen from a trialkylphosphine oxide, dibutyl butyl phosphonate and a trialkyl phosphate, whereby a depleted aqueous phase of uranium and a uranium-laden organic phase are recovered after separation of the phases, from which the uranium is recovered after washing with water, and before the recycling of this second extractive phase, characterized in that prior to washing with the preceding water, said extractive organic phase of the second cycle charged with uranium is treated with an aqueous solution containing sulfuric acid containing less than 40 ppm iron, said solution being, if appropriate, obtained by dissolving concentrated sulfuric acid substantially free of iron r in the aqueous washing solution leaving the water washing stage of the extractive organic phase of the second uranium-loaded cycle, whereby the uranium is recovered in a Fe / U weight ratio of less than 0 , 2%.

The invention will be better understood with reference to the attached figure,
The impure phosphoric acid is typically represented by a crude wet phosphoric acid obtained by phosphate rock attack with sulfuric acid. After filtration of the gypsum, the crude phosphoric juice, introduced through the line (1) usually undergoes in (2) known pretreatments of stabilization, concentration, etc ... from where it comes out in (3), at a weight concentration in P205 usually between 25 and 40%, the uranium content is usually between 80 and 250 mg / liter and the iron content of the order of 3 to 10 g / liter. The previous acid feeds a zone of extraction (4) generally consisting of a battery of mixer-settlers, a packed or pulsed column, against the current or cocurrent of a first organic phase of extraction entering (5) and circulating in a closed loop. The ratio of the flow rate of the impure acid to that of the organic phase is generally between 0.5 and 5 and is generally close to 2. This first organic extraction phase comprises a well-known inert organic diluent such as kerosene, a main extractant selected from di (alkyl) phosphoric acids and a synergistic extractant selected from trialkylphosphine oxides. usually it is preferred to use di (2-ethylhexyl) phosphoric acid (HDEIP) and trioctylphosphine oxide (TOPO). The concentration of the extractive phase in IIDEHP is in general between 0.1 and 1.5 M, preferably close to 0.5 M. The concentration of the phase in
TOPO is in general between 0.05 M and 0.5 M, preferably close to 0.125 M.

 At the outlet of the zone (4), a solution of phosphoric acid depleted in uranium is recovered in (6) and (7) an organic phase loaded with uranitim (VI).

The organic stream (7) then feeds a uranium stripping zone (o) usually comprising a battery of mixer-settlers, a pulsed column or packed where it is treated against the current or cocurrent with an aqueous solution of phosphoric acid (9) containing iron ions (II), the ratio of the flow rate of the stream (9) to that of the stream (7) being generally between 0.015 and 0.10, preferably close to 0.025. Its weight content in P 0 is in general between 28 and
45 eo, preferably close to 35% and the iron (II) ion content is in general between 10 and 40 g / liter, preferably close to 25 g / liter. In a preferred variant, the current (9) is obtained by withdrawing a portion of the spent uranium depleted acid stream (6) leaving the zone (4), the iron ions II being obtainable by dissolution of iron metal introduced by (10).

 From zone (8) comes out in (11) a depleted organic phase of uranium which constitutes the recycled stream (5) and in (12) an aqueous stream enriched with uranium IV and containing iron ions.

The stream (12) then feeds a zone (13) where it is oxidized by means of an oxidizing agent such as hydrogen peroxide, air or a chemical agent such as a chlorate, or by passing through the compartment anode of a DC voltage separator electrolytic cell, from which it leaves at (14) to enter the second cycle.

In the second cycle, the stream (14) feeds an extraction zone (15) consisting of a battery of decanting mixers, together with the stream (16) of the second organic extraction phase. This second organic phase usually comprises a well known inert diluent such as kerosene, a di-alkylphosphoric acid such as HDEHP and, where appropriate, a synergistic extraction agent, preferably
TOPO. However, the molar concentrations of the main extractant and the synergistic extractant in the inert diluent can be substantially different from those of the organic phase of the first cycle. Thus, the concentration of IDEHP is usually between 0 and , 1 M and 1 X, preferably close to 0.3 M and that the concentration of TOPO is between 0.01 M and 0.5 M, preferably close to 0.075 M. The ratio of the current flow (read ) the current (16) usually varies between 0.1 and 5, preferably it is close to 0.5.

From the zone (15) comes out in (17) a depleted aqueous uranium phase which generally feeds the extraction zone (4), and an organic stream (18) charged with uranium. The stream (18) then feeds an iron purification zone (19) generally constituted by a battery of mixer-settlers, where it is treated with the stream (20) consisting of an aqueous solution of sulfuric acid containing less 40 ppm iron.

The sulfuric concentration of this solution is usually between X and 60%, preferably it is close to 45%. In a first variant, this solution is obtained by dilution with water of 95% sulfuric acid containing less than 40 ppm of iron. In another preferred embodiment as shown in the accompanying figure, the concentrated 98 C sulfuric acid entering at (21) is diluted to the required concentration by means of the aqueous wash solution (22) from the wash zone ( 24) as will be explained below. The ratio of the flow rates of the current (20) to the current (18) can vary between 0.2 and 10 and is preferably close to 2.

 The extraction of the iron contained in the organic solution (18) by the sulfuric acid stream (20) being relatively slow, it will be preferable to operate with a sufficient contact time of the two aforementioned phases. An increase in the contact time, for example from 20 to 50 OC, makes it possible to improve this kinetics. However, in view of the fact that uranium coextracts with sulfuric acid becomes more important, it is preferable to carry out the purification at a temperature close to ambient and with a suitable contract time of the phases (18) and (20). ). This time of contract depends on the mixing-settling technology. Similarly, the number of theoretical stages to be used in this lavaSe step can vary in large proportions according to the volume ratio of the s phases. For example, for an aqueous phase / organic phase ratio of 2 to 30 ° C., about six stages are used with a mixing time of 10 minutes at each stage.

 From the iron purification zone (19), an iron-purified organic stream (23) and an iron-enriched aqueous sulfuric and phosphoric solution (25) are produced, which, if appropriate, after concentration in an evaporator, provides an acidic stream, which for reasons of profitability of the process is reintroduced at the stage of the attack of phosphatic rocks. The purified organic stream (23) then feeds a washing zone (24) consisting generally of a battery of mixer-settlers or it is washed with water introduced by (28), whereby the dissolved P205 is recovered in the water. organic phase.

From the zone (24) comes the aqueous wash solution (a2) which can be used to dilute the sulfuric acid (21) used in the purification zone (39) as just described, or the current (22). ) can be added to currents (3) or (14)
From zone (24) there is also a stream (29) of washed purified and organic phase loaded with uranium from which uranium is recovered according to known means. In a preferred embodiment of the invention, it is treated the stream (29) in a two-stage zone comprising in the first stage (30) the treatment by means of a recycled stream (31) of aqueous solution containing carbonate and ammonium ions and in the second stage (32) the treatment by means of an aqueous solution of ammonium carbonate, the concentration of which is preferably lower than that of the stream (31).

It comes out in (33) a depleted uranium organic stream which is recycled to the zone (15) and an aqueous suspension of AUT (34) which is filtered and washed in (35), the mother water being recycled on (31) after adjusting its title to ionscarbonate and ammonium. The filter cake is then calcined to provide U308 containing iron in a weight ratio
Fe / u less than 0.5 5 most often less than 0.2, b.

 The temperature during the entire process is not critical. Usually it is between 10 and 50 OC, preferably between 20 and 50 OC.

 The process of the invention makes it possible to obtain a uranium oxide U308 of high iron purity by means of a treatment with an aqueous solution of iron-free sulfuric acid (less than 40 ppm of iron) during the second cycle of the process, the sulfuric wash solution being recovered for the process, if appropriate after coentration, in the phosphatic rock attack step. In addition it is possible according to the invention to reuse for the process the aqueous P205 recovery solution in the second cycle together with the above sulfuric acid.

 The invention is illustrated below by means of a non-limiting example with reference to the attached figure.

Example
Introduced by (3) a pretreated impure phosphoric acid containing 90% P205, 110 mg / liter uranium and 8 g / I iron in a battery of 5 mixer-settlers at a rate of 100 liters / hour. Also introduced into the battery (4), a stream (5) of 50 liters / hour of a recycled organic phase of concentration 0.5 M IIDEIS and 0.125 M TOPO. The leaving aqueous stream (6) is sent to the concentration. The organic stream (7) contains 160 mg / l of iron. This stream is sent to the uranium regeneration zone (8) comprising four mixer-settlers where it is treated against the current by a stream (9) of phosphoric acid at 30 eo of P 2 O 5 and containing 25 g / l of iron (II) ions at a flow rate of 1 to 35 liter / hour.

 The exhausted organic phase is recycled to the extraction and the outgoing aqueous phase (12) contains 8 g / l of uranium.

After oxidation with hydrogen peroxide, the aqueous phase (14) is treated in a battery of 4 mixer-settlers with a kerosene phase of concentration 0.3 M HDEHP and 0.075M
TOPO at a rate of .02 liter / hour. The resulting organic phase (18) contains 170 mg / l iron and 5.3 g / l uranium. The outgoing aqueous phase (15) is sent to the extractor (4) of the first cycle.

The organic phase (18) then feeds a battery of six mixer-settlers where it is treated countercurrent with an aqueous solution (20) which is the union of the current (21) of 98% sulfuric acid (iron 4). 40 ppm) at a rate of 1.35 liters / hour and the aqueous stream (22) leaving the washing battery (24) and corresponding to the stream of pure water (28) whose flow rate is 2.92 liter / hour. The aqueous stream (25) leaving the battery (19), where appropriate after concentration, is returned to the phosphate rock attack. The organic stream (23) exiting the battery (19) contains 15 mg / l of iron and 4.7 g / liter of uranium. This dying person feeds the battery (24) of two mixer-settlers where it is washed against the current with water as just described. The purified and washed organic stream (29) is then treated to recover the uranium in a two-stage apparatus (30, 32), the first of which is supplied with an aqueous solution of recycle (NH4) 2 CO3.2M. saturated in AUT, the second being fed with a solution of (NH4) 2 CO3.0.5M. At (33) there is an organic stream which is recycled at (15) and an aqueous suspension of AUT which is filtered, the mother water being adjusted and recycled. By calcination of the cake, we obtain
U3O8 with a Fe / U weight ratio of 0.2%.

Claims (9)

1) In a process for recovering uranium (VI) contained in an impure phosphoric acid comprising in a first cycle the treatment of impure acid by means of a first extractive organic layer comprising a dialkylphosphoric acid, a trialkylphosphine oxide and an inert diluent and then phase separation, treating the previous organic phase loaded with uranium with an aqueous solution of phosphoric acid containing iron (II) ions, whereby uranium is extracted ( IV) in said aqueous phase, followed by phase separation and recycling of the spent organic phase to the extraction of the impure acid; in a second cycle, the treatment of the preceding aqueous phase, after oxidation, by means of a second extractive phase comprising an inert diluent, a dialkylphosphoric acid and, where appropriate, a synergistic extraction agent chosen from a trialkylphosphine oxide, the dibutyl butyl phosphonate and a trialkyl phosphate, whereby a depleted aqueous phase of uranium and an organic phase loaded with uranium are obtained after separation of the phases, from which the uranium is recovered after washing. to the water and before the recycling of this second extractive phase, perfected further in that, prior to washing with water the extractive phase of the second cycle loaded with uranium, the latter is treated with an aqueous solution containing sulfuric acid substantially free of iron, said solution being obtained by dissolving concentrated sulfuric acid substantially free of iron in the solution washing water leaving the water washing step of the extractive organic phase loaded with uranium, whereby the uranium is recovered in a weight ratio Fe / U less than 0.5 5 preferably lower at 0.2, 2) Process according to claim i characterized in that the aqueous solution of sulfuric acid used in the second cycle contains less than 40 ppm of iron. 3) Process according to claim 1 characterized in that the extractive organic phase of the second ring comprises an inert diluent, di- (2 ethylhexyl) phosphoric acid and trioctylphosphine oxide. 4) Process according to one of the preceding claims characterized in that the aqueous sulfuric acid solution leaving the treatment of the organic phase is returned, if appropriate after concentration, to the phosphate attack stage of phosphates . 5) Process according to claim 1 or 2 characterized in that the sulfuric acid concentration of the treatment solution of the organic phase is between 25 ', o' and 60, preferably close to 45,. 6) Process according to claim 3 characterized in that the treatment is carried out in a liquid-liquid contact zone comprising from 1 to 10 stages, preferably 6 stages. 7) Method according to one of claims 3 or 4 characterized in that the ratio of the flow rate of the aqueous solution of sulfuric acid free of iron or flow of the organic phase is between 0.2 and 10, preferably close to 2. 8) Method according to one of the preceding claims, characterized in that the uranium is recovered from the purified organic phase of the second cycle for precipitation of AUT by means of an aqueous solution containing ammonium and carbonate ions. 9) Application method according to one of the preceding claims for the recovery of uranium contained in a phosphoric acid obtained by the wet process.