FI66823C - OVERFLOWER CONTAINING OIL ORGANIC PHOSPHORUS - Google Patents

Description

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Patent · och registerttyrelMn 'AiwMun uä ** Dodi utljkriftvn pvbUcvrad 31.00.04 (32) (33) (31) ^ rr> «tr nuoikwn — prior ** 20.07.79

France-Frankrike (FR) 7918781 (71) Rhöne-Poulenc Industries, 22, Avenue Montaigne, 75008 Paris,

France-France (FR) (72) Dominique Foraison, Thann, Alain Leveque, Paris, France-France (FR) (74) Berggren Oy Ab (54) Method for the recovery of uranium from impure phosphoric acid - Förfarande för ti11varatagning av uran ur Oren fosforsyra

The present invention relates to an improvement in the process for recovering uranium present in phosphoric acid, and more particularly to the recovery of uranium from phosphoric acid obtained by a wet process by liquid-liquid extraction.

It is known to recover uranium from aqueous solutions containing it in very low concentrations by separating it from other (potentially valuable) components of treated ores by a series of liquid-liquid extractions and chemical treatments designed to isolate uranium and recover it in the form of an oxide of high purity. , and which can be used as a source of nuclear fuel.

These methods are suitable for the recovery of minerals such as phosphate-bearing rocks, which otherwise provide phosphoric acid, or rocks of various origins, which contain more or less uranium, most often in the form of oxides. The process usually involves treating the ore with a strong and concentrated acid 26823, such as sulfuric acid, phosphoric acid, hydrochloric acid or nitric acid, to give an aqueous solution containing uranyl ions in a well-diluted state together with other ions as impurities, from which uranium is then recovered.

An example of a typical uranium recovery process, phosphoric acid obtained by the wet process, is described in U.S. Patent No. 3,711,591. This process is divided into two successive extraction cycles. In the first cycle of this process, 6 valence uranium in impure phosphoric acid is extracted by means of a first organic extraction phase with an inert solvent, a primary extraction agent - di- (2-ethylhexyl) -phosphoric acid - and a synergistic extraction agent - oxytocin valine, trioctylphosphine concentrations in the solvent. After the phases have been separated, the depleted uranium-depleted acid is returned to the phosphoric acid concentration unit, while the organic phase containing uranium (VI) is treated with a moderate feed rate of phosphoric acid containing metallic iron or iron (II) as a reducing agent. ) salt, which selectively re-extracts the uranium (IV) into the aqueous phase.

In the second cycle of this process, the aqueous solution of uranium-enriched and iron-containing phosphoric acid obtained above, after re-oxidation of the uranium to hexavalent, is continuously treated with a second organic extraction phase similar in nature to the first to obtain a uranium-containing organic phase and the depleted aqueous phase which is returned to the first cycle re-extraction unit or which is passed to the phosphoric acid concentration unit. The above organic phase is washed with water and then treated to recover uranium by precipitation to form a mixed carbonate (AUT) of uranium and ammonium. The resulting uranium-depleted organic phase is returned to the cycle.

The industrial application of this method requires that the concentration of iron in the aqueous phosphoric acid solution be relatively high, about 15-30 g per liter of aqueous solution, in order to

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66823 3 should be effectively re-extracted from the first extraction phase. Under these conditions, and despite the fact that the rate of iron extraction is very low in the organic phase of the second cycle, the uranium obtained contains considerable amounts of iron, up to 4-5% by weight. Therefore, there is a need for an improved method to obtain uranium that is virtually pure iron and on economically viable terms.

It is an object of the present invention to provide an improved process for recovering uranium in impure phosphoric acid by treating the crude acid in a first cycle with a first organic extraction phase comprising dialkylphosphoric acid, triallylphosphine oxide and an inert solvent, followed by the phases are separated; treating the above uranium-containing organic phase with an aqueous solution of phosphoric acid containing iron ions (II), whereby the uranium (IV) enters said aqueous phase, and then the phases are separated and the cycle-depleted organic phase is returned to the crude acid extraction unit; in the second cycle, the above aqueous phase after oxidation is treated with a second organic extraction phase containing an inert solvent, dialkylphosphoric acid and, if necessary, a synergistic extractant such as trialkylphosphine oxide, dibutylbutylphosphonate or ureaphase containing uranium from which uranium is recovered after washing with water before returning it to the second extraction phase cycle, the method being characterized in that before washing with water said uranium-containing organic extraction phase of the second cycle is treated with an aqueous sulfuric acid solution containing less than 40 ppm iron and said solution is obtained, possibly by dissolving concentrated sulfuric acid, which is practically free of iron, in a washing solution which is removed from the aqueous water of the uranium-containing organic extraction phase of the second cycle from the summer stage to recover uranium with a Fe / U weight ratio of less than 0.2%.

The invention is easier to understand with reference to the accompanying figure.

66823 4

Impure phosphoric acid is typically represented by crude phosphoric acid obtained by the wet process by dissolving phosphate-containing ore with sulfuric acid. After the gypsum has been filtered, the crude phosphoric acid solution is passed along line 1 and is usually subjected to the pretreatments known in step 2, such as stabilization, concentration, etc., from which it leaves in step 3 and its P205 concentration is usually 25-40% by weight and uranium content is usually 80-250 mg / liter and an iron content of about 3-10 g / liter. The above-mentioned acid feeds the extraction zone 4, which usually consists of several stirred-settling tanks, packed columns or pulse columns, either upstream or downstream in the first organic extraction stage, and enters through point 5 and circulates in a closed circuit. The ratio of crude acid to organic phase flow rates is usually between 0.5-5 and usually about 2. This first organic extraction step contains a well known inert organic solvent such as kerosene, the main extractant selected from a dialkylphosphoric acid, and a synergistic extractant. a trialkylphosphine oxide is selected. Di- (2-ethylhexyl) -phosphoric acid (HDEHP) and trioctylphosphine oxide (TOPO) are usually used. The HDEHP concentration of the extraction phase is usually between 0.1 M and 1.5 M, preferably about 0.5 M. The TOPO concentration of the phase is usually between 0.05 M and 0.5 M, preferably about 0.125 M.

After zone 4, the uranium-depleted phosphoric acid solution is recovered in step 6 and the uranium-containing organic phase in step 7. The organic stream 7 then feeds the uranium re-extraction zone 8, which usually consists of a stirred-tank tank, a pulse or packing column where it is treated upstream or downstream with an aqueous solution of phosphoric acid 9 containing iron ions (II) and the feed rate of stream 9 the speed of the current 7 is usually 0.015 to 0.1, preferably about 0.025. It has a P 2 O 4 content of usually 28 to 45% by weight, preferably about 35% by weight, and an iron ion (II) content of usually 10 to 40 g / liter, preferably about 25 g / liter. In a preferred variant, stream 9 is obtained by counting a portion of the depleted urine stream 6 from starting at 4; 66823 thiones II are obtained by dissolving metallic iron and are introduced from 10.

The uranium has been removed from zone 8 from the depleted organic phase at 11 and forms a stream 5 returned to the cycle, and from 12 leaves a stream of water enriched in uranium IV and containing iron ions. The stream 12 then feeds a region 13 where it is oxidized by an oxidizing agent such as hydrogen peroxide, air or a chemical such as a chlorate, or passed through an anode field of an electrolytic separation cell with a DC voltage and exiting at 14 and entering to the second cycle.

In the second cycle, stream 14 feeds an extraction zone 15 consisting of a series of stirred-settling tanks, together with stream 16 from the second organic extraction phase. This second organic phase usually contains an inert well-known solvent such as kerosene, a dialkylphosphoric acid such as HDEHP and, if necessary, a synergistic extractant, preferably TOPO. However, the molar concentrations of the main extractant and the synergistic extractant in the inert solvent can be clearly different from those in the organic phase of the first cycle. For example, the concentration of HDEHP is usually 0.1 M to 1 M, and preferably about 0.3 M, and the concentration of TOPO is 0.01 M to 0.5 M, and preferably about 0.075 M. The ratio of the velocity of stream 14 to the velocity of stream 16 varies usually between 0.1 and 5, and is preferably about 0.5.

A uranium-depleted aqueous phase leaves line 15 along line 17, which usually feeds the extraction zone 4 and the organic stream 18, which contains uranium. Stream 18 then feeds an iron purification zone 19, usually consisting of a series of stirred-settling tanks, where it is treated by stream 20, an aqueous solution of sulfuric acid containing less than 40 parts per million of iron. The sulfuric acid concentration of this solution is usually between 25% and 60%, mainly about 45%. In the first variant, this solution is obtained by diluting with water 95% sulfuric acid containing less than 40 parts per million of iron. In another preferred variant, 66823 6 shown in the accompanying figure, the incoming 98% concentrated sulfuric acid from point 21 is diluted to the desired concentration with a wash water solution 22 from wash zone 24, as will be described below. The speed ratio of current 20 to current 18 may range from 0.2 to 10 and is most preferably about 2.

Since the extraction of the iron contained in the organic solution 18 by means of the sulfuric acid stream 20 is relatively slow, it is considered best to work in such a way that the contact time of the two phases is sufficient. Raising the contact temperature, for example from 20 ° to 50 ° C, helps to improve the kinetics. But given that sulfuric acid also extracts more uranium at the same time, it is considered best to carry out the purification at approximately ambient temperature and apply the contact time of phases 18 and 20 to it. This contact time depends on the technology of the mixing and settling operations. In addition, the theoretical number of bases used in this washing step can vary greatly depending on the volume ratio of the phases. For example, when the aqueous phase / organic phase ratio is at a temperature of 2-30 ° C, about six bases are used and the mixing time is 10 min in each base.

The iron scavenger 19 emits an organic stream 23 from which the iron has been purified and an aqueous solution 25 of sulfuric acid and phosphoric acid, which contains iron and is optionally concentrated in an evaporator and forms an acid stream which is recycled to a phosphate-containing leaching unit. The purified organic stream 23 then feeds a scrubbing zone 24, usually consisting of a pool of stirred-settling tanks, where it is washed with water from point 28 to recover the? 2®5 'A 2 solution dissolved in the organic phase, which can be used for sulfuric acid 21 for dilution with cleaning agent 19, as described above, or stream 22 may be combined with streams 3 or 14.

The uranium-containing, purified and washed organic phase stream 29 also leaves area 24, from which uranium is recovered in a known manner. In a preferred embodiment of the invention, a stream 29 is treated in a two-stage region comprising a first stage 30 which is treated with a recycled aqueous solution stream 31 containing carbonate and ammonium ions and a second stage 32 which is treated with an aqueous ammonium carbonate solution. with a concentration preferably below the concentration of current 31. At step 33, the depleted organic stream is removed and taken back to cycle 15 and the aqueous AUT suspension 34, which is filtered and washed at 35, and the mother liquor is returned to cycle 31 after adjusting its carbonate and ammonium ion titer. The filtrate lump is roasted to give U 2 Og containing iron so that the weight ratio Fe / U is less than 0.5% and most often less than 0.2%.

The temperature throughout the process is not critical.

It is usually between 10-50 ° C and preferably between 20-50 ° C.

The process according to the invention makes it possible to obtain uranium oxide UgOg, which is very pure iron, by treating the sulfuric acid solution used in the second cycle of the process with an aqueous solution of sulfuric acid free of iron (less than 40 ppm iron) and possibly concentrated in the phosphate-containing rock solution. According to the invention, it is also possible to reuse in the process the recovery of an aqueous solution Ρ20 ^: η in the second cycle together with the above-mentioned sulfuric acid.

In the following, the invention will be illustrated by a non-limiting example with reference to the accompanying figure.

Example:

In step 3, crude pretreated phosphoric acid containing 30% P 2 Og, 110 mg / liter of uranium and 8 g / liter of iron is introduced into a battery formed by five mixing and settling tanks at a feed rate of 100 l / h. A stream 5, 50 1 / h of cycled organic phase with a concentration of 0.5 M HDEHP and 0.125 M TOPO is also introduced into the radiator 4. The outgoing water stream 6 is led to a concentration unit. Organic stream 7 contains 160 mg / liter of iron. This stream is fed to a uranium regeneration zone 8 comprising four stirred ponds, where it is treated countercurrently with a phosphoric acid stream 9 containing 30% P 2 O 3 and 25 g / liter of iron ions II at a flow rate of 1.35 l / B.

The depleted organic phase is returned to the cycle in the extraction unit and the leaving aqueous phase 12 contains 8 g / liter of uranium.

After oxidation with hydrogen peroxide, the aqueous phase 14 is treated in a four-stirred-tank coil with a kerosene phase with a concentration of 0.3 M HDEHP and 0.075 M TOPO at a flow rate of 2.02 l / h. The resulting organic phase 18 contains 170 mg / liter of iron and 5.3 g / liter of uranium. The outgoing aqueous phase 15 is fed to the extraction device 4 of the first cycle.

The organic phase 18 then feeds a battery of six stirred-in tanks, where it is treated countercurrently with an aqueous solution 20 combined with a stream of 98% (iron 4 to 40 ppm) sulfuric acid 21 at a rate of 1.35 l / h and a stream of water 22 leaving washing coil 24 and corresponds to a clean water flow 28 with a flow rate of 2.92 l / h. The water stream 25 from the radiator 19, if necessary concentrated, is led to a dissolution unit for phosphate-bearing rocks. The organic stream 23 from the radiator 19 contains 15 mg / liter of iron and 4.7 g / liter of uranium. This stream feeds a coil 24 of two mixing-settling tanks, where it is washed countercurrently with the water described above. The washed and purified organic stream 29 is then treated to recover uranium from a device 30, 32 with two levels, the first of which is fed with a recycled (NH 4) 2 00 2 M aqueous solution saturated with AUT and the second is fed ( NH3 ^ COg.0.5 M solution from page 33 leaves an organic stream which is returned to the cycle at position 15 and an aqueous suspension of AUT which is filtered, the mother liquor is adjusted and returned to the cycle.The filtrate clump is returned to give U ^ Ogia with a weight ratio of Fe / U is 0.2%.

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Claims (7)

A process for recovering uranium (VI) impure phosphorus acid by treating, in a first cycle, the impure acid with a first organic extraction phase containing a dialkylphosphoric acid, a trialkylphosphine oxide and an inert solvent, after which the phases are separated ; the uranium-containing organic phase is treated with an aqueous solution of phosphoric acid containing iron (II) ions, whereby uranium (IV) is extracted into the aqueous phase, then the phases are separated and the uranium-depleted organic phase is returned to the cycle for the crude phosphoric acid extraction unit; in a second cycle, the aforementioned aqueous phase, after oxidation, is treated with a second extraction phase containing an inert solvent, a dialkylphosphoric acid and, if necessary, a synergic extractant which may be selected from an oxide of trialkylphosphine, dibutylbutyl phosphonate or a trialkylphosphate, of the phases there is obtained a water phase depleted of uranium and an organic phase containing uranium, after which this organic phase is washed with water and treated for the recovery of uranium and this second extraction phase is characterized, characterized in that prior to washing with water of the second cycle urea-containing extraction phase, it is treated with an aqueous solution containing practically free sulfuric acid and which aqueous solution obtained by dissolving free iron in practically free concentrated sulfuric acid obtained from the washing step. with water of the uranium extraction phase, so that sulfuric acid The concentration of the solution in the treatment solution is in the range of 25-60%, preferably about 45%, whereby uranium is extracted with a weight ratio Fe / U below 0.5%, preferably below 0.2%. Process according to claim 1, characterized in that the aqueous solution of sulfuric acid used in the second cycle contains less than 40 ppm of iron. Process according to claim 1, characterized in that the organic cycle's second extraction phase contains an inert solvent, di- (2-ethylhexyl) -phosphoric acid and trioctylphosphine oxide. Process according to any of the preceding claims, characterized in that the aqueous solution of sulfuric acid extracted from the organic phase treatment step is optionally passed in concentrated form to the phosphate-containing mineral digestion unit. Process according to claim 3, characterized in that the treatment is carried out in a liquid-liquid extraction zone of 1-10, preferably 6 bottoms. Process according to Claim 3 or 4, characterized in that the ratio of the amounts of the streams in the aqueous solution of the iron-depleted sulfuric acid to the organic phase is in the range of 0.2-10, preferably about 2. Process according to any of the preceding claims, characterized in that the uranium is recovered from the purified organic phase of the second cycle and precipitates in the form of ammonium-uranium mixed carbonate using an aqueous solution containing ammonium and carbonate ions.