FR2460889A1 - METHOD FOR RECOVERING PHOSPHORUS AND URANIUM FROM PHOSPHATE ROCKS - Google Patents

Abstract

THE INVENTION RELATES TO THE RECOVERY OF PHOSPHORUS AND URANIUM FROM PHOSPHATE ROCKS. A PHOSPHATE ROCK IS ACIDIFIED WITH AQUEOUS NITRIC ACID TO PRODUCE AN AQUEOUS SOLUTION CONTAINING PHOSPHATES, CALCIUM AND URANIUM. THE AQUEOUS SOLUTION IS CONTACT WITH AN EXTRACTION SOLVENT FOR URANIUM, IN PARTICULAR A SOLVENT CONSISTING OF DI (2-ETHYLHEXYL) PHOSPHORIC ACID AND TRIPHENYLPHOSPHINE OXIDE IN AN ORGANIC SOLVENT WHICH IS NOT MISCIBLE WITH THE WATER. URANIUM IS COLLECTED FROM THE EXTRACTION SOLVENT.

Description

The present invention relates to the treatment of phosphate rocks

  and more particularly it relates to a new and improved process for

  recovery of phosphorus compounds and ura-

  from a phosphate rock.

  Phosphorus compounds are usually

  recovered from phosphate rock by acidification with sulfuric acid, which extracts the phosphorus compounds in the aqueous phase and produces a calcium sulphate residue. The acid is then converted into various forms of fertilizer products, such as diamonium phosphate and others.It is known that traces of uranium present in phosphate rock are an interesting raw material for fuel for power plants. nuclear reactor, and it has been proposed to extract this uranium from the aqueous phosphoric acid produced in the acidification, but the Applicant has found that such a process is not completely effective since uranium which is contained in the residue of solid calcium sulfate formed as a by-product is not extracted, and that the radioactivity of the residue

  calcium sulphate poses a problem for the environ-

ment.

  According to the present invention, provision is made

  a new and improved process for extracting and collecting

  phosphorus and uranium compounds from phosphate rock without loss of some of the potential uranium

  phosphate rock in a solid nhase.

  According to the present invention, the phosphate rock is acidified with aqueous nitric acid so as to produce an aqueous solution containing the phosphate, calcium and uranium present in the phosphate rock. This aqueous solution is then brought into contact with a selective extraction solvent for

  the uranium present in this aqueous solution, from

  that uranium is effectively separated from phosphorus

  phates and calcium. Uranium is then recovered at

  from the extraction solvent. The plaintiff found

  that by using a combination of acidification with nitric acid and extraction of uranium, it is

  possible to improve the recovery of uranium ini-

  tially present in phosphate rock.

  In particular, the phosphate rock

  which may be of any of the varieties

  conventionally used in the art of

  phosphates, which is used in the

  calcination or not, in a ground form, is acidified with nitric acid to produce water-soluble calcium nitrate and water-soluble phosphoric acid, this aqueous portion also comprising the uranium initially present

  in the rock. In general, this acidification is conducted

  at a temperature in the range of about 380 ° C. to about 9 ° C., with nitric acid having a

  from about 50% to about 70%. Neither acid

  It is generally used in an amount that is in excess of about 10 to about 20% of that needed to convert all of the calcium phosphate present in the rock to calcium nitrate. By

  following this use of nitric acid for the acid

  a major portion of the uranium, if not all, is in the aqueous phase in the state

  Hexavalent. Insoluble materials such as stones

  res, clays, etc., are separated from the aqueous acid solution by filtration, and the filter cake

  is washed with a small amount of water.

  According to the preferred embodiment -3-

  of the present invention, the uranium is then recovered.

  from the aqueous acid solution by a solvent

  extracting uranium in the hexavate state.

  slow. Consequently, in the case where any part of the uranium present in this aqueous acid solution is not in the hexavalent state, this uranium

  must be oxidized to the hexavalent state. In general

  Generally, this oxidation can be conveniently carried out by the addition of hydrogen peroxide, sodium chlorate, ammonium persulfate and similar oxidizing agents at temperatures between 380 ° C and 930 ° C. not

  with sufficient time, it is possible to use

  air to make the oxidation at 60-770C.

  The aqueous acid solution, which contains uranium in the hexavalent state, as well as calcium ions, is then contacted with a solvent

  extraction for the selective extraction of uranium.

  The Applicant has found that, surprisingly,

  the uranium extraction solvents used prior to

  in the art to extract uranium from acid solutions could be used effectively in the present invention, despite the

  the acid solution contains calcium ions.

  According to a preferred embodiment of the present invention, this extraction solvent consists of a mixture of an organic diluent which is immiscible with water,

  of a dialkyl phosphoric abide having at least 10 ato-

  carbon and an organophosphorus compound having the structural formula;

R2

R1 - P = O

  Wherein R 1, R 2 and R 3 are each selected from alkyl and alkoxy, preferably alkyl, groups having at least 10 carbon atoms. The compound

  preferred to three identical alkyl groups.

  Organic diluent is usually a

  hydrocarbon, with kerosene being particularly

  Brother. A particularly preferred solvent for

  the extraction of uranium consists of di (2-

  ethylhexyl) phosphoric acid and trioctylphosphine oxide

  in an organic diluent, in particular in ketone

Rosene.

  In the use of the extraction solvent, the ratio of the dialkylphosphoric acid to the organophosphorus compound is generally in the range of about 2 to 1 to about 6 to 1, and preferably about 3.6 to 1 at about 4.4 to 1. In general, both compounds are used in the organic diluent at a

  concentration of about 0.0375 M to 1.0 M-

about.

  Extraction can be carried out at times

  temperatures in the range of about 21 to about 710C, the

  temperature being preferably above 270C,

  typically around 27 to 49 ° C, because the phase separation is improved at these relatively high temperatures. Thus, at these high temperatures, there is a suitable viscosity of the liquid and moreover

  avoid crystallization of calcium nitrate.

  According to the preferred procedure,

  the extraction in several stages in the form

  countercurrent extraction with an organic phase

  continues. Using such a technique of ex-

  at the extraction temperature, the ratios between the phases and the contact times are chosen so as to obtain the extraction of the uranium in the

  organic phase, almost all the phosphates remain

  both in the raffinate phase. Thus, for example, the extraction can be carried out with ratios of the organic phase to the aqueous phase in the range of 2: 1 to 0.25: 1. Any small amounts of phosphate that are extracted into the organic phase can be efficiently recovered by the use of a water wash, which can be recycled to the water.

  washing of the filter cake resulting from the acidi-

nitric acid.

  The aqueous raffinate collected after the ex-

  Traction contains phosphorus and calcium compounds, which can be processed by methods known in the art to provide usable fertilizer products. The organic extract, including the extracted uranium, can be processed for the recovery of this uranium. Thus, for example, the uranium can be recovered from this organic extract by contacting the organic extract with an aqueous solution

  ammonium carbonate, to obtain the complex

  ble uranyltricarbonate ammonium in the aqueous phase.

  The solubility of uranium varies inversely with the concentration of ammonium salt and results

  that by using an excess of ammonium salt in the

  recovery, we can obtain by abandonment

  yellow crystals of ammonium uranyltricarbonate.

  These crystals can be collected by filtration and

  then decomposed by calcination to give a

  U308 duit of relatively superior quality.

  Using ammonium carbonate

  (Ammonium carbonate here refers generically

  carbonate and / or bicarbonate) to recover the uranium from the organic extraction solvent,

  in general only about 1.0 M of carbonate of ammonium

  monium to precipitate ammonium uranyltricarbonate (AUT), but about 1.5 M ammonium carbonate is preferred at about 2.5 M. The ratio (in volume) of the aqueous solution to organic solvents is included

  preferably between about 0.5 and about 5.

  The recovered AUT can be calcined in an oven at temperatures of about 3500C to about 9000C for recovery of uranium oxide. If we

  uses a reducing atmosphere, uranium is

  picked in the form of U02 and if we use a

  oxidizing atmosphere, such as oxygen, we obtain U308.

  The Applicant has found that by proceeding

  according to the present invention, it is possible to recover

  at least 80% of all uranium originally

  in phosphate rock, and in most

  the recovery of uranium is 85% or more

pool.

  The invention will now be further described with reference to an embodiment illustrated in the accompanying drawing, wherein the single figure is a simplified block diagram of one embodiment of the invention.

present invention.

  Wash liquor, containing all phosphates and dissolved uranium compounds, is recycled

  digestion by line 19.

  The acid solution, containing nitrate

  of calcium, phosphoric acid, nitric acid,

  that, as well as compounds of dissolved uranium, primarily

  usually in the hexavalent state, may be subjected to oxidation in line 22 by oxygen or another oxidant introduced via line 23, if

  necessary, so as to transform all other

  put uranium in the hexagonal state.

  worth. The aqueous solution in line 24 is then introduced into the uranium extraction zone, schematically indicated by the reference in which the aqueous solution is brought into contact.

  with a solvent for extracting uranium, of the type de-

  written above. As described above, this extract

  may be carried out in one or more stages, the extraction being preferably carried out in

  a multiplicity of stages by countercurrent extraction

rant.

  An aqueous raffinate containing

  soluble poses of phosphorus and Pu calcium, is evacuated

  of the extraction zone by Line 26.

  An organic extract containing

  dissolved uranium removed from the extractive area.

  25 through line 27, is introduced into a washing zone with water, schematically indicated in FIG.

  28, in which the extract is washed with water, introduced

  through line 29, for the recovery of any phosphorus compounds that may have been dissolved in

  the organic phase. This water, recovered in the cana-

  after the washing operation, can be used

  2o then used to wash solids, as

of writing below.

  The extract collected in line 32 after the washing is then introduced into the uranium re-generation zone, indicated diagrammatically at 33, in which the uranium is recovered from the extract using an aqueous solution of

  ammonium carbonate, as described below. As-

  above, ammonium carbonate is used in such a way that uranium is

  the form of solid crystals of AUT.

  AUT crystallized in an air phase is collected from zone 33 through the pipeline

  34 for introduction into a filtration zone, indi-

  diagrammatically at 35. The organic solvent of

  traction is collected from zone 33 by the -8-

  pipeline 36 for the extraction of uranium from the ef-

  aqueous fluent acidification, as described above.

  The TUE crystals collected at

  from the filtration zone 35 in the pipe 39, are introduced into a calcination zone, indicated diagrammatically at 41, to calcine AUT in U 308

  which is collected by Line 42.

  The filtrate collected from the filtration zone 35 via line 43 is mixed

  with ammonia and carbon dioxide

  point arriving through the pipes 44 and 45, respec-

  and recycled to zone 33 for urethane recovery. The invention will now be described

  again by the following nonlimiting examples.

Example 1

  1000 g of

  Mobil Florida Phosphate Rock (Tables 1 and 2) contains

  32.35% P205, 47.51% CaO, 1.18% Fe2O3, 5.59% SiO2, 3.45% F, and 130μm Uranium. This phosphate rock is reacted with 2000 g of nitric acid, a titre of 61.4% by weight. This amount of acid represents an excess of 20% over what is needed to transform all the calcium

  present in the rock in calcium nitrate. The reaction

  tion is completed in approximately half an hour, during which

  temperature rises from the ambient temperature

  to about 520C. The product is then filtered; the insoluble materials are washed with two portions of water,

  150 g each. A combined liquor of

  viron 3015 g (digestion acid plus washing water).

  The residue of 208 g is discharged to the waste.

  The 3015 g of liquor thus obtained

  contain 10.6% by weight of P205, 15.5% of CaO and 44 ppm of uranium. There is also in the liquor a

24'60889

-9

  certain amount of nitrate, iron and aluminum.

  (See Table 3). Table 4 shows the composition

  sition of insoluble solids. Recoveries

  P205, CaO and uranium are 98%, 97% and 97.7%, respectively, in the acid phase.

nitric acid.

  According to the scheme presented in Perry's

  Chemical Engineers' Handbook, pages 14 to 43,

  kills simulated countercurrent extraction so

  discontinuous, multi-stage, using a-

  di (2-ethylhexyl) phosphoric acid (D2EHPA, 0.5M) and trioctylphosphine oxide (TOPO, 0.125M) in kerosene (AMSCO-460) to collect uranium at

  from the mixture of phosphoric acid and calcium nitrate

  nitric acid. The solvent is placed first in a settling funnel. The aqueous acid mixture with 44 ppm of uranium is obtained from the digestion described in Example 1. It is slowly introduced into

  the solvent phase. The relationship between the phases of

  The organic and acid content is about 0.5 to 1.0 (by volume). The funnel is shaken at room temperature for about 10 minutes. After

  sedimentation, the phases are separated, the

  finat and extract with regard to their uranium contents by a colorimetric method. Raffinat and

  the extract then enter the next stage to ex-

  extra traction. After 5 floors, we collected

93% of the uranium.

-1O-

Table I

  Mobil Florida phosphate rock composition Moisture content 0.8% after drying Phosphoric anhydride (P205) Iron oxide (Fe2O3) Aluminum oxide (A1203) Calcium oxide (CaO) Magnesium oxide MgO) Fluorine Silicon (SiO2) ) Sodium oxide (Na2O) Potassium oxide (K20) Sulphite (SO3) Carbon dioxide (C02) Organic carbon Arsenious anhydride (As203) Uranium (U308)

Table 2

  Particle size analysis of phosphate rock% by weight collected on sieve% by weight 32.35 1.18 1.05 47.51 0.42 3.45, 59 0.56 0.14 1.08 2.86 0, 05 0.001 0.013 sieve nO (opening of mesh, mm)

+ 35 (0.50) 0.20

+60 (0.250) 1.76

+70 (0.210) 1.62

+ 100 (0.149) 6.32

+200 (0.074) 44.12

+ 325 (0.044) 33.78

  Tank 12.20 Total 100.00% by weight -11-

Table 3

  Miobil phosphate rock digestion liquor

Table 4

  Main Residual Solids of Rock Phosphate Mobil Amount of Residue 208 g The present invention is particularly advantageous because it allows efficient recovery of phosphorus present in phosphate rock, while

  allowing a high recovery of uranium present.

  Thus, according to the present invention, it is possible to recover at least 80%, and very generally at least

  % of the uranium present in the phosphate rock.

  This is an improvement over the prior art

  in which uranium recoveries were lower as a result of the loss of uranium

  in the by-product calcium sulfate. The request

  found that these high levels of recovery from% to weight

AT _..

  Phosphoric anhydride (P205) 10.58 Calcium oxide (CaO) 15.47 Iron oxide (Fe203) 0.29 Aluminum oxide (Al203) 0.26 Nitrate (NTO) 16.93 Fluor 0.94 Uranium (U308) ) 44 ppm% by weight Phosphoric anhydride (P205) 3.04 Calcium oxide (CaO) 6.76 Uranium (U308) 15 ppM -12- Uranium can be obtained despite the presence of calcium ions (calcium nitrate ) that would have been expected to interfere with the recovery of uranium. -13-

Claims (13)

R E V E N D I C A T I 0 N S   1. A process for recovering phosphorus   and uranium in phosphate rock, which is   in that the phosphate rock is acidified with aqueous nitric acid so as to produce an aqueous solution of phosphoric acid, nitrate of   calcium and uranium in phosphate rock   ted; the uranium is extracted from the aqueous solution by means of an extraction solvent comprising a water-immiscible organic diluent, a dialkylphosphoric acid before at least 10 carbon atoms and an organic phosphorus compound having the structural formula : R2 R1 - P 0   R 3 in which R 1, R 2 and R 3 are each selected from alkyl and alkoxy groups, said organic phosphorus compound having at least 10 carbon atoms, the acid   phosphoric dialkyl and the organic phosphorus compound   phore being dissolved in the organic diluent   target with water; and we collect the uranium from extraction solvent.   2. A process according to claim 1, characterized in that the title of the nitric acid is between 50% and 70%.   3. A method according to claim 2, characterized in that the nitric acid is used in an amount in excess of 10 to 20% approximately compared to that required to transbreat any   the calcium present in the rock in calcium nitrate.   -14- 4. A process according to claim 1, characterized in that the ratio of dialkylphosphoric acid to organic phosphorus compound is between 2: 1 and 6: 1.   5. A process according to claim 4,   characterized by conducting the extraction at a time more than 27 C.   6. A process according to claim 5, characterized in that the uranium is collected from   extraction solvent in the form of uranyltricarb-   ammonium carbonate by contact with ammonium carbonate aqueous monium.   7. A process according to claim 1,   characterized in that the extraction solvent is   of di (2-ethylhexyl) phosphoric acid and oxide   of trioctylphosphine dissolved in kerosene.   8. A process according to claim 7,   characterized in that at least 85% of the ranium present in the rock.   9. A process according to claim 7, characterized in that the title of the nitric acid is between 50% and 70%.   10. A process according to claim 9,   characterized in that the ratio of the di (2-   ethylhexyl) phosphoric acid trioctylphosphine oxide is between 2: 1 and 6: 1.   11. A process according to claim 10,   characterized by conducting the extraction at a time more than 27 C.   12. A process according to claim 11, characterized in that the uranium is collected from the extraction solvent in the form of ammonium uranyltricarbonate by contact with aqueous ammonium carbonate. 13. A method according to claim 12, characterized in that at least 85% of uranium in the rock.