FR2722701A1 - Molybdenum recovery from impure calcium molybdate - Google Patents

Abstract

Process for recovering the molybdenum present in impure Ca molybdate obtd. during the processing of uraniferous minerals comprises: (a) dissolving the Ca molybdate in aq. H2SO4 soln. having a H2SO4 concn. of at least 2 mol/l; (b) contacting the aq. soln. from (a) with an organic solvent contg. a dialkylphosphoric acid (I); and (c) separating the organic solvent contg. the extracted Mo from the aq. soln.

Description

PROCESS FOR RECOVERY OF MOLYBDENE FROM

  IMPURED CALCIUM MOLYBDATE FROM THE TREATMENT OF

URANIFE ORES.

DESCRIPTION

  -a presen: e -ivention relates to a process of recpera: - s of molybdenum from molyvbdae e ie ca.imr ssu of the treatment of

uranial minerals.

  In 'i-dustr-e of uranium, paricu le- a2s les - ^ hydrometallurgical edés, we crcidut es o' '_ _ carbonate containing uranium e_ meaux universes: es that molybdenum, that

  es. need to separate uranium.

  This seara-icn c can be performed after acdif -ca.cn because pr.c-- _a2ton with lime, which cui_ A 'a forma: a' _n precipeity of molybdate of _2lcim turL, ... n ...: enan e- articular impurities zeú! es that _i, P e / u Y ,, capable of forming with _e molydene es heerocolvanionic type complexes Po.ur r.ccéer The molybdenum of this _-ecic: té, _r ce. uiss ^ "dre it in a su_ uric solution e: ex: -__- e ensui molybdenum present in this s ......, especially in the form of é ..... r. olvanc ns el, - d'i s ccolyanions, by means of a

solvan. org-an-ze a-rspi.

  he -sc ". in: FR-A-2 691 373 describes a crocede of rdcua i i umolybdenum using these

  % after -ei ssEO lt'e of solvent extraction.

  According to this oc_ in :, -n: issut -first the molybdate of sa! Ci ls dcacma-s _ne aqueous solution of sufurcue acid has approx. Rs- .. mo, / 1, or a pH close to 2 after dissc! uion, -us, - extracts the molybdenum dissolved in a sc _--. a-uese in an organic solvent c = mprenant a -rem-e er- -cac: an consisting of a dialkvy- hoshor icue -el as di- (2ethylhexyl) phosphcrique acid and a second extractant chosen pcarmi es salts of tertiary amines, amine onix-c salts, tributyl phosphate and hosphn.e oxides. This croedé? Resente the disadvantage of requiring the em! Oi of u. organic solvent comprising two bottles of ex: rac - a.ts to reach yields

ex: rac ^ nc sanis asa.s.

  _n e e =, e. reason for the presence of deerotic species c. - vs-! in the aqcuous solution e isscil__. We first carry out a transfer of h: rcc: v- 7years of molybdenum in the organic phase at the cen _ s econd extracting in the form of anion cu acie se 'I the nature of the second extracrant, ruls n - ans-crme the protonated form of the ccmpiexe polyu. _ éanrc-.i cue of molybdenum in the? hase cr a .... in complex (MoO22 +) acid _ a1 kylphcsnhor: e au.oyen the first extractant, by soaking the aci e c-osnhoCrizue, vanadic acid and / or rh-csilicic acid as well as water in

has azure phase.

  es cccr.en: s 'JS-A-3 751 555 and US-A-4 275 039 above: the use of an organic solvent ccmren-n- those:', - es of extractants, such as c? -atvlexy -.csohoric acid and t ribu y! e phosphate, to recover the molybdenum from

rolybdite or this sch-eelte.

  -a 2 r-sece: .vention has precisely for cbjet a u r _ _éé e -'_-- erazon of molybdenum from molybda: e of this c .. imur, by dissolution, then extrac: we cans _. so.vant organic, which makes it possible to avoid the f-rma-cc of ccm. heteropolyanioniclexes between moiysdene e: impurities such as silcimc, hc..s_: cre e, / u vanadium, present in the starting calcium molybdate, and thereby simplifying the molybdenum extraction process, while

  obtaining very good extraction yields.

  According to the invention, the process is characterized in that it comprises the following stages: a) dissolving calcium molybdate in an aqueous solution of sulfuric acid having a sulfuric acid concentration of at least 2 mol / l, b ) bringing the aqueous dissolution solution from step a) into contact with an organic solvent comprising a dialkylphosphoric acid, and c) separating the

  organic solvent having extracted molybdenum.

  In this process, the use for the dissolution of calcium molybdate of an aqueous solution comprising at least 2 mol / l of sulfuric acid, for example 2 to 4 mol / l of sulfuric acid, makes it possible to avoid the formation heteropolymolybdic species in the dissolution solution. Therefore, it is no longer necessary to then use for the extraction of molybdenum a couple of extractants to ensure, on the one hand, the transfer of heteropolymolybdic species into the solvent and, on the other hand, their transformation

  complex (MoO22 +) - dialkylphosphoric acid.

  Indeed, it has been discovered according to the present invention that the domain of existence in aqueous solution of heteropolymolybdic species lies in the pH range from 1 to 3, which corresponds to sulfuric acid concentrations of 0.2 to 2 mol / l, and that the degradation of the species formed by subsequent acidification of the solution was very slow. Also, by carrying out according to the present invention the dissolution of calcium molybdate with a sulfuric acid concentration greater than 2 mol / 1, the formation of these species is avoided.

bothersome heteropolymolybdics.

  After dissolution of the calcium molybdate in the aqueous sulfuric acid solution, this solution is brought into contact with an organic solvent

  comprising a dialkylphosphoric acid.

  Generally, the organic solvent consists of a solution of dialkylphosphoric acid

  in an appropriate organic thinner.

  The dialkylphosphoric acids which can be used are dialkylphosphoric acids in which the alkyl radicals are linear or branched radicals having from 4 to

16 carbon atoms.

  By way of example of such an acid, mention may be made of di (2ethylhexyl) phosphoric acid which is

  will hereinafter denote by the acronym HDEHP.

  The organic diluents used are, for example, aliphatic or aromatic hydrocarbons,

  for example hydrogenated tetrapropylene (TPH).

  The dialkylphosphoric acid concentration of the organic solvent is generally high, as the extraction rate increases

with extractant content.

  Preferably, the acid concentration

  dialkylphosphoric content is 15% to 40% by volume.

  According to the invention, after having brought the organic solvent into contact with the dissolution solution, an organic solvent containing

molybdenum extracted.

  Preferably, this solvent is subjected to washing with an aqueous solution of dilute sulfuric acid, for example having an acid concentration

sulfuric from 0.5 to 1 mol / l.

  The molybdenum can then be re-extracted from the organic solvent using an aqueous ammonia solution. The process of the invention can be implemented in conventional co-current or counter-current extraction installations, such as settling mixers, pulsed columns, etc. The contacting can be carried out at ambient pressure and temperature; however, higher temperatures can be used

  in particular to improve the kinetics of extraction.

  Furthermore, it is possible to operate continuously by circulating the organic solvent and the aqueous solutions against the current and by recycling the aqueous solution for washing the organic solvent with the solution.

  starting aqueous containing the molybdenum to be extracted.

  Other characteristics and advantages of the invention will appear better on reading the following examples given of course by way of nonlimiting illustration, with reference to the appended drawings in which: - Figure 1 is a diagram representing the quantities of heteropolymolybdic complexes present in a sulfuric medium depending on the

  concentration of sulfuric acid in the medium (in mol / l).

  - Figure 2 is a schematic representation of an example of implementation of the method

of the invention.

  - Figure 3 is a schematic representation of another embodiment of the

method of the invention.

  In FIG. 1, the behavior of the following hetero-polymolybdic complexes is represented: - phosphomolybdic complex (Mo / P atomic ratio of 20/1) absorbing at 400 nmn, - phosphovanadomolybdic complex (Mo / P / V atomic ratio of 11 / 1/1) absorbent at 490 nm, and - silicomolybdic complex (Mo / Si atomic ratio of 12/1) absorbing at 430 nm, at a concentration of 0.1 mol / 1 Mo (VI) in an aqueous solution of sulfuric acid, depending on the

H2SO4 concentration (in mol / l).

  The abundance of the complex in solution is represented by the optical density of the solution at the wavelength corresponding to the absorption peak of the

complex considered.

  In this figure, curve 1 relates to the phosphomolybdic complex; curve 2 relates to the phosphovanadomolybdic complex and curve 3 relates

  refers to the silicomolybdic complex.

  Thus, we note that beyond a sulfuric acid concentration of 2 mol / l, there is

no more complex in solution.

  This is why, in accordance with the invention, an aqueous solution of sulfuric acid having a solution is used for the dissolution of the calcium molybdate.

  H2SO4 concentration of at least 2 mol / l.

  Thus, the dissolution solution contains practically no heteropolymolybdic species. This result cannot be achieved quickly by carrying out the dissolution with a dilute solution of H2SO4 and then acidifying the dissolution solution, since it has been found that these heteropolymolybdic species, in particular the silicomolybdic species, have kinetics of degradation in concentrated acid medium. too slowly; for example, a period of 15 days at room temperature is necessary to degrade the species

  silicomolybdiques in sulfuric medium 3M.

  The following examples illustrate

  results obtained with the process of the invention.

  EXAMPLE 1 Dissolution of Calcium Molybdate In this example, 1 g of calcium molybdate having the composition given in Table i below is dissolved in 20 ml of an aqueous solution containing 3 mol / l of acid. sulfuric, with stirring, at room temperature, and the composition of the dissolution solution is checked by periodically taking samples and analyzing them by spectrophotometry and emission spectroscopy JCP to determine their contents in Mo, P, V, Si and U. After 45 minutes of stirring, the dissolution yield no longer undergoes any significant variation and a dissolution solution is obtained having the concentrations of Mo, P, V, Si and U given in the

table 1.

  In this table, the results obtained when the dissolution is carried out under the same conditions, but by using a 0.25 mol / l solution of sulfuric acid, have been given for comparison.

(pH = 2) as in FR-A-2 691 373.

TABLE 1

  ELEMENT MOLYBDATE SOLUTION SOLUTION

OF CALCIUM DISSOLUTION DISSOLUTION

  (% in H2SO4 3 mol / 1 H2SO4 (pH = 2) mass) (in mol / l) (in mol / 1) Mo 33.660 0.212 0.159

P 1,360 5.99.10-3 1.10.10-2

V 1.610 1.69.10-2 1.49.10-2

If 0.760 1.81.10-3 5.80.10-3

U 0.378 7.04.10-4 7.10-4

  The results of Table 1 show that, according to the invention, a

increased dissolution of molybdenum.

  EXAMPLE 2 Extraction of the Molybdenum Is brought into contact with stirring, 1 volume of a dissolution solution obtained as in Example 1, either with H2SO42M or with H2SO43M, 4 days after obtaining it, with 1 volume of an organic solvent comprising 30% by volume of di (2-ethylhexyl) phosphoric acid and 70% by volume of

hydrogenated tetrapropylene.

  After 5 minutes of stirring at 23 ° C., the two phases are allowed to settle, and their

Respective molybdenum contents.

  This operation is repeated twice by bringing the aqueous phase separated from the organic solvent coming from the previous contact into contact with 1 volume.

new organic solvent.

  The composition of the starting solution and

  the results obtained are given in table 2.

  In this table, the extraction yields correspond to the cumulative values obtained after 1, 2

or 3 contacts.

  In this table, the results obtained by operating in the same way with a dissolving solution having a

H2SO4 concentration of 1 mol / l.

TABLE 2

  SOLUTION OF H2SO4 (in 1 2 3 DISSOLUTION mol / 1) MO (VI) in 0.161 0.165 0.15 mol / 1) After 1 contact organic Mo (VI) 0.0753 0.135 0.129 (in mol / 1) Mo (VI) aqueous 0.0857 0.030 0.021 (in mol / 1) Extraction yield (%) 46.7% 81.8% 86% After 2 contacts organic Mo (VI) 0.0315 0.0164 0.0129 (in mol / 1) aqueous Mo (VI) 0.0542 0.0136 0.0081 (in mol / 1) Yield 66.3% 91.7% 94.6% extraction (%) After 3 contacts Organic Mo (VI) 0 , 0236 0.0028 0.0017 (in me / I) Mo (VI) aqueous 0.0306 0.0108 0; 0061 (in mol / 1) Yield _. _ extraction (%) 80.9% 93.4% 95.9% The results in Table 2 show that the best results are obtained with the dissolution solutions obtained in accordance with the process of the invention.

Example 3

  In this example, the molybdenum is recovered from a dissolution solution obtained in accordance with the invention, using the installation operating continuously and against the current, shown diagrammatically on the

figure 2.

  This installation comprises an extraction stage 21 and a washing stage 23 in which the organic solvent circulates continuously, being

introduced by line 25.

  In the extraction stage, the organic solvent is brought into countercurrent contact with the solution for dissolving calcium molybdate stored in the tank 27. This solution is introduced by

  line 29 in the extraction stage 21.

  At the end of the extraction stage, there is recovered - via line 31 an aqueous effluent containing P, Si, V, U and practically no molybdenum, and - via line 33 the organic solvent charged with molybdenum containing in addition some impurities . In washing stage 23, this organic solvent is brought into contact against the current with an aqueous washing solution, for example a 0.5 mol / l solution.

  sulfuric acid, introduced via line 35.

  At the end of the washing stage, the organic solvent containing molybdenum is recovered via line 37 and an aqueous effluent through line 39

  containing the impurities extracted from the solvent.

  In this installation, circulation rates can be used such that the volume ratio of the organic phase to the aqueous phase is from 2 to

  extraction stage and washing stage.

  Each stage can consist of several stages each formed by a mixer-settler. For example, the extraction stage can have 12 stages and the

washing 4 floors.

  In Table 3 which follows, the results obtained in this installation are given with a

  dissolving solution containing 3 mol / 1 of sulfuric acid.

  In this table, the results obtained were also given for comparison with a solution of dissolution in a weakly acid medium (pH2), then acidified to have a sulfuric acid concentration of 3 mol / l. In this table, the extraction yields are calculated from the concentrations

  measured on the different aqueous phases.

TABLE 3

  CONCENTRATION IN MB (VI) Rendi Extr. (Mol / l) rate reflux (*) I / O (0) Solution At the entry Effluent Solvent effluent (%) (%) of dissolution (in 29) of organic washing extraction (3 mol / I) (in 31) (in 39) (in 37) H9SO4 dissolution solution 0.212 6.1.10-4 2.2.10-4 0.10 99.7 0.05 1.056 (3 mol / I) Acidified dissolution solution (pH :)

  to 0.138 1.5.10-2 2.90.10-3 5.55.10-2 88.1 1.0 1.08

  (3 moVI) in HSO4 (*) Rate of reflux = Mo flow (mole / h) in the aqueous phase to be treated (*) Rate of reflux = Mo flow (mole / h) in the dissolution solution used in the operation of extractioon Incoming Mo flow E Outgoing Mo flow

B 11985.3 MDT

  The results of Table 3 show that an extraction yield of 99.7% is reached with the process of the invention, while it is clearly lower (88%) when the dissolution is carried out.

  pH2, followed by acidification to 3 mol / l of H2SO4.

Example 4

  In this example, the molybdenum is dissolved and then extracted, from calcium molybdate, using the installation shown.

schematically in Figure 3.

  In this figure, the same references have been used as those in FIG. 2 to designate the

  components common to both installations.

  In this installation, the calcium molybdate is first dissolved in the container 40 using 20 m3 of H2SO43M per tonne of calcium molybdate. Dissolution is carried out with stirring for 1 hour at 23 ° C., then the solution of the solid materials is separated by filtration in

filter 42.

  The separate solution which comprises approximately 0.2 mol / l of molybdenum and impurities (V, U, Si, P) is sent via line 29 to the extraction stage 21 which comprises 6 stages with the washing solution

leaving the washing stage 23.

  The organic solvent (HDEHP 30% -THP 70%) is introduced via line 25 and circulates at

  counter current of the aqueous solution.

  At the exit from the extraction stage 21, it is introduced into the washing stage 23 which comprises 4 stages where it is brought into countercurrent contact with an aqueous solution of 1 mol / l of H2SO4 introduced by

driving 35.

  At the end of the washing stage 23, the organic solvent which contains practically only molybdenum is treated with a view to recovering the molybdenum by stripping in an ammoniacal medium (pH 8.5-9), then subjected to decontamination vis-à-vis screw uranium in carbonate medium. It is then re-acidified with H2SO4 and then recycled to the extraction stage 21. However, this re-acidification of the solvent can be avoided, since it can be carried out by the solution

  aqueous at the first extraction stage.

  Molybdenum can be separated from the ammonia solution by precipitation of molybdate

of ammonium in an acid medium (pHi1).

  In figure 3, the volumes are indicated

  of solutions introduced at each stage.

  With this installation, the molybdenum is recovered with a yield of 99.7%, using a

only extractant.

Claims (5)

  1. A method of recovering molybdenum present in impure calcium molybdate from the treatment of uranium ores, characterized in that it comprises the following successive stages: a) dissolving the calcium molybdate in an aqueous solution of sulfuric acid having a sulfuric acid concentration of at least 2 mol / l, b) bringing the aqueous dissolution solution from step a) into contact with an organic solvent comprising a dialkylphosphoric acid, and c) separating the aqueous solution   organic solvent having extracted molybdenum.   2. Method according to claim 1, characterized in that the concentration of sulfuric acid in the aqueous solution used in step a) is 2 to 4 mol / l.   3. Method according to any one of   claims 1 and 2, characterized in that the acid   dialkylphosphoric is di (2-ethylhexyl) phosphoric acid. 4. Method according to any one of   Claims 1 to 3, characterized in that it comprises   an additional step of washing the organic solvent having extracted the molybdenum with an aqueous solution   consisting of dilute sulfuric acid.   5. Method according to claim 4, characterized in that the sulfuric acid concentration of the washing solution is 0.5 to 1 mol / l.