FR2510541A2 - Molybdenum recovery from uranium and vanadium leach solns. - by pptn. of molybdate, dispersing in acid medium and pptn. of molybdenum tri:oxide - Google Patents

Abstract

The parent patent describes a process for purifying solns. contg alkali metal (bi)carbonate, sulphate and/or hydroxide as well as one or more of vanadium, uranium and molybdenum in the form of the alkali metal salt(s). The process comprises (i) treating the soln. at its b.pt. or above with 0.1-20 times the stoichiometric amt. of lime required to convert the (bi)carbonate content into alkali metal hydroxide (ignoring the amt. of lime required to ppte. insol. calcium cpds. of V,U and MO); (ii) sepg. the alkali metal hydroxide-enriched liquor from the ppte cotg. mainly calcium carbonate and a mixt. of other (in)organic calcium salts, and washing the ppte; (iii) concentrating the combined liquor and wash liquor by evapn. to an alkali metal hydroxide content of at least 50% to form a second ppte; and (iv) sepg. the ppte. to recover the alkali metal hydroxide-rich liquor. In the present invention, the sepd. second ppte, comprising a mixt. of alkali metal molybdate and sulphate, is dispersed in an aq. acid liquor (pref. a sulphuric acid-contg. liquor), which is heated under pressure, to ppte. anhydrous MO3 and the ppte. is sepd. to leave a liquor contg. mainly alkali metal sulphate. Process is used to purify leach solns. for recycling, in the leaching of uranium or vanadium minerals which also contain molybdenum, after sepn. of the metal values. The molybdenum, is recovered directly in the oxide form and the problems of the previous sulphide ppte. method are avoided (e.g. elimination of pollution by hydrogen sulphide, risk of formation of the blue oxide and the requirement for calcining the prod.).

Description

PROCESS FOR THE VALORISATION OF TPLYBENENE FROM MOLE3DENIFEROUS SOLFIONS CONTAINING CARBONATE, SULPHATE, HYDROXIDE OR HYDRO
GENUCARBONATE ALKALINS AS WELL AS, EVENTUELLD {T, URANIUM
The present invention, addition to the patent 2 404 601, relates to a method of upgrading molybdenum from molybdenum solutions containing alkali carbonate, sulfate, hydroxide or hydrozenocarbonate, as well as, optionally, uranium.

In the main patent No. 2,404,601 of September 30, 1977, the Applicant has described a process for purifying solutions containing sodium carbonate, sulfate, hydroxide or hydrogen carbonate and at least one of the metals belonging to the group consisting of uranium and molybdenum in the form of sodium salt.

These solutions came from a cycle of attack of a uranium ore containing as particular impurity of molybdenum, after precipitation and separation of the metal to be valorized according to a known method.

Thus, in the case of a uranium ore, for example, the ore being attacked by a bicarbonate liquor and / or sodium bicarbonate, the solubilized uranium, present in the liquor after attack, was usually precipitated in the form of uranate. sodium. This sodium uranate could be converted - either to crystallized ammonium uranate by a sulfo
ammonic, which consisted of treating sodium uranate with a
ammonium sulphate, or uranium peroxide by sulfuric redissolution and precipitates;
by introduction of hydrogen peroxide.

Whatever the mode of precipitation and separation of uranium, for example in the form of sodium uranate, optionally converted into uranium peroxide, these operations led to the production of solutions containing carbonate, sulfate, hydroxide or sodium hydrogen carbonate, which had to be purified before being recycled to attack the ore. Because, it is indeed known that the impurities normally have an adverse influence on the qualities of the main product sought and their presence at too high concentrations can be troublesome during the attack using a recycled liquor and / or still cause untimely rainfall at various points in the manufacturing circuits.

In the specialized literature, it is often stated that the removal of impurities present in the circulating liquors is carried out at the same time as the waste products, in the form of an impregnation liquor, as a result of an insufficient washing. .

The rejection in the nature of sterile still strongly soda, or liqueurs previously mentioned, is more and more inconceivable and prohibited by the national legislations, because of irremediable degradation that these effluents can cause in the natural environment.

However, if it appears desirable to better perform the washing of the waste to improve the recovery of the reactants and the product to be upgraded, against the amount of impurities present in the circuit increases simultaneously.

Therefore, it becomes necessary to use a method for extracting impurities in sufficient quantities of the liquors to be treated so that their content of impurities can not cause the aforementioned drawbacks.

It is in this spirit that the Applicant had described in the main patent 2 404 601 a purification process of the aforementioned solutions, which was characterized in that said solutions were treated at a temperature at most equal to boiling, by a quantity of lime of between 0.1 and 20 times the stoichiometric quantity necessary to transform the carbonates present in free sodium, without taking into account the quantity of lime necessary for precipitating the insoluble calcium metal compounds, and then producing separating and washing a first precipitate containing essentially calcium carbonate and a mixture of other organic and inorganic calcium salts, and a liquor which has been enriched with sodium hydroxide, in that the mixture of said liquor and washing liquor of the first precipitate was concentrated by evaporation to a sodium hydroxide content of not more than 50 % to cause to obtain a second precipitate, in that the crystals of this second precipitate are separated from their mother liquor rich in sodium hydroxide and in that said liquor rich in sodium hydroxide is recovered . In this process, the second precipitate consisted essentially of sodium sulfate.

Since the mother liquor rich in sodium hydroxide, obtained by separation of the sodium sulphate precipitate, still contained impurities, it seemed desirable to the applicant to carry out a treatment of the said liquor in Mle to extract the elements, such as molybdenum, organic materials and others, troublesome for its subsequent use.

Thus, the applicant proposed, in the context of this invention, a treatment for the removal of molybdenum in the form of a sulphide, a treatment which consisted in acidifying the hydroxyl-rich liquor, obtained after the separation of the sulphate. of sodium, and to precipitate the molybdenum sulphide by the addition of an alkaline sulphide. In spite of the interest offered by such a treatment, there appeared to be major disadvantages which could have led to a limitation of its application. In fact, the treatment necessitated the complete neutralization with sulfuric acid of the mother liquor rich in sodium hydroxide which had just been freed of sodium sulphate. The mother liquor was then purified by molybdenum by precipitation. With the addition of sulphide ions, it was again necessary to remove the SO 4 ions introduced for the neutralization and to reconstitute the recycling liquor intended for the attack by introducing therein the desired amounts of CO 3 and HCO 3 ions.

It is because of these drawbacks that the applicant has proposed, in the patent of addition No. 2,433,482, a new process for extracting molybdenum from the solutions to be purified comprising carbonate, sulphate, hydroxide or sodium hydrogencarbonate, these solutions resulting from an attack cycle of uranium ores containing, as a particular impurity, molybdenum after the alkaline attack of the ore and extraction of the uranium in the form of a concentrate, and intended to be processed by caustification by means of the introduction of lime which was characterized in that the molybdenum was extracted in the form of a sulfur compound by introduction of sulphide ions into an acidified aliquot of said solutions before causing caustification.

In its essential characteristics, this process for the extraction of molybdenum, of solutions to be purified from uranium ore treatments, included the following steps: the removal before caustification of an aliquot of the solubles
catered for the extraction of the largest
part of molybdenum in solution, while the rest of the solutions are
sent, according to the main patent, in caustification - the acidification of the aliquot fraction of the solutions to be treated by a
acidic agent - introduction of sulphide ions into said acidified aliquot; the separation of the molybdenum precipitate impregnated with mother liquors, a
liquor still acid but impoverished in molybdenum, to which are joined
the wash water of the said precipitate - the mixture of the molybdenum-depleted aliquot with the frac
of solutions to be purified having undergone the causative cycle according to
the main patent; - the concentration of the liquid fractions coming from the purification in mo
lybdenum and caustification, until obtaining a second meadow
cipité constituted by sodium sulphate - the separation of the crystals of this second precipitate impregnated with a li
sodium-hydroxide rich mother - washing of the second precipitate with recycling of washing water to
the concentration, and - the recovery of the liquor rich in sodium hydroxide.

This process had the advantage over the main patent of a lower consumption of Ca (OH) 2, a lower introduction of H2SQ4 to neutralize the only aliquot for the extraction of molybdenum, and a lower consumption of carbon dioxide to regenerate liquors recycled to attack.

In addition, this process allowed to eliminate by concentration the SO4 ions initially present in the solution to be purified as well as those introduced into the aliquot fraction to ensure the neutralization and allow the precipitation of molybdenum.

However, the amounts of H2SO4 added for the neutralization of the aliquot for the molybdenum purification, as well as the amounts of CO 3 introduced into the liquor from the separation of sodium sulfate to recycle this liquor to the attack of the ore, were still considered too important.

Therefore, the applicant has proposed in the application 80 07877 addition to the aforementioned main patent, a molybdenum extraction process which avoided the aforementioned drawbacks.

This process for extracting molybdenum from aqueous solutions to be purified containing alkali carbonate, sulphate, hydroxide or hydrogen carbonate and which may also contain ulanilm, which involves a caustifi cation of said solutions by means of lime to transform carbonates into hydroxides alkaline, then the separation and washing of the above-mentioned calcium carbonate, a liquor which had been enriched in alkaline hydroxide, the concentration by evaporation of the mixture of the alkaline hydroxide-rich liquor and the washing liquor of the first precipitate containing essentially calcium carbonate, until a second precipitate was obtained, was characterized in that the second precipitate was a mixture of molybdate and alkali sulphate, which was solubilized in an aqueous liquor redissolution, then the aqueous liquor thus obtained was treated with sulphide ions causing the precipitation of molybdenum , which was later separated from the mother liquor essentially containing alkali sulfate and was washed and dried.

In its essential characteristics, this process of extracting molybdenum from aqueous solutions to be purified from an ore treatment cycle included the following steps: a) A caustification of the solutions by a quantity of lime included
between 0.1 and 20 times and preferably between 0.5 and 10 times the quantity
stoichiometric unit to convert the alkaline hydroxide
carbonate and bicarbonate present.

b) The separation of a first precipitate impregnated with mother liquors and consti
killed by a mixture of organic and inorganic calcium salts,
of a liquor enriched in alkaline hydroxide and containing a sulphate
alkaline.

c) Washing the first precipitate to extract the liquor im
prégnation by giving washing waters which are attached to the li
alkaline above, enriched with alkaline hydroxide.

d) The evaporative concentration of the liquor resulting from the mixing
until obtaining a second precipitate, constituted by the mixture
molybdate and alkali sulphate.

e) The separation of the crystals of this second precipitate impregnated with
mother liquor rich in alkaline hydroxide.

f) The washing of the second precipitate with recycling of the washing water to
concentration d).

g) The recovery of alkaline hydroxide rich liquor which can
to be later carbonated before being recycled to attack
of an ore.

h) Redissolution in water and / or in a liquor recycling the
second precipitate.

i) The introduction of sulphide ions into the redissolution liquor of the
second precipitate.

j) Acidification of the redissolution liquor containing the ions
sulphides causing complete precipitation of molybdenum sulphide
and forming a suspension of this sulfide in the aqueous phase.

(k) The separation of the molybdenum sulphide precipitate from a liquor
aqueous rich in alkali sulfate.

1) The drying and calcination of molybdenum sulphide.

In this process, the valorization of molybdenum was carried out in the form of Mis3, which required, for its obtaining, the use of an alkaline sulphide in an acid medium. As a result, the precipitation medium was the seat of a disengagement of hydrogen sulphide hindering for the exploitation and the environment, and presented the risk of causing a partial reduction of Mo in the form of "molybdenum blue". In addition, the resulting molybdenum trisulphide not being a usual industrial product, required a special calcination treatment to allow its marketing.

That is why, the applicant, continuing his research, found that it was possible to achieve the recovery of molybdenum according to a new process that avoids the aforementioned drawbacks.

The process according to the invention for upgrading the molybdenum of aqueous solutions to be purified containing alkaline carbonate> sulphate, hydroxide or hydrogencarbonate and which may also contain uranium, which involves a caustification of said solutions by means of lime to transform the carbonates into alkali hydroxides, followed by the separation and washing of the aforesaid calcium carbonate, a liquor which has been enriched in alkaline hydroxide, the concentration by evaporation of the mixture of the alkaline hydroxide-rich liquor and the washing liquor of the first precipitate containing essentially calcium carbonate, until a second precipitate formed of a melt is obtained; molybdate and alkali sulfate mixture, characterized in that said solid mixture is dispersed in an aqueous acidic liquor, heated under pressure to precipitate anhydrous NbO.sub.3, and said MbO.sub.3 precipitate is separated from the mother liquor which is concentrated to cause precipitation of the alkali sulfate.

In its essential characteristics, the new process for upgrading molybdenum from aqueous solutions to be purified from an ore treatment cycle involves the following steps: a) A caustification of the solutions by a quantity of lime included
between 0.1 and 20 times and preferably between 0.5 and 10 times the quantity
stoichiometric titer to convert alkaline hydroxide
bonateset the bicarbonates present.

b) The separation of a first precipitate impregnated with mother liquors and cons
by a mixture of organic and inorganic calcium salts,
of a liquor enriched in alkaline hydroxide and containing a sulphate
alkaline.

c) Washing the first precipitate to extract the liquor
of impregnation by giving washing water which is attached to the
aforementioned alkaline liquor, enriched with alkaline hydroxide.

d) The evaporative concentration of the liquor resulting from the mixing
until a second precipitate is obtained consisting of the mixture
molybdate and alkali sulphate.

e) The separation of the crystals of this second precipitate impregnated with
mother liquor rich in alkaline hydroxide.

f) The possible washing of a second precipitate with recycling of waste water
wash at concentration d).

g) The recovery of alkaline hydroxide rich liquor which can
to be later carbonated before being recycled to attack
of an ore.

h) Dispersion in water and / or in a recycling liquor.

i) The acidification of the liquor (h) of dispersion of the second preci
mite.

j) Heating under pressure of said acidified dispersion at a time
such as is precipitated MbO3 anhydrous, and causes the formation of
suspending said oxide in the aqueous phase.

(k) The separation of an aqueous liquor rich in alkali sulphate
precipitate anhydrous NibO3 which is washed.

1) The evaporation of the alkaline sulphate-rich liquor causing
precipitating said alkali sulfate.

m) The separation of this alkaline sulphate and the recycling of the liquor ob
held at evaporation and / or the acidification step.

In the remainder of the description, and for simplicity of understanding, the alkaline salts, which are mentioned, are only those of sodium and potassium.

où M peut être le sodium, le potassium. According to the main patent, the caustification of the solutions is generally carried out by introducing a quantity of lime at least equal to the stoichiometric quantity necessary for the almost complete conversion of the alkali carbonate present in the liquor to free sodium, depending on the reaction.

where M can be sodium, potassium.

In the case where the solutions to be caustic contain metal salts capable of forming, with the lime, and under the operating conditions, an insoluble compound, the total quantity of lime introduced is constituted by the quantity of lime actually necessary for the caustification of the carbonates. in solution and the amount of lime needed to precipitate said metal elements in the form of insoluble calcium compounds. Therefore, and to simplify the understanding of the object of the invention, mention will be made only of the amount of lime actually required for the sole caustification of alcaline carbonates.

 The corresponding temperature of the caustification treatment is at most equal to the boiling temperature of the treated liquor. It is therefore between 200 ° C. and 100 ° C., but preferably between 500 ° C. and 9 ° C., the precipitation and filterability of the residue obtained being, in most cases, improved when the causticization temperature is close to the boiling point. .

The precipitate consists essentially of calcium carbonate and excess lime and> minor amounts of organic and inorganic calcium salts.

The first precipitate and the alkaline mother liquor are separated by known means such as, for example, filtration, spinning, decantation, etc.

The alkaline mother liquor is then evaporated to an alkaline hydroxide concentration of at most 50% causing the simultaneous precipitation of alkali metal sulfate and molybdate. This second precipitate is then collected which is separated from the mother liquor rich in alkali hydroxide by a known means, then washed with water or with a saturated aqueous solution of alkali metal sulfate, the washing liquor being recycled to the concentration.

Since the recovered mother liquor, which is rich in alkali hydroxide, still contains impurities, it may be desirable to carry out a treatment of the said liquor in order to extract the interfering elements for its subsequent use, such as organic and other materials. Similarly, said mother liquor may undergo a processing treatment before being used in the manufacturing cycle.

According to a first variant for extracting organic matter, the mother liquor sodium is treated in a known manner - either by a barium compound by taking advantage of the weak solubili
barium organates in the sodium medium. The compound of the ba
barium is introduced in quantities at least equal to the amount stoechio
metric needed to allow precipitation and elimination
by separating the organates from this metal - either by sodium dioxide causing degradation "in situ"
organic materials, - either by hydrogen peroxide causing this same degradation, - or, finally, by passing said liquor on activated carbon having
the well-known property of retaining the organic elements present
in the treated mother liquor.

According to a second variant, the sodium mother liquor may be partially or completely carbonated by contacting it with carbon dioxide by known means, for example by blowing a large excess of this gas. Depending on the conditions of this operation, it is possible to obtain a precipitate of sodium carbonate which can subsequently be separated.

According to the characteristics of the alkaline mother liquor at the end of the evaporation and the uses to which this purified liquor is subjected, it is possible to use either of these variations, to combine them partially or totally.-
According to the process of the invention, the second precipitate consisting of a mixture of molybdate and alkali sulfate is generally dispersed in water and / or an aqueous recycle liquor containing SO4 ions. Then, this aqueous dispersion is then resumed to perform the upgrading treatment of molybdenum.

The molybdenum beneficiation treatment consists of acidifying the dispersion of the molybdate and alkali sulphate mixture with an acidic aqueous solution, such that the mass of free H 2 SO 4 in the dispersion thus formed is between 2% and 20%. of the mass of the liquid phase of the dispersion.

The consumption of sulfuric acid converted to the alkaline sulfate during the precipitation of anhydrous tet03 is compensated by the introduction of new acid at any point of the molybdenum recovery circuit and, preferably, during the dispersion of the molybdate precipitate. and alkali sulfate in an aqueous acidic liquor, or during the concentration of the liquor resulting from the separation and washing of MbO3.

The temperature at which the precipitation of anhydrous tE03 is carried out is chosen in the range of 1200C to 2500C and, preferably, in the range 1400C to 1800C.

The Applicant has found that the duration of the temperature maintenance in the aforementioned field was between 0.5 hours and 10 hours, but that this duration was not critical in itself.

Finally, in order to improve the physical qualities of the anhydrous BobO3 crystals, qualities having an influence on the filterability of the reaction medium and on the phenomena of encrustation of the reactor walls, it is important to achieve the introduction of a minor amount of germ. anhydrous Mb03 in the precipitation medium of
The invention will be better understood thanks to the description of the attached diagram.

The figure is a schematic representation of the process according to the invention indicating in full lines the circuit used when it is desired to valorize the molybdenum and remove the only carbonate> alkaline sulphate and, in dashed lines, the circuits for producing on the liquor from the caustification and rich in hydroxide, either a complementary purification of the organic materials, or a carbonation, by performing the aforementioned complementary treatment intended for this purpose, or by carrying out a complete treatment by the successive practice of the complementary treatments described above.

The alkaline solutions to be treated "Le" as well as the lime necessary are introduced into (A) by (03 and (R) .The slurry obtained after treatment with lime is introduced into the zone (B) where it carries out the separation. a cake S1 and a liquor L1 containing certain solubilized impurities The mother liquors of the cake St are extracted in (C) by means of a quantity of water introduced The mother liquors L2 thus extracted are mixed with the liquor L1 forming liquor L3 The resulting cake S2, extracted from (C), consists essentially of calcium carbonate.

The liquor L3 constituted by the mixture of liquors L1 and L2 is conducted in (D) where the concentration of alkali hydroxide is carried out by evaporation of water, causing the precipitation of a mixture of sulphate and alkali molybdate.

The L4 blowing out of the concentration is introduced in (E) where the separation of a liquor L5 and cake S5 is carried out.

The cake S> essentially consisting of the mixture of sulphate and alkali molybdate, is driven to (EA) where it is suspended in an acidic recycle liquor L515. The suspension thus prepared being stirred, is heated to the proper temperature to cause the precipitation of anhydrous water.

The L511 slurry thus obtained is treated with (EB) where the separation of an S512 cake consisting essentially of anhydrous MbO3 and a L512 liquor containing in solution the alkaline sulphate and sulfuric acid> which is sent to evaporation (EC).

Sufficient sulfuric acid is also introduced into the zone (EC) and concentrated by evaporation to precipitate most of the alkali sulphate present.

The slurry L513 from the evaporation zone is transferred to an area (ED) where the separation of the solid S514 and liquid L514 phases takes place.

Phase S514, consisting of alkali sulfate, is removed from the circuit.

The liquor L514 is then recycled according to L515 in the acidification zone (EA) and, possibly in part, according to L516> in the concentration zone (D) when it comprises impurities whose accumulation would be --gênante in the circuit precipitation of MoO3.

The cake S512 essentially consisting of anhydrous MoO3 is sent to a washing zone (EE) comprising at least one washing stage.

Said cake is washed with a suitable quantity of water and the liquor resulting from the washing is generally sent to the evaporation zone (EC) according to L517, but all or part of this liquor may possibly be sent to the zone acidification (EA) according to L518.

However, it may be advantageous to take a portion of the cake S512 before washing, to recycle it in the acidification-precipitation zone (EA), this fraction of the cake acting as anhydrous MbO3 crystallization primers.

At the outlet of the washing zone (EE), the cake S519 may, according to the intended uses, be wholly or partly sent into the drying zone (EF) according to S521 or / and in the zone (EG) according to S520 for further purification treatment.

The L5 liquor, rich in alkali hydroxide, from (E), may contain in solution impurities such as, for example, various organic and inorganic salts which it may be desirable to remove.

If it is desired to remove liquor L organic matter present, said liquor is introduced in (I) with, for example, an amount of an adequate amount of a barium compound, causing the precipitation of barium organates. The slurry from (I) is then introduced at (T) where the separation of a cake S8 and a liquor L8 which can be collected in (V)> or recycled to another stage of the process is carried out. process such as (J) for example.

Similarly, if it is desirable to carbonate the liquor L5, rich in alkali hydroxide, this liquor is introduced in (J) to undergo carbonation by blowing CO 2. The slurry obtained can be used as produced or further treated in 0i) to separate the cake Sg consisting of alkali carbonate and a carlyonate liquor L 9 which can be collected in (R) or recycled in (J) for the purpose of obtaining an alkaline-unsaturated carbonate.

 But, it is obvious that the liquor L5, rich in hydroxide, can undergo successively these two treatments depending on the impurities that it is desirable to eliminate and according to the uses for which this liquor is intended after purification.

The method according to the invention is remarkable for its flexibility of adaptation. This is very important because, if the presence of alkali sulfate in the solutions to be purified is general, and also that of the alkali carbonate, the other constituents present may vary qualitatively and quantitatively depending on the origin of the solutions to be treated. Thus, the process is particularly interesting with regard to the environment, due to the absence of liquid discharges into nature.

In addition, this process has other advantages by which we can first mention the possibility of recycling a concentrated solution of alkali hydroxide, or an alkali carbonate solution, optionally a suspension of this salt, or even carbonate alkaline in the solid state, but also to be able to adjust on demand the amount of alkali sulphate recycled, as well as the levels of impurities (molybdenum, organic materials, etc ...).

The advantages of the method according to the invention will be much more perceptible thanks to the example given by way of illustration. EXAMPLE (illustrated by the figure)
According to the process of the invention, a solution rich in sodium hydroxide, taken at the end of an etching cycle of a uranium ore, was treated after precipitation and separation of sodium uranate. The solution "The" had the following composition, in mass
4.7 kg NaOH
Na2C 3 31.88 kg
Nua2504 9.27 kg
Uranium 0.02 kg
molybdenum 3.79 kg
H20 and various 599.34 kg
The 649 kg of this solution were introduced in (A) with 29.67 kg of industrial lime, in order to carry out the almost complete caustification of the carbonate present, by heating and maintaining at 95 ° C. for a time of about 3 hours.

The slurry obtained was then transferred to (B) where the separation of the solid S1 and liquid L1 phases took place.

The cake S1 was then rinsed in (C) with 35 kg of water. The mother liquors which impregnated the cake S1 were thus extracted and joined to the liquor L1 coming from the separation (B).

The cake S2 which had a mass of 70.72 kg had the following composition expressed in mass
Poop, 35.7 kg
Uranium 0.02 kg
Ca (OH) 2 excess 1.5 kg
H20 impregnation and
various 33,5 kg
molybdenum 0.002 kg
The liquor L3 constituted by the mixture of the liquors L1 and L2 represented a mass of 642.95 kg and had the following composition expressed by mass
NaOH 28.05 kg
Na2S04 9.26 kg
Molybdenum 3.79 kg
Water and various 601,85 kg
This liquor L3 was conducted in (D) where a concentration was carried out by evaporation. In addition, in this zone (D), the recycling liquor L516 which had a mass of 3.46 kg and which had the composition was introduced. next expressed in mass
Molybdenum 0.09 kg
H2504 0.68 kg Na2S04 1.11 kg
Water and various 1.53 kg
The total amount of water evaporated during the liquor concentration
L3 and L516 in (D) represented a mass of 540.49 kg.

The slurry exiting from (D) was transferred to (E) where the separation of a cake Sg and a liquor L5 was carried out.

The cake Sg represented a mass of 15.32 kg and had the following composition expressed in mass
Na2504 10.86 kg
Molybdenum 1.49 kg
H20 and various 2.97 kg
The liquor L5, from the separation (E) represented a mass of 90.60 kg and had the following composition NaOH 27.18 kg
Nua2504 0.50 kg
Molybdenum 2.39 kg
Water and various 60,53 kg
The liquor L5 at the outlet of (E) can, according to the main patent, undergo various transformations before being reintroduced into the cycle of operations.

The cake Sg was then introduced into 31.14 kg of the liquor L515 which had the following composition
Molybdenum 0.82 kg
H2504 6.13 kg
Nua2504 9.97 kg
Water and various 14.22 kg
The slurry obtained was treated, after introduction of 10 grams of anhydrous Mb03 acting as a crystallization primer, for three hours at 1600 ° C, to precipitate the anhydrous molybdenum oxide.

The L511 slurry coming out of (FA) was transferred to the zone (EB) where the separation of an S512 cake and an L512 liquor took place.

The cake S512 was subjected to a first scrubbing (EE) with 40 kg of water. The slurry obtained was treated to separate the first wash liquor having a mass of 65.06 kg, having the following composition
Molybdenum 0.45 kg
H2S04 1.67 kg
Na2SO4 17.85 kg
Water and various 45.09 kg of a cake which was again washed with a mass of 5 kg of eatl. A wet cake S514 of anhydrous ttO3 having a mass of 2.96 kg having the following composition was then obtained.
Molybdenum 1.38 kg
Water and various 1.58 kg and 5.49 kg of second wash liquor having the following composition
Siblybdenum 0.01 kg
H2S04 0.03 kg
Na2SO4 0.36 kg
Water and miscellaneous 5,09 ka.

The liquor L517, consisting of the mixture of the two washing liquors mentioned above, was introduced into the evaporation zone (EC) at the same time as the liquor L512. 2.74 kg of sulfuric acid at 96 t were also introduced into this zone. 43.32 kg of water were then concentrated by evaporation and the mixture thus produced was evaporated.

The slurry exiting from (EC) was transferred to (ED) where separation of an S514 cake and an L514 liquor took place.

The cake S514 represented a mass of 12.81 kg and had the following coeI? Osition in mass
Na2SO4 12.37 kg
Water and miscellaneous 0.44 kg
The LS14 liquor from the separation (ED) represented a mass of 34.60 kg and had the following composition
H2S04 6.81 kg
Na24 11.07 kg
Water and miscellaneous 16,72 kg
This L514 liquor was sent in part, according to L515 in the acidification-precipitation zone (EA) of MbQ3, and the remainder, according to L516 in the concentration zone (D).

Claims (6)

10 / - Process for the recovery of molybdenum from aqueous solutions * to be purified according to revendaration1d patent 2 404 601 containing, in addition to said molybdenum, alkaline carbonate, sulfate, hydroxide or hydrogenocatbonate, and may also contain uranium, as well as mineral and / or organic impurities, said solutions being treated at a temperature at most equal to the boiling with lime, to transform the alkali carbonate into hydroxide and precipitate the insoluble calcium salts formed, then to separate and wash the first precipitate containing essentially calcium carbonate, a liquor which has been enriched in alkaline hydroxide which is concentrated by evaporation together with the washing liquor of the first precipitate, until a content of alkaline hydroxide not more than 50% to cause the production of a second precipitate formed of a mixture of molybdate and alkali sulphate, characterized in that this solid mixture is dispersed in an acidic aqueous liquor, heated under pressure, so as to cause the precipitation of anhydrous ttO3, which is subsequently separated from the mother liquor essentially containing alkali sulphate. 20 / - Process for the recovery of molybdenum from aqueous solutions to be purified according to claim 1, characterized in that the alkali carbonate, sulfate, hydroxide and / or hydrogencarbonate are those of sodium and potassium. 30 / - Process for the recovery of molybdenum from aqueous solutions to be purified according to claim 1, characterized in that the aqueous liquor in which the dispersion of the mixture of molybdate and alkali sulphate is carried out, is a sulfuric liquor. 40 / - Process for the recovery of molybdenum from aqueous solutions to be purified according to claims 1 and 3, characterized in that the free H2504 mass in the dispersion of the mixture of molybdate and alkali sulphate in the aqueous acidic liquor, is between 2 and 20% of the mass of the liquid phase of said dispersion.  CLAIMS - - Process for the recovery of molybdenum from aqueous solutions to be purified according to claims 1 and 4, characterized in that new sulfuric acid is introduced at any point of the molybdenum recovery circuit, but preferably during the dispersing the molybdate and alkali sulphate precipitate in the aqueous acidic liquor, or in the concentration of the liquor resulting from the separation of anhydrous No03. 60 / - Process for the recovery of molybdenum from aqueous solutions to be purified according to claim 1, characterized in that the dispersion of the precipitate of molybdate and alkali sulphate in the aqueous acidic liquor is heated at a temperature of between 1200C and 2500C and preferably between 1400C and 1800C. 70 / - Process for the recovery of molybdenum from aqueous solutions to be purified according to claim 1, characterized in that seeds of anhydrous Mo03 are introduced into the MuO3 precipitation medium.