FR2533588A1 - Process for recovering metals from spent hydrotreatment catalysts. - Google Patents

Abstract

Process for metal recovery. The metals consist of at least one metal of Group VIII and at least one metal of Group Vb or VIb. The treated charge is first of all roasted between 400 and 600 DEG C and then placed in contact with a first ammonia/ammonium salt aqueous solution which gives a first laden liquor. The charge which has been leached once is placed in contact with a second aqueous solution of SO2, forming a second laden liquor. The metals are precipitated from the second liquor with H2S and the precipitate is roasted together with the unroasted charge. The metals of Groups Vb and VIb from the first laden liquor are transferred into a first organic solution by ion exchange in liquid phase. The first organic solution is exhausted with the aid of an aqueous solution and the metals are separated by successive precipitations. The metals of Group VIII are separated and purified by ion exchange in liquid phase in series. Application to the treatment of particles of a spent hydrotreatment catalyst.

Description

 The present invention relates to processes for leaching and recovering spent hydrotreatment catalyst metals.

 Modern progress in the processing of crude oil is the improvement of metal and sulfur containing feedstocks, eg crude oils and residues, by hydrotreatment processes. This improvement is necessary to convert the heavy load into more valuable lower boiling fractions and to remove impurities, including metals and sulfur that can pollute the atmosphere during combustion.

 Crude oils contain various dissolved impurities, including nickel, vanadium, iron and sulfur. The lighter fractions are often separated by distillation at atmospheric pressure or partial vacuum, leaving the metals in a high-boiling fraction generally referred to as "waste fraction" or "residues". Residues generally contain at least 35 parts per million metal impurities, whose proportion frequently reaches 100 ppm and in extreme cases exceeds 1000 ppm.

 These metals and all the sulfur present are eliminated thus improving the charge by treating it with a catalyst in the presence of hydrogen. Such catalysts generally consist of a solid support which contains catalytic metals, usually molybdenum or tungsten with either nickel or cobalt. As the catalyst is used, metals from the charge deposit on its outer surface and on the inner surface of its pores, eventually clogging the pores and reducing catalyst activity to such an extent that This catalyst will be referred to herein as the "spent catalysts" and will contain catalytic metals, an inorganic support matrix, metals from the feed, sulfur compounds, and a residue. hydrocarbon.

 The crude oil currently being extracted tends to be heavy, forcing refiners to use more hydrotreatment catalysts than hitherto needed to remove metals and sulfur of the charge. A shortage of catalytic metals of interest, especially cobalt, is therefore possible. In an effort to recycle both catalytic metals and catalyst supports, thereby creating a renewable source of catalytic metals, attempts have been made to extract metals from hydrotreatment catalysts, including hydrodesulphurization catalysts, and hydrodemetallization.

A general process for leaching hydrotreatment catalysts is described in the US Pat.
United States No. 3,567,433. An aqueous leaching solution containing ammonia and an ammonium salt is contacted with particles of the spent catalyst.

System conditions were not optimized, resulting in poor metal recovery.

 Another leaching process is disclosed in Chemical Abstracts, 94: 178649x. A spent catalyst containing aluminum, vanadium, nickel, cobalt and molybdenum was leached with ammonia and ammonium salts at a temperature above 110 ° C. and at a partial pressure of 40.degree. oxygen greater than 0.1 MPa for more than half an hour.

 Other processes for recovering spent catalyst metals from demetallation or desulfurization are known. U.S. Patent No. 4,216,118 discloses spent chlorination catalysts for the conversion of vanadium compounds to vanadium tetrachloride and nickel compounds to nickel chloride for recovery by extraction. using a solvent. U.S. Patent No. 4,145,397 describes the recovery of spent catalyst metals by high temperature scratching and leaching with caustic alkali.

An article in Engineering and Mining
Journal, May 1978, page 105, describes a spent cobalt-free catalyst treatment plant, by first leaching with sodium hydroxide and then with ammonium carbonate.

 Cobalt is a particularly difficult metal to remove from hydrotreatment catalysts by conventional aqueous leaching techniques. Under optimal leaching conditions, an aqueous leach solution containing ammonia and an ammonium salt seldom removes more than about 50% of the cobalt on the spent catalyst. It was found that if spent catalysts were leached with a first aqueous solution of ammonia and an ammonium salt and then leached with a second aqueous solution containing dissolved sulfur dioxide, total recovery of cobalt could be much greater than 90% of the metal present on the original spent catalyst.

The present invention provides a method for recovering the metals of particles from a spent hydrotreatment catalyst, said metals to be recovered comprising at least one Group VIII metal of the Periodic Table and at least one Group Vb and Group VIb metal of the
Periodic Table, consisting of
(a) grilling the particles in an atmosphere containing molecular oxygen, at a temperature in the range of 400 to 6000C
(b) leaching the particles with a first aqueous solution containing ammonia and an ammonium salt at a temperature below the boiling point at atmospheric pressure of said first aqueous solution to form a first charged liquor and particles leached once
(c) separating the leached particles once from the first charged solution;
(d) leaching the leached particles once with a second aqueous solution containing sulfur dioxide to form a second charged liquor and twice leached particles
(e) separating the second charged liquor from the leached particles twice;
(f) precipitating the metal sulfides of the second charged liquor by the addition of hydrogen sulfide;
(g) roasting said precipitated metal sulfides with fresh spent catalyst of step (a);
(h) transferring the metals contained in the first charged liquor of the class comprising Group Vb and Group VIb metals into a first organic solution by ion exchange in the liquid phase;
(i) extracting the metals from said first organic solution with a first aqueous extraction solution;
(j) separating said metals by successive precipitation;
(k) selectively transferring metals from the
Group VIII of the periodic table of the first liquor charged in at least a second organic solution by ion exchange in liquid phase in series
(l) extracting each of said second organic solutions forming aqueous solutions containing a single metal.

 The single figure of the accompanying drawing is a Raman spectrum illustrating a new vanadium bicarbonate complex.

LEACH
Metals deposited on hydrotreatment catalysts and in particular the nickel, cobalt, molybdenum and vanadium group can all be removed simultaneously from spent hydrotreatment catalysts by the use of an aqueous leaching solution containing ammonia. and an ammonium salt. Used hydrotreating catalysts can be considered as a high grade ore with a particular metal composition. Leaching is the method of choice for removing metals from this particular ore, since the supports are porous and the metals - all are individually capable of leaching; however, in order to simplify the downstream separation of the metals and to allow the maximum recovery of the inorganic support matrix intact, the leaching conditions chosen must not allow the leaching of the iron, which is a frequent impurity of the oil or inorganic support.

 One of the most interesting metals of spent catalysts is cobalt. Normally, less than 50% of the cobalt in the catalyst is leached with an aqueous solution of ammonia. It was found that by contacting the leached catalyst once in the ammonia leaching operation with a second aqueous leachate solution containing dissolved sulfur dioxide (SO), it was possible to recover over 90 Do of the initial total amount of cobalt present on the spent non-roasted catalyst.

 To simplify downstream processing, it is preferable to treat a single aqueous stream containing metals. The best choice for treatment is an aqueous ammonia stream. In order to pass the leached metals through the aqueous solution of SO2 into the ammoniacal solution, the metals are precipitated in the form of sulphides.

The metal sulphides recovered in this manner are mixed with the spent non-roasted catalyst and are exposed to further roasting and leaching with the first aqueous ammonia solution. The first charged liquor, that is to say the product containing the metals of the first aqueous solution, therefore has a cobalt content in equilibrium greater than the value it would have if the charge consisted only of spent catalysts. .

 The spent catalyst, as it exits the catalytic reaction vessel, is heavily contaminated with carbonaceous deposits, also known as "coke", and sulfur.

These impurities are easily removed by combustion in an atmosphere containing molecular oxygen, for example air, but it has been found that the amount of metals leached from the catalyst particles, mainly nickel, tends to be reduced if the catalyst was grilled at a too high temperature. The desirable conditions for the reaction with oxygen are below 600 ° C and preferably between 400 and 5000 ° C. The temperature can be adjusted by diluting the oxygen with nitrogen or by other means known to those skilled in the art. The catalyst thus treated lacks a large carbonaceous residue and the metals contained therein can be easily removed by a first aqueous leaching. The first aqueous leaching solution is a solution of ammonia and an ammonium salt. Such a solution will be alkaline, which is recommended for solubilizing vanadium and molybdenum, and it will contain free ammonia, complexing agent. effective for nickel and cobalt. Solutions of ammonia and ammonium carbonate are particularly well suited because they allow the recycling of the reagent by distillation of the charged liquor and reabsorption in fresh or recycled aqueous solution. Ammonium sulphate constitutes another ammonium salt which is preferred for the implementation of the invention. Nickel and cobalt are free cations and form complexes of the ammine type, and the molybdenum and vanadium are in the form of anionic oxide ions and form ammonium salts.

 The catalyst support in spent catalyst particles frequently consists of alumina. However, mixtures of alumina with other refractory inorganic oxides, for example silica, boron oxide, magnesia and titanium oxide, as well as supports which contain natural clays containing alumina, for example kaolin and halloysite can be leached by the process of the invention.

 It should be noted that the catalyst is normally in the form of uniform geometry particles, elongated extrudates or spherical particles. Other forms may be processed by the process of the invention. The catalyst may be milled or otherwise treated to modify its shape prior to the practice of the invention.

 In a buffered system such as a leach system containing ammonia and an ammonium salt, two parameters must be adjusted for optimal extraction: the concentration of the element to be leached and the pH of the solution solutions. leaching. The solution must contain enough ammonia to complex the nickel and cobalt present, and enough ammonium to adjust the pH. The pH must not be less than 9.5, otherwise the molybdenum and vanadium recoveries are disturbed, and it must not be greater than 11, otherwise the disturbance relates to the nickel and cobalt recoveries.An ammonia concentration aqueous NH3 (aq), hereinafter referred to as ammonia, plus Nli4 + (aq), hereinafter referred to as ammonium, not exceeding 6 M, with approximately equal values of the ammonia concentration and the ammonium concentration, meets these requirements . It is preferred that the solution has at least one hexamolecular ratio of ammonia to the amount of cobalt ion plus the amount of nickel ion calculated by the spent catalyst particles.

The molar concentration of the ammonium salt should not exceed about 2 M, otherwise a vanadium complex precipitates. A particularly preferred leaching system is a system in which the concentration of ammonia is initially about equal to the ammonium ion concentration and the two chemical species are present at concentrations of about 2 M.

 It was found that the leaching time was important for obtaining maximum cobalt yield. To maximize cobalt recovery, the catalyst particles should not be in contact with the leach solution for more than 15 minutes.

The temperature of the leaching is also important.

In general, the number of particular species which pass into solution is greater as the temperature is higher; but an upper limit lies in the boiling point of the solution at atmospheric pressure, above which a pressure vessel is required. In practice, a temperature between about 85 and 950C is optimal. After 15 minutes at about 850 ° C., the leach solution normally contains more than 85% of the molybdenum, about 75 to 80% of the nickel, 75 to 85% of the vanadium and at least 45% of the cobalt. (These percentages refer to the amount by weight of metal in solution compared to the amount of metal that was on the used catalyst before leaching). A proportion of less than 0.1% of the alumina and a proportion of less 5% of the iron are extracted.

 The once leached catalyst particles are then separated from the first charged liquor and contacted with a second aqueous solution of sulfur dioxide prepared by bubbling SO 2 directly into the leach tank or by separately forming an aqueous solution of SO2 and passage of this solution prepared in advance in the leaching tank. The temperature of this solution should be between 65 and 1000C and preferably between 80 and 100 C. Since it is recommended to leach as much metal as possible with as little solution as possible, it is preferred that the second solution be as close as possible to saturation in SO2.

 The double leached catalyst is then separated from the second charged liquor and the metals dissolved therein are precipitated by the addition of hydrogen sulfide to the solution. It was observed that the representative metals precipitated were nickel in an amount of about 5 t; molybdenum and vanadium in an amount of about 2%; and cobalt in an amount of about 35 percent, based on the amount on the non-roasted catalyst. The precipitated metal sulfides are separated from the second charged liquor and are mixed with the spent non-roasted catalyst. The mixture is roasted and leached with ammonia. The temperature of the second charged liquor should be lowered between 10 and 300 ° C before precipitation with H2S. A H2S concentration of about 0.1 M in the second charged liquor precipitates the metals of interest.

 The catalyst support alumina tends to be leached into the second aqueous solution. Representative amounts can reach 10% of the total alumina.

Since iron is not precipitated by hydrogen sulfide, the invention provides an easy separation between the catalytic metals of interest and the contaminating metals of less interest.

Extraction of molybdenum and vanadium
The first charged liquor from the ammonia leach is extracted successively with several liquid ion exchange reagents. Interesting metal ions can be divided into two categories.

In the first category are Group metals
VIII, in particular cobalt and nickel, which are present in the cation state in the charged liquor. In the second category are selected metals in the Groups
V and VI, in particular molybdenum, tungsten and vanadium, which are present in the charged liquor in the form of oxyanions. In the practice of the present invention, the oxyanions are extracted first. The metals of Groups V and VI are transferred into the first organic solution by a first ion exchange in the liquid phase. The extraction can be carried out directly on a charged liquor from the leach solution containing ammonia and an ammonium salt. This solution normally has a pH of approximately 10 to 10.5. The organic extraction substance recommended is a quaternary ammonium compound of general formula RR '3 N + Cl in which R is the methyl group and R' is a group having 8 to 12 carbon atoms. Such organic extractants are sold by Henkel Corporation under the trade name Aliquote 336 and Sherex Chemical Company under the trade name Adogens 464, and are available from Aldrich Chemical Corporation under the trade name Aliquote 336. form of an impure compound of methyltricaprylammonium chloride.

dans lequel x et Z sont de petits nombres entiers, normalement compris entre 0 et 10, et M représente tout oxyanion de métal du Groupe V ou VI, et R peut être tout substituant organique qui rend suffisamment hydrophobe l'amine quaternaire.Il a été observé que lorsque le produit A1iquats 336 constituait le réactif d'échange anionique, l'extraction tendait à être limitée à l'équilibre par le molybdène. Dans la pratique, on a trouvé que, par l'utilisation d'installations d'extraction à étages multiples, on extrayait le molybdène plus rapidement que par des extractions à un seul étage.The quaternary ammonium compounds are in organic solution, preferably in hydrocarbon solution, for example in kerosene, which solution can be conditioned by a paraffinic alcohol such as decanol. The contacting of the aqueous phase with the anionic exchange reagent extracts both molybdenum and vanadium. The reaction can be illustrated by the following general scheme

wherein x and Z are small integers, typically 0 to 10, and M is any Group V or VI metal oxyanion, and R may be any organic substituent that sufficiently quaternary amine is hydrophobic.It has been observed that when the product A1iquats 336 was the anionic exchange reagent, the extraction tended to be limited to equilibrium by molybdenum. In practice, it has been found that, by the use of multi-stage extraction plants, molybdenum is extracted more rapidly than by single-stage extractions.

Extraction and recovery of vanadium and molybdenum
The metals are then transferred from the organic phase into an aqueous phase using an aqueous solution of bicarbonate or carbonate or other anion.

A preferred extraction solution is a saturated aqueous solution of ammonium bicarbonate at a pH of about 8 and at a temperature of about 0 to 300C. We have. observed that extraction tended to be limited by vanadium. In the presence of vanadium, it has been found that the bicarbonate extraction solution is particularly suitable for extracting vanadium from the organic phase.

 When the overall process involves leaching spent catalysts with an aqueous solution of ammonia and an ammonium salt, it is preferable that the extraction solution is a saturated solution of ammonium bicarbonate. In this way, new ions are not introduced into currents, which facilitates the recycling of currents to steps which are upstream in the process. The ammonium ion is recommended, since ammonium metavanadate is a preferred product of this process.

 When vanadium is present, it can be recovered from the aqueous solution by adjusting its pH to about 7, by addition of concentrated HCl. The chloride ion was found to be important for the kinetics of vanadium metavanadate precipitation. Reference is made to the process commented in Zhurnal Prikladnoi Khimii, 43, pages 949-954, 1970. Excess ammonium chloride is added to the aqueous solution and any undissolved ammonium chloride is removed by filtration, which creates a saturated solution of ammonium chloride. The solution is heated at 75-80 ° C. for 20 minutes and then cooled slowly over a period of about 30 minutes to about 300 ° C. the solution is further cooled to about 0 ° C for 3 hours. Crystals are collected by filtration while the solution is cooled, and they are washed with cold water.

 The resulting aqueous solution may contain molybdenum or tungsten, or it may not contain metals. Molybdenum or tungsten may be recovered by reducing the volume of the solution until the metals begin to precipitate. Precipitation can be promoted by adding an appropriate ion to form a less soluble salt, for example calcium hydroxide can be added to precipitate the less soluble calcium molybdate.

Extraction and recovery of cobalt and nickel
The Group VIII metals still in solution in the first charged liquor are each selectively placed in an organic solution by ion exchange in the liquid phase in series. Each organic solution thus formed is then extracted to form an aqueous solution containing the Group VIII metal. The Group VIII metals that predominate in the charged liquor of spent hydrodesulphurization or hydrodemetallization catalysts are nickel and cobalt.

 Nickel is extracted with an organic nickel extraction substance. The organic extraction substances recommended include oximes.

dans laquelle R, R' et R" peuvent représenter divers radicaux organiques hydrocarbonés tels que des radicaux aliphatiques et alkylaryliques. R" peut aussi représenter l'hydrogène. R et R' sont avantageusement des hydrocarbures insaturés ou des groupes alkyle à chaSne ramifiée contenant environ 6 à environ 20 atomes de carbone. R et
R' sont aussi avantageusement égaux. Il est également préférable que R" soit l'hydrogène ou un hydrocarbure insaturé ou un groupe alkyle à chaîne ramifiée contenant environ 6 à 20 atomes de carbone.Hydroxyoxime meets the general formula

in which R, R 'and R "may represent various hydrocarbon organic radicals such as aliphatic and alkylaryl radicals R" may also represent hydrogen. R and R 'are preferably unsaturated hydrocarbons or branched chain alkyl groups containing from about 6 to about 20 carbon atoms. R and
R 'are also advantageously equal. It is also preferable that R "is hydrogen or an unsaturated hydrocarbon or a branched chain alkyl group containing about 6 to 20 carbon atoms.

 Suitable oximes are described, for example, in U.S. Patent Nos. 3,224,873, 3,559,775, 3,455,680, 3,428,499, 3,276,863 and 3,319,274. Particularly suitable extraction substances include 2-hydroxy-4-nonylbenzophenoxime, which is a main extractant in a composition also containing an alpha-hydroxyoxime sold by Henkel Corporation under the tradename LIXs 64N; 7-hydroxy-dodecanone oxime which is the main substance of extraction of a composition sold by Henkel Corporation under the trade name of LIX 63, and 2-hydroxy-4-dodecylbenzophenoxime which is the main substance of extraction of a composition also containing an alpha-hydroxyoxime, sold by Henkel Corporation under the trade name LIXe 64.

 The recommended removal agent is LIX 64N. This agent contains about 46 to 50% of beta-hydroxy benzophenone oxime and about 1 to 2% of an aliphatic alpha-hydroxyoxime in a hydrocarbon diluent such as kerosene. This extraction agent allows an almost quantitative extraction of nickel and offers a very high degree of separation of nickel (II) compared to cobalt (III).

 The nickel is separated from the extraction substance by any conventional solution of exhaustion, for example with sulfuric acid.

 The cobalt is then extracted in the series extractions. The cobalt present in the charged liquor is at the +3 oxidation state and must be reduced to the +2 oxidation state before it can be readily extracted by conventional cobalt extraction agents. Cobalt (III) is conventionally reduced to cobalt (II) by contacting the solution of cobalt (III) with metallic cobalt. Cobalt shot is a form of cobalt metal that can be used for this reduction.

dans laquelle n a une valeur de 1 à 4, m est égal à 0, 1 ou 2 et R est un groupe alkyle ayant 1 à 25 atomes de carbone. Les composés et leur préparation sont décrits dans le brevet des Etats-Unis d'Amérique No 4 152 396 cité en référence et la substance préconisée est vendue par la firme Henkel Chemical sous le nom commercial de LIX 51. The cobalt (II) is then extracted with an extractant containing as extraction substance a metal chelating beta-diketone. A preferred extraction substance is a beta-diketone of the formula

wherein n is 1 to 4, m is 0, 1 or 2 and R is an alkyl group having 1 to 25 carbon atoms. The compounds and their preparation are described in the referenced U.S. Patent No. 4,152,396 and the preferred material is sold by Henkel Chemical under the trade name LIX 51.

Other organic cobalt (II) extracting substances include the oximes, dioximes and diketones mentioned above as nickel extractants.

If the same extraction substance is used for both cobalt and nickel, selectivity can be provided by the degree of oxidation of cobalt.

 The N-chelating beta-diketone used as the extraction substance is preferably dissolved in kerosene with about 10-15% of a conditioning agent. The coupling agent is advantageously an alcohol which contains about 10 carbon atoms, decanol being recommended. A preferred hydrocarbon is kerosene. An example of an advantageous hydrocarbon is the product Kermac 470B which is sold by the firm Kerr-McGee. The proportions in which the beta-diketone-chelation of metals, alcohol and hydrocarbon must be used are governed by considerations such as the rate and degree of completion of the phase separations and the concentration of cobalt in the liquor to be extracted When the decanol and the KermacQ 470B product are selected, respectively, as alcohol and as hydrocarbon, the optimum concentration of decanol is about 15% by volume, the effective range of concentrations being about 10 to 20% by volume.

 The maximum loading capacity of cobalt (II) relative to the 5% by volume solution of beta-diketone extractant is about 2.6 g per liter.

 Beyond this threshold, a precipitation takes place in the organic phase. An organic solution containing about 5% by volume of extraction beta-diketone is normally sufficient to remove all of the cobalt from ammonia leaching of spent catalysts. Therefore, it is preferred that the spent catalyst organic substance solution contain about 5% by volume of beta-diketone and about 15% by volume of decanol, and about 75 to 85% by volume of Kermaco 470B. The extraction step is advantageously carried out at a temperature in the range of approximately ambient temperature to about 400 ° C., and is carried out in one or two phases of countercurrent extraction. cobalt (II) when extracted with a beta-diketone is strongly pH dependent. Cobalt (II) begins to charge weakly acidic solutions, the maximum loading occurring at a pH between 7.5 and 9.5. Therefore, adjusting the ammonia evaporation pH of the leach liquor prior to nickel extraction promotes extraction of cobalt (II). If necessary, the pH can be further adjusted at this stage by addition of sulfuric acid or ammonium hydroxide depending on whether the pH should be raised or lowered. Extractions have been found to be favorable in solutions having an ammonia concentration of less than 50 grams per liter.

 The cobalt-containing organic phase can be extracted by any of a variety of methods. A typical extraction technique commonly used is to extract cobalt with sulfuric acid to produce cobalt sulfate in aqueous phase. Another extraction method that has been found suitable is the use of ammonia solution and ammonium salt to extract cobalt from the organic phase.

 Another method is to add other metal ions, for example copper (II) or nickel (II) to "cobalt" the organic extraction phase by releasing the cobalt in an aqueous solution.

 The aqueous solutions of Group VIII metals produced by the present invention can be further processed to produce pure metal or a salt that can be reused directly to form a new catalyst. Nickel or cobalt can be obtained by electrolysis or directly reduced by hydrogen gas. Aqueous solutions of nickel or cobalt can be used directly as a source of metals for the simultaneous impregnation or pulping of new catalyst.

 The following scheme I illustrates in detail the leaching steps of the present invention.

SCHEMA II

<tb><SEP> Toasting
<tb><SEP> Phase <SEP> aqueous
<tb><SEP> Leaching
<tb><SEP> Liquor <SEP> loaded
<tb> containing
<tb><SEP> Co, <SEP> Ni, <SEP> Mn <SEP>, and <SEP> V
<tb><SEP> Ammonia
<tb><SEP> Extraction
<tb><SEP> (ammonium
<tb><SEP> quaternary)
<tb><SEP> Distillation <SEP> Stalker
<tb><SEP> of <SEP> NH3 <SEP> ~ SEP> aqueous <SEP> $ organic <SEP> Exhaustion
<tb><SEP> of <SEP>
<tb><SEP> 3 <SEP> by
<tb><SEP> I <SEP> tER4) HC03
<tb><SEP> Precipitation
<tb><SEP> Extraction <SEP> of <SEP> V <SEP> by
<tb><SEP> with <SEP> with <SEP> LIX <SEP> 64N <SEP> addition <SEP> of
<tb><SEP> HC1
<tb><SEP> Phase <SEP> Phase
<tb><SEP> aqueous <SEP> 8 <SEP> organic
<tb><SEP> Precipitation
<tb><SEP> of <SEP> Mn
<tb><SEP> Reduction
<tb><SEP> in <SEP> in <SEP> CoII <SEP> Exhaustion
<tb><SEP> Extraction
<tb><SEP> with <SEP> LIX <SEP> 51
<tb><SEP> Phase
<tb><SEP> Organic
<tb><SEP> Solution
<tb><SEP> aqueous <SEP> am
<tb><SEP> moniacal
<tb><SEP> of exhaustion
<Tb>
The spent catalyst is roasted at a temperature of 400 to 600 C. The roasted catalyst is then contacted with an aqueous solution containing both ammonia and an ammonium salt. The temperature of this leaching is maintained at about 900C. The first charged liquor is then treated as shown in Scheme I. The once leached catalyst is contacted with a saturated solution of sulfur dioxide at 65 to 1000 ° C and preferably 80 to 1000 ° C. The second charged liquor is separated from the leached catalysts twice, which are discarded. The second charged liquor is then contacted with hydrogen sulfide, precipitating the metals in the solution. The precipitated metals are mainly cobalt and molybdenum.

The precipitated sulphides are reinjected into the roasting operation in order to be roasted again and leached with the ammoniacal solution. In this way, almost all of the cobalt is recovered, and an ammoniacal stream is obtained for subsequent treatment.

 Scheme II is an overall diagram illustrating all the operations of the invention.

SCHEMA II

<tb><SEP> Catal.-se ~ r <SEP> use
<tb><SEP> Toasting <SEP><<SEP> f
<tb><SEP> Contact <SEP> with
<tb><SEP> solution <SEP> nodding
<tb><SEP> dlamgoniac <SEP> and <SEP> from
<tb><SEP> salt <SEP> drammonium
<tb><SEP> b
<tb><SEP> Separation <SEP> of
<tb><SEP> Catalyst <SEP> and <SEP> of
<tb><SEP> the <SEP> liquor <SEP> loaded
<tb><SEP> Solution <SEP> | <SEP> Catalyst
<tb><SEP> aqueous <SEP> leached
<tb> Treatment <SEP> subse- <SEP> Contact <SEP> with <SEP> one
<tb> quent <SEP> of <SEP> the <SEP> solution <SEP> aqueous
<tb> liquor <SEP> charged <SEP> with sulfur dioxide <SEP>
<tb><SEP> Separation <SEP> of <SEP> Precipitation
<tb><SEP> catalyst <SEP> and <SEP> of <SEP> ~~ -c- <SEP> by <SEP> H2S <SEP> of <SEP> lethal
<tb><SEP> the <SEP> the <SEP> solution <SEP> in <SEP> solution
<tb><SEP> aqueous
<tb><SEP> Evacuation
<tb><SEP> of <SEP> support
<tb><SEP> of <SEP> Catalyst
<Tb>
Metals are recovered from spent catalysts known to contain cobalt, nickel, molybdenum and vanadium. The catalyst is first roasted and leached as described above. The first charged liquor is then extracted with a quaternary amine to form a first set of two streams an organic stream containing molybdenum and vanadium and an aqueous stream containing cobalt and nickel. The first organic stream is depleted with an aqueous solution of ammonium bicarbonate. Hydrochloric acid is added to the aqueous solution of exhaustion and ammonium metavanate is precipitated. The volume of the solution is then reduced and ammonium molybdate is precipitated.

 The excess ammonia is removed from the first aqueous stream by heating the solution. The first remaining charged liquor is first exposed to the air, which ensures the existence of cobalt at the trivalent degree of oxidation. It is then extracted with LIX 64N, which removes nickel and creates a second set of two streams: an aqueous stream containing cobalt and all impurities and an organic stream containing nickel. The second organic solution is extracted with sulfuric acid, which forms an acid solution of nickel-containing sulphate. The cobalt present in the second aqueous stream is reduced on cobalt shot and extracted with LIX 51, which forms a third. set of aqueous and organic streams.

 The third aqueous stream is recycled to the ammonia-enriched leach stage from the ammonia distillation step. The third organic stream is extracted with a solution of ammonia and ammonium carbonate.

 Using Scheme I, there is a process that is fully compatible with ammonia leaching. Therefore, the charged liquor from the leaching must be in aqueous ammonia solution.

 The following examples illustrate in detail various steps of the process of the invention.

Example 1
This example illustrates the ammonia leaching step of the present invention.

 A spent hydrodesulphurization catalyst containing 1.45 wt.% Cobalt and 6.75 wt.% Molybdenum was obtained for use in a pilot plant. The catalyst particles contained, in addition to the catalytic metals, 1.62% by weight of nickel and 6.24% by weight of vanadium as well as 9.86% by weight of carbonaceous deposits and 12.3% by weight of sulfur. .

 The catalyst particles were roasted in a bed about 19.05 mm deep at 3100C for 3 hours, then at 4380C for 3 hours. The temperature never exceeded 4500C. At the end of the roasting, the particles had lost 10.2% of their initial weight.

 This loss of weight was attributed to oxidation, and a subsequent loss was attributed to the atmosphere of carbon and sulfur.

 A leach solution was prepared by dissolving 179 g of (NH4) 2CO3-in 1 liter of 2M aqueous NH40H solution. 98 g of catalyst particles, roasted as above, were placed in a 5 liter flask which was heated to 85 ° C. Aliquots were removed every 5 minutes and analyzed by inductively coupled plasma (ICP) to determine the metal content.

 Table I shows the results obtained.

TABLE I
Time (minutes) Extracted metals,% / -Co ~ 7 / Ni 7 / -o 7 / v 7 / Fe 7 rP ~ 7
5 47 73 86 74 3.6 15
10 47 73 86 76 5.7 17
28 44 85 86 84 4.2 28
Concentrations of nickel, molybdenum and vanadium in the leach liquor increase with time, but the concentration of cobalt tends to decrease after about 10 minutes. The leaching time can be varied to increase the amount of any metal desired. Since phosphorus can interfere with the downstream processing of the leach liquor and is not an interesting metal to recover, stopping leaching when the solution contains small amounts of phosphorus is preferable. this example involved leaching at 850C, the spent catalysts could have been leached at any temperature between 750C and the boiling point of the solution, but preferably between 85 and 950C.

Example 2
This example illustrates another ammoniac leaching as performed in accordance with the invention.

 A spent hydrodesulphurization catalyst containing 1.4% by weight of cobalt, 6.3% by weight of molybdenum, 2.2% by weight of nickel and 4.2 g by weight of vanadium was roasted for 2 hours. at 4270C under a gentle draft. When the carbonaceous and sulphurous residue was almost entirely eliminated by combustion, the roasting was stopped. After cooling the particles, they were placed in 1 liter of solution prepared by dissolving 200 g of (NH 4) 2 CO 3 in 1 liter of 2M aqueous NH 4 OH.

 The metal contents of the solution were determined after 2.0 minutes and after 180 minutes. The results are shown in Table II.

TABLE II
Metals extracted,%
Time (minutes) / Co rani ~ 7 / Mo T 1V 7
20 48 71 89 68
180 31 83 97 87
It can be seen that with a strong prolongation of the leaching time, more nickel, molybdenum and vanadium were recovered, but the cobalt yield was considerably lowered.

Example 3
This is another example of ammoniac leaching of the invention.

Particles of an entangled hydrotraite catalyst were roasted at various temperatures; then placed in a 2M NH4OH ammonia solution of (NH4) 2CO3 iN, except that the test conducted at 8500C was placed in a solution of (NX4) 2CO3 0.5M in
NH40H 2M. Aliquots of solution were taken after 15 minutes and after 180 minutes and analyzed by PCI to determine the metal content. The results are shown in Table III.

TABLE III
Toasting temperature
4270C 6000C 760C 8500C
15 180 15 180 15 180 15 180
Metal Min Min Min Min Min Min Min Min
Metals extracted,%
Co 48 31 46 26 32 34 32 15
Mo 89 97 70 74 81 89 52 62
Nor 71 83 45 46 19 28 8 21
V 68 87 70 73 103 107 80 81
The values given are the percentages of metals leached in the solution, compared to the metal content of the non-leached catalyst.

 Nickel recovery is reduced as the scorching temperature of spent catalyst particles is raised above 6000C. No metal is significantly better recovered than if the spent catalyst was roasted at 4270C.

Cobalt recovery is generally better after 15 minutes at each roasting temperature than after 180 minutes at the same roasting temperature. It is generally better to stop the leaching of the present invention after about 1 hour.

Example 4
This example illustrates the sulfur dioxide leaching of the invention. 30.00 g of spent catalyst used in a pilot plant were leached for 60 minutes in 600 ml of a saturated aqueous solution of 502. The leaching temperature was 850C.

TABLE IV
Fe Ni V Al Co Mo
Heads, ppm 6200 7200 21100 353900 14500 13500
Tails, ppm 3900 6200 18300 372400 3900 13400
Percentage leached 49.38 30.71 30.21 17.65 78.36 20.13
The analysis of the heads, tails and final percentage leached is shown in Table IV.

Example 5
This is another example of leaching with sulfur dioxide according to the invention. 9 g spent catalyst used in a pilot plant was leached for 180 minutes in 170 ml of a saturated aqueous solution of 502 to 880C.

 The analysis of heads, tails and percentage of leached metals is shown in Table V.

TABLE V
Fe Ni V Co Mo
Heads, ppm - 8500 13000 23000 8800
Tails, ppm 1914 3064 7527 2577 7869
Percent Leached - 71.28 53.94 91.09 28.86
Example 6
This example shows the degree of metal precipitation in sulfur dioxide leach solutions obtained in the two preceding examples. Metal sulfides were precipitated by bubbling with H2S in cooled solutions. at room temperature and having a pH of between 3.5 and 4.0. The percentages of metals removed from each leach liquor by sulfur dioxide are shown in Table VI.

TABLE VI
Solution Co Mo Ni V
1 97.7>98.6> 96.0 '92.7
2 97.3 90.1> 94.9 58.2
Example 7
This example shows a coextraction of molybdenum and vanadium in a charged liquor. The pH of the aqueous solution was varied. The most efficient extraction was found to be at a pH of 10.4, which is approximately as high as practically permitted in an ammonia solution. The organic extraction solution was a 10% solution of Aliquat 336 in kerosene, with the addition of 10% decanol. The aqueous solution constituting the feed contained 2.4 g / l of molybdenum, 3.1 g / l of vanadium and had a pH of about 10.1. The pH was raised by addition of NH 4 OH and lowered by addition of H 2 SO 4. The aqueous phase and the organic phase were contacted at room temperature in a dropping funnel. The volume of aqueous solution was equal to the volume of organic solution. The results are reproduced in Table VII.

TABLE VII
No V pH to Duration. g / l, g / l, g / l, g / l
250 phase phase D = organic phase phase phase
contact, aqueous organic aqueous-aqueous organol (min) that ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ 10.4 10 1.06 1.28 0.83 2.83 0.43 7.1 10.1 10 0.86 1.62 0.53 2.97 0.40 7.4
9.6 10 0.60 1.88 0.32 3.14 0.43 7.8 10.1 20 0.88 1.63 0.49 3.14 0.41 7.8
Example 8
This example illustrates the effect of variation in bicarbonate concentrations on the ease of extraction of metals from a 10% solution of Aliquat () 336 in 10% decanol and kerosene, charged both with Molybdenum and vanadium. An aqueous solution was prepared containing the following concentrations of NH 4 HCO 3: 6.84, 13.68, 20.52, 100.0 and 200.0 g per liter. A ratio of aqueous phase to organic phase of 1: 1 was used for all concentrations.

 The results of the tests are reproduced in Table VIII.

TABLE VIII
Initial value Final value [NH4HCO3] pH Mo * Organic aqueous organic Mo
g / l (g / l) (g / l) (g / l) pH
6.84 8.29 3.3 2.9 0.26 8.73
13.68 8.20 3.3 2.5 0.68 8.52
20.52 8.20 3.3 2.1 1.1 8.42
100.0 8.21 3.3 0.4 2.9 8.07
200.0 8.34 4.0 0.3 3.7 8.41
Initial value Final value [NH4HCO3] V * V
g / 1 aqueous organic organic pH (g / l) (g / l) (g / l) (g / l)
6.84 8.29 6.3 6.113 0.025 8.62
13.68 8.20 6.3 6.140 0.081 8.45
20.52 8.20 6.3 6.010 0.182 8.36
100.0 8.21 5.2 3.476 2.070 8.07
200.0 8.34 5.2 1.247 3.360 8.45
* The analysis to determine the metal concentrations of the solution was performed by atomic absorption.

Example 9
Two organic solutions were prepared, one charged with 3.367 g / l molybdenum with 10% Aliquat # 336 in 10% decanol in kerosene, the other being charged with 6.292 g / l vanadium with 10 Aliquat # 336% in 10% decanol in kerosene, and two other aqueous solutions, one of which contained 20 g / l of NH4HCO3 and the other contained 200 g / l of NH4HCO3. Various ratios of the organic phase to the aqueous phase were selected; the results are reproduced in Tables IX and X.

TABLE IX
20 g / l of NH4HCO3 200 g / l of NH4HCO3
PH report Phase Phase fold Phase Phase
aqueous organic aqueous organic (g / l) (g / l) (g / l) (g / l)
15/1 8.97 3.019 1.389 8.70 2.517 9.412
10/1 8.93 2.994 1.459 8.52 1.562 14.182
5/1 8,87 3x189 1,540 8,35 1,036 11,871
2/1 8.59 2.606 1.318 8.22 0.431 6.096
1/1 8,40 2,217 1,097 8,09 0,248 3,315
1/2 8.19 0.570 0.808 8.02 0.151 1.743
1/5 8,19 1,182 0,428 8,03 0,100 0,705
1/10 8,19 0.660 0.266 8.00 0.119 0.350
1/15 8.17 0.635 0.179 8.00 0.127 0.234
Table IX shows the results obtained for the extraction of the molybdenum solution.

PAINTINGS
20 g / l of NH4HCO3 200 g / l of NH4HCO3
PH report Phase Phase pH Phase Phase
aqueous organic aqueous organic (g / 1) (g / i) (g / l) (g / l)
15/1 9.03 6.412 0.162 8.52 5.228 *
10/1 8.97 6.306 0.175 8.35 5.326 *
5/1 8,6 6,144 0,179 8,32 3,850 *
2/1 8,44 6,080 0,177 - 2,310 *
1/1 8,53 6,104 0,178 8,10 0,743 5,700
1/2 8.25 5.715 0.151 8.03 0.251
1/5 8.17 5.690 0.137 8.00 0.186 1.112
1/10 8.17 5,131 0.112 8.02 0.352 0.800
1/15 8,20 5,050 0,100 7,99 0,277 0,385
* Presence of a precipitate.

 Table X shows the results obtained for the extraction of vanadium from the organic phase. An exceptional feature observed with regard to the extraction with 200 g / l of NH4HC03 resides in a greenish color not appearing in the charged aqueous solution present in the case of the 20 g / l solution of NH4HCO3.

This is thought to be an indication of the formation of a vanadium compound not previously reported.

Example 10
The green solution of Example 9 was analyzed by Raman spectroscopy.

TABLE XI
Transitional Energy Intensity Attribution (Cm-1) ..

1063 M CO32-
1019 VS HCO3
917 VS Complex of carbonate of
vanadium V
888 accented 2-
674 W C032
633 W HCO3
438 M Complex of carbonate of
vanadium V
347 W Complex of carbonate of
vanadium V
Raman spectroscopy gives a strong proof of the existence of a V vanadium carbonate complex.

Table XI shows the Raman bands of some solutions containing vanadium and their attribution. All solutions were adjusted to pH 8.8 using nitric acid or sodium hydroxide. Solutions of sodium bicarbonate containing vanadium show a band
Intense Raman at 923 cm 1 and moderate bands at 435 cm 1 and 354 cm 1 as shown by curves b and d in the single figure. These bands show neither vanadium-free sodium bicarbonate (curve c) nor a solution of metavanadate without bicarbonate (curve a). In addition, it has been observed that vanadium bicarbonate solutions usually have a characteristic light green color presumably due to the complex.

Example 11
This example shows the results of the coextraction of Mo and V of the organic solvent loaded, with a solution of 200 g / l NH4HCO3. An organic solution was prepared which contained 3 g / l of molybdenum and 6 g / l of vanadium dissolved in kerosene containing in solution 10% Aliquats 336 and 10% decanol. Various ratios of the organic phase to the aqueous phase have been experimented.

The results are shown in Table XII.

TABLE XII
Organic aqueous organic pH (g / l) ratio
(g / l) (g / l) (g / l)
15/1 8.49 0.168 * 5.175 *
10/1 8.51 0.077 * 4.226 *
5/1 8.52 0.104 * 4.664 *
2/1 8.29 0.051 * 2.166 *
1/1 8.16 0.030 * 0.750 *
1/2 8.01 0.015 0.083 0.321 3.048
1/5 8.03 0.008 0.034 0.234 1.305
1/10 8.00 0.007 0.016 0.211 0.603
1/15 8.00 0.012 0.011 0.349 0.393
* an insoluble precipitate has formed.

Example 12
This example illustrates the production of a solution of cobalt (II) from an aqueous solution initially containing nickel and cobalt.

Used catalyst particles, which were used in a hydrodesulfurization pilot plant, containing cobalt and molybdenum, as catalytic metals, were maintained in contact with a feedstock containing high proportions of vanadium and nickel as impurities. metal retentions. The catalyst particles were leached with an aqueous solution of ammonium carbonate and ammonia at a pH of about 10.5. After heating the solution to evaporate enough ammonia so that the sum ammonia plus ammonium is equal to about 25 g / l at a pH equal to 9, nickel was extracted with LIX64N in kerosene.Then, The solution is passed through a column of cobalt shot and the refined phase leaving this column containing 2.975 g / l of cobalt was extracted with 5% by volume of LIX 51 in 10% decanol and 85% Rermac 470B. at 500C-. The resulting organic solution was extracted with a solution of 2M ammonium carbonate in a 15M ammoniacal solution whose pH had been adjusted to 10.27 by the addition of sulfuric acid. About 25% of the cobalt of the LIX 51 product was removed during each contact with the ammonia extraction solution. After several extractions against
As a result, the resulting cobalt (II) carbonate solution was evaporated to give a cobalt-containing brown powder, presumably consisting of a mixture of oxide and carbonate.

 The cobalt (II) carbonate solution can be recycled directly for the production of the catalyst or it can be processed to obtain a product containing cobalt.

Example 13
Various organic solutions containing cobalt dissolved in the product LIXe 51 were extracted with aqueous solutions of ammonia and ammonium carbonate. The organic solutions contained 5% LIXs 51, 85% Kermac 470B and 10% decanol. The concentration of cobalt in the organic phase was 2.65 g / l in the case of the 3M and 5M ammoniacal solutions and 3.1 g / l in the case of the 15M ammoniacal solution.

The volume ratio of the organic phase (O) to the aqueous phase (A) was varied. The results are summarized in Table XII.

TABLE XIII
Extraction of cobalt with an anonic solution
Organic phase: 5% of LIX D1, 85% of Kermac ~ 470B
and 10% decanol, tc: 500C
Organic concentration / aqueous concentrate (g of Cc / liter)
Extraction solutions NH37 M 15 5 5 3 (NH4) 2CO3, M 2 2.5 2.5 1.5
NH3 Kjeldahl (g / l) 206 pHTA 10.27 10.58 10.4 10.27
Phase Volume Report (O / A)
15/1 2.72 / 0.42
10/1 2.69 / 0.31 2.98 / 1.21 3.0 / 1.05 3.08 / 0.23
5/1 2.45 / 0.51 2.94 / 0.82 2.98 / 0.81 3.04 / 0.31
2/1 2.28 / 0.53 2.83 / 0.52 2.86 / 0.47 3.02 / 0.16
1/1 2.00 / 0.97 2.84 / 6.3-2 2.82 / 0.28 3.01 / 0.12
1/2 1.74 / 0.30 2.67 / 0.21 2.77 / 0.17 2.86 / 0.081
1/5 1.49 / 0.23 2.45 / 0.12 2.52 / 0.094 2.88 / 0.045
1/10 1.32 / 0.15 2.34 / 0.077 2.97 / 0 15 2.82 / 0.028
1/15 1.05 / 0.22 2.06 / 0.06 2.61 / 0.03 2.73 / 0.025
The results indicate that cobalt changes from the organic phase to the aqueous phase more easily in the case of the 15M ammonia solution than in the 5M or 3M ammoniacal solutions. As a result, at higher ammonia concentrations, more cobalt is extracted if the pH is maintained at about 10.5.

 It goes without saying that the present invention has been described for explanatory purposes, but in no way limiting, and that many modifications can be made without departing from its scope.

Claims (26)

 A method for recovering the metal particles of a spent hydrotreatment catalyst, said metals comprising at least one metal Group VIII of the Table Periodic and at least one metal belonging to one of the Groups Vb and VIb of the Periodic Table, characterized in that it consists  (a) grilling the particles in an atmosphere containing molecular oxygen, at a temperature in the range of 400 to 6000C  (b) leaching the particles with a first aqueous solution containing ammonia and an ammonium salt at a temperature below the boiling point at atmospheric pressure of said first aqueous solution to form a first charged liquor and particles leached once  (c) separating the lixed particles once from the first loaded solution  (d) leaching the leached particles once with a second aqueous solution containing sulfurous llanhydride to form a second charged liquor and particles lixitized twice  (e) separating the second charged liquor from the leached particles twice  (f) precipitating the metal sulfides of the second charged liquor by the addition of hydrogen sulfide; and  (g) grilling said precipitated metal sulfides with fresh spent catalyst of step (a)  (h) transferring the metals contained in the first charged liquor of the class comprising Group Vb and Group VIb metals into a first organic solution by ion exchange in a liquid phase  (i) extracting the metals from the first organic solution with a first aqueous extraction solution  (j) separating said metals by successive precipitation  (k) selectively transferring metals from the  Group VIII of the Periodic Table of the first liquor  charged in at least a second organic solution by  ion exchange in liquid phase in series  (1) extracting each of said second solids  organic compounds forming aqueous solutions containing  a unique metal.  2. Process for extracting party metals  of a spent hydrotreatment catalyst, characterized  in that it consists  (a) grilling said catalyst particles  in an atmosphere containing oxygen at a temperature  ture in the range of 400 to 6000C  (b) introducing said roasted particles  catalyst in contact with a first aqueous solution  ammonia and a compound selected from the group of salts  ammonia consisting of ammonium carbonate and sulphate  ammonium chloride, maintained at a temperature  the range of 85 to 950C, in the presence of a gas containing  oxygen  (c) separating said catalyst particles  of said first aqueous solution  (d) bringing said catalyst particles into contact with a second aqueous solution of anhy  sulfurous  (e) separating said catalyst particles  of said second solution  (f) precipitating as a metal sulphide  with hydrogen sulphide the metals present in the said  second solution; and  (g) grilling said pre metal sulfides  precipitated with the fresh spent catalyst of step (a).  3. Process for separating metals from a solution  aqueous composition containing at least one metal selected from  Group VIII and at least one metal chosen in Group V  and Group VI, characterized in that it consists  (a) transferring said Group V metals  and VI in a first organic solution by a first ion exchange in the liquid phase  (b) depleting said first organic solution with a first aqueous extraction solution to form an aqueous solution containing said selected metals in Group V and in Group VI  (c) separating said Group V and Group VI in said first aqueous solution of series precipitation extraction  (d) selectively transferring each of said Group VIII metals into a second organic solution by ion exchange in series. in the liquid phase  (e) extracting each of said second organic solutions to thereby form a single aqueous solution containing the metals.  separating said organic extraction solvent and said aqueous exhaustion solution.  bringing said organic extraction solvent into contact with an aqueous solution of exhaustion maintained at a temperature not exceeding 50 ° C, at a pH of between 7 and 9 and containing at least 75 g / l of a salt of a bicarbonate ion for a period of time sufficient to convert said quaternary ammonium dialkyl metal complexes to water-soluble metal complexes  4. Process for exhausting an organic extraction solvent containing extracted metallic constituents and a quaternary alkylammonium compound, characterized in that it consists  5. Process according to one of Claims 1 and 2, characterized in that the spent hydrotreatment catalysts are fixed on an alumina support.  6. Method according to one of claims 1 and 2, characterized in that said first aqueous solution has a pH maintained in the range of 9.5 to 11 and ammonia concentrations plus ammonium not exceeding 6M.  7. Process according to claim 1, characterized in that the pH of said second aqueous solution is maintained between 2.5 and 3.  8. Process according to claim 1 characterized in that the vanadi m constitutes said metal of Group Vb and the bicarbonate are in said first aqueous solution of exhaustion, and is produced in step (i) a green solution having the Raman spectrum corresponding to the curve (b) of the single figure of the accompanying drawing.  9. The method of claim 2, characterized in that the catalyst particles remain in contact with said first aqueous solution for a period not exceeding 15 minutes.  10. Process according to claim 2, characterized in that the pH of said second solution is maintained between 2.5 and 3.  11. The method of claim 2, characterized in that the temperature of said second solution during said precipitation step is about 200C.  12. Process according to one of claims 1 and 3, characterized in that the metal species selected from Group V and from Group VI comprise oxyanions of the group of metals comprising molybdenum, tungsten and vanadium.  13. Process according to one of claims 1 and 3, characterized in that said first liquid phase ion exchange involves a quaternary alkylammonium salt as a phase transfer reagent.  14. A process according to one of claims 1 and 3, characterized in that the first depletion solution comprises the bicarbonate ion.  15. The process as claimed in claim 5, wherein it involves in step (c) the precipitation of the vanadium and the cooling of the exhaustion solution.  16. A method according to claim 7 or claim 15 subordinate to 12, characterized in that it involves the precipitation of molybdenum by reducing the volume of the depletion solution.  17. Process according to claim 1 or 2, characterized in that the metals selected in the group VII include nickel and cobalt.  18. Process according to claim 1 or 2, characterized in that the nickel is in the divalent state and the cobalt is in the trivalent state.  19. A process according to claim 18, characterized in that in step (d) the nickel is extracted with an extraction substance selected from the group of dioximes and hydroxyoximes.  20. Process according to claim 19, characterized in that it consists in reducing the trivalent cobalt to divalent cobalt and extracting the divalent cobalt with an extraction substance chosen from the group comprising dioximes, hydroxyoximes and beta-diketones .  21. Process according to claim 1 or 2, characterized in that the aqueous solution containing the metals contains the ammonium ion and ammonia, the first extraction solution comprises the ammonium ion and the various extraction solutions comprise the ammonium ion and ammonia, the latter being preferably removed by distillation before step (d).  22. Process according to claim 4, characterized in that said salt of the bicarbonate ion is ammonium bicarbonate.  23. A process according to claim 4 characterized in that the organic extraction solution contains tricaprylylmethylammonium chloride.  24. The process as claimed in claim 4, wherein the extracted metallic constituents comprise Group V and Group VI metals, preferably molybdenum and vanadium.  25. The method of claim 4 characterized in that the extracted metal components comprise vanadium.  26. Process according to claim 4, characterized in that the bicarbonate concentration is at least 160 g / l.