LU85010A1 - PROCESS FOR RECOVERING METALS FROM WASTE HYDROTREATMENT CATALYSTS - Google Patents

Description

8C a 1 graxd-duchê de Luxembourg

..... J (j <M

of . 21.js ^ tenbca.2383. Mllg Monsieur the Minister of Economy and the Middle Classes

Title issued ......................................... Intellectual Property Service

vM? LUXEMBOURG

Patent Application I. Application .... The .... company ............ C.HE ¥ RQU ..... RESEÄ, EC.n .. ... CQMEAN.Y. / ....... 525 ..... iferked; ..... S.tx ££ .t .., (l) ^ -jSM ™ FEMCISCOx .... .C.all £ QrniSU ...... United States ..... dkAmerica., ...... reprégen.r .........

.... té.e ..... p.ax .... Mn.S.î..eWr..Jacques ..... ae..Muyser, ...... agissan.t ..... year ..... quality ..... of .......... (2) * .... raandataixa ............. .................................................. .................................................. .................................................. .................................................. ..........................

- depoae <nt) ce ..... tfin.gt-et-un ..... aeptembxe ..... llo..Q ..... quatr.e.-tfin.gt-tr.a .is (3) “at ............. 1.5 ........... hours, at the Ministry of the Economy and the Middle Classes, in Luxembourg: 1. the present request for obtaining a patent of invention concerning: î ..... î.!. Er.Dcé.dé ..... p.Qur ..... r.é.c .upér.er ...... de.s .... iné.taux ..... de ..... catalysts ..... worn .... dlb.y- .. (4 ) _______ âr.Q.tx.aitemenfc "......................................... .................................................. .................................................. .................................................. .........................

2. the delegation of power, dated, .EIQMM) .7 ..... Califomié ..... 2.2 .... Aug. .... .... l9..8.3 ....... ..

3. description in language .............. fxaPÇ.a.iSÊ ....................... of the invention in two copies; 4. .......... 3 .................. drawing boards, in two copies; . 5. the receipt of taxes paid to the Luxembourg Registration Office on ...:. 2.1 ..... September ..... 1.9..8..3 ......... .................................................. .................................................. .................................................. ............................

declares (s) assuming responsibility for this declaration, that the inventor (s) is (are): -..... Gale ....!. · ...... EU.BRED .., ...... 1.9..6.Q ...... Tulax.e ..... Avenue .., ...... to .... RICHMQND .., .. ... C.alif.Qrn ± e ...._ (5) ......... 9.A.8..Q.5 .., ..... Eta.ts.- Un.is ..... d.!. Aiaér.i.que ................................. .................................................. .................................................. .............

...... D.al.a .... A ....... VAN ..... LEIRSBURG., ....:. 1q4..7 ...... Hel. in .... C.cair ±, ...... to .... P.ETALUMA., .. „. Calif ornie ........ 9.4.9.52., ..... .Efcats.-Hn.is ..... from America ..................................... .................................................. .................................................. ..

claim) for the above patent application the priority of one (s) application (s) of (6) _____________ patent .________________________________________ filed (s) eA / (7) ...... aux ..... E.fc .ats.-Dn ± s ...... &.!. Amer.i.gu.e ._____________ on, ._ jv: oir ..... au .... 3ierso ....... .................................................. .................................................. .................................................. ........................................... (8) * em (eïiseiii ) jxrnr him (her) and, if appointed, for his representative, in Luxembourg .................................

35., hl, d .. Royal ......................................... .................................................. .................................................. .................................................. ...................... (io) requests (s) the issue of a patent for the invention for the subject described and represented in, =. -! abovementioned annexes, (- with postponement of this issue to ___________ D ... / ................................... .......... months. (11) ^. ^ anda ^^ ^ II, Minutes of Deposit

The above patent application has been filed with the Ministry of the Economy and the Middle Classes, Intellectual Property Service in Luxembourg, dated: September 21, 1983

Pr. The Minister at 3 p.m. of the Economy and the Middle Classes, -: p-d.

A 68007

CLAIM OF PRIORITY

* of the patent application / M

56 / TO THE UNITED STATES OF AMERICA From September 24, 1982 (No. 422,813)

September 24, 1982 (No. 422,814)

September 24, 1982 (No. 422.987)

From September 24, 1982 (No. 422,761)

From __ (No. 519,18ο) (c-i-p appl.) Descriptive Brief ^ "filed in support of a request for

PATENT

at

Luxembourg

in the name of: CHEVRON RESEARCH COMPANY

"Process for recovering spent catalyst metals for: hydrotreating".

- * · r

The present invention relates to methods of leaching and recovering metals from spent hydrotreatment catalysts.

Modern progress in the treatment of crude oil is the improvement of feedstocks containing metals and sulfur, for example crude oils and residues, by hydrotreatment processes. This improvement is necessary to convert the heavy load into more attractive fractions of lower boiling point and to remove impurities, especially metals and sulfur which 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 under partial vacuum, leaving the metals in a high boiling fraction generally called the "residual fraction" or "residues". generally at least 35 parts per million metallic impurities, the proportion of which frequently reaches 100 ppm and in extreme cases exceeds 1000 ppm.

These metals and all of the sulfur present are removed thereby improving the charge by treatment of the latter with a catalyst in the presence of hydrogen. Such catalysts generally consist of a solid support which contains catalytic metals, generally molybdenum or tungsten with either nickel or cobalt. As the catalyst is used, metals from the charge will settle on its outer surface and the inner surface of its pores, eventually clogging the pores and reducing the activity of the catalyst to such an extent that it no longer gives the desired quality of the product. Such catalysts will be referred to as "spent catalysts" herein, and they contain catalytic metals, an inorganic support matrix, metals from the feed, sulfur compounds and a hydrocarbon residue.

-t 2: r

The crude oil currently extracted tends to be heavy, forcing refiners to use more hydrotreating catalysts than have been necessary to date to remove metals and load sulfur. A shortage of interesting catalytic metals, especially cobalt, is therefore possible. In an effort to recycle both the catalytic metals and the catalyst supports, thereby creating a renewable source of catalytic metals, attempts have been made to extract metals from hydrotreatment catalysts, especially hydrodesulfurization catalysts and of hydrodemetallization.

A general process for leaching hydrotreatment catalysts is described in U.S. Patent No. 3,567,433. An aqueous leach solution containing ammonia and an ammonium salt is contacted with spent catalyst particles. System conditions have not been optimized, resulting in poor recovery of metals.

Another method of leaching 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 25 ° C. and at partial pressure d oxygen greater than 0.1 MPa for more than half an hour.

Other methods of recovering metals. - used catalysts for 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 solvent extraction. U.S. Patent No. 4,145,397 describes the recovery of metals from spent catalysts by scratching at high temperatures and leaching with caustic alkali.

* 3 "

An article published in Engineering and Mining Journal, May 1978, page 105, describes an installation for treating spent catalysts containing no cobalt, by leaching first with sodium hydroxide and then with ammonium carbonate.

Cobalt is a metal that is particularly difficult to remove from hydrotreatment catalysts by conventional aqueous leaching techniques. Under optimal leach conditions, an aqueous leach solution containing ammonia and an ammonium salt rarely removes more than about 50% of the cobalt present on the spent catalyst. It has been demonstrated that if the spent catalysts are leached with a first aqueous solution of ammonia and an ammonium salt, then 15 leached with a second aqueous solution containing dissolved sulfur dioxide, the total recovery of the cobalt could be much greater than 90% of the metal present on the initial spent catalyst.

The present invention provides a process for recovering metals from particles of a spent hydrotreating catalyst, said metals to be recovered comprising at least one metal from Group VIII of the Periodic Table and at least one metal from Group Vb and from Group VIb of the Periodic Table, method comprising: (a) roasting the particles in an atmosphere containing molecular oxygen at a temperature in the range of 400 to 600 ° C; (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 leaching the particles twice; (e) separating the second charged liquor from the leached particles twice; (f) precipitating the metal sulfides from the second charged liquor by the addition of hydrogen sulfide; (g) roasting said precipitated metal sulfides with the fresh spent catalyst from 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 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 the metals from Group VIII of the Periodic Table from the first liquor 20 loaded into at least one 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 in the accompanying drawing is a Raman spectrum illustrating a new vanadium bicarbonate complex,

LEACHING

Metals deposited on hydro-treatment catalysts and in particular the nickel, cobalt, molybdenum and vanadium combination, can all be removed simultaneously from spent hydrotreatment catalysts by the use of an aqueous leaching solution containing ammonia and an ammonium salt. Spent hydro-treatment catalysts can be considered as a high grade ore which has a particular metallic composition. Leaching is the method of choice for removing metals from this particular ore, since the supports are porous and the metals are all individually capable of leaching; however, to simplify the downstream separation of metals and to allow maximum intact recovery of the inorganic support matrix 5, the leaching conditions which are chosen should not allow the leaching of iron, which is a frequent impurity of oil or inorganic carrier.

One of the most interesting metals; 10 catalysts used is cobalt. Normally, less than 50% of the cobalt in the catalyst is leached with an aqueous ammonia solution. It has been found that by contacting the catalyst leached once in the ammonia leaching operation with a second aqueous leach solution containing dissolved sulfur dioxide (SO2), it was possible to recover more 90% of the total initial 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. To pass the metals leached by the aqueous SO 2 solution into the ammonia solution, the metals are precipitated in the form of sulphides.

The metal sulfides thus recovered are mixed with the spent, non-roasted catalyst and are exposed to further roasting and further leaching with the first aqueous ammonia solution. The first charged liquor, i.e. the metal-containing product of the first aqueous solution, a. Consequently, an equilibrium cobalt content greater than the value it would have if the charge consisted only of spent catalysts.

The spent catalyst, as it leaves the catalytic reaction vessel, is heavily contaminated with carbon deposits, also called "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 toasted at too high a temperature. The desirable conditions for the reaction with oxygen are below 600 ° C and preferably between 400 and 500 ° 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 is devoid of any significant carbon residue. so much and the metals contained therein can be easily removed by a first aqueous leaching. The . first aqueous leach solution is a solution of ammonia and an ammonium salt. Such a solution will be alkaline, which is recommended for dissolving vanadium and molybdenum, and it will contain free ammonia, an effective complexing agent for nickel and for cobalt. Ammonia and ammonium carbonate solutions are particularly well suited, because they allow recycling of the reagent by distillation of the charged liquor and reabsorption in fresh or recycled aqueous solution. Ammonium sulphate constitutes another ammonium salt appreciated for the implementation of the invention. Nickel and cobalt are free cations and form amine complexes, and molybdenum and vanadium are in the form of anionic oxide ions and form ammonium salts.

The catalyst support in the 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 carriers which contain natural clays containing alumina, for example kaolin and halloysite, can be leached by the method 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 can be treated by the method of the invention. The catalyst can be ground or otherwise treated in order to modify its shape before implementing 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 leach element and the pH of the solutions leaching. The solution should contain enough ammonia to complex the nickel and cobalt present, and enough ammonium to adjust the pH. The pH must not be lower than 9.5, otherwise the recoveries of molybdenum and vanadium are disturbed, and it must not be higher than 11, otherwise the disturbance relates to the recoveries of nickel and cobalt. A concentration of aqueous ammonia NH ^ (aq), hereinafter called ammonia, plus NH4 + (aq) hereinafter called ammonium, not exceeding 6 M, with approximately equal values of the ammonia concentration and the concentration of ammonium, meets these requirements. It is preferable that the solution has at least a hexamolecular ratio of ammonia to the amount of cobalt ion plus the amount of nickel ion carried, by calculation, by the spent catalyst particles.

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

It has been found that the leaching time is important for obtaining maximum cobalt yield. To maximize recovery of the cobalt, 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 higher the number of particular species which go into solution, the higher the temperature; but an upper limit lies in the boiling point 8 of the solution at atmospheric pressure, above which a container operating under pressure is required. In practice, a temperature between about 85 and 95 ° C is optimal. After 5 minutes at about 85 ° C, the leach solution normally contains more than 85% of molybdenum, about 75 to 80% of nickel, 75 to 85% of vanadium and at least 45% of cobalt. (These percentages refer to the amount by weight of metal in solution compared to the amount of metal which was on the spent catalyst before leaching). Less than 0.1% of the alumina and less than 5% of the iron are extracted.

The catalyst particles leached once are then separated from the first charged liquor 15 and are brought into contact with a second aqueous solution of sulfur dioxide prepared by bubbling SC> 2 directly into the leach tank or by separate formation of a aqueous SO 2 solution and passage of this solution, prepared in advance, into the leach tank. The temperature of this solution should be between 65 and 100 ° C 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 is as close as possible to the saturation in SO 2.

The catalyst which is leached twice is then separated from the second charged liquor and the metals which are dissolved therein are precipitated by adding hydrogen sulfide to the solution. The representative metals precipitated were observed to be nickel, in an amount of about 5%; molybdenum and vanadium in an amount of about 2%; and cobalt in an amount of about 35%; the percentages referring to the amount present on the non-toasted catalyst. The above-mentioned 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 must be lowered between 10 and 30 ° C

9 before precipitation with Ë ^ S. A concentration of approximately 0.1 M in the second charged liquor causes the metals of interest to precipitate rapidly.

The catalyst support alumina tends to be leached into the second aqueous solution. Representative amounts can reach 10% of the total alumina. Since the iron is not precipitated by hydrogen sulfide, the invention offers an easy separation between the catalytic metals of interest and the contaminating metals of less interest.

Molybdenum and vanadium extraction

The first charged liquor coming from the ammoniacal leaching is extracted successively with several liquid ion exchange reagents. The interesting metal ions can be divided into two categories. In the first category are Group VIII metals, in particular cobalt and nickel, which are present as cations in the charged liquor. In the second category are metals chosen from Groups 20 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 interest in Groups V and VI are transferred to the first organic solution by a first ion exchange in the liquid phase. The extraction can be carried out directly on a charged liquor coming from the leaching solution containing ammonia and an ammonium salt. This solution normally has a pH of about 10 to 10.5. The organic substance of extraction recommended is a quaternary ammonium compound of general formula RR'3N + C1 ”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 of Aliquat 336 and by the Sherex Chemical Company under the trade name of Adogen 464, and can be obtained from Aldrich Chemical under the form of an impure compound of methyltricaprylammonium chloride.

10

The quaternary ammonium compounds are in organic solution, preferably in hydrocarbon solution, for example in kerosene, solution which can be conditioned by a paraffinic alcohol such as decanol. Contacting the aqueous phase with the anion exchange reagent extracts both molybdenum and vanadium. The reaction can be illustrated by the following general diagram:

MaY ”+ y R A - R Ma + AX“ X y; - X 3 10 in which x and y are small whole numbers, normally between 0 and 10, and M represents any metal oxy-anion of Group V or VI, and R may be any organic substituent which makes the hydrophobic sufficiently quaternary amine. It has been observed that when the product Aliquat 336 constitutes the anion exchange reagent, the extraction tends to be limited to equilibrium by molybdenum. In practice, it has been found that, by the use of multi-stage extraction facilities, the molybdenum is extracted faster than by single-stage extractions.

Extraction and: recovery of vanadium and molybdenum

The metals are then transferred from the organic phase to an aqueous phase using an aqueous solution of bicarbonate or carbonate or another 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 30 ° C. It has been observed that the extraction tends 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 the leaching of 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 streams, which facilitates the recycling of streams to stages which are located upstream in the process. Ammonium ion is recommended, since ammonium metavanadate constitutes a popular product of this process.

When vanadium is present, it can be recovered from the aqueous solution by adjusting its pH to about 7, by adding concentrated HCl. The chloride ion has been found to be important for the kinetics of precipitation of vanadium metavanadate. We refer to the process commented on in Zhurnal Prikladnoi Khimii, 43, pages 10 949-954, 1970. Excess ammonium chloride is added to the aqueous solution and any undissolved ammonium chloride is removed by filtration, which creates a saturated ammonium chloride solution. The solution is heated to 75-80 ° C for 20 minutes, then cooled slowly over a period of about 30 minutes to about 30 ° 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 can be recovered by reducing the volume of the solution until the metals begin to precipitate. Precipitation can be promoted by the addition of a suitable 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 30 The Group VIII metals which are still in solution in the first charged liquor are each placed selectively in an organic solution by ion exchange in liquid phase in series. Each organic solution thus formed is then extracted so as to form an aqueous solution containing the Group VIII metal. The Group VIII metals which predominate in the liquor charged with spent hydrodesulfurization or hydro-demetallation catalysts are nickel and cobalt.

12

Nickel is extracted with an organic nickel extraction substance. The recommended organic extraction substances include oximes. Hydroxyoxime has the general formula 5 OH NOH

I II

R-Ç - C - R1 R "wherein R, R 'and R" can represent various organic hydrocarbon 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 preferably 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. Patents No. 3,224,873, No. 3,592,775, No. 3,455,680, No. 3,428,499, No. 3,276,863 and No. 3,197,274. Particularly suitable extractants include 2-hydroxy-4-nonylbenzophenoxime which is a primary extractant in a composition also containing an alpha-hydroxyoxime sold by Henkel Corporation under the trade name LIX 64N; 8-diethyl-7-hydroxy-6-dodecanoneoxime which is the main substance for extracting a composition sold by the company Henkel Corporation under the trade name of LIX 63; and 2-hydroxy-4-4-dodecylbenzophenoxime which is the main substance for extracting a composition also containing an alpha-hydroxyoxime, sold by the company Henkel Corporation under the trade name of LIX 64.

The recommended extracting agent is product 35 LIX 64N. This agent contains approximately 46 to 50% of beta-hydroxybenzophenoneoxime and approximately 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) from cobalt (III).

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

The cobalt is then extracted, in serial extractions. The cobalt present in the charged liquor; ‘10 is at the degree of oxidation +3 and must be reduced to the degree of oxidation +2 before it can be easily extracted by conventional cobalt extracting agents. Cobalt (III) is conventionally reduced to cobalt (II) by contacting the cobalt (III) solution with metallic cobalt. Cobalt shot is a form of metallic cobalt that can be used for this reduction.

The cobalt (II) is then extracted with an extractant containing as the extraction substance a metal chelating beta-diketone. A popular extractant is a beta-diketone with the formula igM? - CH2-C- (CP2) mCP3

Zi Rn in which n has a value from 1 to 4, m is equal to 0, 1. - or 2 and R is an alkyl group having 1 to 25 carbon atoms. The compounds and their preparation are described in US Pat. No. 4,152,396 cited in reference and the recommended substance is sold by the company Henkel Chemical under the trade name of LIX 51. Other organic substances Cobalt (II) extractors include the oximes, dioximes and diketones mentioned above as nickel extractants.

If the same extractant is used for both cobalt and nickel, selectivity can be offered by the degree of oxidation of cobalt.

14 ”t

The metal chelating beta-diketone used as an extraction substance is advantageously dissolved in kerosene with about 10-15% of a conditioning agent. The conditioning agent is advantageously an alcohol which contains approximately 10 carbon atoms, decanol being recommended. A popular 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 metal chelating beta-diketone, alcohol and hydrocarbon are to be used are governed by such considerations as the rate and degree of completion of the phase separations and the concentration of cobalt in the mixture. liquor to be extracted. When decanol and product © Kermac 470B are chosen, respectively, as alcohol and as hydrocarbon, the optimum concentration of decanol is approximately 15% by volume, the effective range of concentrations being approximately 10 to 20% by volume .

The maximum loading capacity of cobalt (II) with respect to the 5% by volume solution of beta-diketonic extractant is approximately 2.6 g per liter. Beyond this threshold, precipitation takes place in the organic phase. An organic solution containing about 5% by volume of extracted beta-diketone is normally sufficient to remove all of the cobalt from ammonia leaching of spent catalysts. Therefore, it is preferable that the organic extract solution for spent catalysts contains about 5% by volume of beta-diketone and about 15% by volume of decanol, and about 75 to 85% by volume of Kermac 470B. The extraction step is advantageously carried out at a temperature ranging from approximately ambient temperature to approximately 40 ° C., and it is carried out in one or two extraction phases against the current. The loading of cobalt (II) during an extraction with a beta-diketone strongly depends on the pH. Cobalt (II) begins to charge weakly acidic solutions, maximum loading

> I

15 occurring at a pH between 7.5 and 9.5. Therefore, adjusting the pH by evaporation of ammonia from the leach liquor before nickel extraction promotes the extraction of cobalt (II). If desired, the pH can be further adjusted at this stage by adding sulfuric acid or ammonium hydroxide depending on whether the pH is to be raised or lowered. Extractions have been found to be favorable in solutions having an ammonia concentration of less than 50 g per liter.

The organic phase containing cobalt can be extracted by any of a variety of methods. A conventional extraction technique frequently used is to extract cobalt with sulfuric acid to produce cobalt sulfate in the aqueous phase. Another extraction method which has proved suitable is the use of an ammonia solution and an ammonium salt to extract the cobalt from the organic phase.

Another method is to add other metal ions, for example copper (II) or nickel (II) to "collect" the cobalt from 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 which can be reused directly to form a new catalyst. Nickel or cobalt can be obtained by electrolysis or directly reduced by hydrogen gas. The aqueous solutions of nickel or cobalt can be used directly as a source of metals for the impregnation or simultaneous pulping of new catalyst.

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

t »% 16

DIAGRAM I

Wire mesh

I

Aqueous phase - ^ Leaching

'' ’I

Loaded liquor - - container

’" Co, Ni, Mn and V

Ammonia i

Extraction (quaternary ammonium)

Distillation ^ aculuse ï orqaniaue _, de NH - · —-1 == --- "* - Depletion _3 by i

(NH4) HCO- I

i 4!

Precipitation j

Extraction of V by j

with LIX 64N addition of I

HCl!

Phase r Aqueous phase r | organic y Î]. Precipitation | of Mn "i Reduction in Coll Depletion Ί

Extraction _ with LIX 51

Organic Phase I

Aqueous ammonia solution for exhaustion “t ► · 17

The spent catalyst is roasted at a temperature of 400 to 600 ° C. The roasted catalyst is then brought into contact with an aqueous solution containing both ammonia and an ammonium salt. The temperature of this leaching is maintained at about 90 ° C. The first charged liquor is then treated as indicated in diagram I. The leached catalyst once is brought into contact with a saturated solution of sulfur dioxide between 65 and 100 ° C and preferably between 80 and 100 ° C. The second charged liquor is separated from the double leached catalysts, which are discarded. The second charged liquor is then brought into contact with hydrogen sulphide, which causes the metals to precipitate from the solution. The precipitated metals are mainly cobalt and molybdenum.

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

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

•; c 18

DIAGRAM II

“T -

Wire mesh --— "I"

Contact with aqueous solution of arrmoniac and ammonium salt Separation of the catalyst and the loaded liguer

Solution I Aqueous catalyst | leachate f— - *

Subsequent treatment Contact with an aqueous solution solution laden with sulfur dioxide! F Separation of precipitation __ catalyst and tpar K ^ S of metals the solution in aqueous solution

Evacuation of the catalyst support 19 'J ·

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 exhausted with an aqueous solution of ammonium bicarbonate. Hydrochloric acid is added to the aqueous depletion solution and ammonium metavanadate 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 air, which ensures the existence of cobalt at the trivalent degree of oxidation. It is then extracted with LIX 64N, which removes the 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 acidic sulfate solution containing nickel. 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 leaching step, enriched in ammonia from the ammonia distillation step. The third organic stream is extracted with a solution of ammonia and ammonium carbonate.

Using Scheme I, a pro-cede is available which is fully compatible with ammonia leaching. Consequently, the charged liquor coming from the leaching must be in aqueous ammoniacal solution.

'‘*» 20

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 used hydrodesulfurization catalyst containing 1.45% by weight of cobalt and 6.75% by weight of molybdenum was obtained, having been used in a pilot installation. 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 carbon deposits and 12.3% by weight sulfur.

The catalyst particles were roasted in a bed about 19.05 mm deep at 310 ° C for 3 hours, then at 438 ° C for 3 hours. The temperature never exceeded 450 ° C. By the end of roasting, the particles had lost 10.2% of their original weight.

This weight loss has been attributed to oxidation, and subsequent loss has been attributed to the atmosphere of carbon and sulfur.

A leaching solution was prepared by dissolving 179 g of (NH ^^ CO ^ in 1 liter of 2M aqueous solution of NH ^ OH. 98 g of catalyst particles, roasted as above, were placed in a flask. 5 liters which were heated to 85 ° C. Aliquots were taken every 5 minutes and analyzed by inductively coupled plasma (PCI) to determine the metal content.

Table I shows the results obtained.

30 - TABLE I

Time (minutes) _Metals extracted,% _ Γc ° _7 Γnî_7 Γmo_7 / “v_7 ΓFe_7 /“ p_7 5 47 73 86 74 3.6 15 35 10 47 73 86 76 5.7 17 28 44 85 86 84 4.2 28

The concentrations of nickel, molybdenum and vanadium in the leach liquor increase over time, but the concentration of cobalt tends to decrease after 1 t 21 of about 10 minutes. The leach time can be varied to increase the amount of any metal that is desired. Since phosphorus can interfere with downstream processing of leach liquor 5 and is not a valuable metal to recover, stopping leaching when the solution contains small amounts of phosphorus is preferable. Although this example involved leaching at 85 ° C, the spent catalysts could have been leached at any temperature between 75 ° C and the boiling point of the solution, but preferably between 85 and 95 ° C .

Example 2

This example illustrates another ammoniacal leaching as carried out in accordance with the invention. A spent hydrodesulfurization catalyst containing 1.4% by weight of cobalt, 6.3% by weight of molybdenum, 2.2% by weight of nickel and 4.2% by weight of vanadium was roasted for 2 hours at 427 ° C under a gentle draft. When the carbon and sulfur residue was almost completely removed 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 2 ^ CO-j in 1 liter of 2 M aqueous NH4OH.

The metal contents of the solution were determined after 20 minutes and after 180 minutes. The results are shown in Table II.

TABLE II

_Metals extracted,% _

Time (minutes) ΓCo_7 Γ ~ Ni_7 Γ ~ Mo_7 ΓV_7 30 20 48 71 89 68 180 31 83 97 87

It can be seen that with a long extension of the leaching time, more nickel, molybdenum and vanadium were recovered, but the yield of cobalt 35 was considerably lowered.

Example 3

This is another example of ammoniacal leaching of the invention.

I!

- .. P

i V.- 22

Particles of a spent hydrotreatment catalyst were roasted at various temperatures, then placed in an ammoniacal solution NH ^ OH 2M of (NH ^) 2CO2 1M, with the difference that the test carried out at 850 ° C 5 was placed in a solution of (NH ^^ CO ^ 0.5M in NH ^ OH 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 reproduced in Table III.

~ 10 TABLE III

Broiling temperature

427 ° C 600 ° C 760 ° C 850 ° C

15 180 1.5 .180 15 180 15 180 Metal min min min min min min min min 15 _Metals extracted,% _

Co 48 31 46 26 32 34 32 15

MB 89 97 70 74 81 89 52 62

Ni 71 83 45 46 19 28 8 21 V 68 87 70 73 103 107 80 81 20 The values indicated are the percentages of metals leached in the solution, compared to the metal content of the non-leached catalyst.

The recovery of nickel is reduced as the roasting temperature of the spent catalyst particles is raised above 600 ° C. No metal is much better recovered than if the spent catalyst were roasted at 427 ° C. Cobalt recovery is generally better after 15 minutes at each roasting temperature than after 180 minutes at the same roasting temperature. It is generally best 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 SC> 2. The leaching temperature was 85 ° C.

Î · I

23

TABLE IV

Fe Ni V Al Co Mo Heads, ppm 6200 7200 21100 353900 14500 13500

Tails, ppm 3,900 6,200 18,300 372,400 3,900 13,400 5 Percent leached 49.38 30.71 30.21 17.65 78.36 20.13 Analysis of heads, tails and final percentage leached is shown in Table IV.

Example 5 This is another example of sulfur dioxide leaching according to the invention. 9 g of spent catalyst used in a pilot installation were lixi-viated for 180 minutes in 170 ml of a saturated aqueous solution of SC> 2 at 88 ° C.

15 The analysis of the heads, tails and percentage of leached metals is reproduced in Table V.

TABLE V

Fe Ni V Co Mo Heads, ppm - 8500 13000 23000 8800 20 Tails, ppm 1914 3064 7527 2577 7869

Percentage leached - 71.28 53.94 91.09 28.86

Example 6

This example shows the degree of precipitation of the metals in sulfur dioxide leached solutions obtained in the two previous examples. Metal sulfides were bubbled from solutions cooled to room temperature and having a pH between 3.5 and 4.0. The percentages of metals removed from each sulfur dioxide leach liquor are shown in Table VI.

TABLE VI

Co Mo Ni V solution

1 97.7> 98.6> 96.0 92.7 35 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. We found that extraction ”24

i * t I

the most effective was carried out at a pH of 10.4, which is approximately as high as practice allows 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 charge contained 2.4 g / l of molybdenum,

3.1 g / 1 vanadium and had a pH of about 10.1. PH

was raised by addition of NH ^ OH and lowered by addition of I ^ SO ^. The aqueous phase and the organic phase were brought into contact at room temperature in a dropping funnel. The volume of aqueous solution was equal to the volume of organic solution. The results are shown in Table VII.

TABLE VII

15 _Mo_ _V_ pH at Duration, g / 1, · g / 1, oraanicn._ g / 1, g / 1 omanioue 25 of phase phase D = —phase phase D ~ a ^^ p · contact, organic-aqueous q orga - aqueous ^ _ (min) que___nique__ 20 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 3.11 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 varying bicarbonate concentrations on the ease of extracting metals from a 10% solution of Aliquat® 336 in 10% decanol and kerosene, loaded with both molybdenum and vanadium. An aqueous solution was prepared containing the following NH 2 HCOg concentrations: 6.84, 13.68, 20.52, 100.0 and 200.0 g per liter. A ratio of the aqueous phase to the organic phase of 1: 1 was used for all concentrations.

The results of the tests are shown in Table VIII.

»I

25

TABLE VIII

Initial value _ Final value_ / ~ NH4HC03_7 pH Mo * _Mo_ ,, organic organic aqueous „

5 9/1 _ (q / 1) (q / 1) (q / 1) P

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 10 200.0 8.34 4.0 0.3 3.7 8.41 _ Initial value Final value_ L nh4hco3_7 v * yd / 1 organic organic pH aqueous „_ _ (g / 1) (g / 1) (q / 1) J_ 15 6.84 8.29 6.3 6.132 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 20 * Analysis to determine the metal concentrations of the solution was carried out by atomic absorption.

Example 9

Two organic solutions were prepared, one loaded with 3.367 g / l of molybdenum with 10% Aliquat 336 in 10% decanol in kerosene, the other being loaded with 6.292 g / l of vanadium with 10 % Aliquat 336 in 10% ^ decanol in kerosene, and two other aqueous solutions, one of which contained 20 g / l of NH ^ HCO ^ and the other of which contained 200 g / 1 of NH ^ HCO ^ . Various relationships have been selected from the organic phase to the aqueous phase; the results are shown in Tables IX and X.

26 1 t f »*

TABLE XX

20 g / 1 NH4HC03 200 g / 1 NH4HC03

PH report Phase Phase pH Phase Organic phase aqueous organic aqueous

5 _ _ (l / R (l / D _ (l / D (l / D

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 3.189 1.540 8.35 1.036 11.871 2/1 8.59 2.606 1.318 8.22 0.431 6.096 10 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 / 1 NH4HC03 200 g / 1 NH4HCC> 3

PH report Phase Phase pH Phase Phase 20 organic aqueous organic aqueous (g / 1) (g / 1) (g / 1) (g / 1) 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 * 25 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 ï- “1/5 8.17 5.690 0.137 8.00 0.186 1.112 1/10 8.17 5.131 0.121 8.02 0.352 0.800 30 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 characteristic observed with regard to ex-traction with 200 g / l of NH4HC03 lies in a greenish color which does not appear in the charged aqueous solution present in the case of the 20 g / l solution of NH4HC03.

This is believed to be indicative of the formation of a vanadium compound not previously reported.

Example 10

The greenish solution of Example 9 was analyzed by Raman spectroscopy.

5 TABLE XI

Transition energy Intensity Allocation (cm ~ 1) _ _ 1063 M c032_ 10 1019 VS HC032 ”917 VS Carbonate complex

vanadium V

v · 888 accented? 674 W C032 "15 633 W HC03 ~ 438 M Carbonate complex

vanadium V

347 W Carbonate complex

vanadium V

20 Raman spectroscopy gives strong proof of the existence of a vanadium carbonate V complex.

Table XI shows the Raman bands of certain solutions containing vanadium and their allocation. All solutions were adjusted to pH 8.8 using nitric acid or sodium hydroxide. Sodium bicarbonate solutions containing vanadium show a “1 -1 band

Intense Raman at 923 cm and moderate bands at 435 cm “1 • and at 354 cm as shown by curves b and d of the single figure. These bands show neither sodium bicarbonate free of vanadium (curve c) nor a solution of metavanadate free of bicarbonate (curve a). In addition, it has been observed that vanadium bicarbonate solutions ordinarily have a characteristic light green color presumably due to the complex.

: 1 i 28

Example 11

This example shows the results of the coextraction of Mo and V of the charged organic solvent, with a 200 g / l solution of NH ^ HCO ^. 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 S of Aliquat® 336 and 10% decanol. Various relationships have been experienced from the organic phase to the aqueous phase.

The results are shown in Table XII.

10 TABLE XII

'' Organic pH ratio (g / 1) aqueous organic aqueous (g / D (g / D (g / 1) 15/1 8.49 0.168 * 5.175 * 10/1 8.51 0.077 * 4.226 * 15 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 20 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 cobalt (II) solution from an aqueous solution initially containing nickel and cobalt.

Spent catalyst particles, used in a pilot hydrodesulfurization plant, containing cobalt and molybdenum, as the catalytic metals, were kept in contact with a charge containing high proportions of vanadium and nickel, as impurities metallic. 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 for the ammonia plus ammonium sum to be approximately 25 g / l at a pH of 9, nickel was extracted using LIX 64N in kerosene. Then, the solution was passed over 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 decanol at 10% and 85% Kermac® 470B at 50 ° C. The resulting organic solution was extracted with a solution of 2M ammonium carbonate in a 15M ammonia solution whose pH had been adjusted to 10.27 by addition of sulfuric acid. About 25% of the cobalt of the LIX 51 product was eliminated during each contact with the ammo-10 niacale extraction solution. After several countercurrent extractions, the resulting cobalt (II) carbonate solution was evaporated to give a brown powder containing cobalt, 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 treated to obtain a product containing cobalt.

Example 13 Various organic solutions containing cobalt dissolved in product LIX 51 were extracted with aqueous solutions of ammonia and ammonium carbonate. The organic solutions contained 5% LIX 51, 85% Kermac 470B and 10% decanol. The concentration of cobalt in the organic phase was

2.65 g / 1 in the case of 3M and 5M ammonia solutions

tr, and 3.1 g / 1 in the case of the 15M ammoniacal solution.

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

ê τ 30

TABLE XIII

Cobalt extraction with ammonia solution Organic phase: 5% LIX® 51, 85% Kermac® 470B and 10% decanol, temperature 50 ° C

5 Organizational concentration / aqueous concentrate (g of Co / liter)

Extraction solutions NH3, M 15 5 5 3 (NH4) 2C03, M 2 2.5 2.5 1.5 10 NH3 Kjeldahl (g / 1) 206 "pHTA 10.27 10.58 10.4 10.27

Ratio of phase volumes (O / A) 15/1 2.72 / 0.42 15 10/1 2.69 / 0.31 2.98 / 1.21 3.0 / 1.05 3.08 / 0 , 23 5/1 2.45 / 0.51 2.9.4 / 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 / 6.32 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 20 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 / 0.015 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 passes from the organic phase to the aqueous phase more easily in the case of the 15M ammoniacal solution than in that of the 5M or 3M ammoniacal solutions. Therefore, at high ammonia concentrations, more cobalt is extracted if the pH is kept at around 10.5.

, u.- · It goes without saying that the present invention has only been described by way of explanation, but in no way limiting, and that numerous modifications can be made without departing from its scope.

Claims (26)

31 1. Process for recovering the metals from particles of a spent hydrotreatment catalyst, said metals comprising at least one metal from Group VIII of the Periodic Table and at least one metal belonging to one of Groups Vb and VIb of the Periodic Table , characterized in that it consists of: (a) roasting the particles in an atmosphere containing molecular oxygen, at a temperature in the range from 400 to 600 ° C; (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 loaded solution; (d) leaching the leached particles once with a second aqueous solution containing sulfur dioxide to form a second charged liquor and leached particles twice; (e) separating the second charged liquor from the leached particles twice; (F) precipitating the metal sulfides from the second charged liquor by the addition of hydrogen sulfide; and (g) roasting said precipitated metal sulfides with the fresh spent catalyst from 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; ί 32 *. t (k) selectively transferring the metals of Group VIXX from the Periodic Table from the first liquor loaded into at least one second organic solution by ion exchange in liquid phase in series; 5 (1) to extract each of said second organic solutions forming aqueous solutions containing a single metal. 2. Method for extracting metals from particles of a spent hydrotreating catalyst, characterized in that it consists of: ^ (a) roasting said catalyst particles in an oxygen-containing atmosphere at a temperature included in the range of 400 to 600 ° C; (b) bringing said roasted particles of catalyst into contact with a first aqueous solution of ammonia and of a compound chosen from the group of ammoniated salts consisting of ammonium carbonate and ammonium sulfate, maintained at a temperature in the range of 85 to 95 ° C in the presence of an oxygen-containing gas; (c) separating said catalyst particles from said first aqueous solution; (d) bringing said catalyst particles into contact with a second aqueous solution of sulfur dioxide; (e) separating said catalyst particles from said second solution; .v = „· (f) precipitating the metals present in said second solution as metallic sulfide with hydrogen sulfide; and (g) roasting said precipitated metal sulfides with the fresh spent catalyst from step (a). 3. Process for separating metals from an aqueous solution containing at least one metal chosen from the 35 Group VIII and at least one metal chosen from Group V and Group VI, characterized in that it consists: (a) in transferring said metals from Groups V and VI into a first organic solution with a first 33 * 'r ion exchange in liquid phase; (b) depleting said first organic solution with a first aqueous extraction solution so as to form an aqueous solution containing said metals selected from Group V and from Group VI; (c) separating said Group V and Group VI metals in said first aqueous extraction solution by serial precipitation; (d) selectively transferring each of said Group VIII t-metals to a second organic solution by serial ion exchange in the liquid phase; it is to extract each of said second organic solutions so as to thus form a single aqueous solution containing the metals. 4. A method for exhausting an organic extraction solvent containing extracted metallic constituents and a quaternary alkylammonium compound, characterized in that it consists in: bringing said organic extraction solvent into contact with an aqueous solution of depletion maintained at a temperature not exceeding 50 ° C, at a pH between 7 and 9 and containing at least 75 g / 1 of a salt of a bicarbonate ion, for a period sufficient to convert said metal complexes of quaternary alkyl ammonium in water-soluble metal complexes; separating said organic extraction solvent and said aqueous depletion solution. 5. Method 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 concentrations of ammonia plus ammonium not exceeding 6M. 7. The method of claim 1, charac terized in that the pH of said second aqueous solution is maintained between 2.5 and 3. 34 *. i 8. A method according to claim 1, characterized in that vanadium constitutes said Group Vb metal and the bicarbonate is in said first aqueous depletion solution, and in step (i) a greenish solution is produced having the Raman spectrum corresponding to curve (b) of the single figure of the attached drawing. 9. A method according to claim 2, characterized in that the catalyst particles remain in contact with said first aqueous solution for a period not exceeding 15 minutes. 10. Method 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, charac terized in that the temperature of said second solution during said precipitation step is about 20 ° C. 12. Method according to one of claims 1 and 3, characterized in that the metallic species chosen from Group V and from Group VI comprise oxyanions from the group of metals comprising molybdenum, tungsten and vanadium. 13. Method according to one of claims 1 and 3, characterized in that said first ion exchange in the liquid phase involves a quaternary alkylammonium salt as phase transfer reagent. 14. Method according to one of claims =; 1 and 3, characterized in that the first exhaustion solution comprises the bicarbonate ion. 15. Method · according to claim 5 subor given to 1 or claim 12, characterized in that it involves in step (c) the precipitation of vanadium and the cooling of the exhaustion solution. 16. Method according to claim 7 or claim 15 subordinate to 12, characterized in that it involves the precipitation of molybdenum by reduction of the volume of the exhaustion solution. * 35 17. The method of claim 1 or 2, characterized in that the metals selected from Group VII include nickel and cobalt. 18. The method of claim 1 or 2, 5 characterized in that the nickel is in the divalent state and the cobalt is in the trivalent state. fl 19. The method of claim 18, characterized in that, in step (d), nickel is extracted with an extraction substance selected from the group of "10 dioximes and hydroxyoximes. 20. The process as claimed in claim 19, characterized in that it consists in reducing the trivalent cobalt to divalent cobalt and in extracting the divalent cobalt with an extracting substance chosen from the group comprising dioximes, hydroxyoximes and beta-diketones. 21. Method 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 include ammonium ion and ammonia, the latter being preferably removed by distillation before step (d). 22. The method of claim 4, characterized in that said salt of the bicarbonate ion is ammonium bicarbonate. ,. 23. The method of claim 4, charac terized enuce that the organic extraction solution con- =, * · 'holds tricaprylylmethylammonium chloride. 24. The method of claim 4, characterized in that the metal constituents extracted include Group V and Group VI metals, preferably molybdenum and vanadium. 25. The method of claim 4, characterized in that the extracted metallic constituents comprise vanadium. 26. The method of claim 4, characterized in that the bicarbonate concentration is at least 160 g / 1.