WO1982001369A1

WO1982001369A1 - Stabilization of substituted 8-hydroxyquinoline hydrometallurgical reagents

Info

Publication number: WO1982001369A1
Application number: PCT/US1981/001378
Authority: WO
Inventors: Chem Co Sherex; David L Gefvert; Harvey J Richards
Original assignee: Sherex Chem
Priority date: 1980-10-22
Filing date: 1981-10-19
Publication date: 1982-04-29
Also published as: EP0063137A1

Abstract

Method for substantially maintaining the loading capacity of a 7-(//c-alkenyl)-substituted 8-hydroxyquinoline hydrometallurgical reagent which comprises reducing the //c-alkenyl unsaturation while minimizing the saturation of the hydroxyquinoline group.

Description

STABILIZATION OF SUBSTITUTED 8-HYDROXYQUINOLINE HYDROMETALLURGICAL REAGENTS

Background of the Invention

The present invention relates to substituted 8-hydroxyquinoline hydrometal lurgical reagents useful in selective solvent extraction of metal values from an aqueous solution thereof and more particularly to a method for stabilizing such reagent for maintaining its loading capacity during such solvent extraction process.

Subtituted 8-hydroxyquinoline reagents, such as disclosed in U. S. Patents No. 4,045,441 and 4,066,652, have been shown to be effective in extracting metal values (ions) from aqueous solutions thereof by a solvent extraction process. Briefly, such solvent extraction process comprises contacting the aqueous solution of the metal with a hydrocarbon solvent containing the reagent followed by separation of the resulting organic and aqueous phases. The organic phase containing the metalreagent complex or chelate then is contacted with an aqueous acidic stripping solution in order to concentrate the metal values in the acidic aqueous phase and to regenerate the reagent in the organic solvent phase. By judicious selection of process conditions, desirable metal values can be selectively separated and concentrated from other metal values by this process.

While such hydrometallurgical reagents typically have an acceptable initial loading capacity for the desired metal values to be recovered, the loading capacity of the reagent significantly declines and protracted phase separation times are experienced as the process proceeds with continual regeneration of the reagent. Accordingly, an effective method for stabilizing such substituted 8-hydroxyquinoline reagents for substantially maintaining the loading capacity thereof is needed.

Broad Statement of the Invention

The present invention is directed to a method for substantially maintaining the loading capacity of a 7-(α-alkenyl)-substituted 8-hydroxyquinoline hydrometallurgical reagent. Such method comprises reducing the α-alkenyl unsaturation while minimizing the saturation of the hydroxyquinoline group thereof. Another aspect of the invention is directed to the use of such stabilized substituted 8-hydroxyquinoline reagent in a process for the selective recovery of one metal from the dilute aqueous solution of two or more metals wherein the aqueous solution is intimately contacted with the hydrocarbon solvent containing the stabilized reagent dissolved therein to provide a metal-reagent chelate in the solvent. The chelate- containing solvent then is intimately contacted with an aqueous acidic stripping solution to provide an aqueous phase containing the desired metal values and the solvent phase containing the regenerated reagent.

Advantages of the present invention include the ability to substantiall maintain the initial loading capacity of the substituted 8-hydroxyquinoline hydrometallurgical reagent during the selective solvent extraction process. Another advantage is that the stabilized substituted α-hydroxyquinolme reagent retains the other advantages which they have in the process. These and other advantages will become readily apparent to those skilled in the art based upon the disclosure herein contained.

Brief Description of the Drawings

The drawings depict graphically the results obtained in the examples and will be described in detail in connection therewith.

Detailed Description of the Invention The 7-(α-alkenyl)-substituted 8-hydroxyquinoline reagents of the present invention preferably are those shown and described in U.S. Patent No. 4,045,441 and 4,066,652, the disclosures of which are expressly incorporated herein by reference. Such reagents contain unsaturation in the α ,-β-position of the side chain attached in the 7 position to the 8-hydroxyquinoline group, which side chain unsaturation is reduced according to the precepts of the present invention. Preparation of these unsaturated reagents can be practiced according to the teachings of said patents. The unsaturated reagents which are reduced according to the present invention can be represented conventionally by the following general structural formulae:

where R₁, R₂, R₃, R₄ are alkyl groups, the sum total of carbon atoms in R₁ and R₂ being between 6 and 18 and in R₃ and R₄ being between 4 and 18.

Saturation of the β -, or δ -alkyl branched α -unsaturated side chain attached to the 8-hydroxyquinoline unit stabilizes the reagent in the solvent extraction circuit. The saturated reagents can be represented by the following structures:

Such stability is adjudged by and reflected in the loading capacity of the saturated reagent (the 8-hydroxyquinoline reagent substituted with a saturated alkyl group in the 7 position) being substantially maintained for extended periods of time wherein the reagent is recirculated in the solvent extraction circuit. The instability displayed by the unsaturated reagent (reagent of structure I or II) is believed to be primarily caused by an oxidative cyclization reaction evidenced by large increases in furoquinoline being formed. When the unsaturation in the side chain is reduced, the proportion of such saturated reagent remains substantially constant in the circuit and substantially no increase in furoquinoline by-product is noted. The drawings and the examples will further elaborate on this. Saturation of the side chain of the unsaturated reagent is accomplished by reduction of the double bond therein with hydrogen most preferably under conditions substantially preelusive of reducing the unsaturation in the rings of the 8-hydroxyquinoline substituent of the reagent. While a variety of agents (or catalysts) can be envisioned for the reduction reaction, most simply the unsaturated reagent is selectively hydrogenated in the presence of a selective hydrogenation catalyst. Selective hydrogenation for present purposes connotes saturation or reduction of the double bond in the side chain without substantially hydrogenating or reducing the unsaturation in the rings of the 8-hydroxyquinoline group. A wide variety of catalysts are useful for reducing the side chain of the unsaturated reagent by a conventional catalyzed hydrogenation process. Some observations on judicious selection of the catalyst, though, are important in this context. Because the unsaturated reagent is an effective ehelating reagent, use of homogeneous catalysts probably is not practical as the unsaturated reagent can chelate or complex readily therewith, thus, inactivating the catalyst. For the same reason, conventional heterogeneous divalent hydrogenation catalysts (e.g. Ni, Co, Cu, etc.) are not practical in the process.

Advantageous catalysts for the process, then, can be selected from the supported and unsupported Group VIII metals having an atomic number of 44 or greater (e.g. Ru, Rh, Pd, Os, Ir, and Pt) and the Group VIIb precious metal Re. These metals are fairly recalcitrant to being complexed by the unsaturated reagent in the selective hydrogenation process. The preferred catalyst for commercial implementation of the invention is a supported palladium catalyst. Carbon is the preferred support for the Pd catalyst, though alumina or other conventional support materials may be used in conventional fashion.

Hydrogenation conditions for reducing the side chain of the reagent are conventional. Accordingly, advantageous hydrogenation temperatures range from about 60°-150°C, preferably about 90°-115°C, and advantageous hydrogen pressures range from about 60-400 psig, and preferably about 100-200 psig. It should be noted that intensive hydrogenation of the unsaturated reagent is not desirable as a practical matter because of the resultant difficulty in determining the end point of the hydrogenation reaction. Thus, for ease in controlling the degree of hydrogenation in the hydrogenation process, moderate conditions are preferable so that hydrogenation times in the range of around 2-4 hours will be experienced. Such moderate hydrogenation conditions and times permit GLC or other analytic techniques to be practiced during the hydrogenation process in order to control the degree of hydrogenation of the unsaturated reagent. It should be understood, however, that some saturation of the aromatic ring can occur even with the preferred Pd catalyst. For some reagents (e.g. reagent I with R₁ being a butyl group and R₂ being an ethyl group) subjected to the reduction process, the degree of ring saturation in the final reagent product is sufficiently minimal that such ring saturation has no adverse effects in the extraction circuit as a practical matter. If required for the reagents, however, the rings can be rearomatized rather readily by mere heating of the reduced reagent in the presence of a dehydrogenation catalyst (e.g. Pd or other hydrogenation catalyst, such as listed above) at a temperature of above about 220°C and advantageously between about 220° and 300°C. An inert gas sparge may be used in this rearomatization reaction, though such sparge is not necessary.

The saturated reagents of the present invention find wide use in the solvent extraction of metal values from aqueous solutions wherein the reagent is dispersed in an organic solvent, as such process is disclosed in U.S. Patents Nos. 3,637,711,

4,045,441, 4,066,652, the disclosures of which are expressly incorporated herein by reference. Briefly, such process comprises mixing a dilute aqueous solution of the metal values, of which one of the metals is desired to be selectively separated from a mixture of metal values, with a hydrocarbon solvent containing the reagent dispersed therein. A promoter can be added to the hydrocarbon solvent. The presently preferred promoter is tridecyl alcohol. Other suitable promoters include isodecyl alcohol or other aliphatic alcohols (U. S. Pat. No. 3,224,873), alkylated phenols (U. S. Pat. No. 3,725,046), and other suitable conventional promoters. Upon mixing of the dilute aqueous phase and the organic solvent phase in a mixing-extraction tank, such mixture is permitted to settle for separation into two phases.

The organic phase containing the metal-reagent chelate then is contacted with an acidic aqueous stripping solution under suitable mixing or agitation conditions. This mixture then is permitted to settle for formation of an organic phase containing the regenerated reagent for recycle and an acidic aqueous phase containing the metal values which have been selectively separated by the process.

The metal value of choice to be separated by the reagents of the present invention is copper, though a wide variety of metals can be separated by the reagents, as such metal values are set forth in U.S. Patent No. 3,637,711. Further specific polyvalent metals which can be separated by the reagents of the present invention include, for example, rare earth metals and yttrium (European Patent Application S.N. 79400120.6, filed February 27, 1979, of Rhone-Poulenc Industries, Paris, France); gallium (U. S. Pat. No. 3,971,843); and copper, zinc and nickel (Ritcey et al, "Evaluation of Contactors for the Extraction and Separation of

Copper, Zinc, and Nickel from Ammoniacal Solutions Using Kelex 100," I. Chem E. Symposium Series No. 42, and Hartlage et al, "Kelex^(R) Copper Extraction: A Study of the Stripping Mechanism," I. Chem. E. Symposium Series No. 42, pp. 12.1-12.9 and 13.1-13.7, respectively, 1975). Representative organic solvents which can be used in the process include benzene, toluene, xylene, fuel oil, and a wide variety of other hydrocarbons, but preferably kerosene. Conditions obtaining during the extraction process (eg. temperature, pH, and the like) are conventional and can be found in the various citations referred to above. The following examples show how the present invention can be practiced but should not be construed as limiting. In this application, all units are in the metric system unless otherwise expressly indicated. Also, all citations noted herein are expressly incorporated herein by reference.

IN THE EXAMPLES The unsaturated reagent evaluated can be represented by the formula:

and was made in a procedure substantially as described in Example 1 of U.S. Patent No. 4,045,441. The theoretical loading capacity of this reagent for copper (Cu ²⁺ ) is

1.07. Extensive testing indicated that laboratory prepared samples of this reagent had loading capacities generally ranging from 0.70 to 0.95 gpl. and pilot plant prepared samples had loading capacities of 0.82 to 0.87 gpl.

Loading capacities are determined by a standard control method by extracting copper from a standard solution and measuring the amount of copper in the aqueous phase before and after extraction. The loading capacity of the reagent is the difference in the amount of copper in the aqueous phase before and after extraction and is expressed in grams per liter (gpl).

The standard control method uses a 1% (weight/volume) of the reagent in kerosene (Escaid 200) containing 15% by weight nonyl phenol. 650 ml of the reagent solution is washed twice with 300 ml each of a sulfuric acid solution (200 gms of H₂SO ₄ diluted to 1 liter with distilled water) in order to ensure that no metal values are therein. The washed reagent solution (50 ml) is mixed with a standard copper solution (21.6 gms of CuSO₄.5H₂0 diluted to 1 liter with distilled water and pH adjusted with additional H₂SO₄ to 3.0±0.2), the two layers permitted to settle, and the two layers separated. This extraction step is repeated and the two resulting aqueous phases combined.

Copper determinations are made by adding 10 ml of a potassium iodide solution (150 gms KI diluted with distilled water to 1 L) to the. standard copper solution and to the combined aqueous phases. The two resulting solutions then are titrated separately with 0.1 N sodium thiosulfate solution to a light yellow color, a soluble starch indicator added, and titration continued until the blue color just disappears and remains so for 30 seconds. The copper concentration (gpl) is calculated for each solution by dividing the milliliters of the sample by the product of the milliliters of the titrating solution times its normality times a constant of 63.5. The loading capacity of the reagent is the difference between the copper concentration in the standard and the combined phases multiplied by 2.

Reduction of the reagent was accomplished by charging a reactor with the unsaturated reagent (V) and 0.4% by weight of a wet 5% palladium on carbon (50% H₂O and 50% of 5% Pd/C) catalyst and purging the air from the reactor. The contents of the reactor were heated to about 125 ºC under 60 psig of hydrogen gas. Samples of the reagent were removed periodically and analyzed by GLC (gas-liquid chromatrography) in order to determine the progress of the reduction reaction. Full reduction of the side chain occurs in about 2-4 hours. In order to dehydrogenate the partially hydrogenated quinoline group, the reactor was vented of all H₂, and heated up to a final temperature of about 250°C. At about 190°C, hydrogen begins to evolve from the reduced reagent. The evolved H₂ is vented from the reactor which is maintained at about 250°C for about 2-3 hours until samples of the reagent indicate that the dehydrogenation reaction is complete. Conveniently, the dehydrogenation reaction can be considered complete when the reagent regains a loading capacity which is at least 95% of its pre-reduction loading capacity.

EXAMPLE 1

The unsaturated reagent (V) used in this example had an initial loading capacity of 0.87. Pilot plant extraction of copper with the reagent showed that after 45 hours in the circuit, the loading capacity had dropped to 0.77 (an 11.5% loss of loading capacity). Accordingly, reduction of the side chain unsaturation was tried as a method of reestablishing the initial loading capacity of the unsaturated reagent. In order to generate data points on loading capacity and phase separation times of the organic phase (kerosene, nonyl phenol and reagent) from the aqueous copper solution, the reduction of the reagent was continued until substantial ring reduction had occurred. GLC analysis of the reagent also was conducted. The results of these tests are displayed in Figs. 1 and 2.

Fig. 1 depicts graphically the loading capacity of the reagent and phase separation time as a function of the reduction time. The linear loss of loading capacity shows no sign of leveling off and phase separation times have increased substantially. Figs. 2A and 2B depict the results of GLC analysis of samples of the reagent as a function of reduction time. From Fig. 2A it can be seen that the proportion of reduced reagent increases with increasing reduction time and that two unsaturated components of the reagent decrease with increasing reduction time. Fig. 2B shows that furoquinoline by-product in the reagent is converted to a reduced form also. Since no degradation or generation of a non-copper loading species is evidenced in the GLC analysis, the GLC analysis was modified to split the reduced reagent component into two components. The second component was theorized to be the ring-reduced analogue of the saturated reagent. This was confirmed by dehydro genating the final reduced reagent (250ºC for 3-4 hours in the presence of the Pd on carbon catalyst) which restored the loading capacity of the reagent to within 95% of its initial loading capacity.

Three components isolated from the reduced reagent by fractional distillation on a spinning band column were analyzed by a combination of NMR (nuclear magnetic resonance) and GC-MS (gas chromatography-mass spectrometry). The saturated reagent and furoquinoline were confirmed by such analysis. The third component is believed to be dϊhydrofuroquinoline because all of the furoquinoline was converted to this third component under total reduction conditions. The two unsaturated components in the reagent are believed to be two isomeric forms of the unsaturated reagent wherein the side chain unsaturation is either in the chain as shown for reagent A (structure (V)) or is pendant to the chain as shown below for reagent B (Structure (VI)):

It should be understood that the precise structures for the two isomeric forms of the unsaturated reagent shown herein are merely the most likely structures based on current information and are not a limitation on the present invention as reduction of the unsaturation in either position will result in the saturated reagent of the present invention. Thus, it appears as though the unsaturated reagent actually is a mixture of two (or more) isomeric forms thereof.

EXAMPLE 2 In order to evaluate the stability of the reagents, an accelerated circuit variation test was devised. The reagent being evaluated was mixed continuously with a stripping electrolyte solution (150 gpl of H₂SO₄ and 30 gpl of Cu²⁺ in water) at 45º -50ºC. Periodic samples of the reagent were examined for loading capacity and compositional changes by GLC. The reagent was a mixture of the unsaturated reagent, the side chain-saturated reagent, and furoquinoline. Two circuit runs were conducted on the partially reduced reagent, one being in the presence of air and the other being under an inert nitrogen blanket. The total test time was 382 hours. The proportions of each component in the reagent mixture for each circuit run is given in Figs. 3 and 4.

Fig. 3 depicts the results of the test conducted in air graphically by plotting the concentration of the components in the reagent as a function of time. Note that the unsaturated reagent components concentration decreases during the course of the circuit test. Fig. 4 depicts the results of the nitrogen atmosphere tests. Note that the concentration of the unsaturated components is substantially maintained. It appears that the unsaturated reagents instability is primarily an oxidative cyclization process evidenced by the large increase in furoquinoline in Fig. 3. Note, however, that the saturated reagent is stable both in air (Fig. 3) and in nitrogen (Fig. 4) and that substantially no increase in furoquinoline is evidenced for the nitrogen run (Fig. 4).

Claims

1. A method for substantially maintaining the loading capacity of a 7-[α- alkenyl)-substituted 8-hydroxyquinoline reagent for removing polyvalent metal ions from a mixture of metal ions in a dilute aqueous solution thereof and for regenerating said substituted 8-hydroxyquinoline from the resulting metal complex thereof, which comprises reducing said α-alkenyl unsaturation while minimizing the saturation of said hydroxyquinoline group.

2. The method of claim 1 wherein saidα-alkenyl unsaturation is reduced by selective hydrogenation in the presence of a selective hydrogenation catalyst with hydrogen gas under selective hydrogenation conditions.

3. The method of claim 2 wherein any hydrogen added to said hydroxyquinoline group is removed by dehydrogenation thereof.

4. The method of claim 2 wherein said catalyst is a Group VIIb or Group VIII metal having an atomic number of between 43 and 78.

5. The method of claim 2 wherein said hydrogenation catalyst is palladium.

6. The method of claim 5 wherein said palladium is disposed on an inert support.

7. The method of claim 6 wherein said support is carbon.

8. The method of claim 2 or 5 wherein said hydrogenation conditions include a temperature of between about 60° and 150°C and a pressure of between about 60 and 400 psig.

9. The method of claim 3 wherein said dehydrogenation is conducted in the presence of said hydrogenation catalyst at a temperature of between about 220° and 300°C.

10. The method of claim 9 wherein said catalyst is palladium disposed on an inert support.

11. The method of claim 1 or 10 wherein said 7-(α-alkenyl)-substituted hydroxyquinoline has the formula

or

12. The method of claim 11 wherein said reagent is of formula (I) and has R₁ being a butyl group and R₂ being an ethyl group.

13. The method of claim 11 wherein said reagent is of formula (II) and has R₃ being a 2-ethylhexyl group and R₄ being an ethyl group.

14. In a process for the recovery of polyvalent metal values from a dilute aqueous solution thereof wherein said aqueous solution is intimately contacted with a hydrocarbon solvent containing a chelation reagent dispersed therein to provide a polyvalent metal-reagent chelate in said solvent, said chelate-containing solvent being intimately contacted with an aqueous acidic stripping solution to provide an aqueous phase containing said polyvalent metal values and said reagent regenerated in said solvent, the improvement which comprises using a chelation agent having the formula

or

where R₁, R₂, R ₃, R₄ are alkyl groups, the sum total of carbon atoms in R₁ and R₂ being between 6 and 18 and in R ₃ and R₄ being between 4 and 18.

15. The method of claim 14 wherein said reagent used is of formula (III) and has R₁ being a butyl group and R₂ being an ethyl group.

16. The method of claim 14 wherein said reagent used is of formula (IV) and has R₃ being a 2-ethylhexyl group and R₄ being an ethyl group.

17. The method of claim 14 wherein said hydrocarbon solvent contains an alkylated phenol or an aliphatic primary alcohol promoter, the volumetric ratio of said reagent to said promoter being between about 1:19 and 1:1.

18. The method of claim 17 wherein said promoter is tridecyl alcohol.

19. The method of claim 14 or 18 wherein said hydrocarbon solvent is kerosene.