CA1193267A - 3,5-dicarboxy pyridine compounds - Google Patents

Abstract

ABSTRACT

A 3,5-disubstituted pyridine of the formula:

Description

2 Dx.31682A

This application is a division of Serial No. 395,390 filed February 2, 1982.
This invention relates to a process for the extraction of metal values from aqueou3 ~olu~ion~ of metal salts, and in particular to a proces~ for the extraction o~ metal values from aqueous solutions in the presence of halide anions.
The use of solvent extraction techniques for the hydrometallurgical recovery of metal values from metal ores has been practised commercially for a number of years~ For example copper may be recovered from oxide ores or from ore tailings by treating the crushed ore with sulphuric acid to give an aqueous solution of copper fiulphate which is subsequently contacted with a solution in a water-im~iscible organic solvent of a met~l extractant whereby the copper values are selectively extracted Lnto the organic solvent phaseO
The application of solvent extraction techniques to aqueous solutions containing halide ions however has hitherto presented numerous technical problems.
Of particular importance in this connection is the development of hydrometallur~ical routes (as an alternative to smelting) for the extraction of metal values from sulphur-containing ores such as chalcopyrite. S~lch ores may be leached for example using ferric chloride or cupric chloride solutions; but the solvent extraction of the result~nt leach solutio~ presents formidable difIiculties.
The present in~ention provides a proce6s for the extraction of metal values ~rom aqueous solution~
containing halide ion~ by the use of metal extractants who~e several properties meet the stringent requirements imposed on the extractant by the system.

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According to the present invention there is provided a process for extracting metal values from aqueous solutions of metal salts containing halide or pseudo halide anion which comprises contacting the aqueous solution with a solution in a water-immiscible organic solvent of a substituted pyridine of formula:

(~C ~

wherein X is the group -ORl or -NR2R3, Rl being a hydrocarbyl group containing from 5 to 36 carbon atoms and R2 and R3 being hydrogen or a hydrocarbyl group, R2 and R3 together containing from 5 to 36 carbon atoms, and n is 1, 2 or 3.
When n is 2 or 3, the substituent -X in the respective groups COX may be the same ordifferent. For example, when n is 2, ~he two groups COX may be -CORl and -CORl' respectively where Rl and Rl' are both hydrocarbyl groups containing from 5 to 36 carbon atoms. Similarly, when n is 2, the two groups -COX may be -CORl and -CONR2R3 respectively.
According to a further aspect of the present invention there is provided a process for extracting metal values from aqueous solutions of me-tal salts containing halide or pseudo-halide anion which comprises contacting the aqueous solution with a solution in a water-immiscible organic solvent of a

3~ or 4-substituted pyridine of formula:

~) ~3;~6'7 Dx 31682A

C - X O
C - X

~ ~ or ~ ~

wherein X is the group -ORl or -NR2R3, Rl being a hydrocarbyl group containing from 5 to 36 carbon atoms and R2 and R3 being hydrogen or a hydrocarbyl group, R2 and R3 together S containing from 5 to 20 carbon atoms.
According to a further aspect of the present invention there is provided novel metal extractants. Thus there is provided a 3- or 4-substituted pyridine of formula:
O O

10 ~wherein X is the group -ORl or -NR2R3, Rl being an alkyl group containing from 9 to 24 carbon atoms and having the formula:

- CH - CH
~5 wherein R4 and R5 are alkyl groups, and R4 contains two fewer 15 carbon atoms than R5, and R2 and R3 together containing a ~393~

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total of from 15 to 36 carbon atoms, provided -that when R2 is hydrogen, R3 is a branched chain alkyl group.
There is also provided a substituted pyridine of formula:

~ n ~'N~

wherein X is the group -ORl or -NR2R3, and n is 2 or 3, the respective groups Rl being alkyl groups containing a total of from 16 to 36 carbon atoms, and the respective groups R2 and R3 being alkyl groups wherein the total number of alkyl carbon atoms contained in all the respective groups R2 and R3 is from 20 to 70~
The pyridine ring may carry substituents in addi-tion to the group(s) COX. Examples of suitable substituents are halo~en ~roups, alkyl groups, aryl groups, alkoxy groups, aryloxy groups, aralkyl groups, cyano groups and nitro groups.
The pyridine ring may also carry a carboxylic acid group, ancl the invention includes for example a half ester of a pyridine dicarboxylic acid.
Substitution in the pyridine ring may for example result 2Q from the method of synthesis. For example bis ester of

4-phenylpyridine-3,5-dicarboxylic acid may be prepared from methyl propiolate, aromatic aldehydes and ammonium acetate in acetic acid followed by oxidation to the pyridine derivative and ester exchange (Chennat and Eisner, J~C~So Perkin I, 1975).
When n is 1, examples of compounds which may be used in the process of the invention include esters or amides of nicotinic acids, isonicotinic acids and picolinic acids.

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When n is 2, examples of compounds which may be used in the process of the present invention include bis esters or amides of pyridine~2,4~dicarboxylic acid, o~ pyridine-2,5-dicarboxylic acid, and of pyridi.ne-3~5-dicarboxylic acid. ~Ihen n is 3, examples of compounds which may be used in the process of the present invention include tris esters or amides of pyridine-2,4,6-tricarboxylic acid. Mixtures of such compounds may be used, for example a mixture of bis esters or amides of isomeric pyridine-dicarboxylic acids.
The substituted pyridines of the present invention wherein X is the group -ORl may be prepared by conventional means, for example by the reaction of a pyridine carboxylic acid, for example isonicotinic acids, nicotinic acids or picolinic acids respectively with the appropriate alcohol to form the desired esters. Alternatively the lower esters, for example methyl or ethyl esters may be subjected to ester exchange reactions with higher alcohols, or the acid chlorides may be reacted with the appropriate alcohol or phenol.
Dicarboxylic acid esters of pyridine may conveniently be prepared from lutidines, for example by oxidation and esterification.
Rl may for example be an alkyl group, for example an octyl, nonyl, decyl, dodecyl, tridecyl, pentadecyl, hexadecyl or octadecyl group or substituted alkyl group, for example a group containing one or more propylene oxide residues formed by reacting propylene oxide with an alcohol before esterification to give the substituted pyridine, Rl may be a cyclo alkyl group such as cyclohexyl; Rl may be an aralkyl group such as benzyl; or Rl may be an aryl, alkylaryl or alkoxyaryl group for example p-nonylphenyl or p-dodecylphenyl.
When n is 1 and there are no other substituents in the pyridine ring, R1 is preferably a branched chain alkyl group containing fxom 9 to 24 carbon atoms.
Rl may be an isomeric mixture of groups con-taining the same number of carbon atoms or a rnixture of groups containing , ~j ~3%~i'7 Dx 31682A
different numbers of carbon atoms (which may themselves be an isomeric mixture), for example a mixture of different alkyl groups. If Rl is a mixture of groups containing different numbers of carbon atorns, the average number of carbon atoms is preferably from 9 to 24.
Highly branched groups Rl may usefully be obtained by the reaction of the pyridine carboxylic acid with alcohols prepared by the Guerbet and Aldol condensations. Such alcohols are characterised by branching at the position beta ~ to the hydroxyl group, and have the general formula:

HO - CH2 ~ CH

In general R4 contains 2 fewer carbon atoms than R5, and groups Rl derived from these alcohols include for example, C6Hl3 ~ CH2 ~ CH

Cl oH

- CH - CH

CgHl g , ~3~

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R4 and R5 may be straight chain or branched chain alkyl groups and may be isomeric mixtures of alkyl groups. A
mixture of highly branched alcohols may be oh~ained by Guerbet or Aldol condensations of mixtures of alcohols and aldehydes respectively.
Excellent solubility is conferred upon the compounds of formula I where the alcohol is the product of the aldol dimerisation of commercial nonaldehyde. In this alcohol the group Rl is believed to consist essentially of a mixture of geometrical isomers of a radical of the formula:
I

fH3 fH3 CH2 IH3 IH3 CH3 - C - CH2 -CH - 2 CH2 - CH - CH2 - f - CH

When n is 2, the respective groups Rl (Rl and Rl') may be any of those groups Rl listed previously. Rl and Rl' are conveniently the same and are preferably straight chain or branched chain alkyl groups. When n is 2, we have found that to achieve the desired solubility of the metal complex in preferred solvents, Rl and Rl' preferably together contain a total of from 16 to 36 carbon atoms. The groups may contain a mixture of isomers, for example a mixture of nonyl isomers derived from isononanol obtained by the hydro-formylation of a mixture of octenes, a mixture of decyl isomers obtained from isodecanol r or a mixture of tridecyl isomers obtained from tridecanol.
The substituted pyridines of the previous invention wherein X is the group -NR2R3 may be prepared by conventional means, for example by reaction of pyridine carboxylic acids and their lower esters with higher primary or secondary amines.
Alternatively the acid chloride of the pyridine carboxylic acid may be reacted with the appropriate amine.

~32~;~

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~ he amide group -NR2R3 may be primary (R2 is hydrogen) or secondary. R2 and R3, which may be the same or different may be groups of the type indicated above for R1. R2 and R3 taken together contain from 5 to 36 carbon atoms. Thus R2 may be for example a lower alkyl group, ~or example a methyl group, provided R3 is correspondingly larger. R2 and R3 taken together are preferably alkyl groups containing a total of 15 to 36 carbon atoms. For secondary amides sufficient solubility in preferred organic solvents may generally be achieved if R2 and R3 are straight chain or branched chain alky] groups. However for primary amides (R2 is hydrogen), R3 is pre~erably a branched chain alkyl group. When n is 2, and the groups R2 and R3 are all alkyl groups, the total number of alkyl carbcnatoms preferably does not exceed 70, for example the total number of alkyl carbon atoms is preferably from 20 to 70.
The process of the present invention mav be applied to the extraction from aqueous solutions containin~ halide or pseudochalide ion of any metal capable of forming a stable halide- or pseudochalide-containing complex with the pyridine derivative in the water-immiscible organic solvent. Examples of such metals include copper, cobalt, cadmium and zinc. The process of the present invention is especially applicable to the solvent extraction of copper from aqueous solu-tions obtained by the halide or pseudo halide leaching of sulphur-containing copper ores, for example from solutions obtained by the leaching of ores such as chalcopyrite with aqueous ferric chloride or cupric chloride solutions.
The leaching of ores such as complex sulphide ores, for example chalcopyrite with for example aqueous ferric chloride solution containing hydrochloric acid gives rise to leach solutions containing cuprous and cupric ions, ferrous and ferric ions and excess chloride anion. The ratio of cuprous to cupric ion depends on the leach condi-tions selected. The sulphur content of the ore may be precipitated , ~

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as elemental sulphur. Whilst the scope of the present invention is not to be taken as being limited to the treatment of any particular halide-containing aqueous solution, -t:~pical solutions obtained by the leaching o~ chalcopyrite with acidified ferric chloride may contain between 10 and 60 grams per litre of copper, between 50 and 150 grams per litre of iron, may typically be between O.lM and lM in hydrochloric acid and may be between about ~M and 8M in total chloride ion. Certain leach systems may give total chloride ion contents as high as lOM or 12M. All leach solu-tions encoun-tered in practice will also contain varying quantities of the many other metals present in the ore body. Certain leach solutions may contain high levels of specific metals, for example zinc, in addition to copper.
It will be appreciated that the process oE the present invention may be incorporated into a wide variety of different methods for the overall recovery of metals from their ores or from other metal-bearing sources. Details of these methods will vary depending on the metal concerned and the nature and composition of the leach solution.
Whilst the process of the present invention is not limiied to any single overall method for the recovery of metals, the stringent conditions imposed on the pyridine extractant are best illustrated if the solvent extraction process is seen as a step in an integrated process for the recovery of the metal from the ore. For example an integrated process which is especially suitable for leach solutions containing high levels of cupric ion comprises the fol~owing steps:
1. Leaching of the ore with aqueous ferric or cupric chloride solutions, and removing the elemental sulphur produced;
2. Contacting the leach solution from step 1 (in which the ferric ion i9 at least partially reduced to ferrous ion) with a solution in a water-immiscible solvent of -the extractant, whereby the copper is trans-ferred into the ;~

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organic phase in the form of a chloride-con-taining complex with the extractant;
3. Separating the organic phase containing the complex of copper with the extractant from the aqueous phase containing the ferric/ferrous chloride;
4. Contacting the organic phase from step 3 with an aqueous strip solution which is water, or which contains a reduced concentration of chloride ion, whereby the chloride-containing complex of copper with the extractant is unstable and copper transfers into the aqueous strip solution;

5. Separating the organic phase containing the stripped extractant from the aqueous strip solution containing the copper chloride; and

6. Electrolysing the strip solution from step 5 to recover copper. The electrolysis step is suitably arranged such that oxidation of ferrous ion with transfer of chloride ion takes place in the anode compartment, such that the solution leaving the cathode compartment is denuded in both copper and chloride ion. Alternatively chlorine gas may be evolved at the anode and optionally used as oxidant to regenerate the leach solution.
In order to preser~e the overall stoichiometry of the sequence of reactions, it may be necessary to provide additional oxidation of ferrous to ferric ion, and to remove the iron entering the system continuously from the chalcopyrite (CuFeS2), for example in the form of iron oxide such as goethite.
For a fully integrated process it is highly desirable that the solutions be re-circulated between the various stages.
Thus aqueous strip solution used in step 4 is preferably derived from the electrolysis step 6 and is preferably the solution leaviny the cathode compartment denuded in both copper and chloride ion. Similarly the organic phase containing the stripped extractant which is separated in step 5 is preferably re-circulated to the extraction stage 2.

~3~

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The ferric chloride solution derived from the electrolysis step 6 may be returned for fur-ther leaching of the ore.
Considering first the extraction stage 2 and the strip stage ~, the extraction of for example cupric ivn by the extractant may be represented by an equation such as the following:

2Lorg ~ Cu aq ~ 2Cl aq -~ (L2CuCl2)ory This equation is a grossly oversimplified representation of a very complex process and is not to be taken as in any way limiting the scope of the present invention, but it serves to illustrate the formation of a neutral organic phase complex of copper and the extractant (L) which is believed to predominate in the process of the present invention.
Other equations may be used to represent the extraction and stripping of cuprous ion or of other metals by the extractant.
~ he above equation assumes that the extractant acts as a monodentate ligand, and whilst this is believed to be generally true, esters and amides of 2-carboxypyridines do at least have the potential of acting as bidentate ligands.
Vnder certain conditions other species, for example oligomeric complexes such as L2(CuC12)n may be formed. The formation of oligomeric species is generally undesirable since the efficiency of copper extraction is reduced and in addition the oligomeric complexes tend to have a low solubility in organic solvents. We have found that the tendency to the formation of oligomeric species is especially low with esters and amides of 2-carboxypyridines.
The equation also illustrates the reversible na-ture of the extraction, whereby the cornplex of copper and the extractant in the organic phase can be stripped on contact with water or with an aqueous solution containing a reduced chloride or a reduced copper content such that copper is 332~7 Dx 31682A

transferred to the aqueous phase and the free ex-tractant is at least partially regenerated in the organic phase.
Most efficient stripping will be obtained usiny water itself as the stripping medium, and the proce~s of the present invention may be combined with a water stripping stage. However, i-t will be noted that in a fully integrated process, it is preferred that the loaded extractant be stripped with the solution derived fro~ the electrolysis stage and denuded in copper and chloride ion. In the extreme case, the aqueous phase may be entering the electrolytic cell containing about 40 or 50 grams per litre copper and may leave it still containing as much as 30 grams per litre copper or more. The requirement that the extractant will be able to efficiently extract copper from the leach solution, whilst at the same time be stripped by a solution containing relatively high levels of copper is exacting.
Preferred extractants for use in the process of the present invention are capable of being stripped by an aqueous solution containing relatively high levels of copper, for example from 20 to 35 grams per litre of copper.
Since the leach solution contains high levels of iron, it isclearly important that the extractant should have good selectivity for copper over iron. The extractants of the present invention have this property. Of particular importance in an integrated s~stem, where the copper is recovered by electrolysis of the pregnant aqueous strip solution, is selectivity for copper over silver and other minor extractable constituents of the ore~ The reason for this is that whilst metals such as zinc and cadmium are more electronegative than copper and are not electrodeposited with it, silver is both co-deposited with copper and furthermore adversely affects the physical properties of the copper so that an expensive electrorefining stage is required. Preferred extractants of the present invention have excellent selectivity for copper over silver under appropriate operating conditionsO
.~

~93~
1~

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A yet further property which is of importance for an extractant in ~e process of the present invention is the absence of significan-t protonation by the acidic leach liquGr.
Such protonation may be represented by an equation such as:

L + H + Cl ~- ILH Cl ) org aq aq ~-- org where L is the extractant. Such protonation of the ligand not only carrles hydrochloric acid into the organic phase, building up unnecessary chloride concentration on the strip side, but is also believed to be associated with less of selectivity for copper over silver and other trace components such as antimony and arsenic. Again the preferred extractants of the present invention have excellent resistance to protonation even in contact with relatively acidic leach solutions.
As illustrated by the ~xamples, the extractants of the present invention provide a range of properties so that the optimum extractant may be selected for a given leach solution. In particular, a "strong" extractant, for example, isooctadecyl nicotinate,is capable of extracting high levels of copper from a leach solution containing relatively low chloride ion content (for example about 3.7M) but tends to undergo undesirable protonation and acid transfer at higher acid/chloride ion concentrations (for example H~, O.lM; Cl , 9.8M). On the other hand, a "weak" extractant such as a diester of pyridine-2~5-dicarboxylic acid is found to transfer only low level.s of acid, even ~rom solutions concentrated in chloride ion and acid (for exa~lple lO.7M and lM respectively).
Furthermore, the lower inherent abiiity of the ex~ractant -to transfer copper into the organic phase is offset by the irnproved transfer of copper at these higher chloride ion concentrations.

, ,, ~3;2~7 Dx 31682A
sis esters of pyridine-3,5-dicarboxylic acids, for example/ the bis-nonyl ester, are weak extractants which furthermore show high selectivity for copper over zinc, and provide a potential for recovery of ~inc in leach solutions containing high levels of both copper and zinc.
Examples of suitable water-immiscible organic solvents are aliphatic, aromatic and alicyclic hydrocarbons, chlorinated hydrocarbons such as perchloroethylene, trichloro-ethane and trichloroethylene. Mixtures of solvents may be used. Especially preferred in conventional hydrometallurgical practice are mixed hydrocarbon solvents such as high boiling, high flash point, petroleum fractions (for example kerosene) with varying aromatic content. In ~eneral, hydrocarbon solvents having a high aromatic conten-t, for example ARO~ASOL H
which consists essentially of a mixture of trimethylbenzenes and is commercially available from Imperial Chemical Industries PLC (AROMASOL is a registered trade mark), provide a higher solubility for the extractant and its copper complex, whilst kerosene having a relatively low aromatic content, for example ESCAID lQO which is a petroleum distillate comprising 20~ aromatics, 56.6% paraffins and 23.4% naphthenes con~ercially available from ESSO (ESC~ID is a registered trade mark) may in certain cases improve the hydrometallurgical performance of the extractant. Factors influencing the solubility of the extractant and its copper complex are complicated, but in general extractants having highly branched substituents and/or an isomeric mixture of substituents have comparatively high solubility.
We have found that isonicotinic acid derivatives and 30 their copper complexes, for example (2-hexyldecyl)isonicotinate, have surprisingly high solubility in both high and low aromatic content hydrocarbon solvents.
The concentration of the extractant in the water-immiscible organic solvent may be chosen to sui-t the particular 35 leach solution to be treated. Typical values of extractant concentration in ~he organic phase are between about ~1 to 2 Molar, and an especially convenient range is from 0.2 to 0.~ Molar in the organic solvent.

2~

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The extraction stage and the strip stage of the solvent extraction process may conveniently take place at ambient tempe~ature. However, it is possible to lmprove net copper transfer from the leach solution to the strip solution if the extraction s-tage is operated at ambient temperature, whilst the strip stage is operated at elevated temperature, for example up to 50C. We have also found that the undesirable formation and build-up of oligomeric complexes of the extractant and copper may be alleviated if the strip stage is operated at elevated temperatures, for example up to 50C.
The invention is illustrated by the following Examples in which ali parts and percentages are by weight unless otherwise stated.
Ex~mple 1 (2-(n)Hexyldecyl)nicotinate was prepared as follows:-A stirred mixture of nicotinic acid (61.5 parts),dimethylformamide (0.63 parts) and xylene (174 parts) was heated to 80 below a condenser set for reflux. Thionyl chloride (65.5 parts) was then added during 1-2 hours, the temperature of the reaction mixture being allowed to rise ~o 90-95 during the addition. The mixture was then stirred at 90-95 for 3 hours. The condenser was then set for distillation and the temperature was raised until excess thionyl chloride had distilled and xylene had begun to distil.
The mixture was then allowed to cool to 80-85 and 2-(n~-hexyldecanol (112 parts) was added during 30 minutes. The mixture was stirred at 80-85 for 2 hours and was then cooled to room temperature, and extracted with a solution of sodium hydroxide (40 parts) in water (165 parts). The xylene solution was washed alkali free with more water, and the xylene was distilled under reduced pressure leaving (2-hexyldecyl~nicotinate [147 parts] as a brown oil. The purity was estimated at 95% by titration of a sample with N/lO perchloric acid in acetic acid medium. The compound was distilled, b.p. 176-]84 at 0.4 mm pressure, yielding 109 ,~;, j~, ~32~

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parts of straw-coloured liquid which was 98-99~ pure.
The ability of (2-(n)hexyldecyl)nicotinate to extract copper from aqueous solution containing chloride ion was investigated.
An aqueous solution (A) was made up which was O.lM
in cupric chloride (6.35 gpl copper) t and O.lM in hydrochloric acid, and which contained in addition 250 g/litre of calciurn chloride dihyclrate. This solution was then agitated for 15 minutes with an equal volume of a solution (s) which was a 0.2M solution of (2-hexyldecyl)nicotinate in AROMASOL H. The layers were allowed to separate and settle, and were separately analysed for copper content. I'he percentage of the copper initially present in A which had passed into B, w~s 44.5%. The resultant loaded organic solution B was then stripped with an aqueous solution (C) which was 0.472M in cupric chloridel i.e. one which contained 30 gpl of copper.
It was found that copper passed from the organic to the aqueous solution. The percentage of the copper originally present in ~ which had been transferred to solution C was 25.5%. The transfer of hydrochloric acid from solution A
to solution ~ was negligible.
Extraction of copper by the same extractant from a more strongly acidic solution was also examined. The same solutions and procedure as before were used, except that solution A was l.OM rather than O.lM in hydrochloric acid.
The percentage of copper extracted into the organic solution (B) and the percentage which finally passed into the aqueous solution of cupric chloride (C) were 47.8% and 30.6%
respectively. The amount of hydrochloric acid which passed from solution A to solution B under these extremely acidic conditions was measured. Expressed as a percentage of that which would be transferred if every molecule of the ligand combined with one molecule of hydrochloric acid, the acid transfer was only 1.9~.
The above results are summarised in Table 1.

~1 . "

~3~

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Example 2 Tridecyl nicotinate was prepared using the method of Example 1 from commercial tridecanol (an isome~ic mixture) and nicotinic acid. The procluct had a boiling poin-t of 136 to 140C under 0.05 mm pressure and an estimated purity of 100% based on a molecular weight of 305.5.
The ester was evaluated as an extractant for copper from aqueous solution containing chloride ion using the me-thod of Example 1.
The results are presented in Table 1.
Example 3 N,N-di-(n)- octylnicotinamide was prepared using the method of Example 1 from nicotinic acid and di-(n)-octylamine. The product had a boiling point of 1~0 to 183C
at 0.15 mm pressure and an estimated purity of 95.5%.
The amide was evaluated as an extractant for copper from aqueous solution containing chloride ion using the method oE Example 1.
The results are presented in Table 1.
It will be noted that this compound is a stronger extractant than those shown inthe previous Examples, and would be more suitably employed for the extraction and subsequent recovery of copper from an aqueous solution of lower concentration of chloride ion. It would also be preferable to strip the extractant with a strip solution which was lower in copper and/or in chloride ion than solution C.
Example 4 (2-(_)-hexyldecyl)isonicotinate was prepared using the method of Example 1 from isonicotinic acid and 2-hexyl-30 decanol. The product had a boiling point of 180 to 190C at 0.75 mm pressure and an estimated puri-ty of 97.5%.
The ester was evaluated as an extractant for copper from aqueous solution containing chloride ion using the method of Example 1.
I'he results are presented in Table 1.

~3~7 Dx 316~2A

~::C
o ~
~n h ~ al X h o Q~ ~ ~
_ _ ~

U ~O 1 ~
O
q~ _ ~ !~ ~o 4 o ~
e _ __ __ h 1~>
t.) ~ ~ cO h ~¦ h--~ ~ O ll~ O u~ 1~\ ~1 0 4~ h O _ _ _ 0 O ~ ~ ~ ~ t~ O
~ ~ la . 60 _ _ ~1 ~
~ 0 h E E ~ ~ o '~J~
,.~ .

321~7 Dx 31682A

Example_5 A solvent extraction circuit was assembled consisting of small scale mixer settler units. The circult comprised 3 stages of extraction and 2 stages of stripping and purnping was arranged such that over both the e~trac-tion and stripping parts of the circuit the organic and aqueous solu-tions flowed counter current-wise~
The aqueous feed solution had the following composition of metals:
Copper (Cu ) 16.0 g per litre Iron (Fe ] 40.4 g per litre Silver (Ag ) 18.9 mg per litre In addition, the solution contained 150 g per litre of calcium chloride added as the dihydrate CaC12.2H20 and contained 3.6 g per litre of hydrochloric acid giving a total chloride ion concentration of 4.23 moles per litre.
The strip solu-tion consisted of an aqueous solution containing 28.9 gpl copper as cupric chloride with no added acid.
The solvent phase comprised a 19.2% by weight solution (0.553 moles per litre) of the extractant of ~xample 1 dissolved in~ROMASOL H.
The pumps and agitators in the circuit were started and the flow rates adjusted to give an organic flow of 33.3 25 ml/min and aqueous flows of 13.3 ml/min (2.5 to 1 organic to aqueous phase ratio).
After the circuit had been running successfully for four working days at an average temperature of 15C, samples taken from the aqueous raffinate; from the extraction circuit;
and of the pregnant strip solution were analysed.
The results obtained are sun~arised in Table 2.

.....

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Table 2 __ Fe Ag gpl gpl rng/l _ ... , . (~pl~) Aqueous feed 16.G 40.4 13.9 Raffinate 2.49 3g.8 18.4 Strip solution 28.9 0.24 0 Pregnant strip s~luti~n 44.5 0.3 0.6 Example 6 _ (2-(n)-Octyldodecyl)nicotinate was prepared from nicotinic acid and 2-(n~octyldodecanol using the general method of Example 1 with the following minor changes. The temperature after thionyl chloride addition was maintained at 80C for 2 hours, and after the esterification reaction, the solution was diluted with petroleum ether (60-80), washed with water to remove acidity and the solven-ts removed by distillation. The product had a boiling range of 190-200C
at 0.05 mm mercury pressure and an estimated purity of 87.9%.
The ability oE (2-(n)octyldodecyl)nicotinate to extract copper from aqueous solution containing chloride ion was investigated.
An aqueous solution (A) was made up which was O.lM
in cupric chloride ~6.35 g/l copper), O.lM in hydrochloric acid and contained 250 g/l of calcium chloride dihydrate, providing a total chloride ion concentration of 3.7M. This solution was shaken for 1 minute with an equal volume of a solution (B) which was a 0.2M solution of (2-(n)-octyldodecyl)-nicotinate in ESCAID 100. The layers were allowed to separate~ the aqueous layer was analysed for copper and the solvent layer for acid transferred with the copper. The 3~

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percentage of copper initially presen-t in A which had passed into B was 52%. There was no de-tectable transfer of hydro-chloric acid into B.
These results are summarised in Table 3.
Example 7 Iso-hexadecyl ni.cotinate was prepared from nicotinic acid and a commercial material, iso-hexadecyl alcohol, obtained from Farbwerke ~oechst AG. The general method of Example 1 was used except that the temperature after thionyl chloride addition was maintained at 80C for 2 hours, and after the esterification reaction the solution was cooled and washed with 0.5M sodium hydroxide, 0.5M hydrochloric acid and water.
The solution was treated with activated carbon (2.5% on the expected weight of product) at 50C for 1 hour, filtered and the solvent removed under reduced pressure. The light brown oil had an estimated purity of 93.4% and was distilled (boiling range 141-146C at 0.03 mm mercury pressure) to provide a product of 99.8% estimated purity.
The ester was evaluated as an extractant for copper from aqueous solution containing chloride ion using the method of Example 6~
To evaluate the efficiency of the extractant for use with leach solutions containing higher levels of total chloride ion, the general test method of Example 6 was repeated using a solution (A) which contained cupric chloride (O.lM), hydrochloric acid (O.lM) and 700 g/l calcium chloride dihydrate giving a total chloride ion concentration of 9.8M.
The results are displayed in Table 3, and indicate that the extractant is more suitable for use with leach solutions having relatively low total chloride ion concentra-tions (3.7M), since relatLvely high acid transfer levels occur at high total chloride ion concentrations (9.~M) Example 8 Isooctadecyl nicotinate was prepared using the method of Example 7 from nicotinic acid and a commercial product, isooctadecyl alcohol, obtained from Farbwerke ~ioechs-t ~G. The product had an estimated purity 94.5%.

~932~

Dx 31682A

The i.sooctadecyl alcohol starting material was analysed by capiliary Gas Chromatography and gave traces showing four peaks each of which was approximately the same size. The commercial isooctadecyl alcohol is believed mainly to comprise different geome-tric isomers of 2,2,4,8,10,]0-hexame-thyl-5-methylolundecane.
The ester was evaluated as an extractant for copper from aqueous solution containing chloride ion, using the method of Example 7.
The results are displayed in Table 3 and indicate that the extractant is more suitable for use with leach solutions having relatively low total chloride ion concentrations (3.7M), since relatively high acid transfer levels occur at high total chloride ion concentrations (9.8M).
Example 9 , .. _ l2-~n)Hexyldecyl)picolinate was prepared from picolinic acid and 2-(n)hexyldecyl alcohol by the general method of Example 1 with the following differences. The temperature after thionyl chloride addition was maintained at 80C for 2 hours and after the esterification reaction, the solution was diluted with petroleum ether 60-80C, washed with lM hydrochloric acid and with brine (10% NaCl). The solvents were removed by evaporation and the dark coloured oil distilled (boiling range 176-178C at 0.07 mm mercury pressure) to give a colourless oil of estimated purity 97.5%.
The ester was evaluated as an extractant for copper from aqueous solutions containing chloride ions by the general method of Examples 6 and 7, except that AROMASOL H
was used as solvent. The solution A contained the higher levels of chloride ion (9.8M) indicated in Example 7 and Table 3. Table 3 shows that the extractant is comparatively well suited for operation using leach solutions containing higher levels of total chloride ion since only 9% transfer of hydrochloric acid took place a~ a total chloride ion concentration of 9.8M.

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~3;~

Dx 3168 ple 10 Isooctadecyl picolinate was prepared using the method of Example 7 from picolinic acid and isooc-tadecyl alcohol, the commercial material obtained from Farbwerke Hoechst AG and described in Example 8. The light bro~n, oily product of the reaction had an estimated purity of 93.5%.
The ester was evaluated as an ex-tractant for copper from aqueous solutions containing chloride ion using the method of Example 7, except that AROMASOL H was used as solvent.
The results are displayed in Table 3, and show that whilst a relatively low extraction of copper takes place from 3 7M total chloride ion solution, good extraction of copper with relatively low acid transfer takes place from 9.8M total chloride ion solution.
Example ll -The bis isodecyl ester of pyridine~3,5-dicarboxylic acid was prepared by the method of Example 1 from pyridine-3,5-dicarboxylic acid and commercial isodecanol (obtained fromICI Petrochemicals Division) using modified amounts of reactants as required by the stoichiometry. Toluene was used as reaction solvent in place of xylene and the temperature was maintained at 80-82C for 4 hours after the thionyl chloride addition. Following the esterification reaction, the solution was cooled, washed with dilute sodium hydroxide solution, lM hydrochloric acid, 0.5M hydrochloric acid and water~ The solution was treated with activated carbon (8%
on the expected weight of product), the solvent evaporated at reduced pressure and the residue distilled (boiling range 200-210C at 0.08 mm mercury pressure~ to give a product having estimated purity of 97.5%.
This bis-ester was evaluated as an extractan-t for copper from aqueous solutions containiny chloride ion by the method of Examples 6 and 7.

3~:~7 Dx 31632A

To evaluate the efficiency of the extrac-tallt for use with leach solutions containing both high levels of total chloride ion and high acid levels, the general test method of Examples 6 and 7 was repeated usincJ a solution A which contained cupric chloride (O.lM), hydrochloric acid (l.OM) and calcium chloride dihydrate (700 g/l), giving a total chloride ion concentration of lOo 7M.
The r~sults are displayed in Table 3, and show that whilst a relatively low extraction of copper takes place from 3.7M total chloride ion solution, excel~ent extraction of copper takes place with no acid transfer from solutions containing a total chloride ion concentration of ~.8M, and low acid transfer levels are achieved even when the total chloride ion concentration is 10.7M.
Example 12 The bis nonyl ester of pyridine-2,4-dicarboxylic acid was prepared using the method of Example 1 from pyridine-2, 4-dicarboxylic acid and commercial nonanol (obtained from ICI Petrochemicals Division and containing predominantly 3,5,5-trimethylhexanol), with modified amounts of reactants as required by the stoichiometry. After the thionyl chloride addition, the temperature was maintained at 84-85C for 2 hours whilst a~ter the esterification reaction the product was isolated as described in Example 7. The boiling range of the product was 200-210C at 0.2 mm mercury pressure and the estimated purity was 100%.
The bis-ester was evaluated as an extractant for copper from aqueous solutions containing chloride by the method of Examples 6 and 11, except that AROMASOL H was used as solvent.
The results are shown in Table 3.
Example 13 The bis-isodecyl ester of pyridine 2,5-dicarhoxylic acid was prepared using the method of Example 1 from pyridine-2,5-dicarboxylic acid and commercial isodecanol, obtained ,.::,.:

~326~

Dx 316~2A
from ICI Petrochemicals Division, with modified amounts of reactants as required by the stoichiometry. Toluene was used as solvent for the reaction, in place of xylene, and after the thionyl chloride addition the temperature was maintained at 77-83C for 1~ hours. After the esteri~ication xeaction the product was isolated as described in Example 7, and had a boiling range of 219 221C at 0.08 mm mercury pressure, and estimated purity of 95.5%.
The bis-ester was evaluated as an extrac-tant for copper from solutions containing chloride by the method of Examples 7 and 11.
The resul-ts are displayed in Table 3.

N,N-Di-(n~-octyl picolinamide was prepared using the method of Example 1 from picolinic acid and di-(n)-octylamine. A~ter the addition of thionyl chloride, the temperature was maintained at 79-80~C for 5 hours and then raised to distil excess thionyl chloride and a little xylene.
The acid chloride suspension was cooled to 48C and the molten amine was added at 48-74C over lO minutes. The reaction was continued at 90C for ~ hours and the dark brown solution was cooled and washed with water to remove acidity. The solution was treated with activated carbon (10% on the expected weight of product), filtered, the solvent evaporated and the dar~ brown oil distilled. The product had a boiling range of 175-180C at 0.15 mm mercury pressure and was dark coloured. It was purified by dissolving in toluene, treating with activated carbon (lO~ on expected weight of product) and extracting with 2M sodium hydroxide and water~ The toluene was removed by evaporation under reduced pressure to give a mid-brown coloured oil of estimated purity 91~.
The amide ~as evaluated as an extractant for copper from solutions containing chloride ion as in ~xample 6 and

7, except that AROMASOL H was used as solvent.
The results are displayed in Table 3.

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932~7 Dx.31682 A

A 0.5 molar solution of the extractant of Example 1 in Aromasol H (20 ml) was shaken for 1 minute with an equal volume of a solution containing 37.6 ~l zinc, 3.65 ~l ~Cl and 65 ~l calcium (all as chlorides) ha~ing a total chloride ion concentration of 4.5 molar.
Analysis of the resulting aqueous phase showed that it contained 2801 ~l zinc, indicating a zinc transfer of 2~.~q.
~
The solvent extraction circuit described in Example 5 was used to eYaluate the extractant of Example 1. The feed was:

Copper (Cu2+) 25 ~l Iron ~Fe2 ) 75 ~l Silver (Ag~) 0.028 ~l Lead (pb2 ) 1.5 ~l Arsenic (As3 ) 0.2 g/l Antimony tsb3+) O.10 ~l Merc~r~ ) o.005 8~l With the e~ception of ~ilver, which wa8 added a~
silver nitrate to ~acilitate dissolution, the metals were in the for~ o~ their chlorides. In additionq the solution contained 1.8 ~l of hydroge~ chloride, giving a total c~loride ion concentration of 3.5 moles per litre~
The strip solution consisted of an aqueou~ solution containiag 29 ~l copper as cupric chloride, adjusted to p~ 1~0 with hydrochloric acid.

2~

Dx.~1682 A

The sol~ent phase eomprised 175 ~ 1 (0.5M) o~
the extractant of Example 1 dissolYed in AROMASOL H.
The operati~g conditions were a6 described i~ ~xample 5, except that ~he aqueous feed to the fir~t ~trip mixer-~ettlor wa~ heated, and the 8tripped organic phase returned to the ~xtraction ~ixer-fiettlers was cooled.
~s a result~ the fir6t fitrip 6tage operated at a~ a~erage temperature o~ 45C, whil~t the second 6trip stage operated at an ~er~ge te~perature o~ 34C~ ~he extraction 8tage8 operated at 280G.
The ~ircuit was operated for 53.5 honr6 wit~ steady trans~er o~ copper from the aqueous ~eed solution to the ~trip 801ution throughout the period of operatio~ as indicated by analysi6 of solutions pASSlng through the circuit at the ti~es listed below:
Time ~
(hourJ) R~fi~tes ~ ~ r~ S~ln.

4~ 10 9 49 5~-5 8 10 41 ~ _____~ _ During t~e period o operation, analysis for the minor metals pre~ent i~ the f~ed 6ave the followi~g results ( ~ l):
~ Pb2~ As3~ Sb3 ~
Strip 601~tion 0.001 00015 0.~040.010 0.0002 Preg~ant ~trip 0.001 000~0 o~too8 0.012 0.0002 solution B~ way o~ co~tparifiontt the circuit was operated under identical conditions,t except that no heatL~g of the strip -t~. " j ", ~32~7 Dx.31682 circuit was U6ed ~ and Rll mi%er-6ettlers operated at ambie~t tempe~ature (22C). No preci.pitate ~as ob~erved but a gradual build-up of an oligomeric copper comple~
~pecies was i~ferred from copper loadings on the e~tr~ctant gre~t0r than that expected for the species L2CuCl2~ where L
5 repres~ts the extractant. Tbe circuit wa~ oporated ~or 30 hours, and during this period, the concentration of copper in both the raf~inate and the ~tripped organic phase steadily increa6ed a~ indicated below:
q'ime (hour~) ~finate (CuZ _ ~ ) Stripped or~auic (~u 10.5 11~4 13.4 13.3 33 15.2 15.0 Example 17 The nicotinir acid e6ter of 2,2,4,8,10~10-he~amethyl-5-methylolundecane (the latter being deriqable fro~ the self conden~ation of two ~ol~sules o~
~OC~2C ~C~ - C~2C(~3)~ vi~ the Guerbet reaction) c~3 wa6 prepared U8illg the method o~ E~ample 1~ Tbe product bad a boilirlg point of 145 to. 150C at Ool mm pressure and an e6timated purity o~ 90~a~.
qhe ester was evPluated as an extractant for copper from aqueous solution con~aining chloride ion using the method o~ E~a~ple 1.
The results are as ~o}low~:

~3~

Dx . 316 o2A

%
Transfer of copper ~rom 0.1M ~Cl to B42~5 Tran6fer of copper fro~ 0.1M ~Cl to C2~.6 Transfer o~ copper from 100M ~Cl to B48.o Tran~f~r o~ copper from 1~0M ~Cl to C~0.2 Acid co-extracted from 1.0M ~Cl to B 2.6 Th~ acid co-extracted rrom 0~1M ~Cl to B was negligible.
t~ a~
The effect of different ester groups on the solubility of a ligand-copperII chloride complex in 10 concentr~ted ~olution in a non-polar solvent was examined as follows: Pyridine 3,5-dicarboxylic acid bis esters were prepared by esterifying pyridine 3,5-dicarboxylic acid with a series of different alcohols according to the procedure of Example 11 (see Table 4). Each ester in turn was made up as a 0.5M solutio~ in ESCAID 100 and loaded with copperII chloride (to approximately 75~ of the theoretical amount according to the stoichio~etry of L2CUCl~ where L
is the bis ester) by shaking with twice its ~olume of an aqueous 60lution which was 0.1M in ~Cl, 0.4M in CuC12 aud which in addition contained 250 g/l of calcium chloride dihydrate. Any separation of the metal ligand complex from the organic solution was noted (Test 1). If no separation occurred, the organic solution was loaded to approximately 100% of theoretical by shaking with a second aqueous solution which differed from the first only in containing 500 ~l of calcium chloride dihydrate. Again any separation of complex from the organic solution was noted (Test 2). Results are listed below in Tabl~ 4~

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Dx.31682 A

Table 4 Alcohol used Test 1 Test 2 18 Mixed isomer Immediate iso-octanol precipitation occurred 19 2-e-thylhexanol Commercial nonanol (3,5,5-trimethyl-hexanol) 21 Diisobutyl No Precipitation carbinol precipitation occurred a~ter 2 weeks 22 Mixed iso~er ll No isononanolC precipitation after 2 weeks 2~ Mixed isomer isodecanol 24 Mixed isomer Some tridecanol precipitation occurred but only after . 2 weeks _~_ _ _ _ . _.
~ The mixed isomer isononanol was obtained by h~drofor~ylation of a mixed octene stream.
The results indicate that the bis esters of Example6 18, 19, 20, 21 and 24 would require to be used in more dilute solution or in a more polar solvent than ESCAID 100, for example a solvent having a higher aromatic content, but that the bis esters of Examples 22 and 2~ and their copper complexes have excellent solubility even in conce~trated solution in a very weakly polar solvent of low aromatic co~tent.

~5 3;~

Dx.31682A

N1N,NI,N~-tetraisoamyl pyridine-2,5-dicarboxamide was prepared using the method of EXample 1 from pyridL~e-2,5-dicarboxylic acid and diisoamylamine. The crude product in toluene 60lution was washed several times with 005M aqueous sodium hydroxide ~nd then with 0.5M aqueous hydrochloric acid and water. The solution was then treated with charcoal and filtered. The solvent was distilled under reduced pressure, but the product, a brown oil, wa6 not itself distilled. It was made up as a 0.2M solution in AROMASOL
and tested for extraction of copper in the presence of chloride ion using the method o~ Examples 6 and 7 except that AROMAS0~ ~ was used as solvent. The results are given in Table 3. The results indicate that this is a very weak extracta~t suitable for recovering copper from aqueous solution of high chloride ion concentrations.

3-hexylundecylamine was prepared from Z-hexyldecanol as follows~ The alcohol was heated to 96-107J
ZO and stirred whilst a stream of hydrogen bromide gas was bubbled through it for 4 hours~ The organic layer was separated, and washed first with SS~ sulphuric acid and then with water, aqueous ammonia u~til neutral, and water1 and then distilled yielding 1-bromo-2-hexyldecane (b.p~140 at 1 mm pressure). The bro~o compound was conYerted to 1-cyano-2-hexyldecane by stirring it at the reflux temperature with excess of a 44~ aqueous solution of sodiu~ cyanide, in the presence of methyl trioctyl ammoniu~ chloride as a ~haRe transfer catalyst, following C.M.Starks (Journal of the American Chemical Society, 93, page 195, 1971). After washing with dilute aqueous sodium hydroxide sol~ltion and '''`i:~, , ~

32~7 Dx.31682A

water, the cyano compound (141 gram6) was di6solved in ethanol (1~0 ml~ and poured into an autoclave~ Liquid am~onia (150 6) was added and the autoclave was pressurified to 50 at~ospheres with hydrogen7 sealed, and heated to 170 for 24 hours. The autoclave w~s cooled, a~d most of the ammonia allowed to evaporate. The ~olution was filtered and the solvent was distilled under reduced pressure. It was found by gas chromatography that complete conversion to 3-hexylundecylamine had taken place.
N,N~-bis(3-hexylundecyl)pyridine-2,5 dicarboxamide was prepared using the method of Example 1 from 3-hexyl-undecylamine and pyridine 2,5-dicarboxylic acid. The product which was a brown oil was not distilled but was analysed as being 92~o of theoretical strength (based on MW 642) by titration of an aliquot in acetic aGid with perchloric acid. It was made up as a 0.2M solution in AROMASOL ~ and tested for extraction of copper in the presence of chloride ion using the method of Examples 6 and 7. The results are given in Table 3. They indicated that this compound is a strong extractant for copper which would be best employed in extracting copper fron solutions of relatively low chloride ion concentration and relati~ely low acidity.

Claims (2)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A 3,5-disubstituted pyridine of formula wherein the respective groups R1 and R6 are branched chain or mixed isomer alkyl groups together containing a total of from 16 to 36 carbon atoms, and wherein Y is hydrogen or is one or more of the groups halogen, alkyl, aryl, alkoxy, aryloxy, aralkyl, cyano, nitro or carboxylic acid.

2. A 3,5-disubstituted pyridine according to Claim 1 wherein Y is hydrogen and the respective groups R1 and R6 are the same and are selected from the group consisting of mixed isomer isodecyl, single isomer nonyl, mixed isomer nonyl, 2-ethylhexyl, mixed isomer octyl,di-isobutylcarbinyl and tridecyl.