CA1101444A - Liquid-liquid extraction of metal values - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
2-Hydroxyiminoacetic acids of the general formula

Description

The invention relates to novel 2-hydroxyiminoacetic acids to be specified hereinafter as well as to a process for their preparation. The

2-hydroxyiminoacetic acids according to the present invention have outstand-ing properties as metal-extraction agents. The invention therefore also relates to a process for the extraction o~ metal values with the aid of these 2-hydroxyiminoacetic acids.
One of the processes used for the production of metals from ores comprises grinding the ore and extracting the ground ore with an aqueous solution containing sulphuric acid. The acidic aqueous extract phase thus obtained usually contains a mixture of metal ions. An alkaline material, for example, aqueous ammonia, is added to this extract phase to increase the pH to a value suitable for the selective liquid-liquid extraction of one of the metal values with an extractant comprising an organic solvent and a dis-solved organic extraction agent. This organic extraction agent is more soluble in the organic solvent than in water and forms complexes with the metals to be extracted. These complexes are also more soluble in the organic solvent than in water.
The liquid-liquid extraction can be conducted continuously by bring-ing the acidic aqueous solution into contact with the extractant, preferably by vigorous stirring. Then, the organic phase is separated from the aqueous phase and stripped with an aqueous solution containing a strong mineral acid.
The metal values are thus transferred to the aqueous stripping solution as metal salts and can then be recovered therefrom, for example, by crystalliza-tion, or as metal by electrolysis, while the organic phase containing the released organic extraction agent is advantageously used again for the extrac-tion of further quantities of metal values.
Organic extraction agents are described in:
~1) United States patent specification 3,224,873, disclosing the use, '~

11~)1444 as eopper-extraction agent, of alpha~hydroxy-oximes of the general formula OH NOH
Rl _ C - C R2 (I) wherein R , R and R may represent any of a variety of organic radicals such as aliphatic and alkylaryl radicals, while R3 may also represent a hydrogen atom. Table I in this specification shows that at a pH of 2.63 3.0% of the copper was extracted from the acidic aqueous solution, the logarithm of the distribution coefficient being -1.66.
(2) United States patent specification 3,428,449, disclosing the use, as copper-extraction agent, of 2-hydroxybenzophenone oximes sub-stituted with (a) saturated or ethylenically unsaturated aliphatic group or groups or the corresponding ether group or groups, in combination with alpha-hydroxy-oximes of the general formula I, The acidic aqueous starting solutions in this case usually have a pH between 1.4 and 2.3. For example, the logarithm of the distribution coefficient for copper at a pH of 1.68 has a value of -0.28.

(3) British patent specification 1,322,532 disclosing the use, as metal-extraction agent, of a hydroxy-oxime of the general formula A - C (=NOH) - R (II) in which R represents an aliphatic group and A a cyclic organic group carrying as substituents at least a hydroxyl group at a ring carbon atom in a 2-position - the number 1 being assigned to the ring carbon atom to which the -C(=NOH)~R group is attached - and .x ~ 2 _ 11014g4 ~:~
an organic group. These extraction agents are suitably used for copper extraction from aqueous solutions having a pH between 1 and 1.5 and those in which the group A contains, in addition, one or more electron - attract-ing substituents, from aqueous solutions having a pH between 0 and 1. For ; example, for a representative oxime the logarithm of the distribution co-efficient for copper at a pH of 1.04 has a value of 0.15. The oximes of the general formula II cannot be used for the separation of nickel tII) from cobalt (II), because a mineral acid very difficultly decompose their complexes with cobalt.

(4) German Offenlegungsschrift 2,334,901, disclosing the use, as metal-extraction agent, of certain salicylaldoximes. The acidic aqueous solution used in Examples 1 and 3 of this publication had a pH of 2 and 1.49, respectively. From the results obtained logarithms of distribution co-efficients for copper of 0.14 and -0.1, respectively, can be calculated.

(5) British patent specification 959,813, disclosing the use of certain alkanemonocarboxylic acids for the separation of nickel from cobalt present in aqueous solutions having a pH between 7.5 and 9.5; copper is ~ advantageously extracted from aqueous solutions having a pH between 5 and 6.
; The rate of extraction attained with the organic extraction agents mentioned under (1), (2), (3) and (4) is too low to justify their application in a column contactor such as a rotating disc contactor (dis-closed in British patent specification 659,241). They call for the use of an impeller mixer. The rate of extraction attained with the organic ex-traction agents mentioned under (5) is sufficiently high to justify their application in a column contactor, but they cannot be used for the separation of nickel from cobalt present in acidic aqueous solutions.
The present invention provides novel metal-extraction agents, the advantages of which are illustrated hereinafter.
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1~101444 The novel compounds according to the present invention are 2-hydroxyiminoacetic acids of the general formula R - C - COOH
" (III) NOH

and their salts, in which formula R represents an aromatic hydrocarbyl group substituted with one or more aliphatic side chains possessing in total at least four carbon atoms.
The aromatic hydrocarbyl group in the general formula III may be polycyclic but is preferably monocyclic The aliphatic side chain(s) may contain heteroatoms, for example, an oxygen atom. In particular, R
represents an alkyl-substituted monocyclic aromatic hydrocarbyl group, the alkyl groups possessing in total from seven to twenty carbon atoms. An example of particularly preferred 2-hydroxyiminoacetic acids according to the invention is a mixture of isomeric 2-(p-dodecylphenyl)-2-hydroxyimino-acetic acids, of which the isomerism is caused by the branching of the dodecyl groups which are derived from a mixture of branched dodecenes obtained by oligomerization of propene. Other examples of groups represented by R are 2,4-diisopropylphenyl, p-n-hexylphenyl, p-2-methylheptylphenyl, p-n-heptyl-phenyl, p-2-methyloctyl, p-n-nonylphenyl, p-2-methylnonylphenyl, p-n~decyl-phenyl, p-2-methyldecylphenyl, p-n-tridecylphenyl, p-2-methyltridecylphenyl, p-n-tetradecylphenyl, p-n-hexadecylphenyl and p-n-eicosylphenyl groups. A
mixture of isomeric 2-~p-nonylphenyl)-2-hydroxyiminoacetic acids, of which the isomerism is caused by the branching of the nonyl groups, which are de-rived from a mixture of branched nonenes obtained by trimerization of propene, is also within the scope of the invention.
The 2-hydroxyiminoacetic acids of the general formula III may be prepared by methods known in the art.

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A suitable route to alkali metal salts of 2-hydroxyimioacetic acids of the general formula I, wherein R represents a p-alkylphenyl, an o-alkylphenyl or an o,p-dialkylphenyl group, includes reacting the corresponding alkylbenzene or 1,3-dialkylbenzene (compounds according to formula 1, modified by replacing the HOOC-C=NOH group by a hydrogen atom) with methoxalyl chloride and reacting the methyl 2-oxo-2-(p-alkylphenyl)acetate, methyl 2-oxo-2-(o-alkylphenyl)acetate or methyl 2-oxo-2-~2,4-dialkylphenyl~acetate thus obtained with hydroxylamine and alkali metal hydroxide. The alkali metal salts thus - formed may be converted into the corresponding 2-hydroxyiminoacetic acids by acidification of a solution thereof with a mineral acid such as sulphuric acid or hydrochloric acid.
The invention further relates to a process for the separation of metal values from an acidic aqueous solution thereof by liquid-liquid extraction with an extractant comprising an organic solvent and, dissolved therein, a 2-hydroxyiminoacetic acid of the general formula R-C-COOH
. N , ~III) NOH
wherein R represents an aromatic hydrocarbyl group substituted with one or more aliphatic side chains possessing in total at least four carbon atoms, excluding the carbon atoms of the HOOC-C=NOH group.
The process for the separation of metal values according to the present invention allows the use of acidic aqueous starting solutions having an unusually low pH. This reduces the quantity of alkaline agent required to increase the pH of the acidic solution to be extracted. Furthermore, in most cases the protons liberated during the extraction need not be neutralized.
The process for the separation of metal values according to the invention is preferably conducted with 2-hydroxyiminoacetic acids of the general formula III, wherein R represents an alkyl-substituted monocyclic . . .
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' 11t)1444 aromatic hydrocarbyl group. The aliphatic side chains in the general formula III must have in total at least four car60n atoms, because with decreasing number of carbon atoms in the side chain the 2-hydroxyiminoacetic acids become more soluble in water and less soluble in organic solvents. In view thereof the alkyl side chain~s) preferably possess(es) in total at least seven carbon atoms. No additional advantages are obtained when the number of carbon atoms in the aliphatic side chain~s~ increase above twenty. Examples of suitable 2-hydroxyiminoacetic acids are stated hereinbefore.
The extraction according to the invention is so rapid that it may be conducted in a column contactor such as a rotating disc contactor as disclosed in British patent specification 659,241. The process is very suit-able for the selective extraction of: (a) copper (II) values from an aqueous solution having a pH between 0 and 1.5 and containing copper (II) and iron (III) values; (b) nickel (II) values from an aqueous solution having a pH
between 1.0 and 2.5 and containing nickel (II) and cobalt (II) values; the complexes of cobalt (II) can be decomposed with a mineral acid and, moreover, this separation is more selective than that effected with the alkanemono-carboxylic acids mentioned hereinbefore; (c) calcium values from an aqueous solution having a pH between 3.0 and 4.5 and containing calcium and magnesium values; such solutions become available, for example, when dolomite is dissolved in aqueous hydrochloric acid. Preferably, the mutual miscibility of the acidic aqueous solution and the organic solvent should not exceed 5 %v, and in particular it should be lower than 1 %v. Suitable solvents are, for example, halogenated solvents, such as chloroform, 1,2-dichloroethane, 1,2-dichloropropane, 1,2,3-trichloropropane and di(2-chloroethyl) ether, and in particular hydrocarbons, for example, kerosine, toluene and the xylenes.
A favourable volume ratio o the extractant to the acidic aqueous solution has been found to be 1:3 to 3:1. However, ratios outside this range may also be used. As a rule, the extraction proceeds smoothly at a .

temperature between 15C and 35C. However, higher or lower temperatures, for example, between 0C and 15C and 35C and 5QC, are not precluded.
The extractant may conta;n a compound favouring phase separa-tion, for example, a long-chain alcohol such as a mixture of primary alkanols having from nine to eleven carbon atoms per molecule, of which at least 80%
are linear; such mixtures are known under the trade mark of "LINEVOL". Other examples of such compounds are hexanol, octanol, 2-methyldecanol, tridecanol and alkylphenols possessing alkyl groups having at least six carbon atoms, for example, p-nonylphenol and p-dodecylphenol.
The invention is further illustrated by means of the following Examples.
EXAMPLE I
A. Preparation of ?- ~o-and p-dodecylphenyl)-2-hydroxyiminoacetic acid A flask was charged with 0.1 mol of a mixture of isomeric dodecylbenzenes, 0.1 mol of methoxalyl chloride and 100 ml of tetrachloro-ethylene. The dodecylbenzenes had been prepared by alkylation of benzene with a mixture of branched dodecenes obtained by oligomerization of propylene. The contents of the flask were kept at a temperature between O and 10C and 0.15 mol of powdered aluminium chloride was added with stirring. Then, the temper-ature of the contents of the flask was increased to 40C and stirring was continued at this temperature for a period of two hours. The reaction product thus formed was poured into 100 ml of lN aqueous sulphuric acid, the aqueous phase was separated from the organic phase thus formed and the latter phase was washed twice with 100 ml of lN aqueous sulphuric acid. The washed organic phase was boiled down at a pressure of 0.047 bar and the residue formed was dissolved in 50 ml of ethanol. An amount of 0.1 mol of hydroxyl-amine hydrochloride and 0.2 mol of solid sodium hydroxide and 50 ml of water were added to the ethanolic solution formed and the solution was boiled under ,,~ ,. ,~
~ ~ - 7 --: 1101444 reflux for a period of two hours. Then, the reaction mixture was extracted twice with 5Q ml of n-pentane and the raffinate phase obtained was acidified with 60 ml of 2N aqueous sulphuric acid, the acidified mixture was extracted three times with 50 ml of n-pentane, the extract phases obtained were combined and the combined phases were dried in the presence of anhydrous sodium sulphate and then boiled down at a pressure of 0.047 bar and a temperature of 50C to give a residue containing a mixture of isomeric 2-(o- and p-dodecyl-phenyl)-2-hydroxyiminoacetic acids, of which the isomerism is caused by the branching of the dodecyl groups. The residue was dried in a dessicator with anhydrous phosphorous pentoxide. Table I presents the results of an elementary analysis of the dried residue. The theoretical composition refers to the acid.
Table I
._ Composition, %

theoretical found _ . .
C 72.1 72.1 N 4.2 4.1 H 9.3 9.5 O 14.4 14.3 .
The dried residue had an acid number of 159 mg KOH/g (theory 168) and the amount of it corresponded to a yield of 83%, calculated as residue on dodecyl-benzene. The dried residue mainly consisted of 2-(p-dodecylphenyl)-2-hydroxy-iminoacetic acid, a minor content of 2-(o-dodecylphenyl~-2-hydroxyiminoacetic acid being present.

B. Extraction with 2-(o- and p-dodecylphenyl)-2-hydroxyiminoacetic acid The extrac~ion experiments were conducted in a separatory funnel consisting of a graduated, straight-walled vessel with a capacity of 0.25 1. At the bottom a stopcock was provided for draining the funnel. The ~ - 8 -.

top opening was used to introduce a double-paddle stirrer and it also served as the inlet for the feed. The extractions were carried out by contacting 100 ml of an aqueous solution for a period of 15 seconds wîth 100 ml of an organic extraction solution and stirring at a rate of about 500 rev/min. The aqueous solutions contained metal sulphate or chloride in a concentration of 0.01 - gramion metal per litre together with sodium sulphate or sodium chloride in a concentration of 0.5 mol per litre and sulphuric or hydrochloric acid. The organic extraction solution consisted of a mixture of a kerosine fraction, poor in aromatics, having an atmospheric boiling range from 210C to 240C
(90 %v) and primary alkanols having nine to eleven carbon atoms per molecule of which at least 80% was linear (10 %v) and the 2-(o- and p-dodecylphenyl)-2-hydroxyiminoacetic acid prepared as described above in a concentration of 0.1 mol/litre.
Each aqueous solution contained one metal to be extracted.
Eight starting solutions were prepared which contained Cu , Fe , Ni , Co Cd , Zn (these six were obtained by dissolving the metal sulphate), Ca and Mg (these two were obtained by dissolving the metal chloride). The firs~ six solutions contained sodium sulphate, ~he last two sodium chloride.
The pH of the starting aqueous solutions was adjusted by adding sulphuric acid (for the first six metals) or hydrochloric acid (for the last two metals) and the extraction was started. Then, the two phases were allowed to separate and the concentrations of the metal in the organic and in the aqueous phase were determined. Subsequently, the pH of the aqueous solution was slightly increased by adding 25 %w aqueous ammonia and stirring was continued until equilibrium was again obtained. The two phases were allowed to separate and the concentration of the metal in the organic and in the aqueous phase were again determined. This procedure was continued in this way for each of the eight metals. Table II presents the logarithms of the distribution ~ ~ _ g _ :`
coefficients D found at various pH values. The distribution coefficient is the quotient of the concentrations of the metal in the organic and the aqueous phase.

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O O O O
O N O 1~ ~ 1 ~1 n oO
H ¦ I~ ~i N N N
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O bl) O O O ~ .-1 :~ u~ a~ 1~ 1`

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O O ~1 _l N ~ N .-1 0 CO Lt~ ~ N 00 ~C O O ~ ~ ~

llV14~4 In the graph the pll and the log D have been set out along the hori`zontal and vertical axes, respectively. The values for log D and the pH presented in Table II have been plotted in the graph and are indicated with points. A straight line has been drawn through each set of points thus obtained for one particular metal.
EXAMPLE II
A. Preparation of 2-(2,4-diisopropylphenyl)-2-hydroxyiminoacetic acid The experiment described in Example I, section A, was repeated with 30 g (0.18 mol~ of 1,3-diisopropylbenzene (which also contained max 5 %w of 1,3,5-triisopropylbenzene) instead of the mixture of isomeric dodecylbenzenes. The dried residue had an acid number of 135 mg KOH/g, indicating that 60 %w consisted of hydroxyiminoacetic acid (calculated as diisopropyl derivative) and 40 %w of unconverted starting 1,3-diisopropyl-benzene. The yield was 84%, calculated as 2-~2,4-diisopropylphenyl)-2-hydroxyiminoacetic acid on methoxalyl chloride.
B. Extraction with 2-(2,4-diisopropylphenyl)-2-hydroxyiminoacetic acid The extraction of copper described in Example I, section B, was repeated with the modification that the 2-~o- and p-dodecylphenyl)-2-hydroxyiminoacetic acid was replaced by the 2-(2,4 diisopropylphenyl)-2-hydroxyiminoacetic acid prepared as described in Section A. The extract phasecontained copper, but some of the 2-(2,4-diisopropylphenyl)-2-hydroxyimino-acetic acid had been transferred to the raffinate phase ~aqueous phase), which had acquired a brownish colour.

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Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. 2-Hydroxyiminoacetic acids of the general formula and their salts, in which formula R represents an aromatic hydrocarbyl group substituted with one or more aliphatic side chains possessing in total at least four carbon atoms.

2. Compounds as claimed in claim 1, wherein R represents an alkyl-substituted monocyclic aromatic hydrocarbyl group, the alkyl group(s) possess-ing in total from seven to twenty carbon atoms.

3. A mixture of isomeric 2-(p-dodecylphenyl)-2-hydroxyiminoacetic acids, of which the isomerism is caused by the branching of the dodecyl groups which are derived from a mixture of branched dodecenes obtained by oligomerization of propene.

4. Process for the preparation of aIkali metal salts of 2-hydroxy-iminoacetic acids as claimed in claim 1, wherein R represents a p-alkylphenyl, an o-alkylphenyl or an o,p-dialkylphenyl group, which process comprises re-acting the corresponding alkylbenzene or 1,3-dialkylbenzene (compounds according to formula I modified by replacing the group by a hydrogen atom) with methoxalyl chloride and reacting the methyl 2-oxo-2-(p-alkylphenyl)acetate, methyl 2-oxo-2-(o-alkylphenyl)acetate or methyl 2-oxo-2-(2,4-dialkylphenyl)acetate thus obtained with hydroxylamine and alkali metal hydroxide.

5. Process for the preparation of 2-hydroxyiminoacetic acids as claimed in claim 1, wherein R represents a p-alkylphenyl, an o-alkylphenyl or an o,p-dialkylphenyl group, which process comprises the acidification with a mineral acid of a solution containing an alkali metal salt of this acid prepared by a process as claimed in claim 4.

6. Process for the separation of metal values from an acidic aqueous solution thereof by liquid-liquid extraction with an extractant comprising an organic solvent and, dissolved therein, a 2-hydroxyimino-acetic acid as claimed in claim 1.

7. A process as claimed in claim 6, in which nickel (II) values are selectively extracted from an aqueous solution having a pH between 1.0 and 2.5 and containing Ni (II) and Co (II) values.

8. A process as claimed in claim 6, in which copper (II) values are selectively extracted from an aqueous solution having a pH between 0 and 1.5 and containing Cu (II) and Fe (III) values.

9. A process as claimed in claim 6, in which calcium values are selectively extracted from an aqueous solution having a pH between 3.0 and 4.5 and containing Ca and Mg values.