WO1997030181A1

WO1997030181A1 - Extraction of cobalt and/or nickel from an aqueous feed solution

Info

Publication number: WO1997030181A1
Application number: PCT/GB1997/000091
Authority: WO
Inventors: Domenico Carlo Cupertino; John Campbell; John Robert Lawson; Julie Ann Stocks; Raymond Frederick Dalton
Original assignee: Zeneca Limited
Priority date: 1996-02-17
Filing date: 1997-01-14
Publication date: 1997-08-21
Also published as: AU1392497A; ID15954A

Abstract

A process for the selective separation of cobalt and/or nickel from aqueous acidic solutions is provided, and particularly a process for the selective separation of cobalt from aqueous solutions also comprising nickel. The process comprises contacting the feed solution under controlled pH conditions with an extractant comprising an amidobis(thiophosphoryl) compound of formula (1), wherein R?1, R2, R3 and R4¿ each independently, represents an optionally substituted hydrocarbyl or optionally substituted hydrocarbyloxy group, or R?1 and R2¿ and/or R?3 and R4¿ together with the P atom, form an optionally substituted 5- to 8-membered heterocyclic ring.

Description

EXTRACTION OF COBALT AND/OR NICKEL FROM AN AQUEOUS FEED SOLUTION

This specification describes a process relating to the extraction of one or more metals from an aqueous solution containing the metals, especially in the presence of other metals

It is known from EP 573182A and WO 95/15329 that certain amιdo-bιs(thιo- phosphoryl) compounds ("ABTP") are useful for the selective extraction of certain metals from aqueous acid solution (at or below pH 2) Of thirteen metals, including nickel, contained in a mixed aqueous solution, only bismuth, cadmium, mercury, silver and zinc were reported as being extracted into an organic phase containing the ABTP

There is commercial interest in the extraction of cobalt and nickel from ores in which they occur, and particularly in the selective extraction of cobalt and nickel from ores in which they occur together, especially from 'sulphidic" ores containing nickel and cobalt sulphides and from "latente" ores containing cobalt and nickel, together with magnesium, manganese, iron, aluminium, chromium, zinc and sometimes copper US Patent No 5,378,262 discloses that certain organic dithiophosphinates can be employed to extract cobalt and nickel from aqueous acidic solutions

It has now been found possible to separate cobalt and/or nickel from solutions containing either or both metals, and particularly to selectively separate cobalt, and optionally nickel, from solutions containing both metals, and especially from aqueous solutions derived from "latente" ores containing cobalt, nickel and the other metals mentioned above, using an ABTP

THE EXTRACTION PROCESS (1

According to a first embodiment of the present invention there is provided a process for the extraction of cobalt from an aqueous feed solution comprising cobalt which compπses contacting the feed solution with an extractant comprising an amιdobιs(thιophosphoryl) compound of the formula

Formula (1) wnerein

R¹, R², R³ & R⁴ each independently, represents an optionally substituted hydrocarbyl or optionally substituted hydrocarbyloxy group, or R¹ & R² &/or R³ & R⁴ together with the P atom, form an optionally substituted 5- to 8-membered heterocyclic ring, at a pH of greater than 2

If it is desired to obtain the Co in the substantial absence of any other metals present in the feed medium which are extractable by the present extractant at a pH value of greater than 2, such as bismuth, cadmium, copper, iron, mercury, silver and zinc, these 5 are preferably removed from the feed solution before contacting it with the extractant in the aforementioned pH range Alternatively, the cobalt can be separated from such other metals by selective stripping, in which extractant loaded with cobalt and other metals is contacted with a weakly acidic stπpping solution, the pH of the stripping solution being chosen such that cobalt is transferred into the aqueous phase, but that the undesired 0 metals remain loaded in the extractant The weakly acidic stripping solution may vary depending on the nature of the undesired metals, and their relative concentrations Commonly, the weakly acidic stripping solution is chosen to be such that the final pH of the aqueous solution after stripping is in the range of from 0 5 to 3 and preferably from 1 to 2 5 In many embodiments, acid concentrations, particularly for sulphuric acid, in the 5 range of from 5 to 35 g/1, preferably from 8 to 20 g/1 and particularly from 10 to 15 g/l are employed The metals remaining loaded in the extractant can then be recovered by stπpping with one or more acidic stripping solutions, the pH of the solutions being chosen to achieve any such further separation as desired, for example a stripping solution such that the final pH of the aqueous solution was of pH less than 0 could be employed to strip

The process of the first embodiment is preferably carried out at a pH of the aqueous solution of no less than about pH 2 4 and more preferably no less than about pH 2 5, and although it has been found that Co may be extracted by certain extractants at values as low as about pH 2, the degree of extraction below pH 2 7 is relatively low and it 5 is therefore particularly preferred to operate the present process at or above pH 3 0 especially at least about pH 3 3. The pH of the aqueous solution in the process of the first embodiment is commonly no more than about pH 6 5 and more especially no more than about pH 6

According to a second embodiment of the present invention there is provided a o process for the extraction of nickel from an aqueous feed solution comprising nickel, which compπses contacting the feed solution with an extractant comprising an amιdobιs(thιophosphoryl) compound of the formula

Formula (1 ) wherein R¹, R², R³ & R⁴ each independently, represents an optionally substituted hydrocarbyl or optionally substituted hydrocarbyloxy group, or

5 R¹ & R² &/or R³ & R⁴ together with the P atom, form an optionally substituted 5- to

8-membered heterocyclic ring, at a pH of greater than 4

If it is desired to obtain the nickel in the substantial absence of any other metals present in the feed medium which are extractable by the present extractant at a pH value 0 of greater than 4, such as bismuth, cadmium, cobalt, copper, iron, mercury, silver and zinc, these are preferably removed from the feed solution before contacting it with the extractant in the aforementioned pH range Alternatively, the nickel can be separated from such other metals by selective stripping, in which extractant loaded with nickel and other metals is contacted with a weakly acidic stripping solution, the pH of the stripping 5 solution being chosen such that nickel is transferred into the aqueous phase, but that the undesired metals remain loaded in the extractant The weakly acidic stπpping solution may vary depending on the nature of the undesired metals, and their relative concentrations Commonly, the weakly acidic stripping solution is chosen to be such that the final pH of the aqueous solution after stripping is in the range of from pH 0 5 to 4, and o preferably from 1 to 3 5, when Co is not present When Co is present, the final pH of the aqueous solution is preferably >3, and particularly 3 5 or more In many embodiments, acid concentrations, particularly for sulphuric acid, in the range of from 5 to 35 g/l, preferably from 8 to 20 g/i and particularly from 10 to 15 g/l are employed The metals remaining loaded in the extractant can then be recovered by stripping with one or more 5 acidic stripping solutions, the pH of the solutions being chosen to achieve any such further separation as desired, for example, a stripping solution such that the final pH of the aqueous solution was from 0 5 to 3 5, preferably from 1 to 2 5, could be employed to strip cobalt, and a stripping solution such that the final pH of the aqueous solution was of pH less than 0 could be employed to strip zinc o The nickel extraction process of the second embodiment is preferably carried out at a pH of the aqueous solution of no less than about pH 4 5, especially no less than about pH 5 The pH of the aqueous solution in the process of the second embodiment is commonly no more than about pH 6 5 and more especially no more than about pH 6 According to a third embodiment of the present invention there is provided a 5 process for the selective extraction of cobalt from an aqueous feed solution containing cobalt, in the presence of one or more other metals, especially nickel, which compπses contacting the feed solution with an extractant comprising an ABTP of the formula

Formula (1 ) wherein

R¹ , R², R³ & R⁴ each independently, represents an optionally substituted hydrocarbyl or optionally substituted hydrocarbyloxy group, or

R¹ & R² &/or R³ & R⁴ together with the P atom, form an optionally substituted 5- to 8-membered heterocyclic ring, at a pH in a range from,

(a) a lower value at which Co is taken up by the extractant in order to form a loaded extractant, to

(b) an upper value at which Co and any other metal present in the feed solution (especially Ni) are taken up by the extractant to form loaded extractant in which the ratio of Co to any other metal in the feed solution (especially Ni) in the loaded extractant is higher than in the feed solution By the term "selective extraction" is meant that the selected metal is extracted preferentially to other metals in the feed solution so that the weight ratio of the selected metal to the total amount of metals in the loaded extractant is higher than in the original feed solution

If it is desired to obtain the Co in the substantial absence of any other metals present in the feed medium which are extractable by the present extractant at pH values within or below the pH range from (a) to (b), such as bismuth, cadmium, copper, iron, mercury, silver and zinc, these are preferably removed from the feed solution before contacting it with the extractant in the aforementioned pH range (a) to (b)

In the case of latente ores containing iron and relatively small proportions of zinc and copper, these metals may be removed from the feed medium prior to performing the present process, by any convenient method, for example, cementation in the case of copper extraction with a suitable extractant at about pH 2 or below in the case of zinc, and precipitation at pH 3 5 to pH 4 in the case of iron The remaining components of a feed solution derived from a latente ore may be retained in the feed solution because they are not extracted from the feed solution by the extractant to any significant extent until above the pH at which Co and Ni can be selectively extracted by the extractant

It has been found that the lower value (a) is preferably from about pH 2 4 to about pH 3 3 and more preferably from about pH 2 5 to about pH 3 0 Although it has been found that Co may be extracted by certain extractants at values as low as about pH 2, the degree of extraction below pH 2 7 is relatively low and it is therefore preferred to operate the present process at or above pH 3 0

It has been found that the upper value (b) of the pH range in which Co is selectively extracted from a feed solution containing Co and Ni is preferably from about pH 4 0 to pH 5 0, and more preferably from about 4 0 to about 4 5 although the practical upper pH value depends upon the amount of Nt which can be tolerated in the extracted Co, the specific extractant and certain other environmental factors such as temperature and the nature of other ingredients in the feed solution

However, it is within the skill of the skilled person to determine the practical upper pH value for the extraction of Co for any specific extractant and feed solution, depending upon the specific environmental factors and the level of Ni which is tolerable in the extracted Co

If it is desired to extract Co only, i e without extracting any substantial amount of Ni, it has been found that the optimum pH for the extraction of Co is at or below pH 4 5 and especially in the region from about pH 3 to pH 4 5 though the precise level will depend upon the aforementioned factors It is especially preferred to extract Co, in the substantial absence of Ni, from a feed solution containing Co and Ni, in the region from about pH 3 to about pH 4

According to a preferred feature of the present invention there is provided a process for the selective extraction of cobalt from an aqueous feed solution containing cobalt and nickel and optionally other metals, which compπses contacting the feed solution with an ABTP of Formula (1) in a range from about pH 3 to about pH 4

The Co, and any Ni in the loaded extractant, may be subsequently stripped from the loaded ABTP by contacting the latter with an aqueous strip medium at a pH favouring transport of the Co into the strip medium

After removal of Co from a feed solution originally containing, inter alia, Co and Ni, Ni may be removed from the Co-spent feed solution by contacting the latter solution with fresh extractant at a higher pH.

According to a further feature of the present invention there is provided a process for the selective removal of Ni from a feed solution which is substantially free from Co

(and other metals extractable with an ABTP of Formula (1 ) below pH 5) by contacting the feed solution with an extractant comprising an ABTP of Formula (1 ) at a pH in a range from

(c) a lower value at which Ni is taken up by the extractant in order to form a loaded extractant, to

(d) an upper value at which the ratio of Ni to any other metal in the feed solution, in the loaded extractant, is higher than in the feed solution

In the case of a feed solution originally containing only Co and Ni the pH for the extraction of Ni following removal of Co, is preferably from about pH 4 up to the level at which the Ni is no longer soluble in the feed solution However, where the feed solution is derived from a latente ore, the practical upper value (d) is about pH 6 if it is desired to extract Ni in the substantial absence of the other metals remaining in the feed solution, which are generally only extracted to a significant extent by the extractant at a pH > 6 The Ni, and any other metal in the loaded extractant, may be subsequently stripped from the loaded extractant by contacting the latter with an aqueous strip medium at a pH favouring transport of the Ni into the strip medium

According to a further preferred feature of the present invention, there is provided a process for the sequential separation of Co and Ni from a feed solution containing Co 0 and Ni (especially a feed solution derived from a latente ore from which iron, zinc and any copper have been previously removed), which comprises contacting the feed solution, (i) with an extractant comprising an ABTP of Formula (1) at a pH in a range from

(a) a lower value at which Co is taken up by the extractant in order to form a loaded extractant, to 5 (b) an upper value at which Co, but substantially no Ni, is taken up by the extractant and repeating step (i) sufficiently often to remove substantially all the Co from the feed solution without removing any substantial amount of Ni, and subsequently contacting the spent feed solution from step (i), o (ti) with an extractant comprising an ABTP of Formula (1 ) at a pH in a range from

(d) an upper value at which Ni, but substantially no other metal tn the feed solution is taken up by the extractant 5 It is preferred to repeat step (n) sufficiently often to remove substantially all the Ni from the feed solution

The lower value (a) in step (i) is preferably from about pH 2 7 to about pH 3 3 and more especially about pH 3 and the upper value (b) in step (i) is preferably from about pH 4 to about pH 5 and more especially from about pH 4 to about pH 4 5 The lower o value (c) in step (n) is preferably from about pH 4 to about pH 5 and more especially from about pH 4 5 to about pH 5 and the upper value (d) in step (n) is preferably from about pH 5 5 to pH 6 5 and more especially about pH 6

THE EXTRACTANT 5 The ABTPs employed in the present invention are substantially water insoluble

The extractant may comprise one or more different ABTPs and compositions of ABTPs in which the nature of the substituents groups represented by R¹ to R⁴ differ between component ABTP, especially where the component ABTP are isomeric, are generally preferred because such isomeric compositions often have better solubility in organic solvents than a single ABTP Whilst the invention is described herein with reference to compounds of Formula (1 ), it is to be understood that the invention relates to such compounds in any possible tautomeπc forms, and also to the complexes formed between ABTPs and metals

Optionally substituted hydrocarbyl and optionally substituted hydrocarbyloxy groups which may be represented by R¹, R², R³ and R⁴ preferably comprise optionally substituted alkyl, alkoxy, aryl and aryloxy groups including any combination of these, such as optionally substituted aralkyl and alkaryl groups

Examples of optionally substituted alkyl and alkoxy groups which may be represented by R¹, R², R³ and R⁴, include groups in which the alkyl or alkoxy moieties each contain from 1 to 20, especially from 1 to 10, carbon atoms Examples of optionally substituted aryl and aryloxy groups include optionally substituted phenyl and phenoxy groups

Examples of optionally heterocyclic rings which may be formed by R¹ and R² and/or by R³ and R⁴ together with the P atom include rings wherein R¹ and R² together and/or R³ and R⁴ together have the following structures

wherein each of X¹ and X², independently, represents O or S and in which one or more of the carbon atoms may be substituted by one or more substituents, particularly lower alkyl, such as C1 to C6 alkyl, substituents

When any of R¹, R² R³ and R⁴ is a substituted hydrocarbyl or hydrocarbyloxy group or when the aforementioned heterocyclic ring is substituted, the substιtuent(s) should be such as not to adversely affect the ability of the ABTP to complex with metals, especially cobalt and nickel Suitable substituents include halogen, nitro, cyano, hydrocarbyl, such as C^o-alkyl, especially C_1-10-alkyl, hydrocarbyloxy, such as C-|.₂o- alkoxy, especially C_{1 10}-alkoxy; hydrocarbyloxycarbonyl, such as C_{T 2}o-alkoxy-carbonyl, especially C^o-alkoxycarbonyl, acyl, such as C_T^o-alkylcarbonyl and arylcarbonyl, especially C- o-alkyicarbonyl and phenylcarbonyl, and acyloxy, such as C^ ₂₀- alkytcarbonyloxy and arylcarbonyloxy, especially C_1-10-alkylcarbonyloxy and phenylcarbonyloxy There may be more than one substituent in which case the substituents may be the same or different

A preferred ABTP is one in which each of R¹, R², R³ and R⁴ is alkyl, especially secondary alkyl (s-alkyl) Good solubility in preferred solvents is provided when R¹, R² R³ and R⁴ taken together contain at least 12 more preferably at least 16, and especially at least 20, and up to about 40, more preferably 30, saturated aliphatic, or equivalent, carbon atoms For this purpose, a phenyl or phenoxy group may be regarded as equivalent to about two or three saturated aliphatic carbon atoms In an especially preferred compound each of R¹, R², R³ and R⁴ is 2-pentyl

Another preferred ABTP is one in which at least one and especially at least two of R¹ to R⁴ is optionally substituted phenoxy, preferably an alkyl substituted phenoxy group wherein the alkyl group or groups contain from 1 to 20, and especially from 1 to 10, carbon atoms Such an ABTP, especially one in which each of R¹ to R⁴ independently is optionally substituted phenoxy, ts preferred for both ease of synthesis and because it has been found that it generally has a faster rate of extraction than some of the equivalent alkyl and aryl substituted compounds

In another preferred ABTP, R¹ is an optionally substituted 2-alkylphenoxy group, each of R², R³ and R⁴ is a group selected from optionally substituted 2-alkylphenoxy optionally substituted phenyl, optionally substituted alkyl and optionally substituted alkoxy and at least one optionally substituted 2-atkylphenoxy group has a tertiary alkyl (t-alkyl) substituent

In the optionally substituted 2-alkylphenoxy groups which may be present in the ABTP, the 2-alkyl group preferably contains from 1 to 20, especially from 1 to 10, carbon atoms Such an alkyl group may be primary alkyl (n-alkyl) having one or more carbon atoms, secondary alkyl (s-alkyl) having three or more carbon atoms, or tertiary alkyl (t- alkyl) having four or more carbon atoms The 2-alkylphenoxy group may optionally carry one or more additional alkyl substituents, such as a 4-alkyl substituent

When the optionally substituted 2-alkylphenoxy group contains a t-alkyl group, the latter may be present in addition to the 2-alkyl group and/or the 2-alkyl group may itself be a t-alkyl group

Examples of 2-alkylphenoxy groups include 2-t-butylphenoxy, 2-t-buty!-4-methyl- phenoxy, 2-t-butyl-5-methylphenoxy, 2,4-dι-(t-butyl)-phenoxy, 2,4-dι-(t-pentyl)-phenoxy, 2- methyl-4-t-nonylphenoxy, 2-t-butyl-4-t-nonylphenoxy, 4-octylphenoxy, 4-t-dodecyl- phenoxy, 4-t-dodecyl-2-methylphenoxy, 2-s-butylphenoxy and the like

In particularly useful ABTP, at least one 2-alkylphenoxy group is 2-t-alkylphenoxy and preferably at least two 2-alkylphenoxy groups are 2-t-alkyl-phenoxy Preferred 2-t- alkyl groups include 2-t-butyl

Optionally substituted phenyl groups which may be represented by R² and/or R³ and/or R⁴ in the ABTP include alkyl substituted phenyl groups, for example o-tolyl, m-tolyl, p-tolyl and xytyl groups and mixtures of such groups However, because of the commercial availability of suitable intermediates, a preferred optionally substituted phenyl group is phenyl itself

Optionally substituted alkyl and optionally substituted alkoxy groups which may be represented by R² and/or R³ and/or R⁴, include alkyl and alkoxy groups preferably containing from 1 to 20, especially from 1 to 10, carbon atoms Each alkyl group and the alkyl moieties of each alkoxy groups, taken independently, may be n-alkyl having one or more carbon atoms, s-alkyl containing three or more carbon atoms or t-alkyl containing four or more carbon atoms Examples of optional substituents for such alkyl or alkoxy groups, include halogen, nitro, cyano, hydrocarbyloxy, hydrocarbyloxycarbonyi, acyl and acyloxy groups as hereinbefore more specifically defined More than one substituent may be present in which case the substituents may be the same or different In another valuable ABTP, R is an optionally substituted 2-alkylphenoxy group, each of R², R³ and R⁴ is either an optionally substituted 2-alkyl-phenoxy group or an optionally substituted phenyl group and at least one optionally substituted 2-alkylphenoxy group has a t-alkyl substituent When R¹ alone is an optionally substituted 2- alkylphenoxy group and each of R², R³ and R⁴ is phenyl, it is preferred that the phenoxy group is heavily substituted with aliphatic groups, such as in 2-t-butyl-4-t-nonylphenoxy, in order to provide the extractant compound with good solubility in hydrocarbon solvents However it is preferred that at least one of R², R³ and R⁴ is also an optionally substituted 2-alkylphenoxy group so that the compound of Formula (1) contains at least two optionally substituted 2-alkylphenoxy groups and it is further preferred that at least two of these 2-alkylphenoxy groups have a t-alkyl substituent

The ABTP in which R¹ and R² are both optionally substituted 2-alkylphenoxy and R³ and R⁴ are both optionally substituted phenyl are strong metal extractants An example of such an ABTP is one in which R¹ and R² are both 2-methyl-4-t-nonylphenoxy and R³ and R⁴ are both phenyl Another useful ABTP in which R¹ and R³ are optionally substituted 2-alkylphenoxy groups and R² and R⁴ are optionally substituted phenyl is one in which the 2-alkyl groups are t-alkyl, such as the compound in which R¹ and R³ are both 2-t-butyl-4-methylphenoxy and R² and R⁴ are both phenyl In an especially valuable ABTP, each of R¹, R² and R³ is optionally substituted 2- alkylphenoxy and R⁴ is optionally substituted phenyl In such a compound, at least one of the 2-alkylphenoxy groups is preferably 2-t-alkylphenoxy and the others are preferably 2- t-atkyl and/or 2-s-alkylphenoxy, in which preferred s-alkyl groups have at least four carbon atoms An example of an ABTP containing one 2-t-alkyl substituent and two 2-s-alkyl substituents is the ABTP wherein each of R¹ and R² is 2-s-butylphenoxy, R³ is 2,4-dι-(t- penty!)phenoxy and R⁴ is phenyl An example of a compound containing two 2-t-alkyl substituents and one 2-s-alkyl substituent is the compound wherein R¹ and R³ are both 2- t-butylphenoxy, R¹ is 2-s-butylphenoxy and R⁴ is phenyl In an ABTP in which each of R¹, R², R³ and R⁴ is optionally substituted 2- alkylphenoxy, preferably at least one, and more preferably two and especially three of these is 2-t-alkylphenoxy In a preferred compound R¹ and R² are 2-t-alkylphenoxy, and more preferably R³ and R⁴ are also 2-s-alkylphenoxy

In another valuable ABTP, R¹ is optionally substituted 2-alkyl-phenoxy, at least one of R², R³ and R⁴ is optionally substituted alkyl or optionally substituted alkoxy, any remaining group or groups from R², R³ and R⁴ are selected from optionally substituted 2- alkylphenoxy and optionally substituted phenyl, and at least one optionally substituted 2- alkylphenoxy group has a t-alkyl group

In an especially preferred ABTP of this type R¹ is optionally substituted 2-t- alkylphenoxy, R² is optionally substituted alkoxy and each of R³ and R⁴, independently, is optionally substituted 2-alkylphenoxy or optionally substituted alkoxy, at least one of R³ and R⁴ being preferably 2-t-alkylphenoxy In another preferred ABTP of this type, R¹ is optionally substituted 2-t-alkylphenoxy, R² is optionally substituted alkoxy or optionally substituted phenyl and R³ and R⁴ are the same or different optionally substituted alkoxy groups In another preferred ABTP of this type, R¹ is optionally substituted 2-t- alkylphenoxy, R² is optionally substituted 2-alkylphenoxy or optionally substituted phenyl and R³ and R⁴ are the same of different optionally substituted alkyl groups

The ABTP of Formula (1) can be prepared by the methods disclosed in EP 573182A and WO 95/15329

THE EXTRACTION PROCESS (2)

The extraction process can be effected by contacting the feed solution with the extractant in different physical forms

Thus, the contact can be effected by attaching the extractant to a water-insoluble inert support medium and contacting the supported extractant with the feed solution, whereby the loaded-extractant may be easily separated from the feed solution after contact This would permit either the supported extractant to be stirred with the feed solution and subsequently separated by filtration or the feed solution to be passed througn a column containing the supported extractant However, it is preferred to dissolve the extractant in an inert water-immiscible organic solvent and to effect contact with the metal by intimate mixing of the organic solution and the feed solution. The loaded extractant can then be separated from the feed solution by a cessation of mixing and allowing the immiscible organic and aqueous liquids to separate.

A typical solvent extraction process comprises a sequence of stages in which the target metal is extracted into an organic solution, stripped into an aqueous solution and recovered from the aqueous solution by any suitable means, for example by electrowinning. Thus, as a particular aspect of the invention, there is provided a process for extracting a target metal from an aqueous feed solution by a sequence of stages, comprising:

(1) contacting the feed solution containing ions of the target metal with a solution of an extractant compound as hereinbefore defined in a water-immiscible organic solvent (solvent phase) under pH conditions favouring formation of extraction a complex of the target metal with the extractant (loaded extractant);

(2) separating the solvent phase containing the loaded extractant from the feed solution;

(3) contacting the solvent phase containing loaded extractant with an aqueous strip solution under pH conditions favouring decomposition of the loaded extractant whereby ions of the target metal transfer into the strip solution, and

(4) separating the loaded strip solution containing metal ions from the stripped solvent phase.

This extraction process may be applied to the extraction from aqueous solution of Co and Ni under the appropriate pH conditions, as hereinbefore described. in operating stage (1) of the aforementioned process, the amount of extractant compound to be used will depend to some extent upon the concentration of metal salt in the aqueous solution and also on the plant design. However, it is preferred to use from 5g to 400g of the extractant per dm³ (litre) of organic solution. Higher concentrations may be used but tend to afford organic phases of too high viscosity for convenient handling. Lower concentrations can also be used but may involve the use of unnecessarily large volumes of solvent.

The volume ratio of organic solution to aqueous feed solution in stage (1) of the aforementioned process is commonly in the range of from 100:1 to 1 :100, preferably from 25:1 to 1 :25, particularly from 5:1 to 1:5, and particularly preferably from 2:1 to 1 :2.

For use with aqueous solutions containing 0.1g or more, particularly 1g or more, per dm³ of a metal such as Co or Ni, it is preferred to use from 50 to 400g of the extractant per dm³ of organic solution. If desired, the extractant can be used together with an agent which modifies the behaviour thereof in the extraction process, for example an alkylphenol, alcohol or ester which may be used in an amount of from 10% to 200%, especially from 20% to 100% by weight of extractant compound Such compounds generally weaken the extraction power of the extractant but thereby facilitate the subsequent stripping of metal therefrom In this way, a very strong extractant may be adjusted in strength to the requirements of different feed solutions and different stπpping solutions

Alkytphenols which may be used as modifiers in conjunction with the extractant include alkylphenols containing from 3 to 15 alkyl carbon atoms, for example 4-tert- butyiphenol, 4-heptylphenol, 5-methyl-4-pentylphenol, 2-chloro-4-nonylphenol, 2-cyano-4- nonylphenol, 4-dodecylphenol, 3-pentadecylphenol and 4-nonylphenol and mixtures thereof The preferred phenols contain alkyl groups having from 4 to 12 carbon atoms, especially the mixed 4-nonylphenols obtained by condensation of phenol and propylene tπmer

Alcohols which may be used as modifiers in conjunction with the extractant include saturated and unsaturated hydrocarbon alcohols and polyols containing 14 to 30, preferably 15 to 25 carbon atoms The alcohols are preferably highly branched with the hydroxyl group located approximately midway along the hydrocarbon backbone Especially preferred are the branched chain alcohols that may be made by condensation of short chain alcohols by the Guerbet process, such alcohols sometimes being referred to as Guerbet alcohols Optionally, the alcohols may contain an aromatic group or other functional group, particularly an ester group

Especially useful alcohols may be synthesised from highly branched precursors leading to very highly branched Guerbet alcohols containing a large number of terminal methyl groups Examples of particularly efficient alcohol modifiers include highly branched isohexadecyl alcohol and iso-octadecyl alcohol, the latter being 2-(1 ,3,3- trιmethylbutyl)-5,7,7-trιmethyloctanol

Esters which may be used as modifiers in conjunction with the extractant include saturated and unsaturated aliphatic and aromatic-aliphatic esters containing from 10 to 30 carbon atoms The esters may be mono-esters or polyesters, especially di-esters The esters are preferably highly branched Optionally, the esters may contain other functional groups, particularly a hydroxyl group Especially useful esters include 2,2,4-tπmethyl-1 ,3- pentanediol isobutyrate and the benzoic acid ester thereof

In the context of the present invention, 'highly branched' as applied to the alcohols and esters means that the ratio of the number of methyl carbon atoms to non-methyl carbon atoms is higher than 1 5 and preferably higher than 1 3

If desired, mixtures of alkylphenols and/or alcohols and/or esters may be employed as modifiers

The aforementioned modifiers may be used in the preparation of extractant compositions containing one or more extractant and one or more modifier Stages (1 ) and (2) of the aforementioned process may conveniently be carried out using well known conventional solvent extraction techniques Typically, the aqueous solution containing the target metal at a pH in a defined range (as hereinbefore described) is intimately contacted, in a single stage or in multiple stages but preferably continuously, with the organic phase (for example by agitating the two phases together in a suitable vessel) for a time sufficient to allow substantial extraction of the target metal from the aqueous solution, the two phases then being separated in any conventional manner The extraction is usually carried out at ambient temperature although somewhat higher temperatures, for example up to 100°C but preferably not more than 50°C, may be used if operationally convenient

Organic solvents which may be used for the extraction include any mobile organic solvent, or mixture of solvents, which is immiscible with water and is inert under the extraction conditions to the other materials present Examples of suitable solvents include aliphatic, alicyclic and aromatic hydrocarbons and mixtures of any of these as well as chlorinated hydrocarbons such as tπchloroethylene, perchloroethylene, tπchloroethane and chloroform Examples of suitable hydrocarbon solvents include low aromatic (<1% w/w) content hydrocarbon solvents such as ESCAID 110 commercially available from Exxon (ESCAID is a trade mark), and ORFOM SX1 1 commercially available from Phillips Petroleum (ORFOM is a trade mark) Preferred solvents are hydrocarbon solvents including high flash point solvents with a high aromatic content such as SOLVESSO 150 commercially available from Exxon (SOLVESSO is a trade mark) and includes solvents which consist essentially of a mixture of tπmethylbenzenes such as AROMASOL H, commercially available from Imperial Chemical Industries PLC (AROMASOL is a trade mark) Especially preferred, however, on grounds of low toxicity and wide availability are hydrocarbon solvents of relatively low aromatic content such as kerosene, for example ESCAID 100 which is a petroleum distillate comprising 20% aromatics, 56 6% paraffins and 23 4% naphthenes commercially available from Exxon (ESCAID is a trade mark)

In operating the stripping stage 3) of the aforementioned process, and particularly where the target metal is cobalt, it is preferred for the contact between the solvent phase comprising metal-loaded extractant to be contacted with the aqueous strip solution in the presence of a strip accelerating additive which accelerates the transfer of the metal into aqueous solution Such strip accelerating additives are generally substantially water insoluble compounds which are soluble in the organic phase and examples of strip accelerating additives which can be employed include aromatic and aliphatic amines, particularly pyndmes and azoles, such as benzimidazoles and oxazoles, quaternary ammonium compounds, hydrocarbyl, particularly alkyl and aryl, sulphonic acids, particularly alkaryl sulphonic acids including dinonylnaphthalenesulphonic acid and didodecylnaphthalene sulphonic acid, carboxyiic acids, particularly long chain alkyl and alkenyl acids comprising from 16 to 30 carbon atoms such as versatic acid, oleic acid linoleic acid and stearic acid, hydrocarbyl, particularly alkyl and aryl, phosphoric, phosphonic and phosphinic acids, and the mono and dithio derivatives thereof, such as dι(2-ethylhexyl)phosphoπc acids. Preferred strip accelerating additives include compounds of the formulae

(Formula 3) (Formula 4) wherein R⁵ and R⁶ represent hydrocarbyl groups which may be substituted, and

X, Y and Z each independently represent O or S, and salts thereof

In the compounds of Formula 3 and 4 it is preferred that X represents O, and in compounds of Formula 4, that Z represents O Particularly preferred compounds are those of Formula 3 in which X and Y represent O

Hydrocarbyl groups which may be represented by R⁵ and R⁶ independently include alkyl and aryl groups, and any combination thereof, such as aralkyl and alkaryl groups Alkyl groups which may be represented by R⁵ and R⁶ include linear and branched alkyl groups comprising up to 20 carbon atoms, particularly from 3 to 14 carbon atoms, and preferably from 4 to 10 carbon atoms In many embodiments of the present invention, tt is preferred that alkyl groups represented by R⁵ and R⁶ are branched, especially at the carbon atom alpha to the carbon bonded to the phosphorus atom, or in the case of R⁵-Z- moieties, alpha to the carbon bonded to Z It is especially preferred that alkyi groups represented by R⁵ and R⁶ comprise more than one branch, with alkyl groups comprising 2 or 3 branches being especially advantageous Examples of alkyl groups which may be represented by R⁵ and R⁶ include butyl, including sec-butyl and particularly tert-butyl, pentyl, including particularly 2-pentyl, hexyl, including particularly 2-hexyl, heptyl, including particularly 2-heptyl, and octyl, including particularly 2-octyl A particularly preferred alkyl group is 2,4,4-trιmethylpentyl

Aryl groups which may be represented by R⁵ and R⁶ include phenyl and naphthyl groups, particularly phenyl and naphthyl groups bearing an alkyl substituent at the position ortho to the carbon bonded to the phosphorus atom, or in the case of R⁵-Z- moieties ortho to the carbon bonded to Z

When either of R⁵ and R⁶ is a substituted hydrocarbyl group, the substιtuent(s) should be such as not to adversely affect the ability of the compound to accelerate the transfer of cobalt from the cobalt-ABTP complex into the aqueous phase Suitable substituents include halogen, nitro, cyano, hydrocarbyl such as C ₂o-alM, especially Cι.ιo-alkyl, hydrocarbyloxy, such as C^o-alkoxy, especially C_1-10-alkoxy, hydrocarbyloxycarbonyi, such as C^o-alkoxy-carbonyl, especially C-i ₁₀-alkoxycarbonyl, acyl, such as C^o-alkylcarbonyl and arylcarbonyl, especially C ₁₀-alkylcarbonyl and phenylcarbonyl, and acyloxy, such as d.₂o-alkylcarbonyloxy and arylcarbonyloxy especially C ₁₀-alkylcarbonyloxy and phenylcarbonyloxy There may be more than one substituent in which case the substituents may be the same or different

Although R⁵ and R⁶ may represent different hydrocarbyl groups, it is often convenient for R⁵ and R⁶ to represent the same hydrocarbyl group

The organothiophosphonate or organothiophosphmate compounds which may be employed in the present invention may be employed in the form of the free acid, or may be employed as a water-immiscible salt thereof, for example an alkali metal, alkaline earth metal ammonium or a zinc salt Highly preferred strip accelerating additives are dι(tert- butyHthiophosphonic acid, dι(2,4,4-tπmethylpentyl)thιophosphιnιc acid and dι(2,4,4- trιmethylpentyl)phosphιnιc acid One or more of the strip accelerating additives, preferably compounds of

Formulae (4) or (5) above may be used in the preparation of extractant compositions comprising one or more amιdobιs(thιophosphoryl) compounds and, commonly, at least one modifier

In the extraction processes according to the present invention, or when used in the preparation of extractant compositions, the strip accelerating additives can be present in an amount of up to 30%, particularly up to 15%, by weight of the ABTP, and is usually present tn an amount of at least 0.01 %, particularly from 0 1%, preferably from 0 5% to 5%, and particularly preferably from 1 to 3%, by weight of the ABTP The ABTPs are often present in an amount of up to 50% by weight of the composition, commonly no more than 40%, and usually no more than 30% w/w Often, the ABTP comprises at least 5% by weight, commonly at least 10% by weight and usually at least 15% by weight of the composition The balance of the composition comprises water-immiscible organic solvent(s), often in an amount of from at least 50% by weight Preferred extractant compositions comprise at least 65% by weight of water-immiscible hydrocarbon solvent, an ABTP in an amount up to 30% w/w, and preferably from 5 to 25% w/w and an organothiophosphonic acid, organothiophosphinic acid, organophosphonic acid or an organophosphinic acid in an amount up to 5% w/w, and preferably from 0 01 to 2% w/w Especially preferred compositions also comprise an alkylphenol, alcohol or ester modifier in an amount up to 10% w/w Aqueous strip solutions which may be employed in the process according to the present invention commonly comprise a mineral acid, particularly sulphuric acid, nitric acid or hydrochloric acid A low acid concentration but at least 4M chloride strip solution as descπbed in European Patent application no 93301095 1 (publication no 0 562 709 A2) or Internationai application publication No WO95/04835 (the stripping solutions of both of which are incorporated herein by reference) can be employed Preferred strip solutions can comprise spent electrolytes from arising from an electrolytic cell, which may typically contain from 5 to 100 g/l cobalt and up to 60 g/l sulphuric acid. Except in the cases of the selective stripping of cobalt and nickel discussed above, the strip solutions often have a pH of up to 2, commonly up to 1 , and particularly a pH of no more than 0.5.

The volume ratio of organic solution to aqueous stnp solution in the stage 3) of the aforementioned process is commonly in the range of from 100:1 to 1 100, preferably from 25:1 to 1 25, particularly from 5.1 to 1:5, and particularly preferably from 2.1 to 1.2

The processes according to the present invention are commonly carried out at a temperature of up to 75^βC, particularly a temperature in the range of from 15 to 50°C

The present invention is further illustrated by the following Examples tn which all parts and percentages are by weight unless otherwise indicated

EXAMPLE 1 This example serves to demonstrate the principle of sequential and selective separation of metal values but is not intended to suggest a working process in a large- scale solvent extraction ng where inter-stage neutralisation could also be employed to speed up dwell times in the extraction cell

Zinc sulphate heptahydrate (2.88g, PA Grade, Janssen Chemica), nickel sulphate hexahydrate (2.65g, ACS Reagent, Aldrich) and cobalt sulphate heptahydrate (2 84g, SLR Reagent, Fisons) were dissolved in distilled water and diluted to 100ml in a graduated flask ("Metal Solution A") Analysis of Metal Solution A by atomic absorption gave the following results (see Table 1)

Met Sol A. Zinc: 6425 ppm Cobalt: 6080 ppm Nickel 6200 ppm

A sample of the ABTP, N-[0-(2-sec-butylρhenyl)-0-(2-tert-butylphenyl)- thιophosphoryl]-0-(2-tert-butylphenyl)phenylphosphonamιdothιoate (199.5g), was dissolved in a mixture of ESCAID 100 (600 ml, Exxon Inc) and tπdecanol (30g ICI) and the solution diluted to 1000ml with ESCAID 100 ("Ligand Solution B")

CONTACT 1 An aliquot of Metal Solution A (50 ml, pH 5 6) was stirred vigorously at 25^°C in contact with an aliquot of Ligand Solution B (50 ml) and after 10 minutes the pH of the aqueous phase had fallen to pH 1.25, NaOH solution (0 4 ml, 47%) was added dropwise over 10 minutes and vigorous stirring maintained for a further 10 minutes after which the pH of the aqueous phase had risen to pH 1 8 Agitation was then stopped and the aqueous and organic layers were separated. Analysis of small samples of these layers by atomic absorption gave the following results Organic Layer Zinc 6105 ppm, Cobalt 2 ppm, Nickel 0 ppm

Aqueous Layer Zinc 300 ppm, Cobalt 5990 ppm Nickel 6110 ppm

CONTACT 2 The residual aqueous layer (volume 50 25 ml) from Contact 1 was stirred vigorously and contacted with a further 50ml sample of Ligand Solution B After stirπng for 20 minutes at 25°C with no further addition of base, the pH of the aqueous layer had fallen to pH 1 75 Stirring was stopped and the layers separated Analysis of a sample of the two layers by atomic absorption gave the following results

Organic Layer Zinc 222 ppm Cobalt 5 ppm Nickel 0 ppm

Aqueous Layer. Zinc 10 ppm Cobalt 5990 ppm Nickel 6110 ppm

CONTACT 3 The residual aqueous layer (volume 50 0 ml) from Contact 2 was stirred vigorously and contacted with a further 50 ml sample of Ligand Solution B and NaOH solution (0 6 ml, 47%) was added dropwise over 15 minutes After stirring for a further 5 minutes the pH of the aqueous layer was pH 3 8 and the aqueous and organic layers were separated Analysis of these by atomic absorption gave the following results

Organic Layer Zinc <1 ppm Cobalt 4524 ppm Nickel 0 ppm

Aqueous Layer Zinc 0 ppm, Cobalt 1400 ppm Nickel 6040 ppm

CONTACTS 4 & 5 Two further sequential contacts of 50 ml portions of Ligand Solution B with the residual aqueous layer from Contacts 3 & 4, at pH 3 6 and pH 4 2 respectively, gave an aqueous solution devoid of zinc and cobalt, but still containing 5600 ppm nickel

CONTACT 6 Nickel was transferred to the organic layer by contacting the residual aqueous layer from Contact 5 with a further 50ml of Ligand Solution B and raising the pH to >6 0 Control of pH was very difficult at this pH level and the final pH was 8 1

The results are summarised in Table 1

TABLE 1

Contact PH Organic layer (ppm) Aqueous layer Mass Balance No aqueous (ppm) (%) layer

Zn Co Ni Zn Co Ni Zn Co Ni

Met Sol 1 5 6 0 0 0 6425 6080 6200 100 100 100

1 1 8 6105 2 0 300 5990 61 10 100 100 100

2 1 75 222 5 0 <10 5990 6110 100 100 100

3 3 8 <1 4524 4 0 1400 6040 - 100 100

4 3 6 0 460 0 0 997 5822 - 105 97

5 4 2 0 1005 181 0 0 5600 - 100 100

6 8 1 0 0 51 10 0 0 0 - - 100

EXAMPLES 2 TO 11

In Example 2, an extractant composition comprising a 0 3M solution (200g/l) of an ABTP of Formula 1 in which R1=R3= 2-tert-butylphenoxy, R2 = 2-sec-butylphenoxy and R4 = phenyl in the hydrocarbon solvent commercially available under the trade name ESCAID 100, also containing 30g/l tπdecanol, was prepared In Examples 3 to 11 , extractant compositions were prepared by adding, at the concentrations specified, the strip accelerating compounds given in Table 2 below, to the solution of Example 2.

Example No Additive Concentration (g/l)

3 dinonylnaphthaienesulphonic acid 2 5

4 dinonyinaphthalenesulphonic acid 3 75

5 dinonylnaphthaienesulphonic acid 5

6 dι(2,4,4-trιmethylpentyl)thιophosphιnιc acιd 2 5¹

7 dι(2,4,4-trιmethylpentyl)thιophosphιnιc acid 5¹

8 dι(2-ethylhexyl)phosphorιc acid 1

9 dι(2.4,4-trιmethylpentyl)phosphιnιc acιd 1²

10 dι(2,4,4-trιmethylpentyl)phosphιnιc acιd 2²

1 1 dι(2-ethylhexyl)phosphonιc acid 1³ of the product commercially available under the trade name CYANEX 302

² of the product commercially available under the trade name CYANEX 272

³ of the product commercially available under the trade name IONQUEST 801 200ml of the organic solutions of Examples 2 to 11 were loaded with cobalt by vigorously stirring the solutions in contact with a cobalt solution comprising 10g/l cobalt as CoS0 at ambient temperature (15 -25°C) for 30 minutes at an O/A volume ratio of 1 1 with the pH maintained at 4 8 by dropwise addition of 47% w/w aqueous NaOH solution The loaded organic solutions were then separated from the cobalt solution and stripped by contact with vigorous agitation with an aqueous acidic strip solution comprising 50g/l Co as CoS0 and 50g/l sulphuric acid, at ambient temperature and an O/A ratio of 1 1 Samples of both the organic and aqueous phases were analysed for cobalt content by atomic absorption at intervals over 60 minutes, and the percentage approach to the equilibrium distribution (%ATE) of cobalt between the phases was calculated 100% ATE in this case signifies complete transfer of cobalt from the organic to the aqueous phase The results are given in Table 2 below

TABLE 2

The results in Table 2 clearly demonstrate how the use of a strip accelerating additive reduces the time necessary to achieve a given transfer of cobalt into the aqueous phase In the case of nickel, a repeat of Example 1 above, but employing 10 g/l Ni as NiS0₄ in place of CoS0 resulted in 100% ATE being reached in only 5 minutes EXAMPLE 12

An organic solution having the same composition employed in Example 10 was contacted with an aqueous feed solution containing about 1240ppm zinc and 5500ppm cobalt, both as sulphates, at an organic/aqueous ratio of 1 1 The pH of the aqueous solution was raised to 5 0 with dilute sodium hydroxide solution, thereby effecting the transfer of all the metals from the aqueous to the organic phase This loaded organic solution was separated from the aqueous feed solution, and was found by analysis to contain 1243ppm zinc and 5500ppm cobalt The loaded organic solution was then stirred vigorously at an O/A ratio of 1 1 with vaπous aqueous strip solutions of sulphuric acid for 5 minutes The concentrations of sulphuric acid employed were as detailed in Table 3 below The two phases were separated and analysed for metal content The results of the analyses are given in Table 3 below

TABLE 3

H₂S0₄ Residual aqueous layer Stripped Organic Layer Concentration Zinc cone (ppm) Cobalt cone Zinc cone (ppm) Cobalt cone

(g/i) (ppm) (ppm)

35 299 5500 936 0

30 220 5500 1040 0

25 158 5500 1059 0

20 45 5500 1178 4

15 9 5500 1198 8

10 1 5400 1202 98

5 <1 3300 1260 2183

The results in Table 3 show that a range of sulphuric acid concentrations could be employed to preferentially strip cobalt from ABTP complexes of both Co and Zn Particularly good results, high degrees of stripping of Co and very low stripping of Zn, were achieved with sulphuric acid concentrations in the range of from 10 to 15 g/l

EXAMPLE 13

A sample (85ml) of an aqueous solution containing 273ppm cobalt, and 3144ppr Ni (a ratio of Co/Ni found in typical latente ore leach liquors) was contacted with 85 ml of an organic solution of the same composition as that employed in Example 10 except that the ABTP concentration employed was 0 15M and stirred vigorously at 25°C whilst maintaining the pH of the emulsion at 5 4 to 5 5 using an auto pH controller containing 1N ammonium hydroxide solution (7 4ml required) After 6 minutes, stirring was stopped and the layers were separated The aqueous layer contained 1 160ppm of nickel and < 5ppm of cobalt, as estimated by atomic absorption spectroscopy By difference the organic layer was calculated to contain 273ppm of cobalt and 1883 ppm of nickel A sample of this cobalt-depleted aqueous raffinate (80ml) was then re-contacted with a 70ml of a further sample of organic solution and the pH maintained at 5 5 with vigorous stirring for a further 6 minutes The stirring was stopped and the layers separated The aqueous layer was found by atomic absorption spectroscopy to contain 228ppm of nickel By calculation the loaded organic layer contained 1049 ppm of nickel The organic layers from these two extractions were combined A sample (140ml) of the combined organic layers (calculated metal contents - cobalt 156ppm, nickel 1525ppm) was contacted with distilled water (60ml) and with vigorous stirring, aqueous sulphuric acid (0 5M) was added under the control of an autotitrator set at pH 3 5 After 6 minutes the stirring was stopped and the layers separated The aqueous liquor (69ml) contained 3032ppm (98% theory) of nickel as estimated by uv/visible spectroscopy, and < 5ppm of cobalt (estimated by atomic absorption spectroscopy) The organic layer was found to contain 156pprπ of cobalt (estimated by uv/visible spectroscopy) A sample of the organic layer (100ml) was contacted with a solution (25ml) of 0 1M sodium sulphate to which was added 0 5M sulphuπc acid (2ml) After stirring vigorously for 10 minutes the organic solution was colourless, and the aqueous pH was 1 35 The aqueous liquor was found by atomic absorption spectroscopy to contain 550 ppm of cobalt (99 5% theory)

Claims

1 A process for the extraction of cobalt from an aqueous feed solution comprising cobalt which comprises contacting the feed solution with an extractant comprising an amιdobιs(thιophosphoryl) compound of the formula

Formula (1) wherein

R¹ & R^z &/or R³ & R⁴ together with the P atom, form an optionally substituted 5- to 8-membered heterocyclic ring, at a pH of greater than 2

2 A process for the extraction of nickel from an aqueous feed solution comprising nickel, which comprises contacting the feed solution with an extractant comprising an amιdobιs(thιophosphoryl) compound of the formula

Formula (1) wherein R¹ , R², R³ & R⁴ each independently, represents an optionally substituted hydrocarbyl or optionally substituted hydrocarbyloxy group, or R¹ & R² &/or R³ & R⁴ together with the P atom, form an optionally substituted 5- to 8-membered heterocyclic ring, at a pH of greater than 4

3 A process for the selective extraction of cobalt from an aqueous feed solution containing cobalt, in the presence of one or more other metals, especially nickel, which comprises contacting the feed solution with an extractant comprising an amιdo-bιs(thιo- phosphoryl) compound of the formula

Formula (1 ) wherein

R¹ , R², R³ & R⁴ each independently, repπ hydrocarbyl or optionally substituted hydrocarbyloxy group, 5 or

R¹ & R² &/or R³ & R⁴ together with the P atom, form an optionally substituted 5- to 8-membered heterocyclic ring, at a pH in a range from

(a) a lower value at which Co is taken up by the extractant tn order to form a l o loaded extractant, to

(b) an upper value at which Co and another metal present in the feed solution (especially Ni) are taken up by the extractant to form loaded extractant in which the ratio of Co to the other metal in the feed solution (especially Ni) in the loaded extractant is higher than in the feed solution

15

4 A process for the selective extraction of cobalt from an aqueous feed solution containing cobalt and nickel, and optionally other metals, which comprises contacting the feed solution with an amido-bis(thιo-phosphoryl) compound of Formula (1 ) as defined in Claim 3 in a range from about pH 3 to about pH 4

20

5 A process for the selective removal of Ni from a feed solution which is substantially free from Co (and other metals extractable with an amιdo-bιs(thιo- phosphoryl) compound of Formula (1) at below pH 5) by contacting the feed solution with an extractant comprising an amιdo-bιs(thιo-phosphoryl) compound of Formula (1) at a pH

25 in a range from

(d) an upper value at which Ni and another metal present in the feed solution are taken up by the extractant to form loaded extractant in which the ratio of Ni to the

30 other metal in the feed solution, in the loaded extractant, is higher than in the feed solution.

6 A process according to claim 5 in which the pH range is from about 4 to about 6 7 A process for the sequential separation of Co and Ni from a feed solution containing Co and Ni (especially a feed solution derived from a latente ore from which iron, zinc and any copper have been previously removed), which comprises contacting the feed solution, (i) with an extractant comprising an amιdo-bιs(thιo-phosphoryl) compound of Formula (1 ) at a pH in a range from

(b) an upper value at which Co, but substantially no Ni, is taken up by the extractant; and repeating step (i) sufficiently often to remove substantially ail the Co from the feed solution without removing any substantial amount of Ni, and subsequently contacting the spent feed solution from step (t),

(II) with an extractant comprising an amιdo-bιs(thιo-phosphoryl) compound of Formula (1 ) at a pH in a range from

(d) an upper value at which Ni, but substantially no other metal in the feed solution, is taken up by the extractant

8 A process according to claim 7, wherein the lower pH value (ι)(a) is from 2 7 to 3 3, the upper pH value (ι)(b) is from 4 to 4 5, the lower pH value (tι)(c) is from 4 5 to 5, and the upper pH value (ιι)(d) is from 5 5 to 6 5

9 A process for stripping cobalt and/or nickel from an ABTP complex thereof wherein a solution of the ABTP complex in an organic water-immiscible solvent is contacted with an aqueous acidic strip solution under conditions such that the ABTP complex is unstable, thereby causing transfer of at least a fraction of the cobalt and/or nickel into the aqueous solution, characteπsed in that the contact between the organic solution and the aqueous solution occurs in the presence of one or more substantially water-insoluble strip accelerating additives which are soluble in the organic solution selected from the group consisting of aromatic and aliphatic amines, quaternary ammonium compounds, alkyl and aryl sulphonic acids carboxy c acids, and hydrocarbyl phosphoric, phosphonic and phosphinic acids, and the mono and dithio derivatives thereof

10 A process according to claim 9 wherein the strip accelerating additives are selected from the group consisting of dinonylnaphthaienesulphonic acid, didodecylnaphthalenesulphonic acid, dι(2-ethylhexyl)phosphoπc acid, and compounds of the formulae

X, Y and Z each independently represent O or S, and salts thereof

11 A composition comprising one or more amιdo-bts(thιo-phosphoryl) compounds of the formula

Formula (1) wherein

R¹ , R², R³ & R⁴ each independently, represents an optionally substituted hydrocarbyl or optionally substituted hydrocarbyloxy group, or R¹ & R² &/or R³ & R⁴ together with the P atom, form an optionally substituted 5- to 8-membered heterocyclic ring, and one or more compounds of the formulae

(Formula 3) (Formula 4) wherein R⁵ and R⁶ represent hydrocarbyl groups which may be substituted, and X, Y and Z each independently represent O or S, and salts thereof

12 A composition according to claim 11 which comprises at least 65% by weight water immiscible hydrocarbon solvent, up to 30% by weight amιdo-bιs(thιophosphonyl) compound and up to 5% by weight of organthiophosphonic acid, organthiophosphinic acid organophosphonic acid or organophosphmic acid