CA2040541C

CA2040541C - Method for stripping metals in solvent extraction

Info

Publication number: CA2040541C
Application number: CA002040541A
Authority: CA
Inventors: Thomas J. O'keefe
Original assignee: University of Missouri System
Current assignee: University of Missouri System
Priority date: 1990-04-18
Filing date: 1991-04-16
Publication date: 2002-07-02
Anticipated expiration: 2011-04-16
Also published as: AU649676B2; JPH06500822A; CA2040541A1; EP0525125A1; EP0525125A4; AU7775891A; WO1991016465A1

Abstract

Aqueous solutions containing metal cations, that may include cations of both desired metal and impurity or secondary metal, are treated with an organic liquid extractant suitable for the extraction of cations of the desired metal, cations of at least one secondary metal being co-extracted. After phase disengagement, the loaded organic phase containing cations of either a desired metal or desired metal together with at least one secondary metal is contacted with a solid metal or solid metal alloy capable of reducing in the organic phase cations of either a desired metal or a secondary metal from a higher to a lower state of oxidation. Depending on the extracted metal(s) and the added solid metal or alloy, cations of the at least ane extracted metal are reduced to the lower state of oxidation and either are deposited (cemented) in the metallic state onto the solid metal or alloy, or are partially reduced in the organic phase to a lower oxidation state with the solid metal or alloy being oxidized in part. The methode of galvanic stripping is carried out at ambient pressures and at ambient or slightly elevated temperatures.

Description

METH10D P'OR STRIPPING tdETALS TN SOLVENT EXTRACTION
'this invention relates to the solvent extraction of metals and, more particularly, to a method for the removal of metal cation species in solvent extraction by galvanic stripping with added rnetals.
Background of the Invention Aqueous solutions that contain one or more dissolved metals in ionic Corm may be subjected to solvent extraction for the recovery of one or more desired metals. The desired metal ions are usually extracted from aqueous solution into an organic solvent containing an extractant and are recovered from the loaded solvent by stripping with a suitable aqueous strip solution. The other metals, present as ions in the aqueous solution as impurities, must often be removed from the process as they may cause difficulties in the stripping of the desired metal, and often increase in concentration in the circulating solvent to an extent that affects the efficiency of the extraction process.
Methods that are used alone and in combinations for removing desired and impurity cat.ions present in solvent extraction processes include the conventional stripping or selective stripping with acidic or basic solutions and the more recently developed hydrogen reductive stripping, hydrolytic stripping and electrolytic stripping.

2 ~ ,~ .' in ". !) .~
~ ;:' . , i~ ;_~ _,: ,~.
Stripping is often accomplished with acids or bases under ambient or elevated conditions. Hydrogen reductive stripping is carried out at temperatures between 150~and 350°C under elevated pressure and usually i.n the presence of seed metal.
particles to produce a metal powder. In hydrolytic stripping, loaded solvent is subjected to elevated temperatures (100-250°C) in the presence of water whereby metal oxides or hydroxides are Formed. Elydrogen reductive stripping and hydrolytic stripping have been reviewed by Monh emius, A.J., Mintek 50, pp. 599-609. >;lectrolytic stripping has been applied to a loaded solvent by subjecting the solvent to electrolysis with electrodes placed in the loaded solvent (Wan, R.Y., etal., J. of Metals, Dec. 198b, pp. 35-X10).
Ferric iron may also be stripped From various loaded organic solvents into the aqueous phase with an acid alone or combined with the introduction of sulfur dioxide or hydrogen sulfide to reduce ferric to Ferrous. The stripp7.ng may be carried out at ambient or elevated temperatures and pressures. It is noted that iron is usually present in solvent extraction processes as ferric and that, in many cases, ferrous is the stable form in the aqueous phase.
The above prior art methods have a number of disadvantages.
In conventional stripping, high concentrations of the strip solution are often required. Where lower concentrations are used, the processes are complicated by, for example, the use of combinations of extractants. Hydrogen precipitation and f ~ ' ~ )j ;.'r -''~~:

3 gaseous and/or hydrolytic stripping, especially under elevated pressure and at higher temperatures, are expensive and complex.
In aqueous hydrometallurgical processes use is often made of galvanic reactions between metals that cause reduction of a metal cation and precipitation, i.e. 'cementation, onto an added solid metal. This has not been applied to solvent extraction processes. Any methods disclosed for the reduction of metal cations to reduce and cement metal cations onto an added solid metal have been applied before carrying out the solvent extraction. According to Canadian Patent 1 250 210, a solution containing iron and zinc is treated in tcvo stages caith metallic iron and zinc to reduce ferric to ferrous iron and cementation of copper, arsenic, antimony and bismuth on the iron, followed by precipitation of a sludge of tin, cadmium and lead in the second stage treatment with zinc duet. After this two-stage pre-treatment in an aqueous system, zinc chloride is extracted with an organic liquid. The reduction stages are, therefore, essentially separate t:rom the solvent extraction process. It is noted that no metal is actually deposited onto the zinc powder in the second stage.
Shibata Junji etal. reported that ferric iron can be stripped from di-2-ethyl-hexylphosphoric acid (D2EFFPA) with mineral acid and iron powder (Proc. Symp. Solvent >;xtr. 1986, 139-192).
Shibata et al. only disclose the stripping of ferric iron from D2>;HPA with iron pocader. Shibata et al, do not disclose the galvanic stripping with metals other than iron, or the J
deposition of metals onto added metals, or stripping of metals other than iron from organics other than D2EHPA.
Taking the above-mentioned teachings according to the Canadian Patent and Shibata et al., one could not presume a priori that the Shibata et al. method is operable with zinc pocader or metals other than iron and zinc. Similarly, it could not be presumed that the Shibata et al. method is operable with organics other than D2Ef~PA, or that actual deposition of a metal species dissolved in an organic liquid would occur in the organic phase onto an added solid metal. It could also not be presumed that addition of a solid metal to an organic phase would make it possible to reduce metal ions other than ferric ions in the organic phase From a higher to a lower state of oxidation.
Summary of the :Invention The present invention seeks to provide an excellent and simple way to separate a coanted ration species from another one in an organic liquid, the species being either a desired or an undesired species. Thus, it has been found that many metal rations can be readily reduced in a loaded organic liquid by contacting loaded organic liquid with a suitable solid metal or solid metal alloy causing a galvanic reaction. More particularly, aqueous solutions containing metal rations, that may include rations of both desired metal and impurity or secondary metal, are treated with an organic liquid extractant or solvent suitable for the extraction of rations of the c", ~ ;1 a~ ';' ;'~ A
~~ '.~ .r .
r.r i; -. ~ .. ..
desired metal, rations of at least one secondary metal being co-extracted. After phase disengagement, the loaded organic phase containing either rations of a desired~metal or rations of desired metal together with rations of secondary metal is contacted with a solid metal or solid metal alloy capable of reducing in the organic phase either rations of a desired metal or rations of a secondary metal from a higher to a lower state of oxidation. Depending on the extracted metals) and the added solid metal or solid metal alloy, the rations of an extracted metal are reduced to the lower state of oxidation and are either deposited (cemented) in the metallic state onto the solid metal or solid metal alloy, or are partially reduced in the organic phase to a lower oxidation state, svhich is easily stripped, with the solid metal or solid metal alloy being oxidized in part. The method of galvanic stripping is carried out at ambient pressures and at ambient or slightly elevated temperatures. It .is understood that the term solid metal will ~e used hereinafter to denote and is hereby defined to include Both solid metals and solid metal alloys.
galvanic stripping is v.~seEul For the removal of rations of a esired metal, or cations~ of a secondary metal, From an organic iquid into which it has been extracted from an aqueous elution. Cations of a desired metal or rations of a secondary atal may be galvanically stripped from an organic liquid by position of such a metal onto an added solid .metal capable reducing rations of such a metal to its metallic state, and moving the added solid metal with deposited metal from the ~, .w. ~ .r3 ~,a .~~..

organic liquid. Galvanic stripping is also useful For the partial reduction to a lower state of oxidation and for the removal of rations of secondary metals from ari organic liquid.
Hy adding a suitable solid metal, rations of the secondary metal are reduced to a lower state of oxidation and are removed by stripping into an aqueous phase. Reduction and stripping may be carried out selectively and separately in two steps or simultaneously in one step. Where the organic phase contains rations of both a desired metal and a secondary metal, and rations of the secondary metal are only partially reduced to a lower state of oxidation, the stripping of rations of the desired metal may be carried out either before or after the contacting with solid metal and the removal of catians of the reduced secondary metal from the organic phase. The solid metal is preferably used in particulate form. The use of a solid metal reductant makes it possible to directly reduce rations of a metal, especially rations of those metals that may be difficult to transfer from the org,~nir phase in their normal oxidation state, into the solid state or in a partially reduced form (but usually still in cationic formy to allow easy stripping. The method according to the invention eliminates the use of high temperatures and/or pressures, and the need to deal with stripping solutions that are not easily treated, or axe chemically or environmentally undesirable.
Accordingly, it is an aspect of the present invention to provide a method for the galvanic'stripping of metal ions from loaded organic liquids, It is another aspect to provide a method for the solvent extraction of cations of metals wherein a loaded organic liquid is treated with solid metal reductant, which may be a single metal or an alloy.
It is still another aspect to provide a method for the solvent extraction of cations of metals wherein cations of an extracted metal are precipitated onto a solid metal reductant.
It is yet another aspect to provide a method for the solvent extraction of cations of metals wherein cations of an extracted metal are at least partly reduced.
It is yet a further aspect to provide a method for the solvent extraction of cations of metals wherein cations of a metal are simultaneously at least partly reduced in and stripped from the organic phase.
These and other aspects of the method according to the invention will become clear from the following detailed description.
According to the main embodiment of the invention, there is provided a method for the extraction of cations of at least '?0 one metal from an aqueous solution with an organic liquid capable of extracting canons of said at least one metal in a higher state of oxidation from said solution, said aqueous solution containing cations of metals chosen from the group consisting of a)cations of a desired metal and b)cations of a desired metal together with rations of at least one secondary metal, rations of said at least one secondary metal being co extracted from the aqueous solution by the organic liquid, said method comprising the steps of:
(1) mixing said aqueous solution with said organic liquid for the formation of an aqueous raffinate phase and an organic liquid phase containing rations of said at least one metal in a higher state of oxidation;
(2)separating said aqueous raffinate phase from said organic liquid;
(3)contacting separated organic liquid with a solid metal capable of reducing in said organic phase at least a portion of said rations of said at least one metal from said higher state of oxidation into a lower state of oxidation, said solid metal being chosen from the group consisting of Zn, A1, Cu, Cd, Mn, Mg, Fe and their alloys to provide organic liquid having a reduced content of said canons of said at least one metal;

(4)removing said organic liquid having a reduced content of said rations of said at least one metal from said solid metal;
and

(5)returning organic liquid having a reduced content of said rations of said at least one metal to said mixing of step (1);
wherein solid metal is defined as including both solid metals and solid metal alloys.
According to a first preferred embodiment, there is provided a method according to the main embodiment wherein said rations of metals comprise both rations of a desired metal and rations of at least one secondary metal, rations of said desired metal and rations of said at least one secondary metal are extracted into said organic phase. rations of said desired metal are stripped from separated organic phase with a stripping solution 9 ~ ;1 .? F~; ", ~
~, i; ::: C9 ;_1 i'.
capable of stripping rations of said desired metal frorn separated organic phase prior to said contacting with solid metal while substantially leaving rations of~'said at least one secondary metal in said organic phase, and rations of said at least one secondary metal are reduced to said lower state of oxidation in said contacting.
According to a second preferred embodiment, there is provided a method according to the main embodiment, wherein said rations of metals comprise rations of. a desired metal and rations of at least one secondary metal, rations of said desired metal and rations of said at least one secondary metal are extracted into said organic phase, rations of said at least one secondary metal are reduced to a lower state of oxidation in said contacting while substantially leaving rations of said desired metal in said organic phase to provide organic liquid having a reduced content of rations of secondary metal and having left rations of the desired metal herein, and stripping rations of said desired metal from said organic liquid having a reduced content of rations of secondary metal with a stripping solution capable of stripping rations of said desired metal from said organic liquid prior to returning liquid having a reduced content of rations of secondary metal to said mixing of step (1).
According to a third preferred embodiment there is provided a method according to the main embodiment, wherein rations of metal comprise rations of a desired metal, and wherein rations lu a .? ~~ ;.~ ~~~.
of said desired metal are reduced to said locaer state of oxidation and are deposited onto said solid metal, and said solid metal with deposited desired metal is removed from said organic liquid.
Detailed Description Solvent extraction or liquid-liquid extraction is a versatile method for the selective separation of metals. The separation involves the mass transfer of metal cations across boundary interfaces between two contacting, insoluble phases, i.e. an organic phase and an aqueous phase.
The degree of extraction is influenced by the selectivity among various canons in the solution and the pkk. In many cases, the process functions very well using straight-forward, reversible loading and stripping. In other cases reactions are less easily attained by simple shifts in chemical equilibria, and it is in these cases that the galvanic stripping rnethod of the present invention finds particular application. Although the method of the present invention is applicable in many instances as an alternative to ,or even preferable over hydrogen reduction, or gaseous or hydrolytic stripping, the galvanic stripping of this invention is particularly valuable far the recovery of certain desired cations and for the removal of co-extracted cations of impurity, unwanted or secondary metals, especially iron.

In the galvanic stripping according to the invention, an added solid metal reluctant provides an electrochemical driving force to alter the oxidation state or, in general, modify the equilibrium of inorganic ions dissolved in organic liquids.
These alterations are important because certain separations or recoveries, that are not normally attainable using a standard chemical driving force or technique, become possible using electrochemical reactions. The following simplified equations represent two possible reactions:
( R-) nMln+(org) + xM2(S) -___> x ( R_ )mM2m+(org) .t. M1(5) ( 1 ) ( R ) nMln+(org) + xM2(S) -___~ ( R-) n_mxMl(n-xm)t(org) + x ( R )mM2m+(org) (2) wherein (R-) is the organic and M~ and MZ are different metals or their complexes in the organic pt7ase. equation (1) shows the reduction of.the M~ ion to metal M~~S) by added solid metal MZ(S). This reduction is similar to but by no means the same as the displacement (or cementation) reactions commonly encountered in aqueous chemical processes. In equation (2), the M1 ion is only partially reduced by solid metal M2~5) to a lower oxidation state, altering the equilibrium and allowing easier stripping into an aqueous phase. In both cases, .M2 remains in the organic phase as an oxidized stable species.
The suitability of M2 as a reactant for Ml in such a system then requires that a) added solid metal MZ is capable of forming a stable R-M2 species, and b) Lhe potential of the half cell Mz/R-M2 is less noble than that of M1/R-M~. These conditions are necessary, but not necessarily sufficient, to 6w ~; .~ ? ~-.. -f.~ ':A i~ ,'.' '',: ~IR.

insure reaction, As is often the case for similar reactions occurring in an aqueous solution, the magnitude of the differences in potentials as well as the. reaction kinetics must be considered. Generally, the added solid metal must be capable of reducing a metal extracted into an organic liquid to a lower state of oxidation.
The method is carried out using the conventional process steps in solvent extraction. Aqueous solution containing one or more dissolved metal species, in the form of rations or, in some cases, complexed as anions, is mixed with an amount of an organic liquid capable of extracting rations or complexed anions of a desired metal. The organic liquid is usually premixed with a diluant, a modifier may be added, and the organic liquid may be equilibrated ar conditioned prior to mixing with aqueous solution. Aqueous solution and organic liquid are mixed to form a loaded organic raffinate phase and an aqueous phase, which are subsequently separated, If desired, the loaded organic phase rnay be scrubbed with a scrub solution. Conventionally, a scrub raffinate is separated and loaded (scrubbed) organic phase is stripped with a strip solution to form a strip liquor and a stripped organic liquid.
Cations of the desired metal are recovered from the separated strip liquor and the stripped organic liquid is regenerated, purified and recycled to the extraction.
To strip rations of a metal galvanically, cahether rations of a desired metal or rations of a secondary metal, from loaded 13 ~A ~ ,~ Ei' ;~.~ ::3. ~'.
organic phase, an amount of suitable solid metal is added to the loaded organic phase, after separation from the aqueous raffinate phase. The suitable salid metal must be capable of reducing cations of the metal to a lower oxidation state, either to its elemental Form, i.e. the metallic state, or to a partly lowered oxidation state. The amount of added solid metal should be at least stoichiometric to accomplish the reactions, but is added preferably in excess. of the stoichiometrical amount required to effect the reduction.
The solid metal may be added in the form of sheets or coupons but is preferably added in a particulate form such as chips, pellets, granules or powders. Although coarse reductant effects the reduction, small particle sizes increase the rate and efficiency considerably. A broad range of particle sizes may be used, such as in the range of From about 94 to 6000 microns. The particle sizes are preferably in the range of from about 9A to 600 microns. 'fhe CE:duCtiOn may be carried out in an oxidizing, neutral or reducing atmosphere to suit the needs of the desired reaction. The reduction is preferably carried out in the absence of oxygen, as, in the case of some metals, oxygen (air) tends to re-oxidize cations of the reduced metal and to lower the effic3.ency. If desired, the reduction may be carried out in the presence of nitrogen, cvhich is essential in some cases to avoid re-oxidation.
The galvanic stripping is carried out at ambient pressures and at ambient temperatures. As the reduction is temperature 14 ft ~ t ~ :' " ,~ -~:
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dependent, the rate of reduction may be increased by using elevated temperatures. Preferably, slightly elevated temperatures such as, for example, up to about 60°C may be used. The temperature may, therefore, be in the range of from ambient to about 60°C. Efficiency is increased with good mixing during the contacting and stripping steps.
The loaded organic phase .is contacted with the solid metal for a period of time sufficent to reduce at least a portion of rations of the metal in the organic phase. Contact times may be in the range from about 1 to 90 minutes, preferably about 15 to 60 minutes. The contacting may be carried out continuously or intermittently in a column loaded with reductant by passing the loaded organic phase through the column. Alternatively, the contacting may be carried out by mixing reductant with the loaded organic phase in a suitable vessel provided with agitation.
In the galvanic stripping with a suitable solid metal, whereby rations of the metal extracted into an organic liquid are reduced to the metallic state and deposited onto the added solid metal, rations of certain metals (extracted as rations of desired metal or rations of secondary metal) can be deposited onto suitably selected added solid metals from certain solvents. Cations of more than one secondary metal may be ca-extracted, and rations of at least one of the co-extracted secondary metals may be reduced to a lower state of oxidation and deposited in the metallic state onto the solid ~3 ~. '~ 'Y, f.~ , . ..: Y,f .~~ '~%: .,..
metal. The reduction and deposition are also dependent on the type of anion originating from the aqueous feed solution fed to the solvent extraction process. The following Table I lists extracted metal cations that were extracted from aqueous feed solution with a suitable organic liquid, and were reduced to elemental form in the organic phase from either a sulfate, chloride or cyanide anion system by solid metals.
TABLE T

Organic Extracted Solid Liauid Anion Cation Metal D2EHPA sulfate Cu2+ An,Cd,iron sulfate Ag+ Al,Zn,Cu sulfate Co2-t- Zn*, Mn*

chloride Sn4+ Zn*

chloride Pb2+ Zn AliquatTM sulfate Cu2-H Zn,Al,Cd 336 chloride Cu2+ Zn,Al,Cd sulfate Ni2+ Zn*,iron*

cyanide Au3+ Zn LIXmM622 chloride Cu2+ Zn LTXrM864 chloride Cu2-E Zn, iron * Nitrogen must be present wherein D2EHPA is di-2-ethylhexylphosphoric acid, AliquatTM
336 is tri- (CeClo) methylammonium chloride, LIXTM 622 is a mixture of LIXTM 860 (5-dodecylsalicylaldoxime) with tride-canol, LIXTM 864 is a mixture of LIX.rM 64N, which is 1 vol LIXTM 63 (5, 8-diethyl-7-hydroxy-6-dodecanone oxime) in LIXTr~ 65N (2-hydroxyl-5-nonylbenzophenone oxime), and LIXTM
860, and iron denotes low carbon steel or electrolytic iron.

:.' ~ ,, ~'~ ,.>ui .7 As, unfortunately, the majority of common organic extractants also remove undesirable cations,i.e. rations of secondary metals, from an aqueous solution in addition to the rations of the desired metal, the present method is also useful to remove rations of such secondary metals from the organic phase.
For example, a reaction that may occur in the loading of the extractant with iron as secondary metal in the form of ferric ions from a sulfate solution may be represented by the following equation:
Fe3+(aq) + 3IIR(org) -___> Fe R3(or9) + 3IiF(a~) ( 3 ) The extraction frorn a chloride solution, using a tertiary amine, may be represented by the equation:
Fe3~(a~l) v HCl(aq) -H 3C1-(aO) 't NR3(or9) -__~ FeCl,~-fINR3(or~) ( 9 ) Thus, when aqueous solution containing rations of desired metal and rations of iron as secondary metal is contacted with an organic liquid extractant, the resulting organic phase contains, in addition to rations of the desired metal, the above-noted ferric complexes which are strongly stable. After separation of the loaded organic phase From the aqueous raffinate phase, the loaded organic phase is contacted with a suitable solid metal that is capable of reducing the ferric to the ferrous form. Suitable solid metals are selected t:rom the group consisting of zinc, manganese and magnesium, the use of Zinc being preferred. Certain alloys, such as, for example, low carbon steel or zinc containing a small amount of lead (e. g. 0.2~) may also be used. Small amounts of certain 17 f ~.' ::i~ i ' ~''.
alloying metals favorably affect the reactivity of the so activated zinc. The use of activated zinc is most preferred.
Ca n ons of the desired metal may be stripped from the organic phase with a stripping solution capable of stripping cations of the desired metal from the organic phase, either before or after the contacting caith solid metal, and removing cations of the secondary metal in its partially reduced state of oxidation.
For example, the galvanic stripping reactions of iron with the preferred solid metal, i.e. activated zinc, may be represented by the equations (5), and (6) and (7):
FeR3(or9) + 3E1+(~~~) -H 1/2 Zn° __~ re2~(a~~) (-h 1/2 Zn2~(a~) ) * -f 3HR(or9) (5) and FeR3(or9) v 1/2 Zn° ____~ 1/2 ZnRZ(°r~) v FeRZ(°r~) ( the organic complexes reacting with hydrogen ions (acid) as follows 1/2 ZnR2(°r9) + FeR2(°r9) + 3Ht(°r9) _____> 3HR(org) ( + 1/2 ZnZ+(~~) ) * + Fe2+(~~) ( 7 ) *Zinc may remain in the organic. phase if solution is dilute.
Equation (5) illustrates the reduction and stripping being accomplished simultaneously in one step, and equations (6) and (7) sequentially in two separate steps.
The contacting may be carried out as described above and with similar conditions of time, temperature, pressure and particle ~

.n ~ , ,~ "~ . .
f 1 L;:
a E ~ , sizes to reduce at least a portion of cations of the secondary metal in the organic phase from a higher to a partially reduced lower state of oxidation, i.e. ferric to ferrous ion. The organic liquid may be one of a number of extractants into which iron is co- extracted such as, for example, phosphoric acids such as di-2-ethylhexylphosphoric acid (D2EHPA), mono-2-ethylhexylphosphoric acid (M2EHPA) and mixtures thereof, phosphonics such as the mono-2-ethylhexyl ester of 2-ethylhexylphosphonic acid (PC88A, tradename), phosphinics such as bis (2,4,4-trimethylpentyl) phosphinic acid (CyanexjM272), and (LIX 69N) which is a mixture of LIX 65N (2-hydroxy-5-nonylbenzophenone oxime) and 1~ LIX 63 (5, B -diethyl-7-hydroxy-6-dodecanone oxime).
In the two steps of first reducing ferric to ferrous and then stripping the ferrous, the loaded organic phase is contacted with particulate zinc under the appropriate conditions, as described. After contacting, the solution is stripped with an acid such as sulfuric or hydrochloric acid. For example, the strength of the acid may range from 20 to 100 g/L H2S04 or 30 to 100 g/L HC1, dependent on the organic. For example, the reduction of ferric in the loaded organic phase with zinc powder then allows stripping with a sulfuric acid solution at a value of the pFE of about 3. At this pH value the zinc remains in the organic phase, providing a selective separation from the iron. At a pH below about 3.5, no iron or zinc hydroxides precipitate. Using HC1 as stripping acid, the pH
should also have a value of below about 3.5.

19 ,.
In tile Olle-Step galvanic stripping, zinc metal and acid stripping solution are both added to the loaded organic phase.
After the desired contact time under the desired conditions, as described, the phases are separated, the ferrous iron reporting to the aqueous phase. If desired; using the appropriate conditions, a portion or virtually all of the iron can be removed from the organic phase using either the one-step or the two-step method. It is noted that the reduction substantially takes place in the organic phase, as ferric ions do not readily strip into the aqueous phase.
According to the embodiment wherein an aqueous solution contains rations of a desired metal together with rations of a secondary metal, the method is carried out as follows. The aqueous solution is mixed with an organic liquid capable of extracting rations of the desired metal and co-extracting rations of the secondary metal to form an aqueous phase and a loaded organic phase containing both rations of the desired metal and rations of the secondary metal. The secondary metal is substantially present in a higher oxidation state. The loaded organic phase is separated from the aqueous raffinate phase. Cations of the desired metal are then stripped, if desired after scrubbing, from the loaded organic phase with a stripping solution capable of stripping rations of the desired metal from the organic phase while substantially leaving rations of the secondary metal in the higher oxidation state in the organic phase. The organic liquid is subsequently it :'z i~ J ~'.3 ~ ':
contacted, batch-wise, continuously or intermittently, with a solid metal for the reduction of at least a portion of rations of the secondary metal from the~:higher state of oxidation to a partially reduced state of oxidation. Cations of the secondary metal in the partially reduced state of oxidation are stripped from the organic liquid caith a stripping solution capable of stripping rations of partially reduced secondary metal from the organic liquid with the formation of.
a regenerated organic liquid having a reduced content of rations of the secondary metal. 'Phe regenerated organic liquid is returned to the extraction step. Alternatively, rations of the secondary metal in the higher state of oxidation in the separated loaded organic phase are first partially reduced and stripped from the organic liquid without substantially reducing or stripping rations of the desired metal in the organic, and rations of the desired metal are then stripped from the organic phase, leaving a regenerated organic liquid with a reduced content of rations of secondary metal for return to the mixing step for extraction of metal.
This embodiment may, for example, be applied to a solution containing indium as desired metal and iron as secondary metal, and using commercial grade di-2-ethylhexylphosphoric acid, which contains mono-2-ethylhexylphosphoric acid, dissolved in kerosene. Cations of both metals are substantially extracted into the organic liquid. The indium is stripped from the loaded organic phase with dilute hydrochloric acid (1-3 normal) substantially leaving the iron in the organic phase. The iv ~ b ~! ~~~

organic phase is then contacted, as described, with zinc having particle sizes from about 49 to 6000 microns, preferably about 79 to 150 microns, in the presence of 'nitrogen and at temperatures of from ambient to about 60°C. After allowing adequate contact time and a following solids-liquid separation, the ferrous iron is stripped from the organic phase with a sulfuric acid stripping solution containing 20 to 100 g/L sulfuric acid. The organic liquid with a reduced iron content is returned to the extraction. As explained above, the reduction and the stripping of ferrous iron may be carried out simultaneously in one step or separately in two steps.
Although the partial reduction of a metal ration to a lower state of oxidation has been described mostly with reference to iron, this embodiment may also be used for the partial reduction of other multivalent metal rations such as Ce, Mn and Cr. 'Phe method of the invention may be used in a number of applications. ~Phe method is suitable for the selective removal of rations of a metal from an aqueous solution by solvent extraction, the metal ration being of a desired metal or of a secondary metal; For the removal of rations of a metal from an organic liquid that is difficult to remove in its normally occurring oxidation state; for the removal of rations of one or more co-extracted secondary metals from an organic liquid being used for the recovery of a desired metal; or for the coating of a metal on the added solid metal as a substrate.
In these and modified embodiments, solvent-solid metal r,'~ '.a~'~3~
combinations especially designed to effect such applications may be used. , The invention will now be illustrated by the following non-limitative examples.
Example 1 This example illustrates that the galvanic stripping of certain metal rations from certain organic liquids can be carried out with suitably selected solid metals. In a number of tests, an organic liquid was loaded with a metal ration extracted From an aqueous solution containing rations of the metal. The loaded organic phase was contacted with an excess of solid metal in particulate form for 30 minutes. Some tests were carried out in the presence of nitrogen. The solid metal was removed from the organic liquid. Examination of the removed solid metal with a scanning electron microscope showed that rations of the metal had been deposited on the surface of the added solid metal, the rations of the metal having been reduced to the metallic state. The rations of the metal extracted Prom aqueous solutions, the organic liquids, the anion of the aqueous system and the added solid metal are tabulated in Table II.

23 sy ~ ~~ n -~ ,y .~
fd i. ''.~ 'v° .~ ~f~. .~~.
TABLE II
Organic Extracted Solid Liquid*** Anion Cation Metal D2EHPA sulfate Cu2+ ~ Zn,Cd,iron**

sulfate Ag+ Al,Zn,Cu sulfate Co2+ Zn*,Mn*

chloride Sn4+ Zn*

chloride Pb2+ Zn Aliquat 336 sulfate Cu2-~ Zn,Al,Cd chloride Cu2+ Zn,Al,Cd sulfate Ni2+ Zn*,iron**

cyanide Au3+ Zn LIX 622 chloride Cu2-f Zn LIX 864 chloride Cu2+ Zn,iron**

* Nitrogen must be present ** iron was low carbon steel or electrolytic iron *** For definitions see TABLE I.
Example 2 This example illustrates that the galvanic stripping can be carried out in two stages to achieve 100% iron stripping and removal. An organic liquid loaded with 1.0 g/L iron was mixed with zinc granules for 30 minutes under nitrogen. Metallic zinc was then removed, and the resultipg organic phase was stripped with 10 g/L sulfuric acid for five minutes. Analysis showed that complete reduction and stripping of iron was achieved.
Example 3 To examine the effects of reoxidation of the ferrous iron, the nitrogen was removed from above the organic and aqueous strip solutions obtained in Example 2. The two phases were allowed .: _. , to mix in a vessel open to the air. After 30 minutes, it coas Found that 20~ o~ the stripped iron was re-extracted back into the organic phase.
Exams 1p a 4 A number of tests were done to determine the effect of using nitrogen, an open or a closed reaction vessel, and a one-step or two-step galvanic stripping. Nitrogen was either used or not used; when used, nitrogen was bubbled through the liquid phases, or introduced over the liquid surface. The organic loading was 5 g/L re, the ratio of aqueous to organic phase was 1:1, the strip solution was 100 g/L H2S04, the temperature was ambient and nitrogen (when used) was admitted for 10 minutes. The percentage of iron stripped was determined. The test conditions and results are given in Table III.
TABLE TII
Test Nitrogen Vessel Zn Metal Steps Fe Stripped No. Used Used Used No. $

1 none closed none 1 15 2 none open yes 2 38 3 bubbled closed yes 2 63 4. bubbled closed yes 1 7g over closed yes 1 80 Tt can be seen from the results that mere acid stripping removed only 15~ of the iron from the organic phase, that the presence of nitrogen is necessary, and that galvanic stripping in one step appears to give better results.

b~,, ~'1 .! n ~ ~~ J~ .d ~'.1 :ti ..; ~.., :, ~ ".. .v, In the following Examples 5 to 7, a leach solution containing ferric sulfate and zinc sulfate was mixed: with a solvent consisting of 20 volume percent D2EHPA dissolved in kerosene.
The extraction was done in stages with the pH controlled at a value of 2.6 to prevent the precipitation of iron or zinc hydroxides. The volumes of leach solution and solvent were equal. The organic phase was loaded to metal concentrations of 1 to 7 g/L iron and 0 to 13 g/L zinc. After settling, the loaded organic phase was separated from the aqueous raffinate phase and subjected to galvanic stripping.
The galvanic stripping was carried out in one step with the addition of 99.0 pure zinc granules having particle sizes of 1000 to 2000 microns and a total surface area in the range between 15 and 35 cm2. The galvanic stripping was carried out at temperatures between 20°C and 60°C with the addition of from 2 to 7 g of zinc granules which is in excess of the amount stoichiometrically required For the reduction of the ferric present to ferrous, and in a solution containing from 20 to 100 g/L sulfuric acid.
The loaded organic phase was heated to the desired temperature, sparged with nitrogen for five minutes and zinc and preheated sulfuric acid solution were added. The mixture was then agitated in a closed vessel for 30 minutes. The desired number of samples were taken and analyzed.

nj J, ~ ,, a ~;~ ": ' Example 5 Using the procedure described above, eight tests were done to determine the percentage of iron stripped into the aqueous phase. The values of the variables and. the results are shown in Table IV.
TABLE IV
Total re ( ionic)Zn2~ L'e 'PestH2S04 Zn Area Temp Loading Loading Stripped No. g/L cm2 C g/L g/L $

6 60 15 20 5 8 32

7 20 35 20 5 0 84

8 20 15 2U 1 8 68 The results indicate that the galvanic stripping of iron is strongly dependent on the surFace area of the added zinc metal and the temperature and, to a lesser c9egree, on the iron loading.
Example 6 Using the procedure described above, eight tests were done to determine the percentage iron stripped with varying zinc loadings, temperatures and zinc metal. areas while maintaining the iron loading constant at 1.1 g/L. The values of the variables and percentage iron stripped are given in Table V.

TABLE V
Total Test Zn Loading Zn Area Temperature Fe Stripped No g/L cm2 C
.

The results show that for a given iron loading, increasing the zinc metal surface area resulted in increased amounts of iron stripped. Hy comparing the results given in Tab:Les IV and V, it can be seen that the effect of temperature remains but that the effect of higher zinc metal area decreased in the presence of higher zinc loading in the organic. The effect of higher zinc loadings is more pronounced at the lower temperature.
Example 7 This example illustrates the effects on the percentage of iron stripped and the iron stripping rate of the iron loading of the loaded organic and the surface area of the added zinc metal. Four tests were carried o~.it using the procedure described above. Samples were taken after 5, 10, 15, 20 and 30 minutes and the iron stripped and stripping rates determined. The results are given in Table VI.

f;.~ ~.: " Z j' ~ j ; ' .~~.

TABLL VI
Total Stripping Test Pe Loading Zn Surface Time I~'e StrippedRate No. g/L cmz min, o L
g/ / min.

1 1.1 15' S 13 538 2 1.2 35 5 92 323 15 78 8os 3 6.8 15 5 7 2096

9 6.7 35 Gi 13 3441

10 2B 3925 1.i 37 3763 3(1 84 4570 It follows from the data presented in bitable VT that for a given iron loading, increasing the zinc metal surface area resulted in an increase of the amount of iron stripped. At low initial iron loading and high zinc area, a decline in removal rate occurs with increasing time. The stripping rate is increased virtually proportionally with increasing zinc surface area.
example 8 This example illustrates that iron can be effectively removed in a one-step galvanic stripping from different organic phases using different solid metals added in particulate form. The ratio of organic to aqueous phase was 1:1, and the mixing time was 50 minutes. Test data are presented in Table VTI.

z9 TAHLE VII
Iron , Organic Fe3+ loaded HzSO~ Removed in vol.% in m L Metal added in L in m L

D2EHPA 760 2.5g Zn 20 750 in kerosene 5 D2EHPA 760 3.5g Fe 20 495 in kerosene LIX 69N 985 None 10 0.4 15 LIX 64N 985 Cu 10 371 Example 9 This example illustrates that lead can be effectively removed by galvanic stripping. Lead loaded to 1.5 g/L in 5 vol.%
D2EHPA in 30 mL of organic phase was contacted with 2.5 g of metallic zinc. Samples were taken from the organic at various times, and the samples were stripped with 80 g/L HC1. The amount of lead removed was determined. Examination of the zinc after the tests with a scanning electron microscope showed that metallic lead had deposited on the zinc surface. Test results are given in Table VIII.
TABLE VIII
Pb Removed Time ______________ in minutes in mg in %

10 519 ' 34 b~ W
i ~ ~ ~'n ~
30 ...
hxample 10 This example illustrates that an organic liquid loaded with indium and iron can be selectively stripped of indium, and the iron remaining in the liquid can then be at least partly stripped of iron using added solid metal to yield a regenerated organic liquid with a reduced iron content. In a countercurrent solvent extraction process, a feed solution containing iron and 0.94 g/L indium, and an organic extractant containing one volume $ M21;I~PA, three volume ~ D2l;FiPA, and two volume ~ TBP in tcerosene were used. A loaded organic phase was obtained that contained 0.89 g/L indium and 0.52 g/L iron.
The indium was stripped from the loaded organic liquid with 3N
hydrochloric acid. The organic liquid cvas washed faith sodium sulfate solution to remove chloride and Found to contain <0.003 g/L indium and 0.51 g/L iron. 'Phe washed organic liquid was split in two portions. The first portion caas treated with 100 g/L sulfuric acid solution in a 1:;1 volume ratio, with 10 g activated zinc dust,(0.2'k Pb) per litre of organic liquid, at ambient temperature, and with the addition of nitrogen. All iron was removed From the organic liquid aFter 15 minutes. The second portion was similarly treated with 10 g activated zinc dust (0.2~ Pb) per litre of organic liquid but with the addition o~ 150 g/L return acid (obtained Erom a zinc electrowinning process) in a ratio of organic to acid solution of 30:1. Substantially all iron had been removed after 30 minutes.

~: ; ! '~ p !.,.
3 a f, i,. . ~ ,, ' r1 Example 11 This example illustrates. that iron can be at least partly stripped from an organic phase in a one-step process by continuous circulation of organic phase mixed with stripping solution through a column filled with a solid metal. From a vessel containing a mixture of 6.5 L of an organic phase consisting of 4$ EHP,A, 2$ THP and 99$ ExxsolTM D80 by volume, and 6.5 L of a regenerated raffinate containing sodium sulfate and 60 g/L sulfuric acid, 0.5 L/min of the rnixture was continuously circulated through a column containing zinc granules. The column was 2 m high with a diameter of 1.9 crn, and was filled with 860 g zinc (0.2$ Pb) granules, the void volume being 0.47 L. The temperature was ambient. During the test, nitrogen was sparged into the vessel. Samples were taken from the vessel and from the column effluent at 15 minute intervals, and the iron concentration in the solvent in the aqueous phases of each sample was determined. The results are given in Table TX.
TABLE IX

Iron Concentration in q/L

Time solvent con tinuous aqueous continuous in minutes vessel column vessel column 0 076 0.68 1 0.52 0.55 15 0.69 0.60 16 0.46 0.45 30 0.54 0.52 31 0.36 0.40 45 0.43 0.45 46 0.27 0.30 60 0.34 0.37 61 0.20 0.22 75 0.26 0.29 76 0.15 0.17 b/Z f1 ~ 5' v ~f ;'~
32 ~ - ~; : ... _;
>Jxample 12 This example illustrates that four-valent cerium (Ce'~+) can be effectively galvanically reduced to the two-valent state (Ce3r) in solvent extraction and subsequent stripping.
An aqueous nitric acid solution containing 15 g/L Ce'~+ as ammonium cerium nitrate ( (NHq)2 Ce (N03)6 ) caas mixed with 99~ tributylphosphate (THP) in an aqueous to organic volume ratio of 1:1. After 10 minutes, the loaded organic phase was separated From the aqueous phase. The loaded organic phase was then mixed with zinc either as pieces or as powder having particle sizes of 74 to 150 microns in an amount of 1 gram per 1.0 ml of organic phase and an amount of a dilute acid containing 10 g/h H2SO,t or HN03 added either together with the addition of zinc or after the galvanic reduction was completed. The galvanic reduction was carried out for times ranging from 30 seconds to 30 minutes. The reduction and stripping were carried out in a closed vessel under a flow of nitrogen. During the reduction the colour of the solution changes from dark orange to colourless. The Ce concentrations in the solutions were determined with x-ray fluorescence, and additional analyses were made using atomic absorption spectometry. All cerium analyses have been transformed into g/L Ce. A series of tests were made including a comparative non-reductive stripping. The test data and analytical results were as follows.

n1 r~ v, ,~ .~.
33 h, ;_, ~ !. r ~ s ~:~ '~
Test 1: Comparative nonreductive stripping The loaded organic phase contained 14.8 g/L Ce, and was split in two equal portions. One portion was mixed for 30 minutes with an equal volume of a 10 g/L HN03 solution.
The resulting aqueous solution contained 1.1 g/L Ce, and the stripped organic contained 13.7 g/L Ce for a stripping efficiency of only 8~. The other portion was mixed for 30 minutes with an equal volume of a 10 g/L Fi2S0,~ solution.
The resulting aqueous solution contained 2.5 g/L Ce, and the stripped organic contained 12.3 g/L Ce for a stripping efficiency o.E 17~ into the aqueous phase.
Test 2: One-stage galvanic reduction and separate stripping The loaded organic phase containing 19.6 9/L Ce was mixed with 3 g zinc powder for 30 minutes. After removal of zinc, the reduced organic phase was split in two equal portions which were stripped of cerium as in Test 1. After the nitric acid strip, the aqueous phase contained 7.0 g/L
Ce and the stripped organic phase contained 7.6 g/L Ce for a 98~ stripping efficiency. For the sulfuric acid stripping, these figures were, respectively, 11.1 g/L Ce, 3.5 g/L Ce and 76~.
Test 3: Simultaneous one-stage galvanic reduction and stripping The loaded organic phase containing 19.1 g/L Ce was separated in two equal portions. One portion was mixed for u5 ~ :' rt~ ':w l~ 'i seconds with an equal volume of a 10 g/L HN03 solution and 1 g Zn powder. The resulting aqueous phase contained 9.4 g/L Ce and the stripped organic phase contained 9.7 g/L
Ce for a 62~ efficiency. The second portion was treated in the same manner but mixed for 30 minutes. The stripping efficiency was 60~.
Test 4: Simultaneous multi-stage galvanic reduction and stripping The loaded organic phase containing 14.6 g/L Ce was mixed in a first stage with a volume of a 10 g/L HN03 solution and zinc pieces with a total surface area of 5.6 cm2.
Mixing was continued until the solution was colourless.
After separation, the aqueous phase was found to contain 12.2 g/L Ce for stripping efficiency of B3~. The separated organic phase was then treated in a second stage under the same condition for twice as long a period. The separated aqueous phase contained 2.05 g/h Ce and the stripped organic phase contained 0.35 g/L Ce for a stripping efficiency of 85~. The cumulative efficiency was 97$.
Test 5: Multistage stripping using simultaneous and separate stages A first portion of a loaded organic phase containing 14.5 g/L Ce was mixed caith an equal volume of a 10 g/L HN03 solution and zinc pieces with a total surface area of 5.2 cm2 until the solution had turned colourless. After separation, the aqueous phase contained 12.2 g/L Ce, and the organic phase was mixed in a second stripping stage with an equal volume of a 10 g/L HN03 solution for twice as long but no zinc was present. Separated aqueous phase contained 2.0 g/L Ce and separated twice-stripped organic phase contained 0.3 g/L Ce.
A second portion of the same loaded organic phase was mixed with zinc pieces (6.B cm2) until colourless. The reduced organic phase was then mixed for 10 minutes with an equal volume of a 10 g/L HN03 solution. After separation, the aqueous phase contained 12.5 g/L Ce, and the stripped organic phase containing 2.1 g/L Ce was again treated with zinc pieces (4.2 cm2) and subsequently mixed for 10 minutes with an equal volume of a 10 g/L HN03 solution. After separation the final aqueous phase contained 2.1 g/L Ce and the twice-reduced and stripped organic contained 0.9 g/L
Ce. It follows from the results of these tests that Cerium is very difficult to strip with acid solutions in the four valent state, viz. the low stripping efficiencies of Test 1, but that after a reduction of Ce'~~ to Ce3+ with a solid metal reductant (zinc), the stripping with dilute acid is almost quantitative.
It is understood that variations and modifications may be made in the embodiments of the invention without departing from the scope and purview of the claims.

Claims

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

1. A method for the extraction of cations of at least one metal from an aqueous solution with an organic liquid capable of extracting cations of said at least one metal in a higher state of oxidation from said solution, said aqueous solution containing cations of metals chosen from the group consisting of a)cations of a desired metal and b)cations of a desired metal together with cations of at least one secondary metal, cations of said at least one secondary metal being co-extracted from the aqueous solution by the organic liquid, said method comprising the steps of:
(1) mixing said aqueous solution with said organic liquid for the formation of an aqueous raffinate phase and an organic liquid phase containing cations of said at least one metal in a higher state of oxidation;
(2)separating said aqueous raffinate phase from said organic liquid;
(3)contacting separated organic liquid with a solid metal capable of reducing in said organic phase at least a portion of said cations of said at least one metal from said higher state of oxidation into a lower state of oxidation, said solid metal being chosen from the group consisting of Zn, A1, Cu, Cd, Mn, Mg, Fe and their alloys to provide organic liquid having a reduced content of said cations of said at least one metal;
(4) removing said organic liquid having a reduced content of said cations of said at least one metal from said solid metal;
and (5)returning organic liquid having a reduced content of said cations of said at least one metal to said mixing of step (1);
wherein solid metal is defined as including both solid metals and solid metal alloys.

2. A method as claimed in claim 1, wherein said contacting is carried out at ambient conditions.

3. A method as claimed in claim 1, wherein said contacting is carried out in the absence of oxygen.

4. A method as claimed in claim 1, wherein said contacting is carried out for a time sufficient to reduce at least a portion of said cations of said at least one metal in said higher oxidation state to said lower state of oxidation.

5. A method as claimed in claim 1, wherein said contacting is carried out for a time in the range of about 1 to about 90 minutes.

6. A method as claimed in claim 1, wherein said contacting is carried out at a temperature in the range of from ambient to about 60°C .

7. A method as claimed in claim 1, wherein said solid metal is in a particulate form having particle sizes in the range of from about 44 to 6000 microns.

8. A method as claimed in claim 1, wherein said solid metal is in a particulate form having particle sizes in the range of from about 44 to 600 microns.

9. A method as claimed in claim 1, wherein said solid metal is zinc.

10. A method as claimed in claim 1, wherein said cations of metal in a higher state of oxidation comprise cations of said desired metal, and said cations of said desired metal are reduced from said higher state of oxidation to said lower state of oxidation.

11. A method as claimed in claim 10, wherein cations of said desired metal are reduced to said lower state of oxidation and are deposited onto said solid metal, and said solid metal with deposited desired metal is removed from said organic liquid.

12. A method as claimed in claim 10, wherein said desired metal is chosen from the group consisting of copper, silver, gold, cobalt, nickel, tin and lead, cations of said desired metal are reduced to said lower state of oxidation and are deposited onto said solid metal, and said solid metal with deposited desired metal is removed from said organic liquid.

13. A method as claimed in claim 10, wherein cations of said desired metal are reduced to said lower state of oxidation and are deposited onto said solid metal, and said solid metal with said deposited desired metal is removed from said organic liquid, cations of said desired metal contained in said organic liquid are extracted from an aqueous cation- and anion-containing solution as cations of a desired metal with an organic liquid capable of extracting cations of said desired metal into said organic liquid wherein said organic liquid, said anion, cations of said desired metal and said added solid metal are chosen in combinations as follows:

Desired Organic Metal Solid Liquid Anion Cation Metal D2EHPA sulfate Cu2+ Zn, Cd, iron sulfate Ag+ Zn, Al, Cu Sulfate Co2+ Zn, Mn chloride Sn4+ Zn chloride Pb2+ Zn Aliquat TM sulfate Cu2+ Zn, Al, Cd 336 chloride Cu2+ Zn,Al,Cd sulfate Ni2+ Zn,iron cyanide Au3+ Zn LIX TM622 chloride Cu2+ Zn LIX TM64 chloride Cu2+ Zn, iron and wherein D2EHPA is di-2-ethylhexylphosphoric acid, Aliquat TM, 336 is tri- (C8C10) methyl ammonium chloride, LIX TM622 is a mixture of LIX TM 860 (5-dodecylsalicylaldoxime) with tridecanol, LIX TM864 is a mixture of LIX TM64N, which is 1 vol % LIX TM 63 (5, 8-diethyl-7-hydroxy-6-dodecanone oxime) LIX TM65N(2-hydroxyl-5-nonylbenzophenone oxime), and LIX TM860, and iron denotes low carbon steel or electrolytic iron.

14. A method as claimed in claim 1, wherein said cations of metals comprise cations of said desired metal together with cations of at least one secondary metal, said cations of said secondary metal being in said higher state of oxidation, cations of said desired metal and cations of said at least one secondary metal are extracted into said organic phase, cations of said desired metal are stripped from separated organic phase with a stripping solution capable of stripping cations of said desired metal from separated organic phase prior to said contacting with solid metal while substantially leaving cations of said at least one secondary metal in said organic phase, are cations of said at least one secondary metal are reduced from said higher state of oxidation to said lower state of oxidation in said contacting.

15. A method as claimed in claim 1, wherein said cations of metals comprise cations of said desired metal and said cations of at least one secondary metal, said cations of said secondary metal being in said higher state of oxidation, said cations of said desired metal and said cations of said at least one secondary metal are extracted into said organic phase, said cations of said at least one secondary metal are reduced from said higher state of oxidation to said lower state of oxidation in said contacting with said solid metal while substantially leaving said cations of desired metal in said organic phase to provide organic liquid having a reduced content of said cations of secondary metal and having left cations of said desired metal therein, and stripping said cations of said desired metal from said organic liquid having a reduced content of said cations of secondary metal with a stripping solution capable of stripping said cations of desired metal from said organic liquid prior to returning organic liquid having a reduced content of cations of said secondary metal to said mixing of step (1).

16. A method as claimed in claim 14, wherein said cations of secondary metal are reduced to said lower state of oxidation and are deposited onto said solid metal, and said solid metal with deposited secondary metal is removed from said organic liquid.

17. A method as claimed in claim 15, wherein said cations of secondary metal are reduced to said lower state of oxidation and are deposited onto said solid metal, and said solid metal with deposited secondary metal is removed from said organic liquid.

18. A method as claimed in claim 14, wherein said secondary metal is chosen from the group consisting of copper, silver, gold, cobalt, nickel, tin and lead, said cations of secondary metal are reduced to said lower state of oxidation and are deposited onto said solid metal, and said solid metal with said deposited secondary metal is removed from said organic liquid.

19. A method as claimed in claim 15, wherein said secondary metal is chosen from the group consisting of copper, silver, gold, cobalt, nickel, tin and lead, said cations of secondary metal are reduced to said lower state of oxidation and are deposited onto said solid metal, and said solid metal with said deposited secondary metal is removed from said organic liquid.

20. A method as claimed in claim 14, wherein said cations of secondary metal are reduced to said lower state of oxidation and are deposited onto said solid metal, and said solid metal with deposited secondary metal is removed from said organic liquid, said cations of secondary metal contained in said organic liquid are extracted from an aqueous cation- and anion-containing solution as cations of a secondary metal with an organic liquid capable of extracting cations of said secondary metal into said organic liquid, wherein said organic liquid, said anion, cations of said secondary metal and said added solid metal are chosen in combinations as follows:

Organic Metal Solid Liquid Anion cation Metal D2EHPA sulfate Cu2+ Zn,Cd,iron sulfate Ag+ Zn,Al,Cu sulfate Co2+ Zn+Mn chloride Sn4+ Zn chloride Pb2+ Zn Aliquat TM sulfate Cu2+ Zn,Al,Cd 336 chloride Cu2+ Zn,Al,Cd sulfate Ni2+ Zn, iron cyanide Au3+ Zn LIX TM622 chloride Cu2+ Zn LIX TM864 chloride Cu2+ Zn, iron and wherein D2EHPA is di-2-ethylhexylphosphoric acid, Aliquat TM
336 is tri- (C8C10) methylammonium chloride, LIX TM622 is a mixture of LIX TM860 (5-dodecylsalicylaldoxime) with tridecanol, LIX TM864 is a mixture of LIX TM64N, which is 1 vol % LIX TM63 (5, 8-diethyl-7-hydroxy-6-dodecanone oxime) in LIX TM65N (2-hydroxyl-5-nonylbenzophenone oxime), and LIX TM860, and iron denotes low carbon steel or electrolytic iron.

21. A method as claimed in claim 15, wherein said cations of secondary metal are reduced to said lower state of oxidation and are deposited onto said solid metal, and said solid metal with deposited secondary metal is removed from said organic liquid, said cations of secondary metal contained in said organic liquid are extracted from an aqueous cation- and anion-containing solution as cations of a secondary metal with an organic liquid capable of extracting cations of said secondary metal into said organic liquid, wherein said organic liquid, said anion, cations of said secondary metal and said added solid metal are chosen in combinations as follows:

Secondary Organic Metal Solid Liquid Anion Cation Metal D2EHPA sulfate Cu2+ Zn, Cd, iron sulfate Ag+ Zn, Al, Cu sulfate Co2+ Zn,Mn chloride Sn4+ Zn chloride Pb2+ Zn Aliquat TM sulfate Cu2+ Zn,Al,Cd 336 chloride Cu2+ Zn,Al,Cd sulfate Ni2+ Zn, iron cyanide Au3+ Zn LIX TM622 chloride Cu2+ Zn LIX TM864 chloride Cu2+ Zn and wherein D2EHPA is di-2-ethylhexylphosphoric acid, Aliquat TM
336 is tri- (C8C10) methylammonium chloride, LIX TM622 is a mixture of LIX TM860 (5-dodecylcalicylaldoxime) with tridecanol, LIX TM864 is a mixture of LIX TM64N, which is 1 vol % LIX TM63 (5,8-diethyl-7-hydroxy-6-dodecanone oxime) in LIX TM65N (2-hydroxyl-5-nonylbenzophenone oxime) and LIX TM860 and iron denotes low carbon steel or electrolytic iron.

22. A method as claimed in claim 14, wherein said secondary metal is iron, at least a portion of said iron is reduced from the ferric state to the ferrous state, and said solid metal is chosen from the group consisting of Zn, Mn and Mg.

23. A method as claimed in claim 15, wherein said secondary metal is iron, at least a portion of said iron is reduced from the ferric state to the ferrous state, and said solid metal is chosen from the group consisting of Zn, Mn and Mg.

24. A method as claimed in claim 14, wherein said organic liquid is chosen from the group consisting of di-2-ethylhexylphosphoric acid, mono-2-ethylhexylphosphoric acid and mixture thereof, PC88A (tradename) (mono-2 ethylhexyl ester of 2-ethylhexylphosphoric acid), Cyanex TM 272 (bis (2, 4, 4-trimethylpentyl) phosphinic acid) and LIX TM64N which is a mixture of LIX TM65N (2-hydroxy-5-nonylbenzophenone oxime) and 1% LIX TM63 (5, 8-diethyl-7-hydroxy-6-dodecanone oxime), said secondary metal is iron, said solid metal is zinc in particulate form having particle sizes in the range of from about 44 to 6000 microns, said contacting is carried out in the presence of nitrogen for a time sufficient to reduce at least a portion of said iron from the ferric state to the ferrous state and at a temperature in the range of from ambient to about 60°C, and said iron in the ferrous state contained in said organic phase is stripped from said organic phase with sulfuric acid solution containing sulfuric acid in the range of about 20 to 100 g/L with the formation of organic liquid having a reduced content of iron.

25. A method as claimed in claim 15, wherein said organic liquid is chosen from the group consisting of di-2-ethylhexylphosphoric acid, mono-2-ethylhexylphosphoric acid and mixture thereof, PC88A (tradename) (mono-2 ethylhexyl ester of 2-ethylhexyl phosphoric acid), Cyanex TM 272 (bis (2, 4, 4-trimethylpentyl) phosphinic acid) and LIX TM64N which is a mixture of LIX TM65N (2-hydroxy-5-nonylbenzophenone oxime) and 1 % LIX TM63 (5, 8-diethyl-7-hydroxy-6-dodecanone oxime), said secondary metal is iron, said solid metal is zinc in particulate form having particle sizes in the range of from about 44 to 6000 microns, said contacting is carried out in the presence of nitrogen for a time sufficient to reduce at least a portion of said iron from the ferric state to the ferrous state and at a temperature in the range of from ambient to about 60°C, and said iron in the ferrous state contained in said organic phase is stripped from said organic phase with sulfuric acid solution containing sulfuric acid in the range of about 20 to 100 g/L with the formation of organic liquid having a reduced content of iron.

26. A method as claimed in claim 14, wherein said secondary metal is iron, at least a portion of said iron is reduced from the ferric state to the ferrous state, said solid metal is zinc, said iron in the ferrous state contained in said organic phase is stripped from said organic phase with a stripping solution capable of stripping iron in the ferrous state from said organic phase with the formation of organic liquid having a reduced content of iron, and said contacting and said stripping of ferrous iron are carried out simultaneously.

27. A method as claimed in claim 15, wherein said secondary metal is iron, at least a portion of said iron is reduced from the ferric state to the ferrous state, said solid metal is zinc, said iron in the ferrous state contained in said organic phase is stripped from said organic phase with a stripping solution capable of stripping iron in the ferrous state from said organic phase with the formation of organic liquid having a reduced content of iron, and said contacting and said stripping of ferrous iron are carried out simultaneously.

28. A method as claimed in claim 14, wherein said desired metal is indium, said organic liquid is chosen from the group consisting of di-2-ethylhexylphosphoric acid, mono-2-ethylhexylphosphoric acid and mixtures thereof said secondary metal is iron, said indium is stripped from said organic phase with dilute hydrochloric acid, said solid metal is activated zinc in particulate form having particle sizes in the range of from about 44 to 600 microns, said contacting is carried out in the presence of nitrogen for a time sufficient to reduce at least a portion of said iron from the ferric state to the ferrous state and at a temperature in the range of from ambient to about 60°C, said iron in the ferrous state in said organic phase is stripped with sulfuric acid solution containing sulfuric acid in the range of about 20 to 100 g/L with the formation of organic liquid having a reduced content of iron;
and said contacting and the stripping of ferrous are carried out simultaneously.

29. A method as claimed in claim 10, wherein said desired metal is cerium.