Method for effecting solvent extraction of metal ions using hydrocarbon soluble aminomethylene phosphonic acid compounds

Solvent extraction of one or more metal ions from an aqueous solution in the presence of hydrocarbon-soluble aminomethylenephosphonic acid derivatives.

FIELD OF THE INVENTION
 The present invention relates to the use of hydrocarbon-soluble
 aminomethylenephosphonic acid derivatives comprising the structural
 element of the formula I
 ##STR1##
 where R.sup.1 and R.sup.2 are hydrogen, C.sub.1 -C.sub.30 -alkyl which can
 additionally bear up to 15 hydroxyl groups and/or be interrupted by up to
 14 non-adjacent oxygen atoms, C.sub.2 -C.sub.30 -alkenyl, C.sub.7
 -C.sub.18 -aralkyl or C.sub.6 -C.sub.14 -aryl which can be substituted by
 up to three C.sub.1 -C.sub.12 -alkyl groups, C.sub.1 -C.sub.12 -alkoxy
 groups, halogen atoms, cyano groups, hydroxyl groups or C.sub.1 -C.sub.4
 -alkoxycarbonyl groups, for the solvent extraction of one or more metal
 ions from the group consisting of lithium, sodium, potassium, rubidium,
 cesium, francium, beryllium, magnesium, calcium, strontium, barium,
 radium, scandium, yttrium, lanthanum, cerium, praseodymium, neodymium,
 promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium,
 erbium, thulium, ytterbium, lutetium, actinium, thorium, protactinium,
 neptunium, plutonium, americium, curium, berkelium, californium,
 einsteinium, fermium, mendelevium, nobelium, lawrencium, titanium,
 zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum,
 tungsten, manganese, technetium, rhenium, ruthenium, osmium, cobalt,
 rhodium, iridium, nickel, platinum, copper, silver, gold, zinc, cadmium,
 mercury, aluminum, gallium, thallium, germanium, tin, lead, arsenic and
 polonium from aqueous solutions.
 The invention also relates to the use of these hydrocarbon-soluble
 aminomethylenephosphonic acid derivatives for selectively separating one
 or more of the above metal ions from one another by solvent extraction.
 DESCRIPTION OF THE BACKGROUND
 The removal of undesired accompanying metals from aqueous solutions and the
 separation of metals is particularly important in hydrometallurgical
 nonferrous metal production, eg. in the winning of copper, zinc, noble
 metals or other special metals. Solutions of desired metals are frequently
 obtained from ores by digestion or leaching with aqueous, usually acid
 systems. The interfering or accompanying metals have to be removed from
 these solutions and separated from one another. In addition, the work-up
 of metal-containing wastes or residues (eg. flue dusts or precipitation
 sludges from wastewater treatment) and the recycling of used metal
 products (eg. catalysts) nowadays play an ever more important role in the
 provision of aqueous solutions of desired metals. Regardless of the origin
 of the metal salt solutions, it is always necessary to remove interfering
 elements from these solutions of desired metals and to separate the metals
 into individual fractions so that pure metals can be isolated. Apart from
 improving the quality of the desired metals, recovery of metals and
 reducing contamination of landfill areas is sought in the waste and
 residue processing sector for economic and ecological reasons.
 The solvent extraction of iron ions is known in the literature. Thus, DE-A
 38 01 430 (1) describes the use of a mixture comprising a primary amine
 and an alkylphosphonic monoester such as mono-2-ethylhexyl
 2-ethylhexylphosphonate for the removal of iron(III) ions from acid zinc
 salt solutions by solvent extraction.
 Furthermore, JP-A 1985/077936 (2) discloses that aminomethylenephosphonic
 acid derivatives are suitable for the solvent extraction of uranium,
 antimony or bismuth and of indium.
 U.S. Pat. No. 4,741,831 (3) relates to a process for separating metals such
 as iron, cobalt, copper, vanadium, cadmium, nickel, zinc, lead or aluminum
 from aqueous solutions using water-soluble polymeric complexing agents,
 for example polyethyleneiminephosphonates. The metal complex is
 subsequently separated off by dialysis or ultrafiltration by means of
 membranes.
 WO-A 96/00309 (4) describes the solvent extraction of iron ions from
 aqueous solutions, particularly from solutions of zinc or copper, by means
 of the present hydrocarbon-soluble aminomethylenephosphonic acid
 derivatives.
 In the reference Proc. Symp. Solvent Extr. (1995) 59-60 (5), Y. Baba, Y.
 Kawano and J. Shibata describe the separation of palladium from chloride
 solutions by means of di (2-ethylhexyl) aminomethylenephosphonic acid.
 However, the above processes of the prior art still have disadvantages.
 They are mostly not efficient enough and are too uneconomical. In
 particular, the selectivity of the separation of the interfering metals
 from the desired metals and the loading capacity of the complexing agents
 used are still in need of improvement.
 SUMMARY OF THE INVENTION
 It is an object of the present invention to find an improved system for the
 solvent extraction of metal ions from aqueous solutions which no longer
 has the disadvantages of the prior art.
 We have found that this object is achieved by the use as defined in the
 introduction of the hydrocarbon-soluble aminomethylenephosphonic acid
 derivatives having the structural element I.
 Preferably, use is made of hydrocarbon-soluble aminomethylenephosphonic
 acid derivatives comprising the structural element of the formula Ia
 ##STR2##
 For the purpose described, particular preference is given to
 hydrocarbon-soluble aminomethylenephosphonic acid derivatives of the
 general formula II
 ##STR3##
 where
 R.sup.3 to R.sup.6 are each hydrogen, C.sub.1 -C.sub.30 -alkyl which can
 additionally bear up to 15 hydroxyl groups and/or be interrupted by up to
 14 non-adjacent oxygen atoms, C.sub.2 -C.sub.30 -alkenyl, C.sub.7
 -C.sub.18 -aralkyl, C.sub.6 -C.sub.14 -aryl which can be substituted by up
 to three C.sub.1 -C.sub.12 -alkyl groups, C.sub.1 -C.sub.12 -alkoxy
 groups, halogen atoms, cyano groups, hydroxyl groups or C.sub.1 -C.sub.4
 -alkoxycarbonyl groups, or are each a group of the formula --CR.sup.1
 R.sup.2 --PO.sub.3 H.sub.2, --CH.sub.2 --COOH or --CH.sub.2
 --CH(OH)--R.sup.1, where at least one of the radicals R.sup.3 to R.sup.6
 is the group --CR.sup.1 R.sup.2 --PO.sub.3 H.sub.2 and at least a further
 one of these radicals is C.sub.6 -C.sub.30 -alkyl, C.sub.6 -C.sub.30
 -alkenyl, C.sub.7 -C.sub.18 -aralkyl, unsubstituted or substituted C.sub.6
 -C.sub.14 -aryl or the group --CH.sub.2 --CH(OH)--R.sup.9, where R.sup.9
 is C.sub.6 -C.sub.30 -alkyl, C.sub.6 -C.sub.30 -alkenyl, C.sub.7 -C.sub.18
 -aralkyl or unsubstituted or substituted C.sub.6 -C.sub.14 -aryl, and
 where R.sup.1 and R.sup.2 are as defined above,
 A is a C.sub.1 -C.sub.12 -alkylene group which can additionally bear as
 substituents up to three C.sub.1 -C.sub.30 -alkyl groups, C.sub.2
 -C.sub.30 -alkenyl groups, C.sub.7 -C.sub.18 -aralkyl groups or C.sub.6
 -C.sub.14 -aryl groups which can in turn be substituted by up to three
 C.sub.1 -C.sub.12 -alkyl groups, C.sub.1 -C.sub.12 -alkoxy groups, halogen
 atoms, cyano groups, hydroxyl groups or C.sub.1 -C.sub.4 -alkoxycarbonyl
 groups, where, if a plurality of groups A are present, these can be
 identical or different, and
 p is a number from 0 to 30,000.
 The compounds II can be in the form of monomers (p=0), oligomers or
 polymers.
 Suitable straight-chain or branched alkyl radicals as R.sup.1 to R.sup.9
 and as substituents on aryl groups, which are mentioned as C.sub.1
 -C.sub.30 -, C.sub.6 -C.sub.30 - or C.sub.1 -C.sub.12 -alkyl radicals,
 are, for example, methyl, ethyl, n-propyl, iso-propyl-, n-butyl,
 iso-butyl, sec-butyl, tert-butyl, n-amyl, iso-amyl, sec-amyl, tert-amyl,
 neopentyl, n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, iso-nonyl,
 n-decyl, n-undecyl, n-dodecyl, n-tridecyl, iso-tridecyl, n-tetradecyl,
 n-pentadecyl, n-hexadecyl, n-heptadecyl, n-octadecyl and n-eicosyl.
 Suitable alkyl radicals additionally bearing up to 15, in particular up to
 10, especially up to 5, hydroxyl groups and/or interrupted by up to 14, in
 particular by up to 9, especially by up to 4, non-adjacent oxygen atoms
 are, for example, corresponding polyoxyalkylene chains, in particular
 polyoxyethylene chains, whose terminal hydroxyl groups can be etherified
 by alkyl radicals, for example groups of the formula --CH.sub.2 CH.sub.2
 --OH, --CH.sub.2 CH.sub.2 --O--CH.sub.3, --CH.sub.2 CH.sub.2 --O--CH.sub.2
 CH.sub.2 --OH, --CH.sub.2 CH.sub.2 --O--CH.sub.2 CH.sub.2 --O--CH.sub.3,
 --CH.sub.2 CH.sub.2 CH.sub.2 --OH, --CH.sub.2 CH.sub.2 CH.sub.2
 --O--CH.sub.2 CH.sub.3, --CH.sub.2 CH.sub.2 --O--CH.sub.2 CH.sub.2
 --O--CH.sub.2 CH.sub.2 --OH or --CH.sub.2 CH.sub.2 --O--CH.sub.2 CH.sub.2
 --O--CH.sub.2 CH.sub.2 --O--CH.sub.2 CH.sub.2 --OH.
 Among these, preferred radicals as R.sup.1 and R.sup.2 and as substituents
 on aryl groups are in general lower alkyl radicals, in particular C.sub.1
 -C.sub.12 -alkyl radicals, but especially C.sub.1 -C.sub.4 -alkyl
 radicals, in particular ethyl and methyl.
 Particularly suitable long-chain C.sub.6 -C.sub.30 -alkyl radicals R.sup.3
 to R.sup.9 are C.sub.8 -C.sub.20 -alkyl radicals. Here, radicals having a
 low degree of ranching, ie. having up to 5 methyl or ethyl side chains,
 are often particularly effective.
 Suitable straight-chain or branched C.sub.2 -C.sub.30 - or C.sub.6
 -C.sub.30 -alkenyl radicals as R.sup.1 to R.sup.9 are, for example, vinyl,
 allyl, methallyl and but-2-enyl and also, as long-chain radicals, oleyl,
 linoleyl and linolenyl.
 Suitable C.sub.7 -C.sub.18 -aralkyl radicals as R.sup.1 to R.sup.10 are,
 for example, naphthylmethyl, diphenylmethyl or methylbenzyl, but
 particularly C.sub.7 -C.sub.18 -phenylalkyl such as 1-phenylethyl,
 2-phenylethyl, 1-phenylpropyl, 2-phenylpropyl, 3-phenylpropyl,
 2-phenylprop-2-yl, 4-phenylbutyl, 2,2-dimethyl-2-phenylethyl,
 5-phenylamyl, 10-phenyldecyl, 12-phenyldodecyl or especially benzyl.
 Suitable C.sub.6 -C.sub.14 -aryl radicals as R.sup.1 to R.sup.10 are, for
 example, biphenyl, naphthyl, anthryl and especially phenyl, which can each
 be substituted as indicated. If such substituents are present on phenyl
 rings, the preferred degree of substitution is 2 or in particular 1.
 Monosubstituted phenyl radicals are substituted in the ortho, meta or
 preferably para positions, disubstituted phenyl radicals frequently have a
 2,4 substitution pattern and trisubstituted phenyl radicals often have a
 2,4,6 substitution pattern. If two or three substituents are present,
 these can be identical or different.
 Typical substituents on the aryl radicals, in particular on the phenyl
 rings, are methyl groups (o-, m-, p-tolyl, 2,4-dimethylphenyl, mesityl),
 methoxy groups, methoxycarbonyl and ethoxycarbonyl groups.
 Besides methoxy, further suitable straight-chain or branched C.sub.1
 -C.sub.12 -alkoxy groups, in particular as substituents on the phenyl
 ring, are especially C.sub.2 -C.sub.4 -alkoxy groups such as ethoxy,
 n-propoxy, iso-propoxy, n-butoxy, iso-butoxy, sec-butoxy and tert-butoxy,
 but also n-pentoxy, n-hexoxy, iso-hexoxy, n-heptoxy, iso-heptoxy,
 n-octoxy, 2-ethylhexoxy, iso-octoxy, n-nonoxy, n-decoxy, n-undecoxy and
 n-dodecoxy.
 For the purposes of the present invention, halogen atoms are fluorine,
 iodine, but especially bromine and in particular chlorine.
 Groups of the formula --CH.sub.2 --CH(OH)--R.sup.9 are derived, for
 example, from long-chain epoxidized .alpha.-olefins such as
 1,2-epoxyhexane, 1,2-epoxyoctane, 1,2-epoxydecane, 1,2-epoxydodecane,
 1,2-epoxytetradecane, 1,2-epoxyhexadecane or 1,2-epoxyoctadecane or from
 styrene oxide.
 The bridge A is preferably a C.sub.2 -C.sub.8 -alkylene group, in
 particular a C.sub.3 -C.sub.6 -alkylene group. A can be branched or
 preferably straight-chain, ie. have a polymethylene structure. Typical
 examples of A are methylene, 1,2-ethylene, 1,2-propylene, 1,3-propylene,
 dimethylmethylene, ethylmethylene, 1,2-butylene, 1,3-butylene,
 2,3-butylene, 1,4-butylene, pentamethylene, hexamethylene and
 octamethylene.
 If a plurality of groups A are present, these can also be different, eg.
 the group of the formula
 ##STR4##
 can be present as structural element.
 If A is substituted by the radicals indicated, these substituents are as
 defined above for R.sup.1 to R.sup.6.
 The degree of oligomerization or polymerization p is, in the case of
 oligomers, preferably from 0 to 20, in particular from 0 to 5, especially
 0 or 1, and in the case of polymers is preferably from 20 to 30,000, in
 particular from 20 to 5000, especially from 20 to 100.
 Typical examples of monomeric compounds II (p=0) are structures of the
 following types:
EQU (R.sup.7).sub.2 N--CH.sub.2 --PO.sub.3 H.sub.2
EQU H.sub.2 O.sub.3 P--CH.sub.2 --NR.sup.7 --CH.sub.2 --PO.sub.3 H.sub.2.
 Typical examples of oligomeric compounds II (usually p=1) are structures of
 the following types:
 ##STR5##
 In these formulae, R.sup.7 is C.sub.6 -C.sub.30 -alkyl or C.sub.6 -C.sub.30
 -alkenyl, n is a number from 2 to 6 and R.sup.1 is as defined above.
 Typical examples of polymeric hydrocarbon-soluble aminomethylenephosphonic
 acid derivatives for the purposes of the present invention are
 polyalkylenepolyamines and polyalkylenepolyamides containing at least one
 group of the formula --CR.sup.1 R.sup.2 --PO.sub.3 H.sub.2 and at least
 one further C.sub.6 -C.sub.30 -alkyl radical, C.sub.6 -C.sub.30 -alkenyl
 radical, C.sub.7 -C.sub.18 -aralkyl radical, unsubstituted or substituted
 C.sub.6 -C.sub.14 -aryl radical or a group of the formula --CH.sub.2
 --CH(OH)--R.sup.9, where R.sup.1, R.sup.2 and R.sup.9 are as defined
 above, in particular correspondingly substituted polyethyleneimines,
 polyvinylamines and polyacrylamides, for example of the structure:
 ##STR6##
 In these formulae, R.sup.3 and p are as defined above.
 The polyalkylenepolyamines described can have linear or branched
 structures. The bridges between the nitrogen atoms in the main polymer
 chain are preferably ethylene or propylene groups, but also methylene,
 butylene, pentylene or hexylene groups, or mixtures thereof.
 To slightly modify the properties of the polyalkylenepolyamines described
 for the purposes of optimizing them for the application according to the
 present invention, these polymers can, to an appropriate degree, be
 functionalized with suitable end groups, crosslinked or made available as
 copolymers or graft polymers.
 To introduce suitable end groups, the polyalkylenepolyamines can be reacted
 with C.sub.1 -C.sub.30 -alkyl halides, eg. methyl iodide, ethyl chloride
 or ethyl bromide, with benzyl halides, with halohydrins, eg. chlorohydrin,
 with polyalkylene oxides, with epoxidized .alpha.--C.sub.3 -C.sub.30
 -olefins, with isocyanates or with C.sub.1 -C.sub.30 -monocarboxylic
 acids.
 Suitable crosslinkers are, for example, epihalohydrins, eg.
 epichlorohydrin, .alpha.,.omega.-bis(epoxides), .alpha.,.omega.- or
 vicinal dichloroalkanes, eg. 1,2-dichloroethane, C.sub.2 -C.sub.30
 -dicarboxylic acids, eg. adipic acid, and diisocyanates, eg. hexamethylene
 diisocyanate.
 Suitable polyvinylamine copolymers comprise, for example, as other
 monoethylenically unsaturated monomers, vinyl esters of saturated
 carboxylic acids having from 1 to 6 carbon atoms, eg. vinyl acetate, vinyl
 propionate and vinyl butyrate, monoethylenically unsaturated C.sub.3
 -C.sub.8 -carboxylic acids such as acrylic acid, methacrylic acid,
 dimethylacrylic acid, ethacrylic acid, crotonic acid, vinylacetic acid,
 allylacetic acid, maleic acid, fumaric acid, citraconic acid and itaconic
 acid and also their esters, anhydrides, amides and nitriles. Anhydrides
 which are preferably used are, for example, maleic anhydride, citraconic
 anhydride and itaconic anhydride. Suitable esters are derived, for
 example, from alcohols having from 1 to 6 carbon atoms, for example methyl
 acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate,
 isobutyl acrylate and hexyl acrylate, or from glycols or polyalkylene
 glycols, where in each case only one OH group of the glycol or polyglycol
 is esterified with a monoethylenically unsaturated carboxylic acid, eg.
 hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate,
 hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl
 methacrylate and also acrylic monoesters of polyalkylene glycols having a
 molecular weight of up to 10,000. Also suitable are esters of the above
 carboxylic acids with aminoalcohols, eg. dimethylaminoethyl acrylate,
 dimethylaminoethyl methacrylate, diethylaminoethyl acrylate,
 diethylaminoethyl methacrylate, dimethylaminopropyl acrylate and
 dimethylaminopropyl methacrylate. Suitable amides are, for example,
 acrylamides and methacrylamides such as N-alkylamides and
 N,N-dialkylamides having alkyl radicals of from 1 to 6 carbon atoms, eg.
 N-methylacrylamide, N,N-dimethylacrylamide, N-methylmethacrylamide,
 N-ethylacrylamide, N-propylacrylamide and tert-butylacrylamide and also
 basic amides such as dimethylaminoethylacrylamide,
 dimethylaminoethylmethacrylamide, diethylaminoethylmethacrylamide,
 diethylaminoethylacrylamide, dimethylaminopropylacrylamide,
 diethylaminopropylacrylamide, diethylaminopropylmethacrylamide and
 dimethylaminopropylmethacrylamide. The basic acrylates and acrylamides can
 be used in the form of the free bases, the salts with mineral acids or
 carboxylic acids or else in quaternized form. Also suitable as comonomers
 are acrylonitrile, methacrylonitrile, N-vinylpyrrolidone,
 N-vinylcaprolactam, N-vinylimidazole and also substituted N-imidazoles
 such as N-vinyl-2-methylimidazole and N-vinyl-2-ethylimidazole and
 N-vinylimidazoline and substituted N-vinylimidazolines, eg.
 N-vinyl-2-methylimidazoline. Apart from the monomers mentioned, it is also
 possible to use monomers containing sulfo groups, for example
 vinylsulfonic acid, allylsulfonic acid, styrenesulfonic acid and
 3-sulfopropyl esters of acrylic acid as other monoethylenically
 unsaturated monomers.
 The copolymers specified have K values of from 10 to 300, preferably from
 20 to 200. The K values are determined by the method of H. Fikentscher in
 5% strength aqueous sodium chloride solution at pH 7, 25.degree. C. and a
 polymer concentration of 0.1% by weight.
 It is also possible to use polyethyleneimines grafted onto polyvinylamines.
 For the use according to the present invention of the compounds II and the
 specified polyalkylenepolyamines the presence of at least one
 methylenephosphonic acid group --CR.sup.1 R.sup.2 --PO.sub.3 H.sub.2 and
 at least one hydrophobic radical, ie. an aromatic group or preferably a
 saturated or unsaturated long-chain aliphatic radical (C.sub.6 -C.sub.30
 -alk(en)yl), is of decisive importance. The methylenephosphonic acid
 groups are essentially responsible for the selective complexation
 (extraction) of the metal ions and the hydrophobic radicals make the
 compounds soluble in hydrocarbons.
 The hydrocarbon-soluble aminomethylenephosphonic acid derivatives to be
 used according to the present invention can be prepared by customary
 methods. Compounds having R.sup.1 =R.sup.2 =hydrogen can be obtained most
 simply by reacting appropriate amines with formaldehyde (or
 paraformaldehyde) and phosphorous acid with acid catalysis (eg. inorganic
 acids or mineral acids such as sulfuric acid or hydrochloric acid,
 sulfonic acids such as p-toluenesulfonic acid or methanesulfonic acid or
 carboxylic acids such as a mixture of acetic acid and acetic anhydride).
 Such reactions of amines with formaldehyde and phosphorous acid are usually
 carried out at from 0 to 150.degree. C., in particular from 50 to
 120.degree. C., especially from 80 to 110.degree. C. Amine, formaldehyde
 and phosphorous acid are advantageously used in a molar ratio of
 1:(2-6):(1-4) based on one N--H bond.
 Alternatively, these compounds can also be obtained by hydrolysis of the
 corresponding phosphonic esters, obtainable by reaction with phosphites in
 place of phosphorous acid.
 Another synthetic route which is of particular interest for compounds
 having R.sup.1, R.sup.2.noteq.H starts out from aldehydes (eg. of the
 formula R.sup.1 --CHO) or ketones (eg. of the formula R.sup.1
 --CO--R.sup.2) and the appropriate primary amines which are reacted to
 form imines onto which phosphorous acid is then added.
 The term solvent extraction customarily refers to extraction processes in
 which two liquid phases which are sparingly miscible or immiscible with
 one another are brought into intimate contact and a transfer of one or
 more components, here metal ions, from one phase into the other takes
 place. In this process, an equilibrium dependent on various external
 parameters is usually established. Important parameters in this context
 are the residence time (contact time), the temperature, the concentration
 (composition of the mixture) and the pH.
 The hydrocarbon-soluble aminomethylenephosphonic acid derivatives described
 are particularly suitable for the solvent extraction of one or more metal
 ions from the group consisting of magnesium, vanadium, chromium,
 molybdenum, manganese, cobalt, nickel, copper, zinc, cadmium, aluminum,
 gallium, tin and arsenic from aqueous solutions.
 In particular, the hydrocarbon-soluble aminomethylenephosphonic acid
 derivatives described serve for the separation of one or more metal ions
 from the group consisting of magnesium, vanadium, chromium, molybdenum,
 manganese, iron, cobalt, nickel, copper, zinc, cadmium, aluminum, gallium,
 tin, arsenic and bismuth in aqueous solution from one or more other metal
 ions from the same group by solvent extraction, with the separations of
 iron ions from zinc ions and iron ions from copper ions being excepted.
 The order of extraction of the individual metal ions or groups of metal
 ions from the others of the specified group is dependent on the pH of the
 aqueous solution. One type of metal ion is separated from another by the
 present process if its pH.sub.1/2 value is greater than the pH.sub.1/2
 value of the other type of ion. Details may be found below in the
 experimental examples.
 The aqueous solutions of the metal ions used for the separation or removal
 are generally acid solutions which usually have pH values of from &lt;0 to
 about 7. The metal contents of the aqueous solutions used can vary
 greatly. The metal salt solutions usually contain from 0.1 ppm to 80% by
 weight, usually from 1 ppm to 50% by weight, particularly from 5 ppm to
 30% by weight, of metal. The solutions additionally contain up to 800 g/l
 of free acids, in particular sulfuric acid, hydrochloric acid, phosphoric
 acid, nitric acid and/or hydrofluoric acid), preferably from 1 to 400 g/l
 of free acid. Basic, eg. ammoniacal, solutions can also be used under some
 circumstances.
 In the extraction, one or more metals are together transferred as a
 function of the pH into the organic solutions comprising
 aminomethylenephosphonic acid derivatives and, if desired, modifiers.
 Apart from the pH, the parameters contact time, temperature and
 concentration of extractants, and of modifier if used, play a role in the
 extraction.
 The contact time is usually from 1 to 90 minutes, in particular from 5 to
 45 minutes. The temperature during the extraction is normally in the range
 from 15 to 90.degree. C., in particular from 20 to 60.degree. C.
 For the purposes of the present invention, organic solutions of the
 aminomethylenephosphonic acid derivatives described are used. Suitable
 organic solvents are, for example, aliphatic, cycloaliphatic or aromatic
 hydrocarbons or mixtures of these having a high boiling point, halogenated
 hydrocarbons, ketones or ethers having a high boiling point or else
 mixtures of such compounds. Preference is given to using petroleum
 hydrocarbons such as kerosene.
 The monomeric and oligomeric aminomethylenephosphonic acid derivatives
 described generally have a concentration in the specified organic solvents
 of from 0.01 to 8 mol/l, in particular from 0.05 to 3 mol/l, especially
 from 0.1 to 1 mol/l. Polymeric aminomethylenephosphonic acid derivatives
 such as the corresponding polyethyleneimine or polyvinylamine derivatives
 generally have concentrations of from 0.5 to 800 g/l, in particular from 5
 to 600 g/l, especially from 50 to 300 g/l.
 Finally, the mass ratios of organic and aqueous phases used also play a
 role, with the ratios of organic phase to aqueous phase generally being
 from 1:20 to 20:1, preferably from 1:10 to 10:1, in particular from 1:5 to
 5:1.
 The solvent extraction of the present invention can be carried out on a
 laboratory scale or on an industrial scale, batchwise or continuously (eg.
 in a mixer settler plant or in pulse columns).
 The separation of the metals extracted from the organic solutions and the
 recovery of the extractants (complexing agents) used and any further
 auxiliaries concomitantly used can be carried out by conventional methods.
 In addition to the actual extractants (complexing agents), "modifiers" are
 usually used in the solvent extraction. The term "modifiers" refers to
 compounds which either effect a better or more rapid phase separation,
 accelerate the transfer of the components to be extracted from one phase
 to the other or improve the solubility of the metal complex formed in the
 organic diluent phase.
 Modifiers known from the prior art are, for example, straight-chain or
 branched long-chain alcohols having from 10 to 22 carbon atoms, for
 example isodecanol, isotridecanol or hexadecanol, phenols or esters of
 such alcohols and phenols with lower carboxylic acids or relatively
 long-chain fatty acids. Furthermore, it is possible to use alkoxylated
 alcohols and alkoxylated amines as are described as modifiers in (4).
 The modifiers are used together with the extractant (complexing agent) in a
 weight ratio of extractant to modifier of generally from 99.5:0.5 to
 0.5:99.5, preferably from 95:5 to 5:95, in particular from 80:20 to 20:80.
 Mixtures of various extractants and various types of modifier can also be
 used. They are used in the abovementioned organic solvents.
 The hydrocarbon-soluble aminomethylenephosphonic acid derivatives used
 according to the present invention as extractants in the solvent
 extraction make it possible to selectively remove metal ions or separate
 them from one another to a high degree of efficiency. The loading capacity
 of the extractant used according to the present invention is above
 average.

Extraction
 [M].sub.feed [M].sub.org
 [M].sub.aq. efficiency
 Extractant pH Metal [%] [%] [%] [%]
 Ex. 23a Ex. 1 1.2 Ga 0.19 0.31 0.085 54
 Zn 0.30 0.001 0.29
 Ex. 23b A 1.2 Ga 0.19 0.009 0.18 4
 Zn 0.30 0.002 0.29
 Ex. 23c B 1.2 Ga 0.19 0.069 0.16 15
 Zn 0.30 0.003 0.29
 Ex. 24a Ex. 1 1.75 Ga 0.18 0.47 0.035 80
 Cu 0.29 &lt;0.001 0.28
 Ex. 24b A 1.75 Ga 0.18 0.25 0.10 44
 Cu 0.29 &lt;0.001 0.28
 Ex. 24c B 1.75 Ga 0.18 0.47 0.035 80
 Cu 0.29 &lt;0.001 0.28
 In the Ga/Zn separation (at pH 1.2), the extractant used according to the
 present invention from Example 1 is clearly superior to both commercially
 available extractants (A and B). In the case of the Ga/Cu separation (at
 pH 1.75), the extractant used according to the present invention is
 clearly superior to the commercial extractant A and has the same
 effectiveness as the commercial extractant B.
 Examples 25-26
 (Selective Separation of a Metal From a Mixture)
 The studies were carried out as pH-controlled, stirred batch tests. 200 ml
 of a synthetic aqueous solution (feed) containing four different metals in
 each case (Bi/Zn/Mn/Cu (Example 25) or Mo/Cu/Co/Ni (Example 26) and
 prepared from bismuth(III) oxide, zinc(II), manganese(II) and copper(II)
 sulfate or molybdenum(VI) oxide, cobalt(II), nickel(II) and copper(II)
 sulfate; these solutions additionally contained 100 g/l of free sulfuric
 acid (Example 25) or 200 g/l of free sulfuric acid (Example 26)) were
 mixed for 30 minutes at room temperature (20-25.degree. C.) with 50 ml of
 organic phase (composition: 10% of extractant, 15% of isodecanol, 75% of
 LK.sup.1)) at the pH values shown in Table 23. The phases were
 subsequently separated and the metal contents in the aqueous and organic
 phases were determined. For comparison, two commercial extractants
 (mono-2-ethylhexyl 2-ethylhexylphosphonate (A) and di(2-ethylhexyl)
 hydrogen phosphate (B)) were used. The individual results are shown in
 Table 23.
 TABLE 23

FNT .sup.4) Organic phase: 15% extractant (example 1), 15% isodecanol, diluent
 (lamp kerosene) Aqueous phase: 1.0 g/l As(V) Conditions: O/A=1
 TABLE 24
 As(V) Extraction
 pH As (V).sub.extr. (%)
 0.3 3.0
 0.5 6.7
 1.0 15.6
 1.2 19.6
 2.1 30.3
 2.5 30.6
 As(V) stripping is relatively easy in the presence of Fe(III).
 Fe(III) plays an important role on As(V) extraction from an acidic media
 with the extractant from example 1. Extraction of As(V) in the presence of
 about 20 g/l Fe(III) is 3 times higher than in the absence of this metal;
 As(III) extraction remains unaltered (see table 25).
 Example 28
 Extraction of As(V) and As(III) in the Presence of Fe (III) .sup.5)