NO811552L - PROCEDURE FOR AA REMOVING IRON (III) FROM Aqueous SOLUTIONS - Google Patents

Description

The present invention relates to hydrometallurgy.

More specifically, it concerns the extraction of metals from aqueous solutions by solvent extraction and subsequent treatment of the metal-rich solvent with sulfuric acid.

Removal of iron from aqueous solutions is necessary in many industrial processes. In, for example, leaching treatment of metal-containing ores or concentrates, iron is often dissolved together with the desired metal values and must be removed from the resulting solution before the extraction of the desired metal. Another example is the following: alum solutions (aluminium sulphate solutions) produced by the action of sulfuric acid on clay typically contain iron, and if this is removed, the alum solution can be used for the production of pure alumina for further use as a catalyst support material or in the production of aluminum metals .

In a further example, iron must be removed from certain waste streams due to regulations regarding pollution control.

Conventional practice is to precipitate iron by chemical means, which involves difficult solid-liquid separations and co-precipitations, with consequent loss of valuable constituents. Solvent extract. ion has been found to eliminate or reduce these problems.

The extraction of iron (III) from acidic aqueous sulphate solutions using water-immiscible organic solutions, containing either bis (2-ethylhexyl) hydrogen phosphate, hereinafter abbreviated to BEHP, or tri-n-octylphosphine oxide, in the the following abbreviated to TOPO, is well known: British patent no.

970,885; J. Inorg. Nucl.Chem. 33, 4, 1099-1118: U.S. patent no.

4,168,297; J.Inorg.Nucl.Chem.* 38, 7, 1347-1350 and BRD official publication; no. 26 45 130. However, if the iron(III)-enriched organic solution contains only BEHP, the iron cannot be completely removed with sulfuric acid. If the extraction solvent contains only TOPO, only approx. 25% of the total iron(III) in the aqueous solution is extracted into the organic phase. There is therefore a need for an extractant mixture which will extract most of the trivalent iron into the organic phase and enable the stripping of the trivalent iron from this phase with sulfuric acid. ;Brief description of the invention.;The present invention provides a method for removing iron(III) from an aqueous iron(III)-containing solution, and the method involves bringing said solution into contact with an extraction solvent, which solvent comprises an extraction agent and optionally a water-immiscible organic diluent, which extraction agent comprises a mixture of approx. 1-10 parts by volume of a suitable organophosphoric acid which has at least 6 carbon atoms, and approx. 1 part by volume of a tertiary (C4-C2q)-phosphine oxide; after which the liquid two-phase mixture is allowed to separate and the aqueous phase is separated from the organic iron(III)-enriched phase. ;The present invention also provides a method as described above with the further steps that the remaining iron(III)-enriched organic solution is brought into contact with an aqueous solution of sulfuric acid for stripping the trivalent iron into the aqueous acidic phase; the aqueous acidic phase containing water-soluble iron(III) salts is separated; and the thereby obtained organic phase is recovered for subsequent new use by extraction of another aqueous solution containing iron (III). ;Detailed description of the invention.;When carrying out the method according to the present invention, suitable extraction solvents and stripping solutions are prepared as follows: ;The extraction solvent can preferably be prepared;by mixing approx. 1-50 parts by volume extraction agent with approx. 99-50 parts by volume of a water-immiscible organic diluent, although pure extractant can be used. Said extractant consists of a mixture of an organophosphoric acid with at least 6 carbon atoms and a tertiary (C^-C^q)-phosphinoxide. Suitable organophosphoric acids are selected from alkyl, cycloalkyl, aryl, substituted aryl and aralkyl phosphoric acids. Representative examples include bis(n-hexyl) hydrogen phosphate, bis(n-heptyl) hydrogen phosphate, bis(n-octyl) hydrogen phosphate, bis (2-ethylhexyl) hydrogen phosphate, bis(n-hexadecyl) hydrogen phosphate, bis(n-octadecyl )-hydrogen phosphate, n-butyl (n-hexadecyl) hydrogen phosphate, methyl (n-hexyl)-hydrogen phosphate, n-butyl (2-ethylhexyl) hydrogen phosphate, n-octadecyl (2-ethylhexyl) hydrogen phosphate, diphenyl hydrogen phosphate, phenyl (2-ethyl -hexyl)hydrogenphosphate, n-dodecyl(p-tolyl)hydrogenphosphate, n-decyl-;(naphthyl)hydrogenphosphate, 2-ethylhexyl(p-octylphenyl)hydrogenphosphate, bis(p-octylphenyl)hydrogenphosphate, bis(benzyl)hydrogenphosphate fat, benzyl (2-ethylhexyl) hydrogen phosphate, benzyl (octadecyl) hydrogen phosphate, dicyclohexyl hydrogen phosphate, cyclohexyl (dodecyl) hydrogen phosphate, n-octyl dihydrogen phosphate, phenyl dihydrogen phosphate, benzyl dihydrogen phosphate, (p-chlorophenyl) dihydrogen phosphate, bis (2-ethyl-hexyl)-dihydrogen diphosphate, octyl trihydrogen diphosphate and the like. Any organophosphoric acid with at least 6 carbon atoms in the hydrocarbon chain, with a maximum molecular weight of approx. 600, is generally suitable. In the preferred embodiment, the organophosphoric acid is a dialkyl (C 8 -C 8 -hydrogen phosphate). The most preferred organophosphoric acid is bis(2-ethylhexyl) hydrogen phosphate (BEKP). Suitable tertiary phosphine oxides are selected from alkyl, α-hydroxy-cycloalkyl, cycloalkyl, aryl, substituted aryl, aralkyl, α-hydroxybenzyl phosphine oxides and bridged phosphine oxides. Representative examples include tri-n-butylphosphinoxide, triisobutylphosphinoxide, tri-n-pentylphosphinoxide, tri-n-hexylphosphinoxide, tri-n-heptylphosphinoxide, tri-n-octylphosphinoxide, tri-n-decylphosphinoxide, tri-n-dodecylphosphinoxide , tri-n-hexadecylphosphine oxide, tri-n-octadecylphosphine oxide, tri-n-eicosylphosphine oxide, di-n-octyl(methyl)phosphine oxide, di-n-octadecyl(ethyl)phosphine oxide, di-n-octyl(isobutyl )phosphine oxide, diethyl (n-octadecyl) phosphine oxide, di-n-decyl (n-butyl) phosphine oxide, diisobutyl (n-hexyl) phosphine oxide, di-n-butyl (cyclohexyl) phosphine oxide, dicyclohexyl (n-octyl) phosphine oxide, dicyclohexyl (methyl) phosphine oxide, dicyclo-octyl (ethyl) phosphine oxide, dicyclohexyl (benzyl) phosphine oxide, tricyclohexyl phosphine oxide, di-n-octyl (phenyl) phosphine oxide, di-n-hexyl (p-tolyl) phosphine oxide, diphenyl (ethyl) phosphine oxide, triphenylphosphine oxide, trinaphthylphosphine oxide, diphenyl(cyclohexyl)phosphine oxide, dicyclopentyl (p-tolyl)phosphine oxide, tribenzylphosphine oxide, tris(p-tolyl)phosphine oxide, tris(p-ethylphenyl)phosphine oxide, tri s(p-octyl-phenyl) phosphine oxide, tris(2,3-dimethylphenyl)phosphine oxide, tris(2,4-dimethylphenyl)rphosphine oxide, tris(2,5-dimethylphenyl)phosphine oxide, tris(3,4-dimethylphenyl)phosphine oxide, bis(p-tolyl)n-octylphosphinoxide, di-n-hexyl-(2,4-dimethylphenyl)phosphinoxide, tris(p-chloro-phenyl)phosphinoxide, bis(p-bromophenyl)n-hexylphosphinoxide, tris(3,5 -dimethylbenzyl)phosphinoxide, benzyl-bis(a-hydroxybenzyl)phosphinoxide, dicyclohexyl(a-hydroxybenzyl)phosphinoxide, cyclohexyl(1-hydroxy-cyclohexyl)phenylphosphinoxide, cyclopentyl(1-hydroxycyclopentyl)phenylphosphinoxide, benzyl(a-hydroxybenzyl)cyclohexylphosphinoxide, 1 -(4-heptyl)— 2,6-dihydroxy-1-phosphacyclohexane-1-oxide, 4-heptyIbis(α-hydroxylbenzyl)phosphine oxide, n-octylbis-(p-chlorophenyl)phosphine oxide, 9-octyl-9-phosphabicyclo- 3,3-nonane-9-oxide and the like. Any tertiary phosphine oxide with low solubility in water is generally suitable. The preferred tertiary phosphine oxide is tri-n-octyl phosphine oxide (TOPO). The extractant consists of approx. 1-10 parts by volume of organophosphoric acid, preferably approx. 1-3 volume parts, per volume fraction of the tertiary phosphine oxide. Generally, a number of different organic liquids which are immiscible with water can be used as diluents. Preferably, the diluent is an aliphatic or aromatic mineral oil distillate. The most preferred diluent is kerosene. Suitable diluents include, but are not limited to, benzene, toluene, xylene, kerosene, naphtha and the like.. In carrying out the method according to the invention, the iron(III)-containing aqueous solution is brought into contact with the extraction solvent, either chargewise, continuously co-current or continuously counter-current. The ratio between aqueous and organic phase should be chosen so that the trivalent iron is most effectively removed. Ratios of aqueous phase to organic phase from 1:20 to 20:1 are believed to be effective, although other ratios may prove effective depending on the particular separation. Phase contact is usually achieved in devices termed "mixer-settlers", although many other types of devices are available and suitable. In the mixer, one phase is dispersed in the other by stirring or another suitable method of agitation. The extraction solvent then forms a complex with iron(III), which goes to the organic phase of the liquid two-phase mixture. The dispersion then flows to the separation device, where the phases separate after standing. The extraction is usually carried out between 0 and 100°C, preferably between 20 and 70°C. After extraction, the aqueous solution is free of trivalent iron and ready for further treatment, for example aluminum oxide precipitation. The iron(III)-enriched extraction solvent flows into the stripping circuit, where approx. 0.05-20.0 parts by volume of a solution of a sulfuric acid, preferably 0.01-0.5 parts by volume, are brought into contact with one part by volume of the solvent. The trivalent iron goes to the aqueous phase in the form of a soluble salt of the sulfuric acid used. Phase contact can be achieved with mixing-separating devices or other suitable devices. Several mixing-separating devices, van- . usually approx.- 1-10 and preferably approx. 1-6, connected in series is normally required to achieve the desired degree of iron (III) stripping. Stripping is generally carried out between 0°C and 100°C, preferably at 20-70°C. The post-stripping iron (III)-free solvent is recycled to the extraction circuit for treatment of incoming iron (III)-containing aqueous solutions. Sulfuric acid from the stripping circuit containing the dissolved iron(III) salts can either be discarded or treated to remove iron, for example by electrolysis, and recycled to the stripping circuit. The preferred sulfuric acid contains at least 100 g of sulfuric acid per litres, preferably approx. 150-500 g per litres. Applications for which the method of the invention is suitable include, but are not limited to, extractions from aqueous solutions of cobalt, nickel, rare earth metals, uranium, vanadium, copper, alum, zinc and silver, to name but a few some.; The following examples will further illustrate the invention; and also indicate methods for evaluating the same. All parts and percentages are by weight, unless otherwise stated. ;Example 1.;An oxidized solution of alum containing iron (III)-sulphate corresponding to 1470 micrograms Fe +/ml is produced at a rate of 1000 ml/min. added to an extraction circuit consisting of four stages of mixing-separating devices. Here, at 40°C, continuously and in countercurrent, it is brought into contact with an extraction solvent containing 4.5% by volume BEHP, 3% by volume TOPO and 92.5% by volume kerosene, which is added at a rate of 500 ml per minute to achieve a volume ratio between aqueous phase and organic phase of 2:1. After the four extraction steps at this ratio, an aqueous alum solution containing approx. 5.0 micrograms Fe 3+/ml at a rate of approx. 1000 ml per minute. ;Example 2.;The iron-enriched, organic extraction solution medium from example 1, containing approx. 2955 micrograms of Fe 3+/ml, flows out of the extraction circuit at a rate of approx. 500 ml/min. ; and is fed to a stripping circuit. Here, at 40°C, in three countercurrent mixing-separation steps, it is brought into contact with a stripping solution consisting of sulfuric acid in water. The sulfuric acid solution, containing 200 g of sulfuric acid per liter of solution, is added at a rate of 100 ml/min., whereby a volume ratio between aqueous phase and organic phase is achieved. of 0.2. After the three stripping steps at this ratio, an acidic ;3+ ;stripping liquid containing 14,650 micrograms Fe /ml is obtained at a rate of approx. 100 ml/min. ;The stripped organic phase, containing approx. 25 micrograms of Fe 3+/ml, extracted and recycled at a rate of approx. 500 ml/min. to the extraction circuit in example 1, where it is used for the subsequent extraction of iron from the incoming ferrous alum solution. ;Examples 3- 5.;Iron-enriched organic solutions, each containing 3+ ;ca* 3 g Fe per litres, is produced by extraction of alum solutions containing sulfuric acid with the following extraction solvents

The iron-enriched solutions are then stripped by contact with aqueous sulfuric acid (2000 g/l) in an amount that gives a volume ratio between aqueous phase and organic phase of 0.2 at 40°C, for varying numbers of mixing-separation steps, and the iron (III) content in the organic stripping phase is measured. The results that will be achieved are shown below.

The above results illustrate that the presence of TOPO i

the iron-enriched solvent greatly facilitates the stripping of iron (III) therefrom.

Example 6.

An oxidized solution of alum containing ferric sulfate corresponding to 52 3 micrograms Fe 3+ /ml, which has a pH of 2.6 and contains 8.48% by weight alumina, is extracted at 24°C using a Burrell shaking with an equal volume of an extraction solvent consisting of 5% by volume TOPO and 95% by volume kerosene. The liquid two-phase mixture is allowed to stand until the phases have separated, and the aqueous phase is separated. Analysis of the aqueous phase shows that only 27.4% of the trivalent iron has been extracted into the organic phase.

Examples 7-14.

The procedure in example 6 is followed with the exception that the 5% by volume extractant used is a mixture of BEHP.

The percentage composition of TOPO in the extractant is varied from 0% to 50 vol%. The aqueous phase obtained after separation of the organic phase is analyzed with regard to Fe and aluminium, whereby the extraction coefficients and separation factors (S^) are determined. The results, see Table I, show that the optimal extractant composition for minimizing aluminum extraction while maintaining a high extraction of iron(III) is in the range of 40-50% by volume TOPO.

Example 15.

The procedure of Example 1 was followed in all material detail except that the extraction solvent now contains phenyl dihydrogen phosphate, tris(2-ethylhexyl)phosphine oxide and benzene, and essentially the same results are obtained.

Example 16.

The procedure in Example 1 is followed in all essential details with the exception that the extraction solvent now contains octyl trihydrogen diphosphate, tricyclohexylphosphine oxide and toluene, and substantially the same results are obtained.

Examples 17-19.

The procedure in example 1 is followed in all essential details, with the exception that instead of the sulfuric acid solution, solutions of hydrochloric acid, hydrofluoric acid and nitric acid respectively are now used, and essentially the same results are obtained. Example 20.

An aqueous leaching phase that had a concentration of

35 g/l Cu<2+>, 5 g/l Fe3+, 10 g/l H2S04, 11 g/l Al<3+>and 2 g/l Cl and a pH of 1.5 are brought into contact with. an extraction solvent at 24°C for five minutes in withdrawn, measured volumes (aliquots) with a volume ratio (A/O) between aqueous phase and organic phase of 5.2 and.l. After separation, the pH of the aqueous phase is adjusted to 1.5 with NaOH, and the contact treatment is repeated until a constant equilibrium pH of 1.5 is achieved. Test data and results are given in Table II.

Example 21.

The procedure in example 20 is followed in all essential details with the exception that a different extraction solvent is used. Test data and results are given in Table II.

Example 22.

An aqueous leaching liquid phase with a concentration of

15.2 g/l of Fe<3+>, 22 g/l Cu<2+>, 3 g/l Ag<+>, 20 g/l H2S04 and a pH of 1.5 are brought into contact with an extraction solution -agent at 50°C for ten minutes using withdrawn, measured volumes (aliquots) with a volume ratio between organic phase and aqueous phase (O/A) of 6, 4 and 2. After separation, the pH of the aqueous phase is set to 1, 5 with a 50% solution of NaOH, and the contact treatment is repeated until a constant equilibrium pH is achieved. Test data and results are given in Table III.

Example 23.

An aqueous leaching liquid phase with a concentration of

2 g/l of Fe<3+>, 2 g/lCu<2+>, 2 g/l Zn2+, 2 g/l Co<2+>, 2 g/l Ni<2+>, 2 g/l V <4+>, 2 g/l Eu<3+> and a pH adjusted to 1.0 with H2SO4 are contacted with an extraction solvent at 50°C for ten minutes using withdrawn, measured volumes with a volume ratio between aqueous phase and organic phase t (A/O) of 4.2 and 1. Test data and results are given in Table IV.

Example 2 4.

An aqueous leaching liquid phase with a concentration of

2 g/l of Fe<3+>, 2 g/l V<4+> and a pH adjusted to 1.0 with H2SO4 are contacted with an extraction solvent at 50°C for ten minutes using withdrawn, measured volumes of a volume ratio between aqueous phase and organic phase (A/O) of 4, 2 and 1. Test data and results are given in Table V.

Example 25.

An aqueous leaching liquid phase with a concentration of

2 g/l of Fe3+, 2 g/l Co<2+>and 2 g/l Ni<2>+ and a pH of 1.5 adjusted with H2S04 are brought into contact with an extraction solvent at 50°C for ten minutes using withdrawn, measured volumes with an aqueous phase to organic phase volume ratio (A/O) of 4, 2 and 1. Test data and results are indicated in Table VI.

Example 26.

An aqueous leaching liquid phase with a concentration of

2 g/l of Fe 3+ and 2 g/l Zn 2 + and a pH adjusted to 0.8 with H2SO4 are brought into contact with an extraction solvent. at 50°C for ten minutes using withdrawn, measured volumes with an aqueous phase to organic phase volume ratio (A/O) of 4, 2 and 1. Test data and results are given in Table VII.

Example 27.

An aqueous leach liquid phase with a concentration of 15 g/l Fe3+, 22 g/l Cu<2+>, 3 g/l Ag<+> and a pH of 0.76 adjusted with H2SO4 is brought into contact with an extraction solvent containing 10 %BEHP and 6.7% TOPO in kerosene at 50°C

for ten minutes using withdrawn, measured volumes with a volume ratio between organic and aqueous phase (O/A) of 2.

After separation, the solvent is then contained

the extracted metals are divided into aliquots. An aliquot of this enriched solvent is analyzed and found to contain 2.77 g/l Fe<3+> and 30.0 micrograms/ml Ag<+>. Another aliquot of the enriched solvent is contacted with 5 g/l sulfuric acid for five minutes at 50°C using an O/A ratio of 1. The test results show that 95% of the silver and 0.2% of the trivalent iron is leached from the solvent.

Claims (18)

1. Method for removing iron (III) from an aqueous iron (III)-containing solution, where said solution is brought into contact with an extraction solvent, which extraction solvent comprises an extraction agent and optionally a water-immiscible organic diluent, characterized in that said extraction agent comprises a mixture of approx. 1-10 parts by volume of an organophosphoric acid that has at least 6 carbon atoms, and approx. 1 part by volume of a tertiary (C4-C2q)-phosphine oxide; the liquid two-phase mixture is allowed to separate, and the aqueous phase is separated from the iron(III)-enriched extraction solvent. 2. Method according to claim 1, characterized by the further steps that the remaining iron (III)-enriched extraction solvent is brought into contact with an aqueous solution of a sulfuric acid for stripping iron (III) into the aqueous phase; the aqueous phase containing iron (III) is separated, and the stripped extraction solvent is recovered for subsequent new use in the extraction process. 3. Process according to claim 1 or 2, characterized in that said organophosphoric acid is a dialkyl(C^g-C-^g) hydrogen phosphate. 4. Process according to claim 3, characterized in that said dialkyl (C-^-C-^g) hydrogen phosphate is bis (2-ethylhexyl) hydrogen phosphate. 5. Method according to claim 1 or 2, characterized in that said tertiary (C 2 -C 2 q)phosphine oxide is tri-n-octylphosphine oxide. 6. Method according to claim 1 or 2, characterized in that the water-immiscible organic diluent is an aliphatic or aromatic mineral oil permit. 7. Method according to claim 1 or 2, characterized in that said extraction agent consists of approx. 50-75% by volume bis (2-ethylhexyl) hydrogen phosphate and approx. 50-25% by volume tri-n-octylphosphine oxide. 8. Method according to claim 2, characterized in that . a part by volume of the remaining iron(III)-enriched extraction solvent is brought into contact with approx. 0.05-20 parts by volume of an aqueous solution of sulfuric acid containing more than 100 g of sulfuric acid per liter of solution. 9. Method according to claim 1 or 2, characterized in that the aqueous starting solution of iron(III) contains aluminium. 10. Method according to claim 1 or ^^ characterized in that the aqueous starting solution of iron(III) contains copper. 11. Method according to claim 1 or 2, characterized in that the aqueous starting solution of iron (III) contains vanadium. 12. Method according to claim 1 or 2, characterized in that the aqueous starting solution of iron (III) contains cobalt. 13. Method according to claim 1 or 2, characterized in that the aqueous starting solution of iron (III) contains rare earth metals. 14. Method according to claim 1 or 2, characterized in that the aqueous starting solution of iron (III) contains silver. 15. Method according to claim 1 or 2, characterized in that the aqueous starting solution of iron (III) contains nickel. 16. Method according to claim 1 or 2, characterized in that the aqueous starting solution of iron (III) contains zinc. 17. Method according to claim 1 or 2, characterized in that the aqueous starting solution of iron (III) contains europium. 18. Method according to claim 1 or 2, characterized in that the aqueous starting solution of iron (III) contains uranium.