CA1148367A - Solvent extraction process for the removal of iron (iii) from leach liquors - Google Patents

Abstract

28,201 TITLE: SOLVENT EXTRACTION PROCESS FOR THE REMOVAL
OF IRON (III) FROM LEACH LIQUORS
ABSTRACT OF THE DISCLOSURE
Iron (III) bearing leach liquors may be treated with an extraction solvent comprising an organophosphoric acid, a trialkyl phosphine oxide and a water-immiscible organic diluent to separate the iron (III) from the leach liquor. The iron (III) loaded extraction solvent may sub-sequently be treated with a strong mineral acid to recover the iron (III). as a water-soluble salt.

Description

~ 2~
~836~

PRIOR ART_STATEMENT

.
Pertinent pri~or art uncovered includes U.S. Patent No. 4,168,297, issued to Nagasubramanian et al; British Patent No. 970,885, issued to ~ong et al; and the following articles:
Roddy et al., J. Inorg. Nucl. Chem. 33, 4, 1099-1118; Sekine et al., ~ Inorg~ Nucl. Chem. 38, 7, 1347-1350; and Diaz Nogueira et al., German Offen. 26~5130 [C.A. 87, 26576(4)].
!~' British Patent No. 970,885 discloses on page 3, lines 122-123, etc~ the extraction of titanium and iron from a leach solution with a solution of bis(2-ethylhexyl)-hydrogen phosphate in kerosene, and stripping the iron from the iron-loaded organic extract with hydrochloric acid.
~ The Roddy et al. article discloses the extraction`~ ~ of iron lIII) from acid perchlorate solutions by a solution of b~s(2-ethvlhexyl)hydrogen phosphate in n-octane.
U.S. Patent No. 4,168,297 discloses the extraction ; ! of iron (III) from digested ilmenite ore in aqueous hydro-fluoric acid by using a solution of bis(2-ethylhexyl)hydro-gen phosphate in kerosene.
The~Sekine et al. article discloses the extraction ;~ 20 of iron (III) from acid perchlorate with a solution of tri--n~octylphosphine oxide in hexane.
The Diaz Nogueira et al. article discloses the stripping of iron from organic extracts containing bis(2-ethylhexyl)hydrogen phosphate.

In summary, the extraction of iron (III) from acidic leach liquors by using;a water-immiscible organic solution containing either bis(2-ethylhexyl)hydrogen phos-phate, or tri-n-octylphosphine oxide, is known in the art.
However, the art does not teach, nor is it obvious 3a therefrom, that the use of bis(2-ethylhexyl)hydrogen phos-phate and tri-n-octylphosphine oxide in combination to extract iroll (III) from leach liquors containing sulfuric ` acid would provide a substantially superior process.
~, 35 j;`~ ' ~
,~ ~

;

: ~
~j ~

. ~ ~f~8 3

2~, Jl~

TITLE: SOLVENT EXTRACTION PROCESS FOR THE REMOVAL
: ~ OF IRON ~III) FROM LE~CH LIQUORS
~ .

BACKGROUND OF THE INVENTION

The present invention relates to hydrometallurgy.
More particularly, it relates to the recovery of metals from leach liquors by solvent extraction and subsequent stripping of the metal-loaded solvent with sulfuric acid.
The removal of ferric iron from aqueous solutions ; containing sulfuric acid, particularly alum solutions, is not known to be practiced commercially at the pre~ent time.
The purpose of the removal of iron from alum is to upgrade the final alumina product into a form suitable for use as a catalyst base, such as an al~nina-based hydrodesulfurizing catalyst. Altcrn~tive uses fox this proccss include the use in thc production of aluminum ~etal by thc Hall~Heroult ~` pxocess.
The alum solutions are derived from the action of .~
sul~uric acid on clays, and typically contain from 700 to 1600 micrograms of ircn ~ per milliliter~ To be used as a catalyst sQurce ~ ~ox aluminum metal production, the iron (III~ content o~ the alum solutlon must be reduced to about 10 to 16 m~crograms per milliliter.
The extraction o~ iron (III) from acidic aqueous sul~ate liquors by means of water-immiscible organic solutions, containing either bi3(2-ethylhexyl)hydrogen phosphatP, here-after abbrev~ated BEHP, or tri-n-octylphosphine oxide, here-a~ter abbreviated TOPO, i5 well-known in the art. Lonq et ~ ' , .,. ~ . .

: ,' , ~ , . . ~ ' ' ~: - : , . ,. :

33~7 2 ~

al., Brit~sh Patent 970,885; ~oddy et al., J Inorg. Nucl.
Chem. 33, 4, 1099-1118; Nagasubramanian et al., U.S. Patent 4,158,297; Sekine et al., J. Inorg. Nucl Chem, 38, 7, 13~7-1350; and Diaz Noyueira et al., German Offen. 2645130 [C.A.
87 26576(4]~, Ho~ever, if the iron (III)-loaded organic solution contains only BEHP, the iron cannot be completely stripped therefrom with sulfuric acid. If the extraction ~ solvent contains only TOPO, only about 25~ of the total iron (III) in the leach liquor is extracted into the oryanic phase.
There is a need, therefore, for an extractant mix that will extract most of the iron (III) into the organic phase, and allow most of the iron (IIII to be stripped therefrom with sulfuric acid.
- SUMMARY OF THE INVENTION
.
The present invention provides a process for the removal of iron (III) from an aqueous iron (XII)-bearing solution containing sulfuric acid comprising contacting said solution with an extraction solvent at about 0-50C., about 20 parts by volume of said aqueous solution being employed - ~o per part by volume of said extraction solvent, said extrac-t~on solvent comprising about 1-50 parts by volume of an ~; extractant and about 99~50 parts by volume of a water-im-miscible organic diluent, said extractant comprising a mix-ture of about 1-4 parts by volume of a suitable organophos-~; 25 phoric acid, having at least 6 carbon atoms, and about one part by volume of a trialkyl (C6-C14)phosphine oxide; allow-ing the two-phase liquid mixture to settle; and, separating the aqueous phase from the iron (III)-loaded organic phase.
'rhis process enables most of the iron (III) to be extracted into the organic phase.
The present inVention also provides a process, as descr~bed above, with the additional steps of contacting the residual iron ~III)-loaded organic solution with an aqueous~
solution of a strong mineral acid at about 0-50C. to strip the iron (III~ into the aqueous acidic phase; separa-ting the ~queous acidic phase containiny water-soluble iron .:. .. :
;:;::
~ ~ .
.,; , : :
:;

3 ~

~ salts; andr recovering the stripped oxganic phase for subsequent reuse in the extraction of another aqueous solu-tion containing iron (III).
The present invention allows the iron to be re-moved in a low-cost continuous process and the ferric iron to be subsequently s~ripped from the iron (III~-loaded sol-vent with sulfuric acid.
DETAILED DESCRIPTION OF THE INVENTION
In carrying out the processes of the present inven-t;~on, suitable extraction solvents and stripping solutions are prepared as follows:
The extraction solvent is prepared by mixing about 1-50` parts by volume of extractant with about 99-50 parts by volume of a water-immiscible organic diluent. Said lS extractant consists of a m~xture of an organophosphoric acid h~ving at least 6 carhon atoms and a trialkyl (C6-Cl~)phos-phine oxide.
~- Suitable organophosphoric acids include bis(2-~ ., ethylhexyllhydrogen phosphate, phenyl dihydrogen phosphate, octyl phenyl hydrogen phosphate, octyl trihydrogen diphos-phate, dioctadecyl hydrogen phosphate, bisl2-ethylhexyl~di-hydrogen diphosphate, and the like~ Generally, any organo-phosphoric acid having at least 6 carbon atoms in the hydro-; ~ carbon chain, with a maximum molecular weiyht of about 600, is suitable. In the preferred embodiment, the organophos-phoric acid is a dialkyl(C6-C18~hydrogen phosphate. The most pre~erred organophosphoric acid is the bis(2-ethylhex~l)-hydroyen phosphate ~BEHP).V
Suitable trialkylphosphine oxides include tris~2-ethylhexyl~phosphine oxide, tri-n-hexylphosphine oxide, tri-n-octylphosphine oxide, tri n-dodecylphosphine oxide, tricyclohexylphosphine oxide, and the like. Generally, any trialkylphosphine oxide with a low aqueous solubility, that ;~ is, at lea~t 6 carbon atoms in the hydrocarbon chain, with a maximum molecular weight of about 600, is suitable. The preferred trialkylphosphine oxide is tri-n-octylphosphine oxide (TOPO)~V
., : :,

- 4 ~
The composition of the extractant comprises about 1~4 parts by volume of the organophosphoric acid, preferably - about 1~3 parts by volume, per part by volume of the tri-alkylphosphine oxide, Generally, a wide variety of water-~mmiscible or-ganic liquids may be used as the diluent. Preferably, the diluent is an aliphatic or aromatic petroleum distillate.
More preferably, the diluent is kerosene. Suitable diluents include, but are not limited to, benzene, toluene, xylene, kerosene, naphtha, and the like.
In carry~ns out the process of the present ~nven-ti~on, a~out 1-20 parts by volume of the ~ron (III)-bearing aqueous sulfate soluti~on, is contacted continuously and countercurrently wi`th one part by volume of the extraction solvent. Phase contact is cor~monly achieved in devices called "mixer-settlers", although many other types of devices are ava~lable and su~ta~le. In the mixer~ one phase is dis-persed w~thin the oth~r by stirring or some other appropri-ate form of ag~tat;~on. The extracti`on solvent then forms a ~ complex w~th the iron (III) which reports to t~e organic phase o~ -the two-phase liquid mixture. The d~sparsion then flows to the settler where phase disengagement occurs under quiescent conditions. About 1-10 mixer-settlers, preferably 1-6, are requ~red to achieve the necessary iron (III~ ex-traction. Generally, extraction is carried out between 0-50~C., preferably 20-40C
After extractionr the iron (III) free sulate ~` solution is ready for further treatment, for example, alum-ina precipitation. The iron (III) loaded extraction solvent ~lows into the stripping circuit where about 0 05-1.0 part by volume of a solution o a mineral acid, preferclbly 0.1-0.5 parts by volurne, is contacted continuously and counter-currently with one part by volume of the solvent. As a result the iron (III) reports to the aqueous phase in the fo~m o~ a soluble salt of the mineral acid employed. Phase contact may be achieved with mixer-settlers ox othex suitable - devices. Several mixer~settlers, usually about 1 10 and - :
.

. :

~ 5 .~
preferably about 1-6, connected in series are normally re-quired to achieve the desired amount of iron (III) stripping.
Strippin~3 is generally conducted between 0C.-50C., pre-ferably 20-40C~
The str~pped iron (III)-free solvent is recycled to the extraction c~rcuit for the treatment of incom~ng iron bearing sulfate solutions. Mineral acid from the stripp~ng circuit conta~ning the dissolved iron (III) salts may e~ther be d~sposed o~ or treated for iron removal, for example by electrolys~s and recycled to the stripping circuit.
Suitable mineral acids ~nclude sulfur~c, hydro-chlor~c, hydrofluoric, n~tric, and the like. The preferred ; ~ mineral acid ~s sulfuric acid containing about 100-500 grams of sulfuric acid per liter, preferably about 150-2~0 grams :
, ~ 15 per l~ter.
Applications in wh~ch the process of the present invention may be employed other than in the extraction o~
ron from alum solut~ons include, but are not lim~ted to, ;~ extractions from cobalt nickel, rare eaxth, vanadium and copper sulfate to name ~ut a few.
Whereas the exact scope of the instant invention is set forth in the appended claims, the following specific s;~ examples illustrate certain aspects of the present invention, and more particularly, point out methods of evaluating the same. However, the examples are set forth for illustration only and are not to be construed as limitations on the pre-!~ ~ sent invention except as set forth in the appended claims.
All parts and percentages are by wei~ht unless otherwise ,~ specified.
~, 30 EXAMPLE i An oxidized solution o~ alum containing ferric sulphate equivalent to 1470 micrograms of Fe3~/ml is fed at ! 1000 mls~minute to an extraction circuit consistin~ of four stages o~ mixer settlers. ~here, it is contacted at 40C.
in a continuous, counter-current manner with an extraction ~olvent containing 4.5 volume percent BEHP, 3 volume percent TOPO and 92~S volume percent kerosene, which is added at 500 1~ 1 3~ii7 ~ 6 ~
mls per minute to provide a volume rakio of aqueous phase to organic phase of 2:1. After the four extraction stages at this .ratio, an aqueous alum solution containing about 5 0 micrograms of Fe3 /ml is obtained at a rate of a~out 1000 ml per mi~nute~

The iron-loaded, organic-extraction solvent from Example 1, containing about 2955 micrograms of Fe /ml, exits from -the extracti.on ci~cuit at about 500 mls/minute and is fed to a stripping circuit. Here, it is continuously contacted at 40C., in three counter-current mixer settler stages, with a striP feed consisting of a solution of sul-: phuric acid in water. The sulphuric acid solution, contain-ing ~00 g. of sulphuric acid per liter of solution, is fed at a rate of 100 mls/minute to provide a volume ratio of aqueous phase to organic phase of 0~2~ ~fter the t~ree stripping stages at this ratio, an acid strip liquor contain-~ ing 14,650 micrograms o Fe3~ml is obtained at a rate of ; about 100 mls/minute.
~:~ 20 ~he stripped organic phase, containing about 25 micrograms of Fe3~/ml, is recovered and is recycled at a rate of about 500 mls/minute to the extraction circuit of Example 1, where it serves for the subsequent extraction of iron rom incoming, iron-bearing alum solution.

Iron-loaded organic solutions, each containing about 3 grams per liter of Fe3~, are prepared by extracting alum solutions containing sulfuric acid with the following extraction solvents.
Extraction Extraction Solvent Comp~
Solvent __ (% by volume).
A 4.5% BEHP, 3% TOPO, 92.5%
Kerosene B 7.5% BEHP, 92.5% kerosene C 4.5% BEHP, 95.5~ kerosene The ir~n~loaded solutions are then stripped b~
cont~ct with aqueous sulfuric acid (.200 grams per liter) in .` ' ~

-, -: . ,: .
.
. .
, ~: . "' - ' ~ .

. .
an amount to provide a volume ratio of aqueous to organic phases of 0.2 at 40C., for varying numbers of mixer settler stages, and the iron (III) content of the stripped organic phase is measured. The results obtained are shown below.

5 No. of MixexFe (III) Conc. In Stripped SolventSettler StagesOrganic Phase (ug/ml) B 1~ 700 The above results illustrate that the presence of TOPO in the iron-loaded solvent greatly facilitates the stripping of iron (III) therefrom.

An oxidized solution of alum containing ferric sulfate equivalent to 523 micrograms of Fe ~ml, which has ~ a pH of 2,6 and contains 8~48~ by weight of aluminum oxide, -; is extracted at 24C us~ng a Burrell wrist-action shaker for ~;- 40 minutes with an equal volume of an extraction solvent ,`~ cons~sting of 5% by volume of TOPO and 95~ by volume of ker-r ~ 20 osene. The two-phase liquid mlxture is allowed to settle and the aqueous phase is separated. Analysis of the organic ` ~ phase shows that only 27.4% of the Fe3~ has been extracted from the aqueous phase.

; 25 The procedure Oe Example 6 is followed except that '~ the 5% by volume of extractant used is a mixture of BEHP and TOPO. The percentage composition of TOPO in the extractant is varied from 0% to 50~ by volume. The aqueous phase, obtained after separation of the organic phase, is analyzed for Fe3 and aluminum to obtain extraction coefficients (EA), and calculate separation factors tS~). The results obtained in Table III below indicate that the optimum ex-tractant composition for minimizing aluminum extraction, ' ~ while maintaining high iron (III) extraction, is in the range of 4a to 50~ TOPO by volume.

,~ ,;
;
i;

! - z 3;367 ., ., .
.. _~

('' ` U) ~ ~ ~
, o ~ i~ ~ o o ,1 ~ ,1 ~ ,1 oooooooo , ~
9 ~ o o o o o o o o '; - . ~
~ ~ In r~ ~D O 0~ ~cn :~ o + ~ ~ r~
o o ~5 .
~: o U~ ~ ~ ~ ~~ er r~i ~ ~ ) O
!~' O N t~l ~1 ~-i ~i ~i r-i ~i . I
h ~5`~: ~ ~ t~
,~ Pi ~) ~: . ~ ~ ~ ~ ~ ~-1 ~~ ~
'.'' d~ ~4 o~ ~ 1:~ ~ cs~. ~ ~ (~1 ô o ~
~ O O O Lf) OLO O O ' U? U~ a O r-l N N ~ ~) ~r U~) ~ h f5 1 . ~1 Q
>o u u~ p~ o _ 1; i: ~ ~ ~ O 11 . .~ O O ::) h 1 . ~
o i~C o o o In o u~ o o ~1 ~1 li4 .', ` ~ P~

.. ~ ~ O

U o ~ P~
.,, ~ . ~ U~
.. ~ r-- 00 ~ O ~I N ~1 ~
'~ ~ ~ ~I N

''`; "

., -, .
.; . .

',,: ', r~

t, ' . : , : ' ' ~r,., : ~ ,' . , 3~7 EXAM~LE 15 Following the procedure of Example 1 in every ma-terial deta;l except that the extraction sol~ent now contains phenyl dihydrogen phosphate, tris(2-ethylhexyl)phosphine oxide and benzene, substantially similar results are obtained.

Following the procedure of Example 1 in every ma-terial detail except that the extraction solvent now contains octyl trihydrogen diphosphate, tricyclohexylphosphine oxide and toluene, substantially similar results are obtained.

Follow~ng the procedure of Example 2 in every ma-terial detail except that in place of the sulphuric acid solution there is now employed solutions of hydrochloric, hydrofluoric and nitric acids, respectively, substantially similar results are obtained.

, ~`,' ' ' .
.

~' ~ . ., :
.:
~':
~ , . ~
r ' " ,' ' ` ' ' '', ' ' ' ,

Claims (13)

28,201 I CLAIM:

1. A process for the removal of iron (III) from an aqueous iron (III)-bearing solution containing sulfuric acid comprising contacting said solution with an extraction solvent at about 0°-50°C., about 1-20 parts by volume of said aqueous solution being employed per part by volume of said extraction solvent, said extraction solvent comprising about 1-50 parts by volume of an extractant and about 99-50 parts by volume of a water-immiscible organic diluent, wherein said extractant comprises a mixture of about 1-4 parts by volume of an organophosphoric acid having at least 6 carbon atoms, and about one part by volume of a trialkyl-(C6-C14) phosphine oxide; allowing the two-phase liquid mixture to settle; and, separating the aqueous phase from the iron (III) loaded extraction solvent.

2, The process of Claim 1 wherein said organo-phosphoric acid is a dialkyl(C6-C18) hydrogen phosphate.

3. The process, according to Claim 2, wherein said dialkyl(C6-C18)hydrogen phosphate is bis(2-ethylhexyl)-hydrogen phosphate.

4. The process, according to Claim 1, wherein said trialkyl(C6-C14)phosphine oxide is tri-n-octylphosphine oxide.

5, The process, according to Claim 1, wherein said water-immiscible organic diluent is an aliphatic or aromatic petroleum distillate.

6. The process of Claim 1 wherein said extractant consists of about 50-75% by volume of bis(2-ethylhexyl)-hydrogen phosphate and about 50-25% by volume of tri-n-octylphosphine oxide.

7. The process, according to Claim 1, with the additional steps of contacting the residual iron (III)-loaded extraction solvent with an aqueous solution of a sulfuricacid at about 0°-50°C. to strip the iron (III) into the aqueous phase; separating the aqueous phase containing iron (III); and, recovering the stripped extraction solvent for subsequent reuse in the extraction process.

8, The process, according to Claim 7, wherein one part by volume of the residual iron (III)-loaded extraction solvent is contacted with about 0.05-1 part by volume of an aqueous solution of sulfuric acid containing about 100-500 grams of sulfuric acid per liter of solution.

9. The process of Claims 1 or 7 wherein the start-ing aqueous iron (III) solution contains aluminum sulfate.

10. The process of Claim 1 wherein the starting aqueous iron (III) solution contains copper sulfate.

11. The process of Claim 1 wherein the starting aqueous iron (III) solution contains vanadium sulfate.

12. The process of Claim 1 wherein the starting aqueous iron (III) solution contains cobalt sulfate and nickel sulfate.

13. The process of Claim 1 wherein the starting aqueous iron (III) solution contains rare earth sulfates.