Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
Significant amounts of aluminum may be recovered from
clays and other low grade aluminum-bearing ores by acid leaching
of the ore (for example, a clay which preferably has been calcined)
to yield a solution containing soluble aluminum Al+++ as the
sulfate, the nitrate or the chloride. Such solution normally
may also contain undesirable ions, and, in particular, iron as
Fe ++. Iron is most undesirable since its presence interferes
with the economic production of high purity aluminum metal.
Prior art processes, typified by that disclosed in
United States Patent No. 3,211,521, teach the purification of
liquids containing aluminum and iron ions by the process wherein
an aqueous solution thereof iæ contacted with an alkyl-substitued
phosphoric acid, HRR'PO4 wherein R is a straight chain or
branched chain alkyl radical containing at least 8 carbon atoms
and R' is a hydrogen or alkyl. Typical of such compositions is
dioctyl phosphoric acid. In use of such techniques, the alkyl-
substituted phosphoric acid is contacted with aqueous~ ~
liquor containing aluminum and iron; and the alkyl-substituted
phosphoric acid will become loaded with iron without picking up
any appreciable quantity of aluminum. The result is the aqueous
liquor must still be further treated to separate the aluminum
from the other undesired impurities. The result is extended
processing which is costly in terms of time and capital equipment.
SUMMARY OF THE INVENTION
This invention provid0s a novel process for permitting
rapid, low cost recovery of aluminum from solutions containing
other ions including iron.
Briefly stated, this invention comprises the process of
extracting aluminum from an aqueous solution containing aluminum
ions by~
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(a) contacting said aqueous solution in a contacting
operation with a symmetrically alkyl-substituted aryl hydrogen
phosphate and a C6 to Cg alkanol;
(b) withdrawing from said CQntaCting operation a lean
aqueous solution substantially free of aluminum; and
(c) recovering said aluminum from said complex.
DETAILED DESCRIPTION
In accordance with certain aspects of this invention,
the rich aqueous solution containing aluminum ions may, typically,
be a solution obtained by leaching an aluminum-bearing ore, such
as a calcined alumino-silicate clay, with a dilute mineral acid.
The most common of such aluminum-bearing ores, such as kaolin
and bauxite, may include various aluminum silicates, metal
aluminates, aluminum oxides, and the like together with sub-
stantial amounts of iron and silica and lessor amoun~s of ~her
impurities.
The invention contemplates recovering aluminum from
such ores (after calcining, in the case of clay) by leaching
with an acidic leach liquor in which the acid is preferably
sulfuric acid, although hydrochloric or nitric acid can also be
used. The acid is present in an amount stoichiometrically
adequate to dissolve the alumina (A12O3) content of the calcined
clay or other ore. The residue may be subjected to further
treatment, as by acidic washing, to recover any remaining
solubilized aluminum.
Such calcining, leaching, and washing do not form a
necessary part of the instant invention, for any conventional
procedure which yields an impure aluminum containing solution
can be utilized.
In accordance with the present invention, the aluminum-
containing solution is treated with a symmetrically alkyl-
substituted aryl hydrogen phosphate in the hydrogen form to
e~tract the alumin~m therefrom.
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As used herein, the term "symmetrically alkyl-
substituted aryl hydrogen phosphate" refers to a phosphate
selected from:
R~O-P-O ~ and Y ~O-P-O~Y
wherein each of ~, X and Z is a Cl-C10 alkyl group, ~ is
selected from hydrogen and Cl-C10 alkyl, and R', X', Y' and
Z' correspond, respectively, to R, X, Y and Z.
Specific examples of suitable phosphates are bis(3,5-
xylenyl) hydrogen phosphate, bis(3,4,5-trimethylphenyl) hydrogen
phosphate, bis(3-ethyl-5-methylphenyl) hydrogen phosphate, bis(3,
5 dihexyl) hydrogen phosphate, bis(3-tolyl) hydrogen phosphate,
bis(3-tertiary-butylphenyl) hydrogen phosphate, and the like.
The bis(3,5-xylenyl) hydrogen phosphate is preferred because
of its greater selectivity for aluminum.
The phosphate preferably is used as a liquid ion
exchanger by dissolving it in a water-immiscible organic solvent
such as commercial kerosene, octane, heptane, toluene, xylene,
or the like. Solubility of the phosphate in such hydrocarbons
may be enhanced by the use of an alkanol cosolvent, which
advantageously is a C6 to C12 alkanol such as hexyl, heptyl,
octyl, monyl, decyl, or dodecyl alcohol.
As to proportions, for each 100 parts by weight of
- aluminum contained in the leach solution there is used from
about 3000 parts by weight of bis(3,5) xylenyl hydrogen phosphate.
Alkyl substituted aryl hydrogen phosphates of different molecular
weights will require proportionately different amounts.
In carrying out the extraction, any conventional cocur-
rent or countercurrent scrubbing or contact apparatus now used
for liquid ion extractions can be used to ensure that the
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organic phosphate solution and the aqueous acidic aluminum-
containing solution are thoroughly admixed.
The pH of the aqueous phase is that of the leach
solution at the conclusion of the acid leach opèration; i.e.,
about 1 to about 3.5; and, while ambient temperature and pres-
sure is preferred during extraction, slightly elevated
temperatures and pressures are also suitable.
During this extraction, the phosphate becomes loaded
with aluminum and with some iron, while the aqueous leach
solution is depleted in aluminum. Substantially all other
undesired impurities, save for the co-extracted iron, remain in
solution .
The loaded phosphate is then stripped to remove the
aluminum therefrom. Preferably, stripping is effected by contact
of the loaded organic phase with an aqueous phase containing acid
at a substantially higher strength than that of the leach
solution entering the extraction stage. Typical of such acids
may be hydrochloric acid, nitric acid, sulfuric acid, and the
like, with hydrochloric acid being preferred; and the strength
of the acid solution delivered to the stripping stage in general
is advantageously equivalent to a nearly saturated aluminum salt
solution at the temperature of operation. Thus, a 28~ hydro-
chloric acid solution is equivalent, after the hydrogen-aluminum
exchange, to a saturated aluminum chloride solution. However,
somewhat lower strength acids may be used; for example, 20%
hydrochloxic acid may be used as the stripping acid.
The organic solution recovered from the stripping
operation contains the regenerated acid form of the phosphate
and can be recycled for use in further extraction; and the
aqueous phase from the stripping operation contains an iron-
contaminated aluminum chloride.
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The aqueous aluminum chloride solution may be preferably
treated in an iron-extraction operation, wherein the iron is
removed from the solution by contacting with a tertiary amine
or quaternary ammonium salt of the type now used for iron
extraction. A substantially pure aluminum salt, or alumina, may
be recovered by known procedures from the resulting iron-free
aqueous strip solution.
While the invention has been described in connection
with a preferred embodiment, it is not intended to limit the
invention to the particular form set forth, but, on the contrary,
it is intended to cover such alternatives, modifications and
equivalents as may be included within the spirit and scope of
the invention as defined by the appended claims.
