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A process for isolating tantalum and niobium
Field and Bac~ound of the Invention
The present invention relates to a hydrometallurgical process for isolating
tantalum and
niobium from raw materials which contain tantalum and niobium by treatment
with pure
hy~ofluoric acid or a mixture of hydrofluoric acid and sulphuric acid,
followed by
solvent extraction of the tantalum and niobium complexes from the treatment
solution
using methylisobutyl ketone and steam distillation of the organic ketone phase
containing
tantalum and niobium.
'Tantalum and niobium occur together in most natural sources. Different
proportions of
the two elements, however, characterise the ores and their geological
deposits. Niobium
is in principle obtained from columbite ore and/or pyrochlore ore from Brazil
and Canada
and other regions. These ores, however contain only small amounts of tantalum.
Tantalum-rich ores, such as e.g. tantalite, contain correspondingly small
amounts of
~o~um.
To isolate tantalum and niobium, however, it is mainly slags which are
produced during
the isolation of tin (Thailand, Brazil) which are also used. These tin slags
are now
regarded as the most important raw material source for the two elements,
although they
only contain small amounts of niobium and tantalum. Also, very variable Ta/Nb
ratios are
encountered in these tin stags.
Normally, the two metals and their compounds are isolated indirectly from raw
materials
containing very little tantalum and niobium, such as e.g. tin stags, by fusion
metallurgical
enrichment methods for the two elements. Only the synthetic tantalum/niobium
concentrates obtained in this way are available for economic wet chemical
processing.
Among these tin stags there are now also those which, like natural columbite,
contain
tantalum in a very unfavourable Ta/Nb ratio, i.e. they contain small amounts
of tantalum
but are rich in niobium. The normal hydrometallurgical treatment and
separation
processes cannot be applied to these, for economic reasons, because these
processes
require a Ta/Nb ratio of at least 1:3 in the concentrate which is used.
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20909~J
The conventional hydrometallurgical process for isolating tantalum or niobium,
disclosed
in US Patent 3,117,833, comprises treatment of the tantalum/niobium raw
material in
mineral acids, preferably hydrofluoric/sulphuric acid mixtures. Tantalum and
niobium are
thereby dissolved together as fluoro-complexes and subsequently separated
first from
accompanying elements and then from each other, using a mufti-stage solvent
extraction
with MIBK (methylisobutyl ketone, 2-methyl-pentan -4- one). Here, the
fluoroniobates or
fluorotantalates are selectively re-extracted in sequence and further
processed to give
pure tantalum or niobium compounds.
In detail, this takes place by selectively removing the niobium from the
organic ketone
phi ~'~'~ch contains niobium and tantalum, e.g. with dilute sulphuric acid,
while
tantalum remaining in the organic phase may be re-extracted from that using
water.
However, if materials which are rich in niobium but contain very little
tantalum are used,
then at this point the tantalum is present in very low concentration in the
organic ketone
phase. This means that there is a very poor volume/time yield, which makes the
process
uneconomical.
In addition, US Patent 3,403,983 discloses a process for the preparation of an
aqueous
solution of niobium and/or tantalum fluoro-complexes from a solution of fluoro-
complexes of these metals in a steam-volatile, organic solvent which is
virtually
miscible with water, wherein a solution of the fluoro-complexes of these
metals in the
organic solvent, which is obtained using the known mufti-stage extraction of
the metals
from ores, is subjected to a steam distillation process with quantitative
evaporation of the
solvent to produce a non-distilled aqueous solution which contains the fluoro-
complexes
in a higher concentration than was present in the organic solvent.
.Lms should mean that the problem of emulsion formation is avoided, the
organic solvents
are easily recovered and recycled, an aqueous solution of niobium and/or
tantalum fluoro-
complexes with three- to four-fold higher concentrations than in solution in
the organic
solvent is obtained and the aqueous product solution is highly suitable for
the economic
crystallisation of K2TaF7.
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23189-7470
This does n<at <~pply :i.n part: ici:~lar, therefore, to
niobium/tantalum complexes which conta.ir; very little
tantalum.
'Therefore, t hei_~e is a need t:o~: a process for
economically isolating tantalum from starting materials
which contain very lit~tlE, tantalum arn~ pat the same time are
rich in niobium, using a wet chemi.ca7_ treatment and
extraction process, without an indirect fusion metallurgical
process being required beforehand. xn aGddition, all the
niobium should also be i:;olated..
S umm.a r~
According tc trze invention, thie raw material
containing tantalum and niobium, e.g. t::i.n slugs, niobium
ores and/or concentrat:es, is treaty=c~ wit h pure hydrofluoric
acid or a mixture of ~nydx-ofluoricv ac:,~:id and sulphuric acid
and the acid solution is extracted fi_r~st with MTBK
(methylisobutyl ket.one), wherein rriob:iunc and tantalum pass
into the organi~~ phase together. No:r-mally, t: he sum of the
transition meta:is, ca:lcul.ated as their c.xides, is expressed
as "combined oxides" ~;abf>rev.: "C".O."n. The niobium is not
now selectively re-extracted from the organic phase using
mineral acids or watew, as is usual, but: the ketone phase
containing the C.O. i:~ subjected to ~~team distillation.
This measure means that both valuab=LEa sL:bstances are
converted into an aqueeou~~ pha~~e in <~ kzighly concentrated
form. The tantalum is now select:ivel.y extracted from this
aqueous phase using fresh ketone (MIBK), while the niobium
remains in the aqueou~~ phase.
This .invention thus comprises a hydrometal7_urgical
process for isolating tarutalurn and niobium from :raw
materials containing tarrt.alum and n:i.ob.~.L:~m by treatment with
pure hydrofluor_Lc acid o:r a m:i_xture of lydrof_luo.ric acid and
3 ._
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23189-7470
sulphuric acid, followed by solvent extraction of the
tantalum and niobium flu~~ro-complexes f~:~om the treatment
solution using methylisobut.yl ketc~ne an~:i steam distillation
of the organic ketone ph;~sF~ containing ;.:antalum and .niobium,
wherein the tantalum is selective'y extrvacted from the newly
produced aqueous phase witru fresru metriy.isobutyl ketone,
while all the niobium remains ~.n:~ the aqueous phase.
3 <~ ._
2000910
By selecting the ratio between the organic and aqueous phases, the amount of
tantalum in
the new MIBK phase may be adjusted to the desired concentration. If this
organic phase
is subjected to a further steam distillation process, there is another
increase in the
concentration of tantalum in the new aqueous phase. A preferred embodiment of
the
process according to the invention comprises treating the new organic ketone
phase
~n~g ~~~ ~~ steam and thereby re-extracting the tantalum. The new
concentrated tantalum solution may then be further processed in known ways.
The process according to the invention is advantageously useable for various '
tantalum/niobium raw materials. It confers particular advantages if there is a
Ta:Nb ratio
i 5 of 50.2 in the raw materials containing tantalum and niobium. Preferably,
the process may
be applied to columbite ores and/or tin stags with a Ta:Nb ratio of 1:5 to
1:15.
Detailed Description of Preferred Embodements
The invention is explained in more detail in the following by way of example,
without this
being regarded as a limitation.
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~o~oo~o
Example
A columbite ore with 35% by weight of Nb205 and 4% by weight of Ta205, the
remainder being Si02, FeO, Mn02, Ti02 and other impurities, was treated with
?0%
strength pure hydrofluoric acid. This produced a solution with 135 g/1 of G.O.
i 0 (- Combined Oxides, Nb205 and Ta205) and an acidity of 20 N. The Ta:Nb
ratio in this
starting solution was about 1:9, corresponding to the starting material. This
feed solution
was passed against an organic phase consisting of methylisobutyl ketone (MIBK)
in a
counter-stream solvent extraction unit. The raffinate was sufficiently free of
valuable
material, with 0.3 g/1 of C.O. The ketone phase containing 89 g/1 of C.O. was
now
'"shed with a little 12 normal sulphuric acid, in order to remove residual
impurities of
other elements which had also been extracted. The ketone phase containing
niobium and
tantalum was sluiced out and subjected to steam distillation. 1301/h TaNb MIBK
were
continuously fed to the top of a destillation column whereas 501/h steam were
fed to the
bottom of this column. The MIBK was totally distilled off and 35-401/h of a
concentrated
2o Niobium- and Tantalum solution remained behind. These elements were present
as
fluoro-complexes in a concentration ratio of 20 g/1 Ta205 and 180 g/1 Nb205
(Ta:Nb =
1:9). Due to the relatively low acidity of the aqueous phase of this steam
distillation
process the tantalum now was selectively extracted by contacting 401/h of this
aqueous
solution with 51/h of fresh unloaded MIBK while the niobium (180 g/1 Nb205)
remained
m the aqueous phase and was worked up separately. The resulting organic phase
containing tantalum (with 140 g/1 Ta205) was again treated with steam (31 Ta
MIBK /
11 steam) which totally removed the MIBK from the system and produced the
concentrated aqueous solution of tantalum fluorid (with >200 g/1 of Ta205
equivalent).
This was converted into the endproduct potassium hepta fluorotantalate (1,4
kg) by the
addition of KCl in the usual way as described for example in US Patent
3,051,547.
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Comparison example (according to US Patent 3,117,833)
The niobium/tantalum solution produced from treatment of the ore used in
example 1
was, as in example 1, passed against an organic phase consisting of
methylisobutyl ketone
(MIBK) in a counter-stream solvent extraction unit. The ketone phase,
containing 90 g/1
of C.O., was now washed with a little 12 normal sulphuric acid, in order to
remove
residual impurities of other elements which had also been extracted. The
niobium was
selectively and completely converted into an aqueous phase, in the usual way,
by
stripping it from the ketone phase containing niobium and tantalum with 2 N
sulphuric
acid and this was used as a sulphuric acid niobium fluoride solution to
isolate niobium
hydroxide. The ketone phase, now only containing tantalum, with 7.5 g/1 of
Ta205, was
freed of ketone by steam distillation and converted into an aqueous phase
containing Q5
g/1 of Ta205. This solution, with the relatively low tantalum content, is not
suitable for
economic further processing since it either requires too much heat energy for
evaporation
or leaves behind too much salt-laden waste water, if tantalum hydroxide is
produced from
it.
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