UPGRADING OF TITANIFEROUS MATERIAL
THIS INVENTION relates to the upgrading of titaniferous material. In
particular, the invention relates to a method of upgrading a titaniferous material.
Conventional processes, and in particular conventional commercial
processes, to produce TiCI4 use titaniferous raw materials with a high content of TiO2.
The TiO2 is reacted with chlorine in a high temperature chlorinator (about 900°C) to
produce TiCI , which is used commercially on large-scale to produce TiO2 pigment or
titanium metal. Unfortunately, chlorine reacts unselectively at high temperatures, with
chlorine thus being consumed by other constituents of the titaniferous raw materials.
A method of upgrading titaniferous materials, such as ilmenite, to a form
which consumes less chlorine or produce less chloride wastes from impurities in the
titaniferous feed material and which can produce TiCI4 in a process step conducted at a
lower temperature would be desirable. It would also be advantageous if such a method
is more economical and can upgrade low-grade titaniferous materials, such as lowgrade
titanium-bearing slag.
According to the invention, there is provided a method of upgrading a
titaniferous material, the method including
nitriding and reducing a titaniferous material which includes TiO2 and Fe oxides
in the presence of nitrogen and carbon to convert the TiO2 to TiN and to reduce most of
the Fe oxides to Fe;
oxidising the Fe in preference to the TiN to form Fe2+ ions; and
removing the Fe2+ ions to produce an upgraded low-Fe TiN bearing material.
Typically, the upgraded low-Fe TiN bearing material is an admixture of
TiO, TiN and TiC.
A plurality of Fe oxides, e.g. Fe2+ and Fe3+ will thus be present in the
titaniferous material. The Fe oxides in the titaniferous material are thus carbothermically
reduced to Fe while the T1O2 in the titaniferous material is nitrided to TiN.
Advantageously, the TiN is more reactive than T1O2, and chlorine, other than with Fe,
reacts selectively with TiN at much lower temperatures than with T1O2, e.g. about 170°C
- 250°C, to form TiCI with virtually no waste chlorides, except FeCI2 and/or FeCI3, being
formed.
The method may thus include chlorinating the upgraded low-Fe TiN
bearing material thereby converting the TiN therein to TiCI . The chemical reaction
involved is in accordance with reaction ( 1 ) :
TiN + 2CI2 = TiC + ½N2 ( 1)
As most, if not substantially all of the Fe, as Fe2+ ions, has been removed
to provide the low-Fe TiN bearing material, chlorinating the TiN will lead to little chlorine
being consumed by iron, thus advantageously improving the economics of the method
of the invention.
The chlorination of TiN is selective regarding the bulk of impurities that
may be found in the low-Fe TiN bearing material, such as S1O2, CaO, AI2O3 and MgO.
These compounds do not react with chlorine at the low temperatures, i.e. about 170°C -
250°C, where TiN reacts with chlorine (CI2).
Nitriding and reducing a titaniferous material which includes T1O2 and Fe
oxides in the presence of carbon and nitrogen to convert the T1O2 to TiN and to reduce
the Fe oxides to Fe may be effected by any method known to those skilled in the art,
such as the method described in US 6,629,838. Typically, a large nitriding kiln is used
to effect the nitriding and reduction, producing a carbo-nitrided intermediate which
includes TiN and Fe. As will be appreciated, a source of nitrogen is required for this
method step. Advantageously, if an air separation plant or facility is present to produce
oxygen for downstream processing, nitrogen from the air separation plant may be used
for nitriding purposes. The chemical reaction for the nitriding of TiO2 is as follows, i.e.
reaction (2):
TiO2 + 2C + ½N2 = TiN + 2CO (2)
When the T1O2 is however mostly present as FeO.TiO2, as in the case of
ilmenite, which is the most abundant commercial mineral currently used for the
extraction of titanium values, the FeO.TiO 2 may thus be nitrided carbothermically to
provide TiN and metallic Fe and one or more carbon oxides (i.e. CO and/or CO2). The
nitriding and reducing reaction for the FeO.TiO2 can in simplified form be described as
follows, i.e. reaction (3):
FeO.TiO 2 + 3C + ½N2 = Fe + TiN + 3CO. (3)
In a more complex form, the nitriding and reducing reaction for the
FeO.TiO2 can for example be described by way of exemplary reaction (3a):
FeO.TiO 2 + 2.8C + ½N2 = Fe + TiN + 2.6CO + 0.2CO 2. (3a)
Oxidising the Fe in preference to the TiN to form Fe2+ ions may thus
include reacting a carbo-nitrided intermediate which includes TiN and Fe with an
oxidising anion to convert the Fe to Fe2+. Typically, the oxidising anion is in the form of
an aqueous salt solution.
The aqueous salt solution may be a chloride solution, preferably a FeC
solution. Advantageously, both FeCI3 and FeCI2 have a high solubility in water. It is
however to be appreciated that there are other salts, e.g. nitrates, that are also suitable
for use in the method of the invention. For an efficient and economic process, the ferric
ions must be in the form of a water-soluble salt and the corresponding ferrous salt must
also be water-soluble, allowing water leaching of the ferrous salt from the carbo-nitrided
intermediate.
When FeC is used as the aqueous salt solution, the following reaction,
i.e. reaction (4), describes the oxidation of the Fe in preference to TiN to form Fe2+ ions:
Fe + TiN + 2FeCI3(aq) = 3FeCI2(aq) + TiN (4)
This reaction may conveniently be carried out at ambient temperature, but
higher temperatures up to the boiling point of the ferric chloride solution enhance the
rate of reaction between the Fe3+ ions and the Fe and also increase the solubility of
both ferric chloride and ferrous chloride.
Preferably, during nitriding and reducing of the titaniferous material,
substantially all of the Fe oxides are reduced to metallic iron and not only to the divalent
form. This is typically the case in any event at the highly reducing conditions at about
1300°C used to nitride the TiO2 to produce TiN. Typically, the iron is in the form of
small particles that are intimately mixed with small TiN particles that are sintered
together with a remainder of the titaniferous material, i.e. a carbo-nitrided intermediate
which includes TiN and Fe. This advantageously allows extraction of the iron as Fe2+
using FeC (ferric chloride) in accordance with reaction (4) above, instead of using
hydrochloric acid. No hydrogen is thus formed, unlike the case with extraction by
hydrochloric acid in accordance with reaction (5):
Fe + 2HCI = FeCI2 + H2 (5)
thereby avoiding the dangers of hydrogen formation and problems caused by foaming.
Furthermore, the reaction of FeC is rapid compared to processes where FeO is
leached with HCI, making it possible to use shorter residence times and smaller
reactors. In addition, the oxidation of aqueous ferrous chloride by oxygen, i.e. air, to
regenerate FeCI3 requires much less energy. Advantageously, the ferrous chloride
(FeCI2) can be oxidised (for purposes of recycling Fe3+ and for purposes of removing an
iron oxide by-product) in a separate reactor to a reactor in which the Fe is oxidised to
form Fe2+ ions, providing better separation of iron from TiN and providing the
opportunity to select operating conditions to stimulate the growth of large iron oxide
crystals, which is advantageous for the subsequent use or disposal of the iron oxides.
As will also be appreciated, where HCI is used to leach iron species from TiN, provision
has to be made to contain and scrub HCI vapours. In contrast, the vapour pressure of
HCI over ferric chloride solutions (FeCb solutions) is orders of magnitude less than over
HCI solutions, thus allowing a much simplified mechanical construction of a plant to
employ the method of the invention.
Surprisingly, TiN is remarkably resistant against attack by FeC . The
inventors have surprisingly found that, even though there is a large change in Gibbs
free energy for the reaction, i.e. reaction (6):
8FeCI3 + 2 Ί N + 4H2O = 8FeCI2 + 2TiO2 + 8HCI + N2 AG25°c = -722 kJ (6)
and even though one would expect the very fine TiN particles formed by carbo-nitriding
of titaniferous material such as ilmenite to be highly reactive as a result of their high
surface to volume ratio, the oxidation of fine iron particles in nitrided ilmenite by
aqueous ferric ions (Fe3+) according to reaction (4) above is much faster than the
oxidation of TiN particles by the Fe3+ ions according to reaction (6) above.
Advantageously, metallic iron in nitrided titaniferous material, such as ilmenite, can thus
be converted to Fe2+ ions and leached from TiN, with an aqueous solution of a suitable
Fe3+ containing salt.
Removing the Fe2+ ions to produce an upgraded low-Fe TiN bearing
material typically includes separation of Fe2+ solution from the unreacted carbo-nitrided
intermediate to produce the low-Fe TiN bearing material and a Fe2+ solution. The
separation may be effected by a physical separation step, e.g. filtration, settling or
centrifuging. If required or desirable, the method may include washing the low-Fe TiN
bearing material with an aqueous fluid. Preferably, the low-Fe TiN bearing material is
dried before it is chlorinated.
As intimated hereinbefore, the method of the invention may include the
step of regenerating Fe3+ ions from the FeCI2(aq) obtained by the leaching of the carbonitrided
intermediate with FeCls(aq).
Typically, only a portion (e.g. about two-thirds) of the FeCI is converted to
Fe3+ ions, the balance being in the form of a by-product of the method of the invention
containing iron in a non-chloride form. The regenerated Fe3+ ions may be recycled to
oxidise the Fe in preference to the TiN to form Fe2+ ions.
Regeneration of the Fe ions may include oxidation of the FeCI2 with
oxygen (typically air at about 1 to 2 bar(g) and 90°C), e.g. according to reactions (7) and
(8):
6FeCI2(aq) + 1½O2 = 4FeCI3(aq) + Fe2O3 (7)
6FeCI2(aq) + 1½O2 + H2O = 2FeO.OH + 4FeCI3(aq) (8)
Depending on reaction conditions, Fe3O4 can also precipitate.
Instead, regeneration of the Fe3+ ions may include the electrochemical
oxidation of the FeCI in a cell to produce FeCI3 at an anode of the cell and electrolytic
iron at a cathode of the cell. The electrochemical reactions to regenerate ferric chloride
and to electrowin iron are as follows, i.e. reactions (9), ( 10) and ( 1 1) :
cathode reaction Fe2+ + 2e = Fe (9)
anode reaction 2Fe2+ = 2Fe3+ + 2e (10)
overall electrochemical reaction 3Fe2+ = Fe + 2Fe3+ ( 11)
The titaniferous material may be ilmenite, as hereinbefore indicated.
Instead, it may be a low-grade slag, e.g. a low-grade slag such as that produced by
Highveld Steel and Vanadium Corporation in South Africa or by New Zealand Steel in
New Zealand, containing about 30% TiO2 and 5% Fe. The titaniferous material may
also be a sulphate grade slag for example as produced by Exxaro Limited and Richards
Bay Minerals, both of South Africa, which contains about 80% TiO and 10% FeO.
The invention will now be described, by way of example, with reference to
the accompanying diagrammatic drawings in which
Figure 1 shows a flowsheet of one embodiment of a method in accordance with
the invention of upgrading a titaniferous material; and
Figure 2 shows a flowsheet of another embodiment of a method in accordance
with the invention of upgrading a titaniferous material.
Referring to Figure 1 of the drawings, reference numeral 10 generally
indicates a method of upgrading a titaniferous material. The method 10 includes a
nitriding step 12, an iron oxidation step 14, an Fe2+ ions removal step 16, an Fe2+
oxidation step 18 and an Fe2O3 filtration step 20.
The method 10 is used to treat ilmenite, with a theoretic composition of
FeO.TiO2, to provide a low-Fe TiN product. Ilmenite, nitrogen and a carbon-containing
material, e.g. coal, are fed to the nitriding step 12 where the FeO is reduced to iron
metal and the TiO2 is nitrided to TiN. This is typically effected in a large refractory-lined
kiln operated at a temperature of about 1300°C. The kiln produces a carbo-nitrided
intermediate which includes TiN and Fe which is fed to the iron oxidation step 14.
Carbon monoxide as an off-gas is produced by the nitriding step 12, in accordance with
reaction (3)
FeO.TiO2 + 3C + ½N2 = Fe + TiN + 3CO. (3)
In the iron oxidation step 14, the carbo-nitrided intermediate comprising
TiN and Fe is leached with an aqueous solution of FeC as lixivant. Substantially all of
the iron is converted to ferrous chloride (FeCI2) in accordance with reaction (4)
Fe + TiN + 2FeCI3(aq) = 3FeCI2(aq) + TiN (4)
The ferric chloride solution may be at a temperature of about 80°C.
Surprisingly, substantially none of the TiN is oxidised by the ferric chloride but
substantially all of the iron present is converted to ferrous ions. In order for the method
of the invention to work efficiently, the ferric ions must be in the form of a water-soluble
salt and the corresponding ferrous salt must also be water-soluble. Chlorides are the
preferred salts because of the high solubility of both FeC and FeCI2 in water, but there
are also other salts, e.g. nitrates that are suitable. Sulphates are preferably not used
because of the low solubility of ferric sulphate in water.
The next step of the method 10 requires removal of Fe2+ ions from the
carbo-nitrided intermediate subjected to ferric chloride leaching. This is typically
effected by filtrating a suspension comprising the leached carbo-nitrided intermediate
and the aqueous ferrous chloride solution, producing a low-Fe TiN product and a
ferrous chloride solution stream. Typically, the low-Fe TiN product is dried. If it is
desired to convert the TiN to TiCI4, the TiN is chlorinated with chlorine in a chlorinator at
a temperature of between about 170°C and 250°C, e.g. about 200°C. This step is not
shown in the drawings, but may for example be effected in accordance with the
teachings of US 6,423,291 .
In order to regenerate Fe3+ ions for use in the iron oxidation step 14, the
ferrous chloride solution is oxidised in the Fe2+ oxidation step 18, using air at about 1 to
2 bar(g) and 90°C. Depending on the temperature and oxidation potential at which this
reaction is undertaken, it is possible to form different iron oxides such as FeO.OH,
Fe(OH)3 or Fe2O3. The chemistry of the formation of different iron oxides from ferrous
chlorides is well documented and known to those skilled in the art and will not be
discussed in any further detail.
In the embodiment of the method shown in Figure 1, it is assumed that the
Fe2+ oxidation step 18 produces Fe2O3 in accordance with reaction (7)
6FeCI2 + 1½O2 = 4FeCI3 + Fe2O3 (7)
The Fe2O3 is present in the form of a Fe2O3 suspension and the Fe2O3 is
thus separated from the suspension to provide an Fe O3 by-product and a ferric
chloride solution, with the ferric chloride solution being recycled to the iron oxidation
step 14. Typically, about 2/3 of the ferrous chloride entering the Fe2+ oxidation step 18 is
converted to ferric chloride and the balance forms part of the Fe2O3 by-product.
Referring to Figure 2 of the drawings, another embodiment of a method in
accordance with the invention to upgrade a titaniferous material is shown and indicated
generally by reference numeral 100. The method 100 is similar to the method 10 and
unless otherwise indicated, the same process steps or features are indicated by the
same reference numerals.
As will be noted, instead of having a Fe2+ oxidation step 18 and an Fe2O3
filtration step 20, the method 100 includes an Fe electrowinning step 102. The Fe
electrowinning step 102 comprises an electrolytic cell in which the ferrous chloride
solution from the Fe ions removal step 16 is electrolytically converted to a ferric
chloride solution and iron, using reaction ( 11)
overall electrochemical reaction 3Fe2+ = Fe + 2Fe3+ ( 11)
The method of the invention, as illustrated, shows a number of
advantages compared to conventional processes of which the applicant is aware in
which Ί O 2, instead of TiN, is produced for subsequent chlorination to TiCI4. T1O2 is
stable and the titanium cannot be oxidised any further. In contrast, TiN is in a reduced
form and can readily be oxidised to titanium in the quaternary valence state. This is an
important aspect in the selective chlorination of TiN versus the unselective carbochlorination
of T1O2. The method of the invention enables lower capital costs for
chlorination reactors for the chlorination of TiN as compared to the chlorination reactors
required for the chlorination of T1O2. The method of the invention, as illustrated,
provides lower consumption of chlorine and does not use relatively expensive petroleum
coke, in contrast to conventional processes of which the applicant is aware that use
petroleum coke as reactant. The method of the invention, as illustrated, also does not
require roasting of ilmenite followed by magnetic separation of small amounts of lowgrade
impurities, as the method of the invention can accommodate these impurities.
Furthermore, the method of the invention, as illustrated, allows lower grade titaniferous
materials to be upgraded. In addition, any treatment of chlorinator off-gas when using
the method of the invention, as illustrated, is simpler because the gas volume and gas
temperature are significantly lower than for T1O2 chlorinators, and the gas does not
contain sublimed chlorides, such as FeCI3. It is also expected that the method of the
invention will provide lower T1CI3 losses in off-gas from the chlorinators.
CLAIMS:
1. A method of upgrading a titaniferous material, the method including
nitriding and reducing a titaniferous material which includes TiO2 and Fe oxides
in the presence of nitrogen and carbon to convert the Ί O 2 to TiN and to reduce most of
the Fe oxides to Fe;
oxidising the Fe in preference to the TiN to form Fe2+ ions; and
removing the Fe2+ ions to produce an upgraded low-Fe TiN bearing material.
2 . The method as claimed in claim 1, which includes chlorinating the
upgraded low-Fe TiN bearing material thereby converting the TiN therein to TiCI4 in
accordance with reaction ( 1) :
TiN + 2CI2 = TiC + ½N2 ( 1)
3 . The method as claimed in claim 1 or claim 2, wherein the titaniferous
material is ilmenite in which the T1O2 is mostly present as FeO.TiO2, with the FeO.TiO2
being nitrided carbothermically to provide TiN and metallic Fe and one or more carbon
oxides.
4 . The method as claimed in claim 3, wherein the TiN and Fe obtained from
the nitriding and reduction of the titaniferous material are in the form of a carbo-nitrided
intermediate which includes TiN and Fe, with the step of oxidising the Fe in preference
to the TiN to form Fe2+ ions including reacting the carbo-nitrided intermediate which
includes TiN and Fe with an oxidising anion to convert the Fe to Fe2+.
5 . The method as claimed in claim 4, wherein the oxidising anion is in the
form of an aqueous salt solution.
6 . The method as claimed in claim 5, wherein the aqueous salt solution is a
chloride solution.
7 . The method as claimed in claim 6, wherein the aqueous salt solution is a
FeC solution, with the oxidation of the Fe in preference to TiN to form Fe2+ ions, being
in accordance with reaction (4):
Fe + TiN + 2FeCI3(aq) = 3FeCI2(aq) + TiN (4)
8 . The method as claimed in claim 7, wherein reaction (4) is carried out at an
elevated temperature between ambient temperature and the boiling point of the ferric
chloride solution, to enhance the rate of reaction between the Fe3+ ions and the Fe and
to increase the solubility of both ferric chloride and ferrous chloride.
9 . The method as claimed in claim 7 or claim 8, wherein during the nitriding
and reducing of the titaniferous material, all of the Fe oxide is reduced to metallic iron
rather than to the divalent form, with the iron being in the form of small particles that are
intimately mixed with small TiN particles that are sintered together in the carbo-nitrided
intermediate which includes TiN and Fe, thereby allowing extraction of the iron as Fe2+
using FeCI3 in accordance with reaction (4) above.
10 . The method as claimed in claim 9, which includes the step of regenerating
Fe3+ ions from the ferrous chloride solution obtained by the extraction or leaching of the
carbo-nitrided intermediate with the ferric chloride solution.
11. The method as claimed in claim 10, in which only a portion of the ferrous
chloride is converted to Fe3+ ions, the balance being in the form of a by-product of the
method containing iron in a non-chloride form.
12 . The method as claimed in claim 11, wherein the regenerated Fe3+ ions are
recycled for reuse to oxidise the Fe in preference to the TiN to form Fe2+ ions.
13 . The method as claimed in any one of claims 10 to 12 inclusive, wherein
regeneration of the Fe3+ ions includes oxidation of the ferrous chloride with oxygen
according to reactions (7) and (8):
6FeCI2(aq) + 1½O2 = 4FeCI3(aq) + Fe2O3 (7)
6FeCI2(aq) + 1½O2 + H2O = 2FeO.OH + 4FeCI3(aq) (8)
14. The method as claimed in any one of claims 10 to 12 inclusive, wherein
regeneration of the Fe3+ ions includes the electrochemical oxidation of the ferrous
chloride in a cell to produce ferric chloride at an anode of the cell and electrolytic iron at
a cathode of the cell, with the electrochemical reactions to regenerate ferric chloride and
to electrowin iron being in accordance with reactions (9), ( 10) and ( 1 1) :
cathode reaction Fe2+ + 2e = Fe (9)
anode reaction 2Fe2+ = 2Fe3+ + 2e (10)
overall electrochemical reaction 3Fe2+ = Fe + 2Fe3+ ( 11)
15 . The method as claimed in any one of claims 4 to 14 inclusive, wherein
removal of the Fe2+ ions to produce the upgraded low-Fe TiN bearing material includes
separation of Fe2+ solution from the unreacted carbo-nitrided intermediate to produce
the upgraded low-Fe TiN bearing material and a Fe2+ solution.
16 . The method as claimed in claim 15, wherein the separation comprises a
physical separation step, followed by washing the low-Fe TiN bearing material with an
aqueous fluid, and optionally drying the upgraded low-Fe TiN bearing material.
AMENDED CLAIMS
received by the International Bureau on 4 May 20 2 (14.05.2012)
1. A method of upgrading a titaniferous material, the method including
nitriding and reducing a titaniferous material which includes Ti0 2 and Fe oxides
in the presence of nitrogen and carbon to convert the Ti0 2 to TiN and to reduce most of
the Fe oxides to Fe, the TiN and Fe obtained from the nitriding and reduction of the
titaniferous material being in the form of a carbo-nitrided intermediate which includes
TiN and Fe;
oxidising the Fe in preference to the TiN to form Fe2+ ions, the oxidation of the Fe
in preference to the TiN including reacting the carbo-nitrided intermediate which
includes TiN and Fe with a FeCI3 solution in accordance with reaction (4):
Fe + TiN + 2FeCI3(aq) = 3FeCI2(aq) + TiN (4)
and removing the Fe + ions to produce an upgraded low-Fe TiN bearing material.
2. The method as claimed in claim 1, which includes chlorinating the
upgraded low-Fe TiN bearing material thereby converting the TiN therein to TiCI4 in
accordance with reaction (1):
TiN + 2CI2 = TiCI4 + ½N2 (1)
3. The method as claimed in claim 1 or claim 2 , wherein the titaniferous
material is ilmenite in which the Ti0 2 is mostly present as FeO.Ti0 2, with the FeO.Ti0 2
being nitrided carbothermically to provide TiN and metallic Fe and one or more carbon
oxides.
4. The method as claimed in any of claims 1 to 3, wherein reaction (4) is
carried out at an elevated temperature between ambient temperature and the boiling
point of the ferric chloride solution (FeCI3(aq)), to enhance the rate of reaction between
the Fe ions and the Fe and to increase the solubility of both ferric chloride and ferrous
chloride.
5. The method as claimed in any of claims 1 to 4, wherein during the nitriding
and reducing of the titaniferous material, all of the Fe oxide is reduced to metallic iron
rather than to the divalent form, with the iron being in the form of small particles that are
intimately mixed with small TiN particles that are sintered together in the carbo-nitrided
intermediate which includes TiN and Fe, thereby allowing extraction of the iron as Fe2+
using FeCI3 in accordance with reaction (4) above.
6. The method as claimed in claim 5 , which includes the step of regenerating
Fe3+ ions from the ferrous chloride solution (FeCI2(aq)) obtained by the extraction or
leaching of the carbo-nitrided intermediate with the ferric chloride solution (FeCbiaq)).
7. The method as claimed in claim 6 , in which only a portion of the ferrous
chloride is converted to Fe3+ ions, the balance being in the form of a by-product of the
method containing iron in a non-chloride form.
8. The method as claimed in claim 7 , wherein the regenerated Fe3+ ions are
recycled for reuse to oxidise the Fe in preference to the TiN to form Fe2+ ions.
9. The method as claimed in any of claims 6 to 8, wherein regeneration of
the Fe3+ ions includes oxidation of the ferrous chloride with oxygen according to
reactions (7) and (8):
6FeCI2(aq) + 1½0 2 = 4FeCI3(aq) + Fe20 3 (7)
6FeCI2(aq) + 1½0 2 + H20 = 2FeO.OH + 4FeCI3(aq) (8)
10. The method as claimed in any of claims 6 to 8, wherein regeneration of
the Fe + ions includes the electrochemical oxidation of the ferrous chloride in a cell to
produce ferric chloride at an anode of the cell and electrolytic iron at a cathode of the
cell, with the electrochemical reactions to regenerate ferric chloride and to electrowin
iron being in accordance with reactions (9), ( 10) and ( 1):
cathode reaction Fe + + 2e = Fe (9)
anode reaction 2Fe + = 2Fe3+ + 2e ( 10)
overall electrochemical reaction 3Fe2+ = Fe + 2Fe + ( 1 1)
11. The method as claimed in any of claims 1 to 10, wherein removal of the
Fe2+ ions to produce the upgraded low-Fe TiN bearing material includes separation of
Fe2+ solution from the unreacted carbo-nitrided intermediate to produce the upgraded
low-Fe TiN bearing material and a Fe2+ solution.
12. The method as claimed in claim 11, wherein the separation comprises a
physical separation step, followed by washing the low-Fe TiN bearing material with an
aqueous fluid.
13. The method as claimed in claim 12 , which includes drying the upgraded
low-Fe TiN bearing material.