Method of separating iron and its alloy metals from fine-grained crude oxidic products

Pure ferro-alloy metals are isolated from fine-grained crude oxidic mineral products by reduction melting and subsequent anodic liberation of the iron. The reduction melting is performed in a plasma-heated furnace into which the fine-grained oxide material is blown together with carbon powder and circulating exhaust gas, extremely over-heated in a plasma generator, the quantity of carbon powder being dosed so that most of the alloy metal(s) is converted to carbides during the reduction. After electrolysis, the anode residue will consist primarily of alloy metal carbides from which the metal can be recovered by known methods.

The invention relates to a method of separating iron and one or more 
ferro-alloy metals from fine-grained crude oxidic mineral products by 
means of reduction melting, to produce a ferro-alloy for use as anode 
material in the electrolytic liberation of the iron content therein and 
precipitation of pure iron on the cathodes, at the same time forming an 
anode residue constituting a concentrate of the alloy metal or metals. 
Ferro-alloy metals exist primarily within groups IV a, V a and VI a of the 
periodic system. They often occur in oxidic mineral together with iron 
oxides and cannot be separated from the iron by mechanical enriching. 
Examples of such oxidic minerals are ilmenite FeO.TiO.sub.2, niobite 
FeO.Nb.sub.2 O.sub.5 and chromite FeO.Cr.sub.2 O.sub.3. 
Starting with oxidic mineral of the type mentioned above, for instance, the 
corresponding ferro-ally, that is ferro-titanium, ferro-niobite and 
ferro-chromium in the above cases, can be produced by means of reduction 
melting. Since the alloy metals in the above groups are all less noble 
than iron they cannot be produced in pure form by removing the iron 
through de-slagging. 
Neither does anodic liberation of the iron offer any solution. Although the 
alloy metals are attacked before the iron, they cannot form soluble salts 
in neutral water solution, but will be converted to a fine hydroxide 
slurry forming a suspension not prone to sedimentation. The suspension 
particles are thus combined with and contaminate the cathode iron. An 
electro-chemical unbalance also occurs since both iron and alloy metal are 
oxidized at the anode whereas only iron is precipitated on the cathode. 
This is not compatible with Faraday's law. 
Instead, the object is production of a ferro-alloy for use as anode 
material in the electrolytic liberation of iron to form an anode residue 
which is substantially free from iron. 
By binding the alloy metals as carbides in the reduction process, i.e. by 
producing a carburetted alloy, more favourable conditions are created for 
the electrolytic precipitation of iron. All the alloy metals have a 
greater affinity to carbon than iron does, and carbon in the melt will 
therefore be bound to them by preference. When the melt solidifies, 
carbides, which generally have high melting points, are separated out and 
form separate crystals in the iron matrix. Upon anodic liberation of such 
an alloy, the carbide crystals are exposed without being oxidized and, at 
moderate contents, they form an anode residue consisting of a coherent 
skeleton structure which gives rise to very little current resistance. 
Since electro-chemical balance now reigns, i.e. the only anode reaction is 
liberation of iron and the only cathode reaction is precipitation of iron, 
the electrolysis can continue until practically all the iron has been 
liberated. 
At the time of the present invention reduction melting is normally carried 
out in electric arc furnaces. Fine-grained starting material cannot be 
used for this and must first be agglomerated by pelletization, for 
instance. The oxide materials in question here, however, have extremely 
high melting points and some are even used as refractory material. 
Agglomeration is thus an exremely complicated and expensive process which 
should preferably be avoided. 
The present invention is designed to produce pure ferro-alloy metals from 
fine-grained oxidic starting material by a process in which the above 
drawbacks are subtantially eliminated. 
This is achieved, according to the present invention, by a procedure in 
which the reduction melting process is performed in a plasma-heated 
furnace into which the fine-grained oxide material is blown together with 
carbon powder and circulating exhaust gas extremely over-heated in a 
plasma generator, the quantity of carbon powder being dosed so that a 
substantial proportion of the alloy metal(s) is converted into carbides 
during the reduction process and the anode residue formed after 
electrolytsis consists primarily of alloy metal carbides from which the 
pure alloy metal(s) can be recovered by methods known per se, e.g. direct 
chlorination. 
The invention thus makes it unnecessary to use coke. Coal dust works 
excellently. The circulating exhaust, consisting primarily of carbon 
monoxide, is preferably given a heat content of 4-6 kWh/Nm.sup.3 when 
heated in the plasma-generator, thus enabling the strongly endothermic 
reduction and carbide-forming reactions to proceed. 
According to one embodiment of the invention, nitrogen gas, also heated in 
th plasma generator, is blown into the furnace together with the 
circulating exhaust gas, whereupon a ferro-alloy is formed containing a 
mixture of carbides and nitrides of the alloy metals. This mixture is then 
included in the anode residue formed during the electrolytic treatement. 
As a rule, the alloy metals have a greater affinity to nitrogen than iron 
does and the carbo-nitrides, i.e. the mixture of carbides and nitrides, 
behave in the same way as the carbides. For certain metals such as 
zirconium, carbo-nitridation gives a better yield than just carbide 
formation. The amount of carbon powder should be sufficient for 
substantially all of the alloy metal(s) to be converted, to carbide when 
nitrogen is not used or to carbide/nitride when nitrogen is also used. In 
other words, there should be more than 50% by weight conversion of alloy 
metal(s) and preferably at least 90% by weight conversion. 
The reduction melting process itself can be performed in various ways. 
According to one embodiment of the invention, the oxide-containing 
starting material and the carbonaceous reducing agent are blown into the 
reaction chamber which is continuously produced in a shaft filled with 
coke due to the action of the gases heated in the plasma generator, the 
reaction taking place in said reaction chamber and melts of carburetted 
ferro-alloy and slag formed are caused to flow down to the bottom of the 
shaft to be tapped off and separated. This method gives high carburization 
from the coke column. 
According to another embodiment of the invention, the plasma-heated gases, 
the oxide-containing material and the carbonaceous reducing agent are 
blown in under the surface of the slag bed, whereupon the reactions take 
place in the gas bubbles formed and carburetted ferro-alloy is separated 
at the bottom of the slag bed. In this embodiment the carbide formation 
can be accurately adjusted by controlling the quantity of carbonaceous 
reducing agent added. Oxide material in chunks may, however, also be added 
to the surface of the slag bed. 
According to yet another embodiment of the invention the plasma-heated 
gases, the oxide-containing starting material and the carbonaceous 
reducing material are blown in under the surface of a melt of the 
ferro-alloy in question, from which slag formed is separated out. This 
method also leads to high carburization and allows the addition of solid 
oxide material to the surface of the slag bed.

EXAMPLE 
The invention will first be described in connection with the production of 
pure titanium. However, it should be noted that the invention is in no way 
limited only to the production of titanium but, as indicated above, is 
particularly suitable for the production of all ferro-alloy metals from 
groups IV a, V a and VI a. 
The most usual titanium mineral is ilmenite, for which the full formula can 
be written FeTiO.sub.3. The carburetted alloy formed in the reduction 
according to the invention contains carbide TiC, which is extremely stable 
and has a melting point of ca 3250.degree. C. It is also easy to 
chlorinate to TiCl.sub.4, to which we shall revert later on in the 
Example. 
An ilmenite concentrate having the following analysis is used as oxidic 
starting material: 
______________________________________ 
TiO.sub.2 45% 
FeO 35% 
Fe 35,4% 
Fe.sub.2 O.sub.3 
11,5% 
MgO 4,5% 
SiO.sub.2 2,5% 
other oxides 1,5% 
______________________________________ 
The ore concentrate is reduced in a furnace with coke-filled shaft and the 
necessary energy is supplied by means of a plasma generator. Under the 
extreme reducing conditions prevailing, about 90% of the titanium content 
and about 95% of the iron content are reduced out and form carburetted 
ferro-titanium. The remainder of the oxide content forms a slag. 
Carbonaceous reducing material is added to the reduction furnace, as well 
as ore concentrate. Slag containing primarily MgO and SiO.sub.2 is removed 
separately and the carburetted ferro-titanium is removed for further 
treatment. 
Taking 1 ton ilmenite concentrate as a basis for calculation, the material 
balance shown in the following table is obtained. 
TABLE 
__________________________________________________________________________ 
Concen- Ferro- 
trate Slag Carburette 
Carbide 
Iron 
Oxide (kg) (kg) 
(%) 
(kg) 
(%) 
(kg) 
(%) 
(kg) 
(%) 
__________________________________________________________________________ 
TiO.sub.2 
450 45 29.4 
SiO.sub.2 
25 25 16.3 
FeO 350 23 15.0 
Fe.sub.2 O.sub.3 
115 -- -- 
Converted 
270 27 
-- -- 243 
38.0 
238 
78.3 
to pure 
Ti 
Converted 
354 18 
-- -- 336 
52.5 
6 2.0 
330 
99.5 
to pure 
Fe 
MgO 45 45 29.4 
Other oxides 
15 15 9.8 
C -- -- -- 61 
9.5 
60 
19.7 
Total 1000 153 640 304 330 
__________________________________________________________________________ 
The carburetted ferro-titanium recovered is granulated and placed in net 
baskets of an inert material such as titanium. The baskets are placed in 
cells with an electrolyte suitable for precipitation of the iron, such as 
FeCl.sub.2 -NH.sub.4 Cl with a concentration of 15 g Fe/l and 135 g 
NH.sub.4 Cl/l, the ammonium chloride being present to prevent 
ferro-hydroxide from being precipitated although the pH value is close to 
6. The granules are attacked concentrically, leaving skeleton structured 
carbides with extremely low iron content. These can be considered to 
constitute a concentrate, in this case of titanium. 
The iron cathodes obtained, often known as "flakes" are used as highly pure 
scrap iron. Calculated on th same basis as the above, 304 kg of titanium 
and 330 kg iron are obtained. 
Titanium carbide is an extremely favourable starting material for continued 
treatment. For the production of pure alloy metal, it is often desirable 
to first form metal chloride, and the titanium carbide is extremely easy 
to chlorinate, particularly in comparison with the oxide. 
The oxides require "reducing chlorination", i.e. heating to 
800.degree.-900.degree. C. in briquette form with carbon, whereas carbides 
react directly with chlorine at about 600.degree. C. Pure metal is then 
produced from the chloride, by means of metallo-thermic reduction. 
As mentioned earlier, the invention is equally suitable for separating iron 
and producing other pure alloy-metals. by way of examples, below is 
described the procedure and the advantages of applying the invention to 
alloy-metals other than titanium. However, the list in no way lays claim 
to being complete and many other applications of the invention are also 
feasible. 
Zirconium ZrSiO.sub.4 is the most usual material containing zirconium. It 
is extremely advantageous to use the invention for zirconium rich in iron, 
but not so profitable if the iron content is low. Zirconium easily forms 
carbonitride. The embodiment with a coke-filled shaft should preferably be 
used, enabling the removal of most of the silicon content as gaseous SiO. 
Steel slags often contain vanadium. With relatively high contents of 
vanadium, carburetted ferro-vanadium can be reduced directly from the 
molten slag according to the invention. However, with lower vanadium 
contents a two-step process is advisable in which a gentle reduction is 
performed removing so much of the iron content that a vanadium-rich 
ferro-alloy can be produced in the next step for further treatment 
according to the invention. Magnetite containing vanadium and other 
similar materials can also be treated in a similar manner according to the 
invention. 
Niobium and tantalum generally occur in the minerals niobite and tantalite 
which, besides varying contents of pentoxides of these metals, also 
contain oxides of iron and manganese. According to conventional methods 
iron and manganese oxides are liberated in hydrochloric acid, after which 
the remaining pentoxides must be dissolved in hydrofluoric acid to be 
converted later to chlorides which are separated in a water solution by 
liquid extraction in pure niobium chloride and tantalum chloride. The pure 
metals can finally be produced after hydrolysis to oxides. 
According to the present invention carburetted ferro-niobium-ferro-tantulum 
can be produced immediately, from which a carbide concentrate is produced 
by anode liberation of iron and manganese. The carbide concentrate can be 
directly chlorinated and the niobium and tantalum chlorides are separated 
from the mixture of pentachlorides formed, by means of distillation which, 
since they are free from water, can easily be converted to the pure metals 
by means of metallo-thermic reduction. 
Tantalum is often present in tin ore and remains after tin has been reduced 
out in the slag. If such slag is treated in accordance with the invention, 
carburetted ferro-tantalum can be produced directly from the liquid slag. 
Chromium exists almost solely in the form of chromite (Fe, Mg) O.CR.sub.2 
O.sub.3. Pure chromium is produced by a conventional method according to 
which a type of carburetted ferro-chromium is produced by reduction of 
piece ore or pellets with coke, after which leaching can be performed with 
sulphuric acid. The leaching is performed with return sulphuric acid from 
electrolytic precipitation of chromium and thus contains ammonium 
sulphate, and from the chromium-iron sulphate solution, by means of 
series-crystallization a pure ammonium chromium sulphate can be produced 
which, upon electrolytic cracking, gives chromium cathodes and return 
sulphuric acid. The iron must be rejected as iron sulphate. 
Several advantages are gained by the use of the present invention: that 
fine-grained chromite in the form of concentrate from enrichment of poor 
ore can be used as starting material, the reduction can be performed with 
coal, no liberation of chromium from the anode material in the neutral 
electrolyte appears, the anode residue can be directly leached with return 
sulphuric acid, the production of pure chromium salt for the electrolysis 
is facilitated and, finally, the iron content can be utilized as pure iron 
cathodes. 
It may also be mentioned that chromium ores often contain platinum-group 
metals. These can also be recovered by application of the method according 
to the invention, in which case the process is preferably divided into two 
steps. A gentle reduction is effected in the first step and only some of 
the iron is reduced, whereupon this iron will take the platinum-grpoup 
metals with it in the form of metals, not as carbides. After electrolytic 
liberation of the iron, the platinum-group metals are obtained in an anode 
slam. 
The invention can also be used in the recovery of pure molybdenum from 
waste material containing iron, and even tungsten and uranium can be 
recovered by means of the method according to the present invention.