Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group ivb metal
Reexamination Certificate
2001-06-15
2004-10-12
Bos, Steven (Department: 1754)
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group ivb metal
C423S082000, C423S086000
Reexamination Certificate
active
06803024
ABSTRACT:
1. FIELD OF THE INVENTION
This invention relates to a method of beneficiating titania slag to a high grade titanium dioxide (TiO
2
) product. Preferably the product is suitable for use as a feedstock in titanium dioxide pigment production or titanium metal production by means of the chloride process. The invention also relates to a process for preparing intermediate products suitable for use in the beneficiation of titania slag and also to intermediate products and final products formed by the processes.
More particularly the process of the present invention includes the steps of sizing the slag; oxidizing the sized slag and then reducing the oxidized slag. The treated slag may then be subjected to steps such as acid leaching.
2. BACKGROUND OF THE INVENTION
Commercial Uses of TiO
2
Titanium is widely known for its use as a metal, but the primary use of titanium is in the form of titanium dioxide (TiO
2
). TiO
2
is used as a white pigment in paints, plastics and paper. Two types of pigment with a tetragonal crystal structure are produced, namely rutile and anatase. Rutile is preferred in outdoor paints and anatase is preferred in indoor paints.
TiO
2
Pigment Production
There are two commercial processes for the production of TiO
2
pigment namely, the sulphate process and the chloride process. A sulphate process plant is easier to operate and monitor than a chloride process plant, and is capable of using feedstock with a relatively low TiO
2
content. However, capital costs of a modem sulphate process plant can be higher than that of a chloride process plant of the same pigment capacity. Furthermore there is a higher volume of waste products to be treated and disposed of due to the use of more impure feedstock and the fact that the sulphate used in the process cannot be easily recovered and recycled.
Accordingly the chloride process is a more popular process and is growing in popularity. The feedstock suitable for use in the chloride process usually needs to have a high TiO
2
content and needs to contain fewer impurities than those suitable for the sulphate process.
TiO
2
Bearing Deposits
TiO
2
is commonly found in nature in the form of ilmenite (FeO. TiO
2
) which contains from 40% to 80% TiO
2
. Most deposits being mined produce concentrates with a TiO
2
content between 45% and 67%. Rutile deposits are far more scarce than ilmenite and they contain about 95% TiO
2
in crystalline form and are therefore of sufficient quality to be used directly in the chloride process for TiO
2
pigment production. Deposits of anatase have been discovered but have not yet been commercially exploited. Anatase typically has a TiO
2
content in excess of 95%. Leucoxene, a weathered form of ilmenite, contains up to 85% TiO
2
and is exploited on a limited commercial scale. Brookite (rhombic TiO
2
), perovskite, (CaTiO
2
), sphene (CaTiSiO
5
) and geikielite (MgTiO
3
) also contain titanium.
Beneficiation of Ilmenite
Although natural rutile is suitable for use as a feedstock in the chloride process, the ever. decreasing availability of natural rutile forced chloride process pigment producers to consider other lower grade feedstock. One such alternative is naturally occurring ilmenite. Due to its relatively low TiO
2
content several processes have as their aim the upgrading of the TiO
2
content of ilmenite.
These processes include:
i) Partial Reduction of the Iron in the Ilmenite.
This process is described in U.S. Pat. Nos. 4,038,364 and 4,199,552. In this process ilmenite is reduced at elevated temperatures to convert iron in the ferric state, (Fe(III)), to the ferrous state, (Fe(II)). This renders the iron more amenable to acid leaching of the ilmenite during upgrading of the ilmenite.
ii) Pre-Oxidation Followed by Partial Reduction of the Iron in the Ilmenite.
In a process described in GB1,225,826 the ilmenite is subjected to an oxidation treatment to convert substantially all the iron to the ferric state. The ore is then reduced to convert the iron back to the ferrous state and metallic state. In the examples of the patent the oxidation is carried out at 870° C. for two hours. The reduction is carried out at 870° C. for five minutes. The ore exhibits the original X-ray diffraction pattern of ilmenite after treatment but is more amenable to acid leaching to upgrade the ilmenite.
iii) Pre-Oxidation Followed by Reduction of the Iron to Metallic State.
U.S. Pat. No. 4,097,574 describes a process whereby ilmenite is subjected to an oxidation treatment to convert the iron in the ilmenite to the ferric state. Reduction treatment is then carried out to reduce the iron to metallic iron. The iron is then removed by leaching thereby to upgrade the ilmenite.
iv) Smelting of the Ore.
Ilmenite ore can also be smelted in the presence of a carbonaceous reducing agent in an electric arc furnace. This process is described in U.S. Pat. No. 2,680,681. Two saleable products result from this namely, high quality pig iron and titania rich slag. The slag typically contains 80-85% TiO
2
.
Differences Between Ilmenite Ore and Titania Slag
All of the processes listed above are aimed at beneficiating ilmenite or similar titanium ores. None of these processes were applied to titania slag and there are certain fundamental differences between ilmenite ore and titania slag.
i) The first difference is that ilmenite is a naturally occurring titanium bearing ore, while titania slag is produced by electro-smelting of ilmenite in an electric arc furnace.
ii) The second difference can be found in the amount of the main components that are present. Ilmenite typically contains around 50% titanium oxide and around 45% iron oxide. All the titanium is present as Ti(IV) while around 20% of the iron occurs as Fe(III) and the rest is in the Fe(II) state. Titania slag typically contains around 85% titanium oxide and around 10% iron oxide. In this instance the titanium is in the Ti(III) and the Ti(IV) state, while most of the iron is present as Fe(II).
iii) The third difference lies in the respective mineralogical compositions. In ilmenite concentrates the iron and the titanium is organised into hexagonal ilmenite crystals. As-cast titania slag consists of the following four phases:
a) The most abundant phase is a crystalline phase, known as pseudobrookite or the M
3
O
5
phase. This phase is a solid solution of iron oxide and titanium oxide, with the end members being (Ti,Fe,Al,Cr,V)
2
O
3
.TiO
2
and (Mg,Mn,Fe)O.2TiO
2
and can accommodate the main oxidation states of iron and titanium in its structure, namely Fe(II), Fe(III), Ti(III) and Ti(IV);
b) Rutile (TiO
2
) although not always present in such quantities that allows detection thereof by X-ray diffraction analysis;
c) An amorphous, glassy phase consisting mainly of SiO
2
, TiO
2
, FeO, CaO and Al
2
O
3
and;
d) Finely disseminated metallic iron globules present in the grain boundaries of the rutile crystals and in the silicate-rich glassy matrix.
The pseudobrookite and amorphous glassy phases are characteristic of titania slag and generally do not occur in ilmenite ores. The presence of pseudobrookite and the glassy phases in titania slag may be one of the causes that the processes for beneficiating ilmenite ore are in some cases not applicable to the beneficiation of titania slag. The different compositions of slags may also play a role.
Beneficiation of Titania Slag
Several known processes have as their aim the upgrading of the TiO
2
content of titania slag.
These processes can be classified as follows:
i) Chlorination of the Impurities
A process described in U.S. Pat. Nos. 4,629,607; 4,933,153; 5,063,032 and 5,389,355 to upgrade titania slag containing at least one alkaline earth impurity. Firstly the slag is preheated in a fluidized bed reactor in an atmosphere void of oxygen to prevent the oxidation of the Ti(III) present in the slag to Ti(IV). The slag is then contacted with hydrogen chloride gas. This results in the formation of iron and alkaline earth chlorides in the slag. Finally the chlorides that formed during the chlorination treatment are leached with either w
De Lange Thomas
Nell Johannes
Van Dyk Jacobus Philippus
Vegter Nanne Mattheus
Visser Cornelia Petronella
Bos Steven
Fish & Richardson P.C.
Ipcor NV
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