Description:FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
[See section 10, Rule 13]

A METHOD OF PRODUCING IRON OXIDE SINTER FROM ACIDIC IRON OXIDE CONTAINING CHLORIDE;

THE KERALA MINERALS AND METALS LIMITED, A GOVERNMENT OF KERALA UNDERTAKING, WHOSE ADDRESS IS SANKARAMANGALAM, CHAVARA, KOLLAM, KERALA, PIN - 691583, INDIA

THE FOLLOWING SPECIFICATION DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED.

Field of the Invention
The present invention relates to a method of producing iron oxide sinter from acidic iron oxide containing chloride from chloride contaminated acidic iron oxide generated in ilmenite beneficiation process.

Background of the Invention
Commercially, TiO2 pigment is produced either by chloride route or sulphate route. More than 60% of TiO2 pigment production in world proceeds through chloride technology as the chloride route pigment is much superior in terms of pigmentary properties over sulphate process.
In chloride technology, feed stock material for chlorination is synthetic rutile, titanium slag, natural rutile etc. Major TiO2 plants run with synthetic rutile as feed material due to easy availability which is produced from ilmenite beneficiation process and economic factor. The ilmenite, an ore of titanium contains about 30-40% of iron oxide in FeTiO3 form. Natural rutile is very scarce and in case of titanium slag, the production cost is very high. The synthetic rutile is produced either by Benalite process or Becher process. Benalite process for the production of synthetic rutile in which the first step is carbothermic reduction of ilmenite. During this, the ferric iron in ilmenite is reduced to ferrous at a temperature of 900°C. The reduced ilmenite is then leached with mineral acid to remove the iron content in ilmenite and upgrade the TiO2 value to 92 %. This upgraded ilmenite is called leached ilmenite which is then calcined at a temperature of 600 °C in third stage, produces the synthetic rutile, with a TiO2 content of about 90 to 92 %.
In the second stage, leaching process, the leach liquor produced containing ferrous chloride as the major constituent with a few ferric chloride and free hydrochloric acid. This leach liquor is subjected to high temperature spray roasting to produce hydrochloric acid as main product and acidic iron oxide (2.5% chloride containing iron oxide) as by-product.
The main hurdle for using the iron oxide generated from the chloride process is its fine nature and the high acidic chloride content inherent in it. Typically, iron ore fines have particle size around 100 micron which are sintered to produce iron oxide sinter of particle size in millimeters and such iron ore sinters were used as blast furnace feed. There are different techniques like briqueting, pelletizing, nodulizing, vacuum extrution, or sintering used in pig iron manufacturing industry to convert iron fines to a suitable size feeding material for blast furnace operation. However, the acidic iron oxide generated as the by-product during beneficiation of ilmenite has a particle size of 0.1 to 5 micron and at least 2% of chloride that makes it unsuitable for blast furnace process for the production of pig iron.
Iron oxide pellets are produced by various known process. US patent 7438,730 B2 reveals a method for producing an iron oxide pellet including the steps of adding water to a raw material mixture comprising iron oxide which serves as a primary component, a carbonaceous material in an amount sufficient for reducing the iron oxide, an organic binder and an inorganic coagulant. In the said patent, corn flour, dextrin, potato starch, wheat flour serving as an organic binder. Said patent discloses using iron ore powder of particle size 75 micron for making sinters and does not disclose use of catalyst for sintering.
WO2005/059186 patent application describes a process of producing iron ore agglomerate by agglomerating iron oxide powder with a binder of alkali metal silicate.
A mixture for pelletizing iron ore concentrates and accelerating sintering by adding bentonite, kaolinite, illite and chlorite was reported in patent US 3258327A.
A method of producing sponge iron pellet by mixing iron oxide of particle size 0.033 mm to 0.2 mm with binders like alkaline earth metal oxide, hydroxide or carbonate followed by reduction at a temperature of 1250 to 1350°C was reported in US 3682621A patent application.
US patent application US3754889A discloses iron ore concentrate containing acidic impurities was mixed with a flux of dolomite and limestone. The mix was balled and the green balls are dried and fired at a temperature for a time to form pellets. The pellets can be used as a charge material for metallurgical furnaces.
KR101145603B1 patent invention discloses a method for producing reduced iron pellets for producing partial reduced iron by reducing powder containing iron oxide in the molded article and carbon using a rotary hearth type reduction furnace wherein the iron oxide having average particle diameter of 50 micrometers or less was reduced by the carbon in the molded article to 1000 to 1500°C by radiation of the hot gas. High temperature sintering not only consumes more fuel, but also decreases the life of castable lining and shell life. Further, there is substantially increased break down frequency and hence increased maintenance cost.
There are several patent publications such as GB1104908 that disclose producing pellets of magnetic iron oxide and coke suitable for roasting in a furnace by roasting iron ore to form magnetic iron oxide, separating and agglomerating the oxide with coke in finely divided form. US5401485 discloses process for reducing the residual chloride present in iron oxides, particularly in regenerated iron oxides produced from hydrochloric acid waste liquid generated from steel pickling wherein neutralizing chloride present in iron oxide is done by washing with sulphuric acid and regenerating iron oxide containing 1400 ppm (0.14%) of chloride. However, washing with sulfuric acid would increase the acidity of the iron oxide. Further, the process involves handling and consumption of sulfuric acid.
Iron oxide generated as the by-product during beneficiation of ilmenite has very fine particle size of 0.1 to 5.0 micron and has a higher chloride content of 2.0%. Therefore, due to the low particle size and higher amount of chloride present in the iron oxide, while agglomerating by known methods, the chloride ion inherent in the material will be trapped in crystal lattice and the trapped chloride ion and hence the chloride ion will not be removed during the sintering process. Therefore, the acidic iron oxide and/or the iron oxide sinter with trapped chloride ion is not suitable for use in pig iron manufacturing. Hence, there is a need in the art for producing iron oxide sinter which can be suitable as blast furnace feed material for the production of pig iron by recycling or using the acidic iron oxide generated as the by-product during beneficiation of ilmenite having low particle size of about 0.1 to about 5 micron and at least 2% of chloride.
Summary of the Invention
In one aspect, the present invention relates to a method of producing iron oxide sinter from acidic iron oxide containing chloride comprising agglomerating acidic iron oxide containing at least 2% chloride having a particle size of 0.1 to 5 microns with 1% to 2% of an alkaline binder selected from sodium aluminate and 5% to 15% of water; neutralizing the iron oxide containing chloride by adding an alkali; granulating the neutralized iron oxide forming green pellets; simultaneously reducing and sintering the green pellets with a carbonaceous material at a temperature of about 900°C to 1000°C forming iron oxide sinter. The process comprises sintering and reducing the pellets in the presence of a catalyst selected from gypsum.
In an embodiment, the acidic iron oxide containing at least 2% chloride having a particle size of 0.1 to 5 microns is a by-product during beneficiation of ilmenite in chloride route titanium dioxide synthesis.
The process comprises, neutralizing the iron oxide containing chloride is by adding alkali selected from 1% to 2% calcium hydroxide, preferably 1.2% calcium hydroxide. The process further comprises reducing the green pellets with a carbonaceous material selected from 10% to 20% of non-pulverized fraction of petroleum coke.
In an aspect, the iron oxide sinter produced from acidic iron oxide containing chloride comprises 85% to 86% of iron as Fe, 2.5% to 3% of titanium dioxide (TiO2), 0.5% to 0.75% of silica (SiO2), 0.5% to 0.8% alumina (Al2O3), and less than 0.1% chloride. In an embodiment, the iron oxide sinter has hardness of 8 to 9 and particle size of diameter 5 mm to 10 mm.

Brief Description of Drawings
Figure 1 shows images of the iron oxide sinters produced in accordance with the present invention.

Description of Invention
The present invention provides a method of producing iron oxide sinter from acidic iron oxide containing chloride and a lower particle size. Particularly, the present invention relates to a method of producing iron oxide sinter from chloride contaminated iron oxide generated as a by-product from ilmenite beneficiation process. The iron oxide sinter produced by the present invention has sufficient hardness and particle size making its application as feed stock in blast furnace for pig iron production.
In an aspect, the present invention relates to a method of producing iron oxide from acidic iron oxide containing chloride. The method comprises agglomerating acidic iron oxide containing at least 2% chloride having a particle size of about 0.1 to about 5 microns with 1% to 2% of an alkaline binder selected from sodium aluminate and 5% to 15% of water; neutralizing the iron oxide containing chloride by adding an alkali; granulating the neutralized iron oxide forming green pellets; simultaneously reducing and sintering the green pellets with a carbonaceous material at a temperature of about 900°C to 1000°C forming iron oxide sinter.
The acidic iron oxide is typically produced by the chemical method involving high temperature spray roasting of spent acid generated during the ilmenite beneficiation process. The composition of the acidic iron oxide obtained as a by-product by chloride route titanium dioxide synthesis can have the following composition as shown in Table 1 below.
Table 1
Constituent Composition (%)
Fe2O3 (%) 92.85
TiO2 (%) 2.90
V2O5 (%) 0.46
Al2O3 (%) 0.59
MnO (%) 0.46
Cr2O3 (%) 0.16
CaO (%) 0.20
MgO (%) 0.60
SiO2 (%) 0.27
Total Chlorides (%) 2.40
Moisture (%) 0.50
Sulphur (%) 0.32
Phosporous (ppm) 0.0035
Particle size < 5 miron

Although the iron oxide content in the by-product is over 90%, the presence of chloride and lower particle size makes it unsuitable as a feed material in pig iron process.
In an embodiment, the acidic iron oxide containing at least 2% chloride having a particle size of 0.1 to 5 microns is a by-product during beneficiation of ilmenite in chloride route titanium dioxide (TiO2) synthesis. The present invention provides a process that removes the excess chloride and forms a sintered iron oxide that is suitable as a feed material to blast furnace for manufacturing of pig iron. Agglomerating the acidic iron oxide with alkaline binder not only helps in binding the acidic iron oxide particles but also partially neutralizes the chloride content especially the chloride trapped in crystal of iron oxide. The alkaline binder can be selected from 1% to 2% of sodium aluminate. Other binders such as sodium silicate, or bentonite can be used. Sodium silicate and bentonite can increase the silica content in iron oxide which may be undesirable for blast furnace feed material. Preferably the alkaline binder can be sodium aluminate.
The agglomerated partially neutralized iron oxide can be completely neutralized by adding an alkali selected from 1% to 2% calcium hydroxide. Other alkali such as sodium hydroxide, potassium hydroxide can also be used. However, calcium hydroxide is an economical choice than other alkalis. Further, calcium hydroxide contains two hydroxyl (OH) groups and hence the consumption of alkali can be reduced with calcium hydroxide. Preferably neutralizing the agglomerated iron oxide can be done by using 1.2% calcium hydroxide. In an embodiment the alkali can be added at the agglomeration step where simultaneous agglomeration and neutralization can be achieved. In another embodiment, the agglomerated iron oxide can be neutralized with the alkali. Neutralization removes the remaining chloride from the agglomerated iron oxide thereby completely neutralizing the acidic iron oxide and reducing the chloride content to an acceptable value of less than 0.1%.
The neutralized agglomerated iron oxide can be granulated forming green pellets by a method known in the art. The green pellets can be formed by known methods in a pan mixer.
The green pellets can be subjected to simultaneous sintering and carbothermic reduction at a temperature of about 900°C to 1000°C with a carbonaceous material forming iron oxide sinter. The carbothermic reduction and sintering can be carried out with 10% to 20% of non-pulverized fraction (NPF) of petroleum coke as a reductant. Preferably, the carbothermic reduction can be carried out in the presence of a catalyst gypsum which is easily available and economical. Sintering in the presence of gypsum reduces the sintering temperature. Addition of gypsum thus produces more metallic iron. It has been observed that the Vicar hardness Number (VHN) improved to a value 9 which shows the formation of more metallic iron with addition of gypsum. Formation of more metallic iron from iron oxide indicates elimination of chloride trapped in crystal lattice. Thus, addition of catalyst surprisingly further reduced the chloride content to the acceptable values of less than 0.1%.
Figure 1 shows the iron oxide sinter produced in accordance with the present invention. In an aspect, the iron oxide sinter produced by the process of the present invention particularly from acidic iron oxide containing chloride, comprises 85% to 86% of iron as Fe, 2.5% to 3% of titanium dioxide (TiO2), 0.5% to 0.75% of silica (SiO2), 0.5% to 0.8% alumina (Al2O3), and less than 0.1% chloride. The iron oxide sinter formed by the process of the present invention has hardness of 8 to 9 and particle size of diameter 5 mm to 10 mm. Thus, the iron oxide sinter produced is suitable for blast furnace operation with added advantage of TiO2 values. The titanium dioxide content of at least 2% in the by-product acidic iron oxide produced by the beneficiation process may improve the quality of the iron oxide as the feed material to the blast furnace and the sintered iron. The TiO2 content in the iron oxide sinter produced by the process of the present invention can be about 2% to 3%. The TiO2 in the sinter in turn will be incorporated in pig iron thereby enhancing the metallurgical properties of pig iron. The iron content in the sinter will be above 85.0%. As there is more iron content in the sinter more pig iron is produced.
The process of the present invention thus helps in recycling and/or reusing or converting the acidic iron oxide by-product produced during the beneficiation of ilmenite in chloride route titanium industry to a useful blast furnace feed material having a composition comprising iron oxide with added TiO2 content that enhances the metallurgical property of iron produced from such a feed material with the acceptable chloride content of less than 0.1%.

Examples
Examples are set forth herein below and are illustrative of different amounts and types of reactants and reaction conditions that can be utilized in practicing the disclosure. The following examples are given to describe further the details of the instant invention.
Methods
The raw material used for this study is acidic iron oxide powder generated during the beneficiation of ilmenite. The typical composition of iron oxide is given in Table 1. The chloride content and lower particle size of iron oxide generated in the by-product during beneficiation of ilmenite makes its unsuitable for blast furnaces process for the production of pig iron. The process was developed for the removal of trapped chloride in iron oxide followed by granulation and sintering to enhance the particle size of iron oxide there by makes it suitable as blast furnace feed material. All percentages, on weight basis, were analysed by Volumetric and Atomic Absorption Spectroscopy methods. Hardness was measured by Vicar hardness number (VHN) method.
Table 1
Sl. No. Constituent Composition (%)
1 Fe2O3 (%) 92.85
2 TiO2 (%) 2.90
3 V2O5 (%) 0.46
4 Al2O3 (%) 0.59
5 MnO (%) 0.46
6 Cr2O3 (%) 0.16
7 CaO (%) 0.20
8 MgO (%) 0.60
9 SiO2 (%) 0.27
10 Total Chlorides (%) 2.40
11 Moisture (%) 0.50
12 Sulphur (%) 0.32
13 Phosporous (ppm) 0.0035
14 Particle size < 5 miron

Detailed procedures and steps:
Example 1 (Comparative Example)
Iron oxide powder was mixed with 10% water and made green pellets by granulation using a pan mixer. These green pellets were then subjected to carbothermic reduction at 1000oC using 20% NPF as reductant. The sintered iron oxide was analyzed for composition, hardness, metal content and chloride present in it. VHN value of 5 confirmed the soft nature of the sintered iron oxide. The required hardness was not obtained.
Example 2
Iron oxide powder was mixed with 10% of water and 1.0-2.0% sodium aluminate (binder). From this mixture green pellets were made by granulation using a pan mixer. These green pellets were then subjected to carbothermic reduction at 1000oC using 20% NPF as reductant. Sintering process is a carbothermic reduction process, which was carried out in a rotary furnace. The iron oxide was heated along with the NPF coke. Iron oxide is reduced to metallic iron during carbothermic reduction method. There was a partial neutralization of the chloride content, especially chloride trapped in crystal of iron oxide by the alkaline binder of sodium aluminate. The sintered iron oxide was analyzed for composition, hardness, metal content and chloride present in it. The results are tabulated in Table 2.
Example 3
Iron oxide powder was mixed with 10% of water and 1.0-2.0% sodium silicate. This mixture was made to green pellets by granulation using a pan mixer. These green pellets were then subjected to carbothermic reduction at 1000oC using 20% NPF as reductant. The sintered iron oxide was analyzed for composition, hardness, metal content and chloride present in it. The results are tabulated in Table 2.
Example 4
Iron oxide powder was mixed with 10% of water and 1.0-2.0% bentonite. This mixture was made to green pellets by granulation using a pan mixer. These green pellets were then subjected to carbothermic reduction at 1000oC using 20% NPF as reductant. The sintered iron oxide was analyzed for composition, hardness, metal content and chloride present in it. The results are tabulated in Table 2.
Example 5
Iron oxide powder was mixed with 10% of water, 1.0-2.0% sodium aluminate and a neutralizing agent calcium hydroxide (1.0-2.0%). This mixture was made to green pellets by granulation using a pan mixer. These green pellets were then subjected to carbothermic reduction at 1000oC using 20% NPF as reductant. The sintered iron oxide was analyzed for composition, hardness, metal content and chloride present in it. The results are tabulated in Table 2.
Example 6
Iron oxide powder was mixed with 10% of water, 1.0-2.0% an alkaline binder selected from sodium aluminate and a neutralizing agent selected from calcium hydroxide (1.0-2.0%). To the above mixture 0.80 % to 1.2 % of gypsum (preferably 1.0 %) was added which acts as a catalyst during sintering process. This mixture was made to green pellets by granulation using a pan mixer. These green pellets were then subjected to carbothermic reduction at 900oC using 20% NPF as reductant. As a sintering aid gypsum was added, the sintering temperature was reduced from 1000 oC to 900 oC. The sintered iron oxide was analyzed for composition, hardness, metal content and chloride present in it. The results are tabulated in Table 2.
All the above method (examples 1 to 6) produces iron oxide sinter but the best results are with example 5 and 6.
The comparative experimental results for examples 1 to 6 showing the difference in composition including the major constituent present in iron oxide sinter and the properties are given in table 2 below.
Table 2
Sl. No Parameter Example
1 Example
2 Example
3 Example
4 Example
5 Example
6
1 Iron as Fe (%) > 86.0 > 86.0 > 86.0 > 86.0 > 86.0
> 86.0
2 TiO2 (%) 2.5 3.2 2.7 2.8 2.9 2.8
3 SiO2 (%) 0.4 0.4 1.2 1.0 0.5 0.6
4 Al2O3 (%) 0.5 0.8 0.5 0.5 0.8 0.8
5 Chloride (%) 0.5
0.2 0.3 0.3 < 0.1
< 0.1
6 Particle size (mm) 5 to 10 5 to 10 5 to 10 5 to 10 5 to 10 5 to 10
7 Hardness (VHN) 5 8 8 7 8 9

The chemical analysis above clearly showed that the iron oxide sinter produced is suitable for blast furnace operation with added advantage of TiO2 values. The TiO2 content in the iron oxide sinter varies from 2.5% to 3.2% with an average of 2.9%. This TiO2 incorporated in pig iron thereby enhances the metallurgical properties of pig iron. The iron content in the sinter will be above 86.0 %. As more the iron content in the sinter, more the pig iron is produced. There will be slight enrichment of silica and alumina content in the iron oxide sinter compared to raw iron oxide due to the addition of binder and catalyst. The chloride content in iron oxide sinter showed more desired value of < 0.1%, for iron oxide sinter produced in example 5 and 6. There was a partial neutralization of the chloride content, especially chloride trapped in crystal of iron oxide by using the alkaline binders. The remaining chloride present in the iron oxide was further neutralized with calcium hydroxide (1.0-2.0 %). The addition of suitable alkaline binder to iron oxide for binding and partial neutralization, followed by complete neutralization using calcium hydroxide, and sintering with a catalyst (gypsum) reduces the chloride content to the acceptable values of less than 0.1 %. Moreover, iron oxide sinter produced by the above method showed sufficient hardness (VHN : 8-9) and particle size between 5 mm to 10 mm makes its application as feed stock in blast furnace for pig iron production.
The foregoing description of specific embodiments of the present invention has been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching.
The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others, skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated.
It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.

, C , Claims:
1. A method of producing iron oxide sinter from acidic iron oxide containing chloride comprising:
a. agglomerating acidic iron oxide containing at least 2% chloride having a particle size of 0.1 to 5 microns with 1% to 2% of an alkaline binder selected from sodium aluminate and 5% to 15% of water;
b. neutralizing the iron oxide containing chloride by adding an alkali;
c. granulating the neutralized iron oxide forming green pellets;
d. simultaneously reducing and sintering the green pellets with a carbonaceous material at a temperature of about 900°C to 1000°C forming iron oxide sinter.
2. The method as claimed in claim 1, wherein comprises sintering and reducing the pellets in the presence of a catalyst selected from gypsum.
3. The method as claimed in claim 1, wherein the acidic iron oxide containing at least 2% chloride having a particle size of 0.1 to 5 microns is a by-product during beneficiation of ilmenite in chloride route titanium dioxide synthesis.
4. The method as claimed in claim 1, wherein comprises neutralizing the iron oxide containing chloride is by adding alkali selected from 1% to 2% calcium hydroxide, preferably 1.2% calcium hydroxide.
5. The method as claimed in claim 1, wherein comprises reducing the green pellets with a carbonaceous material selected from 10% to 20% of non-pulverized fraction of petroleum coke.
6. Iron oxide sinter produced from acidic iron oxide containing chloride by the process as claimed in claims 1 to 5, wherein comprises 85% to 86% of iron as Fe, 2.5% to 3% of titanium dioxide (TiO2), 0.5% to 0.75% of silica (SiO2), 0.5% to 0.8% alumina (Al2O3), and less than 0.1% chloride.
7. The iron oxide sinter as claimed in claim 6, wherein has hardness of 8 to 9.
8. The iron oxide sinter as claimed in claim 6, wherein has a particle size of diameter 5mm to 10mm.