FIELD OF THE INVENTION
The present invention relates to utilization of low grade iron ore. The invention is
particular relates to use of iron ore containing high AI203 and SiO2 along with
LD slag. More, particularly, the invention relates to a process for utilization of low
grade iron ore.
BACKGROUND OF THE INVENTION
Integrated steel plants (ISPs) use huge quantity of iron ore and conversion of iron
ore into pig iron (also called hot metal) takes place in the blast furnaces. Hot
metal is refined and alloyed suitably during steelmaking operation to produce
different kind of steel grades.
Blast furnaces are time-tested smelter using sized iron ore along with prepared
agglomerates (in form of sinter or pellet) which gets reduced by coke & coal to
give hot metal. Smelting is a metallurgical process in which reduction and melting
takes place simultaneously.
Indian iron ores and coals are typically of low grade variety which contains high
amount of gangue elements {i.e. SiO2 and AI203). During blast furnace
operation, suitable fluxes are used to take care of gangue elements (fluxes and
gangue react with each other and make slag). Higher gangue elements give
higher slag volume which adversely affects blast furnaces operation. Therefore,
higher limit of gangue elements in iron ore is fixed for each blast furnace
operation. The higher limit for AI203 and SiO2 in the iron ore is typically in the
range of 1.5% and 2.0% respectively. Thus, iron ore containing higher AI203 and
SiO2 is called low grade iron ore and simply treated as waste during mining of

iron ore. There had been a few attempts to blend low and high gangue iron ores,
but, the benefits were marginal. The amount of low grade iron ore generated
during mining operation each year in India is staggering (besides, there are huge
low grade iron ore deposits which are not mined at all). In light of this,
researchers in steel industry are trying to figure out ways to use low grade iron
ore.
OBJECTS OF THE INVENTION
An object of the invention is to develop a process to use low grade iron ore with
high amount of gangue material, the Iron ore having high levels of AI203 (5-15%)
& SiO2 (15-45%) to higher amounts (-900-1300 kg/thm) in the blast furnaces.
Another object of the invention is to develop a process that can make use of LD
(BOF) slag along with low grade iron ore, with mass recycling of LD slag (>750
kg/thm) while gainfully utilizing the useful elements of LD slag (e.g. Fe and CaO),
which is wasted, if LD slag being re-useable for various applications such as
aggregates for roadmaking /construction or ballast for railways tracks.
Yet another object of the invention is to replace Fe-P (a ferroalloy used for
alloying steel) with High Phosphorus Pig Iron (HPPI), to produce HPPI with pig
iron phosphorus varying from 1.5 - 3.0% (pig iron phosphorus varies depending
upon the proportion of LD slag in the burden).
Further object of the invention is to develop a process that overcomes limitations
of the prior art and ensure utilization of low grade iron ore.

Still another object of the invention is to develop a new product i.e. high
phosphorus pig iron (P: 1.5 - 3.0%) for niche applications e.g. cathode of
Aluminum smelters, hard facing powders, brake drums for railways, piston rings
of engines, various high phosphorus requirements of foundry applications.
Summary of the Invention:
The process as per the invention makes use of low grade iron ore along with LD
slag and coal/coke fluxes. The new process entails using low grade iron ore in
higher amount (900-1300 kg/thm) and the feed mixture is treated in normal blast
furnace conditions as in case of normal iron making process in steel industry
The process results in 1:1 Hot Metal & Slag Ratio (hot metal produced has high
phosphorous content varying in the range of 1.5 to 3.0%).
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

A normal blast furnace operation uses iron bearing materials (e.g. prime quality
sized iron/ore and agglomerates in the form of sinter and pellets) along with fuel
(coke and coal) and fluxes (limestone, dolomite, quartz etc.) to produce pig iron
(hot metal) and slag in the typical ratio of 4:1. Hot metal is used for steelmaking
whereas slag is re-used as raw material for cement making.

The new inventive process uses blast furnace with different input raw materials
e.g. iron bearing materials (e.g. low grade Iron Ore and sinter and LD slag) along
with fuel (coke) and fluxes (Dolomite and Quartz) to produce high phosphorus pig
iron (P: 1.5 - 3.0%) and slag in equal amount. Higher fuel rate (100-150 kg/thm
+) is maintained to produce high silicon pig iron (Si: 2.0% +). High phosphorus
pig iron is utilized for foundries as foundry grade pig iron or various other
applications whereas the slag is utilized for cement making.
The inventive process does not demand any change in BF process as such - the
feed mixture is processed as in case of normal iron making process. However,
operation regime will change substantially because of very high slag volume
(typical metal slag ratio from normal to inventive process will change from 4:1 to
1:1).
Fig. 1 shows pictorial view of the normal blast furnace process and new invented
process. While composition and quality of fuel (i.e. coke) and fluxes (Dolomite,
Quartz etc.) remains same in the normal and new invented process, the key
difference lies in the composition of iron bearing materials used in the process
and quality of hot metal and slag produced. The new process uses LD slag in
various proportion (40-80%), as a result slag volume increases which reduces
slag AI203. Lower slag AI203 enables use of low grade iron ore in the form of
lump (e.g. high SiO2 BHJ/BHQ) or sinter from high AI203 iron ore fines/slimes or
both (see Annexure -1 for burden details with low grade iron ores).
The composition of prime and low grade Iron ore is given in the Table below.


Low grade iron ore contains high amount of AI203 and SiO2. Normal blast
furnace process cannot use low grade iron ore/sinter as it adversely affects the
productivity and smooth operation of present day blast furnaces operating in
India or abroad.
The composition of LD slag used for this invention is given in the table below.
The LD slag chemistry may vary to an extent depending upon the steelmaking
operations and depending upon the source of raw materials and their
corresponding compositions used during steelmaking.

Examples:
The new process has been tried out in Mini Blast Furnace (working volume: 55
m3). This trial produced 303 tons of high phosphorus pig iron. The slag produced
with the new invented process has higher basicity (CaO/SiO2) than normal blast

furnace operation (see Table below). Higher basicity slag has higher di-calcium
silicates therefore it serves as better raw material for cement making (di-calcium
silicate provides better bonding properties to cement).

Example 2: In an another example, the proportion of LD slag in the burden was
kept at 40% owing to produce pig iron with target *P': 1.4 - 1.6%. Annexure -1
provides details of burden for the above two batches of production (Case -II and
Case-III.
The proportion of LD slag in the burden can go up to 80% which depends on,
composition of hot metal w.r.t. phosphorus, slag management & granulation
capability on the casting floor, and cost economics.


The new inventive process produces High Phosphorus Pig Iron (HPPI). The
amount of phosphorus depends upon the proportion of LD slag in the burden.
20% and 80% LD slag in the burden produces P: 1.0% and P: 3.0% respectively.
The typical chemistry of HPPI is given below:
C : 3.5-4.0%
Si 1.0-3.0%
Mn 0.4 - 0.8%
P 1.0-3.0%
S 0.03%
Fe 92%
The phosphorus content of HPPI can be varied from 1.0 - 3.0% to suit particular
application. HPPI can be used in Foundry applications and various other niche
applications (e.g. cathode of Aluminum smelters, hard facing powders, brake
drums for railways etc.). Based on pig iron 'Silicon' level, two kinds of pig iron are
defined for Foundry application: steel grade (Si<1.5%) and foundry grade
(Si>2.0%).
HPPI can be used as foundry pig iron in applications where final product
specification w.r.t. Phosphorus is higher i.e. P>0.200%. Depending on the level
of phosphorus specifications, HPPI can be used as 10-20% of the charge mix.
Also, HPPI can be used as a substitute of Fe-P. Many applications/products have
higher amount of phosphorus in steel/iron castings. These applications/products
use Fe-P (ferroalloy of phosphorus) to add phosphorus. HPPI can be used as a
substitute of Fe-P addition. A few of the products requiring higher amount of
phosphorus in steel/iron castings include cathode application of Aluminum
Smelters, Brake shoe/drums in Railways, hard facing powders etc. Besides,
HPPI can replace scrap being used in LD/BOF steelmaking process.

Fe-P alloys (Fe-0.4%P) are used for improving magnetic properties of rotors
used in generators. HPPI can be used in the charge mix to increase phosphorus
level.
The process of the current invention produces slag that has improved
characteristics. Typical blast furnace (using prime iron ore/sinter) produces slag
having lower two component basicity (i.e. CaO/SiO2). The inventive process will
produce slag with higher basicity resulting in improved cementing properties
which will serve as better raw material for cement industries.


WE CLAIM
1. A process for utilizing low grade iron ore, the process comprising:
mixing low grade iron ore with BOF slag and coke/nut coke, quartz and
dolomite to form a feed mixture; and reducing said feed mixture in a
blast furnace set-up wherein the feed mixture gets converted to hot
metal & slag in the ratio 1:1.
2. The process as claimed in claim 1, wherein the low grade iron ore
varies in the feed mixture in the range of 10-60%
3. The process as claimed in claim 1, wherein the BOF slag varies in the
feed mixture in the range of 40-90%
4. The process as claimed in claim 1, wherein CaO/SiO2 ratio in the slag
varies in the range of 1.2 to 1.4.
5. The process as claimed in claim 1, wherein the BOF slag used in the
feed mixture comprises:

6. The process as claimed in claim 1, wherein the hot metal produced is
high Phosphorus pig Iron (HPPI) comprising:
C 3.5-4.0%
Si 1.0-3.0%
Mn 0.4 - 0.8%
P 1.0-3.0%
S 0.03%
Fe 92%

7. The process as claimed in claim 1, wherein the low grade iron ore
comprises AI203 and SiO2 in the range of 5-15% and 15-45%
respectively.