FIELD OF INVENTION
The invention relates to a process of converting a liquid BOF slag being a waste
material generated during steel making, to obtain cementitious properties
suitable for various construction applications. More particularly, the invention
relates to a process of producing iron bearing charge material and hydraulic
binder from liquid BOF slag.
BACKGROUND OF THE INVENTION
During the production of steel, a waste in the form of slag is generated, the
tonnage of which varies with the process of steel production but is typically
between 10 to 20% of the steel produced. Depending on the type of hot metal
and / or steel making practice adopted, the following compounds may be present
in BOF slag: CaO - 45-55%, Fe(t) - 16-20%, SiO2 - 14-16%, P205 - 2.5-3.5%,
etc. Nearly 100 million tones of steel making slags are produced annually
worldwide. This slag is generally put into low-end uses such as land filling, road
making, ballast, etc. directly or subsequent to some treatment. Since steel slags
contain significant amounts of Calcium oxides of silica and iron, such low-end
applications do not do justice to its potential usage.
The recycling of this slag into iron making processes is restricted because of its
higher proportion of P205, which virtually reports to blast furnace hot metal. At
the same time, the fact that nearly half of the slag is made up of CaO and nearly
one - fifth of iron oxide(s), implies that it could be put to use more profitably
than done hitherto.
OBJECTS OF THE INVENTION
An object of the present invention is to propose a process for producing iron
bearing charge material and hydraulic binder from liquid BOF slag.
Another object of the present invention is to propose a process for producing
iron bearing charge material and hydraulic binder from liquid BOF slag which is
suitable for use in part or complete replacement of cement.
A further object of the present invention is to propose a process for producing
iron bearing charge material and hydraulic binder from liquid BOP slag which is
easy to perform and does not require costly machinery.
SUMMARY OF THE INVENTION
Accordingly, there is provided a process of producing iron bearing charge
material and hydraulic binder from liquid BOF slag which comprises the steps of:
treating the slag and suitably cooling the liquid slag by granulation or direct
quenching by pouring it into a pool of water, thereby converting the phases and
their morphology to obtain in the B.O.F slags cementitious properties nearly
conforming to the hydraulic binder.
The ground slag thus produced is suitable for part / complete replacement of
cement depending upon the strength and application requirements. It can be
used as a hydraulic binder in masonry blocks, flat sheets, tiles and as a mortar in
various applications. Also as a blend in cement manufacture.
EX: HOLLOW BRICK
Test results (as per IS 2185) of the hollow bricks made out of the hydraulic
binder using hand moulding equipment are shown below:
P - Ground Slag with 5% Gypsum S - River Sand
D - Chips Dust (-4.5mm) C - Chips (-6mm)
DETAILED DESCRIPTION OF THE INVENTION
After the steel has been tapped into the steel ladle, the slag is removed from the
stee(making vessel in a slag pot. In course of removal of the slag from the
vessel, the slag is fluidized by adding flour spar of sufficient quantity in the slag
pot. This enables the assimilation of the unmixed lime and also to some extent
carryover metal to settle at the bottom of the slag pot. The pot is transferred to
a nearest quenching pit to quench the slag. Alternatively, the slag pot taken to a
granulation pit, where the molten slag is granulated through a runner. Then the
quenched / granulated slag is crushed to -3mm size and passed through a
magnetic separator to separate the metallic fraction of the slag. The rest non -
metallic slag is then crushed with or without gypsum to 3500 blain depending
upon the application. The magnetically separated metallic portion is suitable for
iron bearing charge material in iron and steel making processes. The ground slag
is suitable for varying applications including hydraulic binder in masonry blocks,
flat sheets, and tiles and as a blend in cement manufacture and as a mortar in
various applications.
EXPERIMENTAL WORK
Pilot scale experimentation in a running plant was carried out to establish the
process parameters necessary to obtain the cementecious phases by controlled
cooling. Various aspects of the process that lead to instant flaking of the treated
slag were identified. The range of process parameters has been listed below. The
exact temperatures ranges and method of cooling are shown below:

WE CLAIM:
1. A process of producing iron bearing charge material and hydraulic binder
from liquid BOF slag, comprising the steps of:
-removing the liquid slag having a temperature between 1650°C to
1400°C from the steel making vessel to a slag pot;
-fluidizing the slag by adding fluorspar in a range between 0 to 5 wt% in
the molten slag during the removing step;
-cooling the slag by rapid quenching from a temperature of 1500°C to
1250°C via one of granulation method and water spraying on the slag
layer; the cooled slag being crushed to size between 1 mm to 3 mm size;
-separating a metallic portion of the liquid BOF slag by passing the
crushed slag via a magnetic separator, the separated metallic slag being
useable as charge material in an iron/steel making process; and
-crushing the left-over non-metallic portion out of said liquid BOF slag
along with 5% gypsum to a size range of 3000 to 3500 blain after
separating the metallic portion therefrom, the ground non-metallic slag
being useable as a hydraulic binder.
2. The process as claimed in claim 1, wherein the slag is dried to a minimum
extent after cooling and before crushing.

3. The process as claimed in claim 1, wherein the processed slag exhibits the
phases of a'-2Cao.SiO2(0-25%)/ (3-2Cao.SiO2 (20-50%), 3CaO.SiO2 (0-
15%), 2CaO.Fe203 (20-40%), and complex phases of CaO, MgO, SiO2,
FeO and Al2O3 (minor).
4. A process of producing iron bearing charge material and hydraulic binder
from liquid BOF slag, as substantially described herein.

The invention relates to a process of producing iron bearing charge
material and hydraulic binder from liquid BOF slag, comprising the steps
of:
-removing the liquid slag having a temperature between 1650°C to
1400°C from the steel making vessel to a slag pot;
-fluidizing the slag by adding fluorspar in a range between 0 to 5 wt% in
the molten slag during the removing step;
-cooling the slag by rapid quenching from a temperature of 1500°C to
1250°C via one of granulation method and water spraying on the slag
layer; the cooled slag being crushed to size between 1 mm to 3 mm size;
-separating a metallic portion of the liquid BOF slag by passing the
crushed slag via a magnetic separator, the separated metallic slag being
useable as charge material in an iron/steel making process; and
-crushing the left-over non-metallic portion out of said liquid BOF slag
along with 5% gypsum to a size range of 3000 to 3500 blain after
separating the metallic portion therefrom, the ground non-metallic slag
being useable as a hydraulic binder.