FIELD OF APPLICATION
The present invention relates to a process for conversion of basic oxygen furnace
slag into construction materials like hydraulic binder in masonry blocks flat
sheets and tiles, and as a blend in cement manufacture and as a mortar for
various other applications.
BACKGROUND OF THE INVENTION
During the production of steel, there is a generation of waste in the form of slag.
The tonnage of slag generated varies with the process of steel production. It is
typically between 10 to 20% of the steel produced. Nearly 100 million tonnes of
steel making slags are produced annually worldwide. Depending on the type of
hot metal and / or steel making practice adopted, the following compounds may
be present in basic oxygen furnace slag.
CaO - 45-55%
Fe -16-20%
SiO2-14-16%
P2O5 - 2.5-3.5%, etc.
This slag is generally put to low-end uses such as land filling, road making,
ballast, etc. directly or subsequently to some treatment. Since steel slags
contain significant amounts of CaO, 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 P2O5. The P2O5 content of the basic oxygen furnace slag
can be in the range of 2 to 3.5% based on the steel making practice.
If this slag is recycled into blast furnace as flux the P2O5 content will virtually
report to the blast furnace hot metal. In other words the phosphorus content of
the hot metal will increase. 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.
SUMMARY OF THE INVENTION
The main object of the present invention therefore, is to put basic oxygen
furnace slag to more profitable use than done hitherto.
Another object of the present invention is to process the liquid basic oxygen
furnace slag, a waste material generated during steel making, to obtain
cementitious properties suitable for various construction applications.
These and other objects of the present invention are achieved by increasing the
fluidity of the molten slag during slag off from steel converter and allowing the
carry over steel to settle at the bottom. This can be done by adding fluorspar
(calcium fluoride) to the molten slag.
The liquid slag can then be cooled by granulation or by direct quenching in a
pool of water. By rapid quenching the phases and their morphology can be
managed which enables the slag to have better cementitions properties.

Thus the present invention provides a process for conversion of basic oxygen
furnace slag into construction materials like hydraulic binder in masonry blocks,
flats sheets, bricks and tiles and as a blend in cement manufacture and as a
mortar in various applications, said process comprising the steps of: adding
required quantity of fluorspar for increasing the fluidity of molten slag; cooling
the liquid slag; crushing the slag to -3 mm size; separating the metallic fraction
of the slag using a magnetic separator and grinding the non-metallic fraction to
about 3000 to 4000 blain depending upon its application.
DETAILED DESCRIPTION
After the steel has been tapped into the steel ladle, slag is removed from the
steelmaking vessel in a slag pot. While slag is removed from the vessel, the slag
is fluidized by adding fluorspar (calcium fluoride) of sufficient quantity in the slag
pot. This enables the assimilation of the unmixed lime and also to some extent
carryover metal or settle at the bottom of the slag pot. The pot is transferred to
a nearest quenching pit to quench the slag.
The slag can also be taken to a granulation pit, where the molten slag is
granulated through a runner.
After quenching or granulating the slag is crushed to -3 mm size and passed
through a magnetic separator to separate the metallic fraction of the slag.

The rest non-metallic slag is then crushed 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.
For enhancing calcium silicate network during hydration the -3 mm non-metallic
slag can be crushed with gypsum, which acts as a catalyst.
Pilot scale experimentation carried out in a running plant has established the
process parameters necessary to obtain the cementitious 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 in Table 1
below. The exact temperatures ranges and method of cooling are shown below:


Typical chemical composition obtained are shown in Table 2.

Phases present:
α'-2CaO.SiO2 0-25%
β-2CaO.SiO2 20-50%
3CaO.SiO2 0-15%
2CaO.Fe2O3 20-40%
Ca(H2PO4)2 H2O Minor
• Fe2O3 Minor
• Complex phases of CaO, Mgo, SiO2, FeO, and AI2O3 - Minor
Physical properties:
• Fineness -3000 - 3500 blain
• 1ST (initial setting time) - 35 min
• FST (final setting time) - 45 min
Strengths as per IS - 4031
• 7 day strength : 5-10 MPa
• 28 day strength : 15-30 MPa

The ground slag 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, fiber cement boards, tiles and as a mortar in various
applications.
Solid bricks can be made out of the treated basic oxygen furnace slag using
machine molding test results of the bricks at various loads are shown in Table 3
below:


We Claim :
1. A process for conversion of basic oxygen furnace (BOF) slag into construction
materials, the BOF slag consisting of at least

- adding upto 03% of fluorspar to the molten slag for increasing the fluidity
of said molten slag;
- cooling the liquid slag by quenching using water spray from a temperature
range of 1500 to 1200 degree centigrade.;
- crushing the slag to -3 mm size;
- separating the metallic fraction of the slag using a magnetic separator;
and
- grinding the non-metallic fraction to about 3000 to 4000 blain depending
upon its application.
2. The process as claimed in claim 1, wherein gypsum is mixed with the non-
metallic fraction of the -3mm slag to act as a catalyst before grinding.

3. The process as claimed in claims 1 or 2, wherein the grinding of the slag with
or without gypsum is carried out to about 3500 blain.
4. The process as claimed in claim 1, where the cooling of the fluidized slag is
carried out by granulating through a runner from a temperature range of 1500 to
1200 degree centigrade.
5. The process as claimed in claim 1, wherein the construction materials
comprise one of hydraulic binder in masonry blocks, flat sheets, bricks, tiles,
mortar for several applications, and blend in cement manufacture.

ABSTRACT

A PROCESS FOR CONVERSION OF BASIC OXYGEN
FURNACE SLAG INTO CONSTRUCTION MATERIALS
The invention relates to a process for conversion of basic oxygen furnace (BOF)
slag into construction materials like hydraulic binder in masonry blocks, flat
sheets, bricks and tiles and as a blend in cement manufacture and as a mortar in
various applications, said process comprising the steps of adding required
quantity of fluorspar to the molten slag for increasing the fluidity of said molten
slag, cooling the liquid slag, crushing the slag to -3 mm size, separating the
metallic fraction of the slag using a magnetic separator and grinding the non-
metallic fraction to about 3000 to 4000 blain depending upon its application.