FIELD OF THE INVENTION
The present invention generally relates to a process for production of refractory
bricks from ferrochrome slag. More particularly, the invention relates to an
improved process for production of refractory from ferrochrome slag generated
as byproduct during production of ferrochrome metal in submerged electric arc
furnaces.
BACKGROUND OF THE INVENTION
The hitherto known process to produce magnesia-chrome refractory bricks uses
high quality magnesia and chrome concentrates as main raw material, with
addition of binder and sintering aid. The existing process to produce refractory
bricks consists of grinding, batching, mixing of raw material with binder, sintering
aid and with little amount of water in a mechanical mixer. Then pressing in brick
shape in hydraulic press, drying at 110°C temperature for moisture removal and
sintering at 1550 to 1650°C with 2 hrs. soaking at maximum temperature into
furnace.
Another known process to produce refractory bricks uses white fused alumina,
brown fused alumina, reactive alumina, calcined alumina, tabular alumina with
binder and sintering aid. The existing process to produce refractory bricks
consisting of grinding, batching, mixing of raw material with water in a
mechanical mixer. The process also consists of pressing into brick shape then
drying at 120°C and finally sintering at 1550 to 1650°C.

A still another known process to produce refractory bricks using quartz as main
raw material. The process consists of grinding, batching, mixing, pressing and
drying at 120°C in air drier. Finally firing at a temperature of 1450 to 1550°C
with 2 hrs soaking.
All the basic refractories like magnesia, dolomite chrome, and combinations of
these materials exhibit outstanding resistance to iron oxides and the basic slags
associated with steelmaking. For this reason they find wide employment in the
linings of basic oxygen furnaces, electric furnaces, and open-hearth furnaces.
High temperature burnt directly bonded magnesia-chrome bricks, semi-rebonded
magne-sia-chrome bricks and rebonded magnesia-chrome bricks are made from
low impurity raw materials. The bricks are widely used in large cement rotary
kiln, and secondary refining units such as RH, VOD, AOD furnaces, non-ferrous
metal metallurgical furnaces, glass tanks and so on.
US 4169734, 1979 patent disclosed a process for producing chemically bonded
chrome-magnesia refractories, and method for making same, comprised of
refractory brick making size
graded magnesia and chrome ore grain in weight ratio between 90/ 10 and
30/70, the major portion, and preferably all, of the chrome ore grains being of a
size between —24 and +200 mesh screen. The silica content of the shape should
be from 0.5 to 2.5% SiO2 by weight on the basis of an oxide analysis of the
whole mixture. The CaO/SiO2 ratio is in the range of 0.2 to 2.5. Calcium nitrate
may be employed, particularly in those formulations wherein the Si02; content is
low (0.5 to 1.3%) and the CaO/SiO2; ratio is high (1.8 to 2.5). this invention
comprises the steps of preparing a batch from 30 to 90 parts of size graded

periclase and of 70 to 10 parts of size graded particles of chrome ore, the major
portion of the chrome ore grains being such as to pass 24 mesh screens and stay
on 200 mesh screens; mixing the grains with sufficient amounts of liquid to
temper the batch for efficient forming; forming the mixture into the desired
shapes; and drying the shapes at a temperature of around 120° C. The shapes
of this invention do not require firing step; they are ready for use after having
been dried at a temperature of around 120°C.
Few non-patent literatures by D. Gregurek et al., The Southern African Institute
of Mining and Metallurgy Platinum 2012, pp. 251-260 and Han Bom Kim and
Myongsook S. Oh, Ceramics International, 34, 2008, pp. 2107-2116 are available
on development, properties and performance of the mag-chrome refractory
during applications. This works are based on using natural raw materials like
fused or dead brunt magnesia, fused magnesia chrome grains etc. None of this
work used a waste or byproduct as starting raw material.
Ferro-chrome slag is produced as byproduct during production of ferrochrome
alloy into submerged arc furnace. The typical ferrochrome slag composition is
25-38 % SiO2 , 20-34 % AI2 O3 , 15-26% MgO, 1-6 % CaO, 5-18 % Cr2O3 and
the iron content is 1-5 %. The granulated slag contains three different phases
like amorphous glass phase, crystalline and zonal Fe-Mg-Cr-AI -spinels and metal
drops. The ferrochrome slag products are chemically very stable. They are used
in civil engineering and road construction.
The steel plant byproducts like BF slags, steel slags are used for production of
building materials.
JP 2001323403 of 22.11.2001 provides a road pavement slab using mill slag as a
part of raw material. According to the invention, the road pavement is formed by
mixing with water a mixture containing granular hot metal preliminary treated

slag as mill slag and blast furnace slag fine powder as Si02-containing material,
whose percentage of a content of hot metal preliminary treated slag having a
particle diameter of 1.18 mm or less is 15 to 55 mass % and whose percentage
of a content of blast furnace slag fine powder is 5 is to 40 mass %. The pH of
the contact water is 10 or less after contact.
US Pat. 6805738 of 19th Oct 2004 discloses a process where a road repairing
material is developed using 10-15% steel slag.
The non-patent literature by Masahide Nishigaki, published in Waste
Management 20 (2000) page 185-192, describes a process where paving bricks
are produced using molten slag at a temperature above 1200°C.
The non-patent literature by Yuksel, Isa; Bilir, Turhan, published in March,2007 in
the Book "CONSTRUCTION AND BUILDING MATERIALS; Volume: 21 Issues: 3
Special Issues: SI; Pages: 686-694 DO1:10.1016/j.conbuildmat.2006.06.031;"
described usage of industrial by products to produce plain concrete elements.
According to the process described, sufficient number of briquettes, paving
blocks and kerbs specimens containing GBFS and BA as fine aggregate
replacement were produced in laboratory. Then, a few tests were conducted for
investigating durability and mechanical properties of these specimens. Unit
weight, compression strength and freeze-thaw tests were conducted for
briquette specimens. Compression strength, freeze-thaw, water absorption and
surface abrasion tests were conducted for paving blocks. Surface abrasion and
flexural tensile strength tests were conducted for kerb specimens. While
compression strength was decreased slightly, durability characteristics such as
resistance of freeze-thaw and abrasion were improved. The test results showed

that usage of partially fine aggregate of these industrial by-products has more
beneficial effects on durability characteristics of plain concrete elements.
The use of slag for refractory is new area of work. With this not only waste to
utilize in bulk but at the same time, waste is replacing the natural raw material
like magnesia and chrome. It helps to preserve natural resources.
OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose an improved process for
production of refractory from ferrochrome slag generated as byproduct during
production of ferrochrome metal in submerged electric arc furnaces.
Another object of the invention to propose an improved process for production of
refractory from ferrochrome slag generated as byproduct during production of
ferrochrome metal in submerged electric arc furnaces, which is less energy-
extensive.
A further object of the invention is to propose an improved process for
production of refractory from ferrochrome slag generated as byproduct during
production of ferrochrome metal in submerged electric arc furnaces, which cost-
effective, and preserves natural resources.
SUMMARY OF THE INVENTION
The invention provides solid bricks produced by the inventive process which
process comprises compressing a mixture of ferrochrome slag, dextrin, and
molasses. These solid bricks after firing have a relatively low porosity, high
compressive strength and other refractory properties. This bricks can be used in
high temperature furnace lining.

In the present invention, ferrochrome slag is used as a prime material in the
brick composition. Along with ferrochrome slag dextrin, molasses are added to
the batch composition as binder.
The slag used for present invention is coarser in nature. Sieve analysis result
shows that 10.8% +5 BS mesh size, 66.5% -5+18 BS mesh size, 17.7% -
18+150 BS mesh size and 2% -150 BS mesh size fractions particles. In present
invention three fractions namely coarse (-5+18 BS mesh size fraction), medium
(-18+150 BS mesh size fraction) and fine (-150 BS mesh size fraction) are used
for refractory brick development. As the finer fraction availability is very less into
as received slag so, the coarser ferrochrome slag grinds. Finer fractions obtain
through sieving. The sieved slag of three different fractions is calcined at 900 to
1000°C to avoid undesirable phase formation into final refractory formation. The
calcined slag of three different fractions mix together in a proportion of 4:3:3 to
3:3:4 with 1% dextrin and 2% molasses or 3% molasses or 3% dextrin in mixer
machine for homogenous mixing and then pressed into desired shape into
hydraulic press at a pressure of 1500 to 2200 kg/cm2. The pressed body is dried
at 110-140°C in air oven for removal of moisture. The dried bricks are finally
sintered at high 1220-1350°C with 2-3 hrs soaking.
Accordingly, the present invention provides an improved process for production
of refractory bricks using ferrochrome slag, which comprises the steps of:
(i) sieving of raw ferrochrome slag through BS sieve no. 5, 18 and 150.
Fractions of -5 +18, -18+150 and -150 separate and mark as coarse,
medium and fine,
(ii) mixing homogenously the above three fractions in a proportion in the
range of 4:3:3 to 3:3:4 mix with 1-3% dextrin, 2-3% molasses and 7-8%
water in a mechanical mixer for homogenous mixing for batch
preparation,

(iii) pressing the mixture at a pressure ranging between 1500 to 2200 kg/cm2
in brick shape by known means,
(iv) drying at temperature ranging between 100 to 140°C to remove
moisture,
(v) firing the dried bricks at temperature ranging between 1220 to 1350°C .
The invention provides a unique and useful process for utilization of significant
quantities of ferrochrome slag for refractory applications at high temperature.
Further, the invention saves significant amounts of energy by reducing final firing
temperature of the compressed bricks.
In an embodiment of the present invention the composition of the refractory
brick during batch may have the range of coarse fraction: 30%, medium
fraction: 30%, fine fraction: 40%, binder: 2-5% and water: 6-10%.
In another embodiment of the present invention, the composition of the
refractory brick during batch may have the range of coarse fraction: 40%,
medium fraction: 30%, fine fraction: 30%, binder: 1-4%, water: 5-8%.
In still another embodiment of the present invention, the composition of the
refractory brick during batch may have the range of coarse fraction: 30%,
medium fraction: 40%, fine fraction: 30%, binder: 2-5%, water: 5-10%.
In yet another embodiment of the present invention, the ferrochrome slag may
be selected from the composition range of SiO2: 25-40%, Al2O3: 20-35%, MgO:
20-40%, Fe2O3: 1- 7%, CaO: 0-4%, Cr2O3: 5-25%.

In a further embodiment of the present invention, the binder may be selected
from molasses, dextrin, PVA and like.
DETAIL DESCRIPTION OF THE INVENTION
As indicated above, the invention utilizes ferrochrome slag, the byproducts of
chrome steel production in EAF, as components of a compressed solid refractory
brick. Ferrochrome slag, is a coarser particle with chemical composition of SiO2,
AI2O3, MgO, Cr2O3 along with minor amount of Fe2O3, CaO etc., is suitable for
refractory composition. The slag is typically collected from EAF during the
production of chrome steel and air cooled. Nature of the slag can vary with time
to time depending on process parameters, raw material characteristics.
In one embodiment, the invention provides solid bricks that are useful for
refractory applications. A mixture of coarse, medium and fine ferrochrome slag
fractions in the ratio of 4:3:3 or 3:4:4 or 3:3:4, mixed with binder and water into
the composition. The bricks are produced by compressing under pressures
ranging from about 1,500 kg/cm2 to about 2,200 kg/cm2, preferably from about
1,700 kg/cm2 to about 2,100 kg/cm2, and most preferably from about 1,850
kg/cm2 to about 2,050 kg/cm2. The resultant bricks dry at a temperature of 100-
140°C for removal of moisture. As dried bricks fired at 1220-1350°C temperature
range with 2 hrs soaking for getting dense, less porous and high strength
refractory bricks.

The obtained refractory bricks of the present invention may have the following
range of properties:

According to the invention ferrochrome slag is used as the primary raw material
of composition. Further, the method requires low energy for processing as
compared to the conventional processes.
The following examples are illustrative of the invention and do not in any way
limit the scope of the invention as disclosed above and claimed here below.
Three mixtures were prepared and compressed under pressure into bricks. The
compressive strength and other properties of the bricks were then measured.
Example-1
A mixture containing 40 wt. % coarse, 30 wt. % medium, 30 wt. % finer fraction
was prepared. This was poured into a mold of hydraulic press and subjected to
pressure of 2000 kg/cm2 to shape into a brick. The brick was then dried at 120°C
in oven for moisture removal. The dried bricks were subjected to fire at 1300°C/2
hrs into furnace. Properties were evaluated and given in Table-1.


A mixture containing 30 wt. % coarse, 35 wt. % medium, 35 wt. % finer fraction
was prepared, compressed under 2100 kg/cm2 pressure. Pressed bricks were
dried at 110°C in oven for drying. After drying bricks were fired at 1300°C with 2
hrs soaking. Properties were evaluated and given in Table-2.


Example-3
A mixture containing 30 wt. % coarse, 30 wt. % medium, 40 wt. % finer fraction
was prepared and pressed under 2200 kg/cm2 pressure in hydraulic press. The
bricks were dried in air drier for moisture removal at 120°C. The dried bricks
were subjected to firing at 1300°C with 2 hrs soaking. Properties were evaluated
and given in Table-3.

Example-4
A mixture containing as example-1 and compressed at 2000 kg/cm2 pressure and
the resultant bricks were fired at 1270°C after sufficient drying. Properties were
evaluated and given in Table-4.


ADVANTAGES OF THE INVENTION
1. The method utilizes 100% industrial byproduct, ferrochrome slag to produce
refractory bricks, thereby reducing the load on environment and cost of
disposal of the waste.
2. The method of the present invention is helpful in resource conservation by
replacing costly natural raw materials.
3. The method replaces natural raw materials by industrial waste and reduce the
final firing temperature, thereby considerable reduction in energy
consumption to the known process.
4. The products developed by the method of the present invention are superior
in terms of strength development and high temperature refractory application
wise.

WE CLAIM
1. An improved process for the production of refractory bricks using
ferrochrome slag, comprising the steps of:
(i) sieving raw ferrochrome slag through BS sieve no. 5, 18 and 150 to
separate the fractions of -5 +18, -18+150 and -150 respectively to
identify as coarse, medium and fine;
(ii) mixing homogenously said three fractions in a proportion in the range
of 4:3:3 to 3:3:4, and further mixing with 1-3% dextrin, 2-3%
molasses and 7-8% water in a mechanical mixer for homogenous
mixing for batch preparation;
(iii)pressing the mixture at a pressure ranging between 1500 to 2200
kg/cm2 in brick shape by known means,
(iv)drying at temperature ranging between 100 to 140°C to remove the
moisture; and
(v) firing the dried bricks at a temperature ranging between 1220 to
1350°C
2. The process as claimed in claim 1, wherein the ferrochrome slag has the
following composition range: SiO2- 20 to 40%, AI2O3-18 to 38%, MgO- 22
to 45%, Cr2O3 - 2-10%, Fe2O3- l to 5%, CaO - 0 to 5%.
3. The process as claimed in claims 1 or 2, wherein the obtained product has
a bulk density more than 2200 kg/m3.
4. The process as claimed in any of claims 1 to 3, wherein the refractory
product used have multiple phases such as spinels, fosterite, Mg-AI-
silicates, mullite and glass.

5. An improved process for production of refractory bricks using ferrochrome
slag substantially described herein with reference to the examples.

ABSTRACT

The present invention relates to an improved process for the production of
refractory bricks using ferrochrome slag, comprising the steps of sieving raw
ferrochrome slag through BS sieve no. 5, 18 and 150 to separate the fractions of
-5 +18, -18+150 and -150 respectively to identify as coarse, medium and fine;
mixing homogenously said three fractions in a proportion in the range of 4:3:3 to
3:3:4, and further mixing with 1-3% dextrin, 2-3% molasses and 7-8% water in
a mechanical mixer for homogenous mixing for batch preparation; pressing the
mixture at a pressure ranging between 1500 to 2200 kg/cm2 in brick shape by
known means, drying at temperature ranging between 100 to 140°C to remove
the moisture; and firing the dried bricks at a temperature ranging between 1220
to 1350°C .