FIELD OF THE INVENTION
The present invention relates to the technology of making glazed ceramic tiles from
waste ferrochromium slag. The invention relates to the utilisation of water granulated
ferrochrome slag in making value added ceramic tiles.
BACKGROUND OF THE INVENTION
Ferrochrome slag is a waste by product of ferrochrome production process.
Ferrochrome slag is generated during smelting of chromite ore. The Ferrochrome
slag consists of SiO2, MgO, and Al2O3 in different proportion along with few minor
amount of CaO, chromium and iron oxides. Chromium is generally present in form of
partial altered chromite (PAC) and entrapped alloy. Water Granulated slag is very
homogenous, spongy and glassy in nature. The amount of ferrochrome slag
generated during production of high carbon ferrochrome is equal to 1.2 times of the
quantity of metal produced. Majority of ferrochromium slag is discarded and sent for
landfilling which will create a huge waste deposit over the years. Safely disposal of
such a huge quantity of slag is a major challenge for the ferrochrome producers.
Worldwide ferroalloy producers are attempting for valorisation of ferrochrome slag to
solve the environment issue and reduce the overall cost of their production.
Utilization of ferrochrome slag in building material application such as glazed tiles will
solve the waste disposal problem.
Some of the prior art technologies describes the utilisation of industrial wastes such
as furnace slag, electric arc furnace slag, iron ore tiling, sludges, boron wastes,
municipality waste, wastes from petroleum industries etc.
B.C. Chukwudi et al. studied the production of ceramic tiles from steel slag and using
kaolinite clay. The blended mixture was hydraulic pressed into rectangular moulds,
oven dried and sintered to 1200°C. Steel slag in the range of 20-60 wt. % was added
to kaolinite clay to form good quality usable floor tiles. The tiles contain useful
phases like quartz, wollastonite, enstatite, anorthite. Z.B. Ozturk et al. investigated
on the preparation of wall tiles from the blast furnace slag. They found that addition
of 33% blast furnace slag to ceramic wall tile compositions in ceramic wall tiles
results in 25% increase in strength. The results from their investigation showed that
the blast furnace slag can be used to produce anorthite based quality wall tiles. S.K.
Das et al., investigated the possibility of using iron ore tailing as one of the raw

materials for ceramic floor and wall tile bodies. They found that tiles made from iron
ore tailing possess superior strength and scratch hardness compared to
conventional tiles and conform to most of the EN standards. Ritwik Sarkar et al.
studied the utilization of steel melting electric arc furnace slag for development of
vitreous ceramic tiles. Slag, to the extent of 30-40 wt. % with other conventional raw
materials, was used for the development in the temperature range 1100-1150OC.
The fired product showed relatively higher density due to presence of heavier iron
oxide with shorter firing range and good strength properties
Making of high strength wall and floor tiles from the industry waste is disclosed in
patent application number CN1548398A. Materials used in this method includes
aggregate selected from iron tailing powder, steel slag and waste ceramic in 60-70
wt% and adhering material of shale and/or bauxite in 30-40 wt%. The production
process includes crushing material, rolling into fine powder, adding water glass
solution via stirring, forming in press, and sintering at 1120-1180 0C for 1.5-2 hr.
Patent no US 2003/0183988A1 disclosed a process to produce ceramic tiles in
glazed and unglazed form using industrial wastes such as slime in the range of 30 to
50% by weight, fly ash 10 to 25% by weight, blast furnace slag 5 to 20% by weight,
aluminosilicate minerals 25 to 50% by weight and other low cost minerals. Patent no
CN 103819175 B disclosed a method of producing low cost ceramic floor tiles by the
raw material which includes Bayer red mud 20 to 25 wt. %, chromium slag 20 to 25
wt. %, felsic rock type gold mine tailings 8 to 12wt. %, fly ash 8 to 12 wt. %, slag boil
8 to 12 wt. %, talc 10 to wt. 15% lime wt. 10 to 15%. The chemical composition of
ferrochrome slag used in this process consists of CaO: 2-5%, SiO2:22-30%,
Al2O3:25-30%, MgO:20-30%, Cr2O3: 5-10%. Patent application number US5175134
disclosed the method of making ceramic tiles by using sludge slag by converting it
into ash. The melting point of a sludge slag obtained by separating sludge from
sewage, burning the thus separated sludge into ash, melting the ash, and solidifying
the thus melted ash, can be brought to a temperature lower than the melting point of
the ash of the sludge by adjusting the ratio (CaO/SiO2) of the calcium oxide (CaO)
content to the silicon dioxide (SiO2) content to a desired value. Along with sludge
slag silica sand (1-50%), clay (5-50%), agalmatolite (20-90%), alkaline metal (1-5%)
is used to make tiles.

Y.A.Guloyan et al. studied the utilisation of ferrochrome slag in production of bottle
as colouring agent in addition to lowering the melting temperature of operation. But
none of the prior art technology utilizes ferrochrome slag as colouring agent in glaze
making process.
There are many literatures describing the utilisation of industrial wastes such as blast
furnace slag, fly ash, sludge slag, boron waste, slag from copper extraction process,
municipal waste etc. But there is limited or no prior art available to utilize water
granulated ferrochrome slag to produce glazed ceramic tiles. Ferrochrome slag is
refractory in nature and requires high temperature for sintering and water granulated
slag is porous/ spongy, less dense, glassy in nature and lacks binding property. So
an approach aimed at reducing the sintering temperature and providing binding
property by introduction of clay and additive is adopted in this invention.
Ferrochrome slag is also used for dye purpose in the glaze composition for making
coloured glazes.
OBJECT OF THE NVENTION
The purpose of this development is to use freely available waste materials such as
ferrochrome slag as an alternative raw material to produce value added ceramic
articles such as glazed tiles.
Another objective of the invention is the utilisation of ferrochrome slag for dye
purpose as a source of Cr2O3 for colouring of the glaze.
SUMMARY OF THE INVENTION
In the production of glazed ceramic tiles from ferrochrome slag the process utilizes
waste ferrochrome slag in two steps: (1) to produce unglazed sintered biscuit part of
tile (2) to produce glaze part of the tile where ferrochrome slag act as a source of
Cr2O3 for colouring. The schematic diagram in fig 1 summarizes the process of
producing glazed ceramic tiles from ferrochrome slag.
In this process the ferrochrome slag powders produced by ball milling are mixed with
kaolin clay, moisture and additive followed by compaction and sintering to produce
the sintered part of the tile. In the glaze making process the oxide powders (silica,
borax, ZrO2, ZnO, CaO, and B2O3) are mixed with ferrochrome slag powders

followed by melting of this mixture, water quenching of the melt to produce frits,
milling the frits to make very fine powder, slurry making of the frit powders, painting
and firing of the slurry painted sintered part to develop glaze on the surface.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig 1 shows the process flow chart for glazed tiles from ferrochrome slag
Fig 2: XRD pattern showing the presence of mineral phases in sintered unglazed
tiles from ferrochrome slag
Fig 3: The optical micrograph of the unglazed sintered tile (a) Fecr slag+Kaolin (b)
Fecr slag+kaolin+Boric acid
DETAILED DESCRIPTION OF THE INVENTION
The main object of the present invention is to develop a method to produce glazed
ceramic tiles using water quenched granulated ferrochrome slag.
In the present invention the ceramic tiles made from water granulated ferrochrome
slag consist of 2 parts: (1) unglazed sintered part (biscuit) and (2) glaze part.
The making of unglazed sintered part (biscuit) follows important steps like:
a) Milling of ferrochrome slag to make fine slag powders of size less than
150micron
b) Blending and mixing with clay (kaolin), molasses, additive (boric acid) and
water
c) Compaction under 25-40 MPa pressure to make green compact
d) Drying of the compacted tile at 150 0C for 8-10 hours
e) Sintering at 1150-1250 0C for 2-3 hour
In the present invention dry ball milling of water granulated ferrochrome slag is
employed to achieve very fine slag powder. The ball milling of ferrochrome slag is
performed in a ball mill in dry condition with hardened steel ball as grinding media.
The weight of the grinding media is taken as three times that of the grinding material
(ferrochrome). The sizes of the grinding materials are selected in the range of 0.5 to
2 mm. Approximately 95% of the grinding materials are milled to powder of size
below 150 micron, when the milling is carried out with weight of grinding media
(Hardened steel ball) as three times that of grinding material (ferrochrome slag) at
100 revolutions per minute for 8 hours.

The very fine slag powders obtained from grinding operation are mixed with 20 to 30
parts kaolin clay in ferrochrome slag-kaolin mixture, 3-5% water, 1-2% molasses and
0.5-1% boric acid (as additive). The additive like boric acid was used to introduce low
melting phases to facilitate low temperature sintering during sintering. Use of Kaolin
here serves two purposes: (1) act as clay and provide green strength before
sintering (2) introduces low melting phase to facilitate low temperature sintering. The
green mixture was densified in form of compact tile shape under the pressure of 20
to 40 Mpa in a hydraulic press. The compacted tile body is allowed for drying at 150
0C for 8-10 hour. The dried compacted tile (biscuit) is allowed for sintering in a
furnace/kiln at 1150 to 1250 0C for 2-3 hour. In the initial stage of sintering the
necking formation starts and the growth of neck proceeds as the temperature and
time of sintering increases. Several independent necks on each particle grow during
sintering process. Further sintering and densification takes place by formation of low
temperature melting phases caused by additives and kaolin. During sintering the
necessary crystal phases like spinel (AB2O4 where A=Mg, B=Al, Cr) and enstatite
and corderite phases are developed. The XRD peaks in fig 2 and microstructure in
fig 3 shows the necessary phases of the final sintered tile (sintered biscuit) made
from ferrochrome slag. The chemical composition of the unglazed sintered tile is
shown in table 2.
Example-1
Water granulated Ferrochrome slag (size range 0.5 to 2mm) of chemical composition
mentioned in table 1 are milled together for 8 hour in a ball mill to produces fine
powder of size less than 150 micron. Then 80 parts of ferrochrome slag powder is
mixed with 20 parts of kaolin clay. To this powder mixture 1-2% molasses, 3-5% of
water and 0.5% boric acid were added and thoroughly mixed in a muller. This
mixture was compacted in the form of tile under pressure of 35Mpa by using a press.
The green compact is allowed for sintering at 1250 0C for 2hr followed by furnace
cooling. The firing shrinkage of this composition of the tiles is around 2.4%. The
percentage of water absorption of the unglazed sintered tile is around 14%.
Example-2
0.5% boric acid was added to the mixture composition as explained in example-1.
This mixture was compacted in the form of tiles and sintered as explained in

example-1. The firing shrinkage of the tiles was 2.2%. The percentage of water
absorption of the unglazed tile is around 13%.
Glaze applying method:
In this invention ferrochrome slag powders are also used as a source of Cr2O3 for
dye purpose with other oxide materials source in making the frits for the glaze
application. The ferrochrome slag does not contain free chromic oxide and all the
components of the ferrochrome slag are easily soluble in glass melt. This favours the
homogenous colouring of the glaze during compared to other colouring additives.
The manufacturing of frits material for applying glaze follows:
a) Mixing the oxide materials (SiO2, Zinc oxide, CaO, B2O3) with ferrochrome slag
powder (10-20%)
b) Melting the oxide mix at 1500-15500C
c) Pouring the molten oxides in water for quenching to make frits
d) Grinding the frits to make very fine powders
e) Slurry making
f) Slurry painting on tile surface
g) Firing the slurry painted tile at 1050-1100 0C for 10 min to develop glaze.
The raw materials for making frits for glazing consist of Ferrochromium slag: 5-10%,
Silica: 50-60%, borax: 15-20 wt. %, MgO: 2-5wt. %, CaO: 2-5%, ZrO2: 2-5-wt. %,
ZnO: 5-10%. The oxide powders were mixed with ferrochromium slag powder
thoroughly. 100 gm of the mixed oxide powder composition was taken in a graphite
crucible and kept in a muffle furnace for melting. The mix composition is allowed for
heating for 15-20 minutes till the composition became molten. The molten oxide
composition is taken out of the furnace and poured in to water to allow for sudden
quenching. The quenched silicate products are called frits. These frits were milled to
form very fine powder of size less than 75 micron. Around 20-30 gm of the frit
powders was mixed with 100ml of water and 0.2wt% bentonite to form slurry. The
slurry containing frits was painted on the unglazed sintered tile made previously.
Then this slurry painted tiles is allowed for firing in a furnace at 1050-1100 0C for 10
minutes and then allowed for fast cooling inside furnace by applying nitrogen/argon
gas after switching off the furnace. The chemical composition of the glaze is shown

in table 3. The final glazed tile produced from this method consists of brown coloured
glaze due introduction of Cr2O3 in the glaze composition by using ferrochrome slag.
Example-3
A mixture of oxide powders which consists of 60wt.% Silica, 15 wt.% borax, 5wt.%
ZrO2, 10 wt.% ZnO, 5 wt.% CaO, 5 wt.% B2O3 and 10 wt. % FeCr slag were mixed
thoroughly and melted at 1550 0C. The molten oxide mixure is quenched in water to
make frits. The frits are milled to powders of size below 75 micron. Slurry of the frit
powders was made by mixing 30 gm of frit powders in a 100ml of water with 0.2gm%
bentonite. The slurry painted tile was fired at 1050-1100 0C for 10 min followed by
fast cooling by purging nitrogen/argon gas inside furnace. A brown coloured glaze is
developed on the surface of the tiles.


References
1. B.C. Chukwudi1, P.O. Ademusuru, B.A. Okorie, Characterization of Sintered
Ceramic Tiles Produced from Steel Slag, Journal of Minerals and Materials
Characterization and Engineering, 2012, 11, pp.863-868.
2. Z. B. Ozturk, E. E. Gultekin, Preparation of ceramic wall tiling derived from blast
furnace slag, Ceramic international, 2015, 41, pp.12020–12026.
3. S.K. Das, S. Kumar, P. R. Rao, Exploitation of iron ore tailing for the development
of ceramic tiles, Waste Management 2000, 20, pp.725-729.
4. R. Sarkar, N. Singh, S.K. Das, Utilization of steel melting electric arc furnace slag
for development of vitreous ceramic tiles, Bull. Mater. Sci., 2010, 33, pp. 293–
298.
5. Y.A. Guloyan, K.S. Katkova, V.F. Smirnov, A.F. Sudin, M.A. Basova, S.G.
Korobov, Use of ferrochrome slags in the production of bottles, Glass and
Ceramics, 1972, 29, pp 527-529.

WE CLAIM
1. A method of manufacturing a glazed tile, the method comprising:
Developing a sintered biscuit part of the tile using ferrochrome slag
powder; and
Glazing the sintered biscuit part with an oxide mixture; and
Firing the slurry painted sintered biscuit part at 1050-1150 0C for 10
min to develop glazed tile.
2. The method as per the claim 1, wherein the process of developing the
sintered biscuit part comprises:
Milling of ferrochrome slag to make fine slag powders of size less than 150
micron;
Blending and mixing with clay (kaolin), molasses, water and sintering
additive;
Compacting under pressure to make green compact; and
Sintering of the green compact.
3. The method as per the claim 1, wherein the process of glazing the sintered
biscuit part comprises:
Mixing the oxide materials (SiO2, borax, Zinc oxide, CaO, B2O3) with
ferrochrome slag powder;
Melting the oxide mix at 1500-1550 0C;
Pouring the molten oxides in water for quenching to make frits;
Grinding the frits to make fine powder;
Developing a slurry in water using the fine powder and bentonite; and
Painting the sintered biscuit part with the slurry.
4. The method as claimed in claim 2, wherein the sintered biscuit part
comprises, in weight %, MgO: 16-23, SiO2: 27-32, CaO: 1.5-2.5, Al2O3: 23-30,
Cr2O3: 5-9, FeO: 1.5-3.5, B2O3: 0.4-0.9.
5. The method as claimed in claim 3, wherein the glazed part comprises, in
weight %, SiO2: 50-60, B2O3: 5-15, ZnO: 5-10, Na2O: 2-4, ZrO2: 2-5, CaO: 2-
5, MgO: 2-3, Cr2O3: 0.5-1.

6. The method as claimed in claim 3, wherein ferrochrome slag in glazed part
varies in the range of 5-10 weight % as source of Cr2O3.
7. The method as claimed in claim 2, wherein the sintered biscuit part comprise
at least 50 % (in weight %) of ferrochrome slag.
8. The method as per claim 2, wherein granulated slag when grinded in a ball
mill at 100 revolutions per minute for 8 hour in dry condition with the weight of
grinding ball three times that of ferrochrome slag results in almost 95% of
ferrochrome slag to below 150 micron.
9. The method as per claim 2, wherein compacting is done under a pressure
varying in the range of 25 to 40 Mpa.
10. The method as claimed in claim 2, wherein sintered biscuit part comprises at
least 50% kaolin -preferably 20-30 parts kaolin, 1-2% molasses, and 0.5-1%
boric acid mixture.
11. The method as claimed in claim 2, wherein sintering additive is boric acid.
12. The method as claimed in claim 2, wherein sintering additive is added as
additive to introduce low melting phases during sintering.
13. The method as claimed in claim 2, wherein sintering of the green compact in a
furnace/kiln is done at a temperature in the range of 1150 to 1250 0C for 2 to
4 hours to develop necessary phases such as enstatite (MgSiO3 ), cordierite (
Mg2Al4Si5O18) and spinel (AB2O4 where A=Mg, B=Al, Cr).