FIELD OF THE INVENTION
The present invention relates to a process for reducing oil and moisture content in iron
bearing oily steel mill sludge generated during the rolling operations which contain
wastes/contaminating oil and water that are usually separated in primary settling tank. The
mill scale at the primary settling tank is used in the sintering plant. The secondary sludge-
oil-water emulsion containing fine sized iron bearing particles are difficult to process further.
These are conventionally discarded, although having potential for internal recycling,
including prospective recycling to the sinter plant. The present process of recovery of iron
fines for recycling to sintering plant by reducing its oil and moisture content involve
selective combination of solvent extraction and drying to obtain iron enriched dried sludge
for recycling to sinter making. The solvent extraction is accomplished by vigorous admixing
with water and finally with organic solvent in selective ascertained ratio, to favor more than
86 % reduction of oil content in the sludge. Thus the process according to present invention
is directed to achieve on one hand reliable and faster conversion of secondary waste sludge
to iron enriched solid free of any contamination by oil or water for recycling to sinter
making, and on the other hand, control environmental pollution due to disposal of the
untreated secondary steel mill sludge at the output of primary settling tank, containing high
proportion of oil and other contamination and is therefore having the potential for wide
industrial applications in steel plants or rolling mill operations.
BACKGROUND ART
It is well known in the conventional steel industries, that the mill scales from Ingot casting
and steel rolling mills contains scales rich in iron content that are utilized after adequate
processing for recycling in the sintering plant to be converted to agglomerates/briquette or
pellets along with other additives and binders, with the objective of recovery of the iron
from mill waste to reduce consumption of precious and scarce iron ore used in BF
operations.
The steel mill sludges are the mill scale fines suspended in water and oil obtained as
outcome of processes of the rolling mill and other auxiliary plants. These iron bearing Oily
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mill sludges are generated during the rolling operations. Wastes thus obtained containing oil
and water goes to primary settling tank, wherein the coarse mill scales are already used up
in sintering plant. However, conventionally the secondary sludge-oil-water emulsion bearing
the fine sized particles poses serious difficulty in processing for separation and recycling and
thereby rendering such wastes being disposed to environment at the cost of iron rich
particles on one hand and damaging the ecological balance creating environmental hazard
by disposing oil rich sludge to open ground.
Persons skilled in the art of steel making and its subsidiary operations in steel plants,, are
well aware of the complexities of separating the contaminants from the oily sludges
obtained from the rolling mill operations.
There had been, therefore, a persistent need in the art to obtain a cost effective and faster
method for separation of oil and moisture from the secondary oily steel mill sludge such as
to reduce oil content by about 86% such that the sludge could be rendered suitable for
being recycled to sinter making in steel plants, on a sustainable basis.
OBJECTS OF THE INVENTION:
The basic object of the present invention is thus directed to a sustainable integrated treat-
ment process for the secondary steel mill sludge containing iron fines, which are otherwise
difficult to separate out for productive use and is wasted as pollutant, eliminating
undesirable oil and moisture content in a faster and cost effective way, such that the
treated and dried sludge is fit for recycling to sinter making.
A further object of the present invention is directed to an integrated process involving
solvent extraction for successive reduction of the oil content level in said secondary sludge,
and driving out moisture by heating, to be used as iron enriched solid mass, recycled to
sinter making.
A still further object of the present invention is directed to an integrated sustainable process
for treatment of secondary steel mill sludge containing iron fines, the separation of
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oils/hydrocarbons, is subjected to solvent extraction process such as to favour lowering the
oil content by at least 86%.
Yet another object of the present invention is directed to an integrated process for
treatment of secondary sludge involving a selective solvent extraction method including a
magnetic field for holding the iron containing fines while separating oil containing solvent
layer.
A still further object of the present invention is directed to an integrated sustainable process
for treatment of secondary steel mill sludge containing iron fines wherein the said sludge
after oil separation is subjected to selective heating adapted to drive out moisture in a
faster and cheaper way, such that the dried sludge is fit for use in sinter making.
A still further object of the present invention is directed to an integrated sustainable process
for treatment of secondary steel mill sludge containing iron fines, wherein the disposal of
untreated sludge as industrial waste, rich in oil content being deleterious to environment
and ecology, and also containing iron bearing fines, is gainfully avoided.
SUMMARY OF THE INVENTION
The basic object of the present invention is thus directed to a process to reduce oil and
moisture content in iron fines containing oily mill sludge of steel plant comprising:
(a) subjecting the mill sludge to a step of solvent extraction; and
(b) drying the thus obtained and solvent treated mill sludge to drying to thereby
produce dried sludge with reduced oil and moisture content.
A further aspect of the present invention of said process for treatment of iron fines
containing oily steel mill sludge comprising involving
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According to another preferred aspect of the present invention directed to said process
wherein in said step of solvent extraction water and organic solvents are used as the
solvent.
A still further aspect of the process according to the invention wherein preferably microwave
heating is used for the removal of moisture content, that is faster and cheaper means for
heating and drying of the treated sludge than conventional electrical heating.
According to another aspect of the present process for treatment of oily steel mill sludge
wherein said solvent extraction comprises initial solvent extraction with water followed by
final stage of solvent extraction with organic solvent.
A still further important aspect of the process of the present invention wherein said solvent
extraction comprises vigorous mixing, settling, tilting and involvement of magnetic field for
holding the iron containing fines while separating oil containing solvent.
Said process further comprising recycling the treated sludge to sinter making.
According to yet another aspect of the present process comprising:
vigorous admixing with water and thereafter with water and solvent in
predetermined ratio to thereby achieve > 86% reduction in oil content; and finally
subjecting to microwave heating for removal of moisture.
The objects and advantages of the present invention are described in greater detail with
reference to the following non limiting exemplary illustrative figures.
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BRIEF DESCRIPTION OF THE DRAWING
Figure 1: is the illustration of the process flow diagram for the integrated process of
treatment of iron bearing secondary steel mill sludge, for in plant recycling to sinter making,
according to the present invention.
Figure 2: is the illustration for the apparatus used for the solvent extraction process in
laboratory scale, which is a magnetic unit with stirring and tilting facility.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO THE
ACCOMPANYING DRAWINGS:
The present invention relates to an integrated process for improvement of recyling potential
of secondary sludge of Steel Plants containing iron bearing fines, on a sustainable basis. The
present process is directed to reduce oil and moisture content in iron bearing oily steel mill
sludge generated during the rolling operations which contain wastes/contaminating oil and
water that are usually separated in primary settling tank. The mill scale at the primary
settling tank is already used up in the sintering plant but The secondary sludge-oil-water
emulsion containing fine sized iron bearing particles are difficult for further processing and is
thus conventionally discarded although having potential for internal recycling, including
prospective recycling to the sinter plant.
The present integrated and environment friendly process of recovery of iron fines from
secondary oily steel mill sludges for recycling to sintering plant, involve combination of
steps such as solvent extraction and drying to obtain iron enriched dried sludge for recycling
to sinter making.
Attention is now invited to the accompanying Figure 1, that illustrates the flow diagram for
the integrated process comprising steps as already mentioned. The invention involves a
laboratory scale integrated treatment process that has been developed and utilized to
reduce oil and moisture content in oily mill sludge and recover the iron bearing fines
therefrom for inplant recycling to sinter making, which is difficult to separate and is
otherwise disposed off as wastes, causing industrial pollution on one hand due to high oil
content in the neighbourhoods of the disposal area and on the other hand wasting scarce
and costly iron bearing fines without productive use. The integrated process is a
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combination of biodegradation, solvent extraction and drying such as to obtain dried sludge
having less than 1% oil and less than 5% of moisture, ensuring recycling of the end product
to sinter making.
It may be noted that the process according to the invention for treatment of secondary steel
mill sludge uses said sludge containing about 6.35 % oil as starting material is subjected to
Solvent Extraction (SE) for favored reduction in oil content of the secondary sludge.
Attention is now invited to accompanying Figure 2 that illustrates the apparatus for
laboratory scale solvent extraction process, carried out in a Magnetic unit with stirring and
tilting facility. The solvent extraction process involves mixing of water with secondary
sludge with, stirred vigorously for thorough mixing and dispersion of oil particles in water
and at the final stage a mixer of water and an organic solvent in ascertained ratio of 2:0.5 is
further added to the mix and stirred for desired duration to separate oil in water emulsion
used as solvent and then allowed to settle. The stirring speed is optimized to achieve
desired end results. Finally a magnetic field is applied to retain the iron containing fines
while separating the oil containing solvent layer by tilting the SE unit. The oil content of
sludge is reduced to about 0.87% i.e. by about 86% of the initial oil content of the sludge.
The sludge so obtained, substantially free from oil content is next dried by heating. The
heating is carried out for drying of sludge to drive away moisture by advantageous
Microwave heating which is at least nine times faster and twenty times cheaper than the
conventional electrical heating method. The treated and dried sludge obtained contains less
than 1% of oil and less than 5% of moisture, making it worthy of being in plant recycling to
sinter making in steel plant when applied in industry scale.
It is thus possible by way of this invention to achieve an integrated process for improving
the recycling potential of secondary steel mill oily sludge containing iron bearing fines,
separating the oil and moisture content to desired level such that the dried sludge is capable
of being used for inplant recycling to sinter making and thereby avoiding environmental
pollution and saving waste of secondary sludge containing iron fines as a scarce and costly
resource.
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We Claim:
1. A process to reduce oil and moisture content in iron bearing oily mill sludge of steel
plant comprising:
(a) subjecting the said oily mill sludge to solvent extraction, and
(b) drying the thus obtained and solvent treated mill sludge to drying to thereby
produce dried sludge with reduced oil and moisture content.

2. A process in said step of solvent extraction water and organic solvent are used as the
solvent.
3. A process as claimed in anyone of claims 1 to 2 wherein preferably microwave
heating is used for the removal of moisture content.
4. A process as claimed in anyone of claims 1 to 3, stirring speed is optimized for
desired end results.
5. A process as claimed in anyone of claims 1 to 4 wherein said solvent extraction
comprises initial solvent extraction with water followed by final stage of solvent
extraction with organic solvent.
6. A process as claimed in anyone of claims 1 to 5 wherein said solvent extraction
comprises vigorous mixing, settling, tilting and involvement of magnetic field for
holding the iron containing fines while separating oil containing solvent.
7. A process as claimed in anyone of claims 1 to 6 comprising recycling the treated
sludge to sinter making.
8. A process as claimed in anyone of claims 1 to 7 comprising:
vigorous admixing with water and thereafter with water and solvent in
predetermined ratio to thereby achieve > 86% reduction in oil content; and
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finally subjecting to microwave heating for removal of moisture.
9. A process to reduce oil and moisture content in iron bearing oily mill sludge of steel
plant substantially as herein described and illustrated with reference to the
accompanying examples and figures.

Dated this 7th day of February, 2008
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A process directed to reduce oil and moisture content in iron fines containing oily steel mill
sludge generated during the rolling operations and the like on a sustainable basis. The
present process treats the secondary sludge-oil-water emulsion containing fine sized iron
bearing particles, for recycling to the sinter plant. The present process involves selective
combination of solvent extraction and drying to obtain iron enriched dried sludge for
recycling to sinter making. The solvent extraction consists of vigorous admixing with water
and finally with organic solvent in selective ascertained ratio, reduces oil content to >86 %.
Importantly, magnetic field is used for holding the iron containing fines while separating oil
containing solvent layer. The moisture removal by microwave heating is achieved at less
time and cost to obtain <1% oil and <5% moisture in the treated and dried sludge.