FIELD OF THE INVENTION
The present invention generally relates to an improved process for recovering iron values
from iron ore slime, a waste generated during washing of iron ore. More particularly, the
invention relates to an improved method for utilization of slime by circumventing its
inherent deficiencies so that the same can be utilized as an alternate to the lump iron ore,
being used in blast furnace for production of iron.
BACKGROUND OF THE INVENTION
Iron ore slime is the powdery material (associated with the iron ore), which is removed
during washing of iron ores; typical slime generation is around 20% of the iron ore mined
[Manna et al., 2011]. Though its Fe content, about 54% Fe [Manna et al. 2011], is higher
than that of many ores elsewhere in the world, it is unacceptable to blast furnace iron
making for its fine size and alumina and silica content beyond the acceptable limits;
hence they are discarded in slime ponds. Continued slime accumulation in large
quantities makes the iron and steel sector industries vulnerable to environmental
regulations; besides huge amount iron values is wasted. Utilization of these slimes is
inevitable for the sustainability of iron ore mining industries.
Hitherto known approaches to make use of the iron ore slime involve simple, innovative
mineral processing techniques. One such process [Srivastava et al., 2001] uses a two-
stage hydrocyclone –spiral circuit for processing the ore. The slime could be upgraded up
to 64% Fe with an yield of ~37%. Manna et al (2011) have also used only hydrocyclone
to achieve the purpose; but they have used some dispersing agents to get the desired
product grade. Dey et al. (2015) have used column flotation of the iron ore slime to get a
concentrate having a grade of 64.3% Fe, 1.9% silica and 2.2% alumina with an yield of
~55%. A product having <1% silica and 80% metallic recovery has been reported in

another study using reverse cationic flotation of iron ore slimes [Rocha et al., 2010]. A
combination of hydrocyclone and flotation has yielded a concentrate assaying 64.46% Fe,
2.66% Al2O3, and 2.05% SiO2 and recovering 34.13% of iron values contained in the
slime. Above-mentioned approaches selectively recover usable grade from the slime, but
has the following disadvantages: (1) the fine size still makes it unusable as it is (2) none
of the process recovers the iron values in full, and (3) it generates another stream of
waste, coated with chemicals if dispersion and flotation processes are employed.
For the slime to be made usable even after arriving at a suitable chemistry for use through
beneficiation, it needs to be agglomerated.
The hitherto known process to produce briquettes from iron ore uses inorganic binder
such as hydrated lime or cement. The existing process to produce briquettes consists of
grinding of iron ore in a grinding mill, mixing with binder in a mechanical mixer, roller
compaction for shaping the products, drying and curing in water for 21-28 days.
Another known process to produce briquettes uses organic binder such as pitch, molasses,
and sulfite liquor. The existing process to produce briquettes consisting of mixing of iron
ore with organic binder in a mechanical mixer, roller pressing of the mixed material,
drying in open atmosphere for 1-4 days followed by drying in a drying oven for 1-2 days.
The disadvantages include obnoxious odor of the pitch etc. and high temperature strength
degradation of briquettes as these organic binders are burnt. Pitch needs to be mixed at an
elevated temperature to have a uniform composition of the binder.
A still another known process to produce briquettes uses melting of asphalt at high
temperature and mixing with iron ore in a mechanical mixer and then casting in a mould.
Besides the disadvantages such as odor and low strength, it needs a high temperature
operation for mixing the binder.

A non-patent literature [Qiu et al., 2003] disclosed a process to produce cold bonded iron
ore pellet for direct reduction using organic binder. The process consisted of pretreatment
of iron ore concentrate with organic binder in a roll drum mill. A balling time of 20
minutes was used to get good pellet strength. Drying was carried out at a temperature in
the range of 200-250 °C. These pellets were used in the production of direct reduction
iron. This process would need a much more fine material, all must be below 75 µm or
below; besides the energy requirement for drying, energy is also required for grinding a
part of slime to the requirement of pelletization.
Another non-patent literature by [Anyashiki et al., 2009] disclosed a process wherein iron
carbon composite briquettes were produced by mixing coal and iron ore and densification
by hot briquetting, followed by carbonization of the briquetted materials. A mixture of
40% iron ore and 60% coal has given the good strength to the briquettes and the
reduction ratio of the product exceeded 70%. The disadvantages include the large energy
consumption required for the high press operation and hot briquetting and carbonization.
Gannon et al. (EP 1425427 A4, 2004; US 2005/0050996 A1, 2005) provides a
description of iron ore briquetting suitable for blast furnace. According to this invention,
the briquettes are prepared by mixing ore and a flux to form an ore/flux mixture, then
pressing the ore/flux mixture into a green briquette using a low roll pressure; and
induration of the green briquette to form a fired briquette. Firing is done on granulating
iron ore fines with coke breeze at approximately 1300°C. Bonding takes place between
the grains during combustion, and strong agglomerate is formed. High temperature
induration is the main disadvantage; the particle size of the materials in use, 2 mm size is
significantly larger than that of the slime discussed in the present invention.
A US patent by Roger (US 3295952 A, 1967) describes a process for briquetting hematite
fines with a bituminous coal binder. The hematite fines is heated under reducing
condition at a temperature of 850 to 1050 F. Bituminous coal fines are mixed with the

heated and partially reduced hematite at a temperature of 600 to 800 F and then
briquetted using a briquetting machine. Requirements of a reducing gas and hot
briquetting etc. make the process unattractive.
An Indian patent (DE 01224, 2002) describes an improved inorganic binder matrix,
consisting of a combination of different in-organic binders, useful for cold briquetting of
iron and steel plant wastes such as iron ore fines, flue dust, mill scale, coke fines etc for
use in blast furnace charge. The process does not include fine material such as slime.
Further, disadvantage is that this uses chemicals like sodium silicate.
UA patent 0098787 discloses a process to produce briquettes which contains
metallurgical production slimes, blast-furnace dust, scale, and as binder it comprises
cement.
A hitherto known Russian process (RU2298584) uses cement for briquetting iron-
containing metallurgical process wastes along with dolomite dusts and 1-5% cement. It
needs significant quantities of dolomite dusts. Another Russian patent (UA-61865)
describes a process for briquetting which takes only less than 10% slime.
A hitherto known process (CN 103114201A) describes a process of utilizing the dust and
mud of steel industry; it involves agglomeration of the dust with a mixture of bentonite,
carboxy methyl cellulose and fulvic as binder and is used as a part of the sinter feed. The
process uses costly binders and does not have the disadvantage of high alumina and silica
as with the slime described in the present invention.
A hitherto known process (CA 2789308 A1) involving classification, wet milling of the
coarse fraction (>15 µm) and multiple stage selective flocculation using modified starch
produces a high purity iron for high end application from a poor grade iron ore slime. The
disadvantages are the energy consumption in ultrafine grinding (-15 µm) and the tailings
produced.

A hitherto known process (CN 101293220B) uses a chemical mix consisting of Na2SO4,
Na2B4O7 and Na2CO3 for separating alumina from iron ore. The process involves
carbothermic reduction of the iron ore chemical mix pellets. Metallic Fe with < 1%
alumina and < 1 % silica are obtained by magnetic separation of the reduced pellets after
grinding. There is another patent (CN 101293281 B) on similar lines. The reagent breaks
the crystal structure and helps in releasing the alumina embedded in the structure and
thereby facilitating the separation easier. Main drawback is the significant amount of
energy required for the grinding and high temperature operation. Another process (CN
100540694 C) prepares feed suitable for blast furnace from high alumina ores by
removing the alumina by chemical means (reacting with Na2CO3) at high temperature
followed by soda leaching. This method also is an energy intensive process.
Das et al. (2004) describes a process for utilization of iron ore slime in preparing ceramic
tiles. However, the use is only partial, < 50% and needs firing.
Thus the prior art processes have the following limitations:
a. None of the processes uses iron ore slime, a waste product (with an adverse silica
alumina content) generated during washing of iron ore as it is, i.e. without any
pretreatment. The one that uses [Das et al., 2004] needs high temperature firing and
overall usage is limited when large quantities of other high grade raw materials are
available.
b. The pretreatment processes used to have a suitable grade for further use suffers
from the following: (1) the fine size still makes it unusable as it is, (2) none of the
process recovers the iron values in full, generating another waste with no scope for
reclaim anything, (2) a consequent material loss, (3) it generates another stream of
waste often coated with chemicals, and (4) the processed slime needs to be
transformed to a suitable form for its use.
c. Prior art processes of briquetting of fines generally use a size range -6 mm or less,
significantly greater than the slime or slime + mill scale put together.

d. Prior art briquetting processes uses costly (some of which are foul smelling as well)
organic binders such as pitch, asphalt etc. and/or use of high temperature at some
stage during briquetting or curing.
e. During the high temperature, organic binder often burns out and the briquettes
decomposes giving rise to dust generation.
f. A prior art uses large scale use of slime by briquetting using cold bonding;
however, higher alumina and silica levels of slime, undesirable for iron making is
not attuned. Besides, its limited porosity to effectively complete the reduction of
iron oxides through gas/solid reduction reaction.
Based on literature and patent survey, and prior public knowledge, at present no process
is available for the utilization of iron ore slime (without any prior pretreatment) for iron
recovery in the normal process of blast furnace/mini blast furnace iron making; though
the slime is beneficiated to the desired grade with pretreatment, it has never gone beyond
the level of laboratory scale beneficiation studies. The purpose of this development is to
use abundantly available waste iron ore slime as a resource for iron making. The process
described in this invention synergistically uses large quantity of iron ore slime dumped in
the mine site as waste with mill scale, another waste generated during steel making to
produce cold bonded briquettes. This will reduce environmental pollution while
producing value added product such as briquettes, which can be used as an alternate
resource for iron making.
Many of the prior arts in iron ore slime utilization are limited to enhancing the grade
equivalent to that lump ore used in blast furnace. Neither there has been an attempt to
utilize beneficiated ore as it is or after transforming to briquettes or pellets. The briquettes
produced by the prior art processes for other iron ore materials have two components,
first a binder component such as cement, bitumen or resin, and second an aggregate
component such as hematite powder, iron ore fines, etc. The strength development in
briquettes is achieved either by hardening of binder phase or by reaction of binder with

fines at elevated temperatures. Reduction of iron oxides, on the other hand, also depends
on the porosity of the briquette which in turn is a function of particulate characteristics.
Thus any variation in quantity and quality of binder and heating condition, particulate
characteristics of second component affects the physicochemical properties of resulting
briquettes.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose an improved method, which
eliminates the drawback as detailed above, for utilizing the iron ore slime for recovering
the iron values in it.
Another object of the present invention is to propose an improved method for production
of cold bonded briquettes from iron ore slime and other ingredients, in which the green
density of the briquettes can be achieved by compacting by mechanical pressing and
bringing the grains closer which inter alia increase the product strength.
A still another object of the present invention is to propose an improved method for
production of cold bonded briquettes from iron ore slime using cold setting hydraulic
bonding, which reduces the energy consumption.
Yet another object of the present invention is to propose an improved method for
production of cold bonded briquettes from iron ore slime with sufficient porosity for
gas/solid reactions during reduction and a favourable chemistry in terms silica and
alumina content for iron extraction.
Use of an abundantly available less costly jhama coal as a reducing agent for iron oxides
present in the iron ore slime and other charge materials in the briquette.

A further object of the present invention is to propose an improved method for production
of cold bonded briquettes from iron ore slime, in which naturally occurring iron ore is
significantly reduced in the production of iron.
SUMMARY OF THE INVENTION
The method of the present invention uses iron ore slime as the main component, which is
a waste product generated during washing of iron ore and abundantly available
worldwide in conjunction with mill scale, another waste generated during steelmaking.
The process also incorporates jhama coal, a less costly, abundantly available coal for
reducing the iron oxides present in the iron ore slime and other charge materials in the
briquette. The process further uses hydraulic binder such as cement, which is abundantly
available worldwide. The process requires substantially lower energy consumption. The
products produced by the process of the present invention are of high compressive
strength, good volume stability, good resistance against drop and good abrasion
resistance. The product of the present invention is useful as a feed to mini blast furnace as
an iron resource instead of naturally occurring lump iron ore, which is limited and costly.
The iron ore slime used in the present invention contains iron oxides, calcium oxide
(CaO), silica (SiO2), alumina (Al2O3) and magnesium oxide (MgO).
In the method of the present invention, hydraulic binder such as cement or materials like
that has been added into iron ore slime containing charge mix (iron ore slime, mill scale
and jhama coal) for briquetting. The green strength for handling is achieved by
compaction of the mix to briquette using a hydraulic/ mechanical press. During the
hydration of cement at ambient temperature, the calcium silicate hydrate phase is formed
which has the cementitious properties. The calcium silicate hydrate then reacted with the
clayey alumino-silicate fraction present in iron ore slime which has pozzolanic properties.

Addition of additives such as calcium hydroxide, sodium hydroxide, bentonite or
molasses improves the setting time. During the pozzolanic reaction, the reactive free lime
liberated from the hydration of cement, reacted with silica and formed more
calcium silicate hydrate which bound the remaining iron oxide fractions and resulted into
solid compact body.
Accordingly, the present invention provides an improved method for utilization of iron
ore slime through regulating its chemistry and transforming to a size suitable for charging
to furnace; the method comprising the steps of:
(i) Dewatering the iron ore slime by natural (or in filter press) to reduce the
moisture content less than 15% by weight;
(ii) drying of the iron ore slime as obtained in step (i) by open air drying to
reduce the moisture less than 1-5 % by weight;
(iii) powdering large agglomerate lumps (if any) in the iron ore slime as
obtained in step (ii) by using a roller;
(iv) blending the slime obtained in step (iii) with -1mm mill scale to adjust the
chemistry; presence of -1 mm size mill scale ensures sufficient porosity
required for gas/solid reaction during reduction in the furnace
(v) add the required amount of jhama coal to the blend in step (iv) as reductant
for the iron oxides in blast furnace or any other furnace
(vi) dry mixing a hydraulic binder to iron ore slime blend obtained in step (v)
using a mechanical mixer for a period ranging between 4-10 minutes in the
ratio ranging between 8:2 to 9.4:0.6;
(vii) the binder mix used in the step (vi) is of commercial grade

(viii) mixing the water to the mixture obtained in step (vi) in the range of 5-15 %
for a period ranging between 5-15 minutes using mechanical mixer;
(ix) allowing the mixture obtained in step (viii) for a period of 10-60 min at a
humidity ranging between 60 to 80% so as to start off the initial hydration
reaction;
(x) mixing of additives in the mixture obtained in step (vi) in the range of 1 to
5% by weight for a period in the range of 2 to 4 minutes in the ratio 9.7:0.3
to 9.9:0.1;
(xi) the mix obtained in step (x) is force fed to the roller briquetting press,
wherein the mix is compressed to the shape of the roller cavities (pillow
shape); no extra pressure is applied;
(xii) curing of articles as obtained in step (xi) in closed condition at ambient
temperature for a period of 12 – 48 hours;
(xiii) curing of articles as obtained in step (xii) in water at ambient temperature
for a period of 3-6 days;
(xiv) curing of articles as obtained in step (xiii) in closed condition at ambient
temperature for a period of 3-5 days;
(xv) evaporation of moisture of the articles obtained in step (xiv) by drying in air
at ambient temperature for a period of upto 28 days;
(xvi) charging the dried articles obtained in step (xv) in the mini blast furnace in
the range of 25-100% replacement of iron ore.

In embodiment of the present invention, the iron ore slime may be selected from the
following composition range:

In another embodiment of the present invention, the hydraulic binder cement may be
selected from the following composition range:

In another embodiment of the present invention, additives may be selected from the
calcium hydroxide, sodium hydroxide, bentonite, and molasses and like.

In yet another embodiment of the present invention the briquettes may have the following
range of properties:

According to the invention iron ore slime is used as the primary raw material and is more
than 40% of iron bearing materials in the charge composition comprising of wastes such
as iron ore slime, mill scale. Further, the method requires low energy and less water for
processing as compared to the conventional processes.
The following examples are given by way of illustration and should not be construed to
limit the scope of invention.
EXAMPLE – 1
40 kilograms iron ore slime was taken for the preparation of briquettes. The iron ore
slime was dry mixed with 40 kg of mill scale below -1 mm size and 20 kg of jhama coal
powder (-150 µm size) in a mechanical mixer for 5 minutes. To this mix is added 8 kg
Portland cement of 350 m2/kg specific surface area and continued. The mixture obtained
after dry mixing was mixed with 8 liters of water for 4 minutes and then kept at ambient
condition for reaction to start. After 35 minutes, 1 kg of prewetted bentonite was added
into this mixture and then the ready mix was shaped into a pillow shape of size 40x38x24
mm. The samples produced were kept in ambient condition in a covered tank for 30 hours
and then cured in water for 3 days. Further the samples were taken out from water, kept
again in covered tank for 3 days in ambient condition and then air dried for 28 days. The

properties obtained are furnished in Table 1. The dried briquettes were used in mini blast
furnace.

EXAMPLE – 2
48 kg iron ore slime was taken for the preparation of briquettes. The iron ore slime was
dry mixed with 32 kg of mill scale below -1 mm size and 20 kg of jhama coal powder (-
150 µm size) in a mechanical mixer for 5 minutes. To this mix is added 8 kg Portland
cement of 350 m2/kg specific surface area and continued. The mixture obtained after dry
mixing was mixed with 8 liters of water for 4 minutes and then kept at ambient condition
for reaction to start. After 35 minutes, 1 kg of prewetted bentonite was added into this
mixture and then the ready mix was shaped into a pillow shape of size 40x38x24 mm.
The samples produced were kept in ambient condition in a covered tank for 30 hours and
then cured in water for 3 days. Further the samples were taken out from water, kept again
in covered tank for 3 days in ambient condition and then air dried for 28 days. The
properties obtained are furnished in Table 2.The dried briquettes were used in mini blast
furnace at 820ºC.


EXAMPLE – 3
32 kg iron ore slime was taken for the preparation of briquettes. The iron ore slime was
dry mixed with 48 kg of mill scale below -1 mm size and 20 kg of jhama coal powder (-
150 µm size) in a mechanical mixer for 5 minutes. To this mix is added 8 kg Portland
cement of 350 m2/kg specific surface area and continued. The mixture obtained after dry
mixing was mixed with 8 liters of water for 4 minutes and then kept at ambient condition
for reaction to start. After 35 minutes, 2 kg of prewetted bentonite was added into this
mixture and then the ready mix was shaped into a pillow shape of size 40x38x24 mm.
The samples produced were kept in ambient condition in a covered tank for 30 hours and
then cured in water for 3 days. Further the samples were taken out from water, kept again
in covered tank for 3 days in ambient condition and then air dried for 28 days. The
properties obtained are furnished in Table 3. The dried briquettes were used in mini blast
furnace at 820ºC.


The main advantages of the present invention are:
1. The method utilizes higher proportion of abundantly available industrial waste iron
ore slime and remaining mill scale, another waste generated during steelmaking) in
the ratio 40-60: 70-30 to produce briquettes for recovering iron values, thereby
reducing the load on environment and cost of waste disposal.
2. The method of the present invention ensures resource conservation (of fast
depleting high grade raw materials e.g. hematite or magnetite) in iron/steel
production by an industrial wastes.
3. The briquetting method uses ambient temperature processing, thereby considerable
reduction in energy consumption comparison to the known process.
4. The briquettes produced by the method in the present invention are superior in
terms of strength development and resistance to break in short time than the
products produced by the existing process;
5. The briquettes produced by the method in the present invention are superior in
terms the chemistry and porosity required for gas/solid reaction during reduction in
the furnace.

References
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JFE Technical Report
No. 13 (May 2009)
Banerjee, P.K. and Manna, M. A process for producing high purity Fe2O3 for value-added
applications including blast furnace feed for a poor-grade iron ore slime, Patent
Application No.CA 2789308 A1, 2011
Dey S., Pani, S., Singh, R., Paul, G.M., 2015. Response of process parameters for
processing of iron ore slime using column flotation. Int. J. Miner. Process. 140, 58-65.
http://dx.doi.org/10.1016/j.minpro.2015.04.013
Gannon, J., Salter, C.J., Vining, H.K.R., Meakins, R.L. Iron ore briquetting, US
2005/0050996 A1, 2005; EP 1425427 A4, 2004
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with high alumina iron ore.
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alumina iron ore.
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high-alumina iron ore.
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WE CLAIM:
1. An improved method for utilization of iron ore slime through regulating its
chemistry and transforming to a size suitable for charging to furnace; the method
comprising the steps of:
(i) Dewatering the iron ore slime by natural (or in filter press) to reduce the moisture
content less than 15% by weight;
(ii) drying of the iron ore slime as obtained in step (i) by open air drying to reduce the
moisture less than 1-5 % by weight;
(iii) powdering large agglomerate lumps (if any) in the iron ore slime as obtained in
step (ii) by using a roller;
(iv) blending the slime obtained in step (iii) with -1mm mill scale to adjust the
chemistry; presence of -1 mm size mill scale ensures sufficient porosity required
for gas/solid reaction during reduction in the furnace
(v) add the required amount of jhama coal to the blend in step (iv) for reducing the
iron oxides in blast furnace or mini blast furnace
(vi) dry mixing a hydraulic binder to iron ore slime blend obtained in step (v) using a
mechanical mixer for a period ranging between 4-10 minutes in the ratio ranging
between 8:2 to 9.4:0.6;
(vii) the binder mix used in the step (vi) is of commercial grade
(viii) mixing the water to the mixture obtained in step (vi) in the range of 5-15 % for a
period ranging between 5-15 minutes using mechanical mixer;

(ix) allowing the mixture obtained in step (viii) for a period of 10-60 min at a
humidity ranging between 60 to 80% so as to start off the initial hydration
reaction;
(x) mixing of additives in the mixture obtained in step (vi) in the range of 1 to 5% by
weight for a period in the range of 2 to 4 minutes in the ratio 9.7:0.3 to 9.9:0.1;
(xi) the mix obtained in step (x) is force fed to the roller briquetting press, wherein the
mix is compressed to the shape of the roller cavities (pillow shape); no extra
pressure is applied;
(xii) curing of articles as obtained in step (xi) in closed condition at ambient
temperature for a period of 12 – 48 hours;
(xiii) curing of articles as obtained in step (xii) in water at ambient temperature for a
period of 3-6 days;
(xiv) curing of articles as obtained in step (xiii) in closed condition at ambient
temperature for a period of 3-5 days;
(xv) evaporation of moisture of the articles obtained in step (xiv) by drying in air at
ambient temperature for a period of upto 28 days;
(xvi) charging the dried articles obtained in step (xv) in the mini blast furnace in the
range of 25-100% replacement of iron ore at the temperature in the range of 700-
12000C.
2. The method as claimed in claim 1 wherein the iron ore slime has the following
composition range: SiO2 - 0.5 to 10 wt%; Al2O3 - 0.3 to 7 wt%; Fe2O3- 44 to 62
wt%; S -0.02 to 0.05 wt%; and P - 0.02 to 0.08 wt%
3. The method as claimed in claim 1 wherein the mill scale has the following
composition range: FeO - 60 to 66% wt%; Fe2O3 - 2 to 5%; Fe3O4 - 30 to
34%wt%; Fe (metallic) – 0.1 to 2%.

4. The method as claimed in claim 1 wherein the mill scale has the following particle
size: 75µm-6mm with 90% material below 1mm size.
5. The method claimed in claim 1 where in the jhama coal has a size range -150 µm
and composition range of Fix Carbon- 45-69% Volatile matter 3-25% ash -15 to
30 wt%.
6. The method claimed in claim 1 wherein the hydraulic binder such as cement has
the following composition range: SiO2-19 to 23 wt%, Al2O3-4 to 7 wt%, Fe2CO3 -
2 to 4 wt%, CaO - 62 to 70 wt%, MgO - 0.5 to 1 wt%, Free lime - 0.5 to 1.5 wt
% and Specific surface area - 325-500 m2/kilogram.
7. The method as claimed in one of claims 1 to 3, wherein the additives can be
selected from a group consisting of calcium hydroxide, sodium hydroxide,
bentonite, and molasses.
8. An improved method for production of cold bonded briquettes of iron ore slime
modified to have a chemistry and porosity suitable to iron making in mini blast
furnace by blending with mill scale and jhama coal, as substantially described
herein with reference to the examples