FIELD OF THE INVENTION
The present invention relates to a process for dewatering of furnace sludge
including gas cleaning plant ultrafine particles to produce solid cakes with
reduced moisture applicable to agglomeration process.
BACKGROUND OF THE INVENTION
During manufacturing of ferro-manganese or silico-manganese lumpy Mn ores,
reluctant (coal, coke, charcoal, LAM Coke), and flux
(dolomite/limestone/olivine/pyroxene) are produced. Generally these alloys are
produced in a submerged arc furnace, a blast furnace, a DC plasma furnace.
Feed consisting of the above descends inside the furnace is heated by hot gases
coming from the furnace bottom. During smelting reduction, oxides of Mn, Fe, P
and Si reduce and form molten ferromanganese. Oxides of gangue minerals
(Al2O3, SiO2, MgO, etc.) combine with fluxes to from the slag. Part of the Mn
oxide also combines with the slag.
During smelting of the material, a huge quantity of the gas generated as a off
gas and cleaned in a Gas Cleaning Plant (GCP). The off gas primarily contains
ultrafine particles of manganese ore, manganese oxides, iron oxides, silicates,
aluminum silicates, calcium oxide, and carbon fines at elevated temperature.
These ultrafine particles along with the off-gas are passed through a series of
venture scrubber and collected in a thickener at a very low pulp density of 0-
0.5% solids by wt. The thickener being inefficient produces underflow of slurry
having pulp density less than 1-2% solids by wt. This low concentrated slurry
also contains heavy metal such as zinc, which is deposited in a storage pit. These

are treated as solid waste, and causes a high degree of environmental
degradation, when reach the soil and the ground water level through removal of
oxygen. On the other hand, the process waste contains huge volume of water
which can be reused.
Ferro-manganese/silico-manganese sludge, in the presently available state of the
art production techniques of these alloys, is deposited in landfills, resulting in a
great environmental impact due to the available oxygen in the soil, directly
affecting the bacteria existing in that environment and so hindering the
proliferation of the essential organisms for the continuation of the life cycle.
US patent No. US 6,413,433 Bl describes use of cationic dispersion polymers to
water the microparticles from the sludge. In this patent, the use of above
mentioned polymer is applicable to different industries other than minerals and
metallurgy.
US Pat. No.5209841 discloses a liquid filtering system, comprising a filter belt
along with a pressurized chamber to dewater the material. The above patent
teaches a unique design to dewater the material without emphasis on the
material characteristics.
US Patent No. 6,101,738 talks about a system for dewatering the sludge by
pressurizing air to a moving porous belt conveyor where the capacity of
dewatering of the sludge can be enhanced. The above patent is silent about the
particle size and type of material used for the invention.

Publication No. WO 2005/017216 A2 teaches a recycling process for blast
furnace sludge along with the metallurgical waste from the steel industry. But
the above patent is silent on recovery of the sludge generated from the
ferroalloys industry.
None of the above patents, teaches or suggests dewatering or recycling of the
sludge generated from the ferromanganese industry. Also, there is no indication
of similar process to dewater the sludge of similar composition or particle size
range.
Presently, the sludge generated from the gas cleaning plant of ferromanganese
process contains a huge quantity of water with low solid concentration, which
cannot be utilized further for agglomeration process. A particular moisture level
is suitable for the green mix of the agglomeration process viz: pelletisation,
sintering or briquetting. So the moisture content can be lowered to minimum
amount to mix it with the green mix. In addition to this, the storage of this low
solid concentration sludge is an issue along with the overall water consumption
in the plant.
The ultrafine sludge, presently considered as an industrial waste, has indeed a
tangible storage and handling cost and an enormous intangible value as a
recycle of the process/dewatered water along with the filtered low moisture
cake for agglomeration. Further, a possible use of the industrial waste is likely to
result in a considerable advantage to the recuperation of the degraded
environment along with the recycling of the natural resources and industrial
waste.

OBJECTS OF THE INVENTION
It is therefore an object of the invention to propose a process for dewatering of
furnace sludge including gas cleaning plant ultrafine particles to produce solid
cakes with reduced moisture applicable to agglomeration process.
Another object of the invention is to propose a process for dewatering of furnace
sludge including gas cleaning plant ultrafine particles to produce solid cakes with
reduced moisture applicable to agglomeration process, which is efficient and
economic.
A further object of the invention is to propose a process for dewatering of
furnace sludge including gas cleaning plant ultrafine particles to produce solid
cakes with reduced moisture applicable to agglomeration process, which
contributes in minimizing environment pollution.
SUMMARY OF THE INVENTION
Accordingly, there is provided a process for dewatering of furnace sludge
including gas cleaning plant ultrafine particles to produce solid cakes with
reduced moisture applicable to agglomeration process, comprising the steps of :
conditioning the slurry in a condition tank by adding a pH regulator and stirring
with the agitator to maintain a pH value less than 9; feeding the conditioned
slurry in a flocculating tank and adding a known flocculant to form the floccule of
ultra-fine sludge particles; and pumping the flocculated slurry into a pressure
filter at a pressure between 7-10 bars for solid-liquid separation and allowing air
at a pressure between 5-10 bars to pass for a period about 5-8 minutes to form
solid cakes useable for agglomeration.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The process which is object of the present invention, allows the dewatering of
the gas cleaning plant sludge of ferro manganese/silicomangnese process in a
feasible, efficient, and economical way which can be better understood from
figure 1. The description of the figure allows for a complete and comprehensive
understanding of the process. The Figure shows a flow diagram of a dewatering
process for ferro-manganese/silico manganese sludge.
DETAILED DESCRIPTION OF THE INVENTION
As shown in figure 1, and their numeric reference, the inventive dewatering
process for the ferromanganese/silicomangnese sludge or ultrafine particles
generated from gas cleaning plant of ferromanganese/silicomangnese consists of
the steps of slurry conditioning, flocculation and filtration. The generated sludge
is collected in a conditioning tank having an agitator (1) for maintaining pH, fed
to a flocculating tank (3) from which it is fed into a pressure filter (5) to produce
filtered cake (6) for reuse in the manufacturing process in the form of
agglomeration, and filtered water (7) can be pumped to the system.
As depicted in Figure 1, a method is illustrated to dewater the ultrafine sludge
particle generated from the manganese alloy industry. The process handles the
ultrafine particles of maximum particle size having less than 100 μm and as fine
as 80% (by weight) of the particle having diameter less than 15-30 μm. The
slurry or sludge contains solid of below 0.5% solids by weight with pH value in
the range of 10-12. The sludge is having particle of different elements viz: Mn,
Fe, Si, Al, Zn, Ca, Mg, Ti, Zn, C and the temperature of the slurry varied from 60-
120 degree centigrade. The Mn content was present in the form of Mn and or

MnO and or MnO2. The MnO content is very critical and varied from 60-68%
whereas silica content varied from 8-15%. The CaO and MgO content in the
slurry varied from 3-5% each.
The slurry contained in the above composition was pumped to the condition tank
(1) to maintain the pH. The sludge generated from the process having pH in
between 10-11. The pH of the slurry is controlled and maintained to less than 9
or varied in between 8-9. This is one important step which assists the
flocculation (3) to be more effective. For adjusting the pH in the system to a
required value, pH regulator viz: hydrochloric acid is added based on the
requirement. The slurry is mixed inside the conditioning tank with the agitator.
Furthermore, the slurry is pumped to the flocculation tank (3) and required
amount of flocculent (4) is added to form the floccule of the ultrafine sludge
particles. The main objective of the flocculation is to enlarge the particle size by
utilizing the surface charge of the individual particles. The subsequent process
i.e. filtration of the sludge mainly depends on the degree of the flocculation in
this process. The dosage of the flocculent varied from 0.1 to 0.5 kg/ton of ore to
form the floccule for the subsequent process. A known flocculent such as Nalco
7763 (Nalco Company of Naperville, US) or DEL-DKP700 (Dai-Ichi Karkaria Ltd.)
can be used for carrying out the present invention. The retention time of the
slurry during the process is approximately 5-7 minutes.
The flocculated slurry is pumped to the pressure filter (5) at optimized pressure
for effective solid liquid separation. The optimized pressure is maintained while
feeding and the value varied in between 7-10 bar. After saturation of the feed in
between the filtering chamber, the high pressure air is allowed to pass through
for 5-8 minutes. The pressure during the drying is varied from 5-10 bar. The

cake (6) is allowed to drop from the chamber and can be utilized for
agglomeration purpose. The moisture content in the cake is varied from 20-25%
solids by wt The filtered water (7) can be further utilized for reuse in the plant.
The particulate matter in the clarified filtered water varied from 100 to 200 ppm.
The low moisture sludge cake/recycled product obtained from the process of the
present invention may be reused economically in the agglomeration process in
the manganese alloys industry besides contributing to the preservation of the
environment.
Having generally described the invention, a further understanding can be
obtained by reference to certain specific examples, which are provided herein for
the purpose of illustration only and are not intended to be limited unless
otherwise specified. The following examples are given by way of illustration of
their working of the invention in actual practice and therefore should not be
construed to limit the scope of the present invention.
Slurry generated from the gas cleaning plant having solid concentration of 0.7%
(by weight) was mixed and conditioned in a slurry tank of 200 liters capacity.
The temperature of the slurry was about 80 degree centigrade and the pH of the
slurry was 11.2. Required amount of hydrochloric acid was added to lower the
pH value up to 8.7. Further, it was pumped to another tank of similar capacity
for the flocculation. A known flocculent was added (0.1 kg/ton). It was mixed for
5 minutes with lower turbulence prior to pumping. Then the flocculated slurry
was pumped to the press filter for filtration to obtain the cake. During pumping,
the pressure maintained was 7.2 Bar and pumped for 15 minutes to the press
chamber of 20 mm thickness. After completion of the pumping, the drying was

done for 5 minutes with a pressure of 6.5 Bar. After completion of the drying
cycle, the pressure was released for the discharge of the cake. The
representative sample of about 25 gm of 5 samples were taken from different
cake and subjected for the moisture analysis. The sample was kept in a
laboratory micro-oven for 2 hrs. at a temperature of 200 degree centigrade. The
average weight loss during the heating was used to calculate the moisture level
in the cake. In this test the reported moisture of the cake was 24.2%. The
reported total suspended solid content of the filtrate water was 170 ppm.
Similar experiments on the dewatering system were carried out with gas cleaning
plant sludge. Few results of the study are summarized in the below Table.

The main advantages of the present invention are:
1. Effective dewatering of the gas cleaning plant of ferromanganese/silico
manganese sludge.

2. The sludge containing manganese and its oxides can be reused for ferro-
rnaking process.
3. The low moisture filtrate cake can be mixed with green mix of the
agglomeration process such as: sintering, pelletisation or briquetting.
4. Proper utilisation or gainful utilization of the furnace dust/sludge.
5. The filtrate water can be reused in the system by which, the overall
consumption of water to the plant can be minimized.
6. The environmental hazard such as storage of ultrafine sludge in a pit can
be avoided.

WE CLAIM :
1. A process for dewatering ferromanganese/silicomangnese sludge, the
process comprising:
conditioning the slurry in a condition tank by adding a pH regulator
and stirring with an agitator to maintain a pH value less than 9;
feeding the conditioned slurry in a flocculating tank and adding a
flocculent to form the floccule of ultra-fine sludge particles; and
pumping the flocculated slurry into a pressure filter at a pressure
between 7-10 bars for solid-liquid separation and allowing air at a
pressure between 5-10 bars to pass for a period about 5-8 minutes to
form solid cakes useable for agglomeration.
2. The process as claimed in claim 1, wherein MnO content and silica
content, in the sludge is varied in the ranges 60 to 68 weight %, 8 to
15% weight respectively.
3. The process as claimed in claim 1, wherein calcium oxide and
magnesium content in the sludge is varied in the range 8 to 15%
weight.
4. The process as claimed in claim 1, wherein the sludge temperature is
varied in the range 60 to 120 degree centigrade.
5. The process as claimed in claim 1, wherein the ferromanganese or
silico-manganese sludge is having particle size below 100μm.

6. The process as claimed in claim 5, wherein 80% of the particles
diameter varies in the range 10 to 30 μm.
7. The process as claimed in claim 1, wherein pH regulator is Hydrochloric
Acid (HCI).
8. The process as claimed in claim 1, wherein pH regulator is used to
maintain pH preferably in the range 8.5 to 9.
9. The process as claimed in claim 1, wherein the flocculent is a polymer
based flocculent.
10. The process as claimed in claim 1, wherein the flocculent dosage varies
in the range 0.1 to 0.5 kg/ton.
11. The process as claimed in claim 1, wherein the ultrafine flocculated
sludge (3) is fed into the pressure filter (5) up to a saturated level
when the pressure triggers to a maximum to stop the flow of the
filtration water.
12. The process as claimed in any of the preceding claims wherein, during
filtration (5) of the sludge, thickness of the filtrate cake is varied from
20 to 35 mm.
13. The process as claimed in any of the preceding claims, wherein
moisture content of the filtrate cake (6) varies from 20-25% by wt

14. The process as claimed in any of the preceding claims, wherein, during
filtration (5) of the sludge, the filtrate water (7) is recycled in the
process.

ABSTRACT

The invention relates to a process for dewatering of furnace sludge
including gas cleaning plant ultrafine particles to produce solid cakes
with reduced moisture applicable to agglomeration process, comprising
the steps of : conditioning the slurry in a condition tank by adding a
pH regulator and stirring with the agitator to maintain a pH value less
than 9; feeding the conditioned slurry in a flocculating tank and adding
a known flocculent to form the floccule of ultra fine sludge particles;
and pumping the flocculated slurry into a pressure filter at a pressure
between 7-10 bars for solid liquid separation and allowing air at a
pressure between 5-10 bars to pass for a period about 5-8 minutes to
form solid cakes useable for agglomeration.