FIELD OF THE INVENTION
This invention relates to a process for production of nano/submicron size
monodispersed iron powder from waste chloride pickle liquor. This invention
particularly relates to a process for production of high grade monodispersed
metallic iron powder with varying size and shapes suitable from waste
chloride pickle liquor suitable for high end applications.
BACKGROUND OF THE INVENTION
The iron powder in nano/submicron range has received considerable
attention for its potential application in groundwater treatment and site
remediation. Recent studies have demonstrated the effect of zero valent iron
nanoparticles for the transformation of halogenated organic contaminants
and heavy metals. In addition, nanoscale iron particles are effective for the
transformation of a wide array of common environmental contaminants like
chlorinated organic solvents, organochlorine pesticides, organic dyes, various
inorganic compounds and metal ions M. Nutt, J. Hughes, M. Wong, 2005,
Environ Sci Technol 39, 1346; J. Cao, D. Elliott, W. Zhang, 2005, J Nanopart
Res 7, 499). Several field tests have demonstrated the promising prospective
for in situ remediation (J. Quinn, C. Geiger, C. Clausen, K. Brooks, C. Coon, S.
O'hara, 2005, Environ Sci Technol., 39, 1309)
Several synthetic methods that have been developed and are in use to
produce iron nano particles (Gil-Geun Lee and Sung-Duck Kim, 2003, Mat.
Res. Soc. Symp. Proc. VoL 740, 13.22: D. Prabu, R. Parthiban, 2013, Asian J.
Pharm. Tech. Vol. 3(4), 181; DeCaro, D. et al., 1996, Chemistry of Materials,
8, 1987) with modified surface properties and enhanced efficiency. Chemical
synthesis / reduction methods (Glavee, G.N. et al., 1995, Inorganic

Chemistry, 34, 28; R. Yuvakkumar et al., Digest Journal of Nanomaterials and
Biostructures, 2011, 6(4), 1771) are most widely used as it has several
advantages over conventional methods of preparation such as (1) effective
control of size and shape of the particles (2) incorporation of less impurities
(3) regeneration of lixiviant and (4) relatively low reaction temperature.
Huge quantity of waste pickle liquor (WPL) is generated from steel industries,
generally to the tune of 30-60 L/MT of steel depending on the operating
conditions. About 70-100 g/L of ferrous iron and 50-80 g/L of HCl/H2SO4 are
found in the system. General methods for disposal in practice are :
neutralisation of acid, precipitation of metal values, in some cases
evaporation or pyro-hydrolysis to recover acid and iron as crude grade iron
oxide. These practices are now being questioned with the stringent
environmental regulation related to waste disposal. Therefore it is proposed
to develop a suitable process for recovery of iron as value added products
which will not only generate revenue but also will prevent environmental
pollution.
Though several attempts have been made to produce various grades of iron
oxide from waste chloride pickle liquor mostly by spray roasting and aqueous
precipitation methods. Spray roasting process produce s very crude grade
iron oxide containing chloride, silica etc while recovering hydrochloric acid for
recycling. Various grades of iron oxide with controlled shape and sizes have
been produced from waste pickle liquor by chemical precipitation method
both under atmospheric and pressure conditions. Very uniform
monodispersed powder of iron oxide of different shapes and sizes were
prepared from ferric chloride (Indian patents No. 0251DEL2013 and 247568,
A. Agrawal et al., 2011, Journal of Environmental Management, 92, 3105)
Very little information available production of iron powder from waste chloride
pickle liquor.

OBJECTS OF THE INVENTION
Therefore, the main object of the present invention is to propose a process
for preparation of high pure iron metal powder directly from an impure iron
chloride solution.
Another object of the present invention is to produce monodispersed iron
powder of uniform size and shape from waste chloride pickle liquor.
Yet another object of the present invention is to produce iron oxide of definite
size and shape from waste chloride pickle liquor by hydrothermal precipitation
method.
Still another object of the present invention is to produce iron powder of
different shapes and sizes from iron oxide by hydrogen reduction.
A further object of the present invention is to produce iron powder from ferric
chloride solution with the aim to utilise naturally abundant and waste material
like blue dust, iron scrap and various process residues containing high iron,
which would favour a hydrochloric acid leaching route.
A still further another object of the present invention is to produce high purity
iron metal powder directly from impure waste chloride pickling solution.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a process for preparation of
monodispersed iron oxide of high coercivity, comprising the steps of :
i) Collecting waste pickle liquor cotaining iron and hydrochloric acid in
the range of 20-200 g/L and 5-50g/L respectively including various

other impurities such as Zn : 0-4.0 g/L, Cu – 0-200 ppm, Co : 0 – 200
ppm, Ca : 0-500 ppm, Mg : 0 – 500 ppm, Cr : 0 – 500 ppm and Mn: 0
– 500 ppm,
ii) oxidising the ferrous iron to ferric using chlorine gas by known process,
iii) adding calculated amount of ammonium hydroxide solution to iron
chloride for precipitating iron as iron hydroxide while stirring with the
help of suitable stirrer and maintaining the pH of the hydroxide slurry in
the range 1.0 to 8.5,
iv) aging the iron hydroxide slurry in the temperature range of 90 to 200
oC for a duration of 0.5 – 200 h,
v) cooling the slurry below 50 oC, filtering and washing the precipitate for
complete removal of chloride and drying in the temperature range of 70
to 150 oC for 1-24 hours,
vi) heating the product to in the temperature range of 300 – 800 oC and
passing hydrogen gas/Hydrogen +Nitrogen gas for a duration of 0.5 - 5
h to reduce iron oxide to iron metal powder.
vii) Cooling below 60 oC under inert/reducing atmosphere and charactering
the product for its for its potential use.
In an embodiment of the present invention the concentration of iron in the
starting solution may be in the range of 20 - 200 g/L.
In another embodiment of the present invention the concentration of
ammonia solution used for precipitation of iron from concentrated iron
chloride solution may have concentration in the range of 5 - 20% (w/v).
In still another embodiment of the present invention the pH of the hydroxide
slurry may be adjusted in the range 1.0 - 8.5 by adding ammonia solution.
In still another embodiment of the present invention the heating of the
hydroxide slurry may be carried out in a closed reactor, in the temperature
range of 90 - 200 oC.

In still another embodiment of the present invention the size of the
monodispersed pseudocubic particles prepared is in the range of 50 to 3000
nm.
In still another embodiment of the present invention the produced
monodispersed hematite particles of different shapes and sizes are prepared
by aqueous precipitation directly from waste pickle liquor.
In still another embodiment of the present invention the monodispersed
particles of iron powder produced from the above iron oxide by gaseous
reduction using hydrogen gas / hydrogen + nitrogen gas mixture.
In still another embodiment of the present invention the iron powder by
hydrogen gas / hydrogen + nitrogen gas mixture in the temperature range of
300 - 800 oC.
In still another embodiment of the present invention the magnetization value
of iron powder is in the range of 170 to 219 emu/g.
Novelty of the present invention are (i) production of very uniform size
monodispersed iron oxide powder in different size range and maintaining
dispersity during hydrogen reduction to produce high grade iron powder.
The following examples are given to illustrate how the process of the present
invention is carried out in actual practice.
EXAMPLE – 1
One litre of waste chloride pickle liquor containing 127.6 g/L ferrous iron,
0.28 g/L ferric iron and 17.4 g/L free hydrochloric acid along with 30 ppm Zn,
16.8 ppm Ni, 55.6 ppm Cu, 4.5 ppm Co, 177 ppm Mn and 24.6 ppm Cr was
taken in a 1.2 L glass cylindrical container fitted with an air sparger. To the
above solution chlorine gas was passed from a chlorine gas cylinder in order
to oxidise ferrous iron to ferric state. Intermittent sample was collected and
analysed to check the remaining ferrous iron. Chlorine gas was passed till

complete oxidation of iron from ferrous to ferric state. The experiment was
repeated several times and the oxidised solution were stored as stock
solution for carrying out further experiment.
EXAMPLE – 2
300 mL of above ferric chloride solution (as obtained in Example-1)
containing 128.4 g/L iron and18.7 g/L free hydrochloric acid in a 1 litre
polythene beaker. Under stirring condition, 373.5 mL of 10% ammonia
solution was added slowly to the above iron solution to precipitate iron as
ferric hydroxide and made homogeneous for about 15 minutes. The
hydroxide slurry was transferred to a 1000 mL capacity autoclave and heated
to 150 oC for 2 h. After cooling to about 50 oC, the content was filtered,
washed with distilled water and subsequently with acetone and dried at 110
oC for about 6 h. As observed from the SEM pictures, the prepared particles
were found monodispersed and almost spherical in shape of size about 200
nm (Fig. 1a).
Fig. 1 : Monodispersed nano iron oxide produced hydrothermally from waste
chloride pickle liquor.
EXAMPLE – 3
20 g of above dried particle of hematite (as obtained in example 2) was taken
in a recrystalised alumina boat and kept inside a closed type tubular furnace.
The furnace has the facility for passing gas from one end with the exit in the
other end. The furnace was heated up to 500 oC and hydrogen gas was
passed at a flow rate of 2 L per min. The gas flow under heating at 500 oC
was continued for 2 h. Cooling of the sample was done under reducing
atmosphere to below 50 oC.

X- ray diffraction patterns confirm formation of pure iron powder and
maintain monodispersity. Some pores are developed and size was found
smaller (~150 nm ) than original hematite particle. Metallic iron fraction in
the reduced powder was found >99.5%. The magnetic measurement data
obtained from the coercivity curve of the prepared sample shows
magnetisation value of 218.3 emu/g, which shows almost complete
conversion of the hematite to metallic iron.
Fig. 2 : (a) Iron powder produced from above nano iron oxide produced
hydrothermally, at 500 oC, (b) XRD of nano iron powder produced by gaseous
reduction with hydrogen.
EXAMPLE – 4
20 g of above dried particle of hematite (200 nm) as obtained in example - 2
was taken in a recrystalised alumina boat and kept inside a closed type
tubular furnace. The furnace has the facility for passing gas from one end
with the exit in the other end. The furnace was heated up to 650 oC and
hydrogen gas was passed at a flow rate of 2 L per min. The gas flow under
heating at 650 oC was continued for 2 h. Cooling of the sample was done
under reducing atmosphere to below 50 oC.
X- ray diffraction patterns confirm formation of pure iron powder and
maintain monodispersity. Some pores are developed and size was found
smaller (~150 nm ) than original hematite particle. Metallic iron fraction in
the reduced powder was found >99.5%. The magnetic measurement data
obtained from the coercivity curve of the prepared sample od size about 150
nm shows magnetisation value of 204.4 emu/g, which shows almost
complete conversion of the hematite to metallic iron.

Fig. 3 : (a) Iron powder produced from above nano iron oxide at 650 oC, (b)
XRD of nano iron powder produced by gaseous reduction with hydrogen.
EXAMPLE – 5
300 mL of above ferric chloride solution (as obtained in Example-1)
containing 128.4 g/L iron and18.7 g/L free hydrochloric acid in a 1 litre
polythene beaker. Under stirring condition, 350 mL of 10% ammonia solution
was added slowly to the above iron solution to precipitate iron as ferric
hydroxide and made homogeneous for about 15 minutes. The hydroxide
slurry was transferred to a 1000 mL capacity autoclave and heated to 150 oC
for 2 h. After cooling to about 50 oC, the content was filtered, washed with
distilled water and subsequently with acetone and dried at 110 oC for a period
of 6 h. As observed from the SEM pictures, the prepared particles were found
monodispersed and cubical in shape of size about 2000 nm.
Fig. 4 : Monodispersed cubic shape iron oxide produced hydrothermally from
waste chloride pickle liquor.
EXAMPLE – 6
20 g of above dried particle of hematite (as obtained in example - 5) was
taken in a recrystalised alumina boat and kept inside a closed type tubular
furnace. The furnace has the facility for passing gas from one end with the
exit in the other end. The furnace was heated up to 500 oC and hydrogen gas
was passed at a flow rate of 2 L per min. The gas flow under heating at 500
oC was continued for 2 h. Cooling of the sample was done under reducing
atmosphere to below 50 oC.
X- ray diffraction patterns confirm formation of pure iron powder and
maintain monodispersity. Some pores are developed and size was found
smaller (~1800 nm ) than original hematite particle. Metallic iron fraction in
the reduced powder was found >99.5%. The magnetic measurement data
obtained from the coercivity curve of the prepared sample shows

magnetisation value of 183.6 emu/g, which shows almost complete
conversion of the hematite to metallic iron.
Fig. 5 : (a) Monodispersed Iron powder produced by H2 gas reduction at
500 oC from hydrothermally prepared iron oxide as in example -5.
EXAMPLE – 7
20 g of above dried particle of hematite (2000 nm) as obtained in example -
5 was taken in a recrystalised alumina boat and kept inside a closed type
tubular furnace. The furnace has the facility for passing gas from one end
with the exit in the other end. The furnace was heated up to 500 oC and
hydrogen gas was passed at a flow rate of 2 L per min. The gas flow under
heating at 650 oC was continued for 2 h. Cooling of the sample was done
under reducing atmosphere to below 50 oC.
X- ray diffraction patterns confirm formation of pure iron powder and
monodispersity is lost due to inter particle fusion. Some pores are developed
and size was found smaller (~1800 nm ) than original hematite particle.
Metallic iron fraction in the reduced powder was found >99.5%. The
magnetic measurement data obtained from the coercivity curve of the
prepared sample shows magnetisation value of 174.3 emu/g, which shows
almost complete conversion of the hematite to metallic iron.
Fig. 6 : (a) Iron powder produced by H2 gas reduction at 650 oC from
hydrothermally prepared iron oxide as in example -5.

The major advantages of the process are :
1. Use of ammonia solution for precipitation avoids
ontamination/incorporation of sodium/ potassium in to the host matrix.
Ammonium ion if at all will present that will decompose at about 320 oC
during powder production.
2. Very low temperature is required in the process to precipitate iron oxide
as compared to conventional pyrometallurgical process.
3. Reduced chemical consumption as both ammonia and hydrochloric acid
could be regenerated and recycled in the system.
4. No additional steps like selective precipitation or solvent extraction is
required prior to iron oxide precipitation to produce high purity iron
powder.
5. Very easy to control size and shape of the hematite particle can be
engineered by controlling suitable parameters which can be retained
during iron powder production.
6. Produce very uniform in size monodispersed hematite particles of iron
powder of definite shape and sizes.
7. Produce iron powder with very high green density suitable for specific
application.
8. The preparation techniques can be applied to utilise various waste
material like blue dust, MS scrap and other high iron containing wastes as
a raw material for producing high purity monodispersed iron powder.

WE CLAIM :
1. A process for preparation of monodispersed iron oxide of high
coercivity comprising the steps of :
i. collecting waste pickle liquor cotaining iron and hydrochloric acid
in the range of 20-200 g/L and 5-50g/L respectively including
various other impurities such as Zn : 0-4.0 g/L, Cu – 0-200 ppm,
Co : 0 – 200 ppm, Ca : 0-500 ppm, Mg : 0 – 500 ppm, Cr : 0 –
500 ppm and Mn : 0 – 500 ppm,
ii. oxidising the ferrous iron to ferric using chlorine gas by known
process,
iii. adding calculated amount of ammonium hydroxide solution to
iron chloride for precipitating iron as iron hydroxide while stirring
with the help of suitable stirrer and maintaining the pH of the
hydroxide slurry in the range 1.0 to 8.5,
iv. aging the iron hydroxide slurry in the temperature range of 90 to
200 oC for a duration of 0.5 – 200 h,
v. cooling the slurry below 50 oC, filtering and washing the
precipitate for complete removal of chloride and drying in the
temperature range of 70 to 150 oC for 1-24 hours,
vi. heating the product to in the temperature range of 300 – 800 oC
and passing hydrogen gas/Hydrogen +Nitrogen gas for a duration
of 0.5 - 5 h to reduce iron oxide to iron metal powder.
vii. Cooling below 60 oC under inert/reducing atmosphere and
charactering the product for its for its potential use.
2. A process as claimed in claim 1 wherein the concentration of iron in
the slurry during hydroxide precipitation is in the range of 20 - 200
g/L.

3. A process as claimed in claim 1 wherein the concentration of ammonia
solution used for precipitation of iron from concentrated iron chloride
solution may have concentration in the range of 5 - 20% (w/v).
4. A process as claimed in claim 1 wherein the pH of the hydroxide slurry
may be adjusted in the range 1.0 - 8.5 by adding ammonia solution.
5. A process as claimed in claim 1 wherein the heating of the hydroxide
slurry may be carried out in a closed reactor, in the temperature range
of 90 - 200 oC.
6. A process as claimed in claim 1 wherein the size of the monodispersed
pseudocubic particles prepared is in the range of 50 to 3000 nm.
7. A process as claimed in claim 1 wherein the produced monodispersed
hematite particles of different shapes and sizes are prepared by
aqueous precipitation directly from waste pickle liquor.
8. A process as claimed in claim 1 wherein the monodispersed particles
of iron powder produced from the above iron oxide by gaseous
reduction using hydrogen gas / hydrogen + nitrogen gas mixture.
9. A process as claimed in claim 1 wherein the iron powder by hydrogen
gas / hydrogen + nitrogen gas mixture in the temperature range of
300 - 800 oC.

10. A process as claimed in claim 1 wherein the magnetization value of
iron powder is in the range of 170 to 219 emu/g.
11. A process as claimed in claims 1 - 10 for the production of high pure
monodispersed iron powders of different sizes magnetisation value
from waste pickle liquor herein described with reference, examples and
figures.