FIELD OF INVENTION:
This invention relates to iron powder production by reacting iron oxidewith hydrogen rich gas
and a method of preparing the same.
BACKGROUND AND PRIOR ART:
The branch of powder metallurgy has its impressions long back in the prehistoric era of Egyptian
and Indus valley civilizations. The modern powder metallurgy came into lime light during the
early 20th century and further development took place during the World War-II period. In present
era, from the last three decades this branch has geared up significantly in producing various
grades of metal powders and continued its expansion in all aspects and in all applications to the
industry.
Ferrous powder metallurgy represents almost 80 % of the total metal powder production
comprising applications like sintered automobile parts, welding electrodes, magnetic materials,
friction materials, gas cutting agents, soil purifying agents, etc. The starting material for ferrous
powder metallurgy is iron powder. Ferrous aggregates with in the size range of 20-200 µm are
termed as iron powders. Metal powder manufacturing comprises of majorly three methods;
chemical (Reduction, Decomposition), physical (Atomization, electrolytic) and mechanical
(Comminution). Iron powders on a large scale are manufactured by reduction (Solid/Gas) and
atomization (Air/Water/Gas) techniques.Reduction of iron oxide to iron powder is done by the
use of reducing agents like coal (solid) or nitrogen (gaseous). On the other hand in the
atomization technique, liquid iron melts were atomized by air or water or gas and further
processed to get powdered form of iron. The selection of the method of production always relates
to the type of application and desired property of the iron powder to be produced.
The reduction and atomization of iron ore/ iron oxide for synthesizing iron powder are the most
common and largely patented methods [(JP 910019161), (CN 104259470), (WO 200264844),
(JP 62230406)]. Now-a-days, the interest of the researchers is being shifted to find new source
and methodology for producing iron powders in eco-friendly and economical manner.
Li Ting and co-workers patented (CN 104259470) the production of low apparent density and
fine iron powder from iron scale. The iron scale is reduced in two stages, first in tunnel kiln with
carbon as the reducing agentat 1150-1165 0 C and next in a belt furnace using ammonia
decomposition gas at 760-900 0C with intermediate crushing and grinding between two reduction
stages.

Fang Minxian and co-researchers produced iron powders from smoke and mud of steel making
converter after a series of steps like beneficiation, drying and reduction annealing (CN 1076234).
On the other hand ferrous dust was used as a raw material to synthesize iron powders byOkuno
Yoshio and Kawachi Yuji in which ferrous dust was reduced in a sand fluidized bed with
hydrogen rich gas at 800-900 0C (JP 01283305).
Morishita Tsuyoshi and co-researchers patented their work on iron powder production from
degreased and dehydrated swarf of iron and steel materials. The degreased and dehydrated
swarfis subjected to nitriding- grinding- denitriding- grinding cycle, finally leading to powdered
iron. The denitriding step is performed in a reducing atmosphere at 600-1100 0C(JP 56072106).
On the other hand the slimes of red fume powder produced during the conversion of pig iron in
oxygen blowing converters were used to produce iron powders by Rossi Geremia and co-
researchers. The method of production involves drying and agglomerating the slimes followed
by grinding to required size and further subjecting to heating at 1000 – 1200 0C and reduction in
a fluidized bed or fixed bed or rotary kiln at 800-900 0C using solid (coal, coke, etc.) and gaseous
(hydrogen, carbon monoxide, etc).(GB1127145).
Few authors extracted/ generated iron powders from steel making by products, whose process
majorly deals with simple mechanical process rather than chemical reduction. HigichiNarihisa
and MatsuhistaTetsuma patented their work on iron powder generation from steel making dust
by a series of steps like pulverizing- primary washing- pickling- secondary washing in a batch
type stirring device (JP 2000054010). Similarly, Okimura Toshiaki and co- workers generated
iron powder by a simple treatment process comprising of classification and separation of
granules of specific diameter from steel making converter dust(JP 95094681).
Few researchers also proposed some new methodologies for the preparation of iron powders.
Vladimir and co-workers (RU 2529129) patented a method of iron powder preparation in which
iron –carbon melt is sprayed into water by means of compressed air which is further dehydrated
and annealed under reducing atmospheres to get iron powder.
In another patent (CN 103042223) Liyan and co-workers reported a new method in which iron
ore was pelletized by adding coal and lime and these pellets were further reduced and sized to
get iron powder. Sakai Hitoshi has patented [(JP 06279824)(JP 06116616)] a new method in
which iron ore and carbonaceous mix was reduced using microwave energy and further
processed to give iron powders.

In other patent (JP 03031401) Kishigamikimihisa and Ikezajieiji proposed a new method in
which iron powder is synthesized in a fluidized bed by simultaneous reduction and carburization
of iron ore. A new iron powder in which they have fiber like configuration and the method of
producing them was patented by Grebe kalas and co-workers (US 3975186).
A part from the source and methodology, interest was also laid by the researchers to synthesize
iron powder based on their application. Thus iron powders synthesis based on their application as
bearings (WO 2015048880), magnetic dust core (JP 2009120915), metal ceramics (JP
2008150648), reaction medicine (JP 2008081790), oxygen free absorber (JP 2006263630),
injection moulding (JP 07026304), sintering application (JP 06228603), Ferro magnetic powder
(JP 02159305) and magnetised iron powder (JP 64039302) were patented.
Meng Guangdong and co-workers patented the method by which iron powder can be produced
from titanic magnetite tailings using coke oven gas as reducing agent. The process of reduction
follows pelletizing-drying-reducing-separation steps. The reduction is done in two stages, one at
1050+-10 0C and the other at 1250-1300 0C using different flow rates of coke oven gas (CN
104384520).
Zhao Yu and co-researchers patented their work of iron powder synthesis from iron ore using
coke oven gas as reducing agent. The iron ore is reduced in a reducing furnace at 860-900 0C for
3-5 h, with a supply of coke oven gas (CN 1480539).
MeitusGarye and co-workers used a mixture of coke oven gas and basic oxygen furnace gas
(with minimal CO2) to reduce iron oxide to sponge iron in a shaft furnace (EP 2707511). In a
similar way, Zendejas – Martiner and co-researchers patented their work on reducing iron oxide
to sponge iron in a moving bed reduction reactor using coke oven gas as reducing agent (EP
1984530).
In another patent by Millner Robert and Boehm Christian, the metal oxides are reduced using gas
containing hydrocarbons and hydrogen (WO 2012163628).
RyzhonkovDmitrij and co- workers patented their work on producing iron powders from acid
pickling solution comprising iron hydroxide or calcium hydroxide by using hydrogen gas as
reducing agent. The process steps involve precipitation-dehydration-separation-reduction. The
reduction is carried out at 350-400 0C (RU 2038195).

In another patent, Ruthner Michael J sytnhesized iron powder from spray roasted iron oxide
powder obtained from the spent liquor. The reducing agent used for the process is hydrogen. The
process of production involves chloride removal-neutralization-granulation-pre sintering-
reduction. The pre-sintering step is carried out at 900-1350 0C and the reduction is carried out at
1050 0C.
In another patent, William Tiddy et al., worked on the production of iron powder from calcined
precipitate of iron oxide obtained from waste pickle liquor by reducing with coke oven gas in the
temperature range of 927 oC to 1038 oC keeping the CO2 content of the in the range of 10 to 20%
by recirculating the coke oven gas.
A number of iron bearing by products generated in an integrated iron and steel plant finds
unsuitable for further processing. Thus materials such as iron dust, mill scale, iron oxide from
spent pickle liquor, mill sludge powder, forging scale, etc., are used for the production of iron
powder. In the course of obtaining new source and methodology, the present invention deals with
the preparation of iron powder by granulation and reduction of iron oxide powder obtained from
the spray roasting process during acid regeneration process of spent liquor.
BRIEF DESCRIPTION OF THE INVENTION:
Present invention relates to the method of producing iron powder from potential by product of
steel making industry comprises iron oxide powder (spray roasted/ mill scale/ mill sludge),by
reduction with a coke oven gas. Accordingly, the present invention produces metallic iron
powder having composition and characteristics which is suitable in powder metallurgy where
requirement of purity and fineness is required which is very difficult to obtain in commercial
industrial production. Spray roasted powder is oxide form of iron obtained from the pickling line
of cold rolling mill and mill scale is oxide form of iron by product obtained from the hot rolling
mill.
The iron oxide powder with particle size less than 150 microns is used as a raw material. The
iron oxide powder is first granulated in a high intensity mixer using water and dextrin solution
and then the wet granules are dried at 110oC for 1 hour. The dried granules are heated to 500-
900oCin a reducing furnace and coke oven gas as a reducing agent is introduced into the furnace
to form a sintered iron cake and cooling of the reduced iron powder with the help of nitrogen
gas.The reduction temperature should not exceed 1000oC because beyond this temperature
thermal cracking of hydrocarbons in the coke oven gas takes place that leads to deposition of
carbon on the iron powder. In the presence of iron, which acts as catalyst for the thermal

cracking of hydrocarbons in the coke oven gas, the temperature should be less than 900oC to
avoid any cracking of hydrocarbons in the coke oven gas. This invention provides a process for
producing high purity and fineness iron powder from iron bearing metallurgical by-product
produced in steel plant, reduced with coke oven gas at exalted temperature. The above inventions
stands novel in the source and the methodology of producing iron powder.
DETAILED DESCRIPTON OF THE INVENTION:
A process for reducing iron oxide powder, obtained from spent pickling liquor with coke oven
gas as a reducing agent at exalted temperature comprises of the following steps:
(a) Mixing of fine iron oxide powder with dextrin in the range of 1.0 to 5.0 wt.% and
granulation the mixture in high intensity mixer using water in the range of 1.0 to 5.0
wt.%
(b) Drying of the wet granules at 100 – 150oC for 60 – 90 minutes such that moisture content
is reduced below 0.5%.
(c) Heating the dried iron oxide granules from step (a)in a reduction furnace to the
temperature about 500 - 900oC.
(d) Coke oven gas was introduced into the furnace at exalted temperature in step (b) for 60 –
240 minutes to reduce iron oxide to form a loosely sintered iron cake.
(e) The sintered iron cake in step (c) is the cooled in the furnace to room temperature by
passing nitrogen gas.
(f) The cooled cake in step (d) is then crushed and screened into desired size to produce iron
powder.
Example 1: This example demonstrates the reduction of spray roasted iron oxide powder using
coke oven gas as reducing agent. The chemistry of raw material used in the experiment is shown
in Table 1.

100 gms of iron oxide obtained from spray roasting of pickle liquor is mixed with 1% dextrin
and then granulated in a mixer using water in the range of 4 to 5%. Then the wet granules are
dried at 100 – 150oC for 90 minutes so as to bring the moisture level of less than 0.5% by weight.

The dried granules are placed in the reduction chamber of furnace and heated at rate of
7.5oC/min,to reach to a temperature of 900oC. When the desired temperature is reached, coke
oven gas was introduced in to the furnace with the flow rate of 2 litres per minute for 60 min.
The following reduction lasted for60 min. at a temperature of 900°C resulting in the formation of
loosely sintered iron cake. Thereafter, to eliminate the pyrophoric nature of the iron powder, the
reduced substance was then subsequently allowed to cool in an inert environment preferably
Nitrogen to further lower the oxygen content. The following Nitrogen cooling was carried out at
flow rate of 0.5 liters per minute till the temperature of the furnace reaches to atmospheric
temperature thus yielding 74 grams of reduced iron oxide cake. The cake was then pulverized
into desired size to produce iron powder having apparent density of 0.5 to 1 g/cm3. The XRD
analysis of the iron oxide powder and iron oxide is shown in Figure 1.
Example 2:
This example demonstrates the reduction of spray roasted iron oxide powder using coke oven gas
as reducing agent at different temperatures to demonstrate the carbon deposition at higher
reduction temperature. The chemistry of raw material used in experiment is shown in Table 2.

100 gms of iron oxide obtained from spray roasting of pickle liquor is mixed with 1% dextrin
and then granulated in a mixer using water in the range of 4 to 5%. Then the wet granules are
dried at 100 – 150oC for 90 minutes so as to bring the moisture level of less than 0.5% by weight.
The dried granules are placed in the reduction chamber of furnace and heated at rate of
7.5oC/min, to reach to a temperature of 700oC, 900oC and 1100oC. When the desired temperature
is reached, coke oven gas was introduced in to the furnace with the flow rate of 2 litres per
minute for 60 min. The following reduction lasted for60 min. at a temperature of 700oC , 900oC

and 1100oC resulting in the formation of loosely sintered iron cake in case of 700oC and 900oC
and well sintered cake in case of 1100oC.
Thereafter, to eliminate the pyrophoric nature of the iron powder, the reduced substance was
cooled in nitrogen at flow rate of 0.5 liters per minute till the temperature of the furnace reaches
to atmospheric temperature thus yielding 74 grams of reduced iron oxide cake. The cake was
then pulverized into desired size to produce iron powder having apparent density of 0.5 to 1
g/cm3. The XRD analysis of the iron oxide powder and iron oxide is shown in Figure 2.
The analysis shows that carbon deposition is occurring during the reduction at 1100 oC and not at
lower reduction temperatures viz., 700oC and 900oC. Hence it is important to maintain the
reduction temperatures not more than 900oC to avoid contamination of the final product with
carbon.

We Claim:
1. A method for producing reduced iron powder comprising the following steps;
Mixing iron oxide powder with an organic binding agent;
Granulating the iron oxide powder to produce fine granules of less than 5 mm size
with water and the organic binding agent;
Drying wet granules;
Reacting the dried granulated iron oxide granules with gaseous reducing agent
comprising hydrogen in the temperature range of 500 to 900oC; and
Cooling the reduced iron powder to 25oC in the inert atmosphere.
2. The method as claimed in claim 1, wherein the organic binder comprises dextrin, starch,
starch derivatives and mixture thereof.
3. The method as claimed in claim 1, wherein the iron oxide comprises fine powder of iron
oxide obtained from spray roasting process during acid regeneration process of spent
pickle liquor.
4. The method as claimed in claim 1 wherein the iron oxide comprises mill scale obtained
during the rolling process of steel.
5. The method as claimed in claim 1, wherein the gaseous reducing agent comprises coke
oven gas or cracked ammonia gas.
6. The method as claimed in claim 1, wherein the granulating process comprises intense
mixing of iron oxide and binder mixer in a high intensity mixer to obtain fine granules.
7. The method as claimed in claim 1, wherein the amount of binding agent ranges from 1 to
5 weight percentage of iron oxide powder.
8. The method as claimed in claim 1, wherein the process reduces iron oxide to form a
loosely sintered iron cake.
9. The method as claimed in claim 8, wherein the sintered iron cake cooled in the furnace to
room temperature by passing nitrogen gas.

10. The method as claimed in claim 9, wherein the cooled cake in step is crushed and
screened into desired size to produce iron powder.