Note: Descriptions are shown in the official language in which they were submitted.
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METHOD FOR MANUFACTURING AN AUSTENITIC STAINLESS STEEL
FROM A NICKEL LATERITE ORE AND A CHROMITE ORE
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for manufacturing
an austenitic stainless steel, more particularly to a
method for manufacturing an austenitic stainless steel
from a nickel laterite ore and a chromite ore.
2. Description of the Related Art
In a conventional method for manufacturing an
austenitic stainless steel, scrap and ferroalloy are
used as main raw materials and are smelted into a molten
metal in an electric furnace. The molten metal is then
transferred to a converter along with adding a
ferronickel and/or a ferrochrome into the converter in
a ratio determined according to the specific steel to
be made (for example, 200 or 300 series stainless steel) ,
thereby obtaining an austenitic stainless steel. Since
the cost fora noble metal such as nickel is about 40-50%
of the total cost for the stainless steel, the profit
of the stainless steel manufacturer is easily affected
or even lost due to the price volatility of the noble
metal.
There has been developed a process for producing a
stainless steel master alloy by directly smelting a
nickel laterite ore and a chromite ore as raw materials
in an electric furnace or a blast furnace, as disclosed
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in Chinese Patent Publication Nos. CN 102212691 A and
CN 101701312 A, so as to save the cost for manufacturing
a stainless steel. However, in the process disclosed
in the aforesaid prior art, the nickel laterite ore and
the chromite ore are not pretreated to remove free water
and crystallization water prior to the smelting
procedure, and a relatively great amount of energy is
consumed to remove water during the smelting procedure.
Furthermore, there are other disadvantages in the
process of the aforesaid prior art, such as difficulty
in control of the nickel content in the molten metal,
relatively great amount of impurities, and inferior
recovery rate. Additionally, rare metal such as cobalt
usually contained in the nickel laterite ore cannot be
extracted and recovered in the process of the aforesaid
prior art.
SUMMARY OF THE INVENTION
Therefore, the object of the present invention is
to provide a cost-effective method for manufacturing
an austenitic stainless steel from a nickel laterite
ore and a chromite ore.
According to a first aspect of this invention, there
is provided a method for manufacturing an austenitic
stainless steel from a nickel laterite ore and a chromite
ore. The method includes steps of:
a) crushing, screening, and blending the nickel
laterite ore, followed by roasting the nickel laterite
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ore in a rotary kiln to remove free water and
crystallization water along with charging a reducing
agent into the rotary kiln to obtain a calcine, and
smelting the calcine in an electric furnace to obtain
a molten ferronickel;
b) sintering the chromite ore in a sintering device
to obtain a sintered chromite ore, followed by smelting
the sintered chromite ore along with a coke particle
in another electric furnace to obtain a molten
ferrochrome;
c) hot charging the molten ferronickel and the molten
ferro chrome into a converter to obtain a mol ten stainless
steel; and
d) charging the molten stainless steel into a
continuous casting machine to obtain a stainless steel
slab.
According to a second aspect of this invention, there
is provided a method for manufacturing an austenitic
stainless steel from a nickel laterite ore and a chromite
ore. The method includes steps of:
a) crushing the nickel laterite ore and pulping the
nickel laterite ore with water to form a pulp material,
followed by agitating the pulp material with a sulfuric
acid solution under a high pressure atmosphere to form
a mixture, filtering a leach solution containing nickel
and cobalt out of the mixture, separating the leach
solution by solvent extraction into an extraction
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solution containing nickel and an anti-extraction
solution containing cobalt, and electrolyzing the
extraction solution and the anti-extraction solution
to obtain pure nickel and pure cobalt, respectively;
b) sintering the chromite ore in a sintering device
to obtain a sintered chromite ore, followed by smelting
the sintered chromite ore in an electric furnace to
obtain a molten ferrochrome;
c) transferring the pure nickel into a converter,
and hot charging the molten ferrochrome into the
converter to obtain a molten stainless steel; and
d) charging the molten stainless steel into a
continuous casting machine to obtain a stainless steel
slab.
According to a third aspect of this invention, there
is provided a method for manufacturing an austenitic
stainless steel from a nickel laterite ore and a chromite
ore. The method includes steps of:
a) determining whether a nickel content of the nickel
laterite ore is less than 1.5 wt% based on total weight
of the nickel laterite ore;
b) processing the nickel laterite ore into a
nickel-containing precursor based on the determination
made in step a);
c) sintering the chromite ore in a sintering device
to obtain a sintered chromite ore, followed by smelting
the sintered chromite ore along with a coke particle
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in an electric furnace to obtain a molten ferrochrome;
d) transferring the nickel-containing precursor
into a converter, and hot charging the molten ferrochrome
into the converter to obtain a molten stainless steel;
5 and
e) charging the molten stainless steel into a
continuous casting machine to obtain a stainless steel
slab.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
A method for manufacturing an austenitic stainless
steel from a nickel laterite ore and a chromite ore
according to a first preferred embodiment of the present
invention includes steps of:
i) obtaining a molten ferronickel:
The nickel laterite ore is dried in a drying kiln
at a drying temperature ranging from 600 C to 700 'C
to remove free water contained in the nickel laterite
ore from 30-35% to 10-20%. The nickel laterite ore is
then crushed, screened, and blended, followed by
roasting in a rotary kiln at a roasting temperature
ranging from 800 C to 950 C to remove residual free
water and crystall i zation water from the nickel laterite
ore. When the nickel laterite ore is roasted in the rotary
kiln, a reducing agent such as anthracite coal is fed
into the rotary kiln to obtain a pre-reduced calcine.
The calcine is molten in an electric furnace to obtain
the molten ferronickel. The tapping temperature of the
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slag is controlled in a range from 1550 C to 1650 t
and the tapping temperature of the molten ferronickel
is controlled in a range from 1400 C to 1500 C so as
to obtain a better effect for separating the slag from
the molten ferronickel . The molten ferronickel includes:
8-15 wt% of Ni, less than 4 wt% of C, less than 2 wt%
of Si, and less than 0.06 wt% of P.
ii) obtaining a molten ferrochrome:
The chromite ore (content of Cr203: less than 62 wt%)
is mixed with a coke powder and is pressed in a ball
press machine to form chromite pellets, followed by
drying the chromite pellets to remove water. The dried
chromite pellets are then sintered in a sintering device
at a temperature ranging from 1350 C to 1450 C to obtain
a sintered chromite ore having a particle size less than
30 mm. The sintered chromite ore along with a coke
particle is then molten in another electric furnace to
obtain the molten ferrochrome. The tapping temperature
of the slag is controlled in a range from 1600 C to
1700 C. The molten ferrochrome includes: less than 60
wt% of Cr, less than 9 wt% of C, less than 5 wt% of Si,
and less than 0.03 wt% of P.
iii) obtaining a molten stainless steel:
The molten ferronickel and the molten ferrochrome
are transferred into a converter in a hot charging manner
to obtain the molten stainless steel.
iv) obtaining a stainless steel slab:
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The molten stainless steel is charged into a
continuous casting machine to obtain the stainless steel
slab.
The aforesaid steps iii) and iv) can be conducted
in a manner well known in the art, and thus are not
described in detail herein.
The molten ferronickel and the molten ferrochrome
can be added into the converter in a ratio determined
according to the specific stainless steel to be
manufactured. For example, the 202 series stainless
steel contains 4-6 wt% of Ni and 17-19 wt% of Cr, and
the 304 series stainless steel contains 8-10.5 wt% of
Ni and 17.5-19.5 wt% of Cr. When the molten ferronickel
obtained in step i) contains 8 wt% of Ni, and the molten
ferrochrome obtained in step ii) contains 50 wt% of Cr,
the 202 series stainless steel can be manufactured by
formulating 65 wt% of the molten ferronickel with 35
wt% of the molten ferrochrome. When the molten
ferronickel obtained in step i) contains 15 wt% of Ni,
and the molten ferrochrome obtained in step ii) contains
40 wt% of Cr, the 304 series stainless steel can be
manufactured by formulating 55 wt% of the molten
ferronickel with 45 wt% of the molten ferrochrome.
In the aforesaid preferred embodiment, the molten
ferronickel and the molten ferrochrome are obtained
respectively from the nickel laterite ore and the
chromite ore, the stainless steel of various series can
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be manufactured by formulating the molten ferronickel
with the molten ferrochrome in a specific ratio of the
molten fe rroni cke 1 to the molten ferro chrome , which can
be easily adjusted and controlled according to the
specific stainless steel to be manufactured. Therefore,
the consumption of fuel and electricity can be reduced
due to the reduction of the repeated melting times, and
the manufacturing cost can be effectively controlled
so as to raise the profit for the manufacturer.
A method for manufacturing an austenitic stainless
steel from a nickel laterite ore and a chromite ore
according to a second preferred embodiment of the pre sent
invention includes steps of:
I) obtaining pure nickel and pure cobalt:
The nickel laterite ore is crushed and pulped with
water to form a pulp material, followed by agitating
the pulp material with a sulfuric acid solution under
a high pressure atmosphere to form a mixture. A
solid-liquid ratio of the nickel laterite ore to the
sulfuric acid solution is about 1:4 in the mixture. The
pulp material is agitated with the sulfuric acid solution
under a pressure ranging from 4 to 5 MPa and at a
temperature ranging from 2 5 0 C to 300 C. A leach solution
containing nickel and cobalt is then filtered out of
the mixture. The leach solution is separated by solvent
extraction into an extraction solution containing
nickel and an anti-extraction solution containing
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cobalt. The extraction solution and the anti-extraction
solution are electrolyzed to obtain pure nickel and pure
cobalt, respectively. The purity of the pure nickel is
greater than 99 wt%, and the recovery rate of the pure
nickel and cobalt is greater than 90% in the preferred
embodiment.
II) obtaining a molten ferrochrome:
This step can be conducted in a manner identical
to the aforesaid step ii) in the first preferred
embodiment.
III) obtaining a molten stainless steel:
The pure nickel is transferred into a convertor via
a belt conveyor, and the molten ferrochrome is hot
charged into the convertor to obtain the molten stainless
steel.
IV) obtaining a stainless steel slab:
This step can be conducted in a manner identical
to the aforesaid step iv) in the first preferred
embodiment.
When the pure nickel obtained in step I) has a purity
of 99 wt%, and the molten ferrochrome obtained in step
II) contains 24 wt% of Cr, the aforesaid 202 series
stainless steel can be manufactured by formulating 5
wt% of the pure nickel, 75 wt?, of the molten ferrochrome,
and 20 wt% of a carbon steel scrap. The aforesaid 304
series stainless steel can be manufactured by
formulating 9 wt% of the pure nickel, 7 6 wt % of the molten
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ferrochrome, and 15 wt% of a carbon steel scrap.
In addition to the aforesaid effect achievable in
the first preferred embodiment, in which the stainless
steel of various series can be manufactured by
5 formulating
the pure nickel, the molten ferrochrome,
and the carbon steel scrap in a specific ratio thereof,
valuable pure cobalt can be obtained in the aforesaid
step I) along with the pure nickel so as to obtain an
additional economic benefit.
10 A method for
manufacturing an austenitic stainless
steel from a nickel laterite ore and a chromite ore
according to a third preferred embodiment of the present
invention includes steps of:
A) determining a nickel content of a nickel laterite
ore:
When the nickel content of the nickel laterite ore
is determined to be not less than 1.5 wt% based on total
weight of the nickel laterite ore, the following steps
are performed.
B) obtaining a molten ferronickel:
This step can be conducted in a manner identical
to the aforesaid step i) in the first preferred
embodiment.
C) obtaining a molten ferrochrome:
This step can be conducted in a manner identical
to the aforesaid step ii) in the first preferred
embodiment.
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D) obtaining a molten stainless steel:
This step can be conducted in a manner identical
to the aforesaid step iii) in the first preferred
embodiment.
E) obtaining a stainless steel slab:
This step can be conducted in a manner identical
to the aforesaid step iv) in the first preferred
embodiment.
As described above, the molten ferronickel and the
molten ferrochrome can be added into the converter in
a ratio determined according to the specific stainless
steel to be manufactured.
On the other hand, when the nickel content of the
nickel laterite ore is determined to be less than 1.5
wt% based on total weight of the nickel laterite ore,
the following steps are performed.
B') obtaining pure nickel and pure cobalt:
This step can be conducted in a manner identical
to the aforesaid step I) in the second preferred
embodiment.
C') obtaining a molten ferrochrome:
This step can be conducted in a manner identical
to the aforesaid step ii) in the first preferred
embodiment.
D') obtaining a molten stainless steel:
This step can be conducted in a manner identical
to the aforesaid step III) in the second preferred
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embodiment.
E') obtaining a stainless steel slab:
This step can be conducted in a manner identical
to the aforesaid step IV) in the second preferred
embodiment.
As described above, the stainless steel of various
series can be manufactured by formulating the pure ni ckel
with the molten ferrochrome along with the carbon steel
scrap in a specific ratio, which can be easily adjusted
and controlled according to the specific stainless steel
to be manufactured. Furthermore, other noble metals,
such as pure cobalt, can be obtained along with the pure
nickel in the electrolytic step. Therefore, the economic
value of the method for manufacturing an austenitic
stainless steel of the present invention can be further
raised.
Alternatively, in the third preferred embodiment,
both the molten ferronickel and the pure nickel can be
transferred into the convertor, and the molten
ferrochrome is hot charged into the convertor so as to
obtain the molten stainless steel.
In the method for manufacturing an austenitic
stainless steel of the present invention, the nickel
laterite ore can be effectively treated to obtain a
molten ferronickel or a pure nickel. Therefore, the
method for manufacturing an austenitic stainless steel
of the present invention is relatively flexible and
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cost-effective as compared to the prior art.
The scope of the claims should not be limited by
the preferred embodiments set forth above, but should
be given the broadest interpretation consistent with
the description as a whole.
