AU2017299295B2

AU2017299295B2 - Method for improving iron grade of iron ore

Info

Publication number: AU2017299295B2
Application number: AU2017299295A
Authority: AU
Inventors: Takero Adachi; Tetsushi Deura; Takeshi Maki; Masaki Shimamoto; Takashi TSUSHIMA
Original assignee: Kobe Steel Ltd
Current assignee: Kobe Steel Ltd
Priority date: 2016-07-19
Filing date: 2017-06-29
Publication date: 2019-11-07
Anticipated expiration: 2037-06-29
Also published as: BR112019000977A2; WO2018016292A1; AU2017299295A1

Abstract

Provided is a method for improving the iron grade of iron ore, said method enabling the improvement of the iron grade by efficiently removing gangue included in the iron ore and enabling the iron ore to have a form that is easily usable as a raw material in the manufacture of iron. The present invention is a method for improving the iron grade of iron ore by grinding gangue-containing iron ore that has been reduced using a reducing gas and then removing the gangue by magnetic separation, wherein: said reduction is controlled such that parameter X represented by a function of the reduction time for the iron ore and the partial pressures of the reducing gas satisfies [X=t×(P

Description

METHOD FOR IMPROVING IRON GRADE OF IRON ORE

Technical Field [0001]

The present disclosure relates to a method of improving an iron grade of iron ore by subjecting the iron ore having a low iron grade to grinding and magnetic separation after reduction of the iron ore, in order to use the iron ore as a raw material for iron manufacturing.

Background Art [0002]

Recently, along with an increased global demand for crude steel, it is gradually getting difficult to obtain high-quality iron ore. Thus, there is a need for a technology to allow iron ore having a low T.Fe (total iron content in iron ore), which has not been used conventionally as a raw material for iron manufacturing, to be used as a raw material for iron manufacturing.

However, when the iron ore having a low T. Fe as described above, in other words, low-quality iron ore containing a lot of gangue, is used as it is as the raw material for iron manufacturing, the gangue containing SiCh AI2O3, and the like becomes slag, and an amount of the slag increases, resulting in a rise of operation costs. Thus, when the iron ore having the low T. Fe is used as the raw material for iron manufacturing, it is necessary to remove the gangue by ore dressing in advance.

[0003]

Examples of the technologies to improve an iron grade of iron ore by removing the gangue include those disclosed in Patent Literatures 1 to 7.

[0004]

An object of Patent Literature 1 is to subject reduced iron obtained in a reduced iron production facility using coal as a reducing agent to cooling, finely grinding, dressing by magnetic separation, and reshaping, thereby producing high-purity and high-density reduced iron.

Specifically, the reduced iron obtained by subjecting a mixture containing an iron raw material and coal to a heating and reducing treatment at a high temperature is ground, and thus obtained reduced iron particles are sorted with a predetermined particle diameter as a boundary. Then the reduced iron particles having the predetermined particle diameter or less are magnetically separated into strong magnetic material particles containing a lot of iron and weak magnetic material particles containing less iron. Thereafter, the sorted reduced iron particles having a particle diameter larger than the predetermined particle diameter and such strong magnetic material particles are used as the reduced iron.

[0005]

An object of Patent Literature 2 is to reduce an agglomerate including an iron oxide-containing material and a carbonaceous reducing agent followed by magnetic separation, thereby producing metallic iron having a high iron purity.

Specifically, when a heated material obtained by subjecting a mixture containing an iron raw material and coal to a heating and reducing treatment at a high temperature is separated into metallic iron and slag using a first magnetic separator, a device is used in which a transport mechanism is included as a magnetic separator and a magnetic field intensity in a magnetic field generating region has an inflection point along a flow direction of the heated material.

[0006]

An object of Patent Literature 3 is to prevent production of free carbon without raising a sulfur concentration in a product to efficiently produce iron carbide within a short time, in producing the iron carbide from an iron oxide-containing material.

Specifically, in producing the iron carbide by reducing an iron oxide-containing material followed by carbonizing, the iron oxide-containing material is reduced by a reducing gas including S in which a ratio of a sulfur molarity relative to a sum of H2 and CO molarity (S/H2+CO) is from 0.05 times to less than 1 time of such ratio of the sulfur molarity at the time of Fe/FeS equilibrium, thereby producing a preliminary reduced product having less than 20% by mass of iron carbide and a metallization ratio of 60% or more. The preliminary reduced product is then carbonized by a carbonizing gas to produce iron carbide.

[0007]

An object of Patent Literature 4 is to suppress disintegration during reduction in a direct reduction iron manufacturing process so as to expand freedom of operation.

Specifically, in producing reduced iron by reducing an iron oxide raw material with a reductive gas using a moving bed of a vertical type shaft furnace, compositions of an exhaust gas and a reducing gas to be introduced are controlled to be within predetermined ranges, and the iron oxide raw material is preheated before its introducing, thereby suppressing the disintegration during the reduction. [0008]

An object of Patent Literature 5 is to enhance separability of reduced iron from slag as to a mixture of the reduced iron and the slag which are obtained in a semimolten state in which all of the agglomerates are not entirely melted.

Specifically, a step of agglomerating a raw material in which a melting point adjusting agent is further blended with an iron oxide-containing material and a carbonaceous material, and a step of heating the obtained agglomerates so that the agglomerates are partly melted, thereby reducing the iron oxide included in the agglomerates are included in the above described order. Heating of the agglomerates is performed at a temperature lower than the temperature at which complete melting of the agglomerates occurs, the melting point adjusting agent includes at least a CaO supply material, CaO/SiCg of the agglomerates is 0.2 to 0.9, and also a blending amount of the melting point adjusting agent is adjusted, so that a molten amount of gangue contained in the agglomerate is 50% by mass or more at a temperature 100 °C lower than the maximum temperature when the agglomerates are heated.

[0009]

An object of Patent Literature 6 is to improve productivity of metallic iron and also solve a reoxidation problem, in operation of direct reduction equipment.

Specifically, when iron ore is reduced with a reducing gas including hydrogen and/or carbon monoxide, a supply rate and a discharge rate of the ore are adjusted so that a metallization ratio of semi-reduced ore as a product is 10 to 80%.

[0010]

An object of Patent Literature 7 is to provide a technology to efficiently remove gangue, even in a case where the gangue is solid-solubilized in the iron oxide (iron ore) or fine gangue particles are dispersed in the iron ore, in which a dressing effect cannot be expected with a conventional dressing method such as dressing by magnetic separation (magnetically separating), floating dressing (flotation) or the like.

Specifically, when the gangue is removed, iron oxide is reduced by reduction with carbon containing composite to form metallic iron, and the metallic iron is ground followed by performing magnetic separation.

[0010a]

Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present disclosure as it existed before the priority date of each of the appended claims.

[0010b]

Throughout this specification the word comprise, or variations such as comprises or comprising, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step or group of elements, integers or steps.

Citation List

Patent Literature [0011]

Patent Literature 1: JP 2002-363624 A

Patent Literature 2: JP 2016-14184 A

Patent Literature 3: JP H10-291816 A

6a

Patent Literature 4:

JP 2014-111813 A

Patent Literature 5: JP 2013-127112 A

Patent Literature 6: JP H9-165612 A

Patent Literature 7: JP 2015-101740 A [0012]

In Patent Literature 1, an average particle diameter of the particles to be subjected to dressing by the magnetic separation is as small as 100 pm or less.

In addition, since the premise of Patent Literature 1 is to reduce carbonaceous material interior, heating to 1200°C or higher is needed, and also addition of flux is needed for melting gangue, but the flux becomes an impurity like the gangue. Therefore, there is a possibility that an amount of slag increases. Therefore, this method is hardly an efficient method of producing the reduced iron.

[0013]

Patent Literature 2 is a technology appropriate for producing the metallic iron, but merely discloses that a ground particle diameter is 10 mm or less, and thus, it is considered that particles having a fine ground particle diameter are included.

In addition, since the premise of Patent Literature 2 is to reduce carbonaceous material interior, heating to 1200°C or higher is needed, and addition of flux is needed for melting gangue. The flux becomes an impurity like the gangue. In Patent Literature 2, a heating temperature of 1400 to 1480°C is recommended.

[0014]

Since the object of Patent Literature 3 is to produce the iron carbide, and does not include a grinding step or a subsequent magnetic separation step, it is considered very difficult to improve an iron grade of the iron ore.

[0015]

Patent Literature 4 is a gas reduction technology, and the object thereof is only to improve productivity in the reduction treatment of the iron ore. Also, the technology does not include a grinding step or a subsequent magnetic separation step. It is thus considered very difficult to improve an iron grade of the iron ore.

[0016]

Patent Literature 5 is a technology appropriate for producing a mixture of the reduced iron and the slag, but only discloses that a ground particle diameter is 3 mm or less, and thus, it is considered that the particles having a finely ground particle diameter are included.

In addition, since the premise of Patent Literature 5 is to reduce carbonaceous material interior, heating to 1200°C or more is needed, and also addition of flux is needed for partial melting. The flux becomes an impurity like the gangue.

[0017]

Patent Literature 6 is a gas reduction technology, but the object thereof is only to improve productivity in the reduction treatment of the iron ore. Also, it does not include a grinding step or a subsequent magnetic separation step. It is thus considered very difficult to improve the iron grade of the iron ore.

[0018]

Patent Literature 7 is a technology to reduce the iron ore, and uses to reduce carbonaceous material interior, and S in the carbonaceous material interior intrudes into iron. Therefore, although the iron grade can be improved, it is difficult to use the product as a raw material for iron manufacturing, and there is a problem in that costs for desulfurization are much increased.

In addition, it is necessary to heat iron oxide to

1000°C or higher, and there is a risk that costs relating to operations and facilities for such heating are very high.

Summary [0019]

The present disclosure describes a method of improving an iron grade of iron ore, which efficiently removes gangue contained in the iron ore to improve the iron grade, and at the same time, does not adopt the carbonaceous material interior and allows a form that is easy to use as a raw material for iron manufacturing.

[0020]

Some embodiments relate to a method of improving an iron grade of iron ore, the method comprising: subjecting the iron ore containing gangue to a reduction treatment with a reducing gas, followed by a grinding treatment, and then a magnetic separation treatment, thereby removing the gangue, wherein the reduction treatment is controlled such that parameter X represented by a function of a reduction time of the iron ore and reducing gas partial pressures satisfies the following equation (1):

[0021]

X = t x (Ph2 + 0.3 x Pco) -5 · · · (1) wherein t represents the reduction time [min] of the iron ore, Ph2 represents an H2 partial pressure [atm] of the reducing gas, and Pco represents a CO partial pressure [atm] of the reducing gas.

[0022]

In addition, another method of improving an iron grade of iron ore includes: subjecting the iron ore having an Ig loss > 10 wt% to a reduction treatment with an H2 gas such that the iron ore has a metallization ratio > 60 wt%, and then to a grinding treatment to have a particle diameter of 2 mm or less, followed by dressing with a magnetic separation treatment, thereby improving the iron grade of the iron ore, wherein the particle diameter of the iron ore after the grinding treatment is D50 100 pm.

[0023]

According to the present disclosure, the gangue contained in the iron ore is efficiently removed to improve the iron grade of the iron ore, and at the same time, a form that is easy to use as a raw material for iron manufacturing can be achieved.

Brief Description of Drawings [0024]

Fig. 1 is a graph showing a relationship between a parameter X represented by a function of a reduction time of iron ore and reducing gas partial pressures and an iron recovery ratio.

Fig. 2 is a drawing schematically showing an outline of agglomeration of particles and particle entrainment by a magnetic field.

Fig. 3 is a graph showing a relationship between a particle diameter D₅q of iron ore after grinding and a gangue removal ratio.

Embodiments for Carrying Out the Invention [0025]

Hereinafter, embodiments of methods of improving the iron grade of the iron ore according to the present invention will be described with reference to the drawings.

It is noted that the embodiments described below are examples embodying the present invention, and these specific examples do not limit the constitution of the present invention. Accordingly, the technical scope of the present invention is not limited only to the disclosure of the present embodiments.

[0026]

Examples of a method of solving the above described problem include a method of reducing the iron oxide containing the gangue by, for example, gas reduction such as CO or H₂ reduction or the like at a relatively low temperature range of 1000°C or lower, thereby forming metallic iron, and then grinding and magnetically separating the metallic iron formed by the reduction, thereby separating and removing the gangue.

[0027] <First embodiment>

One embodiment of the present invention (referred to as a first embodiment of the present invention) is a method

of improving an iron grade	of	iron ore,	the method
including:	subj ecting	the iron	ore	containing	gangue to a
reduction	treatment	with a	reducing gas,	a grinding
treatment,	and then	dressing	by	a magnetic	separation
treatment,	thereby	removing	the	gangue, wherein the

reduction treatment is performed using H2 gas and/or CO gas as the reducing gas, and also the reduction treatment is controlled such that parameter X represented by a function of a reduction time of the iron ore and reducing gas partial pressures satisfies the following equation (1):

[0028] [Math. 2]

X = t x (Ph2 + 0.3 x P_co) >5 ---(1) where t represents a reduction time [min] of the iron ore, P_H2 represents an H2 partial pressure [atm] of the reducing gas, and P_co represents a CO partial pressure [atm] of the reducing gas .

[0029]

That is, the first embodiment of the present invention is intended for a technology in which the reduction treatment is performed using the reducing gas, the reducing gas used at the time of performing the reduction treatment is a reducing gas containing at least one of H2 and CO, or both of them, and the gangue (AI2O3, SiO2, and the like) contained in the low-quality iron ore containing a hydroxyl group and a carbonate group such as FeOOH, Fe(OH)2, Fe(OH)3 FeCOs and the like is separated and removed, thereby forming metallic iron (Fe).

In addition, in the first embodiment of the present invention, the reducing gas may contain an inert gas such as N2 or the like.

[0030]

The method as described above is to produce metallic iron by the reduction treatment using the reducing gas and preferentially recover the metallic iron by the magnetic separation. However, when the reduction treatment is insufficient, there is a risk that the yield of the metallic iron recovered by the magnetic separation is drastically deteriorated.

[0031]

In order to avoid the deterioration of the yield of the metallic iron which can be recovered by the magnetic separation, in the present invention, the reduction treatment is controlled so that parameter X represented by a function of the reduction time of the iron ore and the reducing gas partial pressures satisfies equation (1), thereby improving the iron grade. As such, in order to efficiently recover the metallic iron, it is necessary to exceed a threshold value of equation (1).

[0032]

An iron recovery ratio is an indicator representing a ratio of the metallic iron that can be recovered by the magnetic separation, and the higher the numerical value of the iron recovery ratio, the higher the recovery efficiency of the metallic iron. In calculating the iron recovery ratio, equation (2) is used.

[0033] [Math. 3] magnetically captured ratio [wt%]x . . _r (T.Fe [wt%]after magnetic separation) iron recovery ratio [wt%]=y------------------------------------------- · · ’(2)

(.T.Fe [wt%] before magnetic separation) [0034]

In equation (2), T.Fe [wt%] is a concentration of total iron contained in the iron ore, and T.Fe before magnetic separation [wt%] and T.Fe after magnetic separation [wt%] are a concentration of the total iron contained in the iron ore before performing the magnetic separation and a concentration of the total iron contained in the iron ore after performing the magnetic separation, respectively. It is noted that the magnetically captured ratio is represented by the following equation (3).

[0035] [Math. 4] weight after magnetic separation [wt%] magnetically captured ratio [wt%]=-------------------------------------------x 100 · · · (3 weight before magnetic separation [wt%]

In equation (3) , weight is a total weight of the iron ore, and weight before magnetic separation and weight after magnetic separation are a total weight of the iron ore before performing the magnetic separation and a total weight of the iron ore after performing the magnetic separation, respectively.

[0037]

In the reduction treatment, naturally, in a case where the same kind of reducing gas is used, the reduction further proceeds when the reduction time is longer, and in a case where the reduction time is the same, the reduction further proceeds when gas reducing power is stronger.

Thus, in the first embodiment of the present invention, as shown in equation (1), the reduction treatment is controlled based the function of information of the reducing gases and the reduction time t [min] of the iron ore. For the information on the reducing gas, an H2 partial pressure P_H2 [atm] of the reducing gas and a CO partial pressure P_co [atm] of the reducing gas are used. It is noted that the reason why the coefficient of CO is 0.3 is that CO gas has a weaker reduction power than that of H₂gas. Meanwhile, when the conditions of performing the reduction treatment do not satisfy equation (1), the reduction becomes insufficient, and thus, there is a risk that the iron recovery ratio in the subsequent magnetic separation is greatly lowered.

[0038]

It is noted that the first embodiment of the present invention, it is more preferable to adopt the reduction treatment condition and the grinding condition according to the second embodiment as described below.

That is, it is all preferred to perform the first embodiment such that the reducing gas at the time of performing the reduction treatment is H₂ gas, a metallization ratio in the reduction treatment is 60 wt% or more, a particle diameter is 2 mm or less in the grinding performed after the reduction treatment, and a particle diameter after grinding is D₅q 100 pm.

[0039] <Second embodiment>

Another embodiment of the present invention is a method including subjecting the iron ore containing the gangue to a reduction treatment with a reducing gas, to grinding, and then to dressing by the magnetic separation, thereby removing the gangue, wherein when the reduction treatment is performed using an H₂ gas as the reducing gas, and also the iron ore having an Ig loss (ignition loss) > 10 wt% is subjected to the reduction treatment with the H₂gas so that the iron ore has a metallization ratio > 60 wt% subjected to the grinding to have a particle diameter of 2 mm or less, and then subjected to the dressing by the magnetic separation, thereby improving the iron grade of the iron ore, a particle diameter of the iron ore after the grinding is D₅q 100 pm (this method is referred to as a second embodiment of the present invention).

[0040]

That is, the second embodiment of the present invention is intended for a technology to use an H2 gas as the reducing gas at the time of performing the reduction treatment, and also to separate and remove the gangue (AI2O3, SiO2, and the like) contained in low-quality iron ore including a hydroxyl group such as FeOOH, Fe(OH)2, Fe(OH)₃, and FeCO₃ and the like, thereby forming metallic iron (Fe) .

It is noted that in the second embodiment of the present invention, the H₃ gas may contain an inert gas such as N2, or may be a gas containing at least 50% or more of h₂.

[0041]

In addition, for example, as shown in WO 2015/006796, it is known that a technology to separate and remove gangue by gas reduction has a particularly large effect when ore having a lot of water of crystallization such as goethite or pisolite is reduced to a high metallization ratio range with the H₂ gas having a high reducing power.

[0042]

As for the second embodiment of the present invention, it is intended that the iron ore (iron oxide) to be reduced has an Ig loss of 10 wt% or more.

[0043]

It is noted that the Ig loss, which is an abbreviation for an ignition loss, is a mass of a volatile materials (OH group) included in the iron oxide. For example, ore having a lot of water of crystallization such as goethite, pisolite, or Ulrich's hematite has a high Ig loss. In addition, as a method of measuring the Ig loss of the iron ore, a method according to JIS M 8700 8.4 is used for such measuring. That is, the Ig loss is a mass change when the iron ore is maintained at 1000°C, and a weight loss due to hydroscopic water is excluded. The hydroscopic water can be removed by heating at 105°C for 2 hours.

[0044]

In the second embodiment of the present invention, the reduction is performed as to the iron ore to be reduced with the H₂ gas, so that a metallization ratio is 60 wt% or more. Depending on the kind or an amount of the iron ore to be reduced, properties of the H₂ gas to be used, and the like, the metallization ratio can appropriately be adjusted. The metallization ratio is an indicator commonly used for representing a reduction degree of the iron ore.

[0045]

In calculation of the metallization ratio, equation (4) represented below is used.

[0046] [Math. 5] (M.Fe[wt%]) metallization ratio [wt%]=------------x 100 · · · (4) (T.Fe[wt%]) [0047]

In equation (4), M.Fe [wt%] is a concentration of metallic iron of the reduced iron ore, and T.Fe [wt%] is a total iron concentration of the iron ore.

[0048]

In addition, a gangue removal ratio is an indicator representing to what degree the gangue is removed from the original iron ore. The higher the derived numerical value of the gangue removal ratio is, the more the gangue is removed. In calculation of the gangue removal ratio, the following equation (5) is used.

[0049] [Math. 6] gangue removal ratio [wt%]= ^1gangue ratio after \ magnetic separation [wt%] ] inn . . .

I x -LUU * * * () gangue ratio of ore [wt%] / [0050]

In equation (5), the gangue ratio of ore is a gangue ratio of the original iron ore, and a gangue ratio after magnetic separation is a gangue ratio of the iron ore after performing the magnetic separation.

In addition, the gangue ratio is defined by equation (6) represented below.

[0051] [Math. 7] (SiO₂[wt%]+A1₂O₃[wt%]) gangue ratio [wt%]=-----------------------χ 100 · · · (6)

T.Fe[wt%] [0052]

	In	equation (6),	SiC>2 [wt%] and AI2O3	[ wt%	] are	an
SiO₂	concentration and	an AI2O3 concentration	contained	in
iron	ore	, respectively.
[0053	]
	In	the method as	described above, as	a	point	to

increase a removal efficiency of the gangue (gangue removal ratio), for example, increasing single phase particles after the grinding as many as possible can be mentioned, as shown in Fig. 2. This is because, when there are many mixed particles (locked particles) including two or more minerals after the grinding, an amount of the gangue in the magnetically captured materials is increased, and at the same time, an amount of iron that cannot be recovered is increased. Considering the above reason, it is preferred that a particle diameter after the grinding is small, and for example, it is disclosed also in WO 2015/006796 that the ground particle diameter is set to 2 mm or less.

[0054]

However, the present inventors have found that when the ground particle diameter is set too small, that is, when there are finely ground particles, the particles become susceptible to an effect of static electricity so that they are likely to agglomerate, thereby reducing the removal efficiency of the gangue.

[0055]

Thus, in the second embodiment of the present invention, the iron ore after the reduction has a particle diameter of 2 mm or less, and also a particle diameter (median diameter) D₅₀ of the iron ore, in other words, a median diameter thereof after the grinding is 100 pm or more (D₅q 100 pm), and then the iron ore is subjected to the magnetic separation, thereby improving the removal efficiency of the gangue.

[0056]

When the iron ore does not have a particle diameter (median diameter) D₅₀ of 100 pm or more after being ground to have a particle diameter of 2 mm or less, any method capable of removing particles not lager than a predetermined lower limit, for example, a conventional method such as sieving can be used to satisfy D₅q 100 pm.

[0057]

It is noted that D₅q [pm] is a particle diameter at the 50% accumulated volume of the particles starting from the smallest particle side. This value can be easily obtained by a laser diffraction type particle size analyzer such as Microtrac or the like.

[0058]

It is noted that in the second embodiment of the present invention, it is more preferable that the reduction treatment conditions according to the first embodiment are adopted.

That is, in the second embodiment, it is preferred that when parameter Y represented by a function of a reduction time of the iron ore and a reducing gas partial pressure at the time of performing the reduction treatment

with H₂	gas	satisfies	equation	(7) wherein	the reduction
time of	the	iron ore	is t	[min], and	an H₂ partial
pressure	of	the reducing gas is	P_H2 [atm] .
[0059]
[Math. 8	]
Y =	t x	Ph2 - 5 · ·	• (7)

[0060] [Experimental Examples]

Hereafter, Experimental Examples implementing the methods of improving the iron grade of the iron ore according to the present invention will be described.

[0061] [Experimental Example 1]

First, implementation conditions of Experimental Example 1 according to the first embodiment of the present invention are described.

In Experimental Example 1, as the ore used in the method of improving the iron grade of the iron ore, three kinds of ores shown in Table 1 were used.

[0062] [Table 1]

	ore A	ore B	ore C
T.Fe	[wt% ]	51.63	59.29	56.13
SiO₂	[wt% ]	7 . 64	12.72	5.11
Ά12Ο3	[wt% ]	5.32	0.85	6.63
Ig loss	[wt% ]	12.26	0.84	7.25

[0063]

The reduction treatment was performed as described below:

1) It was performed at 950°C using a horizontal resistance heating furnace.

2) As the reducing gas, various mixed gases were used which had a ratio of 132:0:00 of partial pressures described in Table 2 of the reduction conditions.

3) An amount of a sample of the iron ore at the time

of the	reduction treatment	was	50 g	per	1 ch	(charge),	and
a flow	rate of the reducing	gas	was	3 Nl/min.
[0064]
A	grinding method for	the	iron	ore	and	measurement	of

the particle size of the iron ore after the grinding were performed as described below.

1) The grinding of the iron ore after the reduction was performed using a disc mill, thereby forming a particle diameter of 2 mm or less.

2) The measurement of the particle size of the iron ore after the grinding was performed using a laser diffraction type particle size analyzer.

[0065]

The magnetic separation was performed with a magnetic field strength of 200 G using a manually operative magnetic separator .

[0066]

Next, experimental results of the method of improving the iron grade of the iron ore in Experimental Example 1 will be described.

[0067]

It is noted that Nos. 1 and 2 in Table 2 are Comparative Examples performed for the comparison with the Examples of the present invention. In addition, Nos. 3 to

27 in Table 2 are Examples performed based on the method of improving the iron grade of the iron ore according to the first embodiment of the present invention.

[0068] [Table 2]

	No	ore	reduction conditions	before magnetic separation T. Fe	after magnetic separation T. Fe	magnetically captured ratio	iron recovery ratio
time	h₂	n₂	CO	X
[-]	[-]	[-]	[min]	[atm]	[atm]	[atm]	[-]	[wt%]	[wt%]	[wt%]	[wt%]
Comparative Example	1	A	5	0 . 8	0.2	0	4.0	64.2	67.2	55.6	58.2
2	A	15	0	0.2	0 . 8	3.6	64.1	67.0	47.0	49.1
Example	3	A	10	0 . 8	0.2	0	8 . 0	67.8	70.6	80 . 8	84.3
4	A	15	0 . 8	0.2	0	12.0	72.1	73.7	91.6	93.7
5	A	30	0 . 8	0.2	0	24.0	76.5	78.2	92.6	94.6
6	A	30	0 . 8	0.2	0	24.0	76.5	75.6	96.5	95.3
7	A	60	0 . 8	0.2	0	48.0	78.6	80 . 0	96.0	97.7
8	A	60	0 . 8	0.2	0	48.0	78.6	79.0	96.8	97.3
9	A	30	0	0.2	0 . 8	7.2	66.7	69.9	87.7	91.9
10	A	60	0	0.2	0 . 8	14.4	69.6	71.6	86.1	88.6
11	A	60	0	0.2	0 . 8	14.4	69.6	69.1	97.1	96.4
12	A	90	0	0.2	0 . 8	21.6	74.4	77.5	90.6	94.4
13	A	120	0	0.2	0 . 8	28.8	74.9	77.0	92.7	95.4
14	A	60	0.4	0.2	0.4	31.2	76.1	78.2	93.9	96.4
15	A	60	0.4	0.2	0.4	31.2	76.1	76.5	96.1	96.6
16	B	15	0 . 8	0.2	0	12.0	71.4	74.8	86.8	90.9
17	B	30	0 . 8	0.2	0	24.0	78.0	80 . 0	93.0	95.5
18	B	60	0 . 8	0.2	0	48.0	76.4	77.8	95.3	97.0
19	B	60	0 . 8	0.2	0	48.0	76.4	77.8	96.4	98.2
20	B	90	0	0.2	0 . 8	21.6	75.6	78.6	92.1	95.7
21	B	120	0	0.2	0 . 8	28.8	77.7	80.4	93.2	96.4
22	C	15	0 . 8	0.2	0	12.0	73.9	75.7	92.6	94.9
23	C	30	0 . 8	0.2	0	24.0	79.2	80.4	95.6	97.0
24	c	60	0 . 8	0.2	0	48.0	80.5	82.3	94.4	96.6
25	c	60	0 . 8	0.2	0	48.0	80.5	80.5	97.3	97.4
26	c	90	0	0.2	0 . 8	21.6	76.8	79.4	94.9	98.1
27	c	120	0	0.2	0 . 8	28.8	77.4	80.2	95.6	99.1

[0069]

Comparative Example No. 1 shown in Table 2 uses Ore A.

In addition, as the reduction treatment conditions, a reduction time t of the iron ore is 5 [min] , an H2 partial pressure P_H2 of the reducing gas is 0.8 [atm], and an N2 partial pressure P_N2 of the reducing gas is 0.2 [atm] . In addition, the parameter X is 4.0 [-], which does not satisfy equation (1). T.Fe before the magnetic separation is 64.2 [wt%], T. Fe after the magnetic separation is 67.2 [wt%], and a magnetically captured ratio is 55.6 [wt%].

Also, an	iron recovery	ratio is 58.2 [wt%],	which	indicates
a very 1	ow efficiency.
[0070]
It	is noted that	Comparative Example	No. 2	does	not
satisfy	equation (1),	either, indicating a	very	poor	iron

recovery ratio.

[0071]

Meanwhile, Example No. 3 uses Ore A. In addition, as the reduction treatment conditions, a reduction time t of the iron ore is 10 [min] , an H₂ partial pressure P_H2 of the reducing gas is 0.8 [atm], and an N2 partial pressure P_N2 of the reducing gas is 0.2 [atm]. In addition, the parameter X is 8.0 [-], which satisfies equation (1) (X > 5). T. Fe before the magnetic separation is 67.8 [wt%], T. Fe after the magnetic separation is 70.6 [wt%], and a magnetically captured ratio is 80.8 [wt%]. In addition, an iron recovery ratio is 84.3 [wt%], which indicates a very good efficiency.

[0072]

Example No. 7 uses Ore A. In addition, as the reduction treatment conditions, a reduction time t of the iron ore is 60 [min] , an H₂ partial pressure P_H2 of the reducing gas is 0.8 [atm], and an N₂ partial pressure P_N2 of the reducing gas is 0.2 [atm]. In addition, the parameter X is 48.0 [-], which satisfies equation (1) (X > 5). T.Fe before the magnetic separation is 78.6 [wt%], T. Fe after the magnetic separation is 80.0 [wt%], and a magnetically captured ratio is 96.0 [wt%]. In addition, an iron recovery ratio is 97.7 [wt%], which indicates a very good efficiency.

[0073]

Example No. 14 uses Ore A. In addition, as the reduction treatment conditions, a reduction time t of the iron ore is 60 [min] , an H₂ partial pressure P_H2 of the reducing gas is 0.4 [atm], an N2 partial pressure P_N2 of the reducing gas is 0.2 [atm], and a CO partial pressure P_co of the reducing gas is 0.4 [atm]. In addition, the parameter X is 31.2 [-], which satisfies equation (1) (X > 5). T.Fe before the magnetic separation is 76.1 [wt%], T. Fe after the magnetic separation is 78.2 [wt%], and a magnetically captured ratio is 93.9 [wt%]. In addition, an iron recovery ratio is 96.4 [wt%], which indicates a very good efficiency.

[0074]

Example No. 19 uses Ore B.

In addition, as the reduction treatment conditions, a reduction time t of the iron ore is 60 [min] , an H₂ partial pressure P_H2 of the reducing gas is 0.8 [atm], and an N₂ partial pressure P_N2 of the reducing gas is 0.2 [atm]. In addition, the parameter X is 48.0 [-], which satisfies equation (1) (X > 5). T.Fe before the magnetic separation is 76.4 [wt%], T. Fe after the magnetic separation is 77.8 [wt%], and a magnetically captured ratio is 96.4 [wt%]. In addition, an iron recovery ratio is 98.2 [wt%], which indicates a very good efficiency.

[0075]

Example No. 27 uses Ore C. In addition, as the reduction treatment conditions, a reduction time t of the iron ore is 120 [min] , an N₂ partial pressure P_N2 of the reducing gas is 0.2 [atm], and a CO partial pressure P_co of the reducing gas is 0.8 [atm]. In addition, the parameter X is 28.8 [-], which satisfies equation (1) (X > 5). T.Fe before the magnetic separation is 77.4 [wt%], T. Fe after the magnetic separation is 80.2 [wt%], and a magnetically captured ratio is 95.6 [wt%]. In addition, an iron recovery ratio is 99.1 [wt%], which indicates a very good efficiency.

[0076]

It is noted that the Examples other than the above illustrated examples also allow a high iron recovery ratio by controlling the reduction treatment so as to satisfy equation (1).

[0077]

As described above, the first embodiment of the present invention is the technology focused on increasing the iron recovery efficiency, and according to this technology, the gangue in the iron ore having a low T.Fe is efficiently removed, thereby improving the iron grade, while allowing a form that is easy to use as a raw material for iron manufacturing.

[0078] [Experimental Example 2]

Next, the implementation conditions of Experimental Example 2 according to the second embodiment of the present invention will be described.

In Experimental Example 2, as the ore used in the method of improving the iron grade of the iron ore, the ore having the composition shown in Table 3 was used.

[0079] [Table 3]

T. Fe	[wt% ]	51.63
SiO₂	[wt% ]	7.64
AI2O3	[wt% ]	5.32
Ig loss	[wt% ]	12.26
gangue ratio	[wt% ]	25.1

[0080]

The reduction treatment was performed as described below:

1) It was performed at 950°C using a horizontal resistance heating furnace.

2)	As	the	reducing gas,	an H₂ gas having a	ratio of
H₂: 8 0%	and	N₂:	20% was used.
3)	An	amount of a sample	of the iron ore at	the time

of the reduction treatment was 50 g per 1 ch (charge), and a flow rate of the reducing gas (¾ gas) was 3 Nl/min.

[0081]

A	grinding method and measurement	of the	particle size
of the	iron ore after	the	grinding	were	performed as
described below:
1)	The grinding of	the	iron ore	after	the reduction

was performed using a disc mill, thereby forming a particle diameter of 2 mm or less.

2) The iron ore after the grinding was sieved, thereby forming a particle diameter after the grinding of D₅₀ 100 pm.

3) The measurement of the particle size of the iron ore after the grinding was performed using a laser diffraction type particle size analyzer.

[0082]

[0083]

Next, experimental results of the method of improving the iron grade of the iron ore of Experimental Example 2 will be described.

It is noted that Nos. 28 to 30 in Table 4 are the

Comparative Examples performed for the comparison with the

Examples of the present invention. In addition, Nos. 31 to in Table 4 are the Examples performed based on the method of improving the iron grade of the iron ore according to the second embodiment of the present invention. [0084] [Table 4]

	No	D50	composition after magnetic separation [wt%]	gangue removal ratio
[μη]	T. Fe	SiO₂	Ά12Ο3	[wt%]
Comparative Example	28	14.0	78.4	10.47	7.56	8.4
29	13.9	77.28	10.42	7.31	8.6
30	14.4	78.85	10.18	7.42	11.1
Example	31	261.3	78.96	8.95	6.98	19.6
32	255.3	80.84	9.10	7.05	20.4
33	123.5	76.98	8.26	7.11	20.5
34	158.2	78.23	8.35	7.04	21.6
35	452.4	79.99	8.62	7.08	21.8
36	370.6	80.71	8.73	7.01	22.3
37	307.4	80.09	8.57	7.01	22.5
38	488.8	78.21	7.85	6.70	25.9

[0085]

Comparative Example No. 28 shown in Table 4, a particle diameter D₅q after the grinding is 14.0 pm, which does not satisfy D₅q 100 pm as specified. Then, the composition of the iron ore after the magnetic separation is T. Fe of 78.4 wt%, SiCg of 10.47 wt%, and AI2O3 of 7.56 wt%. In addition, the removal efficiency of the gangue is

15	8.4 wt%,	which indicates	a very	poor	efficiency.
	That	is, it has been	. found	that	the	iron ore	after the
	grinding	of Comparative	Example	No .	28	contains	a lot of

too fine particles, thereby causing agglomeration of the fine particles due to the effect of static electricity, and thus, the removal efficiency of the gangue is rather reduced.

[0086]

In addition, also in Comparative Examples Nos. 29 and 30, the particle diameter D₅q after the grinding does not satisfy D₅q E 100 pm as specified, which is very poor in terms of the removal efficiency of the gangue.

[0087]

Meanwhile, in Example No. 31, the particle diameter D₅q after the grinding is 261.3 pm, and satisfies D₅q E 100 pm as specified. In addition, the composition of iron ore after the magnetic separation is T.Fe of 78.96 wt%, SiCg of 8.95 wt%, and AI2O3 of 6.98 wt%. In addition, the removal efficiency of the gangue is 19.6 wt%, which is a very good efficiency.

[0088]

In addition, in Example No. 34, the particle diameter D₅q after the grinding is 158.2 pm, which satisfies D₅q E 100 pm as specified. In addition, the composition of the iron ore after the magnetic separation is T.Fe of 78.23 wt% SiCg of 8.35 wt%, and AI2O3 of 7.04 wt%. In addition, the removal efficiency of the gangue is 21.6 wt%, which is a very good efficiency.

[0089]

In Example No. 38, the particle diameter D₅q after the grinding is 488.8 pm, and satisfies D₅₀ E 100 pm as specified. In addition, the composition of the iron ore after the magnetic separation is T.Fe of 78.21 wt%, SIC® of 7.85 wt%, and AI2O3 of 6.70 wt%. In addition, the removal efficiency of the gangue is 25.9 wt%, which is a very good efficiency.

[0090]

In addition, the Examples other than the above illustrated Examples also had the particle diameter of the iron ore after the grinding of D₅q 100 pm, thereby allowing the removal efficiency of the gangue to be high (see Fig. 3) .

[0091]

As described above, according to the second embodiment of the present invention, the gangue in the iron ore having a low T.Fe is efficiently removed, thereby improving the iron grade, while allowing a form that is easy to use as a raw material for the iron manufacturing.

[0092]

It is noted that all the embodiments disclosed herein are examples in all respects, and should not be considered as being restrictive.

In particular, in the embodiments disclosed herein, the matters which are not explicitly disclosed, for example running conditions and operating conditions, various parameters, dimensions, weights, and volume of the components, and the like are not out of the scopes usually used by those skilled in the art, and adopted values associated with such matters can easily be conceived by

Claims

1. A method of improving an iron grade of iron ore, the method comprising:

subjecting iron ore containing gangue to a reduction treatment with a reducing gas followed by a grinding treatment and then a magnetic separation treatment, thereby removing the gangue, wherein the reduction treatment is performed using H₂gas and/or CO gas as the reducing gas, and the reduction treatment is controlled such that parameter X represented by a function of a reduction time of the iron ore and reducing gas partial pressures satisfies the following equation (1):

X = t x (P_h2 + 0.3 x Pco) ^5 · · · (1) wherein t represents a reduction time [min] of the iron ore, Ph2 represents an H2 partial pressure [atm] of the reducing gas, and Pco represents a CO partial pressure [atm] of the reducing gas.

2. The method of improving the iron grade of the iron ore according to claim 1, wherein the iron ore having an Ig loss > 10 wt% is subjected to the reduction treatment by the H2 gas such that the iron ore has a metallization ratio > 60 wt%, and then subjected to the grinding treatment to have a particle diameter of 2 mm or less and satisfy D50 100 pm.