hydrogen reduction of hematite ore fines to magnetite ore...

Research ArticleHydrogen Reduction of Hematite Ore Fines to Magnetite OreFines at Low Temperatures

Wenguang Du1 Song Yang1 Feng Pan1 Ju Shangguan1 Jie Lu2

Shoujun Liu2 and Huiling Fan1

1Key Laboratory for Coal Science and Technology of Ministry of Education and Shanxi ProvinceInstitute for Chemical Engineering of Coal Taiyuan University of Technology Taiyuan 030024 China2College of Chemistry and Chemical Engineering Taiyuan University of Technology Taiyuan 030024 China

Correspondence should be addressed to Ju Shangguan shanggj62163com

Received 6 December 2016 Revised 30 January 2017 Accepted 8 February 2017 Published 5 March 2017

Academic Editor Maria F Carvalho

Copyright copy 2017 Wenguang Du et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Surplus coke oven gases (COGs) and low grade hematite ores are abundant in Shanxi China Our group proposes a new processthat could simultaneously enrich CH

4from COG and produce separated magnetite from low grade hematite In this work low-

temperature hydrogen reduction of hematite ore fines was performed in a fixed-bed reactor with a stirring apparatus and alaboratory Davis magnetic tube was used for the magnetic separation of the resulting magnetite ore finesThe properties of the rawhematite ore reduced products and magnetic concentrate were analyzed and characterized by a chemical analysis method X-raydiffraction optical microscopy and scanning electron microscopy The experimental results indicated that at temperatures lowerthan 400∘C the rate of reduction of the hematite ore fines was controlled by the interfacial reaction on the core surface However attemperatures higher than 450∘C the reaction was controlled by product layer diffusionWith increasing reduction temperature theaverage utilization of hydrogen initially increased and tended to a constant value thereafterThe conversion of Fe

2O3in the hematite

ore played an important role in the total iron recovery and grade of the concentrateThe grade of the concentrate decreased whereasthe total iron recovery increased with the increasing Fe

2O3conversion

1 Introduction

Shanxi a large coal and coke producing province in Chinahas a large amount of surplus coke oven gases (COGs) [1ndash6]which contain substantial amounts of H

2 CH4 and CO In

2014 the coke output of Shanxi was 8722 million tons whichaccounted for 1829 of the national output If 1t of coke canproduce 430 Nm3 of coke oven gas of which approximately200 Nm3 is returned to a coke oven as a coking heat sourceapproximately 16sim18 billion Nm3 of COGs is produced justin Shanxi Meanwhile the apparent consumption of naturalgas in China was 1786 billion Nm3 in 2014 which imports63 billion Nm3 of natural gas (approximately 339 externaldependency) COGmethanation for CH

4enrichment can be

regarded as a simple andhighly efficientway of producing gaswhich has attracted many specialists and scholars to research

and develop the process However the catalysts which arerequired for both the reactivity and selectivity are sensitiveto sulfide and very expensive Can we economically obtainenriched natural gas from surplus COGs

Due to their natural abundance low cost and usefulnessfor a variety of applications iron ores are considered someof the most promising and important resources for the future[7 8]The rapid development of the steel industry has resultedin the reduction of iron ore resources in recent years theseores have been increasingly explored andutilized At the sametime processed iron ores may be utilized as raw materialsfor the desulfurization sorbents used in gas purification ironoxide is the main component of a renewable desulfurizationsorbent for high-temperature coal gas desulfurization [9ndash12] In addition this new route uses iron ore as an oxygencarrier which transfers oxygen from the combustion air to

HindawiJournal of ChemistryVolume 2017 Article ID 1919720 11 pageshttpsdoiorg10115520171919720

2 Journal of Chemistry

the fuel Direct contact between the fuel and combustion airis prevented through the use of chemical looping combustion(CLC) [13ndash15]

However using the iron ores is quite difficult due to theircomplex structure and nonuniform crystal size A combina-tion of low-temperature reduction roasting and low-intensitymagnetic separation is considered a promising approachfor increasing the usability of these ores [16 17] Low-temperature reduction roasting can convert the weakly mag-netic iron minerals (Fe

2O3 FeCO

3 and FeS) into a strongly

magnetic phase (Fe3O4) which can be easily separated by

a low-intensity magnetic field In addition magnetizationwhich can be readily performed at low operating costs is usedto reduce the hematite (Fe

2O3) tomagnetite (Fe

3O4) H2 CO

CH4 and coal can be used as reducing agents [18 19] and the

corresponding reduction reactions should proceed as follows

3Fe2O3+H2997888rarr 2Fe

3O4+H2O (1)

3Fe2O3+ CO 997888rarr 2Fe

3O4+ CO2 (2)

6Fe2O3+ C 997888rarr 4Fe

3O4+ CO2 (3)

Compared to coal-based reduction gas-based reductioncan be performed at lower reduction temperatures [20] andtypically results in higher quality concentrates which havelower levels of carbon deposits H

2 CO and CH

4are usually

used as reducing agents in these gas-based reductions [21ndash23]

As such our research group has proposed an innovativeprocess which combines low-temperature reduction magne-tization of intractable hematite with the production of substi-tute natural gases (SNGs) fromCOGsThis combined processwas used to remove H

2 CO and H

2S thereby enriching the

methane gas contained in the COG and converting hematiteto easily separated magnetite The ultimate aim of this workwas to use low grade hematite ore and the surplus COGcomprehensively to obtain enriched SNG and high grademagnetite economically Meanwhile the whole process isdescribed in Figure 1

This paper as a preliminary study of the innovativeprocess mainly describes the process of low-temperaturehydrogen reduction of hematite ore and magnetic separationof the resulting magnetite ore since hydrogen which is themain component of COG is an efficient reducing agent Theeffect of this reduction on the properties of the magnetite oreis discussed

2 Materials and Methods

21 Materials The raw hematite ore used in this work wasobtained from Guangling County Shanxi province ChinaGuangling County is located northeast of the Shanxi pro-vince Guangling hematite ore is a Shanxi-type hematiteore

22 Analysis and Characterization Method The chemicalcompositions of the raw hematite ore reduced ore samplesand concentrate ore samples were analyzed according to the

Coke oven gas

Tailing

High grademagnetite

Reduced hematite ore

SNG

Low grade hematite ore

Reactor

Magneticseparation

Figure 1 The schematic diagram of use for the low grade hematiteore and the surplus coke oven gas to produce SNGs and high grademagnetite

National Standards of China number GB 67305-2008 andnumber GB 67308-2008

The crystalline phases of the aforementioned sampleswere determined via X-ray diffraction (XRD) (using Cu-K120572radiation scanning rate of 8∘min and sweeping range of 5∘ndash85∘)

The structural characteristics of the raw hematite orewere examined using an optical microscope and a scanningelectron microscope (SEM)

23 Experimental Procedure A total of 100 kg of the rawhematite ore sample was first crushed using a jaw crusher andthen sieved to a size of 2mm in our laboratory One kilogramof each of the 12 samples of the crushed hematite ore wasthen reduced to magnetite ore under a total volumetric gasrate of 120 Lh using a gas mixture of 50 H

2ndash50 N

2 The

reduction process was performed in a fixed-bed reactor anda stirring apparatus was used to enable full contact betweenthe solids and the gas The samples were reduced for 1 15 2and 25 h at 400∘C Similarly the samples were reduced for05 1 15 and 2 h at both 450∘C and 500∘C

The total Fe content (TFe) and Fe2+ content (TFeO)of each sample were determined using a chemical analy-sis method The titanium trichloride-potassium dichromatetitration method was used to determine the TFe of eachsample the ferric chloride-potassium dichromate titrationmethod was used to determine the TFeO Fe

3O4contains one

Fe2+ and two Fe3+ ions Therefore if all the hematite in theraw ore sample is reduced to Fe

3O4 then the TFe and TFeO

of the reduced sample are related through by TFeO = 37TFeThe conversion of Fe

2O3(119883Fe2O3

) to Fe3O4in each reduced

sample can then be calculated by determining the TFe andTFeO of each reduced sample119883Fe2O3

was calculated from

119883Fe2O3 =7119882TFeO3119882TFetimes 100 (4)

Journal of Chemistry 3

The grain sizes of the newly generated magnetite werecalculated from

119863 =119877119897

120573 cos 119902 (5)

where 119863 is the distance between the atomic layers in thecrystals 119877 is Schererrsquos constant 119897 is the wavelength of the X-ray radiation 119902 is the diffraction angle and 120573 is the full widthat half maximum

As for the low-intensity magnetic separation of thereduced samples the optimal grinding fineness andmagneticfield intensity should be chosen such that the optimal mag-netic separation index is obtained In this paper reduced sam-ples with different degrees of grinding fineness and magneticfield intensities were obtained by varying the grinding timeand the working electrical current of the Davis tubemagneticseparator respectively The experiments aimed at optimizingthe grinding fineness and magnetic field intensity wereperformed for samples reduced at 500∘C for 05 h or 20 hThe reduced samples were drymilled in a rodmill for varioustimes and then separated by a laboratoryDavis tubemagneticseparator with a working electrical current of 2 A in order todetermine the best grinding fineness Furthermore in orderto determine the optimum magnetic field intensity reducedsamples with the best grinding fineness were separated bya laboratory Davis tube magnetic separator operating atvarious electrical currents

Each of the 12 reduced samples was dry milled in a rodmill for 15min and then separated by a laboratory Davistube magnetic separator (model XCGS12059350) operating at aworking electrical current of 2A (magnetic field intensity0156 T)The grades andweights of themagnetic concentrateswere determined and the recovery of iron (119877Fe) which isthe index of magnetic separation was calculated during thelow-intensity magnetic separation 119877Fe the amount of ironrecovered in the final concentrate was calculated from

119877Fe =1198981times 119879Fe11198982times 119879Fe2times 100 (6)

where 119877Fe 1198981 119879Fe1 1198982 and 119879Fe2 are the amount of ironrecovered during the low-intensity magnetic separationquality of the concentrate iron content of the concentratequality of the reduced samples and iron content of thereduced samples respectively

3 Results and Discussions

31 Properties of the Raw Ore Samples The mineral com-position main chemical composition and iron distributionof the raw hematite samples are listed in Tables 1 2 and 3respectively the crystalline phase is shown in Figure 2

The Guangling hematite ore sample consisted of 5883Fe2O3 1953 SiO

2 675 Al

2O3 021 FeO 246 CaO

138 MgO 011 Na2O and 365 K

2O Harmful elements

such as phosphorus and sulfur were present in only lowquantities This hematite ore contained a small amount ofmagnetite hematite is the precious form of iron mineralsThe gangue minerals were composed mainly of quartz and

Table 1 Mineral composition of the hematite ore

Components Content (wt)Hematite 53Limonite 4Quartz 20Mica 5Kaolinite 8Barite Trace

Table 2 Chemical composition of the hematite ore

Components Content (wt)TFe 4114Fe2O3

5883FeO 021SiO2

1953CaO 246Al2O3

675MgO 138Na2O 011

K2O 365

S 018P 066LOI 395lowastLOI loss on ignition

Table 3 Iron distribution of the hematite ore

Components Content (wt) Fraction (wt)Magnetic iron 0057 014Siderite 0057 014Iron sulfide 0057 014Iron silicate 050 121Hematite and limonite 404 9837TFe 4107 100

small amounts of mica and kaolinite Furthermore there wasa 395 loss upon ignition for the Guangling hematite ore AsFigure 2 shows the Guangling hematite ore was composedmainly of hematite and the nonmetallic mineral quartz

The optical micrographs in Figure 3 reveal that the Guan-gling hematite ore mainly had taxitic structure disseminatedstructure and similar oolitic structure the hematite mixedwith quartz or mica hematite quartz and clay (mainlykaolinite) formed an oolitic-like structure quartz formed thecore of the similar oolitic structure and hematite and clay(mainly kaolinite) formed a concentric circle in the similaroolitic structure

The corresponding SEM images (Figure 4) confirmedthat the hematite ore consisted mainly of scaly acicularcryptocrystalline and metasomatic textures with a sandconsolidation structure (rarely with an oolitic structure)Theacicular and scaly hematite ores are bright white whereasquartz shows a grey color The disseminated structure of thehematite was very fine


0 10 20 30 40 50 60 70 80 90

bbb

b

bb

b

b

b

aaa

a

aIn

tens

ity

b hematitea quartz

a

a

a

b

2 theta (∘)

Figure 2 XRD pattern of the raw hematite ore

Therefore the hematite ore used in this studywas a typicalcomplex fine-grained marine-sediment-refractory hematiteore

32 Reducing Magnetization of the Raw Hematite Ore

321Thermodynamics of Reducing Fe2O3withH

2 TheGibbs

free energy function method was adopted for the thermody-namic calculation of the H

2-reduction of Fe

2O3[24 25] the

results are shown in Figure 5Three reduction products were formed namely Fe

3O4

FeO and Fe Moreover Fe2O3reacted with H

2to form

Fe3O4at reduction temperatures of 400∘Cndash600∘C and H

2

concentrations of lt65 vol

322 Effect of the Reduction Temperature and Time onthe Conversion of Fe

2O3 Short low-temperature reduction

processes can reduce the cost of magnetizing the hematiteoreThe dependence of the Fe

2O3conversion in the hematite

ore on the reduction time (Figure 6) was investigated at thetemperatures of 400∘C 450∘C and 500∘C

As Figure 6 shows at 400∘C the amount of Fe2O3con-

verted increased linearly with the increasing reduction timeAt reduction temperatures of 450∘C or 500∘C the amountof Fe2O3converted increased rapidly at the beginning of

the reaction and slowly thereafter The shrinking unreactedcore model stipulates that there is a sharp boundary betweenthe reacted (magnetite Fe

3O4) and the unreacted (hematite

Fe2O3) parts of the particle [26] The hematite is reduced to

magnetite (Fe3O4) via the diffusion of hydrogen through the

product layer on the boundary (reacted-unreacted interface)As reduction proceeds the boundary eventually recedes tothe center the hematite is exhausted and the thickness of theproduct layer (magnetite layer) increases The product layerdiffusion and the interfacial reaction on the surface of the coreconstitute the rate-limiting steps of the process [25 26]

The interfacial reaction on the surface of the coreproceeded very slowly at low reduction temperatures In fact

the rate of the interfacial reaction is significantly lower thanthat of the hydrogen diffusion processTherefore the interfa-cial reaction constituted the rate-limiting step of the processSince the reduction temperature was constant and very lowthe reaction proceeded extremely slowly the conversion ofFe2O3was proportional to the reduction time

When the reduction temperature was high the interfacialreaction on the core surface proceeded rapidly and at asignificantly higher rate than that of the hydrogen diffusionprocess Diffusion into the product layer was therefore therate-limiting step of the process During the beginning ofreduction the reaction proceeded rapidly since the productlayer was very thin and the diffusion resistance of hydrogenwas correspondingly small As the reduction proceededthe thickness of the product layer increased the diffusionresistance of hydrogen which in turn led to a sharp decreasein the reaction rate with the increasing reduction time

The aforementioned results show that the transition ofhematite (Fe

2O3) to magnetite (Fe

3O4) proceeded according

to a shrinking unreacted core model When the reductiontemperature was low the reaction rate was controlled bythe interfacial reaction on the surface of the core whenthe reduction temperature was high the reaction rate wascontrolled by diffusion into the product layer

On average sim186 231 and 234 of the hydrogenwere utilized during the reduction process at 400∘C 450∘Cand 500∘C respectively This indicates that the averageutilization of hydrogen increased initially and tended sub-sequently to a constant value with the increasing reductiontemperature

XRD was used to characterize 12 samples which werereduced for 1 h 15 h 2 h and 25 h at the respective reductiontemperatures of 400∘C 450∘C and 500∘C as shown inFigures 7 8 and 9 As the figures show the intensity of thepeaks corresponding to hematite and magnetite decreasesand increases respectively with the increasing reductiontime This indicates that the rate of reaction increased with


Taxitic structure Taxitic structure Taxitic structure

Hematite

Quartz

0 150휇m 0 150휇m 0 40휇m

(a)

Similar oolitic structure Similar oolitic structure Similar oolitic structure

Quartz core

ClayHematite

0 150휇m 0 150휇m 0 40휇m

(b)

Disseminated structure Disseminated structure0 150휇m 0 150휇m

(c)

Figure 3 Optical microscope images of the raw hematite ore

the increasing temperature Moreover nearly all the hematitewas reduced to magnetite during the process

33 Mechanism of Reduction Magnetization Process Thegrain size of the newly generated magnetite is shown inFigure 9

Figure 10 shows that the grain size of the newly generatedmagnetite increased initially and then decreased slightly andincreased thereafter Based on the structural characteristicsof the hematite this grain size trend also indicates that thetransition of hematite (Fe


3O4) followed

a shrinking unreacted core model [27ndash29] This transitionprogressed in three steps [30]

Step 1 H2molecules diffused through the air and were

absorbed on the surface of hematite these H2molecules were

then activated These active H2molecules combined with

O2minus from the Fe2O3lattice thereby generating H

2O [31]

Moreover the two electrons released during the reactionreduced Fe3+ to Fe2+

H2+O2minus = H

2O + 2eminus (7)

2Fe3+ + 2eminus = 2Fe2+ (8)

Step 2 The new generation of Fe2+ combined with Fe2O3

thereby producing Fe3O4through lattice reconstruction [31

32]

4Fe2O3+ Fe2+ + 2eminus = 3Fe

3O4(Fe2O3∙ FeO) (9)

Step 3 During the above process the reduction reactionextended continuously to the inner layer and the entirehematite particle was completely reduced to magnetite [32]


Quartz

QuartzAcicular hematite

Scaly hematite

Mica

Hematite

Quartz

Acicular hematite

Scaly hematite

MicaMica

MicaHematite

Figure 4 SEM images of the raw hematite ore

400 600 800 1000 1200 1400

0102030405060708090

100

Fe

FeO

H2

H2+

H2O

()

minus10

Temperature (∘C)

H2 + 14Fe3O4 = 34Fe + H2O

H2 + FeO = Fe + H2O(g)H2 + Fe3 O4 = 3FeO + H2 O(g)

H2 + 3Fe2O3 = 2Fe3O4 + H2O(g)

Fe3O4

Figure 5 Gas-phase equilibrium composition of H2-reduced iron

oxide

Figure 11 shows the SEM images of samples reduced for1 h and 25 h at 400∘C as well as for 05 h and 2 h at 500∘C

The grain sizes of the new-generation magnetiteincreased with the increasing reaction time Furthermorethe amount of Fe

2O3converted and the number of grains

generated increased with the increasing reaction temperatureand time

00 05 10 15 20 25 300

20

10

40

30

60

50

80

70

100

90

Reduction time (h)

XFe

2O3

()

400∘C450∘C500∘C

Figure 6 Effect of reaction time on the conversion of Fe2O3at

different temperatures

34 Low-Intensity Magnetic Separationof the Reduced Samples

341 Optimization of the Grinding Fineness and MagneticField Intensity To obtain a high grade concentrate with


0 10 20 30 40 50 60 70 80 90

bb bbbb

bbb c

cc

c

c

ccc

c

c

c

c

c cc

ccc

c

bbb

bbbb

b

bbbbbb

a

a a a a

aaaa

a

aa a a a

aaaa

Inte

nsity

1

2

3

4

c magnetite

a

bc

2 theta (∘)

b hematite

a quartz

4-Reduced 25h sample

3-Reduced 2h sample


1-Reduced 1h sample

Figure 7 XRD patterns of samples reduced at 400∘C

0 10 20 30 40 50 60 70 80 90

ccc

c

c

cccc

c

ccc

c

c

ccc

c

b bbbbbbb

b

bb

b

a

a a a a

aaaaa

a

a a a a

aaaa

Inte

nsity

1

2

3

4a

bc

2 theta (∘)

c magnetiteb hematite

a quartz

4-Reduced 2h sample



2-Reduced 1h sample


excellent Fe recovery experiments on the grinding finenessof the ore were performed prior to magnetic separation ofthe reduced samples The results obtained for the samplesreduced at 500∘C for 05 h and 20 h are shown in Figures 12ndash15

The figures reveal an optimum grinding time of 15minand a corresponding grinding fineness and iron recoveryof minus200mesh and 7078 respectively In addition theoptimum magnetic field intensity (0156 T) for magneticseparation occurred at an electrical current of 2 A

The grain size of the hydrogen-reduced new-generationmagnetite influenced the dissociation of the core and there-fore played an important role in the subsequent magneticseparation Comparing Figure 9with Figures 14 and 15 revealsthat the increases in the grain size for the former and latter

0 10 20 30 40 50 60 70 80 90

ccc

c

c

cc

c c c

ccc

c

c

ccc

c

b

b

b

bbbbb

bb

b

aaaaa

aa a a a

a aa a a

aaaa

Inte

nsity

1

2

3

4

ab

c

2 theta (∘)


a quartz

4-Reduced 2h sample


2-Reduced 1h sample



00 05 10 15 20 25150

200

250

300

Reducing time (h)

Gra

in si

ze (A

)

400∘C450∘C500∘C

Figure 10 Grain size of the new-generation magnetite (Fe3O4)

figures for the new-generation magnetite were favorable andunfavorable respectively to the dissociation of the ore

342 Effect of Reduction on the Magnetic Separation Therelationship between the grade of the concentrate and theconversion of Fe

2O3(in the hematite ore) at a given reduction

temperature was determined by analyzing the total ironcontent the results are shown in Figure 16

As Figure 16 shows the grade of the concentratedecreased sharply with the increasing amount of convertedFe2O3 This indicates that the Fe

2O3conversion played an

important role in determining the grade of the concentrateAccording to the shrinking unreacted core model the

reduction of hematite (Fe2O3) to magnetite (Fe

3O4) pro-

ceeded from the outer surface to the center of the hematite


(a) (b)

(c) (d)

Figure 11 SEM images of samples reduced for (a) 1 h at 400∘C (b) 25 h at 400∘C (c) 05 h at 500∘C and (d) 2 h at 500∘C

5 10 15 20 25 30

46474849505152535455565758

Con

cent

rate

gra

de (

)

Grinding time (min)

Reduced for 05h at 500∘C sample


Figure 12 Effect of grinding time on the grade of the concentrate

ore particle The product layer (magnetite layer) thickenedwith the progression of reduction and the unreacted ganguein the hematite ore particle was inevitably encapsulatedby the new-generation magnetite (Fe

3O4) This enclosure

hindered the dissociation of the gangue and the newlygeneratedmagnetite (Fe

3O4) and as a result the grade of the

5 10 15 20 25 3060

65

70

75

80

85

90

95

Reco

very

of i

ron

()

Grinding time (min)

Reduced for 05h at 500∘C sampleReduced for 20h at 500∘C sample

Figure 13 Effect of grinding time on the recovery of iron

magnetic concentrate decreased with the increasing amountof converted Fe

2O3

The dependence of the iron recovery on the conversionof Fe2O3at specific reduction temperatures was determined

by analyzing the total iron content in both the hematite andconcentrate ores the results are shown in Figure 17


10 15 20 25 30

49

50

51

52

53

54

55

56

57

Con

cent

rate

gra

de (

)

Current strength (A)


Figure 14 Effect of current strength on the concentrate grade

10 15 20 25 30

55

60

65

70

75

80

85

90

95

Reco

very

of i

ron

()




As Figure 17 shows the total iron recovery increasedsignificantly with the increasing amount of converted Fe

2O3

This indicates that the Fe2O3conversion played an important

role in the recovery of ironThe amount of hematite reduced to magnetite increased

with the increasing amount of converted Fe2O3and resulted

in turn in increased total iron recovery Therefore theconversion of Fe

2O3in the hematite ore had a significant

effect on the total iron recovery and concentrate grade Infact the concentrate grade decreased whereas the total ironrecovery increased with the increasing Fe

2O3conversion

The grade of the concentrate reduced at 450∘C for 30minand milled in a rod mill for 15min could be improved (tograde 5699 iron recovery rate 6193) by performing asimple magnetic separation process using a working elec-trical current of 2 A (magnetic field intensity 0156 T) thisprocess could also be used to improve the iron recovery rate of

10 20 30 40 50 60 70 80 90 10050

51

52

53

54

55

56

57

58

59

60

Con

cent

rate

gra

de (

)

XFe2O3 ()

400∘C450∘C500∘C

Figure 16 Dependence of the concentrate grade on the conversionof Fe2O3

10 20 30 40 50 60 70 80 90 10040

50

60

70

80

90

Reco

very

of i

ron

()

XFe2O3 ()

400∘C450∘C500∘C

Figure 17 Dependence of iron recovery on the conversion of Fe2O3

the concentrate (to grade 5206 iron recovery rate 905)which was reduced at 400∘C for 150min and rod-milled for15min

4 Conclusions

We conclude the following

(1) One kilogram of hematite (minus2mm) was reducedunder a total volumetric gas rate of 120 Lh (gasmixture composition 50 H

2ndash50 N

2) At reduc-

tion temperatures lower than 400∘C the rate of thereduction reaction of the hematite ore fines wascontrolled by the interfacial reaction on the coresurface However at temperatures higher than 450∘C


the reaction rate was controlled by the product layerdiffusion With an increasing reduction temperaturethe average utilization of hydrogen increased initiallyand tended to a constant value thereafter

(2) The grade of the concentrate decreased and thetotal iron recovery increased with increasing Fe

2O3

conversion The grade of the concentrate which wasreduced at 450∘C for 30min and rod-milled for15minwas improved (to grade 5699 iron recoveryrate 6193) through a simple magnetic separationprocess using a working electrical current of 2 A(magnetic field intensity 0156 T) this process wasalso used to improve the iron recovery rate (to grade5206 iron recovery rate 905) of the concentratewhich was reduced at 400∘C for 150min and rod-milled for 15min

(3) During the reduction magnetization the grain sizeof the new-generation magnetite increased initiallyand then decreases slightly and increased thereafterThe former and latter increases in the grain sizewere favorable and unfavorable respectively to thedissociation of the hematite ore In addition thetransition of hematite (Fe


3O4)

followed a shrinking unreacted core model

Competing Interests

The authors declare that they have no conflict of interests

Acknowledgments

The authors thank the colleagues from Taiyuan University ofTechnology for their assistance during this work This workwas sponsored by the Taiyuan Green Coke Clean Energy CoLtd (China)

References

[1] W-H Chen M-R Lin T-S Leu and S-W Du ldquoAn evaluationof hydrogen production from the perspective of using blastfurnace gas and coke oven gas as feedstocksrdquo InternationalJournal of Hydrogen Energy vol 36 no 18 pp 11727ndash11737 2011

[2] R Razzaq C Li and S Zhang ldquoCoke oven gas availabilityproperties purification and utilization in Chinardquo Fuel vol 113pp 287ndash299 2013

[3] J M Bermudez A Arenillas R Luque and J A MenendezldquoAn overview of novel technologies to valorise coke oven gassurplusrdquo Fuel Processing Technology vol 110 pp 150ndash159 2013

[4] W G Du S J Liu J Shangguan F Gao and J Chen ldquoMethodfor producing natural gas by reduction magnetizing hematitewith coke-oven gasrdquo PRChina Patent CN102311821A

[5] W-H Chen M-R Lin A B Yu S-W Du and T-S LeuldquoHydrogen production from steam reforming of coke oven gasand its utility for indirect reduction of iron oxides in blastfurnacerdquo International Journal of Hydrogen Energy vol 37 no16 pp 11748ndash11758 2012

[6] J Lu S Liu J ShangguanWDu F Pan and S Yang ldquoThe effectof sodium sulphate on the hydrogen reduction process of nickellaterite orerdquoMinerals Engineering vol 49 pp 154ndash164 2013

[7] P Pourghahramani and E Forssberg ldquoEffects of mechanicalactivation on the reduction behavior of hematite concentraterdquoInternational Journal ofMineral Processing vol 82 no 2 pp 96ndash105 2007

[8] M Challenor P Gong D Lorenser et al ldquoIron oxide-indu-ced thermal effects on solid-state upconversion emissions inNaYF4YbEr nanocrystalsrdquo ACS Applied Materials and Inter-faces vol 5 no 16 pp 7875ndash7880 2013

[9] H Fan K Xie J Shangguan F Shen and C Li ldquoEffect of cal-cium oxide additive on the performance of iron oxide sorbentfor high-temperature coal gas desulfurizationrdquo Journal of Natu-ral Gas Chemistry vol 16 no 4 pp 404ndash408 2007

[10] H-L Fan J Shangguan L-T Liang C-H Li and J-Y Lin ldquoAcomparative study of the effect of clay binders on iron oxidesorbent in the high-temperature removal of hydrogen sulfiderdquoProcess Safety and Environmental Protection vol 91 no 3 pp235ndash243 2013

[11] N Jordan A Ritter A C Scheinost S Weiss D Schild andR Hubner ldquoSelenium(IV) uptake by maghemite (120574-Fe

2O3)rdquo

Environmental Science and Technology vol 48 no 3 pp 1665ndash1674 2014

[12] E Potapova I Carabante M Grahn A Holmgren and J Hed-lund ldquoStudies of collector adsorption on iron oxides by in situATR-FTIR spectroscopyrdquo Industrial and Engineering ChemistryResearch vol 49 no 4 pp 1493ndash1502 2010

[13] Z Yu C Li Y Fang J Huang and Z Wang ldquoReduction rateenhancements for coal direct chemical looping combustionwith an iron oxide oxygen carrierrdquo Energy amp Fuels vol 26 no4 pp 2505ndash2511 2012

[14] Z YuC Li X Jing et al ldquoEffects ofCO2atmosphere andK

2CO3

addition on the reduction reactivity oxygen transport capacityand sintering of CuO and Fe

2O3oxygen carriers in coal direct

chemical looping combustionrdquo Energy and Fuels vol 27 no 5pp 2703ndash2711 2013

[15] Z Yu C Li X Jing et al ldquoCatalytic chemical looping combus-tion of carbon with an iron-based oxygen carrier modifiedby K2CO3 catalytic mechanism and multicycle testsrdquo Fuel

Processing Technology vol 135 pp 119ndash124 2015[16] C Li H Sun J Bai and L Li ldquoInnovative methodology for

comprehensive utilization of iron ore tailings part 1The recov-ery of iron from iron ore tailings usingmagnetic separation aftermagnetizing roastingrdquo Journal of Hazardous Materials vol 174pp 71ndash77 2010

[17] C Li H Sun J Bai and L Li ldquoInnovative methodology forcomprehensive utilization of iron ore tailings part 2 theresidues after iron recovery from iron ore tailings to preparecementitiousmaterialrdquo Journal of HazardousMaterials vol 174pp 78ndash83 2010

[18] W K Jozwiak E Kaczmarek T P Maniecki W Ignaczak andWManiukiewicz ldquoReduction behavior of iron oxides in hydro-gen and carbon monoxide atmospheresrdquo Applied Catalysis AGeneral vol 326 no 1 pp 17ndash27 2007

[19] H L Gilles and C W Clump ldquoReduction of iron ore with hyd-rogen in a direct current plasma jetrdquo Industrial and EngineeringChemistry vol 9 no 2 pp 194ndash207 1970

[20] A Mcgeorge Jr A H Hixson and K A Krieger ldquoLow temp-erature gaseous reduction of iron ore in the presence of alkalirdquoI and E C Process Design and Development vol 1 no 3 pp 217ndash225 1962

[21] J Zielinski I Zglinicka L Znak and Z Kaszkur ldquoReduction ofFe2O3with hydrogenrdquoApplied Catalysis A General vol 381 no

1-2 pp 191ndash196 2010


[22] K-S Kang C-H Kim K-K Bae et al ldquoReduction and oxi-dation properties of Fe

2O3ZrO2oxygen carrier for hydrogen

productionrdquoChemical Engineering Research and Design vol 92no 11 pp 2584ndash2597 2014

[23] N J Welham ldquoActivation of the carbothermic reduction ofmanganese orerdquo International Journal ofMineral Processing vol67 no 1-4 pp 187ndash198 2002

[24] A Pineau N Kanari and I Gaballah ldquoKinetics of reductionof iron oxides by H2 Part II Low temperature reduction ofmagnetiterdquoThermochimica Acta vol 456 no 2 pp 75ndash88 2007

[25] A Pineau N Kanari and I Gaballah ldquoKinetics of reductionof iron oxides by H2 Part I low temperature reduction ofhematiterdquoThermochimica Acta vol 447 no 1 pp 89ndash100 2006

[26] J P Martins and F Margarido ldquoThe cracking shrinking modelfor solid-fluid reactionsrdquo Materials Chemistry and Physics vol44 no 2 pp 156ndash169 1996

[27] X Liu F Song and Z Wen ldquoA novel dimensionless form ofunreacted shrinking core model for solid conversion duringchemical looping combustionrdquo Fuel vol 129 pp 231ndash237 2014

[28] D da Rocha E Paetzold andN Kanswohl ldquoThe shrinking coremodel applied on anaerobic digestionrdquo Chemical EngineeringandProcessing Process Intensification vol 70 pp 294ndash300 2013

[29] Y Yu andCQi ldquoMagnetizing roastingmechanism and effectiveore dressing process for oolitic hematite orerdquo Journal WuhanUniversity of Technology Materials Science Edition vol 26 no2 pp 176ndash181 2011

[30] WV Schulmeyer andHMOrtner ldquoMechanisms of the hydro-gen reduction of molybdenum oxidesrdquo International Journal ofRefractoryMetals andHardMaterials vol 20 no 4 pp 261ndash2692002

[31] K Higuchi and R H Heerema ldquoInfluence of sintering condi-tions on the reduction behaviour of pure hematite compactsrdquoMinerals Engineering vol 16 no 5 pp 463ndash477 2003

[32] H Veeramani D Aruguete N Monsegue et al ldquoLow-temp-erature green synthesis of multivalent manganese oxide nano-wiresrdquo ACS Sustainable Chemistry amp Engineering vol 1 no 9pp 1070ndash1074 2013

Submit your manuscripts athttpswwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


the fuel Direct contact between the fuel and combustion airis prevented through the use of chemical looping combustion(CLC) [13ndash15]

However using the iron ores is quite difficult due to theircomplex structure and nonuniform crystal size A combina-tion of low-temperature reduction roasting and low-intensitymagnetic separation is considered a promising approachfor increasing the usability of these ores [16 17] Low-temperature reduction roasting can convert the weakly mag-netic iron minerals (Fe

2O3 FeCO

3 and FeS) into a strongly

magnetic phase (Fe3O4) which can be easily separated by

a low-intensity magnetic field In addition magnetizationwhich can be readily performed at low operating costs is usedto reduce the hematite (Fe

2O3) tomagnetite (Fe

3O4) H2 CO

CH4 and coal can be used as reducing agents [18 19] and the

corresponding reduction reactions should proceed as follows

3Fe2O3+H2997888rarr 2Fe

3O4+H2O (1)

3Fe2O3+ CO 997888rarr 2Fe

3O4+ CO2 (2)

6Fe2O3+ C 997888rarr 4Fe

3O4+ CO2 (3)

Compared to coal-based reduction gas-based reductioncan be performed at lower reduction temperatures [20] andtypically results in higher quality concentrates which havelower levels of carbon deposits H

2 CO and CH

4are usually

used as reducing agents in these gas-based reductions [21ndash23]

As such our research group has proposed an innovativeprocess which combines low-temperature reduction magne-tization of intractable hematite with the production of substi-tute natural gases (SNGs) fromCOGsThis combined processwas used to remove H

2 CO and H

2S thereby enriching the

methane gas contained in the COG and converting hematiteto easily separated magnetite The ultimate aim of this workwas to use low grade hematite ore and the surplus COGcomprehensively to obtain enriched SNG and high grademagnetite economically Meanwhile the whole process isdescribed in Figure 1

This paper as a preliminary study of the innovativeprocess mainly describes the process of low-temperaturehydrogen reduction of hematite ore and magnetic separationof the resulting magnetite ore since hydrogen which is themain component of COG is an efficient reducing agent Theeffect of this reduction on the properties of the magnetite oreis discussed

2 Materials and Methods

21 Materials The raw hematite ore used in this work wasobtained from Guangling County Shanxi province ChinaGuangling County is located northeast of the Shanxi pro-vince Guangling hematite ore is a Shanxi-type hematiteore

22 Analysis and Characterization Method The chemicalcompositions of the raw hematite ore reduced ore samplesand concentrate ore samples were analyzed according to the

Coke oven gas

Tailing

High grademagnetite

Reduced hematite ore

SNG

Low grade hematite ore

Reactor

Magneticseparation

Figure 1 The schematic diagram of use for the low grade hematiteore and the surplus coke oven gas to produce SNGs and high grademagnetite

National Standards of China number GB 67305-2008 andnumber GB 67308-2008

The crystalline phases of the aforementioned sampleswere determined via X-ray diffraction (XRD) (using Cu-K120572radiation scanning rate of 8∘min and sweeping range of 5∘ndash85∘)

The structural characteristics of the raw hematite orewere examined using an optical microscope and a scanningelectron microscope (SEM)

23 Experimental Procedure A total of 100 kg of the rawhematite ore sample was first crushed using a jaw crusher andthen sieved to a size of 2mm in our laboratory One kilogramof each of the 12 samples of the crushed hematite ore wasthen reduced to magnetite ore under a total volumetric gasrate of 120 Lh using a gas mixture of 50 H

2ndash50 N

2 The

reduction process was performed in a fixed-bed reactor anda stirring apparatus was used to enable full contact betweenthe solids and the gas The samples were reduced for 1 15 2and 25 h at 400∘C Similarly the samples were reduced for05 1 15 and 2 h at both 450∘C and 500∘C

The total Fe content (TFe) and Fe2+ content (TFeO)of each sample were determined using a chemical analy-sis method The titanium trichloride-potassium dichromatetitration method was used to determine the TFe of eachsample the ferric chloride-potassium dichromate titrationmethod was used to determine the TFeO Fe

3O4contains one

Fe2+ and two Fe3+ ions Therefore if all the hematite in theraw ore sample is reduced to Fe

3O4 then the TFe and TFeO

of the reduced sample are related through by TFeO = 37TFeThe conversion of Fe

2O3(119883Fe2O3

) to Fe3O4in each reduced

sample can then be calculated by determining the TFe andTFeO of each reduced sample119883Fe2O3

was calculated from

119883Fe2O3 =7119882TFeO3119882TFetimes 100 (4)



119863 =119877119897

120573 cos 119902 (5)









2 675 Al

2O3 021 FeO 246 CaO

138 MgO 011 Na2O and 365 K

2O Harmful elements






5883FeO 021SiO2

1953CaO 246Al2O3

675MgO 138Na2O 011

K2O 365








0 10 20 30 40 50 60 70 80 90

bbb

b

bb

b

b

b

aaa

a

aIn

tens

ity

b hematitea quartz

a

a

a

b

2 theta (∘)





2 TheGibbs


2-reduction of Fe

2O3[24 25] the


3O4


2to form


2

























Hematite

Quartz

0 150휇m 0 150휇m 0 40휇m

(a)


Quartz core

ClayHematite

0 150휇m 0 150휇m 0 40휇m

(b)


(c)






3O4) followed






2O [31]


H2+O2minus = H

2O + 2eminus (7)

2Fe3+ + 2eminus = 2Fe2+ (8)



32]


3O4(Fe2O3∙ FeO) (9)



Quartz


Scaly hematite

Mica

Hematite

Quartz

Acicular hematite

Scaly hematite

MicaMica

MicaHematite


400 600 800 1000 1200 1400

0102030405060708090

100

Fe

FeO

H2

H2+

H2O

()

minus10

Temperature (∘C)

H2 + 14Fe3O4 = 34Fe + H2O


H2 + 3Fe2O3 = 2Fe3O4 + H2O(g)

Fe3O4


oxide





00 05 10 15 20 25 300

20

10

40

30

60

50

80

70

100

90

Reduction time (h)

XFe

2O3

()

400∘C450∘C500∘C






0 10 20 30 40 50 60 70 80 90

bb bbbb

bbb c

cc

c

c

ccc

c

c

c

c

c cc

ccc

c

bbb

bbbb

b

bbbbbb

a

a a a a

aaaa

a

aa a a a

aaaa

Inte

nsity

1

2

3

4

c magnetite

a

bc

2 theta (∘)

b hematite

a quartz


3-Reduced 2h sample


1-Reduced 1h sample


0 10 20 30 40 50 60 70 80 90

ccc

c

c

cccc

c

ccc

c

c

ccc

c

b bbbbbbb

b

bb

b

a

a a a a

aaaaa

a

a a a a

aaaa

Inte

nsity

1

2

3

4a

bc

2 theta (∘)


a quartz

4-Reduced 2h sample



2-Reduced 1h sample





0 10 20 30 40 50 60 70 80 90

ccc

c

c

cc

c c c

ccc

c

c

ccc

c

b

b

b

bbbbb

bb

b

aaaaa

aa a a a

a aa a a

aaaa

Inte

nsity

1

2

3

4

ab

c

2 theta (∘)


a quartz

4-Reduced 2h sample


2-Reduced 1h sample



00 05 10 15 20 25150

200

250

300

Reducing time (h)

Gra

in si

ze (A

)

400∘C450∘C500∘C










3O4) pro-



(a) (b)

(c) (d)


5 10 15 20 25 30

46474849505152535455565758

Con

cent

rate

gra

de (

)

Grinding time (min)





3O4) This enclosure



5 10 15 20 25 3060

65

70

75

80

85

90

95

Reco

very

of i

ron

()

Grinding time (min)




2O3




10 15 20 25 30

49

50

51

52

53

54

55

56

57

Con

cent

rate

gra

de (

)




10 15 20 25 30

55

60

65

70

75

80

85

90

95

Reco

very

of i

ron

()





2O3







2O3conversion


10 20 30 40 50 60 70 80 90 10050

51

52

53

54

55

56

57

58

59

60

Con

cent

rate

gra

de (

)

XFe2O3 ()

400∘C450∘C500∘C


10 20 30 40 50 60 70 80 90 10040

50

60

70

80

90

Reco

very

of i

ron

()

XFe2O3 ()

400∘C450∘C500∘C



4 Conclusions



2ndash50 N

2) At reduc-





2O3




3O4)


Competing Interests


Acknowledgments


References












2O3)rdquo





2CO3












1-2 pp 191ndash196 2010
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



119863 =119877119897

120573 cos 119902 (5)









2 675 Al

2O3 021 FeO 246 CaO

138 MgO 011 Na2O and 365 K

2O Harmful elements






5883FeO 021SiO2

1953CaO 246Al2O3

675MgO 138Na2O 011

K2O 365








0 10 20 30 40 50 60 70 80 90

bbb

b

bb

b

b

b

aaa

a

aIn

tens

ity

b hematitea quartz

a

a

a

b

2 theta (∘)





2 TheGibbs


2-reduction of Fe

2O3[24 25] the


3O4


2to form


2

























Hematite

Quartz

0 150휇m 0 150휇m 0 40휇m

(a)


Quartz core

ClayHematite

0 150휇m 0 150휇m 0 40휇m

(b)


(c)






3O4) followed






2O [31]


H2+O2minus = H

2O + 2eminus (7)

2Fe3+ + 2eminus = 2Fe2+ (8)



32]


3O4(Fe2O3∙ FeO) (9)



Quartz


Scaly hematite

Mica

Hematite

Quartz

Acicular hematite

Scaly hematite

MicaMica

MicaHematite


400 600 800 1000 1200 1400

0102030405060708090

100

Fe

FeO

H2

H2+

H2O

()

minus10

Temperature (∘C)

H2 + 14Fe3O4 = 34Fe + H2O


H2 + 3Fe2O3 = 2Fe3O4 + H2O(g)

Fe3O4


oxide





00 05 10 15 20 25 300

20

10

40

30

60

50

80

70

100

90

Reduction time (h)

XFe

2O3

()

400∘C450∘C500∘C






0 10 20 30 40 50 60 70 80 90

bb bbbb

bbb c

cc

c

c

ccc

c

c

c

c

c cc

ccc

c

bbb

bbbb

b

bbbbbb

a

a a a a

aaaa

a

aa a a a

aaaa

Inte

nsity

1

2

3

4

c magnetite

a

bc

2 theta (∘)

b hematite

a quartz


3-Reduced 2h sample


1-Reduced 1h sample


0 10 20 30 40 50 60 70 80 90

ccc

c

c

cccc

c

ccc

c

c

ccc

c

b bbbbbbb

b

bb

b

a

a a a a

aaaaa

a

a a a a

aaaa

Inte

nsity

1

2

3

4a

bc

2 theta (∘)


a quartz

4-Reduced 2h sample



2-Reduced 1h sample





0 10 20 30 40 50 60 70 80 90

ccc

c

c

cc

c c c

ccc

c

c

ccc

c

b

b

b

bbbbb

bb

b

aaaaa

aa a a a

a aa a a

aaaa

Inte

nsity

1

2

3

4

ab

c

2 theta (∘)


a quartz

4-Reduced 2h sample


2-Reduced 1h sample



00 05 10 15 20 25150

200

250

300

Reducing time (h)

Gra

in si

ze (A

)

400∘C450∘C500∘C










3O4) pro-



(a) (b)

(c) (d)


5 10 15 20 25 30

46474849505152535455565758

Con

cent

rate

gra

de (

)

Grinding time (min)





3O4) This enclosure



5 10 15 20 25 3060

65

70

75

80

85

90

95

Reco

very

of i

ron

()

Grinding time (min)




2O3




10 15 20 25 30

49

50

51

52

53

54

55

56

57

Con

cent

rate

gra

de (

)




10 15 20 25 30

55

60

65

70

75

80

85

90

95

Reco

very

of i

ron

()





2O3







2O3conversion


10 20 30 40 50 60 70 80 90 10050

51

52

53

54

55

56

57

58

59

60

Con

cent

rate

gra

de (

)

XFe2O3 ()

400∘C450∘C500∘C


10 20 30 40 50 60 70 80 90 10040

50

60

70

80

90

Reco

very

of i

ron

()

XFe2O3 ()

400∘C450∘C500∘C



4 Conclusions



2ndash50 N

2) At reduc-





2O3




3O4)


Competing Interests


Acknowledgments


References












2O3)rdquo





2CO3












1-2 pp 191ndash196 2010
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0 10 20 30 40 50 60 70 80 90

bbb

b

bb

b

b

b

aaa

a

aIn

tens

ity

b hematitea quartz

a

a

a

b

2 theta (∘)





2 TheGibbs


2-reduction of Fe

2O3[24 25] the


3O4


2to form


2

























Hematite

Quartz

0 150휇m 0 150휇m 0 40휇m

(a)


Quartz core

ClayHematite

0 150휇m 0 150휇m 0 40휇m

(b)


(c)






3O4) followed






2O [31]


H2+O2minus = H

2O + 2eminus (7)

2Fe3+ + 2eminus = 2Fe2+ (8)



32]


3O4(Fe2O3∙ FeO) (9)



Quartz


Scaly hematite

Mica

Hematite

Quartz

Acicular hematite

Scaly hematite

MicaMica

MicaHematite


400 600 800 1000 1200 1400

0102030405060708090

100

Fe

FeO

H2

H2+

H2O

()

minus10

Temperature (∘C)

H2 + 14Fe3O4 = 34Fe + H2O


H2 + 3Fe2O3 = 2Fe3O4 + H2O(g)

Fe3O4


oxide





00 05 10 15 20 25 300

20

10

40

30

60

50

80

70

100

90

Reduction time (h)

XFe

2O3

()

400∘C450∘C500∘C






0 10 20 30 40 50 60 70 80 90

bb bbbb

bbb c

cc

c

c

ccc

c

c

c

c

c cc

ccc

c

bbb

bbbb

b

bbbbbb

a

a a a a

aaaa

a

aa a a a

aaaa

Inte

nsity

1

2

3

4

c magnetite

a

bc

2 theta (∘)

b hematite

a quartz


3-Reduced 2h sample


1-Reduced 1h sample


0 10 20 30 40 50 60 70 80 90

ccc

c

c

cccc

c

ccc

c

c

ccc

c

b bbbbbbb

b

bb

b

a

a a a a

aaaaa

a

a a a a

aaaa

Inte

nsity

1

2

3

4a

bc

2 theta (∘)


a quartz

4-Reduced 2h sample



2-Reduced 1h sample





0 10 20 30 40 50 60 70 80 90

ccc

c

c

cc

c c c

ccc

c

c

ccc

c

b

b

b

bbbbb

bb

b

aaaaa

aa a a a

a aa a a

aaaa

Inte

nsity

1

2

3

4

ab

c

2 theta (∘)


a quartz

4-Reduced 2h sample


2-Reduced 1h sample



00 05 10 15 20 25150

200

250

300

Reducing time (h)

Gra

in si

ze (A

)

400∘C450∘C500∘C










3O4) pro-



(a) (b)

(c) (d)


5 10 15 20 25 30

46474849505152535455565758

Con

cent

rate

gra

de (

)

Grinding time (min)





3O4) This enclosure



5 10 15 20 25 3060

65

70

75

80

85

90

95

Reco

very

of i

ron

()

Grinding time (min)




2O3




10 15 20 25 30

49

50

51

52

53

54

55

56

57

Con

cent

rate

gra

de (

)




10 15 20 25 30

55

60

65

70

75

80

85

90

95

Reco

very

of i

ron

()





2O3







2O3conversion


10 20 30 40 50 60 70 80 90 10050

51

52

53

54

55

56

57

58

59

60

Con

cent

rate

gra

de (

)

XFe2O3 ()

400∘C450∘C500∘C


10 20 30 40 50 60 70 80 90 10040

50

60

70

80

90

Reco

very

of i

ron

()

XFe2O3 ()

400∘C450∘C500∘C



4 Conclusions



2ndash50 N

2) At reduc-





2O3




3O4)


Competing Interests


Acknowledgments


References












2O3)rdquo





2CO3












1-2 pp 191ndash196 2010
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



Hematite

Quartz

0 150휇m 0 150휇m 0 40휇m

(a)


Quartz core

ClayHematite

0 150휇m 0 150휇m 0 40휇m

(b)


(c)






3O4) followed






2O [31]


H2+O2minus = H

2O + 2eminus (7)

2Fe3+ + 2eminus = 2Fe2+ (8)



32]


3O4(Fe2O3∙ FeO) (9)



Quartz


Scaly hematite

Mica

Hematite

Quartz

Acicular hematite

Scaly hematite

MicaMica

MicaHematite


400 600 800 1000 1200 1400

0102030405060708090

100

Fe

FeO

H2

H2+

H2O

()

minus10

Temperature (∘C)

H2 + 14Fe3O4 = 34Fe + H2O


H2 + 3Fe2O3 = 2Fe3O4 + H2O(g)

Fe3O4


oxide





00 05 10 15 20 25 300

20

10

40

30

60

50

80

70

100

90

Reduction time (h)

XFe

2O3

()

400∘C450∘C500∘C






0 10 20 30 40 50 60 70 80 90

bb bbbb

bbb c

cc

c

c

ccc

c

c

c

c

c cc

ccc

c

bbb

bbbb

b

bbbbbb

a

a a a a

aaaa

a

aa a a a

aaaa

Inte

nsity

1

2

3

4

c magnetite

a

bc

2 theta (∘)

b hematite

a quartz


3-Reduced 2h sample


1-Reduced 1h sample


0 10 20 30 40 50 60 70 80 90

ccc

c

c

cccc

c

ccc

c

c

ccc

c

b bbbbbbb

b

bb

b

a

a a a a

aaaaa

a

a a a a

aaaa

Inte

nsity

1

2

3

4a

bc

2 theta (∘)


a quartz

4-Reduced 2h sample



2-Reduced 1h sample





0 10 20 30 40 50 60 70 80 90

ccc

c

c

cc

c c c

ccc

c

c

ccc

c

b

b

b

bbbbb

bb

b

aaaaa

aa a a a

a aa a a

aaaa

Inte

nsity

1

2

3

4

ab

c

2 theta (∘)


a quartz

4-Reduced 2h sample


2-Reduced 1h sample



00 05 10 15 20 25150

200

250

300

Reducing time (h)

Gra

in si

ze (A

)

400∘C450∘C500∘C










3O4) pro-



(a) (b)

(c) (d)


5 10 15 20 25 30

46474849505152535455565758

Con

cent

rate

gra

de (

)

Grinding time (min)





3O4) This enclosure



5 10 15 20 25 3060

65

70

75

80

85

90

95

Reco

very

of i

ron

()

Grinding time (min)




2O3




10 15 20 25 30

49

50

51

52

53

54

55

56

57

Con

cent

rate

gra

de (

)




10 15 20 25 30

55

60

65

70

75

80

85

90

95

Reco

very

of i

ron

()





2O3







2O3conversion


10 20 30 40 50 60 70 80 90 10050

51

52

53

54

55

56

57

58

59

60

Con

cent

rate

gra

de (

)

XFe2O3 ()

400∘C450∘C500∘C


10 20 30 40 50 60 70 80 90 10040

50

60

70

80

90

Reco

very

of i

ron

()

XFe2O3 ()

400∘C450∘C500∘C



4 Conclusions



2ndash50 N

2) At reduc-





2O3




3O4)


Competing Interests


Acknowledgments


References












2O3)rdquo





2CO3












1-2 pp 191ndash196 2010
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Quartz


Scaly hematite

Mica

Hematite

Quartz

Acicular hematite

Scaly hematite

MicaMica

MicaHematite


400 600 800 1000 1200 1400

0102030405060708090

100

Fe

FeO

H2

H2+

H2O

()

minus10

Temperature (∘C)

H2 + 14Fe3O4 = 34Fe + H2O


H2 + 3Fe2O3 = 2Fe3O4 + H2O(g)

Fe3O4


oxide





00 05 10 15 20 25 300

20

10

40

30

60

50

80

70

100

90

Reduction time (h)

XFe

2O3

()

400∘C450∘C500∘C






0 10 20 30 40 50 60 70 80 90

bb bbbb

bbb c

cc

c

c

ccc

c

c

c

c

c cc

ccc

c

bbb

bbbb

b

bbbbbb

a

a a a a

aaaa

a

aa a a a

aaaa

Inte

nsity

1

2

3

4

c magnetite

a

bc

2 theta (∘)

b hematite

a quartz


3-Reduced 2h sample


1-Reduced 1h sample


0 10 20 30 40 50 60 70 80 90

ccc

c

c

cccc

c

ccc

c

c

ccc

c

b bbbbbbb

b

bb

b

a

a a a a

aaaaa

a

a a a a

aaaa

Inte

nsity

1

2

3

4a

bc

2 theta (∘)


a quartz

4-Reduced 2h sample



2-Reduced 1h sample





0 10 20 30 40 50 60 70 80 90

ccc

c

c

cc

c c c

ccc

c

c

ccc

c

b

b

b

bbbbb

bb

b

aaaaa

aa a a a

a aa a a

aaaa

Inte

nsity

1

2

3

4

ab

c

2 theta (∘)


a quartz

4-Reduced 2h sample


2-Reduced 1h sample



00 05 10 15 20 25150

200

250

300

Reducing time (h)

Gra

in si

ze (A

)

400∘C450∘C500∘C










3O4) pro-



(a) (b)

(c) (d)


5 10 15 20 25 30

46474849505152535455565758

Con

cent

rate

gra

de (

)

Grinding time (min)





3O4) This enclosure



5 10 15 20 25 3060

65

70

75

80

85

90

95

Reco

very

of i

ron

()

Grinding time (min)




2O3




10 15 20 25 30

49

50

51

52

53

54

55

56

57

Con

cent

rate

gra

de (

)




10 15 20 25 30

55

60

65

70

75

80

85

90

95

Reco

very

of i

ron

()





2O3







2O3conversion


10 20 30 40 50 60 70 80 90 10050

51

52

53

54

55

56

57

58

59

60

Con

cent

rate

gra

de (

)

XFe2O3 ()

400∘C450∘C500∘C


10 20 30 40 50 60 70 80 90 10040

50

60

70

80

90

Reco

very

of i

ron

()

XFe2O3 ()

400∘C450∘C500∘C



4 Conclusions



2ndash50 N

2) At reduc-





2O3




3O4)


Competing Interests


Acknowledgments


References












2O3)rdquo





2CO3












1-2 pp 191ndash196 2010
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0 10 20 30 40 50 60 70 80 90

bb bbbb

bbb c

cc

c

c

ccc

c

c

c

c

c cc

ccc

c

bbb

bbbb

b

bbbbbb

a

a a a a

aaaa

a

aa a a a

aaaa

Inte

nsity

1

2

3

4

c magnetite

a

bc

2 theta (∘)

b hematite

a quartz


3-Reduced 2h sample


1-Reduced 1h sample


0 10 20 30 40 50 60 70 80 90

ccc

c

c

cccc

c

ccc

c

c

ccc

c

b bbbbbbb

b

bb

b

a

a a a a

aaaaa

a

a a a a

aaaa

Inte

nsity

1

2

3

4a

bc

2 theta (∘)


a quartz

4-Reduced 2h sample



2-Reduced 1h sample





0 10 20 30 40 50 60 70 80 90

ccc

c

c

cc

c c c

ccc

c

c

ccc

c

b

b

b

bbbbb

bb

b

aaaaa

aa a a a

a aa a a

aaaa

Inte

nsity

1

2

3

4

ab

c

2 theta (∘)


a quartz

4-Reduced 2h sample


2-Reduced 1h sample



00 05 10 15 20 25150

200

250

300

Reducing time (h)

Gra

in si

ze (A

)

400∘C450∘C500∘C










3O4) pro-



(a) (b)

(c) (d)


5 10 15 20 25 30

46474849505152535455565758

Con

cent

rate

gra

de (

)

Grinding time (min)





3O4) This enclosure



5 10 15 20 25 3060

65

70

75

80

85

90

95

Reco

very

of i

ron

()

Grinding time (min)




2O3




10 15 20 25 30

49

50

51

52

53

54

55

56

57

Con

cent

rate

gra

de (

)




10 15 20 25 30

55

60

65

70

75

80

85

90

95

Reco

very

of i

ron

()





2O3







2O3conversion


10 20 30 40 50 60 70 80 90 10050

51

52

53

54

55

56

57

58

59

60

Con

cent

rate

gra

de (

)

XFe2O3 ()

400∘C450∘C500∘C


10 20 30 40 50 60 70 80 90 10040

50

60

70

80

90

Reco

very

of i

ron

()

XFe2O3 ()

400∘C450∘C500∘C



4 Conclusions



2ndash50 N

2) At reduc-





2O3




3O4)


Competing Interests


Acknowledgments


References












2O3)rdquo





2CO3












1-2 pp 191ndash196 2010
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


(a) (b)

(c) (d)


5 10 15 20 25 30

46474849505152535455565758

Con

cent

rate

gra

de (

)

Grinding time (min)





3O4) This enclosure



5 10 15 20 25 3060

65

70

75

80

85

90

95

Reco

very

of i

ron

()

Grinding time (min)




2O3




10 15 20 25 30

49

50

51

52

53

54

55

56

57

Con

cent

rate

gra

de (

)




10 15 20 25 30

55

60

65

70

75

80

85

90

95

Reco

very

of i

ron

()





2O3







2O3conversion


10 20 30 40 50 60 70 80 90 10050

51

52

53

54

55

56

57

58

59

60

Con

cent

rate

gra

de (

)

XFe2O3 ()

400∘C450∘C500∘C


10 20 30 40 50 60 70 80 90 10040

50

60

70

80

90

Reco

very

of i

ron

()

XFe2O3 ()

400∘C450∘C500∘C



4 Conclusions



2ndash50 N

2) At reduc-





2O3




3O4)


Competing Interests


Acknowledgments


References












2O3)rdquo





2CO3












1-2 pp 191ndash196 2010
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


10 15 20 25 30

49

50

51

52

53

54

55

56

57

Con

cent

rate

gra

de (

)




10 15 20 25 30

55

60

65

70

75

80

85

90

95

Reco

very

of i

ron

()





2O3







2O3conversion


10 20 30 40 50 60 70 80 90 10050

51

52

53

54

55

56

57

58

59

60

Con

cent

rate

gra

de (

)

XFe2O3 ()

400∘C450∘C500∘C


10 20 30 40 50 60 70 80 90 10040

50

60

70

80

90

Reco

very

of i

ron

()

XFe2O3 ()

400∘C450∘C500∘C



4 Conclusions



2ndash50 N

2) At reduc-





2O3




3O4)


Competing Interests


Acknowledgments


References












2O3)rdquo





2CO3












1-2 pp 191ndash196 2010
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




2O3




3O4)


Competing Interests


Acknowledgments


References












2O3)rdquo





2CO3












1-2 pp 191ndash196 2010
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of
























Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

hydrogen reduction of hematite ore fines to magnetite ore...

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