ABSTRACT

This research investigated the sintering characteristics of sinter blends produced from
Agbaja iron ore concentrate of high phosphorus (P2O5 = 1.50 – 2.14%) and low silica
content and Itakpe iron ore concentrate of low phosphorus (P = 0.03%) and high silica in
order to produce fluxed sinters suitable for pig iron production. The ores (Agbaja and
Itakpe) were concentrated using conventional beneficiation techniques and then blended
in the ratios of 10-70% Agbaja and 90-30% Itakpe. The blends were mixed with coke
breeze, limestone and moisture to produce fluxed sinters. The physical and chemical
characteristics of the produced sinters vis-a-visa abrasion resistance, shatter index,
tumbler index, reducibility, reduction decrepitating and chemical composition were
determined. The results obtained revealed that both the physical and chemical properties
of the produced sinters compared favourably with existing blast furnace specifications for
sinters. However, the sinter with 10% Agbaja and 90% Itakpe possessed physical and
chemical properties that are close to the specified properties of sinter for use in the blast
furnace for Pig iron production. Therefore, sinter blend with 10% Agbaja and 90%
Itakpe iron concentrates can be recommended for use in blast furnace for the production
of pig iron.

 

 

TABLE OF CONTENTS

TITLE PAGE ……………………………………………………………………………………………… i
DECLARATION ………………………………………………………………… ii
CERTIFICATION ……………………………………………………………… iii
DEDICATION ………………………………………………………………….. iv
ACKNOWLEDGEMENT ……………………………………………………. v
ABSTRACT ……………………………………………………………………… vi
TABLE OF CONTENTS …………………………………………………… vii
LIST OF TABLES …………………………………………………………….. xi
LIST OF FIGURES …………………………………………………………. xiiii
LIST OF APPENDIX ……………………………………………………….. xiii
NOTATIONS ………………………………………………………………….. xiv
CHAPTER ONE …………………………………………………………………. 1
1.0 INTRODUCTION ………………………………………………………………….. 1
1.1 Statement of problem ……………………………………………………………… 4
1.2 Aims and Objectives of the Study ……………………………………………… 5
1.3 Justification and Significance of the study ………………………………….. 5
1.4 Limitations of the research ……………………………………………………….. 6
viii
CHAPTER TWO ………………………………………………………………… 7
2.0 LITERATURE REVIEW ………………………………………………………… 7
2.1 INTRODUCTION ………………………………………………………………….. 7
2.2 Nigerian Iron Ore Deposits ………………………………………………………. 7
2.3 Agbaja Iron Ore Deposit. Reserve and Chemical compositions ……… 9
2.3.1 Chemical Composition of Agbaja Iron Ore ……………………………………………… 9
2.3.2 Itakpe Iron Ore Deposit, Reserve and Chemical Analysis …………………………. 10
2.3.3 Chemistry and Mineralogy of Itakpe Iron Ore ………………………………………… 11
2.4 Fluxes ……………………………………………………………………………………11
2.4.1 Basic fluxes ……………………………………………………………………………………… 12
2.4.2 Aluminous Fluxes …………………………………………………………………………….. 12
2.4.3 Acid fluxes………………………………………………………………………………………. 12
2.5 Definition and Concept of Sintering …………………………………………..13
2.6 Background of Sintering ………………………………………………………….14
2.7 Reduction Reactions that occurred During Sintering …………………….16
2.8 Process Variables during Sintering …………………………………………….17
2.8.1 Roles of sinter returns in sintering ………………………………………………………… 18
2.8.2 Positive effect of sinter return on gas permeability ………………………………….. 18
2.9 Types of Sinters …………………………………………………………………….18
2.10 Desired Qualities of sinters ……………………………………………………19
2.11 Comparison between sinters and pellets ………………………………….21
ix
2.12 Charge Calculations for sinter production ………………………………..22
2.13 Mechanisms and Kinetics of reduction of blast furnace burden …..23
CHAPTER THREE …………………………………………………………… 30
3.0 EXPERIMENTAL TECHNIQUES …………………………………………..30
3.1 MATERIALS ………………………………………………………………………..30
3.2 Methods …………………………………………………………………………………31
3.2.1 Charge calculation …………………………………………………………………………….. 31
3.2.2 Determination of Abrasion Index Value (AIV) ……………………………………….. 33
3.2.3 Determination of Shatter Index Value (SIV) ………………………………………….. 34
3.2.4 Determination of Tumbler Index Value (TIV) ………………………………………… 34
3.2.5 Determination of Reducibility Index Value (RIV) …………………………………… 34
3.2.6 Determination of Reduction Decrepitation Index Value (RDIV)………………… 35
3.2.7 Determination of Chemical Composition of Sinters …………………………………. 35
3.2.8 Determination of Phosphorous content of the blends by calculation …………… 35
CHAPTER FOUR …………………………………………………………….. 38
4.0 RESULTS AND DISCUSSION ……………………………………………….38
4.1 Results ………………………………………………………………………………….38
4.2.0 Discussion ……………………………………………………………………………..42
4.2.1 Abrasion Index Values (AIV)…………………………………………………………….. 42
4.2.2 Shatter Index Values (SIV) …………………………………………………………………. 43
4.2.3 Tumbler Index Values (TIV) ……………………………………………………………….. 44
x
4.2.4 Reducibility Index Values (RIV) ………………………………………………………….. 45
4.2.5 Reduction Decrepitation Index Values (RDIV) ………………………………………. 46
4.2.6 Chemical Analysis of Sinters ………………………………………………………………. 47
CHAPTER FIVE ………………………………………………………………. 48
CHAPTER FIVE ………………………………………………………………. 49
5.0 CONCLUSION AND RECOMMENDATION ……………………………49
5.1 CONCLUSION ……………………………………………………………………..49
5.2 RECOMMENDATIONS …………………………………………………………49
REFERENCES …………………………………………………………………. 51

 

 

CHAPTER ONE

1.0 INTRODUCTION
In order to ensure the survival of any industry, raw materials input must be critical and
continuously be in supply both in large quantity and in good quality. Even though Nigeria
is blessed with large quantity of iron ore deposit of about three billions (3 x 109) metric
tonnes, these deposit cannot be used directly in pig iron production without beneficiation
because some of them are of low grade and contain impurities, which can be detrimental
to the properties of the steels to be produced. Some researches have already been carried
out on the beneficiation of some of these ores for use for pig iron production by, Adigwe
(1973), and Oloche et al., (1996).
Eventhough Nigeria is blessed with large reserves of proven and unproven iron ore
deposits, only one of the deposits in the proven reserves is currently being exploited and
processed that is the Itakpe iron ore deposit. This deposit has an estimated reserve of
about 200 millions (200 x 106) metric tonnes and has been earmarked to be supplied to
Ajaokuta and Delta steel plants. However, this deposit, based on the designed
requirement of the Ajaokuta plant, will only last for 25 years (Adigwe, 1983). This is
grossly inadequate for the establishment of a formidable foundation for a well- projected
and integrated iron and steel plants. Also the Agbaja iron ore deposit, eventhough the
largest iron ore deposit in Nigeria estimated at over 2 billions (2 x 109) metric tonnes, has
a very high phosphorous content in addition to its extremely fine grained texture. This
feature has discouraged its utilization to date (BRGM Report, 1983). With these apparent
problems it has become very necessary to find ways of using this vast deposit of iron ore.
2
The most probable way to utilize the large quantity of iron ore is by blending with other
iron ores with lower phosphorous content. Therefore, the objective of this work is to
blend Itakpe super concentrate of low phosphorous with the Agbaja concentrate of high
phosphorus so as to produce a sinter mix that can serve as feed to blast furnace for pig
iron production.
Kurt (1980) said that both sinters and pellets are used as feed with iron but sinters are the
common and suitable sources of feeds to the blast furnace. The process of sintering
comprises high temperature-treatment (above 10000C) of iron fines on a moving grate,
blended with fluxes and coke breeze (finely divided coke) to form hard lumps or iron-rich
material suitable for use as blast furnace feed (Williams, 1983). In iron ore sintering, the
aim is always to produce a strong but porous agglomerate from a sandy uncompacted
mass. Tupkary et al., (1998) also noted that in order to obtain smooth and hard “rapid
driving operation”, the burden charged in the furnace should ideally posses the following
physical and chemical properties.
Physical properties
1. A close size range with minimum of fines.
2. An ability to withstand the physical stresses incurred on being transported to
the furnace, charged to the hopper and the bells and, finally in the furnace.
3. Non –decrepitating nature.
4. An ability to withstand mild reducing condition at lower temperature without
breaking.
3
5. A good bulk reducibility so as to obtain closed equilibrium conditions
between solid and gas phases in the stack.
6. Low swelling tendency during reduction.
7. A high softening temperature with a narrow temperature range of fusion.
Chemical properties
1. A high percentage of iron to gangue ratio.
2. A low percentage of silica, alumina and a low alumina to silica ratio.
3. Good overall chemistry of the burden to ensure adequate desulphurization of
metal and absorption of coke ash in slag.
4. Good overall chemistry to ensure clean slag and metal separation at minimum
temperature and free flow of both slag and metal.
In addition, sintering is also carried out to improve size grading and reducibility of iron
ore concentrate to avoid wasting of fines, reduction of the quantity of coke used in the
blast furnace and lastly to use up waste materials from blast furnace flue dust.
The quantity of sinter produced by the integrated blast furnace route has risen from
371.2mt in1982 to 422.7mt in 1994, accounting for 55.0% to 57.9% of total crude steel
production. Therefore more than 50% of the total liquid iron production during this
period was supplied via the blast furnace for which sinters remain the major iron feed
stock. However, Pellets are gradually replacing sinters to a certain degree, depending on
available local process, economic and environmental circumstances with the global
4
output of the two products in 1994 standing at 534.3mt and 224.7mt for sinter and pellet
respectively (Madugu, 2001).
Iron ore sintering is a complex thermo-chemical process and the qualities of sinters being
produced affect the blast furnace performances in terms of fuel consumption, smooth
operation, and rate of production. (Nath et al., 2004). Presently, the proportion of sinters
in the charge of most blast furnaces amounts to 90% of the total weight of charge.
Recently, the use of sinters is gradually increasing as mines produce more dusty,
complex and lean ores, which need to be ground to a very fine particle before
beneficiation. The world trend for use of sinters in pig iron production via the
conventional blast furnace (acid and basic) is given in Appendix 1.0. Ogg et al., (1977)
observes that the production and use of sinter for pig iron and hot metal manufacture
continues to grow in 90% of the world’s steelmaking areas. This expansion is often faster
than the growth of iron production, showing that the use of sinter in the blast furnace will
continue to increase since the iron content of the ores to be sinter is generally rising and
thereby lower the slag volume in the blast furnace.
1.1 Statement of problem
Agbaja ore deposit has an estimated reserve of about 2 billions (2 x 109) metric tonnes,
containing high phosphorus (P2O5 = 1.5-2.14%) and low silica, because of this, the
deposit is not suitable for pig iron production. Phosphorus exists in iron ores as
phosphorus pentoxide (P2O5) and this cannot be reduced during beneficiation technique
and agglomeration. Kudrin (1989) observes that the effects of the phosphorus on the
machined iron properties and steel are enormous. In order to use Agbaja iron ore, it is
5
imperative to blend the ore with Itakpe iron ore with a reserve of about 200-300 million
metric tonnes having low phosphorus (0.03%) and high silica to take care of the high
phosphorus in Agbaja iron ore and also to provide large source of iron ore for sinter
production.
1.2 Aims and Objectives of the Study
The main aim is to determine the optimum-blending ratio, the ratio at which the two ores,
when blended will produce sinters with physical and chemical properties that are suitable
for pig iron production via the blast furnace process. The results obtained will also be
compared with the minimum standard specifications required of sinters for pig iron
production via the blast furnace route.
1.3 Justification and Significance of the study
The Agbaja iron ore deposit exists in large quantity and it is very close to Ajaokuta.
Because of high phosphorus associated with it, there is the need to intensify effort in
order to find the means of utilizing the ore economically. One of such means/alternatives
is by blending which is the main focus of this research work.
If this research is successful, it will find a solution to the use of Agbaja through blending
with Itakpe iron ore for the production of sinters for Ajaokuta Steel Company. This will
augment the source of raw material input for pig iron production at Ajaokuta Steel
Company. Also the sinter to be produced could be exported as this will attract foreign
exchange earning.
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1.4 Limitations of the research
As a result of non-availability of some equipment, certain tests, like swelling index, hot
compression strength and low temperature characteristics may not be carried out.

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