BENEFICIATION, DEPHOSPHORIZATION AND DESULPHURIZATION OF AGBAJA IRON ORE

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CHIME, ONYEJIUWA THOMPSON

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ABSTRACT

Iron ores are used in blast furnace for the production of pig iron; Agbaja Iron ore has
an estimated reserve of over I billion metric tonnes. Unfortunately, this large reserve
cannot be utilized for the production of pig iron due to its high sulphur and
phosphorus contents. In addition, the ore cannot be beneficiated easily like Itakpe
and Oshokoshoko iron ores because of its texture. This work studied the
beneficiation, dephosphorization and desulphurization of Agbaja iron ore. The raw
ore was beneficiated using several techniques namely; oil agglomeration technique,
rapid magnetic separation technique, Humphrey spiral technique, froth flotation
technique and jigging table technique. Chemical leaching, bacteria leaching and
pyrometallurgical methods were used to reduce the phosphorus and sulphur contents
of the ore. Hydrochloric acid, sulphuric acid and nitric acids of different
concentrations were used at various leaching times, acid concentrations and particle
sizes. The parameters varied in bacterial leaching include bacterial loads and
leaching time. Atomic Absorption Spectrophotometer, X-ray fluorescence
spectrophotometer, Digital muffle furnace and Absorbance-concentration technique
were used for experimentation and chemical analysis. Central composite design
technique was applied to obtain optimum conditions of the processes. Surface
response plots were also obtained. Oil agglomeration technique was adjudged the
best beneficiation technique with an iron assay of 67.05%. The percentage degrees
of dephosphorization and desulphurization were found to increase with increase in
acid concentration and leaching time and a decrease in particle size for the three
acids. The experimental results for percentage removal of phosphorus for HCl,
H2SO4 and HNO3 were 98.12%, 99.56% and 98.55% respectively, while that of
sulphur were 85.56%, 87.77% and 84.44%. The optimum % removal of phosphorus from the model for HCl, H2SO4 and HNO3 were 97.97%, 99.87% and 99.74%
respectively and that of sulphur were 89.66%, 87.73% and 84.94%. Results obtained
using bio leaching showed that percentage degrees of biodephosphorization and
biodesulphurization depended on the bacterial load and leaching time and passed
through a maximum with increase in leaching time. The experimental results for %
removal for phosphorus for mixed Colony, Colony I, Colony II, Colony III, Colony
IV, and Colony V were 86.00%, 81.01%, 82.28%, 81.01%, 82.28% and 81.01%
respectively and that of sulphur were 99.88%, 99.78%, 99.78%, 99.78%, 99.89%
and 99.78% respectively. Also the optimum percentage removal of phosphorus
using mixed Colony, Colony I, Colony II, Colony III, Colony IV, and Colony V
were 94.86%, 90.91%, 92.21%, 90.91%, 92.02% and 90.91% while that of sulphur
include, 99.94%, 99.99%, 99.43%, 99.43%, 99.93% and 99.43%, respectively.
Critical observation of the results showed that there was no remarkable difference
between the experimental values and CCD model values confirming the authenticity
of the CCD models. The result of this work has shown that Agbaja Iron Ore if
properly processed can be used in our metallurgical plants and also can be exported
since phosphorus and sulphur contents of the ore have been reduced drastically.

TABLE OF CONTENTS

Title page i
Certification ii
Dedication iii
Acknowledgement iv
Abstract v
Table of Content viii
List of Tables xvi
List of Figures xvii

Chapter One
1.0 INTRODUCTION 1
1.1 Background of the Study 1
1.2 Statement of the Problem 6
1.3 Aims and Objectives 7
1.4 Scope of the Study 8
1.5 Significance of the Study 9

ix
Chapter Two
2.0 LITERATURE REVIEW 11
2.1.1 Past work on beneficiation of iron ores 11
2.1.2 Past work on beneficiation of Agbaja iron ores 13
2.2 Past work on chemical leaching 16
2.2.1 Effects of temperature on chemical leaching 16
2.2.2 Effects of pH on chemical leaching 17
2.2.3 Effects of Surface area/particle size and weight on chemical leaching 20
2.2.4 Effects of redox potential on chemical leaching 23
2.2.5 Effects of concentration of leaching medium Fe(II) and Fe(III) on chemical
leaching 25
2.2.6 Effects of oxygen activity and other oxidant concentration on chemical
leaching 26
2.2.7 Effects of impurity compound and various additive on chemical leaching28
2.2.8 Variation in lattice parameters and density during chemical leaching 29
2.2.9 Thermodynamics of chemical leaching 31
2.3.0 Kinetics of Chemical leaching 37
2.3.1 Effects of temperature on bacterial leaching 40
2.3.2 Effects of pH on bacterial leaching 41

x
2.3.3 Effects of surface area/grain size and weight of sample on
bacterial leaching 43
2.3.4 Effects of concentration of leaching medium Fe(II) and Fe(III) on bacterial
leaching 44
2.3.5 Kinetics of bacterial leaching 46
2.3.6 Effects of different strains of bacteria on leaching 48
2.4 Pass work on dephosphorization of Agbaja iron ore using HCl 92
2.4.1 Past work on H2SO4 dephosphorization 92
2.4.2 Past work on nitric acid dephosphorization 95
2.4.3 Past work on desulphurization using bacteria 96

Chapter Three
3.0 MATERIALS AND METHODS 99
3.1 Materials 99
3.2 Beneficiation of Agbaja iron ore 100
3.2.1 Selective oil agglomerization 101
3.2.2 Gravity separation technique by Jigging table 102
3.2.3 Rapid magnetic separation technique 103
3.2.4 Humphrey spiral technique 103

xi
3.2.5 Froth Flotation method 104
3.2.6 Jigging table run on magnetic separation technique 105
3.2.7 Jigging table and magnetic separation technique run on froth flotation
technique 105
3.3 Dephosphorization and desulphurization of Agbaja iron ore using
hydrochloric acid 105
3.4 Dephsophorization and desulphurization of Agbaja iron ore using sulphurix
acid 107
3.5 Dephosphorization and desulphurization using nitric acid 108
3.6 Dephosphorization and desulphurization of Agbaja iron ore using bacteria 109
3.6.1 Microbial reagents (Nutrient Agar) 109
3.6.2 Microbial culture 109
3.6.3 Isolation of bacteria 110
3.6.4 Microscopic examination of isolation 110
3.6.5 Preparation of inoculums and leaching of scrubbed sample 110
3.7 Factorial design 111
3.7.1 Central composite plan 111
3.7.2 Development of statistical multivariable models 114

xii
Chapter Four
4.0 RESULTS AND DISCUSSION 118
4.1 Analysis of beneficiation of Agbaja iron ore 118
4.2 Dephosphorization of Agbaja iron ore using hydrochloric acid 129
4.2.1 Effect of HCl concentration on the percentage degree of dephosphorization of
Agbaja iron ore 129
4.2.2 Effect of leaching time on the percentage degree of dephosphorization 134
4.2.3 Effect of particle size on the percentage degree of dephosphorization of
Agbaja iron ore 138
4.3 Desulphurization of Agbaja iron ore using HCl 143
4.3.1 Effect of HCl concentration on the percentage degree of desulphurization of
Agbaja iron ore 143
4.3.2 Effect of leaching time on the percentage degree of desulphurization of
Agbaja iron ore 147
4.3.3 Effect of particle size on the percentage degree of desulphurization 151
4.4 Dephosphorization of Agbaja iron ore using sulphuric acid 156
4.4.1 Influence of sulphuric acid concentration on the degree of dephosphorization
of Agbaja iron ore 156

xiii
4.4.2 Influence of leaching time on the percentage degree of dephosphorization of
Agbaja iron ore 160
4.4.3 Influence of particle size on percentage degree of dephosphorization 164
4.5 Desulphurization of Agbaja iron ore using sulphuric acid 169
4.5.1 Influence of sulphuric acid concentration on desulphurization of Agbaja iron
ore 169
4.5.2 Effect of leaching time on the percentage degree of desulphurization of
Agbaja iron ore 173
4.5.3 Effect of particle size on the percentage degree of desulphurization of Agbaja
iron ore 177
4.6 Dephosphorization of Agbaja iron ore using nitric acid 181
4.6.1 Effect of nitric acid concentration on the percentage degree of
dephosphorization of Agbaja iron ore 181
4.6.2 Effect of leaching time on the dephosphorization of Agbaja iron ore 185
4.6.3 Effect of particle size on the percentage degree of dephosphorization of
Agbaja iron ore 189
4.7 Desulphurization of Agbaja iron ore using nitric acid 194
4.7.1 Effect of nitric acid concentration on the percentage degree of
desulphurization of Agbaja iron ore 194

xiv
4.7.2 Influence of leaching time on the percentage degree of desulphurization of
Agbaja iron ore 198
4.7.3 Influence of particle size on the percentage degree of desulphurization of
Agbaja iron ore 202
4.8 Biodephosphorization of Agbaja iron ore using bioleaching 206
4.8.1 Influence of leaching time on the percentage degree of biodephosphorization
for different colonies 206
4.8.2 Influence of microbial population on the percentage degree of
biodephosphorization of Agbaja iron ore for different colonies 214
4.9 Biodesulphurization of Agbaja iron ore using bioleaching 221
4.9.1 Influence of leaching time on the percentage degree of biodesulphurization of
Agbaja iron ore for different colonies 221
4.9.2 Influence of microbial population on the percentage degree of
biodesulphurization of Agbaja iron ore 226
4.10 Surface response plots 231

xv
Chapter Five
5.0 CONCLUSION AND RECOMMENDATIONS 259
5.1 Conclusion 259
5.2 Recommendations 260
5.3 Contributions to Knowledge 261

References 262

Appendix A 278
Appendix B1 279
Appendix B2 281
Appendix B3 282
Appendix B4 330
Appendix B5 331
Appendix C 332

CHAPTER ONE

INTRODUCTION
1.1 BACKGROUND OF STUDY
Iron is one of the most abundant element in the earth’s crust, being the fourth
most abundant element at about 5% by weight (Alafara et al, 2007). Astrophysical
and seisimic evidence indicate that iron is even more abundant in the interior of the
earth and is apparently combined with nickel to make up the bulk of planets core.
Iron ores are mainly composed of iron oxides, and oxyhydroxides, with other
accessory gangue phases. These iron ores cannot be used in the production of steel
in their raw states. For them to be maximally used in the production of quality steel,
they must be upgraded or beneficiated.
Although the terms coarse-grained, intermediate size and fine grained are not
assigned definite or specific dermacative values in mineral processing, a fine grained
iron ore is often construed as one in which mineral matter is so finely disseminated
within the gangue matrix that crushing and grinding, to effect liberation, produce
minute particles that respond poorly to conventional beneficiation equipment and/ or
processes (froth flotation, magnetic separation gravity separation etc) (Uwadiale,
1990).
2

Uwadiale and Whewell (1988) observed that the utilization of Agbaja iron
ore is hampered by its poor response to established industrial beneficiation
techniques, this is as a result of fine grained texture of the iron ore.
Phosphorus may be incorporated either into the crystal lattice of iron oxides
or into the gangue minerals (Dukino et al, 2000). This element has a deleterious
effect on the workability of steel (Muhammed and Zhang, 1989). For that reason, in
most places only premium low phosphorus ores (less than 0.08w%P) are extracted
leaving many iron mines around the world enriched in un-tradable, high –
phosphorus iron ore (Cheng et al, 1999; Dukino et al, 2000).
If steel is produced with high level of phosphorus and sulphur that steel will
be brittle and can easily crack hence the need for dephosphorization and
desulphurization. Depending on the degree of association of phosphorus with the
minerals in the ore body, iron ore can be dephosphorized either physically or
chemically (Kokal, 1990; Fonseca et al, 1994).
In the former case, communition followed by wet magnetic separation or
froth flotation is generally employed when the phosphates gangue minerals appear
as discrete inclusions in the iron oxide matrix (primary mineralization) (Kokal,
1990; Fonseca, et al, 1994). However, when phosphorus is disseminated in the iron
oxide structure, possibly forming cryptocrystalline phosphates or forming solid
3

solutions with the iron oxide phases (secondary mineralization), the
dephosphorization can only proceed by chemical routes (Kokal, 1990); Fonseca et
al, 1994; Dukino et al, 2000).
The chemical dephosphorization and desulphurization involve in the
hydrometallurgical processing of the ore, that is, the selective leaching of
phosphorus and sulphur in the ore with a reagent usually acid or base. Since early in
the 19th century, Jacob (1872) suggested the use of sulphuric acid to remove
phosphorus compounds from lumps of iron ore. Nevertheless, a real scientific
interest in hydrometallurgical processing of high phosphorus iron ores can only be
noticed after the last third of the 20th century, when several papers and patents were
published (Feld et al, 1968; Gooden et al, 1974; Muhammed and Zhang, 1989;
Kokal, 1990; Fonseca et al, 1994; Cheng et al, 1999; Dukino et al, 2000). Ever
since, traditionally low prices of iron ore products had impeded the large-scale
industrial application of chemical dephosphorization. At the present time, an
increase in world steel production has increased demand for iron ore with a
consequent increase in the price for this commodity, making hydrometallurgical
phosphate removal viable (Kokal et al, 2003).
4

In the last eight years, the situation of iron ore markets has changed
dramatically due to an increase in the world steel consumption, pushed up mainly by
the economic growth of China and other Asian emerging markets.
On the search for more environmentally sound technologies for the mining
industry, biological processes to extract metals from ores, pre-treating metallic ores
or removing contaminants from metallic ores or industrial wastes have been
developed for different metallic mineral resources (Jain and Sharma, 2004). The
removal of silica and alumina from iron through biological means has also been
proposed (Natarajan et al, 2001; Pradhan et al, 2006).
The biological treatment of ores to remove contaminants, often referred to as
bioleaching or bio beneficiation (Jain and Sharma, 2004), is another variant of the
above mentioned chemical processing. In such a process, the micro organisms
produce, as a consequence of their metabolism, a chemical by-product (mineral
acids, organic acids, polymers, enzymes). The chemical by-products, in turn attack
the gangue minerals contained in the ore, dissolving them and thus producing their
selective removal (Jain and Sharma 2004). The microorganism may or may not, get
some advantage from this solubilization process (such as a nutrient or energy
source). In the iron mining industry, the use of microorganisms could offer an
5

environmentally friendly alternative to the traditional chemical dephosphorization
processes (Delvasto et al, 2005).
In a phosphorus limited environment, microorganisms will be obligated to
extract phosphorus from mineral sources to supply their growth needs (Banfield et
al, (1999)) and this is the theoretical base for the bio dephosphorization of high
phosphorus iron ores. Organic acids producing filamentous fungi have been used to
remove phosphorus from ores in a series of reports (Parks et al, 1990; Buis, 1995;
and Delvasto et al, 2005).
The use of acidithiobacillus ferrooxidans in the metal extractions including
iron in different media have been extensively reported (Bartels et al, 1989; Boon et
al, 1988). Some researchers previously investigated the simultaneous leaching of
metal oxides and sulphides. Gosh and Imai (1985) have reported that iron-oxidizing
bacterium, Thiobacillus ferrooxidans, leached manganese from manganese dioxide
in the presence of the sulphide ores of copper.
However the main draw back of these investigations was that the used strains
were not associated with the ore being treated. When microorganisms are
inoculated in a familiar environment, the microorganisms, as a general rule compete
better in terms of adaptation and cause fewer ecological distortions than exogenous
micro organisms. Consequently, if an efficient bio dephosphorization process has to
6

be implemented for treating a determined raw material, studies on the micro biota
naturally living in such a substratum and evaluation of its desired properties should
be the starting step.
The mechanism and process analysis of desulphurization of Agbaja iron ore
concentrate using powdered potassium trioxochlorate (v) (KClO3) as an oxidant has
been reported (Nwoye, 2009). Concentrates were treated at a temperature range
500oC – 800oC. The results for the extent of desulphurization reveal that
simultaneous increase in both the percentage of the oxidant added and treatment
temperature used (up to 15g KClO3 per 50g of ore and maximum temperature of 800oC, respectively) are the ideal conditions for the best desulphurization efficiency.
At the point of concluding this research work there has been no published
work on dephosphorization and desulphurization of Agbaja iron ore using nitric acid
and sulphuric acid. Also there is no reported work done on this ore using bacteria
harvested from the ore. These lend credence to the originality of this work.

1.2 STATEMENT OF THE PROBLEM
Agbaja iron ore is the largest iron deposit in Nigeria with an estimated
reserve of over 1 billion tonnes. This iron ore has high phosphorus content and
relative high sulphur content. Consequently, the iron ore deposit is abandoned in
7

both research work and exploitation. The presence of high phosphorus and sulphur
in steel making cause brittleness or crackability depending on the type of steel
products. The conventional beneficiation techniques cannot be used to beneficiate
Agbaja iron ore because of the texture of the ore. Uwadiale (1990) observed that
crushing and grinding the ore to effect liberation, produce minute particles that
respond poorly to conventional beneficiation processes. As a result of these
problems of high phosphorus, relatively high sulphur and the difficulty in using
conventional techniques, there is need to package effective beneficiation,
desulphurization and dephosphorization techniques to solve these problems in order
to make the iron ore economically viable.

1.3 AIMS AND OBJECTIVE
The aims of this work include:
1. To determine the best beneficiating method of Agbaja iron ore that
will yield total iron of 67% – 68%
2. To use different beneficiation techniques to beneficiate Agbaja iron
ore.
3. To dephosphorize and desulphurise Agbaja iron ore using
hydrochloric acid.
8

4. To remove phosphorus and sulphur from Agbaja iron ore using
sulphuric acid.
5. To dephosphorize and desulphurize Agbaja iron ore by nitric acid.
6. To use five different colonies and a mixed colony of bacteria to
dephosphorize and desulphurize Agbaja iron ore
7. To employ central composite design to develop models and to subject
them to optimization processes

1.4 SCOPE OF THE STUDY
1. Chemical analysis of Agbaja iron ore as received and scrubbed or
deslimed will be carried out in order to obtain the chemical
composition of the ore.
2. Different beneficiation techniques will be employed to beneficiate
Agbaja iron ore – gravity separation technique by jigging table, rapid
magnetic separation technique, Humphrey spiral technique, froth
flotation technique, jigging table technique run on magnetic separation
technique, jigging table and magnetic separation technique run on
froth flotation technique and oil agglomeration technique.
9

3. The use of different moles of hydrochloric acid, sulphuric acid and
nitric acid on different particle sizes of the ore at different leaching
times will be employed to dephosphorize and desulphurize the Agbaja
iron ore.
4. Different types of bacteria will be isolated from Agbaja iron ore. Each
of the isolates and combination of the isolates will be used to inoculate
the ore at different bacterial populations, and leaching times, in order
to dephosphorize and desulphurize the ore.
5. The results will also be subjected to central composite design in order
to develop models that will be optimized.

1.5 SIGNIFICANCE OF THE STUDY
The significance of this study stems on the need, reality and possibility of
harnessing the low grade, high phosphorus, high sulphur content Agbaja iron ore
using techniques that will beneficiate, dephosphorize and desulphurize the iron ore
to desired marketable values. When these are achieved it will improve the quality of
the iron ore thereby enhancing the economic potentials of the ore. It will also add to
export potentials of the Nigerian economy.
10

It is expected that this study when carried out would provide relevant data for
reference in similar future studies since no extensive and detailed work had been
carried out on this ore. The developed models will be applied to future works on
these areas.