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. Th
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).
2Uwadiale 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
3solutions 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).
4In 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
5environmentally 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
6be 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
7both 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.
84. 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 processes1.4 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.
93. 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.
10It 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.