Journal of Minerals & Materials Characterization & Engineering, Vol. 4, No. 1, pp 21-30, 2005
jmmce.org Printed in the USA. All rights reserved
21
Effectiveness Of Gravity Concentration For The Beneficiation Of
Itakpe (Nigeria) Iron Ore Achieved Through Jigging Operation.
P. A. OLUBAMBI
1,2*
and J. H. POTGIETER
2
1
Department of Metallurgical and Materials Engineering,
Federal University of Technology, Akure, Nigeria
2
School of Process and Materials Engineering,
University of the Witwatersrand, Johannesburg, South Africa
Abstract:
This study investigates the
1
effectiveness of gravity concentration for the
beneficiation of Itakpe (Nigeria) iron ore achieved through jigging operations. Iron ore
obtained from Itapke Iron Ore Mining Project, Kogi State, Nigeria which contains a very
high amount of quartz as revealed by x-ray diffraction was crushed using the laboratory
dodge crusher and ground in a laboratory ball mill. Particle size analysis was carried
out over the range of +4750 µ m and -75 µ m in 12 different mesh sizes, and the ore was
jigged in a Laboratory Denver Mineral Jig. The operating variables used to determine
the recovery effectiveness of jigging include; particle size, dilution ratio and bedding
thickness. Recovery of iron ore was assessed by determining the percentages of Fe in the
underflow and overflow using the Atomic Absorption spectrometry (AAS) method.
Optimum iron ore recovery of 71% was achieved when the jig was operated at medium
stroke and speed, with a feed slurry of average dilution and at a particle size of 600µm.
Keywords: Iron ore; Jigging; Particle size; Dilution ratio; Bedding thickness.
INTRODUCTION
The Itakpe iron ore deposit has a reserve of about 200 million tonnes with an
average iron ore content of 36%. This has to be beneficiated at a rate of 8 million tonnes
per year to produce 64% Fe concentrate as sinter material for the Ajaoukuta blast furnace
and 68% Fe concentrate as pellet feed for the direct reduction plant at Aladja, all in
Nigeria. At this production rate, large quantities of tailings are obtained as waste product
of the beneficiated iron ore (Adepoju and Olaleye 2001).
Since the goal of every mineral processing operation/technique is to effectively
separate the valuable material from the gangue with minimum metal loss in tailings, the
need to develop and employ a sustainable, effective and relatively economical method of
separation is imperative. The concentration of the valuable minerals from the gangue
involves exploitation of the differences in the mineral properties of the ore after effective
comminution (Akande and Olaleye 2000).
*
Corresponding author; E-mail address: [e-mail], [e-mail] (P. A. Olubambi)

22P. A. Olubambi and J. H. PotgieterVol. 4, No. 1
Magnetic separation and flotation are the most widely accepted technologies for
the upgrading of iron ore particles, but these processes result in iron concentrate with
high amounts of very fine and/or interlocked silica particles (Yang, et al 2003). Mohanty
(2002) also found that the ability of flotation to treat mixed-phase (middling) and weakly
hydrophobic particles is not satisfactory. To address the aforementioned problems and
thus to achieve a higher iron ore recovery, several new attempts and technologies are
being developed with an added aim of achieving economical and environmental benefits
through use of the jigging method (Parkinson, 1989; Yang, 1996; Honaker, et al, 1996;
Galvin et al 2002).
The mineralogical characterization of Itakpe iron ore shows that it contains
mainly hematite, magnetite and quartz whose specific gravities give sound basis for
adopting the gravity concentration technique. In this study, the effectiveness of gravity
techniques for concentrating iron ore from bulk Itakpe (Nigeria) iron ore was studied
using the jigging method and the effects of operating variables on the recovery of iron ore
using the laboratory Denver Mineral Jig were investigated.
MATERIALS AND METHODS
The bulk ore used in this study was obtained from the Itakpe mine, north of
Okene in Kogi State, Middle Belt Region of Nigeria. Its chemical composition as
revealed by X-ray fluorescence is as shown in Table1.
TABLE 1: Chemical Composition of Itakpe Iron Ore
MineralFe
2
O
3
Fe
3
O
4
SiO
2
CaOAl
2
O
3
MgOTiO
2
Composition30.8819.0542.051.253.200.370.20
The ore was broken into sizes that could be fed into the jaw crusher using a
sledgehammer. Crushing was carried out in a laboratory dodge crusher and ground in a
laboratory ball mill. Ore sieving was carried out using the laboratory sieve shaker as
described by Pryor (1965) and Adepoju & Olaleye (2001) by placing 6000g of the ore in
the uppermost ASTM standard sieve. The nest of the ASTM sieves was loaded with the
ore and allowed to vibrate for 5 minutes. After the required time, the nest of sieves was
taken apart and the amount of material retained on each sieve was weighed. Composition
was determined by X-ray fluorescence.
100 grams of the ore of the same size from the product of the sieve analysis was
stored in a tray to form the feed or head material for the jigging operation. Steel balls
were spread to form a layer on the screen of the mineral jig as a bedding material to
varying depths. The spigot of the hutch compartment was plugged with rubber cork and
water was added to cover the ragging in the feeding compartment. The head or feed was
fed into the feeding compartment.

Vol. 4, No. 1 Effectiveness Of Gravity Concentration For The Beneficiation Of 23
Itakpe (Nigeria) Iron Ore Achieved Through Jigging Operation
Feed material mixed with water at varying dilutions was added to the jig and the
jigging process was allowed for 4 minutes. At the end of each jigging operation, the
spigot of the hutch compartment was opened and the product was collected as the
underflow. The overflow materials left in the feeding compartment were scooped and
washed out. The two products (underflow and overflow) were dried, weighed and
recorded. The experiments were repeated with varying bedding thickness, dilution rates
and particle sizes.
The amount of iron ore in each of the underflow and overflows were evaluated by
determining the percentages of Fe in the samples using Atomic Absorption Spectrometry
(AAS) method. A sample weight of 2g was the standard measurement for this
experiment. Samples were dried prior to analysis. Samples were well mixed before
weighing to make sure they were homogenous. The samples were digested with 20 ml of
0.01 M Hydrochloric acid (HCL) solution by shaking in plastic centrifuge tubes for 15-20
minutes. Concentration of each of the samples was measured against standard solutions.
The composition of iron and silicon in each sample was then ascertained using a Buck
Scientific model 200 atomic absorption spectrophotometer with air-acetylene flame.
RESULTS AND DISCUSSION
The results obtained from the particle size analysis are as shown in Table 2 and
the compositional analyses revealed by X-ray are graphically presented in Figures 1, 2
and 3. Tables 3, 4, and 5 show the results obtained from the jigging operations and they
are as graphically illustrated in Figures 4, 5 and 6.
TABLE 2: Particle Size Analysis of Iron Ore
Sieve size
Range (mm)
Normal
Aperture
Size
(µm) N
Weight
Retained
(g)
Weight
%
retaine
d (g)
Cumula
tive
Wt%
Retaine
d (g)
Cumula
tive %
Passing
(g)
P
Log NLog P
+475047504507.657.6592.353.681.96
-4750+20002000110019.0326.6873.323.301.86
-2000+170017005559.47536.15563.8453.231.8
-1700+11801180116019.8555.98544.0153.071.64
-1180+85085078513.4169.41530.8352.931.48
-850+60060066011.2780.68519.3152.781.28
-600+35035072512.4293.1056.8952.540.83
-350+300300951.6294.7255.2752.480.72
-300+2502501803.0897.052.1952.400.34
-250+22022012.5.2198.0151.9852.340.29
-220+11011030.7798.7851.2152.040.08
-110+7575.75.01598.801.201.870.07
-75-75701.21000.000.00.0
5848.22

24P. A. Olubambi and J. H. PotgieterVol. 4, No. 1
Size analysis
It can be observed from Table 2 that the smaller the aperture of the sieve, the
lower the weight% of Itakpe iron ore retained. The aperture range of 1180µm has the
most retained weight% followed by 850µm and then 2000µm respectively. It was also
observed in Table 2 that 2000µm has the most retained quantity of quartz followed by
1180µm then 350µm. The rate of reduction of both iron ore and quartz varies (Figures 1
to 3). Quartz dissipates easily, breaking down to fines with little applied stress. Though
the hardness value of quartz (i.e. 7 on the Mohr’s scale) is a bit higher than the iron ore
(Hematite (5.5-6.5), Magnetite (5.5-6), it is far more brittle than iron ore (Gribble, 1988).
The disparity in the cumulative weight% retained and cumulative passing of the
ore is demonstrated by Figures 1 and 2. From both graphs, it can be seen that the
cumulative weight% retained and cumulative passing graphs are inversely proportional to
each other. The Gate-Gaudin-Schumann’s representation of sieve analysis in Figure 3
shows that the compositional distributions of the materials are linearly and uniformly
distributed over a wide size range.
Separation effectiveness:
The results, as shown in Tables 4, 5, and 6 and Figures 4, 5 and 6, revealed that
iron ore concentrate (underflow) was effectively separated from the tailings (overflow),
Fig. 1 SIZE ANALYSIS GRAPH FOR THE ORE
0
20
40
60
80
100
120
-100001000200030004000500
Sieve size (mm)
Cummulative weight % retained
Size analysis of Iron ore
Size analysis of quartz

Vol. 4, No. 1 Effectiveness Of Gravity Concentration For The Beneficiation Of 25
Itakpe (Nigeria) Iron Ore Achieved Through Jigging Operation
which are essentially quartz. Theoretically, effective separation was possible because the
quotient of the difference in their specific gravities is greater than 2.5 (Equation 1)
Fig. 2 Graph of cummulative passing against Aperture size
0
20
40
60
80
100
120
-1000010002000300040005000
Aperture size (MM)
Cummulative% passing (g) P
Iron ore
Quartz
Fig. 3 GATE-GAUDIN-SCHUMAN REPRESENTATION OF SIEVE ANALYSIS
0
0.5
1
1.5
2
2.5
00.511.522.533.54
LOG N
LOG P
IRON ORE
QUARTZ

26P. A. Olubambi and J. H. PotgieterVol. 4, No. 1
fL
fh
DD
DD
−
−
=
0.161.2
0.150.6
−
−
= 3.42(1)
From the same results, it was observed that the overflow, i.e. the tailings still have
an appreciable percentage of Fe total. This Fe total in the gangue may come from
magnetite in the ore, which was not effectively separated. Recall from the above
equation, as the quotient reduces, the effectiveness of the separation reduces. The specific
gravity of magnetite is between 4.6 and 5.2, indicating that the quotient varies is between
2.4 and 2.8.
0.161.2
0.120.5
−
−
= 2.60
0.161.2
0.160.4
−
−
= 2.24(2)
Should there be more magnetite of specific gravity 4.6, the efficiency of
separation decreases. This will eventually lead to a greater percentage of the Fe
3
O
4
going
to the tailings
TABLE 3: Jigging Operation with Thin Bed, Average Dilution with Medium Stroke and Speed
UNDERFLOWOVERFLOWSieve
Size
(µM)
Feed
(g)
Wt
(g) x
% Fe% SiRatio
of
Conc
entrat
ion
Wt
(g) y
% Fe% SiRatio
of
Conc
entrat
ion
%
Losses
100-
(x+y)
11802004065.434.61.8915030.469.62.2910
85020011067332.039031.568.52.170
60020013070.529.52.397033.466.61.990
TABLE 4: Jigging Operation with Thin Bed, Excess Dilution with Medium Stroke and Speed
UNDERFLOWOVERFLOWSieve
Size
(µM)
Feed
(g)
Wt
(g) x
% Fe% SiRatio
of
Conc
entrat
ion
Wt
(g) y
% Fe% SiRatio
of
Conc
entrat
ion
%
Losses
100-
(x+y)
11802005561.538.51.5912526.572.52.7720
85020011061391.568068.531.52.1710
60020011060.539.51.539067.532.52.080

Vol. 4, No. 1 Effectiveness Of Gravity Concentration For The Beneficiation Of 27
Itakpe (Nigeria) Iron Ore Achieved Through Jigging Operation
TABLE 5: Jigging Operation with Thick Bed, Excess Dilution with Medium Stroke and Speed
UNDERFLOWOVERFLOWSieve
Size
(NM)
Feed
(g)
Wt
(g) x
% Fe% SiRatio
of
Conc
entrat
ion
Wt
(g) y
% Fe% SiRatio
of
Conc
entrat
ion
%
Losses
100-
(x+y)
118020011066.533.51.989031.768.32.150
85020012067332.037030.569.52.2810
60020011066.833.22.018528722.575
Effects of dilution ratio:
The influence of dilution on the recovery of iron ore using jigging is as revealed
in Tables 4, 5, and 6. The volume of water in the hutch compartment of the laboratory
mineral jig provides the necessary dilation required for particles separation. The highest
recovery was achieved with average dilution. Low dilution (higher percent solids) led to
hindered settling, with a decrease in the falling rate of particles leading to overcrowding
in the fixed hutch compartment. Excess dilution gave rise to randomness of particles in
the same fixed hutch compartment. With medium dilution, a state of free settling sets in
where the possibility of particle crowding was very negligible.
FIG. 4 Graph of Ratio of concentrate against particle size
1
1.5
2
2.5
5006007008009001000110012001300
Particle size (Micronmeter)
Ratio of concentration
iron ore underflow with thin bed excess dilution
Iron ore underflow with thin bed average
dilution
Iron ore underflow with thick bed excess dilution

28P. A. Olubambi and J. H. PotgieterVol. 4, No. 1
FIG. 5 Graph of rate of recovery of Fe against particle size.
60
62
64
66
68
70
72
5006007008009001000110012001300
Particle size
Recovery of Fe
Thin bed excess dilution
Thin bed average dilution
Thick bed excess dilution
Fig. 6 FFECT OF FEED SIZE ON RATE OF RECOVERY OF Fe
54
56
58
60
62
64
66
68
70
72
1180850600
FEED SIZE (Micronmeter)
RATE OF RECOVERY OF Fe (%)
thin bed, excess dilution
Thin bed, average dilution
Thick bed, excess dilution

Vol. 4, No. 1 Effectiveness Of Gravity Concentration For The Beneficiation Of 29
Itakpe (Nigeria) Iron Ore Achieved Through Jigging Operation
Effects of bedding thickness
The effects of bedding material and thickness of the bed on the recovery of iron
ore are shown in Figures 4, 5 and 6. The bedding material and the thickness of the
bedding materials used has an effect on the %Fe recovered as shown in Figure 6. Thick
bedding causes more friction action during the suction stage, making concentration less
possible. Thin bedding reduces friction during suction and also, allows easy passage of
the Fe concentrate during jigging.
Effects of Particle size:
The effect of the particle size on the recovery of iron ore is also shown in Tables
4,5, and 6, and Figures 4, 5 and 6. The highest recovery was achieved at 600µm. Lower
separation efficiency in finer particles is believed to be caused by the negligible mass
associated with this size particles. Particles so small, that settle in accordance with
Stroke’s law, are unsuitable for concentration (Wills, 1989). Lower recovery of Fe at
larger particle sizes may be due to the reduced possibilities of the larger particles passing
through the jig screen. A coarser particle will have a reduced chance of passing through
the jig screen and thereby will report to the overflow as tailings (Mohanty, et al 2002).
CONCLUSION
The results of this project work have clearly shown that effective separation of iron
ore concentrate from bulk Itakpe iron ore by jigging operations is possible. It is clearly
revealed that the effectiveness of the separation was greatly influenced by the operating
variables of the jig and the particle size of the ore. The result of the work has also shown
that the optimum Fe recovery could be achieved when the jig is operated at medium
stroke and speed under the conditions of a thin bed with feed slurry of average dilution at
a particle size range of 600µm.
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