Proceedings of the 7th World Congress on Mechanical, Chemical, and Material Engineering (MCM'21)
Prague, Czech Republic Virtual Conference – August, 2021
Paper No. MMME 116
DOI: 10.11159/mmme21.116

Upgrading the Fe Grade of Magnetite Concentrate Using a Magnetic
Hydro-Sizer
Evans Vincent Rissenga1, Willie Nheta1

University of Johannesburg, Department of Metallurgy, Faculty of Engineering and the Built Environment. Mineral
Processing and Technology Research Centre. P.O Box 524 Auckland 2006, Johannesburg, South Africa.
evrissenga@gmail.com; wnheta@uj.ac.za

1

Abstract - In this study, a magnetic hydro-sizer was used to upgrade the final Fe concentration grade of a magnetite ore. The impact ofthe magnetic field intensity and water flow rate on the concentration grade were investigated. The chemical composition, mineralogicalphases and surface topography of the feed to the hydro-sizer were analysed using XRF, XRD and SEM respectively. The results revealed
that the feed to the magnetic hydro-sizer contained 61.25% Fe. Major phases in the feed are magnetite, hongquiite, calcium
magnesium catena-silicate and quartz. SEM results showed that the sample was well liberated. A concentrate containing 63.9% Fe
was produced whilst operating at particle size distribution of 80% passing 180 µm, water flow rate of 290m3/hr and a magnetic intensityof 1350gauss. The higher the magnetic intensity, the lower the Fe grade of the concentrate. The higher the water flow rate, the higher
the Fe grade of the concentrate. For a magnetic hydro-sizer, operating field should be between 1200 and 1350 gauss and a water flowrate above 260m3/hr for the final concentration of magnetite.
Keywords: Magnetic separation, magnetite, low grade iron ore, magnetic hydro-sizer

1. Introduction

Iron forms the bases for the development of the steel industry. Due to increase in demand of steel in recent years incountries such as China, India and Malaysia, gradual depletion of high-grade magnetite ores has been noticed leading to theexploitation of low-grade ores worldwide [1]. However, processing of low-grade magnetite ores is characterised by poor
separation efficiencies due to poor liberation and complexity of the ore. Magnetite is strongly magnetic and magnetic
separation is generally applied in the beneficiation process of magnetic ores [2]. Magnetic separation is one of the methods
that has been used for almost 200 years in the concentration of iron ores and is still used extensively even today. Most
common used magnetic separation process is carried out on a drum separator [3].
Magnetite is commonly produced as a by-product from processing of phosphate and copper minerals. The phosphateand copper minerals are recovered using flotation process, producing a rich concentrate of phosphate and copper minerals,
and tailings containing most of the magnetite [4]. The tailings can be treated further to recover magnetite through a seriesof magnetic separation circuits [5]. The efficiency of separation on drum magnetic separators is not determined by magnetic
field but rather by the product of the magnetic induction and the field gradient. As a result, they are not a good concentrating
equipment for the final concentrate.
A hydro-sizer is a classifier used in mineral processing to classify material in terms of the physical properties of a particle
such as the particle size and density of the particle [6]. Water plays an important role in hydro-sizer as it is used to dilute theslurry to improve concentration of the denser particles from the lighter particles. However, a hydro-sizer can be modified byaddition of magnets (magnetic field) and separation will be depended on particle size, density, and magnetic susceptibility.
Separation of particles in a solution using a magnetic field is more selective and efficient and often much faster thancentrifugation or filtration. The efficiency of a magnetic hydro-sizer is affected by the rate of water injection into the hydrosizer, feed density, particle size distribution, particle density and magnetic intensity of the magnetic units [7].
In this paper, the potential of using a magnetic hydro-sizer for the final upgrading of magnetite concentrate is presented.
The research focused on the effect of magnetic intensity, particle size distribution and dilution water feed rate into themagnetic hydro-sizer on the Fe grade of the final concentrate.

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2. Methodology

2.1. Materials
Magnetite ore samples used for the research are from the slimes dam at Phalaborwa Foskor mine, South Africa.
Foskor treats phosphate ore using flotation process and their tailings material contains 45 to 53% Fe in the form ofmagnetite. The magnetic ore sample used comprised of Silicon Oxide(1,0,1) Magnetite, syn (2,2,2), Hongquiite(1,1,1), diopside high, Calcium magnesium catena-silicate(1,3,1) and most importantly Magnetite, syn(5,1,1) , which
has the metal of value as iron (Fe),with an overall percentage of 46.9 % Fe.
2.2. Methods
The industrial test was carried out at a South African Ore Beneficiation (SAOB) plant. The plant was stabilised in
preparation for sample campaign and all spillage pumps running were stopped. Sampling condition were divided into
three condition for this research, which included the different magnetic field intensity, grind and water injection into themagnetic hydro-sizer. Particle size distribution (PSD) analysis was done to determine the optimum grind at which mostof the non-magnetic minerals are separated from the magnetic minerals. PSD was determine using screen sieves andsieve shaker in the laboratory. Chemical composition of the samples was determined using X-ray fluorescence (XRF).
The mineralogical phases for the three samples: run of mine (ROM), feed to the magnetic Hydro-sizer andunderflow (U/F) which is the final product from the magnetic hydro-sizer, were identified using an X-Ray Diffraction7000, shimadzu corp., China operated at the wavelength of 0.154060 nm, generated at 20KV and 30 mA using Cu Kαradiation. Scanning was conducted at 2 minutes for 2 theta (θ) values between 10 and 90 degrees.
2.2.1 The impact of Magnetic intensity on Fe grade of the final concentration.
The impact of high magnetic intensity on the Fe grade of the final concentration was investigated by operating themagnetic hydro-sizer with varying intensities from 1400 Gauss to 1460 Gauss. The feed PSD were kept constant at 80%
passing 180µm and the water injection flow rate at 290m³/hr. Samples collected from the concentrate were analyzed
using XRF.
The impact of low magnetic intensity on the Fe grade final concentration was investigated by varying magnetic
intensity from 1350 gauss to 1400 gauss. Once again, the water flow rate and Feed PSD were kept constant at 290m³/hr
and 240m³/hr, respectively. The concentrate samples at each intensity were collected and analysed using XRF.
2.2.2 Impact of dilution water flow rate on Fe grade of the final concentration.
The impact of dilution water flow rate on Fe grade of the final concentration was investigated by varying the dilution
water flowrate from 240 m³/hr to 290 m³/hr. Magnetic intensity and PSD of feed was kept constant at 1360 Gauss and
80% passing 180µm, respectively. Samples of the feed, concentrate and tailings were collected at each flowrate andanalysed using XRF and SEM.

3. Results and discussion

3.1 Sample Characterisation
The feed to the hydro-sizer was analysed for elemental composition and the results are shown in Table 1. From
Table 1, it can be seen that the Fe content of hydro-sizer feed was 62.129% which is below the required target of 63.5%
Fe. The results also show that major contaminants are Ti (2,734%), Mg (2,085%) and Si (1,91%). Titanium minerals areparamagnetic, and they can be recovered into the concentrate with the increase in magnetic intensity. Mg and Si minerals
are diamagnetic, and they can only be recovered into the concentrated through entrainment [8].

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Table 1: Elemental composition of the hydro-sizer feed

Element% WtO
30.1

Fe62,129

Mg
2,085

Al
0,052

Si
1,91

Ca
0,684

Ti
2,734

Mn
0,306

3.2. Mineralogical Composition of the Feed to the Hydro-Sizer
The mineralogical composition of the ROM, feed to the hydro-sizer and the hydro-sizer underflow was determined using
XRD and the results are shown in Fig. 1. Major mineral phases in the ROM are quartz and calcium magnesium catena silicate(Ca Mg Si2 O6) which are diamagnetic, magnetite (Fe3O4) which is ferromagnetic material and hongquiite (TiO) which isparamagnetic [9]. Most of the silicate minerals are removed during the first stages of magnetic separation using a drum
magnetic separator prior to the upgrading using the hydro-sizer.
M: Magnetite
Q: Quartz
C: Catena
H: Hongquiite

M

Q

H

M

H

M M

M

M

H

MC

Q

M

CUIFintensity (cps)

M

Q

M Q

Q
010

M
20

M

H

C

FEEDM

Q

Q

H

M
Q

Q
30

C
H
40

M H
5060

2-Theta (degree)

70

80

ROM
90Fig. 1: XRD pattern for ROM, hydro-sizer Feed and Underflow (U/F)

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3.3. Elemental Analysis and Mineral Distribution in the Feed to the Hydro-Sizer Samples
Microstructural characterization was carried out by optical microscopy (Keyence VH-Z50L) and scanning electron
microscopy (Tescan VEGAIILMH) (SEM). A commercial image analysis software was employed for quantitative
measurement of the microstructure parameters.

MagnetiteQuartz

AB

CFig. 2: The hydro-sizer feed sample topography as obtained from SEM and EDS scan.

Different phase structures were determined, mostly magnetite phases and quartz. The SEM micrographs of Fig.
2(a)–(c) present a general view of the tensile deformed microstructures (ε = 5%, 10% and 20%, respectively). Ultrafinebasket-weave microstructural characteristic, with the width of α laths about 1.5 μm was observed. The microstructureof the magnetite and gangue minerals observed via optical microscopy are presented in Fig. 2. Based on the statisticalresults derived via an optical microscopy, the fine microstructure observed was mostly at a content of about 79.8%
magnetite, 5.86% silica and 0.345% hongquiite and other minerals.
3.4. The Impact of Magnetic Intensity on Fe Grade of the Final Concentrate

The impact of magnetic intensity on Fe grade of the final concentrate was investigated and the results are shown inFig. 3. It can be seen that the higher the intensity the lower the grade. This can be due to the paramagnetic material
reporting into the final concentrate as well as entrainment of diamagnetic particles. Apart from magnetic intensity,
magnetic field orientation plays a vital role on the performance of a magnetic separator [10]. The best results of 63.53%
Fe were obtained at a magnetic intensity of about 1200 gauss and at 290 m³/hr flowrate, which indicated an iron upgradeof about 1.4% iron in the product from the hydro-sizer feed.

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63.6

Fe Grade (%)

63.4
63.2
63
62.8
62.6
62.4
62.2
62
1150

1200

1250
1300
1350
Magnetic Intensity (Gauss)

1400

1450

Fig. 3: Impact of magnetic intensity on the Fe grade of the final concentrate, 290 m³/hr flowrate

Fe Grade (%)

3.5. The Impact of Dilution Water Flow Rate on the Fe Grade of the Concentrate
The impact of dilution water flow rate was investigated, and the results are illustrated in Fig. 4. As the water flow rateincreased from 240 m³/hr to 290 m³/hr, the Fe grade in the final concentrate increased from 62.2% to 63.9 % respectively.
The dilution flow rate into the magnetic hydro-sizer plays a very important role in the upgrading of magnetite where a steadyincrease on grade is seen as the flowrate into the separator is increased. High water flowrate into the hydro-sizer increases
the safe area of the material thus reducing the possibility of entrainment of the non-magnetic materials, like silica. The nonmagnetic fines are thus overflown with the hydro-sizer overflow, leaving huge improvement in the grade of iron reportingto the final concentrate. The results have shown an improvement of above 1.7% in Fe grade.

64.2
64.0
63.8
63.6
63.4
63.2
63.0
62.8
62.6
62.4
62.2
62.0

220

240

260
280
Water Flowrate (m³/hr)

300

Fig. 4: Impact of water flowrate injected into the hydro-sizer on the Fe grade of final concentrate, 1350 gauss.

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3.6. The effect of grind on the recovery and grade of Fe
The effect of grind was investigated, and it was found that grind can play an important role on the upgrading of iron in
the concentrate grade, as shown in Fig. 5. The result shows as the amount of solid passing the 180µm increased, the iron
grade of the final concentrate improved. Fine grind results in the liberation of the nonmagnetic material locked in themagnetic materials, which can report into the final product because they were associated with the magnetic material.
9080% passing 80 µm70605040302010054565860626466%Fe-GradeFig. 5: Impact of PSD on the Fe Grade of the final concentrate, 1350 Gauss, 290m3/h water flowrate.

4. Conclusion

The results have shown that the major mineralogical phases in the hydro-sizer feed are magnetite, calcium magnesium
catena silicate, hongquiite and quartz. Most of the titanium (IV) oxide was incorporated into the concentrate with the increasein the magnetic intensity. At particle size distribution of 80% passing 180µm, water flowrate of 290m3/h and magnetic
intensity of 1360 gauss, a concentrate containing 63.9% Fe was produced. For a magnetic hydro-sizer, operating field should
be between 1200 and 1350 gauss and a water flow rate above 260m3/hr for the final concentration of magnetite. The effectof grind on the upgrading of iron in the final concentrate has shown that the finer the grind the better the separation ofmagnetite, which then improve iron in the final concentrate. With the correct operating conditions, a magnetic hydro-sizer
can be used to upgrade the final concentrate of a magnetite concentrating plant. Further studies need to target the interactive
effects of the water flowrate and magnetic intensity on the recovery and grade of magnetite using the design of experiments(DoE) approach.

Acknowledgements

The authors would like to acknowledge University of Johannesburg, and NRF for sponsorship and financial supportof this research.

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