1821
Air-Cooling Technology for Magnetising Roasting of
Limonite Ore
Xinran Zhu, Yuexin Han, Yanjun Li, Yifei Cao
School of Resources and Civil Engineering, Northeastern University, Shenyang, China
National-local Joint Engineering Research Center of High-efficient Exploitation Technology for
Refractory Iron Ore Resources
ABSTRACT: Magnetizing roasting is an effective method to treat limonite ore resources. Cooling is a vital
process for roasted ores before subsequent grinding and magnetic separation. In this study, the feasibility of air-
cooling technology was first investigated for magnetising roasting of limonite ore. The fluidization magnetising
roasting and magnetic separation experiments were conducted, and the effects of air cooling, water quenching,
and nitrogen cooling on the separation index were investigated. The samples were characterized by chemical
element analysis, XRD, and VSM. The mineral phase transformation and magnetism variation of roasted ores
were compared with different cooling processes. The proposed air-cooling technology will have a wide range of
applications for iron ore exploration, particularly in regions with water shortages.
Keywords: limonite ore, magnetising roasting, air cooling, maghemite
INTRODUCTION
Limonite ore, a mixture of iron oxide and iron hydroxide,
is an important iron ore resource and has a widespread
distribution globally (Wu et al., 2017, 2018). However,
the exploitation of limonite ore is a worldwide technical
problem owing to its complex mineral composition, high
water content, low iron grade, high content of impurities,
and processing difficulties from sliming during the crush-
ing and grinding process (Zhou et al., 2016, Zhang et al.,
2017). At present, it is difficult to process limonite ore by
conventional methods such as gravity concentration, mag-
netic separation, froth flotation, and their combinations
(Song et al., 2002, Tang and Valix, 2006).
Currently, magnetization roasting is commonly
regarded as an effective method for treating limonite
ore (Fu et al., 2019, Roy et al., 2020). The main iron
minerals of limonite ore, goethite (α-FeOOH) and hematite
(α-Fe2O3), transform to magnetite (Fe3O4) during magne-
tization roasting (Valix and Cheung, 2002a, 2002b). In this
process, goethite is first dehydroxylated to hematite over a
wide range of temperatures of 150–500 °C (α-FeOOH →
α-Fe2O3 +H2O), and subsequently, hematite is reduced to
magnetite using reductants such as CO or H2 (α-Fe2O3
+CO → Fe3O4 +CO2, α-Fe2O3 +H2 → Fe3O4 +H2O)
(O’Connor et al., 2006, Jang et al., 2014, Ponomar, 2018).
Synthetic magnetite is a ferrimagnetic mineral and is easily
recovered from nonmagnetic gangue by low-intensity mag-
netic separation (Astuti et al., 2017, Maksum et al., 2018).
In practice, cooling of the roasted product is a vital pro-
cess in magnetization roasting (Yang et al., 2016, Sun et al.,
2018). First, the high-temperature roasted product needs to
be cooled prior to magnetic separation. Second, oxidation
Air-Cooling Technology for Magnetising Roasting of
Limonite Ore
Xinran Zhu, Yuexin Han, Yanjun Li, Yifei Cao
School of Resources and Civil Engineering, Northeastern University, Shenyang, China
National-local Joint Engineering Research Center of High-efficient Exploitation Technology for
Refractory Iron Ore Resources
ABSTRACT: Magnetizing roasting is an effective method to treat limonite ore resources. Cooling is a vital
process for roasted ores before subsequent grinding and magnetic separation. In this study, the feasibility of air-
cooling technology was first investigated for magnetising roasting of limonite ore. The fluidization magnetising
roasting and magnetic separation experiments were conducted, and the effects of air cooling, water quenching,
and nitrogen cooling on the separation index were investigated. The samples were characterized by chemical
element analysis, XRD, and VSM. The mineral phase transformation and magnetism variation of roasted ores
were compared with different cooling processes. The proposed air-cooling technology will have a wide range of
applications for iron ore exploration, particularly in regions with water shortages.
Keywords: limonite ore, magnetising roasting, air cooling, maghemite
INTRODUCTION
Limonite ore, a mixture of iron oxide and iron hydroxide,
is an important iron ore resource and has a widespread
distribution globally (Wu et al., 2017, 2018). However,
the exploitation of limonite ore is a worldwide technical
problem owing to its complex mineral composition, high
water content, low iron grade, high content of impurities,
and processing difficulties from sliming during the crush-
ing and grinding process (Zhou et al., 2016, Zhang et al.,
2017). At present, it is difficult to process limonite ore by
conventional methods such as gravity concentration, mag-
netic separation, froth flotation, and their combinations
(Song et al., 2002, Tang and Valix, 2006).
Currently, magnetization roasting is commonly
regarded as an effective method for treating limonite
ore (Fu et al., 2019, Roy et al., 2020). The main iron
minerals of limonite ore, goethite (α-FeOOH) and hematite
(α-Fe2O3), transform to magnetite (Fe3O4) during magne-
tization roasting (Valix and Cheung, 2002a, 2002b). In this
process, goethite is first dehydroxylated to hematite over a
wide range of temperatures of 150–500 °C (α-FeOOH →
α-Fe2O3 +H2O), and subsequently, hematite is reduced to
magnetite using reductants such as CO or H2 (α-Fe2O3
+CO → Fe3O4 +CO2, α-Fe2O3 +H2 → Fe3O4 +H2O)
(O’Connor et al., 2006, Jang et al., 2014, Ponomar, 2018).
Synthetic magnetite is a ferrimagnetic mineral and is easily
recovered from nonmagnetic gangue by low-intensity mag-
netic separation (Astuti et al., 2017, Maksum et al., 2018).
In practice, cooling of the roasted product is a vital pro-
cess in magnetization roasting (Yang et al., 2016, Sun et al.,
2018). First, the high-temperature roasted product needs to
be cooled prior to magnetic separation. Second, oxidation