|Cynta Immanuela Lamandasa||Department of Metallurgical and Materials, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia|
|Agung Setiawan||Department of Metallurgical and Materials, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia|
|Sri Harjanto||Department of Metallurgical and Materials, Faculty of Engineering, Universitas Indonesia, Kampus UI Depok, Depok 16424, Indonesia|
|M. Akbar Rhamdhani||Fluid and Process Dynamics (FPD) Research Group, Department of Mechanical and Product Design Engineering, Swinburne University of Technology, Melbourne, VIC 3122, Australia|
study investigated the effects of adding pulverized biomass from palm kernel
shells as a reductant on phase transformation and microstructure during the
carbothermic reduction of ilmenite. The ilmenite concentrate was reduced at a
temperature range of 1000–1200°C for up to 3 h in an inert atmosphere. The
amount of reducing agents used in this study varied between 6 and 10 wt.%. The
reduced samples were studied using an X-ray diffractometer and optical
microscope to analyze their phase transformations and microstructures. The
results revealed that near-complete dissociation of ilmenite was attained when
biomass was added up to 8 wt.%. Complete dissociation of ilmenite occurred, and
Ti3O5 formed when ilmenite was reduced with 9 wt.%
biomass at 1200°C for 2 h. At this point, the microstructural study showed that
a significant amount of metallic iron, with an average metallic iron size of
241.5 µm2, had
Biomass; Carbothermic reduction; Ilmenite; Palm kernel shell
The world’s rutile reserves are low compared to ilmenite reserves (U.S. Geological Survey, 2021), and their amount is dwindling because rutile is still used in the titanium extraction process. An upgrading process is carried out to increase the titanium content by separating iron from titanium oxide in ilmenite and by increasing TiO2 levels.
Currently, the upgrading process of ilmenite is carried out using the Becher, Murso, Laporte, Benelite, Austpac, Dunn, Kataoka, Altair, and BHP Billiton processes (Nguyen and Lee, 2019). However, the Becher, Murso, and Laporte processes require high energy consumption that yields high CO2 emissions and are less effective due to the need to conduct an acid leaching process after pyrolysis. In addition, in the Benelite process, ilmenite is limited as a feed. The Austpac process is less effective because it requires higher acidity for the leaching of the remaining magnetic iron. The Dunn process is also considered less environmentally friendly because of the highly corrosive Cl2 handling process, while the Kataoka, Altair, and BHP Billiton processes are also considered less environmentally friendly because of the subsequent leaching process (Nguyen and Lee, 2019). The Becher process involves reducing the iron in ilmenite to metallic iron by way of burning coal at 1200°C followed by aeration and leaching to remove the metallic iron (Gázquez et al., 2014).
Many aspects of the carbothermic reduction process of ilmenite have attracted much research. Tripathy et al. (2012) reduced ilmenite at 1000–1150°C using graphite and coke as reducing agents. According to the findings, graphite is effective as a reducing agent at a reduction temperature of 1150°C, and it can work within a shorter time interval. Meanwhile, coke is more effective when heated to 1000°C. El-Hussiny et al. (2008) reduced ilmenite with breeze coke at 800–1200°C and discovered that reducibility increased with the stoichiometric amount of coke. Furthermore, the rate of reduction increased as the temperature rose. Bhalla et al. (2017) carried out the carbothermic reduction of ilmenite with graphite as the reducing agent at temperatures between 1050°C and 1350°C under an argon atmosphere. They reported that the rate of reduction increased with increases in temperature and decreases in particle size. Ilmenite reduction can be accomplished through a step in which iron oxide is first reduced to metallic iron and then to iron carbide, while titanium oxide is initially reduced to TinO2n-1 with the possibility of later lower oxide formation. The particle core (original ilmenite grain) retains its composition, with a slight reduction in iron and titanium oxides in the early stages of reduction and is partially reduced in later stages. According to Wang et al. (2008), the reduced ilmenite phase formed by graphite contains iron, ilmenite, rutile, reduced rutile, pseudorutile, and graphite below 1200°C. From 900–1000°C, however, reduced rutile was absent. Above 1200°C, the Ti3O5 phase appears alongside iron, rutile, reduced rutile, Fe3C, and pseudobrookite solid solution.
The utilization of biomass as an alternative carbon source has been studied in many fields, for example, the co-gasification process with blending fuel (biomass and coal) and reductant agents in the carbothermic reduction of minerals. Ahmad et al. (2020) investigated the effect of a torrefied palm kernel shell and Mukah Balingian coal on product yield and gaseous composition in the co-gasification process. They concluded that pretreatment with this biomass mixture resulted in higher gas yields and lower tar and charcoal yields, thereby improving the co-gasification performance. Meanwhile, many researchers have investigated the use of biomass (including palm oil waste) as a renewable carbon source for the carbothermic reduction process of minerals and ores. Using the biomass of palm kernel shell waste as a reducing agent, iron oxide in low-grade iron ore could be reduced completely to magnetite and partially to wustite when up to 30% of the biomass was used in the reduction process (Abd Rashid et al., 2014). Adding up to 30% of sawdust biomass containing 12.5% fixed carbon and 80.7% volatile matter successfully reduced the iron ore to its metallic iron phase at 1200°C (Strezov et al., 2006). Furthermore, Srivastava et al. (2013) investigated the use of fine wood biomass as a reducing agent in the smelting of magnetite concentrate. They found that pig iron nuggets with metallization of 98.10% and a total Fe of 97.16% could be produced at a temperature of 1450°C and a reaction time of 20 min. In addition, Zhang et al. (2017) studied the roasting process of low-grade limonite ore with biomass at temperatures of up to 750°C for 45 min in a vacuum atmosphere. They reported that after dehydration at high temperatures, the iron-bearing materials in limonite ore became ?-Fe2O3, which was then reduced to Fe3O4 by biomass reduction. Fe3O4 will convert to Fe2SiO4 at temperatures above 650°C, causing magnetic materials to be reduced and the calcined ore’s magnetism to be weakened. Furthermore, at a temperature of 550°C with a biomass ratio of 15%, the recovery rate and iron grade were 72% and 58%, respectively.
However, published reports on the use of biomass as a reducing agent in the upgrading process of ilmenite are still lacking. Ismail et al. (1982) investigated the decomposition of preoxidized ilmenite using sawdust biomass as a reducing agent at 1100°C for 3 h. They reported that two steps occurred during the decomposition process. The first step was the conversion of Fe3+ in ferric pseudobrookite to Fe2+ in ilmenite. At this point, the concentration of ferric pseudobrookite decreased over time, while the concentration of ilmenite increased. This indicates that ilmenite was reformed by a recombination reduction mechanism in the early stages of reduction. The second step was the conversion of Fe2+ to metallic iron. As a result, the concentration of ilmenite gradually decreased, while the concentrations of metallic iron and rutile increased (suboxides of titanium). Recently, Setiawan et al. (2020) investigated the carbothermic reduction of ilmenite using palm kernel shells as a reducing agent. They found that a reduction temperature of 1200°C using a solar furnace promoted pseudobrookite formation, and a unique line morphology in metallic iron was observed instead of the spherical structure found in samples heated in electric furnaces. They found that the mechanisms behind the carbothermic reduction of complex weathered ilmenite using the biomass of palm kernel shells and graphite as reducing agents were based on the diffusion of oxygen atoms (Setiawan et al., 2021).
Thus, this research aims to investigate the effects of biomass addition during the carbothermic reduction of ilmenite on phase transformation and microstructure evolution. The phase characterization and detailed microstructures during the carbothermic reduction of ilmenite at up to 1200°C for different reaction times were observed and discussed.
effects of adding palm kernel shell biomass as a reducing agent on the
carbothermic reduction of ilmenite were studied. The following conclusions were
drawn: (1) The phase analysis showed the near-complete dissociation of ilmenite
at 1200°C for 2 h with the addition of 6 and 8 wt.% biomass. Complete
dissociation was reached as more biomass was added. At this point, the phases
formed were metallic iron, rutile, pseudobrookite, and anosovite; (2) The
morphology of metallic iron consisted of the streak and granule shapes. The
particle size of metallic iron was greatly enhanced with increased added
biomass. The maximum average grain size of metallic iron formed was found to be
241.5 µm2 with the addition of 9 wt.% of biomass at 1200°C for 2 h.
authors would like to express their gratitude for the financial support from
the Directorate of Research and Public Engagement, Universitas Indonesia, under
the PUTI Prosiding Grant 2020 (NKB-1199/UN2.RST/HKP.05.00/2020) and the PUTI
Kolaborasi Internasional 2020 (NKB-797/UN2.RST/HKP.05.00/2020). PT Monokem
Surya, Karawang, Indonesia is thanked for providing ilmenite concentrate. Dr.
Mark I Pownceby (CSIRO Mineral Resources, Australia) is gratefully acknowledged
for providing XRF data.
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