Direct reduction of low grade nickel laterite ore to produce ferronickel using isothermal temperature gradient Zulfiadi Zulhan, and Ian Gibranata Citation: AIP Conference Proceedings 1805, 040003 (2017); doi: 10.1063/1.4974424 View online: https://doi.org/10.1063/1.4974424 View Table of Contents: http://aip.scitation.org/toc/apc/1805/1 Published by the American Institute of Physics Articles you may be interested in Extraction of nickel from nickel limonite ore using dissolved gaseous S 2 air AIP Conference Proceedings 1805, 070004 (2017); 10.1063/1.4974445 Reduction of lateritic iron ore briquette using coal bed reductant by isothermal - temperature gradient method AIP Conference Proceedings 1805, 040007 (2017); 10.1063/1.4974428 Thermochemical analysis of laterite ore alkali roasting: Comparison of sodium carbonate, sodium sulfate, and sodium hydroxide AIP Conference Proceedings 1805, 040008 (2017); 10.1063/1.4974429 Implementation of reverse flotation method to reduce reactive and non-reactive silica in bauxite ore from West Kalimantan AIP Conference Proceedings 1805, 050004 (2017); 10.1063/1.4974435 High-temperature experimental and thermodynamic modelling research on the pyrometallurgical processing of copper AIP Conference Proceedings 1805, 040004 (2017); 10.1063/1.4974425 Atmospheric leaching of nickel and cobalt from nickel saprolite ores using the Starved Acid Leaching Technology AIP Conference Proceedings 1805, 020002 (2017); 10.1063/1.4974408
Direct Reduction of Low Grade Nickel Laterite re to Produce Ferronickel Using Isothermal Temperature Gradient Zulfiadi Zulhan *, Ian Gibranata Department of Metallurgical Engineering, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Jl. Ganesha 10, Bandung, 40132, Indonesia * Corresponding author: zulfiadi.zulhan@gmail.com Abstract. In this study, low grade nickel laterite ore was processed by means of isothermal-temperature gradient method to produce ferronickel nugget. The ore and coal as reductant were ground to obtain the grain size of less than 0.25 mm and 0.425 mm, respectively. Both ground laterite ore and coal were mixed, agglomerated in the form of cylindrical pellet by using press machine and then reduced at temperature of 1000 C to 1400 C in a muffle furnace. The experiments were conducted at three stages each at different temperature profile: the first stage was isothermal at 1000 C; the second stage was temperature gradient at certain heating rate from 1000 to 1400 C; and the third stage was isothermal at 1400 C. The heating rate during temperature gradient stage was varied: 6.67, 8.33 and 10 C/minute. No fluxes were added in these experiments. By addition of 10 wt% of coal into the laterite nikel ore, product of ferronickel nugget was formed with the size varies from 1-2 mm. However, by increasing the coal content, the size of ferronickel nugget was decreased to less than 0.2 mm. The observation of the samples during the heating stage showed that ferronickel nugget grew and separated from the gangue during temperature gradient stage as it achieved the temperature of 1380 C. Furthermore, the experiment results indicated that the recovery of ferronickel can be increased at lower heating rate during temperature gradient stage and longer holding time for final isothermal stage. The highest nickel recovery was obtained at a heating rate of 6.67 C/minute. Keywords: nickel laterite ore, ferronickel, isothermal-gradient temperature INTRDUCTIN Nickel is one of commercially important metal which is mainly used for the production of stainless steel (approximately 60%) 1. The rapid rise in stainless steel demand has led to a dramatic increase in the production of nickel metal in the recent years 2 and strategically, Indonesia has nickel reserve of about 577 million tons that spread in Sulawesi, Kalimantan, Maluku, and Papua 3. To date, pyrometallurgical methods using either rotary kiln electric furnace (RKEF) or mini blast furnace (MBF) has been commercially used to extract nickel from nickel laterite ores in Indonesia. The RKEF plant were constructed since the 1970s to process saprolitic nickel laterite ore to produce ferronickel or nickel matte. More recently, some MBF plants were installed to produce nickel pig iron from saprolitic ore as well as blend of limonite and saprolite nickel ores. In general, pyrometallurgical route requires higher energy consumption for smelting to separate the metal and slag. Therefore, most of limonitic nickel laterite ore is not well utilized until now as it leads to higher production cost of smelting plant. An alternative route of direct reduction followed by physical separation with less energy consumption was introduced and applied at Nippon Yakin Kogyo 4. In this research, the production of ferronickel from limonitic nickel laterite ore was investigated by means of isothermal-temperature gradient method. The method is currently under development at the Pyrometallurgical Laboratory of the Department of Metallurgical Engineering, Institut Teknologi Bandung and has shown its potential to separate iron from oxide impurities in the titanomagnetite concentrate as well as the formation of iron nugget. Proceedings of the 1st International Process Metallurgy Conference (IPMC 2016) AIP Conf. Proc. 1805, 040003-1 040003-9; doi: 10.1063/1.4974424 Published by AIP Publishing. 978-0-7354-1473-0/$30.00 040003-1
EXPERIMENTS Limonitic nickel laterite ore and coal (as reductant) were prepared by griding and sieving to obtain grain size of less than 0.25 mm for the ore and less than 0.425 mm for the coal. The mineral phases and chemical composition of the ore were analyzed by X-ray diffraction (XRD) and X-ray fluorescence (XRF), respectively. The XRD analysis (Fig. 1) shows that the minerals of goethite (FeH), gibbsite (Al(H) 3), and hematite (Fe 2 3) were dominant in the nickel limonite ore. Based on the XRF result (Table 21, nickel and iron content in the ore were 1.49% and 47.65%, respectively. The proximate analysis of the coal is shown in Table 2. FIGURE 1. XRD pattern of limonitic nickel laterite ore TABLE 1. XRF chemical analysis of limonitic nickel laterite ore Element Conc. (wt%) Si 1.060 Al 3.520 Fe 47.65 Mn 0.577 Mg 0.185 P 0.004 S 0.217 Zn 0.034 Ni 1.490 Cr 1.570 Co 0.079 LI 16.76 TABLE 2. Proximate coal analysis (adb) Fixed Carbon (%) Ash (%) Volatile Matter (%) Moisture (%) 43.12 10.12 42.04 4.72 Around 3 grams of the limonite ore was mixed with a certain portion of coal (10 wt%, 20 wt% or 30 wt%) and agglomerated into briquette in the form of a cylindrical pellet using press hydraulic machine. The briquette was placed into a 30-mL crucible with the position as shown in Fig. 2. Before the briquette was inserted into the crucible, alumina and coal layer was prepared at the bottom of crucible. Coal was added again to keep the reduction condition on the whole briquette surface. Finally, alumina powder was added on top to minimize oxygen penetration during the reduction process. In general, the coal addition in this experiment was the combination of self-reducing briquette by coal addition inside the briquette, which is also known as composite briquette, and coal bed reductor where coal was added outside the briquette to cover the surface of the briquette with reductant. 040003-2
Briquette Coal Alumina FIGURE 2. Schematic position of briquette in a crucible The crubible was placed in the muffle furnace where the temperature profile was set as depicted in Fig. 3. The temperature profile, which is known as isothermal-temperature gradient, was divided into three stages: the first stage was isothermal (kept at constant temperature) at 1000 C; in the second stage, the temperature gradually increased at certain a rate from 1000 to 1400 C; the third stage was, again, isothermal at 1400 C. The heating rate during the second stage was varied at 6.67, 8.33 and 10 C/minute. The temperature inside the muffle furnace or outside the crucible was maintained according to this temperature profile. However, the temperature inside the crucible was not measured. There may be temperature difference between the inside and outside of the crucible and in general, temperature inside crucible should be slightly lower than the outside. 1500 1400 Temperature ( C) 1300 1200 1100 1000 900 0 50 100 150 Time (minutes) Heating rate: 6.67 C/min Heating rate: 8.33 C/min Heating rate: 10 C/min FIGURE 3. Temperature profile of isothemal temperature gradient After the reduction process was completed, XRD and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) analysis were conducted on the reduced briquette. The nugget was separated from the slag by manual hand picking. The nugget was analyzed by means of total dissolution and aqueous analysis via atomic absorption spectrophotometry (AAS) to determine its nickel and iron content. RESULT AND DISCUSSIN Coal Addition on Reduction of Limonitic Nickel Laterite re A series of experiments was carried out at a various reductant addition to determine the physical appearances of the briquette after the reduction process. Figure 4 shows the physical appearance of the briquette and nuggets after the reduction. Generally, physical characteristic of the reduced briquettes with 10 wt%, 20 wt%, and 30 wt% coal addition was weak and had hollow texture. With 10 wt% coal addition, the ferronickel nuggets were observed with the size variation from 1-2 mm while with higher coal (20 wt% and 30 wt%), the size of the ferronickel nuggets was 040003-3
decreased to less than 1 mm. This phenomenon might be due to fact that at coal addition of 10 wt%, the possibility for the reductant to contact and react with the metal oxide in the ore is higher; while the rest of unreacted coal and the ash from the coal were smaller for 10 wt% coal addition compared to those with 20 wt% or 30 wt% coal addition, which provide a short path way for metal migration and promote metal nucleation and metal growth to form nugget. If the coal addition is increased, the amount of unreacted coal including the ash will also increase which may block the migration path of the metal and thus extend the pathway for the metal to nucleate and form nugget. (a) (b) 10 wt% coal 20 wt% coal 30 wt% coal FIGURE 4. Effect of coal addition on physical appearance of (a) the reduced briquettes and (b) ferronickel nuggets To determine the minerals as well as the metal phases in the briquettes after the reduction process, XRD analyses were performed. Figure 5 shows that without any treatments, goethite, hematite, and gibbsite were the common minerals in the limonitic nickel laterite ore. In the reduced briquette, ferronickel (FeNi), alumina ( 3), and silica (Si 2) were identified. After the nugget was separated by hand picking, ferronickel metal phase was still exist in the slag for 10 wt% coal addition (Fig. 5). In general, ferronickel metal was formed by the addition of 10 wt%, 20 wt%, and 30 wt% of reductant coal in the briquettes. As it has been shown in Fig. 4, the addition of 10 wt% coal is better in the formation of ferronickel metal nugget. Effect of Heating Rate at the Gradient Temperature Stage and Holding Time at the Final Isothermal Stage on Iron and Nickel Recovery The physical appearance of the reduced briquettes with different holding time at a final isothermal temperature of 1400 C is shown in Fig. 6 for heating rate of 6.67 C/minute during the gradient temperature stage. The coal addition was constant at 10 wt% and the initial isothermal stage was at 1000 C for 30 minutes. As it can be seen in Fig. 6, the size of the produced nuggets tends to be larger with the increase of holding time at final isothermal temperature of 1400 C. The increasing nugget size may be due to the available time for the metal that was formed during the reduction process to migrate and nucleate in order to form larger nuggets. The same results were observed with heating rate of 8.33 C/minute and 10 C/minute. To determine recovery of nickel in the ferronickel, chemical analysis was conducted by AAS and the experiment was repeated three times to obtain reliable results. The nickel recovery as a function of holding time at the final isothermal stage is shown in Fig. 7. These results showed that the nickel recovery increased with the increase in 040003-4
holding time. The highest nickel recovery for 60 minutes holding time was about 53%. The nickel content in ferronickel nugget was in the range of 3% to 7%. Si 2 Si 2 3 3 Si 2 FeNi Slag for 10% coal addition FeNi Reduced briquette for 30% coal additition Si 2 FeNi Reduced briquette for 20% Si 2 FeNi Reduced briquette for 10% coal addition Si 2 Al(H) FeH FeH FeH Fe 2 3 Fe 2 3 Limonitic nickel laterite ore FIGURE 5. X-ray diffraction patterns of the reduced briquette with a reductant dosage Reduced briquette Ferronickel Nugget a. 15 minutes b. 30 minutes c. 45 minutes d. 60 minutes FIGURE 6. Physical appearance of reduced briquette at the heating rate of 6.67 C/minute with different final holding time during isothermal stage at 1400 C 040003-5
60 50 Nickel recovery (%) 40 30 20 10 Heating rate: 6.67 C/min Heating rate: 8.33 C/min Heating rate: 10 C/min 0 10 20 30 40 50 60 70 Holding time at final isothermal stage (min) FIGURE 7. Relationship between holding time at final isothermal stage and nickel recovery Similar with the nickel recovery, the iron recovery. which is shown in the Fig. 8, exhibit the same trend: higher iron recovery can be obtained at longer holding time at 1400 C. In general, the iron recovery was lower than nickel. The highest iron recovery was 24.45%, which was obtained at the heating rate of 6.67 C/minute with holding time for 60 minutes. The iron content in the ferronickel nugget was in the range of 84% to 93%. Lower iron recovery in most cases is desirable in order to achieve higher nickel content in the ferronickel product. However, nickel recovery has to be increased. Iron recovery (%) 40 35 30 25 20 15 10 5 Heating rate: 6.67 C/min Heating rate: 8.33 C/min Heating rate: 10 C/min 0 10 20 30 40 50 60 70 Holding time at final isothermal stage (min) FIGURE 8. Relationship between holding time at final isothermal stage and iron recovery Mechanism of Nugget Formation in the Nickel Limonite Briquette Composite To determine the mechanism of nugget formation during the reduction process, briquette samples were heated according to isothermal temperature gradient curve for heating rate of 6.67 C during the temperature gradient stage and samples were taken out at temperature of 1000 C, 1067 C, 1200 C, 1333 C, 1380 C, and 1400 C as shown in Fig. 9. 040003-6
1500 1400 1380 1400 Temperature ( C) 1333 1300 1200 1200 1100 1067 1000 1000 900 0 50 100 150 Time (minutes) FIGURE 9. Temperature profile to study the nugget formation The visual observation on the surface of the reduced briquette samples did not reveal any differences for the sample taken out at 1000 to 1333 C as can be seen from Fig. 9. At 1400 C, it was clear that nuggets were separated in the form globular. To observe the briquette surface in more detail, these samples were examined by SEM and the chemical composition of some phases on the surface was determined by EDS as shown in Fig. 10. (a) at 1000 C (b) at 1067 C (c) at 1200 C (d) at 1333 C (e) at 1380 C (f) at 1400 C FIGURE 10. SEM image and EDS analysis of reduced briquette at various final isothermal temperatures The surface of the reduced briquette at 1000 C is shown in Fig. 10 (a), which was dominated by phase with the color of white, grey, and black. Based on the EDS results, phases that have white color (spectrum 1) were dominated by iron oxide. The grey color (spectrum 3) indicated gangue oxides such as Al23 and Si2. Meanwhile, carbon was present in the black color (spectrum 2). The same trend was observed with the reduced briquette at 1067 C and 1200 C. No metal in the form of nugget was found on the surface. 040003-7
At 1333 C, metal phases were formed as shown in spectrum 12 in Fig. 10 (d). Those phases were dominated by chromium, sulfur, iron and carbon. However, in general, the surface of the reduced briquette at 1333 C was dominated by grey phases (spectrum 10) that indicated oxide with high iron content. Fig. 10 (e) shows that the nuggets (spectrum 15) were begin to merge with each other and have a size about 100 micron. Based on EDS results, these nuggets were dominated by chromium, iron and nickel but sulfur was still existed with at about 38 wt%. Furthermore, small nuggets were formed and dominated by iron and nickel (spectrum 13). These nuggets are getting bigger with the increase in temperature, as shown in Fig. 10 (f) where the size of produced nugget is about 400 micron. It indicated that the increasing time and temperature cause migration of the small nuggets to form a bigger nugget. Based on the microstructural observation by SEM/EDS analysis, the application of isothermaltemperature gradient method on nickel limonite briquette composite was able to produce metals at 1333 C. Thus, the increasing temperature would cause migration of ferronickel nugget to form bigger size. Ferronickel nugget was analyzed by X-ray mapping to determine the metal distribution in the parts of the nugget. Figure 11 shows the X-ray mapping results of the nugget s cross-section. In the reduction product, inclusion was found and dominated by oxygen, chromium, and sulfur. Distribution of iron seemed more uniform on the nugget cross-section, similarly with nickel and carbon. a. riginal Surface b. Iron c. Carbon d. Nickel e. xygen f. Silicon g. Chromium h. Sulphur FIGURE 11. X-ray mapping result of nugget cross section TABLE 3. Chemical composition of nugget based on EDS analysis Element Fe Ni Si Cr C S Conc. (wt%) 76.5 2.2 2.2 3.0 2.3 13.1 0.6 The chemical composition of the produced nugget is shown in Table 3 based on the EDS analysis. The iron and nickel content in the nugget was 76.5% and 2.2%, respectively. Meanwhile the carbon content in the nugget is high (13.1%). The AAS analysis of the iron and nickel content were 86.5% and 4.3%, respectively. CNCLUSIN Isothermal-temperature gradient method can be applied to reduce limonitic nickel laterite ore to produce nugget which is separated from the slag at 1400 C. The amount of coal addition of 10 wt% is suitable to produce nugget with grain size of 1 2 mm. When the amount of coal addition increased to 20 wt% and 30 wt%, smaller nugget (below 0.2 mm) was obtained. Based on macroscopic observation, the nugget was appeared at 1380 C. However, in microscopic observation with SEM analysis, metal was already observed at 1333 C and started to merge to form 040003-8
bigger nugget by the increasing temperature. Heating rate affects the recovery of nickel and iron. Decreasing the heating rate will result in the increase on ferronickel recovery. Furthermore, recovery of the nickel and iron is affected by holding time at a certain final temperature. The increases in holding time will increase the recovery of nickel and iron. The highest recovery was achieved at heating rate 6.67 C/minute for 60 minutes holding time at 1400 C. ACKNWLEDGMENT The authors would like to thank to Ministry of Research and Higher Education, Republic of Indonesia for supporting and funding this research and to PT Antam (Persero) Tbk. for providing the nickel laterite ore. REFERENCES 1. J. Johnson, B.K. Reck, T. Wang, and T. E. Graedel, Energy Policy 36 (1), 181 192 (2008). 2. http://www.worldsteel.org. 3. Ministry of Energy and Mineral Resources, Republic of Indonesia, 2012. 4. T. Watanabe, S. no, H. Arai, and T. Matsumori, International Journal of Mineral Processing 19 (1-4), 173-187 (1987). 040003-9