ISOTHERMAL REDUCTION SMELTING OF MIXED CHROMITE-LATERITE SAMPLES WITH COCONUT CHARCOAL AS REDUCTANT UNDER ARGON ATMOSPHERE IN A VERTICAL ELECTRIC ARC FURNACE

Jeffrey Ken B Balangao, Feven James C Podiotan, Aaron Exxon C Ambolode, Nathaniel M Anacleto

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Jeffrey Ken B Balangao, Feven James C Podiotan, Aaron Exxon C Ambolode, Nathaniel M Anacleto. ISOTHERMAL REDUCTION SMELTING OF MIXED CHROMITE-LATERITE SAMPLES WITH COCONUT CHARCOAL AS REDUCTANT UNDER ARGON ATMOSPHERE IN A VERTICAL ELECTRIC ARC FURNACE. International Journal of Mechanical Engineering and Technology, 2022, 13 (5), pp.46-53. 10.17605/OSF.IO/9YCRE. hal-03929019

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# ISOTHERMAL REDUCTION SMELTING OF MIXED CHROMITE-LATERITE SAMPLES WITH COCONUT CHARCOAL AS REDUCTANT UNDER ARGON ATMOSPHERE IN A VERTICAL ELECTRIC ARC FURNACE

Jeffrey Ken B. Balangao<fnref n="1" />*, Feven James C. Podiotan², Aaron Exxon C. Ambolode³, Nathaniel M. Anacleto⁴

## ABSTRACT

The traditional production of stainless steel follows a long-way process which requires high energy consumption and increase emissions of CO and CO₂ gases. This study aimed at assessing isothermal reduction smelting of additional mixed samples of chromite/laterite ores to produce directly Fe-Cr-Ni metal alloys in a single route manner. Chromite and laterite ores were obtained at Zambales and Surigao del Norte provinces, Philippines. Isothermal smelting was conducted to samples, 6/94 and 35/65 in addition to 12/88, 25/75 and 50/50, with coconut charcoal as reductant under argon atmosphere at 1600 °C in one hour under a vertical electric arc furnace. Higher Cr contents are obtained at increasing percentages of chromite in the mixtures. Ni contents are in fluctuations at increasing laterite contents. Cr and Ni contents can be greatly attributed to the high dilution activity of iron in the metals. Higher recoveries of metal alloys are manifested at smelting 6/94, 35/65 and 50/50 with 93.67, 95.91 and 99.62%, respectively, at increasing chromite compositions. On the other hand, recoveries are decreasing at increasing laterite contents, clearly shown after smelting 12/88 and 25/75 samples with 69.70 and 78.99%, from that of 35/65 with 95.91%. The flushing out of volumes of slag, which is directly related to slag foaming, is believed to be the reason of the said decreasing recoveries. It can be recommended to use other carbon-based reductants and assess their impacts on the recovery of the metal alloys and on their Cr and Ni contents. Exploring other combinations of Philippines chromite and laterite can also be considered accounting their potential to obtain higher recoveries and higher Cr and Ni contents in the metal alloys. Slag foaming can also be further studied with parameters in this direct route smelting.

<footnote n="1">¹,²,³,⁴Department of Materials & Resources Engineering Technology, College of Engineering and Technology, Mindanao State University-Iligan Institute of Technology, Iligan City, Philippines</footnote>

<footnote n="1">¹College of Engineering and Architecture, University of Science and Technology of Southern Philippines, Cagayan de Oro City, Philippines</footnote>

<footnote>*Corresponding Author</footnote>
**Keywords:** Isothermal, Smelting, Chromite, Laterite

**Cite this Article:** Jeffrey Ken B. Balangao, Feven James C. Podiotan, Aaron Exxon C. Ambolode and Nathaniel M. Anacleto, Isothermal Reduction Smelting of Mixed Chromite-Laterite Samples with Coconut Charcoal as Reductant under Argon Atmosphere in a Vertical Electric Arc Furnace, *International Journal of Mechanical Engineering and Technology (IJMET)*, 13(5), 2022, pp. 46-53.

https://iaeme.com/Home/issue/IJMET?Volume=13&Issue=5

# 1. INTRODUCTION

The traditional production of stainless steel follows a long-way process which requires high energy consumption and increase emissions of CO and CO₂ gases (Fruehan et al., 2000; Norgate et al., 2004; Kapuri et al., 2007). In the process, laterite and chromite ores are first smelted in an electric arc furnace to produce both ferronickel and ferrochromium (Hartman et al., 1992). Then, in the blast furnace happens the sintering of iron ore, coked coal and limestone as flux, to produce pig iron. Lastly, these pig iron, ferronickel and ferrochromium need to be smelted altogether in the electric arc furnace to produce stainless steel (Kapuri et al., 2007).

Yape and Anacleto (2014), in response, introduced a technology which simplifies the long-way process. The said process, which is believed to be first of its kind, establishes a feasible route to produce Fe-Cr-Ni metal alloys from direct smelting of mixed chromite and laterite ores from oxides of iron, chromium and nickel. This implies that the whole process lessens the energy consumption and the CO and CO₂ gases emissions, respectively.

When the said technology was introduced, the idea of utilizing other mixtures of Philippine laterite and chromite ores has been carried out (Yape, 2014; Balangao et al., 2018). Yape (2014) utilized both laterite and chromite ores from Surigao and Misamis Oriental, respectively. Balangao et al. (2018), on the other hand, employed laterite and chromite ores obtained at Surigao del Norte and Zambales provinces. In some studies, manganese ores have been incorporated to the mix to produce Fe-Cr-Ni-Mn alloys (Laranjo & Anacleto, 2017; Laranjo & Anacleto (2018). In particular, Laranjo & Anacleto (2017), in their work, produced Fe-Cr-Ni-Mn alloys directly from laterite (saprolite and limonite), chromite and manganese ores which were obtained at Surigao, Zamboanga del Norte and Zamboanga Zibugay, respectively. Another work of them was carried out, but without that limonitic ore, still producing the desired metallic alloys (Laranjo & Anacleto, 2018).

In this work, a continuation to the work of Balangao et al. (2018) has been carried out. This implies that with coconut charcoal as reductant, the laterite and chromite ores used in the isothermal reduction smelting process were still obtained at Surigao del Norte and Zambales provinces, respectively.

# 2. MATERIALS AND METHODS

## 2.1. Research Materials

The research materials were calcined laterite and chromite ores from Surigao del Norte and Zambales provinces, Philippines. The oxide compositions of the raw ores were shown in Table 1 below. The said ores were sieved directly in a 100-mesh screen for isothermal smelting experiments. The coconut charcoal as reductant for smelting had a proximate analysis of 72.46% fixed carbon, 5.32% moisture content, 21.08% volatile content matter, 1.14% ash and 0.08% sulfur contents. It was sieved in a 100-200 mesh screens (Balangao et al., 2018).
<table><caption>**Table 1** XRF Oxide Compositions Laterite and Chromite Ores (in wt. %)</caption><thead><tr><td>Components</td><td>Laterite Ore</td><td>Chromite Ore</td></tr></thead><tbody><tr><td>NiO</td><td>1.99</td><td>0.182</td></tr><tr><td>Cr<sub>2</sub>O<sub>3</sub></td><td>3.03</td><td>31.01</td></tr><tr><td>Fe<sub>2</sub>O<sub>3</sub></td><td>19.12</td><td>16.81</td></tr><tr><td>Al<sub>2</sub>O<sub>3</sub></td><td>1.74</td><td>26.17</td></tr><tr><td>MgO</td><td>28.74</td><td>15.99</td></tr><tr><td>SiO<sub>2</sub></td><td>43.81</td><td>7.40</td></tr></tbody></table>

## 2.2. Isothermal Smelting

Different chromite and laterite mixtures for isothermal smelting were selected on their feasibility to melt at 1600 °C in the ternary phase diagram of the MgO-Al₂O₃-SiO₂ system at 1 atmospheric pressure as shown in Figure 1 below. It is with this system that actually determines such samples are able to be smelted at the desired smelting temperature. These random chromite/laterite mixtures were 6/94, 12/88, 25/75, 35/65 and 50/50, respectively. These mixtures can possibly obtain higher amounts of chromium and nickel in the alloys to be produced when being melted at 1600 °C, the isothermal smelting temperature of the experiment (Balangao et al., 2018). Balangao et al. (2018) have already conducted direct smelting of 12/88, 25/75 & 50/50 samples. In this work, the other remaining samples, 6/94 and 50/50 have been carried out further.

<figure><img src="image_3.png" /><figcaption>**Figure 1** Point Locations of the Ore Compositions in the MgO-Al₂O₃-SiO₂ Ternary Phase Diagram at 1 Atmospheric Pressure</figcaption></figure>

The isothermal smelting experiment was conducted at 1600 °C in 1 hour in a laboratory fixed bed reactor in a vertical electric arc furnace with a recrystallized alumina work tube equipped with a 6 Kanthal Super 1800 – molybdenum disilicide resistance heating element and
having a maximum temperature of 1,700 °C. The container for the input charge materials, the chromite, laterite and the coconut charcoal, was a graphite crucible. The said crucible was then placed further in an alumina crucible for smelting process. The alumina crucible has an average weight of 27g, a height of 35mm and a top diameter of 38 mm and a capacity of 20 ml of volume. Ninety-nine percent (99%) high purity argon was employed in the experiment and the gas flow rate applied was 100-200ml/min (Balangao et al., 2018). Metal alloys and slags were separated by magnetic separation after isothermal smelting. Wet chemical titration was conducted to determine Cr and Ni contents in the metal alloys. Percentage recoveries were calculated on the basis of the theoretical and actual weights of the metal alloys before and after smelting. The theoretical weight is the sum of all the weights of iron, chromium and nickel in the mixed samples smelted to produce metal alloys. The actual weight is the weight obtained of the metal alloy right after the smelting process.

# 3. RESULTS AND DISCUSSION

## 3.1. Isothermal Smelting

Balangao et al. (2018) conducted isothermal smelting to the following mixed samples, 12/88, 25/75 and 50/50, respectively. In this study, other samples such as 6/94 and 35/65 also underwent reduction in 1600 °C at one hour under argon atmosphere. Figure 2 below shows the obtained metal alloys and slags after magnetic separation. At the same smelting conditions, the given ore compositions produced different amounts of alloys and slags. This is in consonance to the findings of Yape and Anacleto (2014) who determined that crude alloys are produced with different grades and compositions of chromite and laterite ores as main factors.

<figure><img src="image_4.png" /><figcaption>**Figure 2** Metal Alloys and Slags of Different Ore Compositions after Isothermal Smelting at 1600 °C</figcaption></figure>

Metal alloys obtained were subjected to wet chemical titration to determine presence of chromium and nickel contents. As shown in Table 2, higher Cr contents are obtained at increasing percentages of chromite in the mixtures. On the other hand, Ni contents which ranged from 1.78 to 4.00% have been fluctuating at increasing laterite contents. The resulting Cr and Ni contents can be greatly attributed to the high dilution activity of iron in the metals. It is
evident that contents of Fe₂O₃ were basically higher than Cr₂O₃ and NiO in mixed samples so iron is expected to be of high content in the metals diluting both chromium and nickel contents.

Further, iron oxide (Fe₂O₃) is easily reduced to iron at lower temperatures (around 750°C) than chromium oxide (around 1250°C). So, the accumulation of iron in the liquid metal would be greater than that of chromium. Although NiO is easily reduced to nickel at a much earlier temperatures (around 500°C), its accumulation in the melt would only be minimal due to its lower contents present in the mixed samples. Basically, the reduced iron from iron oxide starting at around 750 °C would dilute the entire liquid metal.

<table><caption>**Table 2** Cr and Ni Analyses in the Metal Alloys by Wet Chemical Titrations</caption><thead><tr><td>Chromite/Laterite Ore Composition</td><td>% Cr</td><td>% Ni</td></tr></thead><tbody><tr><td>6/94</td><td>3.71</td><td>2.31</td></tr><tr><td>12/88</td><td>4.66</td><td>4.00</td></tr><tr><td>25/75</td><td>5.15</td><td>1.85</td></tr><tr><td>35/65</td><td>21.20</td><td>2.38</td></tr><tr><td>50/50</td><td>11.20</td><td>1.78</td></tr></tbody></table>

## 3.2. Percentage Recoveries of the Metal Alloys Obtained

Percentage metal alloy recoveries were calculated on the basis of the theoretical and actual weights of the metal before and after smelting. Again, the theoretical weight is the sum of all the weights of iron, chromium and nickel in the mixed samples smelted to produce metal alloys. The actual weight is the weight obtained of the metal alloy right after the reduction process. Table 3 below shows the recoveries of the metals obtained after smelting different compositions. It can be observed that higher recoveries of metal alloys are manifested at smelting 6/94, 35/65 and 50/50 with 93.67, 95.91 and 99.62%, respectively. It can be observed further that higher recoveries were obtained at increasing chromite compositions. On the other hand, recoveries are decreasing at increasing laterite contents. In particular, a sudden decrease of recoveries can be clearly shown after smelting of 12/88 and 25/75 with 69.70 and 78.99%, from that of 35/65 with 95.91%.

<table><caption>**Table 3.** % Recoveries of the Metal Alloys</caption><thead><tr><td>Chromite/Laterite Compositions</td><td>Theoretical Weight (g)</td><td>Actual Weight (g)</td><td>% Recovery</td></tr></thead><tbody><tr><td>6/94</td><td>2.806</td><td>2.628</td><td>93.67</td></tr><tr><td>12/88</td><td>3.033</td><td>2.114</td><td>69.70</td></tr><tr><td>25/75</td><td>3.157</td><td>2.494</td><td>78.99</td></tr><tr><td>35/65</td><td>3.399</td><td>3.26</td><td>95.91</td></tr><tr><td>50/50</td><td>3.761</td><td>3.747</td><td>99.62</td></tr></tbody></table>

From Table 3, it is evident that isothermal smelting of 12/88 and 25/75 compositions resulted to lower recoveries as regards to other samples. Figure 3 below shows that flushing out of volumes of slag was evident after smelting the said samples. It is believed to be the reason of the lower recoveries manifested by the said samples. This phenomenon can be associated to slag foaming which is usually observed in many steelmaking processes (Ito and Fruehan, 1989; Hara and Ogino, 1992; RD et al., 1995; Luz et al. 2018). The said flushing out of slag is believed to be the first occurrence upon applying this direct route smelting process for crude steel production introduced by Yape and Anacleto (2014).
<figure><img src="image_5.png" /><figcaption>**Figure 3.** Dried Slag Flushing out on Crucibles after Smelting of 12/88 and 25/75 Samples</figcaption></figure>

To understand slag foaming, another 12/88 and 25/75 mixing compositions were smelted but this time, using another type of chromite ore obtained at Misamis Oriental, Philippines. Results showed no slag foaming occurrence, that is, no flushing out of volumes of slag occurring on the crucibles. Metals and slags are highly distinguishable as observed in Figure 4 below. This implies that types of ores could be the reason for slag foaming at 12/88 and 25/75 compositions.

<figure><img src="image_6.png" /><figcaption>**Figure 4.** Smelting of 12/88 and 25/75 Samples using Another Type of Chromite Ore</figcaption></figure>

The overall metal recoveries were then calculated as 87.67 and 99.03% respectively as shown in Table 5 below. The obtained recoveries are much greater than the previous recoveries caused by slag foaming. This implies that slag foaming would really cause a reduction on metal recoveries when not properly controlled and monitored in this direct smelting process.
<table><caption>**Table 4** Metal Recoveries after Smelting 12/88 and 25/75 Samples using Chromite Ore from Misamis Oriental, Philippines</caption><thead><tr><td>Chromite/Laterite Compositions</td><td>Theoretical Weight (g)</td><td>Actual Weight (g)</td><td>% Recovery</td></tr></thead><tbody><tr><td>12/88</td><td>3.287</td><td>2.882</td><td>87.67</td></tr><tr><td>25/75</td><td>3.654</td><td>3.619</td><td>99.03</td></tr></tbody></table>

## 4. CONCLUSIONS AND RECOMMENDATIONS

Isothermal reduction smelting was conducted to additional mixed samples, 6/94 and 35/65, in a vertical electric arc furnace using coconut charcoal as reductant under argon atmosphere at 1600 °C in 1 hour. After smelting, results were compared with those of 12/88, 25/75 and 50/50 samples performed by Balangao et al. (2018). Chromium and nickel contents were influenced by the high dilution activity of iron in the metal alloys. It is evident that increasing percentages of chromite resulted to higher chromium contents in the metals. Higher recoveries were obtained at increasing chromite compositions. On the other hand, recoveries are decreasing at increasing laterite contents. The flushing out of volumes of slag, which is directly related to slag foaming, is believed to be the reason of the said decreasing trend especially when not properly monitored and controlled.

It can be recommended to further utilize other carbon-based reductants such as graphite and activated carbon and assess their impacts on the recovery of the metal alloys as well as on their Cr and Ni contents. Moreover, exploring other combinations of Philippines chromite and laterite can also be considered for smelting process accounting their potential to obtain higher recoveries and higher chromium and nickel contents in the metal alloys. Slag foaming can also be further studied along with parameters in this direct route smelting introduced by Yape and Anacleto (2014).

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