Open AccessArticle

Relationship Between Thermodynamic Modeling and Experimental Process for Optimization Ferro-Nickel Smelting

Erdenebold Urtnasan

^1,2,*

Seong-Bong Heo

Joo-Won Yu

⁴,

Chang-Ho Jung

⁴ and

Jei-Pil Wang

^4,*

Industrial Science Technology Research Center, Pukyong National University, Busan 48513, Republic of Korea

Darkhan School of Technology, Mongolian University of Science and Technology, Darkhan City 45051, Mongolia

Department of Civil and Environmental Engineering, Hayang University, Seongdong-gu, Seoul 04763, Republic of Korea

⁴

Department of Metallurgical Engineering, School of Engineering, Pukyong National University, Busan 48513, Republic of Korea

Authors to whom correspondence should be addressed.

Minerals 2025, 15(2), 101; https://doi.org/10.3390/min15020101

Submission received: 16 October 2024 / Revised: 6 December 2024 / Accepted: 16 January 2025 / Published: 22 January 2025

(This article belongs to the Special Issue Slag Valorization for Advanced Metal Production, 2nd Edition)

Download

Browse Figures

Figure 1
XRD pattern of calcined nickel ore. "> Figure 2
SEM-EDS image of calcined nickel ore: (a) SEM image and (b) EDS mapping image. "> Figure 3
Schematic diagram of the experimental apparatus. "> Figure 4
The influence of carbon on smelting products: (a) weight of stable compounds and (b) activity of stable compounds. "> Figure 5
Thermodynamic analysis of reduction smelting of calcined nickel ore with carbon addition: (a) Gibbs free energy and (b) heat of reaction in smelting. "> Figure 6
Samples from reduction smelting test: (a) Segregated metal particles, (b) Small metal particles in the slag. "> Figure 7
XRD pattern of slag during reduction smelting with 3 wt.% C and 4 wt.% C addition. "> Figure 8
Analyzing simulated slag structure on MgO-SiO2-FeO ternary system using FToxid data, Factsage 8.2 at 1550 °C and 1 atm. "> Figure 9
XRD pattern of slag during Ni reduction smelting with flux addition: (a) with SiO2 addition and (b) with MgO addition. "> Figure 10
Slag structure analysis on MgO-SiO2-FeO ternary phase diagram projection using FToxid data, Factsage 8.2. "> Figure 11
Ferrous nickel and small metal particles extracted from slag in a reduction smelting test with 6 wt.% MgO flux. "> Figure 12
Relationship of slag basicity with nickel smelting’s metal grade and recovery degree. (a) Nickel, (b) Iron. ">

Versions Notes

Abstract

Saprolite ores in nickel laterite deposits are pyrometallurgically processed to produce Fe-Ni alloy and Ni matte. The key to achieving the highest recovery degrees from nickel ore in electric arc furnaces and producing top-quality ferro-nickel alloys lies in maintaining optimal carbon consumption and carefully controlling the composition of the slag. This research work focused on finding the optimal smelting procedure for extracting ferro-nickel from calcined nickel ore. Comparing experimental data to the results of thermodynamic modeling using Factsage 8.2 software was a key part of the study. The nickel smelting process, which involved a carbon consumption of 4 wt.%, resulted in ferro-nickel with an Fe/Ni ratio of 4.89 and slag with a nickel content of just 0.017%. The structure and properties of nickel slag in the MgO-SiO₂-FeO system were investigated by observing the changes in the MgO/SiO₂ ratio. This study found a significant nickel recovery degree of 95.6% within the optimal M/S ratio range of 0.65 to 0.7. When the M/S ratio exceeds 0.7, iron-rich magnesium silicates (Mg_xFe_ySiO_2+n) are generated within the slag. These compounds are released downwards due to their higher specific weight, restricting the movement of small metal particles and contributing to increased metal loss through the slag. Optimized slags could revolutionize smelting, increasing metal recovery while minimizing environmental impact.

Keywords:

ferro-nickel; nickel laterite ore; olivine phase; M/S ratio; slag basicity; thermodynamic modeling

1. Introduction

Nickel, with its versatile properties, is a metal that finds extensive applications across various industries. Approximately 65% of nickel is dedicated to the production of stainless steel, while around 12% is allocated for nickel superalloys and ferro-nickel. Another 8% is used in electroplating, leaving the remaining 5% for nickel batteries and chemical compounds [1,2,3]. In recent years, the global consumption of nickel has been on the rise, driven by the growing demand for batteries in electrical technology and the widespread use of stainless steel. Laterite and magmatic sulfide deposits are the primary sources of nickel, accounting for approximately 70% of the nickel resources found in laterite deposits [4,5,6]. The laterite deposits are composed of multiple layers that house a plethora of minerals, including limonite, saprolite, and transition ores. The most commonly used method for extracting ferro-nickel through direct pyrometallurgical reduction smelting is by utilizing saprolite ore, which is an oxidized type of nickel ore with a nickel content ranging from 1.8% to 3.0%. This method is considered to be the most efficient due to the high nickel content in saprolite ore. The impurities found in nickel saprolite ores are primarily composed of magnesium-rich silicates, specifically the oxides of MgO and SiO₂ [7,8]. The nickel ore comprises approximately 10% to 25% iron [9,10,11], and when iron is reduced together with nickel ore through reduction smelting, it brings several benefits. These advantages include simplifying the smelting process and enhancing the economic value of the produced ferro-nickel. The process of producing ferro-nickel from saprolite ore requires the implementation of various steps within the field of pyrometallurgy. The procedure outlined for this process includes several important steps, such as drying and calcining in a rotary kiln, as well as reduction smelting in a DC electric arc furnace [12,13,14].

The largest laterite deposits in the world can be found in New Caledonia, Australia, Indonesia, and South America. Out of a total of 3900 million tons of resources, Indonesia stands as the third-largest producer, with 1.576 million tons of laterite [15,16,17]. During the late 19th century, New Caledonia, Indonesia, and Brazil embraced the pyrometallurgical technique to extract Ni alloys from high-grade nickel saprolite ore. In order to implement this technique, rotary kilns and electric arc furnaces [18,19] were employed. In order to improve the efficiency of the smelting process and reduce energy consumption, it is recommended to prepare the ore beforehand. This preparation involves removing all (30%–40%) of the moisture from the ore, which not only aids in promoting the reduction of iron oxides but also helps in saving processing time during smelting. The recovery of nickel in the ferro-nickel smelting process can reach above 90% [20,21,22], provided that the nickel ore used has a nickel content exceeding 1.5%. The calcined nickel ore goes through a series of conventional processing techniques, including reduction smelting, which ultimately yields an outstanding recovery degree of nickel, reaching 95%. The composition of the final product, which is a ferro-nickel, consists of up to 20% Ni and 80% Fe, making it an ideal material for stainless steel production [23,24,25]. It has been determined that there is a direct correlation between the release of nickel and the release of iron during the smelting process. On the other hand, there is a direct correlation between the quantity of nickel oxide and the quantity of iron oxide in the slag [26,27]. Nickel smelting slag is characterized as a MgO-SiO₂-FeO system slag, where the abundant FeO, serving as a major element, enhances the slag’s physical attributes. Nonetheless, this elevated FeO concentration causes a rise in nickel depletion. For this reason, it is imperative to maintain a minimum FeO oxide content of 10% in the slag [27,28]. By adjusting the MgO/SiO₂ ratio, it is possible to create a slag that not only exhibits enhanced meltability but also possesses decreased viscosity. This facilitates the smelting process and enables the achievement of the highest degree of metal recovery. The primary objective of the present research work was to investigate the correlation between the carbon quantity utilized in the production of ferro-nickel and the resulting Fe/Ni grade, as well as the recovery degree of nickel. Moreover, we analyzed the influence of the slag’s composition and structure on the separation process of metal components, ultimately determining the most favorable composition for the slag. Consequently, the primary focus of this research project was to establish the most suitable approach for nickel smelting. To accomplish this, an extensive thermodynamic modeling analysis was performed utilizing the Factsage 8.2 software. Moreover, the smelting experiments took into account the valuable insights obtained from the modeling, further enhancing the accuracy and reliability of the findings.

2. Materials and Methods

2.1. Experimental Materials

For this experiment, nickel saprolite ore sourced from Indonesia was used. The ore was first calcined before it was tested in the smelting process. The chemical analysis of the nickel ore was carried out using XRF analysis to identify the primary elements and impurities, as well as their concentrations, which were expressed in terms of mass percentages. Additionally, the nickel and iron contents were examined using ICP-OES, and the corresponding findings are presented in Table 1. According to the ICP-OES analysis, the ore had a nickel content of 1.9% and an iron content of 16.5%. Among the impurities of the ore, the most significant ones were 30.14% MgO, 43.76% SiO₂, and 2.82% Al₂O₃, along with other oxides. Through the utilization of XRF analysis, one can precisely ascertain the concentration of elements and acquire the outcomes in the universally accepted oxide form. Additionally, it is important to note that XRF analysis lacks the ability to distinguish between various oxidation states of elements. Unfortunately, the search results only provide details about the most prevalent form of oxide. Fe has the ability to exist in different oxidation states, with FeO, Fe₃O₄, and Fe₂O₃ being some examples. It is crucial to mention that the Fe calculation only considers the Fe₂O₃ state, as stated explicitly in reference [29]. The pure activated powdered carbon used as a reducing agent was sourced exclusively from DaeJung Chemical Company in Siheung, Republic of Korea. The extra-pure powder oxides of MgO and SiO₂, sourced from Junsei Chemical Company, Tokyo, Japan, were used as fluxes.

Figure 1 shows the XRD analysis results of the nickel ore, which exhibit a distinct pattern. The nickel ore primarily consisted of silicates composed of magnesium, silicon, iron, and aluminum elements. These silicates are formed in the chemical structures of Mg_xSiO_y and [MgAl]_xSiO_y(OH)_n. Additionally, certain types of iron oxides are present as distinct phases within the ore [30,31,32]. The moisture present in nickel ore is significantly reduced through calcination, which subsequently leads to the reduction of iron and nickel. Clinoenstatite, a magnesium silicate (DB card number 00-035-0610), was identified as the dominant mineral in the calcined nickel ore used for the experiment. Additionally, nickel was found in the magnesium nickel silicate (MgNiSiO₄—DB card number 01-084-1986), while the magnesium aluminum iron oxide (MgAl₂FeO₄—DB card number 01-071-1233) contained a combination of iron and aluminum. The analysis conducted using the Factsage 8.2 software’s FactPS and FToxid data revealed that nickel has the ability to exist in various forms within the olivine and spinel compounds. Specifically, it was found that nickel can be present as MgNiSiO₄, Ni₂SiO₄, and FeNiSiO₄ in the olivine compound, while in the spinel compound it can exist as FeNi₂O₄ and NiFe₂O₄. These findings align perfectly with the results of the analysis.

As part of the smelting experiment, the calcined nickel ore underwent a pre-grinding process to achieve a particle size of less than 45 µm. Through SEM-EDS analysis of the powdered ore, the distribution of elements in the ore was analyzed. Figure 2 shows both the SEM image and the EDS mapping analysis of the nickel ore. Although the nickel ore particles did not exhibit significant differences, they did vary in terms of grain size, as illustrated in Figure 2a. According to the EDS mapping image (Figure 2b), there was a prominent occurrence of iron, silicon, and magnesium within the ore. On the other hand, the amount of nickel distributed was comparatively smaller.

Table 2 provides an overview of the findings from the EDS mapping analysis. The EDS mapping reveals that the distribution of silicon was found to be 29.17 wt.%, while the distribution of iron was measured at 18.90 wt.% and the distribution of magnesium was determined to be 19.56 wt.%. The detection of oxygen at a weight percentage of 29.66 wt.% suggests that the ore was present in the form of oxides. The results of the EDS analysis were consistent with the predominance of oxide compounds containing Si, Mg, and Fe, as determined by the XRF analysis results, and these specific elements were also detected in the samples. Based on the analysis, it was concluded that the weight percentage of nickel in the sample was 2.71 wt.%. This result indicates that the distribution of nickel in the ore was uniform, and this uniformity could be identified using EDS analysis.

2.2. Experimental Procedures

The smelting experiment occurred in a vertical tube, where the intense heat from molybdenum disilicide (MoSi₂) elements reached scorching temperatures of 1550 °C (Figure 3). The tube furnace, composed of a furnace controller and a heating box, stands tall with a B-type thermocouple inside. Inside the tube, there is a working place constructed from a 75 mm diameter alumina tube, with a length of 900 mm. With the ability to reach temperatures as high as 1800 °C, the tube furnace can be completely sealed off to prevent any air infiltration. Placed at the center of the working place, the sample was contained within a zirconia (ZrO₂) crucible. To conduct the experiment, a carefully regulated stream of argon was directed into the furnace. The thermocouple, with a high level of accuracy, was securely attached to the center zone of the furnace to closely monitor its operational temperature. By incorporating a temperature control system and programmable segments, the furnace grants users the ability to precisely adjust the heating rate, cooling rate, holding, and time settings. Moreover, the furnace is fitted with a temperature controller and alarm system, providing uninterrupted operation without the requirement of supervision. The experimental gas, under precise control from a mass flow controller (MFC), flowed into the furnace from one side. With a precision of ±2 cc, the fluid flowed smoothly through the working place at a controlled rate of 300 cc/min. Upon insertion of the sample into the furnace, the lid was closed tightly, and the furnace was filled with Ar gas. The sample in the furnace was slowly heated at a steady rate of 5 °C per minute until it reached 1550 °C, at which point it was left to hold. The sample was cooled down to room temperature at a rate of 5 °C per minute, without being removed from the furnace, and then it was taken out.

2.3. Analytical Methods

2.3.1. Thermodynamic Modeling

For the thermodynamic modeling in this study, the software Factsage 8.2 was employed. FactSage has the ability to calculate the conditions for equilibria involving multiple phases and components. It offers various output modes, such as tables and graphs, and can handle a wide range of constraints. To determine the concentrations of chemical species in our study of ferro-nickel smelting, we used the Equilib module. The species considered were elements or compounds that reacted or partially reacted until they reached a state of chemical equilibrium. The Equilib module identifies various possible products, such as gas phase, pure solids, slag, spinel, matte, and Fe-Ni alloy solution phases. Furthermore, it was employed to ascertain specific information regarding their composition, temperature, and overall pressure. The Phase Diagram module was used to analyze the slag composition. The Phase Diagram module was used to calculate the plots, capturing the intricate details of ternary and multicomponent phase diagrams. The customized axes were carefully crafted with different combinations of temperature and composition.

2.3.2. Calculating Nickel Recovery Degree

The recovery degree was crucial in determining the effectiveness of nickel extraction from calcined nickel ore through smelting. A calculation was carried out that compared the Fe and Ni mass in the raw material before smelting with the Fe and Ni mass found in the Fe-Ni alloy after the smelting process. Equation (1) represents the nickel recovery degree:

η = \frac{M_{i}}{M_{0}} \times 100 %

(1)

where η is the metal recovery degree (%), M₀ is the Ni or Fe weight in the calcined nickel ore (g), and M_i is the Ni or Fe weight in the Fe-Ni alloy (g).

2.3.3. Chemical and Mineralogical Analysis

To determine the chemical composition of the calcined nickel ore, a Shimadzu XRF-1800 model X-ray fluorescence spectrometer was employed, yielding highly accurate data. Inside the XRF machine, the sample was carefully placed in a platinum crucible before being loaded into the machine. Utilizing an Agilent 5800 ICP-OES model, an inductively coupled plasma optical emission spectrometer manufactured by Agilent Technologies in Australia, a detailed analysis was conducted to accurately assess the precise concentrations of nickel and iron within the sample. An X-ray diffractometer, specifically the X’Pert-MPD PANalytical model (Panalytical, Malvern, UK), featuring a high-intensity 3 kW Cu-Kα X-ray tube, was instrumental in determining the mineral composition of the nickel ore and slag. A scanning range of 10 to 80° was employed for the XRD data collection for the nickel ore, with a time of 10 min and a step size of 0.02°. The carbon content in the ferro-nickel was analyzed using a C/S elemental analyzer as. Utilizing water cooling, small ferro-nickel flakes were cut for sampling purposes. For the C/S analysis, only particles weighing less than 5 mg were used from the prepared flakes. The solid sample of sulfanilamide, with 41.85% C, 16.26% N, 4.68% H, and 18.62% S, was used as the calibration standard for the C/S analysis instrument. XRF, ICP-OES, XRD, and C/S analyses were performed at the Central Laboratory of Pukyong National University. The model used for analysis in this study was the EM-30AX, a scanning electron microscope and energy-dispersive X-ray spectrometer, COXEM, Daejeon, Republic of Korea (SEM-EDS), which allowed for a comprehensive examination of the nickel ore and slag’s morphology and the distribution of their elements.

3. Results and Discussion

3.1. Carbon-Based Smelting for Selective Reduction

3.1.1. Thermodynamic Modeling of Ferro-Nickel Smelting

The quality and composition of the calcined nickel ore used in the ferro-nickel smelting process can differ due to various factors. These factors include the composition and mineral composition of the nickel ore, with a particular focus on the desired elemental nickel content, the conditions during calcination, and the resulting outcomes. In nickel smelting, the Fe/Ni ratio of ferro-nickel and the grade of nickel in the alloy are influenced by the composition of the raw material and the correct amount of carbon in the reducing agent. A high nickel content in the ore is crucial for the production of high-grade alloys, and in this particular case, the ratio of Fe/Ni was 80/20. The primary aim of this research was to extract the highest grade of nickel possible from the ore, while also striving to achieve the highest Fe/Ni ratio. In addition, during the first stage, we conducted calculations to determine the amount of carbon consumption for reduction smelting, as well as conducting smelting tests to verify the results. On the other hand, it is important to note that the content of FeO, which is one of the main constituents of the MgO-SiO₂-FeO-based slag used in nickel smelting, needs to be provided at approximately 10%. The calculation of the amount of carbon required to extract ferro-nickel from the calcined nickel ore at a temperature of 1550 °C and a pressure of 1 atm was performed using the data from FactPS, FToxid, and FSstel in the Factsage 8.2 software. The chemical composition of the calcined ore, as shown in Table 1, guided the input considerations into Factsage. It should be highlighted here that, based on the ICP-OES analysis, the iron content was calculated to be 22.7 wt.% Fe₃O₄, and MnO and Co₂O₃ were excluded from the calculation due to their low contents.

The relationship between the chemical composition of ferro-nickel and the amount of reducing carbon added during the reduction smelting of nickel ore is depicted in Table 3. The data in the table were calculated using the “Equilib” module in the Factsage program. Upon the addition of carbon, both iron and nickel underwent immediate reduction from the calcined nickel ore. Moreover, it is worth mentioning that once the carbon content goes beyond 5 wt.%, there is an estimated likelihood of the reduction of silicon and chromium from the ore, and subsequently, their dissolution takes place in the ferro-nickel. Furthermore, it can be observed that the weight of the extracted ferro-nickel rises proportionally with the addition of carbon. The addition of more carbon leads to a higher reduction of iron, which, in turn, causes an increase in the weight of the ferro-nickel. However, it is important to note that the iron reduction process is not desirable in the current nickel smelting process. Therefore, the optimal Fe/Ni ratio of approximately 4 (80:20) is aimed to be achieved in order to produce high-grade ferro-nickel. By adding carbon at concentrations of 3 wt.% and 4 wt.%, it becomes feasible to produce alloys that fulfill the ferro-nickel objective. The calculation revealed that increasing the carbon addition beyond 5 wt.% results in an increase in the iron content and a decrease in the nickel grade in the alloy. Furthermore, it was observed that the Fe/Ni ratio reaches 7.7 at this stage.

Table 4 provides a comprehensive overview of how the composition of ferro-nickel is influenced by the addition of carbon, while the Factsage 8.2 program allowed us to observe the corresponding alterations in the composition of the slag formed during the melting process of nickel ore. There is a direct correlation between the increase in carbon content and the reduction of nickel. Moreover, if the carbon addition surpasses 3 wt.%, the slag’s nickel oxide content drops to an exceptionally low level of 0.005%. As carbon is added in larger quantities, the content of iron oxide in the slag, which is predominantly in the form of FeO, gradually decreases. In the event that the addition of carbon exceeds 6 wt.%, it will result in a decrease in the iron oxide content to less than 1%. Additionally, the slag composition will primarily consist of mixtures of minor Al₂O₃ and CaO based on the MgO-SiO₂ slag system. By excessively reducing the iron oxide content in the slag, there are several negative consequences that arise. Firstly, the desired structure of the slag is compromised, as its intended role is eliminated. Moreover, this reduction results in the slag having a higher melting temperature and increased viscosity. Consequently, meeting the requirement of 10% iron oxide content in the slag is imperative. In order to meet the specified criteria in the reduction smelting regime, it was found that carbon additions of 3 wt.% and 4 wt.% were the most suitable within this requirement. These carbon additions effectively reduced the iron oxide to the desired level while maintaining an Fe/Ni ratio as close to 4 as possible. The addition of carbon results in the reduction of chromium from the slag, which is then transferred to the metal. Comparing the reduction smelting of ferro-nickel with different carbon additions, it was found that the MgO/SiO₂ ratio in the resulting slag was 0.53 when 3 wt.% carbon was added, and it increased to 0.55 with a 4 wt.% carbon addition.

Figure 4 illustrates the balance of reduction smelting products and the activation of compounds that are formed on the carbon added during smelting, as depicted by the Factsage software. The variation in the calculation of the product material balance, as depicted in Figure 4a, during smelting at a temperature of 1550 °C and under 1 atm pressure, is dependent on the quantity of reducing carbon utilized. With the increase in the amount of carbon added, there is a corresponding decrease in the weight of the slag. Conversely, the amount of liquid metal (Fe-Ni) and the quantity of gas produced during the melting process steadily increase. When the carbon addition is 5 wt.%, the main mineral in calcined nickel ore, olivine, undergoes complete decomposition and transfers its elements to both the liquid metal and slag. On the other hand, when the amount of carbon addition is increased, the iron content in the slag decreases, leading to the enrichment of magnesium in the slag. Consequently, at elevated temperatures, the formation of magnesium-rich orthopyroxene (Mg₂Si₂O₆) occurs. From the balance of products, it is apparent that the breakdown of the olivine structure occurs sufficiently when subjected to melting with carbon reduction levels not exceeding 4 wt.%. Moreover, the nickel oxide present in nickel ore can undergo complete reduction and be converted into metal.

Chemical thermodynamics activityindicates the measure of the free composition of species in a mixture, providing insights into how they may react upon activation [33]. Through the calculation of the smelting product’s activity in relation to the carbon content, one can uncover the range of products that may arise during smelting, as shown in Figure 4b. Upon the addition of carbon, the activity of CO in the gas became equal to 1, resulting in a corresponding decrease in the activity of CO₂. The smelting process occurred in an atmosphere of CO gas. As the activity of the base metals in the spinel decreased to zero, they were observed to be reduced and transferred to the metal. In contrast, the liquid metal’s activity steadily increased and reached a value of 1 when the carbon content exceeded 7 wt.%. As the main mass of the nickel ore was transferred to the absorbed slag, the iron and nickel contents underwent reduction, resulting in a decrease in activity. Furthermore, as the iron and nickel underwent the process of transforming into metal, there was a slight uptick in their levels. The value of metal activity was at 1. Likewise, the slag activity matched the value of 1. As the carbon content increased, the olivine compound, which can include iron (Fe) and nickel (Ni), experienced a reduction in its presence, ultimately disappearing entirely at 6 weight percent carbon. When the slag contains more MgO, olivine has a greater tendency to reform. The fact that the activity of olivine phase decreased as it disappeared but then increased again indicates this.

The compounds identified through Factsage modeling exhibited a correlation with the mineralogical data obtained via XRD analysis. Here, our findings indicated the predominance of magnesium silicate (MgSiO₃) and magnesium nickel silicate in the olivine. The presence of spinel, a compound that corresponds to magnesium aluminum iron oxide, was also noted in the references shown in Figure 4b. The equations (Equations (2)–(8)) provided below serve to represent the reactions that occur during the smelting process. The occurrence of nickel melting at high temperatures initiates the reduction of Ni, Fe, Cr, and Si oxides by solid carbon. Once the smelting medium becomes primarily CO gas, the reduction reaction is driven by the high concentration of CO in the gas (Equation (3)).

Within the nickel laterite deposits, the iron, which is a component of associated minerals, exists predominantly in the form of iron oxides such as hematite (Fe₂O₃) and goethite (FeO(OH)). Before ferro-nickel smelting, the raw material undergoes calcination and reduction. During the reduction process, iron undergoes reduction to yield metallic iron or iron magnetite oxide (Fe₃O₄). The calcined ore used in this experiment did not show any presence of iron in magnetite form, but its compounds were detected. Based on this analysis, it is anticipated that the primary phase of the process will focus on converting iron from its magnetite oxide state. Equations (4) and (5) illustrate the potential reactions that can occur during the reduction of iron magnetite to iron. The process of nickel reduction was carried out according to Equation (6). Equation (7) illustrates the process where the iron and nickel in the ore, which are in the form of silicate with an olivine structure, are decomposed and removed at high temperatures until the ore reaches its melting point. Slag is formed when the iron and nickel are extracted from the ore. This is due to the reaction between silicon oxide and the released iron and magnesium oxides, resulting in the formation of easy-melting eutectics (Equation (8)).

Me_xO_y (s) + C (s) = Me_xO_y−1 (s) + CO₂ (g)

(2)

CO₂ (g) + C (s) = 2CO (g)

(3)

Fe₃O₄ (s) + CO (g) = 3FeO (s) + CO₂ (g)

(4)

FeO (s) + CO (g) = Fe (s) + CO₂ (g)

(5)

NiO (s) + CO (g) = Ni (s) + CO₂ (g)

(6)

Me₂SiO₄ (s) + 2CO (g) = 2Me (s) + SiO₂ (s) + 2CO₂ (g)

(7)

MeO (s) + MgO (s) + SiO₂ (s) = MeMgSiO₄ (s)

(8)

Based on the outputs from the Equilib module for ferro-nickel smelting, which involved analyzing the material balance and the activity of the stable compounds, it was determined that the amount of carbon significantly influenced the process. This led to an investigation into the thermodynamic parameters, including Gibbs energy and the heat of reaction, as shown in Figure 5a. The Gibbs energy (Figure 5a) dropped from −1575 kJ to −1592 kJ when the carbon addition values were at the ideal percentages of 3 wt.% and 4 wt.%. The thermal changes of the reactions during ferro-nickel smelting are visually represented in Figure 5b, providing valuable insights into the process. As carbon amounts rise during nickel smelting, the process generates more heat.

3.1.2. Ferro-Nickel Smelting with Carbon Reduction

The purpose of conducting smelting tests at a temperature of 1550 °C, with a holding time of 3 h, was to analyze the ferro-nickel smelting process from calcined nickel ore. The addition of carbon as a reducing agent was carried out at two different weight percentages, specifically, 3 wt.% and 4 wt.%. These percentages were determined based on the calculated conditioning using Factsage 8.2. Figure 6 shows the manner in which metal is released subsequent to reduction smelting. During the extraction of nickel from the ore, the iron and nickel undergo a reduction process, and as they traverse the molten slag, their small droplets can come together and segregate into a bulk metal part (as illustrated in Figure 6a). In addition, it was noted that the small metal droplets exhibited a tendency to be retained in the slag during the melting process. These observations are clearly depicted by the arrows in Figure 6b. By altering the chemical composition of the slag, it becomes imperative to lower both the melting temperature and the viscosity of the slag in order to minimize the mechanical loss of metals, which occurs due to the retention of metals in the slag as minute droplets.

Once the smelting was finished, the ferro-nickel parts and the slag underwent separation and were then thoroughly analyzed to ascertain their respective chemical compositions. The chemical composition of the ferro-nickel was determined using ICP-OES analysis, with details on the extraction efficiency of smelting shown in Table 5. When the reduction smelting process was carried out using 3 wt.% carbon, it resulted in the release of 6.54 g of ferro-nickel. The composition of this alloy was found to be 78.7% Fe, 20.5% Ni, 0.12% C, 0.43% Cr, and 0.22% Si. The iron and nickel contents of this alloy (76.4% Fe and 23.4% Ni) were found to be quite similar to the calculated results from Factsage 8.2. However, there was a slightly higher carbon content. Moreover, the chromium and silicon contents of the experimentally extracted alloy were observed to be higher than the composition of the calculated alloy. The ratio of Fe/Ni in this sample was measured to be 3.83, a value that closely resembles that of a high-grade ferro-nickel. It is important to note that, during the reduction melting process, specifically with the addition of 4 wt.% carbon, a significant amount of ferro-nickel (10.71 g) was extracted. The results of the chemical composition analysis showed similarities between the iron and nickel contents and the calculation results of Factsage, but there were noticeable disparities in the chromium and silicon contents. A significant increase in the carbon content was observed, measuring 0.31%. With an Fe/Ni ratio of 5.07, it can be concluded that the amount of ferro-nickel was at a lower grade.

XRF was utilized to conduct the analysis of the chemical composition of the slag after smelting, while ICP-OES analysis was employed specifically to determine the iron and nickel contents of the slag. Table 6 provides information on the chemical composition of the slag that was generated during reduction melting using carbon contents of 3 wt.% and 4 wt.%. The Fe₂O₃ content exhibited a noticeable decrease, dropping from 14.18% in the slag with 3 wt.% carbon reducer to 10.14% in the slag with 4 wt.% carbon reducer. This decrease suggests a greater reduction of iron from the slag, aligning with the previously mentioned metal yield and analysis findings. According to research, there is a belief that the iron oxide content found in the slag can satisfy the requirement of around 10%. When the smelting slag was treated with a 3 wt.% carbon reducer, the nickel content was measured to be 0.17%. However, no trace of nickel was found in the slag when a 4 wt.% carbon reducer was utilized, suggesting that the nickel concentration was either extremely low or non-existent in the slag. It was confirmed that the complete reduction of nickel from the ore was achieved by utilizing reduction smelting, wherein 4 wt.% carbon was employed. The ICP-OES analysis results revealed that, for a carbon reducer of 3 wt.%, the slag contains 11.1% Fe and 0.36% Ni, while for a carbon reducer of 4 wt.%, it contains 7.33% Fe and 0.017% Ni, which further supports the conclusions drawn from the XRF analysis. As previously stated, it was noted that the slag’s nickel content was insufficient when the carbon reducer reached 4 wt.%. The chemical composition of the slag, as determined by the results of the 4 wt.% carbon smelting experiment and Factsage calculations, revealed that the iron and nickel contents were remarkably similar to each other (as shown in Table 4). The slags that were formed during the tests, which used 3 wt.% and 4 wt.% carbon reducers, were found to consist primarily of around 30% MgO and approximately 40% SiO₂ oxides. These composition percentages indicate that these oxides are the main constituents of the slags. According to the calculations conducted using Factsage, it was determined that the composition of the slag was remarkably similar; however, there was a notable difference of approximately 10% in the SiO₂ content when compared to the results obtained from the melting test. The reason behind the higher M/S ratios of 0.72 and 0.65 in the experimental slag, in contrast to the calculated slag by Factsage, was the lower SiO₂ content found in the actual test’s slag. Both the experimental and calculated slags were found to contain other impurity elements such as Al₂O₃, Cr₂O₃, and CaO, and no significant differences were observed between them. The ZrO₂ and Y₂O₃ oxides detected in the slag were most likely the result of mechanical mixing during the removal process from the zirconia crucible. There was no indication of any reaction occurring between the zirconia crucible and the slag. The significant differences in ZrO₂ content within the slags strongly support the previously proposed conclusion.

The mineralogy of the slag produced during smelting, using both a 3 wt.% and a 4 wt.% carbon reducer, was analyzed through XRD analysis. The results can be observed in Figure 7. SiO₂, MgO, and FeO oxides were found to be the main constituents of the slag, according to the results obtained from the XRF analysis. Additionally, the XRD analysis confirmed the presence of compounds made up of these oxides as the detected phases. The analysis revealed that the melting slag with 3 wt.% carbon was primarily composed of the dominant compound forsterite ferroan (MgFeSiO₄—(DB card number 01-083-0087)), while some enstatite (MgSiO₃—(DB card number 00-019-0768)) compounds were also present. The analysis determined that forsterite ferroan was the main component in the slag when using a carbon reducer with a weight percentage of 4 wt.%. The process of thermodynamic modeling of reduction smelting also provided insights into the potential formation of olivine and orthopyroxene phases rich in magnesium (Mg₂Si₂O₆) within the slag. Furthermore, experimental results from real-world scenarios demonstrated that the composition of the slag primarily consisted of magnesium silicates. The fact that ZrO₂ was found in the slag as single phase, rather than as a constituent of a compound, provides conclusive evidence that contamination occurred during the physical separation of the slag from the crucible.

3.2. Optimizing Slag Composition for Ferro-Nickel Smelting

3.2.1. Thermodynamic Modeling for Optimal Slag Composition

The ideal carbon content for reduction smelting of calcined nickel ore was determined to be a reduction of 4 wt.%. The ferro-nickel, which was obtained through reduction smelting with a carbon content of 4 wt.%, was found to have a nickel content of 16.1% and an Fe/Ni ratio of 5.07. The nickel smelting slag, which had a MgO/SiO₂ ratio of 0.65, also contained a significant amount of iron oxide (10.14%). The observation revealed the presence of small particles of ferro-nickel in the slag, posing a risk of increased mechanical loss of the metal. Therefore, it is imperative to enhance the physical properties of the slag. This study focused on altering the composition of the slag to lower its melting temperature and viscosity, which involved modifying the contents of MgO and SiO₂—the main constituents of nickel smelting slag—in order to achieve the desired slag properties. The studies [34,35,36,37] conducted on slag basicity (B = MgO/SiO₂) during nickel smelting have shown that the highest nickel recovery was achieved when the MgO/SiO₂ ratio values ranged between 0.5 and 0.8. In order to optimize the melting regime and achieve a high recovery of ferro-nickel, the next step of this research focused on altering the chemical composition of nickel smelting slag while maintaining a constant temperature of 1550 °C. The objective was to find a slag with optimal basicity that facilitates the desired outcome. The calculations in Factsage 8.2 software were conducted using the FactPS, FToxid, and FSstel data. The temperature and pressure conditions for the calculations were set at 1550 °C and 1 atm, respectively. During the calculations, the chemical composition of the resulting slag was modified based on the outcomes of reduction melting with a 4 wt.% carbon reducer. During the reduction melting process, the slag formed had a basicity of 0.65 MgO/SiO₂. To study the impact on the slag’s structure and properties, additional SiO₂ and MgO fluxes were introduced. The objective was to understand the influence of these fluxes on the extraction of metal. The material balance, ferro-nickel chemical composition, and slag composition were determined by utilizing the Factsage 8.2 software. In order to predict these factors, additions of 2 to 10 wt.% SiO₂ and 2 to 10 wt.% MgO were incorporated into the calculations. The main objective was to analyze the slag structure based on these predictions. Table 7 provides information on the weight of stable products that were formed through reduction melting of nickel, with the use of SiO₂ and MgO as additives. According to the weight balance analysis, the amount of additive used does not result in a substantial alteration in the quantity of metal extracted. Additionally, there were no significant differences in the weight of the gases that were released during the melting process. The direct addition of flux had a noticeable impact on the weight of the slag, resulting in both an increase in weight and a structural alteration. According to the calculations, it was determined that the olivine phase, which was initially formed through the smelting process and with the addition of SiO₂, is expected to undergo a transformation into a uniform liquid slag. This transformation consequently leads to an increase in the weight of the slag. On the other hand, when smelting with MgO flux, there was an increase in the amount of direct olivine phases, but there was a decrease in the weight of the liquid slag. The olivine phase, which is a compound consisting of a mixture of elements, including nickel, is projected to have an adverse influence on the extraction of nickel.

Based on the results of the Factsage 8.2 calculations, Table 8 provides an overview of the relationship between the composition of the ferro-nickel to be extracted and the corresponding additive that needs to be added to the slag. The addition of SiO₂ to the slag did not have a significant impact on the nickel concentration in the iron; however, there was a minor increase in the silicon content of the alloy. By increasing the amount of SiO₂ added, it is estimated that the concentration of silicon in the alloy will steadily increase, ultimately reaching 0.046% when the weight percentage reaches 10 wt.%. When smelting with the addition of MgO, it was observed that the level of ferro-nickel did not yield the same effect as the addition of SiO₂. On the other hand, it was noted that there was a slight increase in the content of Cr in the alloy, as well as a slight increase in the presence of other impurities. The results of this calculation indicate that the addition of SiO₂ and MgO into slag does not have a significant effect on the reduction of ferro-nickel.

The changes in the chemical composition of the slag formed during melting with the addition of SiO₂ and MgO are presented in Table 9. When SiO₂ was added to the slag, it was observed that the content of silicon oxides in the slag directly increased. Conversely, it was found that the contents of MgO and FeO oxides decreased as the percentage of total weight increased. The analysis revealed that the nickel content in the slag was extremely minimal, barely reaching 0.002%. When the SiO₂ addition was at 2 wt.%, 4 wt.%, and 6 wt.%, the M/S ratio of the slag reached 0.54, 0.52, and 0.50, respectively. However, as the SiO₂ addition increased to 8 wt.% and 10 wt.%, the M/S ratio decreased to 0.48 and 0.46, respectively. Thus, it is advisable to conduct practical experiments with SiO₂ addition amounts of 2 wt.%, 4 wt.%, and 6 wt.% to assess their convenience. In spite of this, it is important to note that the variation in slag composition due to the addition of different amounts of MgO was not found to be significant. This lack of significant difference can be attributed to the formation of the olivine solid phase, as indicated by the phase balance calculations provided in Table 7. The increase in the weight of the olivine phase can be attributed to the addition of MgO, as the weight of the slag decreases. This is due to the fact that some of the main constituents from the main melting liquid slag combine with MgO, thereby contributing to the formation of the olivine phase. The olivine phase, which is a compound, is known for its high magnesium content. Considering the substantial increase in the formation of a solid olivine phase resulting from the addition of MgO, it is advisable to raise the M/S ratio by an equivalent amount to the addition of SiO₂ for the M/S ratios of 2 wt.%, 4 wt.%, and 6 wt.%.

Depending on its composition, it is crucial to provide an explanation of the structure of nickel smelting slag on the ternary diagram of the MgO-SiO₂-FeO system. By utilizing the FToxid data from the Factsage 8.2 software, a ternary diagram of the MgO-SiO₂-FeO system was created. This diagram showcases the chemical composition of the slag at a specific temperature of 1550 °C and a pressure of 1 atm. Figure 8 displays the outcome of the structure determination, which was based on the calculated slag composition. In the figure, C1 shows the region of slag in the reduction smelting with 4 wt.% carbon without the addition of any flux. In this figure, slag region with varying amounts of SiO₂ (2 wt.%, 4 wt.%, and 6 wt.%) are labeled as S1, S2, and S3, respectively. Similarly, slags with different amounts of MgO (2 wt.%, 4 wt.%, and 6 wt.%) are marked as M1, M2, and M3, respectively. Furthermore, the M/S ratios of the key constituents of the slag, including MgO, SiO₂, and FeO oxides, are presented in Figure 8, where the proportions of these oxides are calculated as 100%. The results of the experiment revealed that the slag generated during the reduction smelting procedure, which involved a carbon addition of 4 wt.% and no addition of flux, was positioned right at the boundary separating the olivine formation zone from the liquid slag. This significant boundary is denoted by the presence of a black triangle symbol. As illustrated in Figure 4, it can be observed that the same conclusion was reached, indicating that approximately 7% of the olivine phase was present in the calculation of the balance of stable phases formed, which varies with the quantity of carbon added. Stated differently, the possibility of solid olivine phases beginning to develop within the slag was suggested. The addition of SiO₂ to the slag led to a notable shift in the slag’s structure, causing it to move towards the SiO₂ peak at the top of the triangular diagram. As a result, the slag was found to reside in the liquid slag region, as observed in the S1, S2, and S3 samples. The conclusion drawn from this analysis aligns with the findings presented in Table 7, which demonstrate that the addition of SiO₂ to the smelting slag results in a 100% presence of the substance in the liquid slag phase. In contrast, the addition of MgO resulted in the movement of the slag towards the olivine zone, indicating that the slag was present in both the olivine and liquid slag zones, as evidenced by samples M1, M2, and M3. The indication is that, with a higher amount of MgO addition, the slag has the capability to undergo a complete conversion into a 100% solid olivine phase. The structural analysis of this slag reached a conclusion that further confirmed the beneficial effect of MgO addition on the formation of a solid olivine phase. This finding aligns perfectly with the results obtained from the previous Factsage calculations. The data obtained from the Factsage software indicate that the olivine phase consists of a combination of metal silicates. Among the different types of minerals analyzed, the one that was found to be the most prevalent was Mg₂SiO₄, a silicate that is high in magnesium content. It was calculated that the coexistence of other silicates, including FeMgSiO₄, MgFeSiO₄, and CaMgSiO₄, is also plausible. Another point to consider is the estimation that nickel can be found in MgNiSiO₄ and FeNiSiO₄ silicates. Based on the findings of this analysis, it can be concluded that the chemical loss linked to the nickel slag might take place due to its association with the olivine phase.

3.2.2. Ferro-Nickel Smelting for Optimizing Slag M/S Ratio

The experiment, conducted using the Factsage 8.2 modeling software, aimed to enhance the physical properties of the slag. This was carried out with the goal of improving the separation of metal from the slag. The experiment involved subjecting the slag to a temperature of 1550 °C for a duration of 3 h. The change in the basicity of the slag—specifically, the ratio of MgO to SiO₂—was identified as the crucial variable in this experiment. The preparation for the smelting test involved combining 100 g of nickel ore with a carbon reductant of 4 wt.% and flux additives of SiO₂ and MgO oxides in quantities of 2 wt.%, 4 wt.%, and 6 wt.%. The metal and slag components underwent a thorough separation process after smelting, followed by detailed chemical and mineralogical analysis. Table 10 showcases the chemical composition of the ferro-nickel, based on the results obtained from ICP-OES analysis, along with details on the extraction efficiency during smelting. A detailed, independent analysis of the efficiencies of iron and nickel extraction during the smelting process, categorized by slag basicity for improved understanding, is provided in Section 3.3. The iron content in the ferro-nickel formed during the smelting process with SiO₂ did not show any significant change. However, there was a noticeable difference in the nickel content, which was approximately 15.7% when 2 wt.% and 4 wt.% SiO₂ were added during the smelting process. The content of chromium in the alloy exhibited erratic fluctuations, whereas the content of silicon progressively increased to 0.17%, 0.21%, and 0.45% in consecutive stages. This can be attributed to the formation of free quartz resulting from the higher silicon oxide content in the slag, along with the facilitated release of silicon at elevated melting temperatures. In the smelting process with the addition of SiO₂, there was a slight reduction in the ferro-nickel grade, resulting in an Fe/Ni ratio of 5.3. When it comes to smelting with the addition of MgO, particularly with 2 wt.% and 4 wt.% MgO, it was observed that the average iron content reached 81.7%, the nickel content amounted to 17.4%, and the Fe/Ni ratio level stood at a relatively high 4.7. However, it should be noted that, as a result of the melting process with the addition of 6 wt.% MgO, the nickel content in the ferro-nickel decreased to 15.9%, while the Fe/Ni ratio increased to 5.15, which suggests a decrease in the overall alloy level. When comparing other impurity elements, there were no notable differences.

The chemical composition of the slag formed during the smelting of nickel ore, under the flux-added slag, is presented in Table 11. Based on the findings from the XRF analysis, it was concluded that the inclusion of 2 wt.%, 4 wt.%, and 6 wt.% SiO₂ in the slag led to an increase in silicon oxide content by 46.39%, 48.18%, and 50.64%, respectively. Conversely, the addition of SiO₂ resulted in a decrease in MgO content by 29.73%, 26.96%, and 26.40%, respectively. In each trial, the M/S ratio of the slag showed a decrease with the increasing addition of SiO₂, with values of 0.64, 0.55, and 0.52 recorded. With the increase in SiO₂ oxide content, there was a slight decrease in the proportion of iron oxide as a percentage of the total mass. The analysis of the slag involved the use of ICP-OES to determine the iron and nickel contents. Upon the addition of SiO₂ oxide, there was a noticeable escalation in the iron content, with percentages of 6.19%, 7.48%, and 10.0% recorded. In a similar manner, the nickel content demonstrated an increase, with values of 0.012%, 0.37%, and 1.0%. Here, it can be seen that the increase in nickel was accompanied by an increase in iron. However, when MgO was added to the slag, the M/S value of the slag increased proportionally. Specifically, as the MgO content in the slag increased, the M/S value reached 0.69, 0.73, and 0.81. The iron oxide content in the slag experienced a substantial rise, with measurements reaching 10.23%, 10.41%, and 12.25%. The ICP-OES analysis revealed that there was an increase in the nickel content in the slag, with values reaching 0.016%, 0.13%, and 1.17%, respectively.

In Figure 9, the mineralogical analysis of the slag resulting from nickel flux smelting is displayed. The analysis reveals two different patterns: one characterized by the addition of SiO₂, and the other by the addition of MgO oxide. By examining the added flux content, the mineralogy of the slag formed in the smelting with SiO₂ flux can be determined, as depicted in Figure 9a. The dominant constitutive phase observed in these slags was identified as forsterite ferroan (MgFeSiO₄), which is an iron magnesium silicate compound with a DB card number of 01-083-1540. The appearance of pigeonite (MgFeAlSiO₆ (DB card number 01-071-2429)) phases can be observed as the slag undergoes an enrichment process with SiO₂, with an additional 4 wt.% and 6 wt.% SiO₂ being introduced. In the case of slag with added MgO (Figure 9b), it was found that the main component phase was identical to forsterite ferroan. However, further analysis revealed the presence of a mixture of enstatite (MgCaSiO₃) and magnesium calcite silicates (DB card number 01-076-0524). It was observed that with an increase in MgO addition to 6 wt.%, there was a noticeable increase in the mixing of pigeonite phases within the slag. The findings from the XRD analysis provide confirmation that there was a change in the composition of the slag.

The structure of the slag was analyzed in the MgO-SiO₂-FeO ternary system using the phase diagram projection of Factsage, which was based on the chemical analysis and mineralogical analysis of the slag formed during flux smelting. The analysis was conducted under isotherm conditions with temperature transition. The isotherm diagram is a valuable tool that visually represents the limit curves, indicating the precise temperatures at which phases undergo solidification or melting. Consequently, researchers can utilize this diagram to experimentally deduce the structure of the slag formed and accurately determine its melting temperature. The slags that were formed during the smelting test were given abbreviated names, similar to the ones described in Figure 8, and represented by various figures. As previously described, in the smelt with 4 wt.% carbon reductant and without any flux addition, the slag formed (represented by label C1) was found at the interface between the liquid slag and the olivine phase. The M/S ratio of this slag fell within the range of slags with SiO₂ addition and slags with MgO addition. The composition and the M/S ratio of the slags, as well as the phase isotherm diagram, are shown in Figure 10. A structural transformation occurred in the slags due to the addition of SiO₂, specifically towards the apex of the triangular SiO₂ oxide. This means that the slag with the 2 wt.% SiO₂ addition, denoted as S1, was located within the liquid slag region. Depending on the FeO component contents, the smelting and solidification temperatures of liquid slag exhibit distinct zoning patterns, which are easily discernible through the colors of the temperature zone. As the FeO content in the slag increases, its melting temperature experiences a decline, leading to a change in the temperature zones. The incorporation of SiO₂ (samples S1 to S3) resulted in a liquid slag state. Decreasing temperatures resulted in alterations to the phase formation within the liquid slag (points 1 to 3) due to the addition of SiO₂, shifting the phase mixing zone toward clinopyroxene and liquid slag.

On the other hand, when the MgO oxide (M1, M2, and M3) was added, the ternary diagram revealed an interesting finding: the presence of the olivine phase in the liquid slag increased. This can be attributed to the transition of the slag structure from the boundary between the liquid slag and the olivine zone, leading to the formation of the olivine phase zone. According to the diagram of the MgO-SiO₂-FeO ternary system, it was observed that the presence of olivine phase in the slag with MgO addition led to an increase in the melting temperature of the slag. The addition of both 2 wt.% and 4 wt.% SiO₂ to the slags resulted in a composition that promotes a high liquid slag phase percentage, which can reach up to 100%. The melting temperature required for these slags to achieve this liquid state ranges between 1400 °C and 1500 °C.

In Figure 11, the products of the reduction smelting process, namely, the slag and the separated ferro-nickel particles, are depicted. This process was conducted with the addition of 6 wt.% MgO to the slag nickel ore. When looking at the solidified structure of the nickel smelting slag, one can clearly see two distinct phases without the need for any magnification. Throughout the smelting, a clear separation occurred, with the magnesium silicates floating to the surface and the iron–magnesium silicates settling at the bottom, resulting in a visually striking contrast. The presence of slag in the lower part of this process was characterized by its relatively high melting temperature and viscosity. These properties of the slag pose a challenge to the movement of small metal particles that are released from the ore, thereby inhibiting their ability to unite and form a cohesive metal structure. Consequently, this phenomenon results in the generation of numerous small metal particles, which are clearly depicted in Figure 11.

3.3. Effect of Slag Basicity on Ferro-Nickel Smelting

The efficiency of metal extraction in the nickel smelting test was compared, and it was found that it is dependent on the basicity of slag. By conducting a comparison between the calculations obtained from the Factsage software and the results of the smelting tests, it was determined that a carbon reducer of 4 wt.% in nickel reduction smelting is appropriate. Previous studies have demonstrated that the chemical composition and structural analysis of slag play a crucial role in influencing the separation of metals. The relationship between the grade of nickel and iron, the rate of recovery, and the basicity of slag formed during smelting is depicted in Figure 12. The relationship between the basicity of the slag and the content of nickel, as well as the rate of nickel recovery, is illustrated in Figure 12a. This demonstrates how fluctuations in these values can be influenced by the basicity of the slag. When the basicity of slag ranges from 0.5 to 0.6, it can be observed that the lowest value of nickel grade reaches 15.7%. Interestingly, despite this, the recovery degree shows an upward trend. The nickel grade reached its maximum value of 17.5% when the basicity was at 0.73. It should be noted that the nickel grade does not have a direct impact on the rate of nickel recovery. The degree of recovery, which reached 93.82%, 94.05%, and 95.61%, corresponded to basicity values of 0.64, 0.65, and 0.69, respectively. Conversely, it is interesting to observe that as the basicity increased to 0.73 and 0.81, there was a notable decrease in the rate of nickel recovery, with values dropping to 87.96% and 65.27%, respectively. These results clearly indicate that the efficiency of nickel smelting is significantly impacted by the characteristics of the slag. According to the analysis of the structure and metal extraction efficiency, it was observed that the nickel smelting slag with a basicity of 0.81 (with 6 wt.% MgO flux) had a two-layer structure with a distinctly different composition.

The observation revealed a general pattern, indicating that as the slag’s basicity increases, there is a corresponding decrease in the iron grade. However, it should be noted that the rate of iron recovery does not demonstrate a straightforward connection. At different basicity levels of slag (0.52, 0.55, and 0.64), there was a consistent trend of increasing iron recovery degrees, with the highest value observed at 58.13%. At a slag basicity of 0.73 and 0.81, the recovery degree of iron experienced a decline, reaching its lowest values at 47.37% and 38.72%, respectively. The significant loss of iron can be understood by examining the conversion of iron in the slag. This conversion results in the formation of a eutectic compound called ferromagnesium silicate (MgFeSiO₄). As mentioned earlier, this compound plays a vital role in forming a dark slag structure that settles at the bottom of the slag. When the slag’s basicity is 0.65, the iron recovery degree reaches its highest point, at 58.13%. Based on the analysis of the rate of metal recovery, it was observed that the extraction of iron and nickel metals yielded slightly varied results. However, the most optimal outcomes were obtained within the range of slag basicity values of 0.65 to 0.69.

4. Conclusions

The main purpose of this research was to determine the exact amount of carbon reductant necessary for the reduction smelting of calcined nickel saprolite ore. Moreover, this study examined the relationship between the grade and recovery degree of ferro-nickel. Furthermore, this research aimed to find the best smelting method for maximizing metal extraction using slag with ideal properties. Factsage 8.2 data (FToxid, FactPS, FSstel) were used to calculate the necessary carbon for nickel ore reduction smelting at 1550 °C and 1 atm. Smelting with 4 wt.% carbon achieved Fe/Ni = 5.07. Moreover, the FeO content in the slag remained consistently around 10%, precisely matching the target composition for optimal slag properties. The level of nickel extraction was directly influenced by the ratio of MgO/SiO₂. The M/S ratios of 0.64, 0.65, and 0.69 exhibited the highest outcomes, with corresponding results of 93.81%, 94.04%, and 95.6%, respectively. Both the lab experiments and the Factsage calculations yielded similar results for slag and metal chemical composition. By demonstrating the relationship between the structure and properties of the slag and its impact on the extraction of ferro-nickel, this research aimed to discover additional practical applications.

Author Contributions

E.U.: methodology, data curation, investigation, writing—original draft, software; S.-B.H.: writing—review and editing, data curation; J.-W.Y.: conceptualization, investigation; C.-H.J.: formal analysis, software; J.-P.W.: project administration, conceptualization, funding acquisition. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Korea Institute of Energy Technology Evaluation and Planning (KETEP) under the Korean government (MOTIE) [Grant Number 20227A10100010].

Data Availability Statement

The original contributions presented in this study are included in the article; further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

References

Dilshara, P.; Abeysinghe, B.; Premasiri, R.; Dushyantha, N.; Ratnayake, N.; Senarath, S.; Ratnayake, A.S.; Batapola, N. The role of nickel (Ni) as a critical metal in clean energy transition: Applications, global distribution and occurrences, production-demand and phytomining. J. Asian Earth Sci. 2023, 259, 105912. [Google Scholar] [CrossRef]
Zhou, X.; Zhang, H.; Zheng, S.; Xing, W.; Yang, H.; Zhao, Y. A study on the transmission of trade behavior of global nickel products from the perspective of the industrial chain. Resour. Policy 2023, 81, 103376. [Google Scholar] [CrossRef]
Maisel, F.; Neef, C.; Marscheider-Weidemann, F.; Nissen, N.F. A forecast on future raw material demand and recycling potential of lithium-ion batteries in electric vehicles. Resour. Conserv. Recycl. 2023, 192, 106920. [Google Scholar] [CrossRef]
Farrokhpay, S.; Cathelineau, M.; Blancher, S.B.; Laugier, O.; Filippov, L. Characterization of Weda Bay nickel laterite ore from Indonesia. J. Geochem. Explor. 2018, 196, 270–281. [Google Scholar] [CrossRef]
Fu, W.; Feng, Y.; Luo, P.; Zhang, Y.; Huang, X.; Zeng, X.; Cai, Q.; Zhou, Y. Weathering of Ophiolite Remnant and Formation of Ni Laterite in a Strong Uplifted Tectonic Region (Yuanjiang, Southwest China). Minerals 2019, 9, 51. [Google Scholar] [CrossRef]
Pandey, N.; Tripathy, S.K.; Patra, S.K.; Jha, G. Recent Progress in Hydrometallurgical Processing of Nickel Lateritic Ore. Trans. Indian. Inst. Met. 2023, 76, 11–30. [Google Scholar] [CrossRef]
Oxley, A.; Barcza, N. Hydro–pyro integration in the processing of nickel laterites. Miner. Eng. 2013, 54, 2–13. [Google Scholar] [CrossRef]
Nurjaman, F.; Astuti, W.; Bahfie, F.; Suharno, B. Study of selective reduction in lateritic nickel ore: Saprolite versus limonite. Mater. Today Proc. 2021, 44, 1488–1494. [Google Scholar] [CrossRef]
Pickles, C.A.; Marzoughi, O. Temperature and frequency dependencies of the permittivities of nickeliferous silicate laterite ores and reaction mixtures. Powder Technol. 2023, 428, 118867. [Google Scholar] [CrossRef]
Vahed, A.; Mackey, P.J.; Warner, A.E.M.; Anderson, C. A Review of Nickel Pyrometallurgy Over the Past 50 Years with Special Reference to the Former Inco Ltd and Falconbridge Ltd. In Ni-Co 2021: The 5th International Symposium on Nickel and Cobalt; The Minerals, Metals & Materials Series; Springer: Cham, Switzerland, 2021. [Google Scholar]
Tian, H.; Pan, J.; Zhu, D.; Yang, C.; Guo, Z.; Xue, Y. Improved beneficiation of nickel and iron from a low-grade saprolite laterite by addition of limonitic laterite ore and CaCO₃. J. Mater. Res. Technol. 2020, 9, 2578–2589. [Google Scholar] [CrossRef]
Zevgolis, E.N.; Daskalakis, K.A. The Nickel Production Methods From Laterites and the Greek Ferronickel Production Among Them. Mater. Proc. 2021, 5, 104. [Google Scholar] [CrossRef]
Uddin, M.H.; Khajavi, L.T. The effect of sulfur in rotary kiln fuels on nickel laterite calcination. Miner. Eng. 2020, 157, 106563. [Google Scholar] [CrossRef]
Park, J.-O.; Kim, H.-S.; Jung, S.-M. Use of oxidation roasting to control NiO reduction in Ni-bearing limonitic laterite. Miner. Eng. 2014, 71, 205–215. [Google Scholar] [CrossRef]
Tamehe, L.S.; Zhao, Y.; Xu, W.; Gao, J. Ni(Co) Laterite Deposits of Southeast Asia: A Review and Perspective. Minerals 2024, 14, 134. [Google Scholar] [CrossRef]
Heijlen, W.; Duhayon, C. An empirical estimate of the land footprint of nickel from laterite mining in Indonesia. Extr. Ind. Soc. 2024, 17, 101421. [Google Scholar] [CrossRef]
Sufriadin, F.S.; Tindoilo, P.D.; Nur, I.; Purwanto, A.R.; Irfan, U.R.; Basir, D.N.; Otake, T. Thermal Beneficiation of a Nickel Laterite Ore from the Obi Island of North Maluku, Indonesia Using Corncob Char as Reductant. Adv. Sci. Technol. 2024, 141, 95–102. [Google Scholar] [CrossRef]
Pintowantoro, S.; Abdul, F. Selective Reduction of Laterite Nickel Ore. Mater. Trans. 2019, 60, 2245–2254. [Google Scholar] [CrossRef]
Li, Y.-J.; Sun, Y.-S.; Han, Y.-X.; Gao, P. Coal-based reduction mechanism of low-grade laterite ore. Trans. Nonferrous Met. Soc. China 2013, 23, 3428–3433. [Google Scholar] [CrossRef]
Tian, H.; Guo, Z.; Zhan, R.; Pan, J.; Zhu, D.; Yang, C.; Pan, L. Effective and economical treatment of low-grade nickel laterite by a duplex process of direct reduction-magnetic separation & rotary kiln-electric furnace and its industrial application. Powder Technol. 2021, 394, 120–132. [Google Scholar] [CrossRef]
Quast, K.; Connor, J.N.; Skinner, W.; Robinson, D.J.; Li, J.; Addai-Mensah, J. Preconcentration strategies in the processing of nickel laterite ores part 2: Laboratory experiments. Miner. Eng. 2015, 79, 269–278. [Google Scholar] [CrossRef]
Zhu, D.; Zhou, X.; Luo, Y.; Pan, J.; Bai, B. Reduction Smelting Low Ferronickel from Pre-concentrated Nickel-Iron Ore of Nickel Laterite. High Temp. Mater. Process. 2016, 35, 1031–1036. [Google Scholar] [CrossRef]
Chen, Y.-F.; Lv, X.-M.; Pang, Z.-D. Effect of basicity and Al₂O₃ on viscosity of ferronickel smelting slag. J. Iron Steel Res. Int. 2020, 27, 1400–1406. [Google Scholar] [CrossRef]
Luo, J.; Li, G.; Rao, M.; Peng, Z.; Liang, G.; Jiang, T.; Guo, X. Control of slag formation in the electric furnace smelting of ferronickel for an energy-saving production. J. Clean. Prod. 2020, 287, 125082. [Google Scholar] [CrossRef]
Rao, M.; Li, G.; Jiang, T.; Luo, J.; Zhang, Y.; Fan, X. Carbothermic Reduction of Nickeliferous Laterite Ores for Nickel Pig Iron Production in China: A Review. JOM 2013, 65, 1573–1583. [Google Scholar] [CrossRef]
Urtnasan, E.; Kumar, A.; Wang, J.P. Artificial Slags with Modulated Properties for Controlled Nickel Dissolution in Smelting Process. Trans. Indian. Inst. Met. 2024, 77, 2293–2302. [Google Scholar] [CrossRef]
Ma, Y.-T.; Yang, P.; Lu, B.-G.; Dou, Y.-L.; Tian, J.-K.; Guo, W.-B.; Zhang, Z.-Q.; Shen, Y.-Y. Effect of FeO content on melting characteristics and structure of nickel slag. J. Min. Metall. Sect. B Metall. 2022, 58, 427–438. [Google Scholar] [CrossRef]
Wang, G.; Cui, Y.; Li, X.; Yang, S.; Zhao, J.; Tang, H.; Li, X. Molecular Dynamics Simulation on Microstructure and Physicochemical Properties of Fe_xO-SiO₂-CaO-MgO-“NiO” Slag in Nickel Matte Smelting under Modulating CaO Content. Minerals 2020, 10, 149. [Google Scholar] [CrossRef]
Rowe, H.; Hughes, N.; Robinson, K. The quantification and application of handheld energy-dispersive X-ray fluorescence (ED-XRF) in mudrock chemostratigraphy and geochemistry. Chem. Geol. 2012, 324–325, 122–131. [Google Scholar] [CrossRef]
Zhang, Y.; Qie, J.; Wang, X.F.; Cui, K.; Fu, T.; Wang, J.; Qi, Y. Mineralogical Characteristics of the Nickel Laterite, Southeast Ophiolite Belt, Sulawesi Island, Indonesia. Min. Metall. Explor. 2019, 37, 79–91. [Google Scholar] [CrossRef]
Abdul, F.; Firdausi, S.; Widyartha, A.B.; Setiyorini, Y.; Pintowantoro, S. The Role of Limestone in Enhancing Selective Reduction of Nickel in the Carbothermic Reduction of Laterite Nickel. Trans. Indian Inst. Met. 2023, 76, 2211–2219. [Google Scholar] [CrossRef]
Mudd, G.M.; Jowitt, S.M. The New Century for Nickel Resources, Reserves, and Mining: Reassessing the Sustainability of the Devil’s Metal. Econ. Geol. 2022, 117, 1961–1983. [Google Scholar] [CrossRef]
Seshadri, S. Fundamentals of Metallurgy; The Institute of Materials, Minerals & Mining: Washington, UK, 2005; pp. 66–72. [Google Scholar]
Zhang, T.; Wu, F.; Yang, J. Effect of basicity on the flow and crystallization behavior of synthetic nickel–iron alloy residue. Ceram. Int. 2023, 49, 17067–17073. [Google Scholar] [CrossRef]
Nurjaman, F.; Handoko, A.S.; Bahfie, F.; Astuti, W.; Suharno, B. Effect of modified basicity in selective reduction process of limonitic nickel ore. J. Mater. Res. Technol. 2021, 15, 6476–6490. [Google Scholar] [CrossRef]
Wang, X.; Zhu, D.; Guo, Z.; Pan, J.; Lv, T.; Yang, C.; Li, S. Efficient Utilization of Limonite Nickel Laterite to Prepare Ferronickel by the Selective Reduction Smelting Process. Sustainability 2023, 15, 7147. [Google Scholar] [CrossRef]
Shen, Y.; Chong, J.; Huang, Z.; Tian, J.; Zhang, W.; Tang, X.; Ding, W.; Du, X. Viscosity and Structure of a CaO-SiO₂-FeO-MgO System during a Modified Process from Nickel Slag by CaO. Materials 2019, 12, 2562. [Google Scholar] [CrossRef]

Figure 1. XRD pattern of calcined nickel ore.

Figure 2. SEM-EDS image of calcined nickel ore: (a) SEM image and (b) EDS mapping image.

Figure 3. Schematic diagram of the experimental apparatus.

Figure 4. The influence of carbon on smelting products: (a) weight of stable compounds and (b) activity of stable compounds.

Figure 5. Thermodynamic analysis of reduction smelting of calcined nickel ore with carbon addition: (a) Gibbs free energy and (b) heat of reaction in smelting.

Figure 6. Samples from reduction smelting test: (a) Segregated metal particles, (b) Small metal particles in the slag.

Figure 7. XRD pattern of slag during reduction smelting with 3 wt.% C and 4 wt.% C addition.

Figure 8. Analyzing simulated slag structure on MgO-SiO₂-FeO ternary system using FToxid data, Factsage 8.2 at 1550 °C and 1 atm.

Figure 9. XRD pattern of slag during Ni reduction smelting with flux addition: (a) with SiO₂ addition and (b) with MgO addition.

Figure 10. Slag structure analysis on MgO-SiO₂-FeO ternary phase diagram projection using FToxid data, Factsage 8.2.

Figure 11. Ferrous nickel and small metal particles extracted from slag in a reduction smelting test with 6 wt.% MgO flux.

Figure 12. Relationship of slag basicity with nickel smelting’s metal grade and recovery degree. (a) Nickel, (b) Iron.

Table 1. Chemical composition of calcined nickel ore.

Ox.	Fe₂O₃	NiO	MgO	SiO₂	Cr₂O₃	Al₂O₃	CaO	MnO	Co₂O₃	ZnO	ICP-OES
Mass, %	19.66	2.19	30.14	43.76	0.52	2.82	0.53	0.30	0.05	0.03	-	-
El.	Fe	Ni	Mg	Si	Cr	Al	Ca	Mn	Co	Zn	Fe *	Ni *
Mass, %	29.25	4.27	26.94	35.04	0.70	2.49	0.72	0.45	0.08	0.06	16.5	1.9

* Analyzed by ICP-OES.

Table 2. Chemical composition of calcined nickel ore by EDS analysis.

Element	Fe	O	Si	Mg	Ni
Mass, %	18.90	29.66	29.17	19.56	2.71

Table 3. Chemical composition of ferro-nickel in reduction smelting with varying carbon additions, as calculated by Factsage 8.2.

C Addition, wt.%	Element, %						Weight, g	Fe/Ni
C Addition, wt.%	Fe	Ni	C	Cr	Si	O	Weight, g	Fe/Ni
1	6.872	93.094	0.004	0.000	0.000	0.030	1.012	0.07
2	50.089	49.832	0.007	0.049	0.004	0.018	3.805	1.0
3	76.401	23.436	0.040	0.097	0.009	0.017	8.193	3.2
4	84.521	15.189	0.086	0.170	0.023	0.012	12.663	5.5
5	87.912	11.353	0.219	0.404	0.106	0.006	16.951	7.7
6	86.529	9.568	0.889	1.664	1.348	0.002	20.120	9.0
7	81.814	8.829	1.511	2.991	4.854	0.001	21.804	9.2
8	77.565	8.334	1.509	3.292	9.299	0.001	23.101	9.3
9	73.782	7.917	1.216	3.295	13.790	0.001	24.318	9.3
10	70.370	7.547	0.905	3.237	17.940	0.001	25.511	9.3

Table 4. Chemical composition of slag in reduction smelting with varying carbon additions, as calculated by Factsage 8.2.

C Addition, wt.%	Oxide, %									M/S
C Addition, wt.%	MgO	SiO₂	CaO	FeO	Fe₂O₃	NiO	CrO	Al₂O₃	Cr₂O₃	M/S
1	22.94	46.53	0.27	24.81	0.436	0.79686	0.94	2.74	0.54	0.49
2	24.68	47.97	0.27	22.89	0.100	0.02705	0.96	2.68	0.42	0.51
3	27.02	50.94	0.27	17.56	0.044	0.00571	1.11	2.75	0.28	0.53
4	29.87	54.10	0.28	11.51	0.018	0.00252	1.20	2.81	0.20	0.55
5	32.95	57.37	0.29	5.15	0.004	0.00106	1.24	2.89	0.10	0.57
6	34.65	59.90	0.32	1.00	0.0002	0.00021	0.94	3.17	0.03	0.58
7	35.41	59.75	0.38	0.25	0.00003	-	0.43	3.77	0.01	0.59
8	35.72	59.62	0.40	0.08	-	-	0.20	3.97	-	0.60
9	35.73	59.63	0.40	0.04	-	-	0.11	4.08	-	0.60
10	35.53	59.17	0.47	0.02	-	-	0.06	4.75	-	0.60

Table 5. Fe-Ni alloy composition and extraction efficiency in smelting.

C Addition, wt.%	Element, %						Fe/Ni	Weight of Metal in Alloy, g
C Addition, wt.%	Fe	Ni	Cr	Si	C	Etc.	Fe/Ni	Fe	Ni	Alloy
3	78.7	20.5	0.43	0.22	0.12	0.03	3.83	5.08	1.32	6.45
4	81.7	16.1	0.82	0.46	0.31	0.61	5.07	8.74	1.72	10.71

Table 6. Chemical composition of slag during reduction smelting with 3 wt.% C and 4 wt.% carbon reducers.

C Addition, wt.%	Oxide, %												M/S
C Addition, wt.%	Fe₂O₃	NiO	MgO	SiO₂	Cr₂O₃	Al₂O₃	CaO	MnO	ZrO₂	Y₂O₃	Fe *	Ni *	M/S
3	14.18	0.17	28.33	38.97	1.05	5.81	4.03	0.29	6.57	0.6	11.1	0.36	0.72
4	10.14	-	30.7	46.73	0.71	6.11	4.32	0.29	1.0	-	7.33	0.017	0.65

* Analyzed by ICP-OES.

Table 7. Stable compounds in nickel smelting with flux additions determined by equilibrium-based Factsage 8.2 calculations.

Flux Addition, wt.%	Amount of Phase Mass.%
Flux Addition, wt.%	Slag	Olivine	Metal	Gas	Sum
No flux, 4 wt.% C	78.409	7.47	12.66	9.416	103.96
With SiO₂
2	83.906	-	12.644	9.41	105.96
4	85.94	-	12.615	9.403	107.96
6	87.975	-	12.589	9.396	109.96
8	90.005	-	12.565	9.39	111.96
10	92.03	-	12.544	9.384	113.96
With MgO
2	73.28	10.59	12.66	9.41	105.94
4	68.18	17.68	12.67	9.41	107.94
6	63.12	24.74	12.67	9.41	109.94
8	58.10	31.76	12.67	9.42	111.95
10	53.12	38.73	12.68	9.42	113.95

Table 8. Composition of Fe-Ni alloy in nickel smelting, determined by equilibrium-based Factsage 8.2 calculations.

Flux Addition, wt.%	Element, %
Flux Addition, wt.%	Fe	Ni	C	Cr	Si	O	etc.
With SiO₂
2	84.49	15.214	0.09	0.16	0.025	0.011	0.004
4	84.45	15.249	0.09	0.16	0.030	0.010	0.005
6	84.407	15.28	0.101	0.16	0.035	0.010	0.001
8	84.366	15.31	0.106	0.16	0.041	0.009	0.001
10	84.328	15.336	0.11	0.16	0.046	0.009	0.003
With MgO
2	84.52	15.18	0.08	0.18	0.022	0.012	0.006
4	84.51	15.17	0.08	0.19	0.021	0.012	0.017
6	84.50	15.16	0.08	0.21	0.020	0.012	0.018
8	84.49	15.15	0.08	0.23	0.020	0.012	0.018
10	84.48	15.14	0.08	0.25	0.018	0.012	0.02

Table 9. Composition of slag in nickel smelting with flux additions calculated by equilibrium-based Factsage 8.2 calculations.

Flux Addition, wt.%	Oxide, %									M/S
Flux Addition, wt.%	MgO	SiO₂	CaO	FeO	Fe₂O₃	NiO	CrO	Al₂O₃	Cr₂O₃	M/S
With SiO₂
2	30.00	54.65	0.26	11.14	0.017	0.0024	1.12	2.633	0.18	0.54
4	29.28	55.68	0.26	10.92	0.016	0.0023	1.10	2.57	0.17	0.52
6	28.61	56.66	0.25	10.71	0.014	0.0022	1.09	2.51	0.15	0.50
8	27.97	57.60	0.24	10.51	0.014	0.0020	1.07	2.45	0.15	0.48
10	27.35	58.51	0.24	10.31	0.013	0.0019	1.05	2.4	0.14	0.46
With MgO
2	29.80	53.90	0.29	11.47	0.018	0.0025	1.27	3.01	0.20	0.55
4	29.72	53.65	0.32	11.44	0.018	0.0025	1.36	3.24	0.22	0.55
6	29.64	53.36	0.34	11.41	0.018	0.0025	1.47	3.50	0.24	0.55
8	29.54	53.0	0.37	11.39	0.018	0.0024	1.59	3.80	0.26	0.55
10	29.44	52.57	0.40	11.37	0.018	0.0024	1.73	4.16	0.28	0.56

Table 10. Fe-Ni alloy composition and extraction efficiency in smelting with flux.

Flux Addition, wt.%	Element, %					Fe/Ni	Weight of Metal in Alloy, g
Flux Addition, wt.%	Fe	Ni	Cr	Si	Etc.	Fe/Ni	Fe	Ni	Alloy
With SiO₂
2	83.8	15.8	0.15	0.17	0.08	5.30	9.59	1.78	11.51
4	84.1	15.9	0.09	0.21	-	5.29	8.58	1.62	10.20
6	83.4	15.5	0.33	0.45	0.32	5.38	8.42	1.59	10.05
With MgO
2	81.6	17.3	0.27	0.16	0.67	4.72	8.57	1.82	10.50
4	81.8	17.5	0.16	0.20	0.34	4.67	7.81	1.67	9.55
6	81.9	15.9	0.21	0.12	1.87	5.15	6.39	1.24	7.8

Table 11. Chemical composition of slag during calcined nickel ore smelting with flux addition, analyzed by XRF.

Flux Addition, wt.%	Oxide, %										M/S
Flux Addition, wt.%	MgO	SiO₂	CaO	Fe₂O₃	MnO	Al₂O₃	Cr₂O₃	NiO	Fe *	Ni *	M/S
With SiO₂
2	29.73	46.39	5.17	11.82	0.32	6.18	0.40	-	6.19	0.012	0.64
4	26.96	48.18	4.45	11.31	0.31	8.35	0.29	0.15	7.48	0.37	0.55
6	26.40	50.64	4.90	10.10	0.31	5.90	1.03	0.71	10.0	1.0	0.52
With MgO
2	30.98	44.49	4.14	10.23	0.30	8.13	1.73	-	7.20	0.016	0.69
4	32.38	44.47	4.75	10.41	0.31	5.79	1.76	0.11	7.04	0.13	0.73
6	33.97	41.08	4.47	12.25	0.30	5.46	1.87	0.30	7.28	1.17	0.81

* Analyzed by ICP-OES.

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

© 2025 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

Share and Cite

MDPI and ACS Style

Urtnasan, E.; Heo, S.-B.; Yu, J.-W.; Jung, C.-H.; Wang, J.-P. Relationship Between Thermodynamic Modeling and Experimental Process for Optimization Ferro-Nickel Smelting. Minerals 2025, 15, 101. https://doi.org/10.3390/min15020101

AMA Style

Urtnasan E, Heo S-B, Yu J-W, Jung C-H, Wang J-P. Relationship Between Thermodynamic Modeling and Experimental Process for Optimization Ferro-Nickel Smelting. Minerals. 2025; 15(2):101. https://doi.org/10.3390/min15020101

Chicago/Turabian Style

Urtnasan, Erdenebold, Seong-Bong Heo, Joo-Won Yu, Chang-Ho Jung, and Jei-Pil Wang. 2025. "Relationship Between Thermodynamic Modeling and Experimental Process for Optimization Ferro-Nickel Smelting" Minerals 15, no. 2: 101. https://doi.org/10.3390/min15020101

APA Style

Urtnasan, E., Heo, S.-B., Yu, J.-W., Jung, C.-H., & Wang, J.-P. (2025). Relationship Between Thermodynamic Modeling and Experimental Process for Optimization Ferro-Nickel Smelting. Minerals, 15(2), 101. https://doi.org/10.3390/min15020101

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Menu

Relationship Between Thermodynamic Modeling and Experimental Process for Optimization Ferro-Nickel Smelting

Abstract

1. Introduction

2. Materials and Methods

2.1. Experimental Materials

2.2. Experimental Procedures

2.3. Analytical Methods

2.3.1. Thermodynamic Modeling

2.3.2. Calculating Nickel Recovery Degree

2.3.3. Chemical and Mineralogical Analysis

3. Results and Discussion

3.1. Carbon-Based Smelting for Selective Reduction

3.1.1. Thermodynamic Modeling of Ferro-Nickel Smelting

3.1.2. Ferro-Nickel Smelting with Carbon Reduction

3.2. Optimizing Slag Composition for Ferro-Nickel Smelting

3.2.1. Thermodynamic Modeling for Optimal Slag Composition

3.2.2. Ferro-Nickel Smelting for Optimizing Slag M/S Ratio

3.3. Effect of Slag Basicity on Ferro-Nickel Smelting

4. Conclusions

Author Contributions

Funding

Data Availability Statement

Conflicts of Interest

References

Share and Cite

Article Metrics

Article Access Statistics

Further Information

Guidelines

MDPI Initiatives

Follow MDPI