Key Takeaways & Executive Findings
- •• Hydrogen pre-reduction of Nchwaning manganese ore effectively reduces higher manganese oxides to MnO, with smaller particle sizes and higher temperatures enhancing the reduction degree. • The use of hydrogen as a reductant in manganese ore pre-reduction can significantly reduce CO2 emissions compared to conventional carbon-based processes. • Decrepitation of ore particles during reduction was measured, providing insights into particle stability and process optimization. • The study demonstrates that complete pre-reduction to MnO is achievable, which is critical for minimizing aluminum consumption in downstream processes like the HalMan process.
Abstract
The application of hydrogen gas in the pre-reduction of manganese ore may replace fossil carbon consumption and reduce CO2 emissions in manganese ferroalloy production. The pre-reduction behavior of Nchwaning manganese ore was investigated using a fixed-bed reactor. The reduction rates at different temperatures and temperature programs were investigated, and the particles were sieved after reduction to measure the decrepitation. The reduction rate was measured by adding a tracer gas to the reducing gas and quantifying the off-gas. Samples with different particle-size distributions of the input material were reduced to investigate the effect of particle size on the reduction rate. Chemical analyses and X-ray diffraction were used to characterize the raw and reduced materials. The effects of particle size distribution and temperature on the oxygen removal rate were investigated. Manganese oxides were mostly reduced to MnO in the samples, whereas some iron oxides and carbonates remained. The degree of reduction was improved by using smaller particles and increasing the temperature.
1. Introduction
Manganese ferroalloys are mostly produced in submerged arc furnaces, where solid carbon reacts with MnO to produce manganese metal and CO gas, and the CO gas reacts with higher manganese and iron oxides ([Mn,Fe]Ox, x > 1), albeit with some excess carbon consumption due to the imperfect reduction of the higher oxides. The use of hydrogen in manganese ferroalloy production has been suggested to alleviate the carbon footprint of the product, and the introduction of hydrogen has been shown to improve the pre-reduction of higher manganese and iron oxides compared to that achieved using CO [1–5]. Manganese metal production cannot be achieved using H2 or CO [6–8]; hence, H2 alone cannot fully displace all of the carbon in the reduction to metal. Recently, the HalMan process was suggested as a sustainable method for the production of manganese alloys through hydrogen pre-reduction followed by aluminothermic reduction of MnO [9]. This process may reduce the CO2 emissions of manganese ferroalloy production, depending on the CO2 emissions associated with the aluminum source.
The complete pre-reduction of manganese oxides can be described by Eq. (1), using either H2 or CO as the reductant. The final reduction of MnO to Mn-metal is described by Eq. (2), where either C or Al is used as the reductant. Higher iron oxides undergo similar reduction to lower iron oxides, as described by Eq. (1) for manganese oxides; however, iron oxides can also be reduced to metal by CO or H2. To minimize the consumption of aluminum in the final reduction process, it is necessary to fully reduce the higher manganese oxides to MnO. Incomplete pre-reduction (Eq. (1)) results in additional oxygen that must be removed by the increased consumption of the solid reductant (Eq. (2)). Aluminum consumption may be further reduced if iron oxides are reduced to metallic Fe by H2. The reduction of FeO in manganese ores is retarded by the reduced activity of iron oxides in solid solutions with manganese oxides [4,10–12]. However, formation of metallic iron has been observed during the pre-reduction of manganese ores using pure H2 [1,13–14].
Fig. 1 shows the phase diagram of manganese and iron oxides as a function of temperature and oxygen partial pressure with the oxygen partial pressure of the selected H2/H2O gas mixtures superimposed on the phase diagram. It is observed that under exposure to H2/H2O gas mixtures in the range of 70vol%–99vol% H2, MnO is the stable manganese oxide, while in the Fe–O system, metallic iron is stable above approximately 550°C if the H2 content is ≥ 80vol%. With 70% H2, Fe3O4, FeO and Fe can be stable depending on the temperature. The reactivity of Mn ores during gaseous reduction has been extensively studied [1,4–5,10,13,15–21], and it has been shown that factors such as temperature, ore type, reducing gas composition, and particle size influence the reactivity of the ores during reduction. Reduction of manganese ores in CO/CO2/H2 gas mixtures has been shown to increase the reaction rate by 20%–30% relative to that obtained using CO/CO2 gas mixtures with the same oxygen partial pressure [5]. The addition of H2O to the CO/CO2 gas mixtures has also been shown to promote the reduction of manganese ore due to the production of H2 in the water-gas shift reaction (H2O + CO = H2 + CO2) [3]. The reduction rate improves in the presence of H2 due to its improved diffusion properties compared to those of CO and CO2 [4]; hence, gas mass transfer
Loading authentic research manuscript (Pages 1–5)...
Trygve Lindahl Schanche, Heiko Gaertner, Frida Vollan, Alok Sarkar, Casper van der Eijk (2025). Hydrogen reduction of lumpy Nchwaning ore in a fixed-bed reactor. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-025-3125-7
Research & Educational Purpose Only:The translations, structured abstracts, analytical annotations, and data reports provided by SinoTechIntel are intended exclusively for academic research, internal corporate R&D, and educational benchmarking. They do not constitute formal engineering, chemical safety, legal, or professional advice.
Copyright & Intellectual Property Notice: Original copyright of the underlying source articles and experimental data remains with the respective authors, institutions, and original publishing journals. SinoTechIntel claims intellectual property only over its proprietary translations, analytical syntheses, and AEO structured enhancements in accordance with international fair use and academic citation principles.
Frequently Asked Questions
What is the main objective of the study on hydrogen reduction of Nchwaning ore?
The study aims to investigate the pre-reduction behavior of Nchwaning manganese ore using hydrogen gas in a fixed-bed reactor, focusing on the effects of temperature and particle size on reduction rates and decrepitation, to potentially replace fossil carbon and reduce CO2 emissions in manganese ferroalloy production.
How does particle size affect the reduction of manganese ore with hydrogen?
Smaller particle sizes improve the degree of reduction because they provide a larger surface area for gas-solid reactions, enhancing the oxygen removal rate and overall reduction efficiency.
What are the key findings regarding the reduction products?
Manganese oxides are mostly reduced to MnO, while some iron oxides and carbonates remain. The reduction degree is improved with smaller particles and higher temperatures, and the formation of metallic iron is possible under certain conditions.
Why is hydrogen considered a sustainable alternative in manganese ferroalloy production?
Hydrogen can replace fossil carbon in the pre-reduction step, significantly reducing CO2 emissions. Although hydrogen cannot fully reduce MnO to metal, it can be combined with processes like aluminothermic reduction to achieve a more sustainable production route.
What is the significance of the HalMan process mentioned in the paper?
The HalMan process is a proposed sustainable method that uses hydrogen pre-reduction followed by aluminothermic reduction of MnO, potentially reducing CO2 emissions in manganese alloy production, depending on the carbon footprint of the aluminum source.
Related Technical Papers & Translations
Direct Repair of the Crystal Structure and Coating Surface of Spent LiFePO4 Materials Enables Superfast Li-Ion Migration
The rapid accumulation of spent LiFePO4 (LFP) cathodes from retired lithium-ion batteries necessitates the development of effective and environmental-friendly recycling strategies. In this context, direct regeneration has emerged as a promising approach for reclaiming LFP cathode materials, offering a streamlined pathway to restore their electrochemical functionality. We report an integrated regeneration protocol that simultaneously repairs the degraded crystal structure and reconstructs the damaged carbon coating in spent LFP. The regenerated cathode material had superfast lithium-ion diffusion kinetics and a stable cathode–electrolyte interface, giving a remarkable rate capability with specific capacities of 122 mAh g−1 at 5C and 106 mAh g−1 at 10C (1C = 170 mA g−1). It also maintained capacities of 110.7 mAh g−1 (5C) and 84.1 mAh g−1 (10C) after 400 cycles. It could be used in harsh environments and could be stably cycled at subzero temperatures (−10 and −20 °C) and in solid-state electrolyte batteries. Life cycle assessment combined with economic evaluation using the EverBatt model reveals that this direct regeneration approach has high economic and environmental benefits.
Oxide Semiconductor for Advanced Memory Architectures: Atomic Layer Deposition, Key Requirement and Challenges
Oxide semiconductors (OSs), introduced by the Hosono group in the early 2000s, have evolved from display backplane materials to promising candidates for advanced memory and logic devices. The exceptionally low leakage current of OSs and compatibility with three-dimensional (3D) architectures have recently sparked renewed interest in their use in semiconductor applications. This review begins by exploring the unique material properties of OSs, which fundamentally originate from their distinct electronic band structure. Subsequently, we focus on atomic layer deposition (ALD), a core technique for growing excellent OS films, covering both basic and advanced processes compatible with 3D scaling. The basic surface reaction mechanisms—adsorption and reaction—and their roles in film growth are introduced. Furthermore, material design strategies, such as cation selection, crystallinity control, anion doping, and heterostructure engineering, are discussed. We also highlight challenges in memory applications, including contact resistance, hydrogen instability, and lack of p-type materials, and discuss the feasibility of ALD-grown OSs as potential solutions. Lastly, we provide an outlook on the role of ALD-grown OSs in memory technologies. This review bridges material fundamentals and device-level requirements, offering a comprehensive perspective on the potential of ALD-driven OSs for next-generation semiconductor memory devices.
Laser powder bed fusion of biodegradable Zn-4Cu alloy: Processing, microstructure and properties
Zn's natural degradability and biocompatibility make it a promising candidate for implants, however, its mechanical properties remain insufficient for bone applications. In this study, the performance of Zn was enhanced by developing Zn-Cu alloys via laser powder bed fusion (LPBF). Optimal LPBF parameters for forming stable tracks were achieved by adjusting laser power and scanning speed. Under optimized conditions of 100 W and 100 mm/s, high-density (99.58%) Zn-Cu alloys with improved hardness (68.2HV) and yield strength (160 MPa) were achieved. These improvements are attributed to solid solution strengthening, segregation strengthening, and grain refinement. The Zn-Cu alloys also demonstrated favorable degradation behavior, with a rate of 0.16 mm/year. This degradation is primarily driven by micro-galvanic corrosion between the CuZn5 phase and Zn matrix, along with refined grains and increased grain boundary density. This work demonstrates a viable strategy for fabricating Zn-based implants with enhanced structural integrity and mechanical performance via LPBF.