Project results

– 2023 –

Hydrogen: The key to a more sustainable manganese production

Summary

Manganese (Mn) is the fifth most abundant metal in the Earth’s crust, widely used in metal alloys and batteries, but difficult to produce.
Current Mn production methods have high energy consumption and CO2 emissions.
Professor Jafar Safarian from the Norwegian University of Science and Technology (NTNU) developed the HAlMan process: a novel, sustainable way of producing Mn, ferromanganese, and manganese–aluminum alloys.
The HAlMan process offers a cleaner conversion of Mn oxides to Mn metal or high-value alloys in the presence of hydrogen, while recovering energy.

Author

Jafar Safarian, Dep. of Materials Technology, Norwegian University of Science and Technology, Norway

Read more on Research Features

The Production of Manganese and Its Alloys Through the HAlMan Process

Abstract

In a new integrated process, HAlMan process, hydrogen, and aluminum are used to produce metallic manganese, aluminum-manganese (AlMn), and ferromanganese (FeMn) alloys with low energy consumption and carbon footprint. In this process, hydrogen gas is used to pre-reduce manganese ores and obtain intermediate Fe- and MnO-containing pre-reduced ore. The MnO content of this material is further reduced at elevated temperatures by aluminum in a smelting-aluminothermic reduction process. The main product of the process is metallic Mn, Al-Mn alloy, or ferromanganese, depending on the process feed chemistry. In the present work, the experimental results on the hydrogen reduction of manganese ore are presented and the effect of process conditions such as reduction temperature is evaluated. It is shown that the microstructural properties of the reduced ore depend on the process temperature, and the rate of ore reduction is higher at elevated temperatures. In addition, the smelting-aluminothermic reduction step is discussed and it is shown that the process is flexible to produce a variety of metallic products. Mass and energy balance calculations are presented and it is shown that the energy consumption for the process is lower than the state-of-the-art technology of the submerged arc furnace. It is revealed that the process is sustainable regarding the valorization of Al-dross industrial waste. It is shown that ferromanganese production by this process will prevent the emission of about 1.5 t CO2/t metal, with less practical challenges to produce low-carbon ferromanganese. The implementation of the HAlMan process on a pilot scale through an EU project is presented and it is shown how the process products can be used to make commercial metal products, and also the process products can be valorized to establish a sustainable process for the future ferroalloy industry.

Author

Jafar Safarian, Professor, Department of Materials Science and Engineering, Norwegian University of Science and Technology

Learn more on Springer

Isothermal pre-reduction behavior of Nchwaning Manganese Ore in H2 atmosphere

Abstract

The application of H₂ to pre-reduce manganese ores is a sustainable approach to performing decarbonization in the ferroalloy industry. The process has been extensively studied and tested in a lab-to-pilot scale in the HAlMan EU project. This work presents the results of an experimental study that was conducted in a lab-scale vertical thermogravimetric furnace for the pre-reduction of a manganese ore by H₂ under isothermal conditions at 500 °C, 600 °C, 700 °C, and 800 °C. The ore and reduced samples were characterized by XRF, XRD, BET and SEM techniques to outline the H₂ reduction behavior of the ore from mineralogical, microstructural, and chemical points of view. The rate and extent of reduction were studied using the continuous mass changes during the reduction. It was found that the pre-reduction at a temperature of 700 °C and 800 °C yields metallic iron formation from Fe₂O₃ and MnO formation from MnO₂/Mn₂O₃. The pre-reduction at lower temperatures did not show a complete reduction in Fe and MnO. The pore structure of the ore was affected by the pre-reduction temperature, and a significant porosity evolution was observed.

Authors

Alok Sarkar, PhD candidate, Norwegian University of Science and Technology

Trygve Lindahl Schanche, SINTEF, Norway

Jafar Safarian, Professor, Department of Materials Science and Engineering, Norwegian University of Science and Technology

Read the article on MDPI

– 2024 –

Computational reacting flow models for the pre-reduction of lumpy Nchwaning manganese ore with hydrogen

Abstract

Solid-state pre-reduction of manganese ores with hydrogen presents many potential advantages that include reduction of greenhouse gas emissions and lower energy consumption of the downstream smelting step. Before designing a pre-reduction reactor, it is crucial to investigate and understand the process kinetics and their influence on the overall pre-reduction reactor performance. Computational fluid dynamics (CFD) reacting flow models are used to predict the influence of kinetics, geometry and flow field on the chemical reaction rates. The current work employs the CFD models to predict the influence of temperature, flow field and kinetics on the degree of manganese pre-reduction with hydrogen. The models allow for the determination of the optimum reduction temperature and reduction time.

Authors

Mopeli Khama, Mintek, South Africa

Quinn G Reynolds, Mintek and University of Stellenbosch, South Africa

Buhle Xakalashe, University of Stellenboch, South Africa

Alok Sarkar, PhD candidate, Norwegian University of Science and Technology

Jafar Safarian, Dep. of Materials Technology, Norwegian University of Science and Technology, Norway

Learn more on Researchgate

An experimentally validated CFD modelling approach for the simulation of alumina precipitation tank reactors

Abstract

The aluminothermic reduction of ores and residues is a process that has gained a lot of interest over the past years. During this process, a metal phase and a calcium aluminate slag are formed. The latter can be leached with Na2CO3 for the recovery of aluminum. The produced sodium aluminate solutions differ from the ones produced through the Bayer process and thusthey can’t be efficiently used for the traditional seeding precipitation. Instead, carbonation precipitation is applied to obtain aluminum, where CO2 gas is inserted, lowering the pH and resulting in alumina trihydrate precipitation. Such a process involves gas, liquid and solid-phase interactions, increasing the degree of complexity. For better understanding the phenomena occurring, a three-dimensional CFD model is developed for the precipitation tank and the impeller, considering the main physicochemical mechanisms of the process and the dynamics of the liquid solution during the precipitation process are simulated. A two-phase dispersed flow approach is employed for the simulation of the CO2 gas flow within the tank, in the form of gas bubbles. The CO2 mass transfer between the two phases, as well as the CO2 dissolution reactions, are also taken into account by the CFD model. The computational approach is validated by comparing theoretical predictions for the CO2 outflow and solution pH with experimental measurements. The model is capable of reproducing the experimental results, illustrating the process dynamics for the CO2 bubble flow and dissolution. More importantly, the good agreement between predictions and experimental measurements provides a solid basis for the development of an integrated model, which will take into account the simulation of the whole chain of chemical reactions, yielding the targeted alumina hydrate precipitate. The integrated model will provide an insight into the effect of the interplay between the different mechanisms occurring within the precipitation tank, such as the impeller rotation, the CO2 bubble flow, the mass transfer between phases and the dissolution reactions. This, in turn, will enable the efficient optimization of the whole process regarding reactor design and process conditions

Authors

G.P. Gakis – School of Chemical Engineering, National Technical University of Athens (NTUA), Greece

I.G. Aviziotis – School of Chemical Engineering, National Technical University of Athens (NTUA), Greece

A.G. Boudouvis – School of Chemical Engineering, National Technical University of Athens (NTUA), Greece

D. Marinos – Laboratory of Metallurgy, School of Mining and Metallurgical Engineering, National Technical University of Athens (NTUA), Greece

D. Panias – Laboratory of Metallurgy, School of Mining and Metallurgical Engineering, National Technical University of Athens (NTUA), Greece

Flux smelting behavior of pre-reduced Mn ore by Hydrogen at elevated temperatures

Abstract

Understanding how ore interacts with flux particles at elevated temperatures to create molten slag is crucial since it governs the dynamics of a chemical reaction. This study explores the smelting behaviour of pre-reduced Nchawaning manganese ore when combined with lime, with the objective of examining the evolving interaction between pre-reduced ore particles and lime over time. The research sheds light on the interaction between solid and liquid and the phases that emerge during this process. To achieve this, a sessile drop furnace was employed to rapidly heat the materials positioned adjacent to each other on an alumina substrate and to observe the smelting process as it unfolded over time. This method allowed for the direct observation of the melting temperatures and the flux-ore reaction progression rate, and the potential disruptive events that might occur. By comparing the molten interfaces of the fluxed materials at various time intervals, this study provides insights into the relative rate of slag formation from the two materials. The results indicate that the main slag formation initiated at approximately 1400 oC and continued to advance with time, with complete mixing occurring around 1500 oC. The possible phases formed were identified using Scanning Electron Microscopy and modelled using Fact Sage thermodynamic software. In addition, the iron particles in the pre-reduced Mn ore were separated and settled from a rich MnO-containing slag.

Authors

Pankaj Kumar, PhD candidate, Department of Materials Science and Engineering, Norwegian University of Science and Technology

Jafar Safarian, Professor, Department of Materials Science and Engineering, Norwegian University of Science and Technology.

Learn more on Zenodo

Mintek’s research into sustainable pyrometallurgy for production of ferroalloys

About event

Project Blue and key government, industry, and finance stakeholders gathered to discuss ferroalloy trends in South Africa’s mining heartland. MINTEK was represented by Sello Tsebe, who delivered a presentation highlighting MINTEK’s contributions and work within the HAlMan project.

Presenter

Sello Tsebe, MINTEK

Presentation

Phase relations in ferromanganese production through the aluminothermic reduction of a pre-reduced manganese ore

Abstract

High-carbon ferromanganese is commercially produced via a carbothermic reduction route which generates a metal typically with 70-80% Mn,1-2% Si and 7.5% C along with significant amount of slag. An alternative sustainable approach to produce ferromanganese is the pre-reduction of the ore by hydrogen followed by an aluminothermic reduction-smelting process, the HAlMan process. In this work, extensive study on aluminothermic reduction of hydrogen based pre-reduced Nchawning manganese ore was done. The study was conducted with varying Al, and the quantity of added lime to obtain molten ferromanganese and slag in a flux-smelting process. The study further extends to find the possibility of forming leachable calcium aluminate slag, to recover further Al2O3 used in the process. The experimental study has shown that a metal with 75-80 % Mn, 0.5-1% Si and rest Fe, could be obtained. Moreover, a slag with SiO2 < 7 wt% , Al2O3 > 47 Wt.% and CaO<42 wt.% could be formed, and it was characterized using XRD, SEM and XRF analysis. The slag was found to mostly contain calcium aluminate phase with small amount of unreduced MnO and significantly lower amount of gehlenite phase. It is shown by experimental and theoretical work that the new approach will provide high quality metal product with high yield.

Authors

Pankaj Kumar – NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group
Jafar Safarian – NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group

Learn more on Zenodo

Characterisation of manganese ores and slags for production of ferromanganese and Al-Mn master alloys

Abstract

Manganese (Mn) ores fluctuate considerably in chemistry and other properties. It is well known that the properties of Mn ore have a large influence on the technology and yield of Mn alloy production. This work aims to characterize Mn ore and slag properties for the production of ferromanganese (FeMn) through a prereduction with hydrogen (H₂) and subsequent aluminothermic reduction. The raw materials for this process can be aluminium (Al) containing dross or scrap and Mn ores. Interesting by-products of the process can be Al-Mn master alloys and a slag enriched in rare earth elements (REE) from the Mn ore. Chemical composition, especially critical raw materials (CRM) including REE, porosity, and melting and softening have been characterized with various methods. The implications of the outcomes on the extraction of critical raw materials are also discussed. It is concluded that the CRM, particularly REE tends to accumulate in the slag. Current slags are approximately 9 times less porous than Mn ores. Mn ores in the current work soften at 970-1800°C, and melt at 1460- 1850°C. All current ores expand maximum 16% and reduce to -70% of the original volume.

Authors

Sarina Bao – SINTEF, Norway
Casper van der Eijk – SINTEF, Norway
Debora FoppianoPankaj Kumar – SINTEF, Norway

Learn more on Norwegian Research Information Repository

About event

The Smelting Symposium was first organized as an online event in 2023 under the name SAF/OSBF Symposium by the Department for Industrial Furnaces and Heat Engineering (IOB) at RWTH Aachen University. The symposium is intended to bring together experts in the field at roughly annual intervals, so that the 2nd Smelting Symposium will take place online on 11 October 2024.

The symposium was used to present the current status of research & development and plant technology for electric smelting furnaces (ESF, including SAF and OSBF) and to discuss the future tasks and challenges of the industries (ferroalloys, steelmaking, recycling, etc.). To this end, specialist lectures from science and industry will be presented and discussions held.

Presenters

Sello Tsebe, MINTEK

Elias Matinde, MINTEK

Presentation

Evaluating the Reaction Kinetics on the H2 Reduction of a Manganese Ore at Elevated Temperatures

Abstract

This study investigates the hydrogen reduction of Nchwaning manganese ore at elevated temperatures to enhance understanding of reaction kinetics and optimize industrial applications. Experimental investigations were conducted across temperatures ranging from 600 °C to 900 °C to observe reduction behavior and identify rate determining steps. Thermogravimetric analysis (TGA) was employed to monitor manganese ore weight loss, facilitating precise measurement of reduction rates. Various kinetic models validated experimental outcomes for H₂ reduction, revealing an apparent activation energy (E_a) of 65.76 kJ/mol and an apparent pre-exponential factor (k₀) of 319.66 min⁻¹. The rate constant (k) exhibited a significant temperature-dependent increase, following the Arrhenius equation where rates approximately doubled every 100 °C, rising from 0.037 min⁻¹ at 600 °C to 0.377 min⁻¹ at 900 °C. Morphological and compositional analyses using scanning electron microscopy (SEM) and X-ray diffraction (XRD) assessed structural changes post-reduction. Results demonstrated that pre-reduction temperature critically influences the physical and microstructural properties of the ore particles, particularly above 700 °C, where a notable reduction in BET (Brunauer–Emmett–Teller) surface area and pore volume indicated sintering within the ore. The rate determining step for this reduction process is most likely the chemical reaction at the gas–solid interface between hydrogen and the manganese ore. These findings highlight advancements in efficient manganese ore reduction processes, with significant implications for metallurgical practices and the hydrogen economy.

Authors

Alok Sarkar, PhD candidate, Norwegian University of Science and Technology

Trygve Lindahl Schanche, SINTEF, Norway

Jafar Safarian, Professor, Department of Materials Science and Engineering, Norwegian University of Science and Technology

Maria Wallin, Department of Materials Science and Engineering, Norwegian University of Science and Technology

Read the article on Springer

Development and demonstration of fit for purpose pyrometallurgical processes and technologies: Mintek’s perspectives

Abstract

Pyrometallurgical processes are responsible for the primary production of most industrial and structural materials such as stainless steel and other structural alloys, battery and energy metals, technology metals, and precious metals. Industrial and technology metals, such as copper, aluminium, and steel provide modern society with structural goods and services that are required to meet the basic human needs. Inasmuch as most primary metal production processes have matured and operate optimised pyrometallurgical processes and technologies, these processes are energy intensive, extensively rely on carbon-based reductants (such as coal and coke) and generate significant amounts of residual hazardous waste streams (such as slags and dusts). The need to mitigate the environmental effects and increase the sustainability of pyrometallurgical processes and technologies therefore increases the impetus to develop flowsheets with low carbon and effluent emissions, including demonstrating flowsheets incorporating alternative and low-carbon reductants coupled with the ability to co-process both primary concentrates and secondary materials. This paper provides a review of Mintek’s research and technology demonstration activities towards demonstrating fit for purpose pyrometallurgical processes and technologies at scale. The contribution of Mintek to research in sustainable pyrometallurgy will be segmented thematically into energy efficient and reduced CO2 emission processes, demonstration of carbon-free processes, and valorization of industrial and urban wastes. Key research findings from specific projects under each respective theme will be discussed to highlight the capabilities and facilities utilized, lessons learnt, and the potential impact of findings to the broader pyrometallurgical industry.

Authors

Sello Tsebe, MINTEK

Elias Matinde, MINTEK

Read the article on Researchgate (SAIMM)

– 2025 –

“Mn og Si Dag” (Mn and Si Day) presentations

A seminar titled “Mn og Si Dag (Mn and Si Day)” was organized by NTNU on the 20^th and 21^st of February 2025. During this event, Elias Trondsen Dahl (Master student), Pankaj Kumar and Alok Sarkar (Ph.D. students) and Manish Kumar Kar (Postdoctoral researcher) from the HAlMan project (NTNU), had the opportunity to present their work.

MnO₂ production from pre-reduced Mn ores for battery applications

Presenter: Elias Trondsen Dahl (Master’s Student, NTNU, Norway)

Isothermal Hydrogen Reduction of Nchwaning Manganese Ore: A Kinetics Study at Elevated Temperatures

Presenter: Alok Sarkar (Ph.D. Student, NTNU, Norway)

Effect of pre-reduction of manganese ore by hydrogen on its smelting behavior and interaction with stable oxides

Presenter: Pankaj Kumar (Ph.D. Student, NTNU, Norway)

Hydrogen Reduction of Dust from a Ferromanganese Submerged Arc Furnace (SAF)

Presenter: Manish Kumar Kar (Postdoctoral Researcher, NTNU, Norway)

Read more

A Macro-scale approach to Computational Fluid Dynamics Modelling of the Reduction of Manganese ore by Hydrogen

Abstract

The carbonaceous reduction of manganese ore is an energy-intensive process that releases large amounts of pollutant gases. In an attempt to circumvent the greenhouse gas emissions, this research investigates hydrogen as an alternative reductant. The reduction of manganese ore with hydrogen results in the structural changes in the intermediate products, which might limit the diffusion of the reactant gases through the pores. Computational fluid dynamics (CFD) models capture the structural changes and predict the rate controlling mechanism and this is key in designing the prereduction reactors. The current work uses CFD models to predict the degree of reduction in a shaft furnace under hydrogen reducing conditions. Manganese ore is described as a collection of scalar and tensor fields such as thermal conductivity of the porous medium, density, and viscous resistance. The results indicate that advection contributes significantly towards the overall transport of hydrogen to the reaction sites. Porosity of the final product was found to be higher than porosity of the raw material.

Author

M.I. Khama – MINTEK, South Africa

Q.G. Reynolds – MINTEK, South Africa

B.S. Xakalashe – MINTEK, South Africa

Learn more on SAIMM

Hydrogen reduction of lumpy Nchwaning ore in a fixed bed reactor

Abstract

The application of hydrogen gas for prereduction of manganese ore may substitute fossil carbon consumption and as such reduce CO2 emissions in manganese ferroalloy production. The pre-reduction behavior of Nchwaning manganese ore was investigated using a fixed bed reactor. Reduction rates at different temperatures and temperature programs were investigated, and particles were sieved after reduction to measure decrepitation. The reduction rate was measured by adding a tracer gas to the reducing gas and quantifying the off-gas by GC-analysis. Different particle size distributions of the input material were reduced to investigate the effect of particle size on reduction rate. Chemical analysis and XRD were used to characterize the raw and reduced material. The influence of particle size distribution and temperature on the oxygen removal rate are discussed. The manganese oxides were mostly reduced to MnO in the samples, while some iron oxide and carbonates remained. The reduction degree is improved by smaller particles and increased temperature.

Authors

Trygve Lindahl Schanche – SINTEF As, Trondheim, Norway
Heiko Gaertner – SINTEF As, Trondheim, Norway
Frida Vollan – SINTEF As, Trondheim, Norway
Alok Sarkar – PhD candidate, Norwegian University of Science and Technology
Casper van der Eijk – SINTEF As, Trondheim, Norway

Learn more on International Journal of Minerals, Metallurgy and Materials

An Integrated, CFD-Based, Analysis of Carbonation in a Stirred Tank Reactor

Abstract

Carbonation precipitation processes have been widely used due to their numerous applications in a wide range of fields. The complexity of these processes lies within the interplay of transport phenomena, multiphase flows, chemical reactions, and solid precipitation, deeming the experimental analysis and in-depth mechanistic understanding of the process dynamics a rather challenging task. In this work, a three-dimensional CFD model is developed, focusing on the carbonation step of the carbonation precipitation process, taking into account the flow dynamics of the liquid solution in the stirred tank, the CO₂ bubble flow, and the dissolution in the liquid solution, as well as its dissociation in water. The model is validated with experimental measurements, and a very good agreement is achieved. Additionally, a parametric analysis is conducted to study the effect of different process parameters, such as temperature, CO₂ flow rate, and rotational speed. The analysis of the different phenomena and their interplay reveals the key mechanisms that dictate the carbonation step, resulting in an in-depth understanding of the process. The presented computational approach can potentially pave the way towards a knowledge-based process and reactor design; thus, assisting the scale-up of such processes in stirred tank reactors.

Authors

Georgios P. Gakis – School of Chemical Engineering, National Technical University of Athens (NTUA), Zografou, Greece
Danai Marinos – Laboratory of Metallurgy, School of Mining and Metallurgical Engineering, National Technical University of Athens (NTUA), Zografou, Greece
Ioannis G. Aviziotis – School of Chemical Engineering, National Technical University of Athens (NTUA), Zografou, Greece
Efthymios Balomenos – Laboratory of Metallurgy, School of Mining and Metallurgical Engineering, National Technical University of Athens (NTUA), Zografou, Greece
Andreas G. Boudouvis – School of Chemical Engineering, National Technical University of Athens (NTUA), Zografou, Greece
Dimitrios Panias – Laboratory of Metallurgy, School of Mining and Metallurgical Engineering, National Technical University of Athens (NTUA)

Learn more MDPI

Kinetics study on the H2 reduction of Nchwaning manganese ore at elevated temperatures

Abstract

Replacing solid carbon with hydrogen gas in ferromanganese production presents a forward-thinking, sustainable solution to reducing the ferro-alloy industry’s carbon emissions. The HAlMan process, a groundbreaking and eco-friendly method, has been meticulously researched and scaled up from laboratory experiments to pilot tests, aiming to drastically cut CO2 emissions associated with ferromanganese production. This innovative process could potentially reduce CO2 emissions by about 1.5 tonnes for every tonne of ferromanganese produced. In this study, a lab-scale vertical thermogravimetric furnace was used to carry out the pre-reduction of Nchwaning manganese ore, where direct reduction occurred with H2 gas under controlled isothermal conditions at 700, 800, and 900°C. The results indicated that higher pre-reduction temperatures (800 and 900°C) effectively converted Fe2O3 to metallic iron and Mn2O3 to MnO. By continuously monitoring the mass changes during the reduction, both the rate and extent of reduction were assessed. A second-order reaction model was applied to validate the experimental outcomes of H2 reduction at various temperatures, showing apparent activation energies of 29.79 kJ/mol for dried ore and 61.71 kJ/mol for pre-calcined ore. The reduction kinetics displayed a strong dependence on temperature, with higher temperatures leading to quicker and more complete reductions. The kinetics analysis suggested that the chemical reaction at the gas–solid interface between hydrogen and the manganese ore is likely the rate-limiting step in this process.

Authors

Alok Sarkar – NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group.
Trygve Lindahl Schanche – SINTEF Industry, Trondheim, Norway
Maria Wallin – NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group.
Jafar Safarian – NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group.

Learn more IJMMM

Evaluation of the Effects of Fluidization Conditions on Hydrogen Reduction in Manganese Ore Fines

Abstract

Hydrogen prereduction of two manganese ores fines was investigated under varied operating conditions in a fluidized bed. The manganese ores used in this study are the Zambian ore and the South African Nchwaneng ore from the Kalahari region. The samples were milled and sized before they were characterized with regard to sphericity, Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) chemical analyses, X-ray diffraction (XRD) analyses and Scanning Electrons Microscope (SEM) analyses. Prereduction experiments were conducted in a laboratory scale fluidized bed with the parameters of interest being minimum fluidization velocity, terminal velocity, elutriation, average bed voidage, residence time, temperature, intrinsic ore properties and cohesive adhesion. Experiments for the determination of fluidization velocity and terminal velocity were conducted at both ambient temperature and elevated temperature (500 °500 °C, 550 °550 °C, 600 °600 °C, 700 °700 °C, 800 °800 °C and 900 °900 °C), and for varied sample masses (100 g, 300 g and 700 g) and varied particle-size ranges (200–300 μ300 μm, 300–425 μ425 μm, 425–500 μ500 μm and 500–600 μ600 μm). The experimentally observed minimum fluidization velocities for particles size groupings of [+106–200 μ200 μm], [+200–300 μ300 μm], [+300–425 μ425 μm], [+425–500 μ500 μm] and [+500–600 μ600 μm] as well as the mix (20 wt% of each) was comparable with the theoretical minimum fluidization velocity. The fluidized bed was heated to a desired temperature at a rate of 10 °10 °C/min under argon whilst logging the pressure drop across the bed with increasing temperature. The convectional cooling during the introduction of cold hydrogen as well as the net energy of endothermic and exothermic chemical reactions were observed to result in a temperature drop in the order of 100 to 250 °250 °C. Thermal mineral transformation under argon was observed to yield iron manganese oxide in the order of 15 to 30 wt/wt%. Prereduction was conducted using hydrogen gas at a desired temperature and terminal velocity. Reduction extent was observed to increase with the increasing temperature and residence time. Increasing reduction temperature beyond 700 °700 °C was not observed to improve reduction, whereas longer residence time (of up to 40 min) was observed to favor the formation of iron manganese oxide, iron manganese and manganosite. For hydrogen prereduction experiment conducted at 900 °900 °C, the reactor was observed to be brittle after the experiment. Cohesive adhesion was observed to be more pronounced at 900 °900 °C.

Authors

Dursman Mchabe – Mintek, Gauteng, South Africa
Sello Tsebe – Mintek, Gauteng, South Africa
Elias Matinde – Mintek, Gauteng, South Africa

Learn more MDPI

Making Medium Mn Steel by Sustainable Ferromanganese Pre-alloy

Abstract

Driving toward net-zero CO2 emissions in steel industry, a more sustainable approach should be adopted in both iron making and steel-making processes. While the sustainability of iron making is supported by the prospering hydrogen-based direct reduction technology [1], research on the sustainability of alloying ingredients used in steel making has been limited.

In this study, we utilized a “green” ferromanganese pre-alloy (FeMn) produced by a novel “HAlMan” process, which ensures lower energy consumption [2], as the Mn alloying ingredient in medium Mn steel production. The chemical composition of the designed steel using HAlMan FeMn (hereafter referred to as “HAlMan steel”) is Fe-0.2C-10.2Mn-2.8Al-1Si (in wt. %). To demonstrate the feasibility of the HAlMan steel, we also produced another medium Mn steel with similar composition using electrolytic Mn (hereafter referred to as “EMn steel”). Both steels underwent identical thermomechanical process. Comparability between the HAlMan steel and EMn steel was demonstrated by a thorough microstructure characterization and mechanical testing.

In summary, the HAlMan steel showcases similar grade of medium Mn steel performance as conventional EMn steel while utilizing a more sustainable alloying ingredient. This research effort aims to reduce the overall energy consumption of steel making without compromising steel performance, contributing to a more sustainable future in the steel industry.

Authors

Shao-Lun Lu –Max Planck Institute for Sustainable Materials, Department of Microstructure Physics and Alloy Design (Germany)
Shaolou Wei – Max Planck Institute for Sustainable Materials, Department of Microstructure Physics and Alloy Design (Germany)
Dirk Ponge – Max Planck Institute for Sustainable Materials, Department of Microstructure Physics and Alloy Design (Germany)

Learn more on Zenodo

The use of green ferromanganese in production of high-manganese steels and its effect on lowering CO2 emissions

Abstract

Steel industry is responsible for approximately 8% of industrial CO₂ emission due to its dependence on the widely used blast furnace (BF) and basic oxygen furnace (BOF) technology. On the other hand, the processes applied to produce bulk ferroalloys are also carbon-based technologies, and these processes contribute in CO₂ emissions. For instance, in ferromanganese production in submerged arc furnace (SAF) about 1.1-1.8 t CO₂/t metal is directly emitted, while considering non-renewable energy use it reaches over 4.5 tCO₂/t metal in the main ferroalloy producing countries. Although the quantity of manganese ferroalloys (about 20 million tonnes) is much less than the crude steel production (about 1.9 billion tonnes), their consumption in steelmaking contributes to CO₂ emission.

In recent years, there has been significant research and development in shifting from BF/BOF technology to hydrogen-based direct reduction (DR) and electric arc furnace (EAF) technology to decarbonize the steel industry. In the ferroalloy industry, however, it is not possible to use hydrogen to reduce more stable oxides than iron (such as MnO and SiO₂) to their metals due to the thermodynamics limitations. In an innovative approach in the newly introduced HAlMan process, which is currently implemented in pilot scale through the HAlMan EU project¹⁾, it is possible to produce green manganese ferroalloys through a combination of hydrogen reduction and smelting-aluminothermic reduction. In this approach, which was described previously²⁾, manganese ore is first pre-reduced by hydrogen gas and the obtained pre-reduced ore contains manganese in the form of MnO and iron in metallic form. Further flux smelting and aluminothermic reduction of the pre-reduced ore by aluminum scrap yields ferromanganese. This process is more sustainable than the SAF process regarding lower power consumption and insignificant CO₂ emission. A very important advantage of the HAlMAn process than SAF is obtaining a higher quality ferroalloy with ultra-low carbon concentration, a valuable feedstock to produce low-carbon steels.

To demonstrate the possibility of producing high-manganese steels with insignificant CO₂ emission, DRI pellets were produced from a commercial iron ore pellet using hydrogen in a lab reactor. This DRI was then smelted in an induction furnace with lime to produce a molten steel. Green low-carbon ferromanganese that was produced through the HAlMan approach was then used to alloy the molten steel. Three high-manganese steel grades were produced, and they were characterized by different techniques to qualify regarding the purities and microstructures. Theoretical calculations show that the use of green ferromanganese in steelmaking is accompanied with lowering CO₂ emissions, and it is more important for producing high-manganese steels.

Authors

Jafar Safarian – NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group

Effect of Pre-reduction of Manganese Ore by Hydrogen on Its Smelting Behavior and Interaction with Stable Oxides

Abstract

The conventional ferromanganese production process is driven by coal/coke utilization and constitutes a substantial source of greenhouse gas emissions. Hydrogen-based pre-reduction process stands out for its substantial carbon reduction capabilities and established technological maturity. Regarding this, a process called HAlMan is proposed, where the manganese ore is pre-reduced with hydrogen and then fed in the smelting furnace for complete reduction with aluminum. As the pre-reduced ore becomes the charge material (feed) it becomes quite necessary to understand how the pre-reduced ore behaves when it meets other stable oxides and refractories for that matter. The present work studies the interaction of Nchwaning Manganese ore with Al₂O₃, SiO₂ and MgO substrates before and after reduction with hydrogen, using sessile drop wettability approach. The formed slag droplet on the substrate were cut through center and the cross-sectional analysis for diffusion depth and microstructure was done using SEM, EDS and mapping. In addition, FactSage thermodynamic software was used to correlate and understand the experimental observation and possible phase formed at elevated temperatures. The study found that both pre-reduction and substrate types significantly influence softening and smelting behavior of ore particles. Pre-reduced ore melted at 1350 °C with a wetting angle of 24.32° on SiO₂ and 1544 °C with 13.62° on Al₂O₃. While the unreduced ore melted at 1285 °C with of 32.15° on SiO₂ and at 1485 °C with 16.12° on Al₂O₃. No complete melting was observed on MgO substrate in either case. Giving an idea that MgO could be a better refractory for smelting of pre-reduced ore. The addition of Al₂O₃ to the pre-reduced and unreduced Nchwaning ore has opposing effect as studied using FactSage. The melting temperature of pre-reduced decreases while that of unreduced ore increases on Al₂O₃ addition. This shows that the aluminothermic reduction of pre-reduced ore is better as the dissolution of Al₂O₃ would decrease the overall melting temperature during operation in HAlMan process.

Authors

Pankaj Kumar – NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group.
Jafar Safarian – NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group.

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Making High Mn Steel by Sustainable Ferromanganese Pre-alloy for Cryogenic Applications

Abstract

Driving toward net-zero CO₂ emissions in steel industry, a more sustainable approach should be adopted in both iron-making and steel-making processes. While the sustainability of iron making is supported by the prospering hydrogen-based direct reduction technology [1], research on the sustainability of alloying ingredients used in steel making has been limited.

In this study, we utilized three Mn alloying ingredients to produce three high Mn steels with similar composition. The first one is electrolytic Mn (hereafter referred to as “EMn”), which is a high purity form of metallic Mn; the second one is a conventional medium carbon ferromanganese pre-alloy (FeMn), which has been used in the steel making industry; and the third one is a “green” FeMn pre-alloy produced by a novel “HAlMan” process, which ensures lower energy consumption during the production of FeMn pre-alloy [2]. These three steels were named as EMn steel, MCFEMn steel and HAlMan steel. The chemical composition is designed with the aid of thermodynamic calculation, aiming for cryogenic applications of high Mn steel.

All three steels are produced by a lab-scale vacuum induction melting furnace, and underwent identical thermomechanical processing. Comparability between these steels were demonstrated by a thorough microstructure characterization, and mechanical testing at either room temperature or cryogenic temperature. From the testing results, all three steels exhibited similar microstructure, similar grade of tensile properties and impact toughness, which demonstrated the feasibility of making high Mn steel by the HAlMan “green” FeMn pre-alloy.

In summary, the HAlMan steel showcases similar grade of high Mn steel performance as EMn steel and MCFEMn steel while utilizing a more sustainable alloying ingredient. This research effort aims to reduce the overall energy consumption of steel making without compromising steel performance, contributing to a more sustainable future in the steel industry.

Authors

Shao-Lun Lu –Max Planck Institute for Sustainable Materials, Department of Microstructure Physics and Alloy Design (Germany)
Shaolou Wei – Max Planck Institute for Sustainable Materials, Department of Microstructure Physics and Alloy Design (Germany)
Dirk Ponge – Max Planck Institute for Sustainable Materials, Department of Microstructure Physics and Alloy Design (Germany)

Learn more Zenodo

Green Manganese steel from remelting of hydrogen based Direct Reduced Iron (DRI) and green Ferroalloy: a CO2 free approach

Description

Manganese is an important alloying element used in steel industry and is mostly used for increasing the strength without compromising the ductility. Currently, manganese is added as ferromanganese in steel to form manganese steel. Hence the final steel formation goes through series of steps after primary raw materials extraction, namely, ironmaking, crude steel production, ferromanganese production, steel refining and alloying to get the desired product. Carbon is used as the major reductant to produce iron and ferromanganese, which causes significant emission of CO2. To reduce this greenhouse gas emission, new innovative technology needs to be adopted using greener reductant as an alternative to carbon. In the present work, hydrogen for the reduction of Iron from iron ore pellets was used. The produced Direct Reduced Iron (DRI) was then flux-smelted in induction furnace with lime acting as a fluxing agent to obtain iron metal with low carbon. The obtained iron was then melted with green ferromanganese in certain proportions to obtain steels with composition close to the composition of Hadfield, Transformation Induced Plasticity Steel) (TRIP) and (Twinning-Induced Plasticity steel) TWIP steel. The results showed that the hardness of the produced steel was similar or better than the conventional steel and the proposed process emits no CO2.

Author

Pankaj Kumar – NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group.

Co-authors

Jafar Safarian – NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group.
Rikke Nordstroem – NTNU Norwegian University of Science and Technology

Learn more on Zenodo

Hydrogen Reduction of Manganese and Iron Oxides in a Commercial Manganese Ore: Thermochemistry and Kinetics

Abstract

The transition from solid carbon to hydrogen gas in ferromanganese production represents a transformative strategy for reducing carbon emissions in the ferroalloy industry. The HAlMan process, an innovative hydrogen-based reduction method, has advanced from laboratory-scale research to pilot-scale validation, demonstrating significant potential for decarbonizing ferromanganese production. This breakthrough technology could reduce CO2 emissions by approximately 1.5 tonnes per tonne of ferromanganese produced, marking a critical step toward sustainable metallurgy. This study examines the thermochemical behavior and the reaction kinetics of a commercial manganese ore during hydrogen pre-reduction in a laboratory-scale vertical thermogravimetric furnace under isothermal conditions. Experiments were conducted at temperatures ranging from 600°C to 900°C to assess the reduction behavior and determine the rate-limiting mechanisms. Thermogravimetric analysis (TGA) was employed to monitor weight loss, enabling precise reduction rate measurements. Reduction progression was evaluated using XRF, XRD, BET, and SEM analyses to investigate compositional, mineralogical, and microstructural transformations. The results indicate that the simultaneous hydrogen reduction kinetics of manganese and iron oxides in the ore are strongly temperature-dependent, with higher temperatures facilitating faster reduction and phase transformations. Complete reduction to metallic Fe and MnO was achieved at 800°C and 900°C within two hours, whereas lower temperatures required extended holding times to reach similar extents of reduction. Additionally, sintering effects were observed above 700°C, as evidenced by a decrease in BET surface area and pore volume. These findings provide valuable insights into the hydrogen reduction mechanisms of manganese ore, supporting the development of an environmentally sustainable pathway for ferromanganese production.

Author

Alok Sarkar – NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group.

Co-author

Jafar Safarian – NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group.

Learn more on Zenodo

Carburization with methane of different iron-bearing oxide pellets reduced by hydrogen

Description

To reduce CO₂ emissions in iron and steel production, the industry is transitioning towards hydrogen-based reduction. However, a key challenge lies in the sustainable production of hydrogen, as most hydrogen is currently derived from hydrocarbon decomposition. Additionally, during the smelting of Direct Reduced Iron (DRI) in steelmaking, a certain amount of carbon in DRI feed is beneficial. In this study, hydrogen was used to reduce iron oxides in two iron-bearing pellets, which were quite different in compositions and physical characteristics. The reduction was conducted at 900 °C, followed by carburization at the same temperature using hydrogen with 10 vol% CH₄ for different durations. XRD, SEM, LECO, and XRF analyses were performed to examine the phase compositions, microstructure, carbon content, and chemical compositions before and after reduction. The results confirmed complete reduction of iron oxides during the reduction stage, and in carburization, DRI mass gains were observed due to the carburization and the formation of cementite and graphite phases. Prolonged carburization led to the decomposition of cementite, further influencing the phases distrubutions and compositions.

Author

Manish Kumar Kar – NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group.

Co-author

Alumina Recovery from Sodium Aluminate Solutions via Carbonation

Abstract

This study explores the recovery of alumina from sodium aluminate, sodium carbonate, and sodium hydroxide solutions resulting from the leaching of calcium aluminate slags generated from pyrometallurgical reduction of various ores/by-products for metallic iron, silicon, and manganese extraction within several EU-funded projects. Such calcium aluminate slags are leached with sodium carbonate, generating a pregnant leaching solution. The entire process is evaluated starting from the carbonation of the pregnant leaching solution, where alumina hydrates (aluminium hydroxides) are precipitated by purging carbon dioxide gas into the solution. The alumina hydrates are calcined to produce alumina (aluminium oxide), which is used for its dissolution in cryolite. The research aims to highlight the key characteristics of this process and the challenges involved in producing smelter-grade alumina. In addition, critical aspects of the process, such as the removal of sodium ions from the hydrated precipitate, are assessed. These are instrumental in attaining the purity and quality of the alumina hydrate. The findings demonstrate the viability of processing industrial by-products into useful products with reduced environmental impact. This study provides information on the efficiency of carbonation and facilitates the development of more sustainable alumina production from alternative raw materials.

Authors

Danai Marinos – PhD student
Dimitrios Kotsanis – Materials Characterization Specialist
Dimitrios Panias – Professor, NTUA – Technologies for Sustainable Metallurgy – Laboratory of Metallurgy, Athens, Greece
Efthymios Balomenos – Assistant Professor, NTUA – Technologies for Sustainable Metallurgy, Laboratory of Metallurgy, Athens, Greece
Casper Van der Eijk – Senior Research Scientist, SINTEF Industry – Department of Metal Production and Processing, Trondheim, Norway

Conference paper

Sustainable production of ultra-low-carbon ferromanganese and calcium aluminate slag from pre-reduced manganese ore using aluminium

Abstract

The production of ultra-low-carbon ferromanganese is both energy- and carbon-intensive, motivating the search for greener alternatives. This study investigates a sustainable process, using hydrogen pre-reduced Nchwaning manganese ore (NPO) and aluminium as a reductant, to produce ultra-low-carbon ferromanganese with leachable mono-calcium aluminate (CaO·Al2O3, krotite) slag. NPO (<1 mm) was blended with CaO to achieve CaO/Al2O3 molar ratios of 1.0, 1.2, and 1.4 and smelted with varying aluminium additions at 1500°C. The resulting alloys (0.005–0.013%C, 74.98–78% Mn, 18.8–24.4% Fe) were of high quality, while slags were dominated by calcium aluminates with minor gehlenite and tricalcium aluminate. During smelting, the slag system transformed from MnO–CaO to CaO–Al2O3, and the metal system evolved from Al–Fe to Mn–Fe–Si through rapid interfacial reactions. Mn and Si distributions between metal and slag were closely linked to slag composition. The optimum condition was a CaO/Al2O3 ratio of 1.2 and 20 wt% excess Al, yielding high metal recovery and desired slag. Excess lime increased Al2O3 dissolution from the crucible (8–13 g), slightly reducing Mn recovery. This process offers a cleaner route to ultra-low-carbon ferromanganese with usable slags. La production de ferromanganèse à très faible carbone est à la fois énergivore et fortement émettrice de carbone, ce qui motive la recherche de choix plus écologiques. Cette étude examine un procédé durable utilisant du minerai de manganèse Nchwaning (NPO) pré-réduit à l’hydrogène et de l’aluminium comme réducteur pour produire du ferromanganèse à très faible carbone avec des scories d’aluminate de mono-calcium (CaO·Al2O3, krotite) lixiviables. On a mélangé le NPO (<1 mm) avec du CaO pour obtenir des rapports molaires de CaO/Al2O3 de 1.0, 1.2 et 1.4 et fondu avec des ajouts variables d’aluminium à 1500°C. Les alliages obtenus (0.005 à 0.013% C, 74.98 à 78% Mn, 18.8 à 24.4% Fe) étaient de haute qualité, tandis que les aluminates de calcium avec des traces de gehlénite et d’aluminate tricalcique dominaient les scories. Lors de la fusion, le système de scories s’est transformé de MnO–CaO à CaO–Al2O3, et le système métallique a évolué d’Al-Fe à Mn–Fe–Si par des réactions interfaciales rapides. La distribution de Mn et Si entre le métal et les scories était reliée de près à la composition des scories. La condition optimale était un rapport CaO/Al2O3 de 1.2 et 20% en poids d’excès d’Al, produisant une récupération élevée du métal et de scories souhaitées. Un excès de lime a augmenté la dissolution de l’Al2O3 du creuset (8 à 13 g), réduisant légèrement la récupération du Mn. Ce procédé offre une voix plus propre pour le ferromanganèse à très faible teneur en carbone avec des scories utilisables.

Authors

Jafar Safarian, Department of Materials Science and Engineering, NTNU, Trondheim, Norway
Pankaj Kumar, Department of Materials Science and Engineering, NTNU, Trondheim, Norway

Read more on the Canadian Journal of Metallurgy and Materials Science

Exploring the potential of secondary resources: LA-ICP-MS for critical raw materials characterization

Abstract

This study compares methodologies and provides insights on best approaches for quantifying EU-listed critical raw materials. Europe’s strategy towards greater resilience involves valorization of secondary resources such as mine tailings or by-products of metallurgical production that are typically discarded as waste, despite containing valuable resources. Thus, identifying the best methods to determine elemental concentrations in various resources is crucial for evaluating their recovery, both environmentally and economically.Elemental content is usually determined using techniques such as inductively coupled plasma (ICP) mass spectrometry (MS) by digesting solid samples into liquid solutions, although challenging for some refractory materials. Direct analysis of solids by laser ablation (LA)-ICP-MS is another alternative and can be used for both bulk analysis and spatially resolved mapping of critical elements throughout the supply value chain, from raw materials to refined products.Here, we compare ICP-MS/MS analysis on dissolved samples, obtained after microwave-assisted acid dissolution, with LA-ICP-MS analysis on solid samples for determining rare earth element (REE) compositions of manganese ores and slags. For LA-ICP-MS, we present two approaches, particularly useful in cases where dissolution proves challenging: (i) analysis of glass beads obtained through borate flux fusion of raw powders, and (ii) direct analysis on pelletized powders using a novel non-matrix matched calibration strategy. Each method’s feasibility and strengths are considered for the specific chemical composition of the samples of interests. The study shows that different methods have advantages and disadvantages related to particle size distributions and preparation costs that need to be considered during characterization of secondary resources.

Authors

Debora Foppiano – SINTEF Industry, Trondheim (Norway)
Einar Jonsson – SINTEF Industry, Trondheim (Norway)
Sarina Bao – SINTEF Industry, Trondheim (Norway)
Øyvind Skår – Geological Survey of Norway (NGU), Trondheim (Norway)
Trond Slagstad – Geological Survey of Norway (NGU), Trondheim (Norway)
Pankaj Kumar – Norwegian University of Science and Technology (NTNU), Trondheim (Norway)
Maria Wallin – Norwegian University of Science and Technology (NTNU), Trondheim (Norway)
Kristina Mervič – National Institute of Chemistry, Ljubljana (Slovenia)
Martin Šala – National Institute of Chemistry, Ljubljana (Slovenia)
Casper van der Eijk – SINTEF Industry, Trondheim (Norway)

Read more on SSRN

Read more on Talanta

– 2026 –

Hydrogen reduction kinetics of a high-carbonate manganese ore in raw and calcined forms under isothermal conditions

Abstract

This study examines the hydrogen-based isothermal reduction behavior of high-carbonate UMK manganese ore in both raw and calcined forms, with the aim supporting cleaner manganese ferroalloy production. Comprehensive characterization was performed using XRF, XRD, optical microscopy, and EPMA to assess the impact of the calcination process on lumpy ore structure, composition, and H2-reduction kinetics. Results show that calcination significantly enhances mineral liberation by decomposing carbonate phases and increasing porosity. Thermogravimetric reduction experiments at 700 °C, 800 °C, and 900 °C under 100 % H2 reveal that calcined samples exhibit higher reduction rates, and improved extent of reduction compared to raw ore. Kinetic modelling using the Avrami-Erofeev equation demonstrates a shift in the rate-controlling mechanism from surface-controlled (dried ore) to diffusion-controlled (calcined ore), with apparent activation energy decreasing from 58.72 kJ/mol to 33.23 kJ/mol. Thermodynamic analysis confirms the active role of hydrogen in enhancing carbonate decomposition via the reverse water-gas-shift reaction (RWGSR), especially aiding calcite decomposition at lower temperatures. These findings highlight that calcination of the ore prior to hydrogen reduction not only improves hydrogen reactivity but also promotes favorable gas-solid interactions and CO2 removal. The study supports hydrogen pre-reduction as a viable pathway to decarbonize Mn-alloy production and optimize furnace performance in high-temperature systems.

Author

Alok Sarkar – NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group.

Kai Tang – SINTEF Industry, Trondheim, Norway

CO2 absorption in NaOH-Na2CO3 solutions: Combined CFD and thermodynamics-based, experimentally validated analysis

Abstract

Carbonation processes find numerous applications; however, the complex nature of their underlying mechanisms has hindered their detailed understanding. The fluid dynamics occurring within stirred tanks, the multiphase CO₂ bubble flow, as well as the interphase mass transfer and chemical reactions, are all simultaneously affecting the carbonation process. Furthermore, the interplay between all those mechanisms and phenomena deems the in-depth mechanistic understanding of the process dynamics via experimental studies a rather challenging task. In this work, a novel combined computational approach, consisting of a thermodynamic and a three-dimensional CFD model, is developed for the CO₂ absorption in NaOH-Na₂CO₃ liquid solutions. Information on the equilibrium conditions is provided by the thermodynamic to the CFD model, which calculates the dynamics of CO₂ absorption in the solution. These results are fed back to the thermodynamic model, enabling the simulation of the chemical reactions, in conditions closer to the actual experiments. The results are validated using experimental measurements for the CO₂ flow and the pH within the solution, achieving good agreement. This approach enables the integration of insights from both methodologies, revealing the relationship between the different phenomena and mechanisms that constitute the carbonation process, which might be challenging to define using solely experimental results. Specifically, it elucidates the process dynamics which unravels key mechanisms during the carbonation process. The combined computational approach can assist the knowledge-based process and reactor design, while it can also pave the way for the optimized scale-up of carbonation-precipitation processes.

Authors

A. Lazou, Laboratory of Metallurgy, School of Mining and Metallurgical Engineering, National Technical University of Athens, Greece
G.P. Gakis, School of Chemical Engineering, National Technical University of Athens, Greece
D. Marinos, Laboratory of Metallurgy, School of Mining and Metallurgical Engineering, National Technical University of Athens, Greece
I.G. Aviziotis, School of Chemical Engineering, National Technical University of Athens, Greece
E. Balomenos, Laboratory of Metallurgy, School of Mining and Metallurgical Engineering, National Technical University of Athens, Greece
A.G. Boudouvis, School of Chemical Engineering, National Technical University of Athens, Greece
D. Panias, Laboratory of Metallurgy, School of Mining and Metallurgical Engineering, National Technical University of Athens, Greece

Hydrogen Reduction Behavior and Kinetic Modeling of a High-Barium Manganese Ore: Effect of Calcination

Abstract

Hydrogen-based reduction of manganese ores has attracted increasing attention as a promising route for low-carbon manganese production. In this study, the reduction behavior, microstructural evolution, and kinetics of a high-barium-rich manganese ore were investigated in both dried and calcined states under isothermal hydrogen atmospheres at 600–800 °C. The ore was characterized using XRF, XRD, optical microscopy, SEM-EDS, and porosity measurements to evaluate mineralogical and structural changes during calcination and reduction. Calcination at 900 °C transformed MnO2 into Mn2O3/Mn3O4, removed volatile components, and generated micro-porosity that improved gas accessibility. Isothermal reduction experiments revealed a rapid initial reduction stage followed by a slower reaction regime, with increasing temperature significantly accelerating the reduction rate. Despite isothermal furnace conditions, a temporary rise in sample temperature was observed due to the exothermic nature of manganese oxide reduction by hydrogen. XRD analysis confirmed that manganese oxides were predominantly reduced to MnO, while iron oxides were converted to metallic Fe. Porosity measurements showed significant pore development during reduction at moderate temperatures due to oxygen removal and gas evolution; however, at higher temperatures, partial sintering led to pore coalescence and densification, reducing the overall porosity. Kinetic analysis showed that the Johnson–Mehl–Avrami–Kolmogorov (JMAK) model effectively describes the reduction behavior. The apparent activation energies were 21.92 kJ.mol−1 for dried ore and 17.40 kJ.mol−1 for calcined ore, indicating diffusion-influenced kinetics. The results demonstrate that calcination enhances hydrogen reducibility by improving gas accessibility and reducing kinetic resistance, highlighting its importance for hydrogen-based manganese pre-reduction processes.

Authors

Alok Sarkar – NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group.
Elias Trondsen Dahl – Norsk Hydro, NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group.
Jafar Safarian – NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group.

Read more on MDPI

Effect of Calcination of Manganese Ore on Reducing Hydrogen and Energy Consumptions in Hydrogen-Based Direct Reduction Process

Abstract

Manganese is a critical raw material and there is currently a great interest in decarbonization in the metallurgical sector for its production. Hydrogen use in manganese and its alloys’ production is in principle possible for sustainable production; however, this requires a technological shift from traditional carbothermic processes to completely new processes; like the HAlMan process. To design a process, it is crucially important to optimize the process conditions (such as temperature) and minimize the quantity of hydrogen gas and the related energy consumptions. In the present work, energy and mass balances for a hydrogen-based reduction reactor were carried out employing thermodynamics software and analytical approaches from room temperatures to 900 °C. It was found that the quantity of hydrogen gas required for the pre-reduction of manganese ore can be significantly reduced via coupling the reduction reactor with a calciner and the hot charge of the calcined ore into the reduction reactor. Moreover, hot H2-H2O gas mixture from the reduction reactor outlet can be used for preheating the hydrogen feed of the reactor, and the calcination of the ore, while a portion or all its hydrogen can be recovered and looped. The integrated coupled calcination-reduction process was found to be operated with no external energy supply, or insignificant fuel use.

Author

Jafar Safarian – NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group.

Read more on MDPI

Effect of Calcination on Hydrogen Reduction Kinetics, Porosity, and Microstructural Evolution of a High-Carbonate Manganese Ore

Abstract

This study investigates the hydrogen reduction behavior of high carbonate manganese ore, focusing on how calcination influences reduction kinetics, microstructural evolution, and gas–solid reaction mechanisms. Isothermal reductions were performed at 700–900 °C on dried and calcined ore using a vertical tube thermogravimetric furnace, supported by x-ray fluorescence (XRF), x-ray diffraction (XRD), scanning electron microscopy (SEM)–energy-dispersive x-ray spectroscopy (EDS), porosity measurements, and JMAK kinetic modeling. Calcination of the ore at 900 °C effectively removed the carbonate and hydroxide phases, producing a more open-pore structure and significantly enhanced early-stage reducibility by hydrogen at 700–800 °C. Fractional-conversion and rate analyses confirmed higher initial reaction rates for calcined samples due to improved gas accessibility at these temperatures. At 900 °C, both raw and calcined ore types exhibited reduced porosity associated with temperature-induced densification, with the calcined ore showing a slower progression toward high conversion, consistent with increased diffusion resistance at advanced stages. Gas-evolution profiles revealed strong CO₂ release in the dried ore and highlighted the accelerating influence of the reverse water–gas shift (RWGSR) reaction during carbonate decomposition. JMAK modeling yielded activation energies of 81.46 kJ/mol (dried) and 24.62 kJ/mol (calcined), indicating a shift in the rate-controlling mechanism from surface-controlled behavior in the dried ore to diffusion-controlled behavior in the calcined ore. These findings provide mechanistic insight relevant to hydrogen-based low-carbon Mn processing.

Author

Jafar Safarian – NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group.
Alok Sarkar – PhD candidate, Norwegian University of Science and Technology

Read more on Springer

Combined hydrogen and aluminothermic reduction of Mn ores in HAlMan process; thermochemistry, products qualities, and sustainability

Abstract

In the new HAlMan integrated process, hydrogen gas and aluminium scrap/dross are used to produce manganese ferroalloys with low energy consumption and carbon footprint. In this process, hydrogen gas is used to pre- reduce manganese ores which contains metallic iron and MnO. The MnO content of this intermediate is further reduced at elevated temperatures by aluminium in a smelting-aluminothermic reduction process, yielding high-Mn alloy and a calcium-aluminate slag. The metal product of the process is manganese, new Mn-Al alloy, ferromanganese, or silicomanganese, depending on the process adjustments. The thermochemistry of the HAlMan process is evaluated in comparison with the state-of-the-art carbothermic process in Submerged Arc Furnace (SAF). Experimental results of the HAlMan process are presented, and the effect of ore type and process conditions on the quality of the metal and slag products are discussed. It is shown that that the process is flexible to produce a variety of metallic products, and a consumable/valuable slag byproduct. Mass and energy balances calculations are presented, and it is shown that the energy consumption for the process is significantly lower than the SAF process. It is shown that ferromanganese production by this process prevents significantly CO2 emission in a more robust approach with less challenges than the current low-carbon ferromanganese production technology. The implementation of the HAlMan process in pilot scale through HAlMan EU project is presented, and it is shown how the process products can be used to make commercial

Author

Hydrogen pre-reduction of different manganese ores in a vertical retort toward demonstration of the HAlMan process

Abstract

Authors

Madinoge Mampurua, Mintek
Sello Tsebea, Mintek
Dursman Mchabea, Mintek
Elias Matindea, Mintek

Hydrogen Reduction of a Pyrolusite-Rich Manganese Ore: Effects of Calcination Prior to Reduction

Abstract

Decarbonizing manganese ferroalloy production requires a quantitative understanding of hydrogen-based pre-reduction and the ore specific risks of densification and liquid-assisted sintering. This study investigates the hydrogen reduction behavior of a pyrolusite-rich manganese ore to support low-carbon manganese processing routes. Comparative experiments were performed on dried ore and ore calcined at 900 °C in air, combining thermogravimetric reduction conducted at 600−800 °C under 100% H₂ with phase, chemical, and microstructural characterization. Calcination decomposes carbonates and hydroxides, transforms higher manganese oxides to Mn₂O₃/Mn₃O₄, and generates a crack network that modifies subsequent reduction pathways. In both routes, reduction proceeds through a rapid initial stage followed by a progressively decelerating regime. Avrami−Erofeev kinetic analysis yields low apparent activation energies (11.90 kJ mol⁻¹ for the dried ore and 14.37 kJ mol⁻¹ for the calcined ore), indicating mixed control, with surface chemical reactions dominating initially and diffusion resistance increasing at higher conversions. XRD confirms MnO and metallic Fe as the final reduced phases. Textural evolution shows pore formation at intermediate temperatures, counteracted at 800 °C by densification and liquid-assisted sintering associated with low-melting silicate phases. The results define critical constraints for hydrogen-based manganese ore processing. These findings highlight the potential of hydrogen-based reduction as a low-carbon and sustainable alternative to conventional carbothermic processing.

Authors

Alok Sarkar, PhD, Norwegian University of Science and Technology
Kai Tang, SINTEF Industry
Jafar Safarian, NTNU Norwegian University of Science and Technology, Department of Materials Science and Engineering, Faculty of Natural Sciences, Resources, Energy & Environment research group.