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

Authors:
Mopeli Khama at Mintek
Mopeli Khama
Quinn Gareth Reynolds
Quinn Gareth Reynolds
Quinn Gareth Reynolds
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Buhle Sinaye Xakalashe at Mintek
Buhle Sinaye Xakalashe
Alok Sarkar at Norwegian University of Science and Technology
Alok Sarkar
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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.
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Computational reacting flow models for the pre-reduction of lumpy Nchwaning manganese ore with hydrog
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... Mn ore heat capacity (Cp s ) and thermal diffusivity (α s ) were evaluated using a laser flash method. An LFA-457 Micro-flash was used, and properties were evaluated at 100 • C increments, from 100 to 800 • C. Thermal conductivity (λ s ) was calculated using Equation (7). Thermal expansion of the Mn Ore up to 600 • C is below 1% as reported in [23]. ...
Numerical and Experimental Study of Packed Bed Heat Transfer on the Preheating of Manganese Ore with Air up to 600 °C
Article
Full-text available
  • Feb 2025
This work studies heat transport in the fluid–solid interface of a packed bed to demonstrate the feasibility of preheating lumpy manganese ores to 600 °C with air at 750 °C. Preheated manganese ores aim to reduce furnace energy consumption during smelting in submerged arc furnaces to produce manganese ferroalloys. The preheating process was experimentally studied in a pilot-scale shaft-type column. The air was heated to 750 °C and used as a heat transfer fluid to heat a packed bed of manganese ore from room temperature to 600 °C. A one-dimensional three-phase (manganese ore, air, and the column wall) numerical model was developed to simulate the preheating process. The energy balance of the three phases was carried across a finite volume using the volume averaging technique. Numerical schemes were applied, and non-dimensional parameters were introduced before applying numerical techniques to solve the systems of linear equations. Python NumPy and SciPy modules were used for the computation of the packed bed temperature fields. Temperature data from the preheating tests were used for model validation. The model prediction of the transfer process agreed with experimental results to least square errors of less than 25 °C. Data from experimental measurements confirmed the feasibility of using air as the transfer fluid in the preheating of manganese ore. Detailed temperature field data generated from the model can be used for the sizing of manganese ore preheating units and the implementation of control protocols for the preheating process.
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... They found that higher temperatures accelerate the conversion of Fe 2 O 3 to Fe and Mn 2 O 3 to MnO, resulting in faster and more pronounced formation. Additionally, they observed that increased porosity enhances the rate of pre-reduction [21]. ...
Evaluating the Reaction Kinetics on the H2 Reduction of a Manganese Ore at Elevated Temperatures
Article
Full-text available
  • Nov 2024
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 H 2 reduction, revealing an apparent activation energy (E a) of 65.76 kJ/mol and an apparent pre-exponential factor (k 0) 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.
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... They found that higher temperatures accelerate the conversion of Fe 2 O 3 to Fe and Mn 2 O 3 to MnO, resulting in faster and more pronounced formation. Additionally, they observed that increased porosity enhances the rate of pre-reduction [21]. ...
THEMATIC SECTION: REACTION KINETICS STUDY OF FERROUS AND NON-FERROUS MATERIALS USING HYDROGEN AND BIOMASS Evaluating the Reaction Kinetics on the H 2 Reduction of a Manganese Ore at Elevated Temperatures Graphical Abstract Keywords H 2 reduction · Manganese ore · Kinetics · Rate constant · Activation energy · CO 2 emission
Article
Full-text available
  • Nov 2024
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 H 2 reduction, revealing an apparent activation energy (E a ) of 65.76 kJ/mol and an apparent pre-exponential factor (k 0 ) 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. Graphical Abstract
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... They observed that elevated temperatures reduction accelerates the conversion of Fe2O3 to Fe and Mn2O3 to MnO, resulting in quicker and more significant formation of Fe and MnO. Furthermore, they highlighted that higher porosity enhances the rate of pre-reduction [21] . In our earlier research, we observed that the kinetics of prereduction of the Nchwaning manganese ore by H2 are influenced by temperature. ...
Kinetics study on the H 2 reduction of Nchwaning manganese ore at elevated temperatures
Conference Paper
Full-text available
  • Oct 2024
The application of H2 gas instead of solid carbon to produce ferromanganese is a sustainable approach to reduce the carbon footprint in the ferro-alloy industry. A sustainable integrated process (HAlMan process) is extensively studied and tested in lab to pilot scale to reduce the CO2 emission during ferromanganese production and this process can prevent the emission of about 1.5Tonne of CO2/ Tonne of ferromanganese produced. In this kinetics study, pre-reduction of Nchwaning manganese ore conducted in a lab scale vertical thermogravimetric furnace by direct reduction through H2 gas under isothermal condition with H2 gas at the temperatures of 700℃, 800℃, and 900℃ respectively. Both ore and reduced samples were characterized by X-Ray Fluorescence (XRF), X-Ray Diffraction (XRD) techniques to interpret the experimental results. The pre-reduction at higher temperatures 800℃ and 900℃ yields metallic iron formation from Fe2O3 and MnO formation from Mn2O3. The rate and extent of reduction were studied using the continuous mass changes during the reduction. Different kinetic models were applied to validate the experimental results for the H2 reduction of the manganese ore at different temperatures and activation energy (Ea) and pre-exponential factor (k0) were calculated. It was found that the process kinetics obeys a third order reaction model yielding an activation energy of 30.33kJ/mol for the hydrogen reduction of the dried ore, while it yielded an activation energy of 41.60 kJ/mol for the pre-calcined ore. The kinetics of the ore reduction with H2 exhibit temperature dependence and higher temperature facilitate a quicker and more comprehensive reduction process.
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Isothermal Pre-Reduction Behavior of Nchwaning Manganese Ore in H 2 Atmosphere †
Conference Paper
Full-text available
  • Dec 2023
The application of H 2 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 H 2 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 H 2 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 Fe 2 O 3 and MnO formation from MnO 2 /Mn 2 O 3. 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.
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Pre-reduction of United Manganese of Kalahari Ore in CO/CO2, H2/H2O, and H2 Atmospheres
Article
Full-text available
  • Jan 2023
The incorporation of hydrogen, which is a relatively unexplored reductant used during ferromanganese (FeMn) production, is an attractive approach to lessen atmospheric gaseous carbon release. The influence of hydrogen on the pre-reduction of carbonate-rich United Manganese of Kalahari (UMK) ore from South Africa was investigated. Experiments were performed in 70 pct CO 30 pct CO 2 (reference), 70 pct H 2 30 pct H 2 O, and 100 pct H 2 gas atmospheres at 700 °C, 800 °C, and 900 °C. Calculated phase stability diagrams and experimental results showed good correlation. The pre-reduction process involved two reactions proceeding in parallel, i.e ., the pre-reduction of higher oxides and the decomposition of carbonates present in the ore. A thermogravimetric (TG) furnace was employed for the pre-reduction of the ore in various atmospheres. The calculated weight loss percentage was used to determine the degree and rate of pre-reduction. It was found that the oxidation state of higher Fe- and Mn-oxides was lowered when treated in 70 pct H 2 30 pct H 2 O and 70 pct CO 30 pct CO 2 , whereas FeO was metalized when using 100 pct H 2 . As for the intrinsic carbonates, the majority thereof were decomposed in the CO/CO 2 atmosphere at 900 °C, and ≥ 700 °C in the H 2 /H 2 O and H 2 atmospheres. Additionally, the degree and rate of reduction were accelerated by increasing the pre-reduction temperature and by employing a hydrogen-containing gas atmosphere (70 pct H 2 30 pct H 2 O, and 100 pct H 2 ). Scanning electron microscopy and electron microprobe analysis revealed the presence of three phases in the pre-reduced ore: (i) Mn- and Fe-rich, (ii) Mg- and Ca-rich, and (iii) Mg-, Si-, K-, and Na-rich. It was also found that there were no appreciable differences in porosity and decrepitation of the ores treated in the CO/CO 2 and hydrogen-containing atmospheres. The use of a hydrogen atmosphere showed potential for the pre-reduction of carbonate-containing manganese ores as it accelerated the decomposition of the carbonates as well as facilitated the metallization of Fe-oxides present in the ore.
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OpenFOAM solver for thermal and chemical conversion in porous media
Article
Full-text available
  • May 2022
  • COMPUT PHYS COMMUN
We present the porousGasificationFoam solver and libraries, developed in the open-source C++ code OpenFOAM, for the comprehensive simulation of the thermochemical conversion in porous media. The code porousGasificationFoam integrates gas flow through a porous media with the models of heterogeneous (drying, gasification, pyrolysis, solid combustion, precipitation) and homogeneous (gas combustion) chemical reactions. Inside porous media transport equations are formulated applying the spatial averaging methodology. The mass and enthalpy transfer between solid and gas phases is suitable for systems out of the thermal equilibrium. The convection and radiation modes of the heat transfer are included for gas and solid phases, and the immersed boundary technique is applied for the porous media inside the computational domain. We validate the elements of the model against a set of experimental and theoretical results. Amongst them, Thermogravimetric Analysis experiments of thermal conversions of two wooden particles: one of millimeter size the other of centimeter size. Simulations feature reaction schemes and physical parameters established in the literature. We show the influence of the porous media size on the gasification process. The millimeter particle remains uniform, while for the centimeter setup, the pyrolysis front is reproduced. The spatial patterns in physical conditions modify the course of chemical reactions and influence media composition and structure evolution. Another important example is a gasifier where we obtain a self-sustaining front propagation due to an exothermic heterogeneous reaction. Program summary Program Title: porousGasificationFoam CPC Library link to program files: https://doi.org/10.17632/s6sj9kgp69.1 Developer's repository link: https://github.com/pjzuk/porousGasificationFoam(foam-extend-4.1); https://github.com/btuznik/porousGasificationFoam(OpenFOAM 8) Licensing provisions: GNU General Public Licence version 3 Programming language: C++ External routines/libraries: OpenFOAM 8, foam-extend-4.1 Nature of problem: The developed software is a solver and a set of libraries for simulating the thermal conversion in porous media, including drying, pyrolysis, gasification, and combustion. The model includes the flow of the reactive gas mixture and the transfer of mass and enthalpy between the gas and solid phases. The porous medium can change during the process. The model is transient and enables three-dimensional simulations.Solution method: The finite-volume method is used in the code for equation discretization. A set of governing equations is solved for the gas and solid phases, including mass conservation of gas species and solid components, momentum conservation in the gas phase, and equations of enthalpy conservation in both phases. The porous media region inside the whole computational domain is defined using the immersed boundary approach.
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Effect of Moisture, Hydrogen, and Water–Gas Shift Reaction on the Prereduction Behavior of Comilog and Nchwaning Manganese Ores
Article
Full-text available
  • Apr 2022
The ore–gas reactions in the prereduction zone in a ferromanganese furnace are largely decisive of the overall energy efficiency, carbon consumption, and climate gas emissions in ferromanganese production. An increased understanding of the prereduction zone is thus vital for optimization of the furnace operation. The ore–gas reactions are well known to be governed by kinetics rather than thermodynamics. The raw materials contain various amounts of both chemically bound and surface moisture when fed to the furnace, which may influence the reaction kinetics. This paper presents the investigation of the potential influence of moisture on the prereduction kinetics of two commercial manganese ores, i.e., Comilog and Nchwaning. TGA experiments were carried out by comparing dry and wet ore, as well as introducing H 2 (g) or H 2 O(g) to the CO–CO 2 gas mixture.
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A Sustainable Process to Produce Manganese and Its Alloys through Hydrogen and Aluminothermic Reduction
Article
Full-text available
  • Dec 2021
Hydrogen and aluminum were used to produce manganese, aluminum–manganese (AlMn) and ferromanganese (FeMn) alloys through experimental work, and mass and energy balances. Oxide pellets were made from Mn oxide and CaO powder, followed by pre-reduction by hydrogen. The reduced MnO pellets were then smelted and reduced at elevated temperatures through CaO flux and Al reductant addition, yielding metallic Mn. Changing the amount of the added Al for the aluminothermic reduction, with or without iron addition led to the production of Mn metal, AlMn alloy and FeMn alloy. Mass and energy balances were carried out for three scenarios to produce these metal products with feasible material flows. An integrated process with three main steps is introduced; a pre-reduction unit to pre-reduce Mn ore, a smelting-aluminothermic reduction unit to produce metals from the pre-reduced ore, and a gas treatment unit to do heat recovery and hydrogen looping from the pre-reduction process gas. It is shown that the process is sustainable regarding the valorization of industrial waste and the energy consumptions for Mn and its alloys production via this process are lower than current commercial processes. Ferromanganese production by this process will prevent the emission of about 1.5 t CO2/t metal.
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Reduction of Manganese Ores by Methane-Containing Gas
Conference Paper
Full-text available
  • Feb 2004
  • ISIJ INT
Reduction of Groote Eylandt (Australia) and Wessels (South Africa) manganese ores using CH4-H2-Ar gas mixture was investigated in a fixed bed laboratory reactor in the temperature range 1000-1200 C. The extent and kinetics of manganese ore reduction as a function of gas composition and temperature were determined by on-line off -gas analysis using mass-spectrometer and dew point sensor. Morphology of ores and its change in the course of reduction was examined by optical and scanning electron microscopy. Phaese of raw materials and reduced samples were analyzed by XRD and EPMA. Manganese oxides were reduced to carbide Mn7C3. High extent and rate of reduction by methane-containing gas in comparison with carbothermal reduction were attributed to high carbon activity in the reducing gas, which was in the range 15-50 (relative to graphite). The reduction of Wessels manganese ore increased with increasing temperature. Reduction rate and extent of Groote Eylandt manganese ore achoieved a maximum of 1050 C. The decrease in rate and extent of reduction of Groote Eylandt at higher temperatures, particularly at 1150-1200 C, was due to sintering and formation of semi-liquid silicate slag. An addition of lime (10-15% CaO) to the Groote Eylandt manganese ore increased melting temperature of slag and significantly increased the rate and extent of reduction at elevated temperatures.
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Metals Production and Metal Oxides Reduction Using Hydrogen: A Review
Article
  • Jan 2022
Hydrogen is projected to be not only a source of clean fuel energy, but also a reducing agent for metals production in the current industrial decarbonization effort. Currently, hydrogen is still not common to be used in many metals production. Hydrogen is only commercially utilized in a limited number of refractory metals (i.e., W, Mo) and partly utilized in Ni and Co metals production. Hydrogen reduction of metal oxides has been extensively studied at laboratory scale, particularly in regard to kinetics and reaction mechanism. These studies provided the fundamental knowledge useful for the development of the industrial metals production process. Recently, experimental approaches, current applications, and technologies related to the hydrogen reduction of metal oxides have been further developed. The current paper reviews selected key studies and provides information on the current status and applications of hydrogen for reduction of metal oxides (with a focus on reduction kinetics and mechanisms of non-ferrous oxides). This study summarized that hydrogen has the potential to be used to recover valuable metal from secondary resources (e.g., Zn from EAF dust, Pb from slag) but further detailed fundamental studies are required for improved processes. The use of hydrogen was also found to be useful for a number of advanced material processing, beyond extractive metallurgy perspective.Graphical Abstract
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Kinetics of Hydrogen Reduction of Manganese Dioxide
Article
  • Apr 1968
Single porous pellets and small beds of particles of synthetic pyrolusite were reduced in hydrogen at various partial pressures in the temperature range of 200° to 500° C. The reaction kinetics were followed by recovering the water product, and the intermediate reduction products were identified by x-ray diffraction analysis. Reduction proceeded topochemically through the sequence MnO2 → Mn2O3 → Mn3O4 → MnO. Below 250° C. reduction subsided with the formation of Mn3O4, and the process was controlled by a gas-solid chemical reaction step. Above 250° C. severe diffusional resistances were encountered, and further reduction to MnO became appreciable. Above 325° C. the over-all reduction process was again controlled by a gas-solid chemical reaction step. Variation of the reduction rate with temperature and with H2 and H2O partial pressures is consistent with the concept that the gas-solid reactions in the low (below 250° C.) and high (above 325° C.) temperature regimes involve adsorption of H2, surface reaction, and desorption of H2O, the surface rearrangement being rate-controlling.
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A Process Model for the Carbothermic Reduction of MnO from High Carbon Ferromanganese Slag—The Model
Article
  • Aug 2006
In the present investigation, novel process modelling techniques have been applied to capture the kinetics of the MnO reduction process. The judicious construction of the constitutive equations makes full use of both dimensionless parameters and calibration methods to eliminate poorly known kinetic constants. The effects of different metallurgical parameters on the reaction kinetics are adequately captured by the model. Moreover, by invoking the concept of an isokinetic reaction, it has been possible to derive solutions where the temperature dependence of the process is uniquely described by the Scheil integral. The model is validated by comparison with experimental data, which following calibration yields an adequate predictive power. The applicability is illustrated in different numerical examples and its relevance will be further documented and explored in another paper.
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Reduction of Low Grade Egyptian Manganese Ore via Hydrogen at 800 ˚ C -950 ˚ C
  • Jan 2014
  • 1-11
  • H H A El-Gawad
  • M M Ahmed
  • M E H Shalabi
El-gawad, H.H.A., Ahmed, M.M. and Shalabi, M.E.H. (2014) 'Reduction of Low Grade Egyptian Manganese Ore via Hydrogen at 800 ˚ C -950 ˚ C', Open Access Library Journal, 1, pp. 1-11. Available at: https://doi.org/10.4236/oalib.1100427.