Reduction Of Magnesium Oxide Research Articles

Analysis of KF behavior and inverse reaction molecular kinetics simulation in the vacuum carbothermic reduction of magnesium oxide

As a new generation of structural materials, magnesium-based materials are expected to replace steel and aluminum. Vacuum carbothermic reduction of magnesium smelting is a novel green technique that has received extensive attention in recent years. For this method, the study of catalysts and the reverse reaction mechanism is crucial. In this paper, the behavior of KF during the vacuum carbothermic reduction of magnesium oxide is thermodynamically analyzed. The experimental findings are characterized using X-ray diffraction (XRD), X-ray photon energy spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and chemical analysis. Furthermore, the molecular dynamics simulation of the inverse reaction are investigated. According to thermodynamic calculations, the reaction temperature for the vacuum carbothermic reduction of magnesium oxide is higher than 1463 K at 80 Pa. Furthermore, KF is not involved in the reaction during the reduction in which F- plays the major role. The experimental analysis shows that the addition of KF and CaF2 significantly improved the reduction, and the degree of KF promotion is higher. The degree of reduction of magnesium oxide is higher under higher addition and lower system pressure conditions. The mass loss rate increases with increasing addition and holding time, and tends to level off when the addition amount is greater than 7 % due to the limited impact of F-. The KF reduction experiment crystallized magnesium with a purity of 90.21 %, with good crystallization and structure. It is notable that KF remains in the residue and functions as a catalyst, and is not involved in the vacuum carbothermic reduction of magnesium oxide. According to the reverse reaction mechanism, when the three CO molecules interact on the surface of Mg(100) to form a carbon chain, oxygen atoms separate from the carbon chain, and the released oxygen atoms combine with magnesium atoms to form MgO.

Analysis of the behavior of NaF in the vacuum carbothermal reduction of magnesium oxide

Vacuum carbothermal reduction method of magnesium has the potential to become a new green process to replace the pidgeon method. Adding catalyst to enhance the degree of reduction is highly significant for this method. In this work, the behavior of NaF during vacuum carbothermal reduction of MgO was thermodynamically analyzed, and the experimental results were characterized by XRD, XPS, SEM and EDS. Thermodynamic calculations showed that the reaction temperature for vacuum carbothermal reduction of MgO was above 1462 K(80 Pa), and NaF did not participate in reaction during the reduction process, which was mainly the effect of F−. Experimental analysis showed that the addition of NaF obviously improved the degree of reduction, the mass loss rate elevated with the increasing of NaF addition and holding time, when the addition amount was greater than 7%, the mass loss rate tended to level off, which is the result of the limited effect of F−. The purity of magnesium in the condensate reached more than 91.11% with a good crystallization and granular structure. NaF did not participate in the carbothermal reduction of magnesium in vacuum, where it plays a catalytic role in the process.

Systematic kinetic study of magnesium production using magnesium oxide and carbonic materials at different temperatures

The main goal of this study was to determine the industrially best reductant for reduction of magnesium oxide to magnesium with wood charcoal and petroleum coke (petcoke) each in molar ratio 1:1 and 1:2 (oxidant:reductant) at high temperatures. In this study, a new and reliable combination of mathematical modeling and discrete numerical optimization theory by presenting 18 “mathematical filters” not relying only on statistical quantities of fitting (contrary to many similar researches) was introduced. The purpose of these filters was the determination of correct kinetic equation and therefore, the corresponding rate coefficient from among 18 equations most used at present in the challenging field of solid state chemical kinetics. With assistance of a new and fundamental mathematical function and the obtained values of rate coefficients, the function of rate coefficient in temperature was attained. The activation energy was then calculated as a function of temperature using the general definition of activation energy and the determined function for rate coefficient. The comparison between different reducing agents in the different conditions and with relevant previous study was accomplished to determine the best reducing agent from industry standpoint. Also, the areas under experimental data were calculated numerically and utilized for method validation and comparison. It turned out finally that relying only on fitting quantities in the solid state chemical kinetics can readily lead to wrong conclusions about the correct kinetic equation and about the most suitable reducing agent. It is obvious that the erroneous calculations and wrong decisions in the laboratory scale become significant and paramount in industry and this reveals the significance of rigorous mathematical analysis.Graphical abstract

Investigation of Electrowinning of Mg from MgO Using a Liquid Metal Cathode in MgF2-CaF2-NaF or MgF2-LiF Molten Salt

A novel magnesium (Mg) production process utilizing an electrolytic method was investigated for the direct reduction of magnesium oxide (MgO). Electrolysis of MgO was carried out with an applied voltage of 3.0 V using a copper (Cu), silver (Ag), or tin (Sn) cathode and carbon (C) or platinum (Pt) anode in magnesium fluoride (MgF2)−calcium fluoride (CaF2)−sodium fluoride (NaF) at 1273 K or MgF2− lithium fluoride (LiF) at 1083−1093 K. After the electrolysis of MgO in MgF2−CaF2−NaF molten salt, Mg alloys such as Mg2Cu, Cu2Mg, or Mg2Sn phases were produced with current efficiencies of 75.8−85.6% when the concentration of Mg in Mg alloys was 9.1−14.6 mass%. In addition, when the electrolysis of MgO was conducted in MgF2–LiF molten salt, Mg alloys such as Mg2Cu or AgMg phase were produced with current efficiencies of 76.2−81.7% when the concentration of Mg in the Mg alloys was 12.5−13.2 mass%. In addition, to produce high-purity Mg metal from Mg alloys, vacuum distillation was conducted. When vacuum distillation was conducted at 1100−1400 K for a duration of 5 h, the concentration of Mg in the Mg alloys feed decreased from 30.2−34.1 mass% to 0.64−1.75 mass%, and Mg metal with a purity of 99.998−99.999% was obtained under certain conditions. Therefore, the molten salt electrolysis using liquid metal cathode (MSE-LMC) process developed here is feasible for the direct reduction of MgO using an effective and environmentally sound method.

Transient light emission from the silicothermic reduction of magnesium oxide with potential for monitoring intermediate compound formation and decay

Small silicon samples were brought into contact with magnesium oxide substrate plates and heated under vacuum. At heating temperatures above 1400 K, a transient light emission effect in the Si/MgO interface was observed. The changes in sample brightness are likely caused by a thermal effect. Typically the sample temperature decreases gradually by 40–80 K and is followed by a very fast rise in temperature. The light emission effect may be correlated to the transient formation and decomposition of an inhibiting layer of magnesium silicate and the endothermic formation of gaseous silicon oxide. Tempering a silicon sample on a magnesium oxide plate for several hours produced an etch pit in the substrate material from which the silicon sample split off during the cooling phase. The etch pit was investigated via electron microscopy. EDXS analysis of the finely structured surface of the reaction zone reports a composition of 2/1/5 (Mg/Si/O). A cross-section of the same area reveals a thin layer of reaction products on top of the substrate material.

Phase transformation involved in the reduction process of magnesium oxide in calcined dolomite by ferrosilicon with additive of aluminum

AbstractMetal magnesium is mainly produced from the calcined dolomite by the silicothermic production. However, in this process, the reduction temperature is higher while the reaction speed is slow, which results in higher energy consumption and serious environmental problems. In this paper, adding aluminum into the ferrosilicon reducing agent is expected to lower the reaction temperature so as to solve the problems above. The phase transition involved in the whole reduction process including with and without aluminum addition were investigated in details by theoretical calculation and experimental research. The influence of aluminum on the magnesium oxide reduction path was analysis to clarify the internal mechanism. The results show that aluminum added into the ferrosilicon would first react with magnesium oxide to form magnesium vapor and alumina under vacuum pressure of 10 Pa when the temperature rises to 720°C. Then, calcium aluminate would be formed by the reaction of aluminum oxide and calcium oxide. Once the temperature reaches 1150°C, silicon begins to reduce the magnesium oxide to create the silicon oxide that will finally react with calcium oxide to form calcium silicate. When the temperature rises above 1150°C, both the aluminum and silicon will participate in the reduction of magnesium oxide. In the process of heating up, the mixture of aluminum, ferrosilicon and calcined dolomite forms Mg2Al4Si5O18 and Ca3Al2(OH)12 phase with the components in calcined dolomite. Mg2Al4Si5O18 and Ca3Al2(OH)12 phase finally form Ca12Al14O33 phase. The interaction between aluminum and ferrosilicon in the mixture is less; the mixture of aluminum and ferrosilicon first forms Al3FeSi2 phase, and finally has the trend of forming Al4.5FeSi phase. There is a great difference between the phase transformation of aluminum in the mixture of aluminum, ferrosilicon and calcined dolomite and that of aluminum in the mixture of aluminum and ferrosilicon.

Development of theoretical foundations for the hot metal desulfurization with magnesium reduced by the heat from exothermal transformations

The process of hot metal desulfurization by magnesium, reduced by the heat from exothermic reactions, has been investigated. Our research into the thermodynamics of magnesium oxide reduction in line with various protocols has established that it is in principle possible to reduce magnesium oxide by carbon, silicon, manganese, iron, and aluminum. We have calculated starting temperatures for MgO reduction by iron, manganese, silicon, aluminum, and carbon, which are 2,956, 2,546, 2,313, 1,585 and 1,875 °C, respectively. It has been determined that the most rational method to reduce magnesium oxide is the process based on binding the products of reduction into a CaAl 2 O 4 compound. Based on the established rational conditions for magnesium oxide reduction, the exothermic mixture for hot metal desulfurization was calculated, %: MgO – 15.0; FeO – 56.0; CaO – 7.0; Al – 22.0. Experimental study has confirmed the most successful technical solution for the introduction of the calculated exothermic mixture to the melt aimed at desulfurization, which implies the application of a device for the introduction of active reagents into the melt, which is equipped with a chamber that collapses under the influence of the heat of liquid hot metal. Its use makes it possible to achieve the mean level of desulfurization of 65–70 %. We have performed, under industrial conditions, an experimental desulfurization of chromium hot metal using the designed exothermic mixture. According to the research conducted, the achieved degree of hot metal desulfurization in a ladle was at the level of 38 %; for the material of castings ‒ at the level of 45.7 %. Thus, there is a reason to argue about resource and energy savings when applying the proposed technology for the out-of-furnace hot metal desulfurization by reduced magnesium

Clean magnesium production using concentrated solar heat in a high-temperature cavity-type thermochemical reactor

The synthesis of magnesium from the corresponding oxide via a solar carbo-thermal and methano-thermal reduction process using high-temperature concentrated solar heat was investigated. The reduction of magnesium oxide (MgO) was experimentally demonstrated in a directly-irradiated prototype solar reactor at reduced pressure and temperature up to ∼1650 °C. The solar reactor was successfully operated with a variety of reducing agents (carbon and CH4) in batch and continuous modes under atmospheric and low pressure conditions (0.1–0.9 bar), thus representing the first process demonstration of MgO carbothermal reduction with continuous reactant injection in vacuum condition. A parametric study regarding operating pressure, carbon feedstock type, and C/MgO molar ratio was conducted to emphasize their effect on products yield (Mg and CO) and solar reactor performance. MgO conversion, reduction rate, and CO yield increased with decreasing pressure, in agreement with thermodynamic analysis. Utilizing activated charcoal as reducing agent showed the highest MgO conversion and CO yield. High MgO conversion over 99% was demonstrated with maximal CO yield up to 24.59 mmol/gMgO, closely approaching theoretical maximum value (24.81 mmol/gMgO). Employing methane as a reducing agent was also shown to be an alternative option to produce Mg, although methane cracking occurred simultaneously at the elevated reaction temperature. Mg recovery in the outlet products was identified as one of the most critical process challenges because of the pyrophoric property of the produced nanopowder and its strong oxidation reactivity with air.

On the prevailing reaction pathways during magnesium production via carbothermic reduction of magnesium oxide under low pressures

This work identifies MgO dissociation and reduction with CO as parallel pathways of Mg production via carbothermic reduction of MgO.

Thermal decomposition of magnesium carbonate with biomass and plastic wastes for simultaneous production of hydrogen and carbon avoidance

Application of biomass and waste plastics as resources for production of hydrogen enables sustainability of the chemical industry. In this step change novel carbon avoidance method, the carbon dioxide produced in a high carbon footprint process is consumed by thermal processing of magnesium carbonate in presence of biomass and plastics, simultaneously producing hydrogen. This study details the thermal decomposition of magnesium carbonate in presence of epoxy resin and biomass, as a renewable resource, at 1000 °C. The epoxy resin of known composition was used as a representative of the waste plastics as well as bio-renewable resource. Significant increase in carbon dioxide avoidance potential of up to 99% is realised in this work. The study promises significant reduction in current reaction temperature (∼1600 °C) for the dead burnt magnesium oxide production and magnesium production via carbothermic reduction of magnesium oxide attributed to the reducing atmosphere presented by hydrogen when biomass and waste plastics are used in the process. This study establishes the conditions for carbon dioxide avoidance, hydrogen enrichment and methane enrichment by merely controlling the ratios of the magnesium carbonate, biomass and epoxies.

Kinetics and mechanism of vacuum isothermal reduction of magnesia by aluminium

The kinetics and mechanism of vacuum isothermal reduction of calcined magnesite by Al were studied in the present paper. The results showed that the aluminothermic reduction process was divided into two stages. The apparent activation energy values of the two stages were determined to be 144.4 and 235.3 kJ mol−1, respectively. The phase MgAl2O4 was formed in the first stage. In the second stage, the intermediate phase Mg0.4Al2.4O4 was formed and the phase Al2O3 was obtained from the further reduction of Mg0.4Al2.4O4. The diffusion of molten aluminium is the rate-determining step of the reduction process. The out diffusion of magnesium vapour has some effect on the reduction ratio at the briquetting pressure between 60 and 120 MPa, but it is not the major rate-limiting step.Dans cet article, on a étudié la cinétique et le mécanisme de réduction isotherme sous vacuum de la magnésite calcinée par l’Al. Les résultats ont montré que le procédé de réduction aluminothermique était divisé en deux étapes. On a déterminé les valeurs d’énergie d’activation apparente des deux étapes à 144.4 et 235.3 kJ/mol, respectivement. La phase de MgAl2O4 était formée dans la première étape. La phase intermédiaire de Mg0.4Al2.4O4 était formée dans la seconde étape et l’on a ensuite obtenu la phase d’Al2O3 par réduction additionnelle du Mg0.4Al2.4O4. La diffusion de l’aluminium fondu est l’étape cinétiquement déterminante du procédé de réduction. La diffusion vers l’extérieur de la vapeur de magnésium a un certain effet sur le taux de réduction à la pression de briquetage entre 60 et 120 MPa, mais il ne s’agit pas de l’étape majeure cinétiquement limitante.

Smelting reduction of MgO in molten slag by liquid ferrosilicon

The smelting reduction of magnesium oxide was researched in this paper. The effect of molten slag composition and reduction temperature on percent reduction of magnesium oxide were discussed, and kinetics of smelting reduction of magnesium oxide in molten slag was studied. The results showed that the reduction extent of magnesium oxide increased by increasing either one of the following factors: the initial mass ratio of Al 2 O 3 /SiO 2 , the addition of CaF 2 , the initial molar ratio of Si/2MgO, and reaction temperature. The overall smelting reduction was controlled by mass transfer in slag with an apparent activation energy 586 kJ mol -1 .

Effects of Briquette Forming Condition on the Extraction of Magnesium from Calcined Magnesite via Vacuum Aluminothermic Reduction

Vacuum aluminothermic reduction of magnesia is multi-phase chemical reaction and the briquette forming condition has a great influence on the extent of the reactions. This paper focused on the effect of briquette forming condition on the extraction of magnesium from calcined magnesite. Briquettes were prepared at different conditions, including two forming pressures, four briquette thicknesses and two briquette diameters. The reduction ratio was calculated from the weight loss of the briquette before and after thermal reduction. The obtained condensed magnesium and briquette residues were mainly characterized via X-ray diffraction analysis and scanning electron microscopy. It was revealed that the briquette preparation condition had a great influence on the reduction ratio of magnesia and the phase constitution of the briquette residues, but had a minor influence on the morphology of condensed magnesium.

Direct reduction of magnesium oxide to magnesium using thermal plasma technology

A direct route for the reduction of magnesium oxide to magnesium using thermal plasma processing, with methane as the reducing gas, has been systematically evaluated. A feasibility study of the reduction reaction has been performed on the MgO-CH4 system at different methane concentrations and temperatures. The effects of changes in the key process parameters, such as the oxide-to-methane ratio and plasma power, on the yield of magnesium have been systematically evaluated. A maximum yield of about 61 mol% Mg was obtained using power of 20.0 kW and a molar ratio of MgO:CH4=1:1. Phase, morphological, elemental and binding energy analyses were performed on the product powders to understand the reduction reaction. Surface oxidation was observed in smaller magnesium particles in all the experiments, while the in-situ sintering of magnesium rods was observed at a molar ratio of MgO:CH4=1:1.5. Magnesium carbide (Mg2C3) was observed in the product, and its mechanism of formation is proposed using phase equilibrium data and a predominance diagram.

Energy-Efficient and Environmentally Friendly Solid Oxide Membrane Electrolysis Process for Magnesium Oxide Reduction: Experiment and Modeling

This paper reports a solid oxide membrane (SOM) electrolysis experiment using an LSM(La0.8Sr0.2MnO3-δ)-Inconel inert anode current collector for production of magnesium and oxygen directly from magnesium oxide at 1423 K (1150 °C). The electrochemical performance of the SOM cell was evaluated by means of various electrochemical techniques including electrochemical impedance spectroscopy, potentiodynamic scan, and electrolysis. Electronic transference numbers of the flux were measured to assess the magnesium dissolution in the flux during SOM electrolysis. The effects of magnesium solubility in the flux on the current efficiency and the SOM stability during electrolysis are discussed. An inverse correlation between the electronic transference number of the flux and the current efficiency of the SOM electrolysis was observed. Based on the experimental results, a new equivalent circuit of the SOM electrolysis process is presented. A general electrochemical polarization model of SOM process for magnesium and oxygen gas production is developed, and the maximum allowable applied potential to avoid zirconia dissociation is calculated as well. The modeling results suggest that a high electronic resistance of the flux and a relatively low electronic resistance of SOM are required to achieve membrane stability, high current efficiency, and high production rates of magnesium and oxygen.

Generation of magnesium for in situ desulphurisation–investigations on influence of inert gas flowrate

In situ generation of magnesium by the reduction of its oxide is being considered by researchers as a possible means of effective desulphurisation of liquid iron. Generation of magnesium in this process will be affected by the flow rate of inert gas. The influence of the flow rate of inert gas on the degree of reduction of magnesium oxide by aluminium was studied. The liberation of magnesium increases with increase in flowrate of inert gas. A mathematical model was developed to predict the influence of argon flow rate on the degree of reduction. The reduction was significantly influenced by temperature. Whereas the degree of reduction was about 30% at 1473 K, it was about 85% at 1673 K. SEM studies showed that the reduction of the oxide with aluminium was a complex process. A part of magnesium vapour generated during reduction was trapped inside the (oxide+aluminium) tablets. Temperature, flowrate of argon, and the porosity of the tablets were parameters that critically influenced the degree of reduction.

Production of magnesium during carbothermal reduction of magnesium oxide by differential condensation of magnesium and alkali vapours

Most of researchers believed that the developments on the condensation of magnesium produced by carbothermic reduction just concentrated on two process routes: the “quench” route and the “solvent” route. But this paper will briefly analyzes the major challenges in magnesium vapor condensation during the vacuum carbothermic reduction of calcined dolomite, on equipment upgrade, heat transfers alter, to achieve condensation control and production collection. Solutions are then proposed using theoretical calculations and experiment results. Comparative analysis of the experiment results shows that the burning and even explosion of condensation products during the vacuum carbothermic reduction of calcined dolomite are mainly due to the burning of crystallized powder magnesium, which results from the self-ignition of alkali metals. Finally, this paper proposes a multistage condensation solution to improve traditional vacuum condensation equipment. And result show that the condensation equipment can effectively mitigate the burning and loss during condensation, also the morphology of the condensation products clearly improved, the grain size increased, and the oxidation rate decreased. The potassium/sodium vapor and the magnesium vapor were separately condensed.

Experimental Study on Carbothermic Reduction of Magnesia with Different Carbon Materials

The structure and composition of carbon materials affect obviously the result of carbothermic reduction of magnesia. Coke, charcoal and graphite were used in reduction experiments under the same conditions. The reactivity ratio of magnesia and XRD pattern of residues were analyzed and compared. The reactivity ratio of magnesia by coke was similar to the one by charcoal. The amorphous carbon in coke graphitized partly in reduction experiments of 1673K. The results show that the effective composition in coke is the amorphous carbon. It also suggests that the temperature of reaction should be control less than 1700K to avoid the amorphous carbon’s graphitization.

Effects of Reaction Temperature and Time on the Aluminothermic Reduction of Magnesia

The present paper focuses on the experimental investigation of the aluminothermic reduction of magnesia under vacuum condition with the fixed magnesia to aluminum molar ratio of 11:6. The influences of reaction temperature and time on the reduction ratio of magnesia were studied. The chemical composition, phase constitution and morphology of the condensed magnesium and the briquettes after thermal reduction were investigated by X-ray diffraction, scanning electron microscopy equipped with energy dispersive spectrometry. The reduction ratio of magnesia increases with the increase in the reaction temperature and time. The briquettes after thermal reduction at 1050°C-1150°C are mainly composed of the spinel, unreacted magnesia and aluminum. The briquette after 1 hrs thermal reduction at 1200°C contains corundum, magnesium aluminium oxide, trace amount of spinel, unreacted MgO and aluminium.

Laser Induced Magnesium Oxide Reduction for Renewable Energy Cycle with Solar Power

We succeeded in producing Mg from MgO without reducing agent using high power cw laser. Mg in turn can react with water to produce hydrogen, heat and MgO, thus natural resources like solar power can be stored as chemical energy. In this study, a focused CO2 laser irradiated MgO target in vacuum, high temperature is exerted in tiny spot thus Mg production in equilibrium is achievable. The resultant Mg vapor is deposited on Cu plate and analyzed by EPMA (electron probe micro analysis); the results showed points of more than 30% mol fraction of Mg deposited, with an average of 8 mol%. So far bulk analysis results showed that 6 mol% of Mg is obtained as solid deposit, which can be translated to energy conversion efficiency of 0.35 mg/kJ. These experiments showed that our scheme can be used for magnesium production with higher efficiency and large throughput.