Previous studies have demonstrated that pre-reductionReduction of manganese ores using CO-rich off-gas can significantly reduce both energy use and carbon consumption. While this processProcess increases the CO2 concentration in the off-gas, substantial amounts of CO typically remain, necessitating further gas conditioning prior to CO2 capture and storage. This work investigates advanced pre-reductionReduction concepts designed to maximize the conversion of CO to CO2 directly within the processProcess, thereby minimizing downstream gas treatment requirements and maximizing energy and carbon savings. The analysis has been carried out using idealised simulationsSimulation in HSC Sim. The results indicate that avoiding CO combustion can potentially reduce the energy required for CO2 capture. In particular, CLCChemical Looping Combustion (CLC)-based cases show potential for delivering nearly pure CO2 streams while generating surplus heat that could offset pre-reductionReduction energy demands.

The aluminiumAluminium casthouseCasthouse is responsible for substantial amounts of CO2 emissionsEmissions. Substituting low-emissionsEmissions hydrogenHydrogen for fossil fuels such as LNG and LPG would significantly reduce the climate impact of aluminiumAluminium castingCasting. Such a fuel-switch would also change the combustion products, eliminating CO2 and increasing the amount of H2O, potentially up to 100

Hydrogen (H2) plays an important role in meeting the demand for carbon-free steels. When reduction is done with H2, harmless water is released as the off-gas, instead of CO2 generated by reduction with carbon. While steel can be produced using H2, many of its alloying elements cannot. As a result, fully carbon-free steel production necessitates a carbon-free production of its alloying elements. An important alloying element for steel, manganese (Mn), is subject to thermodynamic limitations that makes reduction with H2 infeasible. If instead a much more reactive hydrogen plasma is used these thermodynamic limitations would disappear. The current work shows an in-depth investigation into the reduction of manganese oxide (MnO) by a thermal hydrogen plasma under various conditions. By passing H2 through a plasma torch before it contacts an MnO-containing slag, formation of metallic Mn was achieved with a hydrogen-based reductant. Investigating the reduced samples with an electron probe micro analyser (EPMA) the amount of Mn formation in different conditions is mapped out. The reduction was found to be favoured when the torch was operated with a transferred arc mode, and for slags high in MnO, if the melting point was not too high. While the research into reduction of stable oxides with thermal hydrogen plasmas is still in an early stage and there are many unanswered questions, the work presented demonstrates the possibility of hydrogen-based manganese production.

The growing awareness of the climate crisis has increased the political and industrial interest in the topic of how industrial off-gases like carbon dioxideCarbon dioxide and carbon monoxide may be put to use, also known as carbon capture and utilisation (CCUCCU). It is a rapidly changing topic as increasing efforts are made towards research, development, innovation, and implementation of various technological options. This article takes a look at some of the possible ways the CO rich off-gas from sealed submerged arc furnaces producing Mn ferroalloysFerroalloys may be used, with special attention on the options which goes beyond simply burning the gas as fuel or energyEnergy recovery. The discussion covers the potentials, challenges, uncertainties, and technological maturity of different alternatives. It is clear from the current report that it is possible to use CO gas for many things, including some exciting new and immature opportunities. Gas composition (purity) is an important issue for several applications. For many options, it may also be necessary to address the challenges connected to variations in gas pressure, availability/volumetric flow, and composition.

To reach agreed-on climate goals, it is necessary to develop new energy carriers and industrial materials that are carbon-neutral. To combat global warming and keep Earth’s temperature from increasing by 1.5 °C, some of these solutions need to be carbon-negative. This study fulfills this criterion by producing clean hydrogen and biocarbon suitable for the metallurgic industry through the thermal decomposition of methane using biocarbon as a catalyst. Five different biomass samples were used to prepare biocarbons at a pyrolysis temperature of 1000 °C with a holding time of 90 min. When methane was cracked at 1100 °C with a holding time of 90 min, the highest hydrogen production was 105 mol/kg biocarbon, achieved using birch bark. The lowest hydrogen yield, of 68 mol/kg biocarbon, was achieved with steam-explosion pellets. All the biocarbons showed substantial carbon deposition from cracked methane on their surfaces, with the highest deposition on birch bark and spruce wood biocarbons of 42% relative to the biocarbon start weight. The carbon deposition increased with the decomposition temperature, the methane share in the purge gas and the holding time. The steam-explosion pellets, after deactivation, had a CO2 reactivity that was comparable to coke, a reducing agent that is commonly used in manganese-producing industries. About 90% of the potassium and sodium were removed from the biocarbon during catalytic decomposition of methane performed at 1100 °C. The alkali removal was calculated relative to the biocarbon produced under the same conditions, but with 100% N2 purge instead of CH4. After catalytic decomposition, the surface area of the biocarbon was reduced by 11–34%, depending on the biocarbon type.

In the future, biocarbon use and carbon capture is expected to be more common in the ferroalloysFerroalloys industry. This creates possibilities for utilisation of waste heat through industrial symbiosis with industries that require lower quality energyEnergy. This paper presents an overview of some of the concepts that present potential energyEnergy savings in the ferroalloysFerroalloys industry, and the potential for heat and material integration between ferroalloysFerroalloys production and biorefinery applications. A conceptual flowsheet model has been developed and used to evaluate the combined effects of different unit operations on the overall energyEnergy consumption of the integrated plant. Evaluation of these concepts: considering bio-char production and carbon capture as integral parts of metal productionMetal production, potential energyEnergy savings of 38–40

HydrogenHydrogen is a candidate to replace carbonCarbon in metal production, as it can reduce some metal ores (e.g., iron ore). However, for other oxides, such as those of manganeseManganese and chromiumChromium, the situation is much more challenging. As the exotic species found in hydrogenHydrogen plasmaPlasma are much more reactive than molecular hydrogenHydrogen, the use of hydrogenHydrogen plasmaPlasma can improve hydrogenHydrogen reduction for all these oxides. Here, using a plasmaPlasma arc melter, samples of Fe2O3, Cr2O3 and MnO have been exposed to hydrogenHydrogen plasmaPlasma. Reactions between oxides and hydrogenHydrogen have been observed in all cases, producing metallic iron, chromiumChromium, and manganeseManganese, hinting that plasmaPlasma technology can play a part in sustainable metal production, allowing for carbonCarbon free production of chromiumChromium and manganeseManganese. The paper also discusses possible reaction mechanisms.

Hydrogen is increasingly being recognized as a crucial element in reducing carbon emissions in the metallurgical industry. Its use in the steel sector is gaining momentum through various initiatives at high TRL levels. Moreover, hydrogen shows promise in other metal production processes as well. One application involves utilizing hydrogen for effective selective reduction copper from copper slags with a low amount of iron being reduced. Hydrogen can also be employed in the pre-reduction of manganese ore, leading to the carbon-free production of manganese metal through aluminothermic reactions. Additionally, hydrogen can be used in the processing of bauxite residue, where iron is partially or completely reduced to separate an iron-rich fraction, allowing for alumina recovery via leaching.

Hydrogen (H2) gas has been proposed as an attractive candidate to replace carbon in metal production. Oxide reduction with H2 releases water (H2O) as the off-gas rather than carbon dioxide (CO2). This has been shown to be feasible, for e.g., iron oxides and some manganeseManganese oxides. However, common, more stable oxides, such as manganeseManganese monoxide (MnO), are subject to thermodynamic limitations, which prohibit reduction with H2. Utilizing monoatomic or ionized hydrogen (H or H+), abundant in hydrogen plasma, makes the hydrogen-oxide reactions more favorable and allows reactions such as: 2H+MnO→H_2O+Mn H^++MnO→OH+Mn^+ The current work demonstrates experimentally the production of metallic manganeseManganese by exposing sintered MnO to hydrogen plasma. The hydrogen plasma was generated by passing H2 through a plasma torch. This paper will present the experimental setup and method, as well as characterization of the reaction products. Hypotheses for the reaction paths are presented and discussed in the context of thermodynamics and solidification theory. Furthermore, computational fluid dynamics is used to support the discussions via mathematical modeling of temperature- and flow fields. Although substantial research is still needed, the presented results demonstrate that hydrogen plasma allows for reduction of more stable oxides than is possible with H2, and that hydrogen plasma-based technologies can be used for manganeseManganese production.

Molten Oxide Electrolysis (MOEMolten oxide electrolysis (MOE)) is a new CO2-free technology that could alleviate the environmental impactEnvironmental Effects of ferroalloyFerroalloys production. In this work the objectives were to perform (i) experimental lab scale studies of MOEMolten oxide electrolysis (MOE) for Mn from MnO using synthetic raw materials and a commercial Ni–Cr–Fe alloy as oxygen-evolving anode, and (ii) theoretical mass and energy balances for different cases of Mn ore purification for a hypothetical industrial MOEMolten oxide electrolysis (MOE) FeMn process. Low carbonCarbon Mn metal was recovered at lab scale, and the feasibility of MOEMolten oxide electrolysis (MOE) manganeseManganese production proven. While the Ni–Fe–Cr anode performed satisfactory during the electrolysis, some dissolution of Ni, Fe and Cr was detected. Theoretical energy and mass balance calculations gave a total energy consumption of 6.5–7.6 MWh/tonne Mn depending on the purification scenario. The results showed that the purified ore greatly improves the process. Non-purified ore requires large amounts of flux and more hydrogenHydrogen in the pre-reduction step, both aspects increasing the need for energy. Non-purified ore also generates large amounts of spent electrolyte. Despite the above, it is an open question whether the benefits of purifications would outweigh the costs.

Vachaparambil, Kurian J.Einarsrud, Kristian EtienneDalaker, HalvorAndersson, StefanIn this work an OpenFOAMOpenFOAM-based framework to simulate the evolution of microsilicaMicrosilica, which is an important byproduct in the silicon/ferrosilicon industries, is proposed. The framework decouples the combustion reaction of CO and SiO from the microsilica generation based on the assumption that the combustion occurs in an oxygen rich environment - SiO $$_{2}$$ generated by combustion is much larger than its depletion due to particle evolution. The combustion of the reactants in the furnace hood is performed using rhoReactingBuoyantFoam, and its results are used as input to a population balance solver that simulates the particle nucleation and growth (due to mass transfer onto the particle surface) as well as depletion of SiO $$_{2}$$ . The framework predicts particles of size around 30 nm at the outlet which is approximately in the smaller sizes of the particles observed in microsilicaMicrosilica during experiments reported in literature.

Carbon has been deposited on HCFeMn slag from methane-containing gas with and without CO2, creating C-MnO composites and giving a hydrogen-rich off-gas as a by-product. The maximum deposited amount corresponds to 38 ± 6% of the carbon required for reduction of all manganese in the slag to metallic Mn. This was achieved at 1100 °C with a H2-concentration in the off gas of 76%. Temperature was an important parameter. At 790 °C, no deposited carbon was detected, at temperatures ≥ 1000 °C, deposition increased with temperature. A lower gas-flow leads to more methane decomposition. Experiments with CO2 in the process gas gave less deposited carbon than other experiments. This could be caused by dilution of methane or chemical reactions involving CO2, or a combination. Investigations of fines formation indicate that the deposited carbon sticks well to the HCFeMn-slag, and would not fall off easily during transport and handling. This demonstrates that biogas can potentially be a non-fossil source of carbon in manganese production.

Plasma species such as monoatomic hydrogen are much more reactive than diatomic hydrogen gas, H2(g). This means that plasma technology can be a way of introducing hydrogen as a reducing agent for producing metals and alloys, like manganese, where oxide reduction to the metallic state by hydrogen gas is not possible. While still an immature technology, it is nevertheless important to address questions regarding economic relevance. In this work, best estimates are used to describe a hypothetical plasma-based process and plant for manganese production. This description then makes the foundation for a techno-economic analysis comparing this hypothetical process with existing standards. It is found that at present, it seems plausible that hydrogen plasma technology can compete economically, and thus be a viable way to decarbonise manganese production. The most sensitive parameters appear to be hydrogen price, cost of CO2-emissions, and to what extent excess energy from the plasma unit can be captured and used for pre-heating of the ore.

There are several technologies that could help cut greenhouse gas emissions from silicon production, for example increasing the share of biocarbon in the reductant mix. Complete decarbonisation however requires the use of other reducing agents, such as hydrogen, electrolysis or metallothermic reduction. The current article gives an overview of the alternatives to carbothermic reduction; that is to say, the solutions which could remove the need for carbon entirely. The discussion focuses on the possibilities, challenges, and the current technological barriers for these technologies to be applied to produce silicon and silicon alloys. The introduction of new reduction practices would require substantial changes in framework conditions in order to become economically feasible. Most of the alternative processes are more energy demanding than the current carbothermal route so availability of cheap and clean, renewable energy in abundance is an absolute prerequisite for all the new technologies discussed herein

Substituting carbon with hydrogen is one of the few ways metal production can potentially become free of CO2 emissions. Moreover, the metallurgical industry produces significant amounts of waste. The present work presents a circular concept that will be pursued in the HARARE project, based on increasing waste recovery by the use of hydrogen. The project will tackle two example cases: bauxite residue and copper smelter slags. The common theme is to use hydrogen to selectively reduce iron and copper, making it possible to extract these metals. Through a series of pyro and hydrometallurgical steps, as well as mechanical separation, it is also possible to recover secondary valuables like alumina, molybdenum, cobalt, nickel, zinc, and scandium. The final remaining residues can be valorised as building materials for a truly zero-waste concept. In this paper, the different process streams for the two example cases are laid out, including the valorisation of secondary material streams.

The production of silicon with hydrogen is very challenging, although it is possible to get partway there, as SiO gas can form from SiO2 and H-2. For some applications, metallurgical grade silicon is only an intermediary to gas-phase silicon species and "not needed" from a value-chain point of view. This work explores the possibility of going directly from SiO gas to useful Si-based gases with gas-phase chemistry. In particular, it looks into reactions between SiO gas and Cl-2 gas to form SiCl4, which can be turned into raw materials for polysilicon production in the Siemens process. If successfully implemented, this would make CO2-free polysilicon production possible. The work is theoretical in nature and is based on thermodynamical calculations using FactSage. Assessing the process steps in isolation, calculations show that both SiO formation from H-2 and SiO2 and the formation of SiCl4 from SiO are thermodynamically favourable. Combining the two steps in a process is likely to be challenging however, since if H-2/H(2)O( )from the first step is present during the second, this will interfere with the chlorination of SiO, representing a serious bottleneck. Unless SiO can somehow be separated from H-2/H2O at very high temperatures, success seems to be dependent on rapid quenching while suppressing back-reactions.

The iron oxide (typically 20–50%) contained in bauxite residue (BR) can be recovered as pig iron. But this is not economically viable due to the low market price of pig iron. Silicon rich iron alloys have higher value than pig iron, and BR typically contains 5–15% silicon oxide. To increase the value of the produced metal, it is attempted to maximise the silicon content of iron alloys produced from BR. This option has been explored with experiments and thermodynamic models (FactSage) focusing on BR from one legacy site and three alumina refineries, obtaining a maximum of 17 wt.% Si in experimentally produced alloys. The paper discusses the thermodynamics around the results and looks at the influence of slag viscosity.

To secure a future with the development of solar and wind energy, weather-safe roads and cities around the world, we must be able to produce metals in a safe, climate-neutral and responsible way. Obviously, we must prolong the lifespan of our materials, increase the efficiency of current processes, reuse and recycle what is already available, but that may not be enough. If we are to reach the global development goals, the world will most likely need new materials, including metals. There are many possible technologies that can help cut greenhouse gas emissions from the metallurgical industry, such as biocarbon and hydrogen as reducing agents but also electrolytic and metallothermic reduction routes and combinations of these solutions. Within each of these different themes, there are many technological possibilities. The current article gives an overview of the different alternatives to carbothermic reduction, i.e., describes the solutions which could potentially remove the need for carbon entirely. The discussion focuses on the possibilities, challenges, and the current technological barriers for these technologies to be applied to ferroalloy production.

Succeeding with ultrathin silicon wafer sawing by diamond multi-wire saw, is not only a matter of optimization; the challenges of thin wafer production and the capability limit have not yet been fully understood. In this work, we have seen that regular pairing of wires occurs when the wire-wire separation distance is reduced below some critical value. The wire pairing leads to wire jumps on the wire guide rolls, and if the run is not stopped, it leads to wire breakage. Moreover, it effectively obstructs the production of wafers thinner than the critical wire-wire distance.We suggest that the physical explanation to the observed limitations to ultrathin wafer sawing, by diamond multi-wire saw, is related to the capillary force acting on the wires due to the sawing liquid bridge connecting the wires. The hypothesis is supported by simplified mathematical modelling including capillary and spring forces between infinitely long, parallel wires. The calculations suggest that capillary forces are the main reason for wire pairing, and that wire pairing will occur when the wire distance is below some critical distance. This matches the observed, experimental behavior. The critical distance will vary with wafer saw design and operation.To succeed with cutting very thin wafers, we recommend using lower surface tension sawing fluid or even dry in-cut, to reduce the capillary forces and thus decrease the critical wire separation distance, and to reduce wire oscillations to decrease the probability of sub-critical wire-wire separation distance. To reduce the vibration amplitude, shorter distance between the wire guide rolls, thinner wires, and increased wire tension are suggested.

Multicrystalline silicon displays a considerable smaller average grain size and reduced dislocation generation when being seeded by polycrystalline silicon chips or fluidized bed reactor silicon granules. A simple texture analysis shows how the initially random grain structure of the seeds develops a weak preference for near-〈111〉 and near-〈112〉 oriented grains upwards in the ingot. Closer investigations reveal a considerable coarsening of the initial microstructure of the seeds during the directional solidification process, especially for small fluidized bed reactor granules. The irregular shape of polysilicon chips allows for melt penetration into the seeding structure and potential indentation effects that may account for the increased dislocation generation observed in this case. The increased generation may, however, also be related to a higher ratio of ∑27 grain boundaries.