As Sweden transitions to hydrogen-based steel production, excess O2 generated as a byproduct of H2 production through water electrolysis is likely to be available. This presents an opportunity to use extra O2 for reducing fuel consumption during production of iron ore pellets. Considerable heat is released as magnetite is oxidised to hematite during induration. Increased O2 content in the process gas is expected to accelerate the exothermic oxidation reaction, allowing faster intrinsic heating of the bed. This study examines various energy scenarios utilising O2-enriched gas (40 vol% O2) relative to a base case that uses low-O2 gas (13 vol% O2). The focus is the effects of the flow rates and O2 contents in the inflow gas on the temperature development and physicochemical properties (oxidation degree and cold compression strength) of pellets across a 100-kg pot furnace bed. Enriching the inflow gas with O2 has advantages with regard to the aforementioned properties. Notably, utilising O2-enriched gas at a reduced flow rate (in this case, 30% less gas volume compared with the base case) enables improved heat distribution relative to the base case with low-O2 gas. In addition to the effects on the energy and pellet properties, the microstructures are analysed with respect to the underlying oxidation mechanisms.

As the markets for electric vehicles and portable electronics continue to grow, global demand for cathode active materials is increasing significantly. This study investigates the effect of thermal pre-treatment on the black mass from spent Lithium-ion batteries (LIBs) and its impact on the leaching efficiency of cathode active materials. Thermal pre-treatment of black mass samples was carried out using a pit furnace and microwave heating at temperatures ranging from 400 °C to 1200 °C. The thermally treated samples were then leached using both water-based and acid-based solutions to extract the valuable metals. The results indicate that thermal pre-treatment of black mass using both microwave and conventional heating methods improves the leaching of Ni, Co, and copper (Cu). At pre-treatment temperatures exceeding 600 °C, Ni retention in the residues increases for both sulfuric acid and carbonated water leaching processes. X-ray diffraction (XRD) analysis of the leaching residues also revealed the presence of LiF, suggesting that incomplete Li extraction resulted from the formation of insoluble compounds. Thermal pre-treatment in a pit furnace at temperatures above 800 °C promoted selective recovery of Li and Mn, yielding 96.8% Mn at 800 °C. These findings indicate that thermal pre-treatment has a significant impact on the selective recovery of cathode active materials from spent LiBs, therefore, careful optimisation of thermal conditions can enhance the targeted extraction of valuable metals and promote the sustainability of recycling processes for spent LiBs.

The increasing use of lithium-ion batteries (LiBs) in electric vehicles and electronics has made efficient recycling essential for maintaining a reliable and affordable supply of critical metals. Thermal treatment of black mass (BM), the heterogeneous residue from spent LiBs, is a crucial step to improve downstream material separation and recovery. This study investigates the thermal behavior of LiBs BM by analyzing the thermal behavior of its components when heated to 600 °C in an inert (N2) atmosphere or in a mixture of 90 vol % N2 and 10 vol % H2. Thermogravimetric analysis (TGA) was conducted at a heating rate of 10 °C/min with an isothermal hold of 1 h, and coupled with quadrupole mass spectrometry (QMS). The analysis was performed on graphite, activated carbon, lithium hexafluorophosphate (LiPF6), polyvinylidene fluoride (PVDF), synthetic black mass, and lithium nickel manganese cobalt oxide (NMC) industrial BM. Equilibrium calculations conducted in FactSage 8.3 were used to describe and understand the experimental findings. The TGA results indicate that in 100 vol % N2, graphite exhibited the lowest weight loss of 0.1 wt %, followed by activated carbon at 2.9 wt %, PVDF at 56 wt %, and LiPF6 at 81 wt %. Synthetic black mass had a weight loss of 3.4 wt %, while industrial black mass had 1.0 wt %. In 90 vol % N2/10 vol % H2, LiPF6 and PVDF experienced weight losses of 79 and 64 wt %, respectively. Synthetic BM had a weight loss of 15.1 wt %, and industrial BM 15.6 wt % due to enhanced reduction of metal oxides in the presence of hydrogen. 

The amount of waste Li-Ion Batteries (LIBs) is significantly growing. Therefore, scholars and industries are exploring efficient ways to recover their valuable elements. Meanwhile, steel production generates Fe-rich slag, which is often sold for construction purposes without fully utilizing its potential metal content. Reusing this slag in LIB recycling allows simultaneous recovery of valuable elements from both waste LIBs and steel slag. This study investigates the pyrometallurgical recycling of Black Mass (BM) from a mixture of spent LIBs in the presence of Fe-rich slag (set based on Electric Arc Furnace (EAF) slag), with a focus on the evaporation of Li and F, the critical volatile elements in the BM, at 1500 °C. The effects of basicity (B2), MgO content, and flux amount on Li and F evaporation were studied using a central composite experimental design, showing that while the effects of MgO content and flux amount were insignificant, B2 had a linear effect on Li and a quadratic effect on F evaporation. Thermodynamic and viscosity calculations suggest that higher B2 improves ion mobility, facilitating the evaporation mechanism. However, for F, its dual role at different B2 levels leads to an evaporation trend different from that of Li. Keeping B2 within a midrange seems to balance Li evaporation efficiency while limiting F evaporation.

Magnetite concentrates, essential for pellet production, often contain a high proportion of fine particles. These fine particles significantly influence the induration process. Understanding their oxidation behavior is crucial for optimizing pellet quality. Previous research primarily focused on magnetite particles larger than 25 µm. This study extends the investigation to finer size fractions below 7 µm. Isothermal oxidations were conducted on three different size fractions from two different mines, using a thermogravimetric analyzer (TGA) at 973 K and 1073 K, followed by light optical microscopy to observe the structural evolution of hematite. The oxidation of magnetite exhibits a two-step phenomenon: an initial stage characterized by a high oxidation rate, followed by a second stage where the oxidation degree increases at a constant rate. The oxidation behavior of both studied concentrates follows a consistent pattern: finer particles exhibit faster oxidation than coarser particles, resulting in a higher oxidation degree in a specific duration. Particles in the finer size range (< 7 µm) undergo complete oxidation during the initial stage. A predictive model based on the Avrami kinetic equation was developed to assess the effect of particle size on magnetite oxidation. The model demonstrated a high validation (98 pct), indicating that particle size is a reliable predictor of magnetite oxidation behavior. 

The increased use of lithium-ion batteries (LiBs) in electric vehicles (EVs) and other applications due to global efforts to reduce carbon emissions has led to an increase in end-of-life battery production. This has created a demand for efficient recycling methods to control waste and conserve resources. This study investigated the effect of thermal pre-treatment of spent LiBs materials on the liberation of anodic and cathodic materials from the aluminium and copper current collectors and the subsequent graphite recovery by flotation. The samples were pre-treated using a rotating kiln and microwave furnace at temperatures of 200 °C, 400 °C, and 600 °C, with an additional sample containing 10 wt% CaO treated at 400 °C. The results indicated that higher temperatures resulted in the breakdown of the binder, leading to graphite liberation. Specifically, at 600 °C, the anode and cathode materials exhibited significant separation from the Cu and Al current collectors with an almost similar liberation efficiency for both pre-treatment methods. Furthermore, adding 10 wt% CaO to the samples treated at 400 °C significantly lowered the flotation of the cathode materials and improved the flotation selectivity of graphite. The findings indicate that combined thermal pre-treatment with flotation can improve the recycling process, providing a more scalable and environmentally friendly approach to managing the increasing volume of spent LiBs.

This study investigates and presents the analysis of magnetite pellets subjected to hydrogen reduction for potential application in green steel making. Hydrogen-based reduction processes have gained prominence due to their potential as a clean and energy-efficient method for reducing iron ore concentrates. Thermo-gravimetric (TG) experiments were performed at low (580 °C) and high (950 °C) temperatures in a hydrogen atmosphere to assess the reduction behavior of magnetite pellets. The samples were characterized using X-ray Fluorescence (XRF), X-ray Diffraction (XRD), and Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS) techniques for qualitative and quantitative analysis. TG analysis reveals that higher reduction temperatures (950 °C) accelerate the reduction rate but introduce complexity through intermediate wustite (FeO) formation, leading to a lower final reduction degree as compared to the simpler reduction at 580 °C. Detailed examination using SEM-EDS shows that reduction at 950 °C results in complete reduction of the outer shell of magnetite particles forming a dense layer and partially unreduced FeO in its core with the presence of magnesium oxide (MgO). At 580 °C, magnetite particles are fully reduced to iron, displaying both porous and dense morphologies. The presence of MgO is found to influence the morphology by promoting denser iron formations. These findings highlight the significant impact of temperature and impurities on the reduction process and microstructural outcomes, providing valuable insights for optimizing hydrogen reduction processes.

The steel industry’s transition to hydrogen-based ironmaking necessitates a deeper understanding of magnetite ore reduction, a crucial yet underexplored pathway for decarbonization. This study systematically investigates the combined effects of particle size and gangue composition on hydrogen-based reduction behavior of four industrial magnetite ore concentrates with varying CaO and MgO contents. Thermogravimetric analysis at 973 K, interrupted reduction experiments, and post-reduction characterization steps are used to evaluate reduction extent and phase transformations across different particle size fractions and bulk ores. The finer fractions generally exhibit faster and more complete reduction. However, this trend is overridden by gangue effects in certain ores. Magnetite ores with MgO as gangue tend to form magnesio-wustite solid solution (Mg,Fe)O during reduction, resulting in dense microstructures that impede hydrogen diffusion and limit reduction progress. In contrast, magnetite ores with CaO as gangue facilitate the formation of intermediate calcium ferrites, which promote porous morphology and enhanced reducibility. Notably, even the finer particles of ore containing MgO show a lower reduction degree than the coarser particles of the ore containing CaO as gangue. This highlights the dominant role of gangue composition in governing reduction kinetics, intermediate phase formation and final product morphology. These findings contribute to the growing knowledge necessary to enable fossil-free ironmaking by emphasizing the importance of considering both granulometric characteristics and heterogeneity when evaluating magnetite ores for hydrogen-based reduction.

Blast furnace (BF) ironmaking remains one of the most efficient countercurrent processes; however, achieving further CO2 emission reductions through conventional methods is increasingly challenging. Currently, BF ironmaking emits approximately 2.33 tonnes of fossil-derived CO2 per tonne of crude steel cast. Integrating briquettes composed of biochar and in-plant fines into the BF process offers a promising short- to medium-term strategy for lowering emissions. This approach enables efficient recycling of fine residues and the substitution of fossil reductants with bio-based alternatives, thereby improving productivity while reducing energy and carbon intensity. This study investigates the reduction behavior of (i) biochar mixed with pellet fines, (ii) various in-plant residues individually, and (iii) briquettes composed of biochar and in-plant fines. The reduction rate of biochar–pellet fine mixtures was found to depend on biochar type, with pyrolyzed pine sawdust exhibiting the highest reactivity, and pyrolyzed contorta wood chips the lowest. A correlation between reduction rate and the alkali index of each char was established, although other factors such as char origin and physical properties also influenced reactivity. The effect of biochar addition (0, 5, and 10 wt.%) on the reduction of steelmaking residues was also studied. In general, biochar enhanced the reduction degree and shifted the reaction onset to lower temperatures. The produced briquettes maintained high mechanical integrity during and after reduction, regardless of biochar origin. Thermogravimetric and XRD analyses revealed that mass loss initiates with the dehydroxylation of cement phases and release of volatiles, followed by carbonate decomposition and reduction of higher oxides above 500 °C. At temperatures ≥ 850 °C, the remaining iron oxides were further reduced to metallic iron.

Purely solid–solid reactions are encountered during materials processing, e.g., reactive sintering of ceramics, cement production, mechanical alloying, and electronic device fabrication. Driven mainly by Gibbs energy of the reaction, the kinetics of the reactions are broadly controlled by two factors, the rate of diffusion and that of reactions at the interfaces. The reaction mechanism involves the transport of reactants through the product layer, as in the case of a core–shell morphology. Nucleation of the reaction product plays an important role in solid–solid reaction kinetics. In Part 1, the theoretical considerations for these reactions are presented, along with examples from the synthesis of oxide ceramic, silicides, and borides. The mechanism of solid–solid reactions in mechanical alloying and mechanochemical synthesis has been elucidated.

Part 2 deals with the experimental methods for investigating solid–solid reactions. The classical diffusion couple experiments are discussed in detail along with the mathematical analyses of the results. A new method for measuring interdiffusivities in the case of oxide systems by the solid-state galvanic cell method is presented. A novel application of high-temperature X-ray diffraction method for interdiffusion studies of oxide systems by following the characteristic peaks of the products formed is also described in this part.

Part 3 presents a case study of the oxidation of magnetite particles to hematite.