In recent years, technical processes for the sequestration of CO₂ through industrial waste mineral carbonation have been explored and developed. There is a large portfolio of carbon capture, utilisation, and storage (CCUS) techniques that have been employed in laboratories and at pilot scale. These include geological storage, ocean storage, and mineralisation by carbonate ores. In view of this, the main purpose of this research was to investigate and explore chemical variables, particularly ammonium salts as lixiviants for calcium mineral extraction from iron-making slag. The slag in use was acquired from a steel mill in the Vaal Triangle Region in Gauteng, South Africa. The experimental test work was conducted using different ammonium lixiviants, namely, NH₄NO₃, NH₄Cl, and CH₃COONH₄, to understand the influence of anion type as well as possible differences in mechanisms of interactions. Lixiviant concentration as well as reaction time were varied in this research study. The three selected ammonium-based lixiviants showed different extents of calcium extraction owing to differences in the anion groups. NH₄NO₃, NH₄Cl, and CH₃COONH₄ were found to be capable of dissolving 50% to 80% of the calcium from the selected slag for different molar concentrations. Anion type and leaching time also had significant influences on the leaching of calcium from the slag. Rapid pH degradation resulted in better calcium extraction capabilities. This work has shown that the selected ammonium salts have the potential to be lixiviants for calcium dissolution from iron-making blast furnace slags. These lixiviants would, therefore, be important to consider during calcium mineral carbonation for CO₂ sequestration.

This study aims to evaluate the grindability and energy requirements for the liberation of quartz from blast furnace ironmaking slag. Furthermore, the study investigates the efficiency of gravity concentration method by using a shaking table and Falcon concentrator for the separation of quartz from the slag. The grindability of the slag was evaluated using the Bond’s Work Index (BWI) method. The energy required for the liberation of quartz was determined using a Modified Bond’s Work Index (MBWI) method. The results showed that the BWI of the slag was 13.5 kWh/t and the MBWI of the quartz was 22.3 kWh/t. Gravity separation tests were carried out using a shaking table and a Falcon concentrator. The results showed that the shaking table was able to recover 91.2% of the quartz with a grade of 99.5% SiO₂. The Falcon concentrator was able to recover 98.3% of the quartz with a grade of 99.7% SiO₂. In contrast, the study found that the quartz in blast furnace ironmaking slag can be physically separated using gravity separation techniques such as shaking table and Falcon concentrator. The study also provides valuable information on the grindability and energy requirements for the liberation of quartz from the slag, which can be used in the development of more efficient separation processes.

The steel sector is one of the main contributors to carbon dioxide emissions among the industrial activities. It is mostly the use of carbon-rich blast furnaces and natural gas direct reduction processes that cause this. Hydrogen-based direct iron reduction (H-DRI) is a demonstrated method of lowering steel production carbon emissions by using hydrogen rather than carbon monoxide as the reducing agent; therefore, water vapor is released instead of carbon dioxide. This work offers a detailed analysis of the trends, operating concepts, industrial-scale trials, difficulties, and advantages of H-DRI. It is well supported by both energetic and reaction rate considerations that hydrogen is an efficient agent for the reduction of iron oxides to iron metal, giving metallization rates up to those of the traditional processes and at the same time significantly reducing GHG emissions. Moreover, industrial trials confirm that the method is technically feasible on a large scale, which is not yet realized because green hydrogen is very expensive, infrastructure needs are high, and there are still hurdles to be overcome in process optimization, such as water vapor management, pellet quality, and reactor design. According to the studies of product life cycles, if the hydrogen is extracted from renewable sources of energy, then the reduction in CO can be as high as 90%. The article also discusses different aspects of the economy, environment, and law that are already there and the ones that need to be developed so that research, technological breakthroughs, and industrial harmonization can be directed to the right spots. Practical deployment requires control of hydrogen supply, optimizing reduction processes, integrating renewable energy, and regulatory support. The results offer operational insights to the steel industry, policymakers, and academia on the path to sustainable, energy-efficient, and carbon-neutral steel production while retaining the metallurgical quality and industrial scale of the steelmaking processes.

In recent years, technical processes for the sequestration of CO2 through industrial waste mineral carbonation have been explored and developed. There is a large portfolio of Carbon Capture, Uti-lisation and Storage (CCUS) techniques that have been employed on a laboratory and at pilot scale. These include geological storage, ocean storage and mineralisation by carbonate ores. In view of this, the main purpose of this research was to investigate and explore chemical variables, particularly ammonium salts as lixiviants for calcium mineral extraction from iron making slag. The slag in use was acquired from a Steel Mill in the Vaal Triangle Region in Gauteng, South Af-rica. The experimental test work was conducted using different ammonium lixiviants, namely, NH4NO3, NH4Cl and CH3COONH4 to understand the influence of anion type as well as possible differences in mechanisms of interactions. Lixiviant concentration as well as the reaction time were varied in this research study. The three selected ammonium based lixiviants showed different extents of calcium extraction owing to differences in the anion groups. NH4NO3, NH4Cl and CH3COONH4 were found capable of dissolving 50% to 80% of calcium from the selected slag for different molar concentrations. Anion type and leaching time also had significant influences on the leaching of calcium from the slag. Rapid pH degradation resulted in better calcium extraction ca-pabilities. This work has shown that the selected ammonium salts have a potential as lixiviants for calcium dissolution from iron making blast furnace slags. These lixiviants would therefore be important to consider during calcium mineral carbonation for CO2 sequestration.

This research aims to explore a novel preparation and characterization of modified BFIS slag, with magnesium oxide, ammonium chloride as a hydrating agent, and the MgO/BFIS sorbent, all of which were synthesized utilizing an atmospheric hydration procedure. The sorbents were made by altering the hydration conditions, which included the MgO/BFIS slag weight ratio (1:1 to 1:4), hydration temperature (40–90 °C), ammonium chloride (1–4 g), and hydration length (4–12 h). The carbonation process was carried out using thermogravimetric analysis (TGA) at 800 °C. At all preparation conditions, the specific surface area of MgO/BFIS composite ranged between (50.2–53.6 m ² /g) and was more than that of MgO (5.34 m ² /g). The produced MgO/BFIS sorbent had a more porous structure than virgin MgO or BFIS slag, according to SEM micrographs. X-Ray Diffraction (XRD) and Fourier-Transform Infrared spectroscopy (FTIR) analysis revealed the existence of complex compounds comprising magnesium silicate hydrate in the produced sorbents. This helped to explain the large BET-specific surface area. The Brunauer–Emmett–Teller (BET) specific surface area decreased as the amount of BFIS slag increased and increased with the hydration temperature, time, and amount of hydrating agent increased. The shrinking core model was used to fit the kinetics of the carbonation reaction, and the results show that diffusion over the product layer was the rate-limiting step. Graphical Abstract

Beneficiation of iron and steel slags have a great potential in mitigating high levels of anthropogenic carbon dioxide (CO₂) gas emissions owing to their high contents of calcium and magnesium. Carbonation of calcium and magnesium leaching solutions produce precipitates that promise to act as fluxing agents in various industries. There is also a need to study the physico-chemical factors affecting the extraction of these elements and their kinetic behaviour. A calcium-rich blast furnace ironmaking slag milled to 80%—75 µm was used in an experiment to study the effect of reaction temperature on the dissolution of calcium. An orbital shaking incubator was used by applying the one-factor-at-a-time method for a 2 h leaching test. Reaction temperature was controlled at 30 °C, 50 °C, 70 °C, and 100 °C at constant agitation speed of 200 rpm, 0.5 M of lixiviant concentration and solid-to-liquid ratio kept at 200 g/L. CH3COOH, (NH₄)₂SO₄, and NH₄Cl were tested individually as lixiviants. AAS, XRD and EDX were used to analyse the leach filtrate and residue. Consequently, the findings showed that temperature is the critical operating parameter that yielded exceptionally high calcium extraction. CH₃COOH yielded 80–90% of calcium extracted under high reaction temperatures. The kinetic data for the effect of reaction temperature leaching data fitted one shrinking core model equation, which described diffusion-controlled leaching reactions. The diffusion controlled by a product layer model was fitted and the activation energy were calculated as 19.4930 kJ/mol for NH4Cl solvent. (NH₄)₂SO₄ and CH₃COOH did not fit into any model because of undefined kinetic data and formation of gelatinous silica layer during leaching process.