The steel industry is among one of the largest CO2 emitters in the world. To meet climate targets, replacing fossil-based carbon with renewable biocarbon in metallurgical processes, particularly in blast furnaces (BFs) and electric arc furnaces (EAFs), has emerged as a viable short- to mid-term solution. Hydrothermal carbonization is a promising technology that converts low-grade, high-moisture biomass into hydrochar, a carbon-rich material with potential applications in ironmaking and steelmaking processes. This review examines the physicochemical and metallurgical properties of hydrochar—both in its pristine and pyrolyzed forms—derived from various biomass sources, and compares them with those of conventional carbonaceous materials such as fossil coal. This review also evaluates recent experimental and industrial studies demonstrating the application of hydrochar in BF injection and carbon composite agglomerates as well as its use for carburization and slag foaming in the EAF process. It demonstrates the potential of hydrochar as a partial substitute for fossil carbon, contributing to significant reductions in steel production-related CO2 emissions.

Carbon capture and storage (CCS) has evolved from a conceptual mitigation option into a cornerstone of global decarbonization strategies. This review provides a comprehensive synthesis of CCS’s technological, intellectual, and institutional evolution, emphasizing its transition from isolated engineering applications to system-wide integration. Drawing on a bibliometric analysis of more than 19,000 publications (2001–2025) from the Web of Science Core Collection visualized through CiteSpace, we map the global research landscape and reveal the field’s thematic shift from capture and sequestration processes toward integrated approaches that couple CCS with hydrogen, bioenergy, and digital optimization frameworks. Technologically, CCS has advanced through three primary pathways—post-combustion, pre-combustion, and oxy–fuel combustion—each with distinct capture mechanisms, energy penalties, and retrofit potentials. At the deployment level, CCS expansion remains geographically uneven: industrialized economies such as China, the United States, and the United Kingdom dominate operational capacity, whereas emerging and developing economies face barriers related to infrastructure, financing, and governance. By integrating bibliometric, technological, and comparative analyses, this review develops a multidimensional framework encompassing policy design, institutional capacity, and deployment structure. The findings highlight that CCS’s future effectiveness depends not only on technological efficiency but also on coordinated governance, cross-border storage networks, and its alignment with broader innovation ecosystems driving the global net-zero transition.

Hydrogen-enriched shaft furnaces serve as the central reactors in hydrogen metallurgy. The accuracy of the furnace design critically influences the internal operating conditions, including the dynamic variations in the gas distribution, pressure, temperature, and metallization rate. Particular attention should be paid to the injection angle of the reducing gas, which is a key operational parameter that significantly affects the system performance. In this study, a computational fluid dynamics model was established to simulate the internal working conditions of an industrial-scale ENERGIRON shaft furnace, revealing complex heat and mass transfer phenomena. Based on the simulation results, the upper wall of the reduction zone (within the height range of 16.0–16.5 m) withstands a significant temperature difference of 200 K, whereas the lower wall of the reduction zone (at a height of 1.5–2.5 m) experiences a substantial pressure difference (500 kPa). The metallization rate was approximately 93%. In the special cases where the reducing gas blowing angle was deflected from 90° to 30° or 150°, the wall temperature difference increased by approximately 100 K, the maximum pressure difference decreased by approximately 250 kPa, and the metallization rate increased by approximately 0.8%. Considering the balance between the service environment of the furnace wall and the metallization rate, a reducing gas blowing angle of 45° was selected as optimal.

This study investigated the sequestration of CO2 from flue gas using a Ca-rich leachate obtained by leaching steel slag with CH3COOH. Ultrasound was used to accelerate the fixation of low-concentration CO2 in the leachate and to induce the transformation of CaCO3 crystals into the vaterite form with a uniform particle distribution. Ultrasound-induced cavitation bubbles in ethanol reduced the nucleation barrier and prevented clustering by maintaining a uniform dispersion of vaterite CaCO3 crystals, which impeded their conversion to other CaCO3 polymorphs. Experimental results revealed that ultrasonic action could effectively fix low-concentration CO2 in the leachate reaction system. Moreover, the addition of ethanol as a surfactant yielded vaterite CaCO3 with an average particle size of 3.2 μm and uniform granularity of 1.4–5.6 μm. This product meets the industrial standards for light CaCO3 micropowder, which makes it suitable for various applications as a filling material. The proposed method presents a sustainable approach for the valorization of steel slag and low-concentration CO2 from flue gas, and it highlights the potential of ultrasonic technology to improve the chemical processes required for Carbon Capture, Utilization, and Storage technologies.

The steel industry, a critical pillar of global economic development, is highly energy-intensive, accounting for approximately 7%–9% of global energy-related CO2 emissions. The transition from traditional carbon-intensive metallurgy to hydrogen-based metallurgy represents a pivotal pathway for the green and sustainable development of the steel industry. This review elaborates on the evolution of hydrogen direct reduction technologies, highlighting early pilot- and commercial-scale plants that primarily utilized fluidized bed reactors with natural gas reforming or ammonia plant exhaust gases as reducing agents. These early efforts demonstrated the feasibility of hydrogen reduction but could not achieve long-term stable operation. The urgent need for decarbonization has resulted in renewed focus on research and development in hydrogen direct reduction, with steel companies proposing diverse technological solutions and advancing industrial demonstrations globally. Despite significant progress, the cost of hydrogen production has become a significant barrier to its widespread adoption. Strategies to lower costs include enhancing the reaction efficiency, integrating green electricity to supply heat, utilizing low-grade ores, and leveraging renewable, off-peak, and surplus electricity for hydrogen production. As the price of hydrogen is 0.7 ¥·Nm−3 (Standard volume), the cost of the hydrogen direct reduction–electric arc furnace process is comparable to that of the blast furnace–basic oxygen furnace process. Hydrogen direct reduction is expected to gradually replace the conventional blast furnace ironmaking method, which is emerging as a mainstream steel production process that underpins the green, low-carbon, and sustainable development of the global steel industry.

This article is a review of advances in sustainability metric (SM), focusing on life cycle assessment (LCA) and material flow analysis (MFA), the most commonly used among all SMs. The presentations at the past 10 Society and Materials (SAM) conferences were used as a database. LCA, the most popular of these methodologies, is thriving among academics, practitioners and clients. Standardized initially by United Nations Environment Program (UNEP) and the European Commission, it passed from the Global North to the Global South and branched into Environmental Product Declarations (EPDs) that provide LCA-formatted information, initially to the construction sector. Some important issues have progressed but are not completely resolved yet: multifunctional products or processes, circulatory practices, dynamic LCA, regionalization, monetarization, human and eco-toxicity, biodiversity loss or resource availability, and they need more development work. Although LCA focuses on a microscale vision of the economy, MFA, being macroscale, emphasizes strategic and policy issues, thanks to its dynamic version. MFAs are now available for at least one third of the substances in the periodic table and for countless materials, from metals, to composites and construction aggregates for civil engineering. MFA has shed light on many strategic issues, such as (1) the fate of end-of-life goods and of the materials of which they are made, which constitute the so-called urban mine, (2) the role of stocks in driving material demand and long-term evolution of production (the so-called Intensity-of-Stock model), (3) the connections with economic and social models that extend the scope and ambition of MFA, and (4) material flow accounting (MFAc), particularly Total Material Requirement (TMR). These two SMs are entirely devoted to objectifying the connection between human activities and the environment, mostly, based on quantitative indicators originating from Sciences, Technology, Engineering and Mathematics (STEM). However, LCA and MFA have left aside the full depth of society’s dynamics, as described by Social Sciences and Humanities (SSH) disciplines. Contributions from SSH disciplines do not match the indicator-based approach: they explored the concepts of social value of materials and social acceptance, used non-engineering metaphors to report on hard-science issues, called on Humanities, from History to Literary Criticism, on Science and Technology Studies (STS), on Design studies, on Ethics or Gender issues to shed light on sustainability issues. How the divide between SSH and SMs can be bridged is not yet fully clear. However, attempts were made to develop approaches that would mimic SMs: Social Cycle of Materials (SCM) mixes Design philosophy with STS, and ANT-reliant LCA, which posits that materials have agency, takes on board Actor Network Theory (ANT), a sociological model of society as a whole, to report on objects described by LCA. In between STEM and SSH approaches, lie approaches based on thermodynamics, which claim that physics can tackle social and economic dimensions: thermoeconomics is one of them.