Carbon emission reduction and steel slag (SS) treatment are challenges in the steel industry. The accelerated carbonation of SS and carbonated steel slag (CSS) as a supplementary cementitious material (SCM) in cement can achieve both large-scale utilization of SS and CO₂ emission reduction, which is conducive to low-carbon sustainable development. This paper presents the utilization status of CSS. The accelerated carbonation route and its effects on the properties of CSS are described. The carbonation reaction of SS leads to a decrease in the average density, an increase in the specific surface area, a refinement of the pore structure, and the precipitation of different forms of calcium carbonate on the CSS surface. Carbonation can increase the specific surface area of CSS by about 24–80%. The literature review revealed that the CO₂ uptake of CSS is 2–27 g/100 g SS. The effects of using CSS as an SCM in cement on the mechanical properties, workability, volume stability, durability, environmental performance, hydration kinetics, and microstructure of the materials are also analyzed and evaluated. Under certain conditions, CSS has a positive effect on cement hydration, which can improve the mechanical properties, workability, bulk stability, and sulfate resistance of SS cement mortar. Meanwhile, SS carbonation inhibits the leaching of heavy metal ions from the solid matrix. The application of CSS mainly focuses on material strength, with less attention being given to durability and environmental performance. The challenges and prospects for the large-scale utilization of CSS in the cement and concrete industry are described.

Steel slag (SS), as a major solid waste of the steel industry, has CO₂ sequestration potential due to its rich calcium and magnesium alkaline components. SS carbonation is a promising strategy gaining industrial traction to simultaneously treat industrial solid waste and greenhouse gases. This article firstly describes the properties of SS and summarizes the research progress of SS carbonation. The classification of mineral carbonation technology is introduced, and the advantages and disadvantages are analyzed. The key factors affecting the SS carbonation are discussed. Then, the current industrial application status and life cycle assessment results are summarized. Finally, the conclusions are summarized, and the future research direction is proposed. Carbonation of SS can effectively fix CO₂ and produce high-value-added products, realizing a win–win situation of environmental and economic benefits, which is of great significance to the green transformation of the steel industry and the realization of the “double carbon” goal.

Environmental context: Rice straw is generated in vast quantities each year, but although the cellulose structure is stable, only 20% is used effectively. The structure of rice straw gives it high porosity and active functional groups, which means it easily adsorbs metals, but few studies have applied it to metal-contaminated soil. This study showed that composite phosphorylated-rice straw can be highly effective for the immobilization of cadmium in contaminated soils. Rationale: Rice straw is generated in vast quantities each year, but the effective utilisation rate is low. In order to develop full utilisation of rice straw and seek high-efficiency immobilising agents for cadmium contaminated soil, the objectives of this paper was to prepare a new modified rice straw material. Methodology: Composite phosphorylated rice straw (CPRS) and phosphorylated rice straw (PRS) were synthesised, the apparent morphology and functional groups of CPRS and PRS were characterised by SEM-EDS and FT-IR, and the remediation ability of CPRS and PRS on cadmium contaminated soil were studied by pot experiment. Results: The results showed that the order of maximum adsorption capacity (Qmax) for Cd2+ was CPRS > PRS > RS, Qmax of CPRS for Cd2+ was 53.57 g kg−1. CPRS had a richer porosity, evidenced a PO43−EN22041_IE1.gif group stretching vibration and had calcium salt well-dispersed on its surface. The application of CPRS to Cd contaminated soil significantly improved the plant biomass (fresh biomass increased 66.97%, over control) and decreased the Chinese cabbage uptake of Cd (decreased 67.16%, over control). The chemical stability of cadmium in soil was enhanced by applying CPRS due to a decrease in the exchangeable Cd in soil in proportion (decreased 95.38–99.10%) to the increasing fractions of Cd bound to Fe/Mn oxides (increased 141.15–158.90%), and residual Cd (increased 4.76–6.99 times) following the application of CPRS as compared to control treatments. Discussion: CPRS had an excellent immobilisation ability for cadmium contaminated soil, which was related to improved soil pH and cation exchange capacity. It possibly immobilises Cd in the soil via surface complexation through Cd–O groups at the surface of CPRS. Modified rice straw materials could be highly recommended as an efficient stabiliser to immobilise Cd in polluted agricultural soils.

Biodiesel is a green, low-carbon, and renewable fuel with the potential to substitute fossil fuels. The effects of reaction temperature (175–290 °C), residence time (5–75 min), and molar ratio of methanol to palmitic acid (6:1–35:1) on the non-catalytic esterification of palmitic acid with methanol to produce biodiesel were investigated by using a batch reactor. Moreover, the reaction parameters were optimized by using the response surface methodology (RSM), and the reaction kinetics were analyzed. The results showed that the conversion rate of palmitic acid to methyl palmitate increased to 100% as the reaction temperature rose from 175 °C to 225 °C, slightly changed until 275 °C, and then decreased to 94.81% at 290 °C. The conversion rate increased with residence time and reached the maximum value of 94.93% at 60 min. With increasing the molar ratio, the conversion rate rose to a maximum value of 85.46% at 15:1 and subsequently decreased. RSM results indicated the relative influence of factors on the conversion rate as reaction temperature > residence time > molar ratio. The optimal reaction parameters were 224 °C, 26 min, and a molar ratio of 16:1, affording a palmitic acid conversion rate of 99.30%. The esterification reaction between methanol and palmitic acid follows the first-order kinetics model.

The apparent viscosity of the oil–solid interface in steel rolling oily sludge (SROS) is governed by the amount, identity, and size of solid particles. To decouple these factors, oleic acid was used as a model oil phase, and Fe, Fe₃O₄, and Fe₂O₃ were selected as representative iron-bearing minerals. The effects of mineral type, Fe₃O₄ volume fraction, and particle size on the rheological behavior of oleic acid–mineral suspensions were systematically investigated using a rotational rheometer. Pure oleic acid behaved as a Newtonian fluid (24.96 mPa·s), and all suspensions exhibited near-Newtonian behavior with flow indices close to unity (0.959–1.048) and small yield stresses; no shear thickening was observed. At a matched loading of 4 vol%, the apparent viscosity followed the order Fe₃O₄ > Fe > Fe₂O₃. Notably, the Fe₂O₃ system exhibited a viscosity almost identical to that of neat oleic acid, which indicates that the reactivity of the mineral surface towards the carboxyl group of oleic acid, and the resulting aggregation state, dictate the particle–oil coupling, rather than the degree of oxidation. Furthermore, the apparent viscosity increased monotonically with Fe₃O₄ volume fraction (2–6 vol%) and decreased with increasing particle size (Dv(50) = 13.3–29.2 μm). Interestingly, the yield stress was highest for the coarsest powder, revealing that the static network strength and steady-flow viscosity are controlled by different microstructural features. These findings provide a quantitative basis for interpreting the oil–solid contribution to the viscosity of iron-bearing sludges and for developing targeted viscosity-reduction strategies.