Search Results (6)

To address the problems of high moisture content, fine particle size, and limited conventional reutilization of stainless steel slag mud (SSSM), controlled low-strength material (CLSM) was prepared using SSSM as the primary solid component and cement together with ground granulated blast furnace slag (GGBS) as cementitious materials. The effects of GGBS replacing cement and SSSM, respectively, on the properties of CLSM and their variation patterns were investigated. Its solidification mechanism was analyzed through simulated control tests, X-ray diffraction (XRD), thermogravimetric–differential thermogravimetric analysis (TG-DTG), and scanning electron microscopy (SEM). The results show that, when GGBS replaces cement, the water-to-solid ratio and bleeding rate increase, while the compressive strength at all curing ages decreases overall; however, the 28 d strength still meets the requirement for CLSM. When GGBS replaces SSSM, the water-to-solid ratio and bleeding rate increase with GGBS fraction, and the compressive strength at all curing ages increases overall. At a GGBS fraction of 18%, the water-to-solid ratio reaches 0.363, the bleeding rate reaches 5%, and the 28 d and 60 d compressive strengths reach 7.3 and 11.2 MPa, respectively, representing increases of 23.3 and 21.4 times compared with the system without GGBS (0.3 and 0.5 MPa). The simulated SSSM substitution tests show that a synergistic solidification effect exists between SSSM and GGBS and contributes to strength development. Microstructural analysis shows that GGBS undergoes hydration under the alkali–sulfate environment provided by SSSM, generating ettringite (AFt) and calcium silicate hydrate (C-S-H gel), which fill pores and thereby enhance strength, while calcium hydroxide (Ca(OH)₂) provides an alkaline environment and promotes the participation of potentially active components in SSSM in the synergistic solidification process. Full article

Petroleum hydrocarbon (PH) contamination in groundwater necessitates sustainable remediation solutions. This study develops a novel co-encapsulated composite by embedding steel slag (SS) and sodium persulfate (SPS) within an ethyl cellulose (EC) matrix ((SS + SPS)/EC) for permeable reactive barrier applications. The EC matrix enables controlled release of SPS oxidant and gradual leaching of alkaline components (Ca²⁺/OH⁻) and Fe²⁺/Fe³⁺ activators from SS, synergistically sustaining radical generation while buffering pH extremes. Optimized at a 10:7 SS:SPS mass ratio, the composite achieves 66.3% PH removal via dual pathways: (1) sulfate radical (${\mathrm{S}\mathrm{O}}_4^{-}$•) oxidation from Fe²⁺-activated persulfate (S₂${\mathrm{O}}_8^{2-}$ + Fe²⁺→${\mathrm{S}\mathrm{O}}_4^{-}$• + ${\mathrm{S}\mathrm{O}}_4^{2-}$ + Fe³⁺), and (2) direct electron transfer by surface-bound Fe³⁺. In situ material evolution enhances functionality—nitrogen physisorption reveals a 156% increase in surface area and 476% pore volume expansion, facilitating contaminant transport while precipitating stable sulfate minerals (Na₂SO₄, Na₃Fe(SO₄)₃) within pores. Crucially, the composite maintains robust performance under groundwater-relevant conditions: 54% removal at 15 °C (attributed to pH-buffered activation) and >55% efficiency with common interfering anions (Cl⁻, ${\mathrm{H}\mathrm{C}\mathrm{O}}_3^{-}$, 50 mg·L⁻¹). This waste-derived design demonstrates a self-regulating system that concurrently addresses oxidant longevity (≥70 h), geochemical stability (pH 8.5→10.4), and low-temperature activity, establishing a promising strategy for sustainable groundwater remediation. Continuous-flow column validation (60 d, 5 mg·L⁻¹ gasoline) demonstrates sustained >80% removal efficiency and systematically stable effluent pH (9.8–10.2) via alkaline leaching. Full article

The carbonation of industrial calcium-rich byproducts such as steel slag demonstrates significant potential for CO₂ sequestration. This technique aids in reducing carbon emissions while also promoting waste recycling. Despite its advantages, gaps remain in the understanding of how steel slag characteristics and operational parameters influence the carbonation process, as well as the underlying mechanism of direct aqueous carbonation. We evaluated the carbonation performance of three types of steel slag at temperatures below 100 °C. The slag with the highest CO₂ sequestration capacity was chosen for a systematic evaluation of the effects of operating conditions on carbonation efficiency. Thermodynamic analysis indicated that the reactivity of CaO and Ca(OH)₂ with CO₂ exceeded that of CaO·SiO₂ and 2CaO·SiO₂. Under conditions of 85 °C, a particle size less than 75 μm, an initial CO₂ pressure of 0.5 MPa, a liquid-to-solid ratio of 5 mL/g, and a stirring speed of 200 rpm, the steel slag achieved a sequestration capacity (K) of 283.5 g(CO₂)/kg and a carbonation efficiency (ζ_Ca) of 51.61%. Characterization of the slag before and after carbonation using X-ray diffraction, SEM-EDS, thermogravimetric analysis, and Fourier transform infrared spectrometry confirmed the formation of new carbonates. Mechanistic analysis revealed that the rate-limiting step initially involved the mass transfer of CO₂, transitioning to Ca²⁺ mass transfer as time progressed. Our research provides a viable technique for CO₂ capture and a beneficial approach for reutilizing waste steel slag. Furthermore, solid residues after capturing CO₂ have the potential for conversion into carbon-negative building materials, offering a sustainable strategy for steel companies and other enterprises with high carbon emissions. Full article

The high moisture content and low strength of dredged soft soils result in significant difficulties in directly reutilizing them in engineering. Improving their mechanical properties effectively and achieving re-utilization with the maximum benefit in engineering is the key to disposing of dredged soils with high moisture content. This study investigated the influences of cement and steel slag ratio, moisture content, the maximum particle size of steel slag, and curing age on the compressive strength of dredged silty clay in a plastic flow state. The performance improvement of dredged silty clay stabilized with cement and steel slag was discussed by comparing to related previous studies. The strengthening mechanism of dredged soils stabilized with cement and steel slag was explored by microstructural observation. The results show that when the ratio of cement to steel slag was 9:6; namely, using steel slag to replace 40% of cement, the strength properties of dredged silty clay stabilized by cement and steel slag could ensure the minimum requirements of the project greater then 100 kPa, and their economics could achieve the best results. The finer the particle size of steel slag was, the better the stabilization effect was. The compressive strength of dredged silty clay stabilized by cement and steel slag with particle sizes of less than 0.075 mm was 1.06 times, 1.10 times, and 1.16 times that of 0.25 mm, 1 mm, and 2 mm and increased linearly over curing ages earlier than 28 days. The compressive strength of dredged silty clay stabilized by cement and steel slag cured for 28 days was 2.44 times, 1.59 times, and 1.36 times that of 3, 7, and 14 days, respectively. The evolution of microstructural characteristics showed that the internal pore sizes of dredged soil decreased the structural compactness increased significantly due to the formation of more calcium silicate hydrate and other agglomerated flocculent gel materials from the further reaction between steel slag and cement hydration products. The results of this study can provide technological parameters for the re-utilization of dredged soil stabilized with cement and steel slag. Full article

Reutilizing industrial by-products and recycled concrete aggregates (RCA) to replace cement and natural aggregates (NA) in concrete is becoming increasingly important for sustainable development. Yet, experimental evidence is needed prior to the widespread use of this sustainable concrete by the construction industry. This study examines the performance of alkali-activated slag concrete made with RCA and reinforced with steel fibers. Natural coarse aggregates were replaced with RCA. Steel fibers were added to mixes incorporating RCA at different volume fractions. Desert dune sand was used as fine aggregate. The mechanical and durability properties of plain and steel fiber-reinforced concrete made with RCA were experimentally examined. The results showed that the compressive strength did not decrease in plain concrete mixes with 30 and 70% RCA replacement. However, full replacement of NA with RCA resulted in a 20% reduction in the compressive strength of the plain mix. In fact, 100% RCA mixes could only be produced with compressive strength comparable to that of an NA-based control mix in conjunction with 2% steel fiber, by volume. In turn, at least 1% steel fiber, by volume, was required to maintain comparable splitting tensile strength. Furthermore, RCA replacement led to higher water absorption and sorptivity and lower bulk resistivity, ultrasonic pulse velocity, and abrasion resistance. Steel fiber incorporation in RCA-based mixes densified the concrete and improved its resistance to abrasion, water permeation, and transport, thereby enhancing its mechanical properties to exceed that of the NA-based counterpart. The hardened properties were correlated to 28-day cylinder compressive strength through analytical regression models. Full article

The purpose of this work is to carry out an accurate and extensive environmental analysis of the steel production occurring in in the largest integrated EU steel mill, located in the city of Taranto in southern Italy. The end goal is that of highlighting the steelworks’ main hot spots and identifying potential options for environmental improvement. The development for such an analysis is based on a Life Cycle Assessment (LCA) of steel production with a cradle to casting plant gate approach that covers the stages from raw material extraction to solid steel slab production. The inventory results have highlighted the large solid waste production, especially in terms of slag, which could be reused in other industries as secondary raw materials. Other reuses, in accordance with the circular economy paradigm, could encompass the energy waste involved in the steelmaking process. The most burdening lifecycle phases are the ones linked to blast furnace and coke oven operations. Specifically, the impact categories are influenced by the energy consumption and also by the toxicity of the emissions associated with the lifecycle of steel production. A detailed analysis of the toxicity impacts indicates that LCA is still not perfectly suitable for toxicity assessments and should be coupled with other more site specific studies in order to understand such aspects fully. Overall, the results represent a first step to understanding the current levels of sustainability of the steelworks, which should be used as a starting point for the development both of pollution control measures and of symbiotic waste reutilization scenarios needed to maintain the competitiveness of the industrial plant. Full article