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The type of steel furnace slag (SFS), including electric arc furnace (EAF) slag, basic oxygen furnace (BOF) slag, ladle metallurgy furnace (LMF) slag, and argon oxygen decarburization (AOD) slag, can significantly affect the composite properties when used as an aggregate or as a supplementary cementitious material in bound applications, such as concretes, mortars, alkali-activated materials, and stabilized soils. This review seeks to collate the findings from the literature to express the variability in material properties and to attempt to explain the source(s) of the variability. It was found that SFS composition and properties can be highly variable, including different compositions on the exterior and interior of a given SFS particle, which can affect bonding conditions and be one source of variability on composite properties. A suite of tests is proposed to better assess a given SFS stock for potential use in bound applications; at a minimum, the SFS should be evaluated for free CaO content, expansion potential, mineralogical composition, cementitious composite mechanical properties, and chemical composition with secondary tests, including cementitious composite durability properties, microstructural characterization, and free MgO content.

The carbonation of alkaline industrial wastes is a pressing issue that is aimed at reducing CO2 emissions while promoting a circular economy. In this study, we explored the direct aqueous carbonation of steel slag and cement kiln dust in a newly developed pressurized reactor that operated at 15 bar. The goal was to identify the optimal reaction conditions and the most promising by-products that can be reused in their carbonated form, particularly in the construction industry. We proposed a novel, synergistic strategy for managing industrial waste and reducing the use of virgin raw materials among industries located in Lombardy, Italy, specifically Bergamo–Brescia. Our initial findings are highly promising, with argon oxygen decarburization (AOD) slag and black slag (sample 3) producing the best results (70 g CO2/kg slag and 76 g CO2/kg slag, respectively) compared with the other samples. Cement kiln dust (CKD) yielded 48 g CO2/kg CKD. We showed that the high concentration of CaO in the waste facilitated carbonation, while the presence of Fe compounds in large amounts caused the material to be less soluble in water, affecting the homogeneity of the slurry.

The characteristics of argon oxygen decarburization slag (AODS) for smelting stainless steel that has been aged for 10 years were analyzed. Three types of AODSs distributed at three positions in a slag heap were sampled for comparison experiments. Chemical analysis, mineral phase identification, thermogravimetric analysis, and micromorphology analysis were used to study the element migration trends and carbonation behavior of AODS after long-term aging. Sequential leaching tests were performed to study the chromium leachability of the aged AODS. The results show that during the long-term aging process, the AODS heap had undergone oxidation and carbonation, accompanied by element migration and mineralogical evolution. The surface slag had the highest degree of carbonation but the weakest chromium leachability. The chemical composition of the middle slag was the closest to that of the original slag. In the bottom steel slag, in addition to magnesium, certain depositions of other elements were present. The matrix phases in the aged slag were dicalcium silicate and merwinite, and the chromium was mainly wrapped in these matrix phases in the form of oxides, spinels, or alloys. Under the combined effects of carbonation and oxidation, the leaching characteristics of the chromium in the aged slag varied greatly depending on the location. The bottom slag had the strongest chromium leachability, and the hexavalent chromium had long-term continuous leachability.

The purpose of this study was to fully explore the mechanical properties of five different doses of an Argon–Oxygen Decarburization slag mixture in an unconfined compressive strength test. The peak stress, elastic modulus, and stress–strain curve of the mixture were studied for 90 days. Based on the experimental data and according to the theory of damage mechanics, the concept of damage threshold (t) was introduced to construct a damage constitutive model. Referring to the damage threshold of concrete, that of the mixture was determined to be 0.7 times higher than the peak strain, and the correlation coefficient between the established model and the test curve was above 0.85. These results indicate that the addition of AOD slag and fly ash can cause hydration reactions, increase the quantity of hydration products, and enhance the peak stress and elastic modulus of the mixture. The maximum increases were 94.9% and 43.1%, respectively. Parameters a and b reflect the peak stress and brittleness of the mixture, respectively. The incorporation of Argon–Oxygen Decarburization slag can make the mixture less brittle and improve its properties. The incorporation of Argon–Oxygen Decarburization slag can protect the mixture from damage. The maximum decrease is 40.2%.

To promote resourceful utilization of argon oxygen decarburization (AOD) slag, this research developed a new three-ash stabilized recycled aggregate with AOD slag, cement, fly ash (FA), and recycled aggregate (RA) as raw materials. The AOD slag was adopted as an equal mass replacement for fly ash. The application of this aggregate in a road base layer was investigated in terms of its mechanical properties and mechanistic analysis. First, based on a cement: FA ratio of 1:4, 20 sets of mixed proportion schemes were designed for four kinds of cement dosage and AOD slag replacement rates (R/%). Through compaction tests and the 7-day unconfined compressive strength test, it was found that a 3% cement dosage met the engineering requirements. Then, the unconfined compressive strength test, indirect tensile strength test, compressive rebound modulus test, and expansion rate test were carried out at different age thresholds. The results showed that the mixture’s strength, modulus, and expansion rate increased initially and then stabilized with age, while the strength and modulus initially increased and then decreased with increasing R. Secondly, based on X-ray diffraction (XRD) and scanning electron microscopy (SEM) used to analyze the mechanism, it was found that the strength, modulus, and expansion rate of the new material can be promoted by blending AOD slag, due to its ability to fully stimulate the hydration reaction and pozzolanic reaction of the binder. Finally, based on the strength and modulus results, R = 3% was identified as the optimal ratio, which provides a reference point for the effective application of AOD slag and RA in road base materials.

Steelmaking plants are associated with the generation of large quantities of dust streams from unit processes such as the blast furnace, electric arc furnace, basic oxygen furnace, and argon-oxygen decarburisation furnace. The dust streams are commonly recycled to the smelting process step (in-process recycling). In-process recycling of dust results in the build-up of zinc and other volatile heavy metals such as lead, arsenic, and cadmium, which renders the dust unsuitable for further recycling. The unsuitable dust is either discarded in landfills or temporarily stockpiled pending further processing. If the dusts are stockpiled for extended periods, they tend to pose operational challenges. A cost-effective solution is needed to avoid long term stockpiling of these materials. Mintek developed the EnviroplasTM process to treat such technogenic materials to recover valuable metals and generate a non-hazardous slag by-product. A large pilot smelting campaign was completed in a 1 MW electric arc furnace to demonstrate the recovery of zinc-rich dust and pig iron, as well as an innocuous slag from the processing of various steel-plant dusts via the Enviroplas process. The test work was undertaken as a feasibility study for Australian steelmaker, BlueScope, to evaluate the Enviroplas process as a suitable technology for treating historical stockpiles and new arisings of dust from their steel plant in Port Kembla. The test work demonstrated that zinc-rich dust with 63–75 % ZnO, pig iron with 94–98% Fe, and a non-hazardous slag can be produced from the various steel-plant dusts. It was noted that minor operational improvements such as a better feed system design to limit the carryover of feed dust into the gas stream, and efficient control of the bag plant extraction to better define the suction pressure at the gas offtake, can further improve the grade of ZnO in the product dust stream.

The phosphorus (P) removal of five combinations of dual filters consisting of blast furnace slag (BFS), argon oxygen decarburisation slag (AOD) and electric arc furnace slag (EAF) was evaluated in column experiments with domestic waste water. The columns were fed with waste water for 24 days. The column with only EAF had the best P removal performance (above 93% throughout the experiment). The speciation of the bound P was evaluated by P K-edge X-ray absorption near-edge structure (XANES) spectroscopy. In all five columns, the main P species of the slag packed in the outlet chamber was amorphous calcium phosphate (ACP). In samples from the inlet chambers, the contributions from crystalline Ca phosphates, P adsorbed on gibbsite and P adsorbed on ferrihydrite were usually much greater, suggesting a shift of P removal mechanism as the waste water travelled from the inlet to the outlet. The results provide strong evidence that P was predominantly removed by the slags through the formation of ACP. However, as the pH decreased with time due to the progressively lower dissolution of alkaline silicate minerals from the slag, the ACP was rendered unstable and hence redissolved, changing the P speciation. It is suggested that this process strongly affected the lifespan of the slag filters. Of the slags examined, EAF slag had the best P removal characteristics and BFS the worst, which probably reflected different dissolution rates of alkaline silicates in the slags.

Environmental aspects and the sustainable manufacturing of steels require producers to pay more and more attention to the efficient utilization of materials and waste products during steelmaking. This study is focused on the evaluation of possibilities for the recovery of metals (such as Fe, Ni and Cr) from waste products used for slag foaming in the Electric Arc Furnace (EAF) process. Two types of industrial briquettes were produced by mixing mill-scale from the hot rolling of stainless steels with anthracite and pet-coke, respectively. Thereafter, an assessment of the metal reduction processes in briquettes at high temperatures (1500 °C) was made by using laboratory thermo-gravimetric reduction experiments in an argon atmosphere. The amounts of metal, slag and gas obtained from the briquettes were estimated. In addition, the velocity and time for the removal of metal droplets from the liquid slag depending on the size of the metal droplets was estimated. It was found that up to 97% of metal droplets can be removed from the slag during the first 30 min. Moreover, results showed that most of the Cr, Ni and Fe (up to 93–100%) can be reduced from oxides of these metals in briquettes at 1500 °C. Moreover, the anthracite and pet-coke in the investigated briquettes have similar reduction capabilities. It was found that up to 330 kg of Fe, 28 kg of Ni and 66 kg of Cr per ton of added briquettes can be recovered from waste products by the industrial application of those briquettes for slag foaming in EAF.

Argon oxygen decarburization stainless steel slag (AOD slag) has high mineral carbonation activity. AOD slag carbonation has both the resource utilization of metallurgical waste slag and the carbon reduction effect of CO2 storage. This paper aimed to study carbonation reaction characteristics of AOD slag. Under the slurry-phase accelerated carbonation route, the effect of stirring speed (r) and reaction temperature (T) on AOD slag’s carbonation was studied by controlling the reaction conditions. Mineral composition analysis and microscopic morphology analysis were used to explore the mineral phase evolution of AOD slag during the carbonation process. Based on the unreacted core model, the kinetic model of the carbonation reaction of AOD slag was analyzed. The results showed that the carbonation ratio of AOD slag reached its maximum value of 66.7% under the reaction conditions of a liquid to solid ratio (L/S) of 8:1, a CO2 partial pressure of 0.2 MPa, a stirring speed of 450 r·min−1, and a reaction temperature of 80 °C. The carbonation reaction of AOD slag was controlled by internal diffusion, and the calculated apparent activation energy was 22.28 kJ/mol.

To enhance the economic value and utilization of argon oxygen decarburization (AOD) slag, cement/cementitious materials were prepared by roasting AOD slag with calcium oxide, and their compressive and bending strengths were characterized. It was clarified that a phase transition from dicalcium silicate to tricalcium silicate occurs as the calcium oxide content increases. The strength of the cement/cementitious materials (S2) met the requirements of 32.5 ordinary Portland cement (OPC), with a highest compressive strength of 63.18 MPa; and the water requirements for standard consistency, setting time, and stability were determined. Chromium leachability (at 12 days) declined to its lowest value (0.2 mg/l), which is lower than the national requirement for building materials (1.5 mg/l). Therefore, roasting AOD slag with calcium oxide is an effective and feasible method to prepare cement/cementitious materials.