Argon Oxygen Decarburization Slag Research Articles

The effect of slag variability in the attempted manufacture of AYF (alite-ye'elimite-ferrite) cement clinker at both laboratory and pilot scale

The production of AYF (alite-ye'elimite-ferrite) clinker was tested at laboratory and semi-industrial scale using by-products from the metallurgical industry: AOD slag; ladle slag; and fayalitic slag. Alite could be produced with ye'elimite using fluorine originating from AOD (argon oxygen decarburisation) slag as a mineraliser. After a successful laboratory demonstration, the clinker production was scaled to a semi-industrial trial. It was discovered that the reason for the absence of alite formation in a semi-industrial demonstration was that the AOD slag from the specific batch did not perform the designed mineralisation effect for alite formation. This study demonstrates that alite-ye'elimite can be produced at 1260 °C at laboratory scale by using fluorine mineralisation originating from an industrial by-product – in this case, AOD slag. However, the utilisation of by-products for delicate reactions requires detailed determination of the properties of the slag, as the variability from the same source yields different clinker chemistries and mineral phases.

In-Line Co-Processing of Stainless Steel Pickling Sludge Using Argon Oxygen Decarburization Slag Bath: Behavior and Mechanism

Stainless steel pickling sludge (SSPS) is classified as hazardous solid waste, while Argon Oxygen Decarburization (AOD) slag is challenging to utilize due to the leaching toxicity of Cr. This study introduces a novel in-line co-processing technique for AOD slag and SSPS, parallel to the steelmaking process, aimed at metal recovery, sulfur fixation, and slag detoxification: pre-treatment-AOD slag bath approach. The transformations and migrations of sulfur and metal elements, such as Fe and Cr, in the co-processed mixture were analyzed using thermogravimetric–mass spectrometry (TG-MS) and scanning electron microscopy–energy dispersive spectroscopy (SEM-EDS). The results indicated that sulfur in SSPS could be transformed from CaSO4 to CaS under controlled low pre-reduction temperatures (below 800 °C), facilitating its stabilization in the slag and achieving a sulfur fixation rate of over 99%. Metal elements, including iron and chromium, first formed a small portion of spinel (FeCr2O4) during the pre-reduction phase, then Fe-Cr or Fe-Cr-C-based alloy particles were rapidly formed at high temperatures and in the presence of reducers in the slag bath (1550 °C), aggregating and growing spontaneously, ultimately achieving a metal recovery rate of over 95%. Furthermore, a reaction model for SSPS briquettes in the AOD slag bath was established to further reveal the mechanisms of sulfur, iron, and chromium stabilization and migration, thereby providing a basis for the harmless disposal of both materials. The product alloys are expected to be used as additives in stainless steel production, while the harmless slag could be safely utilized in the preparation of cementitious auxiliary materials.

Preparation and Mechanism Analysis of Stainless Steel AOD Slag Mixture Base Materials.

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.

Investigation of the acicular aragonite growth behavior in AOD stainless steel slag during slurry-phase carbonation

This study presents a novel method for producing acicular aragonite using argon oxygen decarburization (AOD) slag while controlling the reaction temperature, reaction time, stirring speed, and the magnesium-to‑calcium stoichiometric ratio. This approach provides steel plants with an opportunity to decrease their CO2 emissions and promote efficient resource utilization and CO2 storage through the production of high-quality value-added products. The experimental results showed that reaction temperature was the most significant factor affecting the carbonation efficiency of AOD slag, followed by reaction time, stirring speed, CO2 partial pressure, and the liquid-to-solid ratio (L/S). The study also found that elevated temperature and prolonged reaction duration favored the preferential precipitation of aragonite. Additionally, raising the temperature and the magnesium-to‑calcium stoichiometric ratio was shown to enhance the formation of aragonite, affecting its crystal growth orientation and dimensions. The optimal combination of reaction parameters for the preparation of acicular aragonite was found to be the reaction time of 8 h, the magnesium-to‑calcium stoichiometric ratio of 0.8, the reaction temperature of 120 °C, and the stirring speed of 200 r·min−1. Under these conditions, the resulting acicular aragonite exhibited excellent overall uniformity, a large aspect ratio, and a smooth crystal surface, with a content of 91.49 %, a single crystal length ranging from 9.86 to 32.6 μm, and a diameter ranging from 0.63 to 2.15 μm. This study provides valuable insights into the efficient production of acicular aragonite from steel slag while reducing CO2 emissions and promoting the sustainable use of resources.

Crystallization behaviors and kinetic of argon oxygen decarburization slag via various SiO2 content: Conditions for obtaining amorphous state

The crystallization behaviors and morphology of industrial AOD slag with various SiO2 levels were studied. The time-temperature-transformation (TTT) and continuous-cooling- transformation (CCT) diagrams of argon oxygen decarburization (AOD) slag were obtained using confocal laser scanning microscopy (CLSM). The results show that the main crystalline phases evolved from dicalcium silicate, merwinite, and bredigite to an amorphous state when the dosage of SiO2 increased to 15 wt% in the quenching slag. Crystallization behaviors of AOD slag follow the Johnson-Mehl-Avrami (JMA) crystallization kinetic model. The Avrami exponent and the activation energy increase to 2.382 and 83.68 kJ/mol, respectively in the 15 wt% SiO2 samples. Thus, the crystal size shrinks, and the crystallization capacity of slag decreases. The critical cooling rate reaches the minimum value of 2052.5±34 °C/min in the 15 wt% SiO2 samples. This research showed that AOD slag modified by SiO2 can enhance the potential of preparing supplementary cementitious materials for added-value applications.

Reuse of vitrified argon oxygen decarburization slag as supplementary cementitious materials: Comprehensive performance and chromium immobilization mechanism

• The virified AOD slag with CaO/(SiO 2 + Al 2 O 3 ) = 0.82 has the higher [SiO 4 ] depolymerization and reactive silicate network. • The vitrified AOD slag based cementitious material reaches to 52.5R strength level of Portland cement. • Higher polymerization degree of glass owning stronger chromium immobilization ability. • Chromium can be physical encapsulated in cementitious material with denser microstructure and higher hydration degree. Using vitrified argon oxygen decarburization (AOD) slag as a supplementary cementitious materials (SCM) provides low carbon consumption and improved slag recycling. We investigated vitrified AOD slags with fly ash (FA) as the SCM. The results show that the vitrified AOD slag with CaO/(SiO 2 + Al 2 O 3 ) = 0.82 has the highest [SiO 4 ] depolymerization. The cementitious materials (CM) dosage with this slag reaches the 52.5R strength level of Portland cement. The chromium can be physically encapsulated in CM with denser microstructures and higher hydration degrees. The amount of chromium leaching from the vitrified AOD slag and CM meet the industrial requirements. Thus, vitrified AOD slag is a promising SCM.

Cement/Cementitious Material Prepared by Roasting Argon Oxygen Decarburization Slag with Calcium Oxide

Cement/Cementitious Material Prepared by Roasting Argon Oxygen Decarburization Slag with Calcium Oxide

Toxicity assessment of the utilization of AOD slag as a mineral fertilizer for pakchoi (Brassica chinensis L.) planting

The application of argon oxygen decarburization (AOD) slag as a mineral fertilizer can be employed as an effective and environment-friendly approach. In this study, batch leaching tests and pot experiments were performed to assess the toxicity exhibited by AOD slag fertilization for pakchoi (Brassica chinensis L.) planting. pH, Eh and element leaching concentration were measured to examine the effect exerted by AOD slag addition on physicochemical properties exhibited by soil. The effect of AOD slag fertilization on pakchoi growth was determined by measuring its physiological and biochemical parameters. Moreover, the heavy metal accumulation, biological accumulation coefficient (BAC), estimated daily intake (EDI) and target hazard quotient (THQ) were identified to assess the health risks. As indicated from the result, adding AOD slag could increase pH and the leaching concentrations of Ca, Si, Cr and Ti, while decreasing the leaching concentrations of Fe, Ni, Cd, Hg and Pb in soil. With the increase in the addition rate, the concentrations of Mg, Al and Mn were elevated and then started to decrease at the rates of 2%, 8% and 2%, respectively. Low rates (≤1%) of AOD slag fertilization positively impacted pakchoi growth, whereas high rates exerted an opposed effect. The calculated EDI and THQ values were all less than 1. The consumption of the pakchoi grown on the AOD slag fertilized soil was at low risk. For plant growth perspective, the utilization amount of AOD slag as a mineral fertilizer for pakchoi planting should not exceed 1%.

Copper and Zinc Removal Efficiency of Two Reactive Filter Media Treating Motorway Runoff—Model for Service Life Estimation

The predominant techniques used for road runoff treatment are sedimentation and filtration. In filtration systems, the ability of the media to adsorb the contaminants is a finite process. Consequently, construction, operation and maintenance managers of such systems should know in advance the service life, i.e., when the used medium should be replaced, and associated costs of operation and maintenance. A batch experiment followed by a packed bed reactor (PBR) experiment addressed the kinetics of the studied media argon oxygen decarburization slag (AOD) and Polonite, followed by the development of a 1D-model to describe the change of concentration of Cu and Zn within time. The batch test results showed that Cu and Zn adsorption followed the Freundlich isotherms for AOD and Polonite. Those results coupled with the linear driving force model and the developed model resulted in good agreement between the PBR results and the simulation. The model was capable to predict (i), the service life at the hydraulic load of 0.18 m/h for AOD (Cu: 395 d; Zn: 479 d) and Polonite (Cu: 445 d; Zn: 910 d), to show (ii) the profile concentration in the PBR within time and the gradient of the concentration along the height of the reactor.

Pressurized in situ X-ray diffraction insights into super/subcritical carbonation reaction pathways of steelmaking slags and constituent silicate minerals

This study explores mineral carbonation of industrial stainless steelmaking slags and relevant synthetic constituent minerals via in situ pressurized X-ray diffraction, to clarify carbonation reaction pathways and efficiency for carbon storage and waste valorization. The primary mineral phases of Argon Oxygen Decarburization (AOD) and Continuous Casting (CC) slags, namely, åkermanite, bredigite, cuspidine, merwinite, and β- and γ-C2S, were reacted in a custom-built beryllium-capped XRD reactor filled with either water-saturated (wet) subcritical CO2(g), or wet supercritical CO2(SC), in a series of carbonation experiments. Formation of calcite and aragonite was observed for most Ca-bearing minerals, transient precipitation of metastable vaterite was observed, while carbonation of AOD and CC slags in CO2(SC) resulted in hydrated crystalline calcium carbonates and indirect evidence of amorphous carbonate. Results obtained suggest that low-pressure subcritical carbonation routes are attractive for standalone slag carbonation processes, while high-pressure supercritical carbonation routes are amiable to symbiotic integration with CO2(SC)-generating green technologies.

Cementitious Behavior of Argon Oxygen Decarburization Stainless Steel Slag and Its Stabilization on Chromium

The study mainly aims at the potential of Argon Oxygen Decarburization Slag (AODS) as a supplementary cementitious material and explores the mechanisms of stabilization/solidification (S/S) of chromium in cement-based composite pastes. The basic cementitious parameters, such as water requirement, setting time, soundness, hydration characteristics, and strength indexes of composite binders, were examined through standard methods. The results showed that the most beneficial mineral phase in AODS for cementitious behavior was beta dicalcium silicate (β-C2S). The utilization of a higher AODS dosage in composite binders increased the water requirement and the setting time, while it decreased the hydration heat and the strength indexes. Although the AODS possessed limited cementitious properties, it conformed the Grade II steel slag powder qualified for concrete and cement. Sequential leaching tests were conducted targeting the leachability of chromium in the pastes with different AODS dosage and curing time. Results showed that with the lower AODS dosage and the longer curing time, the S/S efficiency for chromium leaching from the composite paste was better. Utilization of AODS as a cement substitute not only can recycle this solid waste and decrease the emission of CO2 concerning cement production, but also helps to effectively reduce the chromium leaching risk.

Effect of Carbonation Curing on Physical and Durability Properties of Cementitious Materials Containing AOD Slag

In this study, the physical and durability properties of cementitious materials containing stainless steel argon-oxygen decarburization (AOD) slag were investigated by CO2 curing. Three contents (0, 30, 60%) of ordinary Portland cement (OPC) were replaced with AOD slag. Specimens were cured at four CO2 concentrations and three temperatures. The chloride diffusion coefficient, drying shrinkage, compressive strength, and porosity were measured. The drying shrinkage reduction was proportional to CO2 uptake. The chloride diffusion coefficient increased as contents of the AOD slag increased. At 15% CO2 concentration, the diffusion coefficient was similar to that of the OPC regardless of the AOD slag substitution rate. The durability of cementitious materials mixed with AOD slag can be improved by CO2 curing and can be used in construction.

Kinetic model of chromium release from argon oxygen decarburisation (AOD) slag in a neutral leachate

Valorisation of argon oxygen decarburisation (AOD) slag, a suitable recycling resource, is limited by the release of a notable amount of heavy metals, such as chromium. The mineralogical component of AOD slag was characterised by X-ray diffraction and scanning electron microscopy-energy-dispersive X-ray spectrometry. To explore the release kinetics of chromium from AOD slag, neutral leaching tests were performed at various temperatures. The results indicated the existence of two leaching stages: quick and slow leaching stages. In 2 h, the chromium release fraction increased sharply as the leaching time increased. As the leaching time increased, the chromium release rate gradually decreased. Based on the shrinking core model, chromium release kinetic models for the quick and slow leaching stages from the AOD slag were independently determined. The chromium release was controlled by solid product diffusion during the quick leaching stage and a complicated process in the slow leaching stage. The activation energy of chromium leaching was calculated based on the Arrhenius equation. Solid product diffusion was the velocity-determining step during the 2 h leaching process. In the slow leaching stage, chromium release was controlled by complicated hybrid control dominated by solid product diffusion.

Methods to Determine Characteristics of AOD-Converter Decarburization-Slags

Argon Oxygen Decarburization (AOD) converter slags are known to consist of both liquid and solid phases, but limited information on the slag characteristics has been published in the open literature. Therefore, a new methodology to study the characteristics of slag samples taken from the AOD converter process during production was developed based on petrography. The results show that the preparations of the slag samples using the borax method are suitable to use when determining the chemical composition of AOD slag samples using the X-ray fluorescence (XRF) method. The results also showed that both the light optical microscopy (LOM) method and a method combining scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) can be used to characterize the slag samples and that the correlation between the methods was found to be good. This means that it is possible to use the faster LOM method instead of the more complicated SEM-EDS method to characterize AOD slag samples. Finally, the results show that the difference between calculated values based on stoichiometry and measured data for Ca and Cr in AOD slags are 11.7 mass% and 11.3 mass%, respectively. This is considered to be a good agreement for industrial samples.

Carbonation of argon oxygen decarburization stainless steel slag and its effect on chromium leachability

This study focuses on evaluating the carbonation potential of argon oxygen decarburization (AOD) slag and analyzing influence mechanism of carbonation on chromium leachability. Static thin-film accelerated carbonation and sequential leaching tests were carried out. Results show that the liquid to solid (L/S) ratio was the most influencing factor for AOD slag’s carbonation, and the maximum carbonation ratio of AOD slag was 50–52% (L/S = 0.4 mL/g, PCO2 = 7.5 bar, and t > 6 h). Dicalcium silicate’s carbonation resulted in the generation of amorphous calcium carbonate, crystalline calcite and silica gel. AOD slag’s smooth surface could be eroded by these products gradually with carbonation furthered. The mineral phase evolution clearly influenced the mineral phase hydrolysis and physical encapsulation, and thus affected the hydrolysis behavior of the primary phase and the generation behavior of the secondary phase in the carbonated slags. Chromium leachability (20 days) declined to its lowest value (1.7 mg/kg) as the carbonation ratio growing to 23% and then increased to its highest value (7.9 mg/kg) with the carbonation ratio increasing to 52%. Chromium leachability varies with the carbonation ratio. The optimal carbonation ratio that resulting in minimum chromium leaching risk must be taken full in mind before using AOD slag in carbonation-related production activities.

Investigation of microstructure and mechanical performance of carbon-capture binder using AOD stainless steel slag

The γ-C2S that constitutes stainless-steel argon oxygen decarburization (AOD) slag is known to generate calcite and silicate gel through reaction with CO2. In this study, the mechanical performance and microstructure characteristics of cementitious materials that contained AOD slag were investigated with respect to carbonation. AOD slag that contained 38.1% γ-C2S was used. It was crushed into two different finenesses; and paste specimens were prepared, in which up to 60% of ordinary Portland cement (OPC) was replaced by AOD slag. The specimens were cured in environments with CO2 concentrations of 0%, 5%, 10%, and 15%, to analyze the influence of the CO2 concentration. The compressive strengths were measured for the evaluation of the mechanical performances; and the pore size distributions were measured using a mercury intrusion penetrometer, to examine microstructural changes. Thermogravimetry/derivative thermogravimetry (TG-DTG) analyses were employed for the measurement of the CO2 uptake, and the influences of the CO2 uptake on the compressive strength and microstructure were analyzed. In the non-CO2 curing environment, the compressive strength decreased and the number of pores increased as the substitution rate of the AOD slag increased. However, when the CO2 concentration increased, the specimen with AOD slag exhibited a decrease in the porosity and increase in strength. The influence of the fineness of the AOD slag was significantly different when the substitution rate was 30%, and non-significant when it was 60%.

Production and properties of ferrite-rich CSAB cement from metallurgical industry residues

Blast furnace slag from the steel industry is commercially utilized as a cement replacement material without major processing requirements; however, there are many unutilized steel production slags which differ considerably from the blast furnace slag in chemical and physical properties. In this study, calcium sulfoaluminate belite (CSAB) cement clinkers were produced using generally unutilized metallurgical industry residues: AOD (Argon Oxygen Decarburisation) slag from stainless steel production, Fe slag from zinc production, and fayalitic slag from nickel production. CSAB clinker with a target composition of ye'elimite-belite-ferrite was produced by firing raw materials at 1300 °C. The phase composition of the produced clinkers was identified using quantitative XRD analyses, and the chemical composition of the clinker phases produced was established using FESEM-EDS and mechanical properties were tested through compressive strength test. It is demonstrated that these metallurgical residues can be used successfully as alternative raw materials for the production of CSAB cement that can be used for special applications. In addition, it is shown that the available quantities of these side-streams are enough for significant replacement of virgin raw materials used in cement production.

Briquetting of Wastes from Pulp and Paper Industries by Using AOD Converter Slag as Binders for Application in Metallurgy.

A number of carbon-rich (containing up to 47 wt% C) and lime-rich (containing up to 96 wt% of CaO-compounds) waste products from the pulp and paper industries can be used in iron and steel industry as fuels and slag formers for various metallurgical processes such as blast furnaces (BF), cupola furnaces (CF), argon oxygen decarburization (AOD) converters and electric arc furnaces (EAF). In most cases, these wastes consist of different size powders. In order to facilitate loading, transportation and charging of these powder wastes, briquetting is required. In this study, a pulverized AOD slag was tested as a binder component for briquetting of CaO-containing wastes (such as mesa, lime mud and fly ash) from pulp and paper industries. Moreover, mechanical testing of the possibilities for loading, transportation and unloading operations were done, specifically drop test trials were done for briquettes with different chemical compositions and treatments such as heating and storage. The results showed that an addition of 10–20% of AOD slag as a binder component followed by heat-treatment at 850 °C significantly improved the mechanical properties of the CaO-containing briquettes. An application of these briquettes will significantly reduce the consumption of natural resources (such as nature lime) in the metallurgical processes. Moreover, it can reduce the landfill area of wastes from pulp and paper industries, which is important from an environmental point-of-view.

Stabilization of Stainless Steel Slag via Air Granulation

In stainless steel production, slag from argon oxygen decarburization (AOD) converters is dumped on to the ground and then slowly cooled. The slag undergoes phase transformation from β-dicalcium silicate (β-C2S) to γ-dicalcium silicate (γ-C2S) at approximately 500 °C to 450 °C, resulting in slag volume expansion, disintegration, and dust generation. The dusty slag leads to challenges in material handling, metals recovery, and emissions control. Some operations use slag additives to stabilize slag, but this solution is expensive and can limit the end use of slag due to inclusion of toxic elements. Air granulation was hypothesized as a water-free method for stabilizing AOD slag via rapid quenching. Pilot-scale experiments at Sandvik Materials Technology (SMT) with silicon-reduced AOD slags confirmed that air granulation can produce products which are stable and dust free. Mineralogical analyses further indicated that these air-granulated stainless slags contained either no or low content of γ-C2S and are therefore stable.

Carbon dioxide fixation via accelerated carbonation of cement-based materials: Potential for construction materials applications

This study evaluated the CO2 absorption capacity of various inorganic materials commonly used as construction materials. This study compared and examined changes in the physicochemical properties of argon oxygen decarburization (AOD) slag, research cement (RC), ground granulated blast-furnace slag (GGBFS), and circulating fluidized-bed combustion (CFBC) ash in carbonation reactions. The carbon capture capacity was determined for all four materials. CFBC possessed the highest CO2 uptake (wt%), followed in descending order by RC, AOD slag, and GGBFS. However, the paste that 50% AOD slag mixed with 50% RC (AOD50RC50) featured the greatest improvement (92.95%) in strength development properties after carbonation curing. Compressive strength increased in RC100, GGBFS50RC50, and CFBC50RC50 by 6.05%, 3.29% and 15.92%, respectively. These results arose from differences in carbonation reaction mechanisms and products between the various materials. γ-C2S, the major component of AOD slag, produced CaCO3 and silica gel via carbonation; silica gel increased the compressive strength.