Stainless Steel Slag Research Articles

Slurry-Phase Carbonation Reaction Characteristics of AOD Stainless Steel Slag

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.

Physiological, biochemical and nutritional changes in soybean in response to application of steel slag

Steel slag is a powdery industrial residue that has CaO, MgO and SiO2 in its composition, which enables its use in agriculture for soil acidity correction. Most studies involving this residue have focused on understanding its effects on the soil, not always considering its action on the plant metabolism. Thus, the present study aimed to evaluate physiological, biochemical and nutritional changes in soybean plants due to application of lime and steel slag on the soil surface or by incorporation. The experiment was carried out in the field, with six soil acidity corrective materials: stainless steel slag, steel slag, ladle slag, wollastonite rock, dolomitic lime and calcined dolomite, plus a negative control, which did not receive correctives. Two application methods were adopted: soil surface application or incorporation. Sixty days after application, the soybean crop was established. Soybean response changed with the application method, since incorporation of corrective materials provided greater production of fresh and dry leaf mass and stem fresh mass, increased chlorophyll b and leaf K levels, and contributed to a greater number of plants per hectare and pods per plant, compared to surface application. Besides such benefits, there was no difference between the effect of application methods on soybean yield, indicating that both incorporation and surface application are efficient in increasing soybean grain yield. The correctives steel slag, wollastonite and calcined dolomite provided significant increases in soybean yield

Carbonation of EAF Stainless Steel Slag and Its Effect on Chromium Leaching Characteristics

EAF stainless steel slag (EAF slag) is one kind of chromium-bearing metallurgical solid waste, which belongs to alkaline steel slag, and contains a large number of alkaline mineral phases. The carbonation activity of these minerals gives EAF slag the capability to effectively capture CO2. In this paper, EAF slag samples with different carbonation degrees were prepared by the slurry-phase accelerated carbonation route. The mineralogical identification analysis was used to qualitatively and semi-quantitatively determine the types and contents of the carbonatable mineral phases in the EAF slag. The sequential leaching test was used to study the chromium leachabilities in EAF slags with different carbonation degrees. The results showed that the main minerals with carbonation activity in EAF slag were Ca3Mg(SiO4)2 and Ca2SiO4, with mass percentages of 56.9% and 23%, respectively. During the carbonation process, Ca2SiO4 was the main reactant and calcite was the main product. As the degree of carbonation increased, the pH of the EAF slags’ leachate gradually decreased while the redox potential (Eh) gradually increased. At the same time, a large amount of Ca2+ in the EAF slag combined with CO2 to form slightly soluble calcium carbonate, which led to a significant decrease in the conductivity of the leachate. With the gradual increase in carbonation ratio, the leachability of chromium in the EAF slag first decreased and then increased, and reached its lowest value when the CO2 uptake ratio was 11.49%.

Occurrence and Leaching Behavior of Chromium in Synthetic Stainless Steel Slag Containing FetO

Stainless steel slag has been applied to other silicate materials due to its CaO-SiO2-based system. This is done to improve the utilization rate of stainless steel slag and apply it more safely. This paper investigated the occurrence of chromium in synthetic stainless steel slag containing FetO and its leaching behavior. The phase composition of the equilibrium reaction was calculated by FactSage 7.3 Equlib module. XRD, SEM-EDS and IPP 6.0 were used to investigate the phase compositions, microstructure and count the size of spinel crystals. The results indicate that the increase of Fe2O3 content can promote the precipitation of spinel phases and effectively inhibit the formation and precipitation of α-C2S in a CaO-SiO2-MgO-Cr2O3-Al2O3-FeO system. Fe2O3 contents increased from 2 wt% to 12 wt%, and the crystal size increased from 4.01 μm to 6.06 μm, with a growing rate of 51.12%. The results of SEM line scanning show the Cr-rich center and Fe-rich edge structure of the spinel phase. Comparing the TRGS 613 standard with the HJ/T 299-2007 standard, the leaching of Cr6+ in the FetO samples is far lower than the standards’ limit, and the minimum concentration is 0.00791 mg/L in 12 wt% Fe2O3 samples.

A computational study on the mixing and reduction of slags from ferrochrome and stainless steel production

Large amounts of slags are formed in the production of ferrochrome and stainless steels. Although there are many suitable applications for ferrochrome slag products, some chromium is lost with the slag. On the other hand, utilisation of some stainless steel slags are hindered by the volumetric changes of the dicalcium silicate, which is formed during the solidification and cooling of slags. Furthermore, there is some chromium also in stainless steel slags and its recovery would significantly improve the material efficiency and decrease the environmental impact of the stainless steel production. The purpose of this study was to estimate the possibilities to overcome these hindrances by mixing different slags with different ratios thus creating slags in which no dicalcium silicate is formed during solidification and from which chromium could be reduced in one process step before solidification of the slag. Carbon, methane and ferrosilicion were considered as possible reductants in this study. The study was conducted in three stages in which thermochemical simulations were used to estimate the solidus and liquidus temperatures of different slag mixtures, amounts of reductants required to reduce chromium from the slag mixtures and finally the needs for additional energy in the reduction process. The results of thermodynamic simulations were used to define suitable slag mixing ratios for chromium recovery taking avoidance of dicalcium silicate formation, distribution of chromium between different phases as well as the amounts of different possible reactants required for chromium recovery into account. According to the results, at least 30% of ferrochrome production slags are required in the mixtures in order to avoid the formation of dicalcium silicate, whereas the excessive use of ferrochrome slags increases the amount of solid spinel phase in the system thus making the chromium recovery more challenging.

A Study of Treatment of Industrial Acidic Wastewaters with Stainless Steel Slags Using Pilot Trials.

Different stainless steel slags have been successfully employed in previous experiments, for the treatment of industrial acidic wastewaters. Although, before this technology can be implemented on an industrial scale, upscaled pilot experiments need to be performed. In this study, the parameters of the upscale trials, such as the volume and mixing speeds, are firstly tested by dispersing a NaCl tracer in a water bath. Mixing time trials are used to maintain constant mixing conditions when the volumes are increased to 70, 80 and 90 L, compared to the 1 L laboratory trials. Subsequently, the parameters obtained are used in pH buffering trials, where stainless steel slags are used as reactants, replicating the methodology of previous studies. Compared to laboratory trials, the study found only a minor loss of efficiency. Specifically, in previous studies, 39 g/L of slag was needed to buffer the pH of the acidic wastewaters. To reach similar pH values within the same time span, upscaled trials found a ratio of 43 g/L and 44 g/L when 70 and 90 L are used, respectively. Therefore, when the kinetic conditions are controlled, the technology appears to be scalable to higher volumes. This is an important finding that hopefully promotes further investments in this technology.

Properties of ten-year-aged argon oxygen decarburization stainless steel slag

Properties of ten-year-aged argon oxygen decarburization stainless steel slag

Formation and Evolution of DS-Type Inclusions in 15-5PH Stainless Steel

15-5PH stainless steel castings are key components in fracturing trucks. However, DS-type inclusions can lead to fatigue failure of the material. To elucidate the formation mechanism of large-size DS-type inclusions, the evolution, growth, and aggregation of inclusions during vacuum oxygen decarburization, ladle refining, and vacuum casting were studied. The results show that the DS-type inclusions with sizes larger than 20 μm were CaO–Al2O3–SiO2–MgO–CaS composite inclusions. After Si–Al additions in vacuum degassing, typical inclusions were spinel or Al2O3. After Ca–Si additions during ladle treatment, typical inclusions were liquid or dual-phase Al2O3–CaO–SiO2–MgO. During the solidification process, due to the segregation of S and the decrease in solubility, the typical inclusions in the final casting became Al2O3–CaO–SiO2–MgO–CaS. For optimal fatigue performance of stainless steel castings, slag and refractory composition control were also necessary because the [Mg] contents mainly come from the slag and lining.

Alkali-Activated Stainless Steel Slag as a Cementitious Material in the Manufacture of Self-Compacting Concrete.

This work develops the manufacture of self-compacting concrete (SCC) with 50% cement reduction. As an alternative binder to cement, the viability of using an alkali-activated combination of stainless steel slag (SSS) and fly ash (FA) has been demonstrated. SSS was processed applying three different treatments. Binders were manufactured mixing 35% SSS with 65% FA, as precursors, and a hydroxide activating solution. This binder was replaced by the 50% cement for the manufacture of SCC. The results obtained show good mechanical properties and durability. The study shows a reduction in the use of cement in the manufacture of SCC reusing two wastes.

Carbstone Pavers: A Sustainable Solution for the Urban Environment

To reduce CO2 emissions from the building industry, one option is to replace cement in specific applications with alternative binders. The Carbstone technology is based on the reaction of calcium- and magnesium-containing minerals with CO2 to form carbonate binders. Mixes of carbon steel slag and stainless-steel slag, with tailored particle size distributions, were compacted with a vibro-press and subsequently carbonated in an autoclave to produce carbonated steel slag pavers. The carbonated materials sequester 100–150 g CO2/kg slag. Compressive and tensile splitting strength of the resulting pavers were determined, and the ratio was found to be comparable to that of concrete. The environmental performance of the Carbstone pavers, with an average tensile splitting strength of 3.6 MPa, was found to be in compliance with Belgian and Dutch leaching limit values for construction materials. In addition, leaching results for a concrete mix made with aggregates of crushed Carbstone pavers (simulating the so-called “second life” of pavers) demonstrate that the pavers can be recycled as aggregates in cement-bound products after their product lifetime.

Performance of Self-compacting Concrete with Stainless Steel Slag Versus Fly Ash as Fillers: A Comparative Study

Recently, stainless steel slag -a byproduct of manufacturing stainless steel is accepted as a cementitious material, the chemical characteristics of which are highly variant. This study reuses two types of stainless steel reducing slag with specific surface area of 1766 cm2/g (S1) and 7970 cm2/g (S2) in developing self-compacting concrete (SCC). Particularly, two S2-blended SCCs incorporating with S1 and fly ash as fillers (calling as S-mix and F-mix) were prepared for a comparative investigation. In both SCCs, ordinary Portland cement was replaced by S2 with various ratios (from 0 % to 50 %, increment 10 %). Testing results show that in fresh state, the F-mix exhibits higher workability and longer initial setting time than those of S-mix. In hardened state, 10 % compressive strength loss was realized as increasing S2 content up to 30 % in the both SCCs; the strength of F-mix is up to 1.9 times of S-mix at the same rate of S2 replacement. Water absorption of the F-mix was below 3 %, suggested as a “good” quality concrete; whilst the S-mix could be longs to an “average” one. Resistivity and sulfate resistance of F-mix are considerably higher than those of S-mix. Moreover, based on the obtained data, compressive strength and electrical resistivity are correlated well with a logarithmic form.

Luženje in mineraloška kontrola kroma v žlindri nerjavnega jekla iz elektroobločne peči

This study focuses on evaluating the leachability of chromium in Electric-Arc-Furnace stainless-steel slag (EAFS) from the perspective of mineralogical control. Mineral-phase identification results showed that EAFS mainly comprised merwinite, magnetite, dicalcium silicate, calcium aluminosilicate, eskolaite, spinel, and perovskite. The chromium in the EAFS was mainly present in the Mg-Cr spinel, Fe-Cr alloy, or distributed in the form of oxide in the matrix phase, merwinite. When undergoing leaching, the leachate of the EAFS was alkaline and reducing, and a portion of the chromium in the slag was released into the leachate and existed mainly in a trivalent state. In the early stage of leaching, the rapid dissolution of chromium-bearing silicate minerals led to a rapid increase in the concentration of trivalent chromium. However, in the middle and late stages (> 15 days) of leaching, the chromium concentration reached stable values. The geochemical model of chromium leaching from the EAFS demonstrated that the simulated values of the chromium concentration were consistent with the batch-leaching test values. The primary phase Cr2O3 in the EAFS controlled the chromium concentration in the leachate. After entering the leachate, trivalent chromium could be presented as Cr(OH)4– because Cr(III)-hydroxide was unstable in the alkaline leachate.

Alkali Activation of Metallurgical Slags: Reactivity, Chemical Behavior, and Environmental Assessment.

Alkali-activated materials (AAMs) represent a promising alternative to conventional building materials and ceramics. Being produced in large amounts as aluminosilicate-rich secondary products, such as slags, they can be utilized for the formulation of AAMs. Slags are partially crystalline metallurgical residues produced during the high temperature separation of metallic and non-metallic materials in the steelmaking processes. In the present study, the electric arc furnace carbon or stainless steel slag (EAF) and secondary metallurgical slag such as ladle furnace basic slag (LS) were used as precursors in an alkali-activation process. EAF slag, with its amorphous fraction of about 56%, presented higher contents of soluble Si and Al species with respect to ladle slag R (35%). However, both are suitable to produce AAM. The leaching behavior shows that all the release values are below the regulation limit. All the bivalent ions (Ba, Cd, Cu, Ni, Pb, and Zn) are well immobilized in a geopolymeric matrix, while amphoteric elements, such as As and Cr, show a slight increase of release with respect to the corresponding slag in alkaline and aqueous environments. In particular, for Sb and As of AAM, release still remains below the regulation limits, while Mo presents an increase of leaching values that slightly exceeds the limit for landfill non-dangerous waste.

High-capacity adsorbents from stainless steel slag for the control of dye pollutants in water

Adsorbent materials for the control of dye pollutants in water were synthetized from stainless steel slag (SSS) using different acid-base treatments. Using HCl (SS-Cl) and HNO3 (SS-NO3) produced high-capacity adsorbents, with BET areas of 232 m2/g and 110 m2/g respectively. Specifically, the SS-Cl had a structure of amorphous silica sponge. Treatment with H2SO4 (SS-SO4) did not enhance the adsorption capabilities with respect to the raw sample (SSS). Activated carbon (AC) was also tested as reference. The materials were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), N2 adsorption-desorption isotherms, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) zeta potential, and infrared spectroscopy (FTIR). Batch adsorption experiments with methylene blue (MB) showed that the maximum sorption capacities were 9.35 mg/g and 8.97 mg/g for SS-Cl and SS-NO3 at 240 h, respectively. These values, even at slower rate, were close to the adsorption capacity of the AC (9.72 mg/g). This behavior has been attributed to the high porosity in the range of nanopores (0.6–300 nm) and the high-surface area for both samples. Preferential involvement of certain functional groups in the adsorption of dye ions on their surface indicative of chemisorption has been found. Although optimization, repeatability, and reproducibility of the process and environmental assessment have to be done before practical applications, these preliminary results indicate that application of these cost-effective adsorbents from raw SSS may be used in water pollution treatment and contribute to the sustainable development of the steel manufacturing industry.

Assessing the long term effects on climate change of metallurgical slags valorization as construction material: a comparison between static and dynamic global warming impacts

<abstract> <p>The interest in circular economy for the construction sector is constantly increasing, and Global Warming Potential (GWP) is often used to assess the carbon footprint of buildings and building materials. However, GWP presents some methodological challenges when assessing the environmental impacts of construction materials. Due to the long life of construction materials, GWP calculation should take into consideration also time-related aspects. However, in the current GWP, any temporal information is lost, making traditional static GWP better suited for retrospective assessment rather than forecasting purposes. Building on this need, this study uses a time-dependent GWP to assess the carbon footprint of two newly developed construction materials, produced through the recycling of industrial residues (stainless steel slag and industrial goethite). The results for both materials are further compared with the results of traditional ordinary Portland cement (OPC) based concrete, presenting similar characteristics. The results of the dynamic GWP (D_GWP) are also compared to the results of traditional static GWP (S_GWP), to see how the methodological development of D_GWP may influence the final environmental evaluation for construction materials. The results show the criticality of the recycling processes, especially in the case of goethite valorization. The analysis shows also that, although the D_GWP did not result in a shift in the ranking between the three materials compared with S_GWP, it provides a clearer picture of emission flows and their effect on climate change over time.</p> </abstract>

Stainless-Steel Slag Residue for Fabrication of Cost-Effective Ceramic Membranes

Stainless-Steel Slag Residue for Fabrication of Cost-Effective Ceramic Membranes

Understanding the solidification and leaching behavior of synthesized Cr-containing stainless steel slags with varying Al2O3/SiO2 mass ratios

This study investigated the effect of Al2O3/SiO2 mass ratios on the equilibrium crystallization behavior of synthesized CaO–SiO2–MgO–Al2O3–Cr2O3 stainless steel slags to understand the selective concentration behavior of Cr into a primary Mg(Cr,Al)2O4 spinel phase during slag solidification and to determine the leaching stability of Cr-containing slags. The spinel solid solution was precipitated within the temperature range of 1600-1400 °C, where the Cr/(Cr+Al) mole ratio in the Mg(Cr,Al)2O4 spinel phase gradually decreased for slags with higher Al2O3/SiO2 mass ratios. When the Al2O3/SiO2 mass ratio increased from 0.125 to 0.5, the Cr content in the amorphous glass phase gradually decreased, with a subsequent increase in the Cr content in the crystalline phase. For slags with a unit Al2O3/SiO2 mass ratio and MgO mole percent comprising less than the combined sum of the Cr2O3 and Al2O3 mole percents, the Cr content in the amorphous glass phase increased, which was correlated with the enhanced substitution of Cr3+ with Al3+ in the spinel. The trend of the amount of Cr-related ions in the leachate was consistent with the trend of Cr in the amorphous glass phase: the amount decreased for slags with Al2O3/SiO2 mass ratios from 0.125 to 5 and then increased for slags with an Al2O3/SiO2 mass ratio of 1. The results suggest that the addition of appropriate amounts of Al2O3 to stainless steel slags could be conducive to stabilizing Cr into the primary spinel phase to minimize Cr leaching into the environment.

Recovery of Chromium from Slags Leachates by Electrocoagulation and Solid Product Characterization

Slags produced in the steelmaking industry could be a source of chromium. Slags contain, depending on different types of slags, between 2 to 5 wt.% of Cr. Roasting of slag with NaOH, followed by subsequent leaching can produce leachates which can be efficiently processed using electrocoagulation (EC). This paper provides results from the EC process optimization for Cr(VI) solutions with initial concentration 1000 mg/L of Cr(VI). Influence of pH, current intensity and NaCl concentration on the efficiency of chromium recovery, energy consumption as well as solid product composition is discussed in detail. Optimum of pH = 6 was chosen for EC processing of Cr leachates as well as current intensities of 0.1–0.5 A because of the higher Cr/Fe ratio in solid product compared to higher current intensities. Results of EC processing of four real leachates of electric arc furnace carbon steel slag (EAFC), electric arc furnace stainless steel slag (EAFS), low carbon ferrochrome slag (LC FeCr) and high carbon ferrochrome slag (HC FeCr) were evaluated. Comparison of the results of four real leachate samples is presented. Obtained final solid product was identified as (Fe0.6 Cr0.4)2O3 and with up to 20% of Cr could be used as source of chromium in the ferrochrome production.

Up-Concentration of Chromium in Stainless Steel Slag and Ferrochromium Slags by Magnetic and Gravity Separation

Slags coming from stainless steel (SS) and ferrochromium (FeCr) production generally contain between 1 and 10% Cr, mostly present in entrapped metallic particles (Fe–Cr alloys) and in spinel structures. To recover Cr from these slags, magnetic and gravity separation techniques were tested for up-concentrating Cr in a fraction for further processing. In case of SS slag and low carbon (LC) FeCr slag a wet high intensity magnetic separation can up-concentrate Cr in the SS slag (fraction <150 µm) from 2.3 wt.% to almost 9 wt.% with a yield of 7 wt.%, and in the LC FeCr slag from 3.1 wt.% to 11 wt.% with a yield of 3 wt.%. Different behavior of Cr-containing spinel’s in the two slag types observed during magnetic separation can be explained by the presence or absence of Fe in the lattice of the Cr-containing spinel’s, which affects their magnetic susceptibility. The Cr content of the concentrates is low compared to chromium ores, indicating that additional processing steps are necessary for a recovery process. In the case of high carbon (HC) FeCr slag, a Cr up-concentration by a factor of more than three (from 9 wt.% to 28 wt.%) can be achieved on the as received slag, after a single dry low intensity magnetic separation step, due to the well-liberated Cr-rich compounds present in this slag. After gravity separation of the HC FeCr slag, a fraction with a Cr content close to high grade Cr ores (≥50% Cr2O3) can be obtained. This fraction represents 12 wt.% of the HC FeCr slag, and can probably be used directly in traditional smelting processes.

Selective Extraction of Chromium from EAF Stainless Steel Slag by Pressurized Oxidation in a NaOH Solution

Chromium was selectively extracted from electric arc furnace (EAF) slag by pressurized oxidation in a NaOH solution. The effect of the temperature (T), NaOH concentration, oxygen pressure and reaction time on the extraction ratio of the chromium was investigated. It was found that the chromium extraction rate was significantly impacted by the temperature. At the optimum conditions of T = 170°C, NaOH concentration of 40 wt.%, oxygen pressure of 1.6 MPa and reaction time of 4 h, a maximum chromium extraction rate of 60.04% was obtained. It was observed by scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS) that the residual particles were enclosed by a “secondary precipitation layer” mainly composed of Fe and O, which prevented further extraction of the chromium from the core residues. The leaching process of chromium was controlled by the diffusion of the solid phase product layer, and the activation energy of the extraction reaction was 56.67 kJ/mol.