Characterization of a Chromium-Bearing Carbon Steel Electric Arc Furnace Slag after Magnetic Separation to Determine the Potential for Iron and Chromium Recovery

This study investigates the potential to recover iron and chromium from a chromium-bearing carbon steel Electric Arc Furnace (EAF) slag. This slag contains indeed about 30 wt.% Fe and 2.5 wt.% Cr. However, the minerals are intergrown at small scale (<100 µm) and iron and chromium are mostly contained in spinel phases which makes the separation challenging. Several methods including Mössbauer spectroscopy, X-ray Diffraction, Scanning Electron Microscopy (SEM) and electron microprobe analysis were used in order to fully characterize the products obtained after a low-intensity magnetic separation of this carbon steel EAF slag, with the objective to define a pre-treatment process allowing the recovery of iron-rich particles and of a chromium-upgraded fraction. The results show that even if the magnetic separation seems to be not efficient in a first approach for producing an iron-rich/chromium-poor fraction, this fraction can be obtained by adding an attrition step which means that some separation mechanisms still occurred during the magnetic separation. However, it was not possible to produce a chromium-rich fraction. The main bottleneck for reaching a good separation is most probably the very fine liberation size of the iron and chromium bearing minerals.

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%.

Effect of Different CO2 Treatments on the Metal Leaching in Steel Slag Binders

Carbonation is an effective method to promote the quality of the steel slag binder. In this article, two carbonation approaches, namely hot-stage carbonation and accelerated carbonation, were employed to leach the metals, and the influence mechanism on the metal sequential leachability of the binders composed of 80 wt% of EAF slag incorporating 20 wt% of Portland cement (PC) was revealed. The carbonate products, microstructures, and chemical states were investigated, and the results indicated that chromium, vanadium, and titanium gradually transformed into inactive phases after two carbonation approaches, while zinc appeared the opposite trend. The sequential leachability of chromium declined with the increase of the carbonation efficiency, in which the exchangeable chromium decreased from 1.99 mg/kg in the A2A binder to below the detection limit in the A2C binder and C2C binder. Hot-stage carbonation treatment facilitated particle agglomeration, minerals remodeling, and calcite formation. The carbonation curing of the steel slag paste resulted in the formation of amorphous CaCO3, calcite crystalline and Si-bearing hydrates that covered the pores of the matrix, and silicate structure with a higher disorder. The hot-stage carbonation and accelerated carbonation curing methods were adopted to jointly prevent the leaching of harmful metals and facilitate promising high-volume steel slag-based binders with structural densification and CO2 storage.

Utilization of Industrial Byproducts for Enhancing the Properties of Cement Mortars at Elevated Temperatures

The research on industrial byproducts, such as slags and fly ash, was intense during the last decades in the building sector. Apart from the environmental benefits coming from their exploitation, their application may lead to the production of cost effective and durable building materials, such as mortars and concrete. The impact of industrial byproducts on the resistance of materials to fire and elevated temperatures was assessed by many scientists, however, it is still an open field of research. In this study, locally available byproducts were investigated, including High Calcium Fly Ash (HCFA), coming from lignite-fired power plants, as well as Ladle Furnace Steel (LFS) slag and Electric Arc Furnace (EAF) slag aggregates, originating from the steel making industry. Six mortar compositions were manufactured with substitution of Ordinary Portland Cement (OPC) with HCFA and LFS slag (20% w/w) and of natural aggregates with EAF slag (50% w/w). At the age of 7, 28, and 90 days, the physico-mechanical properties of the specimens were recorded, while they were further exposed at elevated temperatures, concerning 200 °C, 400 °C, 600 °C, 800 °C, and 1000 °C. After each exposure, their physico-mechanical and microstructure characteristics were identified. From the evaluation of the results, it was asserted that HCFA and EAF slag aggregates enhanced the overall performance of mortars, especially up to 600 °C. LFS was beneficial only in combination with EAF slag aggregates.

Mechanical Properties of Coarse Aggregate Electric Arc Furnace Slag in Cement Concrete

The feasibility of using EAF slag aggregate, fly ash, and silica fume in pavement Electric Arc Furnace Slag Concrete (CEAFS) is the focus of this research. EAF slag aggregate is volume stable and suitable for use in concrete, according to the findings of the testing. EAF slag was utilized to replace natural coarse aggregates in the CEAFS mixes. CEAFS was created by blending 50% crushed stone with 50% EAF slag in coarse aggregates, with fly ash (FA) and silica fume (SF) partially replacing cement at content levels (i.e. FA: 0, 20, 30, and 40%; SF: 0, 5, and 10%). The soil compaction approach was used to evaluate the optimal moisture level for CEAFS mixes containing EAF slag aggregate fly ash and silica fume. A testing program was used to investigate the weight of CEAFS units and their mechanical qualities (compressive strength, flexural strength, and elastic modulus). As a result, the fresh and hardened unit weights in the CEAFS are comparable. Moreover, variations in the concentration of mineral additives FA and SF in adhesives, as well as the CEAFS mixed aggregate ratio, have an impact on compressive strength, flexural strength, and elastic modulus at all ages. However, combining EAF slag aggregate with (FA0% +SF10%; FA10% +SF0%; FA10% +SF10%; and FA20% +SF10%) the CEAFS mixtures have improved mechanical characteristics over time. According to this study, CEAFS pavements can be made with EAF slag aggregate fly ash and silica fume. In addition, a formula correlation was suggested to compute CEAFS (i.e. compressive strength with elastic modulus and compressive strength with flexural strength). Doi: 10.28991/cej-2021-03091755 Full Text: PDF

Innovative Reuse of Electric Arc Furnace Slag as Filler for Different Polymer Matrixes

The European steel industry produces about 70 million tons/year of steel by the electric arc furnace (EAF). The slag consists of about 15% by weight of the produced steel, thus from the perspective of the circular economy, it has a high potential as a co-product. This research aims to assess an innovative reuse of EAF slag as filler in different polymer matrixes: thermoplastic (polypropylene), thermosetting (epoxy resin), elastomeric (nitrile butadiene rubber), and recycled end of life rubber tire. A comparison between neat polymer and polymer filled with a certain amount of EAF slag has been carried out by tensile (or flexural), compression, and hardness tests. Experimental results show that slag as a filler increases the composites’ hardness and elastic modulus at the expense of toughness. For a safe reuse of the slag, the leaching of hazardous elements must comply with current legislation. It was found that, although the used EAF slag releases small amounts of Cr, Mo, and V, incorporating it into a polymer matrix reduces the leaching. The EAF slag particles distribution has been observed by scanning electron microscopy (SEM) images. The obtained results show good technical feasibility of this innovative slag application so that it could pave the way to a new industrial symbiosis between dissimilar sectors, bringing economic and environmental benefits.

Application of General Full Factorial Statistical Experimental Design’s Approach for the Development of Sustainable Clay-Based Ceramics Incorporated with Malaysia’s Electric Arc Furnace Steel Slag Waste

This study aims to optimize the composition (body formulation) and firing temperature of sustainable ceramic clay-based ceramics incorporated with electric arc furnace (EAF) steel slag waste using general full factorial design (GFFD). The optimization is necessary to minimize drawbacks of high iron oxide’s fluxing agent (originated from electric arc furnace, EAF steel slag waste), which led to severe surface defects and high closed porosity issue of the ceramics. Statistical analysis of GFFD including model adequacy checking, analysis of variance (ANOVA), interaction plots, regression model, contour plot and response optimizer were conducted in the study. The responses (final properties of ceramics) investigated were firing shrinkage, water absorption, apparent porosity, bulk density and modulus of rupture (MOR). Meanwhile, the factors employed in experimental parameters were weight percentage (wt.%) of EAF slag added and firing temperature. Upon statistical analysis, GFFD has deduced that wt.% amount of EAF slag added and firing temperatures are proven to significantly influence the final properties of the clay-based ceramic incorporated with EAF slag. The results of conducted statistical analysis were also highly significant and proven valid for the ceramics. Optimized properties (maximum MOR, minimum water absorption and apparent porosity) of the ceramic were attained at 50 wt.% of EAF slag added and firing temperature of 1180 °C.