A lot of slag was produced by ancient production processes such as smelting, melting, and refining. Iron slag has information that can be used to determine the characteristics of the site, the ...iron-making process and manufacturing date, but there is a limit to reading information through visual observation and nondestructive analysis. Various slag terms have been used depending on the location and characteristics, but it is necessary to use terms that have exact meaning and unity. Although many scientific analyses have been supplemented by archaeological theses, the iron-making trends of each period have not yet been systematically proven. This study reviewed the type of iron-making process used for 100 ancient slags. The slags were analyzed by XRF, revealing when it was formed and some of the detailed processes. XRD analysis was used to define and classify Tap slag, Bloom slag, and Ceramic-rich slag as relative concepts. From the Three Kingdoms Period to the Joseon Dynasty, the amount of temperature variation in the iron-making furnace decreased and the GAS reaction became uniform. It was observed that the amount of iron oxide remaining decreased and the proportion of ceramic-rich slag increased. The change in iron oxide content kept decreasing while the levels of refining, smelting, and melting were maintained, in that order. The results confirmed that advances in ancient iron-making technology can be interpreted based on a comparative review of the relative changes in iron oxide and silicon oxide content in slag.
(Received 23 August, 2022; Accepted 28 December, 2022)
Chemical Looping Gasification (CLG) is a dual fluidized bed gasification technique where an oxygen carrier is used as bed material instead of sand. An optimized process could have several advantages, ...including i) one concentrated CO2 stream, amiable for carbon capture, ii) less tar formation, iii) additional reaction pathways for syngas production, iv) less corrosion and v) CO2 is generated in one stream from the fuel reactor that could be captured.
Steel converter slag, also called LD slag, is a by-product from the steel industry which, besides iron, contains significant fractions of Ca, Mg, Al and Mn in a complex matrix of phases. The low cost and presence of known catalytic solid phases in the slag makes it interesting as an oxygen carrier in CLG.
In this work, LD slag was investigated using a batch reactor with gaseous and solid fuel as well as with TGA. It was found that during gasification with LD slag, the material can i) transfer oxygen to the fuel, ii) catalyze the water-gas-shift reaction, iii) react with CO2 forming carbonates and iv) split water to hydrogen. The overall result was a raw gas with a higher H2/CO ratio for LD slag than the other tested materials.
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•LD slag successfully transported oxygen to achieve partial oxidation.•Higher char conversion rate was achieved with LD slag compared to sand and olivine.•LD slag may generate syngas with high H2/CO ratio via gasification of biochar.•H2 generation by water splitting was indicated with reduced LD slag.•LD slag catalyze the water-gas-shift reaction.
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•Recycling environmentally hazardous SPW into industry raw material.•Removing the oxide layer of SPW by economically-attractive vacuum sintering.•Na3AlF6-enhanced slag refining ...exhibited a larger reaction interface.•A smoother remove pathway of BO33- was created.•The removal rate of impurity boron has increased by 40.92%.
Recycling of environmentally hazardous silicon powder waste (SPW) is conducive to achieving “carbon neutrality”. However, the high-cost and low-efficiency impurity removal limit the industrial recovery of SPW. Herein, a combination strategy of vacuum sintering and Na3AlF6-enhanced slag refining is demonstrated to upgrade the traditional recycling process. The cost-effective vacuum sintering can remove 89.44% of oxygen in silicon waste, indicating that the oxide layer of SPW is removed effectively. In the Na3AlF6-enhanced CaO–SiO2 slag, the optimal Na3AlF6 content and CaO/SiO2 mass ratio are set to 20 wt% and 1.6 based on thermodynamic simulation. Na3AlF6 reduces the liquidus temperature and increases the interfacial tension of the slag system. Moreover, in Na3AlF6-containing slag, the diffusion pathway of BO33- is dredged. As a result, the silicon-slag interface is adjusted from a half-spherical to a cylindrical surface, and the interface area has increased by 14.69%. The boron removal rate by Na3AlF6-strengthened slag refining is 40.92% faster than that of traditional slag. This work improves the removal efficiency of key impurity boron, reducing the cost of SPW recovery. Based on economic evaluation, this strategy offers a commercially available way to achieve the high-value recycling of silicon waste.
This study aims to provide a better understanding of the autogenous shrinkage of slag and fly ash-based alkali-activated materials (AAMs) cured at ambient temperature. The main reaction products in ...AAMs pastes are C-A-S-H type gel and the reaction rate decreases when slag is partially replaced by fly ash. Due to the chemical shrinkage and the fine pore structure of AAMs pastes, drastic drop of internal relative humidity is observed and large pore pressure is generated. The pore pressure induces not only elastic deformation but also a large creep of the paste. Besides the pore pressure, other driving forces, like the reduction of steric-hydration force due to the consumption of ions, also cause a certain amount of shrinkage, especially in the acceleration period. Based on the mechanisms revealed, a computational model is proposed to estimate the autogenous shrinkage of AAMs. The calculated autogenous shrinkage matches well with the measured results.
•High performance alkali activated slag concrete mixes were developed more effectively using the industrial wastes.•Higher rheological and mechanical properties were achieved for all the HPAASC mixes ...developed here in.•The statistical analysed results showed a very good predictive capabilities for all the mechanical properties tested herein.•Microstructural studies also showed a densified morphology for all the HPAASC mixes.
In the present study, development of a class of High Performance Alkali Activated Slag Concrete mixes (hereafter referred to as HPAASC mixes) is discussed. These mixes are developed using three industrial wastes from Iron and Steel industry. While Ground granulated blast furnace slag (GGBFS) was used as the main binder, in the development of these HPAASC mixes, steel slag sand and Electric Arc Furnace slag (EAF slag) have been employed in the fine aggregate and coarse aggregate fractions of them. Higher flow characteristics, as those of self-compacting concrete mixes, as well as enhanced mechanical strength properties of these mixes are discussed in detail. The alkaline solutions used consist mixtures of sodium hydroxide and sodium silicate solutions, with a constant activator modulus (ratio of SiO2/Na2O) of one maintained in them. Taguchi’ design of experiments methodology was used to reduce the experimental efforts.
The formulation of all the mixes developed herein was based on Taguchi’s L-9 orthogonal array. Flow and strength properties of a set of nine mixes were used for performance evaluation purposes in an initial, calibration phase. Strength prediction equations were derived based on such results, the predictive capability of which were then assessed and ascertained with actual results of experiments on the next six new mixes, in the prediction phase. Test results indicated a higher flowability values for all the mixes (with slump flows greater than 700 mm), good filling and passing abilities, all satisfying the EFNARC (European Federation of Specialist Construction Chemicals and Concrete Systems) recommendations for SCC mixes. Higher compressive strengths (65–90 MPa), split-tensile strengths (4.8–5.3 MPa), flexural strengths (6.5–7 MPa), and Modulus of Elasticity (30.4–36.2 GPa) were observed along with lower water absorption values (2.1–2.7%) for all the HPAASC mixes tested herein. Microstructure studies were conducted on samples from the fractured surfaces of test specimens from different mixes, using advanced SEM, EDX and XRD analyses and the results are discussed.
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•CO2 sequestration potential of steel slag under aqueous medium without the usage of any additive chemicals.•Formation of residue and product layers on the surface of slag ...particles.•Stabilization of steel slags by carbonation process.•Determining the impact of carbonation of slag on environment.
This study strives to achieve a substantial amount of steel slag carbonation without using any harmful chemicals. For this purpose, experiments were performed in an aqueous medium, in a semi-batch reactor, to investigate the effect of varying reaction conditions during the steel slag CO2 sequestration process. Further, studying the effect of dissolution on carbonation reactions and the mineralogical changes that subsequently occur within the slag helps provide insight into the parameters that ultimately have an impact on the carbonation rate as well the magnitude of the impact.
•Response surface methodology (RSM) is used to study ASC’s freeze–thaw resistance.•The influence on the freeze–thaw resistance from high to low is A/S, slag content and sand ratio.•The interaction of ...A/S and slag content is the most prominent.•Air-void structure is a decisive factor, and space coefficient and specific surface area are related well to DF.
Alkali–slag concrete (ASC), with the frost resistant grade of above F300 and frost resistant coefficient DF of about 90%, is prepared using slag and composite activator composed of Na2SiO3 and NaOH. Response surface methodology (RSM) is applied to study the freeze–thaw resistance of ASC. The effects of activator solution–slag ratio (A/S), slag content and sand ratio on the freeze–thaw resistance are analyzed using the softwares of Design Expert and Box-Benhnken Design (BBD). Models are established for DF and the influence of air-void structure of hard concrete on the freeze–thaw resistance, respectively. The result shows that the DF model coincides well with the test results and can be used to analyze and predict the freeze–thaw resistance of ASC. The influence on the freeze–thaw resistance from high to low is A/S, slag content and sand ratio. The interaction of A/S and slag content is the most prominent and air-void structure is the crucial factor. The air bubble space coefficient and its specific surface area have good correlation with DF. The freeze–thaw resistance tends to better with smaller air bubble space coefficient and bigger specific surface area.
•EAF and AOD slag aggregates are more dense but more porous than natural aggregates.•Very few mineral phases can show expansive reaction in EAF and AOD slag aggregates.•The use of EAF and AOD slag ...aggregates improves concrete mechanical properties.•Concretes made of EAF and AOD slag aggregates show a slightly but limited expansion.
The aim of this study is to investigate the opportunity using EAF and AOD slags aggregates in concrete. First, physicochemical and mineralogical properties of these stainless steel slag aggregates are determined. Second, the silico-calcareous aggregates of reference concretes are replaced by each of these steel slag aggregates in different proportions. The results show a slight improvement of the mechanical properties for concretes made of stainless steel slag aggregates. The use of EAF and AOD slag aggregates can slightly decrease concrete durability-related properties and increase linear expansion. But these characteristics fit the standards requested for construction use.
Portland cement tends to exhibit negative environmental impacts; thus, it is required to find measures that will improve its green credentials. In this study, we report a blended Portland slag cement ...as an alternative environmentally-friendly building material in order to reduce the total carbon footprint resulted from the production of the ordinary Portland cement (OPC), which may resolve the environmental issues associated with carbon dioxide emissions. The ordinary Portland cement type I enhanced by basic oxygen steelmaking slag (BOF) is produced and casted into cubic and beam-like samples for the compressive and three-point bending tests, and the compressive and flexural strengths are experimentally measured. Numerical simulations are conducted to compare with the experimental result and satisfactory agreements are obtained. X-ray diffraction (XRD) investigations and porosity tests are then carried out using the semi-adiabatic calorimetry, which indicates that 5% BOF is the optimal ratio to accelerate the hydration process while increasing the amount of hydration products, especially at the early curing age of 3 days. Scanning electron microscope (SEM) images further indicate that BOF can be used to prevent the development of microcracks while mitigating their propagation within cement mortar. Our study indicates that the compressive strength of OPC can be critically increased by BOF at the relatively low concentrations of 5%. The blended slag cement reported in this paper provides advanced understanding on the green building material that uses byproduct wastes for the mechanical and electrical performance.
Copper in discarded slag decreases the profits and copper recovery during the pyrometallurgical extraction processes. The copper losses to slag can be reduced by using a settling furnace, in which ...mechanically entrained copper droplets separate from the slag under the action of gravity. The settling rate of entrained droplets can be increased by modifying the slag composition and, thus, the slag properties, which are known to influence the settling rate. The knowledge of industrial CaO slag modification in a reduced iron silicate slag with a Fe/SiO2 ratio close to unity is limited. An industrial trial was thus conducted in an electric settling furnace, where the slag had been pretreated in a fuming furnace, to investigate the effect of CaO slag modification on the final slag copper content. Slag samples were collected from the ingoing and outgoing slag and from within the furnace of batches modified with CaO up to about 16 wt %. The trial was evaluated by comparing the final slag copper content and the copper recovery in the settling furnace. The results indicate that the settling becomes more efficient with the CaO modification as the final slag copper content decreased with increasing CaO content.
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