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.
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.
•Three slags, electric arc furnace, blast furnace, and copper, were used as asphalt modifiers.•The performance of the slag-modified asphalts was characterized via physical and rheological tests.•The ...addition of the slags improved the short-term asphalt aging properties.•Rheological test results showed an enhancement in permanent deformation resistance of slag-modified asphalts.
Metallurgical slags are residues that are obtained in the manufacturing and smelting processes of metals, such as steel and copper. However, their use is limited because they may cause environmental problems at their disposal sites. This study aims to evaluate the effects of the addition of slag on the properties of slag-modified asphalts using three different slag proportions (3, 6, and 10% by weight of asphalt). Electric arc furnace slag, blast furnace slag, and copper slag were used to evaluate the effects of the addition of slag on their performance properties via physical and rheological tests. The results showed an improvement in the consistency of the slag-modified asphalts, decreasing the penetration rate and increasing the softening point. An enhancement in the short-term asphalt aging characteristics was also observed with the addition of slag. Finally, the rheological test results revealed an improvement in the resistance to permanent deformation with the addition of slag in neat asphalt, whereas no statistically significant results were observed when the slag content was increased.
Slags from the nonferrous metals industry have great potential to be used as feedstocks for the production of alkali‐activated materials. Until now, however, only very limited information has been ...available about the structural characteristics of these materials. In the work presented herein, synthetic slags in the CaO–FeOx–SiO2 system, representing typical compositions of Fe‐rich slags, and inorganic polymers (IPs) produced from the synthetic slags by activation with alkali silicate solutions have been studied by means of X‐ray absorption near‐edge structure (XANES) spectroscopy at the Fe K‐edge. The iron in the slags was largely Fe2+, with an average coordination number of approximately 5 for the iron in the amorphous fraction. The increase in average oxidation number after alkali‐activation was conceptualized as the consequence of slag dissolution and IP precipitation, and employed to calculate the degrees of reaction of the slags. The degree of reaction of the slags increased with increasing amorphous fraction. The iron in the IPs had an average coordination number of approximately 5; thus, IPs produced from the Fe‐rich slags studied here are not Fe‐analogs of aluminosilicate geopolymers, but differ significantly in terms of structure from the latter.
•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.
To solve heavy metals leaching problem in the utilization of various industrial solid wastes, this work investigated the heavy metals immobilization of ternary geopolymer prepared by nickel slag ...(NS), lithium slag (LS), and metakaolin (MK). Compressive strength was measured to determine the optimum and appropriate mix proportions. The leaching characteristics of typical heavy metals (Cu (Ⅱ), Pb (Ⅱ), and Cr (Ⅲ)) in acid, alkali, and salt environments were revealed by Inductively Coupled Plasma (ICP). The heavy metals immobilization mechanism was explored by Mercury Intrusion Porosimetry (MIP), X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and Scanning Electron Microscopy (SEM) tests. The experimental results show that the group with a mass ratio of NS, LS and MK of 1:1:8 exhibits the highest compressive strength, which reaches 69.1 MPa at 28 d. The ternary geopolymer possesses a desirable capacity for immobilizing inherent heavy metals, where the immobilization rates of Cu and Pb reach 96.69 %, and that of Cr reaches 99.97 %. The leaching concentrations of Cr and Pb increase when the samples are exposed to acidic and alkaline environments. Cu and Pb are mainly physically encapsulated in geopolymer. Additionally, immobilization of Cr mainly involves physical encapsulation and chemical bonding.
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•Using multiple industrial solid wastes as precursors to prepare ternary geopolymer.•28-day immobilization rates achieve 96.69 % for Cu and Pb and 99.97 % for Cr.•Compressive strength of the geopolymer with 2.0 wt % Cr decreases by 96.5 % at 28 d.•Acid, alkali, and salt environments exposure for ternary geopolymer.•Immobilization of Cr involves physically encapsulated and chemically bonded.
•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.
•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.
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