Search

The submerged arc welding (SAW) process is complex because multi-phase reactions occur simultaneously across a large temperature interval from 2500 °C in the arc cavity, down to the weld pool liquidus temperare at the slag-weld pool interface. This complexity hinders research on specific process metallurgy aspects, such as gas formation from the oxy-fluoride slag. The main objective of this work is to illustrate a low temperature experimental technique as an accurate reaction simulation experiment of SAW flux oxy-fluoride slag behaviour in terms of gas formation and metal powder assimilation reaction mechanisms as observed in the SAW process. The oxy-fluoride slag behaviour was confirmed by identification and analyses of nano-strand formation in the reacted slag formed from the reaction of welding flux with Al-Fe-Cr metal powders at 1350 °C. The observed nano-strand formation agrees with similar observations in SAW post-weld slags used to confirm of oxy-fluoride vaporisation and re-condensation. Element distribution from energy dispersive X-ray spectroscopy (EDS) maps and thermochemical calculations were used to gain insights into the reactions in nano-strand formation. The nano-strands contained chromium patches and spots of less than 1 μm in scale, confirming that added Cr metal powder assimilated via the gas phase. Cr-fluoride formed part of the oxy-fluoride slag and likely formed Cr-fluoride gas. Cr was recovered via re-condensation of Cr vapour formed from the reaction of Cr-fluoride with Al gas. This work presents an accurate low temperature simulation method of gas formation and metal powder assimilation reactions in oxy-fluoride slags as in the SAW process.

Abstract In order to alleviate environmental problems and reduce CO2 emissions, geopolymers had drew attention as a kind of alkali-activated materials. Geopolymers are easier access to raw materials, green and environment friendly than traditional cement industry. Its special reaction mechanism and gel structure show excellent characteristics such as quick hardening, high strength, acid and alkali resistance. In this paper, geopolymer pastes were made with metakaolin (MK) and ground granulated blast furnace slag (GGBFS) as precursors. The effects of liquid–solid ratio (L/S) and modulus of sodium silicate (Ms) on the performances of MK-GGBFS based geopolymer paste (MSGP) were characterized by workability, strength and microstructural tests. The regression equations were obtained by central composite design method to optimize the mix design of MSGP. The goodness of fit of all the equations were more than 98%. Based on the results of experiments, the optimum mix design was found to have L/S of 0.75 and Ms of 1.55. The workability of MSGP was significantly improved while maintaining the strength under the optimum mix design. The initial setting time of MSGP decreased by 71.8%, while both of the fluidity and 28-d compressive strength increased by 15.3%, compared with ordinary Portland cement pastes. Therefore, geopolymers are promising alternative cementitious material, which can consume a large amount of MK and GGBFS and promote green and clean production.

• MAA introduces unsaturated carboxylate metal salt bonds on the steel slag surface. • MAA etching of steel slag to make it loose and porous. • Steel slag can shorten the vulcanization molding cycle. • The performance of MAA-in-situ-m-SS filled natural rubber was significantly improved. • MAA-in-situ-m-SS can partially replace carbon black as a rubber filler. As a by-product of the steelmaking industry, the large-volume production and accumulation of steel converter slag cause environmental issues such as land occupation and dust pollution. Since metal salts of unsaturated carboxylic acid can be used to reinforce rubber, this study explores the innovative application of in-situ modified steel slag, mainly comprising metal oxides, with methacrylic acid (MAA) as a rubber filler partially replacing carbon black. By etching the surface of steel slag particles with MAA, their surface roughness was increased, and the chemical bonding of metal methacrylate salt was introduced to enhance their interaction with the molecular chain of natural rubber (NR). The results showed that using the steel slag filler effectively shortened the vulcanization molding cycle of NR composites. The MAA in-situ modification effectively improved the interaction between steel slag and NR molecular chains. Meanwhile, the physical and mechanical properties, fatigue properties, and dynamic mechanical properties of the experimental group with MAA in-situ modified steel slag (MAA-in-situ-m-SS) were significantly enhanced compared with those of NR composites partially filled with unmodified slag. With the dosage of 7.5 phr or 10 phr, the above properties matched or even exceeded those of NR composites purely filled with carbon black. More importantly, partially replacing carbon black with modified steel slag reduced fossil fuel consumption and greenhouse gas emission from carbon black production. This study pioneered an effective path for the resourceful utilization of steel slag and the green development of the steelmaking and rubber industries. [ABSTRACT FROM AUTHOR]

Increasing the MgO content in vanadium slag is a prerequisite for implementing slag splashing to protect the furnace. The increase in MgO content will inevitably cause changes in the phase structure of vanadium slag, thereby affecting the extraction of vanadium. In this study, the effect of MgO on the crystallization behavior of the spinel phase in vanadium slag was systematically investigated. It was found that the spinel phases in vanadium slag with high MgO content were mainly FeV2O4, Fe2TiO4, MgV2O4 and Mg2TiO4, and the nucleation and growth rates of the above crystals increased significantly with the increase of FeO/SiO2 ratio and MgO content. With the increase of FeO/SiO2 from 1 to 3, the combined crystallization rate of Fe2TiO4, FeV2O4, and Mg2TiO4 increased by two orders of magnitude, and the total spinel crystallization rate of MgV2O4 and spinel also increased by one order of magnitude. The effect of the MgO content on the crystallization of the crystals was not as significant as the FeO/SiO2 ratio. The optimum crystallization temperature of the total spinel in vanadium slag is determined with MgV2O4, which has the highest melting point, and the optimum crystallization temperature interval is 1500–1650 K. During the cooling process of the vanadium slag, MgV2O4 is first crystallized, then Mg2TiO4 and FeV2O4, and finally Fe2TiO4. When the cooling rate is 5 K min−1 and the temperature drops from 1773 K to 1623 K, the average grain size of the spinel gradually increases, and the growth of the spinel in vanadium slag with high MgO content is controlled by the supply. [ABSTRACT FROM AUTHOR]

In this work, a "turn waste into treasure" strategy is proposed to synthesize Fe2O3 and use it as a lithium-ion battery (LIB) anode from green alum slag, a by-product of TiO2 production in the industry. Through this method, a heteroatom-doped Fe2O3 was obtained and showed a stable specific capacity of 1209 mA h g−1 at 500 mA g−1, which was superior to pure-Fe2O3 that was prepared in the laboratory. Besides, the full battery was assembled with Fe2O3 as the anode, and the specific capacity was maintained at 102 mA h g−1 after 100 cycles of stable cycling at 1.0 A g−1, showing excellent cycling and rate performance. This work offers a green low-cost and promising option for the development of LIBs anode materials and making TiO2 industrial production more economical and environmentally friendly. [ABSTRACT FROM AUTHOR]

The Na2O‐SiO2‐TiO2 system is important for the glass, ceramic, and metallurgical industries. Its features provide information on the composition and melting temperature to be utilized during the production of glass and ceramic and during the processing of TiO2‐bearing material in the metallurgical industry. The liquidus temperatures between 900 and 1600°C in the ternary system at saturation of solid SiO2, TiO2, Na2Ti6O13, Na2SiTiO5, and Na2Ti3O7 were measured using the equilibration‐quenching energy‐dispersive X‐ray spectroscopy/Electron Probe Microanalyzer technique. A wide range of liquidus compositions were obtained with Na2O between 0 and 41.7 mol% in the SiO2‐ and TiO2‐rich regions. The present study provides liquidus data at 1500 and 1600°C for the first time. Liquidus temperatures at various double saturations were also obtained in the present investigation to determine univariant lines in the phase diagram. The present experimental data were compared with previous investigations and computed phase diagrams. The data obtained in the present investigation can be employed to optimize the thermodynamic properties and phase diagrams of the Na2O‐SiO2‐TiO2 system. [ABSTRACT FROM AUTHOR]

Towards the end of the 19th century and the early 20th century, France was the world's largest producer of antimony, especially due to the rich deposits in the Brioude‐Massiac area. Even though all the mining and smelting activities are long gone, there are still some remains of those activities. The most original of those is the use of roasting slags as aggregates in former plant walls or industrial building. They are macroscopically characterised by a black or red colour with a vesicular aspect similar to natural pozzolanas. Common petrography and mineralogy tools have been used to characterise those slags: optical mineralogy, scanning electron microscopy coupled with energy dispersive spectroscopy (SEM‐EDS) and X‐ray diffraction (XRD). To gain an insight into their mineral complexity, a QEMSCAN map has been produced. The mineralogy is typical of high‐temperature slags: cristobalite, quartz, mullite, fayalite‐forsterite series and spinel. The antimony content is quite high, up to seven percent, under the form of various antimony oxides and native antimony. LAY DESCRIPTION: In the Brioude‐Massiac area, France, antimony has been heavily mined at the end of the 19th century, giving rise to the generation of large amounts of wastes from the metallurgy of the ores. Those wastes (scoria and slags) have been used locally as aggregates to build walls. They consist of high‐temperature phases (SiO2 polymorphs: cristobalite and tridymite, dendritic spinel, glass) and illustrate an early example of the reuse of waste materials, nowadays termed as 'circular economy'. [ABSTRACT FROM AUTHOR]

MgO–SiC–C refractories with superior hot strength, oxidation resistance and slag resistance have potential to become substitute refractories for matte smelting furnace. In the present work, the influence of glass powder addition on phase compositions, hot strength, oxidation resistance, and slag resistance of MgO–SiC–C refractories was investigated. The liquid phase introduced by glass powder filled the pores, blocking the channel for the ingress of the oxygen and thus improving the oxidation resistance. Although the oxidation resistance of such refractories was improved with 1–3 wt% glass powder addition, their hot strength and slag corrosion resistance decreased when the glass powder content was 2–3 wt%. To balance the mechanical properties, oxidation resistance and slag resistance, low amount glass powder addition (1 wt%) was considered better choice. [ABSTRACT FROM AUTHOR]

The corrosion behavior and mechanism of nickel slag on semi‐rebonded magnesia‐chrome brick are investigated. The variations in the specimens before and after corrosion were studied using microstructure, phase composition, and thermodynamic simulations. The results reveal that at high temperatures, the metal oxides in nickel slag easily react with Cr2O3 to generate Cr‐spinel, and the isolation layer forms a continuous phase on the surface of the refractory. The appearance of the isolation layer causes the nickel slag corrosion process on semi‐rebonded magnesia‐chrome brick to shift from direct to indirect corrosion controlled by ion diffusion, effectively blocking the continuous penetration of Ca2+ and Si4+ in the slag inside the refractories. As a result, the semi‐rebonded magnesia‐chrome brick resists nickel slag corrosion extremely well. [ABSTRACT FROM AUTHOR]

Ultra-low carbon magnesia refractories used in working lining of ladle are crucial components to meet the smelting requirements for producing purity steel. However, the decreased carbon content weakened thermal shock resistance and slag resistance of refractories, resulting in the hampered practical applications. To resolve the mentioned problems, Al–Si alloy powders were introduced into unfired magnesia refractories with glucose and citric acid as binders to form combination of oxides and non-oxides, and performances of refractories were researched systematically in air and carbon-embedded atmospheres according to different service conditions, respectively. The results show that reaction mechanisms in 2 atm led to different effects on microstructure of refractories with added Al–Si alloy powders. The formation of AlN whiskers and plate-shaped MgAl 2 O 4 and Mg 2 SiO 4 with intersecting structure resulted in higher mechanical strength, fracture surface energy and thermal shock resistance of refractories in air atmosphere than that in carbon-embedded atmosphere. The in-situ formed ceramic phases (AlN, MgAl 2 O 4 and Mg 2 SiO 4) in pores led to enhanced slag resistance for refractories. Meanwhile, in carbon-embedded atmosphere, the reduced reactions of Fe 2 O 3 in molten slag increased slag viscosity, presenting higher slag penetration resistance for refractories than that in air atmosphere. Considering the lowered compactness of refractories with excessive alloy powders by large volume expansion from the formation of ceramic phases, refractories with 3 wt% alloy powders showed high mechanical properties, thermal shock resistance and slag resistance. This study provides a reference for the development of ultra-low carbon magnesia refractories used in working lining of ladle, and the research results also indicated that the evaluation of different atmosphere conditions is important for the design of high performance refractories. [ABSTRACT FROM AUTHOR]

Diopside-Like based ceramics as the main crystalline phase (expressed as 'Diopside') were prepared via one-step sintering using extracted titanium slag (ETS) and coal fly ash (CFA) as raw materials. The effects of CFA content and sintering temperature on the crystal phase composition, microstructure, properties and crystallization kinetics were studied by X-ray fluorescence, X-ray diffraction, scanning electron microscopy, and inductively coupled plasma emission spectrometry. According to the findings, the addition of CFA supplemented the deficiency of Si and Al in ETS and balanced the Ca/Al/Si molar ratio in the system. Moreover, at the CFA doping of 20 %, melilite was gradually transformed into 'diopside' at 800–1100 °C that further remained stable at 1160–1200 °C. 'Despite' the fact that the crystallization activation energy increased and the Avrami index was at its lowest level (1.75), the crystallization temperature was reduced, whereas the crystallization rate increased, causing the ceramic body and surface to crystallize and thereby improving the properties of ceramics. Sintering at 1180 °C for 1 h resulted in ceramics with 'diopside' as the primary crystal phase composition. The water absorption, linear shrinkage, bulk density, bending strength, and acid resistance were respectively 1.3 %, 13 %, 2.89 g cm−3, 141.8 MPa, and 97.36 %. Finally, 'diopside' possessed the higher acid resistance than melilite and anorthite. [ABSTRACT FROM AUTHOR]

Superabsorbent polymers (SAPs) can serve as effective internal curing agents in alkali-activated slag (AAS) systems, mitigating the risk of cracking. However, the influence of SAPs on the properties and microstructure of AAS systems is not yet fully understood. In this study, the effects of SAPs on the properties, reaction products, and internal moisture migration of AAS pastes were investigated. The water released by SAPs during curing supplemented the water consumption in the hydration process, maintained internal relative humidity, and reduced autogenous shrinkage by more than 80%. However, the addition of SAPs not only created voids in the hardened paste, as indicated by the mercury intrusion porosimetry (MIP) results, but also increased the microscopic pore volume of the paste. SAPs did not change the phase composition of AAS hydration products, but increased the differential thermogravimetry (DTG) peak corresponding to the main hydration product C(-A)-S-H gel at 28 days. The increase in chemically bound water in AAS pastes containing SAPs, along with the changes in the transverse relaxation time (T2) peak area corresponding to SAPs in the H1 low-field NMR results, likely are due to the gradual release of water during internal curing by SAPs. [ABSTRACT FROM AUTHOR]

Waste calcium carbide slags (CS), which are widely applied to desulfurisation, are not typically used in denitration. Herein, to well achieve waste control by waste, a facile and high-efficiency denitration strategy is developed using KOH to modify the calcium carbide slags (KCS). Various KCS samples were investigated using a series of physical and chemical characterisations. The performance test results showed that the KOH concentration and reaction temperature are the main factors affecting the denitration efficiency of KCS, and CS modified with 1.5 mol/L KOH (KCS-1.5) can achieve 100% denitration efficiency at 300°C. Such excellent removal efficiency is due to the catalytic oxidation of the oxygen-containing functional groups derived from the KCS. Further studies showed that KOH treatment significantly increased the concentration of oxygen vacancies, nitro compounds, and basic sites of CS. This study provides a novel strategy for the resource utilisation of waste CS in the future. [Display omitted] [ABSTRACT FROM AUTHOR]

Resourceful utilization of coal gasification fine slag (CGFS), a typical coal-based solid waste, has always been a trial and challenge in solid waste treatment. In developing its utilization value, fewer steps and lower energy consumption during treatment are more favorable. Herein, CGFS was modified by combining BiOBr to develop its possible application in the photocatalytic degradation of organic pollutants. The BiOBr/CGFS photocatalysts were synthesized at ambient temperature by a simple hydrolysis method with zero pre-treatment of CGFS. The synthesized composites show improved effective photocatalytic performance in the degradation of organic pollutant and the BOB/CGFS20 showed the best activity, which can remove 89.3% of phenol within 90 minutes, 84.53% of sulfamethoxazole within 75 minutes and 84.96% of bisphenol A within 120 minutes. Moreover, the components in CGFS that may play a positive role were investigated and the results showed that CGFS acted as a carrier, and most likely, the carbon materials and metal oxides such as Fe2O3 and/or TiO2 in it led to the improvement of the quantum efficiency of BiOBr and further promoted the photocatalytic performance. This study aims to provide some references and inspiration for the utilization of CGFS and environmental protection. [ABSTRACT FROM AUTHOR]

Magnesium potassium phosphate cement (MKPC) presents a broad application prospect in engineering fast repairing, reinforcement, hazardous material, and national defense construction, due to its good properties such as fast hardening and early strength, high bonding strength, and wide environmental adaptability. In this work, the effect of slag with different particle size on the workability, mechanical properties, and hydration products of MKPC was investigated. The results showed that the compositions of slag in the particle size range 75–300 µm are quite different. A decrease in the particle size of slag resulted in reduction of the fluidity of MKPC from 175 to 108 mm and shortening the setting time from 1300 to 850 s. The compressive strength of MKPC (curing for 3 h) does no change much as the particle size of slag varies, and slag with the particle size in the range of 115–300 µm slightly increase the 3‐h‐compressive strength of MKPC, since the compressive strength values are in the vicinity of 13 ± 2 MPa. As the curing age increases, physical effect and hydration activity of slag concurrently dominate the mechanical properties of MKPC, and when the hydration activity of the slag exceeds the adverse effect caused by fine particles, the compressive strength increases. Slag particle size can significantly improve the long‐term compressive strength of MKPC, which can effectively reduce the cost and can be used as a repair material with better durability. [ABSTRACT FROM AUTHOR]

As one of the key materials used in the civil engineering industry, concrete has a global annual consumption of approximately 10 billion tons. Cement and fine aggregate are the main raw materials of concrete, and their production causes certain harm to the environment. As one of the countries with the largest production of industrial solid waste, China needs to handle solid waste properly. Researchers have proposed to use them as raw materials for concrete. In this paper, the effects of different lithium slag (LS) contents (0%, 10%, 20%, 40%) and different substitution rates of recycled fine aggregates (RFA) (0%, 10%, 20%, 30%) on the axial compressive strength and stress-strain curve of concrete are discussed. The results show that the axial compressive strength, elastic modulus, and peak strain of concrete can increase first and then decrease when LS is added, and the optimal is reached when the LS content is 20%. With the increase of the substitution rate of RFA, the axial compressive strength and elastic modulus of concrete decrease, but the peak strain increases. The appropriate amount of LS can make up for the mechanical defects caused by the addition of RFA to concrete. Based on the test data, the stress-strain curve relationship of lithium slag recycled fine aggregate concrete is proposed, which has a high degree of agreement compared with the test results, which can provide a reference for practical engineering applications. In this study, LS and RFA are innovatively applied to concrete, which provides a new way for the harmless utilization of solid waste and is of great significance for the control of environmental pollution and resource reuse. [ABSTRACT FROM AUTHOR]

Parts of China are abundant in tar-rich coal (pyrolysis yield of coal tar is more than 7%), if it can be converted into high-quality tar, it is a reliable means to deal with energy problems. This paper takes tar-rich coal in Shenmu area and uses modified granulated blast furnace slag (GGBS) for catalytic pyrolysis, and the effects of different metal oxides and different amounts of modified GGBS on tar yield are explored. The fractions of pyrolysis tar are analyzed by gas chromatography, and the pyrolysis cokes (PC) are analyzed by Fourier transform infrared (FTIR) and X-ray diffraction (XRD). The thermodynamics of modified GGBS with pyrolysis gas and pyrolysis tar of the reaction process is calculated by HSC Chemistry software. The results show that the yield of coal tar increased after catalytic pyrolysis, and the fraction of coal tar is directional transformation to phenolic oil. The modification of GGBS with CaO, Al2O3, and Fe2O3 has a good effect on increasing tar production and improving oil quality. Especially for CaO@GGBS, it can increase the tar yield of tar-rich coal to 15.12% with 97.72% phenol oil, far exceeding the current limit of coal pyrolysis tar yield of around 5%. The crystal structure of pyrolysis coke indicates that different reactions occurred. The possible reaction and equilibrium concentration of the reaction of pyrolysis tar under catalytic pyrolysis are revealed by HSC Chemistry. This provides a foundation for the high-value utilization of tar-rich coal and the comprehensive utilization of GGBS in the future. [ABSTRACT FROM AUTHOR]

The lubrication layer (LL) formed at the concrete–pipe interface plays a crucial role in facilitating concrete pumping. Shear thickening in this layer significantly affects concrete pumping. However, very few studies are available for understanding the onset and intensity of shear thickening of the LL. In this study, the effect of solid volume fraction (SVF), superplasticiser dosage, supplementary cementitious materials and hydration on the shear thickening (continuous and discontinuous) behaviour of cementitious suspensions were investigated. Results show that an increase in SVF reduces the shear thickening intensity for systems using ordinary Portland cement (OPC), whereas the intensity is amplified for systems with fly ash (FA) or ground granulated blast furnace slag (GGBS). An increase in superplasticiser dosage results in an early onset of shear thickening and increases the shear thickening intensity, regardless of the binder used. Systems including GGBS exhibit the highest shear thickening intensity, followed by OPC- and FA-based systems. Based on these results, it is evident that the superplasticiser dosage for OPC-based systems needs to be optimised based on the structural buildup, while, for FA- or GGBS-based systems, the superplasticiser dosage needs to be optimised based on shear thickening behaviour with respect to hydration. [ABSTRACT FROM AUTHOR]

Pervious concrete was prepared with two industrial solid wastes of granulated blast-furnace slag and Bayer red mud as cementitious materials, sodium silicate solution as alkali activator, and limestone gravel as coarse aggregate. The effects of design porosity, water-binder ratio and aggregate size on the strength and permeability of pervious concrete were studied respectively. The optimal water-binder ratio is influenced by the design porosity and aggregate size. When the design porosity of pervious concrete is 15% and the aggregate size is 4.75-9.50 mm, the optimal water-binder ratio of 0.36 and it has a higher strength and has good water permeability. The mechanics and permeability performance of alkali-activated slag-red mud pervious concrete are better than those of cement pervious concrete, which is in line with the development concept of low carbon and green. [ABSTRACT FROM AUTHOR]

Coal gasification fine slag (CGFS) is a significant source of solid waste requiring improved treatment methods. This study primarily investigates the mechanism of ultrasonic treatment in optimising flotation-based decarbonization of CGFS and its impact on CGFS modified with surfactants. The objective is to maximise the carbon ash separation effect to support the clean and efficient utilisation of CGFS. Flotation experiments revealed optimal conditions at an ultrasonication power of 180 W for 2 min and a slurry concentration of 60 g/L, resulting in a residual ash content of 82.59%. Particle size analysis, scanning electron microscopy (SEM), and Brunner−Emmet−Teller (BET) measurements demonstrate the efficacy of ultrasound in extracting inorganic minerals from the surface and pores of residual carbon, consequently reducing both pore and particle sizes. Fourier transform infrared spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS) analyses indicate alterations in the surface chemistry of CGFS induced by ultrasound treatment. The content of hydrophilic groups decreased from 31.64% to 29.88%, whereas the COO- group content decreased from 13.13% to 8.43%, consequently enhancing hydrophobicity. Adsorption experiments demonstrate an increase in surfactant adsorption capacity following ultrasonic treatment. Furthermore, ultrasonic treatment facilitates the desorption of surfactants previously adsorbed onto the surfaces of CGFS residue. Therefore, optimal flotation is obtained by applying ultrasonic pretreatment to CGFS before adding flotation chemicals. Upon the addition of Polysorbate (Tween-80), the residual ash content increased 90.17%. [ABSTRACT FROM AUTHOR]

Release of formaldehyde gas indoors is a serious threat to human health. The traditional adsorption method is not stable enough for formaldehyde removal. Photocatalytic degradation of formaldehyde is effective and rapid, but photocatalysts are generally expensive and not easy to recycle. In this paper, geopolymer microspheres were applied as matrix materials for photocatalysts loading to degrade formaldehyde. Geopolymer microspheres were prepared from red mud and granulated blast furnace slag as raw materials by alkali activation. When the red mud doping was 50%, the concentration of NaOH solution was 6 mol/L, and the additive amount was 30 mL, the prepared geopolymer microspheres possessed good morphological characteristics and a large specific surface area of 38.80 m2/g. With the loading of BiOX (X = Cl, Br, I) photocatalysts on the surface of geopolymer microspheres, 85.71% of formaldehyde gas were adsorbed within 60 min. The formaldehyde degradation rate of the geopolymer microspheres loaded with BiOI reached 87.46% within 180 min, which was 23.07% higher than that of the microspheres loaded with BiOBr, and 50.50% higher than that of the microspheres loaded with BiOCl. While ensuring the efficient degradation of formaldehyde, the BiOX (X = Cl, Br, I)-loaded geopolymer microspheres are easy to recycle and can save space. This work not only promotes the resource utilization of red mud and granulated blast furnace slag, but also provides a new idea on the formation of catalysts in the process of photocatalytic degradation of formaldehyde. [ABSTRACT FROM AUTHOR]

To promote the resource utilization of steel slag and improve the production process of steel slag in steelmaking plants, this research studied the characteristics of three different processed steel slags from four steelmaking plants. The physical and mechanical characteristics and volume stability of steel slags were analyzed through density, water absorption, and expansion tests. The main mineral phases, morphological characteristics, and thermal stability of the original steel slag and the steel slag after the expansion test are analyzed with X-ray diffractometer (XRD), scanning electron microscope (SEM), and thermogravimetric analysis (TG) tests. The results show that the composition of steel slag produced by different processes is similar. The main active substances of other processed steel slags are dicalcium silicate (C2S), tricalcium silicate (C3S), CaO, and MgO. After the expansion test, the main chemical products of steel slag are CaCO3, MgCO3, and calcium silicate hydrate (C-S-H). Noticeable mineral crystals appeared on the surface of the steel slag after the expansion test, presenting tetrahedral or cigar-like protrusions. The drum slag had the highest density and water stability. The drum slag had the lowest porosity and the densest microstructure surface, compared with steel slags that other methods produce. The thermal stability of steel slag treated by the hot splashing method was relatively higher than that of steel slag treated by the other two methods. [ABSTRACT FROM AUTHOR]

According to physical property tests of lead-containing slag, the volatilisation behaviour of lead slag will have adverse impacts on test accuracy and further affect the control of chemical reactions, solidification and removal of inclusions during smelting. To analyse the volatilisation characteristics of lead slag, in this paper, four kinds of lead slags from lead direct reduction smelting with different PbO and ZnO content are taken. thermogravimetry, ISP-TOF were used. Additionally, the changes in volatiles and slag composition and phases were analysed with XRD and ICPS, and the volatilisation reaction mechanism was discussed. The results indicated that the volatilisation of lead slag can lead to a big weight loss of about to the slag with higher PbO content. The weight loss increases with the PbO content in slag increases. The volatile corresponding to the weight loss above 900 °C is mainly PbO and less ZnO. The higher the temperature is, the stronger the volatilisation is. With the increase in temperature and keeping time, most of the PbO can be evaporated and leaves little PbO in the residual slag. This will has great effect to physico-chemical property measurement of the slag with higher PbO content, especially to the property measurement that be kept at high temperature for a long time. Because the volatiles is trend to condense with the temperature decrease, mass spectrometer is limited by the condensation of volatiles, i.e., PbO, ZnO and so on, in the connection pipeline. The device should be modified for this use. [ABSTRACT FROM AUTHOR]

It is thought that geopolymers are easy to carbonate, especially when they are cured in ambient temperatures. Matrix gel's composition and microstructure, and new products of geopolymers (GPs) after carbonation were investigated in this study on the basis of XRD and SEM-EDS measurements and ternary diagram analysis, which were prepared from low-lime fly ash (FA) and ground granulated blast-furnace slag (GGBS) alone or a blend, as a precursor. The specimens were hardened in a 20 °C environment with alkali activator solution (S/N = 1.1 in mole), followed by storage under sealing or accelerated carbonation. XRD patterns show that carbonation products were nahcolite for the sole FA-based GP and calcite for the GPs using GGBS alone or as a blend. The SEM images of carbonated samples show that there were cube-shaped calcite and small calcite particles in the GGBS-based GP, but hail-like particles in the FA/GGBS blend-based GP. The hail-like particles were complexes of calcite and C-A-S-H gels determined by ternary diagram analysis, and were found to plug the top of the pores of the spongy C-A-S-H gels. We also confirmed that combined ternary diagram analysis of S-(C + M + N)-A and A-(C + M)-N are very effective in determining the gel type of a geopolymer, as well as the products and compositional changes after carbonation, in which oxide components of gels are determined by SEM-EDS. In the former diagram, C-A-S-H gels were plotted linearly along the (C + M + N)-albite (Ab) join, while N-A-S-H gels showed a scattered distribution. In the latter diagram, the plots for N-A-S-H and C-A-S-H gels are distributed in different zones. N = Na2O, C = CaO, M = MgO, A = Al2O3, S = SiO2, H = H2O. [ABSTRACT FROM AUTHOR]

To achieve better process control of silicon (Si) alloy production using aluminum as a reductant of calcium silicate (CaO-SiO2) slag, it is necessary to understand the reaction phenomena concerning the behavior of formed phases at the metal-slag interface during conversion. The interfacial interaction behavior of non-agitated melt was investigated using the sessile drop method for varying time and temperature, followed by EPMA phase analysis at the vicinity of the metal–slag interface. The most remarkable features of the reaction were the accumulation of solid calcium aluminate product layers at the Al alloy–slag interface and spontaneous emulsion of Si-alloy droplets in the slag phase. The reduction is strictly limited at 1550 °C due to the slow transfer of calcium aluminates away from the metal-slag interface into the partially liquid bulk slag. Reduction was significantly improved at 1600–1650 °C despite an interfacial layer being present, where the conversion rate is most intense in the first minutes of the liquid–liquid contact. A high mass transfer rate across the interface was shown related to the apparent interfacial tension depression of the wetting droplet along with a significant perturbed interface and emulsion due to Kelvin–Helmholtz instability driven by built-up interfacial charge at the interface. The increased reaction rate observed from 1550 °C to 1600–1650 °C for the non-agitated melt was attributed to the advantageous physical properties of the slag phase, which can be further regulated by the stoichiometry of metal–slag interactions and the composition of the slag. [ABSTRACT FROM AUTHOR]

In this article, the influence of the Fe2O3 addition amount on the dephosphorization kinetics of hot metal at the low slag basicity (CaO/SiO2) of about 1.6 and low temperature of 1623 K is investigated with laboratorial experiments and the kinetic model. Si and P contents in the hot metal during the whole dephosphorization process, and the endpoint FeO content in the slag, show good agreements between the calculated results with the kinetic model and experimental results. The peak value of dephosphorization rate linearly increases from 8.35 × 10−5 to 4.52 × 10−4 mass% s−1 when the weight ratio of Fe2O3 is increased from 5 to 10/100 g hot metal. With the increase in Fe2O3 addition amount, the mass transfer coefficient in the hot metal phase (km) and that in the slag phase (ks) and dephosphorization rate constant (k) all increase. The value of km is found to be 4.34 times that of ks. During the dephosphorization process, the rate‐controlling step converts from the mass transfer in slag phase to the mass transfer in hot metal phase in less than 10 min. With the increase in Fe2O3 addition amount, the value of interfacial oxygen activity of aO*$a_{\text{O}}^{\star}$ increases from 0.0102 to 0.0201. [ABSTRACT FROM AUTHOR]

Geopolymer concrete (GPC) is recently drawing the attention of the research community as it represents a durable and eco-friendly alternative to normal concrete. However, its use with steel fibres as a repair material for concrete substrates is a new area that requires further investigation. In this study, a mixture of fly ash, slag, and undensified silica fume was activated using a potassium-based activator. Then, the highest compressive strength blend was adopted. The effect of the curing regime, either partial saturation or wrap in plastic films, and the fibres ratio on the mechanical properties of GPC was studied. Adding fibres to GPC by volume ratios of 1, 2, and 3% enhanced its ductility and boosted the compression, tension, shear, flexural, and pull-out capacity of the fibrous GPC. Therefore, GPC with 2% steel fibres was selected as an innovative repair material for concrete substrates from practical and economical points of view. The durability of this repair material was evaluated using permeability and fire resistance tests. It showed lower permeability by 39% compared to normal concrete and withstood elevated temperatures up to 600 °C. Moreover, its interfacial bond and shear compatibility with concrete were found to be utterly high. [ABSTRACT FROM AUTHOR]

Electric arc furnace slag (EAF) and sandstone waste (SW) are two of the most abundantly generated industrial wastes whose utilization as precursors and supplementary cementitious materials has not been exhaustively studied. The current research study comprehensively investigates the effects of incorporating varying proportions (0–90%) of re-melted EAF as a co-additive on the engineering properties of elevated (80 °C) and ambient (30 °C) cured alkali-activated SW-based binders. Extensive laboratory tests were conducted to assess the physio-mechanical and durability performance of the resulting alkali-activated materials (AAM). Detailed mineralogical and microstructural characterization of SW, EAF, and alkali-activated samples was carried out using sophisticated analytical techniques. Results advocated that irrespective of the curing temperatures, SW-based AAM showed improved setting behavior, compressive strength, water absorption, and porosity characteristics with the increment of EAF at all substitution levels due to the concomitant development of CASH-CSH-NASH gel phases. Overall, it can be inferred that EAFs as a pozzolanic material successfully augmented the properties of SW-based alkali-activated binders, providing an efficient solution for disposal and negative environmental impacts associated with industrial wastes. [ABSTRACT FROM AUTHOR]

In this paper, the mechanical properties and durability performance of polyvinyl alcohol fibers reinforced lightweight engineered geopolymer composites (EGC) with different fly ash and slag contents exposed to 5% magnesium sulfate solution for up to 120 days were investigated. The results were also compared to lightweight engineered cementitious composites (ECC). Instead of silica sand, recycled glass was employed as a lightweight aggregate to reduce the density of EGC and ECC composites. A combination of NaOH and water glass (Na2SiO3) solutions with a Na2SiO3/NaOH ratio 2.5 was chosen to produce lightweight EGC specimens. The relative slump, density, ultrasonic pulse velocity, visual inspection, weight change, compressive stress–strain diagram, load–deflection responses, and scanning electron microscopy were examined to investigate the normal and sulfate environments of EGC and ECC specimens. The obtained results confirmed that the EGC composites had significant multiple-cracking characteristics, strain-hardening behavior, and high deformation capacity after 120 days of exposure to sulfate environments. Moreover, the results showed that the EGC specimens had higher residual compressive and flexural strengths in normal and sulfate environments than ECC specimens. Including 50% slag and 50% fly ash into the EGC mixture exhibited the optimal deflection capacity; however, the deflection of EGC specimens substantially reduced from 6.97 to 2.52 mm when the slag amount increased from 50 to 100%. Despite all studied samples preserving their multiple-cracking and tight crack width control and deflection-hardening behavior when exposed to sulfate environments for up to 120 days, the reduction in deflection capacity of EGC specimens ranged from 8 to 22%. [ABSTRACT FROM AUTHOR]

Engineered geopolymer composites (EGC) have emerged as a more environmentally friendly alternative to conventional engineered cementitious composites (ECC). These composites offer high mechanical and durability features. However, there is a lack of research on EGC, particularly with basic oxygen furnace (BOF) slag as a precursor and iron ore tailings (IOT) as a partial replacement to fine aggregate. Despite their effectiveness as industrial waste products in conventional concrete, this study aimed to determine the optimal compositions of fly ash (FA), steel fibres (SF), and IOT by varying their percentages. Overall, 150 mix combinations were tested, including six binder combinations, five combinations of fine aggregates, and five percentage variations in SF. Finally, one optimum mix was selected for each binder combination, based on the ultimate compressive strength values corresponding to the six optimal mixes. The compressive strengths of all the mixes were evaluated at both 7 and 28 days of curing, involving three replicate samples after oven curing (initial 24 h) followed by subsequent ambient curing until their respective ages. The highest observed compressive strength after 28 days was 41.77 MPa for 50 mm cubes. This strength was achieved with a composition of 60% FA, 1.5% SF, and 45% IOT. An increase in IOT percentage led to a nearly linear increase in strength, while the strength peaked at 1.5% for steel fibres. The addition of BOF slag significantly enhanced the compressive strength compared to mixes with full FA. A 40% fly ash replacement with BOF slag resulted in an average strength that was 39% higher than the combination with 100% fly ash. However, the strength growth decreased after a 10% replacement. Analysis of variance was conducted using the design of experiments methodology to determine the significance of the parameters and their interactions. All three independent parameters were found to be statistically significant, while their interactions were not. Utilizing Taguchi's analysis method with the L25 orthogonal array, it was concluded that IOT percentage was the most influential parameter. [ABSTRACT FROM AUTHOR]

In geopolymer mixes, the amount of shrinkage is (3–6 times) higher than the OPC. Excessive shrinkage can cause cracking, which is a threat to the durability of the concrete. To that end, a solution must be found to reduce it. Studies on the type and concentration of activators, type of base material and its properties, mixing proportions, applying different curing conditions and use of different additives are among the solutions investigated to decrease the drying shrinkage of geopolymers in previous research. In this study, after a comprehensive investigation, the effects of magnesium oxide, calcium hydroxide, sodium carbonate, and Portland cement additives as well as heat treatment and moist curing conditions were evaluated in geopolymer mortar containing slag activated with sodium hydroxide and sodium silicate. Finally, the performance of polypropylene fibers was examined as well. The effects of mentioned options on compressive strength were also investigated. The results indicate the different behaviors of additives on drying shrinkage and compressive strength depending on their type, substitution content, and age. Eventually, it seems that among the available alternatives, the most effective option is to use heat treatment with complete control of the heat rate. With this approach, not only the amount of drying shrinkage reduction will reach 66% but also the early compressive strength will be increased significantly. Although the use of magnesium oxide, sodium carbonate, and calcium hydroxide improved the compressive strength of the samples, relatively different results regarding shrinkage were observed in the use of these materials. Time-dependent behavior was also evident in their influence process. Polypropylene fibers also caused a slight decrease in compressive strength (less than 7.5%) probably due to the reduced compaction capacity of fresh mortar, but it was effective in controlling shrinkage in the short term. [ABSTRACT FROM AUTHOR]

In this article, steel slag was added into the marine silt to improve its dynamic properties. The characteristics of marine silt that can be studied by XRD, BET surface area, SEM, and FTIR were first described. Then, the influence of the sample density, water content, waste steel slag content, and the confining pressure on the dynamic shear modulus G and damping ratio λ was discussed by conducting resonant column tests. The results illustrated that the dynamic characteristics of the marine silt-steel slag admixtures were considerably improved. Additionally, G increased with the increasing steel slag content and λ increased with the decreasing steel slag content. Moreover, a dynamic model of the admixtures was developed based on the Hardin–Drnevich model. Furthermore, by comparing the dynamic characteristics of the admixtures with Nanjing sand, Fujian sand, Kiyohoro silty clay, and Wenzhou marine clay, it was found that the improved admixtures may be a more suitable geofiller in geotechnical engineering. [ABSTRACT FROM AUTHOR]

Iron ores and iron bloom slags from two iron archaeological sites (Chilgeumdong: 300–600 AD, Wanori: ∼20th century) as well as iron ores from six iron deposits in Chungju, South Korea, were examined to assess the provenance of the raw iron ores. Different ore mineralogy proves to be a useful tool in interpreting the ore provenance of samples from the iron archaeological sites, although limited by the simplicity of the assemblage. The application of Ca + Al + Mn vs. Ti + V diagram for classifying the genetic type of magnetite suggests that the iron ores of the iron archaeological sites may have originated from multiple deposits. Comparing the chondrite-normalized REE patterns and the correlation between Lan and Cen in iron ores and iron bloom slags aids in determining the provenance of samples from the iron archaeological sites. Despite notable deviations, the use of Pb-Sr isotope ratios as a means of identifying the origin of unprocessed iron ores proves to be a meaningful approach. Based on our findings, it appears that the iron ores discovered at archaeological sites were typically sourced from nearby iron deposits like Changdong, Yeonsudong, Daekyo, and possibly Manjeong. This preference for local sources as opposed to more distant ones, such as Obok and Yusang, seems to have remained a constant throughout various historical epochs, spanning from the Baekjae to the Joseon period. Overall, this study demonstrates the effectiveness of integrated interpretation of various complementary approaches, including ore petrography, trace and rare earth element geochemistry, and Pb-Sr isotope analysis, in determining the provenance of raw iron ores excavated from iron archaeological sites. [ABSTRACT FROM AUTHOR]

The effect of nanoparticles and nucleation seeds on the hydration kinetics of alkali-activated materials is not well understood. Implications of nano-TiO2 (nTiO2) and C--S--H nucleation seeds (XSeed) on the early-age hydration and later-age properties of sodium hydroxide-activated ground granulated blast furnace slag were investigated. The effect of NaOH concentration (0.5, 1, 2, and 4 M) in the activator solution was reported. Results indicated the acceleration of early hydration kinetics with mixes of XSeed and nTiO2 when the concentration of the activator solution was 0.5/1 M. No considerable effects were noted with XSeed addition for 2/4 M, whereas there was an acceleration with the addition of nTiO2. These differences were attributed to the lack of dispersion of XSeed at higher activator concentrations. Hydrate phase assemblage did not change with the addition of nanoparticles by 28 days of hydration. Increase in strength, along with pore refinement, was observed with the incorporation of nanoparticles. [ABSTRACT FROM AUTHOR]

The weak mechanical properties of dredged soil can be improved by using cementing agents. Comprehensive investigation of the efficacy of stabilizing methods, including Portland cement (PC) and alkali-activated ground granulated blast-furnace slag (CaO-GGBS), cementing agent content from 12% to 16%, and curing methods in different initial moisture content of soils, organic matter content, and soil types was carried out. Experimental results showed that dredged soils have stronger properties using CaO-GGBS than PC. Maximum strength was found by using the highest CaO-GGBS content of 16%. The increase of organic matter content can weaken the enhanced properties of dredged soils stabilized by CaO-GGBS. The highest shear strength of specimens stabilized by CaO-GGBS occurred in dredged soils with 20% sand while the greatest yield strength in e-log p′ space was found in dredged soils with 30% sand. A modified constitutive model based on the framework for cemented geomaterials proposed by Gens and Nova has been developed. The ability of the model to reproduce the mechanical behavior capturing strength development with curing period was explored. [ABSTRACT FROM AUTHOR]

Pavement engineers are paying attention to the stabilization of granular layers in the modern era of sustainable construction. A well-drained pavement can extend the service life to its design life if properly designed and maintained. The water infiltrating into the pavement causes detrimental effects and reduces the service life of the pavement. The open-graded cement-stabilized macadam (OGCSM) can act as a drainage layer in sustainable pavements. Cement cannot be considered as a long-term sustainable material due to its high carbon footprint. This paper investigated the suitability of a supplementary cementitious material, ground granulated blast furnace slag (GGBFS), as a partial replacement of cement in OGCSM, a drainage layer in pavements. The strength and permeability characteristics of the mix were studied using an unconfined compressive strength (UCS) test and specially fabricated permeameters, respectively. OGCSM was optimized at 7% cement content, and cement in the OGCSM was partially substituted with GGBFS at various replacement levels. The mix was optimized at 80% replacement of cement with GGBFS, which satisfied the specified requirements for strength, permeability, and durability. The UCS, coefficient of effective permeability, and water resistance index of the optimized mix were 2.88 MPa, 60.58 m/day and 96.33%, respectively. The morphology and mineralogy characteristics of the optimized mix were determined to justify the strength gain in cementitious mixtures. The porosity of the OGCSM mix was estimated as 25.86% using computed tomography (CT) scanned images. The subsurface drainage design was carried out using drainage requirements in pavements (DRIP 2.0) software, and the quality of drainage was rated as good. [ABSTRACT FROM AUTHOR]