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Ferronickel (FeNi) slag, as the main solid byproduct of the FeNi industry, has the potential to be utilized other than as roadbed material. To broaden the applications of FeNi slag (such as CO2-capturing materials), there is a need for a treatment that breaks the magnesium silicate bonds and transforms the magnesium into MgO. As an initial study, this research treated FeNi slag by using sodium hydroxide followed by water-washing. The present authors evaluated several alkali treatment variables; such as temperature (523 K and 773 K), time (1–8 h), and mass ratio between FeNi slag and NaOH (1:0.75–1:4). The magnesium in FeNi slag was recovered as MgO. By using a FeNi slag:NaOH mass ratio of 1:2, a temperature of 773 K, and a time of 4 h, 97.34% of the magnesium was recovered, and 83.35% of the silicon was removed. During alkali treatment, the Mg-based compound in FeNi slag undergoes a transformation from MgSiO3to Mg2SiO4to MgNa2SiO4and, finally, to MgO. On the other hand, the Fe-based compound transforms olivine to Fe2O3to spinel (Fe2MgO4and Fe3O4) and, finally, to FeNaO2. The alkali treatment process of FeNi slag using NaOH followed by water washing is also known to make the product morphology porous and has a large surface area (11.62 m2/g). In terms of economics, this process will be economical when considering the by-product (Na4SiO4) generated.

The reaction of Ca(OH)2with hydrogen chloride was studied using single crystals to elucidate the reaction mechanism under simulated bag filter conditions. The X-ray diffraction patterns of the chlorinated single crystals indicated that products at both surfaces ((1010) and (0001) planes on the side and top faces, respectively) were CaCl2anhydrate and CaOHCl anhydrate. The observed chlorination product layer on the single-crystal surface was only several micrometers thick, even after 24 h. Comparing the thickness of the chlorinated product layer on the (1010) side face and (0001) top face of the Ca(OH)2crystals revealed that the reaction proceeded more rapidly on the former than on the latter. H2O strongly promoted the chlorination reaction.

Carbon capture and utilization (CCU) has attracted increased attention as a means to mitigate and adapt to climate change. CCU technology regards CO2as a raw material and reduces CO2emissions. However, purity and pressurization requirements in most CCU technologies are high. Flue gas that is emitted from industries and transportation requires advanced purification and pressurization, which limits the development and decreases the feasibility of CCU application. Hence, a new approach to CCU technology without CO2purification and pressurization is desirable. This study reviews differences between the CO2purity and pressure of waste CO2and feedstock CO2, reviews difficulties of CO2purification and pressurization in recent developments of CCU, and provides several promising examples of CCU technologies without CO2pressurization and/or purification. Various promising CCU technologies and their future research prospects are discussed. Mineral carbonation and biological conversion appear to be possible solutions as CCU technologies without CO2purification and pressurization. For all other CCU approaches, research trials to decrease the required CO2purity and pressure of the feedstock CO2will be required.

We have studied the effect of paramagnetic metal ion(neodymium) on the translational motion (diffusion) ofTrihexyltetradecylphosphonium benzoate ionic liquid using pulsedfield gradient NMR. 1D proton NMR results show that the cationand anion are both affected by the presence of neodymium ion.The paramagnetic lanthanide ion induces a downfield shift in the 1D NMR spectra. The 1H diffusion coefficients of the anion andcation are different and increase with temperature at lowconcentrations of neodymium. At higher neodymiumconcentrations, on the other hand the diffusion coefficients for ofthe cations and anions show the same value, which suggests theformation of aggregates around neodymium.

Mineral carbonation of alkaline wastes is a promising route for carbon dioxide (CO2) capture and utilization. An exploration of the carbonation potential of relatively inert alkaline wastes is important to develop mineral carbonation. Large amounts of coal fly ash are generated from coal-fired power plants and must be treated. A fundamental study of the circular indirect carbonation of coal fly ash was proposed and fly-ash leaching, calcium carbonate (CaCO3) precipitation, and solution regeneration with bipolar membrane electrodialysis (BPED) stages were investigated. In the leaching stage, the nitric acid/calcium ratio affected the solution pH and impurity concentration. The leaching behavior of impurities was related mainly to colloidal precipitation. Approximately 97.3% calcium in solution reacted to form precipitated CaCO3, and a higher-purity CaCO3precipitate was obtained when a lower nitric acid/calcium ratio was used in the leaching stage. The CO2conversion was 92.9% and the CO2uptake efficiency was ~0.011 g-CO2/g-fly ash, which can be improved by optimizing the liquor purification process. Fundamental liquor purification was performed. Solution regeneration by BPED was evaluated by investigating the effect of electric potential and current density on the regeneration yield, current efficiency, and power consumption. A comprehensive assessment, including cost and CO2balance, was conducted, and future interesting research on circular indirect carbonation was suggested.

The flux of the CaO‐Al203‐BaO‐CeO2‐MgO system as a desulphurization flux containing no fluorine for the secondary metallurgy process was evaluated in this study. The flux composition was designed using the eutectic compositions of the binary systems. The melting and desulphurization abilities of the fluxes were evaluated by measuring their liquidus temperatures and the distribution ratios of sulphur between the fluxes and the carbon‐saturated iron or stainless steel. The lowest liquidus temperature of 1325°C was obtained by adding 5.7 mass% MgO to the 80mass%A‐20mass%B flux. (A: 12CaO‐7Al2O3, B: BaCeO3+12mass%Al2O3). The distribution ratios of sulphur and sulphide capacities of the fluxes in this study were higher than those of the commercial product of calcium aluminate flux. This means that the CaO‐Al2O3‐BaO‐CeO2‐MgO fluxes developed in this study have higher desulphurization and melting abilities compared with the commercial product of calcium aluminate flux.

Abstract: The oxidation rates of carbon, phosphorus, and silicon; the desulfurization rate of liquid iron; and the simultaneous reduction rate of MnO from slag were examined at 1450 C to 1550 C by using high carbon iron alloys and CaO-SiO2-CaF2 slags containing MnO and FeO. The reaction rates were well reproduced by a kinetic model describing the reaction between the slag and multicomponent iron alloys. The controlling steps applied for the reactions considered in the present kinetic simulation were as follows. The rate of decarburization is controlled by the chemical reaction at the slag-metal interface, and those of the other reactions are controlled by the transport in slag and metal phases. Both observation and simulation results showed that MnO was not a strong oxidizer compared with FeO in the slag, but was an effective component for desulfurization. The simulation results also showed that the interfacial oxygen activity using MnO-based slag was much lower than that using FeO-based slag. The apparent equilibrium constants of phosphorus and sulfur, which were obtained by the kinetic modeling of experimental results, were found to increase with increasing the (MnO + CaO)/SiO2 ratio of the slag. The controlling step(s) of each element transport across the slag-metal interface was discussed with the aid of the kinetic model.

We have studied the effect of paramagnetic metal ion(neodymium) on the translational motion (diffusion) ofTrihexyltetradecylphosphonium benzoate ionic liquid using pulsedfield gradient NMR. 1D proton NMR results show that the cationand anion are both affected by the presence of neodymium ion.The paramagnetic lanthanide ion induces a downfield shift in the 1D NMR spectra. The 1H diffusion coefficients of the anion andcation are different and increase with temperature at lowconcentrations of neodymium. At higher neodymiumconcentrations, on the other hand the diffusion coefficients for ofthe cations and anions show the same value, which suggests theformation of aggregates around neodymium.