ABSTRACT
A porous geopolymer with adsorption and photocatalytic degradation functions was successfully developed by utilizing Ti-bearing blast furnace slag (TBBFS) as the raw material. The prepared porous geopolymers were characterized by X-ray diffraction, scanning electron microscope, energy dispersive spectrometer, and Fourier transform infrared spectrum. Selective crystallization, water quenching, and natural cooling methods were employed to investigate the influences of these modifications on the applicability of TBBFS as a precursor for geopolymer synthesis. Water-quenched slag with amorphous content was prone to alkali dissolution, and the resulting geopolymer exhibited the highest adsorption capacity (97.18 mg/g) for methylene blue (MB) removal. Selective crystallization at 1400 °C generated a hybrid microstructure consisting of a non-cementitious CaTiO3 crystallization phase and a cementitious amorphous fraction. The retention of CaTiO3 in the final geopolymer enables a bifunctionality in adsorption-photodegradation. Particularly, the adsorption and photodegradation processes under various conditions were investigated. The superior removal efficiency for MB could be attributed to the synergistic effects between the geopolymer matrix and CaTiO3, leading to an enhancement in the formation of hydroxyl radicals. The conversion of TBBFS into porous geopolymer offers an efficient and straightforward solution for slag utilization and dye removal.
ABSTRACT
The disposal and large-scale reutilization of industrial solid waste in construction materials have been gaining considerable interest. Herein, the synthesis of glass-ceramics from low-carbon ferrochromium slag (FCS) and waste glass is reported. The crystallization characteristics, microstructural evolution, and Cr migration mechanisms of the glass-ceramics were investigated through offline quenching experiments. The physical properties and Cr ion leaching performance were tested and evaluated. As the low-carbon FCS content was increased, glass network depolymerization was promoted and the crystallization ability was effectively improved. When 50 wt% low-carbon FCS was added, the compressive strength and Vickers hardness of the glass-ceramics reached maximum values of 160.26 MPa and 736 Hv, respectively. Simultaneously, the dominant crystalline phase in glass-ceramics was transformed from diopside and wollastonite into gehlenite when the low-carbon FCS content was further increased to 60 wt%, thereby reducing the mechanical properties. Cr2O3 primarily existed as a [CrO6] octahedron and Cr-containing spinel in the parent glass, resulting in composition segregation. On combining the growth orientation of diopside and spinel, the resulting specific crystal coating structure improved the Cr ion leaching performance. Considering the physical properties and risk of Cr leaching, the optimal FCS content in glass-ceramics is 40-50 wt%. These findings indicate that the production of glass-ceramics from low-carbon FCS and waste glass is an effective and environment-friendly method for co-utilizing these two solid wastes.
ABSTRACT
Blast furnace (BF) dust is a typical refractory iron resource. A novel technology-based utilization of BF dust as iron carbide and carbon concentrate by applying carburization roasting followed by magnetic separation and acid leaching is proposed. Under optimized conditions, an electric arc furnace (EAF) burden assaying 80.79% Fe and 7.63% C with a corresponding iron recovery rate of 87.26% and a carbon concentrate assaying 67.06% C with a corresponding carbon recovery rate of 81.23% were prepared. Furthermore, the carburization behavior and separation mechanism were revealed using X-ray powder diffraction, scanning electron microscopy, and optical microscopy. The results show that the separation efficiency of iron carbide, gangue, and carbon is very low. Na2SO4 is a highly effective additive to strengthen the separation efficiency as it can enhance the carburization index, enlarge the iron carbide particle size, improve the embed embedded relationship of iron carbide and gangue, and promote the gangue leaching efficiency. The study demonstrates that preparation of iron carbide and carbon concentrate from BF dust using the proposed technology is a feasible method.
ABSTRACT
The fabrication of well densified wollastonite with smooth appearance by direct sintering method is still a challenge due to the competitive behaviors between sintering and crystallization. In this study, the coarser glass frits with a size of 1-4 mm are subjected to heat treatment at different temperatures. An attempt of integrating differential thermal analyzer with a slag melting temperature characteristic tester was exploited to monitor the heat and geometry changes during the heating. The results showed that the addition of CaF2 can significantly promote the crystallization of wollastonite at 940 °C, while hindering the sintering ability. At higher temperature, the increase of CaF2 acts as flux and favors the formation of eutectics, leading to a decline in the precipitation amount of wollastonite. The predominated liquid sintering brought fast shrinkage. It was found out that high content of CaF2 narrows the dense sintering temperature range and results in uneven surfaces. In order to obtain wollastonite glass-ceramics with smooth appearance, the maximum content of CaF2 in sintering glass-ceramics should be limited to 2 wt.%.
ABSTRACT
High volume blast furnace slag (BFS) resulting from iron-making activities has long been considered a burden for the environment. Despite considerable research efforts, attempts to convert BFS into high value-added products for environmental remediation are still challenging. In this study, calcium-magnesium-aluminium layered double hydroxides (CaMgAl-LDHs) and ordered mesoporous silica material (MCM-41) sorbents were simultaneously synthesized from BFS, and their CO2 adsorption performance was evaluated. Calcium (Ca), magnesium (Mg) and aluminium (Al) were selectively extracted from BFS using hydrochloric acid. Leaching conditions consisting of 2 mol L-1 acid concentration, 100 °C leaching temperature, 90 min leaching time and a solid-to-liquid ratio of 40 g L-1 achieved a high leaching ratio of Ca, Mg and Al at 88.08%, 88.59% and 82.27%, respectively. The silica-rich residue (SiO2 > 98.6 wt%) generated from the leaching process could be used as a precursor for MCM-41 preparation. Chemical composition, surface chemical bonds, morphology and textural properties of the as-synthesized CaMgAl-LDHs and MCM-41 sorbents were determined. Both the CaMgAl-LDHs and MCM-41 sorbents were found to be thermally stable and exhibited comparable adsorption uptake and rates over 20 CO2 adsorption/desorption cycles. This work demonstrated that a total solution for the utilisation of BFS can be achieved and the resulting valuable products, i.e. CaMgAl-LDHs and MCM-41 are promising sorbents for CO2 capture.
ABSTRACT
In this paper, high value added NaA zeolite material was prepared from blast furnace (BF) slag by hydrothermal method and its adsorption behavior on the removal of ammonium ion was investigated. It was found out that the synthetic NaA cubic zeolite with smaller crystal size obtained at nSiO2/nAl2O3 = 2 and nH2O/nNaOH = 20 showed better adsorption performance. The kinetics of the adsorption of ammonium ion by synthesized NaA zeolite was fitted by the pseudo-second-order kinetic model. The intra-particle diffusion modeling reveals that two mixed rate-controlling mechanisms were involved in the adsorption process. The relatively high value of activation energy of 92.3 kJ·mol-1 indicates a high impact of temperature on the adsorption rate, and the nature of ammonium adsorption is chemical reaction rather than physisorption. Based on the thermodynamics calculations, the adsorption of ammonium was found to be an endothermic, spontaneous process. The adsorption isothermal analysis showed that the Langmuir model could be well fitted and a maximum adsorption capacity of 83.3 mg·g-1 of NH4+ was obtained. Thus, it was demonstrated that by forming low cost NaA zeolite and using it for environmental remediation, the synchronous minimization of BF slag and ammonia nitrogen contamination could be achieved.
