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With the rapid reduction in NOx emissions and the end of various Al alloy products' lives in recent years, large amounts of spent SCR catalysts (SSCs) and Al alloy scrap (AAS) as important secondary Ti and Al resources have been discarded. The value-added reutilization of Ti and Al from the two wastes is necessary to develop sustainable Ti and Al resources. In this work, an environmentally friendly approach is proposed to simultaneously recycle Ti and Al from the two wastes and then prepare them into TiAl3 and low-Fe Al alloys. First, AAS (1.25 wt% Fe) was used as a reductant to extract Ti and W from the SSC to prepare raw W-containing Ti–Al alloys. The results showed that applying a MgO crucible and electromagnetic force can promote alloy–slag separation and a MgO crucible increased the extraction ratio of Ti and W. Next, the raw Ti–Al melt was separated by electromagnetic directional crystallization for the simultaneous preparation of the two high-value products: W-containing TiAl3 and low-Fe Al (0.41 wt% Fe) alloys. In the separation process, Ca, Mg, and Zn impurities in the alloys were removed via volatilization; Fe and Mn impurities were eliminated through agglomeration at the boundary between the TiAl3 and low-Fe Al alloys and at the top of the Ti–Al alloy. The entire process produces no waste liquid, gas, or slag. This method provides new environmentally friendly insights for sustainable recycling of secondary Ti and Al resources, and provides a new technology for preparing TiAl3 and low-Fe Al alloys. [ABSTRACT FROM AUTHOR]

Abstract Ti-bearing blast-furnace slag is a metallurgical waste but a promising Ti resource. In this study, Ti and Al–Si alloys can be prepared directly by separating a Ti–Si–Al alloy that was prepared by reducing Ti and Si from Ti-bearing blast-furnace slag with Al. The technology of directional solidification with electromagnetic force was employed to carry out the separation of the Ti–Si–Al alloy. When additions of CaO and Al were 24 wt% and 40 wt%, respectively, the composition of the obtained Ti–Si–Al alloy was 31.8 wt% Ti, 22.7 wt% Si, 28.5 wt% Al, and 10.2 wt% Fe. Ti 5 Si 4 , TiSi, Al–Si–Ti (τ 2), Al–Si–Fe (τ 4), and Al–Si alloys were prepared in sequence after separating the Ti–Si–Al alloy using directional solidification with electromagnetic force. However, when the composition of the Ti–Si–Al alloy was changed to 21.2 wt% Ti, 48.5 wt% Si, 19 wt% Al, and 6.8 wt% Fe, the TiSi 2 , Si, Al–Si–Fe and Al–Si alloys were prepared in sequence. This study will propose an approach to employ the metallurgical waste, titanium-bearing blast-furnace slag, to prepare Ti and Al–Si alloys. Highlights • An approach to employ Ti-bearing blast-furnace slag to prepare Ti and Al–Si alloys. • Ti and Al–Si alloys were prepared directly by separating a Ti–Si–Al alloy. • Electromagnetic directional solidification was employed to separate Ti–Si–Al alloy. [ABSTRACT FROM AUTHOR]

Large amounts of Ti-bearing blast furnace slag (TBFS), diamond wire saw Si powder (DWSSP), and Al alloy scrap (AAS) are generated annually. Although these are industrial waste, they contain valuable Ti, Si, and Al resources. In this work, a novel process is developed for the simultaneous recycling of Ti, Si, and Al from these three wastes to prepare TiSi 2 and Al-Si alloys. TBFS, DWSSP, and CaO (flux) were mixed to form a mixed Ti-Si-slag, which was combined with AAS and underwent reduction smelting at 1823 K to prepare Si-Ti-Al alloys. Subsequently, TiSi 2 (98.7%) and low-Fe Al-Si (0.64 wt% Fe) alloys were prepared sequentially by separating the molten Si-Ti-Al melt via electromagnetic directional crystallization with a pull-down rate of 3 µm/s. The impurities in the Si-Ti-Al alloy were removed during the separation process by segregation at the boundary of the solid-liquid phase and volatilization. Furthermore, the entire process produces no waste acid or waste gas. Therefore, this work has introduced an efficient and environmentally friendly method for the value-added recycling of Ti, Si, and Al resources from accumulated TBFS, DWSSP, and AAS. [Display omitted] • A novel approach was proposed to simultaneously recycle three wastes. • Extracting Ti from Ti-bearing blast furnace slag while removing O from diamond wire saw Si powder. • Fe was removed from the Al alloy scrap while the Al alloy scrap was also recycled as an Al-Si alloy. • The entire process produces no waste acid or waste gas. [ABSTRACT FROM AUTHOR]

[Display omitted] • A green approach is proposed for the extraction of valuable metals from wastes. • The entire process produces no carbon, waste acid, or waste gas. • A new approach for preparing Ti 5 Si 3 alloy and Ti 5 Si 4 -TiAl 3 alloy. • Three wastes are cleanly utilized through an approach. Spent SCR catalyst (SSC), Ti-bearing blast furnace slag (TBFS), and Al alloy scrap (AAS) are industrial wastes that are rich in Ti and Al. To utilize Ti and Al resources in these three wastes, here, an efficient approach is proposed to prepare two useful alloys, Ti 5 Si 3 and Ti 5 Si 4 -TiAl 3 , using the three wastes as raw materials. First, AAS was used as a reductant to extract Ti and Si from the SSC and TBFS and simultaneously prepare Ti-Si-Al alloys. The effect of the crucible (Al 2 O 3 and MgO crucibles) and CaO addition (slagging agent) on Al reduction was investigated, and the results showed that a MgO crucible and the addition of CaO increased the extraction ratio of Ti and Si. Then, Ti 5 Si 3 and Ti 5 Si 4 -TiAl 3 alloys were prepared sequentially by the separation of molten Ti-Si-Al melt via electromagnetic directional crystallization. Impurities in the Ti-Si-Al alloy were removed during electromagnetic directional crystallization. No carbon, waste acid, and waste gas were discharged throughout the whole production process. This work provides a green, high-efficiency, and low-cost method that also treats accumulated SSC, TBFS, and AAS wastes. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new approach for clean utilization of the Ti-bearing blast furnace slag. • A new approach for preparation of high-purity TiSi 2 using Si-Ti solvent. • Separation of Si–Ti alloy into TiSi 2 and eutectic Si–Ti alloy via directional crystallization. • Mechanism for separation and purification of Si-Ti alloy was discussed. Titanium-bearing (Ti-bearing) blast furnace slag is not only industrial waste but also an important Ti resource. However, the cleaning of Ti-bearing blast furnace slag for utilization is a difficult problem. In this study, a new process is proposed to prepare Titanium disilicide (TiSi 2) and eutectic Si–Ti alloy (Si/TiSi 2), using Ti-bearing blast furnace slag and low-purity Si as raw materials. Firstly, Titanium oxide (TiO 2) in the Ti-bearing blast furnace slag was reduced by Si and an Si–Ti alloy was obtained. The obtained Si–Ti alloy was then separated into TiSi 2 and eutectic Si–Ti alloy by directional crystallization. In addition, MgO, Al 2 O 3 and graphite crucibles were used and their influences on the results were investigated to obtain the optimal reaction container to prepare high-purity TiSi 2 and eutectic Si–Ti alloy. The results show that the separation of Si–Ti alloy using an MgO crucible as a reaction container has little influence on the purity of the TiSi 2 (>98%) and eutectic Si–Ti alloy (>97%) and that most of the impurities could be eliminated from the bulk TiSi 2 crystal and eutectic Si–Ti alloy. The results of this study provide a theoretical and experimental basis for the simultaneous preparation of TiSi 2 and eutectic Si–Ti alloy materials and proposes a new approach for the comprehensive utilization of Ti-bearing blast furnace slag. [ABSTRACT FROM AUTHOR]

• A new technology for simultaneous recycle of Al-Si scraps and purification of Si. • Two products, high-purity Si and low-Fe eutectic Al-Si alloy, were prepared simultaneously. • Critical concentrations of Fe in the eutectic Al-Si-Fe-(Mn/Cr) alloy were experimentally determined for the first time. Currently, the elimination of Fe from Al-Si alloy for recycling Al-Si scraps, and the purification of Si using Al-Si solvent for recycling Si wafers in solar cells or production of new Si wafers, are two totally different research technologies and topics. A new approach is proposed in this study to combine the two different technologies into a single one which can not only recycle spent Si wafers but also Al-Si scrap simultaneously. The new approach is promising for cost reduction and environmental conservation, because two widely used products, high-purity Si and low Fe eutectic Al-Si alloys, can be prepared simultaneously via electromagnetic directional crystallization. The Al-Si-Fe-(Mn/Cr) melt was separated into a low-Fe eutectic Al-Si alloy (eutectic Al-Si-Fe-(Mn/Cr) alloy) and agglomerated high-purity Si crystals. The critical concentration of Fe (theoretical minimum value of Fe content) in the eutectic Al-Si-Fe-(Mn/Cr) alloys were determined experimentally for the first time, which decreased and increased slightly after the addition of Mn and Cr, respectively. After removing Fe, the residual Fe-containing impurities in the low-Fe eutectic Al-Si-Fe-(Mn/Cr) alloy were modified from their harmful needle-like shape to less harmful Chinese-script-like, and short platelet-like shapes by adding small amounts of Mn and Cr, respectively. After grinding the agglomerated Si crystals and leaching the main impurities, namely Mn, B, Cr , Ca, Al, P, Fe, and Ni, from the Si powders, the purity of Si was upgraded from 99.34% to 99.96%. This new and promising approach can be used for the purifying Si, recycling Si wafers and Al-Si scraps. [ABSTRACT FROM AUTHOR]

To prepare high-purity Ti–Si alloys, we newly used vacuum directional solidification technology to purify and separate Ti–Si alloys, which have different compositions (Ti-8.45 wt%Si, Ti-63.7 wt%Si, Ti-71.6 wt%Si, and Ti-84.1%wt%Si). The pulling-down rates in the directional solidification were to be 3 μm/s, 5 μm/s, and 7 μm/s, respectively, to investigate their effects on the purification. The results showed that vacuum directional solidification can purify Ti–Si alloys efficiently without discharging waste acid, slag and gas, and the slower pulling-down rate could result in better purification results. The impurities, Fe, Al, V, and Ni, could be removed due to their segregation behavior on the boundary of the solid and liquid phases. However, the impurities Ca and Mg could be removed using the vacuum technology because their vapor pressures were significantly higher than those of Si and Ti. TiSi 2 could be precipitated and separated from the Ti-63.7 wt%Si and Ti-71.6 wt%Si alloys. The precipitated TiSi 2 could be agglomerated at the bottom of the Ti–Si alloys, under the effect of gravity. The phases in the Ti–Si alloys, after vacuum directional solidification, were observed and determined using an electron probe micro-analyzer (EPMA). The results showed that the eutectic Ti-8.45 wt%Si alloy consisted of Ti 5 Si 3 and Ti, the Ti-63.7 wt%Si and Ti-71.6 wt%Si alloys consisted of TiSi 2 and eutectic Si–Ti alloy at the Si-rich side, and the Ti-84.1 wt%Si alloy consisted of Si particles and eutectic Si–Ti alloy at the Si-rich side. The study shows that vacuum directional solidification is an efficient and clean technology for the purification of Ti–Si alloys, and for the preparation of TiSi 2 through the separation of Ti–Si alloys. • An efficient approach to eliminate the main impurities in Ti–Si alloys. • No waste slag, acid, and gas were discharged in the process of purification or separation. • Vacuum directional solidification was newly employed to prepare high-purity Ti–Si alloy. • TiSi 2 was prepared directly through the separation of Ti–Si alloys. [ABSTRACT FROM AUTHOR]

The extraction of Ti from Ti-bearing blast-furnace slag (TBFS) via aluminothermic reduction to prepare Ti–Si–Al alloy has several promising applications. However, the refractories of the furnace lining can dissolve into the molten slag and change the composition of the slag, not only shortening the life of the refractories, but also influencing the preparation of Ti–Si–Al alloys for industrial applications. The main purpose of this study was to explore the corrosion behavior of refractories (carbon, alumina, and magnesia bricks) and determine the most suitable refractories for the aluminothermic reduction of TBFS. Herein, for the first time, the dissolution equilibrium of refractories during the aluminothermic reduction of TBFS and its effect on aluminothermic reduction were revealed. The results revealed that the alumina and magnesia bricks were more effective for obtaining bulk Ti–Si–Al alloy and avoiding high mass loss of the Ti–Si–Al alloy compared to the carbon bricks. Furthermore, the corrosion of alumina and magnesia bricks increased with an increase in the content of the added CaO; however, the corrosion of the alumina bricks was more severe compared to the magnesia bricks. In addition, the largest extraction ratio of Ti (maximum value: 99.85%) was achieved when magnesia bricks were employed. The results of this study indicate that magnesia bricks are the optimal refractory for the preparation of Ti–Si–Al alloy via the aluminothermic reduction of TBFS. This work provides important experimental information for the industrial application of the aluminothermic reduction of TBFS in the preparation of Ti–Si–Al alloys. [ABSTRACT FROM AUTHOR]

• The spent SCR catalyst was successfully converted into valuable W- and V- containing Ti–Al alloy. • Optimal catalyst conditions for Al reduction were obtained (The reaction time was 60 min, the addition of Al was 45 wt% and the CaO / Al 2 O 3 was 2 / 3). • After directional crystallization, P, Fe, and Si impurities in the alloy are removed obviously, and S impurities are difficult to remove. • The total impurities content of the resulting W- and V- containing TiAl alloys were less than 1.85% by directional crystallization. • By using hydrogen (90 % Ar + 10 % H 2) to remove O from Ti–Al alloy during directional crystallization, and the O content was reduced from 1500 to 140 ppmw. The wide spread application of NH 3 -selective catalytic reduction (NH 3 -SCR) process has led to the accumulation of large amounts of spent SCR catalyst. In this study, Al reduction–electromagnetic directional crystallization was used to recycle Ti, W, and V from spent SCR catalyst to prepare W- and V- containing TiAl alloys. The effects of the slag composition, reaction time, and amount of reductant added on the recovery ratios were investigated. The maximum recovery ratios of 94.16 %, 81.85 %, and 98.14 % for Ti, W, and V, respectively, were achieved at a reaction time of 60 min, addition of 45 wt.% Al, and CaO / Al 2 O 3 ratio of 2 / 3. Furthermore, directional crystallization was performed on Ti–Al alloy under different atmospheres (99.99 % Ar or 90 % Ar + 10 % H 2 gas) to investigate their effects on deoxygenation. 90 % Ar + 10 % H 2 gas could effectively remove O from the Ti–Al alloys. Si and P impurities were enriched at the bottom of the alloy and Fe impurities at the top. The Ca and Mg impurities contents are approximately 50 and 10 ppmw, respectively, and S was removed difficultly. The total impurities content of the resulting W- and V- containing TiAl alloys were less than 1.85 %. The entire process is low-carbon and environmentally friendly. [ABSTRACT FROM AUTHOR]

Eutectic materials have been widely employed in many high-tech fields, and recently, eutectic high-entropy alloys (EHEAs) have become a research focus of eutectic materials; however, it is challenging to determine/design the eutectic composition of alloys accurately, especially multi-component alloys and EHEAs. In this study, a new electromagnetic directional crystallization approach was proposed to determine/design eutectic alloy compositions. First, standard eutectic Al-Si, Al-Si-Fe, Al-Si-Ti, and Al-Si-Fe-Mn alloys were obtained by directly separating their respective melts using electromagnetic directional crystallization. Then their eutectic compositions were accurately determined by inductively coupled plasma-optical emission spectroscopy. Conflicting reports about the eutectic reactions and phase transformations occurring in the Al-Si-Ti system were also resolved. Thereafter, the application of electromagnetic directional crystallization was extended to EHEAs. The widely investigated AlCoCrFeNi 2.1 EHEA was confirmed to have a eutectic composition, and a new EHEA Al 16.8 Co 12.6 Cr 13.8 Fe 11.8 Ni 45.1 with a combination of high strength and high ductility was obtained in this study by separating the AlCoCrFeNi 3 melt via electromagnetic directional crystallization. Therefore, in the absence of thermodynamic data, electromagnetic directional crystallization provides a promising approach for determining and designing the eutectic composition of alloys, especially EHEAs. This new approach is more direct, efficient, and simpler than the conventional thermodynamic-calculation approach because the application of the latter is significantly limited when thermodynamic data are not available. • A new approach is proposed to design eutectic high-entropy alloys without thermodynamic calculation. • A new eutectic high-entropy alloys, Al 16.8 Co 12.6 Cr 13.8 Fe 11.8 Ni 45.1 , was designed and reported. • Standard eutectic alloys were prepared through one-step electromagnetic directional crystallization. • Controversial research results about AlCoCrFeNi 2.1 alloy and the Al-Si-Ti system were finally solved. [ABSTRACT FROM AUTHOR]

[Display omitted] • Refractory silicides and eutectic Si/MSi 2 (M: Nb, Ta, Mo, or W) alloys were prepared by separation Si–M solvent. • High-purity silicon can be obtained by acid leaching of eutectic Si/MSi 2 alloy. • A new approach for simultaneous preparation of high-purity refractory silicides, eutectic Si/MSi 2 alloys, and Si. • Mechanism separation and impurity removal of Si–M alloy was discussed. Refractory silicides, eutectic Si/MSi 2 (M: Nb, Ta, Mo, or W) alloys, and high-purity silicon are materials that have been used in many high-tech industries. Today, they are prepared using different technologies, i.e., each of them is prepared using an independent technology. This study proposes a new method to simultaneously prepare three high-purity materials (refractory silicides, eutectic Si/MSi 2 alloys, and silicon) using electromagnetic directional crystallization. The Si–M (Si–Nb, Si–Ta, Si–Mo, or Si–W) solvents are separated using electromagnetic directional crystallization, and then the MSi 2 (NbSi 2 , TaSi 2 , MoSi 2 , or WSi 2) and eutectic Si/MSi 2 (Si/NbSi 2 , Si/TaSi 2 , Si/MoSi 2 , or Si/WSi 2) alloys are precipitated in sequence because the crystallization temperature of MSi 2 is higher than that of the eutectic Si/MSi 2 alloys. Additionally, owing to the segregation behavior of impurities between the solid and liquid phases, impurities in the Si–M solvents can be eliminated efficiently to prepare high-purity MSi 2 and eutectic Si/MSi 2 alloys. In addition, as the eutectic Si/MSi 2 alloys consist of Si and MSi 2 phases, high-purity Si powders (>99.98%) can be obtained by separating the Si and MSi 2 phases using acid leaching. The results indicate the feasibility of the new approach in preparing refractory silicides, eutectic Si/MSi 2 alloys, and high-purity Si. [ABSTRACT FROM AUTHOR]