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Spent V2O5-WO3/TiO2 catalyst (SVWTC) is considered hazardous waste and a valuable resource of Ti, W, and V. Herein, Ti, W, and V were recovered from waste via silicothermic reduction to prepare W- and V-containing Si-Ti alloys with potential applications. An optimal reduction slag system (CaO-SiO2-TiO2-20 wt pct MgO) and reduction temperature (1773K) were determined to ensure completion of the Si reduction of spent V2O5-WO3/TiO2. The effects of the reduction time (holding time) and basicity (CaO/SiO2 mass ratio) of the initial slag on the separation of the alloy and reduction of Ti, W, and V oxides were investigated. Extending the holding time and basicity of the initial slag improved the separation of the alloy from the residual slag and increased the extraction ratios of Ti, W, and V. The equilibrium time was determined as 6 hours, and the maximum extraction ratios of Ti, W, and V were 96.9, 95.5, and 93.6 pct, respectively. The corrosion of the refractory material during Si reduction was investigated and was controlled at 2.65 pct with high recovery of the oxides. No waste liquid was discharged, and the residual slag could be recycled. This study introduces a green and efficient method for recycling Ti, W, and V from SVWTC and provides a new method for preparing W- and V-containing Si-Ti 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]

[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]

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]

[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]