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Zr was employed as an impurity getter to enhance removal of impurities from MG-Si because of its strong affinity for a wide range of impurities. Different lixiviants, HCl + HF, HF and aqua regia, were employed to investigate the leaching behavior of MG-Si at 348 K for 2.5 h with and without Zr addition. Typical precipitates at Si grain boundaries before and after acid leaching were observed and analyzed via scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS). The leaching results show that the order of efficiency of the lixiviants, from highest to lowest, is HCl + HF > HF > aqua regia. HCl + HF is the optimal lixiviant for purification of MG-Si with and without Zr addition. The presence of Zr in MG-Si can significantly enhance the efficient extraction of impurities, especially P and Al, which cannot be removed efficiently using conventional hydrometallurgical technologies. The total fraction of impurities removed (Fe, Al, Ca, B, P, Zr, Ti, V, Mn, Cu and Ni) increased from 94.2 to 97.5% after HCl + HF leaching. In addition, 99.9% of the impurity getter Zr was removed, with its concentration decreasing from 50,000 ppmw to 49 ppmw after HCl + HF leaching. The residual amount of Zr in the refined Si can be further removed by directional-solidification purification because of its extremely small segregation coefficient. [ABSTRACT FROM AUTHOR]

In order to strengthen B removal during purification of Si with Al–Si solvent, small amounts (<1100 ppma) of transition metals (Hf, Zr, Ti, and Nb) were employed as additives because of their strong affinity for B. The results showed that the B removal process can be significantly improved by adding small amounts of Hf, Zr, and Ti and that Hf and Zr are more efficient for strengthening B removal than Ti or Nb. Nb had no effect on B removal. These additives could be also efficiently removed because of their extremely small segregation coefficients. [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]

The Si purification mechanism was investigated by using Al Si solvent with small amounts of V to enhance B removal. The results indicated that a small amount of V enhanced the removal of B from the Al Si melt, as it formed the VB X compound. The VB X was determined to be VB 2 via EPMA. The solubility product of the VB 2 in the Al-43at. %Si melt at 1273 K and the Al-35at. %Si melt at 1173 K were initially measured experimentally with equilibrium technology, and were determined to be 8.15 × 10 - 11 (1273 K) and 5.97 × 10 - 12 (1173 K). The relationship between the solubility product of VB 2 and the liquidus temperature of Al Si melt was estimated, which indicated that an excessive V addition or a lower temperature is needed to enhance the efficiency of B removal from the Al Si melt. Based on the thermodynamic analysis, V was used as an additive in the Si purification process with the Al-35at. % Si solvent that had electromagnetic solidification. The results of the Si purification indicated that a small amount of V could enhance the B removal efficiently and VSi 2 was found in eutectic Al Si phase along the Si crystals boundaries. The maximum removal rate of B was about 76%. The supplementary V was completely eliminated together with the B and did not contaminate the refined Si. [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]

Boron separation from metallurgical grade silicon (MG-Si) is still a puzzle for metallurgical route. A purification method to MG-Si using a synthetic CaO-CaCl 2 slag (no SiO 2 addition) treatment combined with an Ar-O 2 -H 2 O gas blowing technique was studied. The mechanism of boron separation from silicon using the synthetic CaO-CaCl 2 slag treatment and the Ar-O 2 -H 2 O gas blowing was analyzed and elaborated. The results showed that the intermediate product SiO 2 , generated by the O 2 gas blowing, was combined into silicate with CaO slag reagent. Boron in silicon can be separated by both gaseous borides HBO, BOCl and borate CaO·B 2 O 3 . It was found that the boron separation can be further improved by separating soluble boron in the refined silicon using the acid leaching treatment. The total separation efficiency of boron in MG-Si reached 94.5% using the combined slag treatment and gas blowing refining technique followed an acid leaching treatment to the refined silicon. [ABSTRACT FROM AUTHOR]

[Display omitted] • New findings on characteristics of spent automotive catalytic converters are reported. • The relations between SACCs' characteristics and the recycling methods are revealed. • Solutions to the problems of current recycling methods are proposed based on the SACCs' characteristics. Numerous spent automotive catalytic converters (SACCs) are being produced annually owing to the increasing number of end-of-life automobiles. Although various methods have been proposed for recycling platinum-group metals (PGMs) and rare-earth-elements (REEs) from SACCs, most achieve low recovery ratios owing to the poor understanding of the characteristics of SACCs. In this study, the characteristics of SACCs and occurrence states, migration, and distributions of elements were in-situ investigated in 3D. The deactivation mechanisms of the automotive catalytic converters (ACCs) and the reasons behind the low PGM recovery ratios were revealed. Interestingly, the typical characteristics of SACCs, such as micro-cracks, blocked channels, molten phases of carrier and coating, molten phase of Fe-PGMs, presence of PGMs oxides, heterogeneous distribution of valuable elements, REE oxides mixed with ZrO 2 and Al 2 O 3 , were observed in the SACCs. The effects of these SACCs' characteristics on purchase of SACCs and some methods of recovering PGMs and REEs were discussed, and solutions to the problems were suggested. [ABSTRACT FROM AUTHOR]

Slag refining is one of the most effective methods to remove impurities from metallurgical grade silicon. In this paper, ZnO was added to a binary 50% CaO-50% SiO 2 slag system with a mass ratio of 2–30% to study the impurities removal from metallurgical grade silicon. The results showed that boron was reduced from 12.94 ppmw to 2.18 ppmw by a 46% CaO-46% SiO 2 -8% ZnO slag system. Compared to the 50% CaO-50% SiO 2 slag system, slag refining with ZnO addition showed a 20% increase in removal efficiency and a 40% increase in the distribution coefficient. After acid leaching, boron was further reduced to 1.52 ppmw with a removal efficiency of 88.25%. By a combined process of slag refining and acid leaching, impurities Al and Fe were reduced from 817 ppmw and 3800 ppmw to 1.2 ppmw and 96 ppmw with removal efficiencies of 99.8% and 97.5%, respectively. The evaporation loss of the generated metallic zinc during slag refining was greater than 99.7%. After acid leaching, the minimum zinc content in silicon was only 4 ppmw. [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]

[Display omitted] • An electromagnetic directional solidification process was proposed to purify Al alloy. • Grain refinement and degassing were realized simultaneously. • Effects of the induction current, moving rate, and remelting were investigated. • Both tensile strength and elongation were improved by remelting process. • The mechanism of bubble transfer process was explained by simulation. The grain size and porosity are two significant parameters to evaluate the properties of the Al alloy. In this work, an electromagnetic-field-enhanced directional solidification process hybridized with the remelting treatment was proposed to refine the grain size of Al alloys and at the same time to remove the residual gas in molten alloys. Furthermore, the effects of several factors on the grain refinement and degassing were investigated. The high induction current is effective for the obtainment of the small homogeneous grain size because of the stirring effect. With the increase of the moving rate, the grain size increased and then decreased due to the nucleation effect. The remelting process enables both the grain refinement and H 2 degassing to obtain regular grain orientations. The simulated pressure field, velocity field and H 2 gas volume fraction show the mechanism of the bubble transfer in the liquid Aluminum alloy. The pressure field depicts a sharp pressure gradient on the upper side of the bubble. The velocity field indicates an increase in the velocity maximum in the bubble. The shape evolution process of the H 2 bubble shows the effect of the interface tension. [ABSTRACT FROM AUTHOR]