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[Display omitted] • Recycling environmentally hazardous SPW into industry raw material. • Removing the oxide layer of SPW by economically-attractive vacuum sintering. • Na 3 AlF 6 -enhanced slag refining exhibited a larger reaction interface. • A smoother remove pathway of BO 3 3 - was created. • The removal rate of impurity boron has increased by 40.92%. Recycling of environmentally hazardous silicon powder waste (SPW) is conducive to achieving "carbon neutrality". However, the high-cost and low-efficiency impurity removal limit the industrial recovery of SPW. Herein, a combination strategy of vacuum sintering and Na 3 AlF 6 -enhanced slag refining is demonstrated to upgrade the traditional recycling process. The cost-effective vacuum sintering can remove 89.44% of oxygen in silicon waste, indicating that the oxide layer of SPW is removed effectively. In the Na 3 AlF 6 -enhanced CaO–SiO 2 slag, the optimal Na 3 AlF 6 content and CaO/SiO 2 mass ratio are set to 20 wt% and 1.6 based on thermodynamic simulation. Na 3 AlF 6 reduces the liquidus temperature and increases the interfacial tension of the slag system. Moreover, in Na 3 AlF 6 -containing slag, the diffusion pathway of BO 3 3 - is dredged. As a result, the silicon-slag interface is adjusted from a half-spherical to a cylindrical surface, and the interface area has increased by 14.69%. The boron removal rate by Na 3 AlF 6 -strengthened slag refining is 40.92% faster than that of traditional slag. This work improves the removal efficiency of key impurity boron, reducing the cost of SPW recovery. Based on economic evaluation, this strategy offers a commercially available way to achieve the high-value recycling of silicon waste. [ABSTRACT FROM AUTHOR]

The surface oxide layer (SiO 2 layer) is still one of the main limitations of the recovery and purification of silicon kerf waste (SKW). Herein, to recycle SKW as the low-boron silicon ingot, an effective combination strategy that digests the surface oxide layer by pretreatment and then removes impurity boron by slag treatment is proposed. In the pretreatment part, the surface oxide layer of SKW was successfully digested into a liquid phase after mixing 10.5 wt% cryolite and sintering at 1400 °C, and the obtained SKW-ceramic has a dense structure. Moreover, when holding at 1400 °C for 2 h, the boron concentration in SKW-ceramic was decreased to 5.75 ppmw, and the removal rate reaches 14.18%. In the slag treatment part, CaO and SiO 2 are selected as slag agents. The CaO/SiO 2 mass ratio and reaction temperature were determined to be 2 and 1600 °C based on thermodynamic simulation. Besides, Na 2 O formed due to the dissociation of cryolite, which can enhance the oxygen ion activity and boron-absorbing capacity of the slag. The experimental result exhibited that the boron removal efficiency reached 86.56%. The simplicity and scalability of this strategy provide a better alternative for the recovery of SKW. [Display omitted] • Hazardous silicon kerf waste is recycled into a useful low-boron silicon ingot. • Mixing cryolite to digest SiO 2 surface layer of silicon kerf waste. • SKW-ceramic sintering can remove impurity boron to a certain extent. • The formed Na 2 O enhanced the boron-absorbing and boron-holding of the slag. [ABSTRACT FROM AUTHOR]