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In order to recover silicon from diamond wire sawing waste, silicon extraction and boron removal are two key issues that need to be addressed. In this study, a combined process of pressure-less sintering and CaO−SiO 2 slag treatment was proposed. Low -boron silicon was prepared and considered as raw materials in solar cell production. The results confirmed that pressure-less sintering was beneficial for the digestion of the silicon oxide layer, and the molar percentage of oxygen in silicon kerf was reduced from 14.83 to 7.24% after pressure-less sintering at 1400 °C for 2 h. The effect of slag composition on boron removal was investigated. It was found that an optimum boron removal efficiency of 86.91% was obtained when the optical basicity reached 0.68 and no CaF 2 was added; the CaO−SiO 2 mass ratio was 1.2, the holding time was 40 min, and the slag to silicon mass ratio was 1. Although the addition of CaF 2 can decrease the viscosity, it affects the activity and the oxygen potential of slag.

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Recycling silicon from environmentally hazardous diamond wire saw silicon powder waste (DWSSP) and effectively removing boron is still an elusive aim. Here, pressure-less sintering and dynamic-slag treatment were used to recover the powder waste. On the basis of thermodynamic simulation, the slag composition was designed. Dense structure of DWSSP ceramics could effectively reduce the oxidation loss. Dynamic-slag treatment can provide higher silicon recovery and better boron removal rate than can traditional one-step slag treatment. Slag-1 (Na 2 O-SiO 2 ) can remove boron while protecting molten silicon from oxidation. Interestingly, after Slag-2 (CaO−SiO 2 −Na 2 O) was added, relative displacement between the mixed slag and silicon can provide more favorable dynamic conditions. Using the dynamic-slag treatment, the boron removal efficiency reached 83.4%, and the silicon recovery rate reached 82.29%. Additionally, by introducing the solute penetration theory, the mechanism of boron removal during convective mass transfer process was discussed in detail. The simplicity of this combined approach provides a new possibility for recovery and purification of intractable fine powdery waste.

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