Abstract: The rapid growth of the photovoltaic and semiconductor industries has dramatically increased the demand for high-purity silicon while generating large amounts of silicon waste during wafer slicing, metallurgical refining, and module decommissioning. Efficient recycling of waste silicon can mitigate environmental pressure and provide a sustainable raw material source for silicon-based industries. This work systematically reviews the purification, recovery, and reuse technologies of waste silicon, focusing on three major categories: silicon cutting waste (SCW), metallurgical-grade silicon refining slag (MGSRS), and end-of-life photovoltaic modules (EoL-PV). The physicochemical characteristics of these wastes, including phase composition, impurity distribution, and structural morphology, are analyzed to establish the relationship between their origins and corresponding purification strategies. Experimental and industrial results reported in recent literature are compared to identify the optimal parameters for impurity removal. For SCW, acid leaching with HF-HCl or HNO₃-HF mixtures achieved Fe, Al, and Ca removal efficiencies exceeding 95% under temperatures of 50–60 ℃ and moderate acid concentrations. In MGSRS refining, CaO-SiO₂-Al₂O₃ or Fe₂O₃-SiO₂-based slags effectively removed Ti, C, and Ca impurities through oxidation and selective slagging reactions, yielding silicon purities above 99.8%. Vacuum refining and zone melting remove volatile impurities (e.g., P) and metallic impurities, respectively; however, removing B remains a challenge due to its segregation coefficient being close to unity. Emerging physical purification methods, including plasma, microwave, and electron-beam treatments, are discussed in terms of heat transfer behavior, impurity volatilization kinetics, and energy consumption. The synergistic combination of chemical and physical refining routes has been shown to markedly improve purification efficiency, shorten processing time, and reduce reagent use. The thermodynamic feasibility and kinetic constraints of impurity reactions are summarized to provide theoretical guidance for multi-step integration. Regarding reutilization, purified silicon waste can be converted into metallurgical-grade, solar-grade, or electronic-grade silicon depending on purity requirements. In addition, secondary utilization pathways include the synthesis of SiC and Si₃N₄ ceramics, Si-C composite anodes for lithium-ion batteries, and porous silicon for energy storage and photothermal conversion. Life-cycle analyses indicate that recycling 1 t of silicon waste saves approximately 8–10 MW·h of energy and reduces CO₂ emissions by more than 5 t compared with primary silicon production. Overall, waste silicon recycling offers substantial environmental and economic benefits, but large-scale industrial implementation is still limited by impurity variability, lack of standardized process control, and the high cost of deep purification. Future work should focus on elucidating the thermodynamic and kinetic mechanisms of impurity removal, optimizing multi-process coupling between refining and solidification, and developing modularized refining-functionalization systems. Establishing unified evaluation criteria and techno-economic models will be key to achieving sustainable, high-value recycling of waste silicon materials.