When ludwigite, which is abundant in China, is smelted in a blast furnace, approximately 70% of the B2O₃ content transitions into the boron slag, while the remaining boron is retained in pig iron. The structure, morphology, and properties of boron slag have been studied experimentally. The results reveal that the boron extraction rate from boron slag is closely related to the slag’s composition and characteristics. A modified treatment utilizing selective enrichment and precipitation was conducted to improve the extraction efficiency. This process led to significant boron enrichment in the suanite (3MgO·B2O₃) phase, with particle sizes ranging between 60 and 70 μm. The modified slag was subsequently separated via flotation to produce a boron concentrate with a B2O₃ grade of 15.8%, which serves as raw material for borax production via CO₂ carbonization.