Nickel is a critical metal with broad applications in stainless steel and nickel-based alloys. In recent years, its rapidly growing use in secondary batteries has become particularly important, underscoring its strategic role in enabling low-carbon, green, and sustainable societal development. As high-grade nickel sulfide resources become increasingly scarce and global demand for nickel accelerates—fueled by the expansion of clean energy technologies—there is a pressing need to develop environme