Sustainable strategies for sphalerite flotation: depressant development, mechanisms, and emerging technologies

Sphalerite (ZnS) is a zinc sulfide mineral commonly associated with other valuable minerals such as chalcopyrite (CuFeS₂) and galena (PbS) in sulfide ore deposits. Separating complex Cu–Pb–Zn sulfide minerals is challenging, largely because sphalerite is activated by soluble metal ions such as Pb²⁺ and Cu²⁺, leading to its unintended recovery alongside galena and chalcopyrite. Depressants are essential for separating sphalerite from associated minerals by flotation. Traditionally, toxic and environmentally harmful reagents have been used to depress sphalerite in flotation systems. Growing environmental concerns have driven significant interest in environmentally friendly flotation reagents. This review discusses challenges in sphalerite flotation, including surface activation and the use of toxic reagents as depressants. It provides a comprehensive assessment of recent advances in sphalerite depressants, systematically examining key organic depressant classes and highlighting their molecular structures and depression mechanisms. A comparative evaluation of their performance is presented in terms of selectivity and environmental compatibility. Considerable advances have been made with organic reagents such as polysaccharides and organic acids, which, due to their abundant hydrophilic functional groups, selectively adsorb onto the sphalerite surface, preventing collector adsorption. Furthermore, this review discusses the latest advances in sphalerite flotation, including emerging computational simulation approaches and machine learning, and provides recommendations for future research. Finally, this review identifies key challenges limiting large-scale application, including process integration, and outlines future research directions toward establishing organic depressants as sustainable alternatives to conventional reagents in sphalerite flotation.