Sulfonated Dextrin-Derived Efficient Flotation Separation of Chalcopyrite and Pyrite Under Low Alkalinity

The selective flotation separation of chalcopyrite from pyrite under low-alkalinity conditions remains a challenge due to their similar surface properties. In this study, a sulfonated dextrin (SD) was synthesized via chemical modification and evaluated as a selective depressant for pyrite in the chalcopyrite–pyrite flotation system. Micro-flotation experiments demonstrated that SD exhibited significantly superior selective depression for pyrite compared to unmodified dextrin. At pH 8.0, SD achieved over 95% depression of pyrite with negligible impact on chalcopyrite flotation. In mixed-mineral flotation, SD reduced pyrite recovery from 75.01% to 27.08% at a dosage of 100 mg/L, while chalcopyrite recovery increased from 80.56% to 87.65%. Contact angle measurements revealed that SD markedly enhanced the hydrophilicity of pyrite surfaces, whereas chalcopyrite surfaces retained strong hydrophobicity in the presence of SBX. Zeta potential and FTIR analyses indicated that SD strongly adsorbed onto pyrite surfaces through the introduced sulfonic groups (−SO3−), effectively hindering subsequent SBX adsorption. XPS analysis further suggested chemical interactions between SD and oxidized iron species on pyrite surfaces, forming a stable organic–inorganic composite adsorption layer. These findings demonstrate SD to be a promising environmentally friendly depressant for selective copper–sulfur separation under low-alkalinity conditions, offering a viable alternative to conventional lime-based processes.