H2O2-mediated surface chemistry converts a non-selective depressant to galena-selective for efficient Cu–Pb flotation separation

The flotation separation of chalcopyrite and galena remains challenging due to their similar surface properties. Here, we demonstrate that H 2 O 2 pretreatment passivates Cu sites (forming Cu–O) while activating Pb sites (forming Pb–O) on mineral surfaces, which transforms sodium 2-(dithiocarboxylato)ethyl acetate (DTCA) from non-selective into a galena-selective depressant. Micro-flotation experiments indicate that with H 2 O 2 oxidation duration of 30 min, pH of 10, and DTCA dosage of 100 mg/g, galena recovery can be reduced to below 5% while maintaining chalcopyrite recovery above 90%. Following oxidation, the adsorption amount of chalcopyrite decreased from 96.54 to 7 mg/g, while that of galena increased from 101.32 to 102.45 mg/g. Multiscale characterizations (FTIR, XPS, ToF-SIMS) indicate that DTCA adsorbs onto the surfaces of chalcopyrite and galena, respectively, via chelation between S–Cu–S and S–Pb–S bonds. Density functional theory (DFT) calculations confirm that oxidation enhanced the adsorption strength of DTCA on the surface of galena, with the adsorption energy shifting from −2.571 to −2.645 eV. Conversely, adsorption strength decreased significantly after oxidation of chalcopyrite, with the adsorption energy shifting from −2.470 to −1.588 eV. Closed-circuit tests on industrial concentrates yielded copper recovery and grade reached 93.13% and 27.43%, respectively, while lead achieved 96.33% recovery and 43.21% grade, with a separation index (SI) of 2.55, surpassing that achieved by the toxic potassium dichromate(K 2 Cr 2 O 7 ) method. This study proposes a Cr (VI)-free flotation strategy for efficient Cu–Pb separation, offering a promising alternative to conventional environmentally hazardous methods.