Trisodium 4-carboxy-5-mercapto-3-hydroxy-isothiazole: A novel selective organic depressant for the flotation separation of CuZn sulfide minerals

The efficient separation of chalcopyrite from sphalerite remains a significant challenge in flotation due to their similar surface properties. In this study, Trisodium 4-carboxy-5-mercapto-3-hydroxy-isothiazole (TCMHI) was introduced as a novel, eco-friendly, and selective organic depressant for sphalerite. Micro-flotation tests demonstrated that TCMHI (73 mg/L) could selectively depress sphalerite flotation (recovery <14%) at pH 7.0 while maintaining high chalcopyrite recovery (> 94%). Successful separation was achieved in artificially mixed mineral tests, yielding a concentrate with a Cu grade of 32.01% and a recovery of 96.65%. To validate its industrial applicability, bench-scale flotation tests were conducted on a real Cu Zn sulfide ore. The results showed that TCMHI achieved metallurgical performance comparable to the conventional depressant zinc sulfate (ZnSO 4 ), maintaining a copper recovery of 71.32% while effectively suppressing zinc recovery to 21.18% in the concentrate. Surface characterization techniques, including contact angle, zeta potential, and Atomic Force Microscopy (AFM), revealed that TCMHI preferentially adsorbs onto the sphalerite surface, forming a dense hydrophilic layer that hinders collector adsorption. X-ray Photoelectron Spectroscopy (XPS) and Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) analyses confirmed that TCMHI chemically adsorbs on sphalerite through the formation of stable Zn-TCMHI surface complexes. Density Functional Theory (DFT) calculations further elucidated the mechanism, showing that TCMHI forms a stable five-membered chelate ring with surface Zn atoms via its nitrogen and endocyclic sulfur atoms. Crucially, the adsorption energy of TCMHI on sphalerite (−209.76 kJ/mol) was found to be significantly more negative than that of the collector (−95.88 kJ/mol), explaining its superior depression performance. This work provides a promising reagent for the sustainable and efficient flotation separation of Cu Zn sulfide ores.