Novel pyrite depressant at low alkalinity: Selective adsorption mechanism and its application in separation of galena from high-sulfur lead ore

Low-alkalinity flotation separation of galena from pyrite is challenging yet important. In this study, N-(2-hydroxyethyl) ethylenediamine-N, N', N'-triacetic acid trisodium salt (HEDTA-3Na) was introduced as a novel organic depressant for pyrite to enable selective depression in galena-pyrite flotation system under low-alkaline conditions. At pulp pH of 9 and a HEDTA-3Na dosage of 30 mg/L, the recovery difference between galena and pyrite reached approximately 81%. Flotation of galena-pyrite mixture produced a high-quality lead concentrate with a lead grade of 73.91% and a lead recovery of 85.47%. Contact angle measurements demonstrate that HEDTA-3Na can significantly reduce the surface hydrophobicity of pyrite and hinders collector adsorption, while exerting negligible influence on the wettability of galena. Zeta potential measurements indicated that after HEDTA-3Na treatment, the surface potential of pyrite shifted more negatively than that of galena. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) characterizations confirmed that HEDTA-3Na adsorbs onto galena primarily via physical adsorption. On the pyrite surface, Fe²⁺ is oxidized to Fe³⁺ active sites, which subsequently hydrolyze to form FeO(OH) and Fe(OH)₃. Meanwhile, Fe³⁺ ions coordinate with the carboxylate and N‐bearing groups of HEDTA‐3Na, forming Fe–O chelate linkages and surface‐bound iron chelates. These species stably cover the pyrite surface and create a hydrophilic film. Ultimately, by replacing lime with HEDTA-3Na, flotation separation of galena from pyrite was achieved for actual ore under low-alkalinity conditions. In contrast to the conventional high‐alkalinity process employing lime, HEDTA‐3Na enables efficient pyrite depression at a lower pulp pH (8.5) and a relatively low dosage. This results in a lead concentrate with higher lead grade and recovery, while greatly reducing lime consumption, thereby providing significant environmental advantages and promising application potential.