Pre‑adsorbed collector induced surface homogenization of galena and pyrite and its impact on lime depression and galvanic interaction

Collector residues pre‑adsorbed during bulk flotation of lead‑sulfide ores can persist on mineral surfaces and induce a homogenization effect that masks the intrinsic differences between galena and pyrite, compromising subsequent lime‑based selective separation. This work examines how this homogenization effect alters lime depression, collector adsorption, and galvanic interactions using galena, pyrite, and their 1:1 mixtures under three conditions: with the pre‑adsorbed collector layer retained, after a desorption step, and after complete collector removal. The retained collector layer uniformly covered both mineral surfaces and suppressed calcium deposition, leading to non‑selective flotation. In contrast, a simple desorption step restored selectivity by allowing calcium species to preferentially adsorb onto pyrite while galena retained hydrophobic collector coverage. Surface analyses and electrochemical measurements revealed that this selective calcium deposition on pyrite was accompanied by surface oxidation and activation of the galvanic interaction between the two minerals, amplifying the electrochemical differentiation that lime exploits for selective depression. This work establishes a mechanistic link between collector management and surface electrochemical behavior in Pb‒S flotation.