Unveiling the dual role of substituted iron in sphalerite flotation depression under alkaline aeration: from solution speciation to interfacial mechanisms

Understanding the effects of oxidation on the flotation of sphalerite with varying iron contents during slurry conditioning is of considerable importance. This paper investigated the impact of substituted iron content on the flotation and reagent adsorption behavior of sphalerite following air aeration in the slurry, and elucidated the underlying mechanisms. The results showed that the inhibitory effect of aeration oxidation on sphalerite flotation intensified with increasing substituted iron content and alkalinity, accompanied by greater reductions in copper and butyl xanthate adsorption. Sphalerite oxidation activity increased with iron content, accompanied by greater metal ion dissolution. In the resulting system, most iron existed as hydroxide precipitates, while Zn(CO3)22−, Fe(OH)4−, and Fe(OH)3− were the dominant anionic species in solution. X-ray photoelectron spectroscopy (XPS) analysis confirmed that oxygen content, polysulfide proportion, and metal oxides/hydroxides on the oxidized surface increased significantly with iron content. Higher iron content enhances sphalerite oxidation, promoting metal ion release and formation of iron hydroxide precipitates and hydroxylated anions. These species adsorb onto the surface, blocking reagent sites, while the hydroxylated anions also repel xanthate through electrostatic effects. Collectively, these factors impair activation and collection, leading to stronger flotation depression of high-iron sphalerite.