PAPE- and Fe3+-Mediated Synergistic Depression Selectivity of Calcite: A Superior Depressant Regimen for Scheelite Flotation

The selective flotation separation of scheelite from calcite is challenging owing to the similarity of calcium active sites present on their surfaces. In this work, a novel depressant system was developed comprising polyamino polyether methylene phosphonic acid (PAPE) as the depressant and Fe3+ as the modifier. Microflotation tests conducted under weakly alkaline conditions demonstrated that the combined reagent system achieved a scheelite recovery of 95.34% while effectively suppressing calcite recovery to only 10.37%. Flotation of artificially mixed minerals yielded a concentrate assaying 62.38% WO3 at a recovery of 88.67%. Mechanistic characterization elucidated a synergistic inhibition mechanism whereby PAPE was preferentially adsorbed at calcite surfaces, inducing Ca2+ dissolution, while Fe3+ promoted further Ca2+ release and its hydrolysis products concomitantly occupied the remaining active sites. The concerted action of these components gave rise to a dense hydrophilic layer that effectively impeded NaOL adsorption while exerting negligible influence on scheelite hydrophobicity. This “dissolution–adsorption–occupation” mechanism provides a novel strategy for the selective separation of calcium-bearing minerals.