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

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Abstract 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.

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