Investigation on the selectivity of N-((hydroxyamino)-alkyl) alkylamide surfactants for scheelite/calcite flotation separation

• Amide hydroxamate was first introduced as a collector for Ca minerals flotation.
• Amide hydroxamates exhibited superior affinity to scheelite against calcite.
• Amide hydroxamates owned unique bond patterns and double hydrophobic groups.
• Amide hydroxamates formed intermolecular hydrogen bonds on scheelite surfaces.

In this paper, novel amide-hydroxamic acid surfactants, such as (N-(6-(hydroxyamino)-6-oxohexyl) benzamide (NHOB), N-(6-(hydroxyamino)-6-oxohexyl) octanamide (NHOO), N-(6-(hydroxyamino)-6-oxohexyl) decanamide (NHOD) and N-(4-(hydroxyamino)-4-oxobutyl) octanamide (NOBO), were introduced as flotation collectors for selective separation of scheelite from calicite. The micro-flotation results demonstrated that compared to NHOO, NOBO and NHOB, NHOD exhibited superior collecting power to scheelite and enabled the separation of scheelite and calcite under pH around 10. The calculation results of density functional theory (DFT) and C log P (octanol–water partition coefficient) indicated that NHOD owned excellent hydrophobicity and affinity to scheelite surfaces. The analyses of FTIR spectra, zeta potential and XPS illustrated that besides the electrostatic attraction with Ca cationic species on scheelite surfaces, NHOD might chemisorb onto scheelite by formation of NHOD-W surface complexes, resulting in a superior selectivity to scheelite compared with calcite. NHOD's unique properties, such as characteristic bond patterns on scheelite surfaces, double hydrophobic groups, and intermolecular hydrogen bonds between neighboring molecules coated on scheelite surfaces, rendered it to be a superior collector for scheelite/calcite flotation separation.

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