Flotation performance and adsorption mechanism of α-hydroxyoctyl phosphinic acid to pyrochlore

The flotation performance and adsorption mechanism of α-hydroxyoctyl phosphinic acid (HPA) on pyrochlore were investigated through micro-flotation experiments, zeta-potential tests, contact angle measurements and XPS analysis. The flotation results demonstrated that, in comparison to N-hexadecylpropane-1,3-diamine (NHDA), HPA exhibited a comparable collecting ability for pyrochlore but displayed superior selectivity against feldspar and quartz. Adsorption experiments revealed that the pyrochlore exhibited a higher adsorption capacity for HPA compared to feldspar and quartz. The contact angle experiments indicated that the treatment with HPA significantly increased the contact angle for pyrochlore and calcite, while only minimal changes were observed for feldspar and quartz. Zeta potential and XPS data provided evidence for the chemical adsorption of HPA onto pyrochlore surfaces. Detailed XPS results showed that P-OH groups in HPA formed P(III)-O-M (M = Ca and Nb) bonds with Ca and Nb species on the pyrochlore surface. Additionally, the P-H bond in the HPA molecule could undergo a Redox reaction with highly oxidized Nb, resulting in the formation of a P(V)-Nb(IV) bond. This P(V)-Nb(IV) bond enhances the adsorption of hydrophobic HPA onto the mineral, making it easier to recover pyrochlore through flotation.