Mapping hydrophobicity combining AFM and Raman spectroscopy

• We investigate the hydrophobization of individual minerals in a ore cross-section.
• The force of adhesion is a stable value to map hydrophobicity.
• We detect the mineral phase with Raman spectroscopy while measuring forces.
• In our measurements the hydrophobic effect is due to gas layers on the surface.
• Sodium oleate has a poor selectivity for a silicate type ore from Norra Kärr.

A new concept to evaluate the floatability of individual minerals in an ore specimen is presented. The method is based on the combination of colloidal probe atomic force microscopy to determine hydrophobic interactions responsible for the flotation of fine mineral particles and Raman spectroscopy to identify the mineral phase at the same location. Both methods show a high spatial resolution and allow investigating even small individual minerals. The ore sample of this study is a syenite rock from south Sweden containing the valuable rare earth mineral eudialyte and gangue minerals mainly comprising feldspars, nepheline, aegirine and zeolites. Using the poor selective collector sodium oleate we demonstrate how hydrophobic interactions become apparent by conducting force distance measurements in the aqueous environment. We discuss different parameters of the force spectroscopy in static and dynamic mode to be used to define a measure for floatability. In contrast to other studies on the hydrophobic interactions in flotation we propose to draw information from the detachment of the hydrophobic probe particle of the atomic force microscope from the mineral surface in contrast to the approach force distance spectroscopy. All the hydrophobic interactions identified can be attributed to the appearance of gas layers on the surfaces leading to capillary interactions.

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