The effect of ultrasound treatment on wettability and floatability

Despite the three-decade study in the ultrasound (US) impact on mineral’s floatabilities, there is still not a clear image regarding its role on mineral surface characteristics. For this purpose, the current investigation studies the wettability, roughness and floatability characteristics of six mono-minerals i.e. quartz (strongly hydrophilic), cassiterite (hydrophilic), calcite (moderately hydrophilic), pyrite (slightly hydrophobic), chalcopyrite (fairly hydrophobic) and talc (strongly hydrophobic) to cover the entire spectrum of mineral hydrophobicity properties.
Ultrasound at variable amplitudes were supplied by an ultrasonic bath (35 kHz, 140/560 W, 1.5 A) and sonotrode Sonopuls (20 kHz, 200 W and 0.9 A). Sonopuls’s time (15, 30, 45, 60 and 90 s) and power levels (30, 60, 90, 120 and 180 W) as well as ultrasonic bath’s time (15, 30, 45 and 60 min) were evaluated while dissolved oxygen, temperature, conductivity and pH were monitored. Micro-flotation tests were carried out on the US pre-treated and during the ultrasound treatment. The wettability of the samples was analyzed by optical contour analysis (OCA). Surface morphology and topography were investigated by optical profilometry and atomic force microscopy (AFM) together with scanning electron microscopy (SEM).
The results obtained for the strongly/relatively hydrophobic and hydrophilic minerals confirm that the ultrasonic pre-treatment creates intensive rough surfaces inducing an increase on the mineral hydrophobicities. However, a longer ultrasonic time led to smoothening particle surface roughness and consequently reduced the mineral wetabilities/floatabilities. Naturally/slightly hydrophilic minerals behaved differently in the presence and absence of ultrasonic vibrations which were argued in detail.