The Influence of Static Pressure on Bubble Size and Contact Angle of Quartz: Mimicking What May Happen Inside a Hypothetical Flotation Column

Abstract

This paper addresses the influence of hydrostatic pressure (Phyd) on bubble diameter (db) and contact angle (θ) of quartz in pure water versus collector solution (Flotigam® EDA, γLG = 57 mN/m) at 20 °C. The pressure range (0–300 kPa) applied against the bubbles’ walls mimics what may happen along the vertical axis of a hypothetical flotation column (HFC) that processes iron ore slurry via cationic reverse flotation of quartz. From the column’s bottom (Phyd≈ 300 kPa) to its top (Phyd≈ 0 kPa), a continuous relief of Phyd occurs steadily. Results indicate that a decrease of Phyd promotes a decrease of θ from 47° to 16° in pure water and from 61° to 42° in the presence of collector. Likewise, db increases approximately 60% from the column’s bottom to its top and, consequently promoting an increase in bubble ascending velocity (vb). Values of vb and db were used to assess the bubble Eötvos number (Eo) and the Weber number (We) aiming at characterizing bubble hydrodynamics. It was found that inertial forces dominate surface forces (We > 1) as db> 1.86 mm. This dominance constitutes a preliminary indication of a greater likelihood of coarse particles (diameter > 100 μm) detaching from bubbles. This situation is typically found in the upper parts of the HFC addressed in this paper.