Mechanism of Flotation of Metallic Droplets in Oxide Melts

Abstract

The flotation of droplets in liquids is a frequent phenomenon. For example, flotation is the basis of the removal of liquid nonmetallic inclusions from steel. However, the mechanism of this phenomenon is still poorly understood. The mechanism of flotation of metallic droplets in a melt is comprehensively studied using gold as an example. The kinetics and stages of formation of a gas bubble–attached gold droplet system and the subsequent gold flotation in a melt are investigated. Once a gas bubble and a droplet are in contact, the gold–gas surface and a wetting perimeter are added to the existing slag–gas and gold–slag surfaces. The time is takes for gold droplets about 3 μm in radius to achieve equilibrium is about 10^–4 s. Therefore, the formation of an equilibrium bubble–droplet system is fast and does not retard the general process of collection and coarsening of gold droplets by gas bubbles. The flotation condition for the fine (Au, Pt, Pd) droplet–oxide melt system is analyzed. This condition is met for metallic droplets up to 3500 μm in radius.