How does flotation separation concentrate zinc sulfide minerals?

Flotation separation is the primary method used to concentrate zinc sulfide minerals from ore, which typically contains only a small fraction of the desired metal. The process relies on manipulating the physicochemical surface properties of minerals to separate them from unwanted constituents, known as gangue.12

The concentration process involves several key steps:

• Preparation: The ore is crushed and ground in a ball mill until the particles are less than 0.1 millimetre in size, creating a slurry with water.1
• Chemical Treatment: Selected chemical reagents are added to the slurry. These agents alter the surface of the zinc sulfide particles, making them hydrophobic (water-repelling), while the gangue remains hydrophilic (water-attracting).21
• Aeration and Agitation: The slurry is agitated in flotation cells where air is introduced to create a suspension of bubbles. The hydrophobic zinc particles adhere to these air bubbles and rise to the surface.12
• Collection: The bubbles form an oily froth at the top of the cell, which is continuously skimmed off to collect the concentrated zinc minerals. Meanwhile, the wetted gangue sinks to the bottom and is removed as tailings.21

This technique allows for the effective separation of complex, intergrown ores.2