How does selective flotation separate nickel sulfide minerals from waste rock?

Selective flotation is a critical mineral processing technique used to separate nickel sulfide minerals from waste rock by exploiting differences in surface chemistry.12

The process involves the following steps:

• Preparation: The ore is crushed and ground to liberate the nickel-bearing minerals from the surrounding waste material.2
• Chemical Conditioning: The ore is mixed with water and specialized reagents. These chemicals bind to the surface of the nickel sulfide particles, rendering them hydrophobic (water-repellent).12
• Agitation and Aeration: The mixture is agitated using mechanical or pneumatic devices to introduce air bubbles. Because the nickel sulfide particles are hydrophobic, they adhere to the rising air bubbles.12
• Collection: The mineral-laden bubbles rise to the surface to form a froth, which is then skimmed off as a concentrate. The waste material, or tailings, remains in the pulp and is discarded or sent for further cleaning.12

In complex deposits, such as those containing both copper and nickel, a second stage of selective flotation may be employed to further separate the minerals into distinct concentrates.2