Activator
In froth flotation, an activator is a reagent that changes a mineral's surface so that a collector can attach to it, making a mineral float that otherwise would not. The classic example is copper sulfate, which activates sphalerite, the main zinc mineral, for flotation with xanthate collectors.
What is an activator?
Froth flotation separates minerals by making the valuable ones water-repellent so they attach to air bubbles. A collector supplies that water repellency, but some minerals do not react well with the available collectors. An activator treats the mineral surface first so that the collector will adsorb.
Activators belong to the group of reagents called modifiers or regulators, together with depressants, which do the opposite, and pH regulators.
The classic example: copper sulfate and sphalerite
Sphalerite, zinc sulfide, responds poorly to short-chain xanthate collectors. When copper sulfate is added, copper ions exchange with zinc at the sphalerite surface, creating a copper-sulfide-like surface that reacts readily with xanthate. This is why sequential lead-zinc flotation plants typically:
- Float galena, the lead mineral, first while sphalerite is depressed.
- Add copper sulfate to activate the sphalerite.
- Float the zinc mineral in a separate circuit.
Other examples
- Sulfidizing agents, such as sodium hydrosulfide, which create a sulfide-like surface on oxidized minerals of copper, lead and zinc so that sulfide collectors can float them.
- Metal ions in non-sulfide flotation, where dissolved calcium or other ions can activate minerals such as quartz toward anionic collectors, sometimes deliberately and sometimes as an unwanted effect.
Why dosage matters
Too little activator leaves the target mineral unfloated. Too much, or activation by metal ions already in the process water, can activate minerals that should stay down, hurting flotation selectivity and concentrate grade.
Frequently asked questions
The collector makes the mineral water-repellent. The activator prepares the surface so the collector can attach.
Yes. Metal ions dissolved from the ore or present in recycled water can activate gangue minerals, one reason water chemistry matters in flotation.
Sources
- Wills' Mineral Processing Technology, 8th edition, B. A. Wills and J. A. Finch, Butterworth-Heinemann, 2016