Flotation selectivity
- Also known as
- selectivity
Flotation selectivity is the ability of a flotation process to recover the target mineral into the concentrate while rejecting gangue and other unwanted minerals. Higher selectivity allows a higher concentrate grade at the same recovery.
What is flotation selectivity?
Every froth flotation circuit tries to do two things at once: recover as much of the valuable mineral as possible, and keep everything else out of the concentrate. Selectivity measures how well it separates the two. A highly selective process produces a clean, high-grade concentrate without giving up much valuable mineral to the tailings.
Selectivity also applies between valuable minerals, for example in circuits that float lead and zinc sequentially or separate copper from molybdenum.
Selectivity, grade and recovery
For a given ore and process, there is a trade-off between concentrate grade and metallurgical recovery, shown by the grade-recovery curve. Operating choices move the plant along that curve. Better selectivity moves the whole curve, allowing more recovery at the same grade or higher grade at the same recovery. That is why selectivity improvements are often worth more than changes in operating point.
What controls selectivity
- Reagents. How specifically the collector attaches to the target mineral, and how well depressants keep other minerals from floating.
- Mineral liberation. Particles containing both valuable mineral and gangue float together and dilute the concentrate.
- Entrainment. Fine gangue carried into the froth with water reduces selectivity, independent of reagent chemistry.
- Froth behavior. Froth depth, drainage and washing affect how much unattached material reports to the concentrate.
- Water and ore chemistry, including pH, dissolved ions, oxidation and clays.
Frequently asked questions
Usually by comparing grade and recovery results, for example by plotting grade-recovery curves from laboratory tests with different reagents, or with separation efficiency indices that combine recovery of the valuable mineral and rejection of gangue.
Yes. Changes that improve selectivity, such as a more selective reagent or reduced entrainment, can raise grade and recovery together by shifting the grade-recovery curve.
Sources
- Wills' Mineral Processing Technology, 8th edition, B. A. Wills and J. A. Finch, Butterworth-Heinemann, 2016
- SME Mineral Processing and Extractive Metallurgy Handbook, Society for Mining, Metallurgy and Exploration, 2019