Reverse flotation

What is reverse flotation?

In most froth flotation, called direct flotation, the valuable mineral is made water-repellent and carried up into the froth, while gangue stays in the pulp. Reverse flotation does the opposite: the gangue is floated and removed, and the valuable mineral is recovered from the underflow.

It makes sense when the gangue is the smaller part of the feed, or when the gangue responds to collectors more selectively than the valuable mineral does.

Iron ore: the main example

Iron ores often contain silica, quartz, that must be removed to meet concentrate specifications. In reverse cationic flotation, commonly used for iron ore:

• Amine collectors, cationic collectors, attach to quartz and float it.
• Starch acts as a depressant for the iron oxides, keeping them in the pulp.
• pH is kept alkaline to promote selectivity.

The iron oxides remaining in the pulp become the concentrate.

Other applications

Reverse flotation is also used for other ores, such as removing carbonate or silicate gangue from phosphate ores and cleaning some industrial minerals.

Challenges

• Slimes, very fine particles that consume reagents and reduce selectivity, often need to be removed before flotation.
• Froth handling. Because the froth is the reject stream, valuable mineral lost to it through entrainment directly reduces recovery.
• Reagent consumption and water chemistry affect selectivity.

Frequently asked questions