activator

In flotation circuits, an activator is a soluble chemical compound applied to mineral pulp to modify the surface properties of otherwise unreceptive minerals, making them hydrophobic enough to attach to air bubbles and float. Most minerals arrive at the flotation cell with surfaces coated by oxidation layers, gangue particles, or conditioning agents that prevent collector molecules from adhering. The activator breaks or alters this barrier, creating a receptive site for the collector to work.

The most common activators are metal sulfates and hydroxides. Copper sulfate (CuSO₄) activates sphalerite (zinc blende) by depositing a thin film of copper sulfide on the mineral surface; this film then accepts the collector, typically xanthate. Lime (CaO or Ca(OH)₂) functions as an activator in reverse, raising pH to deactivate unwanted minerals while keeping target minerals receptive. Sodium carbonate and sodium silicate serve as activators in some circuits by adjusting ionic strength and pH simultaneously.

Dosage is critical and usually ranges from 10 to 200 grams per tonne of ore, depending on mineral type, mineral liberation, and pulp composition. Too little activator leaves the mineral surface unreceptive; too much wastes money and can create competitive effects where multiple minerals activate simultaneously, reducing selectivity. The activator is typically added as a dilute solution ahead of the collector, sometimes in the conditioning tank upstream of flotation, allowing time for surface reaction before the air spargers begin.

Activators struggle when the mineral surface is heavily oxidized or when fine clays blanket the target particles. Temperature, pH, and ionic composition of the mill water all influence activator performance. In operations recycling process water, accumulated salts and dissolved metals can inhibit or accelerate activation unpredictably. Operator control of activator addition, particularly in high-throughput mills, is often manual and inconsistent, leading to flotation instability that is wrongly attributed to ore grade variation.

The term activator derives from its function: it activates a dormant or passive surface. In older literature it is sometimes called a depressant when the chemical suppresses unwanted minerals instead, though modern usage distinguishes between the two. Understanding the activator as part of a three-step surface chemistry sequence, conditioning, activation, and collection, clarifies why flotation circuits demand careful control of all three, not just the collector.