How Flotation Works: The Mechanics

The essential mechanism of flotation is that mineral particles be attached to air bubbles so those particles are carried to the surface of the ore pulp, where they can be removed. The process includes the following steps:

• Grinding the ore fine enough so the valuable mineral particles are separated form those of the adhering gangue (worthless rock).
• creating rising current of air bubbles in the ore pulp.
• Making conditions favorable for adhering the desired mineral to air bubbles.
• Forming a mineral-laden froth on the surface of the ore pulp.
• Removing the mineral-laden froth.

Each step is discussed in turn in the following comments.

• Grinding the ore has an important influence on the flotation process. For optimum flotation results, valuable minerals should be separated completely from the waste rock (gangue) and form each other in the grinding step. However, this is not often economically feasible, and even when complete separation is attained, other complicating factors may arise. Example: with common ball mill or rod mill grinding, gangue slimes may form that will complicate subsequent flotation steps.
• Creating a rising current of air bubbles can be done by a flotation machine that produces bubbles bye the mechanical agitation of the ore pulp, by the direct introduction of air under pressure, or both. These operations are “mechanical” adjuncts of the flotation process.
• To get the desired mineral particles to “stick” to the air bubbles, and to form a mineral-laden froth on the surface of the ore pulp, a hydrophobic (water hating) surface must be formed on the particles to be floated, and a hydropillic (water loving/wettable) film on all others. Materials called “COLLECTORS” and “MODIFIERS” do this and selecting the proper combination of reagents for each particular ore is a principal responsibility of the ore dressing metallurgist.
• -5 The frother must produce a froth that is durable enough to permit removal of mineral-carrying bubbles form the flotation machines. The froth must breakdown in launders, must have minimal collecting properties to allow selectivity of the desired mineral to be recovered, and must allow drainage of unwanted insolubles.