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Unlocking Minerals from Ore – The Value of Froth Flotation

Froth flotation is an important concentration process that selectively separates hydrophobic valuable minerals from hydrophilic waste gangue. In its simplest form, froth flotation is a method where minerals can be “skimmed” from the surface of “slurry” that is “foamed” with the assistance of specific chemicals, water, and air bubbles.

The following is a diagram of a typical froth flotation process –

1. Liberation – Crushing and grinding ores to increase surface area and liberate the mineral particles
2. Conditioning – Adding surfactants or collector chemicals such as xanthates, dithiophosphinates, thionocarbamates to achieve hydrophobic surface charges on the desired mineral particles
3. Flotation – A flotation frother – like Methyl Isobutyl Carbinol, 2-Ethyl Hexanol, or terpenic oil – and a “slurry” of fine powder and water are then introduced to a water bath (i.e., flotation cell) which is aerated, creating bubbles.
4. Frothing – A stable froth is formed on the surface of the flotation cell from the aeration. The minerals and metals (i.e., hydrophobic particles) attach to the air bubbles, which rise to the surface. The remaining material from the ore does not rise to the surface.
5. Separation – The mineral laden froth is then separated from the water bath and the resulting concentrate is further refined to deliver the desired mineral or metal. The remaining “slurry” can be further frothed in a downstream flotation cell. The greatest value of froth flotation, versus other concentration approaches, is when a mine is processing fine-grained ores and for high-value sulfide ores like Copper, Copper-Molybdenum, and Platinum Group Metals. In these cases, the initial ore could contain between 0.1-0.5% of the desired metal or mineral and following the flotation process the grade can increase to 20-25%. However, the froth flotation process is also used to extract coal, iron, potassium chloride, phosphates, and – in the paper recycling industry – for deinking paper fibers.

While the froth flotation process certainly can require significant investment – in equipment, specialty chemicals, etc. – it offers significant flexibility to the mine to tailor the process to their specific ore. Of the options available to a mine, the collector, modifier, frother, and flotation cell design are the major elements that can be adjusted.

• Collectors impart hydrophobicity to increase possibility of bubble-mineral attachment by adsorbing on mineral
• Modifiers have multiple functions; changing pH, altering dispersion, and affecting the rise-velocity of bubbles
• Frothers affect the quality of the froth that enables the separation of metals and minerals from waste gangues

The perfect combination of chemicals and flotation cell design is the key for a high-efficiency flotation process. Further, this ability to make refinements and adjustments to multiple elements of the process is part of what gives froth flotation an advantage over other processes.