Flotation is a mineral processing method used to separate valuable minerals from gangue by exploiting differences in their surface properties. In flotation, chemicals called reagents are added to a slurry of ground ore and water, making valuable minerals hydrophobic (water-repellent). These reagents selectively adsorb onto the surfaces of desired minerals, enhancing their hydrophobicity.
Differences in surface energy and surface chemistry between minerals influence their interaction with air bubbles, which is fundamental to the separation process. Air bubbles are introduced, and the hydrophobic particles attach to the air bubbles and rise to the surface, forming a froth that can be skimmed off as concentrate. Froth flotation is also widely used in other processing industries, such as wastewater treatment and paper recycling, due to its effectiveness in separating fine particles.
Why does flotation matter? It is one of the most widely used methods for concentrating ores, especially for copper, gold, lead, zinc, and rare earth elements. Flotation makes it possible to extract metals from low-grade and complex ores, supporting global industries from electronics to renewable energy.
The History of the Froth Flotation Process
Flotation was first patented in the late 19th century and revolutionized mineral processing in the early 20th century.
Early industrial testing of flotation processes took place in locations such as Salt Lake City, where Charles Butters built an Elmore process plant to test flotation on gold ores. Prior to flotation, many low-grade ores were considered uneconomic.
The introduction of flotation dramatically increased metal recovery, especially during World War I and II when demand for copper and zinc surged.
The rise of mechanized mining, combined with flotation, enabled the efficient extraction of valuable metals from much lower grade ore. Today, flotation remains the dominant method for sulfide ores, with modern advances including column flotation and automated control systems.
Terms to Know
- Flotation Reagents: Chemicals used to modify the surface properties of minerals during flotation.
- Chemical Reagents: Substances added to the flotation process to enhance or inhibit mineral separation.
- Chemical Compounds: Specific chemicals used as reagents to alter particle wettability and facilitate separation.
- Wetting Agents: Surfactants that increase hydrophobicity differences between minerals and gangue.
- Mixing Tank: Vessel where slurry is agitated and air is introduced during flotation.
- Ore Particles: Ground fragments of ore subjected to flotation.
- Gangue Minerals: Non-valuable minerals separated from ore during flotation.
- Undesirable Minerals: Minerals present in ore that are not targeted for recovery.
- Target Minerals: Specific minerals intended for recovery during flotation.
- Valuable Particles: Mineral particles that are economically important and targeted for recovery.
- Flotation Tailings: Residual material left after valuable minerals are separated.
- Final Tailings: Waste material remaining after all flotation stages.
- Rougher Concentrate: Initial product from the rougher flotation step, containing a high proportion of target minerals.
- Rougher Tailings: Material left after the rougher flotation step, often subjected to further processing.
- Flotation Recovery: Percentage of valuable minerals recovered during flotation.
- Tailings Disposal Facilities: Designated sites for the long-term storage of mine waste after flotation.
- Reagents: Chemicals used to condition the ore slurry.
- Collector: A reagent that selectively binds to valuable minerals.
- Frother: A reagent that stabilizes bubbles.
- Concentrate: The valuable mineral-rich froth product.
- Tailings: Waste material left after flotation.
The Pros and Cons of Flotation
Pros:
- High selectivity for valuable minerals. High flotation recovery rates are essential for maximizing the extraction of valuable metals.
- Enables economic processing of low-grade ores.
- Produces high-concentration metal products.
Cons:
- Requires chemicals that may impact the environment.
- Generates tailings requiring safe disposal. Final tailings are typically sent to tailings disposal facilities for long-term storage and environmental management.
- Energy and water-intensive.
According to the International Council on Mining and Metals (ICMM), flotation is used to process over 70% of the world’s copper ores, making it indispensable to global supply chains.
Examples of Flotation in Mining
- Copper: Used in porphyry copper mines in Chile, Peru, and the U.S.
- Gold: Sulfide gold ores are concentrated via flotation before cyanidation.
- Zinc & Lead: Widely processed using selective flotation to separate lead sulfide (galena) and zinc sulfide from ore.
- Rare Earth Elements: Flotation separates REEs from host minerals.
Flotation is also widely used to separate sulfide minerals and other target minerals, with the goal of recovering valuable particles from complex ores.
How a Flotation Cell Works
- Grinding: Ore is ground into fine particles. Controlling particle size is critical for efficient mineral liberation and flotation.
- Conditioning: Reagents are added to modify surface properties. These reagents interact with mineral surfaces and surface layers, changing their hydrophobicity and selectivity. Chemical reactions between reagents and mineral surfaces are essential for modifying surface properties and enhancing flotation.
- Aeration: Air is introduced, forming bubbles. Introducing slurry into the flotation cell allows for the production of bubbles in the liquid phase.
- Attachment: Hydrophobic minerals attach to bubbles. Hydrophobic layers form on mineral surfaces, promoting attachment to air bubbles, while hydrophilic particles remain in the slurry.
- Collection: Froth rises and is skimmed off as concentrate. A stable froth is essential for effective recovery of floated minerals.
A copper ore with 0.6% Cu can be upgraded via flotation to produce concentrate with 30% Cu.
Flotation Equipment
Flotation equipment plays a crucial role in the froth flotation process, enabling the separation of valuable minerals from waste rock. At the heart of this process is the flotation cell, the vessel where the flotation process occurs. Flotation cells come in several designs, but they all serve the same purpose: to create the ideal environment for mineral particles to attach to air bubbles and rise to the surface for collection.
There are two main types of flotation cells used in mineral processing: mechanical flotation cells and pneumatic flotation cells. Mechanical flotation cells, such as cylindrical mechanically agitated cells, use a combination of a mixer and a diffuser mechanism to introduce air and keep the slurry well-mixed. This high shear creates optimal conditions for bubble particle contacting, allowing valuable minerals to attach to air bubbles efficiently. Pneumatic flotation cells, including flotation columns, rely on air spargers to generate fine bubbles at the bottom of a tall column, promoting the selective flotation of minerals based on their surface properties.
The selection of flotation equipment depends on several factors, including the type of valuable minerals being targeted, the particle sizes present in the ground ore, and the specific surface properties of the mineral particles. Flotation machines are often tailored to different flotation stages—such as rougher flotation, scavenger flotation, and cleaner flotation—to maximize recovery and produce higher quality concentrates. By carefully choosing the right flotation cells and optimizing their operation, mineral processing plants can efficiently separate valuable minerals from gangue, even when dealing with complex ores or much lower grade ore.
Whether using conventional mechanically agitated cells or advanced flotation columns, modern flotation technology continues to evolve, helping the mining industry achieve higher recovery rates and better concentrate quality while managing the challenges of waste rock and variable ore characteristics.
Tips and Reminders for Using Flotation Reagents
- Correct flotation reagent selection, including the use of wetting agents, is essential for maximizing flotation recovery and selectivity.
- Froth stability affects efficiency.
- Water quality can impact flotation performance.
Analyzing Flotation Efficiency for Valuable Minerals
Flotation efficiency is evaluated using:
- Flotation Recovery: A key indicator of process performance, representing the percentage of valuable mineral recovered.
- Grade of Concentrate: Purity of the product.
- Reagent Consumption: Costs of chemical inputs, including both flotation reagents and other chemical reagents, which play a significant role in process costs and efficiency.
For example, improving copper recovery by 1% in a large operation can yield tens of millions of dollars in additional revenue annually.
Resources for Flotation
- Books: Froth Flotation: A Century of Innovation by Maurice Fuerstenau.
- Reports: SME publications on flotation advances.
- Organizations: International Mineral Processing Council (IMPC).
Checkout our list of the Best Books every miner should read
Closing
Flotation has transformed the mining industry by enabling the recovery of metals from ores once considered waste. Its efficiency and adaptability make it essential to global resource supply. As demand for critical minerals grows, flotation will remain at the heart of mineral processing.
Call-to-Action: Explore more terms in our [Mining & Mineral Processing Glossary] to understand how flotation works alongside grinding, leaching, and smelting.
