Modern Developments in Froth Flotation: Greener Reagents, New Cells and Smarter Control

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Froth flotation has been the main way to concentrate sulfide ores for more than a century, but it is still changing. Ore grades are falling, ores are more complex and finer-grained, water is scarcer, energy costs more, and regulators and communities are paying closer attention to the chemicals mines use. This article looks at how flotation is responding: greener reagents, new ways of using water, machines that recover very coarse and very fine particles, and better measurement and control.

If you are new to flotation, start with our froth flotation basics. For the full treatment of reagents, kinetics, machines and circuit design, see the complete guide to froth flotation.

Why Flotation Is Changing

  • Lower grades and finer liberation: many deposits now have to be ground finer to free the valuable minerals, which produces more slow-floating fines and uses more energy.
  • Energy and water: grinding is the largest energy user in a concentrator, and many mines are in dry regions where fresh water is limited.
  • Reagent toxicity: some long-established reagents, notably xanthates and cyanide, pose health and environmental risks.
  • Tailings: finer grinding makes tailings harder to dewater and store safely, while coarser tailings are easier to handle.

Greener Flotation Reagents

The problem with conventional reagents

Xanthates are the most widely used sulfide collectors because they are cheap, soluble and effective. However, they decompose to carbon disulfide (CS₂), which is a health hazard, and excess xanthate in discharge water can be toxic to aquatic life. Cyanide, used as a depressant in copper–zinc and lead–zinc separations, needs the same careful handling and destruction as in gold leaching. Lime is not toxic, but large amounts are often needed to reject pyrite when using xanthate, and its total cost in a sulfide plant is often about double that of the collector. These issues are driving the search for “green” alternatives.

What makes a reagent “green”

There is no single agreed definition. In practice, researchers and suppliers judge a reagent on where its raw materials come from (renewable or petroleum-based), how it is made, whether it biodegrades, and how toxic it and its breakdown products are. These criteria do not always agree. A bio-based reagent is not automatically less toxic, and a reagent that biodegrades quickly may also break down in the circuit before it has done its job. A greener reagent also has to match the metallurgy of the reagent it replaces, or the gain is lost through lower recovery.

Directions in reagent development

  • Bio-based collectors: fatty acids from plant and animal oils have long been used for phosphate and other salt-type minerals, and research is testing collectors from other renewable sources. A 2025 review of apatite flotation found these promising, but noted that how well they work varies with ore properties such as particle size and surface chemistry.
  • Biosurfactants: surfactants produced by microorganisms are being studied as collectors and frothers with lower toxicity than conventional reagents.
  • Natural polymer depressants: starch, dextrin, guar gum and carboxymethyl cellulose (CMC) are made from natural polysaccharides and are already standard reagents. Starch depresses iron oxides in reverse flotation of silica, dextrin depresses galena in copper–lead separation, and guar or CMC depresses talc in nickel and platinum ores.
  • More selective sulfide collectors: collectors such as dithiophosphates, thionocarbamates and dithiophosphinates are often used with or instead of xanthate. One aim of developing more selective collectors is to reduce the large lime additions needed to reject pyrite.
  • Designer molecules: understanding how collector structure relates to performance is probably the largest topic in basic flotation research. Molecular modelling is used to design collectors for particular minerals, though modelling the mineral surface under real flotation conditions remains the main difficulty. Researchers are also linking frother structure to bubble size and froth properties, which could shorten the search for a frother with the properties a plant needs.
  • Nanoparticle collectors: hydrophobic nanoparticles that attach to mineral surfaces have been proposed as a new class of collector. Whether they become practical is still an open question.

Using less reagent

The simplest green measure is to use less. Plants keep collector at “starvation” levels, add collector in stages along a bank instead of all at the head, compare dosage per tonne of metal rather than per tonne of ore, and use online analysis to adjust dosing as the ore changes. Over-dosing wastes reagent and also hurts the metallurgy, because it floats unwanted minerals and can make the froth too stable or cause it to collapse. Optimal dosage depends on the ore, its liberation and the circuit design. Swapping lime for soda ash, or using both, can also improve results. Several Peñoles copper–lead–zinc concentrators did better after replacing lime with soda ash, which avoids calcium depressing the valuable minerals.

Saline Water and Water Recycling

Many plants now float in salty water, either because they recycle process water or because their source is bore water or seawater. Seawater use is expanding, notably in Chile. Salt changes flotation in several ways:

  • Smaller bubbles: seawater has an ionic strength of about 0.7 M, which produces fine bubbles even without frother. Frother may still be needed to give the froth the right properties.
  • Molybdenite depression: when copper–molybdenum ores are floated in seawater at around pH 10, magnesium ions form a hydroxide that is thought to depress molybdenite. This is one reason seawater plants may need a different pH strategy.
  • Accumulating reagents and ions: recycled water carries residual frother, collector and dissolved metals back into the circuit, which can change reagent demand and selectivity. Monitoring recycle water chemistry is increasingly part of plant control.
  • Brine flotation: potash is floated in saturated brine, where the frother MIBC appears to help the amine collector work.

A related idea is to control the gas, not just the water. Nitrogen in place of air can depress pyrrhotite away from pentlandite in nickel ores. Open mills and cyclones let oxygen back in, which has hampered commercial use, so enclosing cells and recycling the gas has been proposed.

Coarse Particle Flotation

Conventional cells are poor at floating coarse particles, because turbulence knocks them off the bubbles. Coarse particle flotation (CPF) uses fluidized-bed machines such as the Eriez HydroFloat, in which a gently aerated teeter bed lets coarse, partly liberated particles float without being shaken off. Floating coarser particles means the ore can be ground less, saving energy, and the coarse tailings are easier to dewater.

  • Cadia, Australia: Newmont’s Cadia operation commissioned a full-scale HydroFloat trial in August 2018, scavenging coarse values from tailings. Studies found that expanding coarse particle flotation gave a better business case than more fine grinding. After the expansion was completed in 2022, about 75% of concentrator feed was treated through coarse flotation. The coarse, fines-deficient tailings sand can also be used to build tailings embankments.
  • El Soldado, Chile: Anglo American installed a HydroFloat in its copper concentrator in gangue-rejection mode, rejecting coarse barren material early. The paper describing its commissioning won a CEEC Medal.
  • Modified Jameson cell: in pilot work reported in October 2026, Glencore Technology ran a modified Jameson cell as a scavenger on flotation tailings at Antapaccay’s Tintaya concentrator in Peru. It recovered an average of 24.7% of the copper-bearing particles coarser than 150 µm and upgraded them about 5.3 times. These are vendor-reported pilot results.

Flash flotation, which floats coarse, fast-floating minerals straight from the grinding circuit’s cyclone underflow, is an older route to the same goal. It is widely used for gold, which builds up in the circulating load.

Fine Particle Flotation and High-Intensity Cells

At the other end of the size range, fine particles collide with bubbles too rarely and float slowly. Conventional cells can hold only about 15% gas before they start to “boil”, so they cannot simply add more air. A family of reactor/separator machines puts the energy directly into bubble–particle contact in a small reactor, then separates the froth in a short tank:

  • Jameson cell: a plunging slurry jet entrains air in a downcomer, where gas holdup can approach 60%. It is widely used in coal and base-metal cleaning.
  • StackCell: pre-aerated slurry passes through a high-shear aerator at the centre of the cell. It is designed for particles finer than about 150 µm, mainly coal but also iron ore and copper. Its small footprint and gravity feed let units be stacked in series or placed ahead of overloaded circuits.
  • Cavitation bubble generation: devices such as the CavTube create very fine bubbles by a sudden pressure drop and are used as external spargers on flotation columns.
  • Concorde cell and Reflux Flotation Cell: two designs from the University of Newcastle, Australia, for fine particles. The Concorde cell targets particles below about 20 µm. The Reflux Flotation Cell uses parallel inclined channels to keep mineralized bubbles out of the tailings.

Mechanical cells keep growing too. Tank cells of 300–350 m³ were in service by the mid-2010s, 500 m³ cells were being installed and 600–650 m³ cells were being tested. Fewer, larger cells cut capital and operating costs but depend on good level control and instrumentation.

Smarter Measurement and Control

  • Froth imaging: machine vision systems measure froth velocity, texture and colour online, doing what skilled operators do by eye. Several off-the-shelf packages exist. As of the mid-2010s, froth velocity was the only froth property measured robustly enough to be used as a controlled variable in long-term industrial control.
  • Gas dispersion measurement: instruments such as the McGill Bubble Size Analyzer measure bubble size in operating cells. Together with gas velocity and gas holdup, these measurements let plants compare cells and find poor performers.
  • Online analysis and advanced control: on-stream assays, model-predictive control and expert systems adjust air, froth depth and reagents to hold grade and recovery steady. Machine learning is being applied to the same problem.
  • Diagnostics: automated mineralogy shows recovery by particle size and liberation. Surface analysis techniques such as ToF-SIMS and XPS show what is on particle surfaces, and therefore why particles do or do not float.
  • Modelling: computational fluid dynamics (CFD) is used to design rotors and stators for higher flotation rates, lower power and longer life, and simulators help design circuits.

Better control still depends on basics. Surveys of process plants have found that most control loops are poorly tuned and that only about a quarter perform better in automatic than in manual. Well-installed, well-maintained instruments and properly tuned loops come before advanced control or artificial intelligence.

New Applications Beyond Mining

Flotation and related bubble-based processes are used well beyond traditional ore concentration:

  • De-inking recycled paper: ink particles are floated out of paper pulp.
  • Oil refinery effluent: dissolved air flotation, where fine bubbles under about 100 µm form as dissolved gas comes out of solution, removes oil from refinery wastewater. It is also used for municipal and industrial wastewater.
  • Fine coal and oil sands: fine coal is cleaned by flotation, and bitumen is recovered from oil sands by flotation.
  • Rare earths and battery minerals: hydroxamate collectors have proved more effective than fatty acids for the rare-earth mineral bastnaesite, and flotation is central to producing spodumene (lithium) and graphite concentrates.
  • Electroflotation: an electric current generates very fine hydrogen and oxygen bubbles, mostly 10–60 µm. It is used in wastewater treatment and may have a future role for fine mineral particles.

Future Outlook

Flotation will keep evolving to treat lower-grade and more complex ores. The likely directions are reagents that are both selective and safer, wider use of saline and recycled water, flowsheets that grind coarser and float coarse particles, high-intensity cells for fines, and control systems that combine froth imaging, online analysis and machine learning. The common thread is doing more with less: less energy, less fresh water, less reagent and safer tailings, without giving up grade and recovery.

Operating plants that use froth flotation

These Global Circuits profiles describe operating and planned plants that use froth flotation. Each summary is based on the operation’s public technical report.

  • Kansanshi (Zambia): Three ore-specific flotation circuits alongside leaching, SX/EW and a smelter.
  • Riotinto (Spain): Copper sulphide flotation at more than 15 Mt/a.
  • Vazante (Brazil): Lead sulphide flotation, then amine flotation of the zinc silicate willemite.
  • Lalor and Snow Lake (Canada): Two concentrators, each with zinc and copper flotation circuits.
  • Jiama (China): A 12.6 Mt/a concentrator for copper-molybdenum and copper-lead-zinc ore.
  • Caraíba (Brazil): A 3.2 Mt/a copper flotation concentrator.
  • Valenciana Mines (Mexico): Crushing, milling and flotation to sulphide concentrates at the Cata plant.

Browse all profiles tagged Flotation in Global Circuits.

Related Resources

Equipment

Reagents and testing

Sources and Further Reading

Equipment sizes and industry figures are given as reported in these sources and may have changed since. Online resources were accessed in October 2026.

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