From froth to finish
Flotation remains one of the most powerful methods of mineral separation in processing plants. When dialled in, it delivers high recovery, consistent grade and stable throughput. But when it’s off, even slightly, the knock-on effects can be felt across the whole circuit.
This guide focuses on ten common challenges metallurgists and operational teams encounter with flotation performance. It offers practical advice and solutions from real-world plant experiences across gold, base metals, and rare earth operations. The aim isn’t just to put out fires but to build a more stable and optimised flotation circuit over time.
Each challenge includes a breakdown of symptoms, insights into root causes, and tiered solutions: quick fixes, mid-term improvements, and long-term wins.
1. Inconsistent froth characteristics
Symptoms
You may see froth that changes dramatically from cell to cell, or over time, sometimes too brittle and breaking too early, other times dense and sluggish, like wet concrete. Operators often report that the froth level appears to be fine, but recovery starts dropping, or product grade becomes unstable.
Root causes
Froth behaviour is the result of a tight balance between air flow, level control, reagent chemistry, and slurry properties. A shift in any one of these can cause froth instability. Inconsistent reagent addition, sparger, equipment wear, or even uneven airflow distribution between cells can lead to erratic froth formation.
Action items
- Quick Fix: Inspect and verify level setpoints across cells to stabilise froth depth.
- Mid-Term: Implement froth camera systems and deliver operator training to interpret visual cues better.
- Long-Term: Deploy advanced froth-imaging tools with feedback control to automate stability.
2.Poor air flow distribution across banks
Symptoms
You’ll notice certain banks with vigorous froth while others barely respond, or you get froth cycling, where levels oscillate for no apparent reason. The air flow seems to favour some cells over others, despite equal setpoints.
Root causes
Distribution issues are usually tied to manifold pressure drops, partial blockages, or aging valves that no longer deliver consistent flow. Airflow meters may be uncalibrated, or the manifold design may simply favour certain outlets.
Action items
- Quick Fix: Check air services for stable performance, check air instrumentation performance against setpoints and review PID control loop performance (tuning if necessary, ensuring valves are not chattering)
- Mid-Term: Calibrate airflow meters and standardise settings.
- Long-Term: Install control valves and instrumentation to manage and automate airflow control across the bank actively.
3. Blocked or dirty spargers
Symptoms
When spargers become blocked or clogged, air delivery drops significantly, reducing the bubble surface area available for particle collection. You might see a dull surface, reduced froth volume, or unexplained drops in mass pull and concentrate flow.
Root causes
Spargers can become fouled with scale or sediment, especially in older plants or those without good filtration. Contamination and condensation build-up can block spargers if air delivery systems aren’t maintained.
Action items
- Quick Fix: Replace the faulty air sparger.
- Long-Term: Install inline sparger cleaning systems and monitor airflow to catch underperformance early.
4. Fluctuating pulp level control
Symptoms
Levels bounce up and down within individual cells or across the bank. Operators often struggle to maintain control, and you may observe symptoms like short-circuiting and drops in concentrate grade.
Root causes
Level control is often managed through mechanical linkages or outdated float devices that are slow to respond. Add in poor valve tuning, slurry surges, or worn-out instrumentation, and the whole system becomes reactive rather than predictive.
Action items
- Quick Fix: Inspect and clean level instrumentation, recalibrate sensors, and re-tune PID controllers (if required).
- Mid-Term: Upgrade to more responsive, fine control valves and actuators. Implement advanced control improvements (eg. dual valve control, control valve linearisation)
- Long-Term: Replace mechanical devices with high-resolution, smart level sensors integrated into control systems.
5. Reagent addition inconsistencies
Symptoms
Operators report variable recovery across shifts or sudden changes in concentrate quality, even when other parameters remain steady. A dose that works one day seems completely off the next.
Root causes
This often traces back to variable reagent concentrations, manual reagent addition, unstable ore feed, or poor mixing. Without automation or feedback control, it’s easy to overdose or underdose, especially if reagents are mixed off-site or added in batches.
Action items
- Quick Fix: Check reagent concentrations, Conduct targeted test work to determine the optimal reagent regime and identify sources of variability, such as ore type changes.
- Mid-Term: Install auto-dosing systems that adjust flow based on circuit feedback.
- Long-Term: Integrate real-time reagent control tied to ore characterisation and plant conditions.
Read more about how we...
delivered the rougher flotation expansion at Glencore's McArthur River Mine
6. Slurry density flucuations
Symptoms
The feed to the flotation circuit is sometimes too dense, resulting in sanding and poor air dispersion; at other times, it’s too dilute, overloading downstream equipment and reducing residence time.
Root causes
Density variability is usually driven by upstream instability, cyclone fluctuation, or inconsistent mill control. If dilution water isn’t properly controlled or monitored, fluctuations become chronic.
Action items
- Quick Fix: Manually balance density by adjusting dilution water and checking upstream flows.
- Mid-Term: Install online density meters on the flotation feed.
- Long-Term: Integrate density control within APC systems.
7. Sanding in cells
Symptoms
Operators might experience material building up in the bottom of the cells or experience slow froth collapse and choppy discharge. Cells may start short-circuiting, and mechanical agitation can become less effective.
Root causes
Sanding is often a symptom of thick feed, poor agitation, or grinding circuit imbalances. If the cell isn’t agitating effectively, coarse particles settle, reduce effective volume, and disrupt flotation dynamics.
Action items
- Quick Fix: Check density, grind size and upstream grinding performance.
- Mid-Term: Inspect and maintain agitators to ensure proper suspension.
- Long-Term: Implement integrated control strategies that link grinding, flotation, and tailings handling.
8. Cell-to-cell variability
Symptoms
Despite a consistent feed, cells behave differently to the norm, some producing a thicker froth, others have none. You may observe unusual concentrate flows or unexplained drop-offs in recovery.
Root causes
Wear and tear over time introduces variability, from froth launders to stators and rotors. Poor maintenance schedules or inconsistent calibration between cells compound the problem, which can be hard to notice due to the gradual decline in performance
Action items
- Quick Fix: Rebalance air and level settings across the bank.
- Mid-Term: Conduct a full audit of cell wear and implement a preventative maintenance program.
- Long-Term: Undertake a full circuit mass balance review and consider reconfiguration.
9. Over reliance on operator intuition
Symptoms
And while this one is a bit contentious we’ve all seen it happen. Performance swings between shifts or from day to night. Each operator seems to have their own way of running the plant, and there’s little documentation on why adjustments are made
Root causes
Flotation still relies heavily on the eyes and instincts of experienced operators. Without standardised set points, dashboards, or decision-support tools, knowledge remains tribal, and performance varies.
Action items
- Quick Fix: Enforce stricter set points and increase supervisory oversight.
- Mid-Term: Run refresher training to standardise approaches and build shared understanding.
- Long-Term: Deploy digital dashboards and decision-support systems to guide operator responses.
10. Ageing infrastructure
Symptoms
Older plants require more manual input, consume more energy, and can’t match the performance of newer installations. Even when meeting targets, these cells show declining efficiency compared to modern alternatives.
Root causes
Plants often run flotation cells beyond their intended life cycle. With limited capital for upgrades, they rely on patchwork maintenance and minor retrofits. But mechanical limitations in older designs limit what’s achievable.
Action items
- Quick Fix: Acknowledge limitations and work within them.
- Mid-Term: Conduct project evaluation to quantify the benefits of upgrading.
- Long-Term: Roll out a retrofit or replacement program based on performance and ROI.
Some final thoughts
Flotation circuits are highly sensitive systems where minor issues compound quickly. A blocked sparger or inconsistent level can ripple downstream into significant recovery or grade losses. But with a structured approach, diagnosing symptoms, understanding root causes, and applying tiered solutions, operations teams can move from reactive firefighting to proactive optimisation.
Mipac works closely with processing plants worldwide to improve flotation performance, from advanced instrumentation to circuit-wide control strategies. If you’re ready to take your flotation to the next level, our team can help identify the most significant gains and implement lasting improvements.
Need a hand getting more from your flotation circuit?
Mipac’s team of expert metallurgists work shoulder-to-shoulder with site teams to diagnose, troubleshoot and optimise flotation performance across gold, base metals and rare earth operations.
From sorting out inconsistent froth to designing long-term upgrades for ageing infrastructure, we’ve helped clients overcome the full spectrum of flotation challenges, often turning marginal gains into significant returns.
Explore our flotation project case studies and digital solutions here, and when you’re ready to take a fresh look at your flotation performance, contact us today, and we’ll put you in touch with one of our flotation experts.
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