Introduction: Flotation is often called the “soul” of mineral processing. With the same ore and the same equipment, proper parameter adjustment can lift recovery from 75% to 90%; get it wrong, and even concentrate grade will suffer. This article does not revisit flotation theory (covered in a previous column) but focuses on the five most critical on-site parameters: pulp pH, reagent regime, aeration rate, pulp density, and flotation time. Each parameter has its “empirical window” and “field feel.” Understanding the principles, reading the signs, and knowing how to adjust—that is the true skill of a flotation operator.
1. Pulp pH: The Primary Lever for Surface Electrochemistry
Pulp pH directly affects mineral surface potential, reagent ionisation, and bubble-mineral attachment efficiency. Different minerals have their own optimal pH ranges for flotation; deviation from this range can cause recovery to drop sharply.
pH adjustment methods:
- Raising pH: lime (CaO), sodium carbonate (Na₂CO₃), sodium hydroxide (NaOH)
- Lowering pH: sulphuric acid (H₂SO₄), hydrochloric acid (HCl, less commonly used)
Lime is the cheapest pH modifier in a concentrator, but there is a trap: excessive lime can “passivate” mineral surfaces, rendering collectors ineffective. A field indicator: when tailings grade suddenly rises and the froth layer thins and becomes sticky, lime overdosage is often the culprit.
2. Reagent Regime: The Triadic Balance of Collector, Frother, and Depressant
Flotation reagents are the core variable of the process. For the same reagent, a difference of 0.5 g/t can yield entirely opposite outcomes.
2.1 Collector: The Key to Hydrophobicity
Collector dosage is related to mineral floatability, pulp density, and particle size. An empirical reference formula:
q = K × S / (d × C)
Where:
q = collector dosage (g/t)
K = mineral floatability coefficient (0.5–3.0; lower for easily floating minerals)
S = specific surface area of target mineral (cm²/g)
d = target mineral content (%)
C = collector collecting power coefficient (xanthate = 1.0, dithiophosphate = 0.8, fatty acid = 0.5)
Field signs of correct collector dosage:
- Stable froth layer, bright colour (mineral’s natural hue) → normal
- Thin, weak froth, high tailings loss → insufficient or uneven collector distribution
- Over-thick, sticky froth, falling concentrate grade → collector overdosage or frother interaction
2.2 Frother: The Structural Backbone of the Froth Layer
More frother is not always better. Excessive frothing leads to gangue entrainment; too little makes froth fragile and difficult to scrape.
Empirical frother-to-collector ratios:
- Sulphide flotation: frother/collector = 1:3 to 1:2 (mass ratio)
- Oxide flotation: frother/collector = 1:5 to 1:3 (less frother, as oxides are naturally less floatable)
- Coal flotation: frother/collector = 1:1 to 2:1 (more frother, as coal is easily floated but needs stable froth)
2.3 Depressant: Precision Suppression of Interfering Minerals
Depressant dosages are typically an order of magnitude lower than collectors, but their effect is highly sensitive.
Special note on lime depression: When lime is overdosed, it not only depresses pyrite but also chalcopyrite. Field experience shows that when lime exceeds 2,000 g/t, copper recovery drops significantly.
3. Aeration Rate: The “Mineral Elevator”
Aeration rate determines bubble count, bubble size, and pulp turbulence. Insufficient aeration means insufficient “elevators” to carry minerals upward; excessive aeration causes bubble coalescence and an unstable froth layer.
Field indicators for appropriate aeration:
- Froth layer surges vigorously, bubbles even in size (3–8 mm diameter) → normal
- Froth “boils” violently, bubbles coalesce into large ones (>15 mm) → over-aeration
- Froth layer sluggish, few small bubbles (<2 mm) → under‑aeration or worn impeller
- Froth appears “greyish,” entrapping fine slimes → aeration too high, coalescence with slime carryover
Aeration adjustment for mechanical flotation cells:
- Controlled via inlet valve opening
- Impeller speed also affects aeration (higher speed → more aeration, but wear increases)
- At high pulp density, aeration should be increased to compensate for bubble coalescence losses
Post time: Jul-06-2026
