Mineral Processing: Floatation Technique

Study Notes

Floatation in Mineral Processing

Floatation is a key mineral separation technique, continuously evolving to handle larger tonnages and new mineral types.
Enabled mining of low-grade and complex ore bodies previously deemed uneconomic.
Originated for sulphide minerals like copper, lead, and zinc, now includes nickel, platinum, gold-sulphides, and non-sulphide minerals like hematite, cassiterite, fluorite, talc, phosphate, potash, fine coal, and bitumen.
Applications extend beyond mining to industries like paper and oil refining.

Mechanisms of Floatation

Floatation processes use differences in surface properties between valuable minerals (hydrophobic) and gangue minerals (hydrophilic).
Froth floatation consists of three phases: solid (fine ore powders), liquid (water), and froth.
Key separation mechanisms:
- True flotation: selective attachment of air bubbles to valuable minerals.
- Entrainment: water passes through froth carrying some particles.
- Agglomeration: physical entrapment of particles in froth.
True flotation is pivotal for recovering valuable minerals; entrainment and agglomeration affect separation efficiency.

Floatation Process Summary

The process involves grinding ore to liberate valuable minerals, adjusting conditions for adherence to air bubbles, and creating rising air currents in the ore pulp.
Steps include:
- Grinding to a fine size.
- Making conditions favorable for mineral adherence.
- Creating a rising current of air bubbles.
- Forming a mineral-laden froth.
- Removing the mineral-laden froth.
A surfactant collector is added to enhance hydrophobicity, allowing desired minerals to attach to air bubbles.

Direct vs. Reverse Floatation

Direct floatation: valuable minerals attach to air bubbles, rising to the froth.
Reverse floatation: gangue attaches to the froth, leaving the valuable minerals in the tailings.

Applications of Floatation

Effective for separating:
- Sulphide minerals from silica gangue.
- Potassium chloride from sodium chloride.
- Silicate minerals from iron ore.
- Phosphate minerals from silicates.
- Non-mineral applications like de-inking recycled newsprint.
Ideal for fine-grained ores unsuitable for gravity concentration.

Stability and Efficiency Considerations

The stability of froth is influenced by the strength of bubble attachment to minerals, estimated via the Young-Dupré equation.
Greater contact angles correspond to increased adhesion work, enhancing system resilience against disruptive forces.
Optimal bubble diameter should align with particle size to ensure effective contact and minimize fluid entry, which could lead to undesirable entrainment.

Essential Variables in Floatation

Key components influencing floatation:
- Chemistry: collectors, frothers, activators, depressants, pH.
- Equipment design: cell design, agitators, air flow, cell banks.
- Operational factors: feed rate, mineralogy, particle size, pulp density, temperature.

Role of Chemicals in Floatation

Chemicals are critical for adjusting hydrophilicity levels between particles and maintaining froth characteristics.
Types of chemicals used include:
- Collectors: selectively increase hydrophobicity on particle surfaces.
- Frothers: stabilize froth formation.
- Regulators: control pH and adjust interactions between particles.

Description

Floatation is a crucial mineral separation technique used to treat low-grade and complex ore bodies. It has expanded to cover new areas and is now used to treat various minerals, including copper, lead, and zinc. This technique has made it possible to mine ore bodies that were previously considered uneconomic.