FROTH FLOTATION

BY ABDUL ADDAHARY BIN ABDUL YAHYA

INTRODUCTIONFlotation is the separation of particles from a mixture by causing some particles

to collect on the surface of bubbles.

Floatation is an extractive process where various minerals can be selectively extracted. For example, in poly-metal ores such as Pb-Zn-Cu, floatation allows separate extraction of Pb, Cu and Zn.

The process of separation of mineral includes three important mechanisms :

1. TRUE FLOTATION, i.e., selective attachment to air bubbles.

2. ENTRAINMENT in the water which passes through the froth.

3. AGGREGATION, i.e. physical entrapment between the particles in froth.

CONT…True flotation dominates the recovery of the valuable minerals and the other two

decide the separation efficiency between the valuable and the gangue.

FLOTATION process can be applied to relatively fine particles, because if the particles are coarse and heavy, their weight will be greater than the adhesion between the particle and the air bubble and the particle will detach from the bubble.

There are two ways of flotation :

1. DIRECT FLOTATION- In which the mineral is attached to the froth and the gangue remains in the tailing.

2. REVERSE FLOTATION- in which the gangue is attached to the froth and minerals remain in tailing.

BASIC PRINCIPLESThis process commences with Comminution (to increase the surface area of the ore).

The ore is ground to fine powder and wetted with water to form a Slurry.

A Surfactant chemical (known as COLLECTOR) is mixed with slurry to render the desired mineral HYDROPHOBIC.

This slurry (now PULP) is then placed in the water bath containing FROTHER, which is aerated to create bubbles.

The desired mineral escape water by getting attached to the air bubbles, which rise to the surface and form what is called FROTH. This Froth is then removed and the concentrated mineral is refined.

AIR IN

MINERALISED FROTH

PULP

AIR BUBBLE CELL

AGITATOR

MINERALS’ PARTICLES ATTACHED TO BUBBLE

MECHANICS OF FLOTATIONThe basis of Froth Flotation is the difference in the WETTABILITY of the mineral and

gangue particles.

On the basis of Wettability of particles are classified as HYDROPHOBIC and HYDROPHILIC.

The valuable minerals can attach to the air bubbles , only if they are Hydrophobic. Once they reach the surface, due to the buoyancy of the air bubbles, the particle-bubble contact can sustain only if they form a stable froth.

The stability of the froth depends on the strength of the attachment of the bubble to the mineral surface. This strength can be estimated with the help of YOUNG-DUPRE EQUATION, which relates the strength of attachment to the interfacial energies.

This process is used for sulphide ores. Oils can wet sulphides. Oil floats on water. Sulphide ores are first ground to powder and water is added.

Then pine oil is added and the emulsion is agitated by passing compressed air. Oil and froth float on the surface along with the sulphide ore.

The gangue particles being insoluble in oil remain at the bottom of the water tank. The froth is removed and allowed to settle down

This is called the froth-floating process. This process is used for sulphide ores of Cu, Pb and Zn

ADVANTAGES OF FLOTATION OVER SEDIMENTATION

High rise velocity permits small tankage.

Ability to handle variable solids loading (can adjust air flow).

Can provide high float concentration (good thickening).

Can remove low density particles which would require long settling periods.