The process of froth flotation helps separate materials based on their association with water, that is, substances that are either hydrophilic (water-loving) or hydrophobic (water-repelling). Other than the association with water, froth flotation depends on the density of materials. It is a concentration process. 

A typical froth flotation includes five steps: liberation, conditioning, flotation, frothing, and separation. Minerals or liquids are usually separated by froth flotation using air and wetting agents. Impurities or materials bind themselves with bubbles to levitate, and the latter sinks to the bottom. 

Froth flotation has broad recognition and applications in practical life. Some of the uses of froth flotation include separating minerals, plastics, sewage water treatments, and recycling paper.

Froth flotation

Froth flotation is a concentration process of separating materials based on their density and the nature of their association with water. The process is mainly used to separate desired mineral components from gangues. Various chemicals have different physical and chemical properties; this is the principle for separating minerals using froth flotation.

Froth flotation process

The ore is treated through roughing, cleaning, and scavenging to obtain the most concentrated form of the desired minerals without impurities.

• The ore is separated into various minerals using a process called ‘liberation’.
• A hydrophobic environment for the desired minerals is created using chemicals or surfactants. This process is called ‘conditioning’.
• A sludge form of minerals with water and frother is added to the flotation column called ‘flotation’.
• Frothing occurs with the incorporation of air, and only desired minerals or metals levitate to the surface with air bubbles. This process is called ‘frothing’.
• Segregating the froth with a maximum concentration of the desired mineral is called ‘separation’.

Froth flotation column meaning

The froth flotation process takes place in cylindrical or rectangular tanks provided with mechanical agitation, called ‘froth flotation tanks’. In the beginning, there were two types of froth flotations: pneumatic and mechanical. Pneumatic was cumbersome and resulted in a low-grade concentrate of the desired mineral. The mechanical type used a diffuser and mixer while providing concentrates of low-quality.

The modern froth flotation column provides air from the bottom as gas flushing (spargers). Simultaneously, the sludge form of the ore is introduced from the bottom. The slurry’s whirlpool movement produces excellent mixing caused by the air flushing from the bottom. Flotation columns have been more widely accepted than pneumatic or mechanical cells. The main changes of the froth flotation column from all those previous forms are:

• There is no mechanical agitator to create froth.
• The column cell is tall and narrow, allowing ample mixing time.
• Gas bubbles or air is gas flushed from the bottom (spargers).
• Froth formed is much deeper than the surface since slurry from the top is mixed with the air bubbles from the bottom around the midway of the column. This ensures the complete wetting of mineral molecules and increases the chances of binding with the froth. Also, washing water is poured on the surface above the froth.

Froth flotation column design

Industrial columns typically had a height of 6–14 metres and a diameter of 0.5–5 metres. If the column is meant for large-scale production, the height will be 4–4.5 metres, and the diameter goes up to 12 metres. The column is water washable. The washing water poured forth through a pan having perforated holes 4–8 mm in diameter. This is situated 20–30 cm above the froth. 

Water washing is done to avoid rebinding hydrophilic gangue material from the desired mineral. Retention time is the time a mineral spends in the column. The height of the column is determined by the retention time.

Froth flotation column examples include Metso outotec, FLSmidth, and SGS India.

Limitations of froth flotation columns

• They do not provide fine conditioning as mechanical cells do.
• Flotation of fine particles is not as effective.

Conclusion

Froth flotation separates materials based on their association with water (hydrophilic or hydrophobic). The process also depends on the density of materials. It is a concentration process. A typical froth flotation includes five steps: liberation, conditioning, flotation, frothing, and separation. Some of the practical uses of froth flotation include separating minerals, plastics, sewage water treatments, and recycling paper.

The modern froth flotation column provides air from the bottom as gas flushing (spargers), and simultaneously, sludge form of ore is introduced from the bottom. Due to the air flushing from the bottom, the slurry’s whirlpool movement produces excellent mixing. Limitations of the froth flotation column include not providing good conditioning and an ineffective flotation of fine particles.