Froth flotation definition
Froth flotation is a process frequently in use for separating valuable minerals from gangue minerals. It is definitely the most important and versatile mineral processing technique. Both its use and application are continually being spread out to treat greater tonnages and to cover new areas. In fact today, billions of tonnes by annual of over 100 different minerals are using this method.
Froth flotation development
Originally patented in 1906, froth flotation has permitted the mining of low-grade and complex ore bodies. This kind of ore previously considered as uneconomic ore. In earlier practice the tailings of many gravity plants were of a higher grade than ore treated in many modern froth flotation cell plants.
Froth flotation is a selective process. This method can utilise to achieve specific separations from complex ores such as lead -zinc, copper-zinc, etc. Even though originally developed to treat the sulphides of copper, the field of froth flotation has now expanded to many ores type.
Over the past 50 years, froth flotation has developed in to the most important separation method used in the mineral industry. The froth flotation process continues to become more efficient with many improvements. Starts with innovative flotation cell designs, better chemical reagents and advances in computer control. Even though with a lot of improvements, the mineral processing itself remains virtually unchanged.
Particles, water, bubbles and reagents still hold the keys to successful froth flotation. They are conglomerate in such a way that certain particles attach to the bubbles. Furthermore the bubbles will float and are collect at the surface. Therefore separating from the remaining material.
Froth flotation principles
Froth flotation is a physico-chemical separation process that utilizes the difference in surface properties. Specifically between the valuable minerals and unwanted gangue minerals. The theory is complex, involving three phases (solids, water and froth). The subject has been reviewed comprehensively by a number of authors.
The process of material being recovered by froth flotation from the pulp comprises three main mechanisms:
- Selective attachment to air bubbles, called true froth flotation or just true flotation
- Entrainment in the water which passes through the froth
- Physical entrapment between particles in the froth attached to air bubbles, namely aggregation
The attachment of valuable minerals to air bubbles, the true flotation, is the most important mechanism. Surely it is represents the majority of particles that are recovered to the concentrate. Although this is the dominant mechanism for the recovery of valuable mineral, the separation efficiency between the valuable mineral and gangue is also dependent on the degree of entrainment and physical entrapment.
The first step utilize the differences in physico-chemical surface properties of particles of various minerals. After treatment with froth flotation reagents, such differences in surface properties between the minerals within the true froth flotation pulp become apparent. In order the true froth flotation to take place, an air bubble must be able to attach itself to a particle and lift it to the water surface.
The agitator in froth flotation cell will help to provides enough turbulence in the pulp phase. This turbulence is important to promote collision of particles and bubbles. This will results in the attachment of valuable particles to bubbles and their transport into the froth phase for recovery.
The process can only use to relatively fine particles. In any even when they are too large, the adhesion between particle and the bubble will be less than the particle weight. This condition will result the bubble drop its load.
Froth flotation and liberation
As we have seen, a perfect separation can be illustrated by a good degree of liberation and a straight line on the liberation spectrum. In reality because separations are not perfect,, the line will not be truly vertical.
The things we do to change liberation will affect the distribution of particles on the graph. The things we do to affect conditions in the pulp and froth zones, will change the shape and position of the line. In other words change the separation.