Flotation machine function and evaluation

1. Flotation machine basic functions

A flotation machine is an industrial equipment to achieve flotation. Its key component – the inflatable stirring mechanism, which determines the type, characteristics and effectiveness of the flotation machine. From the point of view of the flotation process, the flotation machine should have the following functions.

1. Flotation machine makes the slurry in turbulent flow to ensure the suspension of the ore particles and the dispersion of the chemicals, and to achieve the adhesion of the ore particles and chemicals with certain kinetic energy movement and collision.

2. Flotation machine introduce air to produce air bubbles of suitable size, sufficient quantity and stability, so that they can be dispersed in the pulp, move with certain kinetic energy, and collide with pharmaceuticals and ore particles to produce selective adhesion and realize mineralization.

3. The mineralization bubbles can rise to the liquid surface, forming a three-phase froth layer and producing secondary enrichment; the froth concentrate and tailings can be discharged in time.
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Pulp density and adjustment in flotation plant

The conditioning of the pulping before flotation is an important operation in the flotation process, including the determination of the pulp density and the selection of the pulp conditioning method and other process factors.

1. Pulp density

Pulp density refers to the content of solid mineral particles in the pulp. There are usually two ways to express: (1) liquid-solid ratio, indicates the ratio of liquid to solid weight (or volume) in the pulp, sometimes also known as dilution; (2) percent solid content (%), indicates the percentage of solids by weight (or volume) in the pulp. Common flotation concentrations in flotation plants are listed in Table1.

Pulp density is an important process factor in the flotation process, which affects the following techno-economic indicators. Read more

Particle size effect on flotation process

There are many factors affecting the flotation process, among which the more important ones are:
particle size (grinding fineness), pulp density, chemical addition and adjustment, bubble and foam adjustment, pulp temperature, flotation procedure, water quality, etc.

Experience has proven that flotation process factors must be determined and selected according to the characteristics of the ore properties and through experimental studies in order to obtain the optimal technical and economic indicators.

1. Particle size effect on flotation

In order to ensure a high process index for flotation, it is important to study the effect of particle size on flotation and to determine the most suitable feed size (fineness) and other process conditions according to the nature of the ore. Flotation requires not only adequate monomeric dissociation of the minerals, but also a suitable feed size. Ore particles are too coarse, even if the minerals have been monomeric dissociation, because more than the bubble flotation capacity, often can not float. The upper limit of flotation size for each type of minerals is different, such as sulfide minerals are generally 0.2-0.25 mm, non-sulfide minerals for 0.25-0.3 mm, for some less dense non-metallic minerals such as coal, the upper limit of particle size can also be improved. However, the grinding size is too fine (such as less than 0.01 mm) is also detrimental to flotation. Practice has shown that there are differences in flotation behavior for various particle sizes(Refer Table 1)

The data in the table illustrate that different minerals have their own optimal particle size range for flotation. Both too coarse (>0.1 mm) and too fine (>0.006 mm) particle sizes are not conducive to flotation and recovery is reduced. Read more

Principles of flotation

Principles of flotation
Flotation is a physico-chemical separation process that utilises the difference in surface properties of the valuable minerals and the unwanted gangue minerals. The theory of froth flotation is complex, involving three phases (solids, water, and froth) with many subprocesses and interactions, and is not completely understood.
The process of material being recovered by flotation from the pulp comprises three mechanisms:
(1) Selective attachment to air bubbles (or “true flotation”).
(2) Entrainment in the water which passes through the froth.
(3) Physical entrapment between particles in the froth attached to air bubbles (often referred to as “aggregation”).

The attachment of valuable minerals to air bubbles is the most important mechanism and represents the majority of particles that are recovered to the concentrate. Although true flotation 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. Unlike true flotation, which is chemically selective to the mineral surface properties, both gangue and valuable minerals alike can be recovered by entrainment and entrapment. Drainage of these minerals occurs in the froth phase and controlling the stability of this phase is important to achieve an adequate separation. In industrial flotation plant practice, entrainment of unwanted gangue can be common and hence a single flotation stage is uncommon. Often several stages of flotation (called “circuits”) are required to reach an economically acceptable quality of valuable mineral in the final product.

True flotation utilises the differences in physicochemical surface properties of particles of various minerals. After treatment with reagents, such differences in surface properties between the minerals within the flotation pulp become apparent and, for flotation to take place, an air bubble must be able to attach itself to a particle, and lift it to the water surface. The following picture illustrates the principles of flotation in a mechanical flotation cell. The agitator provides enough turbulence in the pulp phase to promote collision of particles and bubbles which results in the attachment of valuable particles to bubbles and their transport into the froth phase for recovery.The process can only be applied to relatively fine particles, because if they are too large the adhesion between the particle and the bubble will be less than the particle weight and the bubble will therefore drop its load. There is an optimum size range for successful flotation.

In flotation concentration, the mineral is usually transferred to the froth, or float fraction, leaving the gangue in the pulp or tailing. This is direct flotation and the opposite is reverse flotation, in which the gangue is separated into the float fraction. The function of the froth phase is to enhance the overall selectivity of the flotation process. The froth achieves this by reducing the recovery of entrained material to the concentrate stream, while preferentially retaining the attached material. This increases the concentrate grade whilst limiting as far as possible the reduction in recovery of valuables. The relationship between recovery and grade is a trade-off that needs to be managed according to operational constraints and is incorporated in the management of an optimum froth stability. As the final separation phase in a flotation cell, the froth phase is a crucial determinant of the grade and recovery of the flotation process. The mineral particles can only attach to the air bubbles if they are to some extent water-repellent, or hydrophobic. Having reached the surface, the air bubbles can only continue to support the mineral particles if they can form a stable froth, otherwise they will burst and drop the mineral particles. To achieve these conditions it is necessary to use the numerous chemical compounds known as flotation reagents.