7 Factors Affecting Froth Flotation

Froth flotation is a crucial mineral processing technique that separates materials based on differences in their surface properties. This process uses air bubbles to selectively recover valuable minerals from slurry, with flotation machines playing a vital role in the operation.

The specific flotation process is as follows: various flotation reagents are added to a slurry of a certain concentration, and through agitation and aeration within the flotation cell, a large number of dispersed bubbles are generated. At this point, the mineral particles suspended in the slurry collide with the bubbles; some of the floatable mineral particles attach to the bubbles and rise to the surface of the slurry, forming a foam layer, which constitutes the concentrate; meanwhile, the non-floatable minerals remain in the slurry and become tailings. Through this process, the objective of mineral separation is achieved.

7 Critical Factors Impacting Flotation Performance

The froth flotation machine plays an indispensable role in the mineral beneficiation process. Flotation is susceptible to several factors during the process, including grinding fineness, slurry concentration, pulp pH, pharmaceutical system, aeration and agitation, flotation time, water quality, and other process factors. The factors that affect the flotation process are detailed below.

1. Grinding Particle Size

Both coarse-sized minerals (greater than 0.1 mm) and fine-sized minerals (less than 0.006 mm) can affect flotation efficiency and mineral recovery rates.

During coarse-grain flotation, the high specific gravity of the mineral particles makes it difficult for them to remain suspended in the flotation cell, thereby reducing the probability of collision with bubbles. Furthermore, once coarse particles attach to a bubble, they are highly susceptible to detachment due to the significant detachment forces acting upon them. Consequently, under conventional process conditions, the flotation performance of coarse particles is often poor.

In the flotation separation of fine particles, the small size of the mineral particles reduces the likelihood of collision with bubbles. Furthermore, because fine particles are extremely light, when they do collide with bubbles, they struggle to overcome the resistance of the hydration layer between the particle and the bubble, making it difficult for them to effectively adhere to the bubble surface.

The particle size of coarse individual minerals must be controlled below the upper limit for mineral flotation. Currently, the upper limit for the flotation particle size of sulfide minerals is typically 0.25–0.3 mm; for native sulfur, it is 0.5–1 mm; and for coal, it is 1–2 mm. Furthermore, the generation of excessive slime should be avoided as much as possible. When the flotation particle size is less than 0.01 mm, the flotation performance indicators will deteriorate significantly.

The optimal grinding fineness must be determined through testing and evaluated comprehensively in conjunction with actual production data. For certain specific ores, a staged grinding and separation process is often employed to prevent overgrinding of the ore, thereby ensuring that ore particles that have achieved single-particle liberation can be promptly recovered.

2. Excessive Ore Slurry

If the froth machine contains much ore slurry, it will bring a series of adverse effects on the mineral processing. The main influences are as follows:

• Easy to mix in the foam product, so that the concentrate grade is reduced.
• Easy to cover the coarse-grained surface, affecting the flotation of coarse particles.
• Adsorption of a large number of agents increases drug consumption.
• The pulp is sticky, and the aeration conditions have deteriorated.

3. Flotation Reagent

The type and quantity of the agent added during the flotation process, the dosing place, and the dosing method are collectively referred to as the drug system, also known as the prescription. It has a major impact on flotation indicators.

In the ore dressing, it is necessary to pass the ore selectivity test in order to determine the type and quantity of the agent, and in practice, the number, location, and mode of dosing should be constantly revised and improved.

4. Balanced Aeration & Mixing

In addition to oxygen, nitrogen, and inert gases, there are carbon dioxide and water vapor in the air.
The gas has a selective effect on the surface of the mineral; oxygen is the most important factor affecting the surface of minerals. Oxygen is beneficial to the hydrophobicity of sulphide ores/ sulfine flotation; however, if the action time is too long, the mineral surface will return to hydrophilicity. When the gas adsorption conditions are appropriate, the mineral surface will be drained, and the flotation mineral processing can be done even without a flotation agent. The Galena mine can only float up with the action of xanthate through the initial action of oxygen.

Stirring the slurry can promote the suspension of the ore particles and evenly disperse them in the tank, thus promoting the good dispersion of the air and making it evenly distributed in the tank, further promoting the enhanced dissolution of air in the high-pressure area of the tank, and strengthening the precipitation in the low-pressure area.

Enhanced aeration and agitation are advantageous for flotation separation, but not excessively, as excessive aeration and agitation can have the following disadvantages:

• Promoted the merger of bubbles
• Reduced concentrate quality
• Increased power consumption
• Increased wear of various parts of the flotation machine
• The volume of the slurry in the tank is reduced (this is because the volume of the tank is increased by the portion occupied by the bubble)
• Excessive agitation may also cause the ore particles attached to the bubbles to fall off.
  The optimum amount of aeration and agitation in production should be determined by experimentation, depending on the type and structural characteristics of the flotation machine.

Inflation and agitation are carried out simultaneously in the flotation machine. Strengthening them is beneficial to increase the flotation index, but if it is determined too much, it will cause shortcomings such as bubble merger, degraded quality, increased electric energy consumption, and mechanical wear. Therefore, aeration and agitation must be appropriate.

5. Slurry Concentration

The slurry concentration can affect the following technical and economic indicators:

• Recovery rate. When the slurry concentration is small, the recovery rate is low. As the concentration of the slurry increases, the recovery rate also increases, but the recovery rate exceeds the limit. The main reason is that the concentration is too high, which destroys the aeration condition of the flotation machine.
• Quality of concentrates. The general rule is that the quality of the concentrate is higher in the flotation of the leaner slurry, and the quality of the concentrate is reduced in the flotation of the richer slurry.
• Consumption of pharmaceuticals. When the slurry is thicker, the amount of treatment per ton of ore is less, and when the concentration of the slurry is thinner, the amount of treatment per ton of ore is increased.
• The production capacity of the flotation equipment. As the concentration of the slurry increases, the production capacity of the froth flotation machine, calculated according to the treatment amount, also increases.
• Water and electricity consumption. The thicker the pulp, the smaller the water and electricity consumption per ton of ore processed.

In short, when the concentration of the slurry is thick, it is beneficial to the flotation process. However, if the slurry and bubbles do not flow freely, the aeration will deteriorate, thereby reducing the quality and recovery. In this case, the various ore sections of the flotation should determine the appropriate concentration of the slurry according to the nature of the ore and relevant technical requirements.

6. Process Conditions: Pulp Density, Flotation Conditions & Ore Properties

The most suitable ore pulp concentration during the flotation process is related to the ore property and the flotation processing conditions. The general rules flow as follows:

• Pulp Density. The mineral with a large flotation density uses a thicker slurry, while the mineral with a small flotation density uses a thinner slurry. Flotation of coarse-grained materials with thicker slurry, and flotation of fine-grained and muddy materials with thinner slurry.
• Pulp PH Value. The pH of the pulp refers to the concentration of OH– and H+ in the slurry, which is generally expressed by the PH value. Various minerals have a “floating” and “non-floating” pH when using different flotation agents for flotation. The pH of the critical pH. By controlling the critical pH, it is possible to control the effective sorting of various minerals. Therefore, controlling the pH value of the slurry is one of the important measures to control the flotation process.
• Flotation Time. The flotation time directly affects the quality of the indicator. The time is too long, the grade of the concentrate is reduced; the time is too short, and the grade of the tailings is increased. Therefore, the flotation time required for various Minerals must be determined by experimentation.
• Water Quality. Floating water should not contain a large number of suspended particulates, nor can it contain soluble substances and various microorganisms that may interact with minerals or flotation reagents. This problem should be especially noticeable when using backwater, pit water, and lake water.
• Pulp Temperature. Flotation is generally carried out at room temperature, but sometimes it is necessary to warm the slurry to obtain a good sorting effect. Whether or not it needs to be determined according to the actual situation. If it is heated, it is best to adapt to local conditions and use waste heat and exhaust gas as much as possible.

7. Pulp Quality

The main effects of pulp quality score on the froth flotation process in metallurgy are as follows:

• Recovery rate. Within a certain range, when the pulp mass fraction is low, the recovery rate is low; as the pulp mass fraction is increased, the recovery rate is correspondingly increased. However, the mass fraction of the slurry should not be too large. If it is too large, the flotation machine is difficult to inflate normally in the slurry, which in turn reduces the recovery rate.
• Concentrate grade. The general rule is that the concentrate grade is higher when ore flotation is carried out in a leaner slurry, while the concentrate grade is reduced when it is floated in a thicker slurry.
• The dosage of the agent. The flotation agent should maintain a certain mass fraction in the pulp to have a good flotation effect. When the pulp is thicker, the mass fraction of the medicament is correspondingly increased; that is, the required medicament mass fraction can be achieved with fewer chemicals, and the amount of medicament per ton of ore is correspondingly reduced. Conversely, when the pulp is thinner, the amount of the agent increases.

Custom Flotation Solutions from JXSC

For optimal flotation performance, each factor must be carefully controlled through continuous testing and process adjustment. Proper equipment selection and operation are equally crucial for achieving maximum mineral recovery and concentrate quality.