Mineralization of Bubbles During Flotation

In the context of flotation, bubble mineralization refers to the attachment of mineral particles to air bubbles during the flotation process. Flotation is a widely used technique in mineral processing for separating valuable minerals from gangue (unwanted material) based on their differences in hydrophobicity.

How Bubbles Mineralize in Flotation?

During flotation, the objective is to separate valuable minerals from the gangue selectively. It is achieved by introducing air bubbles into a pulp containing finely ground ore particles, water, and flotation reagents. The air bubbles attach to the hydrophobic mineral particles, carrying them to the froth layer while leaving the hydrophilic gangue particles behind.

Various mechanisms facilitate the attachment of mineral particles to air bubbles. Flotation reagents, such as collectors, frothers, and modifiers, are added to the pulp to modify the surface properties of the mineral particles. Collectors, for example, adsorb onto the mineral surfaces, making them hydrophobic and enhancing their attachment to air bubbles. This phenomenon is often referred to as particle-bubble attachment or mineral-bubble interaction.

Once the mineral particles attach to the air bubbles, they form mineral-laden bubbles that rise to the surface and create a froth layer. This froth, containing the concentrated mineral particles, is then collected as the flotation concentrate.

Bubble Mineralization Affects Flotation Process

The process of bubble mineralization has specific selectivity to ore particles. The hydrophobic ore particles adhere to the bubbles in this process and form a gas-solid complex. Hydrophilic ore particles are difficult to comply with the bubble and remain in the pulp. For the flotation process, the adhesion degree of ore particles on bubbles directly impacts the flotation effect, so improving the degree of bubble mineralization is one of the critical factors in improving the flotation process effect.

How to Improve The Flotation Efficiency by Improving The Bubble Mineralization Process?

The more important factors include bubble size, mineral surface properties, mineral particle density & particle size, etc. We will introduce their role in influencing the flotation mineral processing effect.

Bubble Size

The size of bubbles plays a significant role in the flotation process and can impact its efficiency and performance. Reducing the bubble diameter can increase the probability of the collision between the bubble and the mineral particles so that the mineral particles are easier to adhere to the bubble, and the flotation mineralization process is easier to carry out. The effect of bubble size in flotation can observe in terms of bubble-particle collision, attachment, and transportation of mineral particles within the flotation cell.

In production practice, we determine the size of the bubble according to the size of the mineral particles. When the mineral particle size is fine, we can reduce the bubble size appropriately but not too small. Otherwise, it will reduce the recovery rate and concentrate quality to increase the collision probability between the bubble and the mineral to improve the mineral processing effect.

Mineral Surface Properties

In flotation, the surface properties of minerals play a crucial role in the selective separation of valuable minerals from gangue during the process. The main surface properties of minerals essential in flotation include hydrophobicity, hydrophilicity, surface charge, surface composition, and surface roughness. These surface properties can be modified using flotation reagents, allowing differential attachment to air bubbles or interaction with other minerals.

The wettability of the mineral surface determines whether the mineral can carry out selective adsorption, that is, whether it completes the mineralization process. Generally, surface wettability is determined by the structural properties of minerals. The worse the surface wettability is, the stronger the hydrophobicity is, and the better the natural floatability of minerals is. For this mineral, bubbles easily displace the hydration film on the surface of the mineral, allowing it to adhere to the bubble’s surface stably, thus forming bubble mineralization.

In general, in determining mineral composition, the floatability of constituent minerals can be compared according to their different surface wettability. When the difference in surface wettability between useful minerals and gangue minerals is relatively small, we can enlarge the difference of float-ability between them by adding a suitable medium adjustment agent and collector so that one of them can adhere to the bubble more easily, which convenient for flotation mineral processing.

Mineral Particle Density & Particle Size

Mineral particle density and particle size are essential parameters in flotation as they significantly influence the efficiency and effectiveness of the separation process. 

Particle Density

Differential particle density: Flotation relies on the differences in the density of mineral particles to separate valuable minerals from gangue. Valuable minerals with higher density than the gangue can be selectively recovered by attaching to air bubbles and rising to the froth layer. Gangue particles with lower density tend to remain in the pulp or sink to the bottom as tailings.

Gravity settling: Particle density affects the settling velocity of particles in the pulp. Higher-density particles settle faster, while lower-density particles settle more slowly or may remain suspended in the pulp longer.

Density-based separation: In some flotation processes, density-based separation techniques, such as dense medium separation or hydro cyclones, are used before flotation to remove particles with specific densities, thereby optimizing the flotation performance.

Particle Size

Liberation and exposure: Particle size influences the liberation and exposure of valuable minerals. Smaller particle sizes provide larger surface areas and expose more valuable mineral surfaces for interaction with flotation reagents and attachment to air bubbles.

Recovery and selectivity: Fine particles are more likely to report to the froth layer due to their increased collision and attachment efficiency with air bubbles. However, fine particles may also have a higher probability of detachment from bubbles due to their lower mass and slower settling velocity, which can impact the recovery and selectivity in flotation.

Pulp viscosity: Fine particles can increase the viscosity of the pulp, which affects the hydrodynamics and bubble-particle interaction within the flotation cell. Higher viscosity can hinder the movement of bubbles and particles, potentially impacting flotation performance.

Flotation kinetics: Particle size can influence the flotation kinetics, i.e., the rate at which valuable minerals are recovered. Fine particles may require longer flotation residence times or higher reagent dosages to achieve optimal recovery.

Particle size and density are interconnected factors in flotation. The combination of particle size and density distributions in the feed material can affect the overall flotation performance and separation efficiency. Therefore, particle size reduction through comminution processes and proper control of particle density are important considerations in optimizing flotation processes.

After analysis, it is easy to find that the adhesion and buoyancy of mineral particles should be more excellent than their gravity when they rise to the foam layer. Therefore, for mineral particles, under certain gravity conditions, the smaller the density of the mineral, the larger the diameter of the mineral particles that can be flotation. Therefore, for minerals with poor wettability and low density, the grinding fineness can be appropriately relaxed during flotation mineral processing, such as graphite, molybdenite, etc.