MINERAL FLOATABILITY
Mineral flotability is an important mineral processing application that is used to separate particles by differential behavior in waters. Flotability is usually favorable if a mineral’s own hydrophobicity is increased and the particle’s attachment to water is decreased. Flotation of particles is really complex due to the adsorption of species on particle surfaces, which is affected by many parameters. Most particles that have economic interest display hydrophobicity because of their surface natural characteristics at standard conditions. Due to the relatively similar mineral interaction with the flotation environment, some minerals such as sulfides display different flotability when compared with minerals from other families.
A mineral can either be hydrophilic or hydrophobic, depending on its chemical and physical characteristics. Hydrophilic surfaces generally have a negative charge, while hydrophobic surfaces have a positive charge. Particles that are hydrophilic are more likely to adhere to the surface of other particles because the force between the two surfaces is greater. Hydrophobic particles, on the other hand, repel each other and are not likely to adhere to other surfaces, thus increasing the flotability of these particles. The nature of the mineral affects its hydrophobicity and the attraction of particles to the water.
In flotation, the minerals’ flotability is mainly controlled by the combination of the zeta potential, surface hydrophobicity, and surface area. Generally speaking, higher hydrophobicity surfaces tend to be more flotable in an aqueous system than lower ones. The natural hydrophobicity of particles is determined by both the type of the mineral and its properties (pH, mineralogy, trace elements, surface oxidation…) and is mainly controlled by the nature of the mineral surface.
The main driving forces for mineral flota bility are surface free energy, surface charge mechanisms and surface chemistry. The surface free energy is the balance between forces that bind molecules to the particle surface and forces that repel them away. Surface charge mechanism is mainly related with electrical properties of the particle surface. It is affected by the thermal and electrochemical properties, as well as pH of the flotation pulp. The surface charge is usually determined by the isoelectric point of the mineral and the type of ions present in the pulp. Surface chemistry is mainly involved in the adsorption of species such as xanthates, pyrite, and non-polar hydrocarbons which are used as reagents during flotation. These reagents interact with big molecular groups on the particle surfaces resulting in the formation of an electrically neutral dangling layer that is hydrophobic, allowing for flotation.
In conclusion, mineral flotability is an important application used in the mineral processing industry. It is determined by the hydrophobicity of the mineral, the surface charge mechanisms, and surface chemistry. All these parameters must be considered and optimized in order to achieve the desired flotation separations. In addition, different reagents can be used to enhance the flotability of certain minerals. This might be necessary to achieve a certain separation, such as in a flotation process.
