subject: Description Of Flotation Method In Detail [print this page] Froth flotation commences by Waste water treatment
The flotation process is also widely used in industrial waste water treatment plants, where it removes fats, oil, grease and suspended solids from waste water. These units are called Dissolved air flotation (DAF) units. In particular, dissolved air flotation units are used in removing oil from the wastewater effluents of oil refineries, petrochemical and chemical plants, natural gas processing plants and similar industrial facilities.
Flotation equipment
Flotation can be performed in rectangular or cylindrical mechanically agitated cells or tanks, flotation columns, Jameson cells or deinking flotation machine.
Mechanical cells use a large mixer and diffuser mechanism at the bottom of the mixing tank to introduce air and provide mixing action. Flotation columns use air spargers to introduce air at the bottom of a tall column while introducing slurry above. The countercurrent motion of the slurry flowing down and the air flowing up provides mixing action. Mechanical cells generally have a higher throughput rate, but produce material that is of lower quality, while flotation columns generally have a low throughput rate but produce higher quality material.
Mechanics of flotation
The following steps are followed, following grinding to liberate the mineral particles:
1. Reagent conditioning to achieve hydrophobic surface charges on the desired particles
2. Collection and upward transport by bubbles in an intimate contact with air or nitrogen
3. Formation of a stable froth on the surface of the flotation cell
4. Separation of the mineral laden froth from the bath (flotation cell)
Chemicals of flotation
Collectors either chemically bond ( chemisorption) on a hydrophobic mineral surface, or adsorb onto the surface in the case of, for example, coal flotation through physisorption. Collectors increase the natural hydrophobicity of the surface, increasing the separability of the hydrophobic and hydrophilic particles.
