Air Dissolved Flotation

The flotation process was developed in the mineral processing industry as a way of separating valuable suspended solids from a medium such as a mixture constituted by solids and water. The flotation process has found uses in other fields, such as wastewater treatment and ink removal. The process introduces fine air bubbles into the slurry so that the air bubbles attach to the valuable particles, and transport them to the surface. The process can be also known as dissolved air flotation and use a particular way of introducing the air bubbles into the machine called flotation tank or cell. The process relies upon differences in the surface properties of different particles to separate them. The particles to be floated are rendered hydrophobic by the addition of the appropriate chemicals. Air is then bubbled through the mixture and the desired particles become attached to the small air bubbles and move to the surface where they accumulate as a froth and are collected, or if the non-desired particles float to the surface they are collected and discarded (i.e. reverse flotation).

In flotation the ground ore is sent as an aqueous slurry to the flotation cells. The surfaces of specific minerals in aqueous suspension are treated with reagents called collectors which make hydrophobic surfaces on valuable minerals. Flotation reagents provide the desired mineral to be floated with a water repellent surface which adheres to an air bubble which transports the mineral through the slurry to the surface. Other reagents can be added to the slurry to aid in separation: depressants. These assist in selectivity and minimize displacement of unwanted minerals. Other reagents all the modifiers which change the physiochemical state of the mineral surface. Air is no enough to lift minerals and it is required a reagent called frother which help to transport the valuable minerals.

Flotation has been used generally as process to recover minerals such as chalcopyrite, galena, and sphalerite from raw ores and obtaining concentrates as the material to be sent to smelters of non-ferrous minerals. The process usually comprises a rougher step in order to separate valuable minerals of non-valuable minerals (gangue). The gangue is usually pyrite and quartz which occupy a most portion of the raw ores. The rougher step in not enough for obtaining a final product and is required to the employ several cleaning steps which assure the quality of the final concentrate.

Most of ores generally contain pyrite of low value (i.e. precious metals are no always present in pyrite), if they are present by a high amount in concentrates, the quality of the concentrates is low. Sometimes is required special depressant to minimize the present of pyrite.

Accurate and reliable measurement is crucial during the process as there needs to be a balance between the amount of base slurry and the amount of froth produced. Too much slurry and too little froth leads to an under recovery of minerals, thus affecting the efficiency of the process. Flotation is an art and the personnel must have special skills because some flotation processes are not easily conduced.