flotation process

Flotation Process

One of the most employed methods for concentrating minerals is the called flotationprocess which makes a physiochemical separation whereby an ore is ground toproduce slurry which is then subjected to mixing and very fine bubbles of air areformed into the slurry in order to carry the valuable minerals. It is possible thatprecious minerals which have been liberated from non-precious metals during thegrinding step attach to the bubbles and rise to the surface to form a rich froth that canbe skimmed to form a product called concentrate. 

The possibility of separating various substances by using a flotation process isopened up due to the several changes which can be done on the surfaces mineralswith the assistance of chemical reagents which make the valuable particleshydrophobic. These are called collectors. Through physiochemical adsorption theyare attached with the ends of the molecules at the surface. The adsorption of thecollector could be influenced by adding other reagents which can be either supportiveor inhibitive in effect. In these cases is common to make reference to activators anddepressants. Air is added to move the hydrophobic particles to the surface of theslurry under agitation. Further reagents must be added in order to facilitate theadherence of particles to the bubbles and which hold in a layer of froth the particleswhich have displaced to the water-air interface. These reagents are called frother and can be natural or synthetic.

The flotation is done by following several steps: conditioning of the slurry withappropriate reagents, injection of finely disseminated air bubbles through the slurry,collection of valuable particles on the bubble surfaces and inert rock remaining insuspension, and removal of the mineralized froth and discharge of the unwantedmineral.

 Analysis of flotation process is best approach through consideration of the overallprocess first, and then of its components. An ideal system would be a circuit in asteady state, supplied at a constant rate with ore having constant initial properties, afixed optimum size distribution and its mineral surfaces pretreated to yield optimumfloatability. The feed would flow through machines and circuits selected, designed,and adjusted to give an optimum separation, resulting in production of concentratesat a fixed rate and grade, and with an associated recovery.

In order to do reality a flotation process is necessary to carry out flotation tests at thelab. Also, the tests are a powerful tool for improving an existent process and do aprimary evaluation about some possible changes such as reagents, aeration,cleaning steps and regrinding. Most of tests are done in laboratory flotation cells with500 to 4000 grams of ore. All the data obtained can be used in optimizing the dosageof reagents and retention times in industrial cells. In the basic research is commonuse small cells such as Hallimond tube and micro flotation cell.

Industrial flotation is practiced in the called flotation machines. Although manydifferent machines are currently being manufactured and many more have beendeveloped and discarded in the past, it is fair to state that two distinct groups havearisen; pneumatic and mechanical machines. The type of machine is the greatimportance in designing a flotation plant and is frequently the characteristic causingmost debate.