Flotation initially originated from the field of mineral processing. The importance of this process to the economy of the whole industrial world is considered to be enormous. Since for many years various particulate solids besides minerals have been extracted by using this effective gravity separation method with many interesting applications in the treatment of wastewater, looking for sustainability. Certain significant activities in flotation research were reviewed in the present, with main focus in the contribution of physical chemistry to flotation; i.e. zeta-potential measurements, contact angle etc., including examining the role of bubble and particle size played with regard to the process. Alternative bubble generation methods were examined, such as electro flotation and dissolved-air flotation-the latter technique is mainly intended for water treatment applications.Keywords: Hydrophobicity, Dissolved-air flotation, Electroflotation, Biosorption, Waste water
IntroductionLet us start this chapter by saying that flotation is really an old process: the historian Herodotus in ancient Greece is probably the first person that described a process similar to flotation, in the 5 th century B.C., for the separation of gold particles from sand using fatty substances. And later, in the 15 th century A.D., the Arabs used resins for the selective separation of azurite (a copper mineral) from gangue. These are considered to be the main historical roots of flotation, which is based on the idea of applying rising gas bubbles as the transport medium [1]. The attachment of bubbles to particles transfers the solids from the body of water to the surface.Hydrophobicity refers to the property of a molecule, cluster, micro-organism or mineral surface that is repelled from a mass of water. Further, it was noted that the term hydrophobicity (a Greek word) has been differently understood in various fields [2]. Floatability and hydrophobicity, however, are inter-related, focusing often on the application of collectorless flotation. Attention may be paid to a series of relevant reviews on the area [3][4][5][6]. Below a brief survey is given on selected recent papers for different applications of flotation, from a really vast literatureshowing well (as we believe) that chemistry contributes in various ways in flotation research. Coal beneficiation is one of the most effective methods for removing minerals, such as gangues and pyrite, and pollutants such as sulfur, before the burning of coal.In general, the beneficiation process of low rank coals (about the 50% of the world's total coal deposits) is more difficult to achieve than that of bituminous and/or anthracite coals. Lignite is the most important mineral commodities for Greece, according to Anastassakis [7]; its reserves approach to about 4000 Mt. It was pointed out that in the future effective reagents should be invented for effective flotation process (being a physico-chemical one) [8]. A better understanding of the surface chemistry of sulfidewater interfaces was tried...