**4. Ion-flotation**

The process which uses different surfactants for the destabilization of the metal ions present in the wastewaters, and their transformation into hydrophobic compounds, followed by removal through flotation using air bubbles is called ion-flotation [41, 42]. The principle of the ionic flotation process consists on the one hand of attaching the metal ion to the polar end of the surfactant and on the other hand of the interaction between the nonpolar end of the surfactant and the air bubbles, which leads to the concentration and separation of the metal ions on the surface of the residual water by froth forming. In addition to surfactants, foaming agents/frothers (such as ethanol, polypropylene glycol, and methyl isobutyl carbinol), can also be used, which have the role of obtaining air bubbles of the smallest possible size to increase the surface of

*Heavy Metals Removal from Water and Wastewater DOI: http://dx.doi.org/10.5772/intechopen.110228*

interaction between them and the target metal ions [42]. Ionic flotation can be used both for the treatment of wastewater and for the recovery of precious or rare metal ions. As surfactants/collectors were studied sodium dodecyl sulfate [42], polyethylenimine [43], hexadecyltrimethyl ammonium bromide [44], 4-thiazolidinone derivatives [45], etc. This treatment method does not require high energy consumption and sophisticated and large equipment, it is easy to operate, and can be used for selective separations presenting high efficiency and obtaining low amounts of sludge. Ion-flotation could be conducted at different work conditions (pH, flow rate, treatment time, and molar ratio of surfactant/metal ions), function of the metal ions which need to be removed, and function of the used surfactant/collector. The results presented in the specialty literature describe this treatment method as a simple, rapid, and economic one, but also underline the necessity of developing new low-cost collectors, with greater selectivity, environmentally friendly, and present a higher efficiency using a lower dosage, all these leading to a decreasing of the treatment costs.
