Removal of metal ions from dilute solutions by sorptive flotation

The removal of soluble ionic species, such as toxic metal cations or oxyanions, from dilute aqueous solutions, as most waste waters are, was investigated in laboratory‐scale experiments (batch and continuous mode) by applying the sorptive flotation process. This method involves the preliminary abstraction or scavenging of metal ions using proper “sorbents”, which exist at the fine or ultrafine particle‐size range, followed by a subsequent flotation stage for the separation of metal‐loaded sorbent particles from the treated (cleaned) solution. The main flotation techniques for the generation of the necessary bubbles (dissolved air, dispersed, and electrolytic) were applied effectively. The examined sorbents for the initial stage of the process could be of either inorganic nature, conventional (powdered activated carbon and zeolites) or industrial solid byproducts originated in the mineral industry, or of a biological nature (biosorbents), such as those produced during fermentations, in sewage treatment plants (sludge), etc. As a result of the process application, purified water is produced (underflow) as well as a foam concentrate; the recovery and recycling of removed species is also possible from the latter, leading to an overall clean technology. If required, the sorbents may also be reused and recycled after the application of a suitable metal eluant, which can also be considered to reveal to a certain extent the disposal problem of solid wastes.