REMOVAL OF METAL-IONS FROM DILUTE-SOLUTIONS BY SORPTIVE FLOTATION

The removal of soluble ionic species, such as toxic metal cations or o xyanions, from dilute aqueous solutions, as most waste waters are, was investigated in laboratory-scale experiments (batch and continuous mo de) by applying the sorptive flotation process. This method involves t he 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-l oaded sorbent particles from the treated (cleaned) solution. The main flotation techniques for the generation of the necessary bubbles (diss olved air, dispersed, and electrolytic) were applied effectively. The examined sorbents for the initial stage of the process could be of eit her inorganic nature, conventional (powdered activated carbon and zeol ites) or industrial solid byproducts originated in the mineral industr y, or of a biological nature (biosorbents), such as those produced dur ing fermentations, in sewage treatment plants (sludge), etc. As a resu lt of the process application, purified water is produced (underflow) as well as a foam concentrate; the recovery and recycling of removed s pecies is also possible from the latter, leading to an overall clean t echnology. if required, the sorbents may also be reused and recycled a fter the application of a suitable metal eluant, which can also be con sidered to reveal to a certain extent the disposal problem of solid wa stes.