The application of sorptive flotation for the removal of metal ions

There is a stringent need for the control of toxic metals produced during various production processes and released into the aqueous environment in order to avoid damage relevant to soil or groundwater contamination. Among the available treatment technologies, sorption has been considered of particular importance. In the present study, a synthetic ultrafine zeolite was initially applied as sorbent (in suspension) for the removal of copper and zinc cations, and also chromium(VI) oxyanions - the latter less effectively. The removal of cations by zeolite particles depends mainly on the respective pH value, influencing the aquatic speciation during the process, as well as the zeta-potential values (surface charge) of the system. Flotation was subsequently applied for the efficient (more than 95%) solid/liquid separation of metal-laden sorbents. A suitable surface-active agent(acting as collector) should be added such as sodium dodecyl sulfate, dodecylamine or hexadecyl-trimethyl-ammonium bromide, depending on the specific experimental conditions in order to render hydrophobic and hence, to increase the floatability of solids. As a result, a foam concentrate is produced consisting of the metal-loaded zeolite particles and of purified water as underflow, which could be more easily subjected to further treatment (for instance, by membrane filtration), if necessary. Both the aforementioned technological stages, sorption and flotation, can be operated in the same unit, and the integrated innovative process was termed "sorptive flotation".