Competitive removal of mixed haevy metals from water by multistage foam fractionation

Abstract

In this study, a continuous multistage ion foam fractionation column with 5 bubble-cap trays will be employed to study the removal of (i) individual heavy metal including cadmium (Cd), copper (Cu) and nickel (Ni) and (ii) mixed heavy metals at a low concentration (10 mg/L). Sodium dodecyl sulfate (SDS) will be used as foam generator. In order to achieve a maximum process performance, several parameters affecting the separation performance will be investigated including SDS/Cd ratio, foam height, operating parameters-feed flow rate and air flow rate. The separation efficiency will be evaluated in terms of enrichment ratio, recovery or removal percentage, and separation factor. The system has operated at an air flow rate of 80 dm3/min and a feed flow rate of 60 mL/min, located in the operational zone, were selected to run the multistage ion foam fractionation column and a lowest feed SDS/Cd molar ratio of 8/1. An increase in feed SDS/Cd molar ratio enhanced significantly the removal of heavy metal ions. Under the optimum operational conditions, the studied multistage ion foam fractionation system was able to remove single heavy metal ions greater than 99 %. For mixed heavy metal, The highest separation efficiency of each heavy metal (the SDS recovery ~ 90%, the heavy metal removal ~ 90%) was obtained at a foam height of 60 cm, an air flow rate of 80 dm3min, and a feed flow rate of 60 mL/min. For the mixed heavy metal system operated under the same optimum conditions, the -selective separation of heavy metals was in orders of Cd > Cu > Ni because of larger ions preferentially adsorbed because its outer secondary hydration water molecules are more easily to be lost when interacting with the negatively charged head group of SDS adsorbed at the interface.