Removal of trace cadmium Ions using continuous multistage ion foam fractionation

Abstract

In this work, a continuous multistage ion foam fractionation column with bubble-cap trays was used to remove cadmium ions from water having a low cadmium concentration (10 m g/L) and sodium dodecyl sulphate (SDS) was used to generate the foam. To optimize the removal efficiency of cadmium ion s in terms of enrichment ratio, removal, separation factor and residual factor of cadmium , the system has to be operated to have the highest adsorptive transport with the lowest bulk liquid transport. An increase in feed SDS /Cd molar ratio enhanced significantly the removal of cadmium ions. The molar ratio of SDS /Cd in foam ate was found to be close to the theoretical adsorption molar ratio of 2/1 on the air-water interface of foam . Under the optimum operational conditions, the studied multistage ion foam fractionation system was able to remove cadmium ions greater than 99 %. The presence of added co-ions (SO42', NO3', and CI) was found to exhibit no effect on the removal efficiency of both SDS and cadmium ions. In contrast, the addition of counterions (N a+, K +, Ca2+, and M g2+) decreased the cadmium removal whereas it increased the SDS separation. The added divalent cations (Ca2+ and M g2+) gave the higher effect than the added monovalent cations (Na+ and K +) because the divalent cations can co-adsorb more preferentially than the monovalent ones with the SDS.