Biosorption column performance with a metal mixture

The biosorption of Cu, Cd, and Zn from multicomponent mixtures was studied in equilibrium systems and in a flow-through column packed with potassium-s aturated Sargassum algal biosorbent. Pretreatment of the biomass with calci um-, sodium-, magnesium-, and potassium-hydroxides was examined. KOH washin g resulted in a stable biosorbent with an improved affinity for Zinc. Two-m etal sorption resulted in Zn breaking through the column faster than Cd due to its low affinity. The sharp favorable Zn breakthrough curve can be expl ained by its affinity toward the biomass which is higher than that of K. An overshoot of the Zn exit concentration was observed and explained by the i on exchange between Cd and Zn, whereby the higher-affinity Cd from the solu tion displaces Zn already bound to the biosorbent. The same effect was obse rved for Zn, and to a lesser extent Cd, in three-metal sorption (Zn, Cd, Cu ). The Cd exit concentration also exceeded its feed level as Cu displaced i t on the binding sites of the biomass in the bed. The time interval between Zn and Cd breakthroughs was much shorter than that between the breakthroug h points of Cd and Cu. This is because the relative affinities of Zn and Cd , determined from batch equilibrium experiments, are much closer to each ot her (Zn/K = 1.96 and Cd/K = 3.71) than to Cu (Cu/K = 16.51). The applicatio n of experimental IMPACT computer software examined was only partially succ essful in exactly simulating the biosorption column performance.