A comparison of the properties of polyurethane-immobilised Sphagnum moss, seaweed, sunflower waste and maize for the biosorption of Cu, Pb, Zn, Ni in continuous-flow packed columns

The biosorption of Cu, Pb, Zn and Ni from a mixed solution of the metals was investigated in continuous flow packed columns containing polyurethane immobilised biomass. The characteristics and biosorption properties of Sphagnum moss, the brown seaweed Ascophyllum nodosum, waste biomass from the preparation of sunflower oil, and whole plant maize were compared.All the biomass types showed a preference for the sequestration of Pb followed by Cu, with Ni and Zn having roughly equal affinity. With continuous metal loading to the column there was an initial binding of all metals and then a displacement of the lower affinity metals by those with a high affinity. This led to a chromatographic effect in the column with breakthrough concentrations for low-affinity metals higher than the concentration in the feed. A similar phenomenon was found on desorption using acidic solutions where low-affinity metals were desorbed preferentially. The results also indicated that despite competitive displacement of one metal species by another the biomass appeared to succeed in retaining some low-affinity metal species indicating that there may be selective sites present with different affinity characteristics.When using a multi-metal solution with Cu, Pb, Zn and Ni at equal 10 mg l-1 concentrations as column influent, the total quantities of metal sequestered were: seaweed, 117.3 mg g-1; sunflower waste, 33.2 mg g-1; Sphagnum moss, 32.5 mg g-1; and maize, 2.3 mg g-1. The use of an acid base potentiometric titration showed a relationship between the number of acid functional groups and biosorption capacity, although this was not proportional for the biomass types studied. It can, however, be used in conjunction with a simple classification of metals into high and low-affinity bands to make a preliminary assessment of a biosorption system