A Comparison of Palladium Sorption Using Polyethylenimine Impregnated Alginate-Based and Carrageenan-Based Algal Beads

Two kinds of algal beads were prepared using a carrageenan-based alga (Chrondrus crispus) and an alginate-based alga (Laminara digitata) ionotropically gelled with K(I) and Ca(II), respectively: the process consists of biopolymer partial extraction followed by hydrogel formation. The beads were modified with branched polyethylenimine (bPEI) and glutaraldehyde (GA) using the impregnation method to improve their sorption capacity for Pd(II) in acid solution. SEM-EDX and FTIR techniques were used for characterizing the beads. The impacts of pH and presence of anions, cations, and Pt(IV) were studied in batch experiments. The beads were also applied for Pd(II) recovery from synthesized leaching liquors of a spent catalyst and a car catalytic converter via the sorption-desorption process. Results show that Pd is concentrated in the outer layer of L. digitata-bPEI-GA composite (LD/PEI) beads, while in the case of the C. crispus-bPEI-GA composite (CC/PEI), it is homogenously distributed in the whole mass of the sorbents. The difference is attributed to the repulsive force of the outer Ca(II)-alginate barrier of LD/PEI beads that makes it difficult for the branched polymer PEI to penetrate through the layer and be immobilized in the inner compartment. As a result, LD/PEI beads possess a lower maximum sorption capacity, but a slightly faster uptake at pH 1 than CC/PEI beads. In addition, CC/PEI beads present a better recovery performance compared to LD/PEI beads when applied for the treatment of synthesized leaching liquors.