A Comparison of Palladium Sorption Using Polyethylenimine Impregnated Alginate-Based and Carrageenanan-Based Algal Beads  
[PERSON]  
1C2 MA, IMT Mines Ales, University of Montpellier, 30100 Ales, France; [EMAIL_ADDRESS]  
2 IEM, Institut Europeen des Membranes, University of Montpellier, CNRS, ENSCM, 34090 Montpellier, France; [PERSON]  
3C2 MA, IMT Mines Ales, University of Montpellier, 30100 Ales, France; [EMAIL_ADDRESS]  
4C2 MA, IMT Mines Ales, University of Montpellier, 30100 Ales, France; [EMAIL_ADDRESS]  
5C2 MA, IMT Mines Ales, University of Montpellier, 30100 Ales, France; [EMAIL_ADDRESS]  
6 IEM, Institut Europeen des Membranes, University of Montpellier, CNRS, ENSCM, 34090 Montpellier, France; [PERSON]  
7C2 MA, IMT Mines Ales, University of Montpellier, 30100 Ales, France; [EMAIL_ADDRESS]  
6 IEM, Institut Europeen des Membranes, University of Montpellier, CNRS, ENSCM, 34090 Montpellier, France; [PERSON]  
8C2 MA, IMT Mines Ales, University of Montpellier, 30100 Ales, France; [EMAIL_ADDRESS]  
7C2 MA, IMT Mines Ales, University of Montpellier, 30100 Ales, France; thierry.vincent@mines-ales.  
suffering from a high cost; this method is specially tailored for large-scale recovery with a high target metal concentration (higher than 0.5 g L\({}^{-1}\)[6; 7]). For those leaching liquors containing low metal concentrations, base metals, and a relatively high acidity, the recovery process is rather challenging [8].  
Sorption is a physiochemical process that involves the passive sorption and/or complexation of metals by sorbents and is well-known for its low operating cost, high efficiency in recovering metal ions from low-concentration effluents, and small-occupied space. Polyethylenimine (PEI), which has a unique branched/linear conformation, is a superior ligand to chelate PGMs. To make this material stable, several studies previously incorporated its crosslinked products into biopolymers, such as chitosan [9], carrageenan [10; 11], and alginate [12; 13]. However, very few studies were conducted on the direct use of the raw natural materials as supports for PEI. Very recently, glutaraldehyde(GA) crosslinked PEI (branched) was incorporated in brown algal biomass (_Laminara digitata_) beads through a green and convenient process, during which alginate is simultaneously extracted and used for immobilizing PEI-GA via calcium gelation. Theoretically, beads can also be prepared through this process using a kind of red algae, _Chrondrus crispus_, taking advantage of 60% carrageenan inside this material to gel with potassium. Moreover, the pKa of carboxyl groups on alginate and sulfate groups on _kappa_-carrageenan beads is approximately 4 and 2 [14], respectively, while that of tertiary amine groups on PEI was reported as 11.6 [15]. Therefore, when adjusting the PEI solution pH between 4 and 11, PEI can be loaded through electrostatic interaction between the positively charged amino groups and the negatively charged carboxyl groups on _L. digitata_ (LD) beads or sulfate groups on _C. crispus_ (CC) beads [16].  
Based on the discussion above, this study aims to develop two algal-based sorbents modified with PEI by the impregnation method for recovering palladium from the leaching liquors. To improve their stability, the loaded PEI was crosslinked with GA as a post-treatment [17]. The beads were characterized using FTIR and SEM-EDX and compared for Pd(II) sorption by evaluating the impact of parameters such as solution pH, the presence of co-existing anions and metals, and by investigating the sorption isotherms and kinetics. At the end, the sorbents were applied for Pd(II) recovery from synthesized leaching liquors to assess their feasibility for practical applications.