Innovative conditioning of algal-based sorbents: Macro-porous discs for palladium sorption

- Alginate and algal-based discs were prepared using one pot synthesis procedure.
- A new fixed-bed like system was proposed for palladium recovery.
- Crosslinked polyethylenimine greatly improved sorption capacity of algal discs.
- New functional groups were brought in after desorption using acidic thiourea.
- Sorbents can be regenerated at least 4 times without losing binding affinity.

Algal biomass (AB) was used for green synthesis of porous discs by one-pot extraction and shaping procedure without adding pure alginate. Glutaraldehyde-crosslinked polyethyleneimine (GLA-PEI) was incorporated into AB discs. These two sorbents (AB and AB/PEI) along with alginate discs (as a reference) were applied in a fixed-bed-like system using a recirculation mode or a single-pass flow mode for palladium recovery. Recirculation experiments show that the incorporation of 9% (w/w, dry weight) GLA-PEI remarkably improves (more than 100%) sorption property for Pd(II). The flow rate (5-45 mL min−1) hardly affects the sorption rate regardless of sorbent type. The pseudo-second order rate equation well fits the kinetic profiles. Sorption isotherms of Pd(II) onto alginate and AB discs are well described by the Langmuir equation, while the prediction of that onto AB/PEI sorbent requires the Sips model with a larger number of fitting parameters. The maximum experimental sorption capacity is 46.8 mg g−1 for alginate, 56.9 mg g−1 for AB and 121.6 mg g−1 for AB/PEI discs. The so-called Yan equation fits well the data obtained from single flow experiments. The Pd-loaded discs can be desorbed using 2 M HCl/0.1 M Thiourea as the eluant with desorption efficiency approaching 100%. FTIR analysis confirms that after desorption, the sorbents are chemically modified: thiourea brings amine groups, which improve Pd(II) binding in the next sorption cycle. Sorption/desorption experiments show that all the sorbents can be reused for at least 4 times with a concentration factor (CF) of 7.9-8.4, 7.8-8.1 and 4.2-6.3 for alginate, AB and AB/PEI discs, respectively in the recirculation mode, while CFs in single-pass mode are 5.8, 4.4 and 6.1 for alginate, AB and AB/PEI sorbents, respectively.

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