Recovery of Palladium(II) from nitric acid medium using a natural resin prepared from persimmon dropped fruits residues

• Use a natural, abundantly available and low cost adsorbent.
• Exhibit high capacity and good selectivity for Palladium(Ⅱ).
• Propose the adsorption mechanisms of surface complexation and redox reaction.
• Develop a new strategy of palladium recovery from PCBs in nitric acid medium.

A natural resin, named “PPF resin”, was prepared by cross-linking persimmon tannin with formaldehyde and employed as adsorbents for selective recovery of Pd(II) from nitric acid medium. Parameters such as acidic media, HNO3 concentration, contact time, initial metal concentration and temperature were investigated in detail. The adsorption behavior followed the typical monolayer type of Langmuir model and the maximum adsorption capacity reached 259.7 mg g−1 at 323 K. The obtained thermodynamic parameters (ΔG, ΔH and ΔS) revealed that this adsorption process was feasible, spontaneous and endothermic process. After adequately characterizing the samples by FT-IR, XRD, XPS and SEM-EDS, the adsorption mechanism was proposed to be complex formation and redox reaction. The Pd(II) recovery from industrial nitric acid extract of printed circuit boards was effective and highly selective, and the loaded Pd(II) can be easily desorbed using acidic thiourea solutions. Therefore, the present results provide a new, low cost and effective approach for palladium recovery from e-wastes in nitric acid medium.

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