Efficient separation and recovery process of Pd(II) based on sintering-leaching method by silica-based aluminum hexacyanoferrate

In the present work, several hexacyanoferrates (K2CoFe(CN)6, KAlFe(CN)6 and K2NiFe(CN)6) were theoretically analyzed based on density functional theory (DFT). Their stable structures and adsorption capabilities were compared. A silica-based hexacyanoferrate (KAlFe(CN)6/SiO2) was selected and synthesized for Pd(II) separation and recovery process. Its estimated mode particle size was 67 μm, and its average crystal size was 18.8 nm. The Fe 2p and Pd 3 d X-ray photo-electron spectra (XPS) of Pd-loaded KAlFe(CN)6/SiO2 and density functional theory calculation revealed that the adsorption mechanism is the spontaneous displacement of K+ by Pd2+. A novel sintering-leaching method was developed for the recovery of Pd(II) from spent adsorbent. The effects of different sintering times, leaching temperatures, and leaching media were investigated, indicating that the optimal condition (sintering at 400 °C for 24 h, leaching in 3 M HCl at 50 °C) could reach a Pd(II) recover ratio of 88%. Energy-dispersive spectroscopy (EDS) and XPS tests were performed on the leaching product, and the results confirmed that the recovered product was PdO with purity of 91.8%. [Display omitted] •The structures and free energies of several hexacyanoferrates were calculated by DFT.•The adsorption of Pd(II) on KAlFe(CN)6/SiO2 is a spontaneous monolayer ion exchange.•A separation and recovery process of Pd from high-level liquid waste was proposed.•The sintering–leaching method recovered 88% of the adsorbed Pd(Ⅱ) in the form of PdO.