Highly selective extraction of Pd(II) using functionalized molecule of 2-[(2-ethylhexyl)thio]benzoxazole and its Pd(II) extraction mechanism

• Published in: Journal of molecular structure Vol. 1230; p. 129639
• Main Authors: Feng, Shaoping, Huang, Kun, Huang, Zhangjie, Liu, Guiyang, Zhang, Guowei, Gou, Gaozhang
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.04.2021
• Subjects: 2-[(2-ethylhexyl)thio]benzoxazole; Extraction; Mechanism; Palladium; Separation; 2-[(2-ethylhexyl)thio]benzoxazole; Palladium; Extraction; Separation; Mechanism
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2020.129639

•A functionalized extractant EHBXS with three heteroatoms (S, N and O atoms) which can selectively coordinated with Pd(II) was synthesized by one-step reaction.•EHBXS has high selectivity for Pd(II) and can effectively remove Pd(II) from multi-metal solution at desired extraction conditions.•The coordination mechanism between Pd(II) and EHBXS was proved by slope method, FT-IR, 1H NMR, 13C NMR spectroscopies, and the X-ray crystal structure of Pd(EHBXS)2Cl2. In view of the separation and recycling of Pd(II) from multi-metal aqueous solution, a functionalized extractant of 2-[(2-ethylhexyl)thio]benzoxazole (EHBXS) with excellent selectivity for Pd(II) was synthesized and used to extract Pd(II) for the first time. The effects of EHBXS concentration, HCl concentration, organic/aqueous (O/A) phase ratio, contact time, and regeneration of EHBXS were investigated in detail. The extraction efficiency of Pd(II) was almost 100 % while the co-extraction efficiencies of Pt(IV), Rh(III), Cu(II), Fe(III) and Ni(II) existed in the aqueous solution were less than 10 %, which indicates that EHBXS is an effective extractant and can effectively remove Pd(II) from other metals at desired extraction conditions. Thiourea ((NH2)2CS) solution (1.0 mol/L) could be used as an effective Pd(II) stripping agent and the one-step stripping efficiency of Pd(II) was higher than 98 %. EHBXS has excellent regeneration ability and the extraction efficiency of Pd(II) with regenerated EHBXS reaches to 87% even after 7 cycles. Moreover, the coordination mechanism between EHBXS and Pd(II) has been proven via the slope method, FT-IR spectra, 1H NMR, 13C NMR and single X-ray diffraction. Pd(II) and EHBXS formed a 1:2 complex of Pd(EHBXS)2Cl2 during extraction. Pd(II) was coordinated with two Cl atoms and two EHBXS, and thus formed Pd(EHBXS)2Cl2 molecule, in which EHBXS was coordinated with Pd(II) via the N atom in the benzoxazole ring as neutral unidentate ligand. [Display omitted]