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Ligand exchange adsorption and coordination structure of Pd on $$delta$$-MnO$$_{2}$$ in NaCl solution

Tanaka, Kazuya ; Tanaka, Masato*; Watanabe, Naoko*; Tokunaga, Kohei*  ; Takahashi, Yoshio*

Pd is highly accumulated in ferromanganese nodules and crusts relative to its concentration in seawater but the mechanism by which Pd(II) is incorporated remains poorly understood. We investigated the local coordination structure of Pd(II) adsorbed on $$delta$$-MnO$$_{2}$$, using X-ray absorption fine structure spectroscopy. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses indicated that Pd was adsorbed on $$delta$$-MnO$$_{2}$$ through ligand exchange, from Cl coordination to O coordination. Furthermore, curve fitting of EXAFS spectra demonstrated the formation of two different inner-sphere complexes, bidentate-mononuclear and bidentate-binuclear complexes, and this finding was supported by density functional theory calculations. The formation of inner-sphere complexes is reasonable given the relatively large distribution coefficients obtained from adsorption experiments.



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Category:Geochemistry & Geophysics



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