Analytical Sciences

Abstract − Analytical Sciences, 37(10), 1321 (2021).

Investigations on Adsorption of Inorganic Ions in Aqueous Solution to Some Metal Oxides, Hydroxides and a Carbonate by the X-Ray Spectroscopic Method
Hironori OHASHI,* Kotaro YONEZU,** Daisuke KAWAMOTO,* and Takushi YOKOYAMA*
*Department of Chemistry, Faculty of Science, Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395, Japan
**Department of Earth Resource Engineering, Faculty of Engineering, Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395, Japan
Why does the adsorption and concentration of inorganic chemical species proceed at aqueous–solid interfaces? In this review paper, we discuss the use of X-ray chemical state analysis to elucidate the intrinsic adsorption mechanism. Based on the chemical states of the species adsorbed to solids as determined by X-ray chemical state analysis, possible adsorption mechanisms are discussed. The driving forces of adsorption are represented by the Gibbs free energy change (ΔGchem = ΔGchem,1 + ΔGchem,2) resulting from the formation of covalent bonds between metal ions (M) in metal oxides or hydroxides and adsorbed species (X) (M–O–X bond, ΔGchem,1) and the formation of new phases consisting of M and X (ΔGchem,2). The concept of ΔGchem,2 is proposed based on the experimental results from chemical state analyses. As examples, the following investigations are discussed in this review paper: the formation of mullite precursors by the adsorption of monosilicic acid to Al(OH)3, the spontaneous reduction of Au(III) to Au(0) by adsorption of Au(III) to Al(OH)3, MnO2 and Ni(OH)2 and the mechanism of concentration of Co2+, Tl+, Pb2+, Pt2+, Au+, and Pd2+ in marine ferromanganese crusts.