Microscopic structures of Zn(II) adsorbed at delta-MnO2-water interfaces were studied using extended X-ray absorption fine structure (EXAFS) spectroscopy. In a 0.1 M NaNO3 solution of pH 5.50, hydrous Zn(II) was adsorbed onto the solid surface in the form of octahedral coordination. Adsorbed octahedral Zn(II) was located above and below the vacancy sites of delta-MnO2. Each Zn was coordinated on one side to H2O molecules forming an H2O sheet and on the other side to oxygen atoms shared with layer MnO6 octahedra forming a corner-sharing octahedral interlayer complex. The average Zn-O and Zn-Mu distances were 2.07 +/- 0.01 and 3.52 +/- 0.01 Angstrom, respectively. Macroscopic adsorption-desorption isotherms showed that, in contrast to that of the Zn-gamma-MnOOH system, adsorption of Zn(II) on delta-MnO2 was highly reversible. EXAFS results indicated that the highly reversible adsorption was due to the weak adsorption mode of the corner-sharing linkage between the adsorbate and adsorbent polyhedra. (C) 2003 Elsevier Inc. All rights reserved.