THE KINETICS OF NICKEL SORPTION ON PYROPHYLLITE AS MONITORED BY X-RAY-ABSORPTION FINE-STRUCTURE (XAFS) SPECTROSCOPY

This study investigated the effect of reaction time (minutes to months ) on the surface coordination environment of Ni sorbed onto pyrophylli te using XAFS. The data suggest the appearance of multinuclear Ni comp lexes after a reaction time of minutes. As reaction time progresses, t hese multinuclear Ni complexes increased in size ((NNi-Ni = 1.4-4.5). Ni-Ni bond distances (2.99-3.03 Angstrom) were similar to those for mi xed Ni-Al hydroxides (3.03 Angstrom), but distinctively shorter than t hose for Ni(OH)(2)(s) (3.09 Angstrom). We propose that the formation o f mixed Ni-Al hydroxides may explain the observed bond distances and c oordination numbers.