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