Fig. 8. Effect of equivalent time at 25°C on Ni concentration in solution as affected by first-order kinetics for Ni sorption on (a) pyrophyllite, (b) talc, (c) gibbsite, (d) silica, and (e) gibbsite/silica mixture. Equivalent time was calculated from Eq. [7] and solid lines denote the fitted first-order kinetic model relationship (Eq. [8])