Kinetics of Ni sorption on pyrophyllite

Figure 3.1. Kinetics of Ni sorption (%) on pyrophyllite, kaolinite, gibbsite, and montmorillonite from a 3 mM Ni solution, an ionic strength I = 0.1 NaNOs, and a pH of 7.5. (From Scheidegger et al., 1997a.)...

Figure 3 shows the kinetics of Ni sorption on pyrophyllite, kaolinite, gibbsite, and montmorillonite from a 3 mMNi solution at pH = 7.5 (16). For kaolinite and pyrophyllite relative Ni removal from solution follows a similar sorption trend with -90% Ni sorbed within the first 24 hours. At the end of the experiments, relative Ni removal from solution was almost complete (Ni/kaolinite system, 97% sorbed after 70 hours Ni/pyrophyllite system, 98% sorbed after 200 hours). Nickel sorption on gibbsite and montmorillonite exhibited a fast initial step. Thereafter, relative Ni removal from solution distinctively slowed down. Relative Ni sorption increased from 42-58% for the Ni/montmorillonite system (time range 0.5-7Q hours) and from 15-41% for the Ni/gibbsite system (time range... 

Figure 7 illustrates the kinetics of Ni sorption on pyrophyllite, along with dissolved Si data from the Ni-treated pyrophyllite and from an untreated pyrophyllite (16). The release of Si into solution shows a similar kinetic behavior as Ni sorption on pyrophyllite. When one compares the Si release rate with the dissolution rate of the clay alone, the Si release rate in the Ni-treated system is strongly enhanced as long as Ni removal from solution is pronounced (Figure 7). Although not shown, a similar correlation between Ni sorption and Si release was observed for the Ni/kaolinite system but not for the Ni/montmorillonite system. The dissolution rate of the Ni/gibbsite system was not determined since the [Al] in solution was too low (<50 ppb) to produce reliable ICP measurements.

Figure 7. The kinetics of Ni sorption on pyrophyllite from a 3mMNi solution at pH 7.5. ( ) denotes the amount of sorbed Ni (pmol m ) and (a) the amount of simultaneous dissolved Si (pmol m ). The dissolution of untreated pyrophyllite at pH 7.5 is shown for comparison ( ). From Scheidegger et 2il. (16), with permission.

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