as indicates Eq. (3). The mechanism
of action for iron is extremely efficient since it is expected that
1 g of iron reacts with 300 ml of oxygen in the presence of moisture.
Thus, the absorption of the active kaolinite was tested at two levels of
relative humidity to quantify the effect of humidity in the activity of
iron metallic centers supported on the clay. The active kaolinite
showed strong efficiency at short times (even though a lag time of
few hours was needed for moisture absorption), i.e. after 24 h of exposure
at 100% RH the active kaolinite was able to uptake 30 ml
and of oxygen per gram of additive and up to 43 ml after 60 days.
The oxygen depletion at 50% RH exhibited slower kinetics during the
first 20 days, however, similar equilibrium absorption as at higher relative
humidity was achieved after 60 days (37 ml O2/g clay). The oxygen
scavenging activity of iron kaolinite is consistent with the performance
reported by Charles et al., (Charles, Sanchez, & Gontard, 2006) for commercial
O2 scavenger sachets containing iron powder. The sachets
exhibited a bold O2 absorption performance after 24 h of exposure at
100% RH, and at equilibrium conditions they absorbed 43.5 ml O2/g
and 45.5 ml O2/g, at 5 °C and 20 °C, respectively.