Gibbsite surface reactivity

Discrepancies between the data sets were reconciled as discussed in ( ). The increasing scatter in for gibbsite with falling temperature is attributed primarily to contamination of Bayer process gibbsite with bayerite or other surface reactive precipitates, and is discussed further below. Those measurements which are believed to approach most closely the true solubility of gibbsite are reported by by Kittrick (jj ) and Russell et al. 

In summary, the model proposed on the basis of acid-base characteristics of kaolinite platelets explains the pH-dependent charge primarily to the protonation of the hydroxyl groups at the basal gibbsite and the edge surface. We will later illustrate how this charge characteristics (surface protonation) influences the reactivity (dissolution characteristics) of kaolinite. 

Alumina occurs in nature as corundum, a-Al203, which is noted for its great hardness, high electrical resistance and low chemical reactivity. It can be made by the high temperature treatment (at > 1200°C) of boehmite or gibbsite and normally has a low specific surface area (< 5m2 g-1). 

Surface hydroxyl groups coordinated to pairs of AP" cations appear on the plane perpendicular to the crystallographic c axis in gibbsite (Fig. 1.2). This basal plane makes up most of the surface of the mineral, but it appears that the hydroxyl groups bound to Lewis add sites on the edge plane perpendicular to the basal plane are more reactive.These Lewis acid sites comprise an Al " cation coordinated to a single water molecule. 

In the context of surface complexation, a sorbent with only one reactive siuface group like gibbsite might be a typical example where the actual application of such a model would be reasonable. Otherwise, this approach has been typically applied to generic siuface sites for different models. The model would be characterized by... 

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