『Abstract
The dissolution of well crystallized gibbsite far at from equilibrium
was studied in batch and mixed flow through reactors. The dissolution
experiments were carried out between pH 2 and 6 in the presence
of 10 mmol L-1 citrate, at pH 2 and 3 in the presence
of 10 mmol L-1 chloride, nitrate, and sulfate, and
at pH 2 and 3 in the presence of 1.5 mmol L-1 silica
at 20℃. The dissolution rate of gibbsite, RAl (mol
m-2 s-1), increases in the order of chloride≒nitrate＜silica＜sulfate≒citrate.
In presence of silica, sulphate, and citrate dissolution is catalysed
by the formation of aluminium complexes at the gibbsite surface
(pH 2 and 3). From pH 2 to 3 no effect of RAl
on hydrogen activity is predicted as singly coordinated surface
sites at the edges of the platy gibbsite crystals, [≡AlOH2+0.5]≒[≡AlOH], are almost saturated
with protons. However at pH＞3 dissolution is slowed by a decrease
of [≡AlOH2+0.5].
Gibbsite dissolution rates measured in closed and open systems
were identical within the experimental and analytical uncertainty.
This observation indicates that gibbsite dissolution is a surface
controlled process. If dissolution of gibbsite occurs close to
equilibrium RAl values may be predicted by
an approximately linear function of ΔGr.』
1. Introduction
2. Crystal structure, proton adsorption and dissolution behaviour
3. Experimental
3.1. Gibbsite
3.2. Experimental setup
4. Solubility of gibbsite and Al3+ complexation
5. Dissolution of gibbsite at closed system conditions
5.1. Dissolution far from equilibrium
5.1.1. Acid to near neutral pH in the presence of C6O7H8
5.1.2. Acid pH in the presence of Cl-, NO3-,
Si(OH)4, SO42-,
and C6O7H8
5.2. Dissolution close to equilibrium
5.3. Effect of pretreatment
6. Dissolution of gibbsite at open systems far from equilibrium
7. Discussion
8. Conclusions
Acknowledgments
References