Soil chemical properties are significantly affected by surface charge characteristics of the soil. Interaction between oppositely charged particles in variable charge soils plays an important role in variation of soil electrochemical properties. In this study, effects of Al oxides were investigated on surface charge and acidity properties of kaolinite and Alfisol during electrodialysis. Results indicate that Al oxides, when mixed into kaolinite or Alfisol, decreased the effective cation exchange capacity (ECEC) and exchangeable acidity and inhibited the decrease in pH. Gibbsite showed a less effect than γ-Al2O3 and amorphous Al(OH)3 did in reducing ECEC and acidity of kaolinite and Alfisol and the latter two displayed comparable effects. However, Al oxides didn’t show the same order in this aspect as in the amount of positive charge they carried. Their effect on ECEC of kaolinite and Alfisol varied irreversibly with ionic strength of the bathing solutions. The XRD spectra indicate that amorphous Al(OH)3 and γ-Al2O3 were more effective than gibbsite in decreasing peak intensity of electrodialyzed kaolinite when mixed with these Al oxides at the same rate. The results obtained demonstrate that Al oxides could decrease effectively negative charge and inhibit acidification of kaolinite and Alfisol through diffuse-double-layer overlapping between oppositely charged particles and coating of Al oxides on kaolinite and Alfisol. Both mechanisms intensified with increasing rate of Al oxides mixed into kaolinite and Alfisol. Therefore, Al oxides can act as anti-acidification agents in variable charge soils.
The traditional acidification theory didn’t involve the interaction between oppositely charged particles and its effect on the charge properties and soil acidity. Therefore, it can hardly explain the phenomenon of soil acidification in variable charge soils. The mechanism of Al oxides in inhibiting natural acidification of variable charge soils through interaction of electric double layers and coating may offer an important supplementation to the traditional theory of natural acidification of soils.
(Li JY, Xu RK. 2013. Inhibition of acidification of kaolinite and alfisol by aluminum oxides through electrical double-layer interaction and coating. European Journal of Soil Science 64(1): 110-120.)
