REACTIONS OF HYDROGEN IONS WITH VARIABLE CHARGE SOILS

Abstract

We studied the consumption of hydrogen ions and the accompanying changes in positive surface charge, soluble aluminum, and exchangeable acidity in three variable charge soils and a kaolinite, which had been electrodialyzed previously. We found that the sum of the three mechanisms contributed to approximately 100% of the quantity of hydrogen ions consumed. The magnitude of the increase in positive charge was related to the content of surface Fe-OH and Al-OH groups. The presence of amorphous aluminum hydroxide and illite favored the release of soluble aluminum. The exchangeable acidity increased most markedly in the soil having the highest iron oxide content. For a given soil, the role of the increase in positive surface charge decreased and that of the dissolution of aluminum increased when the amount of hydrogen ions added to the soil was increased.