THE INTERACTION OF ALIPHATIC-ACIDS WITH BASIC ALUMINUM SULFATES IN A FORESTED ULTISOL

The effect of low molecular weight aliphatic acids on aluminum and SO4(2-) activity in the soil solution of two forested Cecil soils (typic Hapludult) was evaluated. A column study was conducted in which soils were selectively leached with malonic, or tartaric acid or with distilled water treatment. Leachate concentrations for SO4(2-) were in the range 2 to 709-mu-mol.L-1, total aluminum 26 to 945-mu-mol.L-1, and pH 4.1 to 6.5. Stability diagrams using aluminum, SO4(2-) and pH suggests that the aluminum and SO4(2-) activities were regulated by solid phases with the chemical composition of jurbanite and alunite. The addition of organic acids to the soil resulted in shifts in the solid phases controlling both aluminum and SO4(2-) activity. In the Cecil (South Carolina) soil, organic acids resulted in a shift from solution equilibrium with basaluminite to that of jurbanite, whereas the Cecil (Virginia) soil shifted in equilibrium from alunite to basaluminite as the controlling solid phase. The number of eluent pore volumes required for a solution to become saturated with respect to basaluminite varied with the organic acid source. For the Cecil (Virginia) soil 6, 10, and 14 pore volumes were required by the oxalic, malonic, and tartaric acid treatments, respectively, for the solution to become saturated with respect to basaluminite. Results from this study suggest the jurbanite provides an upper solubility limit for aluminum and SO4(2-) activities in these soils, whereas alunite provides the lower solubility limit. Solid phase transformations between various basic aluminum sulfate solid phases resulted in increased solution pH and may serve as a secondary source for H+ neutralization.