Some factors affecting anion retention in acid soils

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Virginia Polytechnic Institute

The purpose of this investigation were to use chromatographic methods to study the effects of pH, time of equilibration, and the effect of anions themselves in the anion retention in an acid red soil.

It was found that chloride was held much less tightly than sulfate by soils. It was also noted that more sulfate was retained at higher concentration.

A time factor was also noted in this investigation. It took a longer period to reach true equilibrium when sulfate was used. Results showed a positive correlation between sulfate retention and time to reach true equilibrium. The disappearance of aluminum from the solution added to soil suggested that the continuing hydrolysis of aluminum being the main cause of the time effect. Such hydrolysis produces hydrogen ions which can neutralize the hydroxyl ions exchanged by anions and kept the pH of the system from going up and continuing the reaction.

The non-symmetrical elution patterns indicated the retention of anions• The longer the tail of the elution patterns, the more tightly the anions are retained.

Distribution coefficients (Kd) for Cl⁻, NO₃⁻, and SO₄ showed approximately linear relationships between pH 3 and 6. Chloride and NO₃⁻ exhibited similar Kd values at similar pH values. It also indicated that SO₄⁻ was held much more tightly at low pH values.