Anion adsorption and desorption characteristics of a Piedmont Ultisol : Some implications for the fate of sulfate deposition

Abstract

Batch-type experiments were used to determine the anion (fluoride, nitrate, sulfate, and phosphate) adsorption and desorption characteristics of an Ultisol from the Piedmont Province of Georgia. The results were best described using ‘initial mass’ isotherms when the initial anion concentration was less than two meq l-1. The Langmuir adsorption maximum for sulfate (initial concentration range of 0.2–20 meq l-1) was 24.4 meq kg-1. Oxalate, acetate, nitrate, fluoride, and phosphate were used as exchangeable ‘counter’ anions to investigate the sulfate retention characteristics of this soil. High concentrations (> one meq l-1) of oxalate, phosphate and fluoride were shown to release sulfate from this soil. However, little sulfate desorption resulted when lower and more environmentally realistic concentrations of competing anions were applied. Application of oxalate revealed that a minimum of 19 meq kg-1 of sulfate has been adsorbed on this soil through natural processes. The Langmuir adsorption maximum suggests that this Ultisol, typical of many B horizons within this region, has a large capacity to adsorb additional inputs of atmospheric sulfate.