Anion Exchange Characteristics In a Loess Soil.

Loess soils of East Tennessee contain large amounts of subsoil Fe-oxides which have been shown to retain and restrict the movement of conservative anions, such as nitrate and bromide. The potential utilization of large quantities of flue gas desulfurization (FGD) gypsum on these soils may displace subsoil NO₃, releasing it into groundwater. This research examines the depth distribution of Fe-, Al, and Mn-oxyhydroxides, and of the cation and anion exchange capacity and exchange phase composition. This research also characterizes the thermodynamics of anion exchange in the NO₃-SO₄-Cl system. Metal oxide compositions were determined using the citrate-bicarbonate-dithionite and oxalate extraction methods. The AEC, CEC, and anion exchange phase composition were determined using standard methods. Metal (Fe, Al, and Mn) oxyhydroxide concentrations are found to peak at two different depths within the soil profiles: in the Bt horizons (30 to 46 cm), and in the tertiary sands that underlie the loess deposits (244 to 259 cm). The depth-distribution of CEC and AEC are similar to that of the metal oxyhydroxides. The CEC averages ~9.2 cmol/kg, ranging from ~3 to 13 cmol/kg. The AEC averages ~2.2 cmol/kg, ranging from ~1.7 to 4 cmol/kg. On average, the anion exchange complex is dominated by Cl (61 % of the AEC), while NO₃ accounts for 20 %, and SO₄ for 10 %.