Evaluation of Soils for Use as Liner Materials: A Soil Chemistry Approach

Movement of NH 4 + below animal waste lagoons is generally a function of the whole‐lagoon seepage rate, soil mineralogy, cations in the lagoon liquor, and selectivity for NH 4 + on the soil‐exchange sites. Binary exchange reactions (Ca 2+ –K + , Ca 2+ –NH 4 + , and K + –NH 4 + ) were conducted on two soils from the Great Plains and with combinations of these soils with bentonite or zeolite added. Binary exchanges were used to predict ternary exchanges Ca 2+ –K + –NH 4 + following the Rothmund–Kornfeld approach and Gaines–Thomas convention. Potassium and NH 4 + were preferred over Ca 2+ , and K + was preferred over NH 4 + in all soils and soils with amendments. Generally, the addition of bentonite did not change cation selectivity over the native soils, whereas the addition of zeolite did. The Rothmund–Kornfeld approach worked well for predicting equivalent fractions of cations on the exchanger phase when only ternary‐solution phase compositions were known. Actual swine‐ and cattle‐lagoon solution compositions and the Rothmund–Kornfeld approach were used to project that native soils are predicted to retain 53 and 23%, respectively, of the downward‐moving NH 4 + on their exchange sites. Additions of bentonite or zeolite to soils under swine lagoons may only slightly improve the equivalent fraction of NH 4 + on the exchange sites. Although additions of bentonite or zeolite may not help increase the NH 4 + selectivity of a liner material, increases in the overall cation exchange capacity (CEC) of a soil will ultimately decrease the amount of soil needed to adsorb downward‐moving NH 4 +