Assessment of Copper‐Soil Bond Strength by Desorption Kinetics

Kinetics of copper desorption from the A horizon of Paxton soil was investigated following addition of Cu at the rates of 1.6, 3.9, 6.3, and 7.9 µmol Cu/g soil (100, 250, 400, and 500 µg Cu/g soil). The Cu was allowed to react with the soil for 30 min to 4 d, at which time Na‐citrate was added in a 1:1 Cu/citrate charge ratio. Copper adsorption pH was maintained at 5.6, and desorption occurred at pH 6.0. From the desorption kinetics, it appeared that Cu was initially retained on two types of sites. Up to about 1.6 µmol Cu/g was preferentially retained on high energy sites. If Cu addition exceeded this amount, the excess was retained on low energy sites. Within about 24 h, a portion of the Cu initially bound to low energy sites shifted to sites intermediate in energy between the initially observed low energy and high energy sites.