Adsorption and desorption of zinc in soils

Zinc adsorption in soils conformed to the linear form of the Langmuir equation. Based on the adsorption maxima, the Zn adsorption capacity was found to be greater in smectite-dominant soils as compared with illite and kaolinite-dominant soils. On the basis of the maximum saturation percentage, the sequence was illite > kaolinite > smectite. The selectivity coefficients calculated from the Zn-Ca exchange equation decreased logarithmically as amount of Zn adsorbed increased in the soils. The Langmuir k value, which relates bonding energy of sorpt-ion, was found to be greater in the case of smectite-dominant soils. The amount of Zn desorbed by all extractants significantly correlated with total amount of Zn adsorbed, and DTPA desorbed the maximum amount of Zn adsorbed.