Desorption of Ammonium from Montmorillonite Clay

The clay minerals are extremely important constituents of the inorganic solid phase of the soil primarily because of their ability to adsorb cations. Some clay minerals are capable of adsorbing certain cations so tenaciously, that these ions cannot be readily extracted with a neutral solution of a salt. Potassium and ammonium are nutrient cations that may suffer a decrease in their availability to plants by this phenomenon, which is commonly referred to as cation fixation. This research was undertaken to study the behavior of ammonium ions adsorbed by montmorillonite as affected by heating at various temperatures and to test the hypothesis that ammonium ions are adsorbed with varying levels of energy, depending on the site of adsorption. It is postulated that the fixation of cations is dependent upon the site of adsorption alone, and that fixed cations can be identified by the significantly greater demand for the energy required for desorption of such ions.