The Effect of Exchangeable Cations on Soil Mineral Weathering

The kinetics of dissolution of soil minerals as a function of the ionic composition of the exchange phase were studied using a calcareous soil and a noncalcareous soil. It was concluded that mineral dissolution occurred as a two-step reaction when an exchanger phase is present. The initial fast reaction was completed in < 1 h and was linearly related to the amount of exchangeable sodium. The second slower reaction was independent of the exchangeable cation but dependent on the total mineral surface (soil-to-water ratio) available for weathering. The kinetics of dissolution for the second reaction was diffusion controlled.