Movement of ions in soil, I. Ion exchange and precipitation

Abstract

A one-dimensional equilibrium model for the movement of ionic species through a saturated soil is presented. Physical processes considered include mass flow, ion exchange, precipitation and dissolution. Precipitation involves the cationic species which is desorbed upon ion exchange and the anionic species in the leaching solution. In the presence of a precipitate, ion exchange takes place at two separate interfaces, moving at different velocities through the soil. At the first interface, precipitation takes place in conjunction with ion exchange, and at the second interface the precipitate dissolves and ion exchange proceeds. The conposition of the transition zone between the two interfaces is calculated from the conditions of mass conservation and electroneutrality, a linear ion-exchange equation and a solubility product.