Chapter 4 - Soil Solution – Solid Phase Equilibria

Abstract

The composition of the soil solution dictates important chemical reactions such as dissolution and precipitation, both of which impact ion mobility. Additionally, ions in the soil solution can form complexes, which impact their reactivity and transport in the soil. This chapter discusses the major constituent ions of the soil porewater and how they are impacted by different extraction techniques. A major focus is on the speciation of the ions in soil porewater utilizing thermodynamic and conditional equilibrium constants. A vast number of ion species occur in soil porewater, and computational methods, such as those employed by Visual MINTEQ, are introduced. These methods are used to predict ion species and conduct aqueous equilibrium speciation calculations. Ion activity coefficients and ionic strength are described. Dissolution and solubilization processes are linked to the creation of stability diagrams and the prediction of mineral precipitation.