Calcareous, silicate, and aluminosilicate minerals are common constituents of inorganic soil. These minerals act as buffers against acid attack, either through carbonate neutralization or cation exchange. Previous studies focusing on potassium observed that cations occur in four separate phases: the solution phase, exchangeable phase, non–exchangeable phase, and the mineral phase. Each phase represents a different kinetic mechanism that is incrementally slower for cations deposited deeper in the mineral.
We have observed that when soil is exposed to acid, the pH of the soil slurry drops drastically, followed by a recovery curve on the order of seconds
to minutes. These recovery curves sometimes change curvature as a function of pH, indicating a different kinetic mechanism is dominating. Since real soil samples are a complex heterogeneous mixture, we analyzed soil analogs such as calcium carbonate, magnesium carbonate, calcium silicate, magnesium silicate, and aluminum silicate in the hope of assigning extracted kinetic parameters to specific physical properties of the compounds. We studied the kinetic mechanisms in these soil analogs with a series of hand titrations, designed to give a representation of the general shape of the reaction curve and the position of the equivalence point, and titration curves using an autotitrator, which was modified with a DAQ board in order to follow the recovery curve on a time scale of seconds between injections of acid. Our purpose was to determine the kinetic model for each type of recovery curve in each soil analog.
Overway, Ken and Oates, John, "Acid Rain Kinetics on Calcareous and Silicate Soils" (2017). Chemistry Faculty Scholarship. 10.