Characterization of the Solubility of Aluminum in Soil by X-Ray Diffraction

A procedure to investigate the controlling phase of aluminum solubility in soil was developed. Following pretreatment, X-ray diffraction (XRD) was used to determine the aluminum phases present in soil. Gibbsite, kaolinite, and muscovite were observed as the aluminum phases by XRD. From identification of the aluminum phases, a solubility diagram was created to investigate the phase that controls aluminum activity. The aluminum ion activity was obtained experimentally by determining the activity coefficients of hydrolysis species of aluminum, the pH, total aluminum concentration, and the fluoride activities. Soil conductivity was measured to find the ionic strength that was subsequently used to calculate the values of activity coefficients for different valence states. The results suggest that gibbsite solubility line is far away from the experimental line for the studied soil. Kaolinite was the least soluble phase by XRD but the results show it had a reduced effect upon the aluminum ion activity. If quartz...