Modeling of Salt Sorption in Volcanic Ash Soil

Groundwater pollution by nitrate from agricultural fields is a worldwide problem. To improve the understanding of nitrate transport processes through volcanic ash soils overlying groundwater aquifers, salt sorption experiments were performed. Salt sorption is the process that involves the simultaneous use of cation and anion adsorption mechanisms without changing the pH. Prepared six different concentrations of potassium chloride (KCl) solutions were mixed with soil samples. Anion and cation contents of the liquid and solid phases were determined. Experiments were performed in triplicate of six kinds of KCl solutions for three types of soils. Thus, total 54 of samples were analyzed. Relationships between ionic strength and sorption capacity increments of cations and anions were determined. The results show that if ionic strength of the infiltrating solution to the volcanic ash soil is known, the ECEC (effective cation exchange capacity) and EAEC (effective anion exchange capacity) can be reliably estimated. The resulting prediction equations can be included to improve reactive transport simulation models. Consequently, it will be possible to better understand solute transport with changing sorption capacity for the solid soil phase.