2002 Volume 89 Pages 25-33
The prediction method of ion concentration in the effluent during pH 3 sulfuric acid solution permeation into the air-dried volcanic ash soil column was examined in this study. The method for prediction was composed of chemical reactions between acid solution and soil, and mixing cell model. The chemical reactions were composed of aluminum dissolution, cation exchange between dissolved aluminum and basic cations, bicarbonate formation, sulfate ion adsorption, charge valance and mass balance of sulfate ion and basic cations. Cation exchange between dissolved aluminum ion and soil bases were lumped together with the mineral weathering as acid buffering effect. Mixing cell size depends on dispersivity and that value was determined by the breakthrough curve during KC1 and pH 3 sulfuric acid solution permeation. Characteristics of the variable charge on volcanic ash soil were considered in the simulation model by applying the anion adsorption equation (Wada,1981)in which adsorbed amount of sulfate ion depends on pH and sulfate ion concentration. The simulation results agreed well with the measured values of pH, aluminum ion concentration and cumulative release of basic cations in the effluent. These represent the most serious effects of the acid deposition on the soil. Therefore, parameters used in this simulation model are useful for predicting the main effect of the acid deposition on the Kanto loam subsoil. However, it could not estimate basic cations concentration of the effluent with good accuracy. This discrepancy may reflect the assumptions that cation exchange treated as aluminum-divalent basic cation exchange, the equilibrium constant was assumed and exchange between hydrogen ion and cation was not included. Therefore, it is necessary to describe the cation exchange in more detail.
