Abstract
Dispersion of aggregates for allophanic soil was studied with nitric and sulfuric acid solutions. Aggregate dispersion was enhanced for pH<4 in nitric acid solutions, whereas not significant for all pH ranges in sulfuric acid solutions. Hydraulic conductivity of packed soil was decreased instantaneously due to aggregate dispersion when the nitric acid solutions were applied. Aggregate dispersion enlarged the apparent soil surface area which could contact with acid solutions. Increase in the surface area enhanced the buffering capacity as a result of cation exchange, aluminum solubility, anion sorption and mineral weathering. Smaller aggregate could also make the displacement by diffusion easily. These reactions could lead to pH increases for effluent solutions. On the other hand, the hydraulic conductivity was constant when the low pH sulfuric acid solutions were applied since the aggregate dispersion did not occur. The pH of effluent solutions, therefore, decreased because of the limited buffering capacity at the surface of aggregate. When a higher pH solution such as distilled water was applied, the hydraulic conductivity did not change as well. Although the aggregate dispersion did not occur for distilled water, the buffering capacity for the low hydrogen concentration increased the pH of the effluents. Permeability and buffering capacity of allophanic soil were influenced by the species of acid solutions as well as the concentration of hydrogen ion of percolating acid solutions.
