Because of high burning rate of combustible waste, incineration ash constitutes a large percentage of landfilled waste in Japan. High alkali content in the ash leads to high pH in leachate, which have been seen in many reports of shaking test or lysimeter tests of the ash. However, a couple of lysimeter studies show rapid decrease of pH in leachate, and neutral pH are commonly observed in actual landfill operations. By close analysis of past studies, the authors assumed that carbon dioxide immigration/absorption into ash layer could neutralize pH.
The authors tested the assumption by batch type experiments in this study. Carbon dioxide absorption rate into ash was determined, and good correlation was observed between the absorption amounts and pH decrease in leachate. Though the most experiments were done in carbon dioxide concentration of 30%, the neutralization of pH was also realized in the atmosphere whose concentration is only 0.03%. Finally, model simulation explicitly shows that the neutralization process follows the second order reaction of carbon dioxide and alkali, and the reaction rate constant was estimated.
