Journal of the Japan Society of Engineering Geology

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Gas-liquid mixing experiments under both laboratory and in situ conditions were conducted to evaluate the process of neutralizing alkaline seepage from a tunnel (pH 10 to 11) by facilitating the dissolution of atmospheric carbon dioxide. The results showed that air bubbling of the tunnel seepage was the fastest and most effective method in reducing the pH of the seepage, and that a longer mixing period was also effective in reducing the pH. This indicates that increasing the gas-liquid contact area and contact time effectively induced the dissolution of atmospheric carbon dioxide.
Kinetics of the dissolution of atmospheric carbon dioxide was evaluated by constructing a model that expresses the change in pH as a function of the dissolved carbon dioxide concentration. The dissolution was found to be a first-order reaction with respect to the difference in concentration between the saturated aqueous carbon dioxide with the air and actual aqueous carbon dioxide of the tunnel seepage. Based on the above results and topographical conditions at the tunnel site, we are proposing the use of a channel with a series of weirs as a simple but effective remediation method. The model also successfully simulated pH reduction during the in situ experiments, which makes it useful in the design of an actual channel that will be used at the site.

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