抄録
This paper describes a fundamental examination of a quicklime (calcium oxide) mixing treatment combined with carbon dioxide ventilation for the remediation process of soils contaminated with volatile organic compounds (VOCs). The quicklime mixing treatment is widely applied to remove VOCs in soils using the heat of reaction with calcium oxide and pore water.
To maintain a higher temperature and to ensure that most of the VOCs are volatilized, quicklime is usually mixed at a ratio of 10% with soils in this treatment. However, a surplus of quicklime addition results in higher (alkaline) soil pH and causes serious damage to the soil ecosystems. To solve this problem, the simultaneous ventilation of carbon dioxide during quicklime mixing with contaminated soil was examined. Under these conditions calcium hydroxide was generated by the reaction of quicklime with pore water; the calcium hydroxide then reacted with carbon dioxide to produce additional heat of reaction. It is expected that the heat from the second reaction can be used for the treatment, allowing the amount of quicklime addition for the treatment to be reduced.
Laboratory experiments showed that more than half of the calcium hydroxide was changed to calcium carbonate when the mixed soil sample was ventilated by carbon dioxide, using mixing ratios of 5% quicklime and 5% water in the soil. The maximum soil temperature reached with this treatment was the same as that for the treatment using 10% quicklime. Pilot scale and operational scale experiments confirmed the effectiveness of using carbon dioxide ventilation coupled with quicklime mixing treatment.
