Improvement of quicklime mixing treatment by carbon dioxide ventilation

This paper describes a fundamental examination of a quicklime mixing treatment combined with carbon dioxide ventilation for the remediation process of soils polluted with volatile organic compounds (VOCs). The quicklime mixing treatment is widely applied to remove volatile pollutants in soils using the heat of reaction with quicklime 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 added quicklime 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 polluted soil was examined. Under these conditions calcium hydroxide is generated by the reaction of quicklime with pore water; the calcium hydroxide then reacts with carbon dioxide to produce additional heat of reaction. It is expected that the heat from the second reaction can be used for the pollutant 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. Scale-up experiments confirmed the effectiveness of using carbon dioxide ventilation.