汞污染土壤热解吸处理过程中不同形态汞的温度效应

选择贵州省具有代表性的汞污染土壤样品进行热解吸修复的试验研究,同时采用连续化学浸提法对土壤样品中5种形态的汞分别进行提取,探究了不同形态汞在热解吸修复过程中的浓度变化和转化规律. 结果表明,土壤样品中各形态汞所占比例为w(王水溶汞)(占76.52%)>w(酸溶汞)(占22.40%)>w(硝酸溶汞)(占0.87%)>w(水溶性汞)(占0.14%)>w(碱溶汞)(占0.06%). w(王水溶汞)与w(Σ汞)(各形态汞总量)的相关系数可达0.978 1. 升温过程中,w(酸溶汞)和w(王水溶汞)明显降低,而其余形态汞含量则呈先升后降的趋势. 采用热解吸技术可以有效处理汞污染土壤,在370 ℃条件下能够将土壤中w(Σ汞)降至1 mg/kg以下,处理率可达95.73%,处理后土壤中的汞以残渣态汞为主,环境风险较小. 

Effects of Temperature on Mercury Fractions in Contaminated Soil during the Thermal Desorption Process

Typical soil samples contaminated by mercury in Guizhou Province were taken for thermal desorption testing. Mercury in the soil samples was divided into five fractions by continuous chemical extraction. The variation of content and transformation of the different species of mercury were examined during the thermal desorption process. The percentages of each fraction of mercury were ranked as following:chloroazotic acid soluble mercury (76.52%) > acid soluble mercury (22.40%) > nitric acid soluble mercury (0.87%) > water-soluble mercury (0.14%) > alkaline solubility mercury (0.06%). The correlation coefficient between the chloroazotic acid soluble mercury and gross mercury was 0.9781. With the increase of temperature, the amounts of acid soluble and chloroazotic acid soluble mercury were significantly decreased, but the other three species of mercury were found to increase at first and then decrease. The mercury-contaminated soil could be effectively remediated by the thermal desorption technology. The amounts of all five species of mercury in the soil were decreased to under 1 mg/kg at 370 ℃, which represented a total removal efficiency of 95.73%. After the treatment, the major mercury speciation in the soil was found to be the chloroazotic acid soluble mercury, which causes little environmental risk.