覆煤及粉煤灰回用土壤砷质量比与赋存形态研究

Research on arsenic content and its speciation distribution characteristics in overlying coal and fly ash recycling soil

为了解覆煤及粉煤灰回用土壤砷含量及赋存形态分布特征,选取贵州省兴仁县某村农耕旱地土壤为研究对象,采用逐级化学提取法对土壤样品进行试验。结果表明:研究区土壤中砷质量比为15.71～169.55 mg/kg,波动范围较大;土壤砷质量比最高值为169.55mg/kg,远远高于土壤砷质量比自然背景值(15 mg/kg)、世界土壤砷平均质量比(6.0 mg/kg)及我国土壤砷平均质量比(9.2 mg/kg);对照样土壤砷质量比为15.71 mg/kg,也略高于土壤中砷质量比的自然背景值(15 mg/kg)。研究区土壤砷污染问题已较为严重,这除与该地区地层中砂岩及粉砂岩砷质量比较高所导致的土壤砷背景质量比偏高有关以外,最主要的原因是覆煤广泛存在及粉煤灰大面积回用农田所致。该研究区土壤中砷主要以残渣态存在(72.16%),其次为硫化物结合态(15.45%)、铁锰氧化物结合态(5.89%)、有机态砷(3.06%)、碳酸盐结合态(2.51%),水溶态和可交换态砷均较低(0.93%)。研究区土壤总砷量较高,但迁移转化能力较弱,对环境及人体健康的危害程度尚有待讨论。

In order to understand the arsenic content and speciation distribution characteristics in overlying coal and fly ash recycling soil, dry land farming soils from Xingren County, Guizhou province were studied in this paper with sequential chemical extraction method. The results shows that the range of soil arsenic level in the researched area is within 15.71-169.55 mg/kg, the fluctuation range is very large. It is closely related with the different content of high arsenic contained coal and fly ash in the soil samples. The maximum value of soil arsenic（169.55 mg/kg）is much higher than the soil environmental background values（15 mg/kg）, the world average soil arsenic content（6.0 mg/kg） and soil arsenic average content in China（9.2 mg/kg）. The content of arsenic in the control samples is 15.71 mg/kg, which is also slightly higher than the natural background values of arsenic content in the soil. Soil arsenic pollution of the study area has been becoming more serious. It is caused by the higher arsenic content of sandstone and silty sandstone in the study area, as well as wide distribution of overlying coal and a large amount of reused fly ash in the farmland. Soil arsenic in this study area mainly exists as residue state（72.16%）, which is followed by sulfide combination state, iron manganese oxide combination state（5.89%）, organic state（3.06%）, carbonate combination state（2.51%）and water soluble and exchangeable state（0.93%）. They can be arranged in order as： residue state arsenic〉sulfide combination state arsenic〉iron manganese oxide combination state arsenic〉organic state arsenic〉carbonate combination state arsenic〉water soluble and exchangeable state arsenic. Although the total soil arsenic content of this area is too high, the arsenic transformation ability in residual state which arsenic mainly exists in is relatively weak. Therefore, its harm to the environment and human health has yet been in discussion.