重构土壤垂直剖面重金属Cd赋存形态及影响因素

针对矿业废弃地高背景值-历史矿业源相叠加区下土壤重金属Cd污染问题,以西南地区某历史硫磺矿业废弃地重构土壤为研究对象,采集剖面土壤共30个样品,分析测试土壤样品中镉(Cd)、铬(Cr)、镍(Ni)、砷(As)和汞(Hg),利用电镜扫描-能谱分析(SEM-EDS)和重金属形态连续提取的BCR方法,分析不同土层厚度下Cd的赋存形式,运用风险评价编码法(RAC)和次生相与原生相分布比值法(RSP)对其进行有效性评价,以及对不同理化性质下Cd各形态的变化规律进行了初步探讨.结果表明,研究区5种重金属中Cd全量的富集系数最高,达4以上;通过形貌特征可以发现,样品中存在较多的次棱角状、棱角状颗粒,不同深度下的能谱特征显示结果相似,均含有Cd、Fe、S和As等元素,Cd元素是以类质同象形式存在;对Cd进行潜在风险评价,RAC结果显示为中等风险及以下,RSP结果主要为重度污染;重金属全量是影响Cd各形态含量分布的最主要因素,其次pH、有机质和CEC,对垂直深度的土壤Cd赋存形态也表现出不同程度的影响.该研究结果可为进一步了解Cd在剖面土壤的活性、迁移规律、生物毒性和赋存形式提供科学依据.

Reconstructed Soil Vertical Profile Heavy Metal Cd Occurrence and Its Influencing Factors

Aiming at the problem of heavy metal Cd pollution in mining wasteland under the high background value and superposition area of the historical mining source, a total of 30 samples were collected from the reclaimed soil of a historical sulfur mine in Southwest China. The total contents of Cadmium (Cd), Chromium (Cr), Nickel (Ni), Arsenic (As), and Mercury (Hg) in soil samples were analyzed. Scanning electron microscopy-electron diffraction spectroscopy (SEM-EDS) and BCR method for continuous extraction of heavy metals were used to analyze the occurrence of Cd under different soil thicknesses. The effectiveness of heavy metal Cd was evaluated by the risk assessment coding method (RAC), and the ratio of secondary phase and primary phase (RSP) was obtained. In addition, the changes in Cd morphology under different physicochemical properties were discussed. The results show that the concentration factor of Cd in the five heavy metals is the highest over 4. Through the morphological characteristics, it can be found that there are mainly subangular and angular particles in the samples. The resulting energy spectrum characteristics at different depths were similar, and all sampled contained Cd, Fe, S, and As. Isomorphs of Cd element were observed. According to the potential risk assessment of Cd, the RAC results show that the risk is medium or below, while the RSP results may lead to serious pollution except for the bottom layer. The total amount of heavy metals is the most important factor affecting the distribution of Cd forms, followed by pH, organic matter, and CEC. The results of this study can provide scientific basis for further understanding the activity, migration rule, biological toxicity, and occurrence form of Cd in profile soil.