台州某典型电子废物拆解区土壤中镉污染特征及其迁移规律模拟

SIMULATION OF POLLUTION CHARACTERISTICS AND MIGRATION LAW OF CADMIUM IN SOIL OF A TYPICAL ELECTRONIC WASTE DISMANTLING AREA IN TAIZHOU

典型电子废物拆解区土壤中镉(Cd)的污染特征与迁移特性尚不明确。以浙江台州某典型电子废物拆解区为例,通过污染调查、等温吸附实验、土柱实验与HYDRUS-1D软件探究Cd在土壤中的垂向污染特征与迁移特性。构建降雨淋溶作用下堆积渣体溶出的Cd的迁移模型,预测其在研究区土壤中的迁移情况。结果表明:土壤中Cd污染主要存在于研究区西南侧,该处有近30年的电子废物堆积渣体淋溶历史,Cd污染主要存在于0~40 cm土壤中。Cd在土壤中的等温吸附符合Langmuir方程,KL和qm分别为0.0373 L/kg和5465 mg/kg。调参后的两点模型(TSM模型)对Cd在土柱中的穿透过程拟合效果良好(R2=0.998),利用TSM模型预测了实际情景下Cd在土壤中的垂向污染现状,预测值与实测值较接近(R2=0.970),进一步验证了模型的准确性。堆积渣体淋溶情景下Cd的长期迁移情况预测结果表明:Cd污染主要存在于包气带浅层土壤中。当淋溶液Cd浓度为0.02 mg/L时,淋溶100 a时包气带底端淋出液中Cd浓度为0.0042 mg/L,尚未超过GB/T 14848—2017《地下水质量标准》Ⅲ类标准,该情景下地下水中Cd的污染风险较小。因此,对于浙江台州电子废物堆积渣体,需重点关注Cd在浅层土壤中的污染。建议及时清理拆解渣体,避免其长时间接受降雨淋溶。而对于渣体堆积时间<30年的区域,应重点修复0~40 cm深度土壤。

The pollution and migration characteristics of cadmium(Cd)in typical e-waste disposal areas are still unclear.Thus,the electronic waste dismantling area in Taizhou,Zhejiang,was selected as the research area.The vertical pollution and migration characteristics of Cd in soil were studied through pollution investigation,isothermal adsorption experiment,soil column experiment,and HYDRUS-1D software.The migration model of Cd dissolved from accumulated slag under rainfall leaching was established,and its migration in the soil of the study area was predicted.The results showed that Cd pollution in the soil mainly exists in the southwest of the study area,where there has been a history of leachation of e-waste deposits for nearly 30 years,and soil Cd pollution mainly exists in the depth of 0 to 40 cm.The isothermal adsorption of Cd in the vadose zone soil conformed to the Langmuir equation,with KL and qm of 0.0373 L/kg and 5465 mg/kg,respectively.The two-site model(TSM model)could well simulate the penetration process of Cd in the soil column(R2=0.998).The migration simulation of the accumulated slag in the actual electronic waste dismantling area using the TSM model showed that the measured and simulated values of Cd concentration in the soil of the study area were consistent(R2=0.970),which further verified the reliability of the model.A further 100-year migration simulation was carried out for the Cd dissolved from the accumulated slag.The results indicated that when the Cd concentration eluted from the accumulated slag was 0.02 mg/L,the Cd concentration in the leaching solution at the bottom of the vadose zone in the 100th year was 0.0042 mg/L,which did not exceed ClassⅢwater quality standard specified in Groundwater Quality Standard(GB/T 14848—2017),indicating that there was no risk of Cd pollution in groundwater under this scenario,and Cd pollution mainly existed in the vadose zone soil.In conclusion,for the slag leaching scenario in the informal dismantling area in Taizhou,Zhejiang,it was necessary to focus on the risk of Cd contamination in the vadose zone soil.It is recommended to clean up and disassemble the slag in time to avoid receiving rain leaching for a long time.However,for areas where the accumulation time of the slag body is less than 30 years,the surface soil(with a depth of 0~40 cm)should be prioritized in remediation.