锌冶炼废渣重金属在地块土壤中的垂向迁移特征及归趋

Vertical Migration Characteristics and Fate of Heavy Metals from Zinc Smelting Slag in Soil Profile

为探讨冶炼废渣中重金属对土壤及地下水的影响,开展了90 d持续和间歇淋溶下锌挥发窑渣浸出液中重金属在场地剖面土柱的迁移模拟实验,分析淋出液Cd、Cu、Pb和Zn浓度及其在土壤剖面的累积、赋存形态和粒径分布特征,并探讨重金属在土壤剖面滞留机制.结果表明,土柱淋出液重金属浓度在淋溶初期达到峰值后迅速降低,Cd浓度超过《地下水环境质量标准》(GB/T 14848-2017)Ⅳ类水质限值(0.1 mg·L^(-1)),地下水存在Cd污染风险.剖面土壤对废渣中重金属固持量大,Cd、Cu、Pb和Zn主要累积在浅层土壤(0~10 cm),分别为淋溶前土壤的237~429、1.25~16.2、1.38~2.31和1.79~3.17倍;持续淋溶下废渣重金属较间歇淋溶的迁移距离较长,Cd在土柱深层有明显累积.土壤粗颗粒(0.5~2.0 mm)对Cd、Cu和Zn累积总量的贡献率较大,而Pb更易累积在<0.25 mm粒径.BCR顺序提取结果显示,浅层土壤累积的Cd、Cu和Zn主要以弱酸提取态为主,占比分别高达62.4%~76.7%、72.0%~95.8%和67.6%~85.8%.X射线衍射仪(XRD)和傅里叶变换红外光谱法(FTIR)测定结果表明,废渣中重金属进入土壤后90 d内不会形成稳定矿物相,土壤羟基(—OH)、羰基(c=0)官能团和铁铝硅盐氧化物是其主要固持因子.

To investigate the influence of heavy metals in smelting waste residue on the quality of soil and groundwater,a simulation column experiment was conducted to study the migration characteristics of heavy metals from the leaching solution of zinc volatilizing kiln residue in the site soil profile under continuous or intermittent leaching for 90 days.The concentrations of Cd,Cu,Pb,and Zn in leachate and their accumulation,chemical fractions,and particle size distribution characteristics in the soil profile were analyzed,and the retention mechanism of heavy metals was also discussed.The results showed that the concentration of heavy metals in the soil column leachate decreased rapidly after reaching the peak at the earlier leaching stage,and the Cd concentration far exceeded the threshold limit of 0.1 mg·L^(-1)(classⅣ)of the Quality Standard for Groundwater(GB/T 14848-2017),indicating that there was Cd pollution risk of groundwater.The soil profile had a great adsorption capacity for heavy metals in the waste residue.Cd,Cu,Pb,and Zn were predominately accumulated in the shallow soil depth(0-10 cm),which was 237-429,1.25-16.2,1.38-2.31,and 1.79-3.17 times of the content of corresponding heavy metals in the soil profile before leaching,respectively.The migration distance of heavy metals in the slag under continuous leaching was longer than that under intermittent leaching,and Cd was significantly accumulated in the deep layer of the soil column.The contribution of soil coarse particles(0.5-2.0 mm)to the total cumulative amount of Cd,Cu,and Zn was larger,whereas Pb was more prone to accumulate in the particle size of<0.25 mm.The results of BCR sequential extraction fraction showed that the accumulated Cd,Cu,and Zn in shallow soil depth were mainly present in the weak acid extraction,accounting for 62.4%-76.7%,72.0%-95.8%,and 67.6%-85.8%of total content,respectively.The X-ray diffraction(XRD)and Fourier transform infrared spectroscopy(FTIR)analysis showed that exogenous heavy metals in slag entering the soil would not form a stable mineral phase within 90 days,and the soil hydroxyl(—OH)and carbonyl(C=0)functional groups and iron aluminum silicate oxides were the main retention factors.