锌冶炼地块土壤重金属垂向分布特征及影响因素

Vertical distribution of heavy metals in soils and its influencing factors from a zinc smelting site

从湖南某废弃锌冶炼厂火法炼锌区域不同功能区采集6个土壤剖面(0—8 m),分析重金属镉(Cd)、铬(Cr)、铅(Pb)和锌(Zn)含量和赋存形态的垂向分布特征,探讨其与土壤理化性质相互关系.结果表明,土壤重金属主要累积在0—3 m杂填土层,呈现随土壤深度增加含量下降趋势.整个剖面Cd含量高,可迁移污染至深层土壤,Cr、Pb和Zn含量表现为0—3 m>3—6 m>6—8 m的显著差异(P<0.05).欧共体参比司(BCR)制定的三步连续提取法结果表明,剖面土壤Cr含量以残渣态(79.2%—93.0%)为主,随着剖面深度增加,Pb的残渣态比例呈增加趋势,而Cd和Zn的酸可提取态比例增加,迁移风险高.电镜扫描能谱仪(SEM-EDS)和X射线衍射仪(XRD)分析结果表明,土层样品含有大量硅铝酸盐和SiO2;但沸腾炉区点位S6的1—1.5 m处土壤样品存在ZnO物相,点位S3号4—5 m和6—8 m深度处出现ZnCO_(3)矿物相,表明核心功能区冶炼活动会加剧土壤Zn富集并向下迁移.相关性分析表明,剖面土壤重金属全量与其各赋存形态含量呈显著正相关,非晶质Fe_(2)O_(3)含量与Cd、Pb和Zn活性态含量也呈显著正相关(P<0.05),表现出促进迁移的效应.污染来源、土壤理化性质共同控制重金属的垂向分布及迁移,研究结果可为冶炼地块重金属污染土壤风险管控与修复提供科学依据.

Six soil profiles were collected from an abandoned zinc smelting site in Hunan Province to study the vertical distribution characteristics of contents and chemical fractions of Cd,Cr,Pb,and Zn,and the influence factors of soil physical and chemical properties were analyzed.The results showed that high content of heavy metals was predominately accumulated in 0—3 m soil layer,and decreased with the increase in soil depth.The Cd content in profiles was high and migrated into the deep soil.The geomean contents of Cr,Pb,and Zn in soil profiles were decreased significantly followed the order of 0—3 m>3—6 m>6—8 m(P<0.05).According to BCR(European Community Bureau of Reference)sequential extraction analysis,soil profile Cr content was predominated with residual fraction,accounting for 79.2%—93.0%of total content.The percentage of acid soluble fraction Cd and Zn,residual fraction Pb was increased with the soil depth increasing,indicating that high potential migration risks of Cd and Zn in soil profiles.The SEM-EDS(scanning electron microscope-energy dispersive spectroscopy)and XRD(X-ray diffraction)analysis results showed that there were much peaks of aluminosilicate minerals and SiO2 in soil.The mineral phase of ZnO were found in 1—1.5 m depth soil from point S6,and that of ZnCO_(3) appeared at 4—5 m and 6—8 m soil depth from point S3.This result indicated that critical smelting activities would cause the accumulation of Zn in soil.There was significant relationship between total content and chemical fractions of heavy metals in soil.Soil chemical properties of amorphous Fe_(2)O_(3) promoted the migration of Cd,Pb and Zn in soil profile.The vertical distribution of heavy metals was controlled by pollution sources and soil physical and chemical properties.The results would provide scientific basis for effective prevention,control and remediation of heavy metal contaminated soil from smelting sites.