水铁矿-人工合成类腐植酸复合材料的土壤重金属钝化效果及机制

Heavy metal passivation effect and mechanism of ferrihydrite-synthetic humic-like acid composite in farmland

水铁矿-天然腐植酸复合材料(FH-NHA)已广泛应用于土壤重金属污染修复,但来源不同的天然腐植酸活性位点存在较大差异,导致钝化效果不可控,限制其实际应用。本文以优化的非生物腐殖化工艺合成了结构性质可控的人工合成类腐植酸(SHLA),并进一步制备了水铁矿-人工合成类腐植酸复合材料(FH-SHLA)。基于土壤模拟实验,结合土壤二乙三胺五乙酸(DTPA)提取态和改进的BCR提取态重金属含量的变化,解析了FH-SHLA施用后的重金属钝化效果和对土壤理化性质的影响,结合扫描电子显微镜、傅里叶红外光谱和X射线光电子能谱等手段揭示了其重金属钝化机制。结果表明:FH-SHLA会显著改变土壤理化性质,土壤pH、阳离子交换容量、电导率和有机碳含量等均有不同程度的提高;施加FH-SHLA培养30 d后,土壤中DTPA提取态Pb、Cd和Zn含量分别降低了65.98%、29.68%和60.89%,降低效果均优于FH和FH-NHA;FH-SHLA显著促进了土壤Pb、Cd和Zn由有效态(酸溶态+可还原态)向稳定态(可氧化态+残渣态)转变,钝化效果优于FH和FH-NHA;结合强度系数和钝化效率明显提高,迁移系数和生态风险指数明显降低,FH-SHLA有效降低了重金属污染土壤生态风险。FH-SHLA的土壤重金属钝化机制包括表面络合、沉淀作用和阳离子-π作用。水铁矿-人工合成类腐植酸复合材料在重金属污染土壤修复领域具有很好的应用潜力。

Ferrihydrite-natural humic acid composite(FH-NHA)has been widely used in the remediation of heavy metal pollution in soil.However,the active sites of natural humic acid from different sources vary,resulting in uncontrollable passivation effect and limited practical application.In this study,synthetic humic-like acid(SHLA)with controllable structure and properties was synthesized based on the optimized abiotic humification process.Ferrihydrite-synthetic humic-like acid composite(FH-SHLA)was further prepared.A soil simulation experiment,combined with the change in the contents of DTPA-extractable and BCR extractable heavy metals from the soil,were used to study the heavy metal passivation effect of FH-SHLA application.Furthermore,the impacts of FH-SHLA on physical and chemical properties of the soil were explored,and its heavy metal passivation mechanism was assessed using scanning electron microscopy,Fourier transform-infrared spectroscopy,and X-ray photoelectron spectroscopy.The results showed that FH-SHLA significantly changed physical and chemical properties of soil,such as pH,cation exchange capacity,conductivity,and organic carbon content.These properties improved to varying degrees.After 30 days of incubation with FH-SHLA,the content of DTPA-extracted lead(Pb),cadmium(Cd),and zinc(Zn)in soil decreased by 65.98%,29.68% and 60.89%,respectively.These reductions exceeded those obtained using FH and FHNHA.FH-SHLA significantly promoted the transformation of soil Pb,Cd,and Zn from the effective fraction(acid-soluble fraction+reducible fraction)to stable fraction(oxidizable fraction+residue fraction).The passivation effect with FH-SHLA was better than the effect with FH and FH-NHA.The reduced partition index and stabilization efficiency were significantly increased,and metal bioavailability factor and ecological risk index were significantly reduced.FH-SHLA effectively reduced the ecological risk of heavy metal contaminated soil.The soil heavy metal passivation mechanism of FH-SHLA involves surface complexation,precipitation,and cation-πinteraction.Thus,the FH-SHLA composite has significant implications in the remediation of heavy metal contaminated soil.