低聚合羟基铁离子-蒙脱石复合体吸附砷的实验研究

Adsorption of Arsenic on Fe oxyhydroxide-montmorillonite complex

将提纯的钙蒙脱石与羟基铁离子溶液作用,制备了低聚合羟基铁-蒙脱石复合体。用化学分析、电子探针分析、粉晶X射线衍射分析、差热分析和穆斯堡尔谱分析等手段,对蒙脱石原样、低聚合羟基铁-蒙脱石复合体和相同条件下制备的铁的含水氧化物进行了表征。在实际土壤的酸度(pH=4～7)和温度(18～40℃)条件下,进行了低聚合羟基铁-蒙脱石复合体吸附有害元素砷的实验,探讨了复合体的砷吸附能力与pH值、温度、吸附时间、砷初始浓度、离子强度间的关系,并与蒙脱石和铁的含水氧化物的砷吸附行为进行了对比。研究表明,在实验条件下,低聚合羟基铁-蒙脱石复合体对砷具有明显的亲合力,低聚合羟基铁-蒙脱石复合体吸附砷的过程有可能是地表岩石和土壤中重要的地球化学过程,是影响砷在地表,特别是土壤中迁移、富集的重要因素。

Arsenate has high affinity to solubl e hydroxy-Fe species and Fe-oxyhydr oxide precipitates,and montmorillonite has remarkable eff ect on the hydrolysis of Fe(III)and the growth of the initially precipitated Fe(III)phases.The adsorption of As on Fe oxy hydroxide-montmorillonite comple x is studied.Fe oxyhydroxide-montmorillonite complexes are prep ared by mixing montmorillonite with hydroxy-Fe for 1,3and 6months,respectively.The prepared complex es are characterized by chemical analysis,electron microprobe analysis,x-ray diffraction analysis,differentia l thermal analysis and Mssbauer spectroscopic analysis.The results in dicate that the complexes prepared are combination s of substrate motmorillonite and Fe-oxyhydroxide coating.The amount o f the Fe-oxyhydroxide coating increases with increasing of the reaction dura tion between montmorillonite and hydroxy-Fe.The Fe oxyhydroxide-montmorilloni te complex prepared by reacting mont morillonite with hydroxy-Fe for 3mo nths is chosen for As adsorption study.The e ffects of pH,ionic strength,temperature,initial As concentration,an d adsorption duration on the overall a dsorption of As by Fe oxyhydroxide-m ontmorillonite complex are investi gated.The results show that the adsorption of As increased slightly with increa sing of pH,temperature,ionic stren gth and adsorption duration,and decreases with increasing of initial As concen tration.The variation of the As adso rption of Fe oxyhydroxide-montmorillonite c omplex with ionic strength indicate s that inner-sphere complexation is the dominant adsorption mechanism.Und er all experimental conditions,Fe o xyhydroxide-montmorillonite comp lex displays very strong affinity to ars enate,which is supposed to influence the mobility of As in soil and water.