溶解性有机酸对砷在土壤矿物质表面吸附—解吸行为的影响

Effect of Dissolved Organic Acids on Arsenate Adsorption-desorption onto Soil Mineral

砷在土壤环境中的迁移转化受到土壤中存在的金属氧化物胶体的影响。砷在土壤和土壤溶液之间的吸附-解吸行为受到土壤溶液中存在的低分子量溶解性有机酸的制约。柠檬酸根是土壤常见的有机酸根之一,目前的研究认为:对于特定矿物质有限的吸附位而言,柠檬酸根作为一种与As(V)竞争吸附位的阴离子,可导致As(V)在针铁矿上的吸附量严重下降。结合环境中As(V)和柠檬酸根与土壤矿物质可能遭遇的状况,通过改变As(V)和柠檬酸根加入顺序建立了三种实验体系:第一种是先进行As(V)与针铁矿的吸附反应,平衡后再加入柠檬酸根[(As(V)-针铁矿)-柠檬酸根];第二种情况与此类似,所不同的是先加入柠檬酸根再加入As(V)[(柠檬酸根-针铁矿)-As(V)];第三种情况是柠檬酸根和As(V)同时加入[(柠檬酸根-As(V))-针铁矿]。为进一步考察柠檬酸根对砷吸附行为的抑制作用机理,选择乙酸根和草酸根作为对照进行As(V)吸附实验。结果显示:在酸性条件下,柠檬酸根对As(V)在针铁矿上吸附行为的影响是柠檬酸根溶解作用和竞争吸附位两种机理协同作用的结果,受到这两种机理的制约。

The fate of arsenic in soil environments is influenced by adsorption onto metal （hydr）oxides. The extent of arsenic adsorption is strongly affected by coexisting dissolved natural organic acids, which may be present in soils because of the release by roots and microorganisms and by the decomposition of organic matter. Some studies emphasized that citrate decreased arsenate adsorption as the result of the competitive adsorption between arsenate and citrate on goethite. This study focused on the comprehensive knowledge of the mechanism of the effect of citrate on arsenate adsorption-desorption onto goethite by evaluating adsorbed arsenate change in the equilibrated ternary system： [（arsenate-goethite）-eitrate], [（citrate-goethite）-arsenate] and [（citrate-arsenate）-goethite], combined with arsenate adsorption onto goethite in the presence of oxalate and acetate. These results implied that the reduction of arsenate adsorption onto goethite in acidic pH involved not only competition for binding sites, but the dissolution of goethite by citrate.