铁锰二元氧化物改性粉煤灰对地下水中砷的吸附特性

Adsorption properties of fly ash modified with Fe-Mn binary oxide on As(Ⅴ)/As(Ⅲ)in the groundwater

在我国内陆盆地和河流三角洲广泛分布着高砷地下水,吸附法作为一种简单而高效的除砷方法得到广泛的应用,但大多数吸附材料对As(Ⅲ)的吸附能力弱于As(Ⅴ),因此开发具有氧化和吸附耦合作用的高效吸附剂具有积极意义。采用共沉淀法制备铁锰二元氧化物改性粉煤灰(FMFA),探究其对As(Ⅲ)/As(Ⅴ)的吸附性能及吸附机理;通过批实验探究FMFA对溶液中As(Ⅲ)/As(Ⅴ)的吸附性能,采用XRD、SEM、BET等表征分析其表面形貌和结构,利用XPS和FT-IR分析吸附前后FMFA表面元素和官能团变化。结果表明:铁、锰氧化物均以不定形相负载于粉煤灰表面,极大地提高了FMFA的比表面积(可达166.77 m^(2)/g),为As(Ⅲ)/As(Ⅴ)的吸附提供了更多的活性位点;FMFA在中性条件下对As(Ⅲ)和As(Ⅴ)的理论最大吸附容量分别为68.19 mg/g和24.42 mg/g,As(Ⅲ)/As(Ⅴ)的吸附等温线模型均符合Freundlich模型,As(Ⅴ)的吸附过程遵循准二级动力学模型,As(Ⅲ)的吸附过程更符合Elovich模型;在溶液初始pH=5~9范围内FMFA的稳定性较好,初始pH>9的碱性环境不利于As(Ⅴ)/As(Ⅲ)的吸附;水中常见共存含氧阴离子对As(Ⅲ)/As(Ⅴ)竞争吸附影响大小的顺序为PO_(4)^(3-)>HCO_(3)^(-)>SO_(4)^(2-);FMFA可有效去除地下水样品中的砷,且不会造成铁、锰二次污染,同时具有良好的回收再生能力;在FMFA吸附As(Ⅲ)的过程中二氧化锰主要起氧化作用,铁氧化物起吸附作用,砷通过与FMFA表面金属活性羟基配体交换形成内球络合物而被吸附。本文成功制备了可高效去除地下水中As(Ⅲ)/As(Ⅴ)的绿色经济的新型吸附剂,对保障居民饮用水安全具有重要意义。

High arsenic groundwater is widely distributed in inland basins and river deltas in China,and adsorption method has been widely used as a simple and efficient method for arsenic removal.However,the adsorption capacity of most adsorbents for As(Ⅲ)is weaker than that of As(Ⅴ),so it is of positive significance to develop efficient adsorption with the coupling effect of oxidation and adsorption.The fly ash modified with Fe-Mn binary oxide(FMFA)was prepared by co-precipitation,and its adsorption properties and mechanism for As(Ⅲ)/As(Ⅴ)were studied.The adsorption performance of FMFA on As(Ⅲ)/As(Ⅴ)in solution was investigated by batch experiment.The surface morphology and structure of FMFA were analyzed by XRD,SEM and BET,and the changes of elements and functional groups on FMFA surface before and after adsorption were analyzed by XPS and FT-IR.The experimental results show that both the Fe oxide and Mn oxide are loaded on the surface of fly ash in amorphous form,which greatly increases the specific surface area of FMFA(up to 166.77 m~2/g),and provides more active sites for As(Ⅲ)/As(Ⅴ)adsorption.In neutral condition,the adsorption capacities of FMFA for As(Ⅲ)and As(Ⅴ)are 68.19 mg/g and 24.42 mg/g,and the adsorption isotherm model of As(Ⅲ)/As(Ⅴ)conforms to Freundlich model.The adsorption process of As(Ⅴ)follows the qseudo-second-order kinetic model,and the As(Ⅲ)is more consis-tent with the Elovich model.The alkaline environment with initial pH>9 is not conductive to the adsorption of As(Ⅲ)/As(Ⅴ)by FMFA which is more stable in the range of initial pH=5~9.The effect of the coexisting oxygen-containing anions on competitive adsorption of As(Ⅲ)/As(Ⅴ)in water is PO_(4)^(3-)>HCO_(3)^(-)>SO_(4)^(2-).FMFA can effectively remove arsenic from groundwater samples without causing secondary pollution of iron and manganese,and has good recycling capacity.During the adsorption of As(Ⅲ)by FMFA,manganese dioxides mainly plays the role of oxidation and iron oxide plays the role of adsorption,and arsenic is adsorbed by exchanging with metal active hydroxyl groups on the FMFA surface to form inner complex.This paper has successfully prepared a new green economic adsorbent which can effectively remove As(Ⅲ)/As(Ⅴ)from groundwater,which is of great significance to ensure the safety of drinking water for residents.