桑树杆生物炭/铁锰氧化物复合吸附剂的制备及其对As(Ⅴ)的吸附机理研究

Preparation and arsenic adsorption and its mechanisms by mulberry stem biochar/Fe-Mn oxides composite adsorbent

以桑树杆为原料,通过正交试验设计,利用氧化和共沉淀法制备桑树杆生物炭/铁锰氧化物复合吸附剂（MBFMA）,考察p H值、离子强度、共存离子对吸附剂除As（Ⅴ）吸附性能的影响,并对MBFMA进行了表征,探讨了吸附机理。研究结果表明,制备复合吸附剂的最佳工艺为：KMn O4浓度40 g·L^-1、Fe Cl2浓度40 g·L^-1、浸渍时间24 h,煅烧温度400℃,煅烧时间3 h。在p H范围为2.0～7.0时,吸附剂对As（Ⅴ）的吸附效果最佳;硝酸根、硫酸根、碳酸根和磷酸根溶液对除砷效果有不同程度的影响,其中磷酸盐的影响最大,离子强度对除砷效果影响不大;与Freundlich相比,Langmuir模型能够较好地描述MBFMA对As（Ⅴ）的吸附行为,25℃下最大吸附量为4.87 mg·g^-1。能谱分析表明吸附As（Ⅴ）的MBFMA含有0.34%的砷,FTIR定性分析表明羟基、羧基、内酯基是MBFMA表面的主要特征官能团,XPS分析表明铁、锰和表面含碳官能团参与了吸附反应,MBFMA对As（Ⅴ）的吸附是专性吸附。

A mulberry stem biochar/Fe-Mn oxides composite adsorbent（MBFMA）was prepared from mulberry stems by oxidation and coprecipitation methods through the orthogonal experiment. Effects of p H, ionic strength, and co-existing anions on As（Ⅴ）adsorption by MBFMA were investigated. Results show that the optimal preparation conditions were as follows：the concentrations of potassium permanganate and ferrous chloride were both 40 g·L^-1, impregnation time of 24 h, calcination temperature of 400 ℃,and calcination time of 3 h. The range of the optimal p H values was from 2.0 to 7.0. The ions present in the natural environment, such as nitrate, sulfate, carbonate and phosphoric,had different degrees of effects on arsenic adsorption, with phosphoric having the biggest impact. The ionic strength had no obvious side ef-fects on arsenic adsorption. The adsorption behavior of As（Ⅴ）on MBFMA was fit better with Langmuir equation than Freundlich equation.Adsorption capacity is 4.87 mg·g^-1under 25 ℃. Spectrum analysis showed that MBFMA had 0.34% of arsenic after adsorbing As（Ⅴ）. FTIR spectra indicated that MBFMA contained hydroxy, carboxyl, and lactone functional groups. X-ray photoelectron spectroscopy analysis indicated that iron, manganese, and carbon surface functional groups involved in the adsorption reaction, and adsorption of As（Ⅴ）by MBFMA was specific process.