MnCl_2-NaOH改性硅藻精土吸附剂的制备及其对As(Ⅴ)的吸附机制

Preparation of MnCl_2-NaOH modified diatomite adsorbent and adsorption mechanism of As(Ⅴ)

以硅藻精土为基体,MnCl_2和NaOH为复合改性剂制备了针对As(Ⅴ)离子的吸附剂。研究了MnCl_2-NaOH/硅藻土吸附剂用量对As(Ⅴ)去除率的影响,通过SEM、FT-IR、XRD、XPS对改性前后及吸附后的样品进行了微观分析。结果表明:随着吸附剂投量的增加,溶液中As(Ⅴ)的去除率从44.9%增加到93.9%。改性后硅藻基体未发生改变,MnCl_2-NaOH/硅藻土吸附剂平均孔径变大,比表面积增大近7倍。硅藻土经改性后红外活性羟基峰消失,表面新生成Mn—O—Si吸收峰,在XRD数据上显示新生成含有MnO_2的物相,表面Mn得到电子,通过氧化与硅藻表面形成复合接枝,吸附剂吸附溶液中含As(Ⅴ)的离子后,出现Mn_3(AsO_4)(OH)_4等物相,吸附过程中As得电子,Mn失电子,O、Si表面电子向As偏移,As在吸附剂表面的吸附方式有配位吸附、电荷吸附等。

As（Ⅴ）ion adsorbent was prepared by using diatomite as matrix,MnCl2 and NaOH as the complex modifiers.The effect of adsorbent dosage on the removal rate of As（Ⅴ）was studied.The samples of the adsorbent before and after the modification were analyzed by SEM,IR,XRD and XPS.The results show that the removal rate of As（Ⅴ）increases from 44.9%to 93.9% with the increase of MnCl2-NaOH/diatomite adsorbent.After modification,the diatom matrix is not changed,and the average pore size of MnCl2-NaOH/diatomite adsorbent increases and the specific surface area increases by nearly seven times.After the diatom modification,the active hydroxyl peak disappears,and the new Mn—O—Si absorption peak appears on the surface.XRD data show that Mn—O—Si phase is newly formed.The surface of Mn gets electrons,through oxidation and diatom surface formation of MnO2 composite grafting.The adsorption of As（Ⅴ）ions on the adsorbent results in the formation of Mn3（AsO4）（OH）4.As in the adsorption process,As gets electrons,Mn losses electrons,while O and Si surface electrons shift to As.Adsorption on the surface of MnCl2-NaOH/diatomite adsorbent is coordination adsorption,charge adsorption,and so on.