Removal of arsenic from water using multifunctional micro-/nano-structured MnO2 spheres and microfiltration

In this work, multifunctional micro-/nano-structured MnO2 spheres were developed and applied in the removal process of As species from water. Morphology studies indicated that the synthesized material possesses microstructure and nanostructure, which endow the material with excellent oxidation, adsorption and separation properties. Batch experiments showed that As(III) species can be effectively oxidized by the synthesized MnO2 followed by the adsorption of As(V) species. Investigation on operation parameters revealed that removal of As(V) using the MnO2 spheres was evidently dependent on pH and ionic strength, while co-existing anions such as CO32-, SO42-, and PO43- induced suppressive effects. FTIR and XPS studies were used to further identify the surface changes of the synthesized MnO2 after reactions with As(III) or As(V), indicating that As(III) and As(V) interacted differently with the synthesized MnO2. The determination of oxidation states of As and Mn by XPS indicated the reductive dissolution of Mn in the conversion of As(III) to As(V). Furthermore, a dead-end microfiltration process was conducted to evaluate the seperation property of the synthesized MnO2 spheres from treated water. Membrane fouling study showed that the synthesized MnO2 spheres caused little membrane pore blocking. Besides that, the material also formed a porous cake layer on the membrane which kept a relatively high flux.