Efficiencies And Mechanisms Of Removing Heavy Metal Ions From Aqueous Solutions Using Montmorillonite/Zero Valent Iron Nanocomposites

Naturally occurring montmorillonite (Mt) was applied as carrier with good dispersion and absorption properties to synthesize Mt/zero valent iron (Fe0) nanocomposites (Mt/Fe0) by chemical reduction method using sodium borohydride. The particle distribution, particle size and structural condition were analyzed by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), and scanning electron microscopy (FESEM) techniques. These obtained nanocomposites were then used to remove heavy metal ions including Cu2+, Pb2+and Zn2+from aqueous solutions. The adsorption mechanisms as well as the related factors were investigated using the X-ray photoelectron spectroscopy (XPS) technique for the nanocomposites before and after adsorption.The results showed that these obtained Fe0particles were well dispered on the surface of Mt, and the core of the Fe0was a-Fe coated by shells consisting of magnetite and/or hematite iron oxides which made Fe0resistent well to oxidation. The discernable hysteresis loop indicated the ferromagnetic properties of the nanocomposite. A20mL aliquot of Cu2+(20mg/L), Pb2+(50mg/L) and Zn2+(20mg/L) was treated with0.02g Mt/Fe0respectively. After a period of30min, the adsorption rate could reach93.3%,95.5%and81.8%, respectively. In the range of15-45℃, temperature changes had no obvious effects on adsorption. Nevertheless, pH values and initial concentrations of heavy metals had great impact on the adsorption. The adsorption rates increased with pH values and decreased with initial concentrations. Comparison tests among Mt, Fe0and Mt/Fe0implied that the most efficient adsorption material is Mt/Fe0. Adsorption reactions were fitted well with pseudo-second adsorption kinetics for all the heavy metals. Freundlich adsorption isotherm other than Langmuir adsorption isotherm fits more suitable for Cu2+and Zn2+adsorptions. However, Pb2+was fitted well by both Freundlich and Langmuir isotherm. XPS analyses indicated that the reaction mechanisms of Mt/Fe0adsorption for Cu2+involved adsorption-reduction interactions, whereas complexation-adsorption interactions were dominant for Pb2+and Zn2+adsorption. These fundamental results would be of importance and potential for the theoretical and practical studies of Mt/Fe0nanocomposites used for decontamination of heavy metals from aqueous solutions.