Magnetic nanoscale Fe–Mn binary oxides loaded zeolite for arsenic removal from synthetic groundwater

• A magnetic adsorbent MFM can be potentially used for arsenic removal in groundwater.
• MFM shows good adsorption capacities and convenient solid/liquid magnetic separation.
• As(III) oxidization to As(V) on MFM enhances its adsorption capacity.
• Heterogeneous distribution of adsorption site energy on MFM is found.

The removal of arsenic in contaminated groundwater on magnetic nanoscale Fe–Mn binary oxides loaded zeolite (MFM) is evaluated in this study. MFM is produced by an improved precipitation method; and is easily separated from water by an external magnetic field after arsenic removal. With the measured surface area of 340 m2/g by the BET method, the removal efficiency of MFM for arsenic is more than 99.0% at pH 7.0. The adsorption kinetics is well fitted with pseudo-second-order, as well as Weber–Morris model. Results show that arsenic adsorption on MFM is predominantly regulated by surface diffusion in initial 15 min, followed by intraparticle diffusion in later stage. Adsorption and oxidation occur simultaneously in the process of arsenite removal, while adsorption is the sole driving process during arsenate removal. MFM exhibits a strong adsorption affinity to arsenic, and the adsorption isotherms are well described by Freundlich and Redlich–Peterson models. A thermodynamic analysis indicates that the adsorption is spontaneous and endothermic. An adsorption site energy analysis illustrates a distribution of adsorption energy to exhibit the heterogeneous distribution nature on MFM for arsenic removal. This study proves MFM as a promising adsorbent for arsenic removal in contaminated groundwater.

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