This study investigated the effectiveness and mechanisms of a novel composite adsorbent, prepared through in situ coating and regenerated through in situ embedding with Fe-Mn binary oxides onto porous diatomite (FMBO-DE), for the simultaneous removal of As(III) and As(V) from drinking water.
FMBO-DE was prepared in situ by interactions between equivalent amount of KMnO4 and FeSO4 (3:1) with suspended porous diatomite. Zeta potential analysis showed the zero point of charge was pH 7.0, slightly higher than Fe-Mn binary oxides (pH 6.1). No X-ray diffraction peaks were observed, confirming that FMBO-DE was amorphous; SEM/EDX analysis showed the surface elemental ratio of Fe to Mn was 3:1, indicating that ferric and manganese oxides were evenly homogeneous in Fe-Mn binary oxides.
Kinetics studies showed As was quickly removed by FMBO, up to 80% of equilibrium capacity within initial 60 minutes. Additionally, it exhibited strong potential for removing both As(III) and As(V), with maximum adsorption capacities as high as 350 mgAs(III) /g FMBO and 200 mgAs(V)/g FMBO, respectively. It was noteworthy that FMBO showed higher potential of removing As(III) than As(V).
Continuous column tests demonstrated significant removal of both As(III) and As(V). At an initial As concentration of 100µg L-1 and empty bed contact time of 5 min, freshly prepared FMBO-DE could treat 3000 bed volume (BV) of As(III) and 2000 BV of As(V) and the effluent As concentration was consistently below 10 μg L-1. The in situ embedded regeneration processes obviously increased the capability of removing As from water. After three regenerations, the adsorbing potential was as high as 4500 BV of As(III) and 3100 BV of As(V), respectively.