Effective roxarsone (ROX) and arsenate (As(V)) sequestration from water with magnetic hollow Fe3O4-based Mg/Al layered double hydroxide: Performance and mechanism

Magnetic hollow Fe3O4-based Mg/Al layered double hydroxide (Fe3O4@SiO2@LDH) was successfully synthesized and subsequently the laboratory scale tests were conducted to systematically investigate the sequestration of roxarsone (ROX) and arsenate (As(V)). Owing to its abundant surface metal hydroxyl (M-OH) groups and exchangeable CO32- groups in the interlayer of MgAl-LDH nanosheets, the obtained Fe3O4@SiO2@LDH exhibited remarkable behavior for As(V) and ROX removal. Both As(V) and ROX could be effectively immobilized at a relatively wide pH range (3-8), and the maximum adsorption capacities of As(V) and ROX were 96.47 and 71.67 mg/g, respectively. Meanwhile, the negligible mutual effect demonstrated the Fe3O4@SiO2@LDH can simultaneously remove inorganic and organic arsenic compounds. The competitive cations/anions (except for PO43- ions) and ionic strength were negligible on As(V) and ROX removal, whereas the inhibitory effect stem from humic acid (HA) seemed to be more seriously for As(V) than that of ROX. Adsorption mechanism of As(V)/ROX were attributed to electrostatic attraction and ion/ligand exchange process, whereas hydrogen bonding and pi-pi interaction may also involve in the ROX removal. Furthermore, the excellent performance in fix-bed column tests and prominent reusability indicated this magnetic Fe3O4@SiO2@LDH was a promising candidate adsorbent and of great potential application in organic/inorganic As-contamination wastewater treatment.