Composite of magnetite and Zn/Al layered double hydroxide as a magnetically separable adsorbent for effective removal of humic acid

In the present study, we synthesized a magnetically separable adsorbent, i.e., composite of magnetite and Zn/Al layered double hydroxide(Fe3O4-Zn/Al LDH), for effective removal of humic acid (HA). The composite was synthesized through conventional co-precipitation method using NaOH as precipitating agent. The presence of well-dispersed Fe3O4 outside the interlayer space of Zn/Al LDH made the Fe3O4-Zn/Al LDH magnetically active and thus the adsorbent was easily separated from aqueous solution by application of an external magnetic field. The adsorption test on HA demonstrated that Fe3O4-Zn/Al LDH was optimum in removing HA at pH 4.0 with removal capacity estimated according to the Langmuir isotherm model was 1.21 x 10(-4) mmol g(-1) or equivalent to 35.28 mg g(-1), while the removal rate constant according to the pseudosecond order kinetic model was 443.6 (mol/g)(-1) min(-1). The results strongly suggest that the removal of HA on Fe3O4-Zn/Al LDH occurs solely through simple adsorption on the outer surface through an electrostatic interaction. In addition, when the material was tested in a real raw water sample from a drinking water