Investigating the role of the morphology of the Zn-Al LDH on the adsorption of humic acid from aqueous solutions

Abstract

Flake Zn-Al layered double hydroxides (FLDHs) and microspheres of LDH (MLDHs) were fabricated with a simple hydrothermal method to investigate the role of the morphology of Zn-Al LDH for humic acid (HA) adsorption from synthetic solutions and natural water. The effect of process variables, i.e. contact time, initial concentration of HA, pH, and competitive ions on the adsorption was investigated. HA removal mechanism was also studied. The two adsorbents exhibited different adsorption behaviors for HA in the presence and absence of background ions, which may be highly correlated with the various adsorption mechanisms involved. Comparison of the HA removal capacity of these two adsorbents implies the superior adsorption capability of FLDH for removal of HA from synthetic solutions (9.5 mg/g), while the adsorption capacity of MLDH was higher for natural organic matters present in natural water samples containing co-existing ions (8.9 mg/g). The pseudo-second-order kinetics model and Longmuir isotherm model could adequately interpret the HA adsorption process for the studied adsorbents. Both LDHs exhibited good regeneration and recycling abilities. HIGHLIGHTS Morphology of LDH and presence of salts affect the removal mechanism of HA.; Presence of electrolytes in solution resulted in reducing the size of the HA.; In the absence of salts, removal of HA by MLDH was more through ligand exchange.; For FLDH, removal mechanism was an equal combination of both ligand and ion exchange.; MLDH could be a promising adsorbent for HA removal in multi-salt solutions.;

Keywords

• adsorption
• flake zn/al ldh
• humic acid
• water treatment
• zn/al ldh microspheres