Flocculation inspired combination of layered double hydroxides and fulvic acid to form a novel composite adsorbent for the simultaneous adsorption of anionic dye and heavy metals

Abstract

Currently, simultaneous removal of anionic and cationic pollutants from combined pollution wastewater is a challenging subject. Here, a novel composite adsorbent which can simultaneously adsorb anionic azo dye and heavy metal cations was developed by flocculation inspired assembly of Mg2Al layered double hydroxides (LDH) and fulvic acid (FA). The results show that the negatively charged macromolecule FA is firmly intertwined with the positively charged LDH through electrostatic attraction and adsorption bridging. This composite adsorbent (Mg2Al LDH-FA) can effectively capture anionic Orange II by anion exchange adsorption derived from LDH component with the maximum adsorption capacity of 604 mg/g. Mg2Al LDH-FA also exhibits good adsorption performance for heavy metals due to the complexation with FA and surface precipitation on LDH. The adsorption isotherms of heavy metals coincided with Langmuir model or Freundlich model, and the adsorption capacities for Pb2+, Cu2+, Ni2+, Cd2+ could reach up to 661.5 mg/g, 116.3 mg/g, 117.3 mg/g, 235.2 mg/g respectively. Particularly, Mg2Al LDH-FA can simultaneously uptake Orange II and heavy metals from the stimulated combined pollution wastewater, moreover it shows higher adsorption capacity for each pollutant than that in the single pollutant case as the result of the synergistic adsorption effect between LDH and FA.