Magnetic Fe3O4/MgAl-LDH composite for effective removal of three red dyes from aqueous solution

Magnetic material as adsorbent can provide effective remove and quickly separate of pollutant in wastewater treatment. A magnetic Fe3O4/MgAl-layered double hydroxide (LDH) composite was prepared by low saturation coprecipitation in the dispersed Fe3O4 suspension. The characterization of XRD, TEM and FTIR revealed that the Fe3O4/MgAl-LDH composite was combined with Fe3O4 and MgAl-LDH. This provided the composite of magnetic property which improved the separation of solid from aqueous solution. The adsorption of reactive red (RR), congo red (CR) and acid red 1 (AR1) by magnetic Fe3O4/MgAl-LDH composite depended upon the adsorbent dosage, contact time, initial concentration and temperature. The adsorption of the three red dyes reached equilibrium at 30 min and followed the pseudo-second-order kinetic equation. The equilibrium adsorption isotherm data well fitted the Langmuir model for RR, Freundlich model for CR and AR1. Thermodynamic results demonstrated that the adsorption processes were spontaneous, endothermic for RR and CR or exothermic for AR1. The adsorption capacities changed insignificantly between solution pH 2–10 and the maximum were 97, 253 and 92 mg/g for RR, CR and AR1, respectively. Moreover, the solid composite can be quickly separated from the aqueous solution by an external magnet before and after adsorption process. This indicated that the magnetic Fe3O4/MgAl-LDH composite was an effective adsorbent for red dyes removal with quick separation.