Anionic surfactant enhanced phosphate desorption from Mg/Al-layered double hydroxides by micelle formation

Abstract

Desorption of interlayer hydrogen phosphate (HPO4) from hydrogen phosphate intercalated Mg/Al-layered double hydroxide (LDH–HPO4) by anion exchange with surfactant anions has been investigated under controlled conditions. Three types of surfactant, Dodecylbenzenesulphonate (DBS), Dodecylsulphate (DS) and 1-Octanesulphonate (OS), anions were used for intercalation experiments over a range of concentrations, and for all solutions, it was shown that the desorption of hydrogen phosphate is enhanced at concentrations close to the critical micelle concentration (CMC). Intercalation of the surfactant anions into LDH–HPO4 was confirmed by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR) and Scanning electron microscopy (SEM). More than 90% removal of the hydrogen phosphate was achieved at CMC. Repeat adsorption tests to investigate recyclability showed that desorption with 0.005M DBS improved subsequent phosphate re-adsorption, allowing around 90% of the original adsorption over three cycles. This is much higher than when desorption was conducted using either Na2CO3 or NaCl–NaOH solutions, even at much higher concentrations. This study suggests potential economic and environmental advantages in using these surfactants in improving the cycling performance of LDH materials as absorbents for clean-up of water systems.