The enhancement roles of sulfate on the adsorption of sodium dodecylsulfate by calcium-based layered double hydroxide: microstructure and thermal behaviors.

As a commonly used surfactant, sodium dodecyl sulfate (SDS) usually coexists with inorganic anions in the industrial wastewater. These anions have a significant influence on SDS removal, indirectly threatening the environment. It is important to understand the relationship between the adsorption of SDS and inorganic anions. In this study, calcium-based layered double hydroxide (CaAl-LDH-Cl) as an efficient adsorbent was synthesized for investigating the effect of SO42- on SDS removal. The SDS adsorption capacities were enhanced to 3.21 and 4.21 mmol g-1 in the presence of SO42- with low/high SDS concentration, respectively. The phenomenon and mechanism were confirmed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and Scanning electron microscopy (SEM). Anionic exchange played a dominant role in the adsorption of SDS onto CaAl-LDH-Cl at DS-/SO42- < 2, while both anion exchange and precipitation occurred when DS-/SO42- exceeded 2. Moreover, the thermal analysis (TG-DTA) was employed to further reveal the interaction mechanism. The results showed the highest total mass loss and the lowest loss temperature of interlayer water in the sulfate coexist system, confirming the enhancement of SDS adsorption amount in the presence of SO42-.