Kinetic, thermodynamic and equilibrium studies on chloride adsorption from simulated concrete pore solution by core@shell zeolite-LTA@Mg-Al layered double hydroxides

Abstract The novel type of core@shell Linde type A zeolite@Mg-Al layered double hydroxides (zeolite-LTA@Mg-Al LDH) was synthesized by in-situ co-precipitation method. The kinetic, thermodynamic and equilibrium studies on the chloride adsorption of the as-fabricated zeolite-LTA@Mg-Al LDH were performed by a comparative experiment in simulated concrete pore solution. The morphology and microstructure of as-fabricated zeolite-LTA@Mg-Al LDH were observed by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectrum (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller (BET) technique. The results show that the zeolite-LTA@Mg-Al LDH core@shell structure can effectively adsorb the chloride ions from the simulated concrete pore solution, and its chloride adsorption capacity is obviously higher relative to pure Mg Al LDH powder. The initial pH value, additional SO42− and adsorbent dosage exert a remarkable influence on the chloride adsorption capacity. Furthermore, the adsorption process can be described by the Langmuir model and Pseudo-second-order kinetic. The negative values of Gibbs free energy (ΔG0) and standard enthalpy change (ΔH0) confirm the adsorption process spontaneous and exothermic in nature. In addition, the excellent chloride adsorption capacity of zeolite-LTA@Mg-Al LDH is attributed to the anion exchange of highly dispersed LDH with large surface area on the zeolite-LTA support.