Removal of Cr(VI) and Pb(II) from Aqueous Solution Using Mg/Al Layered Double Hydroxides-Mordenite Composite

Mg/Al layered double hydroxides-mordenite nanocomposite (LDH@mordenite) was prepared via the in-situ method to enhance the Cr(VI) and Pb(II) removal efficiency. The results showed that the Cr(VI) and Pb(II) removal efficiency was enhanced by the formation of core-shell structure (mordenite core-LDH shell). The synthesized material with an LDH content of 30% had the highest removal efficiency for both metals at the pH of 5.0. The pseudo-second-order model was the best model for describing the adsorption kinetics of Cr(VI) and Pb(II) on LDH@mordenite. The calculation from the intra-particle diffusion model suggested that the adsorption processes included several steps. Fitting experimental data to the Langmuir, Freundlich, and Temkin models revealed that the Langmuir model was the best model for predicting the isotherms of the adsorption processes. The calculated maximum adsorption capacity at 25 celcius was 54.80 mg/g for Cr(VI) and 67.91 mg/g for Pb(II). Based on the thermodynamic study, the Cr(VI) and Pb(II) adsorption on LDH@mordenite was endothermic and spontaneous. The adsorption mechanisms were studied using the statistical physics model and the calculated parameters indicated that Cr(VI) and Pb(II) ions could interact via one and two adsorption sites of the adsorbent.