Cadmium sequestration with MgCuAl-layered double hydroxide@montmorillonite nanocomposite in batch and circulated fluidized bed column experiments

In this study, montmorillonite cationic clay coated with MgCuAl-Layered double hydroxide nanoparticles was investigated for its capacity to adsorb cadmium ion ( Cd 2 + ) from aqueous solutions. Montmorillonite, MgCuAl − LDH , and a novel MgCuAl-Layered double hydroxide@montmorillonite nanocomposite ( MCA − LDH@MMt ) were characterized using various mechanisms including BET surface areas, XRD, TEM, FTIR, and SEM/EDS analysis. The adsorption behaviour of MCA − LDH@MMt towards Cd 2 + ion was studied using batch and continuous flow systems. pH, contact time, initial Cd 2 + concentration, MCA − LDH@MMt dose and particle size, agitation speed, and temperature were examined in the batch system. The higher removal efficiency of Cd 2 + was reported at pH 5 at 70 mg/l initial concentration and 0.2 g/100 ml best adsorbent dose with 150 rpm. The adsorption of Cd 2 + on MCA − LDH@MMt followed Langmuir model and yielded a maximum adsorption capacity of 129.82 mg/g. While the pseudo-second-order model better simulates the cadmium kinetics data, and adsorption rate parameters values showing that the adsorption process was chemisorption and the rate-determining step of controlling cadmium adsorption onto MCA − LDH@MMt not intra-particle diffusion. A three-phase, commonly known as gas-liquid-solid circulated fluidized bed column was used to continuously eliminate Cd 2 + . Four influencing parameters were studied: liquid and air flow rate, bed height, and initial Cd 2 + concentration. The adsorption efficiency of Cd 2 + in a continuous system increased when the liquid flow rate decreased and the bed height increased. The time required for MCA − LDH@MMt to reach saturation increases as the bed height and the air flow rate increase. Column data were described using Bohart-Adams, Thomas, and Yoon and Nelson models of adsorption for given experimental conditions. The Bohart-Adams could represent the initial regime of the breakthrough curves, while the Thomas model was better at describing the whole curve of metal ion adsorption for a given experimental condition.