Synthesis,characterisation of ternary layered double hydroxides (LDH) for sorption kinetics and thermodynamics of Cd2+

Kinetic and thermodynamic studies were carried out on the sorption of Cd²⁺ on three synthesised and characterised layered double hydroxides, namely: Ni-Co-Ti, Ni-Co-La and Mn-Ni-Al-CO₃. Sorption kinetics were investigated through time-dependent studies. Thermodynamics were determined by the effect of temperature on adsorption. Kinetic modelling of the adsorption of Cd(II) ions on the LDHs was determined using the first-order, pseudo-first order, pseudo-second order and Elovich kinetic models, as well as additional diffusion models. The results showed that the pseudo-second-order model best correlated the adsorption data with R² values of 1.000, 0.998 and 1.000 for NiCoTi, NiCoLa and MnNiAl-LDH respectively. Diffusion of the adsorbate was best correlated by the Weber-Morris intraparticle diffusion model with R² values of 0.9753, 0.8472 and 0.9412 for NiCoTi, NiCoLa and MnNiAl-LDH respectively. Thermodynamic studies showed that the adsorption was spontaneous and exothermic with a high probability of sticking.