Equilibrium and kinetic study of simultaneous removal of Cd (II) and Ni (II) by acrylamide-based polymer as effective adsorbent: optimisation by response surface methodology (RSM)

In the current study, the equilibrium and kinetic isotherms of simultaneous removal of Ni (II) and Cd (II) using acrylamide-based polymer adsorbent were investigated and the effects of different parameters on the adsorption efficiency were considered using the method, called central composite design (CCD), to determine optimal values of the parameters. The function of overriding parameters such as the initial nickel concentration (A), initial cadmium concentration (B), pH (C), adsorbent dose (D) and contact time (E) on Ni (II) and Cd (II) simultaneous removal were evaluated using response surface methodology (RSM). Maximum Ni (II) and Cd (II) simultaneous estimated removal of 84.5285% and 81.0137% and actual amounts of 84.5% and 83%, were achieved experimentally under the optimal conditions. The equilibrium behaviour of the adsorption process was tested using Langmuir, Freundlich, and Temkin isotherm models, which Langmuir isotherm model provided the closest fit for the experimental data. According to the Langmuir model, the maximum adsorption capacities of 37.87 mg/g and 33.89 mg/g obtained for Ni (II) and Cd (II), respectively. Also, different kinetic models, including the pseudo-first-order equation, pseudo-second-order equation, as well as the intraparticle diffusion equation, were applied to evaluate the kinetic data, which resulted in significant conformity between the kinetic data and the pseudo-second-order kinetic equation.