Adsorption mechanism and mass transfer modeling of cesium and europium ions adsorption onto hematite-loaded polyacrylamide-gel composite: Pore Volume and Surface Diffusion Model Approach

The overall adsorption rate of cesium (Cs+) and europium (Eu3+) ions onto hematite-loaded polyacrylamide-gel composite (HPAC) in single and binary pollutant systems was explained with diffusional model that takes into consideration both external mass transfer and intra-particle diffusion. The influence of changing system temperature on the overall adsorption rate of Cs+ and Eu3+ onto HPAC was studied. The fitting process of the experimental data with the three studied isotherm models (Langmuir, Freundlich and Prausnitz–Radke (P-R)) showed that Prausnitz–Radke model has the highest correlation coefficients with the smallest average relative error percentage. The maximum P-R adsorption capacity of HPAC decreased from 2.06 and 3.35 L/g in single pollutant solution to 1.02 and 1.51 L/g in binary pollutant solution at 298 K for Cs+ and Eu3+,respectively. The values of surface diffusion coefficient (DS) ranged within 10−8 for Cs+ and 10−8-10−9 cm2/s for Eu3+ in both studied single and binary pollutant systems. The external mass transfer coefficient (KF) was in the range of 10−4 for Cs+ and 10−3 cm/s for Eu3+ in both studied systems. Lastly, the Biot number (Bi) exposed that the diffusion inside the particle controlled the studied cations's adsorption onto HPAC material.