Removal of thorium by modified multi-walled carbon nanotubes: Optimization, thermodynamic, kinetic, and molecular dynamic viewpoint

Abstract

One of the crucial aspect of nuclear waste management is the radioactive waste stream released from the nuclear fuel cycle. In radioactive waste treatment, adsorption is one of the most powerful methods for the pre-concentration process. In this study, functionalization of multiwalled carbon nanotubes (MWCNTs) using potassium permanganate (KMnO4) and citric acid (C6H8O7) as oxidizing agents was investigated for adsorption of thorium from aqueous solutions named PPM-MWCNTs and CA-MWCNTs, respectively. The central composite design technique was used to examine the initial thorium concentration, pH, and temperature as the adsorption parameters. The thermodynamic parameters (standard enthalpy (ΔH°), entropy (ΔS°), and free energy (ΔG°)) were determined and the results indicated that both adsorption systems were endothermic processes. The adsorption isotherms of modified MWCNTs were investigated using the Langmuir, Freundlich and Dubinin-Radushkevich isotherm models for characterizing the process. According to the high correlation coefficients, the Langmuir model described well the adsorption of thorium on PPM-MWCNTs and CA-MWCNTs and adsorption capacities were found to be 105.28 and 50.67 mg g−1, respectively. In addition, molecular dynamics simulations were successfully performed on the Th bonded modified MWCTNs.