Abstract:

Modified multi-walled carbon nanotubes(MWCNTs) were chosen as adsorbents for the adsorption of rare earths. Nitric acid (HNO₃), sodium hypochlorite(NaClO), hydrogen peroxide(H₂O₂), and potassium permanganate(KMnO₄) were used for the modification of MWCNTs. The concentrations of rare earths were determined with UV-Vis spectrometry. The adsorption capacities of rare earths on MWCNTs treated with different modification methods were compared with each other. The experimental results indicate that MWCNTs modified with NaClO has the highest adsorption capacity of rare earths. As representitives, the adsorptions of samarium(Sm), gadolinium(Gd), and ytterbium(Yb) on MWCNTs modified with NaClO were investigated in detail. Effects of various parameters such as the rare earth concentration, pH value, ion strength, amount of MWCNTs, and experimental temperature were investigated. The adsorption of Sm, Gd and Yb onto MWCNTs modified with NaClO increased with pH value in a range of 2~7. However, the adsorption capacity of the three rare earths decreased with increasing solution ion strength and MWCNTs mass. The adsorption reactions of all the three rare earths on MWCNTs modified with NaClO were exothermic processes. The thermodynamic functions, ΔH, were calculated to be -6.44 kJ/mol, -5.63 kJ/mol, -8.31 kJ/mol for Sm, Gd, and Yb, respectively. Furthermore, the adsorption data were fitted with Langmuir and Freundlich isotherm models, indicating that both the models can fit the adsorption of Sm, Gd, and Yb well.

Key words: Multi-walled carbon nanotubes, modification, rare earths, adsorption