Study of 63Ni adsorption on NKF-6 zeolite

The adsorption of 63Ni from aqueous solutions using NKF-6 zeolite was investigated by a batch technique under ambient conditions. The adsorption was investigated as a function of contact time, pH, ionic strength, foreign ions, humic substances (FA/HA) and temperature. The kinetic adsorption was well described by the pseudo-second-order rate equation. The adsorption of 63Ni on NKF-6 zeolite was strongly dependent on pH and ionic strength, and the adsorption of 63Ni increased with increasing NKF-6 zeolite content. At low pH values, the presence of FA enhanced the adsorption of 63Ni on NKF-6 zeolite, but the presence of HA had no drastic effect. At high pH values, the presence of FA or HA decreased the adsorption of 63Ni on NKF-6 zeolite. The adsorption isotherms were well represented by the Langmuir model. The thermodynamic parameters (i.e., ΔH0, ΔS0and ΔG0) for the adsorption of 63Ni were determined from the temperature dependent isotherms at 293.15, 313.15 and 333.15 °K, respectively, and the results indicate that the adsorption reaction was favored at high temperature. The results suggest that the adsorption process of 63Ni on NKF-6 zeolite is spontaneous and endothermic.

Research highlights
► As an economical and efficient method, adsorption technique has been widely applied in the disposal of wastewaters. The study of 63Ni on NKF-6 zeolite, especially the thermodynamic data of 63Ni adsorption on NKF-6 zeolite and the effect of humic substances on 63Ni uptake to humic–zeolite hybrids, is still scarce. In this paper, the sorption of 63Ni on NKF-6 zeolite is studied as a function of various environmental conditions such as contact time, pH, ionic strength, foreign ions, humic substances and temperature. Based on the obtained experimental results, the adsorption mechanism of 63Ni on NKF-6 zeolite is stated in detail. This study will have an important reference value in evaluating the physiochemical behavior of radionuclide 63Ni.