According to Eq. (7), ΔH° and ΔS° parameters can be calculated from the slope and intercept of the plot of ln KL versus 1/T, respectively [6], [22] and [38]. The calculated values of Gibbs free energy change (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) are given in Table 6. The negative ΔG° values indicate that the process is thermodynamically feasible, spontaneous and corresponding to a chemical process of Ni(II) adsorption. Moreover, the decrease in ΔG° values with increase in temperature shows a decrease in feasibility of sorption at higher temperatures. The positive value of ΔH° indicates that the nature of adsorption process is endothermic in all cases. This behavior indicates that higher temperatures are more preferred for higher sorption. This is also supported by the increase in value of uptake capacity of the sorbent with the increase in temperature ( Fig. 4). The positive value of ΔS° shows the increased randomness at the solid–solution interface during the sorption process.