Kinetic and Thermodynamic study of removal of Ni (II) ions from aqueous solutions using low cost adsorbents

Adsorption studies of Ni (II) ions on different natural materials were carried out by batch experiments. The parameter studied includes initial metal ion concentration, adsorbent dose, pH, contact time, and temperature. The linear regression coefficient R² was used to elucidate the best fitting isotherm model All isotherm models were found to be best fitting models. The monolayer (maximum) adsorption capacities (q_m) were found to be between 4.975 to 10.101 mg g⁻¹ for natural adsorbents under study. Lagergen pseudo -second order model best fits the kinetics of adsorption. R² for all absorbents ≍ 1 and q_e(the) values are in good agreement with q_e(exp) showed that adsorption of Ni (II) ions on these natural materials followed second order kinetics and chemisorption playing role in rate determining step. Intra particle diffusion plot showed boundary layer effect and larger intercepts indicates greater contribution of surface sorption in rate determining step. pH was found to be an important factor in controlling the adsorption of Ni (II) ions. Adsorption of Ni (II) ions on adsorbents was found to increase on increasing pH and increasing temperature. Thermodynamic analysis showed that adsorption was favourable and spontaneous, endothermic physical adsorption and increased disorder and randomness at the solid- solution interface of Ni (II) ions with biosorbents. Teak tree (Tectona grandis) bark powder was found have excellent adsorption capacity towards Ni (II) ions than other natural materials under study.