Adsorption and Desorption Studies of Cadmium (II) ions from aqueous solutions onto Tur pod (Cajanus cajan)

The effective removal of Cd (II) ions from aqueous solutions using Tur Pod (Cajanus cajan), cost effective biosorbent was carried out in batch system. The effects of operational factors including solution pH, biosorbent dose, initial cadmium (II) ions concentration, contact time and temperature were studied. The optimum solution pH for cadmium (II) ions adsorption by biosorbent was 7.0 with the optimal removal 84.62 %. The adsorbent dose 10 mg/ml was enough for optimal removal of 81.25 %. The adsorption process was relatively fast and equilibrium was achieved after 90 min of contact. The Cd (II) ion easily eluted from biosorbent loaded with cadmium with acids. The desorption efficiency was found to be 97 % (0.1 M nitric acid), 92 % (0.1 M hydrochloric acid) and 89 % (0.1 M sulphuric acid). The experimental equilibrium biosorption data were analysed by four widely used two-parameters Langmuir, Freundlich, Dubinin-Kaganer-Redushkevich (DKR) and Temkin isotherm equations. Freundlich isotherm model provided a better fit with the experimental data than Dubinin-Kaganer-Redushkevich (DKR), Langmuir and Temkin adsorption isotherm models by high correlation coefficient value (R2 = 0.8903). The maximum adsorption capacity determined from Langmuir isotherm was found to be 9.2165 mg per g of biosorbent. Simple kinetic models such as pseudo-first-order, pseudo-second-order, Elovich equation and Weber and Morris intra-particulate mixing equation were employed to determine the adsorption mechanism. Results clearly indicates that the pseudo-second-order kinetic model (R2 = 1.000) was found to be correlate the experimental data strongest than other three kinetic models and this suggests that chemical adsorption process was more dominant. Thermodynamic study revealed that the biosorption process was spontaneous, endothermic and increasing randomness of the solid solution interfaces. Tur Pod (Cajanus cajan) was successfully used for the adsorption and desorption studies of Cd (II) ions from aqueous solutions and can be applied in waste water technology for remediation of heavy metal contamination.