Essay --

Batch biosorption isotherm parameters were determined using the Langmuir isotherm, Freundlich isotherm, Dubinin – Radushkevich isotherm and generalized isotherm models. Non-linear regression process gives better results for the determination of isotherms parameters [21]. Hence the isotherm parameters were determined using MATLAB tool ‘nlinfit’ for nonlinear regression. The Langmuir isotherm model is very often used to compute and compare the efficiency of different biosorbents. This model was originally developed for description of adsorption of gas on the activated carbon [26]. The empirical relationship is based on the assumptions that the biosorption is a monolayer, and biosorbent have the finite number of homogeneous binding sites. The Langmuir isotherm relation is basically hyperbolic and given in Eq. (2) [23]. (2) where qe is equilibrium biosorption uptake capacity, Cf is equilibrium concentration (mg l-1) of the residual sorbate, qmax is maximum sorbate uptake (mg g-1) under the given conditions and bL is Langmuir constant (l mg-1). Langmuir constant represents the energy and affinity of the biding sites. The Langmuir isotherm model can be expressed in terms of dimensionless equilibrium parameter ‘RL’ which is also known as separation factor as given in Eq. (3). Separation factor value helps to determine the nature of the biosorption process to be either unfavorable (RL>1), linear (RL=1), favorable (0 (3) The values of Langmuir constant and maximum biosorption capacity are summarized in Table 1. ICTB showed better performance as compared to other two biosorbents i.e. ICUB and ICLB. The maximum biosorption capacity of ICTB, ICUB and ICLB was found to be 197.68, 178.06 and ... ... isotherm is a combination of Langmuir and Freundlich isotherms models and is given below. (7) where qm is maximum biosorption capacity (mg g-1), nG is the cooperative binding constant and KG is the saturation constant (mg l-1). The values of Generalized isotherm constants, i.e. KG and nG along with maximum biosorption capacity were determined. The values of constants are summarized in Table 5. Generalized isotherm model gives a better fit to the equilibrium experimental data for biosorption of nickel ions. The values of MSE were found to be smaller and ranged between 0.88 to 10.27. Table 5: Generalized isotherm parameters for biosorption of nickel ions After comparing all the isotherm models it is revealed that Langmuir isotherm model and Generalized isotherm model represent the equilibrium biosorption data slightly better as compared with other isotherms.