The

equilibrium data for the adsorption at constant temperature are commonly known

as adsorption isotherms. In the present work results obtained after

experimental study were analyzed using Langmuir (1918) and Freundlich (1906) isotherms.

Langmuir adsoption isotherm model is

valid for monolayer adsorption. The adsorbent surface consists of finite number

of identical active sites and all the adsorption sites have equal affinity for

the adsorbate molecules. A linearized form of Langmuir model is represented by

the equation (5):

Ce/qe = 1/(KLqm) + Ce/qm (5)

Where, Ce is the metal ion

concentration in (mg/L) at equilibrium, qe is the metal adsorption

capacity of the adsorbent in (mg/g) at equilibrium; qm and KL

are the Langmuir constants that are obtained by plotting a graph between Ce/qe and Ce as shown in

fig. 6 (a). The intercept and the slope will give the values of qm and

KL.

The Freundlich isotherm is used to

describe the adsorption equilibrium between adsorbent and adsorbate in aqueous

systems. It is applicable on heterogeneous surfaces and gives the idea of

multilayer adsorption. Linearized form of Freundlich adsorption isotherm is

represented by the following equation (6).

ln(qe) = ln(KF) + (1/n) lnCe (6)

Where, qe is the monolayer

adsorption capacity of the adsorbent at equilibrium (mg/g), KF is the Freundlich constant and 1/n is the characteristic constant of the

system that indicates adsorption capacity. From the plot lnqe vs lnCe

as shown in fig. 6 (b) ln KF and 1/n can be calculated as intercept

and slope, respectively.

Langmuir

and Freundlich adsorption isotherms for Cu (II) from aqueous solution are

presented in above fig. 10. It indicates that the experimental data fitted well

to all the isotherm models. By comparing the correlation coefficients (Table 3),

it was observed that Langmuir isotherm is more favorable for adsorption of Cu

(II) by activated Parthenium which is

based on monolayer sorption on to the surface restraining finite number of

identical sorption sites.