Studies On The Treatment Of Coal And Brewery Wastewater Using Adsorption And Coagulation– Flocculation Techniques

Freundlich Isotherm model is expressed as:
qe = KCe
1/n…….. (3.6)
In linear form. It is written as

In qe = ln k + 1 In Ce …. (3.7)
n
Where
Qe = amount of adsorbate (TSP) adsorbed per unit weight of adsorbent,
mg/g.
Ce =Equilibrium concentration of the adsorbate, mg/l
In k= a measure of adsorbent capacity
1/n = Sorption intensity

K and n are calculated from the intercept and slope of the plot of ln qe versus ln Ce respectively (Nath et al, 2006). The value 1/n indicates how favourable the adsorption will be and how strong the bond is between the adsorbate and adsorbent (Kushwaha et al, 2008).

Lagergren proposed a pseudo –first order kinetic model as
Log (qe-q) = Log qe – Kad t . . . .(3.8)
2.303
where
q = amount of TSP adsorbed
qe = amount of TSP adsorbed at equilibrium ,mg/g
Kad = equilibrium rate constant of pseudo first order adsorption

The plot of log (qe-q) versus t gives a straight line for the first order adsorption kinetics. First order rate constant kad is obtained from the slope of the linear graph (Nath et al, 2006). The correlation coefficient values suggests whether a pseudo first –order kinetics held (kushwaha et al, 2008).

The effect of temperature and thermodynamic parameters of adsorption are determined as:

Experimental data considered for calculation of thermodynamic parameters (ΔGo, ΔSo and ΔHo) are in the linear range of equilibrium adsorption isotherm. Hence, eqn (3.10) can be used with the experimental data to evaluate entropy of adsorption ΔSo and enthalpy of adsorption ΔSo and enthalpy of adsorption ΔHo from a plot of log (qe/ce) versus 1/T. Gibbs free energy is then calculated from eqn(3.9) (Nath et al, 2006; Kushwaha et al, 2008).