3.6.1. Langmuir isotherm
The Langmuir equation [23] is given as:
Ce
qe
= 1
qmkL
+ Ce
qm
(5)where Ce(mg L−1) denotes the equilibrium concentration of RhBin solution, qm(mg g−1) is the maximum adsorption capacity, kL(L mg−1) represents the Langmuir constant related to energy ofadsorption. kLand qmare calculated from slop and intercept of theplot of Ce/qeversus Ce. The feasibility of adsorption process can bedetermined by separation factor RL, which is defined by:
RL = 1
1
+
kLC0
(6)where C0(mg L−1) is the initial RhB concentration, kLdenotes theLangmuir constant mentioned above.3.6.2. Freundlich isotherm The Freundlich isotherm [5] is described as:
ln qe =
ln kf + 1
n
ln Ce