The adsorption behavior between the
adsorbate and adsorbent is described by Langmuir, Freundlich and D-R isotherm models.
where q is the amount of the
adsorbate adsorbed (mg/g), t is the agitation time (min), and [k.
Thermodynamic parameters related to the energy changes associated with the adsorption process between the
adsorbate and adsorbent including [DELTA]H (enthalpy variation), [DELTA]S (entropy variation), and [DELTA]G (variation of Gibbs' energy) were also determined.
At low
adsorbate concentration, it turns into Freundlich isotherm, while at high
adsorbate concentration, it reduces a monolayer adsorption capacity characteristic of Langmuir isotherm [15].
This could be due to very slow
adsorbate diffusion and more time required reaching inner pores from the surface (Mohan et al.
Initial concentration provides an important driving force to overcome all the mass transfer resistance between the
adsorbate and the adsorbent surface.
Equilibrium relationships between adsorbent and
adsorbate are described by adsorption isotherms.
Adsorption data for a wide range of
adsorbate concentrations are most conveniently described by adsorption isotherms, such as the Langmuir or Freundlich, which relate amounts adsorbed to the equilibrium
adsorbate concentration in the bulk fluid phase.
Second step involves the boundary layer diffusion of
adsorbate molecules on the biosorbent surface which is called film diffusion.
In an ideal breakthrough curve it is assumed that removal of
adsorbate is complete in the early stages of operation.
After a certain period of time, the rate of adsorption decreases due to accumulation of
adsorbate in the vacant sites.
3+] was used as a model
adsorbate for heavy metals removal process.
