CONCLUSION
These experimental studies have indicated that
chitosan silica composite (CSC) has the potential to
act as an adsorbent for the removal of humic acid from
peat water. The results from this work showed that the
adsorption of humic acid was found to increase with
increase in contact time and temperature while acidic
pH was more favourable for the adsorption of humic
acid from peat water. The optimum dosage of CSC was
10 g. Equilibrium data were fitt ed to non-linear models
of Langmuir, Freundlich and Sips, and the equilibrium
data were best described by the Langmuir isotherm
model, with maximum monolayer adsorption capacity
of 120.2 mg/g at 25 o
C and pH 4.12. Kinetic data were
tested using the pseudo-first-order, pseudo-second order kinetic models and intra-particle equations. The
kinetics of the adsorption process was found to follow the pseudo-second-order kinetic model, with a rate
constant in the range of 0.034 - 0.105 g/mg/min. Intraparticle diffusion model was applied to identify the
adsorption mechanism and this model indicated that
intra-particle diffusion was the main rate determiningstep in humic acid removal process. The value of
adsorption energy, Ea
, gives an idea about the nature
of sorption. From the value of the activation energy of
the process, it was concluded that the adsorption of
humic acid by CSC is physical sorption. The adsorption dependence of humic acid on temperature was
investigated and the thermodynamic parameters were
calculated. Thermodynamic parameters data indicated
that the humic acid sorption process was nonspontaneous and endothermic under the experimental
conditions, with the Gibbs free energy (∆Go
) in the
range of 1.05-3.89 kJ/mol, enthalpy (∆Ho
) and entropy
(∆So
) of 24.69 kJ/mol and 69.62 J/mol, respectively and
the activation energy was 23.23 kJ/mol. The results
revealed that the process of humic acid adsorption is
favoured at high temperatures.