Adsorption of methyl red on local kaolin from spiked aqueous solution

Abstract

Presence of colour in natural water is aesthetically undesirable. It retards growth of aquatic organisms. However,
the soil serves as an important filtering medium for scavenging coloured substances and other pollutants from
industrial effluents and runoff waters. The clay component of soil plays a significant role in this case.
Considering the possible harmful effects of methyl red in water, a study was conducted for removal of the
synthetic dye from spiked aqueous solution by adsorption on Kaolin. The kaolin-dye interaction was studied
under laboratory conditions with respect to kaolin obtained from local sources. Kaolin was used in six different
forms. The effect of methyl red concentration, amount of kaolin, pH, temperature and time was investigated. The
results indicate that kaolin can be very effective in removing an acidic dye like methyl red from water. The pure
kaolin showed the highest adsorption capacity. The raw kaolin itself showed considerable adsorption of 43 –
58%. Optimum adsorption occurred between pH 3.0 and 4.0. Thermal treatment of kaolin resulted in reduction
of adsorption capacities while treatment with NaOH enhanced the same. The adsorption data fitted Freundlich
and Langmuir adsorption isotherms. Computation of thermodynamic parameters such as DH0, DS0 and DG0
showed that the adsorption of methyl red on kaolin was a favourable and spontaneous process. The process of
adsorption was found to follow simple first order kinetics.