Abstract:
Methylene blue is a cationic dye, identified as a one of the pollutants in many industrial waste
water especially in textile industry. It also can be used to develop a model to study adsorption
behavior of raw Laterite. Therefore, the study was mainly focused on removal of methylene blue
in an aqueous solution using raw laterite as the adsorbent material. Natural raw Laterite was
collected from South West region of Sri Lanka. Initially, physical and chemical properties were
analyzed by using standard methods. In order to prepare powdered material, soil samples were
crushed and sieved through 53 μm standard sieve. After that, 30 ppm methylene blue aqueous
solution was prepared. Effect of adsorbent dose, operating pH, ionic strength and contact time on
the removal of methylene blue process were examined by contacting raw laterite with methylene
blue aqueous solution. All the experiments were carried out in batch experiment system.
Equilibrium concentration of methylene blue aqueous solution was measured using UV-Visible
spectrometer at 663 nm. Before and after the experiment, the laterite soil were characterized with
X-Ray powder Diffraction (XRD), X-Ray Fluoresce (XRF), Fourier Transform Infrared
Spectroscopy (FTIR), Scanned Electron Microscopy (SEM) and Energy-dispersive X-ray
spectroscopy (EDS). The adsorption behavior of laterite was evaluated using Langmuir,
Freundlich and Temkin isotherm models. For that, methylene blue solutions which contain
10,20,30,40 and 50 ppm concentration were used. In order to investigate the mechanism of
methylene blue adsorption on to the laterite soil pseudo first order and pseudo second order
kinetic models were used. The recorded optimum adsorption dosage was 2.0 g and contact time
was 60 minute while the maximum removal efficiency was recorded in higher pH than 10.When
increasing the ionic strength of the methylene blue aqueous solution, removal efficiencies were
significantly decreased. The experimental adsorption isotherm complies with Freundlich
isotherm model (R2=0.99) and the maximum amount of adsorption (qmax) was recorded as 3.45
mg/g. The kinetic studies revealed that the adsorption of methylene blue is rapid and complies
with the pseudo second-order kinetic model (R2=0.99). Based on the obtained results from the
study, it can be concluded that raw laterite is effective in removing methylene blue from aqueous
solutions. Finally, raw laterite can be recommended as a cost effective alternative for
commercially available expensive adsorbents to remove methylene blue.
