Abstract:
The ability of composite prepared from bentonite and ackee apple seed (CBAAS) to
remove Congo Red (CR) and Malachite green (MG) dyes from aqueous solution was investigated.
The CBAAS was characterised using Fourier Transform Infrared spectroscopy, pH pzc , Scanning
Electron Microscopy, Energy Dispersive X-ray and Nitrogen adsorption-desorption techniques
respectively. The effects of operational parameters such as contact time, initial dye concentration,
temperature, and initial pH of dye solutions were studied using batch adsorption process. The pH
has a profound influence on the adsorption process. Maximum dye adsorption was observed at pH
2.0 for the two dyes. The reaction was fast, reaching equilibrium in 90 min. Adsorption data were
best described by Langmuir isotherm and the pseudo-second-order kinetic model. The maximum
monolayer coverage are 1428.57 and 370.370 mg g -1 for CR and MG, respectively. Both boundary
layer and intraparticle diffusion mechanisms were found to govern the adsorption process.
Thermodynamic parameters such as standard free energy change (∆G°), standard enthalpy change
(∆H°), and standard entropy change (∆S°) were calculated. Values of ∆G° indicate spontaneous
nature of the adsorption for both dyes. The value of ∆H° (-10.56 KJ mol -1 ) for Congo red
adsorption using CBAAS implies that adsorption is exothermic while the value of ∆H° (14.04 KJ
mol -1 ) for malachite green signifies endothermic process. Regeneration and reusability studies
were carried out using different eluents. The CBAAS, when treated with water gave the best value
for CR and for MG, 0.05 mol
-1
NaCl gave the best regeneration value. Simulation studies show
that CBAAS could be utilised as adsorbent for excellent treatment of industrial textile effluents.
Conclusively, the composite prepared from bentonite and ackee apple seed could serve as
alternative adsorbent for the removal of CR and MG dyes from aqueous solutions.
