DEVELOPMENT OF ADSORBENTS AND PHOTOCATALYSTS USING NIGERIAN PINDIGA BENTONITIC CLAY

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Department of Engineering

ABSTRACT
The potential of Pindiga bentonitic clay for phenol adsorption from aqueous solution and photocatalytic degradation was studied. Pindiga bentonic clay was treated with oxalic acid and calcined at a temperature of 1000oC and was successfully used as an adsorbent and for the degradation of phenol under visible light illumination. The processes were investigated by X-Ray Fluorescence (XRF), X-Ray diffraction (XRD), and surface area analysis. The clay treated with acid for 60 min (PB-60) and 5 min (PB-5) gave higher surface areas of 363.61 m2/g and 265.99 m2/g respectively compared with the raw (PB) and the raw calcined (PBC) with surface areas of 151.69 m2/g and 47.13 m2/g respectively. The adsorptions of phenol by the acid treated clays were studied using pseudo-first order, pseudo-second order kinetic models and intra-particle diffusion model. The adsorption data does not fit well with pseudo-second order kinetic model. The Freundlich and Langmuir adsorption models were used for the mathematical description of adsorption equilibrium and it was found that the experimental data fitted very well to the Freundlich model. The clay treated with acid for 60 minutes (PB-60) showed a better monolayer coverage capacity and greater affinity for phenol compared with the PB, PBC and PB-5. The increase in pH values from 5 – 11 was observed to hinder adsorption processes. Better adsorption was observed at lower pH value. Increase in catalyst dosage increases the adsorption rate. Langmuir-Hinshelwood kinetic model was employed for photocatalysis processes and the values of krand KLH were calculated as 6.8483 mgl-1min-1 and 0.0034lmg-1 for PB-60. PB-60 degraded phenol better than PB, PBC and PB-5 under visible light illumination. Catalyst dosages of 1.5, 2.0, 2.5 and 3.0g were used and the optimum catalyst dosage was found to be 2.5g/l for the photocatalytic degradation.