Removal of textile dyes from aqueous solutions using clay minerals and agricultural waste (carica papaya seeds)

Abstract

In most developing countries, many textile dyes known to be toxic for the environment, are released directly into rivers and other environmental compartments. The effluent streams, containing dyes and other toxic materials, are generally treated with activated carbon to remove these toxic materials from wastewater streams originating from different industries. However, the cost of activated carbon is very high and most small to medium size textile dye houses in developing countries cannot afford to use this adsorbent material for the treatment of effluent streams. Hence, to reduce the impact of dispersed textile dyes into the environment, easily accessible and affordable wastewater treatment materials need to be used. In this research work, the adsorption of Methylene blue and Reactive blue 4 in aqueous solution onto uncalcined and calcined adsorbents prepared using kaolin clay (KC), bentonite clay (BC) and carica papaya seeds (CPS) were studied. These adsorbents were prepared using different proportions of clay and CPS mixtures. Five experimental parameters studied to optimise these adsorbents, viz:, calcination temperature (100-600OC), contact time (2-30 mins), solution pH (2-10), adsorbent dosage (0.4-1.8 g) and initial concentration (150-300 mg/L) of dye. Experimental data were analysed using Langmuir and Freundlich isotherm models to evaluate the maximum adsorption capacities. The adsorbents were characterised using scanning electron microscopy (SEM), Fourier-transform infrared (FTIR) spectroscopy and energy-dispersive x-ray (EDX) spectroscopic techniques. Experimental data obtained indicated that uncalcined kaolin (T0), 100% bentonite (T500), CPS/BC for 25/75 and 75/25 proportion (T300) are suitable adsorbents for the adsorption of Methylene Blue in aqueous solution. For Reactive Blue 4, results showed that uncalcined kaolin (T0), CPS/KC at 25/75 (T300) and CPS/KC at 25/75 (T400) are suitable adsorbents. Adsorption kinetics were compared to Lagergren pseudo-first-order and pseudo-second-order curves and results found to agree better with pseudo-second-order. This study showed that adsorbents prepared using clay minerals (kaolin and bentonite) and CPS could be used as alternative adsorbents to remove Methylene blue and Reactive blue 4 present in aqueous solutions.