Bentonitc clay adsorption affinity for anionic and cationic dyes

Abstract

The incidence of dye pollution in South Africa is quite alarming, requesting effective and affordable techniques to curb further degradation of the limited water resource. Adsorption is an attractive technique due to a better removal efficiency of contaminants. Bentonite also known as montmorillonite clay, has a very large surface area, suitable for adsorption; however the availability of binding sites on the clay is dependent on the geochemical transformation undergone during the genesis, making the geographical source of the clay an important parameter determining his adsorption potential. This consideration has motivated the need to test the adsorption potential of local bentonite clay for the removal of anionic and cationic dye from solution. The clay was characterized using XRD, XRF and FTIR. The adsorption affinity was tested using isotherm and kinetic models. According to the FTIR spectroscopy profile, dyes attached to the clay through interaction between the cetonyl group of the clay and the amines-primary and -secondary functional groups of methyl orange (MO) and methylene blue (MB) respectively. The adsorption capacity values obtained from the pseudo-second order kinetic model indicate that our bentonite clay has higher affinity for MB (qe = 147.06 mg/g) than MO (qe = 11.82 mg/g). It therefore ensues that our clay is suitable for the removal of MB from polluted water, but will require activation to improve the affinity for MO