Abstract
In order to broaden the application of Bentonite clay, an easily obtainable and bio-available low cost adsorbent, it was employed for the decolourization of synthetic wastewater consisting of single and binary basic dyes (Malachite green and Rhodamine b). The adsorbent was used as obtained without any further modification and also characterized for its specific surface area, point of zero charge and its surface functional groups pre and post dyes sorption was determined using Fourier Transform Infrared Spectroscopy (FTIR). Batch adsorption methods were employed in order to study the effects of pH, Ionic strength and contact time in the single solute system. The parameters of sorption of Rhodamine B (RDB) and Malachite green (MG) were obtained and fitted to three isotherm models; Freundlich, Langmuir and Temkin. The Freundlich plot analysis indicated the process occurred via heterogeneous coverage of adsorbent by both dyes. The kinetics of adsorption data were analyzed using the; pseudo-first order, pseudo-second order, Intraparticle diffusion, film diffusion, and Boyd kinetic models. Over the study of these parameters, the film diffusion mechanism was found to predominate in the sorption process of the dyes. Competitive sorption studies were carried out by using both dyes as either the adsorbate of interest or as the interfering specie. The competitive co-coefficient values obtained from interfering MG in RDB removal were significantly lower than those obtained from interfering RDB in MG removal, indicating that the presence of RDB in the aqua matrix had antagonistic effect on MG adsorption by Bentonite.
Highlights
Years of increased industrial activities have resulted in the generation of large amount of wastewater containing a number of coloured toxic pollutants, which are polluting the available fresh water continuously
A large relationship co-exists between the amount of adsorbate adsorbed to the surface of the sorbent and the pH zero point of charge (pHZPC) of the adsorbent, which is that; adsorption of positively charged adsorbates will be favoured at pH values higher than the pHZPC when the surface of the adsorbent is predominantly negatively charged while adsorption of negatively charged sorbent will be favoured at pH values lower than the pHZPC when the surface of the adsorbent is predominantly positively charged [16]
In the determination of the surface charge of Bentonite used in this study, this showed that it possesses a pHZPC of 2.14 which was supported by literature to be between 2.0 and 3.0 [17,18]
Summary
Years of increased industrial activities have resulted in the generation of large amount of wastewater containing a number of coloured toxic pollutants, which are polluting the available fresh water continuously. Dye pollutants are a major source of environmental contamination and colour is the first contaminant that is recognized in wastewater [1] These water-soluble dyes are recalcitrant, carcinogenic and offer considerable resistance to biodegradation due to their complex structures and high thermal/photo-stability, there removal is paramount. Industries such as the textile industries, dye manufacturing industries, paper and pulp mills, tanneries, electroplating factories, distilleries, food companies, and a host of other industries generate and discharge this coloured wastewater [2]. More than 10,000 dyes are commercially available and about 5-10% of these are somehow discharged as wastewaters by these industries directly or indirectly into our water bodies [4]
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