Adsorption of crystal violet on sludge produced from refinery wastewater treatment: characterization of sludge equilibrium and kinetic studies

Abstract

Removal of dye pollutant from wastewater is very important. In the present study, the removal of Crystal Violet (CV) dye from aqueous solution by adsorption on sludge generated from waste treatment is reported. The characteristics of sludge were studied via thermal analyses (DTA, TGA), spectroscopic analyses (X-ray fluorescence-XRF, X-ray diffraction-XRD) and infrared spectroscopy (IR). The empirical formula for the sludge was determined from XRF data. The effect of pH on adsorption was studied, with the highest adsorption being found at pH 5. The adsorption equilibrium data were fitted to Langmuir, Freundlich, Dubinin–Radushevich and Temkin for calculation of adsorption isotherm parameters. The kinetic studies were conducted by fitting the data obtained to pseudo-first order, pseudo-second order and Elovich models. The adsorption of CV was found to obey a pseudo-second order model and the rate-limiting step was intraparticle diffusion. The effect of temperature on adsorption was also investigated. Adsorption was found to be an exothermic process. Thermodynamic parameters were also determined.