Kinetic, Isotherm and Mechanism Investigations of the Removal of Basic Violet 3 from Water by Raw Spent Coffee Grounds

This work examines the possibility of removing the crystal violet (a cationic dye), used in the dyeing of cotton, wood, and silk, onto untreated coffee waste. The influence of various experimental parameters on the adsorption of crystal violet has been analysed: pH, adsorbent dose and initial dye concentration. Optimum adsorption of crystal violet took place at pH 6 and at lower temperatures. Further, the adsorbent was characterised by Fourier Transform Infrared Spectroscopy (FTIR). FTIR analysis revealed the presence of several functional groups that are responsible for the adsorption process. Adsorption equilibrium follows Langmuir’s model with maximum retention of 63.3 mg/g. The kinetics of the crystal violet adsorption were studied using the pseudo-first order and pseudo-second order equations. Adsorption of the dye can be described by pseudo-second order kinetics, reaching the equilibrium at 40 min. The value of the activation energy shows that adsorption is physisorption. Weber-Morris model indicates that this adsorption occurs in two steps. Thermodynamic parameters suggest that the adsorption is spontaneous and exothermic.