Separation of Malachite Green and Methyl Green cationic dyes from aqueous medium by adsorption on Amberlite XAD-2 and XAD-4 resins using sodium dodecylsulfate as carrier

This present work reports a study about the adsorption of some cationic dyes (Malachite Green and Methyl Green) by polymeric resins called Amberlite XAD-2 and XAD-4, in a medium containing sodium dodecylsulfate (SDS). The effect of several parameters (SDS concentration, pH, ionic strength and temperature) on the adsorption of each dye by the resins was investigated. Also, the adsorption was characterized in relation to thermodynamic and kinetic aspects in order to define the nature of the process. For Malachite Green, the SDS concentration did not affect the adsorption efficiency, only changing the adsorption rate at the process occurs, happening faster in the presence of the surfactant. On the other hand, the adsorption efficiency of the Methyl Green was increased with the increase of the surfactant concentration when both Amberlite XAD-2 and XAD-4 resins were tested. For both dyes, the Amberlite XAD-4 resin showed higher efficiency than the Amberlite XAD-2. According to the obtained thermodynamic data, the adsorption of the dyes by the two resins appeared to be a physical process, once adsorption enthalpies values of approximately 20 kJ mol−1 were obtained in all cases. The kinetic study also showed that the whole adsorption process was governed by a pseudo first-order kinetics and that the adsorption rate was regulated by an intraparticle diffusion mechanism.

► The use of the Amberlite XAD resins for the removal of Malachite Green and Methyl Green is reported.
► The fundamental role played by the sodium dodecylsulfate in the adsorption process is shown.
► The adsorption process followed a pseudo first-order kinetic.
► Amberlite XAD resins presented high efficiency for the cationic dyes removal from aqueous medium.