Adsorption of Crystal Violet dye from aqueous solutions onto low-cost untreated and NaOH treated almond shell

In the present study, comparative batch adsorption of basic dye namely Crystal Violet (CV) using the almond shell as an adsorbent in untreated form and activated with sodium hydroxide was carried out in search of optimum adsorption conditions. The operation parameters investigated was contact time (10 to 80 min), initial dye concentrations (40-240 mg/L), temperature, (20-50 oC) and pH, (2-12). From the experimental results, it was found that the adsorption of crystal violet dye from aqueous solution onto both types of adsorbent (treated and untreated) was highly dependent on solutions pH, and its maximum adsorption was observed in basic medium. The adsorption equilibrium of CV was attained very rapidly after 40 min of contact time. Pseudo-first and second orders were used to examine the kinetic adsorption and found that the kinetic adsorption data were best fitted to pseudo-second order. Langmuir and Freundlich isotherm models were applied to equilibrium adsorption data, which were best fitted to Langmuir isotherm model. The thermodynamic analysis was carried out for dye-adsorbent systems. It was found that the adsorption nature of CV onto both adsorbents were endothermic. The performance of both adsorbents to adsorb CV was also compared. It was found that the adsorption capacity of almond shell activated by base was higher than untreated almond shell. Surface morphology and elemental composition of both adsorbents were examined using Scanning Electron Microscopy (SEM), and energy dispersive X –ray spectroscopy.