Crystal violet adsorption on industrial waste (hog fuel ash): equilibrium kinetics with process optimization by response surface modeling

The adsorptive removal of crystal violet from aqueous solution utilizing hog fuel ash, an industrial solid waste, available abundantly is reported in this article. The adsorbent is characterized by various physicochemical methods. Batch experiments are performed as functions of different process variables. The maximum removal (99.99%) was observed at equilibrium time (90 min). Results follow Freundlich isotherm (among five isotherms) and pseudo-second-order kinetics (among four kinetic models). The observed adsorption capacity of 17.002 mg/g is higher than many other reported waste materials. A three-factor full factorial central composite design scheme is adopted for optimizing different process variables and their interactions. The maximum removal predicted by response surface modeling is 99.99%, while corresponding experimental value is 99.13 ± 0.8895% (mean ± standard deviation of five replicates). The removal improves in the presence of NaCl (by 5%) and at higher temperature. Results on the effect of temperature favor spontaneity of adsorption and physisorption that follows from isotherm studies. The temperature effect is investigated exploiting the seasonal variation that does not seem to have been reported before and is the novelty of the present study. The advantages of the present investigation are the use of the adsorbent without pre-treatment, final pH falling well within the safe discharge limit and increased removal in the presence of NaCl. This study could be extended for gainful utilization of the industrial solid waste for similar application.