Adsorptive removal of hazardous azorhodanine dye from an aqueous solution using rice straw fly ash

The objective of this study was to assess the suitability and efficiency of rice straw fly ash (RSFA) for the removal of hazardous azorhodanine dye (AR) from aqueous solution. The effect of different variables in the batch method as a function of solution pH, contact time, concentration of adsorbate, adsorbent dosage and temperature were investigated and optimal experimental conditions were ascertain. More than 85 % removal efficiency was obtained within 75 min. at adsorbent dose of 0.07 g for initial dye concentration of 20-100 mg/L at pH 3.The experimental equilibrium data were tested by the isotherm models namely, Langmuir and Freundlich adsorption and the isotherm constants were determined. The kinetic data obtained with different initial concentration and temperature wasanalyzed using a pseudo-first-order and pseudo-second-order equations. The activation energy of adsorption was also evaluated and found to be +11.09 kJ.mol-1indicating that the adsorption is physisorption.Various thermodynamic parameters, such as Gibbs free energy, entropy and enthalpy of the on going adsorption process have been calculated and found to be spontaneous and exothermic, respectively. The results indicate that (RSFA) could be employed as low-cost material for the removal of acid dyes from aqueous solution.