Adsorption Performance of Acidic Modified Fly Ash: Box–Behnken Design

Abstract

Fly ash (FA) and modified fly ash (mFA) were used as adsorbents to remove methylene blue (MB) dye from aqueous solutions. The adsorbents were characterized using crystal structures with XRD, surface functional groups with FTIR, and surface morphologies with SEM. Response surface methodology (RSM) with Box-Behnken design (BBD) was used to optimize adsorption parameters such as MB dye concentration (A: 10-20 mg/L), solution pH (B: 3-11), and contact time (C: 30-180 min). ANOVA analysis shows the significant interactions between initial concentration, solution pH value, and solution pH value, contact time was found to be significant in the removal of MB (p-value=< 0.0001, 0.0040), whereas between the effect of initial concentration and contact time was not significant (p-value = 0.0881). The adsorption kinetics followed the pseudo-second-order (PSO) kinetic model and the adsorption isotherm followed the Langmuir model. At 28°C, the adsorption capacity of fly ash-HNO3 for MB was found to be 7.67 mg/g.