Adsorption of safranin-O dye on CO2 neutralized activated red mud waste: process modelling, analysis and optimization using statistical design

Abstract

Response surface methodology (RSM) was applied to examine the removal of hazardous safranin-O dye from aqueous solution by CO₂ neutralized activated red mud. A 2⁴ full factorial central composite design (CCD) was used to evaluate the effects of adsorption parameters such as, adsorbent dose (X₁), temperature (X₂), solution pH (X₃) and initial safranin-O concentration (X₄) on percentage removal of safranin-O dye from aqueous solution. Analysis of variance (ANOVA) exhibit a high R² value of 0.9655, indicating second-order regression model excellently evaluate the experimental data. The interaction effects of the main factor and optimum condition of the process were determined from contour and response surface plots, respectively. In addition, the isotherm study revealed that, the adsorption data were best fitted to Langmuir model with high correlation value of 0.994 and adsorption capacity of 9.7680 mg g⁻¹. The optimum operating condition for adsorption of safranin-O dye were obtained as adsorbent dose (0.62 g), temperature (29.06 °C), pH (8.3) and initial safranin-O concentration (37.3 mg L⁻¹). At the optimum condition, the adsorption of safranin-O from aqueous solution was found to be 94.5 ± 0.1%.