A comparative removal of two dyes from aqueous solution using modified oak waste residues: Process optimization using response surface methodology

Abstract

In this study, optimization of adsorptive removal of two cationic (methylene blue (MB)) and anionic (acid red 73 (AR 73)) dyes with modified oak waste (MOW) adsorbent was carried out using response surface methodology (RSM). The input variables included initial solution pH (2–10), contact time (20–200min), adsorbent dosage (0.5–2.5g/L) and initial dyes concentrations (10–90mg/L). Furthermore, the surfaces of the adsorbent were modified with different modifiers to find the most efficient adsorbent. The obtained results of comparative studies on dyes adsorption confirm that sodium hydroxide, compared to other modifiers, has the highest ability to activate the surfaces of the oak waste (OW) to remove dyes from the solution. Using NaOH, the removal efficiency of MB and that of AR 73 were obtained to be 96% and 29%, respectively. In addition, results of the optimization study showed that RSM could significantly predict the experimental data of dyes removal with a high correlation coefficient (0.991 for MB and 0.993 for AR 73). The optimum experimental conditions for dyes removal were pH of 6.2, 160min contact time, 2.0g/L adsorbent dosage and 70mg/L initial dye concentrations. Under this condition, the removal efficiency for MB and AR 73 reached 85.36% and 41.27%, respectively. Ultimately, from the findings of this study, it is observed that MOW can be used as an efficient and cost-effective adsorbent for the removal of dyes from the contaminated aqueous solution.