Process optimization of methylene blue adsorption onto eggshell-treated palm oil fuel ash

Palm oil fuel ash (POFA) and eggshell (EG) were explored towards efficient methylene blue (MB) removal. Calcined EG, with a high content of CaO was used as a low-cost activation replacement for the alkali treatment of POFA. The adsorption performance of EG-POFA was studied by comparing its performance with untreated POFA, calcined EG and commercially treated Ca-POFA, and the competency was following the order of EG < POFA < EG-POFA approximate to Ca-POFA, indicating that EG effectively enhanced the efficiency of POFA. The response surface methodology (RSM) was executed to optimize the operating conditions of MB adsorption onto EG-POFA by investigating the effect of EG-POFA dosage (X-1), initial pH (X-2) and initial MB concentration (X-3) towards MB removal (Y). X-1 ( )= 1.18 g/L, X-2 = 6, and X-3 = 182 mg/L, with Y = 80.36% were found to be optimal conditions. The experimental data disclosed that the MB adsorption onto EG-POFA was in accordance with the Langmuir isotherm model (q(m) = 714.29 mg/g) and followed pseudo-second-order kinetic model. The thermodynamic study discovered the endothermic and spontaneous natures of MB adsorption onto EG-POFA. This study discovered the feasibility of EG as an eco-friendly activation alternative for the alkali treatment towards remarkable MB adsorption. (C) 2018 Elsevier B.V. All rights reserved.