Low-cost magnetic char derived from oily sludge for Methylene Blue dye removal: optimization, isotherm, and kinetic approach

The excessive increase of dye-contaminated wastewater has become an environmental challenge worldwide, menacing human beings, the environment, and the ecosystem. In light of this subject, the current study for the first time evaluated the potential of oily sludge with its intrinsic magnetic characteristics for Methylene Blue adsorption. A single-step pyrolysis approach was employed to convert oily sludge to magnetic char (Fe3O4/Char). The effects of operational parameters such as pH, contact time, Methylene Blue concentration, and adsorbent dose were examined. The maximum adsorption was 84% with a capacity of 88.71 mg/g at a pH of 3, 100 mg/L Methylene Blue concentration, 100 mg Fe3O4/Char concentration, and 120 min contact time. The Redlich-Peterson isotherm model (R2= 0.9854) best described the adsorption experiment, which revealed that the adsorption process followed a mixed adsorption mechanism, namely physical and chemical adsorption. Moreover, the Elovich kinetic model was more suitable to represent the Methylene Blue adsorption onto Fe3O4/Char, confirming a chemisorption process. The significant function of the sludge-based char with high iron content in the adsorption of Methylene Blue provides insight into the inherent potential of oily sludge as a promising approach for removing hazardous dyes.