Malachite green and methylene blue dye removal using modified bagasse fly ash: Adsorption optimization studies
Azeb Gebre Meskel, Muhajir Mussa Kwikima, Beteley Tekola Meshesha, Nigus Gabbiye Habtu, S.V. Chinna Swami Naik, Bhanu Prakash Vellanki
Abstract
Utilizing Bagasse Fly Ash (BFA) as an adsorbent, a byproduct from the sugar industry, proved effective in removing a mixture of Malachite Green and Methylene Blue dyes from aqueous solutions. To enhance its efficacy, the fly ash underwent chemical modification and underwent detailed characterization using FTIR, XRD, SEM, and TGA analyses. Subsequently, adsorption studies were conducted to optimize critical parameters—initial dye concentration, contact time, and pH levels—employing a Mixed-Level Factorial design to pinpoint the most favorable conditions for efficient dye removal. The modified Bagasse Fly Ash (BFA) resulted in a maximum adsorption capacity of 18.75 mg/g (71.5%) for Malachite Green and 15.5 mg/g (67.2%) for Methylene Blue at initial dye concentration of 100 mg/L, pH of 9.6, and time of 51.5 min. Analysis of the sorption data involved rigorous application of both Langmuir and Freundlich isotherm models, revealing a strong fit of the linear representation to the data for both dyes. Specifically, R2 values of 0.97 and 0.93 were observed for Malachite Green, while notably higher values of 0.99 and 0.96 were obtained for Methylene Blue, affirming an excellent model-data agreement. Additionally, a kinetic study revealed that the dye adsorption process (MB and MG) followed the pseudo-second-order kinetic model (R2 > 0.99), indicating that chemisorption as dominant adsorption mechanism and providing valuable insights into the dynamic behavior of the process.