Effective removal of different dyes using run-of-mine and processed coal samples

Abstract

Coal, traditionally utilised solely for combustion, is now being investigated for its potential as an adsorbent in purifying drinking water by eliminating hazardous metal ions. Limited research exists regarding its effectiveness in reducing organic dye levels. Presented here are the outcomes of an extensive investigation into various carbon samples' efficacy as adsorbents for wastewater color removal. Samples of coal sourced from Western Coalfield Limited (WCL) were meticulously processed and characterized, encompassing run-of-mine coal and acid-leached coal. A comprehensive array of techniques, including scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (PXRD), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy, was employed for coal characterization. Proximate analysis and gross calorific value (GCV) were employed to assess coal's physical attributes. The adsorption behavior of methylene blue (MB) and crystal violet (CV) on coal was scrutinized, varying factors such as contact time, pH, initial MB and CV concentrations, and adsorbent doses. Optimal adsorption parameters for MB were determined as pH 2, initial concentration of 1 ppm, 0.2 g adsorbent dose, and 60 min contact time. For CV, optimal conditions were pH 8, initial concentration of 6 ppm, 0.4 g adsorbent dose, and 45 min contact time. MB adsorption kinetics favored the pseudo-second-order reaction model, with Freundlich isotherms providing a better fit than Langmuir isotherms. Conversely, CV adsorption kinetics favored the pseudo-second-order reaction model, with Langmuir isotherms exhibiting a superior fit compared to Freundlich isotherms.