Sulfate removal from acid mine drainage using adsorbents derived from drinking water treatment plant residue: synthesis, characterization and comprehensive analysis.

This paper focuses on the utilization of drinking water treatment plant residue (DWTPR) for sulfate removal from synthetic and real acid mine drainage (AMD) from the mine sumps of an Opencast Project (OCP) in Ib Valley Coalfields, MCL Odisha, India, and compares it with modified DWTPR. The physicochemical behavior of the adsorbents was analyzed by SEM, EDS, XRD, FTIR, BET, and pH_ZPC. The optimum parameter for sulfate removal was obtained from varying initial concentrations, dosages, contact time, and pH of the solution. The findings showed that the modification introduced some new functional groups and altered crystallinity. The pH_zpc of raw DWTPR, EDTA-DWTPR, and Chitosan-DWTPR were found to be 6.4, 7.1, and 8.8, respectively. The maximum sulfate removal (77.93%) was achieved using chitosan-modified DWTPR at pH 7.1 with a dosage of 5 g/100 mL and a contact time of 300 min in synthetic sulfate solution (Solution A). Chitosan-DWTPR removed 77.93%, 71.68%, and 62.76% of sulfate from Sump 1, Sump 2, and simulated AMD solution (Solution B), respectively. Additionally, up to 90% of other pollutants (Fe, Mn, Cu, Ni, and Al) were removed from both synthetic and real AMD samples. The Langmuir isotherm and pseudo-second-order kinetic model accurately described the experimental data. The thermodynamic analysis revealed that the process was non-spontaneous, exothermic, and associated with low randomness. Both raw and chitosan-modified DWTPR demonstrated remarkable neutralization ability for AMD. The study highlighted the significant role of chitosan in enhancing adsorbent properties for effective sulfate removal and mine effluent neutralization. Adsorption and chemical precipitation were identified as the primary mechanisms for the removal of sulfate and other pollutants.