Sulfate removal from acid mine drainage using polypyrrole-grafted granular activated carbon

A novel method of removing sulfate from acid mine drainage (AMD) water was developed by depositing polypyrrole into the pores of wood-based activated carbon (RGC) using in situ chemical oxidative polarization. This polypyrrole-tailored activated carbon hosted positively charged polypyrrole functionality that offered sorption capacity for sulfate. Specifically, in batch tests, the polypyrrole-grafted RGC achieved a sulfate loading of 48 mg/g, this being 8 times higher than for pristine RGC. Rapid Small Scale Column Tests appraised the polypyrrole-tailored RGC for removing 773 mg/L sulfate from AMD water. The more favorably tailored carbon removed sulfate to half-breakthrough at 24 bed volumes (BV). This compared to 1.5 BV for pristine activated carbon. Per mass and charge balance, 9% of the nitrogen in the polypyrrole functionality was active for capturing sulfate. On this tailored carbon, the nitrogen content was 12.9%, as characterized by X-ray photoelectron spectroscopy. With this polypyrrole tailoring, the carbon’s pore volume distributions diminished to one-third, as characterized by argon adsorption.