Electrochemical regeneration of polypyrrole-tailored activated carbons that have removed sulfate

A novel method has been developed for immobilizing (tailoring) polypyrrole (PPy) into activated carbon (AC) in a manner that facilitates the removal of sulfate, and then electrochemically regenerating the tailored activated carbon. This tailoring was achieved by sorbing pyrrole into AC pores, then oxidizing the pyrrole by means of either a FeCl3 oxidant or electrochemical oxidation. The resultant oxidized PPy hosted a positive charge that sorbed sulfate from acid mine drainage (AMD) water. Next, the spent AC/PPy was electrochemically reduced such that the nitrogen functionality became neutrally charged, and released the sorbed sulfate. This AC/PPy was then electrochemically oxidized such that it regained a positive charge, and again sorbed sulfate. When processing rapid small scale column tests (RSSCTs) with AMD water that contained 773 mg/L SO42− the media processed 23 bed volumes before breakthrough occurred. Subsequent to these RSSCTs, electrochemical reduction at −2.0 V (vs Ag/AgCl) released 95% of this sorbed sulfate, and subsequent oxidation at 0.4 V yielded a media that had restored 61.5% of its initial sulfate-sorption capacity.