Sulfate Removal From Acid Mine Drainage Using Polypyrrole-grafted Activated Carbon

Many companies use hydro fracture to release petroleum from the shale underground.The fracking water demand is large, and the precipitate should be prevented. An energycompaniy has sought acid mine drainage water as a viable alternative to municipally-developed water. The rationale for this is that the locations of fracking wells oftenoverlaps geographically with regions of abandoned coal mines and acid mine drainage.The traditional acid mine drainage contains500-1000mg/L sulfate. There are severallimits in current technology for sulfate removal. The adsorption method is rapid and easybut it has limited sorption capacity.A novel method of removing sulfate from acid mine drainage water was developed bydepositing polypyrrole into the pores of activated carbon via in situ chemical oxidationpolarization. This polypyrrole-tailored activated carbon hosted positively chargedpolypyrrole functionality that offered sorption capacity for sulfate. Next, after thissorption, the same polypyrrole-GAC was electrochemically reduced such that thenitrogen functionality became neutrally charged, and released the sorbed sulfate. Then,this same polypyrrole-GAC was electrochemically oxidized such that it regained apositive charge, and again sorbed sulfate.When polarizing polypyrrole on activated carbon, three different activated carbonswere selected, namely bituminous carbon (UC1240), hard-wood carbon (RGC40) andwood-based carbon (Gran C). Specifically, in batch tests, the polypyrrole-grafted RGCachieved a sulfate loading of44.7mg/g, which was8times higher than for pristine RGC.Rapid small scale column tests (RSSCTs) appraised the polypyrrole-tailored activatedcarbons for removing773mg/L sulfate from acid mine drainage water. The morefavorably tailored carbon removed sulfate to full-breakthrough at36bed volumes. Thiscompared to1.5bed volumes for pristine activated carbon. In this tailored carbon, thenitrogen content was12.9%, as characterized by X-ray photoelectron spectroscopy. Permass and charge balance,9%of the nitrogen in the polypyrrole functionality was activefor capturing sulfate. In this tailored carbon, the nitrogen.Subsequent to these RSSCTs, electrochemical reduction at-2.0volts released95%ofthis sorbed sulfate. Next, subsequent oxidation at+0.9volts yielded a media that hadrestored60%of its initial sulfate-sorption capacity. Overall, the tailored activated carbon by polypyrrole can remove sulfate from acidmine drainage water. The spent activated carbon can be regenerated by electrochemicalreduction. The study herein guided a new orientation for modification of activated carbonand regeneration and it provided a fundamental theory of sulfate removal as well.