Can contaminated water from abandoned mines be turned into a viable water supply for hydraulic fracturing operations? The results of a recently completed demonstration project in Pennsylvania suggest that the answer is yes.
Battelle recently completed a demonstration project at Fawn Mine in Sarver, PA. The two-year project, sponsored by the Department of Energy, utilized a novel water treatment technology called Floatation Liquid-Liquid Extraction (FLLX) that removes both metals and sulfates from contaminated water. Now commercialized by Winner Water Services as HydroFlex, the technology uses a dual solvent extraction process to remove contaminants from wastewater. In the demonstration project at Sarver, HydroFlex was shown to reduce sulfate concentrations in Acid Mine Drainage (AMD) by up to 90%—a significant improvement over competing technologies.
With a single gas well requiring up to 5 million gallons of water between initial fracturing and well completion, water use has become a point of contention between oil and gas developers and local communities. At the same time, millions of gallons of water are collecting in abandoned mines throughout the Appalachian area. Left untreated, AMD from these mines can have significant environmental and economic consequences. With HydroFlex, abandoned mine pools can become an economical and convenient source of water for hydraulic fracturing and other operations—a double win for oil and gas companies and the environment.
The technology has been under study since 2008 and was previously validated in bench-scale experiments. The Sarver demonstration project is the first to put the technology to the test in the field for the supply of water to the oil and gas industry. The project used semi-portable, modular treatment units that are capable of processing 100 gallons of water per minute. The resulting water was shown to meet requirements for use in hydraulic fracturing. ArcelorMittal provided access to the Fawn Mine site during the course of the DOE project.
Removing sulfates from mine water has proved to be problematic for companies and agencies engaged in remediation work. Methods for sulfate reduction generally fall into two categories: thermal processes and membranes. Both work by concentrating the dissolved components of the feed water for removal via precipitation or as a concentrated waste stream. Conventional precipitation methods generally are not able to reduce sulfate concentrations much below 1,200 mg/L. Membrane-based processes are more effective, but are very costly, are subject to fouling, and generate a large waste stream.
The FLLX process encompasses two distinct stages – water purification and sulfate recovery. In the water purification stage, sulfates are removed from the wastewater through contact with an organic extractant phase. The sulfate anions associate with the positively charged extractant, which is then separated from the water in a settler. The sulfate is typically reduced by about 70–90%.
The sulfate is then stripped from the extractant phase in a separate extractant recovery stage. A high pH carbonate solution exchanges sulfate anions with carbonate anions, recharging the extractant. A sodium sulfate byproduct solution with potential commercial applications is also generated within this stage.
Winner Water Services will use the results of these studies to make system improvements and optimize HydroFlex for oil and gas and other industrial applications.