Marcellus shale. Image credit: Lvklock / CC BY-SA 3.0A multidisciplinary team of researchers from Penn State has discovered that pressure, temperature and fluid composition significantly affect the amount of metals and other chemical found in hydrofracking wastewater. These results have implications for mining wastewater management and for methodologies for studying fracking processes.

The fracking process causes chemicals used in the fracking fluid and dissolved metals associated with shale to surface in wastewater in high concentrations. These solutes can have a deleterious effect on human health, so it is important to understand the contents of the wastewater when building wastewater management systems.

The research team set out to determine where the metals were concentrated in shale samples, how the composition of hydraulic fracturing fluids affected metal mobility and how hydraulic fracturing fluids are transformed under high pressure and temperature conditions.

They determined where metals are concentrated in shale by sampling six Pennsylvania locations and exposing the samples to the same high temperature and pressure conditions caused by fracking, along with a typical fracking fluid. More metals leached from shale when miners used fluids with acids, oxidizers and high salinity.

The only test conditions that completely removed fracking chemicals from the fluid were high pressure combined with high temperatures. The study also discovered that, while many fracking fluid additives degrade downhole, surfactants and other hydrophilic compounds return to the surface.

Travis Tasker, lead researcher, pointed out that the team’s work “showed that the fracturing fluid chemistry does influence metal leaching from the shale that can lead to secondary mineral precipitation. It is important to understand how mineral precipitation and other mineralogical changes would affect overall gas recovery."

The study was published in the journal Environmental Engineering Science .