Enhanced evaporative flux to remediate soils contaminated with produced water brine

Abstract

Hydraulic fracturing rates have shown significant growth in the past few years and this trend is expected to continue in years to come. As hydraulic fracturing occurs, accidental spills of highly saline produced water have severe impact on nearby soils. The release of large concentrations of salts into the soil profile can destroy plant and microbial life, as well as disperse soil clays causing erosion. Current remediation techniques for this problem, such as excavation or soil washing, are destructive or only partially effective. This study explores a novel technique using surface evaporation to draw salts in solution toward the soil surface when ferrocyanide is added to promote efflorescence. NaCl has the most potential to cause soil pore clogging due to its high concentration and ferrocyanide interacts with NaCl to form dendritic efflorescence that can be effectively removed. Beaker sand column experiments were conducted using produced waters from the Permian Basin to simulate spill sites. Prussian yellow was found to be the most effective form of ferrocyanide. The composition of the produced water was found to have large effect on the capability of Prussian yellow to induce efflorescence. Produced waters with higher background ion concentrations required ten times as much Prussian yellow to cause significant efflorescence. Alternatively, it was found that EDTA could be added to a produced water as a chelating agent to effectively reduce competition for the ferrocyanide ion so that it can promote NaCl efflorescence. Spectrophotometry was used to determine that on average 73% of the Prussian yellow added was removed from the sand profile with the efflorescence. PHREEQC was utilized to model speciation of ferrocyanide and EDTA within the produced waters and this highlighted a need for a predictive model to determine the most efficient dosage of additives for a given produced water spill.