title: Chemical modeling for precipitation from hypersaline hydrofracturing brines.
abstract: Hypersaline hydrofracturing brines host very high salt concentrations, as high as 120,000-330,000 mg/L total dissolved solids (TDS), corresponding to ionic strengths of 2.1-5.7 mol/kg. This is 4-10 times higher than for ocean water. At such high ionic strengths, the conventional equations for computing activity coefficients no longer apply; and the complex ion-interactive Pitzer model must be invoked. The authors herein have used the Pitzer-based PHREEQC computer program to compute the appropriate activity coefficients when forming such precipitates as BaSO4, CaSO4, MgSO4, SrSO4, CaCO3, SrCO3, and BaCO3 in hydrofracturing waters. The divalent cation activity coefficients (γM) were computed in the 0.1 to 0.2 range at 2.1 mol/kg ionic strength, then by 5.7 mol/kg ionic strength, they rose to 0.2 for Ba(2+), 0.6 for Sr(2+), 0.8 for Ca(2+), and 2.1 for Mg(2+). Concurrently, the [Formula: see text] was 0.02-0.03; and [Formula: see text] was 0.01-0.02. While employing these Pitzer-derived activity coefficients, the authors then used the PHREEQC model to characterize precipitation of several of these sulfates and carbonates from actual hydrofracturing waters. Modeled precipitation matched quite well with actual laboratory experiments and full-scale operations. Also, the authors found that SrSO4 effectively co-precipitated radium from hydrofracturing brines, as discerned when monitoring (228)Ra and other beta-emitting species via liquid scintillation; and also when monitoring gamma emissions from (226)Ra.
authors.affiliation: Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, PA 16802, United States.
authors.forename: Maria I
authors.initials: MI
authors.lastname: Zermeno-Motante
authors.affiliation: Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, PA 16802, United States; División de Ciencias Ambientales, Instituto Potosino de Investigación Científica y Tecnológica (IPICyT), Camino a la Presa San José 2055, Col. Lomas 4(a), Sección, San Luis Potosí, SLP 78216, México. Electronic address: cesar.nieto@ipicyt.edu.mx.
authors.forename: Cesar
authors.initials: C
authors.lastname: Nieto-Delgado
authors.affiliation: Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, PA 16802, United States.
authors.forename: Fred S
authors.initials: FS
authors.lastname: Cannon
authors.affiliation: Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, PA 16802, United States.
authors.forename: Colin C
authors.initials: CC
authors.lastname: Cash
authors.affiliation: Hydro Recovery, LP, State College, PA 16803, United States.
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Wunz
mesh_terms: D011232:Chemical Precipitation; D000067071:Hydraulic Fracking; D008956:Models, Chemical; D009994:Osmolar Concentration; D013431:Sulfates; D014875:Water Pollutants, Radioactive
chemical_list: D013431:Sulfates; D014875:Water Pollutants, Radioactive
keywords: Activity coefficients; Hydrofracturing groundwater; Hypersaline brines