Travis L. Tasker

Information on the aqueous chemistry of rare-earth elements and yttrium (REE) is required (1) to predict their environmental form and transport, and (2) to identify and optimize treatment technologies for recovery of REE from acid mine drainage (AMD) or leachate from other sources. REE and associated aqueous complexes may form surface complexes (i.e., adsorption) with hydrous ferric oxides (HFO), hydrous aluminum oxides (HAO), and hydrous manganese (III-IV) oxides (HMO). However, the governing reactions and equilibrium constants for REE sorption to those hydrous metal-oxide (HMeO) solids are not fully defined in available surface-complexation models. The work herein describes laboratory experiments and computations used to develop applicable equilibrium constants for surface-complexation reactions between REE and HMeO sorbents that are common in environmental and AMD systems. Titration experiments were performed to investigate the potential for co-precipitation and/or adsorption of REE with iron (Fe), aluminium (Al), or manganese (Mn) and the effects of sorbent availability, composition, pH, and SO4. The empirical data were used with parameter estimation software, coupled with geochemical modeling software, to calculate equilibrium constants for applicable surface-complexation reactions. Most notably, surface complexation reactions with HFO_wOMe(SO4) ternary complexes were important for simulating REE aqueous concentrations at low-pH with SO4, where adsorbed SO4 is hypothesized to lower the effective pH of REE binding by HFO and HAO. The new surface-speciation data were incorporated into a comprehensive thermodynamic database file to predict potential distributions of aqueous, sorbed, and precipitated REEs concentrations in environmental water samples or treated AMD effluent. The geochemical model with the new thermodynamic database can accurately simulate changes in REE concentrations as functions of pH, aqueous and surface speciation, and sorbent availability and characteristics.

While development of the Utica/Point Pleasant Shale (UPP) is extensive in Ohio (U.S.) and increasing in Pennsylvania and West Virginia, few studies report the chemistry of produced waters from UPP wells. These data have important implications for developing best management practices for handling and waste disposal, or identifying the fluid in the event of accidental spill events. Here, we evaluated the elemental and isotope chemistry of UPP produced waters from 26 wells throughout Ohio, Pennsylvania, and West Virginia to determine any unique fluid chemistries that could be used for forensic studies. Compared to the Marcellus, UPP produced waters contain higher activities of total radium (²²⁶Ra + ²²⁸Ra) and higher ²²⁸Ra/²²⁶Ra ratios. As with the Marcellus Shale, elemental ratios (Sr/Ca) and isotope ratios (⁸⁷Sr/⁸⁶Sr) can distinguish UPP produced waters from many conventional oil and gas formations. Sr/Ca and ⁸⁷Sr/⁸⁶Sr ratios can fingerprint small fractions (∼0.1%) of UPP produced water in freshwater. However, because Marcellus and UPP produced waters display similar major elemental chemistry (i.e., Na, Ca, and Cl) and overlapping ratios of Sr/Ca and ⁸⁷Sr/⁸⁶Sr, ²²⁸Ra/²²⁶Ra ratios may be the best tracer to distinguish these waters.

Radium measurements in high total dissolved solids (TDS) fluids from oil and gas extraction can have unfavorable precision and accuracy, in part because these high-level impurities incur attenuation. γ spectroscopy is often recommended for determining radium activities in these fluids, but even this method can produce a range of reported activities for the same sample. To reduce measurement duration and to maintain or improve accuracy, we propose a method to rapidly assess both ²²⁶Ra and ²²⁸Ra and to account for the self-attenuation of γ rays in high-TDS oil and gas fluids when they are monitored by a well detector. In this work, comparisons between a NaCl-only and a multi-cation-chloride synthetic brine spiked with known amounts of ²²⁶Ra and ²²⁸Ra indicated that both the TDS concentration and the type of TDS (i.e., Na only vs Na–Mg–Ba–Ca–Sr) influenced self-attenuation in well-detector γ spectroscopy, thus highlighting the need to correct for this TDS-influenced self-attenuation. Radium activities can be underestimated if the correction is not applied. For instance, ²²⁶Ra activities could be ∼40% lower in a sample when measured directly at the 186 keV energy level if the attenuation of the high TDS of the fluid is not considered. We also showed that using a NaCl-only brine to match the matrix of high-TDS oil and gas brines is inadequate to produce accurate measurements, rather, the full set of cations should be included.

Accurate and precise analyses of oil and gas (O&G) wastewaters and solids (e.g., sediments and sludge) are important for the regulatory monitoring of O&G development and tracing potential O&G contamination in the environment. In this study, 15 laboratories participated in an inter-laboratory comparison on the chemical characterization of three O&G wastewaters from the Appalachian Basin and four solids impacted by O&G development, with the goal of evaluating the quality of data and the accuracy of measurements for various analytes of concern. Using a variety of different methods, analytes in the wastewaters with high concentrations (i.e., >5 mg L⁻¹) were easily detectable with relatively high accuracy, often within ±10% of the most probable value (MPV). In contrast, often less than 7 of the 15 labs were able to report detectable trace metal(loid) concentrations (i.e., Cr, Ni, Cu, Zn, As, and Pb) with accuracies of approximately ±40%. Despite most labs using inductively coupled plasma mass spectrometry (ICP-MS) with low instrument detection capabilities for trace metal analyses, large dilution factors during sample preparation and low trace metal concentrations in the wastewaters limited the number of quantifiable determinations and likely influenced analytical accuracy. In contrast, all the labs measuring Ra in the wastewaters were able to report detectable concentrations using a variety of methods including gamma spectroscopy and wet chemical approaches following Environmental Protection Agency (EPA) standard methods. However, the reported radium activities were often greater than ±30% different to the MPV possibly due to calibration inconsistencies among labs, radon leakage, or failing to correct for self-attenuation. Reported radium activities in solid materials had less variability (±20% from MPV) but accuracy could likely be improved by using certified radium standards and accounting for self-attenuation that results from matrix interferences or a density difference between the calibration standard and the unknown sample. This inter-laboratory comparison illustrates that numerous methods can be used to measure major cation, minor cation, and anion concentrations in O&G wastewaters with relatively high accuracy while trace metal(loid) and radioactivity analyses in liquids may often be over ±20% different from the MPV.

Thirteen states in the United States allow the spreading of O&G wastewaters on roads for deicing or dust suppression. In this study, the potential environmental and human health impacts of this practice are evaluated. Analyses of O&G wastewaters spread on roads in the northeastern, U.S. show that these wastewaters have salt, radioactivity, and organic contaminant concentrations often many times above drinking water standards. Bioassays also indicated that these wastewaters contain organic micropollutants that affected signaling pathways consistent with xenobiotic metabolism and caused toxicity to aquatic organisms like Daphnia magna. The potential toxicity of these wastewaters is a concern as lab experiments demonstrated that nearly all of the metals from these wastewaters leach from roads after rain events, likely reaching ground and surface water. Release of a known carcinogen (e.g., radium) from roads treated with O&G wastewaters has been largely ignored. In Pennsylvania from 2008 to 2014, spreading O&G wastewater on roads released over 4 times more radium to the environment (320 millicuries) than O&G wastewater treatment facilities and 200 times more radium than spill events. Currently, state-by-state regulations do not require radium analyses prior to treating roads with O&G wastewaters. Methods for reducing the potential impacts of spreading O&G wastewaters on roads are discussed.