Enhanced Transport of 2,2′,5,5′-Polychlorinated Biphenyl by Natural Organic Matter (NOM) and Surfactant-Modified Fullerene Nanoparticles (<i>n</i>C₆₀)

Stable colloidal suspensions of buckminsterfullerene (<i>n</i>C₆₀) in aqueous environments can significantly affect the fate and transport of hydrophobic organic contaminants by serving as a contaminant carrier. In this study, we examined enhanced transport of 2,2′,5,5′-polychlorinated biphenyl (PCB) in saturated sandy soil columns by a variety of <i>n</i>C₆₀ samples, including an <i>n</i>C₆₀ sample prepared by the typical solvent exchange method, as well as eight natural organic matter (NOM) or surfactant-modified <i>n</i>C₆₀ samples, prepared by phase-transferring C₆₀ from toluene to an NOM or a surfactant solution. Whereas the NOM- and surfactant-modified <i>n</i>C₆₀ samples have mobility similar to the unmodified <i>n</i>C₆₀, their contaminant-mobilizing capabilities are significantly greater: breakthrough of PCB increases by 47.2 to 227% with the surfactant-modified <i>n</i>C₆₀ samples and by 233 to 370% with the NOM-modified <i>n</i>C₆₀ samples. The significantly enhanced contaminant-mobilizing capability of the modified <i>n</i>C₆₀ is likely due to a combined effect of increased adsorption affinities and increased tendency of desorption nonequilibrium, likely caused by the changes of <i>n</i>C₆₀ aggregation properties induced by the presence of NOM or surfactant. Findings in this study indicate that <i>n</i>C₆₀ formed in different processes might have vastly different effects on contaminant fate and transport

Laboratory Evaluation and Mechanistic Understanding of the Impact of Ferric Species on Oilfield Scale Inhibitor Performance

Scale inhibitor chemicals are widely used in oilfield operations for mineral scale control. However, the presence of iron species in oilfield produced water can considerably impair the performance of scale inhibitors. To date, few studies have been conducted to experimentally investigate the mechanism of iron effect on scale inhibitors. Although Fe­(II) is the major form of iron species in oilfield produced water, Fe­(III) can be formed in produced waters due to oxidation of Fe­(II). In this study, Fe­(III) effect on various scale inhibitors was evaluated by examining the inhibitor performance to control barium sulfate (barite) scale formation. This study finds that Fe­(III) can significantly impair the performance of both phosphonate and polymeric inhibitors with an iron concentration below 1 mg L^–1. Moreover, the mechanism of the influence of Fe­(III) on scale inhibitors was studied by investigating the adsorption capacity of ferric hydroxide solid of phosphonate scale inhibitor and also examining the efficacy of the unadsorbed inhibitor in aqueous solution. It can be concluded that the Fe­(III) impact on phosphonate inhibitor is due to the adsorption of inhibitor to the surface of ferric hydroxide solids. Furthermore, two common chelating chemicals (EDTA and citrate) were tested for their effects in reversing the adverse impact of Fe­(III) on scale inhibitor. Experimental results suggest that citrate is more effective than EDTA in reversing the detrimental impact of Fe­(III) despite the fact the EDTA is a stronger chelating agent. The mechanisms of these two chelating chemicals in terms of interacting with Fe­(III) were discussed and compared. This study provides the theoretical basis and technical insights for oilfield iron control to minimize iron impairment on scale inhibitor performance

Transport of Fullerene Nanoparticles (<i>n</i>C₆₀) in Saturated Sand and Sandy Soil: Controlling Factors and Modeling

Understanding subsurface transport of fullerene nanoparticles (<i>n</i>C₆₀) is of critical importance for the benign use and risk management of C₆₀. We examined the effects of several important environmental factors on <i>n</i>C₆₀ transport in saturated porous media. Decreasing flow velocity from approximately 10 to 1 m/d had little effect on <i>n</i>C₆₀ transport in Ottawa sand (mainly pure quartz), but significantly inhibited the transport in Lula soil (a sandy, low-organic-matter soil). The difference was attributable to the smaller grain size, more irregular and rougher shape, and greater heterogeneity of Lula soil. Increasing ionic strength and switching background solution from NaCl to CaCl₂ enhanced the deposition of <i>n</i>C₆₀ in both sand and soil columns, but the effects were more significant for soil. This was likely because the clay minerals (and possibly soil organic matter) in soil responded to changes of ionic strength and species differently than quartz. Anions in the mobile phase had little effect on <i>n</i>C₆₀ transport, and fulvic acid in the mobile phase (5.0 mg/L) had a small effect in the presence of 0.5 mM Ca²⁺. A two-site transport model that takes into account both the blocking-affected attachment process and straining effects can effectively model the breakthrough of <i>n</i>C₆₀

Development and Application of a New Theoretical Model for Additive Impacts on Mineral Crystallization

Additives play an important role in crystallization controls in both natural and industrial processes. Due to the lack of theoretical understanding of how additives work, the use and design of additives in various disciplines are mostly conducted empirically. This study has developed a new theoretical model to predict the additive impacts on crystallization based on the classical nucleation theory and regular solution theory. The new model assumes that additives can impact the nucleus partial molar volume and the apparent saturation status of the crystallization minerals. These two impacts were parametrized to be proportional to additive concentrations and vary with inhibitors. As a practical example, this new model has been used to predict barite induction times without inhibitors from 4 to 250 °C and in the presence of eight different scale inhibitors from 4 to 90 °C. The predicted induction times showed close agreement with the experimental data published previously or produced in this study. Such agreement indicates that this new theoretical model can be widely adopted in various disciplines to evaluate mineral formation kinetics, elucidate mechanisms of additive impacts, predict minimum effective dosage (MED) of additives, and guide the design of new additives, to mention a few

Calcite and Barite Solubility Measurements in Mixed Electrolyte Solutions and Development of a Comprehensive Model for Water-Mineral-Gas Equilibrium of the Na-K-Mg-Ca-Ba-Sr-Cl-SO₄‑CO₃‑HCO₃‑CO₂(aq)‑H₂O System up to 250 °C and 1500 bar

Calcite and barite are two of the most common scale minerals that occur in various geochemical and industrial processes. Their solubility predictions at extreme conditions (e.g., up to 250 °C and 1500 bar) in the presence of mixed electrolytes are hindered by the lack of experimental data and thermodynamic model. In this study, calcite solubility in the presence of high Na₂SO₄ (i.e., 0.0407 m Na₂SO₄) and barite solubility in a synthetic brine at up to 250 °C and 1500 bar were measured using our high-temperature high-pressure geothermal apparatus. Using this set of experimental data and other thermodynamic data from a thorough literature review, a comprehensive thermodynamic model was developed based on the Pitzer theory. In order to generate a set of Pitzer theory virial coefficients with reliable temperature and pressure dependencies which are applicable to a typical water system (i.e., Na-K-Mg-Ca-Ba-Sr-Cl-SO₄-CO₃-HCO₃-CO₂-H₂O) that may occur in geochemical and industrial processes, we simultaneously fit all available mineral solubility, CO₂ solubility, as well as solution density. With this model, calcite and barite solubilities can be accurately predicted under such extreme conditions in the presence of mixed electrolytes. Furthermore, the 95% confidence intervals of the estimation errors for solution density predictions are within 4 × 10^–4 g/cm³. The relative errors of CO₂ solubility prediction are within 0.75%. The estimation errors of the saturation index mean values for gypsum, anhydrite, and celestite are within ±0.1 and that for halite is within ±0.01, most of which are within experimental uncertainties

Carbon-Based Nanoreporters Designed for Subsurface Hydrogen Sulfide Detection

Polyvinyl alcohol functionalized carbon black with H₂S-sensor moieties can be pumped through oil and water in porous rock and the H₂S content can be determined based on the fluorescent enhancement of the H₂S-sensor addends