High‐pressure Raman and X‐ray diffraction data on single crystals of hydrous layer‐structure minerals, dickite and gibbsite, reveal structural phase transitions occurring between 2.0 and 2.5 GPa. In the case of dickite, this is the first documented occurrence of a pressure‐induced phase transformation in a 1:1 phyllosilicate. Above the transition the structure of individual 1:1 layers remains unchanged, whereas the stacking of individual layers and the interlayer topology change significantly. Similar to dickite, single‐crystal Raman spectra of gibbsite show large perturbations in the v (OH) region and suggest that the interlayer OH groups play a critical role in the phase transformation.
In aqueous suspension, the affinity of many pesticides for smectites is influenced by the clay properties such as surface area, surface charge density and location, exchangeable cations, and hydration status of exchangeable cations in clay interlayers. The amount and the type of salts present in the aqueous phase influence clay quasicrystal structures and hydration status, which we hypothesize as major determinants of pesticide sorption. To test this hypothesis, we measured sorption isotherms of alachlor, atrazine, dichlobenil, and diuron by K + –saturated smectite (K‐SWy‐2) in KCl solution and Ca 2+ –saturated smectite (Ca‐SWy‐2) in CaCl 2 solution at several ionic strengths. The results indicated that pesticide sorption by K‐SWy‐2 significantly increased with increasing aqueous KCl concentration. In contrast, sorption by Ca‐SWy‐2 at different CaCl 2 ionic strengths remained nearly constant. The “salting‐out” effect on the reduction of dissolution of pesticides failed to account for the significantly increased sorption by K‐SWy‐2 in aqueous KCl solutions. We conclude that formation of better‐ordered clay quasicrystals and shrinkage of clay interlayer distance owing to increased KCl ionic strength facilitate the intercalation of pesticides leading to greater sorption by the clay, while the salting‐out effect plays a minor role (if any) in the observed sorption enhancement.
Although condensate oils are neither well defined nor have a known chemical composition, they are considered by the petroleum industry to be good candidates for the dilution of heavy crude oil as this generates a blend with a lower viscosity. This dilution helps alleviate challenges in heavy crude oil transportation, separation, and processing that are mainly caused by the high concentration of asphaltenes in heavy crude oils. However, asphaltenes in these oil blends are susceptible to precipitation after dilution. Many factors can affect this precipitation, including the amount of polar and heteroaromatic compounds present in the diluent. To facilitate the proper selection of condensate-like oils for heavy crude oil dilution, the chemical compositions of these diluents should be determined. As a proof of concept, five condensate-like oils with different API gravities were analyzed using the previously developed distillation, precipitation, fractionation mass spectrometry method. This method involved fractionation of the samples into five different compound classes (volatile hydrocarbons, heavy saturated hydrocarbons, alkyl aromatic hydrocarbons, heteroaromatic compounds, and polar compounds) and determination of the chemical compositions of compounds in each compound class and in the whole condensate-like oils by using optimized ionization and high-resolution mass spectrometry methods. Further, the average gravimetric weight percentage (wt %) of compounds in each compound class, the average molecular weight, and the average ring and double bond equivalence values of compounds in each class, as well as the overall average molecular weight and ring and double bond equivalence values of the compounds in the entire condensate-like oils, were determined. Additionally, in-source collision-activated dissociation was utilized to determine the average total number of carbon atoms in the alkyl chains of the alkyl aromatic hydrocarbons (ranging from 14 up to 22). Since the API gravity is generally used to make decisions about the quality and price of hydrocarbon products of the petroleum industry, correlations between the API gravity and the chemical compositions of the condensate-like oils were examined. In general, the average wt % of heteroaromatic compounds was greatest in the condensate-like oil with the lowest API gravity (greatest density), while that of saturated hydrocarbons was found to directly correlate with the API gravity. Moreover, consideration of the average wt % of compounds of different elemental composition types in each compound class revealed trends related to the API gravity. For instance, compounds with the elemental composition type CcHhSs were most abundant in the condensate-like oil with the lowest API gravity and their abundance decreased with the increase in the API gravity. Further, condensate-like oils with greater API gravities appeared to have a larger number of carbon atoms in the side chains of the alkyl aromatic hydrocarbons than the condensate-like oils with lower API gravities.
The compound 4,6‐dinitro‐ o ‐cresol (DNOC) is an important pesticide that is strongly adsorbed by smectite clays. Because DNOC is a weak acid with an acid dissociation constant (p K a ) of about 4.4, pH was hypothesized to be a dominant state variable controlling sorption. In this study, we quantified the effect of pH, saturating cation (K + and Ca 2+ ), and freeze‐drying on adsorption of DNOC by two reference smectites with different charge densities (SWy‐2 and SAz‐1) in dilute aqueous suspensions. The smectite–DNOC systems were adjusted from pH 3 to 7. Nearly 100% of added DNOC was adsorbed by K + –saturated SWy‐2 at pH 3, and sorption decreased with increasing pH to 62% at pH 7. Sorption of DNOC on K + –saturated SAz‐1 decreased from 94% at pH 3 to 31% at pH 7. Suspended Ca 2+ –saturated SWy‐2 adsorbed 82% of added DNOC at pH 3 but sorption decreased to 18% for pH 4 and above. Across the entire pH range, Ca 2+ –saturated SAz‐1 sorbed about 12% of added DNOC. Slightly larger amounts of DNOC were adsorbed by the “never dried” (not freeze‐dried) smectites compared with the freeze‐dried and rehydrated smectites. Analysis of supernatants from the K + –saturated SAz‐1–DNOC systems indicated co‐adsorption of K + with DNOC in the phenolate form at pH values above the p K a of DNOC. At lower pH values, DNOC adsorption and complexation with interlayer K + resulted in less K + exchange by H + compared with the control without DNOC. These mechanisms explain the minimal influence of pH on the adsorption of DNOC by the K + –saturated smectites.
The loss of N and P by leaching is an important issue, especially on agricultural fields with subsurface tile drainage. The objective of this study was to evaluate how gypsum amendment and soil exchangeable Ca2+ and Mg2+ could affect the movement of P, NH4–N, and NO3–N in infiltrated water and soil. A column experiment was performed using a Miami silt loam soil, and the treatments were (i) control, (ii) gypsum applied at the surface, (iii) gypsum mixed into the 2.5-cm depth, and (iv) alteration of five different target exchangeable Ca/Mg ratios. A clear Plexiglas cylinder was filled with a 15-cm layer of soil; N, P, and K were applied in solution at the surface after the soil had been wetted and drained. Deionized water at a flow of 0.5 mL min−1 was applied and eight leachate fractions, totaling about five pore volumes, were collected. Gypsum (5000 kg ha−1) applied at the surface and mixed into the 2.5-cm depth significantly decreased P and increased NH4–N concentration but had no significant effect on NO3–N leaching. Exchangeable Ca/Mg ratio treatments did not affect soluble nutrient losses; however, leaching of particulate P was significantly less in the Ca-treated soil than the Mg-treated soil. The overall practical conclusion of this study is that to control P transport, it is necessary to add gypsum even with a high soil exchangeable Ca/Mg ratio. The application of gypsum to the soil could be recommended as a best management practice to avoid water pollution by P; on the other hand, this could cause environmental problems by increasing the NH4 soil mobility.
Chemically enhanced oil recovery (cEOR) is an expensive endeavor that yields modest levels of oil recovery. In order to make it economically viable, an improved understanding of the process is needed. For example, knowledge of the types of compounds in crude oil that are strongly bound to reservoir surfaces would facilitate the design of more efficient cEOR formulations. In this research study, the fractionation step of the previously published distillation, precipitation, and fractionation mass spectrometry (MS) method was utilized to determine the types of compounds in crude oil that are strongly or weakly bound to kaolinite, a prevalent clay mineral found in many oil reservoirs. The results obtained using high-resolution MS experiments revealed that the average molecular weight and the number of aromatic rings were similar for both the strongly and weakly bound compounds. On the other hand, hydrocarbons with no heteroatoms were ∼2.5 times more abundant in the strongly bound compounds than in the nonbound compounds, while heteroatom-containing compounds were more abundant in the nonbound compounds. An analogous binding study performed on a model compound mixture corroborated the above findings that nonpolar compounds prefer to bind to kaolinite than polar compounds. These results suggest that more valuable oil components (nonpolar hydrocarbons) remain in the reservoirs after water flooding, and therefore, cEOR efforts with the appropriate formulation could increase the economic feasibility of the process. The method described herein should also be applicable for the characterization of compounds that bind strongly to different types of mineral surfaces, and the role of temperature, salinity, and pH is studied.
Soil aggregates low in organic matter and clay contents are generally susceptible to disintegration at low rainfall energies. This study was conducted to evaluate the effectiveness of ferrihydrite (Fe5 HO8·4H2O) at stabilizing such aggregates, using five soils with a wide range of physical and chemical properties. The soils were amended with ferrihydrite at rates equivalent to 0, 0.34, 3.36, 16.80, and 33.60 Mg ha−1, packed to a depth of 7.6 cm in plexiglass cylinders, and then exposed to simulated rainfall at an intensity of 64 mm h−1 for 1.5 h. The erodibility data indicated that as ferrihydrite increased from 0 to 16.80 Mg ha−1 on acid soils, infiltration increased an average of 21.5% while runoff and soil loss decreased 20 and 40%, respectively. Conversely, infiltration decreased 37% while runoff and soil loss increased 21 and 34%, respectively for alkaline soils. Further, sediment size distributions measured at these same ferrihydrite rates indicated that the >250-, and 250- to 53-μm fractions increased 24 and 22% for acid soils and decreased 15 and 14%, respectively in alkaline soils. The <53-μm fraction decreased 21% in the acid soils and increased 46% in the alkaline soils. These results suggest ferrihydrite develops a net positive charge in acid soil environments that leads to formation of bonds with negatively charged soil particles and an increase in water stable aggregation. Conversely, in alkaline soils, ferrihydrite becomes negatively charged which results in dispersion and aggregate instability. Thus, ferrihydrite appears to be an effective amendment for reducing runoff and soil loss from acid pH soils at amendment rates between 3.36 and 16.80 Mg ha−1
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