Investigation of the different binding edge sites for Zn on montmorillonite using P-EXAFS - The strong/weak site concept in the 2SPNE SC/CE sorption model

The 2 site protolysis non electrostatic surface complexation and cation exchange (2SPNE SC/CE) sorption model has been used over the past decade or so to quantitatively describe the uptake of metals with oxidation states from II to VI on 2:1 clay minerals; montmorillonite and illite. One of the main features in this model is that there are two broad categories of amphoteric edge sorption sites; the so called strong (S^SOH) and weak (S^W1OH) sites. Because of their different sorption characteristics, it was expected that the coordination environments of the surface complexes on the two site types would be different. Zn isotherm data on two montmorillonites, Milos and STx-1, were measured and modelled using the 2SPNE SC/CE sorption model. The results were used to define the most favourable experimental conditions under which Zn sorption was either dominated by the strong (S^SOH, ∼2 mmol kg⁻¹) or by the weak sites (S^W1OH, ∼40 mmol kg⁻¹). Highly oriented self-supporting films were prepared for polarised extended X-ray absorption fine structure (P-EXAFS) investigations.Montmorillonites often contain Zn incorporated in the clay matrix. The Zn bound in this form was quantified and the results from the analysis of the P-EXAFS spectra were taken into account in the interpretation of the spectra measured at low Zn loadings (∼2 mmol kg⁻¹) and medium Zn loadings (∼30 mmol kg⁻¹). The Zn spectra on the “strong sites” exhibited a pronounced angular dependency and formed surface complexes in the continuity of the Al-octahedral sheets at the montmorillonite edges. In contrast, the Zn “weak site” spectra showed only a weak angular dependency. The spectroscopic evidence indicates the existence of two distinct groups of edge surface binding sites which is consistent with a multi-site sorption model and in particular with the strong/weak site concept intrinsic to the 2SPNE S/CE sorption model.     

Dislocation structure of the crust-mantle boundary and low-velocity body within the crust beneath the Dabie Shan collision orogen

The Dabie Shan is located on the eastern side of the Qinling-Dabie orogenic belt, which marks a geological boundary between the Sino-Korean and Yangtze cra- ton. Since the 1980s, the discovery of coesite and mi- crodiamond in the Dabie Shan orogen motivates an extensive interest to the ultra-high pressure (UHP)metamorphism and its exhumation[1,2]. Many results about them were published, which deal with different disciplines, including tectonics, petrology and chro- nology[3?8]. Up to now,…     

Influence of heterogeneous air entry pressure on large scale unsaturated flow in porous media

The paper presents numerical simulations of water infiltration in unsaturated porous media containing coarse-textured inclusions embedded in fine-textured background material. The calculations are performed using the two-phase model for water and air flow and a simplified model known as the Richards equation. It is shown that the Richards equation cannot correctly describe flow in the presence of heterogeneities. However, its performance can be improved by introducing appropriately defined effective capillary and permeability functions, representing largescale behaviour of the heterogeneous medium.     

Hydraulic fracturing in unconventional gas reservoirs: risks in the geological system, part 2

Hydraulic fracturing is a method used for the production of unconventional gas resources. Huge amounts of so-called fracturing fluid (10,000–20,000 m³) are injected into a gas reservoir to create fractures in solid rock formations, upon which mobilised methane fills the pore space and the fracturing fluid is withdrawn. Hydraulic fracturing may pose a threat to groundwater resources if fracturing fluid or brine can migrate through fault zones into shallow aquifers. Diffuse methane emissions from the gas reservoir may not only contaminate shallow groundwater aquifers, but also escape into the atmosphere where methane acts as a greenhouse gas. The working group “Risks in the Geological System” as part of ExxonMobil’s hydrofracking dialogue and information dissemination processes was tasked with the assessment of possible hazards posed by migrating fluids as a result of hydraulic fracturing activities. In this work, several flow paths for fracturing fluid, brine and methane are identified and scenarios are set up to qualitatively estimate under what circumstances these fluids would leak into shallower layers. The parametrisation for potential hydraulic fracturing sites in North Rhine-Westphalia and Lower Saxony (both in Germany) is derived from literature using upper and lower bounds of hydraulic parameters. The results show that a significant fluid migration is only possible if a combination of several conservative assumptions is met by a scenario.     

Sodic Pyroxene and Sodic Amphibole as Potential Reference Materials for In Situ Lithium Isotope Determinations by SIMS

Two large pegmatitic crystals of sodic pyroxene (aegirine) and sodic amphibole (arfvedsonite) from the agpaitic igneous Ilímaussaq Complex, south Greenland were found to be suitable as reference materials for in situ Li isotope determinations. Lithium concentrations determined by SIMS and micro‐drilled material analysed by MC‐ICP‐MS generally agreed within analytical uncertainty. The arfvedsonite crystal was homogeneous with [Li] = 639 ± 51 μg g^?1 (2s, n = 69, MC‐ICP‐MS and SIMS results). The aegirine crystal shows strongly developed sector zoning, which is a common feature of aegirines. Using qualitative element mapping techniques (EPMA), the homogeneous core of the crystal was easily distinguished from the outermost sectors of the crystals. The core had a mean [Li] of 47.6 ± 3.6 μg g^?1 (2s, n = 33) as determined by SIMS. The seven micro‐drilled regions measured by solution MC‐ICP‐MS returned slightly lower concentrations (41–46 μg g^?1), but still overlap with the SIMS data within uncertainty. Based on MC‐ICP‐MS and SIMS analyses, the variation in δ⁷Li was about 1‰ in each of the two crystals, which is smaller than that in widely used glass reference materials, making these two samples suitable to serve as reference materials. There was, however, a significant offset between the results of MC‐ICP‐MS and SIMS. The latter deviated from the MC‐ICP‐MS results by ?6.0 ± 1.9‰ (2s) for the amphibole and by ?3.9 ± 1.9‰ (2s) for the aegirine. This indicates the presence of a significant matrix effect in SIMS determinations of Li isotopes for amphibole and pyroxene relative to the basalt glasses used for calibration. Based on the MC‐ICP‐MS results, mean δ⁷Li values of +0.7 ± 1.2‰ (2s, n = 10) for the arfvedsonite crystal and of ?3.7 ± 1.2‰ (2s, n = 7) for the core of the aegirine crystal were calculated. Adopting these values, SIMS users can correct for the specific IMF (instrumental mass fractionation) of the ion probe used. We propose that these two crystals serve as reference materials for in situ Li isotope determinations by SIMS and pieces of these two crystals are available from the first author upon request.     

Assessment of the Intake and the Pretreatment Design in Existing Seawater Reverse Osmosis (SWRO) Plants by Hasse Diagram Technique (HDT)

Seawater desalination is a rising technology intended to overcome water scarcity and is increasingly being used for the production of drinking water. A good quality pretreatment process is prominent to the successful operation of a Seawater Reverse Osmosis (SWRO) plant. The tasks of the intake and the pretreatment modules are to prevent fouling and to extend the lifetime of the reverse osmosis membranes. To practice the method of assessment design, 19 seawater plants with 11 different design strategies have been evaluated. The assessed strategies consist of: (i) Intake treatment, (ii) pretreatment aid (coagulation, flocculation, clarification), and (iii) pretreatment unit. Every possible combination of the design elements has been evaluated by a set of 15 attributes. The comparative evaluation has been conducted by Hasse diagram technique (HDT) using PyHasse software. The result of the HDT application includes 7 favorable incomparable design strategies. In order to solve the incomparability, the Condorcet–Kemeny–Young–Levenglick (C–K–Y–L) ranking procedure was additionally used and rendered the optimal design that is based on subsurface intake and membrane (ultrafiltration) pretreatment facilities. According to the results, both mathematical methods, i.e., the HDT in combination with the C–K–Y–L, procedure can be powerful and helpful tools to assist decisions concerning design strategies.     

Possible Effects of Altered Growth Behaviour of Norway Spruce (Picea abies) on Carbon Accounting

Implementing the Kyoto Protocol necessitates precise and practical inventory methods for estimating the carbon reservoir in forests. An analysis of the German state North Rhine-Westphalia forest inventory data showed enormous deviations from the yield tables of Wiedemann (1936, 1942). Specifically the ratio of height/diameter at breast height was up to 30% lower than in the yield tables, which indicated wider annual rings and a lower basic density. Such differences most likely pose consequences for the calculation of the amount of carbon in these forests. In this study the aboveground green weight, moisture and the carbon content of fifteen 46-year old Norway spruces (Picea abies) were measured, and two approaches for calculating the aboveground carbon content of trees were discussed: the common methodology of applying expansion and conversion factors as well as using optimized regression equations. The average expansion factor deviated approximately 1.2% from the yield tables of Grundner and Schwappach (1906). The wood density was 368 kg/m³ and within the European scope of 320–420 kg/m³ (Bosshard, 1984; Hakkila, 1989; Knigge and Schulz, 1966; Trendelenburg and Mayer-Wegelin, 1955). The woody carbon content was found to be 50.42%, which corresponded well with reference values of 50.3% (Bosshard, 1984) and 51.4% (Knigge and Schulz, 1966). However, the average percentage of crown material carbon content was 0.75% higher than in the tree boles. This study demonstrated that the most reliable methodology for calculating aboveground tree carbon was a power regression function, which calculated the growing stock volume, converting it directly into tree carbon content. The results deviated by less than 1.3% (R² = 0.99) from the measured tree carbon. Using volume expansion factors and factors of basic density and carbon percentage, as in Burschel et al. (1993), the calculated results diverged –3.7% from the measured outcome. The adapted form according to Fang et al. (2001) deviated –1.2% (R² = 0.63) and the form following Brown and Schroeder (1999) about –2.5% (R² = 0.61) from the measured carbon of the sample trees. However, coefficients of variation from 12% and 13% for the presented algorithm illustrated that in reality the calculated carbon of single trees could diverge considerably from the model results.