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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jenvman.2005.12.005 Byline: Biswajit Mukhopadhyay (a), Jon Sundquist (b), Rodney J. Schmitz (c) Keywords: Electrochemical process; Hexavalent chromium; Groundwater contamination; Groundwater remediation Abstract: The conventional chemical reduction-precipitation technique in the removal of Cr(VI) from contaminated groundwater involves a two-step process whereby Cr(VI) is first reduced to Cr(III) at an acidic pH by a reducing agent and in a subsequent step, Cr(III) is precipitated as insoluble hydroxide at an alkaline pH. In a variation of this method, Fe(II) is added electrochemically to the Cr(VI) containing water. From a pure iron electrode, Fe.sup.2+ ions are released into the solution and bring forth the reduction of Cr(VI). At the cathode, H.sub.2O is reduced whereby the OH.sup.- ions entering the solution keep the pH of the solution in the alkaline range. This latter fact greatly facilitates simultaneous reduction of Cr(VI) to Cr(III) and co-precipitation of hydroxides of trivalent Cr and Fe. On the basis of a set of experimental data, it is shown that this process is both thermodynamically and kinetically efficient, meaning, with the electrochemical method, rapid and nearly complete removal of Cr(VI) from a groundwater source with both high and low levels of Cr-contamination can be achieved. These factors make the electrochemical process superior to the conventional chemical process in remediation of Cr-contaminated groundwater. Author Affiliation: (a) Ecology and Environment, Inc. 1412 Main Street, Dallas, TX 75202, USA (b) Ecology and Environment, Inc. 368 Pleasantview Drive, Lancaster, NY 14086, USA (c) Andco Environmental Processes, Inc. 595 Commerce Drive, Buffalo, NY 14228, USA Article History: Received 18 January 2005; Revised 24 October 2005; Accepted 13 December 2005

The garnet-biotite geothermometer has been recalibrated using recently obtained Margules parameters for iron-magnesium-calcium garnet, Mn interactions in garnet, and Al interactions in biotite, as well as the Fe oxidation state of both minerals. Fe-Mg and [Delta][W.sub.Al] Margules parameters for biotite have been retrieved by combining experimental results on [6]Al-free and [6]Al-bearing biotite using statistical methods. Margules parameters, per mole of biotite are [Mathematical Expression Omitted], [Mathematical Expression Omitted], [Mathematical Expression Omitted]. Based on this model, the exchange reaction [Delta]H is 41952 J/mol and [Delta]S is 10.35 J/(K mol). Estimated uncertainty for this geothermometer is 25 [degrees] C. This geothermometer was tested on two data sets. The first consisted of 98 specimens containing garnet and biotite from west-central Maine, which formed under reducing [f.sub.[O.sub.2]] with graphite, a limited range of P ([approximately] 3 to 4.5 kbar), and a moderate range in T ([approximately] 550-650 [degrees] C), and which were all analyzed on a single microprobe using the same standards. Results indicate that the Maine staurolite zone averages 574 [degrees] C compared with 530 [degrees] C previously calculated and that the muscovite-breakdown T is consistent with experimental data. The second set consisted of cordierite-garnet granulites without hypersthene from Ontario. Results here suggest an average T of 662 [degrees] C, compared with significantly lower or higher Ts calculated from other geothermometers. This model reproduces the Perchuk and Lavrent'eva (1983) experimental Ts with a standard deviation of 12 [degrees] C and discriminates the assemblages in the Maine data set better than other models.

At present the most widely used models of thermodynamic mixing properties of garnet are those that are optimized to fit the experimental phase-equilibrium data along various binary garnet joins using the method of mathematical programming. We conducted a thorough weighted regression analysis of the available volumetric, calorimetric, and phase-equilibrium data. This resulted in a much improved set of a-X relationships with the following Margules parameters (in joules, kelvins, bars). [Mathematical Expression Omitted], [Mathematical Expression Omitted], [Mathematical Expression Omitted], [Mathematical Expression Omitted], [Mathematical Expression Omitted], [Mathematical Expression Omitted] (all pfu containing 12 O atoms). The robust regression analyses allowed us to obtain the uncertainties associated with each of the parameters, quantities not available by mathematical programming analysis of phase-equilibrium data. Uncertainty estimates are essential for rigorous quantification of errors associated with mineralogic thermobarometers. From the probabilistic model developed here, we present detailed formulations for ascertaining errors of activity coefficients of the end-member components in any garnet solid solution. This provides an opportunity to evaluate the uncertainties in mineralogic thermobarometers involving garnets of compositions dissimilar to those used in the experiments on which the garnet mixing models are based. The results of this study elicit several significant points. The analysis strongly suggests that there is an excess entropy of mixing along the Fe-Mg join because Fe-Mg mixing in garnet is substantially nonideal. The excess entropy of mixing along the Ca-Mg and Ca-Fe joins is asymmetric and therefore assumption of a large symmetric entropy parameter or no entropy along these joins is an oversimplification. Large uncertainty in the mixing properties exists for Ca-rich garnets. There should be a Ca-Mg-Fe ternary interaction parameter (7110 J/mol).

A self-consistent set of thermodynamic data for common staurolite is developed. In the data end-member molar volume, specific heat, and calorimetric entropy are based on the previous results. Trial and error method is used for enthalpy and entropy retrieval. Compositional data including H ion concentration is not available for the staurolite. Staurolite equilibrium can be calculated using this set of improved data.

Energy Fe-end member reaction depicts a positive dp/dT slope and its position is related to the water content of the equilibrium cordierite. The anhydrous breakdown curve has been constructed based on the determination of H2O content. The P-T position of the anhydrous curve varies depending on the context of H2O, which has been maximized and experimentally verified to be unity.

Pressure-temperature (P-T) information is obtained by the study of pelitic rocks during tectonism and the movement of metamorphic fluids through the accurate methods of geothermobarometry. Thermodynamic databases, crystal structure determination, site assignments and analyses of positively charged ferrous ions and light elements for many minerals within a petrogenetic context have been developed.

A reevaluation of the results of studies conducted on the stability relations of andalusite since 1966 indicate that experimental difficulties are encountered due to difficulties in measuring small amounts of reaction, the effect of fibrous sillimanite and intergrown quartz, and the effect of Fe3+ impurities in the elevated sillimanite. The analysis also show valid, self-consistent reversals and half-reversals for the kyanite = andalusite and andalusite = kyanite systems.

The relationship between unit-cell parameters and composition was examined. Unit-cell parameters from 22 natural staurolite samples were expressed as linear chemical composition functions using multiple linear regression and according to two models. In Model A, ions substituting for each other at the T2 site and predicting unit-cell volume to 0.3 angstrom were examined. In Model B examined all major ions and put cell volume at 0.45 angstrom. Model A constants could be used to produce estimates of natural and chemical end-member staurolite unit cell parameters and molar volumes.

Quantitative measures of adiabatic lapse rate, equilibrium line altitude (ELA), and accumulation-area ratio (AAR) are important to understand the hydrological processes and conduct hydrological modeling in a highly glaciated watershed. We present a detailed analysis of temperature data from 21 climatic stations, hypsometric analyses of glacier distributions, and a method to analyze ablation gradients and runoff curves concurrently to quantify these parameters for the watersheds of the Upper Indus Basin (UIB), with 15,062 km2 of glacierized area and an elevation range of 361-8,611 m. We show that the ELA varies considerably from one watershed to another, implying a highly variable upper elevation limit up to which melting of snows and glaciers takes place throughout the basin. This is in sharp contrast to the assertions made by previous researchers. We show that the ELA is as low as 4,840 m in Astore watershed and it is as high as 6,200 m in Shyok watershed. In accordance with the variation of ELA, the AAR also varies considerably from one watershed to another. It is as low as 0.10 in Gilgit and as high as 0.65 in Zanskar watersheds. We ascribe 15-20% uncertainty to these estimates of ELA and AAR in UIB. [ABSTRACT FROM AUTHOR]

Satellite-geodetic altimetry investigations in the Karakoram have indicated slight mass gain or loss of the glaciers during the early part of 21st century. Equivalent discharge in the upper Indus Basin due to these mass changes has been estimated at 5 to 10% of mean annual flow. However, satellite altimetry and geodetic glacier mass estimates in the extreme topography of the Karakoram have not yet been counter-validated by hydrological analysis. Therefore, we present a first cross validation of three to five decades of river flow data from the three major watersheds in the Karakoram, with matching series of monthly precipitation, temperature, and evaporation provided by six atmospheric reanalysis products for 1979-2014. The analyses suggest that in most cases river flows have been increasing steadily from the end of the 1960s and 1970s to the middle of the 1990s and have stabilized or are in decline since then. Hunza watershed in Karakoram West shows consistently declining flows over the first half of the analysis period and stable flows during the second half for most of the summer melting season, suggesting mass accumulation. Rising river flows in the Shyok and Shigar watersheds, followed by stabilizing or slightly declining flows from 1995 onward, can be explained by consistently increasing precipitation during the first half of the analysis period, and successive stabilization or minor decline thereof. Flow data do not necessarily suggest considerable loss or gain of glacial mass in the Karakoram during the late 90s and early 2000s as suggested by satellite-based altimetry studies. [ABSTRACT FROM AUTHOR]

In this paper, we present and discuss our new WSi–WSiN–Pt metallization scheme for SiC-based microsystems for applications in harsh environments. Stoichiometric material WSi was selected as contact material for SiC. The diffusion barrier material WSiN was deposited from the same target as the contact material in order to limit the number of different chemical elements in the scheme. Our scheme was kept as simple as possible regarding the number of layers and chemical elements. Our scheme shows very good long-term stability and suitability for SiC-based microsystems. The experimental evaluation concept used here includes a combination of physical, electrical, and mechanical analysis techniques. This combined advance is necessary since modern physical analysis techniques still offer only limited sensitivity for detecting minimal changes in the metallization scheme. [ABSTRACT FROM AUTHOR]

Water resource in Upper Indus Basin is highly vulnerable to climate change because seasonal snows and glacial melts are the principal components (70%) of river flows in this basin. Here, we apply the concept of Boltzmann–Shannon entropy to long-term discharge records along the main stem of the Upper Indus and its most important tributary Shyok River to determine the relative stability of flows in the four main seasons of the basin. Spring flows are most unstable possibly due to variations in onset of snow melting time in a changing climate. Summer flows, which account for bulk of the annual flows, have remained relatively stable, indicating general stability of the cryosphere of the basin during the past six decades. We draw support of this conclusion from observation of the trend of long-term time series (1962–2013) of summer inflows at the Tarbela reservoir located at the outlet of Upper Indus Basin. Within the summer flow regime, August flows show greatest instability possibly due to changing rate of production of glacial melts under a changing climate. Upper Indus flows are stabilized by flows from the Karakoram where glaciers have either mostly remained stable or gained mass slightly in the recent decades in spite of widespread glacier wastage or ice losses in the western Himalayas. The approach presented here can be used to determine predictabilities of monthly and seasonal flows in water resources management and planning challenged by changes in climate and by land and water usage in concert with economic and social changes. [ABSTRACT FROM PUBLISHER]