wo-dimensional reactive transport modeling of the Maqarin Eastern Springs site, a natural analogue for the alteration of a fractured limestone by high-pH Portland cement waters, has been performed using the CrunchFlow code. These 2D calculations included transport by advection–dispersion–diffusion along a single fracture and diffusion in the wall rock. Solute transport was coupled to mineral dissolution and precipitation. A limited sensitivity analysis evaluated the effect of different values of primary mineral surface areas, flow velocity and sulfate concentration of the inflowing high-pH solution.
Major secondary minerals include ettringite–thaumasite, C–S–H/C–A–S–H and calcite. C–S–H/C–A–S–H precipitation is controlled by the dissolution of primary silicates. Ettringite precipitation is controlled by diffusion of sulfate and aluminum from the wall rock to the fracture, with aluminum provided by the dissolution of albite. Calcite precipitation is controlled by diffusion of carbonate from the wall rock. Extents of porosity sealing along the fracture and in the fracture-wall rock interface depend on assumptions regarding flow velocity and composition of the high-pH solution. The multiple episodes of fracture sealing and reactivation evidenced in the fracture infills were not included in the simulations. Results can qualitatively reproduce the reported decrease in porosity in the fractures and in the wall rock next to the fractures. Instances of porosity increase next to fractures caused by carbonate dissolution were not reproduced by the calculations.
Speciation is the process of evaluating the concentrations of all the species in a chemical system from equilibrium conditions and measured data such as total concentrations of components, electrical conductivity, pH, redox potential or gas partial pressure. It is essential for analyzing geochemical data and defining the chemical composition of waters for geochemical modeling problems like evaluating the chemical composition of evaporating, diluting, mixing waters or reactive transport. We present an algorithm that reduces estimation errors in chemical speciation calculations by means of the use of redundant data. Redundant data are measurements and assumptions that exceed the minimum required, and therefore are not strictly necessary, to speciate a water sample. The proposed method was compared with the classical speciation algorithm on two synthetic examples. Our results show that using redundant data improves speciation results reducing the estimation error between computations and measurements. In fact, the larger the amount of redundant data, the better the speciation in terms of errors of the estimated concentrations. (C) 2014 Elsevier Ltd. All rights reserved.
We studied the effects of evaporation and groundwater flow on the formation of salt minerals in the Sabkha of Oum El Khialate in South East Tunisia, which contains large amounts of sulfate sodium mineral deposits. Due to the fact that there are no important surface water bodies present in this sabkha, transport of solutes is dominated by advection rather than mixing in lakes. For our study we used both analytical conservative and numerical reactive transport models. Results showed that salinity varies with distance and may reach very high levels near a watershed where the groundwater flux is zero. As a consequence, reactive transport simulations results showed that more minerals precipitate and water activity decreases values near this watershed. Model results also showed that a sequence of precipitating minerals could be deduced after 140,000 years. From the boundary of the sabkha towards the watershed the mineral sequence was dolomite, gypsum, magnesite, bloedite, halite and mirabilite. It was found that the amounts as well as the mineral precipitation distribution strongly depend on salinity and rates of inflowing water. (C) 2014 Elsevier Ltd. All rights reserved.
A Human Health Risk Assessment (HHRA) was required for a closed landfill located in Cerdanyola del Valles (Barcelona, Spain). The FIHRA had two objectives, to evaluate the present risk of the identified receptors in the area and to safely develop the future urban planning of the area, therefore 3 scenarios for the current situation and 4 for the future situation were developed.; After reviewing the existing data and exploring the needs of information, the assessment in this study was focused on the measurement of volatile organic compounds (VOCs) fluxes from the subsoil (emission from the landfill at 5 points), concentrations of VOCs in the air (immission in 4 urban sites) and concentration of VOCs in soil-gas (measurements at 5 m below ground surface outside the landfill at 8 sites). Around 70 VOCs were analyzed by using multi-sorbent tubes and Thermal Desorption Gas Chromatography (TD-GC-MS). The VOCs that were detected and quantified include alkanes, aromatic hydrocarbons, alcohols, ketones, halocarbons, aldehydes, esters, terpenoids, ethers and some nitrogenated and sulfur compounds, furans and carboxylic acids. Specific mercury flux measurements were performed in a hot spot by using carulite tubes, that were also analyzed by using Thermal Decomposition, Amalgamation, and Atomic Absorption Spectrophotometry.; Results showed average values of volatile emission fluxes ranging from non-detected to 331 mu g m(-2) day(-1) (dichlorodifluoromethane). In the case of immission, the concentration of VOCs measured in the air of populated area surrounding the landfill ranged values from non-detected to 42.0 mu g m(-3) (acetic acid). The soil-gas measurements in piezometers around the landfill showed individual VOC values with a maximum 830 mu g m(-3) for dichlorodifluoromethane.; With the obtained fluxes and concentrations in air and soil-gas, USEPA methodology and modeling was used to evaluate equivalent concentration in the scenarios considered. Toxicity values from IRIS database were used to finally obtain chemical risk indicators. Admissible risk indicators were obtained in all scenarios. The VOCs that contributed more to risk indexes in RH2 were trichloroethylene, trimethylbenzene, chloroform, 1,2-dichloroethane and carbon tetrachloride. The carcinogenic risk in RH7 was linked to the presence of benzene and chloroform. The comparison of the measurements of the present work with other landfills evidence that HHRA in ambient air would be needed in order to perform a correct landfill management. (c) 2014 Elsevier Ltd. All rights reserved.
Gimenez, F.; De Pablo, J.; Casas, I.; Martinez, X.; Rovira, M.; Martinez, A. Applied geochemistry Vol. 49, p. 42-45 DOI: 10.1016/j.apgeochem.2014.07.004 Data de publicació: 2014-10-01 Article en revista
The knowledge of the characteristics of the U(VI)-peroxide chemical system is of importance because of the relevance of the uranyl peroxide solid phases studtite (UO2O2 center dot 4H(2)O) or metastudtite (UO2O2 center dot 2H(2)O) as uranyl secondary solid phases during the leaching of the spent nuclear fuel as well as to the formation in alkaline waters of soluble nanoscale uranyl peroxo cage clusters. In this work, the solubility of studtite was determined for the first time as a function of pH (from 3 to 11) by means of studtite undersaturation experiments. The results obtained showed a V-shaped solubility curve, which was modelled considering the uranyl complexes formation constants (database of the Nuclear Energy Agency, NEA) and recently published formation constants of uranium hydroxo-peroxo-complexes. The best fit of the model to the experimental solubility data was obtained with log K-sO = -2.7 +/- 0.2 for the studtite solubility reaction:; UO2O2 center dot 4H(2)O(s) + 2H(+) reversible arrow UO22+ + 4H(2)O + H2O2; On the other hand, the so-called immersion methodology was used in order to determine the pH(pzc) of studtite, which resulted to be 4.0 +/- 0.2. This value would corroborate a sorption mechanism based on electrostatic interactions described for previously published sorption data of cations (Cs+, Sr2+) on studtite. (c) 2014 Elsevier Ltd. All rights reserved.
The integrated use of hydrogeologic and multi-isotopic approaches (d15N, d18ONO3, d34S, d18OSO4 and d13CHCO3) was applied in the Selva basin area (NE Spain) to characterize NO -3 and SO-2 -4 sources and to
evaluate which geochemical processes affect NO -3 in groundwater. The studied basin is within a basinand-range physiographic province where natural hydrodynamics have been modified and different scale flow systems converge as a consequence of recent groundwater development and exploitation rates. As a result, groundwaters related to the local recharge flow system (affected by anthropogenic activities) and to the generally deeper regional flow system (recharged from the surrounding ranges) undergo mixing processes. The d15N, d18ONO3 and d34S indicated that the predominant sources of contamination in the basin are pig manure and synthetic fertilizers. Hydrochemical data along with d15N, d18ONO3, d34S, d18OSO4 and d13CHCO3 of some wells confirmed mixing between regional and local flow systems. Apart from dilution processes that can contribute to the decrease of NO -3 concentrations, the positive correlation
between d15N and d18ONO3 agreed with the occurrence of denitrification processes. The d34S and d18OSO4 indicated that pyrite oxidation is not linked to denitrification, and d13CHCO3 did not clearly point to a role of organic matter as an electron donor. Therefore, it is proposed that the mixing processes between deeper regional and local surface groundwater allow denitrification to occur due to the reducing conditions of the regional groundwater. Thus, isotopic data add useful complementary information to
hydrochemical studies, especially in those areas where hydrochemical data is not conclusive.
Martinez, L.; Dentz, M.; Carrera, J.; Fernandez, D.; Nardi, A.; Saaltink, M. Applied geochemistry Vol. 27, num. 2, p. 479-489 DOI: 10.1016/j.apgeochem.2011.09.016 Data de publicació: 2012-02 Article en revista
Caraballo, M.; Roetting, T.; Macias, F.; Nieto, J.M.; Ayora, C. Applied geochemistry Vol. 24, num. 12, p. 2301-2311 DOI: 10.1016/j.apgeochem.2009.09.007 Data de publicació: 2009-12-01 Article en revista
Roetting, T.; Serrano, J.; Caraballo, M.; Ayora, C.; Carrera, J. Applied geochemistry Vol. 23, num. 6, p. 1660-1674 DOI: 10.1016/j.apgeochem.2008.02.023 Data de publicació: 2008-06-01 Article en revista
Rey, A.; Gimenez, F.; Casas, I.; Clarens Blanco, F.; De Pablo, J. Applied geochemistry Vol. 23, num. 8, p. 2249-2255 DOI: 10.1016/j.apgeochem.2008.03.008 Data de publicació: 2008-04-08 Article en revista
he dissolution of UO2 (a chemical analog of uraninite and of spent nuclear fuel) has been studied by using a flow-through reactor. The UO2 dissolution rates at total View the MathML source concentrations of 10−4, 10−5, and 10−6 mol dm−3 have been determined to be: 1.3 × 10−10 mol m−2 s−1, 6.7 × 10−11 mol m−2 s−1, and 2.0 × 10−11 mol m−2 s−1, respectively. The dissolution rates determined are found to be higher than the ones determined for similar carbonate concentrations. Moreover, the surface of the UO2 has been studied in static tests by means of the scanning force microscopy technique (SFM) in order to follow the formation of any secondary solid phase on its surface. The formation of chernikovite (H2(UO2)2(PO4)2 · 8H2O) has been observed at a 10−4 M total View the MathML source concentration, while no uranyl-phosphate secondary phases have been found at lower View the MathML source concentrations. In experiments performed in the presence of both carbonate and phosphate, no precipitation of secondary phases has been observed. It is postulated that this is due to the formation of the highly stable uranyl-carbonate complexes in solution.
Smelting slags associated with base-metal vein deposits of the Sierra Almagrera area (SE Spain) show high concentrations
of Ag (<5–180 ppm), As (12–750 ppm), Cu (45–183 ppm), Fe (3.2–29.8%), Pb (511–2150 ppm), Sb (22–620 ppm) and Zn (639–8600 ppm). The slags are mainly composed of quartz, fayalite, barite, melilite, celsian, pyrrhotite, magnetite, galena and Zn–Pb–Fe alloys. No glassy phases were detected. The following weathering-related secondary phases were found: jarosite–natrojarosite, cotunnite, cerussite, goethite, ferrihydrite, chalcanthite, copiapite, goslarite, halotrichite and szomolnokite. The weathering of slag dumps near the Mediterranean shoreline has contaminated the soils and groundwater, which has caused concentrations in groundwater to increase to 0.64 mg/L Cu, 40 mg/L Fe, 0.6 mg/L Mn, 7.6 mg/L Zn, 5.1 mg/L Pb and 19 lg/L As. The results of laboratory leach tests showed major solubilization of Al (0.89–12.6 mg/L),
Cu (>2.0 mg/L), Fe (0.22–9.8 mg/L), Mn (0.85–40.2 mg/L), Ni (0.092–2.7 mg/L), Pb (>2.0 mg/L) and Zn (>2.5 mg/L), and mobilization of Ag (0.2–31 lg/L), As (5.2–31 lg/L), Cd (1.3–36.8 lg/L) and Hg (0.2–7 lg/L). The leachates were modeled
using the numerical code PHREEQC. The results suggested the dissolution of fayalite, ferrihydrite, jarosite, pyrrhotite,
goethite, anglesite, goslarite, chalcanthite and cotunnite. The presence of secondary phases in the slag dumps and contaminated soils may indicate the mobilization of metals and metalloids, and help to explain the sources of groundwater contamination.