Alteration kinetics of natural stones due to sodium sulfate crystallization: can reality match experimental simulations?

Salt decay is a very destructive mechanism that affects frequently the porous building materials of our architectural heritage. Sodium sulfate is one of the salts found in this context. It usually demonstrates high destructive power in salt crystallization tests because it can crystallize not only during evaporative processes but also when the temperature drops or when the salt solution comes into contact with pre-existing crystals. However, the use of extreme temperatures or successive wet/dry cycles also makes these tests unrepresentative of reality. To verify whether sodium sulfate can also be so destructive in field conditions, we have performed crystallization tests consisting of a single isothermal drying event. Three natural stones, relevant for the architectural heritage, were used for the purpose: Bentheimer sandstone, Ançã limestone, and a current Portuguese limestone of low porosity. The stones gave rise to distinct salt decay patterns: efflorescence, multilayer delamination and unilayer delamination, respectively. These morphological alterations were characterized at the micrometer scale by a new method based on what we have called the alteration kinetics curve. Such curve is calculated from topographic profiles obtained by a non-contact optical technique. The multilayer and unilayer delamination decay were also monitored by time-lapse photography. The work led us to conclude that sodium sulfate can indeed be also very destructive in field-representative conditions. Moreover, it showed that the optical method can be a valuable aid in the development of more realistic salt crystallization tests.     

Influence of geology in the geochemistry signature of Itacolomi State Park waters,Minas Gerais-Brazil

In all geological scenarios, mineral water reactions will affect the water chemistry. As such, water resources in different rocks commonly involve different hydrogeological compartments. The aim of this work is to evaluate the influence of geology in the geochemistry signature of Itacolomi State Park waters. To do so, a survey of the geological units in the area was carried out, a geological/stratigraphic division was made, and its correlation with the main geological events was determined. Using the advantages of GIS, all the catchments were delimited. Based on this division, near 30 stream and lake segments were chosen for analyses. In each point, all physiochemical properties of the water were measured, and samples were collected to determine the concentrations of major and trace elements by ICP–OES. The dynamics of the Itacolomi State Park rock-soil and stream water solutions suggest that mixing of drainage waters from different bedrock and soil sources regulates stream water physical–chemical parameters and solute concentrations. The analytical data showed a clear correlation between the chemical compositions of the solute and the geological characteristics of the catchment. Units that are covered by iron oxide hardpan (Manso unit) and iron-banded formations (Custódio unit) show a large amount of soluble elements, including high values of Fe and Mn. On the other hand, the presence of high values of Al and K (Itacolomi unit) are a direct consequence of the presence of quartzite associated with low pH values.     

The behavior of arsenic and antimony at Pezinok mining site,southwestern part of the Slovak Republic

Arsenic and antimony contamination is found at the Pezinok mining site in the southwest of the Slovak Republic. Investigation of this site included sampling and analysis of water, mineralogical analyses, sequential extraction, in addition to flow and geochemical modeling. The highest dissolved arsenic concentrations correspond to mine tailings (up to 90,000 μg/L) and the arsenic is present predominately as As(V). The primary source of the arsenic is the dissolution of arsenopyrite. Concentration of antimony reaches 7,500 μg/L and its primary source is the dissolution of stibnite. Pore water in mine tailings is well-buffered by the dissolution of carbonates (pH values between 6.6 and 7.0) and arsenopyrite grains are surrounded by reaction rims composed of ferric iron minerals. Based on sequential extraction results, most solid phase arsenic is in the reducible fraction (i.e. ferric oxyhydroxides), sulfidic fraction, and residual fraction. Distribution of antimony in the solid phase is similar, but contents are lower. The principal attenuation mechanism for As(V) is adsorption to ferric oxide and hydroxides, but the adsorption seems to be limited by the competition with Sb(V) produced by the oxidation of stibnite for adsorption sites. Water in mine tailings is at equilibrium with gypsum and calcite, but far from equilibrium with any arsenic and antimony minerals. The concentrations of arsenic and antimony in the surrounding aquifer are much lower, with maximum values of 215 and 426 μg/L, respectively. Arsenic and antimony are transported by ground water flow towards the Blatina Creek, but their loading from ground water to the creek is much lower compared with the input from the mine adits. In the Blatina Creek, arsenic and antimony are attenuated by dilution and by adsorption on ferric iron minerals in stream sediments with resulting respective concentrations of 93 and 45 μg/L at the site boundary south of mine tailing ponds.     

Spectral dependence on the correction factor of erythemal UV for cloud,aerosol, total ozone,and surface properties: A modeling study

Radiative transfer model simulations were used to investigate the erythemal ultraviolet(EUV) correction factors by separating the UV-A and UV-B spectral ranges. The correction factor was defined as the ratio of EUV caused by changing the amounts and characteristics of the extinction and scattering materials. The EUV correction factors(CFEUV) for UV-A[CFEUV(A)] and UV-B [CFEUV(B)] were affected by changes in the total ozone, optical depths of aerosol and cloud, and the solar zenith angle. The differences between CFEUV(A) and CFEUV(B) were also estimated as a function of solar zenith angle, the optical depths of aerosol and cloud, and total ozone. The differences between CFEUV(A) and CFEUV(B) ranged from-5.0% to 25.0% for aerosols, and from-9.5% to 2.0% for clouds in all simulations for different solar zenith angles and optical depths of aerosol and cloud. The rate of decline of CFEUV per unit optical depth between UV-A and UV-B differed by up to 20% for the same aerosol and cloud conditions. For total ozone, the variation in CFEUV(A) was negligible compared with that in CFEUV(B) because of the effective spectral range of the ozone absorption band. In addition, the sensitivity of the CFEUVs due to changes in surface conditions(i.e., surface albedo and surface altitude) was also estimated by using the model in this study. For changes in surface albedo, the sensitivity of the CFEUVs was 2.9%–4.1% per 0.1 albedo change,depending on the amount of aerosols or clouds. For changes in surface altitude, the sensitivity of CFEUV(B) was twice that of CFEUV(A), because the Rayleigh optical depth increased significantly at shorter wavelengths.     

The measurement of coal porosity with different gases

Sorption processes can be used to study different characteristics of coal properties, such as gas content (coalbed methane potential of a deposit), gas diffusion, porosity, internal surface area, etc. Coal microstructure (porosity system) is relevant for gas flow behaviour in coal and, consequently, directly influences gas recovery from the coalbed.This paper addresses the determination of coal porosity (namely micro- and macroporosity) in relation to the molecular size of different gases. Experiments entailed a sorption process, which includes the direct method of determining the “void volume” of samples using different gases (helium, nitrogen, carbon dioxide, and methane). Because gas behaviour depends on pressure and temperature conditions, it is critical, in each case, to know the gas characteristics, especially the compressibility factor.The experimental conditions of the sorption process were as follows: temperature in the bath 35 °C; sample with moisture equal to or greater than the moisture-holding capacity (MHC), particle size of sample less than 212 μm, and mass ca. 100 g.The present investigation was designed to confirm that when performing measurements of the coal void volume with helium and nitrogen, there are only small and insignificant changes in the volume determinations. Inducing great shrinkage and swelling effects in the coal molecular structure, carbon dioxide leads to “abnormal” negative values in coal void volume calculations, since the rate of sorbed and free gas is very high. In fact, when in contact with the coal structure, carbon dioxide is so strongly retained that the sorbed gas volume is much higher than the free gas volume. However, shrinkage and swelling effects in coal structure induced by carbon dioxide are fully reversible. Methane also induces shrinkage and swelling when in contact with coal molecular structure, but these effects, although smaller than those induced by carbon dioxide, are irreversible and increase the coal volume.     

Paleoenvironmental dynamics in central-eastern Brazil during the last 23 000 years: tropical peatland record in the Cerrado biome

The Cerrado biome is the second largest in Brazil, but the evolution of the Cerrado during the late Quaternary is not yet fully known. This study identifies paleoenvironmental changes during the last 23 000 years, based on a tropical mountain peatland record, in the Serra do Espinhaço Meridional in central-eastern Brazil. A multi-proxy approach was used that involved palynological analysis, stable isotopes (δ¹³C, δ¹⁵N), geochemistry, radiocarbon dating and multivariate statistics derived from a peatland core from Rio Preto (Minas Gerais state). The study reveals a very humid and cold climate during the late Pleistocene, with an increase in temperature and decrease in humidity at the Pleistocene–Holocene transition. During this period there was strong instability in the landscape (episodes of erosion). At the beginning of the Holocene there was a reduction in humidity with greater landscape stability. The current sub-humid climatic conditions seem to have been established in the mid-/late Holocene, with periods of landscape instability. Our findings agree with other Cerrado records that contradict previously established hypotheses, such as the Amazonian Refuge and the Pleistocene Arc.     

AsteroFLAG: First results from hare‐and‐hounds Exercise #1

We report on initial results from the first phase of Exercise #1 of the asteroFLAG hare and hounds. The asteroFLAG group is helping to prepare for the asteroseismology component of NASA's Kepler mission, and the first phase of Exercise #1 is concerned with testing extraction of estimates of the large and small frequency spacings of the low‐degree p modes from Kepler‐like artificial data. These seismic frequency spacings will provide key input for complementing the exoplanet search data. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)