Spatial evolution of an AMD stream in the Iberian Pyrite Belt: process characterization and control factors on the hydrochemistry

This paper presents hydrochemical data of an AMD stream in the Iberian Pyrite Belt, obtained from its source, in the Poderosa Mine Portal, till its confluence at the Odiel River. The main objective is to establish potential interdependent relations between sulfate and metals’ loads and the following physical-chemical variables: pH, electric conductivity (EC), redox potential (EH), and dissolved oxygen (O2). All the parameters show a global increasing tendency since the tunnel’s exit to the confluence at Odiel River. The TDS and EC are two relevant exceptions. They behave similarly, showing a decreasing trend and a strong inflection that describes a minimum immediately after the discharging point. The spatial analysis combined with statistical tools put in evidence the typical AMD processes and the respective physical-chemical implications. Inputs with distinctive hydrochemical signatures impose relevant modifications in the Poderosa creek waters. This indicates low hydrochemical inertia and high vulnerability to external stimulus.Financial support for this research was provided by DGCICYT National Plan, project CGL2010-21268-C02-01 and the Andalusian Autonomous Government Excellence Projects, Project RNM-6570

Determination of Melanterite-Rozenite and Chalcanthite-Bonattite Equilibria by Humidity Measurements at 0.1 MPa

Melanterite (FeSO4•7H2O)-rozenite (FeSO4•4H2O) and chalcanthite (CuSO4•5H2O)-bonattite (CuSO4•3H2O) equilibria were determined by humidity measurements at 0.1 MPa. Two methods were used; one is the gas-flow-cell method (between 21 and 98 °C), and the other is the humidity buffer method (between 21 and 70 °C). The first method has a larger temperature uncertainty even though it is more efficient. With the aid of humidity buffers, which correspond to a series of saturated binary salt solutions, the second method yields reliable results as demonstrated by very tight reversals along each humidity buffer. These results are consistent with those obtained by the first method, and also with the solubility data reported in the literature. Thermodynamic analysis of these data yields values of 29.231 ± 0.025 and 22.593 ± 0.040 kJ/mol for standard Gibbs free energy of reaction at 298.15 K and 0.1 MPa for melanterite-rozenite and chalcanthite-bonattite equilibria, respectively. The methods used in this study hold great potential for unraveling the thermodynamic properties of sulfate salts involved in dehydration reactions at near ambient conditions

Secondary sulfate minerals associated with acid drainage in the eastern US: recycling of metals and acidity in surficial environments

Weathering of metal-sulfide minerals produces suites of variably soluble efflorescent sulfate salts at a number of localities in the eastern United States. The salts, which are present on mine wastes, tailings piles, and outcrops, include minerals that incorporate heavy metals in solid solution, primarily the highly soluble members of the melanterite, rozenite, epsomite, halotrichite, and copiapite groups. The minerals were identified by a combination of powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron-microprobe. Base-metal salts are rare at these localities, and Cu, Zn, and Co are commonly sequestered as solid solutions within Fe- and Fe–Al sulfate minerals. Salt dissolution affects the surfacewater chemistry at abandoned mines that exploited the massive sulfide deposits in the Vermont copper belt, the Mineral district of central Virginia, the Copper Basin (Ducktown) mining district of Tennessee, and where sulfide-bearing metamorphic rocks undisturbed by mining are exposed in Great Smoky Mountains National Park in North Carolina and Tennessee. Dissolution experiments on composite salt samples from three minesites and two outcrops of metamorphic rock showed that, in all cases, the pH of the leachates rapidly declined from 6.9 to \u3c3.7, and specific conductance increased gradually over 24 h. Leachates analyzed after 24-h dissolution experiments indicated that all of the salts provided ready sources of dissolved Al (\u3e30 mg L‒ 1), Fe (\u3e47 mg L‒ 1), sulfate (\u3e1000 mg L‒ 1), and base metals (\u3e1000 mg L‒ 1 for minesites, and 2 mg L‒ 1 for other sites). Geochemical modeling of surface waters, mine-waste leachates, and salt leachates using PHREEQC software predicted saturation in the observed ochre minerals, but significant concentration by evaporation would be needed to reach saturation in most of the sulfate salts. Periodic surface-water monitoring at Vermont minesites indicated peak annual metal loads during spring runoff. At the Virginia site, where no winter-long snowpack develops, metal loads were highest during summer months when salts were dissolved periodically by rainstorms following sustained evaporation during dry spells. Despite the relatively humid climate of the eastern United States, where precipitation typically exceeds evaporation, salts form intermittently in ope

Dynamic global-to-direct irradiance conversion models

This paper presents two models for converting hourly global into hourly direct beam irradiance based on a new parameterization of insolation conditions (Perez et al. 1990a). This parameterization does not require any additional input data than those already contained in a global irradiance time series but attempts to better utilize available information. The models are capable of using surface dew-point temperature as an additional input when this is available. The models are derived statistically from a large multiclimatic experimental data base. The two models differ technically but should be functionally equivalent: The first is a correction to the physically based DISC model(Maxwell 1987); the second consists of a set of simple linear relationships. Validation results are presented in reference to three existing models (Maxwell 1987; Erbs et al. 1982; Randall and Whitson 1977). The validation benchmarks consist of root mean square and mean bias errors as well as the ability of the models to recreate the skewness and kurtosis of actual direct irradiance distributions

Ethics and advance care planning in a culturally diverse society

Emerging international research suggests that in multicultural countries, such as Australia and the United States, there are significant disparities in end-of-life care planning and decision making by people of minority ethnic backgrounds compared with members of mainstream English-speaking background populations. Despite a growing interest in the profound influence of culture and ethnicity on patient choices in end-of-life care, and the limited uptake of advance care plans and advance directives by ethnic minority groups in mainstream health care contexts, there has been curiously little attention given to cross-cultural considerations in advance care planning and end-of-life care. Also overlooked are the possible implications of cross-cultural considerations for nurses, policy makers, and others at the forefront of planning and providing end-of-life care to people of diverse cultural and language backgrounds. An important aim of this article is to redress this oversight.<br /