R. Álvarez

XANES speciation of mercury in three mining districts – Almadén, Asturias (Spain), Idria (Slovenia)

The mobility, bioavailability and toxicity of mercury in the environment strongly depend on the chemical species in which it is present in soil, sediments, water or air. In mining districts, differences in mobility and bioavailability of mercury mainly arise from the different type of mineralization and ore processing. In this work, synchrotron-based X-ray absorption near-edge spectroscopy (XANES) has been taken advantage of to study the speciation of mercury in geological samples from three of the largest European mercury mining districts: Almadén (Spain), Idria (Slovenia) and Asturias (Spain). XANES has been complemented with a single extraction protocol for the determination of Hg mobility. Ore, calcines, dump material, soil, sediment and suspended particles from the three sites have been considered in the study. In the three sites, rather insoluble sulfide compounds (cinnabar and metacinnabar) were found to predominate. Minor amounts of more soluble mercury compounds (chlorides and sulfates) were also identified in some samples. Single extraction procedures have put forward a strong dependence of the mobility with the concentration of chlorides and sulfates. Differences in efficiency of roasting furnaces from the three sites have been found.

Arsenic pollution and fractionation in sediments and mine waste samples from different mine sites

A characterization of arsenic pollution and its associations with solid mineral phases in sediments and spoil heap samples from four different abandoned mines in Spain is performed. Three of them were mercury mines located in the same mining district, in the province of Asturias, and the other one, devoted to arsenic mining, is in the province of León. A sequential extraction procedure, especially developed for arsenic, was applied for the study of arsenic partitioning. Very high total arsenic concentrations ranging 300-67,000 mg·kg(-1) were found. Arsenic fractionation in each mine is broadly in accordance with the mineralogy of the area and the extent of the mine workings. In almost all the studied samples, arsenic appeared predominantly associated with iron oxyhydroxides, especially in the amorphous form. Sediments from cinnabar roasted piles showed a higher arsenic mobility as a consequence of an intense ore treatment, posing an evident risk of arsenic spread to the surroundings. Samples belonging to waste piles where the mining activity was less intense presented a higher proportion of arsenic associated with structural minerals. Nevertheless, it represents a long-term source of arsenic to the environment.

Asturian mercury mining district (Spain) and the environment: a review

Mercury is of particular concern amongst global environmental pollutants, with abundant contaminated sites worldwide, many of which are associated with mining activities. Asturias (Northwest of Spain) can be considered an Hg metallogenic province with abundant epithermal-type deposits, whose paragenetic sequences include also As-rich minerals. These mines were abandoned long before the introduction of any environmental regulations to control metal release from these sources. Consequently, the environment is globally affected, as high metal concentrations have been found in soils, waters, sediments, plants, and air. In this paper, a characterization of the environmental affection caused by Hg mining in nine Asturian mine sites is presented, with particular emphasis in Hg and As contents. Hg concentrations found in the studied milieu are similar and even higher than those reported in previous studies for other mercury mining districts (mainly Almadén and Idrija). Furthermore, the potential adverse health effects of exposure to these elements in the considered sites in this district have been assessed.

Hydraulic and Thermal Modelling of an Underground Mining Reservoir

Flooded mines are a groundwater reservoir that can be used geothermally. Modelling such a reservoir can be complicated because it is necessary to simultaneously solve the equations of flow and heat transport within the mine voids and the surrounding medium, whose hydraulic parameters may have been affected by mining. We present a numerical model developed for the reservoir formed by the Barredo and Figaredo shafts in the Central Coal Basin of Asturias (Spain), using FEFLOW software. Both 2- and 3-D versions of the model were used to simulate the flooding of the mine. They were calibrated by comparing the results with actual water levels measured during flooding. The hydrogeological and thermal characteristics of the reservoir were adjusted to predict the long-term temperature of the water under different scenarios of water extraction and injection.ZusammenfassungGeflutete Bergwerke bilden ein Grundwasserreservoir, welches geothermisch genutzt werden kann. Die Modellierung solcher Speicher ist jedoch kompliziert, da bei der Simulation Fließ- und Wärmetransportgleichungen sowohl in den Grubenhohlräumen als auch in den umgebenden Gesteinen gemeinsam gelöst werden müssen, wobei die hydraulischen Parameter zudem durch den Bergbau beeinflusst sind. Es wird ein numerisches Modell präsentiert, welches für das Grundwasserreservoir der Bergbaufelder von Barredo und Figaredo im zentralen Kohlebecken von Astriuas (Spanien) entwickelt worden ist. Sowohl 2-D als auch 3-D Versionen der Software FEFLOW wurden verwendet, um die Flutung des Untertagebergbaus nachzubilden. Die Modelle wurden kalibriert, indem die Modellergebnisse mit aktuellen Wasserständen während der Flutung verglichen wurden. Die hydrogeologischen und geothermischen Parameter des Reservoirs wurden angepasst, um langzeitliche Temperaturentwicklungen im Wasser bei verschiedenen Entnahme- und Injektionsszenarien vorherzusagen.ResumenLas minas inundadas constituyen un embalse de agua subterránea, del que se puede hacer un aprovechamiento geotérmico. Modelizar este tipo de embalses puede resultar complejo, ya que es necesario resolver simultáneamente las ecuaciones de flujo y transporte de calor en los huecos mineros y el medio circundante, cuyos parámetros hidrogeológicos pueden haber resultado afectados por la actividad minera. Se presenta un modelo numérico desarrollado para el embalse constituido por los pozos mineros Barredo y Figaredo en la Cuenca Carbonífera Central de Asturias (España), por medio del software FEFLOW. Se realizaron versiones del modelo en 2 y 3 dimensiones para simular la inundación de la mina, que fueron calibradas comparando los resultados con los valores reales de nivel de agua medidos durante dicha inundación. Las características hidrogeológicas y térmicas del embalse fueron ajustadas para predecir la temperatura a largo plazo del agua bajo diferentes escenarios de extracción de agua y reinyección.抽象闭坑(或废弃)淹没矿坑可用作提供地热的地下水库。由于需要同时求解矿坑及周围介质的水力学和热力学方程以及方程水文地质参数受矿坑严重影响,地下水库的水力与热力学数值模拟比较复杂。利用 FEFLOW建立了西班牙阿斯图里亚斯地区(Asturias)中央聚煤盆地(Central Coal Basin)Barredo井与Figaredo竖的地下水库模型。同时利用二维和三维模型模拟了矿坑淹没过程,用矿坑淹没期间实际观测水位进行了模型识别。地下水库模型经水文地质学及热力学特征校正后用以预测不同抽水、注水情形下的水温长期预测。

Hydrochemical characterization of a mine water geothermal energy resource in NW Spain

Abandoned and flooded mine networks provide underground reservoirs of mine water that can be used as a renewable geothermal energy source. A complete hydrochemical characterization of mine water is required to optimally design the geothermal installation, understand the hydraulic behavior of the water in the reservoir and prevent undesired effects such as pipe clogging via mineral precipitation. Water pumped from the Barredo-Figaredo mining reservoir (Asturias, NW Spain), which is currently exploited for geothermal use, has been studied and compared to water from a separate, nearby mountain mine and a river that receives mine water discharge and partially infiltrates into the mine workings. Although the hydrochemistry was altered during the flooding process, the deep mine waters are currently near neutral, net alkaline, high metal waters of Na-HCO3 type. Isotopic values suggest that mine waters are closely related to modern meteoric water, and likely correspond to rapid infiltration. Suspended and dissolved solids, and particularly iron content, of mine water results in some scaling and partial clogging of heat exchangers, but water temperature is stable (22°C) and increases with depth, so, considering the available flow (>100Ls-1), the Barredo-Figaredo mining reservoir represents a sustainable, long-term resource for geothermal use.

Prediction of the flooding of a mining reservoir in NW Spain.

Abandoned and flooded mines constitute underground reservoirs which must be managed. When pumping is stopped in a closed mine, the process of flooding should be anticipated in order to avoid environmentally undesirable or unexpected mine water discharges at the surface, particularly in populated areas. The Candín-Fondón mining reservoir in Asturias (NW Spain) has an estimated void volume of 8 million m3 and some urban areas are susceptible to be flooded if the water is freely released from the lowest mine adit/pithead. A conceptual model of this reservoir was undertaken and the flooding process was numerically modelled in order to estimate the time that the flooding would take. Additionally, the maximum safe height for the filling of the reservoir is discussed.

Soil pollution related to the mercury mining legacy at Asturias (Northern Spain)

Asturias (NW Spain) is regarded as an important metallogenic province with particular emphasis on mercury (Hg) and arsenic (As). Different Hg mineral species, as well as As-rich minerals, are found in the ore deposits in this part of Spain. Metallurgical activity to extract Hg from these ores was also carried out at many sites. Consequently, the combination of emissions during mining of the ore and additional releases during the inefficient roasting operation gave rise to significant releases of Hg and As to the surrounding soils. All the Hg mines of the district were abandoned before the introduction of any environmental regulations; consequently, the environment is globally affected. Mean Hg contents in soils range from 42 to 155 mg kg−1, whereas average As concentrations range from 17 to 831 mg kg−1.

Wetland-based passive treatment systems for gold ore processing effluents containing residual cyanide, metals and nitrogen species

Gold extraction operations generate a variety of wastes requiring responsible disposal in compliance with current environmental regulations. During recent decades, increased emphasis has been placed on effluent control and treatment, in order to avoid the threat to the environment posed by toxic constituents. In many modern gold mining and ore processing operations, cyanide species are of most immediate concern. Given that natural degradation processes are known to reduce the toxicity of cyanide over time, trials have been made at laboratory and field scales into the feasibility of using wetland-based passive systems as low-cost and environmentally friendly methods for long-term treatment of leachates from closed gold mine tailing disposal facilities. Laboratory experiments on discrete aerobic and anaerobic treatment units supported the development of design parameters for the construction of a field-scale passive system at a gold mine site in northern Spain. An in situ pilot-scale wetland treatment system was designed, constructed and monitored over a nine-month period. Overall, the results suggest that compost-based constructed wetlands are capable of detoxifying cyanidation effluents, removing about 21.6% of dissolved cyanide and 98% of Cu, as well as nitrite and nitrate. Wetland-based passive systems can therefore be considered as a viable technology for removal of residual concentrations of cyanide from leachates emanating from closed gold mine tailing disposal facilities.

Mercury Soil Pollution in Spain: A Review

Spain has been the main mercury producer worldwide, with mines or mining districts scattered across its geography. In particular, two main areas show generally higher contents of this element in the soils, namely, Asturias (or the Cantabrian Zone in geological terms) and the Almaden area in the Southern Central Iberian Zone. In this review six different aspects are considered: (1) distribution of total concentrations, (2) mercury mobility and availability, (3) soil to plant transfer, (4) mercury transfer to animal biota, (5) soil to atmosphere transfer and (6) possibility of remediation for sites polluted by mercury. The conclusions drawn from the available results highlight significant differences in contents, mobility and transfer processes depending on the different types of mercury pollution and different climatic conditions. A general background level for Spanish soils can be established at 20 μg kg−1, but very different ranges can be found in different areas according to the volumetric importance of each source and depending on other local factors. Mercury mining appears to be the most important source of soil pollution, and studies on the possible mobility and transfer to other environmental compartments demonstrate the highest levels at which mercury affects the population living in the proximity of such sources.

Environmental risk assessment of cobalt and manganese from industrial sources in an estuarine system

A total of 74 samples of soil, sediment, industrial sludge, and surface water were collected in a Mediterranean estuarine system in order to assess the potential ecological impact of elevated concentrations of Co and Mn associated with a Terephthalic (PTA) and Isophthalic (PIPA) acids production plant. Samples were analyzed for elemental composition (37 elements), pH, redox potential, organic carbon, and CaCO3 content, and a group of 16 selected samples were additionally subjected to a Tessier sequential extraction. Co and Mn soil concentrations were significantly higher inside the industrial facility and around its perimeter than in background samples, and maximum dissolved Co and Mn concentrations were found in a creek near the plant’s discharge point, reaching values 17,700 and 156 times higher than their respective background concentrations. The ecological risk was evaluated as a function of Co and Mn fractionation and bioavailability which were controlled by the environmental conditions generated by the advance of seawater into the estuarine system during high tide. Co appeared to precipitate near the river mouth due to the pH increase produced by the influence of seawater intrusion, reaching hazardous concentrations in sediments. In terms of their bioavailability and the corresponding risk assessment code, both Co and Mn present sediment concentrations that result in medium to high ecological risk whereas water concentrations of both elements reach values that more than double their corresponding Secondary Acute Values.