Nieves Roqueñí

Occurrence and speciation of arsenic and mercury in estuarine sediments affected by mining activities (Asturias, northern Spain)

Sediments contaminated by Hg and As from two historical mining areas have been deposited in the Nalón estuary (Asturias, northern Spain) since 1850. Total mercury (Hgtotal) concentrations in the sediments range from 0.20 μg g-1 to 1.33 μg g-1, most of it in the form of sulphides. Concentrations of methylmercury (303.20-865.40 pg g-1) are up to two orders of magnitude lower than the concentration of Hgtotal. Total As concentration (Astotal) is enriched compared to the background level for the area. The relative abundance of As(V) on As(III) in the sediments ranges from 97.6% to 100%, whereas inorganic Hg accounts for more than 99% of the total Hg. The occurrence of the most toxic species, inorganic As(III) and organic methylmercury, seem to be related to redox conditions together with the amounts of sulphur which act as natural barriers which inhibit the biological and chemical speciation processes. Despite the high amounts of Hg and As present in the sediments, their transference to the water column appear to be limited thus converting sediments in an effective sink of both elements. Special attention should be paid to potential variations of the environmental conditions which might increase the element mobility and exchange between sediments and the water column.

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.

Seasonal and spatial distribution of mercury in stream sediments from Almadén mining district

The spatial and temporal distributions of Hg in different fractions of sediment samples from the Valdeazogues River (Almadén) were investigated. Almadén is widely known as the worlds largest Hg mining district. A total of nine sites during six time periods were monitored using a BCR (Community Bureau of Reference) sequential extraction procedure. The results showed that Hg is mainly present as residual cinnabar but there is another important organic fraction in which Hg is primarily incorporated. Higher proportions of Hg in the residual fraction were found in wet seasons, while the opposite is true in the organic fraction. The exchangeable/carbonate and Fe-Mn oxide phases are the minor Hg fractions, and they were found less susceptible to seasonal changes. The potential risk for the aquatic medium was evaluated based on the proportions of non-residual (exchangeable/carbonate + Fe-Mn oxides + organic) fractions. The high proportions of Hg potentially (bio)available, together with the Hg total concentrations, indicated an important risk, especially in areas close to the mines. Although the risk is important in all seasons, it is particularly noticeable during dry periods due to the increase in the organic fraction, which may favor potential transference from the sediments to the environment due to the physic-chemical river conditions.

Incidence of the Almadén historical mining district on the hydrochemical characteristics of Valdeazogues Basin (Spain)

The distribution of dissolved potentially harmful elements (PHEs), major ions and physico-chemical parameters in the Valdeazogues river basin was studied during 9 surveys, carried out between 2010 and 2013. The observed physico-chemical parameters depend on the season, the major ions depend of the nature of the lithological materials and the PHEs depend of the characteristics of the mine inputs. The Principal Component Analysis performed on the analysed dataset, distinguished the sources of contaminants introduced into waters and that nowadays mine runoffs play a role higher than the played by the natural inputs.