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In the salth-marshes of the Tinto River (Huelva estuary, SW Spain), are stored in stacks around 100 Mt of PG, covering a surface of 1000 ha without any type of isolation, which produce an important impact in the surrounding environment. On the other hand, this ecosystem it is affected by acid mine drainage (AMD) from sulphide mines located upstream the Tinto River. The aim of this study is to evaluate the deep pollution of the underlain salt-marsh sediments due to leachates from the PG stacks. For that purpose, 7 cores were collected from zones 2 and 3 of the stacks, and PG and salt-marsh sediments samples from different depths were analyzed. The physicochemical parameters, mineralogy, granulometry and the concentration of the main elements of interest were determined in the samples. Most analysed salt-marsh sediments are not affected by PG stacks pollution, because sediments act as a “barrier” for the leachates from the PG, concentrating the contaminants in the first decimetres (0.5 m) under PG-sediments contact, and the deep infiltration is very limited. The obtained results suggest that the perimeter channel which is projected to build in the restauration project, should has a depth of 1 m below the level of the PG stacks for assuring the complete collection of leachates from the stacks, and avoid their liberation into the Tinto River estuary. more...

The Odiel and Tinto rivers show singular characteristics due to the significant acid mine drainage (AMD) generated in the first section of their basins and the phosphogypsum (PG) stacks located on their common estuary. AMD leads to low pH and high redox potential, which keep high amounts of toxic elements and radionuclides in dissolution. The objective of this work was to analyse the seasonal evolution of U-Th isotopes and 210Po in these rivers and the estuarine mixing zone. Four sampling points were selected (a fluvial point and an estuarine one for each river) and water samples were collected monthly throughout a year. The concentrations of natural radionuclides in the dissolved and particulate phases were determined by alpha spectrometry. The Odiel and Tinto rivers show concentrations of U-Th isotopes and 210Po from one to three orders of magnitude higher than background continental waters due to the strong effect of AMD, and 234U/238U activity ratios up to 2. The studied radionuclides show a clear seasonal behaviour in these rivers, with three different stages during the year: (1) concentration peaks observed during November and December due to the “washing effect” produced by the first rainfalls of the hydrological year, (2) a “dilution effect” by runoff in the rainy winter, and (3) a progressive “concentration effect” during the spring and summer. A non-conservative behaviour of the analysed radionuclides in the estuaries was demonstrated due to precipitation processes produced by the increase of pH. The polluted outflows from the PG stacks located in the Tinto estuary produce a significant radioactive impact, mainly during the rainiest months, increasing the concentration of U-isotopes and 210Po in the particulate phase. more...

This paper addresses the behaviour of several technology critical metals (TCMs), i.e., rare earth elements (REEs), Y, Sc, Ga and Tl, in the Tinto River (SW Spain), quantifying their fluxes to the Atlantic Ocean and unravelling the governing geochemical processes controlling their solubility. To accomplish this goal, a high-resolution (2–24 h) sampling was performed during the hydrological year 2017/18. Mean dissolved concentrations of 380 μg/L of REE, 99 μg/L of Y, 15 μg/L of Sc, 9.2 μg/L of Ga and 4.8 μg/L of Tl were found. Most TCMs followed a behaviour similar to that of sulphate and base metals throughout the year, exhibiting a quasi-conservative behaviour due to acidic conditions. However, dissolved Tl concentrations seem to be strongly controlled by Tl incorporation onto secondary minerals and diatoms deposited on the riverbed, especially during the dry season. The remobilization of riverbed sediments led to the transport of significant amounts of TCMs associated with particulate matter, especially Al oxy-hydroxy-sulphates or Al-silicates rather than Fe precipitates (except for Tl and Ga). Around 5.8 t of REE, 1.3 t of Y, 248 kg of Sc, 139 kg of Ga and 138 kg of Tl were delivered annually in their dissolved forms by the Tinto River to the Atlantic Ocean, which constitutes around 0.09% of the dissolved global flux into the oceans of Y, 0.02% of the REE flux, 0.01% of the Ga flux and 0.001% of the Sc flux., This work was supported by the Spanish Ministry of Economy and Competitiveness through the research projects SCYRE (CGL2016- 78783-C2-1-R),CAPOTE (CGL2017-54686050- R) and VALOREY (RTI2018 -101276-J-I00).The authors thank to Dr. Damiá Barceló (Co-Editor- in-Chief) and three anonymous reviewers for their helpful comments that notably improved the quality of the original manuscript., This work was supported by the Spanish Ministry of Economy and Competitiveness through the research projects SCYRE (CGL2016-78783-C2-1-R), CAPOTE (CGL2017-86050-R) and VALOREY (RTI2018-101276-J-I00). The authors thank to Dr. Damiá Barceló (Co-Editor-in-Chief) and three anonymous reviewers for their helpful comments that notably improved the quality of the original manuscript. more...

The Olivargas River drains materials from the Iberian Pyrite Belt with a large number of abandoned sulphide mining complexes that produce highly contaminated acid mine drainages (AMD). The Olivargas River is regulated by a reservoir that receives these acid leachates through its three main tributaries. In this study, the chemical composition of the waters from the reservoir and the water courses in its watershed are investigated based on samples taken throughout a hydrological year. We calculated the contaminant load for Al, Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn, SO4 and other elements entering the reservoir by two methods, establishing the relations of the dissolved element concentrations with 1) the water flow and 2) the specific conductance. The most extreme conditions were found in the tributary Los Peces Creek, with a mean pH value of 2.8 and concentrations of up to 736 mg/L of Zn and 291 mg/L of Al, making it the main source of metals in the reservoir (up to 65 t/year of Zn). Given that the volume of acid mine water pouring into the reservoir is relatively low, the water pH in the reservoir remains neutral. Under these conditions, most of the mine-derived metals (especially Al and Fe) form precipitates that accumulate in the bottom sediments, while dissolved concentrations are low (0.2 mg/L of Al and more...

The R&iacute, o Tinto, located in the Iberian Pyrite Belt (SW Spain), constitutes an extreme case of pollution by acid mine drainage. Mining in the area dates back to the Copper Age, although large-scale mining of massive sulfide deposits did not start until the second half of the 19th century. Due to acidic mining discharges, the R&iacute, o Tinto usually maintains a pH close to 2.5 and high concentrations of pollutants along its course. From a detailed sampling during the hydrological year 2017/18, it was observed that most pollutants followed a similar seasonal pattern, with maximum concentrations during autumn due to the washout of secondary soluble sulfate salts and minimum values during large flood events. Nevertheless, As and Pb showed different behavior, with delayed concentration peaks. The dissolved pollutant load throughout the monitored year reached 5000 tons of Fe, 2600 tons of Al, 680 tons of Zn, and so on. While most elements were transported almost exclusively in the dissolved phase, Fe, Pb, Cr, and, above all, As showed high values associated with particulate matter. River water quality data from 1969 to 2019 showed a sharp worsening in 2000, immediately after the mine closure. From 2001 on, an improvement was observed. more...

The Tharsis mine is presently abandoned, but the past intense exploitation has left large dumps and other sulphide-rich mining wastes in the area generating acid mine drainages (AMD). The main goal of this work is to study the effect of hydrogeochemical processes, hydrological regime and the waste typology on the physicochemical parameters and dissolved concentrations of pollutants in a deeply AMD-affected zone. Extreme leachates are produced in the area, reaching even negative pH and concentrations of up to 2.2 g/L of As and 194 g/L of Fe. The results of the comparison of ore grades of sulphide deposits with dissolved concentrations in waters shows that Pb is the least mobile element in dissolution probably due to the precipitation of Pb secondary minerals and/or its coprecipitation on Fe oxyhydroxysulphates. Arsenic, Cr, and V are also coprecipitated with Fe minerals. Seasonal patterns in metal contents were identified: elements coming from the host rocks, such as Al, Mn and Ni, show their maximum values in the dry period, when dilution with freshwater is lower and the interaction of water-rock processes and evaporation is higher. On the other hand, As, Cr, Fe, Pb and V show minimum concentrations in the dry period due to intense Fe oxyhydroxysulphate precipitation. In this sense, large sulphide rich waste heaps would be a temporal sink of these elements (i.e. Pb, As, Cr and V) in the dry period, and a significant source upon intense rainfalls., This work was supported by the Spanish Ministry of Economic and Competitiveness through the projects CGL2016-78783-C2-1-R (SCYRE) and by H2020 European Institute of Innovation and Technology (EIT RawMaterials) through the projects Modular recovery process services for hydrometallurgy and water treatment (MORECOVERY). The authors thank to Prof. Yong Sik Ok (Associate Editor) and five different reviewers for their helpful comments that notably improved the quality of the manuscript. more...

Opencast mining operations frequently lead to the creation of large voids that become anthropogenic lakes when the water table recovers. In the case of sulfide mining the stored water is of an acidic nature with significant concentrations of toxic metals and, therefore, a high pollutant potential. The main goal of the present work is to characterize the hydrological functioning and evolution of four acidic mine pit lakes in the abandoned mines of Tharsis, which is the second most important mine district in the Iberian Pyrite Belt (IPB). We present a simple methodology based on the use of the available orthophotographs and a Digital Terrain Model (DTM) together with the water balance of the pit lakes, which could be applied to other abandoned mining sites, where there is often a lack of hydrogeological information that prevents the application of more complex models. The accumulation of large volumes (5.2 × 10 6 m 3 ) of acidic and metal-rich waters in these pit lakes poses a serious environmental concern, with dissolved concentrations up to 2000 mg/L of Fe, 223 mg/L of Al, etc. Sierra Bullones and Filon Norte are connected underground and present the same evolution, with water transfers from Sierra Bullones to Filon Norte. The water level in both pit lakes is increasing, with an average rise of 2.8 m/yr since the beginning of flooding. However, the increase in the evaporation rate, as a result of the larger flooded area as the water level rise, would induce a hydrological equilibrium before reaching the overflow level, leading to the formation of a terminal lake. On the other hand, the water level in Filon Centro and Filon Sur pit lakes remain approximately stable. The first behaves as a flow-through or terminal lake, depending on the annual rainfall, while the second acts permanently as a flow-through lake. more...

Total and dissolved rare earth elements (REE) were studied in a river reach affected by several inputs of acid mine drainage. The first four acidic discharges were of lesser importance compared to the last (Agrio River, coming from the Rio Tinto mines), which transported high loads of Fe and Al (2.1 and 4.2 ton/day, respectively) together with REE (16.4 kg/day) and other trace elements. In the acid mine drainage (AMD) sources, practically all the REE were dissolved and the North American Shale Composite (NASC)-normalized patterns showed an enrichment in medium REE, although some differences exist between the patterns of each source. The pH values in the river reach upstream of the confluence with the Agrio River ranged between 8.01 and 7.03, and most of the Fe and Al from the AMD sources precipitated. Downstream of this acidic discharge, the pH decreased to 2.98. Upstream of the first AMD input, the dissolved and total concentrations of ΣREE were very low ( 7, concentrations of ΣREE increased (up to 25 μg/L), mainly transported by the particulate phase. In the reach downstream of the Agrio River with acidic conditions, REE behaved conservatively. The REE NASC-normalized patterns of the river samples resemble that of the AMD sources, although an enrichment of heavy REE in the dissolved phase is observed linked to complexation by carbonates. Cerium and particularly La also show higher dissolved percentages, similar to HREE, which must be due to the lower affinity of these elements to be sorbed onto Fe oxyhydroxides. Variations in Ce and Eu anomalies are observed along the river reach as a consequence of the different AMD inputs. However, the values of the Ce anomaly are higher in total samples than in dissolved samples. Speciation results indicate that these differences are not caused by differences in oxidation states but by slight differences in the hydrogeochemical behaviour of Ce with respect to La and Nd. more...

This study aims to characterize geochemically the acid mine drainage (AMD) sources causing deterioration of the water quality of a river reach with extreme hydrologic variability and to identify the patterns of dissolved and particulate contaminants along the reach. The hydrochemistry of the river reach is exposed to dramatic seasonal and spatial changes. The levels of sulfate and metals increase progressively along the reach due to the input of the first AMD discharges. However, the confluence with the Agrio River, which collects extremely acidic and metal-rich AMD from Riotinto mines, causes the total depletion of alkalinity and a dramatic decrease of pH values (down to 3.3), which strongly enhances the solubility of metals. A pH-controlled pattern of metal transport prevails in the river. Above pH 6, particulate Al and Fe is the predominant form of transport in the river; below pH 5, Al is chiefly transported in dissolved form, while the water velocity may control sedimentation of Fe precipitates. Particulate Cu, Zn, and Mn exhibit a similar pattern although with some differences. Above pH 6, Cu is generally transported by the particulate phase, while Zn and to a greater extent Mn, are mostly carried by the dissolved phase. Cobalt and Ni are mostly transported in dissolved form, even at circumneutral pH values, showing a more conservative behavior. Geochemical modeling results and analysis of high-energy X-ray diffraction patterns point to schwertmannite and ferrihydrite as the mineral phases responsible for the solubility control of Fe. Schwertmannite may precipitate close to mixing zones, where lower pH values and higher sulfate concentrations are found, while ferrihydrite probably precipitates farther from these zones, at higher pH values and lower sulfate concentrations. Metal and sulfate loadings are strongly linked to rainfall events. The highest dissolved loads were observed during floods in May 2016, when up to 48 t day−1 of Al, 16 t day−1of Fe, 8.4 t day−1of Zn, and so on, were transported by the river, values noticeably higher than those observed in other mining areas. more...

Fluxes of acidity and contaminants from acid mine drainage (AMD) sources to the receiving surface water bodies were studied in a mining-impacted watershed (Meca River, SW Spain) using a novel methodology based on the joint application of EMMA and MIX codes. The application of EMMA and elemental ratios allowed delimiting the end-members responsible for water quality variations at a catchment scale. The further application of MIX quantified the significant impact of AMD on the river quality; less than 10% of AMD relative contribution is enough to maintain acidic conditions during most of the year. The mixing model also provided information about the element mobility, distinguishing those elements with a quasi-conservative behavior (e.g., Cu, Zn, Al, Co or Ni) from those affected by mineral precipitation/dissolution (e.g., K, Si, Na, Sr, Ca, Fe, Pb, or As). Floods are the main driver of dissolved and, mainly particulate, contaminants in the catchment. Thus, the first rainfall events in November only accounted for 19% of the annual Meca flow but yielded between 26 and 43% of the net acidity and dissolved metal loads (mainly, Fe, As and Pb). Concerning particulate transport, around 332 tons of particulate Fe, 49 tons of Al, 0.79 tons of As and 0.37 tons of Pb were recorded during these first floods. The particulate As concentration can be up to 34 times higher than the dissolved one during floods and between 2 and 4 times higher for Fe, Pb and Cr. This integrated modeling approach could be a promising and useful tool to face future restoration plans in derelict mines worldwide. This approach would allow prioritizing remedial measures, achieving an environmental and cost-effective restoration of degraded areas. more...

Acid Mine Drainage (AMD) generates a great concern worldwide due to its severe impact to water resources during hundreds and even thousands of years after the cessation of mining activity if control measures are not implemented. AMD treatment is an environmental necessity, but also constitute a tremendous opportunity for the valorization of potential secondary sources of elements of economic interest. The knowledge of the hydrogeochemistry of REE in AMDs and their distribution using normalized patterns would help discrimination of the most potentially marketable AMD sources. To achieve this goal and to estimate the total economic potential of a severely AMD-affected region, chemistry and flow data were determined in spatially and temporally-distributed samples of numerous AMD sources collected throughout the Iberian Pyrite Belt (IPB). Due to high anual metal loads of elements such as Al (6600 ton), Zn (1600 ton), Cu (600 ton), Co (26 ton), Ni (10 ton), LREE (10.7 ton/yr), MREE (2.1 ton/yr), HREE (1 ton/yr), Y (3.7 ton) or Sc (0.7 ton), AMDs of the IPB would have an economic potential of 24.1 M$/yr (being REE 22.6% of this potential). Although the technical and economic limitations would impose a more realistic value of 4.2–10.3 M$/yr. The magnitude of this economic potential cannot be compared with active mines, however the longevity of the AMD generation processes and the need to achieve an environmental improvement make valorization of these leachates an interesting option to recover metals, which would help to treatment plants costs, improving notably the quality of water bodies in abandoned mining sites., This work was supported by the Spanish Ministry of Economy and Competitiveness through the research projects SCYRE (CGL2016-78783-C2-1-R) and CAPOTE (CGL2017-86050-R); and the MORECOVERY (H2020-EIT-PN 18190) project of the European Institute of Technology Raw Materials programme. F. Macías was funded by the R&D FEDER Andalucía 2014–2020 call through the project RENOVAME (FEDER; UHU-1255729). We would also like to thank Dr. Stefano Albanese (Editor-in-Chief), Dr. Annika Parviainen (Guest Editor) and two anonymous reviewers for the support and suggestions that significantly improved the quality of the original paper. more...

Waters affected by acid mine drainage (AMD) can contain high concentrations of rare earth elements (REE) which have a great interest not only by its application as tracers in hydrogeochemical processes but also as a potential economic resource. The Iberian Pyrite Belt (IPB) is rich in sulfide deposits which have been exploited intensively since ancient times, generating numerous AMD discharges. This work studies the REE content in five different AMD sources located in the upper reach of the Odiel River (SW Spain). The concentration of REE in these sources ranged from 113 to 7208 ppb. Differences in NASCnormalized REE patterns were observed among AMD sources that remained constant along the year despite the variability in REE concentrations, being lower during the rainy season due to dilution processes., This work was financed by the Spanish Ministry of Economy and Competitiveness through the project EMPATIA (Ref. CGL2013-48460-C2-1-R) and the grant BES-2014-068354. more...

Summary The Odiel watershed drains materials belonging to the Iberian Pyrite Belt, where significant massive sulfide deposits have been mined historically. As a result, a huge amount of sulfide-rich wastes are deposited in the watershed, which suffer from oxidation, releasing acidic lixiviates with high sulfate and metal concentrations. In order to reliably estimate the metal loadings along the watershed a complete series of discharge and hydrochemical data are essential. A hydrological model was performed with SWAT (Soil and Water Assessment Tool) to solve the scarcity of gauge stations along the watershed. The model was calibrated and validated from daily discharge data (from 1980 to 2010) at the outlet of the watershed, river inputs into an existent reservoir, and a flow gauge station close to the northern area of the watershed. Discharge data obtained from the hydrological model, together with analytical data, allowed the estimation of the dissolved pollutant load delivered annually by the Odiel River (e.g. 9140 t of Al, 2760 t of Zn). The pollutant load is influenced strongly by the rainfall regime, and can even double during extremely rainy years. Around 50% of total pollution comes from the Riotinto Mining District, so the treatment of Riotinto lixiviates reaching the Odiel watershed would reduce the AMD (Acid Mine Drainages) in a remarkable way, improving the water quality downstream, especially in the reservoir of Alcolea, currently under construction. The information obtained in this study will allow the optimization of remediation efforts in the watershed, in order to improve its water quality. more...

The aqueous oxidation of sulphide minerals leads to the generation of acid mine drainage (AMD), one of the main causes of water pollution worldwide. Mineral reactivity is greatly enhanced as a result of extraction and processes such as blasting, crushing, and grinding that increase rock surface area. The exposition of sulphide mine wastes to atmospheric conditions enhances AMD generation. However, a large number of processes and factors (e.g., pH, redox conditions, aqueous and surface complexation reactions) may control the mobility of elements in solution. In particular, the formation of soluble secondary minerals may act as transient storage of metals and acidity during AMD generation, leading however to their release upon rainfalls. To study the influence of mineralogy and grain size on the metal release from a variety of sulphide mine wastes collected in the Iberian Pyrite Belt, different grain size samples were treated with distilled water (S:L ratio 1:10) for 24 h simulating rainfall weathering. Results reveal that grain size plays a major role on metal mobility from sulphide mine wastes. However, mineralogical and geochemical evidence points at the partitioning of highly soluble secondary minerals among grain size fractions as the key factor controlling the metal release rate from these wastes. The results obtained show the importance of grain size on the reliability of the different leaching test procedures, and thus encourage standardizing these procedures worldwide., The authors thank two anonymous reviewers for helpful comments that clearly improved the quality of the manuscript, and Associate Editor Encarnación Ruiz-Agudo and Chief Editor Carlos Rodriguez-Navarro for their handling. This work was supported by the Spanish Ministry of Economic and Competitiveness through the projects CGL2016-78783-C2-1-R (SCYRE) and ERAMIN PCIN2015-242. C.R. Cánovas was funded by the Talent Consolidation Program of the University of Huelva. MD Basallote also thanks the Spanish Ministry of Economy and Competitiveness for the Postdoctoral Fellowship granted under application reference FJCI-2015-24765. more...

Efflorescent sulfate salts constitute a transient storage of acidity and metals during the dry season in mining areas affected by acid mine drainage, especially under semiarid climates. The main goal of this work was to study the metal partitioning among the dissolved and solid phases through the evaporative precipitation sequence of extremely metal-rich mine waters. The evaporative sequence was induced in the laboratory under controlled conditions for 24 days. The loss of water caused a progressive decrease of pH values (from 2.71 to 1.33) and increase of metal concentrations (e.g., from 1826 to 17800 mg/L of Al, 836 mg/L to 9783 mg/L of Fe and 301 to 2879 mg/L of Zn), which caused the precipitation of efflorescent sulfate salts. The precipitated salts were mainly composed of a mixture of minerals of Ca (gypsum, CaSO4·2H2O), Al (alunogen, Al2(SO4)3·17H2O), Fe (copiapite, Fe2+Fe3+4(SO4)6(OH)2·20H2O and melanterite Fe2+SO4·7H2O) and Mg (hexahydrite, MgSO4·6H2O), although the proportion of each mineral phase varied throughout the experiment. A preferential precipitation of Al and Mg sulfate salts, together with melanterite, was observed until the second week of the experiment, with evaporation rates lower than 70%. The precipitation of gypsum predominated with higher evaporation rates, reaching values higher than 80% of the mineral assemblage. The evaporative precipitation sequence was modeled using PHREEQC, obtaining good agreement with experimental data for gypsum, but failing in turn to accurately reproduce the evaporative sequence of other minerals such as hexahydrite, alunogen and melanterite. A metal partitioning pattern was observed during the evaporative precipitation sequence. Fe-sulfate minerals (e.g., copiapite and melanterite) present a higher affinity for Cu, Y and Th (and other trace metals such as Mn, Cd or Sc) while Al and Mg sulfate salts would retain Zn, Co, Ni and to a lesser extent Cr. In the case of gypsum, found prominently in the mineral assemblage during the experiment, it seems to have affinity for REE. This metal partitioning pattern is not observed in field data reported in literature. Such discrepancies, as well as those observed between modeled and experimental results, must be investigated in further studies. more...

In May 2017, a spill from La Zarza pit lake (SW Spain) resulted in the release of approximately 270,000 m3 of extremely acidic waters to the Odiel River. Around 780 × 103 kg of Fe, 170 × 103 kg of Al, 2.15 × 103 kg of As and high amounts of other trace metals and metalloids were spilled. The purpose of this study is to explain the causes, consequences and impacts of the mine spill on the receiving water bodies. To this end, an extensive sampling along the mine site, river and estuary as well as a hydrological model of the pit lake was performed. Around 53 km of the Odiel River's main course, which was already contaminated by acid mine drainage (AMD), were affected. The mine spill resulted in an incremental impact on the Odiel River water quality. Thus, dissolved concentrations of some elements increased in the river up to 450 times; e.g. 435 mg/L of Fe and 0.41 mg/L of As. Due to low pH values (around 2.5), most metals (e.g., Cu, Zn, Mn, Cd) were transported in the dissolved phase to the estuary, exhibiting a conservative behavior and decreasing their concentration only due to dilution. However, dissolved concentrations of Fe, Cr, Pb, Se, Sb, Ti, V and especially As decreased significantly along the river due to Fe precipitation and sorption/coprecipitation processes. At the upper zone of the estuary, a noticeable increment of metal concentrations (up to 77 times) was also recorded. The water balance illustrates the existence of groundwater inputs (at least 16% of total) to the pit lake, due probably to local infiltration of rainwater at the mining zone. The probable existence of an ancient adit connected to the pit lake indicates that potential releases could occur again if adequate prevention measures are not adopted. more...

The Ri o Tinto drains the eastern part of the Iberian Pyrite Belt (IPB), an area with a huge amount of massive sulphide deposits that has been mined for the last 4500 years. This river presents extreme conditions, with very high concentrations in solution of metals and metalloids and low pH values. Mining activities in the upper part of the watershed of the Ri o Tinto have been documented since historical times and a huge amount of widespread acid-producing mine residues exist in this area. Nevertheless, there is no consensus among the scientific community as to whether the extreme conditions of the Ri o Tinto are the result of natural processes or the intense mining activity in the region. Here we show, using numerous geological, archaeological and historical records, that the present quality of the Ri o Tinto is the result of mining activities, especially during the period 1850-2001, while natural processes of formation of acid rock drainage can be considered negligible. more...

Compared with pit lakes originated by coal mining, little is known about in-lake neutralization processes in pit lakes from sulfide ore mining in hard rock substrates, which are typically very deep and acidic and receive low carbon (C) inputs and groundwater flows. Physicochemical processes in water and sediments from a pit lake (San Telmo, 130 m deep) in the Iberian Pyrite Belt were investigated. San Telmo is a meromictic and highly acidic (pH 2.8) pit lake due to pH buffering by precipitation of Fe(III) minerals (schwertmannite and jarosite). The sediments have a low abundance of C (below 0.60%) and iron minerals (below 0.12%) compared to most coal-mining pit lakes. In San Telmo sediments, iron reduction and sulfide oxidation may be thermodynamically favored due to low pH values in pore waters (below 3.8) and the presence of reactive iron. Although schwertmannite is the main ferric mineral precipitating in the water column, mineralogical analyses reveal a low abundance of schwertmannite in the sediment. This may be due to the preferential use of this mineral in reduction reactions mediated by bacteria, together with a low replenishment rate of the schwertmannite pool in the sediment. The transformation of reactive iron (schwertmannite and jarosite) into goethite may limit sulfate reduction, promoting acidic conditions in the sediment. As long as the acid mine drainage continues to discharge into the lake, the pH buffering exerted by ferric minerals in the sediments will limit the neutralization of the pH by sulfate reduction. more...

Extensive extraction of technology critical elements (TCEs) from the lithosphere and their use results in a growing dispersion and remobilisation of these elements within the environmental compartments. We investigated the concentration and mobility of different TCEs (rare earth elements (REEs), Sc, Y, Ga and Tl) in acid mine drainage (AMD) outflows from a massive sulfide underground mine in south-west Spain for around 2 years. High levels of TCEs were observed; average concentrations of 8.2 mg L-1 of REEs, 1.5 mg L-1 of Y, 80 g L-1 of Ga, 53 g L-1 of Sc and 42 g L-1 of Tl were reported, several orders of magnitude higher than those observed in natural waters. The TCEs source in the study site is primarily accessory minerals in the host rocks, although the contribution of Ga and Tl by sulfides cannot be discarded. A seasonal variability in TCEs is observed in AMD waters, although their maximum concentrations do not coincide with those of sulfide-related elements. TCEs seem not to be controlled by the precipitation of secondary minerals, but by the intensity of chemical weathering inside the mined zone. A positive correlation between REEs and the Si/Na+K ratio seems to indicate that these elements are linked to resistant minerals to weathering. © 2019 CSIRO., This work was funded by the H2020 EIT Raw Materials program through the project MORECOVERY “Modular recovery services for hydrometallurgy and water treatment (H2020-EIT-PN 18190)” and by the Spanish Ministry of Science, Innovation and Universities through the SCYRE project (CGL2016-78783-C2-R). C.R. Cánovas was funded by the Talent Consolidation Program of the University of Huelva. MD Basallote also thanks the Spanish Ministry of Science, Innovation and Universities for the Postdoctoral Fellowship granted under application reference FJCI-2015-24765. more...

The Tinto and Odiel rivers in southwest Spain drain the world's largest sulfide mineral formation: the Iberian Pyrite Belt which has been worked since 2,500 BC. The Tinto and Odiel estuarine zones include both an extensive area of salt marsh and an intensively industrialized urban area. As a consequence of pyrite oxidation, the Tinto and Odiel rivers are strongly acidic (pH 3) with unusually high and quite variable metal concentrations. In this study, seasonally varying concentrations of dissolved major and trace elements were determined in the acid mine drainage affected estuary of the Ría de Huelva. During estuarine mixing, ore-derived metal concentrations exhibit excellent correlations with pH as the main controlling parameter. As pH increases, concentrations of dissolved ore-associated elements are attenuated, and this process is enhanced during the summer months. The decrease in Fe and Al concentrations ranged from 80 to 100 % as these elements are converted from dissolved to sediment-associated forms in the estuary. Coprecipitation/adsorption processes also removed between 60 and 90 % of the originally dissolved Co, Cu, Mn, Pb, Zn, and Th; however, Cd and Ni exhibited a greater propensity to remain in solution, with an average removal of approximately 60 %. On the other hand, As and U exhibited a different behavior; it is likely that these elements remain in dissolved forms because of the formation of U carbonates and soluble As species. Concentrations of As remain at elevated levels in the outer estuary (average = 48 μg L(-1)) which exceeds concentrations present in the Tinto River. Nevertheless, the estuary has recently witnessed improvements in water quality, as compared to results of several previous studies reported in the 1990s. more...

The Odiel River Basin (SW Spain) drains the central part of the Iberian Pyrite Belt (IPB), a world-class example of sulfide mining district and concomitantly of acid mine drainage (AMD) pollution. The severe AMD pollution and the incipient state of remediation strategies implemented in this region, coupled with the proximity of the deadline for compliance with the European Water Framework Directive (WFD), urge to develop a restoration and water resources management strategy. Furthermore, despite the presence of some reservoirs with acid waters in the Odiel basin, the construction of the Alcolea water reservoir has already started. On the basis of the positive results obtained after more than 10 years of developing a specific passive remediation technology (dispersed alkaline substrate (DAS)) for the highly polluted AMD of this region, a restoration strategy is proposed. The implementation of 13 DAS treatment plants in selected acid discharges along the Odiel and Oraque sub-basins and other restoration measurements of two acidic creeks is proposed as essential to obtain a good water quality in the future Alcolea reservoir. This restoration strategy is also suggested as an economically and environmentally sustainable approach to the extreme metal pollution affecting the waters of the region and could be considered the starting point for the future compliance with the WFD in the Odiel River Basin. © 2016, Springer-Verlag Berlin Heidelberg., This work was supported by the Spanish Ministry of Economic and Competitiveness through the projects EMPATIA (CGL2013-48460-C2-1-R) and SCYRE (CGL2016-78783-C2-1-R) and LIFE-ETAD project (LIFE12 ENV/ES/000250) and partially financed by Program U-INICIA VID 2014, grant 193, University of Chile, and by CONICYT, Program Fondecyt Iniciacion, Project Nº 111500002. R. Pérez-López also thanks the Spanish Ministry of Science and Innovation and the “Ramón y Cajal Subprogramme” (MICINN-RYC 2011). M.A. Caraballo gratefully acknowledges the support from the Advanced Mining Technology Center of the University of Chile. C.R. Cánovas was funded by the European Union’s Seventh Framework Program, Marie Skłodowska-Curie actions, and the Ministry of Economy, Innovation, Science and Employment of the Junta de Andalucía by the program Talent Hub (COFUND-Grant Agreement 291780). We would also like to thank Dr. Philippe Garrigues (editor in chief) and an anonymous reviewer for the support and comments that significantly improved the quality of the original manuscript. more...

The Iberian Pyrite Belt (IPB) is rich in sulfide deposits which have been intensively exploited, generating a huge problem of contamination of the Odiel River by acid mine drainage (AMD). At its source is a clean river, but along a 7 km-long reach receives five discharges of acid mine waters: Concepción, San Platón, Esperanza, Poderosa and the Agrio River, which drains the AMD contaminated water from the Río Tinto mines. The flows and hydrogeochemical characteristics of these AMD sources have been studied. The Agrio River is the main contributor of acidity, sulfate and metals to the Odiel River due to its high flows and pollutant concentrations. San Platón and Poderosa mines have high sulfate and metal concentrations although both sources are characterized by low or moderate flows while Concepción has the lowest concentrations but higher flows. The composition of AMD sources seem to be controlled by the mineralogy of the deposits and by geochemical processes. Strong seasonal variations are observed for some AMD sources while others are more constant throughout the year., This work was financed by the Spanish Ministry of Economy and Competitiveness through the project EMPATIA (Ref. CGL2013-48460-C2-1-R) and the grant BES-2014-068354. more...

The Tinto River estuary is one of the most contaminated coastal systems in the world due to the high amounts of pollutants this acidic river transports. The tidal influence and the fluvial discharges control the water mixing, which include a salt-induced process (that is typical of all estuaries) and an acid neutralization process (pH-induced mixing). These processes affect the geochemical behavior of uranium, which has a non-conservative pattern. Despite the high concentrations of dissolved uranium in the Tinto River, 234U/238U shows that uranium stems mostly from seawater (between 80 and 100%). Riverine uranium is adsorbed onto both Fe and Al precipitates when the acidic river water is mixed with seawater. Distribution coefficients (Kd) show that dissolved and particulate uranium are controlled by adsorption–desorption processes and the formation of carbonate complexes, both depending on pH. At low pH, uranium tends to be dissolved, and the adsorption by suspended particles is low. As the pH increases, the adsorption processes onto Fe and Al particles are more intense, increasing particulate uranium which reaches a maximum at pH 5.5, where the uranium solubility minimum occurs. At higher pH values, dissolved uranium increases by carbonate complexation. more...

The accurate estimation of metal loads transported by streams is necessary to calculate reliable mass transfers of metals between compartments, both at local and global scales. This estimation is particularly relevant in the case of the Tinto and Odiel Rivers (SW Spain) due to their significant contribution to the total metal transfer from continents to the ocean. At a local scale, the metal load transported by streams plays a key role in predicting the biogeochemical evolution of water reservoirs affected by Acid Mine Drainage (AMD). This work uses the relationships between specific conductivity (SC) and dissolved elements to calculate the metal load of the River Meca, a tributary of the Odiel. The SC and the water level were continuously monitored from April 2009 to June 2010. Water samples were also collected and measurements of the discharge were carried out manually once a month. The relationships between the SC and the concentration of dissolved elements are, in general, very good (R2 > 0.90). However, some key elements such as Fe show a very poor correlation. A simple methodology based on the MIX code (a maximum likelihood method to estimate mixing ratios) was used to elucidate their different behaviours. During the dry period (April–December, 2009) the Fe concentration was lower than that deduced from the SC recorded value due to the precipitation of Fe-oxihydroxides, which also reduced the concentrations of As, Cr, Pb and, to a lesser extent, Cu. At the same time Na, Sr, Ca and Li were enriched because of the higher interaction with the riverbed materials. Correlations between the SC and the metal concentration improved significantly when each period was considered separately. A second dry period (April–June 2010) shows high SC values, although no dissolution/precipitation of solid phases is evidenced. This indicates that SC alone is not enough to predict the dissolved metal loads in Mediterranean AMD streams. The metal load transported by the River Meca was determined for the hydrological year 2009/10 as 1933 ± 129 tonnes of Fe, 990 ± 155 of Al and 378 ± 41 of Zn. more...

Several experiments were conducted to evaluate zinc-tolerance of sulfate-reducing bacteria (SRB) obtained from three environmental samples, two inocula from sulfide-mining districts and another inoculum from a wastewater treatment plant. The populations of SRB resisted zinc concentrations of 260 mg/L for 42 days in a sulfate-rich medium. During the experiments, sulfate was reduced to sulfide and concentrations in solution decreased. Zinc concentrations also decreased from 260 mg/L to values below detection limit. Both decreases were consistent with the precipitation of newly-formed sphalerite and wurtzite, two polymorphs of ZnS, forming2.5-μm-diameter spherical aggregates identified by microscopy and synchrotron-μ-XRD. Sulfate and zinc are present in high concentrations in acid mine drainage (AMD) even after passive treatments based on limestone dissolution. The implementation of a SRB-based zinc removal step in these systems could completely reduce the mobility of all metals, which would improve the quality of stream sediments, water and soils in AMD-affected landscapes. more...

In 1998, the Agrio and Guadiamar rivers underwent an enormous environmental disaster caused by the rupture of the Aznalcóllar tailings dam and the release of 6 hm(3) of pyrite sludge and acidic water. Both rivers run over recent alluvial materials which form a small-sized aquifer which is however important because underground water feeds the flow of the rivers. This work analyzes the state of groundwater 10 years after the spill. Before the dam failure, this aquifer was already contaminated in the zone nearest to the mine, to which the impact of the spill was added. Contamination levels in the alluvial aquifer of the Agrio River have decreased remarkably. However, they are still important, with acidic pH values and high concentrations of toxic elements (maximum values of 16 mg/L of Zn and 15 mg/L of Al). There are also important levels of contamination in the Guadiamar alluvial area closest to the mine, as well as in specific zones located further south. The concentration of toxic elements is mainly controlled by pH. The evolution of contaminant levels show a sharp decrease after the first years following the spill, followed by a subsequent stabilization. It is necessary to take measures for the recovery of the aquifer because, otherwise, groundwater will continue contributing contaminants into the Agrio and Guadiamar rivers. more...

The Odiel River is located in southwestern Spain; the greater portion of its basin is composed of materials from the Iberian Pyrite Belt (IBP), an area with numerous massive sulfide deposits that have been highly exploited since the third millennium BC. As sulfides come into contact with the atmosphere due to mining activity, oxidation occurs, generating a highly toxic acidic leachate with large concentrations of sulfates and metals, a process which is known as acid mine drainage (AMD). As a result, the Odiel River and most of its tributaries are severely contaminated. The construction of two large dams in the Odiel River basin is planned. The most advanced project is that of the Alcolea reservoir, with a storage capacity of 274 hm3, whose construction has already begun, with a total budget of around €164 million. There are reasonable doubts about the final quality of the reservoir water, as this dam will regulate a river with a mean pH close to 3.5 and large concentrations of toxic elements. This paper analyzes the data of water quality in the Alcolea reservoir. The results show that the reservoir water will be acidic and not useful at all, although more specific studies are necessary to obtain the exact estimation of its hydrochemical characteristics. It seems unwise to start building the dam, which requires a large economic investment and will have a vast environmental impact, without first conducting these studies. This proves that water management in Spain is still based on political motivation rather than on technical criteria and good management of natural and economic resources. more...

Summary The Meca River is highly contaminated by acid mine drainage coming from the Tharsis mining district, belonging to the Iberian Pyrite Belt. This river is regulated by the Sancho reservoir (58 hm3), with a pH close to 4.2. In this work, the load transported by the Meca River to the Sancho reservoir has been assessed. Due to the lack of streamflow data, the hydrological behaviour of the Meca River basin has been simulated using the SWAT model. The model has been calibrated against registered daily inflows of the Sancho reservoir (1982–2000), excluding the hydrological years 2000/2001 and 2001/2002 that were kept for the validation. The results were satisfactory; the evaluation coefficients for monthly calibration were: r = 0.85 (Pearson’s correlation coefficient), NSE = 0.83 (Nash–Sutcliffe coefficient) and DV = 1.08 (runoff volume deviation). The main uncertainty was the calibration during low water because of the poor accuracy in the measurement of the inputs to the reservoir in these conditions. Discharge and dissolved concentration relationships for different elements were obtained from hydrochemical samplings, which allowed us to estimate the element pollutant load transported to the reservoir: 418 ton/year of Al, 8024 ton/year of SO4, 121 ton/year of Zn, etc. Based on these loads, concentrations in the reservoir were calculated for some elements. Apart from Mn and Sr, good adjustment between calculated and measured values was observed (±20% for Ca, Co, Li, Mg, Na, Ni, Zn and SO4). Capsule: Hydrological model combined with water quality data show how pollution by AMD can generate huge loads of contaminants acidifying streams and reservoirs. more...

The Odiel river Basin is heavily affected by acid mine drainage (AMD) from the sulphide mining areas in the Iberian Pyrite Belt (IPB). A thorough study has been conducted along this fluvial system, monitoring the seasonal influence on the pollution level and its hydrochemical characteristics. From 2002 to 2006, surface water samples were collected at 91 different points throughout the Odiel river Basin and analyzed by field and laboratory methods for dissolved metals and metalloids. Acid mine drainage affects 37% of the length of the drainage network, which shows a great diversity of geochemical conditions as well as significant variations through the hydrological year. Unaffected streams show different water types depending on the lithological substrate and the marine aerosol influence. Mean concentrations in the contaminated streams are very high: 231 mg/L of Fe, 135 mg/L of Al, 56 mg/L of Zn, 16 mg/L of Cu, etc. Four types of contaminated streams were recognized based on hydrochemical and physicochemical characteristics. There are important seasonal variations depending on the precipitation regimen, level of pollution and proximity to the AMD sources. In the more contaminated samples the M/Fe ratio (M = metals other than Fe) decreases during the summer season. Slightly contaminated samples show an inverse evolution as this ratio increases in spring and summer due to substantial Fe precipitation. A recomparison of contaminant loads suggests that the Odiel river Basin (including the Tinto river) accounts for 15% of the global gross flux of dissolved Zn and 3% of the global gross flux of dissolved Cu transported by rivers into the ocean. more...

The aim of this work is to study the hydrochemical variations during flood events in the Rio Tinto, SW Spain. Three separate rainfall/flood events were monitored in October 2004 following the dry season. In general, concentrations markedly increased following the first event (Fe from 99 to 1130 mg/L; Q(max) = 0.78 m(3)/s) while dissolved loads peaked in the second event (Fe = 7.5 kg/s, Cu = 0.83 kg/s, Zn = 0.82 kg/s; Q(max) = 77 m(3)/s) and discharge in the third event (Q(max) = 127 m(3)/s). This pattern reflects a progressive depletion of metals and sulphate stored in the dry summer as soluble evaporitic salt minerals and concentrated pore fluids, with dilution by freshwater becoming increasingly dominant as the month progressed. Variations in relative concentrations were attributed to oxyhydroxysulphate Fe precipitation, to relative changes in the sources of acid mine drainage (e.g. salt minerals, mine tunnels, spoil heaps etc.) and to differences in the rainfall distributions along the catchment. The contaminant load carried by the river during October 2004 was enormous, totalling some 770 t of Fe, 420 t of Al, 100 t of Cu, 100 t of Zn and 71 t of Mn. This represents the largest recorded example of this flush-out process in an acid mine drainage setting. Approximately 1000 times more water and 1408 200 times more dissolved elements were carried by the river during October 2004 than during the dry, low-flow conditions of September 2004, highlighting the key role of flood Events in the annual pollutant transport budget of semi-arid and and systems and the need to monitor these events in detail in order to accurately quantify pollutant transport. (c) 2007 Elsevier B.V. All rights reserved. more...

The Tinto and Odiel Rivers are strongly affected by acid mine drainage (AMD) due to the intense sulphide mining developed in their basins over the past 5000 years. In this study the results obtained from a weekly sampling in both rivers, before their mouth in the Ría of Huelva, over three and a half years of control are analysed. In the Tinto River, the concentrations of sulphates, Al, Cd, Co, Li and Zn are double to those of the Odiel as a consequence of lower dilution. However, the concentration of Fe in the Odiel River is 20 times lower, since the precipitation of Fe oxyhydroxysulphates caused by neutralisation processes is more intense. Lower As, Cr, Cu and Pb concentrations are also found in the Odiel River as, to a greater or lesser extent, they are sorbed and/or coprecipitated with Fe. Other elements such as Be, Mn, Ni and Mg show similar values in both systems, which is ascribed to lithological factors. The seasonal evolution of contaminants is typical of rivers affected by AMD, reaching a maximum in autumn due to the dissolution of evaporitic salts precipitated during the summer. Nevertheless, in the Tinto River, Ca, Na and Sr show a strong increase during the summer, probably due to a greater water interaction with marly materials, through which the last reach of the river flows. Barium has a different behaviour from the rest of the metals and its concentration seems to be controlled by the solubility of barite. Iron, As and Pb show different behaviours in both rivers, those for Fe and As possibly linked to the prevalence of different dissolved species of Fe. The different Pb pattern is probably due to the control of Pb solubility by anglesite or other minerals rich in Pb in the Tinto River. more...

Scarcity of waters is the main limiting factor of economic development in most arid and semi-arid regions worldwide. The construction of reservoirs may be an optimal solution to assure water availability if the drainage area shows low disturbances. This is the quandary of mining areas where economic development relies on water accessibility. Water acidification trends were investigated in the Sancho Reservoir (SW Spain) in the last 20 years. The acidity (pH3-5) and high dissolved metal concentrations (e.g., 4.4 mg/L of Al, 2.1mg/L of Mn, 1.9 mg/L of Zn) observed in the Sancho, together with the large volume stored (between 37 and 55 Mm(3)), makes this reservoir an extreme case of surface water pollution worldwide. A progressive acidification has been observed since 2003, as evidenced by decreasing pH values and increasing dissolved metal concentrations, especially noticeable after 2007. The increase in the net acidity in the reservoir originates from the higher input of metals and acidity due to the rebound effect after the mining closure in 2001. This trend was not detected in the river feeding the reservoir due to its great hydrological and hydrochemical variability, typical of the Mediterranean climate. Chemical analysis and absolute dating of sediments identified a progressive enrichment in S and metals (i.e., Fe, Zn Cu, Ni, Co and Cd) in the upper 20 cm, which reinforce the year 2002/03 as the onset of the acidification of the reservoir. The decrease of pH values from 4-5 to 3-4 occurred later than the increase in sulfate and metals due to pH-buffering by Al. The acid mine drainage (AMD) pressure has caused an increment of dissolved Fe and other metals, as well as a change in the pH buffering role, exerted now by Fe. These processes were simulated by PHREEQC, which confirms that the acidification trend will continue, causing pH values to reach 2.5 if AMD pressure persists. more...

The Tinto and Odiel rivers are heavily affected by acid mine drainage (AMD). However, the exact quantities of contaminants transported into the Huelva estuary and the Gulf of Cadiz are unknown. The existing previous investigations are, in general, based on studies with few data or incorrect methodology, and are therefore unreliable. This study aims to present a reliable estimation of the dissolved contaminant load transported by both rivers for the periods 1995/96 to 2002/03. The methodology used is based principally on the correlation between contaminant concentration and flow rate. The results show that both rivers transport enormous quantities of dissolved contaminants: 7900 t a −1 of Fe, 5800 t a −1 Al, 3500 t a −1 Zn, 1700 t a −1 Cu, 1600 t yr −1 Mn and minor quantities of other metals. These values represent 60% of the global gross flux of dissolved Zn transported by rivers in to the ocean, and 17% of the global gross flux of dissolved Cu. more...

In April 1998, a spill of 6 hm3 of pyritic mud and acidic water was released into the Guadiamar River due to the rupture of the Aznalcóllar tailings dam. Before the spill, the river was already strongly affected by acid mine drainage (AMD). In this study, the water quality of the Guadiamar River is analysed from a periodic sampling started after the spill. Previous data of the water quality have also been obtained. A recovery of the water quality is observed from 2002 on. The distribution of arsenic is opposed to that of the rest of metals, with the lowest concentrations to the north, due to the adsorption and/or coprecipitation on ferric oxyhydroxides. In the southern area, when pH values are close to 8, arsenic desorption occurs. There is a seasonal pattern of the trace metal content evolution, different in the northern and southern zones of the river. In the northern area the highest polluting levels occur in summer, due to a lower dilution of the mining leachates. In the southern area, the highest metal levels occur during the winter, since during the summer metals remain held by surface sorption processes in the hyporheic zone of the river. more...

In April 1998, the Aznalcollar mine tailings dam spilled 2 hm3 of slurry and 4 hm3 of acid waters into the Agrio River (affluent of the Guadiamar River). The pollutants reached the proximity of the Donana National Park, 60 km downstream. The state of contamination of groundwaters and surface waters, from several samplings made subsequent to the spill, is described. Although the Guadiamar valley groundwaters remain contaminated, this situation cannot be attributed to the mining spill, but to the long history of pollution from mining activity at Aznalcollar. Three zones can be distinguished: the most polluted zone, with pH values close to 4 and very high concentrations of metals (up to 18 mg/l of Al and 7 mg/l of Mn) and sulfates (up to 1263 mg/l); a second zone where pH values are higher (close to neutral) and, as a result, the concentration of metals is significantly lower; and a third zone, with pH exceeding 7, in which the concentration of metals has already fallen to normal levels but sulfate concentrations remain high (above 500 mg/l). The waters of the Agrio River present characteristics similar to those of the most-polluted groundwaters; on mixing with the waters of the Guadiamar River they are neutralized, precipitating firstly Al and then the rest of the metals. These metals remain deposited on the river-bed, where they are readily remobilized in later spates. Analysis of changes in groundwater quality shows a trend toward a lower content of Zn and the other metals in most wells. more...

This work analyses the spatial distribution, the origin, and the shale-normalised fractionation patterns of the rare earth elements (REE) in the alluvial aquifer of the Guadiamar River (south-western Spain). This river received notoriety in April 1998 for a spill that spread a great amount of slurry (mainly pyrites) and acid waters in a narrow strip along the river course. Groundwaters and surface waters were sampled to analyse, among other elements, the REEs. Their spatial distribution shows a peak close to the mining region, in an area with low values of pH and high concentrations of sulphates and other metals such as Zn, Cu, Co, Ni, Pb, and Cd. The patterns of shale-normalised fractionation at the most-contaminated points show an enrichment in the middle rare earth elements (MREE) with respect to the light (LREE) and heavy (HREE) ones, typical of acid waters. The Ce-anomaly becomes more negative as pH increases, due to the preferential fractionation of Ce in oxyhydroxides of Fe. more...

On 25 April 1998 the tailings dam of the Aznalcollar mine burst, a great quantity of pyrite waste sludge and acid water was spilled reaching the vicinity of the Donana National Park. In surface and ground water samples taken a week after dam breaking, metals, trace elements and Pb isotopic ratios (206Pb/207Pb and 208Pb/206Pb) were analysed. In September 1998 a second sampling survey was carried out. The surface waters have a similar isotopic composition as the lead contained in the pyrite from the Aznalcollar mine. The polluted groundwater of the Guadiamar aquifer also shows the influence of the mining origin of the lead. Lead isotope ratios (206Pb/207Pb and 208Pb/206Pb) in the groundwater of the Almonte-Marismas are very low and they differ clearly from the rest of groundwater samples. A further group of wells has a lead isotope composition intermediate between the Aznalcollar mine and the atmospheric aerosols of the Iberian Peninsula. more...

The Tinto River estuary is highly polluted with the acid lixiviates from old sulphide mines. In this work the behaviour of dissolved and particulate trace metals under strong chemical gradients during a tidal cycle is studied. The pH values range from 4.4 with low tide to 6.9 with high tide. Precipitation of Fe and Al is intense during rising tides and As and Pb are almost exclusively found in the particulate matter (PM). Sorption processes are very important in controlling the mobility (and hence bioavailability) of some metals and particularly affect Cu below pH 6. Above pH ~ 6 Cu is desorbed, probably by the formation of Cu(I)–chloride complexes. Although less pronounced than Cu, also Zn desorption above pH 6.5 seems to occur. Mn and Co are affected by sorption processes at pH higher than ca. 6. Cd behaves conservatively and Ni is slightly affected by sorption processes. more...

This study deals with the hydrogeochemical changes and metal(loid) attenuation processes along the extremely acidic Rio Tinto (SW Spain). The geochemistry of Tinto headwaters is determined by the variability of mining discharges due to different geological, geochemical and hydrological controls. Downstream of the mining area, a decrease in most dissolved element concentrations is recorded. However, not all elements decreased its concentration to the same extent, and even some did not decrease (e.g., Ba and Pb). A group of elements formed by Al, Cd, Co, Cr, Cu, Li, Mg, Mn, Ni and Zn behaved quasi-conservatively; mainly affected by dilution, except at the lower part of the catchment where seem to be affected by sorption/coprecipitation (e.g., Cd, Cu, and Zn) or mineral dissolution processes (e.g., Al, Mg). Iron and As exhibited a non-conservative behaviour due to ochre precipitation and sorption processes, respectively. A group of elements formed by Ca, Na, Sr and Li did not behave conservatively; waters were enriched in these elements by dissolutive reactions of carbonates and aluminosilicates from bedrocks. The behaviour of Pb in the Rio Tinto is complex; values fluctuate along the river course and its solubility may be related to the nature of Fe precipitates. more...

The abandoned mining districts of the Iberian Pyrite Belt (IPB, SW Spain) are an extreme source of pollution by acid mine drainage (AMD) to the Tinto and Odiel rivers. The pollutant flux transported by the Odiel River during a high stage period was assessed using concentration–discharge relationships and concentration–conductivity relationships, for the hydrological year 2009/10 (which was especially wet). Both correlations were high (R2 > 0.80) for most of the elements studied. The two methods for flux calculation gave similar results with differences generally lower than 10%. The dissolved contaminant flux transported by the Odiel River just before its mouth mainly includes sulphate (257,534 ± 13,464 t/yr), Al (13,259 ± 1071 t/yr), Zn (4265 ± 242 t/yr), Mn (2532 ± 146 t/yr) and Cu (1738 ± 136 t/yr), and minor amounts of other elements. These findings confirm that, up to our knowledge, the Odiel River can be considered to be the largest contributor of mining-related pollutants to the world's oceans. more...

Acid mine drainage in the Iberian Pyrite Belt is probably the worst case in the world of surface water pollution associated with mining of sulphide mineral deposits. The Iberian Pyrite Belt is located in SW Iberian Peninsula, and it has been mined during the last 4,500 years. The central and eastern part of the Iberian Pyrite Belt is drained by the Tinto and Odiel rivers, which receive most of the acidic leachates from the mining areas. As a result, the main channels of the Tinto and Odiel rivers are very rich in metals and highly acidic until reaching the Atlantic Ocean. A significant amount of the pollutant load transported by these two rivers is delivered during the rainy season, as is usual in rivers of Mediterranean climate regions. Therefore, in order to have an accurate estimation of the pollutant loads transported by the Tinto and Odiel rivers, a systematic sampling on a weekly basis and a high temporal resolution sampling of floods events were both performed. Results obtained show that metal fluxes are strongly dependent on the study period, highlighting the importance of inter-annual studies involving dry and wet years. more...

The Tinto River is an extreme case of pollution by acid mine drainage (AMD), with pH values below 3 and high sulphate, metal and metalloid concentrations along its main course. This study evaluates the impact of releases from a freshwater reservoir on the Tinto River, identifying the metal transport mechanisms. This information is needed to understand the water quality evolution in the long term, and involves the comprehension of interactions between AMD sources, freshwaters, particulate matter and sediments. This work proposes a methodology for quantifying the proportions in which the different sources are contributing. The method is based on the mass balance of solutes and accounts for the uncertainty of end-members. The impact of the releases from the Corumbel Reservoir on the hydrochemistry of the Tinto River was significant, accounting up to a 92% of river discharge. These releases provoked a sharp decrease in dissolved metal concentrations, especially for Fe (approximately 1000 fold) due to dilution and precipitation. Cadmium, Zn, Cu, Co, Ni and Al suffered a dilution to a 12–16 fold decrease while Ca, Sr, Na, Pb and Si were less affected (2–4 folds decrease). However, these releases also gave rise to an increase in particulate transport, mainly Fe, As, Cr, Ba, Pb and Ti, due to sediment remobilisation and Fe precipitation. Aluminium, Li, K, Si, Al, Ni and Sr, together with Cu were present in the particulate phase during the discharge peak. The proposed 2-component mixing model revealed the existence of non-conservative behaviour for Al, Ca, Li, Mn, Ni and Si as a consequence of the interactions between the acidic Tinto waters and the clay-rich reservoir sediments during the bottom outlet opening. These results were improved by a 3-component mixing model, introducing a new end-member to account the chemical dissolution of clay-rich sediments by acidic Tinto waters. more...

Characteristics of water profiles and sulphide formation processes in sediments were studied in two water reservoirs affected by acid mine drainage in order to investigate the mechanisms controlling the physical and chemical processes that, under favourable conditions, act to reduce the toxicity, mobility and concentration of metals and metalloids in the water column. Water columns and pore-waters from sediments were analysed for Fe species, trace elements (As, Cd, Co, Cu, Mn, Ni, Pb, Zn, Cr), sulphide, sulphate and bicarbonate. Inorganic reduced sulphur compounds (acid volatile sulphur, pyrite sulphur and elemental sulphur) and reactive Fe were determined in the sediments. A sequential extraction was also performed. Both reservoirs behave like holomictic and monomictic lakes, with a summer thermal stratification that disappears during winter. pH values between 4 and 7 can be observed along the water columns. Pore-water concentrations of up to 25 mg/l of Fe, 4 mg/l of Al, 1.3 mg/l of Zn, 170 µg/l of Pb, 11 µg/l of As, etc. have been found. The results suggest that toxic elements such as Cu, Zn, Co, Pb, Cr, As, etc. are mainly found in the bioavailable fraction which is the most hazardous for the environment. The calculated degree of sulphidization (DOS) and degree of pyritization (DOP) values indicates that removal of trace elements from anoxic pore-waters occurs by coprecipitation and/or adsorption on newly formed Fe sulphides (framboidal pyrite), attenuating the contamination. However oxidation of the sediments during turnover periods also occurs, which releases toxic elements back into the water column. more...

The Tinto and Odiel rivers are seriously affected by acid mine drainage (AMD) from the long-term mining activities in Iberian Pyrite Belt (IPB). As a consequence, the Huelva estuary is heavily contaminated by metals and metalloids. This study presents an estimation of the seasonal variation, and the dissolved contaminant load transported by both rivers from February 2002 to September 2004. Besides, toxicity and bioaccumulation tests with the sediments of the estuary have been conducted in order to measure the mobility of the toxic metals. Results show that the Tinto and Odiel rivers transport enormous quantities of dissolved metals to the estuary: 7900 t yr−1 of Iron (Fe), 5800 t yr−1 Aluminium (Al), 3500 t yr−1 Zinc (Zn), 1700 t yr−1 Copper (Cu), 1600 t yr−1 Manganese (Mn) and minor quantities of other metals and metalloids. These values represent 37% of the global gross flux of dissolved Zn transported by rivers in to the ocean, and 15% of the global gross flux of dissolved Cu. These metals and metalloids usually sink in the estuarine sediments due to pH and salinity changes. The increase of salinity in the estuary favours the adsorption and trapping of metals. For this reason, the mobility and bioavailability of metals such as Zn, Cd and Cu is higher in sediments located in the area of fresh water influence that in sediments located in the marine influenced area of the estuary, showing a higher percentage of fractionation and bioaccumulation of these metals in the station influenced by the fresh water environment. Keywords: Tinto and Odiel rivers, Acid mine drainage, Water and sediment pollution, Huelva estuary, Iberian Pyrite Belt more...

This paper intends to analyse seasonal variations of the quality of the water of the Odiel River. This river, together with the Tinto River, drains the Iberian Pyrite Belt (IPB), a region containing an abundance of massive sulphide deposits. Because of mining activity dating back to prehistoric times, these two rivers are heavily contaminated. The Odiel and Tinto Rivers drain into a shared estuary known as the Ria of Huelva. This work studies dissolved contaminant data in water of the Odiel River collected by various organisations, between October 1980 and October 2002, close to the rivers entry into the estuary. Flow data for this location were also obtained. The most abundant metals in the water, in order of abundance, are zinc (Zn), iron (Fe), manganese (Mn) and copper (Cu). Arsenic (As), cadmium (Cd) and lead (Pb) are also present but in much lower quantities. The quality of the river water is linked to precipitation; the maximum sulphate, Fe, Zn, Mn, Cd and Pb concentrations occur during the autumn rains, which dissolve the Fe hydroxysulphates that were precipitated during the summer months. In winter, the intense rains cause an increase in the river flow, producing a dilution of the contaminants and a slight increase in the pH. During spring and summer, the sulphate and metal concentration (except Fe) recover and once again increase. The Fe concentration pattern displays a low value during summer due to increased precipitation of ferric oxyhydroxides. The arsenic concentration displays a different evolution, with maximum values in winter, and minimum in spring and summer as they are strongly adsorbed and/or coprecipitated by the ferric oxyhydroxides. Mn and sulphates are the most conservative species in the water. Relative to sulphate, Mn, Zn and Cd, copper displays greater values in winter and lower ones in summer, probably due to its coprecipitation with hydroxysulphates during the spring and summer months. Cd and Zn also appear to be affected by the same process, although to a lower degree than Cu, experiencing a slight reduction in summer with respect to Mn and sulphates. more...

The Iberian Pyrite Belt (IPB) is one of the most famous sulfide mining regions in the world. Mining activity in the IPB dates back to prehistoric times, and though today there is no active mining, the pollution continues to generate. The result is acidic drainage containing elevated concentration of sulfate and heavy metals. This is responsible for the pollution and degradation of the Odiel River basin in south-western Spain. In this work we have conducted a study along the entire Odiel basin. During the years 2002 and 2003 we have collected water samples at 69 points in order to characterize and quantify the pollutants that the Odiel River receives as a consequence of the AMD inputs within its watershed. The contaminant load transported by the Odiel River into the Huelva Estuary has also been calculated. Due to the great quantity of samples and analyses, the use of statistical multivariate techniques (Principal Component Analysis) was used to interpret the results. PCA of the samples showed strong interrelationships between the generation of acid by sulfide mineral weathering and metal loads. In downstream reaches, the rock forming elements (K, Ca, Na, Mg, etc.) dominate as the acidic waters dissolve the rocks in the stream bed. The contaminant load transported by the Odiel River to the Huelva Stuary is dominated by SO4 2- , Al and Fe, with lesser quantities of Zn, Cu, Cd, etc. more...