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This research reports the effects of pH increase on contaminant mobility in acid mine drainage from the Iberian Pyrite Belt by seawater mixing in the laboratory, simulating the processes occurring in the Estuary of Huelva (SW Iberian Peninsula). Concentrations of Al, Fe, As, Cu and REY in mixing solutions significantly decreased with increasing pH. Schwertmannite precipitation at pH 2.5–4.0 led to the total removal of Fe(III) and As. Subsequently, iron-depleted solutions began to be controlled by precipitation of basaluminite at pH 4.5–6.0, which acted as a sink for Al, Cu and REY. Nevertheless, as the pH rises, schwertmannite becomes unstable and releases back to solution the previously retained As. Moreover, other elements (S, Zn, Cd, Ni and Co) behaved conservatively in mixing solutions with no participation in precipitation processes. Some toxic elements finally end up to the Atlantic Ocean contributing to the total pollutant loads and environmentally threatening the coastal areas., Spanish Ministry of Science and Innovation (PID2020-119196RBC21), Spanish Ministry of Science and Innovation RYC2019-027949-I, IJCI-2016-27412 and IJC2018-035056-I, Universidad de Huelva/CBUA

This study evaluates for the first time the impact of a large wildfire on the hydrogeochemistry of a deeply AMDaffected river at the beginning of the wet season. To accomplish this, a high-resolution water monitoring campaign was performed within the basin coinciding with the first rainfalls after summer. Unlike similar events recorded in AMD-affected areas, where dramatic increases in most dissolved element concentrations, and decreases in pH values are observed as a result of evaporitic salts flushing and the transport of sulfide oxidation products from mine sites, a slight increase in pH values (from 2.32 to 2.88) and decrease in element concentrations (e.g.; Fe: 443 to 205 mg/L; Al: 1805 to 1059 mg/L; sulfate: 22.8 to 13.3 g/L) was observed with the first rainfalls after the fire. The washout of wildfire-ash deposited in the riverbanks and the drainage area, constituted by alkaline mineral phases, seems to have counterbalanced the usual behavior and patterns of the river hydrogeochemistry during autumn. Geochemical results indicate that a preferential dissolution occurs during ash washout (K > Ca > Na), with a quick release of K followed by an intense dissolution of Ca and Na. On the other hand, in unburnt zones parameters and concentrations vary to a lesser extent than burnt areas, being the washout of evaporitic salts the dominant process. With subsequent rainfalls ash plays a minor role on the river hydrochemistry. Elemental ratios (Fe/SO4 and Ca/Mg) and geochemical tracers in both ash (K, Ca and Na) and AMD (S) were used to prove the importance of ash washout as the dominant geochemical process during the study period. Geochemical and mineralogical evidences point to intense schwertmannite precipitation as the main driver of reduction in metal pollution. The results of this study shed light on the response of AMD-polluted rivers to certain climate change effects, since climate models predict an increase in the number and intensity of wildfires and torrential rain events, especially in Mediterranean climates., This research was supported by the AIHODIEL project (PYC20 RE 032 UHU) within the 2020 call for grants for the implementation of projects of collaborative interest in the field of innovation ecosystems co-financed by the FEDER program in Andalucía for the period 2014-2020. Jonatan Romero is financed by a FPU program of the Spanish Ministry of Education of Vocational Training (FPU20/04441). C.R Cánovas thanks the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowship granted under application reference RYC2019–027949-I. Funding for open access charge: Universidad de Huelva / CBUA. The authors gratefully appreciate the constructive comments and suggestions from the editor Mark van Loosdrecht and two anonymous reviewers.

Opencast mining of sulfide ore deposits may lead to the formation of anthropogenic acidic lakes with highly polluted waters. In these systems, it is crucial to understand the hydrological connections between surface and groundwater and their contribution to the pollutant load delivered to the downgradient streams. This study characterizes the interactions between surface and groundwater in an acidic pit lake using different geochemical tracers (i.e., REE and other trace metals). The San Telmo pit lake, located in one of the most pollutant sources of the Iberian Pyrite Belt (IPB), can be considered as a flow-through pit lake except during dry periods, when it behaves as a terminal lake due to lower inputs by surface waters and higher outputs by evaporation. Results based on geochemical tracers indicate that the main inputs to the pit lake come from surface waters, with minor groundwater inputs rich in As, Cr, Cu, Fe and Pb. The contaminant load released from the mining area is very high (e.g., median values of 520 kg/day of Fe and 38 kg/day of Zn), causing the degradation of the fluvial network downstream. Most of released pollutants come from waste dumps located at the W of the mining zone (~50–70% of Al, Cd, Mg, Mn, Ni, SO4 and Zn and > 70% for Cu, Cr, Fe and, V), while the contribution of the water coming out the pit lake and other dumps is much lower. Thus, remediation efforts to improve the area and fluvial courses downstream must focus on the W waste dumps., 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). C.R Cánovas thanks the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowship granted under application reference RYC2019-027949-I. F. Macias was funded by the R&D FEDER Andalucía 2014–2020 call through the project RENOVAME (FEDER;UHU-1255729).The commentsand helpful criticisms of two anonymous reviewers and the support of Dr. Jose Virgilio Cruz (Associate Editor) have considerably improved the original manuscript and are also gratefully acknowledged. Funding for open access charge: Universidad de Huelva / CBUA.

Los ríos que drenan la Faja Pirítica Ibérica (FPI) presentan un grave problema de contaminación por aguas ácidas procedentes de minas de sulfuros abandonadas. La construcción de la presa de Alcolea, localizada en el río Odiel, se empezó en 2014 pero se paralizó en 2017, aunque actualmente hay una fuerte presión de los regantes para que se retome. Debido a la acidez que presenta el río Odiel existe una gran polémica sobre la calidad del agua de este embalse. En este trabajo se investiga la calidad del agua en los grandes embalses de la FPI a partir de la información analítica de la red oficial de control de calidad. Los embalses no afectados por aguas ácidas (Jarrama y Corumbel) tienen valores de pH próximos a neutros y muy baja concentración de sulfatos (, The rivers of the Iberian Pyrite Belt (IPB) have a very serious problem of contamination by acid waters from abandoned sulphide mines, intensely exploited in the past. The most extreme and well-known case is the Tinto river, but this problem affects a much greater length of fluvial courses in the Odiel river basin. Other rivers in the IPB that also receive acid leachates, although with less intensity, are the Rivera del Chanza and the Guadiamar. In 2014, the Alcolea dam began to be built on the Odiel River, mainly for agricultural use. This construction was stopped in 2017 but currently there is a strong pressure from the irrigators to resume it. Due to the conditions of the Odiel River in this area, with pH values below 4 and high concentrations of toxic metals, there is great uncertainty about the quality of the water that this reservoir will store. In this work, the quality of the water in the large reservoirs of the IPB is investigated from the analytical information of the official quality control network (period 2008 to 2021). The reservoirs not affected by acid mine waters (Jarrama and Corumbel) have pH values close to circumneutral and very low concentrations of sulphates (

Unlike acidic sulfide mine wastes, where metal/loid mobility and bioaccessibility has been widely studied, less attention has been paid to alkaline cyanide heap leaching wastes. Thus, the main goal of this study is to evaluate the mobility and bioaccessibility of metal/loids in Fe-rich (up to 55%) mine wastes resulting from historical cyanide leaching activities. Wastes are mainly composed of oxides/oxyhydroxides (i.e. goethite and hematite), oxyhydroxisulfates (i.e. jarosite), sulfates (i.e., gypsum, evaporitic sulfate salts), carbonates (i.e., calcite, siderite) and quartz, with noticeable concentrations of metal/loids (e.g., 1453–6943 mg/kg of As, 5216–15,672 mg/kg; of Pb, 308–1094 mg/kg of Sb, 181–1174 mg/kg of Cu, or 97–1517 mg/kg of Zn). The wastes displayed a high reactivity upon rainfall contact associated to the dissolution of secondary minerals such as carbonates, gypsum, and other sulfates, exceeding the threshold values for hazardous wastes in some heap levels for Se, Cu, Zn, As, and sulfate leading to potential significant risks for aquatic life. High concentrations of Fe, Pb, and Al were released during the simulation of digestive ingestion of waste particles, with average values of 4825 mg/kg of Fe, 1672 mg/kg of Pb, and 807 mg/kg of Al. Mineralogy may control the mobility and bioaccessibility of metal/loids under rainfall events. However, in the case of the bioaccessible fractions different associations may be observed: i) the dissolution of gypsum, jarosite and hematite would mainly release Fe, As, Pb, Cu, Se, Sb and Tl; ii) the dissolution of an un-identified mineral (e.g., aluminosilicate or Mn oxide) would lead to the release of Ni, Co, Al and Mn and iii) the acid attack of silicate materials and goethite would enhance the bioaccessibility of V and Cr. This study highlights the hazardousness of wastes from cyanide heap leaching, and the need to adopt restoration measures in historical mine sites., This work was supported by the Spanish Ministry of Economic and Competitiveness through the projects TRAMPA (PID2020–119196RBC21) and by H2020 European Institute of Innovation and Technology (EIT RawMaterials) through the project Modular recovery process services for hydrometallurgy and water treatment (MORECOVERY). This work was partially supported by FCT (Portugal) through contract UID/ Multi/04349/2019. C.R C´anovas thanks the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowship granted under application reference RYC2019–027949-I. M.D. Basallote thanks the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowship granted under application reference IJC 2018–035056-I. The authors would also like to thank to Prof. Edward D. Burton, Ph.D (Editor) and three anonymous reviewers for the support and comments that notably improved the quality of the original paper.

This study deals with the potential release of metal/loids from sulfide mine wastes upon weathering and the health risks associated with their accidental ingestion. To address this, a complete chemical and mineralogical characterization of a variety of sulfide mine wastes was performed alongside a determination of metal/loid bioaccessibility through leaching tests simulating human digestive and lung fluids. The mine wastes consisted predominantly of Fe (35–55% of Fe2O3) and exhibited high concentrations of trace metalloids such as As (382–4310 mg/kg), Pb (205–15,974 mg/kg), Cu (78–1083 mg/kg), Zn (274–1863 mg/kg), or Sb (520–1816 mg/ kg). Most wastes with high concentrations of soluble compounds are considered hazardous according to the European regulations due to the exceedance of threshold values for As, Pb, Cr, Cu, Sb, sulfates, and Zn determined by standardized tests. In general terms, the absorption of waste-hosted metals through both digestive and respiratory routes was low compared to the total metal contents of the wastes, with values below 8% of the total concentration in wastes for most metal/loids including Cu, Zn, As, Cd, Tl, or U. However, some metals exhibited a significantly higher absorption potential, especially through the respiratory route, reaching values of up to 17% for Cr and 75% for Pb, highlighting the strong bioaccessibility of Pb in certain sulfide wastes. Despite the high metal/loid concentrations observed in the studied wastes, a health risk assessment indicated that some noncarcinogenic effects could be observed in children only following the accidental digestion of Pb., This work was supported by the Spanish Ministry of Economy and Competitiveness under the research project TRAMPA (MINECO; PID2020-119196RB-C21). C.R C´anovas thanks the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowship granted under application reference RYC2019-027949-I. BCL, AAB and TGB were supported by projects PG2018-096608-B-C21 from the Spanish Ministry of Science and innovation (MINECO) and P20-00366 (Ministry of Economy, Knowledge, Business and Universities, Regional Government of Andalusia, Spain). We would also like to thank to the Editor Dr. Hefa Cheng and five anonymous reviewers for the support and comments that notably improved the quality of the original paper. Funding for open access charge: Universidad de Huelva / CBUA.

This works investigates the origin, behavior and fate of Tl in acid mine drainage (AMD) affected areas at catchment scale, following the path from rocks to the ocean. To address this issue, comprehensive data set of Tl in rocks, waters, secondary minerals, plants and other environmental compartments is presented, using the Iberian Pyrite Belt (SW Spain) as representative example. The content of Tl in host rocks (mean of 0.51 mg/kg) exhibits moderate positive correlations with elements such as K and Rb, whereas no correlations were observed in sulfides (27 mg/kg) between Tl, Fe and other metal/loids commonly found in these minerals, such as As, Pb, Cd, Cu or Zn. During sulfide oxidation processes, Tl is mobilized from sulfides, as evidenced by the depletion of Tl in gossans (1.8 mg/kg), and host rock minerals, leading to a Tl enrichment in AMD leachates (mean of 242 μg/L), with concentrations of up to 8.3 mg/L, several orders of magnitude higher than those reported in natural waters. The precipitation of secondary minerals, with large surface areas, may be a sink for Tl, especially in jarosite minerals (8.4 mg/kg). Thallium can be also removed during the treatment of AMD in alkaline passive treatment systems due mainly to sorption processes onto Fe and Al secondary minerals (i.e., schwertmannite and basaluminite, respectively). Mean Tl contents of 13 mg/kg have been observed in wastes dumped in abandoned mines of the IPB, mainly spoil heaps, slags, roasted pyrite, heap leaching wastes and tailings. However, there is no clear relationship between Tl content and the type of mining wastes. These wastes can suffer weathering, leading to an enrichment of Tl in soils. Previous studies reported that, This work was supported by the Spanish Ministry of Economy and Competitiveness under the research project TRAMPA (MINECO; PID2020-119196RB-C21) and the Andalusian Regional Government under the AIHODIEL project (PYC20 RE 032 UHU) within the FEDER program. C.R Canovas thanks the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowship granted under application reference RYC2019-027949-I. M.D. Basallote thanks the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowship granted under application reference IJC2018-035056-I. Funding for open access charge: Universidad de Huelva /CBUA

Sulfide-mining wastes may lead to severe environmental and human health risks, especially challenging in abandoned mines without environmental regulation. This work is aimed at discussing the environmental problems associated with this type of wastes, the risks posed by metal(loid) exposure to living organisms, as well as the measures available to mitigate such risks, taking the case of the Iberian Pyrite Belt (SW Iberian Peninsula), as an example, worldwide. The release of metal(loid)s from these wastes upon weathering is strongly controlled by mineral assemblage, processing technique, grain size distribution, and occurrence of highly reactive secondary minerals. Exposure to these wastes may pose a severe risk for humans and animals, and thus, remediation measures must be adopted in abandoned mines. Among these measures, recovery of valuable metals from sulfide wastes could be a promising environmentally friendly solution; however, grade and mineralogical siting of valuable metals, as well as selective recovery methods, must be site-by-site investigated., 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). C.R Ca ́novas and M.D. Basallote thank the Spanish Ministry of Science and Innovation for the Postdoctoral Fellowships granted under application references RYC2019- 027949-I and IJC2018-035056-I, respectively. F. Macı ́as was funded by the R&D FEDER Andalucı ́a 2014e2020 call through the project RENOVAME (FEDER; UHU-1255729). The authors would like to thank to the Guest Editor Dr. Georgios Bartzas and two anonymous reviewers for their helpful comments that notably improved the quality of the original manuscript., Funding for open access charge: Universidad de Huelva / CBUA

Este trabajo estudia la viabilidad de la tecnología conocida como Sustrato Alcalino Disperso (DAS) para el tratamiento pasivo de efluentes extremadamente ácidos y contaminantes procedentes de la balsa de fosfoyesos localizada sobre las marismas del río Tinto (Huelva, SO España). El estudio consiste en hacer fluir el agua ácida a través de una columna rellena con una mezcla de un reactivo alcalino (i.e. Ca(OH)2 ) disperso en una matriz inerte (i.e. virutas de madera) capaz de elevar el pH del lixiviado y precipitar los contaminantes disueltos. El sistema de tratamiento DAS-Ca(OH)2 logró la retirada total de PO4 , F, Fe, Zn, Al, Cr, U y As de las soluciones. La precipitación de brushita [CaHPO4 ∙2H2 O] y yeso [CaSO4 ·2H2 O] fue el principal mecanismo responsable de la eliminación de los contaminantes. Los sólidos retenidos en la columna DAS después del tratamiento fueron sometidos al test de lixiviación EN 12457-2 de la EU para su clasificación y gestión de acuerdo a su peligrosidad. Algunos de estos sólidos podrían ser clasificados como residuos peligrosos, debido a la alta concentración de SO4 lixiviado. Este estudio contribuye al diseño de un tratamiento efectivo y sostenible de los lixiviados procedentes de la industria fertilizante, This work studies the feasibility of the Dispersed Alkaline Substrate (DAS) technology for the passive treatment of highly acidic and polluted effluents from the phosphogypsum stack located on the Tinto river marsh soils (Huelva, SW Spain). The study consists of flowing the acidic water through a column filled with a mixture of an alkaline reagent (i.e. Ca(OH)2 ) scattered on an inert matrix (i.e. wood chips) capable of raising the pH of the leachate and precipitating the dissolved pollutants. The Ca(OH)2 -DAS treatment system achieved the total removal of PO4 , F, Fe, Zn, Al, Cr, U and As from the solutions. The precipitation of brushite [CaHPO4 ∙2H2 O] and gypsum [CaSO4 ∙2H2 O] seems to be the main mechanism responsible for the removal of contaminants. The solids collected from the DAS column were subjected to the EU EN 12457-2 leaching test for their classification and management according to their hazardousness. Some of these solids could be classified as hazardous wastes due to the high release of SO4 . This study may contribute to the design of an effective and sustainable treatment of leachates from the fertilizer industry

Este trabajo trata de explorar el potencial de los fosfoyesos generados en una planta de fertilizantes en el SO España como fuente de elementos de interés económico, estimando las reservas disponibles y evaluando las limitaciones tecnológicas y económicas en la valorización de estos residuos. Las leyes de elementos de interés económico observadas en estos residuos están por debajo de las leyes explotadas actualmente en depósitos convencionales. Sin embargo, el gran volumen de residuos depositados (100 Mt) constituye una gran fuente secundaria de elementos. Alrededor de 304001 de B, 280001 de tierras raras, 18001 de U, 14001 de Cr, 1300 t de V y cantidades inferiores de otros elementos (Cu, Ni, Se, Ga, etc.) están contenidas en los fosfoyesos de Huelva. El elevado precio en el mercado de alguno de esos elementos justificaría su explotación. La recuperación de estos elementos es técnicamente posible, aunque se precisan mejoras en los procesos de refinado para incrementar la pureza del producto final This paper addresses the potential of the phosphogypsum generated by a fertilizer plant in SW Spain as a source of elements of economic interest, estimating the available metal reserves and discussing the technological and economic pros and cons of this potential source of raw materials. In general, elements of economic interest are found in these wastes below h e grades commonly reported in conventional deposits. However, the huge tonnage of wastes stockpiled constitutes a significant secondary source of elements. Around 30,4001 of B, 28,0001 of rare earth elements (REE), 1800 t of 1400 t of Cr, 1300 t of V and lesser amounts of other elements of economic interest (e.g. Cu, Ni, Sc and Ga) are enclosed in the phosphogypsum. The high market values for some of these elements could justify their exploitation. The recovery of these elements is technically feasible, although intense research in refining processes is needed in order to increase the purity of the final product

Este trabajo trata de explorar el potencial de los fosfoyesos generados en una planta de fertilizantes en el SO España como fuente de elementos de interés económico, estimando las reservas disponibles y evaluando las limitaciones tecnológicas y económicas en la valorización de estos residuos. Las leyes de elementos de interés económico observadas en estos residuos están por debajo de las leyes explotadas actualmente en depósitos convencionales. Sin embargo, el gran volumen de residuos depositados (100 Mt) constituye una gran fuente secundaria de elementos. Alrededor de 304001 de B, 280001 de tierras raras, 18001 de U, 14001 de Cr, 1300 t de V y cantidades inferiores de otros elementos (Cu, Ni, Se, Ga, etc.) están contenidas en los fosfoyesos de Huelva. El elevado precio en el mercado de alguno de esos elementos justificaría su explotación. La recuperación de estos elementos es técnicamente posible, aunque se precisan mejoras en los procesos de refinado para incrementar la pureza del producto final, This paper addresses the potential of the phosphogypsum generated by a fertilizer plant in SW Spain as a source of elements of economic interest, estimating the available metal reserves and discussing the technological and economic pros and cons of this potential source of raw materials. In general, elements of economic interest are found in these wastes below h e grades commonly reported in conventional deposits. However, the huge tonnage of wastes stockpiled constitutes a significant secondary source of elements. Around 30,4001 of B, 28,0001 of rare earth elements (REE), 1800 t of 1400 t of Cr, 1300 t of V and lesser amounts of other elements of economic interest (e.g. Cu, Ni, Sc and Ga) are enclosed in the phosphogypsum. The high market values for some of these elements could justify their exploitation. The recovery of these elements is technically feasible, although intense research in refining processes is needed in order to increase the purity of the final product

This work quantifies the impact of the first acid mine discharges to the Odiel River and studies the variation of the dissolved and particulate pollutant load. The acid mine discharges cause the progressive deterioration of the river water quality, resulting in processes that favor the precipitation of the non-conservative elements (Fe, Al, As or Pb), while the more soluble ones (Mn, Co or Ni) remain in solution. Cu and Zn have an intermediate behavior due to be affected by sorption/coprecipitation processes. The dissolved pollutant load at the end of the reach is around 5000 kg/day of Al, 1900 kg/day of Fe, 860 kg/day of Zn, 643 kg/day of Mn, 385 kg/day of Cu and lower amounts of other metals. The total metal load may be up to 21 times the dissolve load in the case of Fe and among 3-4 times for As and Pb Este trabajo cuantifica la repercusión de los primeros vertidos de mina en un tramo del Río Odiel y se estudian las variaciones de la carga metálica disuelta y particulada. La confluencia de las sucesivas descargas ácidas de mina provoca el empeoramiento progresivo de la calidad del agua, dando lugar a procesos que favorecen la precipitación de elementos no conservativos (Fe, Al, As o Pb) mientras que los elementos más móviles (Mn, Co o Ni) permanecen en disolución. Cu y Zn poseen un comportamiento intermedio debido a que están afectados por procesos de adsorción/coprecipitación. La carga disuelta transportada al final del tramo es aproximadamente 5000 kg/día de Al, 1900 kg/día de Fe, 860 kg/día de Zn, 643 kg/día de Mn, 385 kg/día de Cu y cantidades inferiores de otros metales. La carga metálica total es hasta 21 veces superior a la disuelta en el caso del Fe y entre 3-4 veces superior para As y Pb

This work quantifies the impact of the first acid mine discharges to the Odiel River and studies the variation of the dissolved and particulate pollutant load. The acid mine discharges cause the progressive deterioration of the river water quality, resulting in processes that favor the precipitation of the non-conservative elements (Fe, Al, As or Pb), while the more soluble ones (Mn, Co or Ni) remain in solution. Cu and Zn have an intermediate behavior due to be affected by sorption/coprecipitation processes. The dissolved pollutant load at the end of the reach is around 5000 kg/day of Al, 1900 kg/day of Fe, 860 kg/day of Zn, 643 kg/day of Mn, 385 kg/day of Cu and lower amounts of other metals. The total metal load may be up to 21 times the dissolve load in the case of Fe and among 3-4 times for As and Pb, Este trabajo cuantifica la repercusión de los primeros vertidos de mina en un tramo del Río Odiel y se estudian las variaciones de la carga metálica disuelta y particulada. La confluencia de las sucesivas descargas ácidas de mina provoca el empeoramiento progresivo de la calidad del agua, dando lugar a procesos que favorecen la precipitación de elementos no conservativos (Fe, Al, As o Pb) mientras que los elementos más móviles (Mn, Co o Ni) permanecen en disolución. Cu y Zn poseen un comportamiento intermedio debido a que están afectados por procesos de adsorción/coprecipitación. La carga disuelta transportada al final del tramo es aproximadamente 5000 kg/día de Al, 1900 kg/día de Fe, 860 kg/día de Zn, 643 kg/día de Mn, 385 kg/día de Cu y cantidades inferiores de otros metales. La carga metálica total es hasta 21 veces superior a la disuelta en el caso del Fe y entre 3-4 veces superior para As y Pb

This study provides information on the physicochemical processes of water and sediments from San Telmo pit lake. It is a valuable tool to evaluate best treatment remediation options in the long term. This lake has a meromictic nature, is highly acidic (pH of 2.8) and pH- buffered by Fe(III) precipitation. In San Telmo sediments, iron reduction and sulphide oxidation may be thermodynamically favoured due to low pH values in pore waters and the abundance of schwertmannite. The transformation of schwertmannite into goethite may limit sulphate reduction. As far as the Acid Mine Drainage pressure on the lake remains, the pH buffering exerted by schwertmannite in sediments will limit natural attenuation processes by sulphate reduct Este trabajo estudia los procesos físico-químicos en las aguas y sedimentos de la corta minera de San Telmo, que supone una información valiosa para adoptar las medidas óptimas de remediación a largo plazo. Este lago de origen minero presenta meromixis, una elevada acidez (pH 2.8) y sus aguas están tamponadas por la precipitación de Fe(III). Los bajos valores de pH y la abundancia de schwertmannita en los sedimentos favorecen termodinámicamente los procesos de reducción de Fe y oxidación de sulfuros. La transformación de schwertmannita en fases minerales más cristalinas, como la goethita, parece tamponar el pH en el agua de poro, limitando los procesos de reducción de sulfatos. La neutralización de la acidez en los sedimentos por reducción de sulfatos no será posible en tanto no disminuya el aporte actual de AMD a la corta

An understanding of pollutant processes in rivers under different hydrological conditions is essential to assess its long-term evolution. This is especially relevant in Mediterranean rivers during rain events, when most of the water, suspended particulate matter (SPM), and pollutants are delivered. This study investigates the hydrochemical changes and pollutant fluxes in the Odiel River (SW Spain) during rainy conditions. For this purpose, high-resolution sampling (6 h) was performed to monitor dissolved and total concentrations of pollutants. During the rises in discharge, most dissolved elements had decreased concentrations due to the dilution effect of runoff waters and Fe precipitation processes. However, the particulate concentrations of some elements (As, Fe, Pb, Cr, Ti, V, and Ba) increased due to Fe-rich sediment remobilization, and to a lesser extent, direct precipitation. A two end-member mixing model applied to the collected data showed that the contribution of nonaffected waters was ∼85%–98% of the total discharge, highlighting the importance of mining lixiviates in the deterioration of Odiel water quality. An innovative methodology was applied to estimate dissolved and total pollutant loads, based on the relationships between dissolved concentrations and electrical conductivity (EC), and total concentrations and river flow. The importance of particulate metal transport during rain events in the Odiel River was significant. The total transport of Fe was 37 times higher than dissolved Fe, was almost 7 times higher for Pb, and 5 times higher for Cr, while As (1.1 t) was totally transported by particulate matter., This work has been financed by the Spanish Ministry of Education and Science through project CGL2010-21956-C02. CRC was financially supported by the Spanish Government with a research contract within the "Juan de la Cierva" program. The authors wish to thank the Environmental Council of the Andalusian Regional Government for the information provided for this study. We are grateful to John Selker, three anonymous reviewers and the associate editor Heidi Nepf for their insightful comments.

This study provides information on the physicochemical processes of water and sediments from San Telmo pit lake. It is a valuable tool to evaluate best treatment remediation options in the long term. This lake has a meromictic nature, is highly acidic (pH of 2.8) and pH- buffered by Fe(III) precipitation. In San Telmo sediments, iron reduction and sulphide oxidation may be thermodynamically favoured due to low pH values in pore waters and the abundance of schwertmannite. The transformation of schwertmannite into goethite may limit sulphate reduction. As far as the Acid Mine Drainage pressure on the lake remains, the pH buffering exerted by schwertmannite in sediments will limit natural attenuation processes by sulphate reduct, Este trabajo estudia los procesos físico-químicos en las aguas y sedimentos de la corta minera de San Telmo, que supone una información valiosa para adoptar las medidas óptimas de remediación a largo plazo. Este lago de origen minero presenta meromixis, una elevada acidez (pH 2.8) y sus aguas están tamponadas por la precipitación de Fe(III). Los bajos valores de pH y la abundancia de schwertmannita en los sedimentos favorecen termodinámicamente los procesos de reducción de Fe y oxidación de sulfuros. La transformación de schwertmannita en fases minerales más cristalinas, como la goethita, parece tamponar el pH en el agua de poro, limitando los procesos de reducción de sulfatos. La neutralización de la acidez en los sedimentos por reducción de sulfatos no será posible en tanto no disminuya el aporte actual de AMD a la corta

Pirítica Ibérica (FPI), una de las principales regiones metalogénicas del mundo, por lo que ambos ríos están profundamente degradados por los lixiviados generados por el Los ríos Tinto y Odiel discurren en su mayor parte por materiales de la llamada Faja proceso conocido como drenaje ácido de mina (AMD).El río Tinto recibe, en relación a su caudal, aproximadamente el doble de contaminantes que el Odiel, por ello las condiciones en el Tinto son más extremas. En ambos sistemas los bajos valores de pH, muy constantes a lo largo del año se deben a las reacciones de hidrólisis de Fe disuelto, y posibilita la presencia en disolución de elevadas concentraciones de metales tóxicos. La calidad del agua de los ríos Tinto y Odiel sigue un patrón estacional, la concentración de la mayoría de elementos es menor durante el invierno y aumenta progresivamente durante la primavera y el verano.---------------------------The Tinto and Odiel rivers drain one of the most important mining regions in the world, the Iberian Pyrite Belt (IPB), an as a consecuence both rivers are deeply affected by acid mine drainage (AMD). The Tinto river receives, in relation to its discharge, twice as much pollutants than the Odiel, being this the reason why more extrem conditions can be found in the Tinto. Low pH values in both systems througthout the year are due to Fe hydrolysis reactions that buffer pH and contribute to reach high dissolved toxic metal concentrations. Water quality in both rivers follows a seasonal pattern. Most elements show lowest values during winter, increasing progressively in spring and summer.

The Odiel River drains the central part of the Iberian Pyrite Belt, an area with many polymetallic massive sulphide mines that have been worked since prehistoric times. As a consequence of the oxidative dissolution of the sulphides exposed in the surface associated to mining activities, acid mine drainage pollution is an important processes in the Odiel basin that lower considerably the water quality of the river. In fact, near its mouth, the Odiel river has a very low pH and high concentrations of metals and metalloids in solution. Two reservoirs are planned in the Odiel river within the National Hydrologic Plan: Alcolea and Coronada. The construction of the Alcolea dam is suppose to start this year, with a total planned investment of 200.000.000 . After the study and analysis of the water quality in the watershed of the Alcolea dam, and the study of the chemical evolution with time in others water dams in the Odiel basin, the inferred longterm quality for the water in the Alcolea dam will not allow its direct use for agriculture or industrial uses. Therefore, taking into account the important investment planned and the poor quality of the water expected, it is necessary an important re-evaluation of the original project that takes into account, in a more rigorous way, the final quality of the water accumulated in the dam

The Odiel River drains the central part of the Iberian Pyrite Belt, an area with many polymetallic massive sulphide mines that have been worked since prehistoric times. As a consequence of the oxidative dissolution of the sulphides exposed in the surface associated to mining activities, acid mine drainage pollution is an important processes in the Odiel basin that lower considerably the water quality of the river. In fact, near its mouth, the Odiel river has a very low pH and high concentrations of metals and metalloids in solution. Two reservoirs are planned in the Odiel river within the National Hydrologic Plan: Alcolea and Coronada. The construction of the Alcolea dam is suppose to start this year, with a total planned investment of 200.000.000 . After the study and analysis of the water quality in the watershed of the Alcolea dam, and the study of the chemical evolution with time in others water dams in the Odiel basin, the inferred longterm quality for the water in the Alcolea dam will not allow its direct use for agriculture or industrial uses. Therefore, taking into account the important investment planned and the poor quality of the water expected, it is necessary an important re-evaluation of the original project that takes into account, in a more rigorous way, the final quality of the water accumulated in the dam

The estuary known as Ría of Huelva receives the flow of two rivers intensely affected by acid mine drainage (AMD), the Odiel and Tinto rivers. The aim of this work is to evaluate the quality and the seasonal variations of the surface waters, no affected by AMD, which drain into the Ría of Huelva. We carried out a sampling campaign during one year in seven streams which drain an agricultural area with some small villages. The hidrochemistry of these streams depends on the lithology of the catchment and anthropogenic inputs. The seasonal dilution of organic discharges and the leaching of nitrates from agricultural activities are the main parameters affecting the quality of the water of these streams

The estuary known as Ría of Huelva receives the flow of two rivers intensely affected by acid mine drainage (AMD), the Odiel and Tinto rivers. The aim of this work is to evaluate the quality and the seasonal variations of the surface waters, no affected by AMD, which drain into the Ría of Huelva. We carried out a sampling campaign during one year in seven streams which drain an agricultural area with some small villages. The hidrochemistry of these streams depends on the lithology of the catchment and anthropogenic inputs. The seasonal dilution of organic discharges and the leaching of nitrates from agricultural activities are the main parameters affecting the quality of the water of these streams

The Tharsis mining district is the second most important of the Iberian Pyrite Belt (IPB). The intense exploitation of sulphides carried out since the Copper Age but, above all, since the second half of 19th century to the end of the 20th century, has left large dumps and other sulphide-rich mining wastes in the area, where acid mine drainages (AMD) are generated, together with four acid pit lakes (Filón Norte, Sierra Bullones, Filón Centro y Filón Sur) A characterization of the hydrological functioning and evolution of the pit lakes (was carried out. A simple methodology based on the use of the available orthophotographs and the Digital Terrain Model (DTM), together with the water balance of the pit lakes was developed, which could be applied to other abandoned mining sites. The accumulation of large volumes (5.2 hm3) of acid and metal-rich waters in these pit lakes poses a serious environmental concern. The results showed that Sierra Bullones and Filón Norte open pits are connected underground and present the same evolution, with a water transference from Sierra Bullones to Filón 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 Filón Centro and Filón 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. In addition, the influence of hydrogeochemical processes and the waste typology on the physicochemical parameters and dissolved concentrations of pollutants in the acid waters generated were studied during three different hydrological conditions (dry, wet and intermediate). Extreme leachates are produced in the area, reaching even negative pH values and concentrations of up to 2.2 g/L of As and 194 g/L of Fe. Lead was 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, showed their maximum concentrations in the dry period, when dilution with freshwater is lower and the water-rock interaction and evaporation is higher. On the other hand, As, Cr, Fe, Pb and V showed minimum concentrations in the dry period due to intense Fe oxyhydroxysulphate precipitation. The highest pollutant load from the Tharsis mines occurs in the wet period (139 ton/day of SO4, 44 ton/day of Fe, 6.7 ton/day of Al, etc.) while in the intermediate period, it is only a quarter, and in the dry period, it is minimal due to the low flows. Approximately half of the pollutants released reaches the Meca River basin, while the other half joins the Oraque River, although some differences occur depending on the element and the season. These discharges acidify the water of the Sancho Reservoir and will compromise the quality of the new reservoir waters, currently in construction downstream the Oraque River The concentrations and normalised patterns of rare earth elements (REEs; subdivided into light (LREEs: La to Sm), middle (MREEs: Eu to Dy) and heavy (HREEs: Ho to Lu)), their behaviour in the fluvial network, and the REEs contributions from AMD sources were also analysed. High concentrations of REEs were observed, with a mean value of 1,747 μg/L. The concentration of REEs shows a positive correlation with electrical conductivity (EC). However, the highest concentrations of REEs occurred in samples with intermediate levels of pollution and EC values. The highest correlations of middle REEs (MREEs) and heavy REEs (HREEs) occurred with elements related to hydrothermal mineralisations of Mn and Ni. The normalised patterns of the AMD showed an enrichment of MREEs over light REEs (LREEs) and HREEs in all samples. The use of REEs patterns as geochemical tracers confirmed the conservative behaviour of REEs in the fluvial network under low acid pH. The quantification of REEs released from AMD sources to water bodies revealed that the main load of REEs occurs during the wet period with 6.6 kg/day of LREEs, 1.1 kg/day of MREEs, and 0.5 kg/day of HREEs., El distrito minero de Tharsis es el segundo más importante de la Faja Ibérica de Pirita (IPB). La intensa explotación de sulfuros llevada a cabo desde la Edad del Cobre pero, sobre todo, desde la segunda mitad del siglo XIX hasta finales del XX ha dejado grandes escombreras y otros residuos mineros ricos en sulfuros en la zona, donde los drenajes ácidos de minas (AMD) son generados, junto con cuatro lagos mineros ácidos (Filón Norte, Sierra Bullones, Filón Centro y Filón Sur). Se realizó una caracterización del funcionamiento hidrológico y evolución de los lagos de mineros. Se desarrolló una metodología simple basada en el uso de las ortofotografías disponibles y el Modelo Digital de Terreno (DTM), junto con el balance hídrico de los lagos mineros, que podría ser aplicado a otros sitios mineros abandonados. La acumulación de grandes volúmenes (5.2 hm3) de aguas ácidas y ricas en metales en estos lagos mineros plantea una grave preocupación ambiental. Los resultados mostraron que las cortas mineras de Sierra Bullones y Filón Norte están conectadas subterráneamente y presentan la misma evolución, con una transferencia de agua de Sierra Bullones a Filón Norte. El nivel del agua en ambos lagos mineros está aumentando, con un aumento promedio de 2.8 m/año desde el comienzo de las inundaciones. Sin embargo, el aumento en la tasa de evaporación, como resultado del incremento del área inundada a medida que aumenta el nivel del agua, induciría un equilibrio hidrológico antes de alcanzar el nivel de desbordamiento, lo que conduciría a la formación de un lago terminal. Por otro lado, el nivel del agua en los lagos mineros de Filón Centro y Filón Sur se mantiene aproximadamente estable. El primero se comporta como un lago flow-through o terminal, dependiendo de la precipitación anual, mientras que el segundo actúa permanentemente como un lago flow-through. Además, se estudió la influencia de los procesos hidrogeoquímicos y la tipología de residuos sobre los parámetros fisicoquímicos y concentraciones disueltas de contaminantes en las aguas ácidas generadas en tres periodos hidrológicos diferentes (seco, húmedo e intermedio). En la zona se producen lixiviados extremos, alcanzando incluso pH negativos y concentraciones de hasta 2.2 g/ L de As y 194 g/L de Fe. El plomo es el elemento menos móvil en disolución probablemente debido a la precipitación de minerales secundarios de Pb y/o su coprecipitación sobre oxihidroxisulfatos de Fe. El arsénico, Cr y V también se coprecipitan con minerales de Fe. Se identificaron patrones estacionales en los contenidos metálicos: elementos provenientes de las rocas hospedantes, como Al, Mn y Ni, mostraron sus concentraciones máximas en el período seco, cuando la dilución con agua dulce es menor y la interacción agua-roca y evaporación es mayor. Por otro lado, As, Cr, Fe, Pb y V mostraron concentraciones mínimas en el período seco debido a la intensa precipitación de oxihidroxisulfato de Fe. La carga contaminante más alta de las minas Tharsis ocurre en el período húmedo (139 ton/día de SO4, 44 ton/día de Fe, 6.7 ton/día de Al, etc.) mientras que en el período intermedio, es solo una cuarta parte, y en el período seco, es mínimo debido a los bajos caudales. Aproximadamente la mitad de los contaminantes liberados llega a la cuenca del río Meca, mientras que la otra mitad se une al río Oraque, aunque se producen algunas diferencias según el elemento y la temporada. Estos vertidos acidifican el agua del Embalse Sancho y comprometerán la calidad de las aguas del nuevo embalse, actualmente en construcción aguas abajo del río Oraque. Las concentraciones y patrones normalizados de elementos de tierras raras (REEs; subdivididos en ligeros (LREEs: La to Sm), medios (MREEs: Eu to Dy) y pesados (HREEs: Ho to Lu)), su comportamiento en la red fluvial y las contribuciones de REEs de fuentes AMD también fueron analizadas. Se observaron altas concentraciones de REEs, con un valor medio de 1,747 μg/L. Las concentraciones de REEs muestran una correlación positiva con la conductividad eléctrica (CE). Sin embargo, las concentraciones más altas de REEs ocurrieron en muestras con niveles intermedios de contaminación y valores de CE. Las correlaciones más altas de REEs medio (MREEs) y REEs pesado (HREEs) ocurrieron con elementos relacionados con mineralizaciones hidrotermales de Mn y Ni. Los patrones normalizados de AMD mostraron un enriquecimiento de MREEs sobre REEs ligero (LREEs) y HREEs en todas las muestras. El uso de patrones REEs como trazadores geoquímicos confirmó el comportamiento conservador del REEs en la red fluvial en condiciones de pH ácido bajo. La cuantificación de REEs liberado de fuentes de AMD a cuerpos de agua reveló que la carga principal de REEs ocurre durante el periodo húmedo con 6.6 kg/día de LREEs, 1.1 kg/día de MREEs y 0.5 kg/día de HREEs.