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Basaluminite is a poorly crystalline aluminum hydroxysulfate that precipitates in waters affected by acid mine drainage (AMD) and in acid sulfate soils (ASS). Its ability to sequester potentially toxic elements, such as Cu and As, makes it an important component of these systems, with strong environmental implications. Although it was initially described as a mineral, basaluminite is now considered a nanoscale variety of felsöbányaite, a rare mineral. In the present study, chemical analyses of natural and synthetic basaluminites are combined with data from advanced nanoscale characterization techniques such as high-energy X-ray diffraction (HEXD) and their corresponding pair distribution function (PDF) analyses, extended X-ray absorption fine structure (EXAFS), and solid-state nuclear magnetic resonance (ssNMR) spectroscopy. X-ray scattering data are analyzed with reverse Monte Carlo (RMC) modeling to obtain an atomistic representation of the disorder presents in this nanomineral. Sulfur K-edge EXAFS results show that sulfate is coordinated to the aluminum-octahedral framework of basaluminite mainly through outer-sphere ligands, though the existence of inner-sphere ligands seems to be significant in synthetic samples. PDF analyses show that both synthetic and natural basaluminites have identical short-range order, with ~1.2 nm coherent domain size, and share structural characteristics with felsöbányaite. Interestingly, 27Al ssNMR reveals the presence of, respectively, ~1 and 5% of tetrahedral and pentahedral coordinations. RMC models of basaluminite highlight the presence of structural point defects. The understanding of this nanocrystalline character has important implications in terms of the reactivity of this nanomineral in AMD and ASS. The lack of correlation between the spatial and temporal occurrence of basaluminite and felsöbányaite suggests that the similarities between both mineral structures could be fortuitous, and highlights the need for a re-evaluation of the status of basaluminite as a nanomineral. [ABSTRACT FROM AUTHOR]

In the Iberian Pyrite Belt (IPB), especially within the Tinto and Odiel River basins, there is a large number of sources of acid mine drainages (AMD), characterised by very extreme pH conditions and pollution levels. This paper studies the main factors governing the composition of the different leachates, based on ionic relationships. Statistically there are no differences between leachates from adits and shafts and other types of AMD sources. The most extreme conditions (pH values near 1, 35 g/L of Fe and 104 mg/L of As) are found in an area of Riotinto covered by milled pyrite wastes, used for the production of copper through leaching. The Cu and Zn ore grades deduced from the leachates are in line with the usual values of the IPB, which indicate a geological control in the composition of the acid mine waters. The lowest SO 4 /Cd and Zn/Cu ratios in the acid leachates are found in the NE of the study area, whereas the minimum values of SO 4 /Ni ratios occur in the center and SW. This seems to be related with the type of deposit: shale-hosted at the southern part of the IPB and felsic volcanoclastic-hosted at the northern part, although there are exceptions to this general pattern. Likewise, the proportions of Fe, Al, Mg, Co, Ni and other elements in the leachates are influenced by the mineralogy and the degree of hydrothermal alteration of each deposit, the latter related with Co/Ni ratio. [ABSTRACT FROM AUTHOR]

It has been estimated that the acid mine drainage (AMD) impacted Odiel river basin in southern Spain supplies 0.37% and 15% of the global riverine fluxes of Cd and Zn to the oceans, respectively (Sarmiento et al., 2009). However, the behaviour of Cd and Zn in the Ria of Huelva estuary, which connects the Odiel and Tinto watersheds with the Gulf of Cadiz, has yet to be fully investigated. Furthermore, very few studies have investigated Cd and Zn isotope behaviour in estuaries worldwide. This study presents Cd and Zn concentrations and isotopic compositions for the Ria of Huelva estuary and surrounding watersheds, sampled in 2017 and 2019. Sulfide-rich rock samples extracted from three mines yield Cd and Zn isotope compositions that range from –0.14‰ to +0.07‰ (n = 4) for δ114Cd and –0.01‰ to +0.29‰ (n = 4) for δ66Zn. However, a uniform riverine signal of about +0.02‰ for Cd and +0.17‰ for Zn indicates that tracing of individual mining regions using Cd and Zn isotopes is challenging. Limited variability was observed in dissolved δ114Cd values throughout the watershed, including AMD, the estuary, and the Gulf of Cadiz, with a mean value of ±0.00 ± 0.13‰ (n = 25, 2 SD; excludes one AMD outlier, at +0.48‰), including both 2017 and 2019 data. By contrast, δ66Zn values ranged from –0.12‰ to +0.35‰ (n = 28) for the same geographical and temporal scope. In May 2017, a large spill from an abandoned mine, La Zarza, resulted in a drastic increase in the concentrations of trace metals reaching the estuary compared to 2019, but no impact of this mine spill on Cd or Zn isotope compositions is observed. In 2019, an increase in δ66Zn values in the estuary coincided with high pH values (up to pH = 8.8) and chloride concentrations (2.73%), which may reflect an alkaline anthropogenic input from the active neighbouring industrial complex. Overall, Cd concentrations and isotope compositions in the estuary are largely consistent with conservative mixing behaviour. By contrast, Zn behaviour is non-conservative, with removal of 49–97% of dissolved riverine Zn in the estuary during the period 2017–2019, associated with a relatively small isotopic shift to lighter Zn isotope compositions. Removal of Zn to the particulate phase in the Ria of Huelva estuary therefore largely attenuates high riverine Zn fluxes from AMD, indicating that previously estimated Odiel river basin Zn fluxes were overestimated. Nevertheless, the variable but generally light AMD Cd and Zn isotope compositions, coupled with high dissolved metal concentrations, suggest that Cd and Zn isotopes may be useful tracers of regionally averaged AMD inputs to the Gulf of Cadiz and beyond. [ABSTRACT FROM AUTHOR]

Abstract: Rare earth elements (REE) were analyzed in surface sediments from the Guadiana Estuary (SW Iberian Pyrite Belt). NASC (North American Shale Composite) normalized REE patterns show clearly convex curvatures in middle-REE (MREE) with respect to light- and heavy-REE, indicating acid-mixing processes between fluvial waters affected by acid mine drainage (AMD) and seawater. However, REE distributions in the mouth (closer to the coastal area) show slightly LREE-enriched and flat patterns, indicating saline-mixing processes typical of the coastal zone. NASC-normalized ratios (La/Gd and La/Yb) do not discriminate between both mixing processes in the estuary. Instead, a new parameter (EMREE) has been applied to measure the curvature in the MREE segment. The values of EMREE >0 are indicative of acid signatures and their spatial distribution reveal the existence of two decantation zones from flocculation processes related to drought periods and flood events. Studying REE fractionation through the EMREE may serve as a good proxy for AMD-pollution in estuarine environments in relation to the traditional methods. [Copyright &y& Elsevier]

During 20 months of proper operation the full scale passive treatment in Mina Esperanza (SW Spain) produced around 100 mg/L of ferric iron in the aeration cascades, removing an average net acidity up to 1500 mg/L as CaCO3 and not having any significant clogging problem. Complete Al, As, Cd, Cr, Cu, Ti and V removal from the water was accomplished through almost the entire operation time while Fe removal ranged between 170 and 620 mg/L. The system operated at a mean inflow rate of 43 m3/day achieving an acid load reduction of 597 g·(m2 day)−1, more than 10 times higher than the generally accepted 40 g·(m2 day)−1 value commonly used as a passive treatment system designing criteria. The high performance achieved by the passive treatment system at Mina Esperanza demonstrates that this innovative treatment design is a simple, efficient and long lasting remediation option to treat highly polluted acid mine drainage. [Copyright &y& Elsevier]

Acid mine drainage remediation is an unresolved matter in abandoned mining districts around the world. Development and implementation of passive treatment systems in these areas are commonly focused on engineering and water quality aspects. Neoformed mineral phases precipitated within the reactive material of these passive treatments account for the removal of pollutants but also can cause clogging and passivation of the reactive substrate. After 20 months of operation and monitoring, the limestone-based passive treatment system implemented in Mina Esperanza (SW Spain) was sampled to study the relationship between water chemistry, mineral composition of the neoformed precipitates, and treatment performance. Water chemical profiles show the existence of three precipitation zones controlled by Fe, Al, and Zn hydrochemistry and also a migration with time of precipitation zones downward into the reactive material. These precipitation zones were also confirmed by a mineral study performed on the solid samples where either schwertmannite and goethite or hydrobasaluminite and Zn-rich green rust were the mineral phases that controlled the metal removal in the three precipation (Fe, Al, or Zn) zones. Iron and Al precipitates were observed to play a critical role in the time evolution of the reactive material hydraulic conductivity. Furthermore, Al precipitates passivated to some extent the limestone grains by armoring, although migration of the Fe precipitation zone and Al redissolution later activated the limestone grains. A higher proportion of limestone in the reactive mixture and the addition of new reagents to the bottom section of the reactive material (to enhance the reducing environment and to promote divalent metal removal) are proposed on the basis of this hydrochemical and mineralogical study for a future design for the Mina Esperanza passive treatment system. [ABSTRACT FROM AUTHOR]

Metal removal and neutralization of acid mine drainage (AMD) in treatment systems is often controlled by addition of alkaline reagents and metal hydrolysis reactions. To overcome the disadvantage of high cost by conventional treatments, the use of paper mill wastes was evaluated as an alkaline additive to treat AMD at sites within the Iberian Pyrite Belt (IPB) through batch experiments in the laboratory. Paper wastes include three by-products from kraft pulping in a nearby mill: green liquor dregs, slacker grits, and lime mud. When paper mill wastes interacted with AMD, the initial pH increased up to circumneutral values and enhanced greatly the metal removal, reaching average ratios of up to 100% for Al, 98% for Fe, and 66% for Zn (major elements) and 100% for As, Cr, and Cu, 84% for Cd, and 75% for Ni (minor elements). After reaction, gypsum and poorly crystalline Fe-Al oxy-hydroxides and oxy-hydroxysulfates were the main precipitates identified by X-ray diffraction and scanning electron microscopy. Trace metal uptake is mainly attributed to co-precipitation and/or adsorption onto the newly formed Fe-Al precipitates. Geochemical modeling of solutions using the PHREEQC code predicted supersaturation of the observed phases. The experimental results were optimized with the PHREEQC code and combined with the annual production of each waste to quantify the extent of a possible treatment at field-scale. According to our estimations, the system proposed is able to treat effectively an annual total volume of 11.6 hm³, which is equivalent to a mean discharge of 368 L/s. Green liquor dregs alone would be able to treat 86% of the total volume. This result demonstrates the possibility of using alkaline paper mill wastes for treatment and restoration of worldwide natural resources extremely contaminated by AMD such as the IPB. [ABSTRACT FROM AUTHOR]

Abstract: 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: 231mg/L of Fe, 135mg/L of Al, 56mg/L of Zn, 16mg/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. [Copyright &y& Elsevier]

In the present study, experiments in non-saturated leaching columns were conducted to characterize the neoformed phases that precipitate at the interface between two waste residues having different chemical characteristics: an acid mine drainage producer residue (i.e., pyritic sludge) and an acidity neutralizer residue (i.e., coal combustion fly ash). A heating source was placed on top of one of the columns to accelerate oxidation and precipitation of newly formed phases, and thus, to observe longer-scale processes. When both residues are deposited together, the resulting leachates are characterized by alkaline pH, and low sulfate and metal concentrations. Two mechanisms help to improve the quality of the leachates. Over short-time scales, the leaching of pyrite at high pH (as a consequence of fly ash addition) favors the precipitation of ferrihydrite, encapsulating the pyrite grains and attenuating the oxidation process. Over longer time scales, a hardpan is promoted at the interface between both residues due to the precipitation of ferrihydrite, jarosite, and a Ca phase-gypsum or aragonite, depending on carbonate ion activity. Geochemical modeling of leachates using PHREEQC software predicted supersaturation in the observed minerals. The development of a relatively rigid crust at the interface favors the isolation of the mining waste from weathering processes, helped by the cementation of fly ash owing to aragonite precipitation, which ensures total isolation and neutralization of the mine residues. [ABSTRACT FROM AUTHOR]

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. [Copyright &y& Elsevier]

The production of Acid Mine Drainage (AMD) as a result of the oxidative dissolution of sulphides is one of the main pollution problems affecting natural watercourses in mining environments with sulphide-rich residues. In this work, the generation of AMD was prevented by means of the addition of fly ash to sulphide-rich residues in non-saturated column experiments. A column experiment filled with a pyrite-rich sludge with artificial irrigation leached acid drainages (pH approx. 2) containing high concentrations of sulphate, iron and other metals. However, non-saturated column experiments filled with pyritic-rich sludge and fly ash drained leachates characterized by alkaline pH (pH up to 10), low sulphate concentration, and lack of iron and other metals in solution. The pyrite oxidative dissolution at high pH, as a consequence of the leaching of fly ash, favours the metal precipitation inside the column (mainly iron), the coating of pyrite grains, and the attenuation of the oxidation process, resulting in a great improvement in the quality of the leachates. [Copyright &y& Elsevier]

A preservation study has been performed for arsenic speciation in surface freshwaters affected by acid mine drainage (AMD), a pollution source characterized by low pH and high metallic content. Two sample preservation procedures described in the literature were attempted using opaque glass containers and refrigeration: i) addition of 0.25 mol L−1 EDTA to the samples, which maintained the stability of the arsenic species for 3 h; and ii) in situ sample clean-up with a cationic exchange resin, in order to reduce the metallic load, which resulted in a partial co-adsorption of arsenic onto Fe precipitates. A new proposed method was also tried: sample acidification with 6 mol L−1 HCl followed by in situ clean-up with a cationic exchange resin, which allowed a longer preservation time of at least 48 h. The proposed method was successfully applied to water samples with high arsenic content, taken from the Aguas Agrias Stream (Odiel River Basin, SW Spain), which is severely affected by AMD that originates at the nearby polymetallic sulfide mine of Tharsis. The speciation results obtained by liquid chromatography–hydride generation–atomic fluorescence spectrometry (HPLC-HG-AFS) indicated that during the summer the main arsenic species was As(V) at the hundred μg L−1 level, followed by DMA (dimethyl arsenic) and As(III) below the ten μg L−1 level. In winter, As(V) and As(III) increased at least fivefold, whereas the DMA was not detected. [ABSTRACT FROM AUTHOR]

The Río 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 Río 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. [ABSTRACT FROM AUTHOR]

Acid mine drainage (AMD) generated from coal and sulfide mining has attracted much interest due to the high concentrations of rare earth elements (REE) observed. However, the origin of REE in AMD and particularly the mechanism of enrichment in medium REE remain uncertain. The combined study of Sr and Nd isotopes can be used to trace the processes that control the mobility and fractionation of REE in aquatic systems such as AMD. This work reports for the first time worldwide isotopic data of Sr and Nd in AMDs from sulfide mining (Iberian Pyrite Belt, SW Spain) and compare with those in host rocks. Additionally, leaching experiments have been carried out to simulate the water–rock interactions found in these acidic systems. The results obtained strongly suggest that the origin of REE in AMDs from metal mining may be related to the preferential dissolution of shales and felsic rocks. The suitability of Sr and Nd isotopic signatures to trace the REE source in AMD-affected systems has been proven, it provides a new environmental and geochemical prospecting tool which could be useful in different geological water–rock interaction systems. [ABSTRACT FROM AUTHOR]

Water resources management and restoration strategies, and subsequently ecological and human life quality, are highly influenced by the presence of short and long term cycles affecting the intensity of a targeted pollution. On this respect, a typical acid mine drainage (AMD) groundwater from a sulfide mining district with dry Mediterranean climate (Iberian Pyrite Belt, SW Spain) was studied to unravel the effect of long term weather changes in water flow rate and metal pollutants concentration. Three well differentiated polluting stages were observed and the specific geochemical, mineralogical and hydrological processes involved (pyrite and enclosing rocks dissolution, evaporitic salts precipitation-redisolution and pluviometric long term fluctuations) were discussed. Evidencing the importance of including longer background monitoring stage in AMD management and restoration strategies, the present study strongly advise a minimum 5-years period of AMD continuous monitoring previous to the design of any AMD remediation system in regions with dry Mediterranean climate. [ABSTRACT FROM AUTHOR]

Abstract: As acid mine drainage (AMD) remediation is increasingly faced by governments and mining industries worldwide, the generation of metal-rich solid residues from the treatments plants is concomitantly raising. A proper environmental management of these metal-rich wastes requires a detailed characterization of the metal mobility as well as an assessment of this new residues stability. The European standard leaching test EN 12457-2, the US EPA TCLP test and the BCR sequential extraction procedure were selected to address the environmental assessment of dispersed alkaline substrate (DAS) residues generated in AMD passive treatment systems. Significant discrepancies were observed in the hazardousness classification of the residues according to the TCLP or EN 12457-2 test. Furthermore, the absence of some important metals (like Fe or Al) in the regulatory limits employed in both leaching tests severely restricts their applicability for metal-rich wastes. The results obtained in the BCR sequential extraction suggest an important influence of the landfill environmental conditions on the metals released from the wastes. To ensure a complete stability of the pollutants in the studied DAS-wastes the contact with water or any other leaching solutions must be avoided and a dry environment needs to be provided in the landfill disposal selected. [Copyright &y& Elsevier]

Acid mine drainage (AMD) from the Iberian Pyrite Belt has high acidity and metal concentrations. Earlier pilot experiments, based on limestone sand dispersed in wood shavings (dispersed alkaline substrate; DAS) have been shown to be an efficient treatment option. However, complete metal removal was not achieved, principally due to the high ferrous iron concentration in the inflow AMD. In order to oxidize and remove iron, a natural Fe-oxidizing lagoon (NFOL) was added prior to treatment with limestone–DAS. The NFOL comprises several pre-existing Fe-stromatolite terraces and cascades, and a lagoon with a volume of 100 m3 built near the mine shaft. Downstream of the NFOL, the limestone–DAS treatment consists of two reactive tanks of 3 m3 each filled with limestone–DAS reactive substrate, connected in series with two decantation ponds of 6 m3 each and several oxidation cascades. The AMD emerging from the mine shaft displayed a pH near 3, a net acidity of 1800 mg/L as CaCO3 equivalents, and mean concentrations of 440 mg/L Zn; 275 mg/L Fe (99% Fe(II)); 3600 mg/L SO4; 250 mg/L Ca; 100 mg/L Al; 15 mg/L Mn; 5 mg/L Cu; and 0.1–1 mg/L As, Pb, Cr, Cd, Co, and Ni. The oxidation induced in the NFOL enhanced ferric iron concentration, showing an average of 65% oxidation and 38% retention during the monitoring period. The whole system removed a mean of 1350 mg/L net acidity as CaCO3 equivalents (71% of inflow); corresponding to 100% of Fe, Al, Cu, Pb and As, and 6% of Zn. [Copyright &y& Elsevier]

Abstract: Metal contamination from acid mine drainage (AMD) is a serious problem in the southwest of the Iberian Peninsula, where the Iberian Pyrite Belt is located. This zone contains original sulfide reserves of about 1700Mt distributed among more than 50 massive sulfide deposits. Weathering of these minerals releases to the waters significant quantities of toxic elements, which severely affect the sediments and surface waters of the region. The main goal of this paper is to evaluate the toxicity and the potential risk associated with the mining areas using Microtox test and different factors which assess the degree of contamination of the sediments and waters. For this, a natural stream polluted by AMD-discharge from an abandoned mine has been studied. The results show that elevated concentrations of Cu, As and Zn involve an important potential risk on the aquatic environment, associated both with sediments and waters. Microtox test informs that the sediments are extremely or very toxic, mainly related to concentrations of Fe, As, Cr, Al, Cd, Cu and Zn. Pollution is mainly transferred to the sediments increasing their potential toxicity. A natural creek affected by AMD can store a huge amount of pollution in its sediments while exhibiting a not very low water pH and low water metal concentration. [Copyright &y& Elsevier]

Abstract: Gossan, disseminated orebody waste, other mining wastes, minesoils and acid mine drainage (AMD) in the abandoned São Domingos mine area (Iberian Pyrite Belt, IPB) have been analyzed for rare earth elements (REE). The main aim is to understand REE mobility during sulphide weathering so that the lanthanide series can be used both as a record of the water–rock interaction and as a tool for identifying impacts of AMD on natural ecosystems. North-American Shale Composite (NASC)-normalized REE patterns corresponding to the disseminated orebody waste are relatively flat (E MREE =−0.01±0.12). However, NASC-normalized REE distributions in AMD from sulphide oxidation tend to be enriched in middle-REE (MREE) compared to light-REE (LREE) and heavy-REE (HREE). As a consequence, gossan resulting from supergene alteration of massive sulphide presents an evident NASC-normalized MREE-depleted signature. Thus, the overall water–sulphide interaction defines complementary convex (E MREE =+0.72±0.25) and concave (E MREE =−0.31±0.12) NASC-normalized patterns in draining waters and oxidation products, respectively. Solutions extracted from minesoils have also NASC-normalized patterns with MREE-enriched signature (E MREE =+0.62±0.22) similar to AMD. The E MREE parameter is proposed to measure the curvature in the MREE segment, and its size is quantified as the normalized maximum vertical difference between the polynomial curve fitting of the MREE region and its theoretical Y-axis position in the absence of enrichment or depletion (E MREE >0 for MREE-enriched signatures; <0 for MREE-depleted signatures; and =0 for horizontal patterns). The São Domingos stream, although it has been highly affected by AMD, flows into the Guadiana river that has an estuarine system where pollution is considerably attenuated due to the mixing, according to the metal geoaccumulation indexes currently used in the literature. However, sediments of this estuary were also analyzed and reflect MREE-enriched signatures (E MREE =+0.25±0.03), which demonstrate that this apparently non-polluted estuarine system is being certainly affected by historical mining activities from the IPB. The E MREE index is more sensitive to recognize curved MREE-signatures than other normalized ratios such as (La/Gd)NASC, validating the use of REE patterns as a proxy for environmental pollution by AMD. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

Abstract: São Domingos is one of the most emblematic Portuguese mining districts in the Iberian Pyrite Belt (IPB). The beginning of mining exploitation in the area has been dated back to pre-Roman times, remaining in activity until 1966 when it was definitely halted. The intense mining labours are reflected in the presence of a huge amount of sulphide-mining wastes and downstream production of acid mine drainage (AMD). The mining wastes in the area are highly heterogeneous, and numerous different types may be recognized, including slags, iron oxides, smelting ashes, brittle and blocks of pyrite, leaching tank refuses, industrial landfill and other residues coming from ore extraction (gossan wastes and country rocks). The chemical speciation of potentially toxic elements (As, Cd, Cr, Cu, Fe, Mn, Pb, S, Sb and Zn) in all mine wastes from São Domingos was determined by modified BCR-sequential extraction procedure (European Community Bureau of Reference) and combined with the mass/volume proportions of each waste to quantify the potential risk of this mining district at regional scale. Analytical recoveries by sequential extraction, with respect to a pseudo-total metal content digestion, were generally acceptable (100±17%). The oxidizable fraction corresponds with metals bound to sulphides and released easily under oxidizing conditions in AMD production processes. This is the most polluting fraction for the environment in this type of residues. Part of this fraction is retained by precipitation of soluble secondary minerals in warm periods, moving to the bio-available fraction that is dissolved in rainy periods. Just considering the bio-available fraction, all mine wastes from São Domingos may leach up to 172514ton of Fe, 10564ton of S, 6644ton of Pb, 2610ton of Zn, 1126ton of Mn, 1032ton of Cu, 183ton of Cr, 109ton of As, 34ton of Sb and 0.9ton of Cd. The process of precipitation and re-dissolution of efflorescent salts formed directly by oxidation of the oxidizable fraction is seasonally repeated, which causes an annual self-feeding and releasing of the bio-available fraction. Thus, the present study shows the pollutant potential of this IPB mining district and explains the spoiled state of the fluvial courses in the region. [Copyright &y& Elsevier]

This study evaluates the effectiveness of dispersed alkaline substrate (DAS) technology to treat highly acidic and contaminated leachates from the oxidation of sulfide-rich mining wastes under wet temperate oceanic climate conditions. To address this issue, leachates from the abandoned mine at Parys Mountain (NW Wales) were passed through two sets of multistep columns filled with a mixture of a fine-grained alkaline reagent (i.e., limestone, MgO, or BaCO 3) scattered in an inert matrix. The set of columns with the limestone-DAS plus MgO-DAS combination achieved a near total removal of Fe, Al, Zn, Cu, Mn, As, Co, Cd, and Ni. However, the elimination of SO 4 was not significant (around 7%). The limestone-DAS plus BaCO 3 -DAS combination also achieved a high effectiveness for base metal/loids, allowing the removal of Fe, Al, Zn, Cu, As, and Cd with rates of nearly 100%. In addition, the system with the BaCO 3 -step had a higher effectiveness in eliminating SO 4 (around 53%) than the combined treatment with the MgO-step. According to PHREEQC code calculations, the precipitation of oxy-hydroxy-sulfates (i.e., schwertmannite and basaluminite) and carbonate (i.e., malachite, hydrozincite and calcite) phases may have controlled the solubility of pollutants during the passive treatment. The chemical compositions of the treated waters complied with the threshold values defined by irrigation standards, except for Mn in the BaCO 3 -DAS output. [Display omitted] • Multistep DAS treatment systems improved notably the chemical water quality. • Total metal removal was achieved with the limestone-DAS plus MgO-DAS combination. • MgO is more effective than BaCO 3 for the removal of divalent metals contained in AMD. • Metal concentrations in the MgO-DAS output are below the limits for irrigation water. • Solids from DAS systems could be considered a secondary source of base metals. [ABSTRACT FROM AUTHOR]

Lanthanide series have been used as a record of the water–rock interaction and work as a tool for identifying impacts of acid mine drainage (lixiviate residue derived from sulphide oxidation). The application of North-American Shale Composite-normalized rare earth elements patterns to these minority elements allows determining the origin of the contamination. In the current study, geochemical patterns were applied to rare earth elements bioaccumulated in the soft tissue of the freshwater clam Corbicula fluminea after exposure to different acid mine drainage contaminated environments. Results show significant bioaccumulation of rare earth elements in soft tissue of the clam after 14 days of exposure to acid mine drainage contaminated sediment ( ΣREE = 1.3–8 μg/g dw). Furthermore, it was possible to biomonitor different degrees of contamination based on rare earth elements in tissue. The pattern of this type of contamination describes a particular curve characterized by an enrichment in the middle rare earth elements; a homologous pattern (E MREE = 0.90) has also been observed when applied NASC normalization in clam tissues. Results of lanthanides found in clams were contrasted with the paucity of toxicity studies, determining risk caused by light rare earth elements in the Odiel River close to the Estuary. The current study purposes the use of clam as an innovative “bio-tool” for the biogeochemical monitoring of pollution inputs that determines the acid mine drainage networks affection. [ABSTRACT FROM AUTHOR]

This study assesses the environmental impact and the potential valorization of metal-sludge waste generated by the active neutralization of extremely metal-polluted acid mine drainage (AMD). To this end, two regulated leaching tests (EN 12457-2 and 1311 USEPA TCLP), a standardized sequential extraction protocol (BCR sequential extraction) and single leaching tests were performed using dilute common industrial acids. The results of the two standardized leaching tests showed a complete discrepancy, classifying the waste as both inert (according to the TCLP) and not suitable for disposal at landfills for hazardous waste (according to EN 12457-2). In this regard, the environmental characterization of the waste using the BCR sequential extraction lined up with interpretations made by the EN 12457-2 leaching test, reinforcing the hazardousness of this type of residue. This waste requires careful management, as evidenced by the release of high concentrations of metals (e.g., Cd, Zn, Al) when interaction with rainfall and organic acids take place, exceeding the risk threshold values for aquatic life. The easy extraction of base, industrial- and tech-metals that is possible with dilute acids encourages the consideration of this type of sludge as an interesting alternative metal source with great economic potential. The joint application of remediation treatments and metal recovery schemes could contribute to the goal of zero waste production in mining activities, which would help to develop sustainable mining practices worldwide. [ABSTRACT FROM AUTHOR]

[Display omitted] • Preferential leaching evidence of REE-rich minerals has been observed. • REE-rich minerals (phosphates and carbonates) seem to be REE source in the AMD. • Ce and Eu anomalies are inherited in leachate from rock, serving as REE source tracer. • REE fractionation during water–rock interaction produces MREE-enriched patterns. • Shales and igneous rocks show the highest REE release rate in the IPB. Acid mine drainage (AMD) is a worldwide pollution problem of watersheds. In addition to toxic metal(oid)s and acidity, many elements of economic interest are released into the environment, which make AMD a potential strategic secondary source of these elements such as rare earth elements (REE). Despite the importance of these metals, their origin in AMD is still uncertain. Recent hypotheses suggest preferential leaching of REE-enriched minerals as a possible source. Leaching tests with H 2 SO 4 have been developed to simulate the interaction under AMD formation conditions with sulfide bodies and host rocks from two representative mining areas in the Iberian Pyrite Belt: the Perrrunal and Poderosa mines (SW of Spain). The REE patterns and Ce and Eu anomalies of the rock leachates have confirmed the geochemical relationship between the AMD and certain country rocks (felsic and mafic volcanics, and shales). A detailed chemical and mineralogical study has confirmed the existence of a diversity of minerals with high concentrations of REE. Thus, the minerals with the highest REE contents are also those with the fast dissolution kinetics under acid conditions: REE phosphates (monazite and xenotime type) and carbonates (parisite type). Finally, petrographic evidence of the selective leaching of these minerals clearly supports these minerals as the main source of REE in the AMD. [ABSTRACT FROM AUTHOR]

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 <25% of total Tl is easily extractable, being mainly adsorbed to crystalline Fe oxides in acidic soils and Al oxides in neutral-alkaline soils. Despite this, Tl may be translocated by plants. The translocation of Tl in plants of the IPB has not been properly addressed, however previous studies in other areas showed a low phytoavailability of Tl compared to Cd and Zn, although Tl translocation appears to be strongly controlled by plant species or by differences in Tl speciation. The weathering of rocks, mine wastes and soils may lead to the release of notable amounts of both dissolved and particulate Tl to the hydrosphere. In acidic conditions, Tl seems to be mainly transported by the dissolved phase in AMD-affected streams and rivers, with <15% being transported by the particulate matter. This latter Tl transport may be associated to its incorporation into diatoms and Fe minerals such as jarosite after replacement of Tl+ by H+ in their structure. Subsequent release by desorption processes from jarosite and diatoms in acidic conditions can occur. This process has also been observed in estuaries affected by AMD, thus, Tl transported by jarosite minerals in the particulate matter and diatoms are released back to the estuarine waters across the salinity gradient due to the increasing proportion of unreactive TlCl0 and K+ ions, which compete for adsorption sites in jarosite with Tl+. Thus, enhanced transport of Tl to the oceans is observed in AMD-affected systems. [Display omitted] • The origin, behavior and fate of Tl in mineralized catchment was investigated. • Tl in rocks, waters, secondary minerals, plants and other reservoirs was analyzed. • High Tl concentrations in acid mine drainage due to intense sulfide oxidation. • Tl mobility controlled by the precipitation of secondary minerals and sorption. • Sorption competition between Tl+ and K+ controls Tl mobility in estuaries. [ABSTRACT FROM AUTHOR]

Abstract: A 44 m-thick lacustrine succession of silty-clay banded ochres and subordinated sandstones, and conglomerates (known as the Corral Amarillo Formation) is superbly exposed within the Famatina Belt (Central Andes of Argentina) after deep entrenchment by the present-day Amarillo river due to strong recent uplifting and consequent relative drop in base level. The unusual ochreous-rich succession was produced by natural damming (3.48–3.54 14C kyr BP) of an acid drainage system linked to the alteration cap of polymetallic deposits. Facies of silty-clay ochre (wet season) and banded ochre (dry season) from the paleolacustrine setting are composed of jarosite + goethite and goethite respectively. Geochemically, these layers record high concentrations of Fe2O3 (25–55 wt. %) and trace elements (Cu, Zn, Co, As, and Mo with mean concentrations of 2759; 2467; 109; 375 and 116 ppm, respectively). Their origin is inferred from a comparative analysis with the present-day Amarillo river, which has a pH of ∼3, (SO4)2− concentrations of ∼5000 mg/l, and jarosite as the dominant phase, in the upper catchments. Waters downstream have pH values of 3–4.5, (SO4)2− concentrations of ∼3000–480 mg/l, and schwertmannite as the dominant phase. Thus goethite in the paleolake facies is likely related to schwertmannite transformation by an aging process, whereas jarosite is probably transported from the river but could also be associated with post-depositional formation regulated by variations in grain size and the pore fluid chemistry. The Corral Amarillo Formation offers a Natural model, which may be employed to infer the effect on nature of acid drainage of mineralized areas. [Copyright &y& Elsevier]

Abstract: The role of metastable nanocrystalline precursors, like schwertmannite, in iron and sulfate rich acidic waters is commonly underestimated or even neglected. In addition to schwertmannite metastability, its heterogeneous chemical composition and the current use of disparate solubility products result in an incongruous understanding of this mineral. In order to characterize schwertmannite stability in acid mine drainage settings, we used coincident schwertmannite and solution samples to determine how its solubility product is related to its composition. The solubility products (as log K sp) for 30 natural samples of this study span a range of log K sp values from 5.8 to 39.5. These values show a gradual distribution on the pH–pe space from pH1.93 to 4.71 and pe values from 8.5 to 13.7. A set of three predictive equations to select the best schwertmannite solubility product for each new specific case study was obtained. This approximation allows generating an appropriate solubility product for schwertmannite despite the lack of information in certain environments (e.g., absence of former water chemistries on Mars). The trend observed for Fe and S contents in schwertmannite can be interpreted as a pseudo-solid solution ranging from high to low S and Fe concentrations. The polyphasic nature of schwertmannite was studied by means of a thermodynamic model assuming equilibrium between a hydrous ferric oxide (HFO), schwertmannite, and solution. All the results obtained in this study support the understanding of schwertmannite as a polyphasic nanomineral and encourage using a broad log K sp range to model the solubility of schwertmannite in nature. [Copyright &y& Elsevier]

Abstract: Pilot-scale field experiments were conducted to test a strategy for the treatment of acid mine drainage by addition of an alkaline cover of coal combustion fly ash on two sulfide mine tailings impoundments (Iberian Pyrite Belt, SW Spain). During the pilot-scale treatment, calcium-rich alkaline solutions from fly ash interacted with metal-rich acidic solutions from the mine tailings, leading to the massive precipitation of newly-formed phases mainly in the fly ash close to the interface between both materials. Over time, the interaction between fly ash and pyrite sludge promoted the formation of a chemically cemented zone or hardpan, which was analyzed at high spatial resolution by micro-X-ray diffraction (μ-XRD) and micro-X-ray fluorescence (μ-XRF) based on synchrotron radiation. These micro-characterization techniques extensively identified poorly-crystalline Fe oxyhydroxysulfates, jarosite and gypsum as newly-formed phases in the hardpan, and gypsum in the fly ash. As deduced from Principal Component Analysis of the fluorescence intensity data, these phases seem to exert a significant mineralogical control on element mobility; in particular, jarosite showed high affinity for As, whereas poorly-crystalline Fe-rich assemblages selectively concentrated Mn, Ni and Pb. Sequential extractions indicated that the application of a fly ash cover significantly reduced the bioavailability of most of the elements by modification of their chemical speciation into less mobile forms under typical oxidizing conditions. As an additional advantage, the development of the hardpan hindered the penetration of oxidizing agents to sulfide mine tailings. This effect significantly reduced the sulfide oxidation rates, therefore attenuating the release of potentially pollutant elements to the environment. [Copyright &y& Elsevier]

Abstract: A detailed study of two adjacent mine tailings impoundments comparing mineralogical and geochemical analyses of the solids with geochemical analysis of the pore-water and -gas was carried out in the Monte Romero sulfide mining district (Iberian Pyrite Belt, SW Spain). Since 1978, both facilities have been exposed to weathering in a semi-arid climate with dry-warm and wet-rainy seasons. In these impoundments, sulfide oxidation releases sulfate and contaminants to the pore-water that are transported and concentrated by evaporation in the top surface of the tailings, causing precipitation of soluble iron sulfate salts in dry seasons. These salts act as temporary sinks for minor elements such as Cd, Co, Zn, Ni, Cu and Mn, which are again released during rainfall events in wet seasons. Stored flotation tailings have an average pyrite content of 30wt.% although average amounts up to 80% are present in the upper 50cm of one of the impoundments. According to the results of the current study, this difference is key to control the oxidation model in both tailings. In the impoundment containing 30wt.% of pyrite, pore-water pH increases in wet periods to 3.1 average by rainwater dilution, causing supersaturation and precipitation of secondary Fe(III) phases such as jarosite, goethite and schwertmannite. Consequently, this impoundment shows a 20–25cm thick yellowish oxidation layer in the top part. In contrast, in the impoundment containing 80wt.% of pyrite in the top part extremely acidic pore-waters (pH<0.5) are present in both dry and wet seasons, and no precipitation of secondary Fe(III) phases occurs in the oxidation zone. The absence of secondary precipitates explains the apparent unweathered aspect of these tailings, in spite of its much higher remobilization of contaminants to the surface runoff or groundwaters. [Copyright &y& Elsevier]

Abstract: Intensive mining has taken place in the Iberian Pyrite Belt since 3000 B.C. generating Acid Mine Drainage (AMD) and releasing high amounts of SO4, acidity, metals and metalloids into surface water. Concentrations of elements in AMD-impacted waters are regulated by the precipitation of Fe-rich materials and particulate matter can influence the mobility and the bioavailability of metals. In this paper a study on the dissolved As species concentration along a polluted stream has been performed. Two sampling campaigns were conducted during the dry and the rainy seasons. Concentrations of dissolved elements are higher during the dry season and increase progressively along the water course in both seasons. Concentrations up to 80μgL−1 of As3+ and 5mgL−1 of As5+ were determined. The concentration of As species increases and the As3+/As5+ ratio decreases downstream. The Fe2+/Fe3+ and As3+/As5+ ratios show the same pattern with respect to pH for all the examined samples, except those taken from Au cyanidation wastes. The particulate phase is mainly composed of Fe, As and Pb, with As being associated with the Fe minerals while Pb seems to be associated with the clay colloids. [Copyright &y& Elsevier]

Abstract: 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 (R 2 >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. [Copyright &y& Elsevier]

Abstract: Complete metal removal from highly-polluted acid mine drainage was attained by the use of a pilot multi-step passive remediation system. The remediation strategy employed can conceptually be subdivided into a first section where the complete trivalent metal removal was achieved by the employment of a previously tested limestone-based passive remediation technology followed by the use of a novel reactive substrate (caustic magnesia powder dispersed in a wood shavings matrix) obtaining a total divalent metal precipitation. This MgO-step was capable to abate high concentrations of Zn together with Mn, Cd, Co and Ni below the recommended limits for drinking waters. A reactive transport model anticipates that 1m3 of MgO-DAS (1m thick×1m2 section) would be able to treat a flow of 0.5L/min of a highly acidic water (total acidity of 788mg/L CaCO3) for more than 3years. [Copyright &y& Elsevier]

Abstract: The city of Huelva and surrounding areas are affected by several sources of pollution such as acid mine drainage, industrial complexes, urban wastes and agriculture activities that could pose an important environmental risk. For this reason, the modified BCR (three steps) sequential extraction method was applied to evaluate the mobility and bioavailability of the trace elements in 25 representative samples of the study area. The operational scheme of the BCR was classified into three steps: water/acid soluble fraction, reducible and oxidisable fraction. The mobility sequence based on the sum of three first phases was: Cu (82.01%)>Zn (71.14%)>Cd (68.35%)>Ni (50.44%)>Pb (36.39%)>Cr (29.22%)>As (18.82%). Among metals, Cd poses a serious threat to human health and the environment due to the calculated high percentage of mobility. Additionally, multivariate statistical techniques (principal components and cluster analyses) were applied to the chemical results to evaluate the degree of metallic pollution and the levels of association between the variables (metal-metalloids) at the different steps of sequential extraction and to recognise possible sources of potential contamination. The PCA suggests that the study area is influenced by four sources of anthropogenic contributions: acid mine drainage, industrial activities, traffic, and agriculture, aside from the natural sources characteristic of the zone. Calculated environmental risk index reveal a considerable-high ecological risk in the saltmarshes of the Huelva estuary probably related to acid mine drainage and the industrial complexes located in these areas, while in the north sector of Huelva the metallic content is more closer to the natural sources values. The results obtained suggest the need for corrective remediation measures due to the higher accumulation of potentially dangerous metals, which in most cases exceed the limits established by certain legislation. [Copyright &y& Elsevier]

Abstract: The study of the different biotic and abiotic processes involved in the current formation of Fe-stromatolites in rivers affected by acid mine drainage (AMD) is essential not only to understand this unique and extreme environment, but also to achieve a better understanding of the past iron formation on the Earth and on Mars. The Fe-stromatolites studied in the highly polluted AMD in Tharsis, SW Spain, revealed a unique mineral assemblage with jarosite and rostite as the most unexpected Fe and Al phases and goethite and schwertmannite as the main constituents. Seasonal variations in this region greatly affected the composition of the precipitates and the distribution of diatoms within the Fe-stromatolites. Drought and flood events were also recognized in the sedimentary textures and in the mineral assemblages observed of particular layers within the Fe-stromatolites. The characterization of the chemical and mineralogical composition of Fe-stromatolites in Tharsis as well as the different formation mechanisms proposed complement the existing literature on newly-formed Fe-stromatolites and provides new observations to increase our understanding of those extreme environments. [Copyright &y& Elsevier]

Abstract: At present, environmental geochemical cartography using GIS-GeoDAS combined software has become an important tool in the study of polluted soils. Huelva Township, where several sources of pollution (related to acid mine drainage, industrial complexes, urban wastes…) take place is a singular environment to determine the geogenic natural content (background) and the anthropogenic contribution (baseline) applying the GIS-GeoDAS analysis. For this purpose, 150 surficial soil samples and 6 soil profiles were collected and analyzed using ICP-MS and ICP-ES for major and trace elements. The statistic analysis and the background values established have allowed to discriminate two ground of elements: a) anthropic sources (F1: Ag, As, Cd, Cu, Pb, Zn and Hg, among others) and b) natural sources (F2: mainly Al, Co, Cr, Ni, V and Be). Additionally, baseline maps show several elements sources related to AMD processes in the floodplain of the Tinto–Odiel estuary (As, Cd, Cu, Pb, and Zn, among others) and also associated with those areas where intense industrial activity has been developed. Arsenic, Cd, Cu, Pb, Ag and Zn baselines values are above the threshold values recommended by the Directive Commission of the European Community for soils and sludge and therefore represent a risk to human health. The established background and baseline values by GIS-GeoDAS could be used as generic values for the proper application of environmental soil regulations in the future. [Copyright &y& Elsevier]

Abstract: In this study, experiments were conducted to investigate the applicability of low-cost alkaline paper mill wastes as acidity neutralizing agents for treatment of acid mine drainage (AMD). Paper wastes include a calcium mud by-product from kraft pulping, and a calcite powder from a previous study focused on sequestering CO2 by carbonation of calcium mud. The neutralization process consisted of increase of pH by alkaline additive dissolution, decrease of metals solubility and precipitation of gypsum and poorly crystallized Fe–Al oxy-hydroxides/oxy-hydroxysulphates, which acted as a sink for trace elements to that extent that solutions reached the pre-potability requirements of water for human consumption. This improvement was supported by geochemical modelling of solutions using PHREEQC software, and observations by scanning electron microscope and X-ray diffraction of reaction products. According to PHREEQC simulations, the annual amount of alkaline additive is able to treat AMD (pH 3.63, sulphate 3800mgL−1, iron 348mgL−1) with an average discharge of about 114 and 40Ls−1 for calcium mud and calcite powder, respectively. Likewise, given the high potential of calcium mud to sequester CO2 and of resulting calcite powder to neutralize AMD, paper wastes could be a promising solution for facing this double environmental problem. [Copyright &y& Elsevier]

Abstract: Passive treatment systems have become one of the most sustainable and feasible ways of remediating acid mine drainage (AMD). However, conventional treatments show early clogging of the porosity or/and coating of the reactive grains when high acidity and metal concentrations are treated. The performance of fine-grained reagents dispersed in a high porosity matrix of wood shavings was tested as an alternative to overcome these durability problems. The system consisted of two tanks of 3m3 filled with limestone sand and wood shavings, and one tank of 1 m3 with caustic magnesia powder and wood shavings, separated by several oxidation cascades and decantation ponds. The system treated about 1.5m3/day of AMD containing an average of 360mg/L Fe, 120mg/L Al, 390mg/L Zn, 10mg/L Cu, 300μg/L As and 140μg/L Pb, a mean pH of 3.08 and a net acidity of 2500mg/L as CaCO3 equivalent. The water reached pH 5 and 6 in the first and second limestone tanks, respectively (suitable to remove trivalent metals); and pH 8–9 in the MgO tank (suitable to remove divalent metals). After 9months of operation, the system achieved an average removal of 100% Al, Cu, As, Pb, more than 70% Fe, about 25% Zn and 80% acidity. Goethite, schwertmannite, hydrobasaluminite, amorphous Al(OH)3 and gypsum were the main precipitates in the two limestone tanks. Precipitation of divalent metals (Fe (II), Zn, and traces of Cd, Ni and Co) were complete inside the third tank of MgO, but preferential flow along the walls was responsible for its low treatment performance. Goethite, gypsum, Zn-schulenbergite and sauconite are the crystalline solid phases identified in the MgO tank. [Copyright &y& Elsevier]

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. [Display omitted] • Almost all acid waters differ from the typical REE normalized pattern expected. • Samples from the same mining complex show a similar HREE/MREE/LREE ratio. • Most of the samples are enriched in the REEs with the highest economic potential. • Acid Mine Drainage could be an almost renewable source of raw materials. • Elements contained in AMD have an annual potential value of around 24.1 million USD. [ABSTRACT FROM AUTHOR]

This paper tries to analyse the technical and economic performance of a full-scale passive Disperse Alkaline Substrate (DAS) treatment plant steadily operating for 28 months (840 days) to treat extremely acidic and metal rich mine waters in the Iberian Pyrite Belt (SW Spain). For the first time, an economic evaluation of this technology and its comparison with other passive treatments is reported. During this period, around 56,000 m3 of mine waters have been treated, without significant clogging or exhaustion of the alkaline substrate. The efficiency of the system is demonstrated by a significant decrease in the average net acidity (from 2005 to −43 mg/L as CaCO 3 equivalent) and the total elimination of Al, Cu, REY, Zn, As, Cr, Mo, V, Cd, Pb, Co and other trace metals. Water quality of the treated output discharge meets the threshold values for irrigation and drinking standards, except for Fe, Mn and sulphate. The accumulation of elements of economic interest in the waste (e.g., 32 t of Fe, 6.1 t of Al, 0.8 t of Cu, 0.8 t of Zn, 39.4 kg of REE, 20 kg of Co or 1 kg of Sc), easily extractable with diluted acids, may turn a hazardous waste into a valuable resource. The benefits associated with the revalorization of this metal-rich waste could reach a total of 27478 USD, but is more reliably estimated to be around 8243 USD due to technologic limitations. This benefit would help to defray the maintenance costs (8428 €) and make DAS an economically self-sustainable treatment. The annual treatment cost for DAS was 0.27 €/m3, being the lowest value found among other reported conventional passive schemes, and from 8 to 12 times lower compared to active technologies. The results obtained prove that the DAS technology is the most technically and economically sustainable way to decontaminate acid and metal-rich mine waters in abandoned mines. Image 1 • A long-term and eco-friendly treatment for highly polluted mine waters was tested. • Removal of total acidity and most metals was achieved during 840 days. • The technology showed an optimal cost-effectiveness (0.27 €/m3). • Around 100 t of recoverable metals were retained in the tanks. • DAS technology is a promising sustainable upcycling solution for AMD pollution. [ABSTRACT FROM AUTHOR]

• An evaporative precipitation sequence of an acid mine drainage was simulated in laboratory under controlled conditions. • Efflorescent salts were composed of Ca (gypsum), Al (alunogen), Mg (hexahydrite), Fe (copiapite, melanterite) minerals. • A preferential pattern of efflorescent salts precipitation was observed: Ca >>> Mg > Al > Fe. • Fe-sulfate minerals presented higher affinity for Cu, Y and Th while Al-Mg sulfate salts retained mainly Zn, Co, and Ni. • Discrepancies between observed and modelled (PHREEQC) results of precipitation sequences were reported. 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, CaSO 4 ·2H 2 O), Al (alunogen, Al 2 (SO 4) 3 ·17H 2 O), Fe (copiapite, Fe2+Fe3+ 4 (SO 4) 6 (OH) 2 ·20H 2 O and melanterite Fe2+SO 4 ·7H 2 O) and Mg (hexahydrite, MgSO 4 ·6H 2 O), 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. [ABSTRACT FROM AUTHOR]