A Numerical Multi-Component Reactive Model for Pyrite Oxidation and Pollutant Transportation in a Pyritic,Carbonate-Rich Coal Waste Pile in Northern Iran

A one-dimensional numerical finite volume model is presented to simulate pyrite oxidation and reactive transportation of the oxidation products in a pyritic, carbonate-rich, coal waste pile. The proposed model incorporates the shrinking core concept for describing pyrite oxidation, pyrite surface area reduction, oxygen diffusion, and transport of the oxidation products through the waste pile. The model governing equations were solved using the PHOENICS computational fluid dynamics model. The accuracy of the model was verified with field data. Pyrite oxidation was more intense at shallower depths where oxygen decreased almost linearly from the pile surface to an approximate depth of 2 m. The lowest pH, 3.5, was predicted at a depth of 0.5 m. The waste pile has high neutralisation potential due to buffering by carbonate minerals. The maximum concentration of SO₄ ^2?, 31.6 mol/m³, was predicted at an approximate depth of 4 m and to remain constant throughout the rest of waste profile. Simulation of a scenario with a cap shows that iron and sulphate was removed from the upper parts of the pile; their peak concentrations shifted downward due to dilution. Oxygen source removal limited iron and sulphate production. These results will be useful for developing an appropriate remediation scheme.     

Hydrogeochemistry and Contamination of Trace Elements in Cu-Porphyry Mine Tailings: A Case Study from the Sarcheshmeh Mine,SE Iran

Geochemical and hydrochemical investigations were performed to understand the contamination potential of the Sarcheshmeh mine tailings. The geochemical mobility for the tailings is as follows: Cu > Cd > Co > Zn > Ni > Mn > S > Cr > Sn > As > Se > Fe = Bi > Sb = Pb = Mo. Highly mobile and contaminant elements (Cd, Cu, Zn, Mn, Co, Ni, S, and Cr), which significantly correlated with each other, were mainly concentrated in the surface evaporative layer of the old, weathered tailings, due to the high evaporation rate, which causes subsurface water to migrate upward via capillary action. The contamination potential associated with the tailings is controlled by: (1) dissolution of secondary evaporative soluble phases, especially after rainfall on the old weathered tailings, accompanied by low pH and high contamination loads of Al, Cd, Co, Mg, Cr, Cu, Mn, Ni, S, Se, and Zn; (2) processing of the Cu-porphyry ore under alkaline conditions, which is responsible for the high Mo (mean of 2.55 mg/L) and very low values of other contaminants in fresh tailings in the decantation pond; (3) low mobility of As, Fe, Pb, Sb, Mo, and Sn due to natural adsorption and co-precipitation in the tailings oxidizing zone. Speciation modeling showed that sulfate complexes (MSO₄ ⁺, M(SO₄)_(aq), M(SO₄) ₂ ^?2 , and M(SO₄) ₂ ^? ) and free metal species (M⁺² and M⁺³) are the dominant forms of dissolved cations in the acidic waters associated with the weathered tailings. In the alkaline and highly alkaline waters, trace element speciation was controlled by various hydroxide complexes, such as M(OH)⁺, M(OH) ₃ ^? , M₃(OH) ₄ ⁺² , M₂(OH) ₃ ⁺ , M(OH)_2(aq), M(OH) ₄ ^?2 , Me(OH) ₂ ⁺ , Me(OH) ₄ ^? , Me(OH) ₂ ⁺ , Me(OH)_3(aq), and Me(OH) ₄ ^? (where M represents bivalent and Me represents trivalent cations). The speciation pattern of As, Mo, and Se is mainly dominated by oxy-anion forms. The obtained results can be used as a basis for environmental management of the Cu-porphyry mine tailings.     

Tailings Weathering and Arsenic Mobility at the Abandoned Zgounder Silver Mine,Morocco

The abandoned Zgounder Mine (Morocco) was exploited for Ag from 1982 to 1990 and generated nearly 490,000 t of mill tailings before it was closed without being reclaimed. The tailings contain low concentrations of sulfide (mainly as pyrite, sphalerite, and galena) and carbonates (mainly dolomite). Silicates (muscovite, albite, chlorite, labradorite, actinolite, and orthoclase) occur in high concentrations. The most abundant trace elements are As, Ti, Fe, Mn, Zn, and Pb. We studied the geochemical behavior of the mine wastes to identify the main factors controlling drainage water chemistry. Particular emphasis was put on sorption phenomena to explain the low As concentrations in the leachates despite significant As levels in the tailings. Weathering cell tests carried out on various tailings produced two types of contaminated drainage: acidic and neutral. The kinetic test leachates contained high concentrations of some contaminants, including As (0.8 mg L^?1), Co (11 mg L^?1), Cu (34 mg L^?1), Fe (70 mg L^?1), Mn (126 mg L^?1), and Zn (314 mg L^?1). Acidity and contaminants in the leachates were controlled by dissolution of soluble salts and Fe hydrolysis rather than sulfide oxidation. Batch sorption tests quantified the significance of As sorption, and sequential extraction showed that most of the As sorption was associated with the reducible fractions (Fe and Mn oxides and oxyhydroxides).     

Mineralogical and Geochemical Characterization of Mine Tailings and Pb, Zn, and Cd Mobility in a Carbonate Setting (Northern Tunisia)

Millions of tonnes of Pb–Zn ore flotation tailings and waste rock have been discharged at sites in northern Tunisia without concern for environmental issues. The tailings are dominantly fine grained (<125 μm), with high porosity and permeability. The tailings were characterized to assess base metal (Pb, Zn, and Cd) mobility. The relatively low percentage of iron sulphide and the dominance of carbonates in the matrices of the tailings indicated that only neutral mine drainage is likely. Batch sequential testing showed that the calcium and sulphate, which are the major ionic species in solution, are derived mainly from the dissolution of gypsum and not from neutralization of acidity generated by pyrite oxidation. Yet, despite the carbonate setting, the resultant neutral to slightly alkaline pH, and prolonged weathering, the studied flotation tailings maintain their capacity to release contaminants, notably Zn and Cd, into the environment. The amount of Zn that dissolves (2,400 μg L^?1, on average), though significant, is below the background concentrations in the Mejerda River and the environmental norms established for surface waters. Pb concentrations come close to the standards, but only Cd (18 μg L^?1, on average) sometimes exceeds current river water concentrations and environmental standards.     

Pyrite Weathering in Reclaimed Shale Overburden at an Oil Sands Mine near Fort McMurray,Canada

Saline-sodic shale overburden associated with oil sand mining is a potential source of salt release to surface water and groundwater and can lead to salinization and/or sodification of reclamation covers. Weathering of shale overburden due to oxidation of sulphide minerals within the shale leads to sulphate (SO₄ ^2?) production and increased salinity. The controls on the rates of weathering of a shale overburden dump in the oil sands region of northern Alberta were determined from soil chemistry sampling and in situ monitoring of pore gases (O₂, CO₂, CH₄) in three shallow profiles (1.9–4.45 m deep) and one deep (25 m deep) profile under reclamation covers of varying thickness. Oxidation, defined by the depth over which O₂ concentrations were depleted, reached depths of approximately 1.1 m under the reclamation soil covers over a 6 year period after dump placement. Calculations of SO₄ ^2? production rates and weathering depths were consistent with numerical simulations of the diffusion and subsequent consumption of atmospheric O₂ in the overburden. The rate of SO₄ ^2? production during the 6 year weathering period estimated from direct measurements of solids chemistry ranged from 0.70 to 8.3 g m^?2 day^?1. The rates calculated from the oxygen diffusion models were within that same range, between 1.6 and 4.1 g m^?2 day^?1.     

Heavy metal pollution diagnosis and ecological risk assessment of the surrounding soils of coal waste pile at Naluo Coal Mine,Liupanshui, Guizhou

In accordance with the National Soil Environmental Quality Standards of China, Grade I and Grade II (GB15618-1995), this study adopted single pollution index (SPI) and Nemeiow synthetical pollution index (NSPI) methods to analyse and assess the ecological risk of the seven heavy metals, namely Cd, Hg, As, Cu, Pb, Cr and Zn, contained in the surrounding soils of one coal waste pile at Naluo Coal Mine, Liupanshui, Guizhou, China. The results revealed that (1) Cd had higher SPI than any other heavy metal and the maximum Cd SPI, indicative of serious pollution, was found in the soil sample collected from the 150 m distant from the centre along possible coal gangue alluvial flow; (2) synthetical pollution assessment of heavy metals per Grade I found that soil sample collected from sites 150 m from the centre along possible coal gangue alluvial flow had the maximum NSPI, which suggests that the soil is seriously polluted, and that there is a link between heavy metal pollution level in the surrounding soils of the coal waste pile and the sampling direction; (3) synthetical pollution assessment of heavy metals per Grade II revealed that sampling distance had a bearing on the pollution level in the surrounding soils of the coal waste pile, and the soil samples collected from 100 or 150 m distant in all the sampling paths had minor pollution.     

Chemical Fractionation and Contamination Intensity of Trace Elements in Stream Sediments at the Sarcheshmeh Porphyry Copper Mine, SE Iran

This paper presents chemical fractionation and contamination intensities of trace elements in stream sediments at the Sarcheshmeh mine, southeastern Iran, which is one of the world’s largest Oligo-Miocene porphyry copper deposits. Evaluation of environmental pollution indices and maximum probable background concentrations revealed that As, Cu, Cd, Mo, Pb, Sb, Se, S, and Zn are highly concentrated in the contaminated sediments, while Cr, Co, Ni, Fe, and Mn show lower enrichment values. Discharges of industrial effluents (especially those contaminated by tailings), reject waste from the semi-autogenous mill, and rock waste drainages are the main anthropogenic contaminant sources. High values of As, Cu, Fe, Mo, Pb, and Zn were associated with the oxidizable, primary sulfide, and residual sediment fractions. Relatively high percentages of Co (>92?%), Cr (>58?%), Cu (>79?%), Fe (>40?%), Mn (>97?%), Ni (>87?%), and Zn (>83?%) in the sediments associated with the rock waste drainages were readily released during the extraction of water-soluble, exchangeable, and carbonate fractions. Sediments that received reject waste drainages were also polluted by As (>351.7?mg?kg^?1), Cu (>1.58?%), Mo (>91.8?mg?kg^?1), Pb (>291.8?mg?kg^?1), and Zn (>762.4?mg?kg^?1). A large percentage of these contaminants were found to be adsorbed and co-precipitated with amorphous Fe-oxides and carbonate phases. The chemical fractionation pattern of the potentially hazardous trace elements corresponded well with the mineralogical composition of the contaminated sediments.     

Evaluation of Hydraulic Conductivity of Itabirites of the Alegria Centro and Alegria Sul Open Pits,Samarco Mineração S.A., Minas Gerais State,Brazil

Itabirites in Samarco Mineração S.A.’s open mine pits in the Quadrilátero Ferrífero region, Minas Gerais State, Brazil, were hydrogeologically characterized. Itabirites, which represent the main aquifer in the region, were divided into four lithotypes based on their mineralogical composition. Statistical analysis of fracture frequency and rock quality designation were evaluated and correlated to hydraulic conductivity results. Preliminary analysis showed a highly fractured rock mass with relatively constant fracturing with depth, regardless of lithology. Field experiments were performed to determine the hydraulic conductivity and provide input data for an analysis of fracture frequency. Infiltration tests showed a median hydraulic conductivity of 1.2 × 10^?7 m/s, while packer tests indicated a median hydraulic conductivity of 9.6 × 10^?7 m/s. Fracture frequency was related to hydraulic conductivity through the cubic law. Median hydraulic conductivity values for the rock types at the mine were found to range from 1.2 × 10^?7 to 1.0 × 10^?6 m/s.     

Geochemical Behavior of Mine Tailings and Waste Rock at the Abandoned Cu–Mo–W Azegour Mine (Occidental High Atlas, Morocco)

The abandoned Azegour mine is located in the High Atlas Mountains of Marrakesh (Morocco), and was mined for Cu, Mo, and W. About 850,000 t of waste rocks and tailings were deposited on the surface and have been exposed to weathering for 40 years. The remaining acid-producing potential (AP), acid-neutralizing potential, and geochemical behavior of the Azegour Cu-and Mo-rich tailings were investigated. The tailings were found to contain 9.6–19 wt% sulfur, mostly as sulfate (gypsum, anhydrite, and jarosite) while the waste rocks contain less (1.25–6.58 wt%) sulfur. The waste rocks and tailings contain 0.21–9.24 wt% Mo and 0.003–2.78 wt% Cu. The gangue is mostly composed of quartz, talc, chlorite, pyrophyllite, actonolite, clinoptilolite, and alusite. Lead, zinc, cobalt, arsenic, titanium, and nickel are also present. The calcium, which is mainly expressed as calcite, gypsum, scheelite, and powellite, is present at higher concentrations in the waste rocks (18–22 wt% Ca) than in the tailings (4.7–8.6 wt% Ca). Static ABA determinations showed that the Azegour mine wastes still have high AP, 38–205 kg CaCO₃/t in the waste rocks and 46–387.7 kg CaCO₃/t in the tailings. This was confirmed in weathering cell tests, where the Azegour tailings leachate had a pH range of 1.98–3.19 and high concentrations of SO₄ (468–45,400 mg/L), Ca (230–675 mg/L), Fe (3–55,900 mg/L), Mn (0.1–1,430 mg/L), and Cu (2.3–9,000 mg/L). The Mo concentrations were high (35 mg/L) during the two first weeks of kinetics tests; W concentrations were below the 0.005 mg/L detection limit.     

Assessment of Metals Pollution from Tailing Sites in the North Caucuses Region,Russia

The concentrations of metals were determined in the water and bottom sediments of both the Urup and Kuban Rivers near tailings sites in the North Caucasus region of southern Russia. The average concentrations in the Urup followed the order Fe?>?Mn?>?Pb?>?Cu?>?Zn?>?Cd?>?Ni?>?Co, while in the Kuban, the order was Fe?>?Pb?>?Zn?>?Ni?>?Mn?>?Cd, with copper and cobalt not detected. The levels of Zn, Cu, Pb, Cd, and Ni were above Russia’s maximum permissible concentration in both rivers. The water pollution index (WPI) values in Urup ranged from 12.97 to 28.17, indicating that the river is extremely polluted (Class VII), while the WPI value for Kuban ranged from 2.34 to 4.33 downstream of the tailings site, which corresponds to Class IV (contaminated). Calculating the coefficient of accumulation in sediments (CAS) revealed that in Urup, the CAS values for Ni and Cu were 3046 and 11638, respectively, which indicates an emergency environmental situation, while for Co, Fe, and Mn, the situation is high level chronic pollution (CAS?>?10⁴). The Kuban CAS values of Fe and Mn were also >?10⁴, again highly and chronically polluted. Most of the metals in both rivers are bound to the sediments, with minimal mobility. The potential ecological risk is moderate to considerable in Urup, and low in the Kuban River.     

Water quality variation of mining-subsidence lake during the initial stage: cases study of Zhangji and Guqiao Mines

Four quarters?? water collecting and monitoring samples were done in the mining subsidence lakes of different water storing periods (2 to 7 years), considering the water storing time and pollution sources state of the subsidence lakes. The following indexes were discussed such as organic indexes (TOC, COD_Mn, BOD, COD), nutrient salts (TN, NH ₄ ⁺ , NO ₃ ^? , NO ₂ ^? , Kjeldahl Nitrogen, TP, PO ₄ ^3? ), etc. It is shown that water quality of the mining subsidence lake during the initial stage (2 years to 7 years) can stay relatively stable with a fluctuation during different quarters in a year, which can reach class III or IV of the Surface Water Environmental Quality Standard.     

Evaluation of Metal Attenuation from Mine Tailings in SE Spain (Sierra Almagrera): A Soil-Leaching Column Study

A laboratory study was undertaken using mine tailings and soil columns to evaluate some of the natural processes that can control the mobility of metals at Pb–Ag mine tailings impoundments. The effects of buffering, pH, and salinity were examined with tailings from the El Arteal deposit. Al, Ba, Cd, Cu, Fe, Mn, Ni, Pb, Sr, and Zn were mobilized when the tailings were leached. However, when the mine tailings were placed above alluvial soils, Al, Ba, Cd, Cu, Mn, Pb, and Zn were retained, although Fe and Sr clearly remained mobile. Most of the metal retention appears to be associated with the increase in pH caused by calcite dissolution. The sorption of some metals (Cu, Pb, and Zn) onto oxyhydroxides of Fe and Mn, sulphates, clay materials, and organic matter may also explain the removal of these metals from the leachate.     

Column Kinetic Tests Assessing Geochemical Behavior of Mine Wastes in the Jerada Coal District (Morocco)

The Jerada anthracite mine in Morocco was abandoned in 2001 after producing approximately 20 million tonnes of solid waste. The acid generating potential of these wastes was determined by performing tests on five samples collected from relatively older and more recent waste deposits. No carbonate minerals were identified. Pyrite was the only sulphide mineral observed and much of it had been completely transformed into Fe-oxides. Analysis of the waste indicated low levels (<1 %) of Ca and Mg, while Fe and Al concentrations generally exceeded 5 %. Modified Sobek static tests and column kinetic tests were conducted for 24 months. The static test results were not conclusive (20 <net neutralising potential <20 Kg CaCO₃/t). Leachates from the kinetic tests for three of the five samples showed an initially acidic pH, while those of the remaining two became acidic by the end of the tests. Sulfate concentrations (SO₄ ^2?) decreased over time from 5000 to 200 mg/L.     

Carbothermal Reduction of Barium Sulfate-Rich Sludge from Acid Mine Drainage Treatment

The alkali–barium–calcium (ABC) desalination process is basically an integrated lime/limestone neutralisation process combined with a sulfate removal stage using barium carbonate (BaCO₃), and a sludge processing stage. The BaSO₄/CaCO₃ sludge generated during the desalination stage is treated to recover BaS and CaO by dewatering and thermal processes, with the ultimate goal of producing sulfur and recovering BaCO₃. BaCO₃ is the main raw material used for sulfate removal and its recovery ensures that the ABC process is environmentally and financially sustainable. South Africa is also a large importer of sulfur. We evaluated the optimum conditions for the thermal treatment of BaSO₄/CaCO₃ sludge to recover by-products. A high temperature tube furnace was used to reduce BaSO₄/CaCO₃ sludge obtained from a pilot plant test conducted at a gold mine shaft. We used response surface methodology to investigate the combined effects of relevant process variables (time, temperature, and the carbon/barium sulfate (C/BaSO₄) molar ratio to maximize the reduction of BaSO₄/CaCO₃ sludge. At optimal process conditions (T = 1,028 °C; molar ratio of C/BaSO₄ = 2.8 mol/mol), the tube furnace yield of BaS from waste sludge was over 78.5 % after 35 min. Furthermore, the results were similar to those generated by roasting a laboratory-grade mixture of barite and calcite concentrates.     

The Oxidative Precipitation of Thallium at Alkaline pH for Treatment of Mining Influenced Water

Thallium (Tl) may exceed regulatory limits in mining-influenced water (MIW) associated with processing cadmium, copper, gold, lead, and zinc ores. It is a toxic metal that is soluble over a wide pH range, resulting in both persistence in the environment and poor removal by conventional lime precipitation. This study evaluated the effect of potassium permanganate (KMnO₄) at alkaline pH on Tl removal from MIW in batch experiments. The oxidation of Tl⁺ to Tl³⁺ by KMnO₄ and subsequent Tl removal was explored at Tl concentrations of ≤1 mg/L in synthetic and actual MIW. In addition to Tl, the synthetic MIW contained ≈5 mg/L of Mn, while the actual MIW contained >10 mg/L of Al, Cu, Fe, Mn, and Zn and had a pH ≈ 2.5. Dissolved Tl <2 μg/L in synthetic MIW was achieved at a pH ≈ 9 (CaO addition) and ≥5 mg/L of KMnO₄. In the actual MIW, dissolved Tl <2 μg/L was achieved at pH ≈ 9 and ≥12 mg/L of KMnO₄. The Tl removal mechanism is complicated due to the presence of reduced Mn in the synthetic MIW and multiple metals in the actual MIW. However, effective Tl removal was achieved by adding KMnO₄ to synthetic and actual MIW at alkaline pH.     

A DFT study on the effect of lattice impurities on the electronic structures and floatability of sphalerite

The electronic structures of bulk sphalerite containing 14 typical kinds of impurities were studied by density-functional theory (DFT). The calculated results show that the presence of Cd, Hg, Ga, Ge, In, Ag, Sn, Pb and Sb could increase the lattice parameter of sphalerite. Ag, Sn, Pb, Sb, Cd and Hg impurities narrowed the band-gap and increased the conductivity of sphalerite. Moreover, Mn, Fe, Ga, In, Sn and Sb impurities changed the semiconductor type of sphalerite from p-type to n-type. All of the impurities except Cd and Hg made the Fermi level shift to higher energy and led to the occurrence of an impurity state in the forbidden band.Analysis of the frontier molecular orbital showed that the impurities Mn, Fe, Cu, Ge, Sn, Pb and Sb contributed greatly to the highest occupied molecular orbital (HOMO) and greatly influence the nucleophilicity of sphalerite. On the other hand, the impurities of Fe, Cu, Co, Ni, Cd and Ga greatly contributed to the lowest unoccupied molecular orbital (LUMO) and greatly affected the electrophilicity of sphalerite. The interactions of O₂ and xanthate with sphalerite are discussed. Results suggest that Mn, Fe, Ni, Cu, Sn and Pb impurities favored the oxidization of sphalerite; however, the impurities of Cd, Hg, Ga and In had the opposite effect. Impurities of Mn, Fe, Co, Ni, Cu, Hg and Pb could enhance the reactivity of xanthate with sphalerite.     

Competitive Removal of Metals from Wastewater by Maghemite Nanoparticles: A Comparison Between Simulated Wastewater and AMD

Maghemite nanoparticles (γ-Fe₂O₃) produced using a recently developed, single-step method proved to be highly effective for selective removal of Cu, Ni, Mn, Cd(II), and Cr(VI) from acid mine drainage (AMD) and simulated wastewater. An average particle size of about 14 nm was estimated for the maghemite nano-particles using transmission electron microscopy. Their adsorption characteristics proved to be highly pH dependent, allowing facilitated selective adsorption of the studied metals, all of which followed the Langmuir adsorption model. In both simulated wastewater and AMD, Cr(VI) adsorption was best at 70 °C and pH = 2.6. Adsorption peaked at pH = 8.5 for Ni(II), 10 for Cd(II), 8.5 for Mn(II), and 6.5 for Cu(II).     

A Bench-scale Assessment of a Combined Passive System to Reduce Concentrations of Metals and Sulphate in Acid Mine Drainage

Abstract  Passive treatment of acid mine drainage (AMD) requires a combined strategy to minimize the effect of climatic variability on the treatment performance of the system. A vertical-flow combined passive treatment system was developed and evaluated in a bench-scale laboratory test for a 290-day period. The combined system consisted of four components with specific treatment functions: an oxidation/precipitation basin for excess iron removal; a peat biofilter for heavy metal sorption and the establishment of anoxic conditions; a bioreactor for alkalinity generation and sulphate reduction; and an anoxic limestone drain for alkalinity addition. The benchscale system was dosed with moderate strength synthetic AMD at a surface loading of 95 L/m²/d, and operated under continuous flow conditions. Removal efficiencies were 99.7%, 99.9%, 99.9%, 98.6%, 98.2%, and 99.9% for Fe, Al, Zn, Mn, Ni, and Cu, respectively, while Cd remained more mobile with a removal efficiency of 66.5%. Sulphate concentrations were reduced from 3030 mg/L to 814.9 mg/L and the acidic drainage was neutralized to an effluent pH of 7.2 and an alkalinity of 1353.6 mg/L (as CaCO₃).     

Effect of loess for preventing contamination of acid mine drainage from coal waste

Acid mine drainage (AMD) that releases highly acidic, sulfate and metals-rich drainage is a serious environmental problem in coal mining areas in China. In order to study the effect of using loess for preventing AMD and controlling heavy metals contamination from coal waste, the column leaching tests were conducted. The results come from experiment data analyses show that the loess can effectively immobilize cadmium, copper, iron, lead and zinc in AMD from coal waste, increase pH value, and decrease Eh, EC, and SO ₄ ^2? concentrations of AMD from coal waste. The oxidation of sulfide in coal waste is prevented by addition of the loess, which favors the generation and adsorption of the alkalinity, the decrease of the population of Thiobacillus ferrooxidans, the heavy metals immobilization by precipitation of sulfide and carbonate through biological sulfate reduction inside the column, and the halt of the oxidation process of sulfide through iron coating on the surface of sulfide in coal waste. The loess can effectively prevent AMD and heavy metals contamination from coal waste in in-situ treatment systems.     

Pollution of Water and Stream Sediments Associated with the Vale De Abrutiga Uranium Mine,Central Portugal

Abstract.   The Vale de Abrutiga uranium deposit, located in Central Portugal near the Aguieira dam reservoir, was surface mined. Low-grade ore and waste rock were deposited on permeable ground, close to the mine, and were not revegetated. A lake has formed in the open pit. Surface waters draining the mine site are acidic, have high conductivity, and high concentrations of U, SO42-, Zn, Fe, Mn, Ra, Cu, Th, and Pb. The groundwater and the water from the reservoir cannot be used for human consumption or irrigation. The sampled waters show higher contaminant concentrations in winter than in summer. Stream sediments have high geoaccumulation indices for U, Fe, Ag, Zn, Cr, Co, and Pb. In general, sediments bordering the dam reservoir have higher metal contents in winter than in summer.