Sulfide-bearing Mine Tailings Research Articles

Legacy copper/nickel mine tailings potentially harbor novel iron/sulfur cycling microorganisms within highly variable communities.

The oxidation of sulfide-bearing mine tailings catalyzed by acidophilic iron and sulfur-oxidizing bacteria releases toxic metals and other contaminants into soil and groundwater as acid mine drainage. Understanding the environmental variables that control the community structure and metabolic activity of microbes indigenous to tailings (especially the abiotic stressors of low pH and high dissolved metal content) is crucial to developing sustainable bioremediation strategies. We determined the microbial community composition along two continuous vertical gradients of Cu/Ni mine tailings at each of two tailings impoundments near Sudbury, Ontario. 16S rRNA amplicon data showed high variability in community diversity and composition between locations, as well as at different depths within each location. A temporal comparison for one tailings location showed low fluctuation in microbial communities across 2 years. Differences in community composition correlated most strongly with pore-water pH, Eh, alkalinity, salinity, and the concentration of several dissolved metals (including iron, but not copper or nickel). The relative abundances of individual genera differed in their degrees of correlation with geochemical factors. Several abundant lineages present at these locations have not previously been associated with mine tailings environments, including novel species predicted to be involved in iron and sulfur cycling.IMPORTANCEMine tailings represent a significant threat to North American freshwater, with legacy tailings areas generating acid mine drainage (AMD) that contaminates rivers, lakes, and aquifers. Microbial activity accelerates AMD formation through oxidative metabolic processes but may also ameliorate acidic tailings by promoting secondary mineral precipitation and immobilizing dissolved metals. Tailings exhibit high geochemical variation within and between mine sites and may harbor many novel extremophiles adapted to high concentrations of toxic metals. Characterizing the unique microbiomes associated with tailing environments is key to identifying consortia that may be used as the foundation for innovative mine-waste bioremediation strategies. We provide an in-depth analysis of microbial diversity at four copper/nickel mine tailings impoundments, describe how communities (and individual lineages) differ based on geochemical gradients, predict organisms involved in AMD transformations, and identify taxonomically novel groups present that have not previously been observed in mine tailings.

Current State of the Gold Mining Waste from the Ores of the Ursk Deposit (Western Siberia, Russia)

The article presents the original results of the investigation of sulfide-bearing mine tailings dumps (Ursk, Western Siberia, Russia), the adjacent territory, and acid mine drainage flows. The novelty of this study is related to integration of geophysical and geochemical data. The geoelectrical structure of the dump and the drainage valley was determined using the electrical resistivity tomography (ERT) method. Magnetic anomalies above the surface of the site were identified using ground magnetic surveys. The orthophotomap and a digital elevation model were obtained on the basis of aerial photography from an unmanned aircraft. The model of thermal imaging allows us to identify a number of temperature anomalies in the upper part of the dump slope and filtration zone in the drainage valley, caused by exothermic reactions. The digital relief model was constructed comprising three zones: (1) oxidation, (2) leaching, and (3) mixing and dilution. The oxidation zone is marked by low electrical resistivity (1–10 Ω·m), low pH values of the drainage waters (pH 3.61), low values of the modulus of the magnetic induction vector, and heating by +5 °C compared to the solid dump material that is not actively exposed to water. The oxidative conditions and low pH values favor the dilution of the Fe2+ compounds in the drainage solutions, which also contain Cu (3000 μg/L), Pb (1200 μg/L), As (1300 μg/L), and Hg (34 μg/L). The zone of the primary geochemical barrier is formed within the first 400 m, where the major proportion of dissolved elements if deposited. The second iron–aluminum sorption geochemical barrier is formed at a distance of 1000 m at the mixing zone with the Ur River. The stable geochemistry of surface waters, formed due to the inflow of drainage waters into the Ur River and further into the reservoir, persists at a distance of up to 7.7 km from the dump.

Time-Lapse Electrical Resistivity Tomography and Soil-Gas Measurements on Abandoned Mine Tailings Under a Highly Continental Climate, Western Siberia, Russia

Mine tailings are a very active system in which the processes of oxidation, dissolution, and the re-deposition of substances occur in real-time. Time-lapse electrical resistivity tomography and soil-gas measurements have been used on abandoned mine tailings under a highly continental climate, Western Siberia, Russia. The electrical resistivity tomography method allows the structure of the tailings to be determined, namely, its electrophysical parameters, which are related to the chemical composition and geochemical characteristics of the subsurface substance. The aim of this work is to determine the variations in the geoelectrical zoning of sulfide-bearing mine tailings depending on fluctuations in environmental conditions, i.e., ground and air temperature, in conjunction with volatile compounds of environmental concern emanating from the tailings (SO2, CS2, C2H6S). The hourly observations revealed that the configuration of the geoelectrical section varies during the day. The concentration of gases in the surface air layer varied in accordance with the ambient temperature conditions. In general, the minimum gas concentrations were determined at night, and the increase in gas concentrations began when the temperature increased. The dependence of gas formation on temperature conditions differed during the daytime and nighttime. In warmer hours, gas concentrations are highest. At night, when there was a decrease in the temperature of air and then in the ground temperature, a local increase in the concentration of all measured gases occurred at the maximum temperature difference in the air (14.1 °C), and the ground remained relatively warm (20.8 °C). There is a close relationship between ground temperature, electrical resistivity, and the rate of gas production. Local anomalies with the greatest variation in electrical resistivity are associated with the zones that have the most active gas emanations.

Determination of acid forming potential of massive sulfide minerals and the tailings situated in lead/zinc mining district of Balya (NW Turkey)

Weathering of sulfide minerals is a major source of acid production in nature and especially in mining territories. Pyrite is not the only principal mineral that generates acid drainage: other sulfide minerals (sphalerite, galena, chalcopyrite, etc.) may also be responsible for acid production. In addition to massive sulfide minerals, sulfide-bearing mine tailings may also produce acid drainage due to oxidation and hydrolysis reactions in waste dumps. The lead/zinc (Pb/Zn) mining region in Balya and Balıkesir, in Turkey, has operated mines intensively since the 1860s; so that characterization of the sulfide minerals and tailings situated and formed around the mining site is of great importance to secure a sustainable environment. For this purpose, acid production and neutralization potentials of massive sulfide ores of the region, and in the Pb/Zn process facility mine tailings from ten different points of tailings dam, have been determined by applied conventional Acid-Base Accounting (ABA) and Net Acid Generation (NAG) static tests after chemical and mineralogical analysis. The NAG pH and net acid production potential (NAPP) values were compared on a chart in order to classify the samples as either acid generating or non-acid generating. According to the comparisons, the sulfide minerals were classified as potentially acid forming (PAF). Massive pyrite had the highest NAPP and NAG pH value of 1966.6 kg H2SO4/ton and 1.91, respectively and the galena had the lowest NAPP value of 558.9 kg H2SO4/ton. However, the sphalerite NAG leachate pH value of 4.30 was the highest in sulfide minerals so that the sphalerite plotted near the uncertainty reference border in the PAF zone. In the mine tailings, NAPP values of 105.9 kg H2SO4/ton on average and the NAG pH values of over 7.5 were determined. In addition to these tests, water leaching (agitation test) was carried out on tailings in order to generate more information. The tailings did not generate acidic leachates as they lie on limestone bed rock which neutralized the acidity.

Alternative waste residue materials for passive in situ prevention of sulfide-mine tailings oxidation: A field evaluation

Novel solutions for sulfide-mine tailings remediation were evaluated in field-scale experiments on a former tailings repository in northern Sweden. Uncovered sulfide-tailings were compared to sewage-sludge biosolid amended tailings over 2 years. An application of a 0.2m single-layer sewage-sludge amendment was unsuccessful at preventing oxygen ingress to underlying tailings. It merely slowed the sulfide-oxidation rate by 20%. In addition, sludge-derived metals (Cu, Ni, Fe, and Zn) migrated and precipitated at the tailings-to-sludge interface. By using an additional 0.6m thick fly-ash sealing layer underlying the sewage sludge layer, a solution to mitigate oxygen transport to the underlying tailings and minimize sulfide-oxidation was found. The fly-ash acted as a hardened physical barrier that prevented oxygen diffusion and provided a trap for sludge-borne metals. Nevertheless, the biosolid application hampered the application, despite the advances in the effectiveness of the fly-ash layer, as sludge-borne nitrate leached through the cover system into the underlying tailings, oxidizing pyrite. This created a 0.3m deep oxidized zone in 6-years. This study highlights that using sewage sludge in unconventional cover systems is not always a practical solution for the remediation of sulfide-bearing mine tailings to mitigate against sulfide weathering and acid rock drainage formation.

Modeling the effect of stratification on cemented layer formation in sulfide-bearing mine tailings

Abstract Reactive transport simulations have been applied to investigate possible effects of stratification on the potential of sulfide-bearing mine tailings to form protective cemented layers. The simulations are based on characteristic strata found at a German tailings site, including sulfide-enriched heavy mineral layers, mica-enriched silt layers, and homogeneously mixed layers. The simulated secondary phases (jarosite, gypsum, amorphous ferric arsenate, amorphous Fe hydroxide, alunite, amorphous silica, and kaolinite) are similar to those observed in the field. Using scanning electron microscope analyses of cemented layers, it has been observed that the pore area becomes disconnected if the porosity is decreased to values below 15%, which would indicate a strong decrease in permeability. Stratification was found to play a crucial role in cemented layer formation. Cemented layers are absent or insignificant in systems with a homogeneous distribution of Fe-bearing sulfides. They are extensively developed in systems with (a) an arsenopyrite-rich layer or (b) a mica-enriched layer situated immediately below an Fe-sulfide enriched layer. The modeling results have clearly demonstrated that the key processes operating in scenario (a) are very different from the key processes in scenario (b). In scenario (a), the oxidation of arsenopyrite is followed by the precipitation of amorphous ferric arsenate, which can be solely responsible for significant pore reduction. In scenario (b), the presence of a large amount of reactive aluminosilicates (e.g. biotite and Ca-bearing plagioclase) immediately below the Fe-sulfide rich layer appears to be crucial. Key processes are extensive formation of Acid Rock Drainage (ARD) followed by enhanced (pH-driven) weathering of aluminosilicates, resulting in the accumulation of secondary phases directly below the Fe-sulfide rich layer. In both scenarios, a cemented layer is formed that effectively retards the further downward movement of the oxidation front. The presented details on the role of stratification in the formation of cemented layers could be considered in the construction of mining heaps as a possible measure to stimulate natural attenuation.

Zn and Pb release of sphalerite (ZnS)-bearing mine waste tailings

Background, aim, and scope Contaminated mine drainage water has become a major hydrogeological and geochemical problem. Release of soluble metal contaminants and acidity from mining sites can pose serious chemical risks to surface and groundwater in the surrounding environment, and it is an important socio-economic factor addressed by working groups like SUITMA Morel and Heinrich (J Soils Sediments 8:206–207, 2008). The release of Zn and Pb from sulfide-bearing flotation residues of a small scale mine in Western Germany is investigated with focus on metal transfer to soil solution. Total contents of the soil material as well as soil water sampled with suction cups were analyzed. The influence of pH on leaching behavior was investigated with pHstat tests. Isotopic analyses helped assessing seepage water velocity. The aim of this study was the assessment of the environmental behavior of zinc and lead caused by the weathering of sulfide-bearing mine tailings. Especially, we address in this paper the dissolution of sphalerite (ZnS) in contrast to the well-known dissolution processes of pyrite (FeS2).

Comparison of laboratory testing protocols to field observations of the weathering of sulfide-bearing mine tailings

A laboratory weathering study using a humidity cell procedure was conducted on two sulfide-bearing tailing samples from a metallurgical site in Ontario (Canada). The test was accompanied by microbiological studies to enumerate the major groups of sulfur-oxidizing bacteria and determine their potential role at different stages during the oxidation process. To evaluate the utility of this method, results were compared with those of previous laboratory and field studies on the same materials. The mineralogy of the laboratory samples differs only by the addition of a small amount of hydronium-bearing natrojarosite [(Na,H 3O)Fe 3(SO 4) 2(OH) 6] to one sample. The progress of sulfide oxidation and the rates of solute release were determined to evaluate the extent of mineral dissolution. These processes were influenced strongly by the capacity of the material to generate acidity, which was enhanced by the presence of hydronium-bearing natrojarosite. Acid-neutralization processes occurring during the laboratory tests were affected by reaction kinetics, consistent with field observations. In particular, the extent of carbonate-mineral dissolution appears to be different in the laboratory than in the field, where more prolonged rock–water interaction allowed more complete chemical equilibration. As a consequence, the capacity of this test procedure to predict weathering reactions in mine tailings is limited by its inability to reproduce the weathering sequence observed in the field. The results of the microbiological study showed that distinct groups of sulfur-oxidizing bacteria operate at different stages of the oxidative process, as was observed in field studies where tailings oxidation occurred under natural conditions, suggesting that microbiological tests performed for laboratory studies are reflective of field conditions.

Formation of sequences of cemented layers and hardpans within sulfide-bearing mine tailings (mine district Freiberg, Germany)

The roles of mineral dissolution, precipitation, transformation and mass transport processes related to formation of characteristic cemented layer–hardpan sequences were studied in low sulfide and low carbonate Freiberg polymetallic mine tailings. Using high resolution profiling, combined geochemical, geomicrobiological and geophysical methods allowed description of the process of weathering of reactive mineral phases and the position of the oxidation front in detail, as well as revealing the mechanisms of cementation of tailings predominantly by the formation of gels/poorly crystalline phases. Autochthonous and allochthonous gels reduced the porosity of cemented layers to values ⩽1%, whereas secondary crystalline phases were less efficient in filling the pore space. Electron microprobe analysis of cemented tailings showed that common jarosite-group minerals contained up to about 8 wt.% PbO and 0.2–1.9 wt.% As 2O 5. Iron–As–Si gels reached contents of up to ∼44 wt.% As 2O 5 in gel-rich cemented layers. Zinc was below the detection limit in the studied secondary phases. Sequential extraction of cemented and related oxidized brown silt layers confirmed that the bulk of As was bound to amorphous/poorly crystalline hydrous oxides of Fe, whereas Pb was often bound to jarosite. Zinc was found preferentially in the water-soluble and the exchangeable fractions. In the grey silt and the sand directly underlying the oxidized layers, As, Pb and Zn occurred as sulfide minerals. The main effects of the cemented layer–hardpan sequences at the studied site are (1) a temporary natural attenuation of the toxic compounds, (2) a restriction of the downward movement of the oxidation front, and (3) a reduction of the extent of the erosion of the surface of the tailings impoundment by wind and water. The potential of a heap to form cemented layers and hardpans is greatly increased by a heterogeneous distribution of grain sizes and reactive materials in the topmost zone, as well as by the occurrence of sulfide-rich tailings on top of layers with low permeability.

Erosion characteristics and resuspension of sub-aqueous mine tailings

The use of shallow water covers for containing sulfide bearing mine tailings in non-arid climates has gained importance over the years due largely to their effectiveness as oxygen barriers. In spite of the numerous documented benefits of these covers, some fundamental questions on the application of the technology still remain; a major one being the contribution of the nature of the tailings particles to the overall performance of the cover. Many of the existing tailings ponds have been designed assuming cohesionless sediment behavior. Total suspended solids and sediment trap measurements at some existing water cover sites, designed using the cohesionless sediment approach, have indicated significant resuspension at these sites. The present study provides information on the cohesive nature of sulfide mine tailings particles using particle size and mineralogical data and results of laboratory erosion experiments. The results show that the erosion patterns for tailings particles are similar to those reported for cohesive natural sediments. A power law erosion equation is proposed for calculating erosion rates and estimating the optimal water cover depth for flooded mine tailings.Key words: sulfide mine wastes, subaqueous disposal, erosion character, cohesive sediments, erosion shear stress relationship.

Vertical Distribution and Speciation of Trace Metals in Weathering Flotation Residues of a Zinc/Lead Sulfide Mine

Sulfide-bearing mine tailings are a serious environmental problem around the world. In this study, the vertical distribution and speciation of Zn and Pb in the fine-grained flotation residues of a former sulfide ore mine in Germany were investigated to assess the inorganic weathering processes that effect the environmental risk arising from this site. Total metal contents were determined by X-ray fluorescence spectroscopy (XRF). Mobilizable fractions of Zn, Pb, Fe, and Mn were quantified by sequential chemical extractions (SCE). Furthermore, the speciation of Zn was analyzed by Zn K-edge extended X-ray absorption fine structure spectroscopy (EXAFS) to identify the residual Zn species. The variations in pH and inorganic C content show an acidification of the topsoil to pH 5.5. EXAFS results confirm that Zn is mainly bound in sphalerite in the subsoil and weathering reactions lead to a redistribution of Zn in the topsoil. A loss of 35% Zn and S from the topsoil compared with the parent material with 10 g kg-1 Zn and neutral pH has been observed. If acidification proceeds it will lead to a significant release of Zn, S, and Pb to the ground water. In contrast to Zn, Pb is enriched in the mobile fraction of the topsoil by more than a factor of two compared with the subsoil which contains a total of 2 g kg-1 Pb. Thus, the high bioavailability of Pb and the potential for Pb uptake by plants and animals currently represent the most severe threat for environmental health.

English

Waste rock, tailings, and slag from a mine in Sudbury, Ontario were blended to create a material with superior physical and hydraulic properties for the potential construction of a cover system on a large tailings impoundment. The new material, termed Co-Mix, has a low hydraulic conductivity, a high Air Entry Value, and low compressibility. These properties indicate that the Co-Mixed waste rock, tailings, and slag can be used to restrict oxygen entry and water seepage, thus minimizing acid generation and metal leaching within the sulfide bearing mine tailings. The results of laboratory testing for various blend ratios together with soil cover model simulations are used to design a field scale experiment. Field scale test trials using selected Co-Mix blends of waste rock, tailings, and slag were constructed in October, 2004 at the Copper Cliff mine in Sudbury, Canada. The field scale test trials consist of 5 lysimeters measuring 15x15 m, with a total depth of about 2500 mm. These test trials are currently being used to evaluate the performance of the new material for cover systems that may potentially be constructed on the tailings impoundment upon closure. The lysimeters were constructed with thicknesses of Co-Mix cover material ranging between 600 mm and 1000 mm along with various blend ratios of waste rock, tailings, and slag. The lysimeters will be used to measure seasonal net infiltration rates together with oxygen fluxes to the underlying tailings. The construction of the lysimeter was recently completed and early results with respect to field performance during the spring snow melt period and summer months are presented in this paper for comparison with model predictions.

The physical, chemical and mineralogical properties of three cemented layers within sulfide-bearing mine tailings

The oxidation and subsequent dissolution of sulfide minerals within mine tailings impoundments releases H +, Fe(II), SO 4 and trace elements to the tailings pore water. Subsequent pH-buffering and hydrolysis reactions result in the precipitation of secondary phases such as gypsum, goethite and jarosite. In areas of intense precipitation, cemented layers or “hardpans” often form within the shallow tailings. Three cemented layers within pyrrhotite-bearing mine tailings at the Fault Lake, Nickel Rim and East Mine impoundments located near Sudbury, Canada, were examined. The location of the three cemented layers within the tailings stratigraphy varies as does their location relative to the water table. The morphology, mineralogy and chemical composition of the cemented layers also vary between sites. The bulk density within the three cemented layers all showed an increase relative to the surrounding uncemented tailings ranging from 9% to 29%. The porosity of each cemented layer decreased relative to the surrounding uncemented tailings ranging from an 8% to 18% decrease. The cemented layers also showed relative enrichment of total sulfur, carbon and trace elements relative to the surrounding uncemented tailings. Arsenic concentrations showed an enrichment in the cemented layers of up to 132%, Cd up to 99%, Co up to 84%, Cu up to 144%, Ni up to 693% and Zn up to 145% relative to the surrounding uncemented tailings. All the cemented layers studied show an evolution of the secondary phases with time from a gypsum–jarosite-based cement to a goethite-rich cement. The formation of these layers could potentially have a significant effect on the environmental impacts of sulfide-bearing mine waste.