Mine Tailings Site Research Articles

Indicators of Microbial Sulfate Reduction in Acidic Sulfide-Rich Mine Tailings

Sulfate-reducing bacteria (SRB) are thought to be actively involved in the cycling of sulfur in acidic mine tailings. However, most studies have used circumstantial evidence to assess microbial sulfate activity in such environments. In order to fully ascertain the role of sulfate-reducing bacteria (SRB) in sulfur cycling in acidic mine tailings, we measured sulfate reduction rates, sulfur isotopic composition of reduced sulfide fractions, porewaters and solid-phase geochemistry and SRB populations in four different Cu-Zn tailings located in Timmins, Ontario, Canada. The tailings were sampled in the summer and in the spring, shortly after snowmelt. The results first indicate that all four sites showed very high sulfate reduction rates in the summer (∼100–1000 nmol cm− 3d−1), which corresponded to the presence of sulfide in the porewaters and to high SRB populations. In some of the sites, zones of microbial sulfate reduction also corresponded to a decline of organic carbon and to an apparent pyrite (with slightly negative δ34S values) enrichment around the same depth. Microbial sulfate reduction was also important in permanently acidic (pH 2–3) mine tailings sites, suggesting that SRB can be active under very acidic conditions. Secondly, the results showed that microbial sulfate reduction was greatly reduced in the spring, suggesting that temperature might be a key factor in the activity of SRB. However, a closer look at the results indicated that temperature was not the sole factor and that acidic conditions and limited substrate availability in the spring appeared to be important as well in limiting microbial sulfate par reduction in sulfidic mine tailings. Finally, the results indicate that sulfur undergoes rapid cycling throughout the year and that microbial sulfate reduction and metal sulfide precipitation do not appear to be a permanent sink for metals.

Copper and health status of cattle grazing high-molybdenum forage from a reclaimed mine tailing site

High concentrations (21–44 mg kg-1 dry matter) of Mo have been identified in forage in several reclaimed mining areas in British Columbia. Since Mo concentrations greater than 5 mg kg-1 in forage dry matter may result in molybdenosis because of a secondary Cu deficiency in ruminants, a study was undertaken to determine if cattle can safely graze the reclaimed land. For 12-wk grazing periods in 1994, 1995 and 1996, 32 cow/calf pairs grazed high-Mo forage at a reclaimed mine tailings site located at the Highland Valley Copper mine near Logan lake, BC. Half of the animals in the trial received a Cu supplement (All-Trace copper bolus) and the other half served as a control group. There were no significant differences (P < 0.05) in weight gain, liver Mo, serum Cu and Mo, and milk Cu and Mo between the two treatment groups of cows. Liver Cu was higher for the Cu bolus group at certain time periods in 1994 and 1995, indicating that the bolus was effective at supplying Cu. At all times, the liver Cu levels for the animals remained above the recommended critical level of 25 mg kg-1 dry matter. Animals appeared healthy and no signs of Cu deficiency were observed. Key words: Molybdenum, molybdenosis, copper, mine tailings, reclamation, animal health

Development of a functionalized polymer-coated silica for the removal of uranium from groundwater.

A new active material for the treatment of uranium-contaminated groundwater using permeable reactive barriers has been developed. This material, called PANSIL, is an example of a tailored ligand system that selectively removes a contaminant from solution. The active medium in PANSIL is a polyacryloamidoxime resin derived from polyacrylonitrile, which is deposited from solution onto the surface of quartz sand to form a thin film coating. PANSIL is highly effective at sequestering UO2(2+) from solution when the pH is between about 5 and 8 and can preferentially sequester UO2(2+) from solutions that are typical of the groundwater from a mine tailings site, due to the stability of the polyacryloamidoxime uranyl complex formed. Uranium sequestration capacity will depend on the surface area of the sand that is resin coated, but in the batch of PANSIL tested (<2% resin by weight), it exceeds 4000 mg of UO2 per kg of PANSIL at pH 4.5 when the dissolved UO2(2+) concentration is greaterthan 300 mg/L. PANSIL largely retains the permeability and strength of the sand employed and therefore has suitable engineering properties for permeable reactive barrier applications.

Tailings erosion and resuspension in two mine tailings ponds due to wind waves

One of the approaches used for environmental management of mine tailings is the implementation of shallow water covers, typically up to 2 m. As oxygen is one of the key factors in the oxidation of reactive iron-bearing sulfide minerals present in the tailings, water covers provide an effective control measure, owing to the low diffusivity and solubility of oxygen in water. However, wind-induced waves can resuspend flooded tailings, thus increasing the possibility of oxidation and acid generation. Summer field measurements of wind velocity and wave heights at two mine tailings sites in New Brunswick and Ontario are presented and discussed. Frequency diagrams of winds show that in summer wind speeds as high as 15 m/s are anticipated at these sites. Bottom shear stresses are calculated using measured wave heights and compared to critical shear stress of the tailings. Calculated bottom shear stresses exceeded the critical shear stress of the tailings at wind speeds higher than 9 m/s. Based on sediment trap data at the two sites, it is shown that resuspension is not a function of depth and wind-generated stresses alone, but also depends on other factors, such as cohesion and self-consolidation of tailings and site topography. Areas of erosion and accumulation were delineated at the two sites using particle size distribution, metal concentrations and an erosion–transportation–accumulation (ETA) diagram. The findings confirm resuspension work carried out by previous researchers at these two sites.

Spatial analysis of radiometric fractions from high-resolution multispectral imagery for modelling individual tree crown and forest canopy structure and health

Research was conducted in a forest adjacent to an abandoned acid mine tailings site to assess forest structural health using high spatial and spectral resolution digital camera imagery. Conventional approaches to this problem involve the use image spectral information, basic spectral transformations, or occasionally spatial transformations of image brightness. This research introduces fractional textures and semivariance analysis of image fractions. They were integrated with conventional image measures in stepwise multiple regression modelling of forest structure (canopy and crown closure, stem density, tree height, crown size) and health (a visual stress index). The goal was to conduct a relative comparison of the potential of the various image variable types in modelling of forest structure and health. Analysis was conducted for both canopy (crowns and shadows) and individual tree crown sample data sets extracted from 10 nm bandwidth spectral bands at three resolutions (0.25, 0.5, 1.0 m). Spatial transformations (texture, semivariogram range) of image brightness (DN) and image fractions (IF) were consistently the most significant and first entered variables in the best models of the forest parameters. At the canopy-scale, despite a limited number of available plots (6), stable models were produced that demonstrated the potential for spatially transformed variables. Semivariogram range explained 88% of the total variation of 9 of the 18 models and represented 56% of the variables used in all models while texture variables explained 51% of model variance in 8 of the 18 models and represented 40% of the variables used. At the tree crown scale ( n=31), 88% of the total variation of six of eight models was explained by texture variables and 6% by semivariogram variables. DN and IF variables that were not spatially transformed contributed little to the models at both scales. They represented 4% and 6%, respectively, of the variables used in all models. Spatial information in image fractions and image brightness has proven to be more significant than spectral information in these analyses. Of the spatial resolutions evaluated, 0.5 m consistently produced similar or better models than those using the 0.25 or 1.0 m resolutions. These results demonstrate the potential for integration of spatial transforms of image fractions and raw brightness in high-resolution modelling of forest structure and health.

Air–surface exchange of mercury in natural and anthropogenically impacted landscapes in Atlantic Canada

Understanding the relative importance of various sources of mercury within ecosystems and their subsequent impact on biota requires a thorough understanding of the biogeochemical cycling of mercury. An important component of the biogeochemical mercury cycle involves the exchange of gas-phase mercury between the atmosphere and various landscape surfaces. This study examines air–surface exchange (flux) of gaseous elemental mercury in selected undisturbed and anthropogenically impacted aquatic and terrestrial landscape settings. The objective of this study was to quantify air–surface mercury exchange rates in these contrasting landscape settings, to put constraints on these rates and provide insight into physical processes controlling mercury flux. Mean daily mercury flux was typically low over natural forest soils varying from −0.4 (net deposition) to 2.2 ng m −2 h −1 (net evasion). Minimum and maximum flux rates measured at these sites over the diurnal cycle ranged from a minimum of −1.3 to a maximum of 5.7 ng m −2 h −1 . Low flux rates from forest soils was partially due to poor light penetration through the forest canopy. Average daily mercury flux over undisturbed glacial till soil at an open field site with full sun exposure was also low (0.9 ng m −2 h −1 ) compared to the same soil mixed over a depth of 2 m (8.0 ng m −2 h −1 ). Mean daily mercury flux rates measured over pristine freshwater lake surfaces were also low (0.7–6.5 ng m −2 h −1 ), although the overall range in flux varied more widely (−0.3 to 44 ng m −2 h −1 ). Total mercury concentrations in marine water at a moderately polluted coastal harbour site (mean c. 0.8 ng l −1 ) and mean daily mercury flux rates over salt water (0.7 ng m −2 h −1 ) were similar to those measured over freshwater lakes. The highest daily average and diurnal range in mercury flux rates were measured at two abandoned gold mine tailings sites (130 and 237 ng m −2 h −1 ). The abandoned mine sites comprised tailings high in mercury content due to the past use of the mercury amalgamation process in gold extraction from the ore. Flux rates from tailings were two orders of magnitude higher than those observed over undisturbed native soils of similar parent material. Higher flux rates at the mine tailings sites were accompanied by ambient air concentrations 5–10 times background levels at 20 cm above the tailings. Mercury flux from vegetation has not been widely considered. A preliminary study of mercury flux from a white pine tree ( Pinus strobus ) indicated that actively growing trees might play a role in the atmospheric mercury cycle.

Field assessment of metal and sulfate fluxes during flooding of pre-oxidized mine tailings

This paper presents a field experiment performed at the Mattabi mine tailings site near Ignace, Ontario, Canada, to assess the evolution of water chemistry over flooded sulfide mine tailings. The tailings had oxidized for approximately 10 years prior to flooding. The experiment involved the construction of a 70 m 2 test cell and a monitoring program that extended over more than 2 years. Metal and sulfate fluxes towards the water cover were calculated using measured solute concentrations, water cover volumes, and seepage rates. Results indicate that directly flooding pre-oxidized tailings can initially lead to the release of metals and sulfate to the water cover. However, dilution of the water cover by rain and snowmelt, flushing of the oxidation products by infiltration into the tailings, and removal of some metals by precipitation and sorption progressively reduced concentrations in the water cover below regulatory discharge limits. Because the tailings pore water was rich in ferrous iron, a thin layer of hydrous ferric oxide precipitated on the surface of the tailings, following the establishment of the water cover. The precipitate is believed to have removed zinc from the water cover through sorption or co-precipitation reactions.

The Impact of Spectral Band Characteristics on Unmixing of Hyperspectral Data for Monitoring Mine Tailings Site Rehabilitation

RÉSUMÉCette étude démontre l'importance de la position, du nombre, et de la largeur des bandes spectrales sur les résultats de déconvolution spectrale des données de réflectance du Compact Airborne Spectrographic Imager (casi). Les données ont été acquises dans le visible et le proche infrarouge pour le site de rejets miniers de la mine Copper Cliff près de Sudbury (Ontario, Canada). Afin d'étudier l'effet du nombre de bandes spectrales, les données casi ont été réduites de façon systématique de 65 à 33, 17, 8 et 4 bandes en maintenant la largeur de bande initiale de 8,7 nm à mi-hauteur. Pour étudier l'effet de la largeur des bandes, une série de données interpolées par une fonction cubique a été créée à partir des spectres des données originales casi de 65 bandes. Une image de six bandes spectrales pré-sélectionnées a été produite pour chaque largeur de bande à mi-hauteur variant entre 8,5 nm et 76,5 nm avec un intervalle de 8,5 nm. Les données multispectrales à haute résolution spatiale Ikonos 2 (comportant des fenêtres spectrales plus larges et moins nombreuses que casi) ont été simulées afin d'étudier l'effet combiné du nombre et de la largeur de bande. Une déconvolution spectrale linéaire a été appliquée sur les données à partir de la signature spectrale de 5 composantes élémentaires: végétation, chaux, rejets miniers oxydés, et deux types de surfaces d'eau. Les résultats montrent une différence absolue moyenne allant jusqu 'à 0,02 (écart-type: ±0,05) entre les fractions des composantes élémentaires des données simulées et celles provenant de la série de données originales casi de 65 bandes lorsque que les bandes spectrales sont sélectionnées selon des propriétés physiques et spectrales. La différence absolue moyenne est beaucoup plus élevée lorsque les bandes sont positionnées de façon aléatoire. En général, la déconvolution spectrale des données simulées produit des résultats semblables à ceux obtenus avec la série de données originale casi de 65 bandes dans la mesure où la position des bandes spectrales est déterminée d'après des propriétés physiques et spectrales. De tels résultats, entre autre ceux de la simulation de bandes larges, sont réalisables en grande partie parce que les composantes élémentaires ont des signatures spectrales très distinctes.

A deterministic-empirical model of the effect of the capillary fringe on near-stream area runoff 2. Testing and application

The testing and application of HECNAR, a deterministic-empirical model that can account for the hydrologic effect of the capillary fringe on the near-stream area runoff, was carried out in several steps. The model was tested against the response of a laboratory model which resembled a near-stream saturated region of a cross-section, and the results of a field experiment. In each case, the simulated flow components were compared with the separated hydrograph components using a conservative tracer and the predictions of an unsaturated-saturated numerical model. The results were in reasonably good agreement. The model was then applied to a mine tailings site and the predictions were compared with numerical simulations, measured streamflows and the components of the stream hydrograph separated using 180 as a conservative tracer. The predictions of HECNAR and the numerical model were in good agreement, as were the trends of the simulated and the measured hydrographs. However, some discrepancies existed between the measured and the simulated flows. This study shows that HECNAR is computer efficient and has a relatively modest input requirement. Incorporation of the model into a larger-scale and more comprehensive watershed model could provide a valuable tool to quantify total flows and runoff source components to the stream, in watersheds in humid environments.

Flooding of a mine tailing site: Suspension of solids - Impact and prevention

ABSTRACT Acid generating tailings is a problem to be solved in the mining industry. By limiting the available oxygen for the oxidation process, water covers is one of the methods to control the acid generation. This study evaluates the optimum height of water required to prevent the resuspension of solid particles and thus reducing the environmental impact on a specific site (Solbec Cupra). Based on the experimental results, it has been found that the minimum height of water above the reactive tailing should be 1.34 m. However, with a layer of sand on top of the tailings, the required level may be reduced to 0.74 m. Also, it has been calculated that a layer of sand can reduce the total sediment load from 331.10 to 41.80 m3/m/day.

Experimental fluoride accumulation and toxicity in the short‐tailed field vole (Micvotus agrestis)

Vegetation established naturally on three industrial sites contaminated by either airborne or soilborne fluorides was used to formulate dietary feed for a laboratory‐reared population of field voles (Microtus ugrestis L.), an herbivorous species indigenous to all three locations. Animals exposed to laboratory diets containing 100–300 mg F kg‐1 derived from vegetation from around the aluminium smelter and fluorochemical works showed reduced live weight gain, between 40 and 100% mortality and developed marked dental lesions. These comprised banding of the enamel, loss of colour and erosion of the cutting surfaces of the incisors, and dentine cavitation and erosion of the grinding faces of the molar teeth. These morphological changes were accompanied by excessive accumulation of fluoride in the teeth. Voles consuming a diet of vegetation from the mine tailings site with a similar level of fluoride (100 mg kg‐1) as for the other industrial locations, showed only slight dental changes and no weight loss or early mortality. This pattern for laboratory‐bred voles is similar to that experienced in populations of this species in the wild, and the contrast in the severity of the dental lesions is ascribed to intersite differences in the chemical speciation and bioavailability of fluoride.

Algal uptake of U and some other metals: Implications for global geochemical cycling

Freshwater green algae Ankistrodesmus sp, cultured in dilute solutions of metals chelated with EDTA, revealed massive uptake of U. Examination of Thames River waters and selected micro-organisms of its aquatic ecosystem revealed an average dissolved U concentration of 1.46 ppb, representing about twice the global mean riverine solute concentration of 0.6 ppb U. Suspended particulates, principally algae, contain U at 10 3 to 10 5 times that of their river habitat, averaging 28 300 ppb U. One community of the filamentous algae Spirogyra sp. contained intracellular crystals tentatively identified as the Ca-oxylate weddelite. Studies of algae from a variety of environments have shown large concentration factors for a wide range of elements. Algae from an acid U mine tailings site contain up to 2.7% U (dry weight) plus very high concentrations of other metals. Micro-organisms may act as an important sink for metal solutes in the hydrosphere.