Mill Tailings Research Articles

Correction to Mineralogical Controls on Aluminum and Magnesium in Uranium Mill Tailings: Key Lake, Saskatchewan, Canada

W have noticed that in Table 2 of the manuscript for the pH 4.4 step (11-KL-03_SeMo thickener), the Fe value in the solid is not correct. For now it reads Fe 2078 mg/L in the solid but this should be Fe 20748 mg/L in the solid. It should be noted that from a neutralization process aspect this makes sense and is important to have corrected as the previous step of pH 4.3 also shows a similar Fe solid concentration. Moreover, it is important to note that this correction in no way affects any of the ideas or concepts presented in this work.

Recycling of Metal Ore Mill Tailings

The problems of ore mill tailings disposals and eco-economic efficiency of their use are considered. The paper provides the fundamentals of geo-mechanical control of the rock mass by low-strength solidifying mixtures of recyclable tailings. The essence and results of mechanochemical experiments on non-ferrous, ferrous metals and coal tailings are considered. A model to determine the economic and environmental efficiency of this technology is developed.

A comparison of analytical methods for determining uranium and thorium in ores and mill tailings

Three different methods for determining uranium and four for determining thorium in an apatite ore, black schist and mill tailings are compared. The aim of the comparative study is to obtain analytical verification of field results so that site characterization could be optimized without compromising reliability of the analysis. The samples were collected from a former pilot scale phosphate mine in Sokli, northern Finland and the Talvivaara nickel mine in Eastern Finland. A non-destructive, portable X-ray fluorescence (XRF) spectrometer was used on site to measure, semi-quantitatively, the composition of major elements, including thorium in each material. The samples were then analyzed by X-ray diffraction (XRD) to identify the main mineral components and electron probe micro-analysis (EPMA) used to identify the uranium and thorium-bearing minerals. Gamma spectrometry was used for direct determination of uranium and thorium isotopes in powdered samples. Thereafter, sample digestion experiments were performed with various acids to optimize the method for microwave digestion allowing determination of uranium and thorium by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and alpha spectrometry. For the latter method, uranium and thorium were separated using anion exchange resin filled in a column. The results show that overall a sample mass of 0.1–0.5g with addition of 20mL concentrated nitric acid is the most efficient means for extracting uranium and thorium simultaneously from apatite ore, black schist and mill tailings. The results for uranium and thorium concentrations determined by gamma spectrometry, alpha spectrometry and ICP-MS were in good agreement. Also the on-site measurements with portable XRF gave comparable results to other methods used in this study for thorium even without prior sample preparation.

Abiotic U(VI) reduction by aqueous sulfide

Reactions with aqueous sulfide are important in determining uranium (U) geochemistry under sulfate reducing conditions. This paper reports on abiotic reduction of U(VI) by aqueous sulfide under a range of experimental conditions using batch reactors. Dissolved U concentration was measured as a function of time to study the effects of chemical variables including pH, U(VI), S(−II), total dissolved carbonate (CARB=H2CO3*+HCO3−+CO32−), and Ca2+ concentration on the U(VI) reduction rate. Solid phase reaction products were characterized using X-ray diffraction, X-ray absorption spectroscopy, and transmission electron microscopy. The chemical variables had impacts on the solid phase U(VI) reaction products as well as the reduction rates by aqueous sulfide. The solid U reaction product at circumneutral pH was identified as uraninite (UO2+x(s)). Under basic pH conditions, whether a precipitate occurred depended on Ca2+ and CARB concentrations. U(VI) reduction was faster under higher S(−II) concentrations but was slowed by increased dissolved Ca2+ or CARB concentration. In the absence of dissolved CARB and Ca2+, a rapid decrease in dissolved U concentration occurred at circumneutral pH, while virtually no decrease was observed at pH 10.7 within the experimental timeframe of two days. The U(VI) reduction rate was proportional to the total concentration of free uranyl plus its hydrolysis complexes even at minor to trace concentrations. Dissolved Ca2+ and CARB slow abiotic U(VI) reduction by forming stable Ca–U(VI)–carbonato soluble complexes that are resistant to reaction with aqueous sulfide. U(VI) reduction was slow in a synthetic solution representative of groundwater at a uranium mill tailings site. This study illustrates that abiotic U reduction by aqueous sulfide can significantly vary under typical ranges of chemical conditions in groundwater and newly demonstrates the importance of dissolved Ca2+ in the abiotic U(VI) reduction by aqueous sulfide. The results contribute to our understanding of the impact of sulfate reducing conditions on U speciation in groundwater systems undergoing bioreduction conversion of U(VI) to less mobile U(IV) solid phases.

Field analyses of 238U and 226Ra in two uranium mill tailings piles from Niger using portable HPGe detector

The radioactivities of 238U and 226Ra in mill tailings from the U mines of COMINAK and SOMAÏR in Niger were measured and quantified using a portable High-Purity Germanium (HPGe) detector. The 238U and 226Ra activities were measured under field conditions on drilling cores with 600s measurements and without any sample preparation. Field results were compared with those obtained by Inductive Coupled Plasma Atomic Emission Spectroscopy (ICP-AES) and emanometry techniques. This comparison indicates that gamma-ray absorption by such geological samples does not cause significant deviations. This work shows the feasibility of using portable HPGe detector in the field as a preliminary method to observe variations of radionuclides concentration with the aim of identifying samples of interest. The HPGe is particularly useful for samples with strong secular disequilibrium such as mill tailings.

Characterization of hematite nanoparticles synthesized via two different pathways

Hematite is one of the most common and thermodynamically stable iron oxides found in both natural and anthropogenic systems. Owing to its ubiquity, stability, moderate specific surface area, and ability to sequester metals and metalloids from aquatic systems, it has been the subject of a large number of adsorption studies published during the past few decades. Although preparation techniques are known to affect the surface morphology of hematite nanoparticles, the effects of aging under environmentally relevant conditions have yet to be tested with respect to surface morphology, surface area, and adsorptive capacity. We prepared hematite via two different pathways and aged it under highly alkaline conditions encountered in many mill tailings settings. Crystal habits and morphologies of the hematite nanoparticles were analyzed via scanning electron microscopy and transmission electron microscopy. X-ray diffraction, Raman spectroscopy, and Brunauer–Emmett–Teller surface area analyses were also conducted on the hematite nanoparticles before and after aging. The hematite synthesized via an Fe(III) salt solution (average particle size ~37 nm) was morphologically and structurally different from the hematite synthesized via ferrihydrite aging (average particle size ~144 nm). Overall, our data demonstrate that the crystallinity of hematite produced via ferrihydrite transformation is susceptible to morphological alterations/modifications. In contrast, the hematite formed via hydrolysis of an Fe(III) salt solution remains very stable in terms of structure, size, and morphology even under extreme experimental conditions.

Environmental-Friendly Process for Recovering Copper and Nickel from Jinchuan Tailings by Silica-Based Selective Adsorbents

Contamination of heavy metals from mill tailings is a global problem. China’s Jinchuan Group Limited has stored approximately one billion tons of mill tailings which contain toxic levels of copper, nickel, and other metal compounds. To solve the problem, this work extended the principle of hydrometallurgical extraction to the recovery of copper/nickel from Jinchuan tailings and designed an environmental-friendly recovering process. Synergetic leaching by sulfuric acid and ferric ion was proposed to achieve the efficient leach of copper, nickel, and other metals in Jinchuan tailings. Novel silica-based 2-aminomethylpyridine and iminodiacetic acid functionalized adsorbent were used to selectively recover copper and nickel from the leachate of Jinchuan tailings, respectively. The stable adsorption capacity on semi-industrial scale operation after 700 continuous adsorption-regeneration runs promises the achievement of copper and nickel recovery from Jinchuan tailings.

An Experimental Study on the Mechanical Properties of Cemented Rock-Tailings Fill

This paper outlines an effective approach to making composite backfill using mine waste material. Composite materials are widely used in many areas of engineering because of their unique structural properties. Cemented rock-tailings are one of the most prevalent materials used for composite backfill because they can effectively make use of mine waste rock and mill tailings that would otherwise be simply considered waste. This backfill method has the capability of maintaining the mine environment while still allowing for continued mine development. An experimental study is being conducted in a cooperative mine research project to investigate the properties of backfill material and specifically the mechanical characteristics of cemented waste rock-tailings fill. This study details the characteristics of the composite backfill aggregate with respect to the compressive strength of the cemented rock-tailings fill and the backfill mix-proportion, as well as outlines a new method of study for cemented rock-tailings fill mechanics. The study results show the compressive strength of cemented rock-tailings fill is dependent mainly on the cement and waste rock content. Ensuring a precise backfill mix proportion can effectively reduce the cement dosage, thereby decreasing the backfill cost realized for the mine.

Identification of elite native plants species for phytoaccumulation and remediation of major contaminants in uranium tailing ponds and its affected area

Uranium mill tailings are the crushed rock residues of the uranium extraction process from ores. The tailings effluent and tailings solids from the mill are discharged as slurry to a waste retention pond, called tailing pond. Natural radionuclides’ and trace metals are present in mine tailing/soil in varying concentrations, and some of these are found in elevated concentrations in uranium waste tailings. Uranium mine tailing ponds at Jaduguda and Turamdih receive waste from ores mined at the six mine stations at Jharkhand state, India. A study was undertaken to evaluate the potential of native plant species for the phytoremediation of these site. Three sampling stations were selected at Jaduguda (TP1, TP2, TP3) and Turamdih and at the downstream of effluent treatment plant. pH, electrical conductivity, metals (12-Al, V, Cr, Mn, Fe, Ni, Cu, Zn, As, Se, Cd, Pb) and radionuclides’ (3-Co, Sr and U) were analyzed using inductively coupled plasma mass spectrophotometry. From the analysis, four elements—Al, Mn, Fe and U—were found to be much higher in concentration in water with range (mg/kg) of 0.02–2.38, 0.30–31.67, 0.00–0.75 and 0.03–5.50, respectively, and 10 elements—of U, Mn, Al, V, Fe, Ni, Cu, Zn, Co and Se—were found to be higher in concentrations in soils with range (mg/kg) of 22–99, 1,072–8,065, 14,053–21,213, 66–139, 15,163–44,640, 149–240, 135–350, 89–191, 34–140 and 12–122, respectively. Among them, U and Mn were identified as predominant contaminants. Out of all the native plants, 21 species were screened for phytoaccumulation and transfer factor study. P. digitalis (for Al, V, Ni and Co), E. ferox (for Mn and Cu), A. indica (for Fe), B. vitisidae (for Zn), P. hydropiper (for Se) and S. spantanium (for U) were identified for hyper-accumulation, and A. indica (for Al, Co, Se and U), C. bunplandianus (for Mn, Fe, Ni and Cu), E. ferox (for V) and C. procera (for Zn) were listed for non-accumulation of respective contaminant. Besides this, taking consideration of the parameters such as shallow-rooted plant species, easy to adapt, growth, harvest and biomass production and simultaneous accumulation of multiple contaminants, following plants were found to be candidate species for phytoremediation of tailing ponds of uranium mines: For hyper-accumulation: P. vittata (can accumulate Al, V, Ni, Co, Se and U simultaneously) followed by P. digitalis, C. compressus and S. spantanium. For non-accumulation: C. bunplandianus (can non-accumulate Al, Mn, Fe, Ni, Co, Cu, Zn, Se and U simultaneously) followed by B. moneri, C. procera and A. indica.

Depositional characteristics of uranium tailings from Saskatchewan, Canada

The management of uranium tailings, generated as a by-product of ore processing, is particularly important to minimize the environmental footprint of the industry. A clear understanding of tailings slurry behavior is required at the time of deposition to help evaluate the storage capacity and life span of the containment facilities. The main purpose of this study was to investigate the segregation and self-weight settling properties of uranium tailings. Detailed laboratory investigations were conducted on tailings from 4, 5, and 6 % nominal mill feeds (high-grade McArthur River ores blended with special wastes on site) from the Cameco Key Lake operation. The results indicate that the three uranium tailings can be characterized as a sandy silt material with a negligible amount of clay. Their depositional behavior is governed by the initial solids content of the slurry. The investigated tailings showed insignificant segregation between 25 and 40 % initial solids content. The initial hydraulic conductivity during settling was about 10−4 m/s at a void ratio of 4 and was increased by half an order of magnitude for the 4 % mill feed, and by almost two orders of magnitude for the 5 and 6 % mill feeds at a void ratio of 8. Over the same range of initial void ratio, the settling potential increased threefold: from 8 to 24 % for the 4 % mill feed and from 12 to 36 % for the 5 and 6 % mill feeds. The better rate and amount of dewatering of future high mill feed tailings as compared to the current low mill feed tailings means that the onsite containment facility can store more tailings thereby supporting a longer life span of the mill.

Classification of genetic variation for cadmium tolerance in Bermudagrass [Cynodon dactylon (L.) Pers.] using physiological traits and molecular markers.

Cadmium (Cd) is one of the most toxic pollutants that caused severe threats to animal and human health. Bermudagrass is a dominant species in Cd contaminated soils, which can prevent Cd flow and spread. The objectives of this study were to determine the genetic variations in major physiological traits related to Cd tolerance in six populations of Bermudagrass collected from China, and to examine the genetic diversity and relationships among these accessions that vary in Cd tolerance using molecular markers. Plants of 120 accessions (116 natural accessions and 4 commercial cultivars) were exposed to 0 (i.e. control) or 1.5 mM CdSO4·8/3H2O for 3 weeks in hydroponic culture. Turf quality, transpiration rate, chlorophyll content, leaf water content and growth rate showed wide phenotypic variation. The membership function method was used to comprehensively evaluate Cd-tolerance. According to the average subordinate function value, four accessions were classified as the most tolerant genotypes and four accessions as Cd-sensitive genotypes. The trend of Cd tolerance among the six studied populations was as follows: Hunan > South China > North China > Central China > West South China and Xinjiang population. Phylogenetic analysis revealed that the majority of accessions from the same or adjacent regions were clustered into the same groups or subgroups, and the accessions with similar cadmium tolerance displayed a close phylogenetic relationship. Screening genetically diverse germplasm by combining the physiological traits and molecular markers could prove useful in developing Cd-tolerant Bermudagrass for the remediation of mill tailings and heavy metal polluted soils.

Assessment of eco-hazard of copper-nickel ore mining and processing waste

The authors examine oxidation of sulfide minerals in mine waste and the associated ecological problems. The highest environmental hazard is produced by fine-dispersed mill tailings, especially where sulfide content is comparable with nonmetal content of low-chemical activity. In terms of some production waste accumulations in Murmansk Region, it is shown that the eco-hazard source can be not only fine but also coarse particle waste (Allarechensky mine waste) and ore concentration waste with low sulfide content but highly chemical-active nonmetals (Pechenga ore field).

Characteristics Variation of Tailings Using Cemented Paste Backfill Technique

Cemented paste backfill has been proposed in the mining industry for managing metal mill tailings. Low sulfide tailing (0.49 wt%) samples were prepared into different cemented pastes that were mixed with flocculants (polymerized aluminum chloride). The best mixing proportions of tailings, binder, flocculant, and filling structure (containing 0.5 wt% of ordinary Portland cement in one paste layer, 100 g/L polymerization aluminum chloride) were determined through leaching experiment. The addition of polymerization aluminum chloride improved the mechanical property of the paste. The strength of the cemented pastes by adding 100 g/L flocculant met the requirement of mine backfill. The cemented paste could also fix heavy metals, as shown in the paste leachate analysis of copper (Cu, about 0.01–0.08 mg/L of concentration) and chromium (Cr, about 0.03 mg/L of concentration). In summary, results from this study demonstrate that tailings can be managed by cemented paste backfill technique, preventing its contamination of the environment.

Mapping Changes in a Recovering Mine Site with Hyperspectral Airborne HyMap Imagery (Sotiel, SW Spain)

Hyperspectral high spatial resolution HyMap data are used to map mine waste from massive sulfide ore deposits, mostly abandoned, on the Iberian Pyrite Belt (southwest Spain). Mine dams, mill tailings and mine dumps in variable states of pyrite oxidation are recognizable. The interpretation of hyperspectral remote sensing requires specific algorithms able to manage high dimensional data compared to multispectral data. The routine of image processing methods used to extract information from hyperspectral data to map geological features is explained, as well as the sequence of algorithms used to produce maps of the mine sites. The mineralogical identification capability of algorithms to produce maps based on archive spectral libraries is discussed. Trends of mineral growth differ spectrally over time according to the geological setting and the recovery state of the mine site. Subtle mineralogical changes are enhanced using the spectral response as indicators of pyrite oxidation intensity of the mine waste piles and pyrite mud tailings. The changes in the surface of the mill tailings deserve a detailed description, as the surfaces are inaccessible to direct observation. Such mineralogical changes respond faithfully to industrial activities or the influence of climate when undisturbed by human influence.

Metal mobilization under alkaline conditions in ash-covered tailings

The aim of this study was to determine element mobilization and accumulation in mill tailings under alkaline conditions. The tailings were covered with 50 cm of fly ash, and above a sludge layer. The tailings were geochemically and mineralogically investigated. Sulfides, such as pyrrhotite, sphalerite and galena along with gangue minerals such as dolomite, calcite, micas, chlorite, epidote, Mn-pyroxene and rhodonite were identified in the unoxidized tailings. The dissolution of the fly ash layer resulted in a high pH (close to 12) in the underlying tailings. This, together with the presence of organic matter, increased the weathering of the tailings and mobilization of elements in the uppermost 47 cm of the tailings. All primary minerals were depleted, except quartz and feldspar which were covered by blurry secondary carbonates. Sulfide-associated elements such as Cd, Fe, Pb, S and Zn and silicate-associated elements such as Fe, Mg and Mn were released from the depletion zone and accumulated deeper down in the tailings where the pH decreased to circum-neutral. Sequential extraction suggests that Cd, Cu, Fe, Pb, S and Zn were retained deeper down in the tailings and were mainly associated with the sulfide phase. Calcium, Cr, K and Ni released from the ash layer were accumulated in the uppermost depletion zone of the tailings.

ChemInform Abstract: A Review of Binders Used in Cemented Paste Tailings for Underground and Surface Disposal Practices

AbstractReview: 123 refs.

Once Upon a Mine: The Legacy of Uranium on the Navajo Nation

On a low, windswept rise at the southeastern edge of the Navajo Nation, Jackie Bell-Jefferson prepares to move her family from their home for a temporary stay that could last up to seven years. A mound of uranium-laden waste the size of several football fields, covered with a thin veneer of gravel, dominates the view from her front door. After many years of living next to the contamination and a litany of health problems she believes it caused, Bell-Jefferson and several other local families will have to vacate their homes for a third round of cleanup efforts by the U.S. Environmental Protection Agency (EPA). Decades of uranium mining have dotted the landscape across the Navajo Nation with piles of contaminated mine waste. The EPA has mapped 521 abandoned uranium mines on the reservation, ranging from small holes dug by a single prospector into the side of a mesa to large commercial mining operations.1 The Navajo people did not have a word for “radioactivity” when mining outfits looking for vanadium2 and uranium3 began moving onto their land in the 1940s, and they did not understand that radiation could be dangerous. They were not told that the men who worked in the mines were breathing carcinogenic radon gas and showering in radioactive water, nor that the women washing their husbands’ work clothes could spread radionuclides to the rest of the family’s laundry. Bell-Jefferson and her brother Peterson Bell played in and around the mines, splashing and swimming in pools of radioactive water that had been pumped out of the mines and then collected on their property. The contaminated water looked and tasted perfectly clean. Families used it for cooking, drinking, and cleaning. Hogans and corrals were built with mine wastes, as were roads. All that changed on 16 July 1979. Just about a mile and a half from Bell-Jefferson’s home, a dam broke at the United Nuclear Corporation mill, where workers processed ore from the nearby Northeast Church Rock uranium mine. The spill dumped 94 million gallons of mill process effluent and 1,100 tons of tailings—an acidic, radioactive sludge—into a large arroyo that emptied into the Puerco River.4 The Church Rock spill occurred less than four months after the partial meltdown of the Three Mile Island nuclear reactor, and it released three times as much radiation, making it the biggest nuclear spill in U.S. history, yet it received only a tiny fraction of the news coverage.5 Declared a Superfund site in 1983, the heaps of waste around the mill still cause radiation survey instruments to squeal from the invisible uranium atoms that remain active 30 years later.6 “This area used to be my playground,” Bell-Jefferson says. “Now it’s just a huge wound.” For the Bells and other Dine (the term by which many Navajo people refer to themselves), the Church Rock spill was a turning point. When corporate and government officials appeared in the spill’s aftermath and began inquiring into exposure to the slurry and potential health problems, the Navajo people finally learned the truth—far from being harmless, these uranium mines were poisoning people, and researchers say they will continue to do so for decades to come.

Radon emanation from backfilled mill tailings in underground uranium mine

Coarser mill tailings used as backfill to stabilize the stoped out areas in underground uranium mines is a potential source of radon contamination. This paper presents the quantitative assessment of radon emanation from the backfilled tailings in Jaduguda mine, India using a cylindrical accumulator. Some of the important parameters such as 226Ra activity concentration, bulk density, bulk porosity, moisture content and radon emanation factor of the tailings affecting radon emanation were determined in the laboratory. The study revealed that the radon emanation rate of the tailings varied in the range of 0.12–7.03 Bq m−2 s−1 with geometric mean of 1.01 Bq m−2 s−1 and geometric standard deviation of 3.39. An increase in radon emanation rate was noticed up to a moisture saturation of 0.09 in the tailings, after which the emanation rate gradually started declining with saturation due to low diffusion coefficient of radon in the saturated tailings. Radon emanation factor of the tailings varied in the range of 0.08–0.23 with the mean value of 0.21. The emanation factor of the tailings with moisture saturation level over 0.09 was found to be about three times higher than that of the absolutely dry tailings. The empirical relationship obtained between 222Rn emanation rate and 226Ra activity concentration of the tailings indicated a significant positive linear correlation (r = 0.95, p < 0.001). This relationship may be useful for quick prediction of radon emanation rate from the backfill material of similar nature.

Vegetation composition and 226Ra uptake by native plant species at a uranium mill tailings impoundment in South China

A field investigation was conducted for the vegetation composition and 226Ra uptake by native plant species at a uranium mill tailings impoundment in South China. 80 species belonging to 67 genera in 32 families were recorded in the sampling sites. The Poaceae and Asteraceae were the dominant families colonizing the impoundment. The number of the plant species and vegetation community composition in the sampling sites seemed most closely related to the activities of 226Ra and the pH value of the uranium tailings. The plant species in the sampling sites with relatively low activities of 226Ra and relatively high pH value formed a relatively stable vegetation community. The plant species in the sampling sites with medium activities of 226Ra and medium pH value formed the transitional vegetation community. The plant species in the sampling sites with relatively high activities of 226Ra and relatively low pH value formed a simple unstable vegetation community that was similar to that on the unused grassland. The activities of 226Ra and transfer factors (TFs) varied greatly with the plant species. The high activities of 226Ra and TFs were found in the leaves of Pteris multifida (150.6 Bq/g of AW; 9.131), Pteridium aquilinum (122.2 Bq/g of AW; 7.409), and Dryopteris scottii (105.7 Bq/g of AW; 6.408). They satisfied the criteria for a hyperaccumulator for 226Ra. They may be the candidates for phytoremediation of 226Ra in the uranium mill tailings impoundment areas and the contaminated soils around.

Landslides at a uranium mill tailing deposit site Boršt (Slovenia) detected by radar interferometry

This paper presents a comparison of persistent scatterer interferometry (PSI) monitoring results with in situ displacement measurements at the November 1990 landslide at the Borst uranium mill tailing deposit site after heavy rain. Although the landslide did not directly endanger people, site remediation works were undertaken due to the subsequent environmental problems. Additionally, in situ monitoring with benchmarks was established in order to detect the ground motion of the landslide body. PSI campaigning in the Skofjelosko-Cerkljansko area, where the uranium mill tailing is situated, performed for the purpose of measuring displacements of natural targets near the active landslide area, also detected displacements, most probably indicating a creeping process. When comparing the pre- and post-remediation velocities at the benchmarks located on the landslide with persistent scatterers (PSs) located near the landslide, the rates could be regarded as background. The results show that the remediation works in the form of a drainage tunnel were very effective as post-remediation velocities at the landslide closer to the PSs resembled the velocities of the PSs, while the velocities of the landslide mass above the drainage tunnel slowed down, even to below the background velocities. The high correlation values between the movements of the benchmarks and the PSs also confirm that the remediation works were effective as the fluctuations in the displacement values of the landslide were very similar to those of the PSs. Nevertheless, although there are several limitations in comparing the two different datasets, the PSI technique can be complementary to conventional in situ methods.