Fine-grained Mine Tailings Research Articles

Consolidation testing of tailings in a slurry consolidometer using constant rate and accelerated loading

A high rate of rise of fine-grained mine tailings slurry on disposal in a tailings storage facility (TSF) may maintain their condition as underconsolidated. The proper simulation of such field deposition of tailings in conventional laboratory consolidation testing is challenging. A slurry consolidation test using a high constant rate of loading (CRL) simulates a faster rate of tailings disposal in a TSF. A better simulation is achieved, however, by applying accelerated loading in a slurry consolidometer to allow for the increased drainage path length as tailings are built up in the TSF. CRL and accelerated loading were used in a purpose-built, large, instrumented, stress-controlled slurry consolidometer to examine and compare the consolidation behaviour of coal tailings, red mud and gold tailings. At the end of the CRL and accelerated loading tests, the excess pore water pressures had not fully dissipated and the maximum applied stress was maintained to achieve full primary consolidation. The findings of this study showed that the consolidation behaviour of the tailings studied varied with the nature of the tailings and with the loading applied.

A study on the mechanical behaviour of three different fine-grained mine tailings

Mine tailings stored in the tailings storage facility (TSF) are normally loose and failure-prone for several reasons, such as liquefaction, erosion, overtopping, piping, and high excess pore water pressure (PWP). The investigation of the mechanical behavior of tailings material is essential for engineering design and safety evaluation of the TSF during mining operations, closure, and rehabilitation. As such, laboratory compaction, consolidation, and direct shear strength experiments are carried out on three different fine-grained mine tailings, named coal tailings (CT), red mud (RM), and gold tailings (GT). Compared to CT and RM, GT showed higher dry density at the optimum moisture content (OMC) and lower compressibility. The permeability of GT is similar to RM but much higher than that of CT. CT and GT showed the highest cohesion and angle of internal friction, respectively, among the tested materials. The direct shear test, among all the methods used, provided the highest dry density and lowest void ratio. The final state parameters obtained in compaction, consolidation, and direct shear tests are critically compared, which is the novelty of this study. This research explored useful information on the geotechnical properties of different tailings that can help mining operators and researchers effectively design and manage the tailings in the TSF.

Characterization of Self-Weight Consolidation of Fine-Grained Mine Tailings Using Moisture Sensors

Abstract This paper presents an experimental procedure and testing results on the consolidation of saturated tailings based on measurements made with moisture sensors. A special calibration procedure has been developed for precise volumetric water content measurements to reflect the progressive change of density and void ratio in the loose tailings. The moisture sensors’ readings are used to evaluate key parameters during self-weigh consolidation, which allow an assessment of the settlement’s rate and magnitude. The results indicate that the proposed technique can be useful to assess the tailings slurry characteristics, which significantly evolve during self-weight consolidation. The experimentally determined parameters are in the range provided by other investigations conducted on the same materials. It is also shown that pore-water pressures deduced from the volumetric water content measurements during the laboratory tests correlate well with the profiles obtained from the one-dimensional consolidation theory.

Stabilisation of iron mine tailings through biocalcification

Mine tailings consist of fine-grained particles that are deposited into large impoundments. Seasonal temperature and moisture fluctuations can result in dust emissions, an environmental hazard. Accordingly, there is a need for efficient and economical means for controlling dust emissions. Biogeotechnics provides one innovative approach to modifying soil properties. For example, Sporosarcina pasteurii has been studied for its ability to promote biocalcification in sand-sized particles by way of ureolysis. The application of this process to fine-grained materials, however, poses unique challenges. The goal of this work was to demonstrate biocalcification in fine-grained mine tailings to promote the formation of a crust that increased the surface strength of the tailings. Soil box experiments coupled with multiple lines of evidence collected using novel analytical techniques were used to confirm (a) the successful formation of the surface crust by way of ureolysis mediated by inoculated S. pasteurii and native urea-degrading microbes and (b) the impact of the crust on the surface strength of tailings. The crust formation and increased surface strength demonstrated in tailings inoculated with S. pasteurii and with native microbes provide a foundation for further research to advance the application of biogeotechnics in fine-grained materials for purposes such as dust mitigation.

Laboratory Study on Strength Development in Cemented Paste Backfills

Cemented paste backfills (CPBs) are widely used in backfilling underground mine voids. They are fine-grained mine tailings with significant clay content, with a small dosage of a general purpose cement (GPC) or pozzolanic binder such as blended cement (BC) containing slag or fly ash. This paper summarizes the findings from an extensive laboratory test program carried out to understand the effects of binder dosage and solid content on the strength development over 56 days of curing. Ten different mixes were studied using 80 specimens, and it was shown that the blended cement mixes give an early gain in strength and stiffness, along with higher long-term values compared with the GPC mixes. It was also shown that the E/UCS, which is the ratio of Young’s modulus (E) to uniaxial compressive strength (UCS), values for the CPB throughout the curing period were in the range of 150–350, with an average value of 250. Two simple mathematical expressions were developed to express UCS as a function of time and the 14-day UCS value (UCS14). In the case of BC mixes, the relative effect of increasing the solid content or binder dosage was studied through separate UCS tests carried out at 28 and 56 days using 40 additional specimens.

Windborne transport and surface enrichment of arsenic in semi-arid mining regions: Examples from the Mojave Desert, California

Abstract Gold and silver mining conducted throughout the state of California has left an environmental legacy of exposed mine wastes containing elevated levels of toxic metals and metalloids including arsenic (As), a known carcinogen. These mine tailings, particularly the fine-grained size fractions, are susceptible to weathering and windborne transport, significantly increasing the spatial extent of contamination in topsoils and potential exposure of humans to toxic metal(loid)s. Depth-based field sampling of soils surrounding several abandoned mines in the Mojave Desert (Southern CA) have identified an exponential decline in As soil enrichment with both depth and increasing distance from tailings piles to the east, consistent with prevailing west-to-east wind directions. In vitro extraction studies using a phagolysosomal simulant fluid (PSF), mimicking the inhalation of the most finely sieved size fraction of selected samples (⩽20 μm), indicate that initial solid As concentration is the strongest indicator in predicting the concentration of As released in the lung. When extraction data are incorporated into exposure risk assessment calculations, the majority of samples investigated exceed both cancer risk thresholds and non-cancer-related minimal risk levels (MRLs) based on long-term chronic exposure to airborne mine tailings dusts. This suggests that long-term residents of communities located close to these abandoned mine sites, especially those who reside downwind (i.e. east) of mine tailings piles, face possible health effects due to the inhalation of fine-grained mine tailings mobilized through aeolian processes.

Development and Calibration of a Quantitative, Automated Mineralogical Assessment Method Based on SEM-EDS and Image Analysis: Application for Fine Tailings

Quantitative mineralogy has seen significant developments from the combination of scanning electron microscopy (SEM) with automatic image analysis and energy dispersive X-ray spectrometry (EDS). The mining industry is one of the fields that has benefited from this progress. In this paper, the authors present a newly developed quantitative method based on SEM-EDS and image analysis (IA), which is used to determine the mineralogical and environmental characteristics of mine tailings. The main objectives of the method are to be able to characterize sulphides and carbonates as monomineral particles, which control the acid generation from the tailings. Pure sulphides, calcite and quartz were blended to make mineralogical standards that represent typical mine tailings environmental behavior. The SEM-EDS-IA method achieved good mineralogical precision for medium (1-20 Wt%) and abundant (> 20 Wt%) minerals, with a relative error below 10 %. However, some corrections had to be applied to account for typical stereological effects (apparent particle diameter from polished surface) and preparation modes (particle segregation during resin hardening). Particle size analysis was used to calibrate the method and identify the corrections to be applied. Since mineralogical quantifications are based on the area of the observed particles, the most reliable particle size analyses (also obtained from particle area) typically lead to the best mineralogical characterization. However, the SEM based techniques may show some limitations for fine-grained particle quantification (< 10 μm), which required additional corrections. In this article, the technique is described, and it is applied to characterize fine-grained mine tailings with a size-by-size mineralogy (with sulphides and carbonates content). These results have been used by the Authors to propose an environmental management strategy for acid generating tailings using desulphurization by flotation.

Geochemistry of waters associated with the old mine workings at Fonte Santa (NE of Portugal)

The quartz veins containing scheelite from Fonte Santa mine cut the Lower Ordovician quartzites. A muscovite–biotite granite (G1) and a muscovite granite (G2), both S-type, crop out close to the Fonte Santa mine and are related to the Moncorvo–Bemposta shear zone. The most altered samples of G2 show intense muscovitization and microclinization and contain chlorite, columbite–tantalite, wolframite, W-ixiolite and Fe-oxides. The tin-bearing granites contain 18 ppm (G1) and 73 ppm (G2) Sn. The most altered samples of G2 correspond to a tungsten granite. The quartz veins contain muscovite, chlorite, tourmaline, scheelite, pyrrhotite, pyrite, sphalerite, chalcopyrite, galena, arsenopyrite, iron oxides, Fe sulfates, phosphates of Pb, Fe and Al. The Fonte Santa mine area was exploited for W between 1942 and 1982. At the end of November 2006, a flood event damaged the tailings dam of Fonte Santa mine, releasing contaminated material and increasing contaminant levels in water within the area of influence of the mine. The waters related to the Fonte Santa mine are poorly mineralized, with electrical conductivity of < 965 µS/cm, and of a mixed type or HCO 3 − and SO 4 2− types. Most pH values (5.0−8.5) indicate that there is no significant acidic drainage in the region, as found in other areas. More acidic values (pH = 3.4) were found in the mine's lagoon. Waters associated with mineralized veins and old mine activities have Fe and Mn concentrations that forbid their use for human consumption and agriculture. Natural Na, Mg and K water contents are associated with the alteration of albite, chlorite and muscovite of country rock, while Ca with the W-bearing quartz veins. Weathering agents are carbonic and sulphuric acids and the latter has a strong influence in areas draining fine-grained mine tailings.

Cyclic shear response of fine-grained mine tailings

The mechanical response of three different types of fine-grained mine tailings is examined using data from constant-volume cyclic direct simple shear (DSS) tests. Under cyclic DSS loading, fine-grained tailings typically exhibit a cumulative decrease in effective stress along with progressive degradation of shear stiffness. The observed shear strain development due to cyclic mobility is similar in form to that of the previously observed cyclic shear response for natural silts. The cyclic resistance ratio (CRR) of laterite tailings is observed to increase with an increase in the initial effective confining stress (σ′vc). For this material, the dilative tendency due to stress densification seems to have overridden the contractive tendency due to the increase in confining stress. In contrast, the CRR of copper–gold–zinc tailings is insensitive to the initial effective confining stress, suggesting a response similar to that of normally consolidated clay. The postcyclic maximum shear strength ratio (Su-PC/σ′vc) obtained from constant-volume monotonic DSS tests is noted to increase with a decrease in the void ratio. For the fine-grained tailings considered in this study, the liquefaction susceptibility predicted using commonly used empirical criteria is not always in agreement with the liquefaction triggering determined from cyclic DSS tests.Key words: tailings, liquefaction, cyclic stress ratio, postcyclic shear strength, direct simple shear testing.