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ABSTRACT The environmental risks posed by mine tailings suggest the necessity of recycling tailings as cemented paste backfill (CPB) and constitutive modelling is an important step to understand its mechanical [...]

ABSTRACTThis experimental study was carried out to investigate the influence of polypropylene (PP) fibre on the compressive behavior and microstructural properties of tailings (classified as CL - lean clay) cemented [...]

ABSTRACT Cemented paste backfill (CPB) has been widely used to prevent and mitigate hazards produced during the excavation of underground stopes. In practice, the strength of CPB is often an [...]

The rapid concentration of tailings is a crucial initial step in the cemented paste backfill (CPB) process, as it ensures the stability of the backfilling slurry concentration and the continuity of the backfilling process. The structure of flocs plays a pivotal role in tailings concentration, directly contributing to such critical technical parameters as settling speed and bottom flow concentration. However, most of the current studies focus on flocculant addition rather than the tailings slurry itself. Also, there is a lack of uniform characterization of the flocculant structure in the flocculation and settling system. This study establishes a semi-quantitative assessment system for evaluating the fine structure of tailings flocs based on indicators such as the exposure state of coarse particles, floc size, and floc compactness (porosity). The findings reveal that, during the settling process, the higher true density of tailings (3.156 g/cm3) and intermediate particles (40 wt% of 38 μm–74 μm particles) attenuates the clamping effect of turbulence on settling, leading to a faster settling rate to 0.65 cm/s and 0.29 cm/s respectively. Moreover, in the thickening process, tailings located at the bottom of the mud layer expedite the precipitation of interstitial water within the floc structure through the combined influence of gravity and rake frame shear. Consequently, a denser floc structure forms, as evidenced by a higher concentration of bottom flow at a macroscopic level. This conclusion provides a theoretical basis for faster preparation of highly concentrated tailings slurry in CPB.

Cobalt (Co) has been recognized as one of the most hazardous elements by the United Nations Environmental Program; however, it has received limited attention in previous studies of identifying heavy metal contamination and has been limited to small, site-scale datasets and few machine learning algorithms. To fill this research gap, eight machine learning algorithms were combined with visible and near-infrared reflectance spectroscopy in this study to develop a large-scale model for classifying Co content in soil. In total, 18,675 topsoil samples were used to train and validate the models. Spectral preprocessing, principal component analysis, and hyper-parameter tuning were utilized to improve the tested models’ performance, which was evaluated using multiple indicators. The optimal model was then applied to the United States soil spectral dataset. The results show that the eXtreme Gradient Boosting (XGB) performed the best on both the training and testing sets, with an area under the curve value of 0.901 on the training set and 0.904 on the testing set. The application of XGB revealed that Utah, Arizona, New Mexico, North Dakota, Arkansas, Mississippi, and Alabama were at higher risk of Co contamination. In summary, XGB can be used to effectively identify areas of potential Co contamination. The approach presented here not only fills a gap in terms of large-scale identification of Co contamination but can also greatly assist environmental managers in risk assessment and reclamation strategies.

The improper stockpiling of lead/zinc mine tailings results in significant toxic impurities releasing, which threatens both the surrounding environment and human health. Cemented paste backfill (CPB) is considered an effective in-situ remediation way for managing lead/zinc mine tailings. In this study, the mechanical performance and heavy metal retention of CPB were evaluated by comparing the different binder strategies of ordinary Portland cement (OPC), Ca-bentonite, and Na-bentonite. The engineering properties of the mixtures were verified by uniaxial compressive strength (UCS) tests. The phase composition and internal microstructure were obtained by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Toxicity characteristic leaching procedure (TCLP) was performed to ascertain the effectiveness of heavy metal retention capacity. The results showed that the use of bentonite effectively optimized the UCS at early ages. Despite the deterioration is observed at 28 days, the UCS values are still qualified for the engineering application. With XRD and SEM analysis, a great content of amorphous was quantitatively characterized, highlighting the importance of amorphous content in the regulation of mechanical properties. TCLP results indicate that all the Pb, Cd, and As are predominantly incorporated within the cementitious matrix, whereas the Zn is the only concern in which the leachability decreases with the Ca-bentonite proportion. The leachates met the regulation limits (0.1 mg/L) at the CPB samples with 1.28 wt% of Ca-bentonite. Overall, bentonite could be an attractive alternative for the in-situ remediation of lead/zinc mine tailings to revive the stockpile site and reduce the environmental influence of this solid waste.

Triplet fusion (TF) and singlet fission (SF) are two important spin-coupled exciton interactions that occur in rubrene-based organic light-emitting diodes (OLEDs). TF produces additional singlets, which increases fluorescence efficiency, while SF consumes singlets and lowers the fluorescence efficiency. In an effort to adjust the SF and TF processes in rubrene-based OLEDs, we changed the average molecular spacing (d) of rubrene by doping it at varying concentrations in the high triplet energy material 1,3-bis(9-carbazolyl)benzene (mCP). Using magneto-electroluminescence (MEL), we observed that TF increased, while SF decreased at ambient temperature as dwas increased from 1.8 to 5.0 nm. This was further confirmed using MEL at different temperatures and current intensities. We found that the efficiency of rubrene-based OLEDs was improved by altering the value of d, with the highest efficiency being observed at d= 3.8 nm because of complete conversion of SF to TF (SF → TF). The SF → TF was explained using a model that describes Dexter- and Förster-energy transfer in SF and TF processes with functions that have a different dependence on d. This difference causes the rate constant of SF to decrease more rapidly than that of TF. The TF will be primary when dgoes between the Dexter and Förster radii, leading to complete SF → TF at ambient temperature. This work presents a promising approach to improve the efficiency of rubrene-based OLEDs.

Granulated copper slag (GCS) is currently applied to partial cement replacement as a supplementary cementitious material (SCM), but with a low rate due to its low pozzlanic activity. In this contribution we introduce an approach to enhance the reactivity of GCS by modifying the mineral structure using calcium oxide (CaO) and aluminum oxide (Al2O3) both by 10 wt.%, in a molten state. Blended cement pastes were formulated using cement (70 wt.%) and the modified GCS (30 wt.%). The development of hydration heat and strength were examined using isothermal calorimetry and strength tests, respectively. The mineral composition and microstructure of hydration products for different reaction periods were examined using X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). Also, toxicity characteristic leaching procedure (TCLP) was performed on the samples. Results showed an increase in the hydration heat emission rate from the early hydration and the compressive strength of blended cement paste after curing for 28 days, indicating that the addition of CaO and Al2O3in GCS improves pozzolanic activity. XRD and SEM-EDS analysis indicated that the modified GCS consumed more calcium hydroxide (CH) accompanied by increased generation of calcium silicate hydrate (C–S–H) gels in blended cement with a microstructure containing more gel phases and fewer pores, forming a more compact structure. Leaching of heavy metals of paste samples was lower than Environmental Protection Agency (EPA) limit. It is possible to apply the modified GCS as a sustainable material to promote cleaner production for cement and concrete industries.

With the development of deep mining and cemented paste backfill (CPB), high stress or soft-rock mines often encounter conditions that emphasize the creep behavior of rock mass (CBRM). This paper presents numerical models to analyze the interaction between excavation and backfill of adjacent stopes while considering CBRM. Results indicated that stope excavation and backfill had an important influence on the stress and displacement distribution of a previously backfilled adjacent stope. The excavation and backfill of the second stope also affected the horizontal and vertical displacement of the first stope. For example, in the adjacent stopes case, the maximum downward displacement of the first stope was 10.1 cm, compared to 6.7 cm for a single stope. Similarly, the maximum upward displacement increased from 21.6 cm for a single stope to 22.8 cm following the excavation and backfill of a neighboring stope. Moreover, the numerical models were used to analyze the influence of pillar width and filling interval time on the stability of adjacent stopes. In general, the study aimed to understand the effects of creep behavior on adjacent stopes in underground backfill engineering and provide suggestions for real-life engineering applications.

Here, the simulation of the physical fields in an n‐type ferroelectric thin‐film transistor (FeTFT) with a bottom contact bottom‐gate configuration is demonstrated. In the off‐state, the intensity of the lateral electric field in the space charge region near the edge of the drain electrode is several times higher than the coercive field of the ferroelectric film, pinning the direction of polarization near the drain electrode along the channel. While the FeTFT switches from off‐state to on‐state, the vertical component of polarization near the drain edge is stronger than other parts near the channel. This enhances the depolarization field in this area so that the retention performance of the on‐state is worse than the off‐state. These results and methods benefit FeTFTs and are also valuable for floating‐gate memory and light‐emitting field‐effect transistors. In ferroelectric thin‐film transistors (FeTFT) with bottom contact bottom‐gate configuration, intensity of lateral electric field near the edge of drain electrode can reach several times higher than the coercive field of the ferroelectric film in the off‐state. The depolarization field of this region is enhanced while the FeTFT switches from off‐state to on‐state.