This paper studies mechanical properties and energy damage evolution of fiber-reinforced cemented sulfur tailings (CSTB) backfill. The effects of fiber length and fiber content on the stress, ...toughness and failure properties of the CSTB were systematically revealed. In addition, the energy index evolution law was studied, and the energy damage evolution mechanism of CSTB was revealed. The results show that the deformation failure of fiber-reinforced CSTB mainly goes through four stages: initial crack compaction, linear elastic deformation, yield failure and post-peak failure. The peak stress and residual stress of the CSTB firstly increase and then decrease with the increase of fiber content and the addition of fiber can promote the change from brittle failure to ductile failure of the CSTB. Adding appropriate amount of fiber can improve the toughness of CSTB, and the influence degree of fiber length on the toughness index of CSTB is 6mm>12mm>3mm. The total strain energy increases linearly along the variation of fiber content, while the elastic strain energy and dissipated energy increase exponentially at the peak stress point. In the process of CSTB deformation and failure, "gentle-linear growth-slow growth-rapid decline" is for elastic strain energy, while "gentle-slow growth-rapid growth-linear growth" is for dissipation energy. The damage and failure of CSTB mainly experienced four stages: initial damage, slow growth of damage, accelerated damage and damage failure, and the damage evolution curve also showed the changing characteristics of "gentle-slow growth-rapid growth-linear growth". The CSTB without added fiber showed obvious "Y-type" and "linear-type" shear failure characteristics and the phenomenon of shear cracks penetrating the backfill appeared. No big shear crack occur when it is damaged, showing that the fiber addition restrain the crack growth and improve the overall crack resistance of the CSTB. Hydration products are obviously distributed on the surface of the fiber, which indicates that the fiber will be evenly dispersed in the CSTB and form a certain bonding force with the cement-tailings matrix, thus improving the overall mechanical properties of the CSTB.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
An experimental study was conducted to investigate the effect of fly-ash(FA) as a fine aggregate on filling performance. The effect of FA content on the gradation distribution and compactness of the ...dry mixture is tested. Slump, bleeding rate, and unconfined compressive strength (UCS) of cemented waste rock-FA backfill (CWFB) samples were also tested at different FA content, solids content, and cement-sand ratio conditions. Results show that FA as a fine aggregate can effectively improve the mixture gradation performance. Short-term (3d/7d) strength increases with FA content, while long-term (28d) strength and slump first increase and then decrease, reaching a maximum value of 8.58 MPa and 27.4 cm respectively at 30% FA content. The bleeding rate first decreased and then stabilized (about 5.2%) with FA content. The UCS showed higher sensitivity to high solid content. The slump reduction rate of samples with high FA content decreases with solid content. Larger cement content will weaken the fluidity. When the cement-sand ratio increased from 1:6–1:4, the slump decreased from 27.5 cm to 23.5 cm, and the bleeding rate decreased to 4.05%. However, the mechanical properties are significantly improved with cement content. This study has positive implications for recycling the FA.
•CWFB is made of water, waste rock, fly-ash, and cement.•The bleeding, slump, and mechanical properties of the CWFB were observed.•The early strength of CWFB samples increased slowly with the FA content.•Soil grading theory cannot accurately evaluate the mixed aggregates.•This study has positive implications for recycling the FA.
Mineral resources provide an important material foundation for industrial construction and are important for the economy, thus being closely integrated into our daily lives and near future ...
Bacterial community dynamics and copper leaching with applied forced aeration were investigated during low-grade copper sulphide bioleaching to obtain better bioleaching efficiency. Results ...illustrated that appropriate aeration improved bacterial concentrations and leaching efficiencies. The highest bacterial concentration and Cu
2+
concentration after 14-d leaching were 7.61 × 10
7
cells·mL
−1
and 704.9 mg·L
−1
, respectively, at aeration duration of 4 h·d
−1
. The attached bacteria played a significant role during bioleaching from 1 to 7 d. However, free bacteria dominated the bioleaching processes from 8 to 14 d. This phenomenon was mainly caused by the formation of passivation layer through Fe
3+
hydrolysis along with bioleaching, which inhibited the contact between the attached bacteria and ore. Meanwhile, 16S rDNA analysis verified the effect of
Acidithiobacillus ferrooxidans
and
Acidithiobacillus thiooxidans
on the bioleaching process. The results demonstrate the importance of free and attached bacteria in bioleaching.
The ore agglomerations could ameliorate intra-particle pore network, homogenize flow paths, and improve leaching efficiency of heap leaching. This paper innovatively develops a novel ore granulator ...with adjustable inclined angle and rolling speed. To comprehensively evaluate granulation procedure, the effects of physical (crushed feeds particle size distribution, rolling speed, inclined angle), chemical (binder type, curing time) and biological factors (bacterial concentration) on bonding performance of crushed feeds are analyzed. The objective of this paper is to obtain the optimal granulation conditions by studying the influence of various factors on the bonding ability, strength, and stability of granulated ores, in order to improve the pore structure of the heap leaching system, and increase the leaching rate of the ore. The results show that well-shaped agglomeration (WAs) does improve minerals leaching efficiency, and the uniaxial compressive strength of WAs is positively related to curing time, binder concentration, inclined angle, and rolling speed. The excessive lower or higher rolling speed is not suitable to get a higher extraction rate due to undesirable disintegration or compaction. The higher concentration (0.5–10 %) sulfuric acid solution could obviously increase WAs strength from 32.6 KPa to 48.3 KPa. The organic binders such as polyacrylamide are benefit for powders bonding and increase the compressive strength, but does not good for the desirable leaching reaction rate. The bacterial pre-adding has no significant positive influence on bonding and leaching efficiency. Relied on the 3D response surface, the preferred preparing condition is: 78.9 rpm rolling speed, 30° inclined angle, 7-days curing time and 9.3 % H2SO4 solution. Future studies should focus on exploring the intrinsic correlation between the various factors and evaluating the granulating and leaching effects from the perspective of chemical detection and leaching bacteria.
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•A novel lab-scale ore granulator with adjustable inclined angle (0–30°) and rolling speed (30–150 rpm) is firstly developed.•Influence of physical, chemical, biological issues of copper sulfides agglomeration is revealed;•Powder bonding, leaching and structural feature of well-shaped agglomeration (WAs) is evaluated.•Multi-factor 3D response features of WAs preparation is carefully discussed.
The clogging of drainage facilities, which reduces the permeability coefficient, raises the phreatic line, and increases the possibility of seepage damage, seriously impacts the safety of tailings ...dams. The core cause of clogging is the oxidation of active minerals or ions and the formation of gelatinous materials. These materials, the most typical of which are active iron minerals (such as pyrite or ferrous ions), are adsorbed in the percolation passage to block the flow of liquid. This paper aims to study the effect of ferrous ions on the hydraulic conductivity of fine tailings. First, we introduce a new apparatus based on the column experiment to examine the permeation characteristics of fine tailings. Second, a systematic experimental study was conducted to obtain the effect of ferrous ion content, nonwoven geotextile layer number, and specimen height (reflecting the length of the seepage path) on the tailings permeability ratio using this apparatus. Third, scanning electron microscopy (SEM) was performed on selected geotextile samples that underwent filtration to assess the clogging mechanism. The results show that the ferrous ions were oxidized to form the low solubility iron(III) oxide-hydroxide (Fe(OH)3), which was deposited or adsorbed in the percolation channel and caused chemical clogging. Meanwhile, in the case of more geotextile layers or slower seepage rates, the blockage of the fine tailings formed faster in the penetration experiment. According to the results of the SEM, there were glue coverings on the fiber surface, and ultrafine tailings particles (−10 μm) were adsorbed, adhered and deposited on it and formed a chemical-physical clogging.
•Clogging formation is more sensitive to ferrous ions content in the tailings sample.•Geotextile thickness (or number of layers) has a significant impact on the formation of clogging.•The ultrafine particles (−10 μm) are more easily adsorbed, banded, and even encapsulated by colloidal compounds.•Clogging formation seems to be dependent on the hydraulic environment.
In order to study the static and dynamic flocculation settlement characteristics of fine total tailings and the influence law of flocculant on the mechanical properties of fine tailings backfill, the ...experimental research on the flocculation settlement and mechanical properties of fine total tailings was carried out in the laboratory. The static flocculation settlement test of fine total tailings was carried out by orthogonal test scheme, and the influence law of the full-tail mortar concentration (FTMC), flocculant unit consumption (FUC) and flocculant solution concentration (FSC) on the concentration of underflow and sedimentation rate was analyzed, and the best static flocculation settlement parameters were obtained. Secondly, the dynamic flocculation test was carried out on the basis of static flocculation settlement parameters to reveal the influence law of dynamic flocculation settlement on underflow concentration. Finally, the compressive strength of fine tailings backfill under different flocculant unit consumption were tested, and the microscopic evolution of backfill was investigated by scanning electron microscopy. The results show that: Anionic flocculant has better flocculation effect than non-ionic flocculant, so anionic flocculant can be preferred as flocculant for flocculation settlement of fine full tailings. The flocculation settlement process of fine tailings slurry can be divided into four regions: clarification region, settlement region, transition region and compression region. The influence degree of the three factors on settling velocity and underflow concentration is full-tail mortar concentration > flocculant unit consumption > flocculant solution concentration, and full-tail mortar concentration and flocculant unit consumption are significant influencing factors on settling velocity and underflow concentration. The flocculation settlement parameters of fine full tailings slurry are not only affected by single factor, but also by the interaction between factors. The optimal static flocculation sedimentation parameters are as follows: the full tailings slurry concentration is 20 %, the flocculant unit consumption is 10 g/t and the flocculant solution concentration is 0.3 %. The dynamic flocculation settlement can greatly increase the underflow concentration, and the underflow concentration increases with the residence time, but there is no significant change in the underflow concentration when the residence time exceeds 5 h. The compressive strength of fine tailings backfill decreases with the increase of flocculant unit consumption, and the microscopic test results show that the increase of flocculant unit consumption will weaken the compactness of the microstructure of the backfill, which leads to the decrease of the compressive strength of the backfill.
To address the stress–structural failure phenomenon that can be induced by the excavation of a left-side tunnel section of a 610 m crushing station, an unmanned aerial vehicle was used in this study ...to collect the geological conditions and rock mass information of the working face, and important geometric information such as the attitude and spacing of rock mass were extracted. Based on the identified attitude and spacing information, a three-dimensional rock mass structure and numerical simulation model of the 610 m crushing station left-side tunnel section were constructed using discrete element numerical simulation software (3DEC) (version 5.0). The results show that the surrounding rock instability of the left-side tunnel section of the 610 m crushing station is controlled by both the stress field in the contact zone between reddish-brown granite stratum and the gray-black-gray gneiss stratum. The cause of stress–structural failure is that the joint sets (JSet #2 and JSet #3) are most likely to form unfavorable blocks with the excavation surface due to unloading triggered by the excavation. Therefore, stress–structural failure disasters in jointed strata sections are one of the key issues for surrounding rock stability during crushing station excavation. It is suggested to adopt ‘optimized excavation parameters + combined support forms’ to systematically control stress–structural failure after unloading due to the excavation from three levels: surface, shallow, and deep. The stress–structural failure mechanism of deep rock mass is generally applicable to a large extent, so the results of this research have reference value for engineering projects facing similar problems around the world.
The surface deformation caused by underground mining seriously affects the normal life and personal safety of local residents and also causes unfavorable factors for the safe and efficient ...exploitation of underground resources. While the study of surface deformation caused by underground mining of metal mines requires a large amount of measured data as support, the measured data is particularly scarce, which severely hinders the study of surface deformation caused by underground mining. In this paper, in order to study the impact of underground mining on surface structures in metal mines, we take the Fu Lao Zhuang Iron Mine in Anhui Province, China, as the research object and put forward a comprehensive measurement method based on the flat plate beam theory. Using empirical formulas combined with the methods of thickness-to-span ratio and the relaxation coefficient, etc., we carry out numerical simulation calculations for the displacement of the surface triggered by the mining of the ore body by using FLAC3D software. We calculate the maximum inclination deformation, curvature, and horizontal deformation values of the ground surface by referring to the displacement and deformation with reference to the displacement and deformation formula; the maximum tilt deformation, curvature, and horizontal deformation values of the ground surface are calculated, and finally, the permissible values of the design specifications are combined to make a judgment. The research results of this paper put forward the prerequisite for improving the surface deformation induced by underground mining.
Filling mining with solid waste resources as aggregates is an important development direction for cleaner production in mines. The hydration products have an important effect on the mechanical ...properties of superfine tailings cemented paste backfill (SCPB). This paper investigates the mechanism of hydration product formation and thermal decomposition properties of SCPB by a series of experiments combined with thermal decomposition kinetics. Also, to optimize the mechanical properties of SCPB, the effect of Nano SiO2 (NS) on the related properties of SCPB is investigated. The results show that there are two main stages of the thermal decomposition of SCPB, and the kinetic models of these two stages are both reaction order models. After adding NS, the kinetic model of the second stage of thermal decomposition of SCPB is changed to random nucleation and growth model. The substances that undergo thermal decomposition reactions in the first stage are mainly hydration products such as ettringite and C-S-H, while the substances that undergo thermal decomposition reactions in the second stage are carbonates. The activation energy E and pre-exponential factor A of the first stage of thermal decomposition of SCPB with NS added are significantly improved, which indicates a more stable structure of its hydration products. The microscopic test results show that NS can promote the hydrolysis of C3S and gypsum and increase the production of hydration products, which in turn improves the strength of SCPB. In addition, the addition of NS to SCPB decreases the Ca/Si and increases the average silica chain length of C-S-H gels, while the H2O/Si decreases and the silica group increases, resulting in the enhancement of the structure of C-S-H gels.
