Mine Fill Research Articles

Microstructure evolution and mechanical behavior of foamed cement-based tail backfills under varying fiber types and concentrations.

Industrial solid waste (mine tailings) management has emerged as the key universal ecological challenge as a result of the unceasing creation of rising waste by-products. Employing tailings makes mine fill production economical and assists resolve disposal problems. Foamed cement-based tailings backfill (FCTB) is a mine fill consisting of tailing, cement, water, and foaming agents. It provides certain advantages such as lightweight, good fluidity, and thermal insulation yet is relatively weak in strength. Additionally, FCTB's strength properties can be intensely improved by adding fibers. A total of three diverse fibers: polypropylene (PP), glass (G), and basalt (B) as well as dodecyltrimethylammonium bromide (DTAB) as a foaming agent were used to prepare fiber-reinforced foamed cementitious tailings backfill (FR-FCTB). The mechanical properties, energy evolution, ductility, and microstructure of FR-FCTB were elaborately investigated by uniaxial compression tests (UCS) and SEM. Laboratory findings demonstrate the reinforcing effect of three fibers on FCTB specimens: glass > polypropylene > basalt. FR-FCTB showed the best strength features as a fiber content of 0.3% was adopted in FCTB. At this time, the UCS performance of glass fiber-reinforced FCTBs was 0.85MPa increased by 18.1%. The addition of fibers can increase the fill's energy storage limit, slow down the discharge of elastic strain energy within the backfill, and enhance the fill's ductility and toughness. The ductility factor evaluates the degree of deterioration of filling in terms of post-peak drop, with all FR-FCTB values being greater than CTB. FR-FCTB's chief hydration product is the C-S-H gel. Fiber's bridging effect significantly rallies crack extension and thus fill's strength features. Lastly, the study's main results are instructive for the industrial application of FR-FCTB used in metallic mines.

Predicting long-term impact of cementitious mine fill considering sand as a copper-tailings substitution

It is of great importance to use different materials or techniques to enhance the quality/behavior of cementitious mine fill (CMF). This leads the mining industry to evaluate new production techniques or resources that will improve CMF performance by choosing easier, cheaper, faster, and reliable approaches. This study captures the effect of sand employed as tailings substitution on CMF properties by destructive and non-destructive methods. The mechanical (UCS), ultrasonic (UPV) and microstructure (XRD, FTIR, SEM) properties of the backfills, which were prepared with a fixed binder (3 wt%) and two different solids (70 and 75 wt%) content, cured up to 360 days were investigated. The amount of sand used in the mixtures was chosen to be 0% (control), 10%, 20%, 30, 40% and 50% of the tailings by weight. Results exposed that the growth in solid concentration, curing time (up to 90 days) and the amount of sand in the mixtures (up to 30%) had a boosting consequence on the fill's performance. However, both in long curing times and in the use of >30% sand, CMF's performance decreased. Moreover, perfectly compatible correlations were found between the UCS and UPV results, depending on the solid content of CMF and the sand substitution rate. The UCS results measured and predicted by these correlations were also obtained from the current work. As a result, this study presents the contribution of ultrasonic non-destructive testing as an alternative way and the link between them to the backfill technology.

Strength and microstructure evolution in cemented mine backfill with low and high pH pyritic tailings: Effect of mineral admixtures

To properly dispose mining-induced tailings, diverse techniques including cemented paste fill (CPB) have been already employed. Indeed, tailings are manufactured by using different admixtures which are poisonous to the environment and need to be closely explored by considering its effects. This study dealt with the quality of CPB containing low pH (4.9) and high pH (10.8) pyritic tailings. Besides, employing ground blast furnace slag (GBFS) and fly ash (FA) in diverse rates instead of ordinary Portland cement (OPC) and their effects on fill performance were explored. Strength and microstructure of CPB made with constant solid content (72 wt%) and different OPC/GBFS-FA ratios (e. g., 90/10, 70/30 and 50/50) were carried out by several laboratory tests. Results showed that the lowest UCS performance was obtained from CPB having 50%FA and acidic tailings. It was also observed that GBFS-based backfills gave better strength than FA-based ones, irrespective of tailings, owing to the former’s high pozzolanic activity and grain shape. Regardless of additives, the highest strengths were gained from basic tailings-based backfills. pH of pyritic tailings affected fill’s performance due to its aggressive effects on cement hydration. To sum up, this study has provided relevant information and technical evidence that will subsidize the engineering design of a low-cost, zero-waste, and viable mine fill system.

Study on Solidification and Stabilization of Antimony-Containing Tailings with Metallurgical Slag-Based Binders

Blast furnace slag (BFS), steel slag (SS), and flue gas desulfurized gypsum (FGDG) were used to prepare metallurgical slag-based binder (MSB), which was afterwards mixed with high-antimony-containing mine tailings to form green mining fill samples (MBTs) for Sb solidification/stabilization (S/S). Results showed that all MBT samples met the requirement for mining backfills. In particular, the unconfined compressive strength of MBTs increased with the curing time, exceeding that of ordinary Portland cement (OPC). Moreover, MBTs exhibited the better antimony solidifying properties, and their immobilization efficiency could reach 99%, as compared to that of OPC. KSb(OH)6 was used to prepare pure MSB paste for solidifying mechanism analysis. Characteristics of metallurgical slag-based binder (MSB) solidified/stabilized antimony (Sb) were investigated via X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). According to the results, the main hydration products of MSB were C-S-H gel and ettringite. Among them, C-S-H gel had an obvious adsorption and physical sealing effect on Sb, and the incorporation of Sb would reduce the degree of C-S-H gel polymerization. Besides, ettringite was found to exert little impact on the solidification and stabilization of Sb. However, due to the complex composition of MSB, it was hard to conclude whether Sb entered the ettringite lattice.

Characterization of Strength and Quality of Cemented Mine Backfill Made up of Lead-Zinc Processing Tailings

Predicting the reactions of the backfill materials exposed to the effects of air and groundwater will eventually ensure an efficient and accurate mine fill system for sustainable mining operations. This paper reveals the effect of the mobility of sulfur ions within lead-zinc processing tailings on strength and quality of cemented mine backfills. Some laboratory tests such as X-ray diffraction, ion chromatography, scanning electron microscopy, combustion tests, chemical analysis, pH and zeta potential measurements were performed to better characterize the backfill’s mechanical and microstructural properties. Moreover, CEM II/A-P Portland pozzolan and CEM IV/A pozzolanic cements as ready-to-use cement products were used for cemented mine backfill preparation. To ensure the carrier of the lead-zinc tailings and to prevent the mobility of the sulfurous components, a binder content ranging from 3 to 7 wt% were employed in mine backfills. The experimental findings demonstrate that the used cement type and proportions were insufficient and some fractures are occurred in the samples due to the sulfur ion mobility. Accordingly, one can state clearly that the elemental analysis through the combustion test method can provide fast and reliable results in the determination of sulfur within lead-zinc processing tailings.

Enhancing Arsenic Solidification/Stabilisation Efficiency of Metallurgical Slag-Based Green Mining Fill and Its Structure Analysis

To dispose of arsenic-containing tailings with low carbon and high efficiency, sodium sulphate (Na2SO4), sodium hydroxide (NaOH), calcium nitrate Ca(NO3)2 and calcium hydroxide Ca(OH)2 were independently added to metallurgical slag-based binder (MSB) solidification/stabilisation (S/S)-treated tailings (MSTs) to enhance the MST arsenic S/S performance. Results showed that only Ca(OH)2 could increase the unconfined compressive strength of MST from 16.3 to 20.49 MPa and decrease the leachate As concentration from 31 μg/L to below 10 μg/L. Na3AsO4·12H2O and NaAsO2 were used to prepare pure MSB paste for mechanism analysis. The results of microstructure analyses showed the high specific surface area and amorphous properties of calcium–sodium aluminosilicate hydrate facilitated the adsorption or solid-solution formation of As(V) and As(III). As(V) formed an inner-sphere complex in ettringite, whereas As(III) formed an outer-sphere complex, and the relatively larger size and charge of As(V) compared with SO42− restrict substitution inside channels without affecting the ettringite structure under high loading of As(V). The added Ca(OH)2 promoted the hydration reaction of MSBs and facilitated the formation of a Ca–As(V) precipitate with low solubility, from Ca4(OH)2(AsO4)2·4H2O (Ksp = 10−27.49) to Ca5(AsO4)3(OH) (Ksp = 10−40.12). This work is beneficial for the application of cement-free MSB in the S/S process.

Influence of industrial solid waste as filling material on mechanical and microstructural characteristics of cementitious backfills

Use of industrial solid wastes (e.g., fly ash, desulfurization gypsum, steel slag) as mine fill material not only solves the environmental risks dictated by the sustainable management of these wastes, but also reduces the operational costs of backfilling. Utilization of backfill in underground mining enhances both local and regional ground support, leading to maximum ore extraction and minimum solid wastes storage. In this study, the mechanical and microstructural characteristics of cementitious backfill (CB) with fly ash-FA, desulfurization gypsum-DG, and steel slag-SS were studied by both uniaxial compressive strength (UCS) and scanning electron microscope test. CB samples were made at a constant solid content of 70 wt% and subjected to UCS testing after a curing time of up to 14 days. Cement-to-solid waste ratio for all CB samples was kept as 1:12. Results reveal that: the UCS value of 14-day cured fills ranges between 1.32 and 2.60 MPa, and the optimal ratio of solid waste was 2:4:4 (DG: FA: SS). The strength performance of backfilling increases with increasing DG and FA values and decreases with increasing SS value. The failure form of backfills is manifested as a tensile failure, and at the bottom of the phenomenon of varying degrees of loose expansion. Microstructural analyses showed that the hydration products in CB samples includes AFt and C-(A)S-H gels. The mineralogical name of AFt is Ettringite (3CaO·Al2O3·3CaSO4·32H2O). The cementing performance of the latter is better than the first (AFt). With the increased FA contents and curing times, hydration products in CB increased and porosity decreased. The outcome of this work will afford a theoretical support for using solid waste as backfilling, advance the management techniques for employing the fill and also propose significant savings in the cement-related costs without negotiating on the safety.

The mechanism of hydrating and solidifying green mine fill materials using circulating fluidized bed fly ash-slag-based agent

This study focused on classifying and disposing Circulating fluidized bed (CFB) fly ashes from the level of its origin, and proposed an optimal formulation system for clinker-free cemented backfill materials. CFB fly ash-blast furnace slag (BFS)-based cemented backfill materials with unequal strength grades are used in different locations of the goaf that require more than 1 Mpa and 4 Mpa, respectively, and the leaching levels of all toxic components are lower than the underground III water quality standard limit when the additional amount of CFB fly ash does not exceed 60 wt.%. The stable S/S of Cl− is due to the combined effect of chemical fixation of HCC and physical adsorption of the C-S-H/C-A-S-H phase. B2(20 wt.% CFB fly ash) exhibits more functional hydration products and higher degree of polymerization with the hydration age extension. Ettringite is the major effective product of CFB fly ash-BFS-based cemented system due to low level of chlorine environment and HCC transformation. CFB fly ash with appropriate active Al2O3 can dissolve and promote [AlO4]5- to substitute [SiO4]4- to form the C-A-S-H phase with longer chains and higher degree of polymerization with increase in Al/Si ratio of C-A-S-H/C-S-H phase.

Experimental Development of a Novel Mine Backfill Material: Foam Mine Fill

This study aims to develop a novel mine backfill material called foam mine fill (FMF). A cellular structure is achieved by incorporating a premade foam into the backfill mixture using an air-entraining agent. FMF samples were prepared with copper-nickel mine tailings and normal Portland cement. Experiments were designed to investigate the effect of binder dosage, volume of entrained air, and foam mixing time on FMF unconfined compressive strength (UCS) and dry density. Moreover, a qualitative microscopic assessment investigated the effect of foam mixing time on air bubble structure. The pore size distribution and porosity of selected samples were investigated through mercury intrusion porosimetry. Relative to reference samples without entrained air, the UCS of FMF samples was 20–50% lower. However, the concomitant lower dry density (by up to 360 kg/m3) could enhance the safety of the underground working environment, especially in underhand cut-and-fill mining where miners and machinery work beneath the backfilled stope, and lower-density fill material would minimize the adverse effects of potential backfill failure. Prolonged foam mixing time led to a significant loss in UCS and total collapse of the air bubble structure. Other potential applications for FMF are areas where there are tailings shortages and as an alternative to hydraulic fill.

Influence of calcium hydroxide addition on arsenic leaching and solidification/stabilisation behaviour of metallurgical-slag-based green mining fill

In this study, metallurgical-slag-based binder (MSB) with different dosages of calcium hydroxide (CH) was mixed with high-arsenic-containing mine tailings (HAMT) to form green mining fill samples (GMFs) for As solidification/stabilisation (S/S). The As leaching characteristics of the GMFs were evaluated using pH-dependent leaching tests, semi-dynamic leaching tests and toxicity leaching tests. The effective diffusion coefficient (De) decreased from 6.98 × 10−14 to 5.90 × 10−15 cm2/s and the leachability index (LI) increased from 13.53 to 14.73 after 3 wt.% CH was added to the GMFs. The GMFs containing 0 wt.% CH (GMF-0C) and those containing 3 wt.% CH (GMF-3C) reached pH = 2 with acid addition amounts of 9.0 meq/g-dry and 9.3 meq/g-dry at 90 d curing time, and the maximum As leaching concentrations of GMF-0C and GMF-3C reached 10.47 mg/L and 7.47 mg/L, respectively, indicating that GMF-3C exhibited better acid neutralisation and As retention capacities than GMF-0C. Further, a Tescan Integrated Mineral Analyser (TIMA) was used to analyse the dominant hydration products of GMF-3C, which revealed that calcium silicate hydrate, CASH, ettringite and zeolite phases represented approximately 22.5 wt.% of the products. These results provide an understanding regarding the safe large-scale utilisation of GMFs.

Coupled chemo-hydro-mechanical effects in one-dimensional accretion of cemented mine fills

Mine waste-cement mixtures have been extensively used for filling underground mined-out cavities worldwide as a sustainable solution to tailings disposal and for ground control. The pressure that a mine fill imposes on its retaining structures would dictate the stability of a subsurface backfill system. The pressure is influenced by the coupled consolidation and chemical shrinkage processes of a cemented mine fill. Various benchmark results have become available for understanding and predicting such coupled processes during the deposition of cemented mine fills in an ideal one-dimensional (1D) condition. Nevertheless, there has been a paucity of studies where the coupled chemo-hydro-mechanical effects in their entirety are rationally considered. In this paper, the coupled chemo-hydro-mechanical behaviour of fluid-saturated cemented mine fills during 1D accretion is investigated with a new chemo-poroelasticity framework. The present approach is conceptualized by extending Biot's poroelasticity to accommodate the water volume changes induced by cement hydration. The analyses performed in the study have brought new practical insights into the chemo-poromechanical behaviour of accreting cemented mine fills. In particular, the study has shown quantitatively for the first time how the consolidation of a hydrating mine fill is dictated by the specific evolution of its properties, rate of deposition, as well as backfill mix design during sedimentation. The study suggests that a case-specific analysis with coupled numerical tools, rather than the simple application of benchmark results, is mandatory for rationally assessing the nonlinear consolidation process.

Loading rate effect on uniaxial compressive strength behavior and acoustic emission properties of cemented tailings backfill

To understand the quality and behavior of cemented tailings backfill (CTB) subjected to dynamic loads, the influence of change in the rate of loading should be accurately determined for an efficient mine fill design. In this study, the compressive strength behavior and acoustic emission (AE) characteristics of 180-day cured CTB samples are investigated by using four different loading rates: 50 N/s, 100 N/s, 150 N/s, and 200 N/s. Samples were prepared with the classified tailings and cementitious material of a gold mine as raw materials and subjected to the uniaxial compressive test using mechanical testing machine (GAW-2000) and AE equipment (PCI-2). Experimental results indicate that: (1) the loading rate has a strengthening effect on long-term strength behavior of CTB samples, and there is a power function between peak compressive strength of CTB samples and loading rate. The stress state of the backfill mass is “stepped” growth before the peak compressive strength, and the whole process displays a multi-cycle of “surge-steady-surge-steady”; (2) during the loading process, the ring count distribution has a regular peak-spacing effect, and the cumulative ring counts are also “stepped” and inclined to be stable. (3) With the increase of loading rate, the failure mode of CTB is a transition from tensile and shear mixing (mainly shear stress) to X-type shear failure. Ultimately, the essential findings of this experimental work will provide a scientific reference for studying the dynamic characteristics of CTB samples.

A model for one-dimensional deposition and consolidation of shrinking mine fills

The consolidation of a cemented mine fill is controlled by the rate of backfilling in regard to its permeability as well as the companion chemical shrinkage due to hydration reaction. A unified equation is derived in the study to delineate the one-dimensional (1D) deposition and consolidation of shrinking mine fills based on a generic description of the entangled chemo–hygro–mechanical processes. The proposed equation has taken into account the compressibility of each phase and the refinement of pore space due to phase exchange of water during hydration, which are lacking in other 1D formulations. The resulting equation would thus allow for more rational and convenient analyses of mine-fill consolidation during accretion and after deposition with a unified model. The improvement is practically at the mere expense of introducing only one additional parameter (the stiffness of solid grains) compared with existing benchmark equations. Parametric analyses performed with the proposed equation have revealed the limitations of the original Gibson and other 1D solutions in realistic assessment of mine-fill consolidation due to the lack of considerations for internal couplings. The proposed equation could also provide more reliable benchmark solutions for verification of complex numerical tools that incorporate coupled modelling of mine-fill behaviours.

Effect of bottom ash at different ratios on hydraulic transportation of fly ash during mine fill

This study examines the suitability of Durgapur Steel Thermal Power Station fly ash and bottom ash for mine fill material based on their physiochemical and rheological properties. The physiochemical properties of both fly ash and bottom ash are suitable for mine fill. Hydraulic transportation of fly ash for mine fill is a challenge for engineers due to its poor flow properties at higher solid concentration. Rheological properties of fly ash are shown that beyond 40% solid concentration hydraulic transportation may not be effective. Therefore an attempt has been made in this study by adding bottom ash to fly ash at various solid to liquid ratios to improve flow behaviour. Viscosity and rheological properties are studied for this purpose. The results show that the mixture of fly ash and bottom ash at 7:3, 6:4 and 5:5 at 50% solid concentration provides the best result by reducing the shear stress and viscosity. These combinations not only improve the rheological properties in terms of energy consumption, but also decrease the use of water for hydraulic transportation. Therefore, the present study shows that the addition of bottom ash can improve rheological properties of fly ash at higher solid concentration.

Stope depth effect on field behaviour and performance of cemented paste backfills

Cemented paste backfill (CPB) has been extensively used as a popular mine fill system for underground mining operations. Understanding the CPB’s in situ properties as an element of ground support is indeed really important for developing a well-organised mine design in terms of costs and security. In this paper, a comprehensive experimental work was conducted to better understand the effect of stope depth on in situ behaviour and performance of CPB having three different binding agents (ordinary Portland cement alone, slag-based cement and fly ash-based cement) over different curing times. A stope depth of 0 (it replicates the stope’s top), 5, 10, 15 and 20 m (it replicates the stope’s bottom) were virtually simulated by using an improved laboratory set-up, escorting with conventional plastic moulds. Results show that the highest compressive strength is obtained from CPB having slag-based cement. The strength of CPB increases with increasing stope depth mainly due to resulting improved geotechnical properties, such as reduced water content, degree of saturation and porosity as well as increased specific surface area retained at the bottom of a simulated stope. Geochemical testing shows that sulphate SO4−2 and calcium Ca contents increase with increasing curing time and reduce with increasing stope depth. As a critical point, a number of experimental relationships considered typically for different curing times, overburden pressure, arching stress and binder contents within CPB material were expressed and discussed.

Coal Combustion Product: Nonhazardous Material for Mine Fill

As is the case in many other countries around the world, India's main source of electricity is coal‐fired power plants. In addition to providing energy, the burning of coal also results in large amounts of coal combustion products (CCP), the incombustible material, such as fly ash, left after the coal is burned. These materials are produced in large volume, and if they are not managed or utilized properly, they can pose a danger to the environment. This article discusses the uses of CCP, with a special emphasis on fly ash, and the role that it is currently playing and can continue to play as a mine filler for India's depleted opencast and underground coal mines.

Vertical Stress Isobars for Silos and Square Backfilled Mine Stopes

AbstractOften granular materials are stored in vertical containers with circular or square cross sections. The storage material can be food grains, pharmaceutical powders, chemical pellets, or geomaterials such as mine fills. The design and analysis of these containers require adequate knowledge of the stresses developed within the filled material. The stress isobars developed herein enable the designers to estimate the vertical stress at any point within the fill contained in a silo. The same isobars can also be used for square cross sections, as in the case of backfilled underground mine stopes, without sacrificing the accuracy much. The same method was previously followed by the authors in developing isobars for plane-strain situations. On the basis of the two sets of isobars for trenches and square stopes, it is possible to interpolate the stresses for other rectangular mine stopes, which can serve as good first estimates in the designs.

Research of Geological Environment Remediation and Reconstruction of Coal Mining Area in Western of Shijiazhuang City, China

Improper exploitation of mine would lead to a series of geological disasters, such as surface subsidence, collapse, landslide, debris flow, water pollution, earthquake and etc., the results would endanger the safety of life and property, and caused serious economic losses to the state. As a case of Jiazhuang coal mining area of western of Shijiazhuang City based on the ecological problems, on the basis of PSR model, mine geological environment remediation basis, principles and objectives have been set. We puts forward a series of concrete measures of functional areas of governance for remediating of destruction problem of geological environment in western of Shijiazhuang coal mining area, taking comprehensive protection measures, soil formation, shelterbelt, slope shrub, wastewater, waste liquid emission in the mine production process must fit for standard of country. planting vegetation and the scarps leaved by mining reclamation or fill soil in the mine tailings, taking restoration of the original landform governance when constructed buildings and roads destroy the landform in field area.

Accelerated aqueous leaching of selenium and arsenic from coal associated rock samples with selenium speciation using ultrasound extraction

Ultrasound extraction was used to compare the accelerated release rates of selenium and arsenic from three rocks (BT700, BT 571 and BT 60) that are associated with mountaintop mining and valley fill coal mining practiced in southern parts of West Virginia, USA. The concentrations of arsenic released from rocks were found to be three orders of magnitude higher than that of selenium. The accelerated leaching rate constants were ten times higher for arsenic compared to selenium. Se (IV) was found to be stable under ultrasound extraction conditions used whereas As (III) was quickly oxidized to As (V). BT700 was found to have more Se (IV) compared to BT571 while BT60 did not have any significant Se (IV) concentrations. Such compositional and kinetic information becomes important when determining suitable mining waste treatment protocols that have to be undertaken to different types of overburden before it is dumped in valleys.

CERULEAN WARBLER (DENDROICA CERULEA) MICROHABITAT AND LANDSCAPE-LEVEL HABITAT CHARACTERISTICS IN SOUTHERN WEST VIRGINIA

Abstract The Cerulean Warbler (Dendroica cerulea) is a species of conservation concern in eastern North America, where declines in its population have been documented over the past several decades. A high proportion of the population occurs in forested areas of southern West Virginia, where it may be threatened by loss and degradation of forested habitat from mountaintop mining and valley fill (MTMVF). We examined, from a landscape perspective, the effects of forest fragmentation (in particular, effects of fragment size and response to edges) on Cerulean Warblers, using territory mapping techniques and geographic information system (GIS) technology in portions of four counties in southwestern West Virginia. We quantified landscape characteristics from digitized aerial photographs and measured microhabitat characteristics on spot-mapping plots. Territory density of Cerulean Warblers was 4.6 territories per 10 ha in intact forest and 0.7 territories per 10 ha in fragmented forest. The best habitat model inc...