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By K. Wu, X. Yuan, R. Du, C. Chao

"Lump coals are currently employed to replace part of coke in the COREX melter-gasifier for ironmaking. In order to optimize the process, the pyrolysis kinetics of Datong coal used in the COREX process was studied. A sectioning method is proposed to overcome certain shortcomings of traditional methods for studying the pyrolysis of coal. Based on the sectioning method and the characteristics of the coal pyrolysis process, the temperature range was divided into three intervals. In the first, the adsorbed gas and water of crystallization were removed; in the second, the coal was transformed into semi-coke; and finally, the semi-coke was further coked. Three models of reaction were then established to study the different stages of the pyrolysis process: an interfacial chemical reaction model, a random pore model, and internal diffusion with shrinking volume. The results showed that the experimental data fitted the models well, with all correlation coefficients (r2) exceeding 0.97. Finally, the mechanisms of reaction and kinetic parameters for each temperature range were derived, which laid a necessary foundation for optimizing the usage of non-coking coal in the COREX process. IntroductionIn view of environmental concerns and the shortage of good-quality coking coal, the COREX process was designed as a new ironmaking technology, attracting wide attention (Fang et al., 2005). In this process, lump coal and a small quantity of coke are directly charged into the melter-gasifier, where a high-quality reducing gas is generated for the reduction of the iron ore (Kumar et al., 2009). In contrast to the conventional blast furnace (BF) process, non-coking lump coal is used as the reducing agent and as the energy source, and the iron charge consists of lump ore and/or pellets, which results in the elimination of the coke oven and sintering plant as well as a decrease in investment (Kumar et al., 2009; Liu et al., 2012).Although the COREX process has made great progress, in current production practice the energy consumption greatly exceeds that of the BF, and it requires a certain amount of coke to maintain permeability of the semi-coke bed (Wang et al., 2008). In addition, the process consumes a lot of good-quality lump ore and lump coal. The pyrolysis of coal is the first step in most coal conversion processes, such as carbonization, gasification, and combustion (Aboyade et al., 2013). The reaction behaviour of lump coals in the COREX melter-gasifier is crucial, as it determines energy utilization and gas composition, as well as the metallurgical properties and particle size of the semi-coke produced (Prachethan et al., 2011; Zhang et al., 2014). In order to optimize the process and improve its competitiveness, the pyrolysis kinetics of Datong coal used in Baosteel’s COREX C-3000 facility was studied."

Jan 1, 2016

By M. Seerane, R. Machaka, P. Ndlangamandla

"Metal injection moulding (MIM) is a near-net-shaping powder metallurgy technique suitable for the cost-effective mass production of small and complex components. In this paper, the effects of the metal powder particle size on the final properties of 17-4 PH stainless steel are reported. Three different particle sizes (d50 33.0, 7.91 and 4.04 µm) were used to prepare the injectable MIM feedstocks using a CSIR-developed wax-based binder system at a fixed solids loading of 60 vol.%. The distribution slope parameter and the rheological flow index behaviour were used to predict the flowability of the feedstocks. The effects of the particle size on MIM products were established. The results are discussed in terms of the subsequent microstructural and mechanical properties of MIM 17-4 PH stainless steel against the established MPIF Standard 35. IntroductionMetal injection moulding (MIM) is a near-netshape manufacturing process established as an alternative to produce complex small-tomedium shaped components that were previously fabricated by conventional methods at higher costs (Attia and Alcock, 2011; Todd and Sidambe, 2013).Although recent advances in micromanufacturing (mainly machining and electrodeposition-based) have enabled the fabrication of complex micro-size geometries directly into miniaturized parts, these processes are generally neither routine nor easily accessible at present (Attia and Alcock, 2011).Typically, the MIM process consists of four steps: mixing, injection moulding, debinding and sintering. Mixing involves blending of the desired metal powder composition with carefully selected multicomponent organic binders at the right proportion. This mixture, which is called feedstock, is then injected into a mould of a required shape to form a ‘green part’. Debinding is the removal of the binders by chemical, thermal, or catalytic means while maintaining the shape of the part. Finally, the debound part is sintered to a full or near-full density part (Sotomayor, Varez and Levenfeld, 2010). The MIM process is essentially a combination of plastic injection moulding with conventional powder metallurgy technologies."

Jan 1, 2016

By R. W. O. Kersten

"The aim was to investigate stable pillar design procedures currently in use on chrome and platinum mines, subject them to a critical appraisal, and review some of the alternatives proposed in the literature. It is concluded that these pillar design methodologies suffer from drawbacks that can be detrimental to the mining industry and that an improvement is essential.It was decided that the increased availability of analytical models and failure criteria could be exploited to update the empirical to an analytical/empirical method. The proposed methodology adopted FLAC2D simulations using the Hoek-Brown failure criterion to calculate full stress-deformation curves for typical pillars. The mine stiffness concept was introduced to determine the pillar load, integrating the influence of the pillar and strata stiffness and mining geometry.The proposed methodology was calibrated by comparing experimental and predicted deformations and failure depth of pillars in one hard-rock mine. The conclusion was that the methodology is an improvement over the one currently in use. An improved factor of safety is given by the intersection point of curves for the stiffness of the system and the pillar strength. IntroductionThe paper describes part of the findings of a PhD thesis (Kersten, 2016) on an alternative stable pillar design methodology. This publication contains sufficient information to implement the method for further interpretation and testing. A detailed comparison of measured and predicted data is dealt with in the thesis, and the results show that there is promise in the methodology.The design of stable pillars in mining is of fundamental importance, not only in the Bushveld Complex mines but throughout the mining industry. Wherever mining occurs, pillars are formed at some stage and it is essential to predict their behaviour, i.e. whether they will burst, yield, or remain stable. Although of crucial importance, pillar design still suffers from major shortcomings and weaknesses."

May 1, 2019

By T. M. Louw, L. Auret, S. M. Bradshaw, F. F. Noelle

Modern industrial processes undergo frequent process state shifts due to changes in demand, feedstock or maintenance operations. Multimodal continuous process monitoring is therefore required for effective plant operation. Steady state analysis is a key component in effective multimodal monitoring. Various issues still remain in determining the starting and ending times of transition states. High dimensionality of process data is a characteristic that makes it difficult to select variables to consider when conducting steady state analysis. In order to address these problems, steady state detection on the principal component space is proposed. First, data undergoes principle component analysis to reduce dimensionality, then existing multivariate steady state detection algorithms are applied on the principle component scores. A novel algorithm, threshold PCA-SSD, is proposed and compared to an existing technique for steady state detection. The algorithms are investigated on high dimensional synthetic data Keywords: Multimode process, steady state detection, principle component analysis

Jan 1, 2020

By F. D. Agrensa, J. Hadjigeorgiou, E. Storimans, S. J. Thorpe

Reinforcement and surface support are part of an integrated system that transfers and shares loaduntil the excavation surface is stabilized or until the ground support system fails. Steel mesh is the most popular primary surface support element in underground hard rock mines in Canada. Mesh straps are a secondary surface support that provide additional containment as they distribute the load between and across the reinforcement elements. This investigation addresses the role of steel properties, and in particular steel chemistry, in the long-term performance of mesh and mesh straps when exposed to an aggressive corrosive environment. It reports on comparative accelerated corrosion studies to compare the resistance to corrosion of different surface support elements. This has significant implications on the choice of surface support and the anticipated rehabilitation requirements.

Oct 9, 2024

By I. Çinar

Cappadocia is not only a region of Turkey with historical and touristic importance. During the cutting and processing of volcanic tuff, quarries in this region release large amounts of tuff into the environment that is viewed as waste. The release of this waste constitutes an economic loss and contributes to environmental pollution. However, through experimentation with deformation, weight per unit of volume, water absorption, uniaxial compression strength, modulus of elasticity, and point load strength index, volcanic tuff and marble dust composite materials can be produced for use in the building sector. In this study it was observed that, as the percentage of volcanic tuff dust in the mixture increased, the water absorption rate of the material increased, and uniaxial compression strength and point load strength decreased. The produced composite samples used in this study were kept for a predetermined number of times per day, and no deformation in the surface characteristics of the materials was observed. In a statistical parameter analysis, averages, variances, standard deviations, coefficients of variation, and skewness coefficients were calculated. Covariance changes between experimental parameters were also determined. In this study, two types of volcanic tuff dust, that is, yellow and red, were produced during the production of tuff-marble dust composite material. When the percentage of either type of volcanic tuff dust was increased, an increase in water absorption was observed. It was also observed that when the percentage of volcanic tuff dust was increased, uniaxial compressive strength and point load strength decreased. Furthermore, the physical and mechanical properties of the materials obtained by mixing different colored tuff powders and marble powders in different proportions were evaluated using statistical parameter analysis.

Mar 5, 2025

By Jürgen Antrekowitsch, Harald Osthof, Stefan Steinlechner

"In the case of feasibility assessments or feasibility studies, an important point of discussion is often how to calculate the capital (CAPEX) and operating expenditure (OPEX) of a plant. Generally, there is also the request to know how the CAPEX varies when the size of the plant is increased. Nowadays, many databases give an indication of specific equipment costs in relation to the production rate. These data are based on cost information from equipment suppliers and have to be continuously updated by the owner of the database. The approach presented here is a model which allows sizing of process equipment, for example a leach tank, based on process data in combination with the calculation of mechanical properties. Furthermore, it calculates the CAPEX based on construction material cost and adequate machining surcharges. Thus, a single cost model for a leach tank is adequate for both copper and other hydrometallurgical plants and stays valid with changing construction material prices. To summarize, the advantage of this model is the more versatile approach and thus the flexibility due to the inclusion of design aspects, process and mechanical engineering aspects and an updatable database. The database, which is in regard to material cost and is the basis for the cost estimation, is easily updatable from commonly accessible data. This model thus approaches the procedures of an engineering company when designing a plant and executing a cost calculation. INTRODUCTION Hydrometallurgy nowadays plays an important role in processing of primary and secondary resources. In copper metallurgy, hydrometallurgy accounts for roughly 20 % of worldwide primary production, especially in the case of oxide or low copper-containing ores. Zinc smelters changed their method of production from a pyrometallurgical-dominated concept decades ago to mainly hydrometallurgical routes today. Gold production processes using leaching, especially, have a long history without any development which would not be competitive if not based on hydrometallurgical concepts (Pawlek, 1983; Winnacker-Küchler, 2006)."

Jan 1, 2015

By R. C. Nkhoma, K. A. Annan, S. Ngomane

The effects of welding current, electrode force, and welding time in a resistance spot weld were studied to investigate the effectiveness of welded joints between a thin EN10130: DC04 material and a thicker 817M40 part, through analysis of the microstructural and mechanical properties. All welded specimens were subjected to tensile testing at room temperature (25°C) and sub-zero temperature (–46°C) to test the strength of the welded joints. No full button failure was observed at either room temperature or sub-zero temperature after optimization of the weldng parameters. The fusion zone was observed to consist mainly of martensitic phase, due to rapid quenching, while the HAZ was composed of clusters of martensite in a ferrite and bainite matrix. The base 817M40 metal remained fully ferritic after welding. The hardness was found to increase with increasing welding current. An increase in nugget size, indicating good fusion of the weld, was observed with an increase in the welding current.

Oct 1, 2021

By B. M. V. Baloyi, D. Mchabe, D. Chetty

South Africa accounts for the largest global manganese ore production share, primarily from its Kalahari Manganese Field deposit. Despite this, domestic smelting is beset by energy constraints, resulting in most ore being exported for smelting. Mintek is investigating energyefficient pathways for ore reduction, specifically undertaking prereduction tests to reduce energy consumption for manganese smelting. The present contribution considers the effect of methane, anthracite, and holding time, at a fixed temperature, on the extent of reduction of Mamatwan-type ore, primarily from a mineralogical perspective. In particular, the aim was to carburise the monoxide Mn phase to Mn carbide, as this is less energy intensive than producing metallic Mn from the monoxide. Based on thermogravimetric test results, the ore and products from three experiment sets were analysed using X-ray diffraction and scanning electron microscopy to assess the phases and textures present. The findings show that carburisation of manganese monoxide and its equivalents is most advanced under conditions of 8% anthracite, 10% methane, and 60 minutes of holding time, thus confirming with the thermogravimetric data. These results show promise for reducing energy consumption for Mn smelting in ferromanganese production.

Mar 4, 2025

By N. Duda, P. Śliwiński, P. Stefaniak, B. Jachnik

Ventilation and air-conditioning are some of the most energy-consuming processes in deep underground mining. Additionally, the energy consumption of these processes systematically increases along with the expansion of the mine. Therefore, proper energy efficiency assessment and consumption forecasts of these systems are particularly important in modern mines for ongoing tracking and planning of the likely costs. In the article, a short-term prediction model for surface air–conditioning stations is described. This model takes into account dependencies that were identified, based on the data from the supervisory control and data acquisition (SCADA) systems. These dependencies between the response value and the external conditions are then incorporated into the model. This way, for example, the ambient temperature or the total number of specific days of the week (with sometimes significantly lower or higher than the weekly average energy consumption levels) are included. Taking into account these dependencies, and e.g. forecasted average monthly temperatures allow us to include the seasonality of energy consumption in the presented model. In the article, a sample energy efficiency analysis of the A/C system based on an example of the KGHM Polish Copper Polkowice-Sieroszowice mine is performed. The results of the solution proposed in the article are then evaluated, and compared to the currently functioning, more basic forecasting methods. However, given the general nature of the dependencies used in the model, similar solutions could be used in other case studies.

Sep 1, 2021

By V. V. Getman, V. A. Chanturiya, T. N. Matveeva

Most of the Au and PGM ores in Russia are characterised by a thin mineral impregnation of noble metals in sulfide minerals, and a large variety of mineral forms that lead to high loss of precious metals with fine fractions during flotation. In modern flotation technology, the rational choice of reagents is one of the main trends for selective separation of minerals and effective metals recovery. New data on the selectivity of the thermo-sensitive polymer with specific functional groups (TMPPh) as a flocculant and collector of Au and Pt fine fractions are available. The selective modified collector (DEDTCm) for the recovery of Au and Pt from complex ores is discussed in this paper. Scanning electronic microscopy (SEAM), laser SIM and AFM microscopy, UV and IR spectroscopy were applied to study the adsorbed layer of new reagents on the mineral surface. Flotation tests of TMPPh on the gold-bearing ore of the Olimpiada deposit showed an increase in Au extraction and Au content in the concentrate of the rougher flotation. Using a combination of reagents TMPPh and ButX, the quality of the Au and Pt concentrates increased in 1.7 time with an increase in recovery up to 15 % compared with the traditional reagent mode. Testing of TMPPh polymers in flotation of Pt-Cu-Ni ore at Norilsk Nickel has shown the ability to obtain a concentrate with a higher Pt content. Recovery of platinum is 17% higher than recovery in an experiment without polymer. Application of DEDTCm helped to achieve higher technological parameters in flotation of lowgrade Rt-Cu-Ni ore. Compared to the basic mode Pt recovery was plus 13%, Pd recovery was plus 9% and the content of precious metals in the rougher flotation concentrate increased in 2,5 - 4 times. The studies have been supported by Grants of the President of RF “Scientific School of Academician V.A. Chanturiya” NSh-220.2012.5, NSh-748.2014.5. Keywords: Au and Pt complex ores, flotation, flocculation, thermo-sensitive polymer TMPPh, modified collector

Jan 1, 2020

By D Olivier

De Beers' Finsch Mine is situated in the Northern Cape province, 170 km northwest of Kimberley. The concentrator facility, designed and constructed by Bateman Engineering, was commissioned in 1967 and upgraded in 1979 using diamond liberation and extraction technology available at the time of design. Since then significant advances in diamond processing and technology have been made and these -have been incorporated into the new main treatment plant and recovery plant flowsheets, making diamond liberation and recovery from the Pre-1979 dumps a viable economic option at Finsch."

Jan 1, 2010

By C. O’Donova, E. Adam, L. A. Torres-Cruz

High-profile failures of tailings dams illustrate the significant safety challenge they pose. The decant pond of such facilities plays an important role in their mechanical stability. This study investigates the feasibility of using public multispectral data collected by the Sentinel-2 satellite mission to monitor the area of the decant pond. The Sentinel-2 mission has a revisit time of 5 days and the data used herein has a spatial resolution of 10 m/pixel. We considered two water-detection metrics: the normalized difference water index (NDWI) and the near-infrared (NIR) reflectance. Implementation of the method at a South African platinum tailings dam illustrates the capabilities and limitations. Public, sub-metre resolution true-colour imagery served as validation data. There is good agreement between pond area measurements based on Sentinel-2 and the validation imagery. These results suggest the feasibility of using Sentinel-2 data to supplement the monitoring of the decant pond.

Apr 2, 2022

By I. O. Ondicho, E. K. Mutinda, B. O. Alunda, E. Agyekum

Driven by the necessity to improve blast performance regarding fragment size distribution in limestone mines, this paper introduces the prediction and measurement of blast fragmentation distribution through the modified Kuz-Ram (MKR) and Kuznetsov-Cunningham-Ouchterlony (KCO) models. Precise prediction and measurement of rock fragmentation resulting from blasting play a critical role in hard rock ore extraction. This is due to the substantial influence of post-blast ore size distribution on the efficiency of all subsequent downstream rock handling and processing operations. Additionally, employing secondary breakage of boulders, when necessary, leads to an unjustified rise in production costs. In this paper, the MKR and KCO models were utilised to identify the most appropriate model for application in Bisil and Simba quarries situated in Kajiado County, Kenya. Split-Desktop was used for blast fragment measurement by processing digital images obtained after blasting and computing the fragment size distribution of the blasted rock. As per the investigation, the recorded percentages of boulders generated at the sites ranged from 7% to 12.3% for the Simba quarry and from 11.2% to 23.9% for the Bisil quarry, respectively. Regression, correlation, and root mean square error (RMSE) were employed as the primary performance indicators. The study concluded that KCO outperformed MKR in accurately predicting blast fragment sizes in the examined quarries.

Mar 5, 2025

By L. Prosch

"The word 'sustainability' has gotten such a work out lately that the whole concept is in danger of floating away on a sea of inoffensiveness" Michael Pollon. It is estimated that approximately 65% of the roughly 130 million carats of diamonds mined globally per annum originate in Africa and has an annual value of US$ 8.4 billion', Many of these mines are located in remote areas of the continent where the directly affected project community's income is often well below the poverty line. Often associated with these communities are occurrences of localized over exploitation of natural resources, environmental destruction and the abundance of social ills.

Jan 1, 2010

By M. G. Maruma, L. A. Mampuru

"Mill liner wear is a major cost item in the mining industry and there is continuous research to prolong the life of the liners. Over the years it has become apparent that even though high-chromium white cast irons are highly efficient as abrasion-resistant materials, a combination of wear resistance and fracture strength remains difficult to achieve. Increasing the hardness of the high-chrome white cast iron (HCWCI), which improves the resistance to abrasion wear, is often accompanied by a deterioration in fracture strength. Operational conditions inside the mill require that the liner should be made of highly wear-resistant material with some fracture strength. Vanadium additions ranging from 0.2 to 3 wt% were made to HCWCI in an attempt to refine the microstructure. It was found that an increase in vanadium content promotes grain refinement. A content of 1.5-3 wt% gave the best results as measured by the maximum breaking strength.IntroductionOver the years it has become apparent that even though high-chromium white cast irons are highly efficient abrasion-resistant material, a combination of excellent wear resistance and fracture strength remains difficult to achieve. The exceptional wear resistance of highchromium white cast iron (HCWCI) is attributed to hard chromium carbides embedded in an austenitic/martensitic/pearlitic matrix. When the chromium contents exceed 12 wt%, interconnected MC3-type carbides of conventional cast irons are replaced by rodshaped and isolated M7C3 carbides (Powell, 1980), leading to an improvement in the impact toughness, ductility and fatigue resistance. However, the main M7C3 carbides in HCWCI are hard and brittle and can provide an easy path for crack propagation. This limits the applications of HCWCI, particularly in severe impact conditions. Most operations involving HCWCI are in crushing and grinding and the life of a part/liner is limited by its wear resistance. However, improving the wear resistance of HWCI comes at the cost of a significant reduction in fracture strength. Concerns about premature failure of HCWCI mill liners in the mining industries prompted a study to improve the wear resistance and mechanical properties of HCWCI."

Jan 1, 2016

By M. E. Rossi, C. Badenhorst

Conditional bias occurs when the expected value of the true grade conditional on the estimated grade is not equal to the estimated grade. It is a quantification of how the average of estimates differs from the true value. Conditional bias is present in all resource estimates due to the unavoidable properties of kriging, and indeed all linear estimation (regression) methods. In a mining resource estimation context, the degree of conditional bias is dependent on the spacing of the conditioning data; more data leads to the expectation of less conditional bias This paper discusses conditional bias from two perspectives: 1. 2. Estimates seeking to eliminate, as much as possible, conditional bias; and Estimates that accept a larger amount of conditional bias in resource models, in order to achieve a specific outcome. The problem of conditional bias in estimation can only be fully appreciated if the objective or purpose of a resource model is understood. There are instances where conditional bias should be avoided because it is not reasonable to make decisions using estimates that are known to be wrong in expected value; for example, when making a final decision in grade control with respect to the destination of the material. In most instances in the mining resource estimation context, however, the estimated values will not be “final estimates”, but “interim estimates”, meaning that in the future more data will be obtained, and the ”interim estimate” will then be updated. In this context, the most useful resource model is an interim model that is able to predict the final model estimates, despite not having all the data available that will be collected in the future. This is the objective, for example, of a recoverable “long-term” model developed prior to operating a mine, for example at the feasibility stage. It attempts to predict the ore that a processing plant will receive, well into the future. In such cases, it can be unequivocally demonstrated that conditional bias is not only unavoidable, it is a necessity.

Sep 1, 2021

By S. Liaghat, J. Rosenkranz, P. Semsari Parapari, S. Chehreh Chelgani, A. Tohry

It is commonly accepted that the energy consumption for comminution within mineral processing is responsible for around 3% of the global electrical energy usage. However, it was clearly noted that inside mills, less than 1% of this energy efficiency is actually consumed for particle size reduction. Therefore, monitoring of grinding parameters and modelling of product particle size distribution (e.g. characterised by the 80% passing size P80) play an essential role in operating costs of a mineral processing plant. Several empirical models have been introduced for the prediction of the P80. Since in the industrial scale usually a few numbers of grinding variables are monitored, these models cannot identically be used in plants. In addition, these empirical models do not always indicate the magnitude of correlations between milling variables. This study proposes to introduce the Hilbert-Schmidt independence criterion (HSIC) as an intelligent model for exploring linear and nonlinear relationships between grinding variables and P80 for an industrial scale data assessment. HSIC can rank variables based on their importance and help to select the most effective one for the generation of predictive models. HSIC modelling through various monitored grinding variables (ball charge, feed input rate, F80, power draw and work index) of an industrial plant indicated that F80 as a feed property has the highest effect on P80 of the ball mill products. Modelling results highlighted that the P80 can be accurately predicted, based on effective variables by using a HSIC model. These outcomes showed that HSIC as a powerful modelling tool can assess the relationships between monitored grinding parameters, select the most effective grinding parameters and satisfactorily predict the P80. Keywords: Product particle size, variable importance measurement, Hilbert-Schmidt independence criterion, mill charge

Jan 1, 2020

By M. A. El-Sayed

"Double oxide films (bifilms) are significant defects in light alloy castings that occur when, during melt handling, the oxidized surface of the melt is folded over onto itself and then entrained into the liquid metal, encapsulating a portion of the local atmosphere. These defects create crevices in the final castings and have been shown to decrease tensile and fatigue properties, and also to increase their scatter, making casting properties unreproducible and unreliable. This paper reports on two different experiments performed to study the behaviour of such defects in Al alloys. In the first experiment and as a proxy for a bifilm, air bubbles were held in an Al-5Mg alloy melt for varying periods of time before the melt was allowed to solidify. The composition of the gas content of the bubbles was subsequently analysed using mass spectrometry to ascertain how it changed with time. In the other experiment the influence of the age of bifilms on the mechanical properties of Al-5Mg castings was assessed by holding castings in the liquid state for different times before solidification, followed by mechanical property testing and SEM and EDX studies of the fracture surfaces of tensile test bars. This research could provide a better understanding of the behaviour of double oxide film defects, and may lead to the development of new techniques by which these defects could be eliminated, or at least deactivated, in light alloy castings. Introduction One of the major structural defects affecting the reproducibility of mechanical properties of aluminium castings is the double oxide film defect (El-Sayed and Essa, 2017; El-Sayed and Ghazy, 2017). This type of defect is usually created as a result of poor filling system design. Owing to the very high reactivity of liquid Al-Mg alloy with oxygen in the air, the surface of the liquid metal can be considered to be permanently coated with an oxide film (Weigel and Fromm, 1990). As a consequence of surface turbulence, the oxidized metal surface can become folded over onto itself, but not fused, and then submerged into the bulk liquid, with a portion of the mould atmosphere being entrapped within it (Campbell, 2003; Al- Sayed, 2016; El-Sayed, Hassanin, and Essa, 2016)."

Nov 1, 2018

By J. Bal, V. D. Dao, W. Li

"SynopsisThis study proposes a methodology for evaluating the risk of coal bumps in multiple-seam longwall mining. Both the stress field and the total energy release (TER) during retreat were evaluated in the specified case involving multiple-seam mining using the LaModel program. The results of numerical simulations indicated that both the peak vertical stresses on the panel edges and the peak TERs in the outby longwalls increased significantly as the horizontal offsets were reduced from 60 m to zero. With the comprehensive consideration of the stress field and TERs, a conservative offset of 60 m was ultimately adopted when developing the gateroads of the lower panel in the field. The field measurements indicated that coal bumps were avoided completely by employing the proposed design, and the maximum roof-to-floor and rib-to-rib convergences of the tailgate during retreat were only 360 mm and 576 mm, respectively.IntroductionCoal bumps – sudden, violent bursts of coal – pose a serious threat to the safe excavation of coal. Their occurrence depends on the properties of the surrounding rocks, stress field, and dynamic disturbance. The complexity of the mechanism of coal bumps is further enhanced in multiple-seam mining due to seam interaction. Multiple-seam mining is most frequently found in the coalfields in eastern China, such as Xuzhou, Xinwen, Zaozhuang, and Huainan. In the past, due to issues of availability, economics, and ignorance of the potential risk in multipleseam mining, coal seams in such conditions were mined without proper planning to account for seam interaction. Fortunately, studies published over the past three decades have raised awareness of the problems associated with multiple-seam mining, and indicated that the ground control issues induced by multiple-seam mining can be avoided and/or minimized with proper planning.A number of technical studies pertaining to the design of multiple-seam mines have been published. These studies can be divided into two groups based on their methodologies of design: empirical (Chekan and Listak, 1993; Haycocks and Zhou, 1990, Matetic et al.; 1987a, 1987b) and numerical approaches (Li et al., 2000; Maleki, 2007; Mark, 2007; Peng, 2007; Zipf, 2005). The majority of the extant studies on the interaction mechanisms in multiple-seam mining have focused on the load transfer during operation, resulting in the proposal of the pressure bulb theory (Forrest et al., 1987; Haycocks and Karmis, 1983; Peng, 2008; Peng and Chandra, 1980) and pressure arch theory (Holland, 1973; Oram and Ponder, 1997) to guide multiple-seam mine design. However, neither, of these theories can be used to evaluate the potential for coal bumps."

Jan 1, 2015