Search Documents

By Matej Petružálek, Tomáš Svitek, Tomáš Lokajícek

"Migmatite from the Skalka region (Czech Republic) was chosen as the experimental rock material. It has macroscopically visible plane parallel structure (foliation). The foliation was caused mainly by biotite grains arrangement. The cylindrical samples of migmatite with subhorizontal, subvertical and oblique foliation were uniaxially loaded up to the failure. Network of 8 broad band sensors was employed for acoustic emission monitoring and ultrasonic sounding. A grid search method with anisotropic velocity model was used for AE hypocenters localization. The source types of successfully localized events were determined from the average first arrival amplitude. Structural anisotropy of tested rock material caused the anisotropy of its mechanical properties (peak strength, Young’s modulus) as well as a different way of fracturing process in dependence on the angle between axial stress and foliation plane. The combination of splitting, shearing and sliding was found to control the fracturing of sample with subhorizontal foliation. The shearing and sliding was dominant in fracturing of samples with oblique foliation. With greater dip of foliation, the role of sliding increased at the expense of shearing. Due to the favorably oriented system of microcracks already present, the shearing and splitting was at the same level during fracturing of the sample with subvertical foliation before nucleation began.INTRODUCTIONThe process of failure of low porosity rocks depends on their mechanical properties and actual stress and temperature condition. At the low pressure and low temperature, the most common way is brittle failure, which is a progressive process requiring the initiation, growth and coalescence of cracks (Lockner, 1993). Stress strain behavior of low porosity crystalline rocks, during the laboratory compression experiments, is divided into four characteristic stages: crack closure, elastic region, stable crack growth and unstable crack growth which leads to the brittle failure, Brace et al. (1966) , Bieniawski (1967), Lajtai (1974), Cai et al. (2004), Nicksiar and Martin, 2012 and 2013.The fracturing process of stressed rock begins with the crack initiation (sci), which for low porosity rocks occurs approximately at 40-50% of peak strength (sp) (Cai et al., 2004; Nicksiar and Martin, 2013). After the sci, the dilatancy begins and stable crack growth follows up to the crack damage threshold (scd), which is approximately at 80% of sp (Cai et al., 2004). After crossing the crack damage level, there is an unstable crack growth accompanied with nucleation of fault plane (sn) at 97-100% of sp. (Rao et al., 2011). The stress drop accompanied with formation of macro scale shear failure plane follows after peak stress is crossed."

Jan 1, 2015

By E. Heikkinen, J. Suikkanen, T. Siren, J. Valli, M. Hakala

Diametrically faced borehole breakout observations are a fairly good indication of magnitude of the secondary stresses acting perpendicular to the borehole. In cases of low in situ stresses, where borehole breakouts are not observed naturally, it is possible to increase the prevailing stress state around the borehole by increasing the rock temperature. When the temperature is increased sufficiently, thermally induced borehole breakouts will occur. By implementing the temperature increase in boreholes located at excavated tunnels, it is also possible to study the effect of the near-field stresses caused by the excavation. The near-field stress state changes as a function of borehole depth, thus increasing the information available from experiment. To study the feasibility of this proposed low cost method, a Borehole Thermal Spalling (BTS) experiment was executed in ONKALO Underground Rock Characterization Facility, in Western Finland in 2014. The first borehole pilot test with the method was conducted in ONKALO at the POSE niche in already at May 2010, with the second pilot test following in August 2010 at Äspö HRL. The major objective of the experiments was to define the trend of the maximum in situ stress component, while also providing knowledge of the in situ spalling strength of the ONKALO rock mass. The stress state in ONKALO is nearly isotropic in horizontal layer, causing problems for the use of more traditional stress measurement methods. With boreholes heated over long interval, the weakest rock parts are observed to fail, thus providing statistical confidence. For these reasons, continuous test sections have an advantage in ONKALO, compared to spatially limited stress measurement methods such as overcoring and hydraulic fracturing. The BTS experiment is conducted in 9 meter deep vertical boreholes located at the POSE niche, situated -345 m depth below the ground surface. The boreholes used within the BTS experiment are located in migmatitic granite, in an experiment area where the surrounding stress state and the rock strength are fairly well known. The prior knowledge of the stresses is favourable for the experiment, as it requires careful planning and iterations to determine the appropriate heating power domain. Too low heating power will not be sufficient to cause borehole breakout, while too high heating power causes breakout in all directions thus making determination of stress direction hard or impossible. The initial state of the borehole and induced borehole breakouts will be monitored using acoustic televiewer logging (ABI) and optical borehole logging (OBI) imaging techniques. Fracture mechanics modelling is used in planning of the experiment, also in back-analysis to link the observed breakout angle to stress state. Both the pilot test in 2010 and BTS test in 2014 resulted in similar borehole breakout direction. The results are in line with so called EDZ & VT1 stress interpretation, revealed the maximum horizontal component bearing the magnitude of 21.5 MPa, with the trend of 166°.

Jan 1, 2015

By Parissa Mirjafari, Ron Martel, Susan A. Baldwin, Luke Moger

Mine drainage contains metals and sulfate, which may be toxic to aquatic life at certain concentrations and should be removed to acceptable levels before release of any drainage to the environment. One method for treating mine drainage is passive treatment, which is increasing in popularity due to lower construction and operating costs. This method is based on the activity of sulfate reducing bacteria (SRB) respiring on sulfate while using fermentation products from decomposing complex organic materials. The product of this biological process is hydrogen sulfide, which reacts with metals in mine drainage and precipitates them as metal sulfides. However, in practice passive treatment systems are not always effective, reducing the reliability of this approach. In this study, a mixture of hay, cow manure and wood chips was tested in continuous flow experiments for efficacy at sustainable treatment of sulfate and selenium containing water from a mine tailings pond. Factors that contributed to a decline in performance included lowering of the pH due to acids leaching out of the organics, re-oxidation of sulfide back to sulfate and a reduction in dissolved organic compounds over time. In this paper methods are described to overcome these problems so that treatment is made more reliable.

Jan 1, 2011

By J. W. Choung, T. Fu, Z. A. Zhou

An on-line visualization technique and methodology was developed to investigate the role of fine sphalerite (< 10 um) aggregation in flotation. The images of particle aggregates under different operating conditions were recorded and analyzed. The effect of impeller design on particle aggregation was demonstrated. This difference was not mainly due to the energy input into the system, but due to the resultant hydrodynamic conditions created by the impeller and their effect on particle interactions. The recorded image showed that adding fine silica (- 5 um) did not interfere with fine sphalerite aggregation, thereby showing no effect on the sphalerite recovery. Effect of the enlarged aggregate size on increasing flotation recovery was confirmed. Although Malvern Mastersizer produced consistently lower estimates of aggregate size than those by the image analysis, both methods responded to the changes in operating conditions in the similar trend. It was shown from this study that on-line visualization technique is a powerful tool for studying fine particle aggregation and morphology in the context of diagnosis for the flotation separation.

Jan 1, 2004

By I. Demers

The abandoned Manitou mine site covers an area of approximately 190 ha near Val d?Or, Quebec. This old site has been generating acid mine drainage for several decades. In 2006, a partnership was established between the Quebec Ministry of Ressources Naturelles (MRN) and Agnico-Eagle Mines to reclaim the Manitou site using tailings from the nearby Goldex mine. These neutral tailings were to be deposited on top of the Manitou site. An extensive study was performed to evaluate specific reclamation scenarios to control acid mine drainage using Goldex tailings as cover material. The article first describes the global approach used for this evaluation, which includes in-situ hydrogeological monitoring, tailings characterization, laboratory column tests, and numerical modelling. Of the thirteen column tests, three were conducted to evaluate the parameters affecting the performance of covers made of Goldex tailings placed over the spillage area of the Manitou site. Geochemical and hydrogeological parameters were assessed during the leaching column tests for almost two years. The tests aimed at evaluating the effect of water table level and monolayer cover thickness on the overall performance. The testing procedure involved monthly leaching and measurement of geochemical parameters. Results indicate that water table position is the most important factor affecting the monolayer cover performance to control AMD. Based on these results, it was established that the water table must be located near the interface between the Goldex and Manitou tailings to effectively reduce AMD generation. Cover thickness also has an impact on cover performance, which is however less significant than the water table position. The testing scenario with a water table located at the interface with a one-meter Goldex tailings cover showed progressive improvement in effluent quality.

Aug 1, 2013

By P. D. Hanson, H. Colijin

"New procedures and techniques are now available for the design of bulk storage bins. These new methods have essentially eliminated guesswork in the gravity flow of bulk solids, and have provided a sound basis for the quantitative analysis of alternate designs of hoppers and bins. This paper will discuss the practical application of the Solids Flow Theory (Jenike & Johanson) and illustrate the required design procedure with a few examples of actual bin operations."

Jan 1, 1970

By M. Nejati, A. Paluszny, R. W. Zimmerman

A numerical method is proposed to propagate multiple discrete fractures leading to primary fragmentation in a mine that is being worked using block caving. Deformation is computed using the finite element method, fractures are represented explicitly, and the mine domain is discretized by an unstructured mesh. Bedding planes are represented by systematically varying the elastic modulus of the rock and by defining horizontal weakness planes. Fractures and matrix are represented using parametric surfaces, and tips are defined by their boundary curves. Tip advance is controlled by a failure criterion, and a criterion for propagation direction and magnitude, based on the evaluation of the modal stress intensity factors. A novel domain integral approach is applied to accurately compute stress intensity factors (K) ahead of fracture tips in three dimensions. The method does not require a structured volumetric mesh structure around the crack tip, as integration is performed over a series of virtual surface domains along the crack front. The method is efficient, as it makes direct use of automatically generated, arbitrary tetrahedral meshes, and approximates stress intensity factors (KI, KII, KIII) along each crack front using Interaction-integrals. As opposed to the JIntegral, the method does not decompose K a-posteriori, but instead uses an auxiliary field to directly compute modal K. When using this method, numerical approximations of K do not exhibit dependence on the mesh layout, and require meshes that can generally be ten times coarser than are required by displacement- and stress-based methods. Volumetric meshing requires only, on average, 17% of each computation step. Thus, cracks do not follow any pre-existing mesh structure, and the method is well suited for high-density fracture datasets. The method is demonstrated for primary fragmentation of a mine area covering 110 initial draw points, immediately beneath a 2m high undercut. Displacement is constrained at all boundaries except the surface of the undercut. The growth of the fractures is investigated at the onset of the undercut. Ninety initial disc-shaped fractures are taken into account, each having an initial radius of 10 m. Fractures grow around the undercut, intersect the bedding plane boundaries, and the domain is fragmented as a result.

Jan 1, 2015

By M. S. Diederichs, G. Walton

"Developments in understanding the brittle fracture of rock over the past two decades ultimately led to the acceptance of a cohesion-weakening-friction-strengthening model as an appropriate strategy for the modelling of spalling using a continuum approach. This strength model has been used to replicate observed failure depths and geometries for a number of case studies in the literature, most notably the AECL Underground Research Laboratory in Manitoba. One thing which these case studies typically ignore, however, is the influence of rock dilatancy on the evolution of brittle failure. Physically, this phenomenon is the volumetric expansion of the rock due to fracture opening; numerically, this phenomenon is captured by the flow rule, which is often characterized by the dilation angle, ?. Accurately modelling rock dilatancy in conjunction with strength evolution is necessary both to predict the magnitude and distribution of ground displacements, as well as the exact depth and shape of the fracturing zone. Both of these factors can have significant implications for support design. This paper is focussed on presenting some of the recent developments in this field in the context of a number of numerical modelling case studies. Initially, a new model for the dilatancy of brittle rock is presented, as well as some representative data and model parameters for different rock types. Next, several case studies of highly stressed tunnels and shafts are presented. The results of continuum numerical models are presented to demonstrate the ability of the back analyses to match observed in-situ measurements and obtained. The predictive capabilities of the material model are also highlighted for cases where sufficient “a priori” information (such as laboratory compression testing data) are available. The issues of model nonuniqueness and strain-localization/bifurcation are also addressed."

Jan 1, 2015

By J. I. Gazzarri

A model of solid oxide fuel cell AC impedance behaviour has been developed and is used to simulate the frequency response of a single cell with and without mechanical damage. The results indicate that the presence of mechanically induced damage within the components of a solid oxide fuel cell can be detected by comparing the frequency response of the undamaged cell with that of a cell in which in-plane cracking or delamination has occurred. The presence of such defects manifests itself as a new semicircle in the Nyquist impedance diagram of the full cell. A parametric study reveals the resolution capabilities of the method in terms of the geometrical characteristics of the defects.

Jan 1, 2005

By T. Wajima

"A novel carbonaceous adsorbent for recovery of nickel from nickel plating waste solution was prepared from rice straw using sulfur impregnation. The rice straws were cut to 1 cm pieces, and then immersed in 0.01 - 3 M K2S solution to prepare sulfur-immersed materials. The immersed-materials were heated at 100-700 ºC in nitrogen gas to produce the sulfur-impregnated carbonaceous adsorbent by pyrolysis. The contents of carbon and sulfur in the adsorbent and abilities of adsorbent to recovery nickel from aqueous solution were examined. The contents of carbon and sulfur in sulfur-immersed materials are almost same as those in raw material. In pyrolysis, with increasing the heating temperature to 200 ºC, the contents of carbon and sulfur are almost constant, and then above 300 ºC those increase. The recovery for nickel using raw material, sulfur-immersed material and the product pyrolyzed at 100 - 200 ºC are almost same, and with increasing the heating temperature to 400 ºC, that of the product increases, and above 500 ºC that of the product decreases. In immerse step, with increasing K2S concentration, the carbon content of the product at 400 ºC gradually decreases, the sulfur content of the product increases, and the recovery for nickel using the product gradually increases and then above 1 M K2S decrease. The product prepared from material immersed in 1 M K2S solution at 400 ºC indicates a maximum recovery for nickel ion. The product can adsorb nickel ion in nickel plating waste solution coexisting with phosphate ion, and adsorbed nickel ion in the product was deposited as nickel metal after heating at 1000 ºC under N2 atmosphere.INTRODUCTIONRice is the second world’s largest cereal crop after wheat, but produces large amount of straw residues, of about 330 million metric tonnes. Rice is a widely grown crop in Asia, and rice straw is produced as a by-product of rice production. In most parts of rice fields, open-field burning of rice straw is commonly practiced in the region when there is limited time to prepare a field for the next crop. However, open-field burning of crop residues is an uncontrolled combustion process during which air pollutants are emitted into atmosphere. These air pollutants have significant toxicological properties and are potential carcinogens (Gadede et al., 2009). Although wildfires are prohibited in cultivation fields of most countries, farmers usually keep on burning their crop by-products. Biomass burning is an important source of aerosol particles which may affect local and regional air quality (Gao et al., 2011), and also contribute to global climate changes."

Jan 1, 2016

By I Wilkomirsky

The neutralization of S02 from copper smelter gases to produce calcium sulphate (anhydrite) is considered an attractive alternative to sulphuric acid production. To develop the required technology for the process, a three-stages fluidized bed reactor prototype was designed and operated using both high and low grade limestone and gases with 2, 8 and 12 vol -% S02. The results obtained shows that at 800°C and up to 8 vol-% S02 in the gases, the capture of S02 reaches near 99% with limestone conversion to anhydrite of 45 to 48%. A larger pilot plant is presently being built at the Codelco El Teniente-Caletones Smelter to demostrate the technology and to evaluate the economics of the process. Cu2007

Jan 1, 2007

By M. Mbonimpa

Field experimental cells were constructed in 2007 to assess the performance of different cover scenarios for the reclamation of the Parc 1 tailings disposal facility at the Westwood-Doyon Mine site (Abitibi, Quebec). Three configurations of cover with capillary barrier effects (CCBEs) with different thicknesses and material types for the moisture retention layer (MRL) were studied. MRL with 80 cm till, 40 cm till, and 40 cm clayey silt were used for cell nos. 2, 3, and 5, respectively. The capillary barrier layer (CBL) and drainage and protection layer (DPL) of the CCBE consisted of 30 cm gravel. A reference cell without cover was also constructed to compare the geochemical performance of the CCBEs. Due to an unexpected flooding in the leachate exit area of the cells in spring 2008, the cell instrumentation for hydrogeotechnical monitoring was postponed to spring 2009. Changes with time in volumetric water content, suction, soil oxygen concentration, and temperature were measured at different depths. This paper presents and discusses preliminary results obtained from spring 2009 to autumn 2010. In all cases, the degree of saturation Sr is lower in the CBL than in the MRL, indicating the presence of capillary barrier effects at the interface of these layers. Cell nos. 2 and 5 showed hydrogeotechnical behavior typical of an effective CCBE, with Sr maintained above 85% in the MRL and lower than 30?50% in the DPL and CBL. Based on the obtained results, and as expected, MRL thickness and the type of construction material used appear to affect the hydrogeotechnical behavior of the CCBE. Oxygen concentration profiles through the CCBEs were used to estimate the oxygen flux, and results indicate that cell nos. 2 and 3 performed better than cell no. 3. CCBE performance is currently being investigated using the geochemical monitoring data.

Aug 1, 2013

By Mengsu Hu, Yuan Wang, Jonny Rutqvist

Material interfaces and typical boundary conditions are boundaries influencing the existence, uniqueness and stability of numerical solutions of water flow in heterogeneous media. The Numerical Manifold Method (NMM) with a two-cover-meshing system is an ideal method to handle boundaries, considering its flexibility with no need to adjust mathematical nodes onto boundaries, the meshing efficiency, and its integration precision. In this study, we derive and compare two new approaches for boundary constraints, i.e., a discontinuous approach with Lagrange multiplier and a continuous approach with jump function in the frame of NMM. In the discontinuous Lagrange multiplier method (LMM), Dirichlet boundaries or the material interfaces are regarded as discontinuities which are linked by Lagrange multipliers. In the continuous Jump function method (JFM), the material interfaces are regarded as inner interfaces, where the refraction law is realized by constructing jump terms with discontinuity of hydraulic gradient in its normal direction. Both the continuous and discontinuous approaches make full use of the aforementioned advantages of NMM and are established based on a clear physical meaning of water flow by our energy-work seepage model. The newly derived boundary-constraint approaches were coded into an NMM water flow model and tested for precision and efficiency on different simulation examples. We first tested both LMM and JFM for an idealized heterogeneous model, comparing the numerical results with analytical solutions. Then we tested both approaches with a heterogeneous model and compared the results of hydraulic head and specific discharge. We proved that both approaches are very suitable for material boundaries considering the accurate realization of the boundary constraints and the flexibility with no need for mesh-conforming.

Jan 1, 2015

By Michael Samis

Conventional project valuation techniques, such as discounted cash flow (DCF) method, are more frequently being criticised for the manner in which they consider the interacting effects of uncertainty and project structure (including management flexibility) on project value. Modern asset pricing (MAP; often called ?real options valuation? when applied to the analysis of flexibility) is a more general valuation framework that corrects many of the shortcomings of common valuation methods. Previous mining applications of MAP have tended to treat the ore deposit as a homogenous entity. While useful for demonstration purposes, this is inadequate for practical application in industry. This paper presents a MAP valuation example that allows for the heterogeneous nature of an ore deposit. It shows that deposit structure may increase the complexity of the mine planner?s decision so that results of a standard DCF analysis, or a simple MAP analysis that ignores the details of deposit structure, are misleading. In the example, a management is considering the development of an adjacent low-grade zone while mining operations in a high-grade zone are ongoing. If the low-grade zone is developed before high-grade reserves are exhausted, the proposed development will include both low-grade zone development and a capacity expansion to handle additional low-grade reserve production. If development of these reserves is delayed until the high-grade reserves are depleted, then the low-grade reserves can be developed without a capacity expansion. A typical DCF analysis would reduce the management?s decision problem to three alternatives: 1) continue mining only in the highgrade reserves, 2) immediately develop the low-grade reserves and expand capacity, and 3) delay low-grade zone development until the high-grade reserves are exhausted. The model presented here allows the management to reconsider the development and capacity expansion decision on a discrete half-year basis. It delineates price regions, for given levels of high-grade zone reserves, in which it is optimal to develop the low-grade zone, defer low-grade zone development and abandon the mine irrevocably. The model presented here extends the ability of mine planners to describe actual project structure while using the MAP valuation framework that is already noted for its capacity to combine project uncertainty and risk insights with a dynamic project description.

May 1, 2001

By Mario E. Rossi

Geostatistical conditional simulations are becoming increasingly popular as tools that provide models of uncertainty at different stages of a mining project. They have been used as grade control tools in daily operations, to assess the uncertainty of minable reserves at the project?s feasibility stage, and to assess mineralization potential in certain settings. Other applications include assessment of recoverable reserves, resource and reserve classification, and drill hole spacing optimization studies. All large-scale applications of conditional simulations intend to benefit from the ?correct? (or ?accurate?) characterization of uncertainty, adequately describing the variability observed from the data and its impact on the final objective. The objective of this paper is to compare the ad-hoc ?uncertainty model? provided by a traditional classification scheme with the probability intervals resulting from a conditional simulation model. It is argued that the uncertainty model derived from the use of classification schemes is of little practical use to the mining company or operation. The paper emphasizes differences in uncertainty based on the size of the mining unit considered and the extraction method, and local geological differences. Most importantly, it discusses confidence intervals for these mining units, as compared to the relative precision envisioned by a typical classification scheme. The application described in this paper is taken from a medium-sized Cu open and underground mine in northern Chile, and it demonstrates the impact of several variables on the resulting conditional simulation models. It also compares a more ?traditional? resource classification scheme applied, and the wide difference in local confidence intervals for each mining unit.

May 1, 2001

By C. P. Jenney

"Exploration for copper, in a region of 7,000 square miles on the Arctic coast between longitudes 114 and 118 degrees west, has covered a period of nearly 200 years. Occurrences of native copper, used by the natives for tools and weapons, have been reported since the early part of the eighteenth century. In J 771 Samuel Hearne of the Hudson's Bay Company, in the course of his classic 3-year journey from Fort Churchill, became the first white man to see the deposits, and incidentally the first to reach the Canadian Arctic coast by land. During the next 140 years the deposits were mentioned by every explorer and traveller who passed through the area. A good historical summary of this literature has been presented by Tyrrell (1912).In 1911-12 the Douglas-Sandberg party did the first geological mapping along the Coppermine River and Dismal Lakes (Douglas, J., 1913; Douglas, G. M., 1914), and described the copper occurrences there. In 1914 J. J. O'Neill (1924) of the Canadian Arctic Expedition investigated the showings on Bathurst Inlet. In 1929-31 two Canadian exploration companies sent prospectors and geologists to the area (Gilbert, 1931; Norrie, 1931; Duncan, 1931). Since that time only brief references have been published (Kidd, 1931; Stockwell and Kidd, 1931; Lord, 1941, 1951; Washburn, 1947). In 1943-45 an area of more than 1,500 square miles was prospected by American Metal Co. of Canada, Ltd., under the direction of the writer. Forty-nine showings were examined; seven of these were mapped in detail by plane-table and two were sampled by 27 short diamond drill holes totalling 3,061 feet. All holes were in permanently frozen rock, and the deepest vertical distance reached was 206 feet. Five groups of claims were staked. These later lapsed, but one of the groups was restaked in 1951, and assessment drilling and some trenching were carried out in 1952-53. Results were disappointing, and the claims have been allowed to lapse.The area is within the Arctic Circle, northeast of Great Bear Lake and 360 miles north of Yellowknife on Great Slave Lake. For exploration purposes, access is by aircraft from Yellowknife. During the short open season heavy freight can be brought by sea to Coppermine at the mouth of the river, either from Aklavik at the mouth of the Mackenzie or around Alaska. Concentrates would have to be moved by these routes.Although none of the deposits so far found is mineable under present conditions, the total volume of copper in the numerous showings marks the district as a major area of copper mineralization, which may some day be of economic importance."

Jan 1, 1949

By Rick J. Chalaturnyk

In Alberta, oil sands bitumen is utilized for synthetic crude oil production by surface mining, bitumen extraction followed by primary (coking) and secondary (catalytic hydrotreating) upgrading processes, or by catalytic hydrocracking and hydrotreating replacing the primary and secondary upgrading processes. Oil sands tailings, composed of water, sands, silt, clay and residual bitumen, is produced as a byproduct of the bitumen extraction process. Several processes have been proposed for the treatment of oil sands tailings, resulting in different recovered water characteristics, consolidation rates and consolidated solid characteristics, which may have effects on the performance of the overall plant operations. A process for the same purpose has been developed by treating the oil sands tailings with CaO lime and CO2 and thickening it using a suitable thickener. In this process a release water of acceptable properties is recovered in a short retention time, which makes it possible to recycle the recovered water, probably after a reconditioning treatment, as warm as possible to improve the thermal efficiency of the extraction process. The paper presents the theory and laboratory results for the CaO and CO2 thickening of low temperature flotation tailings. The water release rates, segregation potential of the thickened underflow and chemistry of the release water are shown and discussed. It is suggested that in using the proposed process, the thickened tailings underflow can be disposed for further consolidation, or combined with the coarse tailings to produce Blended Composite Tailings, corresponding to the Composite Tailings process in the existing hot water extraction plants.

May 1, 2002

By W. Dziurzynski, St. Wasilewski, T. Palka, A. Krach

"Air parameter monitoring systems, regardless of gasometrical protections, provide a significant number of measurement data. The obtained data broadens the knowledge on processes taking place in underground workings and shows the relationships and influence of machines and technological processes on the variability of ventilation parameters in the areas of longwalls. Nowadays, computer simulation methods are increasingly used to reproduce the flow of air and methane mixture in the area of longwalls equipped with shearers. The paper presents the results of a research experiment covering a long-term observation of a longwall area during mining with a shearer using sensors from the mine's monitoring system. Data from sensors for methane concentration, pressure and velocity were used and additional ventilation measurements were taken to determine the parameters characterising the air flow in the area. The influence of different machine cycles in the longwall on the changes of air parameters in the area of the longwall was shown. A numerical model of the ventilation area was developed and the computer program VentZroby was used for the calculations, which allows for the simulation of the process of ventilating the area of the active longwall during the extraction of coal with the use of a shearer and haulage of the run-of-mine. Computer simulation of the influence of the shearer's operation and the methane inflow associated with the distribution of the mixture of air and methane was carried out. The results of the simulation were compared with the data recorded by the monitoring system’s sensors during the measurement experiment. Comparison of the recorded methane concentration courses with the results of a computer simulation of the air and methane flow conditions in the mining area showed changes in the gassiness. INTRODUCTION Studies carried out in the Polish and global mining industry show that methane is an obvious factor in limiting mining production due to the loss of continuity in the operation of longwall complexes in hard coal mines under methane emission hazard (Schatzel et al., 2008). In addition, methane hazards have a significant impact on the safety of the operators of machinery in the longwall. The requirements of Polish regulations and the practice of safe operation of mining longwalls require correct determination of gas concentration, volume flow, as well as pressure and temperature of the flowing air. As part of the research undertaken in the Budryk (Wasilewski, 2010) and Bielszowice (Dziurzynski et al., 2009) mines to assess the methane hazard in the longwalls and workings in the vicinity of the longwall, research experiments were carried out, during which air parameters were recorded by the mine monitoring system and additional testing equipment in different cycles of shearer operation."

Jan 1, 2019

By Junhyun Choi, Allan Gomez-Flores, Chonbuk National University, Siyoung Q. Choi, Gahee Kim, Seungkon Kim

In this study, to confirm the effect of depletion attraction on the flotation, we theoretically and experimentally investigate the effect of the depletion attraction force on flotation. While varying the concentration of the depletion agent (polyethylene glycol), three different systems are studied: pure malachite, pure silica, and a 1:1 mass ratio of malachite and silica binary system. We find that recovery increases significantly as the concentration of the depletion agents increases for all three systems, as the depletion agent facilitates the adsorption of the particle on the bubble surface. However, the recovery suddenly decreases in a certain concentration range, which corresponds to the onset of the decreased surface tension when high concentrations of the depletion agent are used. This non-monotonic overall recovery trend implies the surface adsorption of the depletant on a surface. The decreased surface tension of the air/water interface suggests that the recovery rate is lowered due to the adsorption of the depletion agent to the bubble surface, acting as a polymer brush. Based on our observations, we conclude that the depletion force can greatly improve particle adsorption, as predicted in the accompanying theory paper, while simultaneously the adsorption of the depletion agent on the bubble surface plays an important role because it hinders particle adsorption. We also perform experiments in the presence of a small amount of a collector, sodium oleate. An extremely small amount of the collector leads to the increase in the overall recovery, which eventually reaches nearly 100 percent. Nevertheless, the grade worsens as the depletant provides the force to silica particles as well as target malachite particles.

Jan 1, 2016

By K. Scalise, M. Teixeira, K. C. Kocsis, J. Parrish

"This paper aims to introduce and discuss a newly developed algorithm, which can be uploaded on smart watches and other mobile devices to inform and protect underground personnel working in hot and humid environments. Using this algorithm, the metabolic rate (M) of a worker can be determined in “real-time”. In addition, besides warning signs and alarm signals emitted by the smart watch, the algorithm has the ability to determine work-rest time periods based on the worker’s physiological parameters (e.g. age, height, weight, gender) and the climatic parameters (Td, Tw, flow velocity). This paper also investigates whether a re-designed auxiliary ventilation system can provide appropriate work conditions in the production stopes. INTRODUCTION An underground environment with high temperature and humidity conditions generated from various heat and moisture sources can significantly affect the thermoregulation processes of the human body. This can lead to heat-related illnesses such as heat rash, heat cramps, heat exhaustion, and heat stroke. Heat stroke is a serious illness that carries a high risk of fatality, if the underground workers are not immediately treated and the climatic conditions are not corrected (McPherson, 1993). There are two methods used to control the climatic conditions in underground mines: (1) Using ventilation and cooling systems to reduce the thermal stress on the mine workers, and (2) Reducing the heat transferred to the ventilating air from major sources such as: strata, auto-compression, mining equipment, groundwater, blasting, etc. The heat from strata and auto-compression is transferred to the ventilating air at varying degrees, based on factors such as the virgin rock temperature (VRT), the thermal properties of the surrounding rock formations, and the surface air temperature. However, the use of mining equipment and blasting processes can be managed to reduce their contribution to the mines’ overall heat load. To provide appropriate work conditions, selecting the most suitable cooling method depends on the level of heat to be removed, the location of the problem areas, and economic constraints (Brake & Bates, 2002; McPherson, 1993). Because every mine is unique, it is essential to monitor the climatic conditions to select the most appropriate method of cooling. A majority of the time, simply adjusting or re-designing the auxiliary ventilation system can efficiently remove the heat and dilute the contaminants. This may involve moving the ducting system, changing the size of the duct, changing the size of the auxiliary fan, or switching from forcing to an exhausting fan arrangement. If the required air volumes are higher than the existing primary ventilation system can supply, other measures may need to be taken to increase the airflow delivery. This may include regulating the flow in some areas of the mine to increase airflow to the desired area, adding booster fans, or replacing the primary fans."

Jan 1, 2019