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By L. Kulik, J. den Drijver

Rhenish lignite will continue to play an indispensible role in the energy mix of the German Federal Republic for a long time to come. The use of lignite for electricity generation, upgrading and, if necessary, as a raw material is geared to the long term. The holistic management of opencast mines underpinned by approval law in the long term and a stronger focus on man, the environment and nature contribute to the acceptance of the mines by the local population. The same is true of state-of-the-art lignite uses: as regards their operational flexibility, lignite-fired power plants are ideal partners for the expansion of renewables. It is along these lines that RWE is continuing its power plant renewal programme as planned. With a view to that which will be conceivable the day after tomorrow, RWE is researching future technologies today in order to meet objectives such as security of supply, profitability and environmental compatibility to the same extent in the long term. Another important contribution to acceptance is public transparency and communications as means to support approval procedures and the implementation of measures in all areas related to lignite mining and utilization.

Jan 1, 2011

By Wm. Mark Hart

High horizontal stresses and shear failure have been considered the major reasons that cause entry roof failure and falls for underground mining. Therefore, reorientation of the current mining systems or layouts or using angular crosscuts in mains or gate entries becomes more popular if a greater than normal horizontal stress is measured. However, reorientation of the current mining systems or layouts is always expensive and use of the angular crosscuts may weaken the pillar structure at corners. Therefore, cautions must be taken before any decision related to reorientation of the current mining systems or layouts or use of angular crosscuts is going to be made. In order to prevent entry roof failure and falls, the following two issues must be carefully examined and fully understood: 1. Which one, shear stress or tensile stress, is going to be blamed for entry roof failure? 2. Which one, horizontal stress, vertical stress, or local geological weakness plays a major role in entry roof failure and falls? This paper analyzes the mechanisms of entry roof failure and falls for underground mining in general examines the roof fall history at Springvale Colliery, and proposes the means of preventing roof failure and controlling roof falls for Spingvale Colliery in particular.

Jan 1, 1996

By David G. Borg

"Although researchers have realized varying degrees of success in numerics modeling, computer blast simulations and small scale in-situ testing, most will agree that the greatest uncertainty in total success stems from the uncontrollable field variables. Given the diverse nature of field conditiorencountered, no reliable and proven method of evaluating fragmentation quantitatively, and the lack of adequate field controls found in many operations, it is unlikely that a universal plug-in model will be developed for all blasting in the imediate future. This does not imply that all research devoted to modeling should cease, for it is precisely here where more research efforts are desperately needed."

Jan 1, 1989

Queensland?s underground coal industry, as a whole, has arguably the best gas monitoring systems in the world. Each mine utilizes real time, tube bundle and onsite ultra fast gas chromatograph systems. Queensland?s mining legislation has specific requirements for mine gas monitoring but there is no requirement for all three techniques. Industry has however identified the need for all three and adopted this as a standard, resulting in over sixty thousand gas results collected each day. Automated monitoring systems are programmed to alarm for gas concentrations, gas ratios and explosibility. These alarms are then used to initiate predetermined actions to take control of the situation and prevent the compromise of safety to workers and the loss of resources. Dedicated software packages have been developed to assist in the interpretation of the large volume of results generated. The real time systems are used for real time warning, essential for incidents such as belt fires. Tube bundle systems suit long term trending used for identification of the onset of spontaneous combustion or for the determination of explosibility during the routine sealing of worked areas. Gas chromatograph analysis is used to provide a complete analysis and provides results for hydrogen and ethylene, key gases used in the assessment of spontaneous combustion. It is also crucial during significant spontaneous combustion events and coal fires to use gas chromatography to determine the explosibility status of the underground atmosphere otherwise the severity of the situation is likely to be under estimated. This paper outlines the need for all three techniques for assessing the underground status and outlines advantages and disadvantages of each.

Jan 1, 2009

By Gabriel S. Esterhuizen, Anthony T. Iannacchione

The roof rock in underground limestone mines in Northern Appalachia can be subject to high horizontal stresses in spite of the shallow depth of the workings. The high stresses can cause roof stability problems. The National Institute for Occupational Safety and Health staff have observed a distinctive asymmetrical mode of failure at the pillar-roof contact in two underground stone mines, which is different from the typical failure mode observed in response to excessive levels of horizontal stress. A dip of greater than 5° was identified as a possible cause of this mode of failure. Numerical model experiments showed that an increase in the dip of the workings can cause an increase in the stress at the up-dip corner of the roof beam. A case study is presented in which failure at the pillar-roof contact was observed where the dip of the workings was 7° in a high horizontal stress field. Numerical modeling showed that the relatively small dip of the workings could have induced stresses changes in the immediate roof that would explain the failures. The model results also showed that this mode of failure is less likely to occur if the limestone pillars contain weak bedding planes that provide stress relief. In addition, the results showed that for the conditions at the case study site, the stress in the roof beam was not sensitive to the thickness of the roof beam or to the excavation span. The high horizontal stresses at this site are an important contributing factor to the observed failures.

Chelopech Mining EAD and Best Available Techniques for Management of Waste Rock in Mining Activities

Sep 13, 2010

By George Goble

I hope that after the long evening and all the exercise that some of you took you won't be completely exhausted to listen to a little bit about pile testing. The topic that 1 have been given is pile testing. It seems to me useful to break this topic into some smaller pieces so that we can try and organize our thought a bit. As I understand the terms "pile testing", I believe we are really referring always to capacity, one way or another, so I am suggesting that we organize the things we are doing in terms of measurement of soil capacity and pile capacity. There are obviously two failure modes and we frequently speak of pile integrity rather than structural pile capacity, but it's really capacity that we are concerned about. Further within these breakdowns I am suggesting that we might look at the topic of soil capacity in terms of static methods and dynamic methods and, finally, within each one of these, measurements of axial capacity and measurement of lateral capacity. Also here some of these subdivisions might be there for the purpose of symmetry and finally the same sorts of breakdown in Pile Capacity area.

Jan 1, 1994

By Dan A. Brown

This paper describes a method of conducting rapid lateral loading tests of deep foundations in which the load is applied to the foundation with a time duration of less than one second. For purposes of this paper the loading is applied using a pyrotechnic loading system commonly referred to as Statnamic. However, the method should apply to any lateral loading system which produces a force time history with a loading duration of 20 msec to 1 second. The test provides a measure of the dynamic and static response of the soil/foundation system and must be evaluated as a dynamic loading. Interpretation of the test includes a simple single degree of freedom (SDOF) model which can account for the inertial effects of foundation mass, system damping, and static foundation stiffness. The results of the test measurements are compared with four case histories in which comparative static load test data are available, including pile group foundations and large diameter drilled shaft foundations.

Jan 1, 2007

By Samuel Frimpong

The interaction of oil sands with a ground articulating pipeline (GAP) system has been simulated with the dynamic model established in this work by combining the multi-body and soil dynamics with the Automatic Dynamic Analysis Mechanical Systems (ADAMS) software. Mathematical models governing the interaction of the GAP system with the oil sand terrain have been modeled based on the theory of multi-body and soil dynamics. These models consist of GAP track-oil sand contact model for generating the contact force between oil sands and track and load-deformation oil sand model for capturing the dynamic behavior of oil sands. A virtual prototype has been created and simulated in the ADAMS environment. The simulation result of the effect of load on oil sand deformation indicates that maximum deformation value increases non-linearly with load varying from 0 to 60t. This study provides a solid foundation for further research and the GAP technology development.

May 1, 2004

Roof falls in coal mines typically occur in or around intersections and this has not changed in the last two decades. This research develops an improved scientific understanding of stress distribution and associated failure behavior around 4-way and 3-way coal mine intersections. Three-dimensional numerical analyses were performed to determine factors that influence intersection stability. The analyses used Hoek-Brown failure criterion. Failure zones around 3-way and 4-way intersections were developed. Intersection span and horizontal stress have a major influence on intersection stability. For the 4-way intersection, pillar corners across the intersection fail first and lead to progressive failure of immediate roof and floor layers. The mechanism of failure is similar for the 3-way entry but the shape and extension of failed zones differ. Coal ribs mostly fail due to tensile stress, while roof and floor strata fail due to shear stresses. Rib corners fail due to a combination of shear and tensile stresses. In addition to stress distribution; safety factor contours analysis was performed to assess stability of intersections.

Feb 27, 2013

By G de Jong, W Sunyoto, K Sari, P Silalahi

"An EXTENDED ABSTRACT is available for download. A full-length paper was not prepared for this presentation. The Big Gossan mine is operated by PT Freeport Indonesia and is one of the largest stope-and-fill mining systems in the world. The Big Gossan deposit is a ~200 m wide, 1200 m long and 500 m high steeply north-east-dipping to subvertical skarn body at the Cretaceous-Tertiary Ekmai-Waripi contact. The copper-gold mineralisation, with a 1.3 per cent copper equivalent cut-off grade, occurs mainly proximal to the Ekmai-Waripi contact in the garnet-clinopyroxene prograde skarn at the base of the Tertiary Waripi formation and partly distal to the contact in the tremolite-actinolite retrograde skarn of the Tertiary Waripi formation.The Big Gossan stope mine is designed from 2540 m to 3020 m above sea level. Present active stoping operations occur at level 2540 mL to level 2640 mL and are done in a primary and secondary stoping sequence. The width and length of the stopes is 15 m and 20 m respectively, while the height of the stope varies between 20 m and 40 m, depending on the ground conditions. The stability of the stopes is visualised in the Mathew’s Stope Stability graphs. These graphs and actual Cavity Measurement Scanner measurements on the stope will predict and show the overbreak and underbreak, which affect the reconciliation of the mined stope and also the pillar stability between the primary stopes. Geological factors like major structures, joints, veins and alteration intensity are important factors that correlated with the stability of the Big Gossan stopes.CITATION:Sari, K, de Jong, G, Silalahi, P and Sunyoto, W, 2015. Stope stability at the Big Gossan skarn deposit, Papua, Indonesia, in Proceedings PACRIM 2015 Congress, pp 139–146 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Mar 18, 2015

By P. Wells

"In the past decade, there have been many developments in processing of nickel/copper sulfide ores. Improved pentlandite/pyrrhotite flotation selectivity with the use of new reagents, fine regrinding and Redox measurement (control) has led to increased pyrrhotite rejection and thus higher concentrate grades. Flash flotation has increased overall nickel and associated precious group metal recoveries. Recovery of both fine and coarse particles has been improved through an understanding of flotation cell hydrodynamics. The separation of copper from nickel in such ores has seen a similar level of development. From the late 80s to very recently, the use of flotation columns, the use of pyrrhotite depressing reagents and the improved understanding of the complex mineralogy of chalcopyrite, pentlandite and pyrrhotite have considerably increased copper / nickel separation efficiency. Copper concentrate with more than 30% copper and less than 0.5% nickel grade is now obtainable at 80-85% copper recovery from mill feed compared to 70-75% copper recovery with 30% copper and 1% nickel grade only a few years ago. Improved copper / nickel separation in milling operations has the potential to substantially improve the processing of the resulting concentrates and thus the overall return from the extraction of nickel and copper from sulfide ores.INTRODUCTIONNickel metal by itself or in alloys with other metals and materials makes a significant contribution to modern society. The relatively high price that nickel commands compared to other base metals is a reflection of the fact that, although abundant in the universe, nickel is sparingly distributed in the earth’s crust. There are two types of nickel deposits that are currently being exploited: complex sulfide ores and lateritic oxide ores. Lateritic contain no copper but in sulfide deposits, nickel– bearing minerals, principally pentlandite (Pn, [Ni,Fe]8S9), some millerite (NiS) and violarite ([Ni,Fe]S) are often found in association with copper-bearing minerals, mainly chalcopyrite (Cp, CuFeS2) and cubanite (CuFe2S3). The copper content of such ores can vary considerably from as high as 5-8% (in some Sudbury basin ores) to as low as 0.1% (in ores mined by Western Mining at Mount Keith, Western Australia and by Inco in Thompson, Manitoba). The valuable minerals Pn and Cp are almost invariably found associated with pyrrhotite (Po, Fe7S8) which along with nonsulphide rock has to be rejected to tails in the primary milling stage. The bulk concentrate from the primary stage is then treated to depress Pn and float Cp. A complete Cu/Ni separation at the mill would be highly desirable but this is not possible because of locking between a small fraction of the valuable minerals. As a result, Cu/Ni separation has to be carried out both during milling and during refining of the matte following smelting. At Inco, Jinchuan and in Norilsk, a chalcocite / heazlewoodite separation is made by flotation following slow cooling of the matte. In the present Sudbury Inco operations, Cu/Ni separation has not been conducted at the mill since 1991 and all Cu/Ni separation takes place at the matte processing plant. Because of the rising ratio of Cu to Ni in the ore, this strategy is under review and this paper describes some recent studies of circuits in preparation for possible installation of a copper / nickel separation circuit at Inco’s Clarabelle Mill in the Sudbury area."

Jan 1, 2004

By Michael B. Cortie

The young field of nanotechnology has as its objective the design and construction of useful devices made of nanoscale materials. Objects or structures which have at least one important dimension in the range 0.5 to perhaps 50 nm may be considered to be in the nanoscale domain. These sizes lie far below the 200 nm or so that can be resolved with an optical microscope, and are closer in size to the 0.3 nm diameter of individual atoms. Nanotechnology, which is the study and exploitation of these tiny structures, is attracting keen interest at present. The excitement is motivated by the observation that control of matter at the nanoscale holds the promise of faster computing, better medicines, and smarter materials. In this paper, the physical phenomena on which this optimism is based are broadly discussed and explained. Where appropriate, examples of the rather different and curious properties of gold at the nanoscale are used to illustrate the points covered.

Oct 1, 2003

By D. M. Lane, J. M. Berkoe

Engineers and Owners share a common desire to build reliable, efficient plants on schedule at reasonable costs. This paper describes one tool that Bechtel finds can integrate these objectives by “putting innovation into practice”. Examples of such innovative engineering practice include the use of computational fluid dynamics (CFD) to determine efficient designs. This paper outlines several examples of CFD applications on actual Mining and Metals Projects from around the world. The focus here is to highlight the modeling objectives, analysis strategy, actual benefit obtained from the work, lessons learned to improve future efforts and the common mistakes that can obscure the correct or best results, despite impressive graphics. The tools are powerful, and the results are more powerful when applied with skilled and well-directed human effort and ingenuity.

Jan 1, 2000

By Neo Molelekeng, Jocelyn Bouchard, Rebecca Monnapula, Martin Émond

"Xstrata Alloys – Eland Platinum concentrator (South Africa) has recently been commissioned and is now initiating a challenging optimisation program encompassing the entire operation. Process control improvements are key elements of the program and initial results have demonstrated how leveraging from current assets can bring significant improvements through overall reduction of variability. This paper gives a brief overview of the operations and details how Eland is striving to become a top tier leader with advanced regulatory control strategies recently implemented. Results reveal that what can be achieved in a standard control system (PLC or DCS) should not be underestimated as the first interventions led to a steadier operation of the primary ball mill circuit. Following the improvements, significant and sustained reductions of standard variation were observed for key process variables around their set-point: primary ball mill feed rate (72 %), rougher feed density (58 %), and rougher feed flow rate (47 %). A path forward has been identified to tackle further opportunities around the primary grinding circuit: water balance management, throughput optimisation as well as charge and power draw control.INTRODUCTIONThere are numerous approaches to mineral processing plant optimisation. As the benefits of determining the right reagent types, mix, dosage and addition points, or the proper charge of grinding media in a mill are fully appreciated, there is still nowadays some misunderstanding and misconceptions about process control in general and how it can contribute to the whole optimisation process. The confusion between the various disciplines involved, i.e. instrumentation, control system programming, automation and process control, certainly does not serve the best interest of the industry with this regard."

Jan 1, 2010

By Garry M. Johnston, Matthew L. Sutcliffe, Nicholas J. Welham

"The predominant current processes for the treatment of oxidized copper–cobalt ores use a reductive acid leach to bring the desired metals into solution. However, the indiscriminate nature of acid leaching results in a solution, akin to a metal soup, containing not only the Cu and Co but also an extensive suite of other metals. These other metals, notably Fe, Mn, Al, Ca, Mg and Si, all have to be eliminated from solution before the copper and cobalt can be recovered. Generally precipitation processes are used, but these tend to result in significant losses of copper and/or more usually cobalt from solution, leading to reduced recoveries. The AmmLeach® process uses ammonia-based chemistry to selectively leach the target metals, leaving the rest behind in the leach residue. This approach eliminates any need to clean the solution of unwanted metals and the consequent metal losses. After solid–liquid separation, the leach solution is immediately subjected to separation and concentration of the copper and cobalt using solvent extraction and electrowinning. INTRODUCTION The Copper Belt extends through the northern part of Zambia and the southern province of Katanga in the Democratic Republic of Congo (DRC) and contains the richest and highest grade deposits of copper and cobalt remaining in the world. Whilst there are a number of mines that produce sulphide concentrates, using froth flotation, the largest deposits are those where near-surface sulphides have been weathered over time to form oxides. The oxides cannot be concentrated by conventional physical means to give high recoveries. Despite this, a number of dense medium separation plants have been installed and used to produce a higher grade concentrate which is typically exported (while the rejects, typically 2 to 3% Cu are stockpiled for treatment at a later date). These plants generally have low recoveries and can only be used on the dwindling supply of high grade materials. In exporting the concentrate, little value adding is undertaken within the country, thus greatly reducing the economic benefits to the country. Recent changes to the regulations in the DRC will effectively ban the export of low value ores, concentrates and intermediates in favour of high value metals. This will necessitate mines to install new processing circuits in order to comply with these regulations. The head grade of ores currently being treated in the DRC is slowly decreasing as the extremely high grade materials are being selectively mined out. In many cases, the removal of a small volume of high grade materials leaves a much larger volume of economically marginal ore behind. This is due to a desire for short-term profits overtaking long-term prosperity. The remaining ore, which in many cases is still of relatively high value by world class standards, is likely to be only treatable by low cost heap leaching. There are some initial trials of heap leaching within the DRC, but implementation at a large scale has yet to be adopted."

Jan 1, 2015

By Liqun Liang

Various nondestructive testing (NDT) inspection methods are available to evaluate the structural integrity of cast-in-place shafts. The widely used methods include Cross Hole Sonic Logging Testing and Low Strain Testing. Due to its advantages such as low cost, easy operation, quickness and flexibility (no need to plan ahead and prepare inspection tubes or other devices), Low Strain Test is frequently specified in quality assurance programs of many countries or when doubts arise as to the integrity of the finished shafts/piles. The method is well suited for small to middle sized shafts. However it is an indirect NDT testing method and has certain limitations. Data interpretation requires proper training, experience and judgment and, therefore, inconsistent conclusions and reporting may be provided by different testers. To avoid or reduce such inconsistencies, it is best to follow a standardized data interpretation and record classification system. In this paper, a new classification method is presented with examples. A step-by-step data evaluation and interpretation procedure is proposed with examples of real cases to help understand the LST data. The paper also makes recommendations for measures to be taken when anomalies are detected in tested production piles.

Jan 1, 2011

By S. du Plessis

Nationalization is high on the policy agenda in South Africa. This paper considers the case for nationalizing the local mining sector from an evidence-based perspective, which is derived from theoretical considerations and related to the known features of the South African mining sector and economy. A strong case against nationalization emerges, which can be summarized as follows. The mining sector is competitive and therefore a poor candidate for public ownership. Furthermore, the resources sector does not dominate the South African economy nor does it create the risk of a decrease in the competitiveness of the industrial sector via the unintended adverse impact of an appreciating real exchange rate due to a commodity boom (Dutch Disease). Nationalizing the mining sector will cost the government more than it receives. This is not only a bad idea in itself, but it will limit the scope for distributive policies on the national budget. The contemporary international experience demonstrates the risks of fiscal imprudence. Finally, nationalizing the resources sector will undermine support for those very market-based institutions required to achieve a higher long-run growth trajectory.

Jan 1, 2013

By P. J. Mehrfert

"Recovery of mineralized coarse particles is notoriously low in conventional concentrators that treat copper porphyry ores. The application of coarse particle flotation techniques has the potential to achieve comparable metallurgical performance at significantly coarser primary grind sizings. ALS Metallurgy has been conducting both internal research and commercial test programs to investigate the potential of Eriez HydroFloatTM technology on copper sulphide ores. Test data indicates that significant improvements in the recovery of copper sulphide bearing particles between 200µm to 850µm can be achieved using Hydrofloat technology compared to conventional flotation techniques. This paper summarizes the results from a selection of test programs that includes recovery by size data from both conventional flotation and HydroFloatTM tests. An explanation of the apparatus and test procedure will be given. Mineralogical analyses of the test products and characteristics that limit metallurgical performance will be discussed.Description of Apparatus and Test ProtocolThe HydroFloatTM laboratory cell is a clear plastic column with an internal diameter of 14 cm. Water and air are introduced to the cell through a circular manifold located in the lower portion of the cell. The cell has a conical bottom which directs slurry to a pinch valve that controls the discharge of tailings. Feed solids are introduced to the upper portion of the cell in slurry form. The cell is operated in a manner such that the manifold water creates a teeter bed zone of suspended solids in the middle portion of the cell. Tailings exit the bottom of the cell at a high pulp density, and most of the introduced water overflows the top of the column and is collected in a launder. Particles with a hydrophobic surface may attach to air bubbles that percolate through the teeter bed, rendering them sufficiently buoyant to be transported to the overflow launder.Three significant features of this arrangement enhance the potential to recover coarse, low grade particles by flotation techniques. Firstly, the hindered settling conditions created by the rising column of water allow coarse particles to become buoyant once attached to a modest sized air bubble. Secondly, the flow conditions within the cell are relatively quiescent compared to a conventional flotation cell that utilizes an agitator. This allows particles that have limited hydrophobic portions of their surface, due to a low content of exposed sulphide mineral, to maintain a somewhat fragile attachment to air bubbles long enough for successful recovery to the overflow. Finally, the absence of a froth phase at the top of the cell allows particles attached to air bubbles to immediately exit the vessel, reducing the potential to drop back into the pulp phase as bubbles burst or coalesce."

Jan 1, 2017

By D. G. Krige

Using chip sample data and spatial structure parameters from a large mined-out section of a South African gold mine the advantages to be gained from a regular underground borehole drilling programme have been investigated for short- and medium- to long-term planning based on block valuations. The results have been compared with the current position, which relies invariably on the extrapolation of limited peripheral sampling data from raises, gullies or stope faces. Some preliminary work has also been done regarding the implications of such underground drilling on costs used for the present pay limit calculations. The results of the study, though preliminary, show that the net advantage of advance regular underground drilling could be substantial and that a more intensive follow-up research is warranted.

Jan 1, 2003