Search Documents

By T Vizcarra, G Sandoval, C L. Evans

One of the challenges in the development of mineral processing simulators is modelling the liberation characteristics of particles produced by comminution circuits. Understanding the mineral characteristics of these particles is one of the keys to predicting their behaviour in separation circuits. While more fundamental research seeks to model the non-random breakage of ores this work examines whether we can move forward now by using observed characteristics of ores to model the composition of particles generated in comminution processes. Several researchers have noted the similarity of the liberation characteristics for a selected size fraction of particulate material, whether the fraction comes from a coarse material, such as the product from a jaw crusher, or a more finely ground material, such as the product from a ball mill. In most cases these observations were reported as an aside and were not the main focus of the published work. This observed behaviour has the potential to be a useful tool for modelling the particle characteristics in mineral comminution and separation circuits, particularly as we move towards the development of multi-component models. However, before the behaviour can be used widely we need to understand which ore types follow the observed pattern and which do not. The current work examines a range of ores and identifies which exhibit the pattern of similarity of composition for particles in a given size class that has been produced as the result of a variety of breakage conditions. The impact of mineralogy and texture on the evolution of liberation characteristics for both valuable and gangue minerals is discussed.

Jan 1, 2008

By K Friese, H P÷llmann

Clinoptilolites, modified with sodium, produced a material which has been tested for the ability to remove Hg (II) from aqueous nitric acid. The amount of adsorption depends on contact time, acid concentration of aqueous solution and initial mercury concentration. The study of the kinetics of mercury uptake revealed that all sorbents exhibit a fast rate of sorption. The highest sorption capacities were observed for sodium forms, and were up to five times higher than for the unmodified zeolite. The maximum sorption capacity toward mercury is determined as 0.093 ¦g/g at an initial concentration of 10.0 ¦g/L for a clinoptilolite from Tsagaantsav deposit (Mongolia). The sorption of Hg (II) has an ion-exchange nature and consists of three stages, ie the adsorption on the surface of microcrystals, the inversion stage and the ion exchange in the interior of the microcrystal. Sorption capacity decreases with the increase of mercury concentration. The presence of other metal ions such as Cd (II), Cu (II), Ni (II) and Zn (II) increases Hg (II) uptake capacity. Finally, sorption for Hg (II) was investigated in batch systems to evaluate the short-term stability of the sorption properties.

Jan 1, 2008

By Frank P. Frandina

The Heartland Corridor Clearance Improvement Project is part of a regional Public-Private initiative to allow double stack container trains a direct route from the Port of Norfolk through Virginia, West Virginia, Eastern Kentucky and into Central Ohio. The project involves clearance improvements to twenty-eight tunnels, twenty-one of which require structural modification. With construction of the first Package of tunnels just underway at press time, this paper summarizes the program implementation from design through the initial stages of construction.

Jan 1, 2008

By A Kindred

The Bogong Hydropower Development is a 140 MW high head power project currently under construction in Northern Victoria. The project is the final link in the Kiewa hydroelectricity scheme, which was originally constructed in the 1950s. Due to its location in the Alpine National Park, the waterway for the Bogong project must be located entirely underground. A series of shafts and tunnels is being constructed to transfer the water from the headworks at McKay Creek to the new power station located on the shores of Lake Guy in Bogong village. The difference in elevation between the headworks and the power station is greater than 420 m, which poses particular issues for the design and construction of the waterway. The purpose of this paper is to describe the design and construction planning aspects of the tunnelling and shaft excavation and lining works for the waterway. The tunnelling works includes 5.7 km of hard rock tunnel boring machine (TBM) driven tunnel, 1.1 km of drill and blast tunnel and two deep shafts. The tunnels and shafts are lined with a mixture of permanent rock bolts and shotcrete, concrete lining and steel lining. The viability of the Bogong Hydropower Development relies heavily on the ability of the TBM to excavate at high speed through the East Kiewa Grandiorites. Particular attention was given during the construction planning stage to understanding the excavation characteristics of this material, and designing a suitable hard rock TBM that would be capable of meeting the program requirements of the project.

Jan 1, 2008

By C MacDonald

There are many technologies available today in terms of fire and life safety in road tunnels. So many in fact that it is becoming more and more difficult for clients and contractors alike to determine what they want and what they need. From a clientÆs perspective, fire and life safety is about protection to its infrastructure and to the public at large. Conversely, the contractor is looking to meet its æfit for purposeÆ or ædeem to complyÆ requirements in the most economic and practicable way. Practices regarding fire and life safety in road tunnels have undergone a degree of transformation during the last decade or more throughout the world. This transformation has largely been driven by a series of catastrophic accidents such as the major fires in Europe including the Mont Blanc Tunnel, Tauern Tunnel, Saint-Gothard Tunnel, and now most recently in the CityLink Tunnels in Melbourne. International guidelines produced by organisations such as the Permanent International Association of Road Congresses (PIARC), the European Union, the International Tunnelling Association (ITA) and the US National Fire Protection Authority (NFPA) now provide clients, owners and designers with the tools required to define and specify the required fire and life safety systems in road tunnels. The majority of these tools are based on risk assessment and risk management. Recent road tunnel projects within Australia, however, have not referred solely to such guidelines. Clients have opted to prescribe different or additional fire and life safety requirements within the projectÆs technical specification documentation (project requirements), leaving designers and contractors with little room to implement alternatives or substitutions. Further, these project requirements are largely dictated by practice established on previous road tunnel projects within Australia. This paper looks at the current international guidelines and practices and undertakes a comparison with the EastLink tunnels in Melbourne and other road tunnels within Australia and makes assessment on whether Australian methods are the most appropriate for clients and contractors alike. Focus is directed to the key elements of fire and life safety such as:traffic envelope, barrier arrangements and emergency walkway provisions;deluge systems;drainage systems;fire rating requirements;tunnel ventilation systems;cross passage provisions;fire safety assessment;critical intelligence systems including help phones, CCTV, incident detection, tunnel signage, etc; andexternal tunnel control systems.

Jan 1, 2008

Knowledge of the crystal chemistry of carbonate apatites is very important for the development of the concept of biomineralisation and the creation of a scientific base for new biocompatible materials for medical purposes. The present work is devoted to research results on various synthetic and biological carbonate apatites obtained at Saint Petersburg University over many years. All-important problems will be considered such as the location of CO32- ions in the apatite structure, the ionic substitutions in various biological apatites and the development of synthesis methods for their analogues. Syntheses of apatites were realised by precipitation methods and under hydrothermal conditions (from solid compounds and by calcite treatment). Biological samples used in this study were physiogenic and pathogenic apatites formed in the human organism, eg in teeth and in renal and salivary stones and dental calculi as well as apatites from fossils of different taxonomic families (brachiopods, conodonts, fishes, reptiles, mammal) with different geological ages and burial conditions. The study of the crystal chemistry of carbonate apatites has been carried out by powder (including high-temperature measurements) and single-crystal X-ray diffraction methods, IR-spectroscopy, thermal analysis and various chemical analytical techniques.

Jan 1, 2008

By N J. Grigg

Gekko Systems has developed an underground pre-concentration plant (Python) to reduce mine operating costs. Many ores liberate favourably using either high pressure grinding rolls (HPGR) or vertical shaft impactors (VSI). Using these comminution circuits for mineral liberation; rather than for the final recovery process and by utilising a high mass pull, high recovery process route (gravity/flotation), a narrow, low head, compact processing plant was developed that can sensibly be operated underground. The Python underground processing plant can provide a number of advantages for narrow vein mines including lower haulage costs, improved mine call factor and lower operating costs. The focus on fine crushing reduces the power requirement of the plant to approximately 8 kWh/tonne. The Python underground processing plant has been designed to be towed down the decline or lowered down a shaft, and is capable of being installed in sloping, non-linear drives for placement close to the working face. The overall benefit to mining companies of this concept has been estimated to be a saving in mining costs and a significantly smaller environmental footprint.

Jan 1, 2008

By Wenbin Liu

A novel route for rapid synthesis of ultrafine WC-Co cemented carbides with homogeneous binder phase distribution is reported. The composite powder is produced by in situ reduction-carbonization reactions by using WO2.9, Co3O4 and carbon black as raw powders. The reaction equilibrium and phase stability are studied by thermodynamic calculations. The WC-Co composite powder is condensed by spark plasma sintering (SPS) to obtain the cemented carbides bulk. The sintering temperature is lower than that in the conventional sintering methods by 1500C, while the sintering time is remarkably reduced by 3-5 times. The high performances of the hardness and the fracture toughness are obtained. The experimental results confirm that the present processing scheme of in situ reduction-carbonization reactions and subsequent SPS sintering is an efficient way to prepare WC-Co cemented carbides, and is apparently superior to the conventional long-period techniques of preparing composite powder and cemented carbides bulk.

Jan 1, 2008

By J. Kang

To obtain microbial cultures with the ability to efficiently leach copper ion from chalcopyrite, microbial samples from acid mine drainage sites were mixed and then subjected to mutation using sodium nitrite (NaNO2), diethyl sulfate (DES), ultraviolet light (UV) and their combinations. Mixed cultures with a much stronger ability to leach copper ion (identified as mixed cultures A, B, C, D and E) were obtained by screening on leaching media. Leaching tests showed that mixed culture E had the best leaching performance and increased the Cu2+ content by 120.5% in 20 days, compared to a control without mutation treatment. Mixed culture E grows well on Leathen leaching medium supplemented with Cu2+ (at a final concentration of 32 g/L), reaching 3.2 × 107 cells/L after 15 days, while the unmutated control culture cannot survive beyond 15 days, indicating that mixed culture E is more tolerant of high concentrations of Cu2+. In addition, continuous leaching by mixed culture E is very effective at a pulp density of 1%. These results suggest that it has the potential for industrial applications.

Jan 1, 2008

By H. Palkowski

Recent trends in the automotive industry lead to increasing interest in advanced high strength steels (AHSS). Those steels often have a high bake hardening potential (BH), giving additional contribution to the strength of structural parts, subjected to the paint baking process. For hot rolled AHSS, namely dual phase and martensitic steels, the effect of process conditions on mechanical properties had been investigated. However, the influence of chemical composition within the range in industrial production has not been investigated sufficiently yet. In the current research, samples with different chemical compositions within the characteristic interval for industrial production are under investigation under different preload conditions and simulating the thermo-mechanical production process. The samples were then subjected to BH process. Tensile tests were performed to study the influence of varying chemical composition on the BH effect. The results of investigations on dual phase steels will be presented in this paper.

Jan 1, 2008

By R Riquelme

The El Salvador porphyry Cu deposit (26¦ 15Æ Lat S, ~2700 masl) and associated exotic mineralisation is situated at the back-scarp of the late middle Miocene Atacama pediplain in the western Precordillera. New, together with published 40Ar-39Ar data from El Salvador combined with morphologic analysis reveal that the palaeospring plumbing system related to exotic mineralisation at the Damiana exotic Cu deposit and the local geomorphology has not changed fundamentally between the late Eocene and late Miocene. Stable H/D isotope data on supergene alunite from El Salvador indicate an overall increase in dD values (VSMOW) from -74ë at 35.82 ¦ 0.95 Ma to -23ë at ~11 Ma. The transition from strongly to moderately negative deuterium values occurred between ~16 and ~13.5 Ma. Supergene alunite from the El Hueso (3950 masl) sedimentary rock-hosted epithermal deposit ca 35 km SE from El Salvador was dated at 8.19 ¦ 0.01 Ma and yielded a dD value of -25ë. We interpret the increasing deuterium excess as the result of strong evaporation and recycling of meteoric water after ~15 Ma and as indicative for a change in precipitation patterns and climate desiccation. In contrast, the strongly negative dD value for late Eocene supergene alunite points to a more humid climate and an elevation similar to the present. The late Miocene supergene activity at El Hueso is probably related to an uplift of the Precordillera to elevations sufficient for capture of orographically controlled precipitation. An EXTENDED ABSTRACT is available for download. A full-length paper was not prepared for this presentation.

Jan 1, 2008

By Carrie Pourvahidi

The California High Speed Rail Authority (Authority) was created by the State of California through legislation in 1996. The purpose of the Authority is to plan, construct, finance and operate a statewide intercity high speed passenger rail system. In 2004 the Authority prepared a programmatic level environmental document in compliance with the California Environmental Quality and National Environmental Protection Acts (CEQA and NEPA).The Authority and Federal Railroad Administration (FRA) were the lead agencies overseeing the development of the environmental documentation. The resulting document includes two volumes and 64 supplemental technical reports analyzing the transportation needs for California and the selection of an approach to meeting the project transportation needs. The Programmatic Environmental Impact Report and Environmental Impact Statement (EIR/EIS) identified High Speed Rail as the most environ-mentally protective, sustainable and economical approach to meeting the state?s projected transportation needs.

Jan 1, 2008

By E Giles

Pike River Coal Limited (PRCL) is opening a new underground coal mine in the Paparoa Ranges north-east of Greymouth. To access the coal reserves, PRCL have had to build a 13 km access road through regrowth and virgin forest, and appointed McConnell Dowell Constructors Limited, with URS New Zealand Limited as their consulting engineers, to construct the final access link: a 2.3 km long, 5.5 m wide and 4.5 m high incline tunnel. This paper discusses the logistical issues of construction in an isolated pristine forest in mountain land and how they were addressed. It provides an overview of the 90 per cent complete tunnel and how challenging rock conditions have been mastered. It outlines briefly the remaining work which is construction of pit bottom workings where the mine infrastructure will be housed and construction of a 110 m deep, 4.0 m diameter, vertical ventilation shaft.

Jan 1, 2008

By E Niva

The IsaMillÖ is challenging the way that plants are designed and operated. This paper challenges existing designs of concentrator flow sheets, particularly focusing on magnetite circuits.   From what has started out as a small scale ultra fine grinding mill in the pharmaceutical and pigment industries, it has been redesigned and improved upon for mineral processing, and has been the mainstay of fine grinding applications for over ten years. These applications have required energy efficient grinding to succeed, and have been predominately in the base metals industry.   Further development of the IsaMillÖ has now resulted in the machines being able to treat larger tonnages, with higher capacity motors. This development, along with the introduction of purpose designed ceramic media, has allowed the mill to treat courser feed sizes. At the same time, the mill still offers highly efficient grinding, and has enabled it to be operated in coarser tertiary and secondary grinding applications.   The acceptance of the mill in coarser applications, predominately in base metals and PGM applications, has enabled the IsaMillÖ to be a serious contender for beneficiation in other minerals. One such application is the potential for IsaMillsÖ to be part of magnetite flow sheets, which are being considered in Australia to meet the growing iron demand of China. The high energy efficiency of the IsaMillÖ compared to conventional technologies, as well as the smaller infrastructure requirements, provides a great opportunity to reduce the power intensity of magnetite circuits.   This paper will examine the use of IsaMillÖ technology in conventional grinding applications, including recent testwork in a primary grinding base metal circuit, as well as testwork on magnetite ore comparing a lab scale IsaMillÖ with a lab scale Tower Mill.   The growing demand for minerals over the next decade, coupled with higher energy cost, will result in energy efficient technology, such as the IsaMillÖ, being included in standard circuit design.

Jan 1, 2008

By William W. Edgerton

The California Department of Transportation (Caltrans), the Contra Costa Transportation Authority (CCTA), and the Alameda County Congestion Management Agency (Alameda CMA) are involved in a unique partnership on the planning and design of the fourth bore of the Caldecott Tunnel, located on State Route 24 in Alameda and Contra Costa counties. The project will add a two-lane bore north of the existing three bores. The project will alleviate traffic congestion in the non-peak direction. This paper provides background on the existing facility, summarizes the need for the new fourth bore, describes the proposed improvements, sets forth the approach for project delivery, and lists some of the challenges that are expected during construction.

Jan 1, 2008

By Filiz Sahin

This paper presents a synthesis of TiB2 via carbothermal reduction method using a mixture of TiO2, B4C and C prepared in molar ratio of 2:1:3. Reduction experiments were carried out in a high temperature graphite furnace in a graphite crucible under argon atmosphere at different time (0, 15, 30 and 60 min.) and temperatures (1400, 1500 and 1600 °C). The products obtained were investigated using XRD technique.

Jan 1, 2008

By Andreas Prucker

The Greater Vancouver Water District (GVWD) is currently constructing the largest water treatment plant in Canada. As part of this treatment scheme twin water transfer tunnels are being constructed. Work commenced with the 11 m diameter, 185 m deep Seymour Shaft which was excavated by drill and blast using a mobile crane for hoisting. The Seymour Shaft is the first large diameter shaft that has been sunk in Western Canada in recent years. The operational aspects associated with the hoisting, the drill-blast-support cycle and water control in the shaft are the focus of this paper.

Jan 1, 2008

By Klaus Rieker

The main train station of Leipzig in Germany is currently being upgraded from a head station to a partially thru station. In order to achieve this, significant ground improvements are necessary. Soil freezing for example is used to create the excavation box retaining walls. The freezing works will be carried out from two tunnels with an inner diameter of 2.4 m (~ 8ft). The tunnels were constructed by the pipe jacking method. The cutter head of the machine was equipped with discs and scrapers. Driving and excavation was carried out using a bentonite supported face. Due to the small arrival shafts, the machine had to be lifted out in components. The essential limitation of settlements during the drives was achieved even better than expected.

Jan 1, 2008

By Hugo E. Camargo

Noise Induced Hearing Loss (NIHL) is the most common occupational disease in the U.S. with devastating consequences particularly in the mining industry. A study conducted by the National Institute for Occupational Safety and Health (NIOSH) revealed that 90% of coal miners have hearing impairment by age 50, compared to only 10% of those not exposed to occupational noise. According to the Mine Safety and Health Administration (MSHA), Continuous Mining Machine (CM) operators account for 30% of workers exposed to noise doses exceeding the Permissible Exposure Level (PEL). This number becomes more dramatic considering that 49% of the total national underground coal production is extracted using these machines. In this context, NIOSH is conducting research to identify and control dominant noise sources in CMs. Previous noise source identification was performed using a Brüel &Kjær (B&K) 1.92-m diameter, 42-microphone phased array. These measurements revealed that the impacts from the conveyor chain onto the tail roller, and the impacts from the conveyor chain onto the upper deck are the dominant noise sources at the tail-section of the CM. The objectives of the work presented in this paper were: 1) To rank the noise radiated by the different sections of the conveyor, and 2) to determine the effect of a urethane-coated tail roller on the noise radiated by the tail-section. This test was conducted using an Acoustical and Vibrations Engineering Consultants (AVEC) 3.5-m diameter, 121-microphone phased array. The results from this new test show that a urethane-coated tail roller yields reductions in the tail-section of 2 to 8 dB in Sound Pressure Level in the frequency range of 1 kHz to 5 kHz. However, integration of the acoustic maps shows that the front-section and mid-section of the conveyor also contain dominant noise sources. Therefore, a urethane-coated tail roller in combination with a chain with urethane-coated flights that reduces the noise sources in the front and mid sections of the conveyor is required toyield a significant noise reduction on the CM operator?s overall exposure. These results show the applicability of phased array technology for low frequency noise source identification.

Jan 1, 2008

By M. Schafer

The 6-m- (20-ft-) diameter cast-in-place tunnel lining for Phase 3 of the Mill Creek Tunnel (MCT3) has been completed. This article summarizes aspects of liner design and ad-dresses the construction approach in placing the liner in areas of tunnel that experienced crown overbreak. Tunnel lining production rates, installation procedures and form buoyancies experienced during concrete placement will also be presented. The Mill Creek Phase 3 tunnel (MCT-3) is expected to be completed this year. It is one of the largest tunneling projects undertaken by the Northeast Ohio Regional Sewer District (NEORSD) to date. The tunnel horizon is situated within the Devonian Chagrin Shale rock formation at an average depth of 85 m (280 ft). The tunnel was excavated using a two-pass method. A full face, fully shielded, Robbins 7.2-m- (23.8-ft-) diameter tunnel boring machine (TBM) was used to excavate approximately 4,500 m (15,000 ft) of tunnel and facilitate installation of initial supports (first pass). The final lining (second pass) consists of 305-mm- (12-in.-) thick cast-in-place reinforced concrete and integral low flow channel. Seven shafts were constructed on the project. The excavation of the tunnel commenced at Shaft 14 and proceeded down grade to Shaft 9, the terminus shaft. Because of the presence of overbreak in the tunnel crown, measures were required to support the form and counteract the effects of buoyancy during concrete placement.

Jan 1, 2008