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By E H. O Meyer, K van Dyk

Fine powders normally exhibit, to a more or lesser extent, some ability to participate in dust explosions. Zinc dust as used in the extractive metallurgy of zinc, is not known to be a reactive powder in the industry. No evidence could be found in the literature where zinc dust was involved in an explosion or explosive type event. On 3 May 2002 an explosive type incident occurred at Zincor in Springs, South Africa, which led to a fatal accident. Given the history of relative benign behaviour of zinc powders under conditions conducive to dust explosions, it was decided to share the information of this incident with industry in an effort to prevent similar incidents. Therefore, the purpose of this paper is to describe the incident that occurred at Zincor, discuss the major findings, report on corrective actions, as well as publish the results of subsequent tests that were performed to determine the conditions under which zinc powder exhibits explosive characteristics.

Jan 1, 2005

By T Connor

Alkali emissions are one of the environmental challenges facing alumina refineries. Queensland Alumina Limited (QAL) is undertaking a number of initiatives to continuously improve its environmental performance. One of these is a program aimed at the reduction of alkali emissions. Alkali emissions originate from a number of sources (eg elevated open tanks), and its level depends on a number of process parameters/ mechanisms (ie splash filling, thermal currents in tanks, streams discharged from a pipe, tank temperatures, atomisation) and climatic conditions (eg wind speed and direction, rain, etc). Under normal operating conditions, there is a continuous low level of alkali emissions from the plant. Certain vessels within the plant have been identified as major contributors to this level of emission, while certain activities within the plant contribute to a temporary elevation (æspikeÆ) of alkali emissions. QAL developed a method using phenolphthalein-treated pads to measure emissions within and outside QAL boundaries. These provide no information about mass emission rates but are important for detecting if alkali material is present. Since mass emission rates are important for determining if improvements in emissions are made, QAL identified the need to design an improved sampling method. Following the development and implementation of a sampling and analysis method to monitor alkali emission concentrations, QAL is conducting a number of feasibility studies evaluating a range of alkali emission reduction options. The alkali measurement method will be used to track and demonstrate progress in this environmental initiative. This paper will discuss the measurement method and emission reduction options being evaluated.

Jan 1, 2005

By Steve Kral

Led by a surge in coal production and prices in recent years, Colorado’s mining industry is taking part in the same revival as others states and the world. Not too many years ago, the state’s industry was languishing in the same doldrums as the rest of the mining world. Ironic for a state whose history was based on mining. Now, however, Colorado’s mining can boast increased production in all commodities produced, along with prices that allowed companies to expand, increase work forces and post improved shareholder value. So there was a lot of optimism at the Colorado Mining Association’s (CMA) 107th National Western Mining Conference in February. The conference, held in Denver, attracted more than 500 attendees and 39 exhibitors. The theme was Colorado Mines the World.

Jan 1, 2005

Ongoing rockpass problems on mines within the South Africa region, prompted AngloGold Ashanti to embark on a risk assessment of major rockpasses. This commenced with the collection of relevant data to identify gaps in the available knowledge and identify existing problems. This was followed by an assessment of rockpass layouts to determine existing and potential interactions with other excavations. An initial risk assessment has been completed and the rockpasses have been ranked in terms of their risk profile. The lack of geological data and an easy and reliable method of surveying rockpasses have been identified as problem areas. Shortcoming is terms of rockpass management procedures have also been identified. Further work is required to quantify the risk in terms of probability of occurrence and consequences.

Jan 1, 2005

Improved roof control in high deformation tailgate environments has been achieved over the last decade through development of stiffer and increased capacity standing support products. æThe CanÆ is one such development, being a steel cylinder containing a weak cementitious fill, designed to essentially fold in upon itself whilst maintaining strength. A laboratory study to better define the relative load contributions of the steel cylinder and fill, the confining interaction between these components and most importantly, the potential impact of varying the steel and/or fill properties is described. This would enable the support engineer to ædial-upÆ the desired strength and stiffness properties and optimise the standing support design with respect to load capacity, stiffness, weight (handling) and cost. Design curves to optimise strength based on steel casing thickness, fill strength (confined and unconfined) and æCanÆ geometry were established. Scaled-down (one-third) samples were used in the test program and found to adequately reflect the loading behaviour of full-scale versions, thereby providing significantly greater scope for further product development at less expense compared with testing full-scale products.

Jan 1, 2005

By Jim Owens

The methodology of quarrying changed significantly in the Indiana limestone industry in the 60 years between Sept. 11, 1941 and Sept. 11, 2001. The former was the date of the Pentagon groundbreaking ceremony, while the latter was when the building was damaged by American Airlines Flight 77. So too, though to a lesser degree, did the machinery and methods used to fabricate the stone. The rededication ceremony on Sept. 11, 2002 marked the end of the Phoenix Project, as the rebuilding effort was named. The story of this remarkable project illustrates what the American construction(and Indiana limestone) industry can accomplish when working toward a common goal.

Jan 1, 2005

By Bill Elverman

Randy and Kenny Robison have visited every coal mine that would let them in the door, to survey the best mining practices. The brothers have spent nearly their entire lives working in coal operations. The Robison’s started out on lube and grease trucks and worked their way up to respected industry leaders in Alabama. The Robisons have owned MS&R since 1989. Since then, they have created a niche for themselves in providing coal for Alabama’s metallurgical coal market. A great deal of the knowledge the Robisons have amassed throughout the years has come from observing — taking note of what works and what does not. In early spring 2004, they commissioned a Komatsu America PC3000 Super Shovel. Outfitted with a backhoe attachment and a 16-m3 (21-cu yd) bucket, MS&R’s PC3000 is currently one of the largest mining excavators working in Alabama.

Jan 1, 2005

By D. W. Olson

Garnet has been used as a gemstone for centuries. However, garnet’s angular fractures, relatively high hardness and specific gravity, being chemically inert and non-toxic and free of crystalline silica, and its ability to be recycled make garnet ideal for many industrial applications. Garnet is the general name given to a group of

Jan 1, 2005

By G M. Evans, C M. Phan

This paper presents an analysis on the dynamic adsorption of frothers and collectors onto air bubbles in flotation. The analysis was carried out using the theory on the surfactant transfer by diffusion and adsorption. The bubble size was considered when solving the diffusion equation for the dynamic surface excess. The adsorption kinetics was modelled employing the Langmuir adsorption isotherm and its extension with the inclusion of the lateral interaction of the adsorbed molecules (the Frumkin adsorption isotherm). The numerical computation was applied to solve the governing equations. The dynamic adsorption of the surfactants was measured in terms of the dynamic surface tension for sodium dodecylbenzene sulfonate (SDBS) and Dowfroth 250, using pendant bubble tensiometry. The results show that for air bubbles with diameter of the order of 1 mm, the bubble size effect on the dynamic surface tension is small and the solution of the diffusion equation for a planar gas-liquid surface can be used to describe the dynamic adsorption onto the air bubbles. The experimental data obtained with SDBS were well described by the Frumkin adsorption isotherm and the molecular diffusion. The model description for the experimental data obtained with Dowfroth 250 required the kinetic equations. The paper is relevant for further analysis of the role of the adsorbed surfactants in the particle collection.

Jan 1, 2005

By WU Jian-hui

Keywords: metallic material, precursor synthesis, precipitation, nickel, fibrillar powder The composition and morphology of the precursor of fibrillar nanocrystalline nickel powder prepared by oxalate precipitation are characterized by XRD,IR and SEM analysis, and the effects of temperature, nickel concentration, pH, surfactant and drying process on the morphology and the dispersion of the precursor are investigated. By the experiment results, the fibrillar precursor is a complicated nickel salt. The precursor prepared in the of 60~70°C,0.6~0.8 mol/L nickel ion, pH=8.4~8.6 and with addition of PVP surfactant is well dispersive and in fiber form. The powder dried by azeotropic distillation is dispersive.

Jan 1, 2005

By John H. Raymer

Groundwater inflow into hard rock tunnels is strongly affected by recharge and drawdown of the water table. Previous analytical and empirical methods for estimating inflow have generally not accounted for these factors in an accurate or systematic way, resulting is wrong conclusions about inflow and the effects of the tunnel on the surrounding environment. This paper discusses these issues and provides some simple analytical equations to estimate inflow and water table drawdown around the tunnel. Examples from tunnels in the Atlanta area are provided.

Jan 1, 2005

By Thomas Schwind, Pamela S. Moran

For short tunnels, a reinforced cast-in-place lining is not economical and shotcreteis a logical substitution. In the past, reinforced shotcrete linings have been constructed with lattice girders and welded wire fabric. For the Russia Wharf Tunnel in Boston, MA, the Contractor, with the help of the Dr. G. Sauer Corporation offered the MBTA a VECP to substitute the reinforced cast-in-place concrete lining with a steel fiber reinforced shotcrete lining. The challenge was to adequately model the ductility of the steel fiber reinforced shotcrete and to test the shotcrete prior to and during construction to assure quality control. To our knowledge, this type of numerical simulation has not been used on any other tunnels in the US.

Jan 1, 2005

By Axel Nitschke, Josef Arnold

Bochum’s Underground Lot 306 was characterised by a confined site and unique tunnelling methods. A highly mechanized construction concept was developed to achieve high progress rates. Bespoke backup systems for muck disposal and material supply were used. For the first time in suburban tunnelling, wet shotcrete, batched onsite, was applied. A three-storey underground car park had to be undermined with only1.5 m of overburden and had to be lifted several times by “compensation grout in.” An existing operational two-lane metro tunnel was enlarged without any major impact on train operation.

Jan 1, 2005

By S Bourke, R Stone, B Hill

Since Jameson Cell flotation technology was first installed in a coal flotation application in 1988/89 at Newlands Coal Handling and Preparation Plant (CHPP) there have been fundamental improvements to its design which has led to its current status as the leading technology in Australia for fine coal flotation. These improvements, which include key hardware modifications, consist of the re-development of the orifice plate to produce considerable increase in wear life and reduction in power consumption for a given air entrainment and a significant increase in the amount of air that is entrained. Modifications to the downcomer allow maximisation of residence time and air entrainment while changes to the feed and air distribution system allows a reduction in installation cost and a reduction of solids ingress into the air line. Additionally, operational improvements such as the use of recycle to maintain constant flow to the cell feed are discussed. The recent installation at Hail Creek in the Bowen Basin, which consists of three B6000/20 Jameson Cells (6 m diameter bottom-fed distributor with 20 downcomers) will be reviewed as a case study. The latest design and operability of the cells are summarised and compared against one of the original designs at Riverside CHPP also in the Bowen Basin.

Jan 1, 2005

By H. A. Taylor

Graphite is elemental carbon that crystallizes in the hexagonal system as six-sided platelets. It occurs naturally and is mined. And it can be made artificially from petroleum coke in the form of shapes (electrodes) and powders. The market for most kinds of graphite in most end-uses was good in 2004. The 2005 graphite market looks positive. The major graphite prices, as given in Industrial Minerals, remained unchanged throughout the year. The preliminary 2004 U.S. Geological Survey (USGS) prices for natural graphite showed almost no change for crystalline flake. They were $600/t ($544/st) in 2004 and$622/t ($564/st) in 2003. Mexican amorphous graphite was almost unchanged at $150/t ($136/st) in 2004 from$152/t ($138/st) in 2003.

Jan 1, 2005

By Paul Grady, Martin Froehling, Curtis Mohns, Eliab Roman

"Since the idea of processing rock to unlock the valuable minerals inside was put into practice, efforts to improve production began. Methods have been learned that allow for operation in environments and under circumstances where it would not have been possible until now. All existing operations have experienced at least some form of productivity improvement measures. The objective is simple: generate more product of better quality in less time and at lower unit cost. Since the year 2000, various modifications have been made at the Kemess Concentrator in efforts to improve productivity. The following is a discussion of these modifications and their contributions to the success of the operation.INTRODUCTIONThe Kemess South Mine, a major producer of gold and copper, is located in north-central British Columbia. Kemess was brought into production in May 1998 by Royal Oak Mines with a modern mill controlled by a fully integrated Foxboro IA DCS system and employing 134 people. On February 11, 2000 Northgate Exploration Limited (now Northgate Minerals Corporation) acquired Kemess Mine from receivership. Since acquisition in 2000, Kemess has seen many accomplishments, including the reduction of costs by 40% site wide.The mill has a nameplate capacity of approximately 56,000 tonnes per day which is processed through a Metso (Svedala) 60” x 89” Primary Gyratory Crusher and then conveyed by a 60” conveyor to a stockpile with 48 hours of total storage capacity. The nominal minus 6” rock from the stockpile is fed to two parallel grinding circuits (A & B). Each section consists of a 10.4 m F x 4.7 m SAG mill with dual drive motors (4,480 kW apiece) discharging onto a 2.4 m x 7.3 m Metso (Svedala) single deck vibrating screen to remove the coarse material for recycle to the SAG mill by a Continental 45º high angle sandwich conveyor. Screen undersize is pumped along with ball mill discharge to a cyclopac consisting of twelve Krebs 66 cm F cyclones to classify flotation feed to a size of approximately 65% minus 200 mesh. Cyclone underflow feeds a Metso (Svedala) 6.8 m F x 11.0 m ball mill, also with dual drive motors (4,480 kW apiece). The primary grinding circuit has 35,840 kW available for grinding."

Jan 1, 2005

By Andrew Budek

"Analytical and experimental work has shown that achieving the full inelastic lateral capacity of a pile may require the formation of a plastic hinge below ground level, in the pile shaft. The confining action of soil about the pile shaft was further been shown to greatly enhance the ductility capacity of the pile. An experimental program was therefore undertaken to build in the effect of external confinement through the addition of a GFRP jacket to the subgrade plastic hinge region. Two piles were thus modified, and compared to an unjacketed pile in a test rig which simulated a subgrade moment pattern and soil confinement. The ductility achieved by the jacketed piles was found to be substantially lower than an unjacketed control specimen. Failure mode of the jacketed specimens was also undesirable, involving complete tendon rupture and sudden loss in capacity IntroductionSeismic loading of concrete pile shafts can result in a demand for inelastic response. In the case of a superstructure supported by a single pile (i.e., a pile-column forming a single-column bridge pier, in which there is no rotational restraint at the top of the pile}, a plastic hinge will form below grade, at a depth which varies with soil properties and above-grade height of the center of seismic mass.In the case of a superstructure supported by multiple piles, there is rotational restraint, and the connection will experience inelastic action first. However, development of the full lateral inelastic capacity of the pile may call for the formation of a second, subgrade plastic hinge (fig. 1 )."

Jan 1, 2005

By Lawrence M. Gochioco

One of the best kept technology secrets in U.S coalmining history involved a robust coal geophysics program used by a local coal company to detect and map various geologic anomalies and man-made structures ahead of mining for nearly 15 years. Several original mine plans were changed as a result of findings from two-dimensional (2D) and three-dimensional (3D) seismic data. They indicated the presence of geologic anomalies in reserve areas that could adversely impact future mine development and longwall production. By combining the surface seismic and exploratory drilling methods, the coal company learned how to properly leverage its risk by gathering a lot of useful subsurface information before making major commitments.

Jan 1, 2005

By Bart Bartholomew, Randall J. Essex

INTRODUCTION In June of 2004, at the North American Tunneling Conference in Atlanta, an all-day workshop was conducted to review the application of Geotechnical Baseline Reports (GBRs) for underground construction. The moderator for the program was Bart Bartholomew, former President of Fruin Colnon Construction Company. The program involved commentary by a panel of engineers, owners, contractors, and legal representatives within the North American tunneling industry, as well as an extended audience discussion. The panelists were: Peter Douglass, President, Peter Douglass, Inc. Randall Essex, Executive Vice President, Hatch Mott MacDonald Joseph Gildner, Deputy Director for Technical Services, Sound Transit Randall Hafer, Esq., Kilpatrick Stockton Robert Fitzgerald Esq., Watt, Tieder, Hoffer, & Fitzgerald Kirk Samuelson, Senior Vice President, Kiewit Construction Group DEVELOPMENT OF PROGRAM FORMAT The focus of the program was to assess the state of the practice in the preparation of GBRs, and to discuss improvements that could and should be made with regard to their preparation, interpretation, and application. The approach used to achieve this focus in the broadest possible way was unique, in that it involved the panelists’ preparation of the workshop format and materials months before the presentation of the workshop. First, each of the six panelists was selected by the moderator based on their reputation and involvement in their respective fields of expertise, taking care to maintain balance and contrast within the collective pool of talent assembled. Following selection and agreement to serve on the panel, each panelist was asked to independently submit to the moderator a list of the six most pressing issues involving GBRs that they each frequently encountered in their individual professional experience. Each was asked to rank their issues in descending order of perceived importance. This process resulting in a pool of thirty-six potential or “candidate” issues for use in the workshop program. Contrary to the moderator’s expectations, there was surprisingly little duplication among the thirty-six issues submitted.

Jan 1, 2005

By Robert J. F. Goodfellow, William A. T. Meakin, Kevin Clarke, Eric Cole

INTRODUCTION New York City Water Supply—Background and History Since the 1840s New York City has been developing the largest, and perhaps, the best urban water supply and distribution system in the world in terms of quality and reliability. One of the engineering marvels of the modern world, the New York City water supply and distribution system serves a population of almost nine million, including residents in nearby Westchester, Putnam, Ulster, and Orange Counties of New York State. The average daily supplies presently are running at almost 60 m3/sec(about 1,350 million gallons per day). The watershed for the New York City water supply system, under the jurisdiction of the New York City Department of Environmental Protection (NYCDEP), consists of19 reservoirs and three controlled lakes, and covers an area of approximately5,000 square kilometers (about 2,000 square miles) north of New York City. The watershed total available storage capacity is about two billion cubic meters (560 billion gallons) and is divided into three reservoir systems: the Catskill and Delaware watersheds located West of the Hudson River; and the Croton watershed, located east of the Hudson River, see Figure 1. The first element of the system, the Croton Aqueduct, started operations in 1842.Through several updates and expansions, the present-day Croton system was in place by 1911, providing a potential maximum supply of about 15 m3/s (about 340 mgd). The system includes ten reservoirs and three controlled lakes. In the late 1800s, with the tremendous growth of the City, New York City water engineers began to look for additional sources. Between 1907 and 1929, the City acquired water rights and constructed a new 148 km (92 miles) Catskill aqueduct to convey water from the Ashokan Reservoir to the City. The Catskill system also included the construction of the Kensico and Hillview Reservoirs just north of the City,

Jan 1, 2005