Search Documents

By B. Hart, D. J. Miller, J. T. Francis, M. C. Biesinger, Smart. R. St. C.

Diagnosis of the surface chemical factors playing a part in flotation separation of a valuable sulfide phase requires measurement of the hydrophobic and hydrophilic species that are statistically different between the concentrate and tail streams. Time of flight secondary ion mass spectrometry (ToF-SIMS) can be used to identify sufficient particles of a specific mineral phase for reliable statistics determining a mean value for each species with 95% confidence intervals (1). Using the region of interest (ROI) facility in the Tof-SIMS software, a mass spectrum from each particle, at 1-2 monolayer sensitivity, is recorded and stored. This analysis is reported for a chalcopyrite / pyrite / sphalerite mineral mixture conditioned at pH 9 for 20 minutes in order to study transfer of copper from chalcopyrite via solution to the other two mineral surfaces since this mechanism can be responsible for their inadvertent flotation in copper recovery. Analysis from mineral selection based on specific ToF-SIMS signals (eg. Pb, Zn, Cu, Fe, Fe/Cu) indicated no statistical difference in the copper intensities on pyrite and sphalerite after this conditioning. Principal component analysis (PCA) of the ToF-SIMS imaging data identifies combinations of factors strongly correlated (positively or negatively) in images or spectra from mass spectra recorded at each of 256x256 pixels in a selected area of particles. PCA is a better method of selecting minerals due to multi-variable recognition. It has clearly separated a statistical difference in copper intensities between the sphalerite and pyrite phases. The method has been extended to samples from an operating plant again with excellent phase recognition and diagnostic surface chemistry.

Jan 1, 2004

By Jeffrey M. Taylor, Arturo Ressi di Cervia

"Construction of the drilled shafts for the Brightman Street Bridge Replacement Project were not only challenging due to working over the water but were also challenged by changed soil conditions, concurrent work being performed by an adjacent contractor on the same project, environmental restrictions and severe winter conditions. A total of 36 x 8 foot (2.44m) diameter drilled shafts with 7.5 foot (2.31m) rock sockets were installed for the East and West bascule piers. This project also included Osterberg Cell load testing on two production drilled shafts at both the East and West bascule piers. The results from the load test program were used to fine tune the design of the drilled shaft rock sockets. From a constructability standpoint the reverse circulation drilling method with a pile top drill rig proved to be an excellent choice for drilling the overburden and rock sockets of the large diameter deep drilled shafts. INTRODUCTIONThe replacement Brightman Street Bridge spans the Taunton River between Fall River and Somerset in Massachusetts.The new crossing is located approximately 1500 feet (450m) upstream from the existing Brightman Street Bridge, which was built in 1908. The new mainline bridge includes nine spans totaling 1725 feet (525m). A bascule type moveable span will be located in the middle of the Taunton River and provide a 200 foot (61m) open channel centered about the 400 foot (122m) navigational channel. The bascule span, which has a span length of 409 feet (124.7m), will be a trunnion-type four leaf structure with a solid deck. A site plan is shown in Figure 1 Contract 3, which includes construction of the foundations for the East and West bascule piers, was bid on December 19, 2000 and was awarded to Modern Continental Construction Company (MCC) on January 24, 2001. MCC in turn awarded the subcontract for the installation of the drilled shafts to TREVIICOS Corporation, which started mobilizing in June of 2001.The scope of work for the drilled shafts of Contract 3 consisted in installing 18 drilled shafts in three rows on each side of the river to support the bascule piers located in the middle of the Taunton River.The foundation plan for the bascule span is shown in Figure 2."

Jan 1, 2004

Jan 1, 2004

By Shawn A. Cefalu, Matthew J. M. Krane, Kent J. VanEvery

"Segregation during electroslag remelting (ESR) of a nickel-chromium-molybdenum alloy (Ni-8 wt% Cr-25 wt% Mo) has been modeled. Features of the model include species transport and AC electromagnetic effects coupled with fluid flow, heat transfer, and solidification. The effect of varying ingot diameter and melt rate, on macrosegregation patterns, local solidification time, and liquid pool profiles obtained from this model are demonstrated. The results show that the macrosegregation in the ingots correlates to the filling velocity.IntroductionElectroslag remelting (ESR) is a secondary melting process used to refine the chemical composition and the microstructure of metals. Macrosegregation of solute elements causes defects in ESR ingots, including freckles and the maldistribution of phases. These defects are not correctable through heat treatment due to the large length scales over which they occur. However, the frequency and distribution of these defects may be minimized, or even prevented, through process control based on an understanding of the conditions that lead to their formation.In the past, studies have been conducted on the effect of the process parameters on the shape of the melt pool and the thickness of the mushy zone [1-7]. In these studies, the shape of the liquid pool is determined by consideration of the heat and fluid flow induced by electromagnetic (Lorentz) force and thermal buoyancy. The transport of solute and the resultant solutal buoyancy effects were not considered in these macroscopic models. Defect formation is tied to formation of secondary phases (e.g., freckling and white spots in nickel superalloys) [5,8]. In cases where secondary phase formation is calculated (e.g., [6]), phase fractions are determined using a micro-scale model given the local solidification time (LST) and local thermal history from the macroscale model.Using the local thermal history from the macroscopic transport model to predict microstructure increases the importance of the accuracy of those results. This investigation models the macrosegregation of molybdenum during the ESR of a Ni-Cr-Mo alloy. The effect of macrosegregation on pool shape and depth is demonstrated, along with its effect on the local solidification time. By comparing the relative effects of the melt rate and ingot radius, a better understanding of the factors that affect macrosegregation, and ultimately secondary phase formation may be obtained."

Jan 1, 2004

By M R. Davidson, M P. Schwarz

A model for column bioleaching is investigated to identify and understand aspects of bacteria in bioleaching applications, which have implications in heap bioleaching operations. The model is used to simulate scenarios that would otherwise be time consuming to perform experimentally. This study uses a model of bacterial transport and attachment/detachment to ore particles, with a bioleaching model for the depletion of a copper-sulfide, also accounting for liquid and gas flow and gas/liquid oxygen mass transfer. The model includes aspects such as oxygen and ferrous ion consumption, coupled with leaching of a copper-sulfide via the shrinking core model. The model is used to investigate how the rate of leaching is affected by the bacterial concentration in the columns, by the bacterial regeneration of the leaching oxidant ferric ions. The model is also used to assess the impact of oxygen limitation and inoculation method on the copper leaching. Some comparison of the model with experimental data will be shown.

Jan 1, 2004

By D. Lunt

Telfer bulk concentrates typically contain 8% chalcopyrite, 8% chalcocite, 45% pyrite and 80-120 g/t gold. Although very high copper and gold recoveries can be obtained by subjecting the concentrate to a "conventional" high temperature pressure oxidation step followed by copper recovery by solvent extraction and electrowinning, and cyanidation of the leach residue for gold recovery, the cost of lime required for neutralisation and power for oxygen generation was such that the process was uneconomic in terms of operating costs. The challenge therefore was to develop an alternative flowsheet that maximised copper and gold recovery in which the reagent costs were commercially attractive. An additional objective was to reduce the capital cost so that the overall NPV and IRR values would enhance the economic viability of the total project. Following a series of batch and locked cycle testwork programs, supported by Metsim modelling, it was established that the same high levels of overall copper and gold recoveries can be obtained by use of a novel two-stage split leaching circuit in which the chalcocite component is leached in a low temperature (90-110°C) circuit with the chalcopyrite component treated in a high temperature (220-250°C) circuit. This split circuit has a number of advantages, including minimising the required capacity of the high temperature autoclave, as well as reducing the overall lime consumption and simplifying the total process water balance. The paper outlines the basis for the development of the flowsheet and discusses the integration of the leaching stages into the overall circuit.

Jan 1, 2004

By C. C. Russelll, V. T. McLemore

The Metals Mining Sector of the Acid Drainage Technology Initiative (ADTI-MMS) addresses technical drainage-quality issues related to metal mining and related metallurgical operations, for future and active mines, as well as, for historical mines and mining districts. One of the first projects of ADTI-MMS is to develop a handbook describing the best sampling, monitoring, predicting, mitigating, and modeling of drainage from metal mines, pit lakes and related metallurgical facilities based upon current scientific and engineering practices. One of the important aspects of planning a new mine in today’s regulatory environment is the philosophy of designing a new or existing mine or expansion of operations for ultimate closure. The holistic philosophy taken in the ADTI-MMS handbook maintains that sampling and monitoring programs should be designed to take into account all aspects of the mine-life cycle. Data required for the closure of the operation are obtained throughout the mine-life cycle, from exploration through post-closure.

Jan 1, 2004

By J. B. Rubenstein

This work demonstrates the feasibility of using confocal surface profilometry to measure and characterize wear of graphite anode surfaces. This method was tested using anode samples that were electrolyzed for 24 hours in a laboratory-scale magnesium cell with a high oxide molten salt electrolyte. The oxide produced accelerated wear on anodes designed for low oxide electrolytes. Contour maps, which are effective at displaying non-uniform wear, and total graphite consumption values were generated from the collected surface coordinates. Along with both qualitative and quantitative analysis capabilities, this measurement system was shown to have a fine resolution and a low detection limit.

Jan 1, 2004

By J M. Santini, I C. A Streimann

Arsenic is a naturally occurring element in the environment and is toxic to biological systems. Arsenic can exist in the environment in the following redox states, arsenite (+3), arsenate (+5), arsine (-3) and elemental (0) (Oremland and Stolz, 2003). Arsenic is released into the environment by natural and anthropogenic activities such as rock weathering and ore mining, respectively. Such activities result in the release of the soluble inorganic arsenic oxyanions, arsenite and arsenate. The redox state of arsenic in the environment is influenced by a number of factors including, redox potential, pH and microorganisms (Irgolic et al, 1977; Genc-Fuhrman, Tjell and McConchie, 2004). Recently, the ability of microorganisms to influence the cycling of arsenic in the environment has attracted much attention. Microorganisms that can oxidise arsenite and reduce arsenate have been isolated and the mechanisms of arsenic metabolism are currently being investigated. The differences between arsenic resistance and arsenic metabolism are being revealed. The role of microorganisms in the release of arsenic into the environment is of particular importance with arsenic contamination of waters causing the death of millions of people worldwide, due to the consumption of contaminated water (Vasken Aposhian et al, 2003; Islam et al, 2004).

Jan 1, 2004

By Dennis J. Kemp

Laterite projects are found in the tropical and sub-tropical regions of the world. As a result severe meteorological situations accompany such projects, often in regions of high seismic activity and political uncertainty. Frequently, socio-economic development supported by political interest is a major driver for development, while environmental protection imposes numerous stresses on the project. This paper will review and examine the many social, environmental, technical and financial issues that a mining and extraction process is subject to during development. The options that must be evaluated will be discussed in the context of sustainable development. Issues of project standards and cultural impact through to long-term issues such as greenhouse gasses and climate change will be assessed in redirecting project environmental norms. Although a rationale for sustainable project can be developed many long- term uncertainties around issues remain. Keywords: sustainable development, communities, social issues, standards, energy, waste management, consultation, agreements

Jan 1, 2004

By Mustapha Zergoun

This paper presents the results of load tests to assess the vertical load carrying capacity of concrete expanded base piles, or pressure injected footings, for various projects located near Vancouver, British Columbia, Canada. The site subsurface conditions and load test methods are described for the Vancouver International Airport site and the test results are reviewed under both compression and tension loading conditions. The pile load tests at Vancouver International Airport are compared to load tests at other sites near Vancouver. The pile load test results are reviewed with respect to available methods of estimating the vertical capacity of this type of piles. The effect of ground improvement by densification on the load test results is considered. The limitations of tension load tests on single piles with respect to uplift resistance of pile groups under seismic conditions are pointed out. Recommendations are proposed regarding pile load test methodology to estimate ultimate vertical load carrying capacity of plies for limit state design.

Jan 1, 2004

By W. Pietsch

For a number of reasons, solids entering and leaving facilities for the treatment of minerals are becoming increasingly finer. Such materials pose problems throughout processing. Solids featuring small particle sizes tend to dusting, result in losses and segregation, exhibit various storage, transportation, and metering problems, and fine particulate effluents can not be easily captured, used and/or recycled. Sustainable mineral processing must minimize the exploitation of natural resources and avoid the need for disposal of wastes. The first requires the use of lower quality raw materials and upgrading, which typically results in the production of fine grained concentrates, and the latter encourages the recycling of wastes and byproducts or efforts to investigate them as sources for secondary raw materials or other beneficial applications. To overcome the difficulties associated with fine particulate solids, size enlargement by agglomeration is necessary. The resulting products have free flow characteristics, do no longer dust or segregate, and are sized and shaped as required for optimum processing. In addition, agglomerated materials may be engineered to feature desirable structure, composition, and a number of related, improved properties. Such engineering may be applied for the modification of fine run-of-mine and up-graded minerals as well as the production of secondary raw materials from by-products or wastes. By the interdisciplinary application of size enlargement by agglomeration waste-free processing of minerals becomes feasible.

Jan 1, 2004

By J. R. Kiji

The Cerro Matoso S.A. mine and smelter, in the Cordoba lowlands of northwestern Colombia, consist of a dedicated laterite nickel mine, ore blending, drying and an RKEF process to produce high-quality ferronickel. At a project investment of $400M, first production of ferronickel was in September 1982, and in its inaugural year CMSA produced 6,150 tons of contained Ni from a mined ore grade of 3.2% Ni. Initial operational difficulties resulted in a number of furnace run-outs, which impacted ramp up to design ore throughput of 128 dry t/h Since then CMSA has steadily incorporated process improvements and initiatives to take the single line operation to an ore throughput of 175 dry t/h. A second 175 dry t/h line was added in 2001 (investment of US$ 300M) to consolidate CMSA as one of the world's lowest cost Ni producers with an installed annual production capacity of 50-55,000 tons Ni. The most recent addition is commissioning of Phase I of an ore-upgrading project to counteract the effect of declining ore grades. Keywords: Laterite, ferronickel, pyrometallurgy, smelter.

Jan 1, 2004

By S. Hoskins, S. Chiovelli

"The annual budget for the repair and maintenance of equipment at Syncrude Canada Ltd. is in excess of $450 million. Of this amount, a significant portion can be attributed to the loss of material on various pieces of equipment throughout the operation. In order to effectively battle the different wear and corrosion mechanisms that lead to material loss, it is important to understand how materials behave in the environments in which they are used. Through the work carried out at Syncrude, and work conducted with various external collaborators, significant improvements in both equipment reliability and productivity have been achieved. This paper will review some recent field trials where materials research has demonstrated the potential for significant improvements in equipment run life and reduced maintenance costs. These field trials will demonstrate the need for understanding the interaction between various damage mechanisms and the materials used in different services. The paper will also discuss current areas of focus along with future directions for further work. IntroductionSyncrude Canada Ltd, located in northern Alberta, Canada, operates a mining, extraction, and upgrading facility that removes bitumen from oil sand to produce synthetic crude oil. Oil sand is mined from the orebody using conventional open pit mining techniques. Recently, the mining scheme has changed from a dragline/bucketwheel/conveyor system to a shovel/truck/crusher/hydrotransport operation as depicted in Figure 1. Since the start of production in 1978, the identification, development and application of wear protection has been an ongoing challenge due to the abrasive nature of the oil sands and the massive volumes of materials that are moved. The use of various materials and application processes along with component design modifications has resulted in significant improvements in both productivity and reliability (Adamic et al., 1995; Llewellyn, 1996, 1997; Anderson et al., 1998; Chiovelli et al., 1998).In an effort to continuously improve the operation, Syncrude has been quick to adopt new wear technologies. As seen in Figure 2, since the start of operation, a variety of materials have been used to increase wear performance and ultimately equipment reliability and availability. Although Figure 2 does not show a time axis, the bottom axis may also be used to represent a time progression for the predominate use of these materials at Syncrude. Tungsten carbide metal matrix composite (WC-MMC) overlays are currently the materials of choice for most of Syncrude’s critical production applications. Metal matrix composite overlay technology has potential for significant improvements and Syncrude is actively working with powder consumable manufacturers to advance this technology."

Jan 1, 2004

By A J. Minns

This paper addresses the question: how can the minerals industry remain viable; viable in the sense that we are able to access land for exploration and discovery, we are able to develop and operate mines (and processing plants) safely and profitably and we are able to close operations in a responsible manner, so that modified landscapes are restored to acceptable community standards?Many of the answers to this question can be addressed through the theme of this conference û that of eco-efficiency. The eco-efficiency concept is very useful, since it does help to translate principles of sustainability into business value at the operational level. To provide some context to how this can be achieved, the paper discusses what is happening at the international level, outlines some key industry initiatives within Australia and then discusses what work is being done within companies.

Jan 1, 2004

Organisations are starting to develop processes for achieving sustainability principles they have defined for their organisation. The foundation for these principles is now well accepted. The definition of a sustainability framework is a good starting point for any project. The delivery of the framework requires the organisation to think differently about how project objectives can be met. New tools are becoming available to help achieve the sustainability outcomes for the projects. This paper will examine the project building blocks that are necessary to ensure the sustainability framework can be achieved for the project. These include new approaches to decision-making processes and evaluation tools and when to apply them. An integrated approach with shared expertise to project delivery, which is applicable to the whole supply chain, will be discussed. This will cover sustainability procurement, integrated waste management, cleaner production and eco-efficiency, sustainable products and disposal. A project toolkit will be presented and some key project tools identified. The need for management support in undertaking these new approaches is critical, as is the need to develop partnerships and cooperative management to facilitate delivery.

Jan 1, 2004

By R. Boom

Corus Umuiden, formerly Hoogovens, was the first steel plant in Europe after Voest to introduce oxygen steelmaking. In the decision-making process contacts with Dofasco in Canada about the production of formability steel grades were crucial. In developing oxygen (LD-) steelmaking high liquid steel output rates had to be combined with accurate process control. For ingot casting static models with input control and sampling during interrupted blowing were sufficient to deliver liquid steel within the required carbon, phosphorus, sulphur and temperature windows. Computers were introduced to perform the complicated charge calculations. Continuous casting called for strict control of composition and temperature at process end point and made predictable timing crucial. Dynamic control was introduced based upon sub lance measurements and waste gas analysis. Reliable disposable measurement sensors were developed in a concerted international action. Dissolved oxygen at blow end deteriorated the quality of low carbon aluminium killed steel grades. Blowing gases through the converter bottom improved process kinetics, resulting in lower carbon-oxygen products, yield increase and better phosphorus removal and generated new families of hybrid blowing processes. Introduction of secondary metallurgy facilities such as argon stirring stations, vacuum degassers and ladle furnaces relieved the demands for strict BOF end point control. Desulphurisation of hot metal became standard practice. In regions with scrap shortage hot metal desiliconisation followed by dephosphorisation, was introduced in the blast furnace cast house and hot metal transfer ladles. Later redundant converter vessels were used for pre-treatment, resulting in a two-stage process. The fundamentals of oxygen steelmaking are described and a vision on the future is presented.

Jan 1, 2004

By T Clemens, D Trumm

Adopting environmentally acceptable practices in New Zealand is a crucial requirement for mineral wealth development. Recent planned expansions in the coal and gold industry have increasingly placed mining in the media spotlight. A lack of appropriate standard environmental guidelines has resulted in inconsistent responses and assessments of current and proposed mines. These inconsistencies have lead to delays in decisions on developing economic mineral deposits that may have only minor short-term impacts, and have also allowed unacceptable environmental management practices to continue elsewhere. A research collaboration between CRL Energy, Landcare Research, University of Canterbury and University of Otago aims to provide regulator groups and the mining industry with a unified approach to the requirements of the Resource Management Act 1991,the legislation that largely drives the nationÆs environmental policies and guidelines. The tangible outcome of this research program will be water quality and impact management guidelines integrated into a decision-making framework. The result of this unification will assist in the development of viable mineral deposits and minimise environmental impacts. The framework will be derived from a synthesis of three objectives. Objective 1 identifies potential water quality impact. This objective is based on a targeted geochemical study of the lithology and waterways of the West Coast and Southland regions. Objective 2 categorises the degree of impacts on the ecology of receiving aquatic ecosystems and determines the processes that drive aquatic ecosystem recovery. Objective 3 identifies best strategies to sufficiently manage impacted ecosystems, and to prevent future unacceptable impacts. Wide consultation with representatives of the mining industry and regulator groups will occur frequently during the development stages of the framework. It is anticipated that this multidisciplinary approach will provide a robust and coherent, standardised system that will assist in achieving industry and environmental targets.

Jan 1, 2004

By S G. Gatehouse

Extensive gold mining activity û dominantly alluvial û has taken place in the Sofala-Wattle Flat district since the 1850s.This work will have located most, if not all, of the visible sources for the gold in current stream systems.Also, there are many gold bearing elevated Tertiary alluvial terraces in the district which may confuse possible gold signals from primary hard rock sources in the streams.Associated element signatures eg As and other chalcophiles, will discriminate non-alluvial signatures but will not necessarily distinguish non gold bearing mineralisation.Both trace elements and conventional gold analyses will dominantly re-identify known occurrences. Conventional BCL sampling is considered misleading as experience from the Oberon area to the south of Sofala demonstrated that BCL sampling was very sensitive û perhaps too sensitive.All occurrences û major or minor û of gold will be detected (Gatehouse, 1992). To improve on BCL sampling, a small, -120# sample with selective duplication was recommended to screen coarse-grained gold anomalism and a program of sampling covering an area thought to be prospective was enacted.Samples returning anomalous Au were analysed in duplicate and if the results demonstrated reproducibility, indicating fine gold only, the sample site was assigned a high priority.It was found that most of the reproducible samples clustered in one area û Spring Gully. The results of this sampling program led to immediate identification and, ultimately, the successful delineation of the Spring Gully gold deposit near Wattle Flat.

Jan 1, 2004

By M Stewart, J Petrie, L Basson

This paper explores tools which have the potential to promote and assess the formation of partnerships between the minerals and energy industries to enhance the economic, environmentally responsible and socially acceptable use of energy. There is a need to look at energy provision and energy services in an integrated manner with key drivers for economic development û both locally and regionally. The minerals sector will remain highly significant to regional economic development in a number of globally significant regions in the medium term. Furthermore, mining, minerals and metalsÆ projects are both consumers and, in some cases (potential), generators of large amounts of energy (electricity included). It is therefore appropriate to focus on the promotion of partnerships between energy providers and the minerals sector which seek to improve resource efficiency within the combined minerals/energy envelope, guided by the tenets of Sustainability.Whilst there has been considerable development of systems analysis tools in recent years to address this sort of æcomplex systemsÆ analysis (Life Cycle Management, Cleaner Production and Industrial Ecology arguments for example), there is no effective roadmap available to decision makers to guide the selection and exploitation of these tools in different contexts. Our previous work developed a Decision Support Framework (DSF) which provides some guidance here, but only within the context of coal-based power generation. The DSF employs the tools of Multi Criteria Decision Analysis (MCDA), within which trade-offs between competing objectives are explored in such a way that alternatives can be compared without necessarily reducing all the different cost and benefits to a common basis (eg a monetary basis). Even if the existing DSF is extended to include all aspects of supply-side management, it is still lacking the necessary tools to analyse energy providers as dynamic network partners within minerals projects (or indeed any resource or manufacturing sector). New models are required for this, which firstly, seek to characterise such network structures, and secondly, enable the application of the necessary analytic tools to exploit these partnerships and networks for optimal performance.This paper explores the development of such an integrated set of network analysis tools, and their relation to the DSF. Due consideration is given to the choice of the attributes needed to characterise partnership linkages and network integrity (eg security of supply of electricity), and the efficiency of material transformations within any node of the network (as a function of energy consumption), and the impact that this has on the viability of other linkages (eg due to reduced availability of raw materials). We discuss how these perspectives help shape the form of objectives to be considered by MCDA.

Jan 1, 2004