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By C. Keefe, O&apos

Measurements of the quantity of entrained air within processes have challenged instrumentation developers for years. This is particularly true in the unique and demanding operating environment and applications seen in minerals processing. In minerals processing applications, entrained air plays a role in errors seen within nuclear density gauge measurements and in pumping efficiency. It is also the major component of flotation processes. The measurement of the quantity of entrained air, known as the gas void fraction, can now be performed from the outside of a process pipe through CiDRA?s patented passive sonar array-based technology. Within column cells, the need for a robust, no maintenance, accurate means of measuring the entrained air, known as gas holdup, has resulted in a submersible version of this technology. CiDRA?s meter technology calculates the gas void fraction by first measuring the speed at which naturally occurring sound in the process slurry propagates past an axial array of sensors. These sensors are incorporated in a band that is wrapped around the outside of the pipe, resulting in no process downtimes for installation and unprecedented reliability. A known relationship between this speed of sound and the entrained air captured in the form of bubbles within the slurry is then applied in CiDRA?s meter to calculate the gas void fraction. This paper will present the measurement technology, its operation, its calibration and its application in a variety of gas void fraction and gas holdup measurement situations such as pumping efficiencies, hydrocyclone operation, external sparging, and column cells.

Jan 1, 2008

By A. Barba, M. P. Gómez, F. Puertas, M. Palacios, M. F. Gazulla, S. Martínez-Ramírez, I. García-Díaz

"The present study explores the reactivity and burnability of cement raw mixes containing fired red or white ceramic tile wastes or combinations of the two as alternative raw materials. The results showed that the new raw mixes containing these wastes are technically viable. The reactivity and burnability of the new raw mixes have been evaluated; confirming very good results when the particle size of wastes was less than 90 µm. The chemical and mineralogical compositions of the new clinkers were comparable to clinker manufactured with conventional raw materials. The mix of red and white ceramic tile waste was found to perform as well or better than each type of waste separately, a promising indication that separation of the two would be unnecessary for these purposes.IntroductionPortland cement clinker production consumes large amounts of energy (850 kcal/kg clinker) and has a considerable environmental impact. This involves massive quarrying for raw materials (limestone, clay etc), as it takes 1.7 tonnes to produce one tonne of clinker, as well as the emission of greenhouse and other gases (NOx, SO2, CO2) into the atmosphere. Around 850 kg of CO2 are emitted per tonne of clinker produced.The cement industry is looking for solutions to these problems, to attain sustainability and comply with the Kyoto Protocol commitments [1,2]. For that reason, experimental ways are being explored to develop cements whose manufacture is less energy-intensive, less damaging to the surrounding environment and with lower tendency to emit polluting gas. One of the reach this objective is the use of industrial waste and by-products as alternative materials for cement manufacture. Such alternative materials may partially replace fuel [3,4], conventional raw materials [5-8] or clinker in the final composition of the cement [9]."

Jan 1, 2008

By M. Pérez-Tello

A mathematical model to represent the expansion and fragmentation of copper matte particles oxidized under flash converting conditions is presented. The model assumes that the particles are initially nonporous, have a constant mass prior to fragmentation and travel at a constant velocity throughout the reaction chamber. The model requires the specification of the following five parameters: the particle expansion rate, a fragmentation diameter factor, a fragmentation size distribution parameter and the fractions of the finest and the coarsest particles in the feed that undergo fragmentation. The model predictions show good agreement with the experimental data collected in a laboratory furnace over a wide range of experimental conditions. The evolution of the size distribution of the particles along the reactor length was computed, and the model parameters were correlated with the experimental operating variables. Model predictions indicate that particle residence time is an important factor in the generation of dust. The presence of two maxima in the particle density function may be attributed to turbulent conditions prevailing in the furnace, which cause particles to follow different trajectories within the furnace even if they are injected at the same location.

Jan 1, 2008

Process mineralogy is an inter-discipline in the fields of mineralogy and mineral processing. As a predicting and trouble-shooting tool, process mineralogy helps address all mineralogical issues and problems related to mineral processing. It provides useful information on process design and optimisation, flow sheet development and cost reduction. As more and more complex and refractory ores are being discovered and processed, it is believed that process mineralogy will gain more attention and play a more important role in process design and optimisation. This paper will first discuss the scope of process mineralogy and mineralogical factors that may affect mineral processing of various ores, and then focuses on the application of process mineralogy in process design and optimisation through case studies.

Jan 1, 2008

By L. Parthasarathy, S. K. Pan, M. P. Srivastava

"Total iron ore reserves in India, as reported by the Indian Bureau of mines, are 23.6 billion tons. Hematite iron ore reserves constitute about 45 % of the total reserve. If we go by the National Steel Policy-2005 projections, India’s supply of hematite iron ore would not last more than 40 years. Laboratory investigations were carried out for the development of a process flow sheet for treating low grade as well as Banded Hematite Quartzite (BHQ) iron ore. The purpose of these investigations was to aim for better resource utilization.Beneficiation studies were conducted on samples of low grade and siliceous iron ore from the Dalli mines, a captive mine of the Bhilai Steel Plant and BHQ ore from Southern states of India. The process flowsheet, developed for upgrading of low grade iron ore, incorporates wet screening of the ore at 0.5 mm, followed by grinding of the +0.5 mm fraction to below 0.5 mm. The whole –0.5 mm fraction, after grinding, was treated in a conventional hydro-cyclone and stub cyclone followed by treatment in Wet High Intensity Magnetic Separator (WHIMS). This resulted in a concentrate product having >66% Fe content from a feed containing 55.5% Fe with an iron recovery of 48 %. The process flowsheet developed for treating BHQ ore in the laboratory resulted in an increase in iron grade in the concentrate from 43.4 to 61.3 Fe % with a yield of 51.7 % .INTRODUCTIONThe classification of Indian iron ore resources have been made compatible with United Nations Framework Classification (UNFC), which is more scientific and has been adopted in most countries in the world. Iron ore reserves and resources estimated using the UNFC classification system, as of April 01,2000 are about 12,906 million tons of hematite ore and 10,628 million tons of magnetite ore. The Indian Bureau of Mines (IBM) has given a breakdown of these reserves by designation as either lumps or fines of hematite iron ore (Table 1). The percentage of the reserves reported lumps and fines are 42 and 34% of the total reserves respectively. High grade iron ore is less than 10% of the total reserve."

Jan 1, 2008

By A. K. Mukherjee

The roles of pulsating mechanisms such as the amplitude and frequency of the jig cycle are well established in jigging. Also well established are the roles of the size ratio and the volume fraction of the feed. In iron ore beneficiation plants, these process parameters are optimized to achieve the highest efficiency. However, the role of one of the more important feed characteristics, the liberation characteristic of the feed, has not been studied in detail. Evaluation of the liberation characteristics is difficult because the required washability test is not viable for iron ore feed. In this paper, a new method is proposed in which the liberation characteristics are measured through a separation efficiency value. In the new evaluation method, jigging parameters such as amplitude and frequency of the jig cycle are optimized from the fundamental understanding of the process dynamics and feed characteristics such as size distribution. Then, feeds with different liberation characteristics are tested to evaluate the liberation characteristics of feed in jigging.

Jan 1, 2008

Nickel laterite HPAL circuits are known for their complexity and have presented a large number of challenges to process engineers worldwide. An attitude commonly encountered by the author is that the beneficiation of the ore is relatively simple and that the difficult problems are in the realms of hydrometallurgy. On a number of occasions beneficiation has become the 'poor cousin' in the process design phase. Another common theme is that significant difficulties are encountered when beneficiation circuits are started up, invariably slowing the ramp-up of the remainder of the circuit. In some cases the problems impact on throughput for a long period and can require major rectification capital. The HPAL Ni laterite projects encountered each have their own set of beneficiation problems that need to be understood before an appropriate circuit can be designed. This paper will discuss a range of design issues including geometallurgy, ore characterisation through laboratory testing, the application of appropriate sizing and analytical procedures, the selection of appropriate unit operations, materials handling of plant feed and products and setting meaningful plant design requirements.

Jan 1, 2008

By A. Amiel

Tarkwa Gold Mine is owned by Gold Fields Ghana, IAMGOLD and the Government of the Republic of Ghana in a 71%, 19% and 10% ratio. The mine is operated by Gold Fields Ghana. This large, low-grade, open pit, gold mining operation is located in Tarkwa, in the Western Region of Ghana, approximately 320 kilometres by road, west of Accra, the capital of Ghana, West Africa. In the Financial year ended June 2007, the operation mined a total of 108 million tons of which 22 million tons was ore. The mined ore is processed through three gyratory crushers supplying two heap leach pads (north and south) and a carbon-in-leach (CIL) plant. Before the 6 Sigma project commenced, the current fragmentation was resulting in sub-optimal feed size to these crushers. It was decided to use 6 Sigma methodology to improve the fragmentation. A defect was defined as a fragmentation analysis indicating less than 95% passing 750 mm. The objective was to improve fragmentation in order to achieve a constant throughput to the north heap leach crusher of 1500 t/h, a 5% increase in pit loading efficiency and a 50% decrease in rock breaker hours, equipment damage costs and in-pit sheeting costs respectively. However, this was not to be achieved at the expense of grade control as Tarkwa is exploiting a low grade, high volume deposit and therefore ore dilution must be kept to a minimum. This paper is intended to take the reader through the various 6 Sigma phases of the project (define?measure?analyse ?improve?control), which have resulted in a 10% reduction in loading times, of which half has been attributed to improved fragmentation, as well as a substantial increase in blasted stocks. The focus has been on both drilling and blasting parameters as both processes had to be taken into account. These parameters are technical but personnel factors were also identified and dealt with as they arose. In order to measure the impact of any change in the process parameters on the fragmentation size distribution, cameras have been acquired. One has been installed looking into the bowl of the north crusher and the other one was dedicated to field observation, of individual blasts. Both are used for ongoing fragmentation analysis. At Tarkwa, mining efficiency is strongly dependent on good fragmentation as well as the presence of unblasted ?toes? on the pit floors. Crusher throughput depends on an acceptable ore fragment size. Compliance with plan for actual hole depths was temporarily monitored by manual hole dipping, but this is now being replaced with a fully automated drill data management system developed by Sandvik and Modular Mining. The Six Sigma methodologies, using control charts based on data collected in the field, allowed the mine to improve methods for the control of blasted material. It also enforced the implementation of a quality control programme encompassing the entire drill and blast process.

Jan 1, 2008

By S. Y. Fantaye

This paper discusses the design, construction and performance of a 30 inch thick diaphragm wall recently constructed in Baltimore, Maryland at Inner Harbor East. The project site is an established marina and waterfront property. The geologic profile consists of fill, alluvial silt and clay, Potomac sand and clay, decomposed rock, and weathered rock on top of gneiss bedrock. The approximately 1,300 ft long perimeter diaphragm wall serves as a water cut-off, perimeter basement wall and support of excavation for the high rise project?s five levels of below-ground parking. Due to the fast track construction and the tight schedule, the initial design of the diaphragm wall was based on a limited amount of geotechnical information. Supplemental borings were then performed along the alignment of the wall to verify the design assumptions and wall depths. Additionally, the design criteria required that the wall be keyed into a competent stratum with low permeability. The Engineer of Record for the diaphragm wall, Mueser Rutledge Consulting Engineers (MRCE) completed the design and produced accelerated construction documents allowing the developer to release the drawings early for bid. This paper describes the theoretical soil parameters used to develop the loads, moments, and shears for the design of the diaphragm wall and the temporary tieback anchors. It also discusses the refinement of these soil parameters using the observed wall displacements and tieback pre-stressing forces as a baseline. This paper compares the calibrated parameters to the values used in the design of the wall. It explains how the soil structure interaction model was developed and the soil parameters calibrated using PLAXIS 2D non-linear finite element software. The paper also discusses the use of the proprietary CWS joint by Soletanche/Inquip JV as end stop between consecutive wall panels and the unique top-down construction utilized to support the diaphragm wall at the Southeast double re-entrant corner.

Jan 1, 2008

By A Castleden, G Cavanough, M Kochanek, J Cunningham

ROES« is a proposed new mining system for underground hard rock mines. Ore is accessed from within a shaft, which is located close to or within the stope, and pitched either vertical or within approximately 20 degrees of vertical. The shaft is designed to exclude personnel entry so production drilling and explosive placement is done using remotely controlled or automated machines. Routine remotely controlled survey of the shaft, stope back and broken rock within the stope is typically done following each blast. The survey may include excavation geometry, rock fragmentation and geotechnical characteristics. Blastholes are surveyed before placement of explosives. This provides mine operators and engineers with real-time data, allowing them to monitor production performance and risk factors so that they can make rapid changes as required. ROES« is designed to apply to open stoping or sublevel caving situations either in disseminated, geologically defined, thick tabular or narrow vein orebodies. The technologies developed for ROES« will also have potential applications to block caving operations to reduce the risk of frozen ore and poor fragmentation. In a typical sublevel open stope application, ROES« will reduce the amount of stope-associated development by about half and therefore will allow ore to be brought on-stream sooner and at significantly reduced cost. Other savings are expected to flow from the centralisation of mining activities and operational data, reduction in mining fleet, reduction in ventilation requirements, improved occupational safety and reduced mine complexity. CSIRO and Orica Mining Services are developing the required technology and AMIRA is seeking sponsorship for a project to trial the mining method. This paper details the ROES« method, expected benefits and applications and includes typical stope and mining block designs and design requirements.

Jan 1, 2008

By C Dell

Hillgrove, situated on the New England plateau of New South Wales, is an area rich in history and resources. Key resources are predominantly antimony, gold and scheelite and the area surrounding the historical field is environmentally sensitive and topographically challenging. Since acquiring the Hillgrove leases, Straits Hillgrove Gold has undertaken a significant exploration program on these historical mining areas with the goal to return the field to production. This exploration program has enabled Straits to significantly increase the resource base and has subsequently enabled the planned redevelopment of Hillgrove to be realised. In October 2006, installation of mining infrastructure and the initial stripping of existing development had commenced. To successfully redevelop Hillgrove, Straits has had to adopt a highly mechanised, trackless, diesel mining operation which will see the production rate commence at an initial rate of 250 kt/a of ore from a narrow vein environment. This ore will be processed on site to produce antimony metal, gold bullion and a scheelite concentrate.

Jan 1, 2008

By R Badreddine, J Rose, L De Windt, P Chaurand, L Raimbault

Municipal solid waste of incineration (MSWI) bottom ashes are recycled as aggregates in civil engineering. These heterogeneous materials are composed of crystalline and glassy solid phases which contain trace metals, presenting a potential risk to the environment. Secondary ion mass spectrometry (SIMS) can provide quantitative chemical information, in particular the localisation of metals at trace level. Unstable glassy phases formed during incineration are present in relatively high proportions. Their analyses suggest a continuum between melilite-bearing glasses and dark glasses enriched in iron with abundant spinel aggregates. These primary glasses are enriched in zinc (~4500 ppm) but depleted in lead (~800 ppm) by comparison with the bulk chemical composition and reference materials. Heterogeneous cementing and encrusting admixtures on coarse grains are studied in a second step. SIMS imaging suggests a superposition of band zones including an intermediate layer enriched in iron oxyhydroxides and a superficial layer with calcium accumulation. A strong spatial association between lead and iron is systematically observed. Extended X-ray absorption fine structure (EXAFS) supports these observations by demonstrating that lead co-precipitation within iron oxyhydroxides, or sorption on their surfaces, may be a main containment process in the cementing and encrusting admixtures, whereas lead speciation is globally more complex in MSWI bottom ash.

Jan 1, 2008

By Alexandra Amiel

Tarkwa Gold Mine is owned by Gold Fields Ghana, IAMGOLD and the Government of the Republic of Ghana in a 71%, 19% and 10% ratio. The mine is operated by Gold Fields Ghana. This large, low-grade, open pit, gold mining operation is located in Tarkwa, in the Western Region of Ghana, approximately 320 kilometres by road, west of Accra, the capital of Ghana, West Africa. In the Financial year ended June 2007, the operation mined a total of 108 million tonnes of which 22 million tonnes was ore. The mined ore is processed through three gyratory crushers supplying two heap leach pads (North and South) and a carbon-in-leach (CIL) plant. Before the 6 Sigma project commenced, the current fragmentation was resulting in sub-optimal feed size to these crushers. It was decided to use 6 Sigma methodology to improve the fragmentation. A defect was defined as a fragmentation analysis indicating less than 95% passing 750 mm. The objective was to improve fragmentation in order to achieve a constant throughput to the north heap leach crusher of 1500 t/hr, a 5% increase in pit loading efficiency and a 50% decrease in rock breaker hours, equipment damage costs and in-pit sheeting costs respectively. However, this was not to be achieved at the expense of grade control as Tarkwa is exploiting a low grade, high volume deposit and therefore ore dilution must be kept to a minimum. This paper is intended to take the reader through the various 6 Sigma phases of the project (Define ? Measure ? Analyse ? Improve ? Control) which have resulted in a 10% reduction in loading times, of which half has been attributed to improved fragmentation, as well as a substantial increase in blasted stocks. The focus has been on both drilling and blasting parameters as both processes had to be taken into account. These parameters are technical but personnel factors were also identified and dealt with as they arose. In order to measure the impact of any change in the process parameters on the fragmentation size distribution, cameras have been acquired. One has been installed looking into the bowl of the north crusher and the other one was dedicated to field observation, of individual blasts. Both are used for on-going fragmentation analysis. At Tarkwa, mining efficiency is strongly dependent on good fragmentation as well as the presence of un-blasted ?toes? on the pit floors. Crusher throughput depends on an acceptable ore fragment size. Compliance to plan with regards to actual hole depths was temporarily monitored by manual hole dipping, but, this is now being replaced with a fully automated Drill Data Management system developed by Sandvik and Modular Mining. The Six Sigma methodologies, using control charts based on data collected in the field, allowed the mine to improve methods with regards to the control of blasted material. It also enforced the implementation of a quality control programme encompassing the entire Drill and Blast process.

Jan 1, 2008

Drill and blast operations account for 12 - 15 per cent of total mining costs. This paper looks at a comparison between electronic detonators and non-electric detonators, focusing on the cost benefits associated with the high precision of the timing sequences of electronic detonators. An analysis of the total mining costs was made on two main case studies; one on a quarry in South Australia (Martin, 2007) and the other on a project undertaken at Sunrise Dam (Vaughan et al, 2007). The criteria used in the analysis included; the resulting fragmentation, a vibration analysis, crusher throughput and productivity analysis such as excavator cycle times, dig rates of the excavator and bucket fill factor. The results indicate that there were consistent production improvements and hence reductions in total mining costs attributed to the use of electric detonators. An increase in the degree of fragmentation gives lower crushing costs as more material passes through as undersize. This reduces truck delay time at the crusher, which in turn gives higher truck and shovels productivity as well as higher dig rates for the excavators.

Jan 1, 2008

By C Bartle

In many operations the use of less electrochemically reactive grinding media in the first grinding stage (for example, rod milling and high aspect ratio SAG milling) is rarely considered. Therefore, in reality a plant may inadvertently be using a 'mixed' media charge. That is, whilst employing inert grinding media during secondary grinding, electrochemically active forged steel grinding media may be used in the primary grinding stage. This paper discusses the impact of such a circuit on the pulp chemistry and flotation response of a refractory gold ore. The Wiluna concentrator has two grinding circuits operating in parallel. Line 1 operates a single ball mill in closed circuit with cyclones, and utilises high chrome grinding media, while the second circuit (Line 2) consists of a rod mill (with forged steel rods) in series with a ball mill, which also utilises high chrome grinding media. The cyclone overflows from both circuits are combined to feed a sulfide flotation circuit. Pulp chemistry surveys were completed around both grinding circuits, and laboratory flotation tests were conducted on the cyclone overflows. The results demonstrate clearly that the rod mill/ball mill circuit operated at significantly lower Eh and dissolved oxygen values, while the percentage EDTA extractable iron was considerably higher, when compared to the single stage ball milling circuit. These variations in pulp chemistry had a marked negative impact on the laboratory rougher flotation response, and suggests that plant performance may be affected.

Jan 1, 2008

By Robert Hopler

That some time in the year 1872 there was organized an association composed of practically all of the manufacturers of gunpowder and other high explosives in the United States, the members of which said association were as follows: E. I. du Pont de Nemours & Co., The Hazard Powder Company, Laflin & Rand Powder Company, Oriental Powder Mills, American Powder Company, The Miami Powder Company, and Austin Powder Company of Cleveland, all of which or their successors are defendants herein; that the object and purpose of said association was the elimination of all competition between the members thereof in the shipment and sale of gunpowder and other high explosives among the various States and Territories of the United States; that the only manufacturers of gunpowder and other high explosives which did not join such association at the time of its organization were the California Powder Works, The Sycamore Manufacturing Company, and The Lake Superior Powder Company, but your petitioner alleges that each of said three last named companies

Jan 1, 2008

By J Wallis

The stability of a raise bore is often assessed using the rock mass classification system published by McCracken and Stacey as a modification of the Q system. Often the assessment is done using a spreadsheet to manipulate geotechnical log(s) of boreholes. This paper discusses the inherent difficulties with this approach. Recent work by others to provide guidelines to the classification system is discussed. A recent example of the design and raise bore performance at Macraes Gold Mine, New Zealand is presented. A key issue is that a visual assessment of the drill core and/or core photographs is necessary to æground-truthÆ the classification.

Jan 1, 2008

By Bhaskar B. Thapa

The proposed Caldecott fourth bore will consist of a two lane highway tunnel along California State Route 24 near the City of Oakland. The proposed design and construction sequence for the 15-m-diameter tunnel are based on the New Austrian Tunneling Method (NATM). The initial support system incorporates combinations of shotcrete, rock dowels, lattice girders, spiles, and grouted steel pipe canopies. The final lining is cast-in-place reinforced concrete. A waterproofing membrane and drainage system are placed between the initial and final linings. State Route 24 is a lifeline route, required to be open to emergency vehicles within 72 hours after a major earthquake, defined as having a return period of 1,500 years and a peak ground acceleration of 1.2 g. Although the seismic design criteria are stringent, the design of the tunnel lining system is ultimately controlled by static ground loads in the weak rock along the alignment.

Jan 1, 2008

By T. T. Chen

The behavior of gold in a conventional copper electrorefinery anode slimes treatment process is expounded on in this study. In the raw anode slimes generated in a copper electrorefinery, gold occurs mainly as tiny particles of metallic gold, which are commonly attached to selenide particles. Some gold is also present in selenide form. Decopperizing the anode slimes retains much of the metallic gold, but also promotes the incorporation of gold in the structure of silver-rich selenide species. A greater fraction of the gold is converted to (Ag,Au)2Se or Ag3AuSe2 when high-Se and high-Ag anode slimes are decopperized at elevated temperatures and pressures. After pelletization and roasting of the slimes, the gold is converted to a (Ag,Au)-alloy and Ag3AuSe2. Smelting of the roaster products eliminates the selenium and converts the gold to a silver-rich (Ag,Au,Pd)-alloy in the dore metal. In the subsequent silver electrorefining process, gold collects as a gold-rich (Au,Ag,Pd)-alloy in the gold mud. Dore smelting rejects many impurities as a silica slag; minor amounts of gold are present as a (Ag,Au,Pd)-alloy in the silica slag. This gold is recovered by flotation and is recycled to the dore furnace. Gold is identified in both the tellurium caustic leach residue and the parting plant wash water mud as tiny particles of metallic gold. These products are also recycled to the dore furnace to recover their gold values.

Jan 1, 2008

By T Rock

This paper looks at recent advances in the United Kingdom (UK) tunnelling industry with particular reference to the A3 Hindhead Project. A 1.8 km long twin bore tunnel is the centrepiece of the A3 Hindhead scheme, which commenced construction in 2007 and is being delivered under a UK Highways Agency early contractor involvement (ECI) contract. The proposed construction methodology is progressive mechanical excavation of a horseshoe-shaped tunnel with shotcrete installed close behind the face using robotic spraying equipment. The tunnelling medium is a æsoft rockÆ sandstone for which there was little previous tunnelling experience, requiring extensive geotechnical investigations and an innovative approach to lining design. A 240 m long section though sandy material utilising a steel pipe umbrella is also required. This paper describes the development of the tunnel planning and design including the most recent developments in UK road tunnels. The innovative approach to the design of the following is discussed:the æpermanentÆ primary lining,an observational technique allowing optimisation of the steel pipe umbrella design,a plain concrete secondary lining designed for resistance to a hydrocarbon fire, anda spray-applied membrane.

Jan 1, 2008