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By W T. Pate, A V. Potapov, J K. Lichter

Even though flotation is one of the most important unit operations of mineral processing, accurate modelling of this process for plant performance prediction has remained elusive. In the last four to five years dramatic changes have occurred in our ability to make credible model based predictions. This paper briefly traces the history of flotation modelling from simple (lumped pulp-froth) æchemical kinetic analogueÆ models for single cells to more detailed multi-phase, multi-component population balance models for banks of cells. It then focuses on recent developments in physics-based modelling tools. This includes current efforts to model the forces of attachment and detachment at the individual event level as well as multi-event levels in individual cells and circuits. Two examples of these tools are presented. The first is DEM modelling of the mechanics of motion of bubbles in froths. The second is population balance modelling of the dynamics of flotation circuits describing how they are influenced by upstream processes (such as crushing and grinding) as well as internal process variables (such as aeration, agitation and reagent addition). Applications of each of these tools are discussed.

Jan 1, 2005

By J. Abrahams, A. Nesbitt

Over the past half-century, researchers have commented on the complexities of ion-exchange processes, but have been forced to use gross assumptions to simplify the associated mathematics sufficiently for mathematical models to be of practical use, given the available computational power. This paper reviews the development of increasingly complex models as computational power has increased over the past half-century, from the direct application of Fick's Law in 1947, through to today's models requiring finiteelement methods. The assumptions required for and the associated limitations of the various models are presented and the associated computational complexities are discussed. A case study is presented in which a continuous loss of capacity in an acid resin was observed over about sixty cycles of loading and elution. Resin poisoning does not explain this observation. This paper presents the capacity loss data, speculates on possible causes of the phenomenon, discusses why conventional kinetic and equilibrium mechanisms cannot explain it and concludes that the need to develop a more rigorous model is apparent. The significance of this observation is that standard tests done for a new resin application could significantly overestimate the commercial performance of the resin concerned, highlighting the importance of computer simulation in this field of process engineering.

Jan 1, 2005

By Ben V. Petersen

Surveying is to tunneling, as a steering wheel is to a car—somewhat essential if you want to end up in the right place. The principles of tunnel surveying have remained unchanged since the first tunnels were constructed: To mathematically connect the selected start and end points of a tunnel and physically translate that alignment onto the ground. The alternative is just dead-reckoning and leaves the probably less than satisfying end results to chance. Today’s laser-guided tunnels often have to thread the needle through a maze of soil types, utilities, structural features and other underground considerations. Surveying makes it possible.

Jan 1, 2005

By D Thomas, B Gallagher

Valuable data for geotechnical interpretation and integration into effective Australian underground mine planning may often be available, yet is not always fully appreciated or utilised, particularly in the early stages of mine planning or in due diligence studies. There may be considerable benefits associated with early prioritisation of geotechnical evaluation and impact on mine planning. Unidentified, misinterpreted, or ill-defined adverse geological and related geotechnical resource characteristics can pose significant business risk to underground coal projects and operations. Preliminary resource definition in the early conceptual mine planning stages attributes significant focus (entirely warranted) on resource quality and structural geology constraints. Yet detailed geotechnical data analysis and interpretation, which may have a substantial down stream impact and sensitivity with respect to future mine planning strategies, at times is given lower priority, or scoped and resourced in the later stages of a bankable feasibility study. Through extensive mine planning experience and observation of downstream process impacts, it has been found there is often data available for geotechnical analysis that does not readily stand out or is not adequately understood or utilised, available at the early (conceptual) stages of mine planning. Part of the issue may be that exploration geologists are not necessarily experienced geotechnical engineers and do not necessarily recognise or understand all important parameters. Subject to appropriate application of experienced professionals data can be manipulated to provide key geotechnical hazard assessment at minimal cost, and provide a framework for understanding and optimising the mine planning process. Although there is no single prescribed strategy for resource evaluation from a geotechnical perspective, potential business risks and mitigation approaches can and should be adopted at the conceptual mine planning stage. There has been a recent focus in the metals industry to provide a reporting framework for geotechnical classification of mining projects. This paper outlines the strategies and gives examples of key analyses adopted in mine planning and discusses the relative merits of adopting a reporting framework as a tool for geotechnical classification in mine planning.

Jan 1, 2005

By J Krawcz, S Wasilewski, W Mironowicz

Barometric pressure and its variation in deep underground workings have a considerable effect on ventilation conditions. Pressure changes which create transient states of air flow and air parameters in workings are especially significant. Experiments have shown that pressure changes have a remarkable effect on air parameters at mine workings and hence, attempts to evaluate the scale of this phenomenon are of value. Continuous monitoring of the barometric pressure on the surface of mines allows for the detection of changes in pressure which undoubtedly influence alternations of pressure in the underground areas of mines. Very important factors are the internal disturbances of pressure within a mine ventilation system due to variable conditions of fan operation and the operation of a winding machine where a mine cage moving in a shaft causes piston like disturbances. Local transient disturbances caused by temporary opening/closing of air stoppings due to personnel or underground transport traffic are of importance. The results of over two years of observations of barometric pressure and its influence on pressure variation in underground mine workings are presented in this paper. The observations were possible through the installation of pressure sensors at selected points of the downcast shaft in a mine. Of interest are the observations of the transient states of pressure and other air parameters caused by emergency fan stoppage, movement of a mine cage and changes due to the opening of air stoppings. Data acquired during experiments of opening and closing air stoppings were used for the validation of a flow model in a long working.

Jan 1, 2005

By Marilia S. de Magalhaes

Keywords: sinter, characterization, agglomeration, iron ore Iron ore sinters are the main burden of blast furnaces for pig iron production. The evaluation of these agglomerates is very important due to their properties affect indirectly the productivity and costs of production of the steel industry. In the sintering plants, the standard procedure of sinter assessment has been carried out by particle size control, bulk chemical analyses, tumbler and/or shatter tests and determination of reduction degradation and reducibility indexes. Microscopy techniques have just been applied to characterize sinters produced in pilot conditions, however, these techniques, the classical ones and the less traditional, allow enhancing the industrial sintering process assessment. For investigation of the phases, microstructures and fabric, reflected-light and scanning electron microscopy(backscattered electrons images) were used; for micro analytical chemical examination, energy-dispersive X-ray spectrometry; for Kikuchi patterns registers, electron backscattering diffraction. In addition to the microscopy techniques, the magnetic behavior was depicted by means of magnetic susceptibility measurements. Iron ore sinters are made up by hematite, magnetite, silicoferrite of calcium and aluminium and silicates. These phases develop either during sintering or, in some proportion, represent remnants of ores and fluxes; this is the case of some hematite and Mg-bearing silicate, respectively. From the magnetic susceptibility results, three different behaviors were determined, which are directly related to the magnetiteproportion in the samples. The phase association and proportion, the sintering conditions andthe quality assessment are some features appraised by such procedures, which reveal themagnitude of this proposal in sintering plants.

Jan 1, 2005

By Gary L. Seider, Dana A. Wesolek, Fred C. Schmednecht

"A new condominium project, The Atelier, developed by Pickus Companies located at the corner of Bryn Mawr and Sheridan in Chicago, IL required an earth retention system to protect the surrounding roads, alley, and existing neighboring apartment bui lding during its construction. Slurry Systems, Inc. (SSI) and Ground Engineering Consultants, Inc. designed the earth retention system using cantilevered sheet piling for three of the four sides: two sides bordering major streets and one side bordering an alley. For the fourth side, which borders an existing occupied brick building, a combination of sheet pil ing and AB. CHANCE® helical screw piers were used. SSI was actively involved in the review process of its earth retention system with the City of Chicago and quickly learned that there was no specific code for hel ical piers/anchors. (It appears that this is the case with most metropolitan cities throughout the United States). Consequently, the approval of underpinning for this project became the critical path, as much testing, calculations, meetings, and other details were required prior to its approval.SSI and AB. CHANCE® recognized that this process for underpinning approval must be seen by other contractors/suppliers who wish to use helical piers/anchors in the City of Chicago. Consequently, this project served as an opportunity to work with the City of Chicago and the City's Building Code Committee in furthering the development of the Helical Piers/Anchors Code, Section 1814. INTRODUCTION - HELICAL PIERSDefinition. A helical pier or anchor consists of one or more helix-shaped steel bearing plate(s) attached to a central steel stem (solid bar or pipe), which is installed by rotating or ""torquing"" into the ground. Each helix is attached near the tip, is circular in plan , and is formed into a screw thread with a defined pitch. Helical piers/anchors are pre-fabricated and can derive their load-carrying capacity through both end bearing and skin friction. The helical piers/anchors can be augmented with grout."

Jan 1, 2005

By Charles Stone, Madan Naik, Drupad Desai, Karel Rossler

Planning of New York’s new subway line dictated the location of shallow underground station caverns and track crossovers. Clear span openings ranging from70 feet to 100 feet and lengths in excess of 1000 feet, coupled with low rock cover ranging from 25 feet to 40 feet required judicious selection of construction methods, equipment, and proper sequencing of the excavation stages. Rock classifications alone could not predict the behavior of the rock mass during construction. A robust design procedure that considered most of the important aspects of rock behavior and elements of shallow tunnel design, minimized the negative impacts of variable geotechnical data. This paper describes the intricacies of the planning and design of the $16 billion Second Avenue Subway with insight into how to overcome the design complexities and construction challenges of the urban underground.

Jan 1, 2005

By W. Z. Rogers

U.S. feldspar output sold or used in 2004 was estimated to be 790 kt (871,000 st), valued at $43 million free-on-board plant. This was below 2003 and about the same volume as 2002. The strong housing market in the United States maintained demand for ceramic tiles, plumbing fixtures, and fiberglass insulation requiring feldspar and shipments of glass containers increased by about 4 percent. Imports of ceramic tiles and plumbing fixtures continue to increase, taking the place of U.S. produced goods, and the feldspar required to make them. Output included flotation concentrates, feldspar content in feldspar-silica mixtures, potash feldspar and aplite.

Jan 1, 2005

By Bradford F. Townsend, Colin R. Speers

INTRODUCTION This is the first in a series of papers addressing practical tunnel lining design. The format for this and future papers is to present a particular topic and support the presentation of the guidelines by the practical application of a case history. The primary intent is to provide guidelines for the geotechnical and structural design of tunnels where the tunnel size and/or ground conditions dictates that systematic support of the excavation is required following each increment of excavation. This method of tunneling is commonly referred to as Sequential Excavation and Support(SES) and is also commonly termed the New Austrian Tunneling Method (NATM) The authors developed the design guidelines from experience gained over the past two decades during the design and construction of several major railway, highway and water-transfer tunnel projects in Africa and Asia. During this time it has been possible to compare the performance of the as-constructed structures to the predicted performance as given by the design process. Excavation was typically carried out in widely varying ground conditions (weak-bedded rock, jointed hard rock, and soil-like poorly cemented rock with groundwater). It is therefore intended that the design guidelines could be applied, in general terms at least, to any tunnel excavated in any ground mass condition with any ground material type (hard rock, soft rock, bedded rock, soft ground, and soil) with or without ground water. This first paper is an introductory paper that defines the scope and a brief outline of the design issues that may be presented in detail in later papers. What is design? It may be thought of as any rational/verifiable/justifiable process whereby a concept is transformed into information that can be used to bring the concept to reality. In the case of a civil structure, design may be defined as that process, which is documented and can be audited, that determines information such as the shape (form) of the structure, the dimensions (size) of the structure, the thickness and strength of structural members that comprise the structure, etc. This information can be used to compute the time, money and resources required for

Jan 1, 2005

By Jan E. Nesset, Antonio DiFeo, James A. Finch, Jose Hernandez-Aguilar, Cesar O. Gomez

"The gas dispersion measurement sensors and methodology developed by the mineral processing group at McGill University have to-date been employed at a number of plants in Canada, Australia, the U.S., South Africa and South America. In some cases the measurements have been directly linked with metallurgical performance while in others the gas dispersion surveys on their own have proved very useful in understanding the behaviour of the flotation cells. In addition to reviewing the current state of the gas dispersion measurement technology, the paper will present a series of case studies from the various plants and will show how this technology brings a remarkable new level of understanding to flotation behaviour. The influence of the bubble size distribution on recovery and grade are emphasized in the paper.INTRODUCTIONBackgroundThe advent of new sensors to characterize gas dispersion parameters in flotation cells is a development that is long overdue. While the chemistry of flotation has been studied since the early 1900’s, it is only now that the significance of bubble size distribution, gas rate and gas holdup can be meaningfully measured in-plant with robust and precise sensors. Early researchers, like T.A. Rickard (1916) recognized the importance of understanding the role of air and bubbles in flotation when he wrote in 1916 “we know that the key to the flotation process is to be found not in the oil, the acid, or the apparatus, but in the bubbles. The man who understands the mystery of a soap bubble has mastered the chief mystery of flotation”. In his 1999 review paper on The Froth Flotation Century D.W. Fuerstenau laments the fact that due to their “inert nature”, bubbles have never received their due attention from researchers who tended to focus on the chemical, physical, surface and colloidal aspects, rather than the physics of the process. It is perhaps fitting that now, 100 years after the inception of industrial flotation practice at Broken Hill, Australia, researchers and industry have turned their attention toward the importance of truly understanding the role of bubbles in flotation."

Jan 1, 2005

By A Suokas

Boliden Tara Mines Ltd, located in County Meath Ireland, produce in excess of 2.5 million tonnes per annum of ore from the underground resource located 40 miles north west of Dublin. The zinc-lead ore is mined using long hole open stoping techniques, with ore treated on site. The operation is continually searching for new ways to improve productivities at the mine, and have employed a detailed data acquisition and reporting system on site to provide feedback around performance. One area where both Boliden Tara Mines Ltd and Orica Mining Services believed improvements could be made was in the application of bulk emulsion technology through an Orica supplied but Tara operated Maxipump Delivery System for all production and development blasting at the mine. Both parties committed to the evaluation of this technology at the mine, however the capital cost and technical and economic changes meant the project needed to be diligently investigated and any improvements documented. The first stage of this project was for Orica Mining Services personnel to visit the operation, and conduct a detailed analysis of the operationÆs performance over the past 12 months. The next step in moving forward was then to commission and utilise the customer operated emulsion system at the mine. This was then followed with the collation and analysis of data from the demonstration period to examine and document the benefits of the system. This paper is a summary of the observations made during the site inspection and the data analysed to date, and has been used in determining operational and financial improvements in the comparison between a Maxipump Emulsion Service and the current ANFO loading systems.

Jan 1, 2005

By D. Newman

The objective of this is paper is to review the current state of knowledge and practice in highwall mining (HWM). HWM has become a standard method in surface mining, commonly used alone or in conjunction with contour or slot mining. It provides 800-feet to 1,200-feet of additional recovery when the economic stripping ratio is reached in contour mining or in slot mining when surface access to a reserve is limited. A significant attribute of the highwall miner is its versatility. HWM has been used successfully to mine abandoned pre-reclamation law highwalls, points or ridges uneconomic to mine by underground or other surface methods, outcrop barriers left adjacent to underground mines, separate benches of the same seam where the parting thickness or quality differences between benches render complete extraction uneconomic, previously augered areas containing otherwise inaccessible additional reserves and close or widely spaced multiple seams. The theory and design methods to assess roof; pillar, and floor stability are presented followed by three case histories. Simple design charts for sizing HWM web and barrier pillars are also presented. A recommended web pillar width may be obtained from the design charts given the overburden depth, the HWM cut width, and the mining height. Given the depth and panel width for a set of HWM cuts, another set of charts gives a suggested barrier pillar width. The case histories, hm Northern and Southern Appalachia are used to illustrate the application of rock mechanics to quantify the stability of the highwall, roof, web pillars, and floor. The case histories involve 1) mining through a previously augered highwall, 2) mining under back-stacked spoil and 3) selective mining of closely spaced benches of the same seam. Because each site is unique, the appropriate pre-mining geotechnical analyses range from the calculation of roof, web pillar, and floor bearing capacity stability factors to detailed numerical modeling of the auger and underground mine workings. When operating in the vicinity of existing underground mine or auger workings, the determination of ground deformation and strains resulting from highwall mining is a necessary facet of a ground control investigation.

Jan 1, 2005

By F. Freme

Coal production in the United States increased in2004 by 36 Mt (39.7 million st) to end the year at 1 Gt(1.11 billion st), according to the U.S. Energy Information Administration (EIA). This was a 3.7-percent in-crease from 2003’s 971.6 Mt (1.07 billion st) (Table 1).(All percentage change calculations are done at the short-tons level.) Although U.S. coal consumption rose in 2004, not all coal-consuming sectors had increased consumption for the year. Coal consumption increased in the electric power sectors by 1 percent and declined slightly in the other industrial sector, while coking coal consumption dropped by 2.4 percent. U.S. coal exports rose for the second consecutive year, while coal imports again increased to record levels. Coal stocks declined during the year, as electric generators used their stockpiles to helpmeet increased demands and missed shipments. Coal producers used their stockpiles to supplement their production levels.

Jan 1, 2005

By R. Minango

Solvent extraction of Cu from acidic leach, using an oxime extractant, e.g. LIX 984 or Acorga is a well-known and establishedprocess. As the process advances, Cu is extracted to the solvent and is replaced by H+in the aqueous phase. At high acidity the distribution coefficient of Cu between the solvent and the aqueous phase decreases, and eventually a relatively high concentration of Cu remains in the raffinate, regardless of the number of equilibrium stages. In many processes this phenomenon is immaterial, as the raffinate returns to the leaching and no copper is lost. But when the copper raffinate is used for processing of additional metals, minimal concentration of Cu in the raffinate is essential for an effective process. The recommended process includes three steps: SX-1?standard extraction of Cu with oxime. The resulting raffinate contains about 6?8 g/lCu and 50 g/lH2SO4. SX-N?Extraction of most of the acid into an amine-based solvent, and stripping it with a base, e.g. aqueous ammonia, caustic, Na2CO3etc. The extraction removes no metals, but decreases the concentration of acid from 50 to10 g/l. SX-2?Extraction of the neutralized solution once more with oxime, to remove the residual copper. Such a process enables one to get down to 100?150 ppm Cu in the final raffinate. This process was developed and tested in the R&D facility at Chambishi Metals plc, by a joint team of Chambishi & Bateman, using Cognis LIX 984N and real solutions from the plant. In the laboratory the equilibrium isotherms for SX-1, SX-2 and the neutralization were developed. Computer simulation of the results showed that the optimal configuration is two stages for both extraction and stripping for SX-1. For SX2, 2?3 stages of extraction and two stages of stripping are needed. The stripping stages may be common to both SX-1 and SX-2. The neutralization of SX1 raffinate was tested both by conventional precipitation with lime and by extraction with alamine-based solvent extraction and stripping with a solution of 10% NaOH. For the SX-N only one stage was needed for both the extraction and stripping. The bench scale pilot plant was run for both SX-1 and SX-2. The results were very similar to the simulated ones, and the configuration of 2E2S for SX-1 and 3E2S for SX 2 delivered the required raffinate with less than 150 ppm Cu.

Jan 1, 2005

By M. Ramström

"In 2002, Atlas Copco Rock Drills AB released the new rig control system (RCS) technology for all of its drill rig types. RCS opened the way for a new generation of computerized drill rigs based on modern, standard PC-computer technology. Drilling accuracy, information logging, reduction in manpower in some types, and serviceability have all taken a quantum leap forward when compared with previous generations of drill rigs. RCS is modularized and distributed by means of CAN-bus technology. This technology, which is well proven in automobile applications, forms the communication backbone of the rig. The modularity facilitates almost unlimited possibilities for the expansion and adaptation of drill rig functions."

Jan 1, 2005

By Robert E. McIvor

The Functional Performance Equation for Ball Milling” was first presented in 1988. It now has been used successfully in more than a dozen mineral processing plants. This powerful, yet simple tool provides a new level of understanding of closed circuit grinding. It shows how grinding circuit efficiency is in reality comprised of two distinct efficiencies. It demonstrates how circuit production rate is related, collectively, to these two efficiencies, mill energy input, and the grindability of the ore. It links circuit performance to design and operating variables that can be manipulated, and creates an effective strategy for making plant improvements. This paper covers the derivation and industrial validation of this equation. As part of an engineering and management system that also incorporates suitable metrics and process control, other operators can now use this tool to make improvements and to manage the performance of their grinding operations with clarity and confidence.

Jan 1, 2005

By S J. Neethling and, S J. R Simons

In this paper the effect of humic substances (natural surfactants), electrolytes and solid particles on bubble coalescence, and as a consequence on froth stability, have been investigated. In this study two bubbles of equal size were formed and forced to collide using a novel experimental apparatus. The interactions were recorded by a high-speed camera, the images of which helped to determine the coalescence frequency and the coalescence time, as well as the mechanisms of the interactions. Two types of humic substances were used, along with three different electrolytes. Humic substances appeared to have a considerable effect on bubble coalescence, while the effect of electrolytes was minimal. Moderate and high hydrophobic glass spheres were used between two bubbles. Very hydrophobic spheres promoted fast bubble coalescence, while moderate hydrophobic spheres had no effect. Data of coalescence frequency and time is presented, as well as images of the coalescence events. The coalescence frequency was used to validate a parameter, Pf, known as the film failure frequency, used in a simulation model to predict foam height in a gas-sparged vessel. Predictions determined using Pf were then validated by experimentation.

Jan 1, 2005

By Balladares V. Eduardo

Most of the arsenic contained in copper concentrates is removed in the gas phase during the smelting and converting processes and, according to recent environmental regulations, it is required to fix it in a solid stable form. In this regards, ferric arsenate has been reported as thermal and aqueous stable compound. Therefore, various alternatives for treating gas containing arsenic were considered in this work. From data obtained at laboratory scale on fixation of arsenic using iron oxide, a new process to treat copper concentrates containing arsenic was evaluated. The effect of temperature, oxygen potential and the sample porosity on the fixation of arsenic contained in a gaseous stream was studied, and the iron oxide converted into ferric arsenate was up to 10%. The obtained results suggest a new alternative for gas treatment with an interesting and attractive technical development. The arsenic was retained as ferric arsenate with thermal and aqueous stability, and it allows a safe disposal keeping the environmental restrictions. The kinetics parameters are used to scale up laboratory results to higher processing rates.

Jan 1, 2005

By Gavin Beer

The Chelopech Copper/Gold Mine, located in west-central Bulgaria, has been in operation since 1953 producing a low-grade copper/gold concentrate containing up to six percent arsenic by weight. The penalties and restrictions imposed on smelting this concentrate, have seen the past operators of the mine strive to find a balance between achieving acceptable metal returns from the smelters and installing novel or unproven technologies in the face of changing political and economic climates. This paper documents the colourful history of the concentrate processing alternatives that have been investigated and implemented over the 45 year life of the Chelopech Mine, culminating in the high pressure oxidation option that is now the focus of a Definitive Feasibility Study (DFS) presently being undertaken by GRD Minproc Limited. The fundamental chemistry of the preceding alternatives is outlined followed by a discussion as to why each was ultimately not employed. A detailed description of the technology proposed in the DFS is given including: pressure oxidation, arsenic fixation, SX/EW copper recovery, CIL gold recovery and AVR/SART cyanide/copper recovery processes. Keywords: Arsenic, Scorodite, HPOX, Chelopech, Dundee

Jan 1, 2005