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By K. L. Riemer

The West Wits Line first began yielding gold in the mid-1930s and is among South Africa's leading gold-producing areas. Gold mining operations are carried out amidst the occurrence of seismic events which cause both damage to underground excavations and injury and loss of life to production personnel. The feasibility of establishing a system to minotor the seismicity on all the Gold Fields mines was investigated during the early 1980s. This led to the establishment of a centralized seismic network in 1981. The system was structured around three major objectives. It uses Perkin Elmer (now Concurrent Computer Corporation) 16 and 32 bit mini-computers. The hardware in use at both the central and remote sites is outlined, giving a good insight into the role of computers in the system. The system software reveals the fast flow of data through the network; it can be divided into three categories: (1) data logging and transmission - remote sites, (2) data capture and communications - central site, (3) applications and research - central site. Several examples are given which show how the system is measuring up to its objectives. These case studies also indicate how the computers are effective in representing the seismic data collected. It is concluded that the use of computers enables the pin-pointing of seismic events on the West Wits Line within about 3 -4 minutes of their occurrence. The choice of hardware is largely dependent on the objectives of system, and the Gold Fields Network has chosen mini-computers because of the speed of communication and the large amount of data and storage required for research applications.

Jan 1, 1987

By D. Sager

Middleburg Ferrochrome (MFC), a company in Samancor Chrome, commissioned a new ferrochrome smelter in March 2009. This is a 60 MW DC-arc furnace with a DC power supply for the smelting of Transvaal chromite ore fines. With the benefit of 12 years' experience with this technology while operating a 44 MW DC-arc furnace, MFC mitigated all known challenges and considered up-scaling risk in the new plant, which had a rapid ramp-up to full power in 02 of 2009. Good operating practices, as made possible by robust equipment selection, including a thyristor rectifier set of proven technology, and operation with optimal slag chemistry, leads to a safe and effective plant operation. With the optimized furnace design and a correctly sized power conditioning system, using only standard (static) harmonic filters and a correctly sized smoothing reactor, the arc furnace is not a 'dirty load' for the utility, staying well within IEC limits for power quality. A patented arc compensation system is installed and allows for full arc position control (to compensate for magnetic field induced arc deflection) so that a symmetrical crucible is maintained, significantly benefiting refractory life. The principal benefits gained from the MFC process is the fact that ore fines are processed, without metallurgical coke, and higher chrome recoveries are achieved compared to other smelting technologies when using a DC open arc for smelting. Keywords Samancor Chrome, Middelburg Ferrochrome, ABB, smelting, DC arc furnace, arc compensation, power factor correction, anode, harmonics, thyristor, reactor, maintenance, refractory, ores, reductants.

Jan 1, 2010

By D. J. Stanton

The objective of this study was to develop, install, and test a small underground mobile refrigeration plant (MRP) to deal with some of the real problems associated with mine cooling in an operating mine. The requirement for cooling the underground environment is discussed with particular emphasis on the need for this method of cooling, with the concomitant benefits. The research investigated current methods of cooling and reasons for previous failures in MRP. Both static and dynamic simulations were conducted to increase the confidence level under operating conditions. Implementation and testing, resulted in ?lessons learnt? requiring modifications, which are documented. Actual results have been recorded. These results have proved that significant cooling via MRP is feasible. Main benefits include positional efficiency, cost per kilowatt of cooling and cooling opportunities for remote hot areas of a mine. Finally, a proven technology is now available for large-scale implementation in the mining industry. Now the ventilation engineer has another system of cooling, which can be utilized in the quest to create an occupational environment, which meets the physical and mental health requirements of the worker.

Jan 1, 2004

By D. -X. Li

The paper covers many literature reports of processes using nitrogenous species as an oxidant for processing refractory gold ores, especially development in the pretreatment of refractory gold minerals by nitric acid. These processes include the high-pressure and the atmospheric-pressure oxidation methods. High-pressure oxidation processes are difficult to carry out, because they require high-capital cost autoclaves. Atmospheric-pressure oxidation processes are easier to manipulate, but complete absorption and reuse of NOx is difficult or multiple-stage absorption must be established for its reuse. So, some new methods were developed, such as catalytically oxidizing technology of NOx to allow subsequent recovery of gold. Keywords: nitric acid; pretreatment; refractory gold

Jan 1, 2009

By B. Geelhoed

Gy's formula for the variance of the fundamental sampling error (FSE) is based on a model that assumes independent selections of particles. A generalization of this model, which can theoretically lead to more realistic representation of actual sampling processes, was, for the first time, experimentally verified by repeated sampling from a well-mixed batch consisting of particles of zirconium silicate of two different sizes. The predictions for the sampling variance made in Gy?s theory and in the more general model were compared with the experimentally observed sampling variance. During the experiment performed here, the variance prediction made in the theory of Gy ranges from 0.96 × 10?7(g2/g2) to 0.95 × 10?7(g2/g2), which is approximately a factor 60 lower than the experimentally observed variance (5.76 × 10?6(g2/g2)). The difference between the Gy prediction and the experimentally observed variance cannot be fully explained by the uncertainty in the experimentally obtained variance due to the finite number of degrees of freedom. Therefore, the difference is likely to be a significant effect. This shows that, under the experimental conditions, Gy?s formula for the variance of the FSE probably undervalues the sampling variance, unless an empirical correction factor for grouping and segregation is applied in the theory of Gy. The new theory resulted in a variance prediction of 6.00 × 10?6(g2/g2), which is much closer to the observed variance than the Gy prediction. This indicates that the generalization of Gy?s theory offers an outlook for providing a better variance prediction than the Gy predictor in the case of dependencies between particle selections. The results are discussed. Keywords: sampling, variance, parameter for the dependent selection of particles, Gy, experiment.

Jan 1, 2009

By Y. H. Hatzor

ABSTRACT: A fully dynamic, two dimensional, stability analysis of a highly discontinuous rock slope is demonstrated in this paper. The studied rock slope is the upper terrace of King Herod’s Palace in Masada, situated on the western margins of the seismically active Dead Sea Rift. The dynamic deformation of the slope is calculated using a fully dynamic version of DDA in which time dependent acceleration is used as input. The analytically determined failure modes of critical keyblocks in the jointed rock slope are clearly predicted by DDA at the end of the dynamic calculation. It is found however that for realistic displacement estimates some amount of energy dissipation must be introduced into the otherwise fully elastic, un-damped, DDA formulation. Comparison of predicted damage with actual slope performance over historic time span window of 2000 years allows us to conclude that introduction of 2% kinetic damping should suffice for realistic damage predictions. This conclusion is in agreement with recent results of Tsesarsky, Hatzor and Sitar (2002) who compared displacements of a single block on an inclined plane subjected to dynamic loading obtained by DDA and by shaking table experiments. Using dynamic DDA it is shown that introduction of a simple rock bolting pattern completely stabilizes the slope. RÉSUMÉ : On présente dans cet article une analyse bidimensionnelle complète de la stabilité d’une pente rocheuse très fracturée. La pente rocheuse étudiée est la terrasse supérieure du Palais du roi Hérode à Massada, située sur la rive Ouest du Rift sismiquement actif de la Mer Morte. La pente est constituée de blocs de dolomite raide présentant une stratification sub-horizontale et des joints sub-verticaux. La déformation dynamique de la pente est calculée en utilisant une version entièrement dynamique de l’Analyse de Déformation Discontinue (DDA) où l’accélération dépendant du temps est utilisée comme donnée. Les modes de rupture déterminés analytiquement des blocs clés dans la pente rocheuse fracturée sont clairement prévus par l’approche DDA à la fin du calcul dynamique. On trouve cependant, que pour obtenir des estimations réalistes du déplacement, il faut introduire un facteur de dissipation énergétique sans lequel la formulation DDA serait totalement élastique et sans amortissement. En comparant l’endommagement prévu avec les caractéristiques de la pente sur une période historique de 2000 ans, nous pouvons conclure que l’introduction d’un amortissement cinématique de 2% suffit pour obtenir de prévisions réalistes. Cette conclusion est conforme aux résultats récents de Tsesarsky, Hatzor and Sitar (2002) qui ont comparé les déplacements d’un bloc isolé sur un plan incliné sous chargement dynamique obtenus avec l’analyse DDA et à partir d’essais sur table vibrante. ZUSAMMENFASSUNG: En utilisant une modélisation DDA dynamique on montre que l’introduction d’un système simple de boulonnage stabilise la pente.In dieser Veroeffentlichung wird eine vollstaendig dynamische, zweidimensionale Stabilitaetsanalyse eines hoechst diskontinuierlichen Steinhangs dargestellt. Der untersuchte Hang ist die obere Terrasse des Herodespalastes in Massada, welche in den westlichen Randgebieten des seismisch aktiven Toten Meer Grabens liegt.Die dynamische Deformation des Berghangs wird mit Hilfe einer vollstaendig dynamischen DDA-Version berechnet, in welcher als Input die zeitabhaengige Beschleunigung eingegeben wird. Die analytisch bestimmten Versagensarten kritischer Schluesselbloecke in diesem zerkluefteten Steinhang werden durch Anwendung von DDA am Ende der dynamischen Berechnung klar vorausgesagt. Es zeigt sich jedoch, dass fuer realistische Dislozierungs-Abschaetzungen ein gewisses Mass an Energieverlust in der sonst vollstaendig elastischen, ungedaempften DDA-Fassung einbezogen werden muss. Der Vergleich des vorhergesagten Schadens mit dem aktuellen Verhalten des Berghangs waehrend einer historischen Zeitspanne von 2000 Jahren erlaubt uns zu schliessen, dass ein Zusatz von 2% kinetischer Daempfung fuer eine realistische Vorhersage des Schadens ausreichen sollte. Diese Schlussfolgerung steht im Einvernehmen mit neuen Ergebnissen von Tsesarsky, Hatzor und Sitar (2002), welche die Dislozierung eines einzelnen Blocks auf geneigter Ebene unter dynamischer Belastung – unter Anwendung von DDA und “shaking table”-Versuchen – verglichen. Mit Hilfe der dynamischen DDA wird gezeigt, dass der Steinhang durch Anwendung einer einfachen Steinschraubenstruktur vollkommen stabilisiert werden kann.

Jan 1, 2003

By A. Koning

Pressure hydrometallurgy operations require vessels to be lined with an impermeable membrane for corrosion protection and one or more courses of refractory or ceramic brick. Examples of unit operations that utilize composite lining systems include pressure oxidation autoclaves, sulphide precipitation autoclaves, chloride leach reactors, flash vessels, cyclone separators, and direct contact condensers (heater vessels and quench vessels). The refractory lining must satisfy multiple requirements: it must thermally insulate the membrane from process fluid, be structurally stable, provide erosion resistance, be chemically compatible with process fluid, and provide an economic service life. New hydrometallurgical processes are pushing the pressure, and temperature with each new generation of plants. A fundamental understanding of all factors affecting the mechanical stability of the lining system is essential as lining designs move further away from the industry?s experience base. The method of designing a refractory lined vessel is examined taking into account the impact of irreversible chemical swell, operating factors, design factors, and installation factors. The effect of geometry and incorporating additional degrees of freedom to the analysis is explored using two-dimensional and three-dimensional finite element analysis (FEA). The effect of these additional degrees of freedom on the results of the one-dimensional model are discussed. Keywords refractory lining design,autoclave, finite element analysis.

Aug 1, 2013

By S. V. Mkhatshwa

The purpose of the study was to investigate the factors which affect the performance of the loading and hauling fleet and also find possible solutions to eliminate these factors, so that the daily tonnages required could be produced .This is due to the high demand of manganese required by clients. The investigation strongly focuses on the performances of the three 777D Caterpillar trucks and the R984 C Liebherr Litronic Hydraulic Excavator. In the content of the study, these machines are used to remove and move the low grade manganese (also known as the top cut overburden) in order to expose the high grade manganese from north pit to dump 4. The objectives of the project were to determine the actual performance of the loading and hauling fleet per shift, compare the actual and the theoretical performance and identify areas that need to be improved. To achieve the goals set for the project, a number of activities were carried out. ?Perform a time study to compare the performance of the loading and hauling fleet with the manufacturer specifications ?Match the equipments analysis for Loading and hauling ?Road conditions analysis ?Rolling resistance and Road Gradients analysis ?Operating cost analysis.

Jan 1, 2009

By G. D. Rosales, P. F. A. Braga, S. C. A. França, C. P. Pinto

The growing market demand for lithium is mainly due to its use in the manufacture of batteries for electric or hybrid vehicles and portable equipment (smartphones, tablets, power tools, notebooks, etc.). Currently there is great interest in finding new sources of lithium and technologies for its utilisation. Li-S batteries have received attention due to their theoretically high specific energy density, which is 3 to 5 times greater than that of Li-ion batteries. Unlike Li-ion batteries, of which the main raw materials are lithium carbonate and lithium hydroxide, the main raw material for Li-S batteries is lithium chloride. The anode used in Li-S batteries is metallic lithium, produced by a molten lithium chloride electrolysis process. The extraction of lithium from pegmatites such as spodumene, previously abandoned in the 1990s for being uneconomical, has become attractive due to the increase in prices as well as the need for greater lithium purity of products made from lithium-bearing minerals. The main methods used for lithium recovery from spodumene ore include the sulfuric acid process, the alkaline process (lime or limestone as raw material) and the chlorination roasting process. Thermodynamic modelling using HSC software 5.1 was conducted to predict different reactions that could occur during chlorination roasting of the spodumene/MgCl2+CaCl2 system. Lithium extraction from the solid obtained after the chlorination roasting was also investigated. The results of thermodynamic analysis provided a better understanding of the chlorination roasting process for lithium extraction. Metallurgical tests with a mass ratio of 1:6 (spodumene:chlorides) and molar ratio of 2:1 (MgCl2:CaCl2) allowed over 95% recovery of the lithium contained in the spodumene concentrate. Keywords: Spodumene, lithium chloride, chlorination roasting

Jan 1, 2020

By H. D. Mtegha

The Southern African Development Community (SADC) aims to harmonize mineral policies and regulatory regimes in the minerals sector. This paper provides a review of the progress made towards harmonization of mineral regimes in the region. It singles out only the mining fiscal environment, as this is normally one of the key issues of interest to potential investors as well as the host state. Indications are that the region is slowly progressing towards a more harmonized approach, and there is evidence that the ?race to the bottom? has been prevented, which is the basis for an integrated mineral sector that the region aspires to.

Jan 1, 2011

By W. P. C. Duyvesteyn, J. R. Cutland, J. R. L. Russell

In 1970 it was decided to build a large new plant at the Chingola Division of N.C.C.M., Ltd., to treat concentrator tailings and leach residues with a low copper content by a leach-solvent extraction-electrowinning process. In order to assist in the establishment of the design parameters for the new plant, and to study the interaction of this plant with the existing leach-electrowinning plant, mathematical models, formulated as linear programs, have been developed and used extensively. The paper outlines the metallurgy of the plants and describes briefly the way in which the models have been formulated and used. The formulation involved the use of separable programming to form the products of some variables.

Jan 1, 2014

By J. Dvorácek

Mine water poses a significant problem in lignite coal mining. The drainage of mine water is the fundamental prerequisite of mining operations. Under the legislation of the Czech Republic, mine water that discharges into surface watercourse is subject to the permission of the state administration body in the water management sector. The permission also stipulates the limits for mine water pollution. Therefore, mine water has to be purified prior to discharge. Although all mining companies operate mine water treatment plants, there is hardly any utilization of the final effluent. The high expenditure involved in the more sophisticated methods of mine water treatment has fuelled the search for the commercial utilization of the effluent.

Jan 1, 2012

By J. O. Claassen

A study was initiated and solutions implemented to address the root causes of a 30%?40% lower than predicted product yield achieved at a Mpumalanga coal mine. A holistic MRTM approach, which focused on improving exploration, geological sampling and analysis, geological modelling, planning, mining, and beneficiation practices, was used. The study indicated that deviations in the planned versus actual yields at the DMS plant were caused mainly by incorrect geological yield predictions, high and variable levels of dilution, and near-dense material, as well as the textural properties of the ore. Keywords MRTM, mining value chain improvement, Witbank coalfields, complex geology.

Oct 1, 2013

By T. Bednarski, L. Thomas, G. Banza, D. Muteba, P. Cole, M. Soderstrom

"In copper solvent extraction, aqueous-in-organic entrainment results in the carry-over of unwanted species into the electrowinning process with negative cost implications. The need to bleed is increased and the purity of the copper cathode is potentially compromised, depending on the impurities being transferred (Cl, NO3, Fe, Mn). In some cases, entrainment results in elevated levels of manganese in the electrolyte which can cause oxidative conditions to develop and degradation of the organic phase. Degraded organic phase detrimentally affects the physical performance of the copper solvent extraction process, contributing to even higher aqueous-in-organic entrainment. Aqueous entrainment may be minimized through good operating practices and maintenance of the organic quality, but the accurate measurement of entrainment remains a challenge. This paper presents coalescing devices designed to provide more exact measurements of aqueous-in-organic entrainment. IntroductionMany copper solvent extraction (SX) plants experience high aqueous-in-organic (A-in-O) entrainments but are unaware of the extent of the problem because entrainment is often not measured. Aqueous entrainment results in the carry-over of unwanted species into the electrowinning (EW) process and the need to bleed to maintain acceptable concentrations in the electrolyte. The costs associated with the bleed are exacerbated in copper plants where aqueous entrainment levels are high. Other than these direct costs, there are operational consequences of the build-up of certain species in the EW circuit that can have deleterious effects on plant performance.Minimizing aqueous entrainment in operating plants requires an understanding of the factors that affect entrainment levels. Both chemical and operational influences are discussed in this paper. The difficulty of obtaining a representative sample makes it challenging to obtain an accurate measure of aqueous entrainment from a continuous process like SX. Coalescing devices used to get a more precise measurement of A-in-O entrainment are useful to complete mass balances around the SX circuits. Alternatively, mass balances can be used to estimate aqueous entrainments and are helpful as a tool to troubleshoot operations with a view to improving plant performance."

Jan 1, 2016

As part of a broad program to optimise the performance of their grinding circuit, BHP Billiton Cannington have installed an OCS© Expert system together with three VisioRockTM online particle size analysis cameras. The main purpose of the system is to stabilise grind size and feed to the flotation circuit. This particular application of OCS© is the first installation to incorporate Metso Minerals Process Technology-Asia Pacific's (MMPT AP) Dynamic SAG/AG Mill Model, which is able to predict numerous mill parameters that were previously unable to be measured with the existing plant instrumentation. Integrated into the logic of the control algorithm are online vision based, particle size measurements of the AG mill feed and recycle crusher product. This paper will describe the history of the project from initiation to date, the model and OCS© logic configuration, and demonstrate the significant benefits realised at Cannington mine.

Jan 1, 2007

By C. Norden

The purpose of this article is to show how a representative overall equipment effectiveness (OEE) measurement can be calculated for an underground coal mining bord and pillar batch process. The calculation method, the typical losses (which include planned and unplanned availability losses, coal quality losses, and process rate losses) and the underlying logic are presented and discussed. It is argued that the current traditional underground bord and pillar mining process can currently provide a maximum theoretical OEE of only 49 per cent, while a realistic benchmark target should be in the order of 37 per cent, which relates to an average of 2400 t per shift or 1.2 Mt/a. In addition, it is argued that the current bord and pillar process is the current bottleneck to further improvement past the 2400 t per shift benchmark, and that fundamental process changes will be required to eliminate this bottleneck.

Jan 1, 2012

By E. J. Magri, A. Couble

Kriging estimates of geological resources are sometimes conditionally biased because the kriging plan contains too few samples. This may be done purposely in order to match the variance of the estimates to the true block dispersion variance. This work aims at evaluating the influence of conditional bias over the ultimate optimum pit design in relation to its shape, size and NPV (Net Present Value of profits). It has been restricted to two real case studies: a ‘carrot shaped’ gold porphyry in northern Greece and a manto-typeexotic copper deposit located in northern Chile. The methodology applied to each deposit consisted of generating a ‘real block model’ and four resource estimates by the use of conditional simulation and the application of four different kriging plans to the drillhole databases respectively. The estimation models vary in smoothness and conditional bias. Ultimate optimum pits were determined for the ‘real’ and the four different kriging models. Pit comparisons lead to the following conclusions: •In the worst case, conditional bias overestimated the project's NPV by 32% and 5% for the gold and copper deposits respectively. •The overestimation of high grades is more relevant than the underestimation of low grades. This resulted in a tonnage over-extraction of 148% and 1% for the gold and copper deposit respectively. This difference was attributable to the vastly different geometry of the deposits. •The smoothing effect of kriging, without or very little conditional bias, produced open pits that were different to the ‘true’ (ideal) ones and furthermore, underestimated the project's NPV by 10% and 6% for the gold and the copper deposits respectively. •Other factors that influence the optimum open pit design and to some extent control the effect of conditional bias are: the cut-off grade, the orebody geometry and distribution of grades within it and the amount of over-burden. Keywords: conditional bias, ultimate pit design

Jan 1, 2003

By W van Drunick, S Naik

To date, Anglo Research has carried out several projects, based on the techniques developed in the AMIRA P9 (AMIRA International Limited), to develop comminution and flotation models for several Anglo Base Metals and, to a lesser degree, Anglo Platinum flotation plants. Plant optimization is thus achieved through steady-state sampling, model-fitting and simulation using the JK SimMet and JK SimFloat software packages. The surveys can vary depending on the needs of the plant/client. The survey can therefore include as little as a single piece of equipment, an entire milling/flotation circuit, or a complete circuit from primary comminution to final flotation concentrate (i.e. the ?integrated survey?). The presence of the AR team on-site usually precipitates in face-value observations that can lead to initial improvements. This stems from the knowledge-sharing on best practice that exists in parallel with the surveys. Numerous (reasonable) changes can then be simulated, thus indicating the optimization step most likely to result in the best efficiency improvements. The simulations can include changes in the flowsheet, ore characteristics, mill loads, grinding media size, change in grind, flotation residence time, air hold-up and several more. Plant surveys can result in process changes that provide the plant with either: higher plant tonnage, improved plant grind, additional flotation recovery and/or improved product grade. The additional benefit of performing an integrated plant survey is that the effects of an optimization change in the comminution circuit can be simulated using the flotation model. This paper describes a number of case studies where individual and integrated plant surveys were conducted by AR for Anglo Base Metals.

Jan 1, 2007

By Keith Rowley, Neal Harries, David Noon

The management of risks associated with slope instability is an essential process in the safe and economic operation of open cut mines. The ?slope stability radar? (SSR) has been developed to better manage those risks. The SSR remotely scans rock slopes to continuously measure any surface movement and can be used to detect and alert users of wall movements with sub-millimetre precision. The high level of movement precision and broad area coverage of the rock face can allow for a better understanding of the geomechanics of slope deformation, including magnitude of potential failures and additional warning time of impending instability. Additionally, radar waves adequately penetrate through rain, dust and smoke to give reliable measurements, 24 hours a day. SSR systems have been deployed in many mines in Australia, Indonesia, South Africa, Zambia, Chile and the United States. Greater than 70 rock falls and waste dump failures (from several to millions of tonnes) have been monitored, and on every occasion precursor ?warning? movements were recorded by the SSR. This technology enables a radical change in the management of risks in open cut mining. This paper will present recent case studies of the SSR operation in coal and metalliferous mines.

Jan 1, 2006

By C. M. G. Wortley

One of the major deliverables of the AMIRA P754 Project, which was sponsored by several major mining companies, was a code of practice and guidelines for metal accounting for the mining and metallurgical industry. These had the objective of improving the auditability and transparency of metal accounting from mine to product, thus assisting in good corporate governance. The overriding objective of mass measurement for metal accounting is to establish the mass of the particular material or component present at a specific time, or the mass flow of that component over a defined time period, to a defined accuracy suitable for metal balancing. As such, it is the first measurement in the chain that includes sampling, sample preparation and analysis, each of which introduces its own errors. Materials often contain moisture, the proportion of which must also be established in order to obtain the dry mass. They may also have to be measured as a volume or mass/mass flow of slurry, or in stockpiles or storage areas, in which case the relative density must be measured. Both the density and moisture measurement often introduce significant error. Whereas a great deal of effort has been directed at sampling, sample preparation and analysis to improve accuracy and establish the error, the same can seldom be said for the mass determination, including the moisture and density measurements. The possible major causes of error are highlighted and methods of reducing them discussed. Mass measurement can be classified into those measurements necessary for custody transfer and primary accounting of the input and output streams to a plant or operation, and measurements required for secondary accounting, or management control. The latter include intra company transfers and plant area performance, and those required for plant control only. This paper is concerned only with primary accounting measurements. The code and best practice state that the equipment should be certified (as sized) as is required for custody transfer. The most accurate and precise of the various possible methods is the static measurement of mass on a weighbridge, platform scale or a weigh bin. If static measurement is not possible, which is often the case for ore fed to a plant, possible alternatives are electromechanical conveyor belt weighers or in-motion weighing of rail trucks. In all cases the material must be adequately sampled to enable a representative moisture content to be determined to calculate the dry mass. Where material is flowing inside conduits, only certain types of the multiplicity of flow meters available may be used and, in the case of slurries, very few flow meters are suitable. As most flow meters measure volume or velocity, the density of the material must also be measured. The basic requirements in order to achieve satisfactory results for the mass, of the component of interest, are listed, as well as common problems and pitfalls encountered in practice. The measurement of the mass of stockpiles and in-plant stocks, often required for metal accounting, is often the largest source of error in metal balances. The reasons for this and methods for reducing and managing the effect are discussed.

Jan 1, 2009