Search Documents

By Klaus Hasselwander

Fluctuating SO2 gas streams represent a difficult task for designers of SO2 removal systems (with respect to designing the plant), but in spite of the designers great efforts to solve the problems, the operation of such plants requires much care and attention. A fluctuating gas flow usually results from metallurgical smelting processes. Both gas composition and gas flow rate may vary. The first part of this paper outlines some existing technical solutions and presents the Pros and Cons of the different solutions. These solutions outline are: - Sulphuric acid plants operated with a preheater permanent in operation - Sulphuric acid plants with concentration increase of SO2 gas either using regenerative SO2 removal or cryogenic partial condensation of the SO2 - Sulphuric acid plants with additional burning of sulfur to increase SO2 content - Single-stage sulphuric acid plants followed by a tail gas system (which is) designed for periods of low SO2 input In the second part, this paper describes some existing technical solutions for removal of SO2 at low concentrations (i. e. less than 0.1 - 2 %-by volume), which could be used as tail gas treatment system for acid plants. While selecting an appropriate solution, special attention should be given to operating costs, which usually to a large extend depends on the type of absorption agent and the costs for disposal of the sulfur compound produced.

Jan 1, 2009

By Klaus Hasselwander

Fluctuating SO2 gas streams represent a difficult task for designers of SO2 removal systems (with respect to designing the plant), but in spite of the designers great efforts to solve the problems, the operation of such plants requires much care and attention. A fluctuating gas flow usually results from metallurgical smelting processes. Both gas composition and gas flow rate may vary. The first part of this paper outlines some existing technical solutions and presents the Pros and Cons of the different solutions. These solutions outline are: - Sulphuric acid plants operated with a preheater permanent in operation - Sulphuric acid plants with concentration increase of SO2 gas either using regenerative SO2 removal or cryogenic partial condensation of the SO2 - Sulphuric acid plants with additional burning of sulfur to increase SO2 content - Single-stage sulphuric acid plants followed by a tail gas system (which is) designed for periods of low SO2 input In the second part, this paper describes some existing technical solutions for removal of SO2 at low concentrations (i. e. less than 0.1 - 2 %-by volume), which could be used as tail gas treatment system for acid plants. While selecting an appropriate solution, special attention should be given to operating costs, which usually to a large extend depends on the type of absorption agent and the costs for disposal of the sulfur compound produced.

Jan 1, 2009

For resources projects with healthy net present value (NPV) and low cash flow volatility, conventional discounted cash flow (DCF) analysis will continue to provide the dominant investment decision-making criteria. However, DCF analysis can be biased because it often applies a single risk-adjusted discount rate (RADR) to compare the value of projects with different risk characteristics. Many of the difficulties with DCF modelling arise from analysts' inability to determine appropriate risk discounts and to estimate expected spot prices inputs for the commodities produced over the life of the project. Modern asset pricing (MAP) is a very valuable complement to DCF analysis in addressing some of these issues. Most papers dealing with MAP, however, while academically rigorous, tend not to be explicit in terms of practical application of this methodology in routine project evaluation. This paper has the objective of reviewing the MAP methodology and of demystifying its complexity, by providing a simple but realistic step-by-step evaluation of a mining project, comparing its DCF and MAP NPV values. The paper concludes that MAP provides a minimum, risk-adjusted `floor' value, thus representing a valuable complement to any DCF valuation.

Jan 1, 2007

By G. P. Dyke

With the removal of the majority of the shallow mineral reserves there has been an increase in the mining depths in the South African mining industry. This has, in turn, changed the industry?s and stakeholders? perceptions of risk associated with mining-induced instability. In recent years the increased mining depth, particularly in open pits, has led to an increase in pit slope failures, which has highlighted the need for appropriate and effective pit slope management programmes. Such a programme comprises many facets, including mine hazard plans, regular slope inspections, cleaning of interim and final pit faces, blasting practices, histories of failures, pit depressurization, stormwater control and evacuation procedures. However, it is arguably in the field of slope monitoring that the most significant strides have been made in terms of new technologies and best practice in open pit mining geotechnics, with the introduction of technologies such as laser scanners and slope stability radar. This paper seeks to illustrate the operational benefits associated with the implementation of new technologies into open pit mining, using AngloGold Ashanti?s Geita Gold Mine in Tanzania as an example.

Jan 1, 2009

Mr G H Park was born and brought up in Zimbabwe, in mining from the University of the Witwatersrand. Starting as a Learner Official at Rand Mines, he went Mr D J van Niekerk was educated at Helpmekaar Boys' High School in Johannesburg and the University of Pretoria. Mr C J C Janse van Vuuren was educated at Klerksdorp High School, Pretoria Technical Colege, the University of Pretoria, and Unisa. He holds the folowing degrees: BSc (I&S), BSc Hons (Met Pta), ND (Met Tech), AEP (Unisa). Prof. R F Sandenbergh was educated at the Afrikaanse Hoerskool Germiston and the University of Pretoria. He holds the degrees of B Ing (Chem), M Ing (Chem), and D Ing (Metal). President's Award Professor Jannie van Deventer, Head of the Department of Metalurgical Engineering at the University of Stelenbosch, has been honoured with one of the five President's Awards for 1990. These awards are made by the CSIR's Foundation for Research Development. G R Bozzoli Awards* Prof. Alan Kemp, Dean of the Faculty of Engineering at the University of the Witwatersrand, has appealed to industry not to cut bursary funding during recessionary times.

Jan 1, 1990

The key functions of project evaluation are to assess potential profitability and to develop an effective operational design. For mining projects, design aspects include mining methodology, ore treatment methodology and production rates. All of these characteristics impact on project economics and overall value. Resource models, which form the ultimate basis of project evaluation, typically consist of tonnes above cut-off, grade above cut-off and the spatial distribution (connectivity) of tonnes/grade above cut-off, for one or more variables. Dilution, ore loss and metallurgical recovery are all modifying factors applied to the resource model during evaluation and determination of profitability. A key issue is: how is the value determined? In addition to traditional combination of in situ tonnes/grade, the following merit serious consideration: the concentration of deleterious elements, throughput rates, mining/processing costs and - importantly - metallurgical recovery. Geometallurgy is an emerging field targeted at integrating these issues by identifying either direct measures or proxies for throughput (hardness, grindability), recovery (liberation, mineral shape/texture, etc) and concentrate quality from easily collected macro-, meso- and microscopic data. These 'geometallurgical variables' drive project costs and revenues in a fundamental way. For geometallurgical characterisation to have a real impact on business design, it must enable improved mine planning. When creating spatial estimates for such variables, it is preferable to find proxies that can be measured as close to the intact rock mass as possible. However, spatial estimation of proxies for geometallurgical properties and responses is complex and requires special consideration. Unlike grades, both proxies and absolute measures of geometallurgical variables are not necessarily linear or additive and therefore require very careful geostatistical consideration. In some cases, models must predict extreme values of geometallurgical attributes rather than averages. Incorrect characterisation of metallurgical recovery/throughput can (and has) led to misspecification of the scale of projects, and thus can be seriously value destructive. Aspects of geometallurgy have long been important in iron, bauxite, manganese and coal deposits and are increasingly on the radar for base and precious metal miners. However, as more metallurgically complex deposits are developed and mining of large-scale, low-grade deposits becomes more commonplace, the importance of characterising the metallurgical response in order to generate properly optimised projects will rapidly increase. It is possible that in many `traditional' (ie grades and tonnes) reserve models, the variables that drive the project are missing!

Jan 1, 2007

By A. M. Clegg

In general, overall experience has shown that the approach to the appointment of a project manager is given much attention, but little specific attention is given first to the risk associated with the project conceptual design and its overall executability within either the new legislative framework or the sustainability of the outcome. The risk in project executability and sustainability within the ?new age? legislative framework of the Mining Charter, etc, is itself however, of far greater importance. The degree of importance being defined by the intended projects impact on the business going forward. This is particularly the case where the intention of the implementation is effectively to turn around or even enhance a loss-making strategic investment like a mine or process plant operation in an ?old-order rights? or Brownfield?s operation. This paper attempts to highlight the importance of a ?pre-project project? (PPP) to mitigate the risk in the ?new age?, with specific reference to operational due diligence (ODD) and project conceptual design.

Jan 1, 2005

The corrosion behaviour of a low carbon steel was investigated in synthetic seawaters with and without Sr2+. It was found that strontium substitutes for calcium in aragonite, rather than precipitating as discrete strontianite (SrCO3). The aragonite deposits that formed in the presence of Sr2+ were finer than those that formed in the absence of Sr2+. It is believed that an increase in the strontium content of aragonite induces a decrease in its solubility, which in turn results in a higher nucleation rate of the precipitates. Furthermore, the growth rate of aragonite is decreased by the presence of Sr2+in the solution. It is concluded that Sr2+is an essential ingredient in any artificial seawater when calcareous deposits are investigated on steel. Keywords: corrosion, seawater, calcareous deposits, strontium, aragonite.

Jan 1, 2007

Electrochemical measurements are presented on electro-deoxidation of silica in molten calcium chloride at 900°C, with porous silica pellets as starting material. Measurements during pre-electrolysis (to remove water from the melt) showed electrochemical noise, which is consistent with the evolution of hydrogen. Throughout, the dominant anodic reaction appears to be CO2formation, based on the observed potential at the anode, and measured anode wear. Because of the presence of dissolved CaO in the melt, some of the CO2 candissolve in the melt; the resulting calcium carbonate formation was confirmed by electrolyte analysis after reduction runs. Reduction of dissolved CO2 at the cathode is likely to contribute to the background current during the reduction process. For the electrode and cell configuration used here, most of the over potential arises from polarization of the anode, and ohmic potential drop in the electrolyte.

Jan 1, 2006

By M. B. Cortie

An account is given of the development of ferritic stainless steels since their discovery in the early years of this century. The alloys became very widely used in the 1950s, the market during that decade being driven strongly by a demand for automobile trim made of ferritic stainless steel. The production of ferritic stainless steel declined as a proportion of the total at the end of the 1950s as consumer preferences changed. However, the market is now growing strongly again, this time driven by a demand for oxidation-resistant alloys for motor-vehicle exhaust systems. The tonnages produced, applications, and market shares of the various alloys are discussed and compared. Trends in world stainless-steel production, product forms, technological development, and usage are examined.

Jan 1, 1993

By L. Andrews

Mineralogy, traditionally associated with concentrator studies, is being increasingly applied to problems in pyrometallurgy. Such investigations commonly make use of a number of techniques, and the results are combined for a meaningful interpretation, which can lead to a successful solution for the problem. Mineralogical techniques are described for various pyrometallurgical operations. Examples are given of studies and investigations involving mineralogy in chemical-looping combustion, feed monitoring to platinum-smelting furnaces, and losses to slag in base metal and platinum smelting.

Jan 1, 2011

The optimal design of production phases and ultimate pit limit for an open pit mining operation may be generated using conventional or stochastic approaches. Unlike the conventional approach, the stochastic framework accounts for expected variability and uncertainty in metal content by considering a set of equally probable realizations (models) of the orebody. This paper evaluates the performance of a new stochastic network flow approach for the development of optimal phase design and ultimate pit limit using a gold deposit as the case study. The stochastic and conventional frameworks as considered here utilize the maximum flow and Lerchs-Grossman (LG) algorithms, respectively. The LG algorithm is restricted to considering an estimated (average-type) orebody model, while the stochastic maximum flow algorithm is developed to simultaneously use a set of simulated orebody realizations as an input. The case study demonstrates that, when compared to the conventional LG algorithm as used in the industry, the stochastic approach generates a 30 per cent increase in discounted cash flow, a 21 per cent larger ultimate pit limit, and about 7 per cent more metal, while it maintains a consistency in phase size.

Jan 1, 2012

By M. J. King, W. K. B. Loftus, H. S. Simpson

SYNOPSIS The history of the early diamond fields and primitive methods of diamond recovery are traced, giving a brief description of the improvements made in final diamond recovery processes and techniques up to the present day. In particular the emphasis is on the effect of improved equipment in reducing final hand sorting time and labour, better security and greater recovery of fine diamonds.

Work undertaken in the field of cut-off grade optimization has not advanced much beyond the work undertaken by Lane in 1988. His definitive work is based on the calculus of the Net Present Value criterion which is the most widely understood, consistent, and appropriate method by which sequential cash flows arising from the extraction of mineral reserves from an exhaustible resource can be represented. Although the mathematics is not complex Lane’s method is not a widely appreciated or applied approach to maximizing the value of a mining operation through selection and balancing of operational cut-off grades. Three stages in a mining operation namely, mining, processing and marketing were defined by Lane and the economics of each stage are identified and isolated to provide an optimum cut-off for each stage. Points of intersection along the present value curves for each stage of a mining operation are used to identify balancing cut-off grades at points where the capacity of the mining, processing and marketing stages is fully utilized and the Net Present Value of the operation is optimized. Data that simulate a small, deep-level Witwatersrand-type gold mine with an average grade of 6 g/t Au and a logrithmic variance of 1.2,are applied to the model to illustrate the benefits of representing cut-off grades in terms of present value curves for different segments of a mining operation. Keywords: Cut-off grade, Net Present Value, grade-tonnage curve, balancing cut-off grade, mining, processing, marketing.

Jan 1, 2003

By M. Pelser, J. Hagemann

"The Anglo American Platinum Rustenburg Base Metals Refiners (RBMR) is the largest producer of nickel cathode in South Africa. It treats slow-cooled matte to recover a platinum group metal-containing magnetic fraction for downstream processing and a nonmagnetic fraction to produce nickel and copper cathode, cobalt sulphate, and sodium sulphate. The refinery was recently expanded from 21 to 33 kt/a nickel. During the ramp-up phase, the sulphur removal section was found to be a constraint to throughput. Nickel hydroxide is precipitated from nickel spent electrolyte by addition of sodium hydroxide, and filtration of the nickel precipitate allows sulphur to be removed from the circuit as aqueous sodium sulphate in the filtrate. The filtration fluxes were found to be limiting the circuit’s capacity. An obvious solution would have been to install additional filtration capacity at significant capital cost and long lead times. RBMR chose rather to first initiate a collaborative project with Anglo American Technical Solutions to better understand the impact of process conditions on filtration characteristics and to evaluate whether the filtration flux could be increased by improving the quality of the nickel precipitate.A deeper understanding of nickel hydroxide precipitation chemistry and kinetics in the context of high nickel and sodium hydroxide concentrations was developed, guided by precipitation theory and confirmed by laboratory tests and plant observations. It was found that the filtration rate could be significantly improved by modifying the precipitate characteristics. A new precipitation process was engineered and retrofitted into the existing plant. Since start-up of the new precipitation system, the available capacity of the sulphur removal section has more than doubled, and control of the process has improved with the better agitation. This paper describes the theory and results used to design the new agitation system, as well as the impact of the change on capital investment, operability, and process efficiency."

Jan 1, 2016

This paper provides a review of the chemical reactions occurring in the submerged arc processing of chromite ores. The excavations of industrial furnaces have shown that the charge, as it descends through the furnace, passes through a number of distinct reaction zones. Each zone is characterised by differing process conditions and reaction products. The phase equilibria, reaction steps and mechanisms occurring as the charge progresses through the furnace are examined, and the potential influences of these factors on the process outcomes are discussed.

Jan 1, 2004

By M. Syamujulu

In 1994, Nkana smelter commissioned a multimillion US Dollar Chilean Teniente converter (CT) in its operations in order to improve its smelting technological base. The main objective was to reduce the overall smelting energy costs and increase the sulphur capture for sulphuric acid production to support the company?s leaching operations at Nchanga tailings leach plant. A decade of CT operations have since ensued following its installation and start-up. This paper provides a technical and operational audit of the performance of the CT in the first 10 years of its operations at Nkana smelter.

Jan 1, 2005

By A. Lane

The socio economic risks of mining in South Africa have been emerging for some time now, and have been brought into sharp relief by recent events in the platinum sector. The slow pace of social upliftment in the country has lead to widespread social unrest with consequent calls for different forms of resource nationalism. Fundamentally, the key stakeholders are not fully aligned, and are not engaging productively. This poses significant above-the-ground risk to mining companies. Measuring social impact, deploying inclusive solutions and engaging effectively with stakeholders are three ways in which mining companies can mitigate this risk.

Jan 1, 2013

By W. U. Reimold, R. Armstrong, R. G. Charlesworth

For many years rockbursts have plagued the mining industry. Although much research has gone into studying this phenomenon only a small proportion of it has been on the actual source mechanism. A study was recently carried out to compliment the previous work done on the micro-structure of these features and to compare it to the micro-structures seen on shatter cones, from meteorite impacts. Both optical and electron-microscopy were used during the study. Samples were collected from rockburst sites by the CSIR Miningtek Rockburst Investigation Unit, and from the collar of the Vredefort Impact Crater. In the optical-microscopy study, the pinnate fractures observed in previous studies were seen in the shatter cones, through all the material. In the rockburst samples, the fractures were observed only in the quartz grains. Quartz micro-crystals were present in the rockburst samples and appeared to be the product of comminution rather than crystallisation. Cataclasite was present on rockburst and shatter cone fracture surfaces. The observations of the shatter cone surfaces with the scanning electron microscope are in agreement with previous work, including the observed presence of melt features, spherules and spheroidal material. The deformation in the rockburst samples is concentrated in the quartz grains, highly complicated with brittle features like sub-conchoidal structures and step structures present. A quartz spherule was identified on one rockburst sample and rhombic-dodecahedra type micro-crystals were present and seen fracturing off quartz grains. It is clear that the rockburst and shatter cone fracture surfaces are quite different; the shatter cone deformation is equally distributed across the sample and involves plastic-deformation, while the deformation in the rockburst material is concentrated in the quartz grains and, with the exception of spherule formation, is brittle. This study agreed with the current explanation for the formation of the rhombic-dodecahedra, and disproved the possibility of it being coesite or fine-grained meta-chert. Although there is no definite evidence of the mechanism of formation of the spherule, it is believed to be the product of vaporization and condensation, and the presence of this material indicates the extreme conditions under which this event occurred.

Jan 1, 2003

In the previous chapters we did not concern ourselves with the fact that the geostatistical properties of the regionalized variable x (z) are affected by the size of the support w. Ideally, when analysing an ore body O, we would like to determine the properties of point values in O, i.e. the properties of a regionalized variable with an infinitely small support, say w°. In practice, point values are never known. To measure the value of x at a point z we must take a sample of size w centred at z. For example, if we are interested in the grade at point z, w will be the volume of the sample 'centred in z; if we are interested in the metal accumulation at point z, w will be the area of the cross-section of the sample centred in z. We say that the measured property is a regularized variable, and so the semivariogram (or covariogram) calculated from the values obtained is also regularized. In the majority of the mining problems which can be solved by geostatistical methods, we are interested in the properties of blocks of ore and of samples with a finite non-point support. It will be shown in the following chapters that these problems can be solved by calculating the average value of the point sernivariogram in volumes or areas of finite dimension, or between such volumes or areas. These calculations would be simple if we knew the point semivariogram. This means that the point semivariogram has to be estimated from the observed regularized semivariogram(s).

Jan 1, 1978