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By Glen Mc Gavigan

The roof of the Sishen cave is being mined in order to exploit 6.8Mt of high grade ore. The cavity is filled with quartzite backfill in order to support the roof in the event of collapse. The cave dips at approximately 37o, is 260m along dip and 70m along strike and has a total volume of 261,391m3. GPS and optical monitoring techniques were attempted to detect subsidence but proved to be impractical. The GroundProbe Slope Stability Radar (SSR) uses differential interferometry to measure sub millimetre movement in a rock face. The SSR was applied in a non production situation and detected subsidences of 38mm/day before visual signs of instability were detected. The rate of deformation detected was slowing as a result of the roof coming to rest on underlying backfill. Monitoring during production drilling detected a sudden subsidence of 18.6mm/hour which resulted in the evacuation of personnel from the area. Further inspection of data showed that the rate of deformation was slowing and production was allowed to continue without further incident. The SSR has helped dispel the fears of workers and has proven that subsidence can be accurately measured and delineated with the SSR.

Jan 1, 2006

By N. Anacleto, S. Ganguly

Reduction of Groote Eylandt (Australia) and Wessels (South Africa) manganese ores using CH4-H2-Ar gas mixture was investigated in a fixed bed laboratory reactor in the temperature range 1000?1200oC. The extent and kinetics of manganese ore reduction as a function of gas composition and temperature were determined by on-line off-gas analysis using mass-spectrometer and dew point sensor. Morphology of ores and its change in the course of reduction was examined by optical and scanning electron microscopy. Phases of raw materials and reduced samples were analysed by XRD and EPMA. Manganese oxides were reduced to carbide Mn7C3. High extent and rate of reduction by methane-containing gas in comparison with carbothermal reduction were attributed to high carbon activity in the reducing gas, which was in the range 15 - 50 (relative to graphite). The reduction rate of Wessels manganese ore increased with increasing temperature. Reduction rate and extent of Groote Eylandt manganese ore achieved maximum at 1050oC. The decrease in rate and extent of reduction of Groote Eylandt ore at higher temperatures, particularly at 1150-1200oC, was due to sintering and formation of semi-liquid silicate slag. The optimum conditions for the reduction of manganese ores were established as follows: a) temperature: 1150-1200oC for Wessels and 1050-1100oC for Groote Eylandt ores, b) methane concentration: 10-15 vol%, c) hydrogen concentration: above 30 vol%, (d) size: 1-3 mm. An addition of lime (10-15 wt% CaO) to the Groote Eylandt manganese ore increased melting temperature of slag and significantly increased the rate and extent of reduction at elevated temperatures.

Jan 1, 2004

By W. G. Huang

To recover the coal resources of high-sulphur anthracite in Jincheng Mining Area, underground coal gasification (UCG) of No. 15 seam in Fenghuangshan Coal Mine was proposed. The feasibility of the project was confirmed by investigations of occurrence conditions, coal properties, and roof conditions, as well as experimental studies and theoretical analysis. It was found that UCG technology is appropriate to be adopted in the mining of the No. 15 seam, due to the stable rock conditions, simple geological structure and hydrogeology, the high carbon content of the coal, non-cohesiveness, medium-thermal stability, high ash fusion temperature, and weak reactivity with CO2. Further factors are the characteristics of the immediate roof, which consists of 9.11 m of limestone and mudstone with a compact structure and low permeability, and 4.27 m of dominantly mudstone with low permeability.

Jan 1, 2012

By S. Budavari, F. M. C. C. Vieira

For several decades, the deep, gold-bearing reefs of the Witwatersrand basin have been mined predominantly according to layouts characterised by longwalls with strike pillars to provide regional support. During the past few years, a new generation of mining layouts has been introduced. These layouts are based on the concept of grid-type, scattered mining with dip pillars for regional support. As the extraction of the gold reefs extends to depths below 3500 m, the hazards associated with mining at these ultra-depths are expected to increase to unacceptable levels. Therefore, the question arises as to, which of the currently applied mining layouts is most acceptable for the economic and safe extraction of an ultra-deep orebody. The purpose of this paper is to describe a research investigation carried out to evaluate the degree of acceptability, from the rock engineering view point, of four currently used mining layouts for application at a depth-range of between 3500 and 5000 m. Pendant plusieurs décades, les filons d’or profonds du bassin du Witwatersrand ont été exploités d’une manière prédominante selon des dispositions caractérisées par des longues tailles avec des piliers directionnels pour donner un support local. Les dernières années ont vu la naissance d’une nouvelle génération de dispositions de mine. Ces dispositions sont basées sur le concept d’extraction type grille, éparpillée, avec des piliers au pendage pour le support local. Comme l’extraction des filons d’or va à des profondeurs en dessous de 3500m, il faut s’attendre à ce que les risques associés à l’exploitation à ces profondeurs extrêmes atteignent des niveaux inacceptables. Par conséquent, la question se pose de savoir laquelle des dispositions de mine couramment utilisées est la plus acceptable pour l’extraction rentable et sans danger d’un gisement ultra profond. Le but de l’étude présente est de décrire les recherches exécutées pour évaluer le degré d’acceptabilité, du point de vue d’ingénierie de roche, de quatre dispositions de mine couramment utilisées pour application à un rayon de profondeur entre 3500 et 5000m. Die tiefen, goldträchtigen Riffs des Witwatersrandbeckens wurden über einige Jahrzehnte hindurch vorwiegend nach jenen Layouts abgebaut, die von Langfrontstreben mit Schlagpfeilern charakterisiert waren, um regionale Unterstützung zu gewährleisten. Während der letzten Jahre wurde eine neue Generation von Grubenlayouts eingeführt. Diese Layouts basieren auf dem Konzept der Rasterfeld-Art, gestreuter Bergbau mit Neigungspfeilern für regionale Unterstützung. Es kann erwartet werden, daß auf Grund der Tatsache, daß sich die Extraktion der Goldriffs auf Tiefen unterhalb 3500 m verlagert, die Gefahren, die mit dem Bergbau an diesen Ultratiefen verbunden sind, sich auf ein nicht annehmbares Niveau erhöhen. Folglich erhebt sich die Frage, welche der gegenwärtig angewendete Abbaulayouts für die ökonomische und sichere Extraktion eines ultra-tiefen Erzkörpers am annehmbarsten ist. Zweck dieser Arbeit ist es, eine durchgeführte Untersuchung zu beschreiben, die vom Gesichtspunkt der Gesteinstechnik gesehen, vier gegenwärtig angewandte Abbaulayouts für den Einsatz in einem Tiefenbereich zwischen 3.500 und 5.000 m evaluiert.

Jan 1, 2003

By S. K. Murphy, K. B. Le Bron, A. K. Ward, S. Hayes, T. Rangasamy

A process for evaluating different options for extraction of mining blocks is presented. The process is described and an example of the application of the process to a case study is presented. Un procédé pour évaluer différentes options pour l’extraction de blocs d’exploitation est présenté. Le procédé est décrit et un exemple de l’application du procédé à un cas particulier est présenté. Ein Prozeß für das Auswerten der unterschiedlichen Optionen für die Extraktion von Abbaublöcken wird dargestellt. Der Prozeß wird beschrieben und ein Beispiel der Anwendung des Prozesses zu einer Fallstudie wird dargestellt.

Jan 1, 2003

By T. Scheldt, M. Lu, A. Myrvang

Abstract: In this paper both continuous and discontinuous modelling are utilised in order to analyze the stability of the Gjøvik Olympic Mountain Hall. The large span cavern (62 m) was built for the 1994 Winter Olympic Games at Lillehammer, and is a unique case study because of the large amount of available input data, through a comprehensive pre-investigation, stress and deformation monitoring program before, during and after the excavation. Phase2, a two-dimensional non-linear finite element program, and the Discontinuous Deformation Analysis (DDA) are used as representative tools for continuous and discontinuous modelling, respectively. The analysis results are compared and discussed taking the reliability of the models, time-consumption and costs into consideration. Some guidelines for the total modelling process, from field measurements to final results, are also presented. Zusammenfassung: In diesem Artikel werden sowohl kontinuierlich als auch diskontinuierlich Modellierung verwendet, um die Stabilität, der in den Berg gebauten Olympiahalle in Gjøvik zu analysieren. Die Olympiahalle wurde 1994 zu den Olympische Spielen in Lillehammer errichtet. Ihr Dach erstreckt sich über eine Breite von zweiundsechzig Meter. Für den Bau wurden umfangreiche Daten durch Voruntersuchungen, und Überwachung von Gebirgsspannungen und Deformationen bevor, während und nach Exkavation eingesammelt. Auf Grund dieser großen Datenmenge stellt die Olympiahalle ein herausragendes Beispiel für den Bau ähnlicher Projekte dar. Für die kontinuierlichen Modellierungen wurde „Phase2“, ein zwei-dimensionales, nicht lineares „endlich Element“ Rechnerprogramm angewandt. Die diskontinuierlichen Modellierungen erstellte man mit Hilfe von der „Diskontinuierliche Deformations Analyse“ (DDA). Die Analysenergebnisse sind mit Rücksicht auf die Zuverlässigkeit der Modelle, Zeitverbrauch und Kosten verglichen und diskutiert worden. Im Artikel werden Richtlinien für den Modellierungsprozess von Dateneinsammlung bis Schlussfolgerung gegeben. Résumé: Dans cet article la modélisation continue et discontinue sont utilisés pour analyser la stabilité de Gjøvik Olympic Mountain Hall. Cette caverne de grande portée (62 m) a été construite pour les Jeux Olympiques d’Hiver de 1994 à Lillehammer, et est une étude de cas unique grâce à la grande quantité de données disponibles, de par un programme de pré-investigation compréhensive, monitorage des contraintes et déformations avant, pendant et après l'excavation. Phase2, un code d’éléments finis non linéaire à deux dimensions, et l’Analyse en Déformations Discontinues (DDA) sont utilisés comme outils représentatifs de la modélisation continue et discontinue, respectivement. Les résultats d'analyses sont comparés et sont discutés, prenant en compte la fiabilité des modèles, la consommation en temps de calcul et les coûts. Quelques indications pour le procédé total de modélisation, des mesures sur place aux résultats finaux, sont aussi présentées.

Jan 1, 2003

By T. Fabritius, L. Hekkala, J. Härkki

The Outokumpu steel belt sintering technology is used for manufacturing chromite pellets that are charged into smelting furnace for ferrochromium production. Hot air is blown through the moving bed of raw pellets. Direct temperature and flow measurements are difficult to do in the bed of a real scale belt sintering process. Therefore, a tested and reliable mathematical model would be a valuable help for optimising operational parameters of the process and designing new constructional improvements. The aim of this work is to present a mathematical model that calculates the gas flow and temperature distribution in the bed of pellets and the atmosphere. Computational fluid dynamics program FLUENT is used to calculate the gas flow, composition and temperature of the gas in the sintering bed during processing. Energy equation for the bed, containing the effects of evaporation of water and oxidation of carbon and iron oxide, will be added to the model to obtain the temperature of the pellets. The porous media model used for pressure drop calculations in the bed is shortly discussed. A comparison between CFD-calculations and experiments with a pilot scale batch-sintering reactor are also presented. The final model can be used as an engineering tool when developing the process and the equipment further. Different designs can be easily tested with the model and the effects of the changes to the flow pattern and temperature distribution can be studied.

Jan 1, 2004

By D. M. Walters

To achieve safe and healthy working conditions in shaft sinking operations, ventilation, and where necessary cooling, must be provided. These requirements are considered for sinking vertical, sub-vertical and decline shafts. Regulatory requirements, determining air volumes and amount of cooling required, the various ventilation methods used such as force, exhaust, twin columns, air reversal using four gate systems and the equipment required to achieve this, are discussed. Consideration is also given to the sinking of single and twin declines using diesel equipment, calculating the air volumes required to dilute pollutants and the various methods for achieving this. Also discussed is the importance of having early ventilation design input to the overall design of the mine. In many cases ventilation can be the prime determinant for the size and configuration of the shafts or declines that have to be sunk.

Jan 1, 2009

By D. M. Walters

To achieve safe and healthy working conditions in shaft sinking operations, ventilation, and where necessary cooling, must be provided. These requirements are considered for sinking vertical, sub-vertical and decline shafts. Regulatory requirements, determining air volumes and amount of cooling required, the various ventilation methods used such as force, exhaust, twin columns, air reversal using four gate systems and the equipment required to achieve this, are discussed. Consideration is also given to the sinking of single and twin declines using diesel equipment, calculating the air volumes required to dilute pollutants and the various methods for achieving this. Also discussed is the importance of having early ventilation design input to the overall design of the mine. In many cases ventilation can be the prime determinant for the size and configuration of the shafts or declines that have to be sunk.

Jan 1, 2009

By P. den Hoed, R. I. Rambiyana

"Four sulphide minerals - pyrite (FeS2), pyrrhotite (Fe1-xS), pentlandite ([Ni,Fe]9S8), and chalcopyrite (CuFeS2) - contain the base metals and most of the iron in concentrates of platinum group metals (PGMs). In the pyrometallurgical processing of PGM concentrates these sulphides form a matte during smelting, and iron and sulphur are removed from the matte during the converting process. This paper discusses the roasting of Merensky concentrate in air before smelting, with the purpose of reducing the matte load to the converter.Roasting tests were conducted in a bench-scale rotary kiln at temperatures from 350°C to 700°C. The concentrate tested contained 17.4% sulphur and consisted of 23% pyrrhotite, 16% pentlandite, 11% chalcopyrite, and 2% pyrite. The particles were fine (d50 = 22 µm), and all the sulphide particles were liberated. Roasting in air at 550°C and 650°C for 20 minutes removed respectively 60% and 70% of the sulphur. The iron in the sulphides was oxidized to Fe3O4 (magnetite) at temperatures below 500°C and to Fe2O3 (haematite) at temperatures above 550°C. At 700°C the bed sintered and copper oxides formed. At temperatures below 450°C oxidation was incomplete: pyrrhotite remained and only 30% of the sulphur was removed. Smelting tests were conducted to assess matte fall and the deportment of copper and nickel to matte. It was evident that roasting resulted in lower matte falls (a drop of approximately 60%) compared with matte falls from unroasted concentrate. The iron and sulphur levels in the matte were reduced to below 3.5% and 22% respectively.This paper also briefly describes the mechanisms by which pyrrhotite, chalcopyrite, and pentlandite are oxidized during roasting. For chalcopyrite, the mechanism proceeds through an intermediate solid solution phase, which extends from Cu1.02Fe1.04S2 to Cu2.04Fe0.72S2 to a copper-rich solid solution of bornite (Cu4Fe1.4S4-Cu2S). The oxidation of pentlandite proceeds through a monosulphide solid solution (Ni0.39Fe0.53S-Ni0.74Fe0.15S) to a solid solution of heazlewoodite ([Ni,Fe]3}xS2). These mechanisms are explored in relation to chemical thermodynamics and microstructures."

Jan 1, 2015

By G. Song

"SynopsisAccording to the overlying rock strength and thickness of 10 shallow coal seams in China, the strata are classified into four types: weak and laminated strata (hereinafter referred to as WL), weak and massive strata (WM), strong and laminated strata (SL), and strong and massive strata (SM). The four types of strata, together with longwall panel height (M), panel length (L), and seam depth (H) are factors that influence the loads on hydraulic power supports. Principal component analysis was used to study the seven influencing factors. It turns out that seam depth (H) is multicollinear with WL, WM, SL, and SM. Thus the enumerated seven factors are divided into two models. In Model 1, six factors; panel height, panel length, and layer thickness of the four type strata are involved. In Model 2, three factors; panel height, panel length, and seam depth are included. Using multivariate regression analysis, two equations to calculate loads on supports are obtained for each model. The equations were applied to shallow coal seams. The equation of Model 1 is more accurate than that of Model 2, but Model 2 could be further used in deep coal seams. The equations were coded through VB programming to simplify the calculation.IntroductionTo ensure coal production in the long term, the focus of coal mining has been gradually shifted to the western areas of China in recent years due to rich coal resources in this region. Most of the coal seams in this area are shallow but the support loads are abnormally high. In these circumstances, the chock loads estimating methods used in the past do not work. If the rated working resistance of a support is larger than needed, the shield is unable to fully perform, while a lower working resistance would lead to accidents like shield crushing or even casualties. This problem is frequently found in shallow coal seams such as Shenfu-Dongsheng, Yulin, Tuha, Lingwu etc. (Zhang, 2011). Thus, to ensure safety and efficiency during mining, the estimation of support loads and selection of supports are of great significance."

Jan 1, 2015

By Simon St J Tose

The objective of this paper and presentation is to review the different criteria and methodology used by AEL and other organisations to create a pre-split design which delivers a stable highwall for the life of that part of the mining operation. It will look at the need to adapt and change the way, size and direction of the production blasts as the mining phase approaches the highwall position for which a pre-split has been created. Key Words: Pre-split: Design; Highwall; Perimeter

Jan 1, 2006

By A. Bothma

The Impala No. 1A ventilation shaft is located approximately 15 kms north of Rustenburg and is accessed via the R510road from Rustenburg to Northam/Thabazimbi. This situation is shown on the location plan in Figure 1. The geology at the site consists of an upper layer of black turf of about 1 metre in thickness, grading into weathered norite. The depth of weathering is generally less than 5 metres. Zones of deeper weathering may occur along fracture zones associated with faults and dykes. Groundwater occurs mainly within the weathered/fractured aquifer system. The ventilation shaft is a 5.1 m diameter upcast shaft ,and forms part of a system of ventilation shafts to complement the existing infrastructure as mining progresses down the new twin decline extension of Impala 1 shaft. The principal reason for these shafts is to lessen the risk of an extended RAW and also to counter the effects of the heat build-up as the mining goes deeper, with the resultant effect that the existing cooling centre (fridge plant) becomes more remote from activities. The No. 1A shaft (upcast) is positioned approximately 1,2 km on down dip from the main shaft and the No. 1Bshaft (downcast) approximately 1,2 km further. Geological information was used from a borehole 1,2 km away on strike from the upcast shaft. The first shaft (1A) is a 5,1 m diameter hole to be fitted with two 2,2 MW fans, whilst the second shaft (1B) is 4,1 m diameter to accommodate a 7MW fridge plant.

Jan 1, 2001

By T. Tholana, P. N. Neingo

"Mining companies globally are currently facing severe economic and financial challenges. In addition to global challenges, the South African mining industry has to face other operational challenges that are unique to the country and which threaten the survival and competitiveness of the industry. Profit margins are being squeezed by rising costs and decreasing commodity prices, while labour productivity is greatly affected by intermittent labour unrest. This paper analyses how the South African gold mining industry has performed pre-, during, and post the global financial crisis of 2008. The competitiveness of the industry in terms of labour productivity and industry cost curve position is analysed for the period 2006–2013 to assess the impacts of both the global financial crisis and labour unrest. An analysis of the South African gold mining industry is presented at company as well as mine level. Productivity measure in this paper is limited to labour productivity, in line with limited reporting on productivity. All the data analysed was obtained from the public domain. IntroductionSouth Africa dominated the world as the number one gold producer until 2009 when China took that position, and today South Africa ranks fifth after China, Australia, Russia, and the USA. According to Statistics South Africa (2009), South Africa still had about 30 years of production in the gold sector, a forecast that fluctuates based on the day’s modifying factors. Although South Africa has a comparative advantage in terms of minerals endowment, there are challenges faced by the mining industry that hinder translation of the comparative advantage into a competitive advantage. The industry continually seeks to address these challenges to remain competitive in global markets while addressing national and community needs.Neingo and Cawood (2014) argued that stakeholders in mining are continually concerned with mine management’s ability to translate use inputs effectively into quality outputs. They further suggested close monitoring of effective utilization of people, materials, and money to obtain maximum production of commodities under given conditions. Productivity is measured in various ways, including unit cost, output per employee, and output per unit capital equipment"

Jan 1, 2016

By Darelle T. Janse van Rensburg

Some of the more recent developments in Paint Technology are solvent free materials. These coatings have mainly been formulated to overcome the negative attributes of solvent-based coatings, i.e. environmental, safety and health risks, potential for solvent entrapment and osmotic blistering, as well as the formation of micro-pores during the curing process. Two solvent free liquid epoxy coatings have been used extensively on power generation plant. However, very little is known regarding their long-term performance under different exposure conditions, as well as whether these coatings actually perform better than their solvent-borne counterparts. In addition, solvent free materials are generally used where outage periods are restricted and coatings need to be applied within a very short period. Though these materials have reportedly much shorter curing times than other conventional solvent-borne coatings, little is known regarding their limits with respect to maximum film thicknesses and being put into service while still being wet/partially uncured. The latter has become common practice at many power stations in the past two years or so. In addition, the application and curing methods of solvent free materials are different to that of solvent-borne materials, and may require equipment and application process changes. This paper covers the application and performance properties of solvent free coatings in comparison to solvent-borne materials primarily intended for immersion service. Numerous coatings were evaluated under immersed static and cyclic hydrostatic pressures. Other tests included short curing / early immersion tests, dry-to-touch and dry-through curing times, adhesion tests, surface tolerance tests, etc. The results show that the solvent free materials have clear benefits with respect to safety, health, environmental and long-term performance, but will be more difficult to apply compared to solvent-borne materials.

Jan 1, 2006

By R. E. Wilmot

The problem of corrosion of reinforcement in concrete structures is internationally recognised and represents the single biggest expenditure in the preservation of steel reinforced concrete structures. While the corrosion protection of the reinforcing steel is no substitute for design and the placement of good quality concrete, it does provide for a viable and economical extension of structural integrity and service life in the day-to-day and practical environment in which concrete structures are constructed. The mechanism of corrosion attack and consequent deterioration of reinforced concrete structures is well understood and documented. New structures can be designed and built to withstand corrosion. However, due to short-term economical restraints, many new reinforced concrete structures continue to suffer as a result of corrosion damage, which results from the corrosion of the steel reinforcing. This paper explores the economic and practical benefits offered by the application of hot dip galvanizing as a viable means of protecting reinforcing steel concrete structures. The paper also discusses technical misconceptions that exist with respect to the application and performance provided by the use of hot dip galvanized reinforcing steel.

Jan 1, 2006

By R. A. Puchner

The location of a decline shaft portal can have far reaching implications if the geotechnical conditions are not suited for safe and cost effective excavation. Ideally the portal should be positioned in an area where the excavation requires minimal support and the portal can be formed in reasonably competent rock. In many cases, however, the shaft is linked to an underground mining plan and the shaft may have to pass through poor ground conditions. Determining the optimal position at which tunnelling can commence i.e. the portal, is critical and requires a thorough geotechnical investigation. Methods used to acquire information for the assessment of the ground conditions are discussed in this paper. Selection of the appropriate methods is dependent on the anticipated ground conditions, the phase of investigation and restrictions due to site access and budget. Non-invasive techniques are often used during preliminary phases and invasive techniques for the detailed investigation. The methods used during each phase of investigation are discussed. Two case studies are then presented to provide examples of the investigative methods used in two different environments. The first being a flat featureless site with thick soils and deeply weathered bedrock, while the second is a mountainous site with differentially weathered rocky outcrops. Based on these cases, it is clear that an understanding of the geology and geomorphology of the site is vital to the final geotechnical assessment. Key words: Decline shaft, boxcut, geology, geomorphology, geotechnical, portal.

Jan 1, 2009

By R. A. Puchner

The location of a decline shaft portal can have far reaching implications if the geotechnical conditions are not suited for safe and cost effective excavation. Ideally the portal should be positioned in an area where the excavation requires minimal support and the portal can be formed in reasonably competent rock. In many cases, however, the shaft is linked to an underground mining plan and the shaft may have to pass through poor ground conditions. Determining the optimal position at which tunnelling can commence i.e. the portal, is critical and requires a thorough geotechnical investigation. Methods used to acquire information for the assessment of the ground conditions are discussed in this paper. Selection of the appropriate methods is dependent on the anticipated ground conditions, the phase of investigation and restrictions due to site access and budget. Non-invasive techniques are often used during preliminary phases and invasive techniques for the detailed investigation. The methods used during each phase of investigation are discussed. Two case studies are then presented to provide examples of the investigative methods used in two different environments. The first being a flat featureless site with thick soils and deeply weathered bedrock, while the second is a mountainous site with differentially weathered rocky outcrops. Based on these cases, it is clear that an understanding of the geology and geomorphology of the site is vital to the final geotechnical assessment. Key words: Decline shaft, boxcut, geology, geomorphology, geotechnical, portal.

Jan 1, 2009

By H. F. Niemand, C. J. Postma, P. L. Crouse

"SynopsisThe separation of zirconium and hafnium is essential in the nuclear industry, since zirconium alloys for this application require hafnium concentrations of less than 100 ppm. The separation is, however, very difficult due to the numerous similarities in the chemical and physical properties of these two elements.Traditional methods for separation of zirconium and hafnium rely predominantly on wet chemical techniques, e.g. solvent extraction. In contrast to the traditional aqueous chloride systems, the AMI zirconium metal process developed by Necsa focuses on dry fluoride-based processes. Dry processes have the advantage of producing much less hazardous chemical waste.In the proposed AMI process, separation is effected by selective sublimation of the two tetrafluorides in an inert atmosphere under controlled conditions, and subsequent selective desublimation. Estimates are made for the sublimation rates of the two tetrafluorides based on the equilibrium vapour pressures. A sublimation model, based on the sublimation rates, was developed to determine if the concept of separation by sublimation and subsequent desublimation is theoretically possible.IntroductionZirconium requires several purification steps to conform to nuclear-grade specifications. Little information is available on the sublimation separation of Zr and Hf compounds, especially in the fluoride form, the majority of which deals with sublimation under vacuum conditions. On the industrial scale, only vacuum sublimation of ZrF4 has been reported. No records were found for the sublimation of ZrF4 in an inert atmosphere. Information on the sublimation rate of ZrF4 or HfF4 in an inert atmosphere is also limited. The rate is assumed to be dependent on several factors, of which temperature, area, and composition are considered the most important."

Jan 1, 2015

By T. Lindstad, V. Myrvågnes

In the production of high silicon alloys, carbonaceous materials like coal, coke, charcoal and woodchips are utilized as reducing agents. Primarily based on historical prices of charcoal compared to fossil reduction materials, the Norwegian Ferroalloy Industry has mostly been using coal and coke (char) as carbon source. The most important role of the carbonaceous material is to react with the SiO gas to produce SiC. The ability of the reduction materials to bind SiO gas can be measured and the value is recognised as the reactivity of the carbon source. This reactivity is one of the most important parameters in the smelting process in order to obtain a high yield of metal. The reactivity of the carbon materials is directly correlated to the material properties. It is known that the rank of the coal influences the SiO reactivity where low rank is beneficial. Coals of the same rank have however proven to have varying reactivity. In order to investigate how the micro-constituents of coal influence the reactivity towards SiO gas, three single seam unwashed coals of different origin which fulfil the requirements of the Norwegian Ferroalloy producers have been chosen. As the structure in the carbonized product is a function of petrographic constitution and carbonization parameters, the coals have been separated into different density fractions. The various density fractions of the same coals proved to have significantly different petrographic composition. The coals were carbonized according to a procedure simulating the conditions the coals experience when charged to an industrial furnace. Chemical-, physical- and petrographical properties of both the coals and the resultant chars have been thoroughly examined and correlated towards the SiO reactivity.

Jan 1, 2007