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By M Bilodeau, G Caro, R Beaudoin, D Labrie

In 2005, Dyno Nobel Canada Inc, DynoConsult and CANMET-MMSL used their pool of expertise in blasting, ground control, open pit and underground mining, mineral processing, information technology and applied mineralogy to launch a research project aimed at evaluating the role of electronic detonators in the development of a sustainable energy-efficient rock reduction process. The overall objectives were to improve health and safety in a mining environment and reduce energy consumption and greenhouse gas (GHG) production in the Canadian mining industry. The study was conducted in a quarry located in Nova Scotia, Canada, with the objective of taking advantage of the higher accuracy and flexibility of electronic detonators towards improving blast efficiency and measuring its impact on productivity in a quarry environment and energy savings. Optimising the blast sequence was the first aspect to be considered before starting to look at designing bigger blasts and achieving productivity improvements, without creating additional environmental concerns, as the quarryÆs location was representing a challenge in itself in the surrounding community. The use of high-speed cameras (500 fps) was an improved means of analysing blast dynamics during the firing sequence. Seismic monitoring and linear superposition techniques were also applied to validate the sequences to be tested in all three specific geological areas. The combination of field measurements allowed to identify the optimal blasting sequences that would then be delivered accurately with the electronic initiation systems. The data from 12 blasts (six with electronic detonators and six with pyrotechnic detonators) carried out in three different geological formations (soft, medium and hard rock) showed that the electronic blasting technology could increase rock fragmentation by 15 to 20 per cent. A more uniform distribution of rock fragment size was also obtained. Blast improvements on downstream processes resulted in a five per cent productivity increase in rock excavation and transportation, a ten per cent energy reduction in primary crushing and a 15 per cent increase in the primary crusher throughput. A prototype soft-sensor based on primary crusher data (eg energy consumption, throughput, feed and product size distribution) and a simplified computer process model were developed for online measurement of a rock operating work index. Furthermore, rock samples were collected and specimens were prepared in order to determine the tensile and compressive strength of the rock materials, evaluate the aggregate crushing work index and examine the development of micro and macro-fractures under binocular and scanning electron microscopy (SEM). Blast-induced rock damage was evaluated at the end of the laboratory testing program. A reduction in rock hardness by about 30 per cent was observed after blasting. However, the impact of the blasting method (eg using electronic versus pyrotechnic detonators) on the induced rock damage was either absent or not perceptible within the measurement technique accuracy and the number of samples analysed.

Jan 1, 2007

By Ormsby W. R, Nicholson P. M

Woodcutters is a polymetallic vein-style deposit hosted by sediments of the Palacoproterozoic Whites Formation which forms part of the sedimentary sequence in the central Pine Creek Geosyncline. Past production and identified resources total over eight million tonnes at 5.5 per cent lead, 12.1 per cent zinc and 110 gA silver. The local geology is influenced by Archaean basement highs; the Rum Jungle and Waterhouse Complexes. Unconformably overlying basement are interbedded clastic and crystalline carbonate units (Batchelor Group) representing cyclic changes in the depositional environment. These exhibit onlapping features with the underlying rocks. Sediments of the overlying Frances Creek Group suggest a quiet period during subsidence and subsequent increase in water depth (the carbonaceous dolomitic shales and the interbedded dololutites of the Whites Formation) followed by proximal uplift resulting in the inundation of turbiditic flows (Acacia Gap Quartzite). All of the Palaeoproterozoic rocks show evidence of being affected by penecontemporaneous, basement circling faults with steep dips. The stress regime during the deposition of the Frances Creek Group was characterised by alternating episodes of thrusting and transpression. Periods of relaxation also occurred. The compression resulted in major NS strike-slip (transpressional) faulting, en-echelon NNE trending folds and NW-SE tensional cross faults. Thrusting produced N-S striking, steep dipping reverse faults and a possible decollement immediately above the Batchelor Group. Relaxation is evidenced by the intrusion of lamprophyre dykes and dolerite sills (Zamu Dolerite). Mineralisation at Woodcutters occurred in faults within the Whites Formation, probably synchronous with deformation and the deposition of the upper parts of the Frances Creek Group. Greenschist facies metamorphism occurred as the rocks were further buried. Several massive sulphide bodies occur at Woodcutters. A number of features influence the location and shape of these bodies. They are: ò the N-S transpressional faults and in particular associated dilation zones; ò intersection of the N-S transpressional faults with the axial plane of the NNE trending Woodcutters Anticline; ò intersection of the N-S transpressional faults with the NW-SE cross-faults; ò intersection of dololutite rich units with the NS transpressional faults where local replacement takes place; ò thickening of the lithological units in the vicinity of the anticlinal axis; and ò the anticline doubly plunging to both the north and south. The mineralisation exhibits vein-like features as well as epigenetic textures. Its boundaries are sharp, its thickness varies rapidly down dip and along strike, and no alteration halo exists though stringer veins of quartz-carbonate-pyrite ¦ sphalerite/galena occur in close proximity. A number of sulphide mineral assemblages have been recognised, each separated by periods of deformation and partially replacing the earlier assemblages. Vertically continuous zonation patterns highlight the presence of rich galena-sphalerite-silver in zones of maximum dilation and pyrite-arsenopyrite-gold concentrated at the along strike peripheries. The genetic model proposed has the mineralisation occurring whilst the transpressional regime was active. It was deposited from the same fluid that elsewhere in the Geosyncline formed the stratiform deposits higher in the sedimentary pile. Hydrocarbons sourced from the organic-rich Whites

Jan 1, 1994

Mineral Processing Education in China

Sep 13, 2010

By R Wedmaier

Henty Gold Mine is an underground operation producing 100 000 ounces of gold per annum. The original mining method used was flatbacking with paste fill. However, a non-entry method û uphole benching û was introduced in 1998 to recover the deteriorating crown pillars. Initial challenges were encountered, including poor drilling accuracy, difficulty in charging holes and poor rise performance. These challenges were overcome by a Continuous Improvement Team, consisting of mining engineers, supervisors and miners. Following this, the Team implemented further changes aimed at reducing ore loss and dilution. A second area addressed by the Team was development blasting, where innovative detonator technology known as the ExelTM DevelDetTM was introduced and rapidly accepted by the operators. Continued use of the ExelTM DevelDetTM resulted in a number of benefits, such as easier bogging, less perimeter damage, faster charging and hook-up and decreased wastage. Finally, improvements were made in the area of explosive handling, where competency-based training of operators was conducted and manual handling of ANFO has been significantly reduced by the introduction of the MiniMoverTM into the underground magazine.

Jan 1, 2001

The problem of stability of the development working at the great depths of coal winning is of great seriousness. Numerous researches of the problem were carried out in the USSR, the results of which determined that raising of resistance of existing support will not lead to a considerable rise of working output. It is necessary to try to find ways at the expense of heightening the support ability of rock massif. For these purposes it is necessary to direct it correctly and in proper time. While carrying the development working the most intensive deformations of rock occur at a depth of 30m from the entry face. The zone of destruction of rock around the work is realised here for 60 to 70 percent. These facts show that in influence zone of entry face a kind of embryo of the working steadiness is forming, which greatly determines its following conditions. Therefore, it is necessary to begin direction of mining pressure around the work directly in a face.Complex research of the mechanism was carried out starting with the effect of moving face upon the surrounding rock massif. It was ascertained, that the zone influenced by the face is a section of 5 equivalent diameters of the work by the length within which the rock of the sides, roof and floor, experience the cyclical influence of stresses at the time of cyclical shift of the face. The elastoplastec deformation is occurring with it at the moments of rock removal and the deformation of creeping takes place at such intervals.

Jan 1, 1991

By R Riquelme

The El Salvador porphyry Cu deposit (26¦ 15Æ Lat S, ~2700 masl) and associated exotic mineralisation is situated at the back-scarp of the late middle Miocene Atacama pediplain in the western Precordillera. New, together with published 40Ar-39Ar data from El Salvador combined with morphologic analysis reveal that the palaeospring plumbing system related to exotic mineralisation at the Damiana exotic Cu deposit and the local geomorphology has not changed fundamentally between the late Eocene and late Miocene. Stable H/D isotope data on supergene alunite from El Salvador indicate an overall increase in dD values (VSMOW) from -74ë at 35.82 ¦ 0.95 Ma to -23ë at ~11 Ma. The transition from strongly to moderately negative deuterium values occurred between ~16 and ~13.5 Ma. Supergene alunite from the El Hueso (3950 masl) sedimentary rock-hosted epithermal deposit ca 35 km SE from El Salvador was dated at 8.19 ¦ 0.01 Ma and yielded a dD value of -25ë. We interpret the increasing deuterium excess as the result of strong evaporation and recycling of meteoric water after ~15 Ma and as indicative for a change in precipitation patterns and climate desiccation. In contrast, the strongly negative dD value for late Eocene supergene alunite points to a more humid climate and an elevation similar to the present. The late Miocene supergene activity at El Hueso is probably related to an uplift of the Precordillera to elevations sufficient for capture of orographically controlled precipitation. An EXTENDED ABSTRACT is available for download. A full-length paper was not prepared for this presentation.

Jan 1, 2008

Miners and explorers in New Zealand are expected to consult with stakeholders, keep out of core conservation areas, and operate a high standard of environmental management and rehabilitation. These requirements are not difficult to meet, but many of the industry's own actions have brought it to a low level of general public esteem in New Zealand. Reasons for this are discussed, drawing examples from the Maruia Society's experiences with the industry since the mid-1980s. The boundary between core conservation areas and other land is not easily drawn, and the Maruia Society has sought to work with the mining industry to promote legislation for net conservation benefit trade-offs. However this initiative was not successful. Today the industry, unlike most other major industry sectors in New Zealand, has no accord with the country's conservation movement.

Jan 1, 1997

The blasting process involves a complex interaction of a delayed sequence of moving sources of seismic energy which produce nonlinear behaviour near the blast holes. A deterministic description of this nonlinear behaviour represents a formidable problem. The modelling of blast vibrations remote from the blast source may use some of the primary features of the blast design such as charge type, charge weight and initiation sequence. Such modelling of blast vibrations usually assumes linear behaviour remote from the blast holes. Site specific charge weight scaling laws may be used to predict the blast vibration levels with relatively poor accuracy. An important ingredient which is missing from charge weight scaling laws is the seismic source wavelet emanating from each blast hole. The present paper considers some approaches which may be used to determine a suitable source wavelet. The wavelets are suitable for use in the region where linearity may be assumed. In that region, it is possible to model the attenuation and scattering of the seismic wave as it propagates from the blast source to the measurement location.

Jan 1, 1990

By K S. Smith, J Woodhead, K Olson Hoal

Mineralogy is the link between ore formation and ore extraction. It is the most fundamental component of geomet programs, and the most important aspect of a life-of-project approach to mineral resource projects. Understanding orebodies is achieved by understanding the mineralogy and texture of the materials, throughout the process, because minerals hold the information required to unlock the value they contain. Geomet mineralogy programs absolutely require the appropriate expertise and at least three steps of mineral characterisation prior to using semi-automated or other methods: field examination, thorough core logging, and optical microscopy. Economic geological inputs for orebody characterisation are necessary for orebody understanding, and are exemplified by current research in the Zambian Copperbelt, where revised sequence stratigraphy and understanding of alteration, metasomatism and metamorphism can be used to predict topical issues at mine sites. Environmental inputs for sustainability characterisation are demonstrated by recent work on tailings from the Leadville, Colorado, USA area, including linking mineralogy to water quality issues. Risk assessments need to take into account the technical uncertainties around geological variability and mineral extractability, and mineralogy is the only metric that can be used to make this risk contribution.CITATION:Olson Hoal, K, Woodhead, J and Smith, K S, 2013. The importance of mineralogical input into geometallurgy programs, in Proceedings The Second AusIMM International Geometallurgy Conference (GeoMet) 2013 , pp 17-26 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 29, 2013

By W R. Adamson

Cerro Vanguardia SA (CVSA), property of AngloGold Ashanti, mines gold and silver from a system of vetiforme orebodies located in the south of the Argentine Patagonia, in the Province of Santa Cruz.Surface mining techniques are applied to develop a series of narrow pits with an average waste to ore ratio of 26:1. This quite unique constraint brings into focus the need to maximise inter-ramp and final wall angles, leading to a strong need to optimise wall control drilling and blasting in order to reduce back-break damage to an absolute minimum.The paper describes a program of applied investigation and design modification implemented during?2008?and?2009 in?two?separate pits of Cerro Vanguardia. Three distinct yet complementary damage mechanisms were identified and observed during the field components of the work; vibration induced strain fracturing, surface cratering around blasthole collars and quasi-static loading and unloading of the surrounding rock mass as a consequence of poorly controlled confinement.With these mechanisms identified, a measurement, modelling and modification campaign was conducted in order to reduce the incidence of each source of damage. Interactive design analysis and modelling, near-field vibration measurement, video capture and the application of electronic initiation technology were supported by seed wave modelling and topographic evaluation of the achieved results.Results point to the usefulness of simulation techniques for determining optimum delay timing to reduce vibration impact, while the visualisation of explosive energy distribution produced by drilling and explosive loading decisions assists in reducing the probability of over-confinement.This paper presents relevant aspects of the two fieldwork campaigns:1) describing the application of the techniques, and2) summarising the results obtained.

Nov 8, 2011

The minerals industry focus over much of the past twenty years has been on cost reduction and production growth supported, but not driven, by technology improvements. Mergers and acquisitions, and the demands of financial markets, have been high priority items whereas research and development and technology based innovation have received less attention and have been cut back in many companies. Technology improvements will be critical if the industry is to make progress on the stated aims of improving energy efficiency, reducing water usage and maximising recovery from deposits. They will also be important for improving capital efficiency and in treating difficult deposits. However the role technology based innovation will play both in the overall industry, and within individual companies, during the next decade is quite uncertain. There are major challenges in progressing technology based innovation in an industry with limited technical resources which is dominated by long life high capital operations. Specific opportunities for energy and productivity improvements exist but face significant technical and structural barriers that need to be overcome if the industry is to significantly improve performance. Current evidence suggests that changes in approach will be needed for these improvements to be realised. Recent studies in the United States and Canada have highlighted the wide range of energy performance across the industry and the scope for marked improvement from both incremental improvements and increased research and development. Comminution, material transportation and underground mine ventilation were identified as high priority areas. Opportunities within these areas are discussed both in respect of specific technologies and in how they may change performance. The role of open innovation as a source of new technology is also discussed. This is an abstract only. No full paper was prepared for this presentation.

Sep 13, 2010

Large mining operations need equipment that consistently performs as expected. The most effective way of ensuring this is to have a defined life cycle with an optimised maintenance strategy. The determination of this life cycle is an economic decision, influenced by the construction and utilisation of the equipment. An effective life cycle costing (LCC) tool must be able to process the many variable factors involved.Many factors influence the costs that are associated with a machine over its life. The most variable of these are the costs of maintaining the equipment. Maintenance costs are dependant not only on the utilisation of the machine, but also on the strategy that has been developed to support the machine through its life. A combination of supplier support, component changes, regular servicing and unscheduled maintenance needs to be modelled, based on a variety of drivers. Traditionally spreadsheets have been used to model these factors, but the increasing complexity of the situation can make spreadsheets unwieldy and difficult to manage. A database solution that breaks each activity into its constituent components, links them to an associated mine plan driver and then aggregates the result is the ideal tool to provide a time based cost profile. The evaluation of a number of scenarios, representing different maintenance strategies/life cycles can be rapidly undertaken. Auditability through inbuilt tools is required to provide easy tracing of data. Use of the host company's account structure allows for reporting against the standard chart of accounts.

Dec 6, 2010

By G B. Smith, D Hillier, T Gibbons, D B. Donato, M D. Adams, S Davies, R S. Schulz

Responsible management of cyanide solutions and tailings on gold processing plants worldwide is an important aspect to these operations and is regulated via guidelines provided by the International Cyanide Management Code, an industry initiative designed to minimise cyanide risk to operators and the environment. Here we demonstrate the unprecedented causal relationships surrounding the saline (>14 000 mg/L total dissolved solids - TDS) and hypersaline (>50 000 mg/L TDS) cyanide solutions in gold plant tailings in the Central Goldfields of Western Australia, resulting in zero wildlife mortalities on three sites over the study period of almost one year. Wildlife interaction and ingestion is significantly lower than that experienced at other gold mine sites, with more rapid degradation of weak-acid dissociable (WAD) cyanide within the tailings storage facility (TSF). A rigorous chemical sampling using a novel æminimal accessÆ robotic sampler device and wildlife observation exercise was carried out at two hypersaline mine sites: Barrick Kanowna Belle (BKB) and Gold Fields St Ives (GSI) and one saline site, Barrick Granny Smith (BGS). The data was compared with available reported chemical sampling and wildlife observation data from a previously operational fresh water site (<2000 mg/L TDS) that had experienced wildlife mortalities, Case Study D (CSD). The comprehensive body of work, along with cyanide degradation test work carried out in the laboratory, was analysed via hypothesis development and testing, causation analysis and dynamic chemical modelling. The non-mortality effect on these sites appears to hold over a further four years of routine wildlife and cyanide monitoring by site personnel. This study has helped these three mine sites achieve and maintain full Compliance Cyanide Code status over a significant period while removing the need for operating the detoxification plants they would otherwise have required.CITATION:Adams, M D, Donato, D B, Schulz, R S, Smith, G B, Gibbons, T, Davies, S and Hillier, D, 2013. Hypersaline-induced reduction in cyanide ecotoxicity at gold operations, thereby obviating detoxification plants, in Proceedings World Gold 2013, pp 489-502 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By Booth S. A, Milton D. W

Stratabound/stratiform and remobilised mineralisation have been recognised as the two dominant styles of mineralisation which constitute the Broken Hill ore deposit. Recognition of prospective sites for accumulation of ore depends on understanding the heterogeneity of the ore environment and the distribution of the two styles of mineralisation. The internal stratigraphy of the Broken Hill ore deposit and its enveloping rocks, is described, and a generalised stratigraphic setting of the stratiform mineralisation is outlined. Fhiphasis is placed on the existence of closely-spaced sub-basins as potential sites for ore accumulation close to the Broken Hill ore deposit. Further from the immediate ore environment, recognition of the same diagnostic stratigraphic sequence

Jan 1, 1983

The Cannington silver lead zinc deposit is located near Mt Isa in North West Queensland. This world class orebody is owned by BHP World Minerals (BHP) and is estimated to contain 45 million tonnes of ore at an average grade of 11 per cent lead, four per cent zinc and 500 grams/tonne silver. At BHPÆs planned 1.5 Mtpa extraction rate, the mine life will exceed 20 years. Construction of the underground mine, which commenced in August 1993, was carried out by Peabody Resources Ltd (Mining Services Division) (PRL) for BHP Minerals Pty Limited (BHP) under contract packages totalling approximately $100 M using several innovative techniques to deliver safety, quality and time related project goals. Client/Contractor Partnering, resulting in harmonious working relationships, a combined commitment to the achievement of an excellent safety record, and a seamless transition from the construction phase to operation of the mine, has been a feature of the project.

Jan 1, 1998

One of the major changes in the resource industry in the nineties has been the re- internationalisation of the industry. The history of the resource business has been one of companies from the developed world utilising the cash flows from their operations to explore and develop mines in less developed regions of the world. This resource development has progressively generated wealth and economic development, which in tum, has led to a new generation of exploration and mining projects.   InSouth America, Chile had led the way in a mining resurgence, now closely followed by Argentina, Brazil, Venezuela and Peru. Although Chile has long had a significant copper mining industry, the pre-nationalisation phase was driven by American capital; the current phase has been spearheaded by RTZ - BHP at Escondida with Canadian junior companies, in particular, providing major speculative impetus. The Australian junior companies have not been significant in South America.   Although Canadian and USA exploration appears to be in decline, the mining industry, particularly in gold, is buoyant in North America. Interestingly, a number of listed and unlisted Australian companies are active, particularly in United States exploration.   Australian-based companies have dominated the South-East Asian exploration scene, especially in the Vietnam region. To date, the combination of political and legislative uncertainties have failed to lead to significant resource developments in this region. The area remains one of great potential, as exemplified by the exciting developments in Indonesia.   The Philippines has a history of mining, and this has been dominated by both local and North American operators. Both large and small Australian resource companies have a presence in the Philippines, and the development of the copper-gold potential could be impressive over the next decade.   The tales of the undeveloped mineral potential of China are probably rivalled only by the supposed strings of virgin Russian orebodies! Many Australian companies appear to have looked but few have chosen to proceed with Chinese developments. There seems little likelihood that China will, in the foreseeable future, rival South America as a target for Australian and North American resource capital.   Papua New Guinea has had an active, albeit chequered history in mining, with Australia long being the predominant source of exploration and development funds. The developing nation status of PNG has generated extreme uncertainty, with the current exploration scene all but dead. Most recently, the international flotation of Lihir Gold has tested the international and Australian investment community's commitment to PNG resource development.   The Australian exploration scene continues buoyant, although dominated by gold. The base metals scene is generating, on average, one significant base metal mine developed every couple of years. This is probably the fastest rate of significant base metal development in Australia's history.   The gold scene has been one of incredible dynamics, and there is no evidence that this momentum is waning. The development of new exploration techniques, together with a number of the companies reaching a critical size, has added to the momentum in the industry.

Jan 1, 1995

The Resource Management Act has been in force now for approximately ten months. This Act, and the Crown Minerals Act which accompanied it, have substantially changed the manner by which mining operations and other resource uses obtain access to resources and are subject to controls of their environmental effects. This paper briefly summarises the key elements of the regulatory provisions of the Resource Management Act. It identifies the types of resource consents required, and discusses these and procedural matters in relation to mining in Otago. It addresses the transitional provisions and highlights inconsistencies and difficulties in the implementation of these provisions. This paper identifies potential future developments in the planning and regulatory environment relating to mining in Otago.

Jan 1, 1992

By P B. Hills

Increasingly over the past couple of decades, the importance of understanding the in situ stress regime in underground hard rock mines has become accepted by all. Providers have responded to this requirement and various techniques for undertaking the measurements have been honed while others have slipped from use. It is a simple, though not inexpensive task to engage a provider to undertake the require measurements, and a comprehensive report will ensue. So, what has actually been obtained? What should the geotechnical engineer do next? What tools are necessary to do so? Regardless of the method of measurement, the report will describe the location of the measurement site and describe the basis of the methodology used in undertaking the measurements and a log of the measurement program. Finally, it will include the results, which should incorporate the normal and shear stress components of the full stress tensor. Ground control management plans (GCMP’s) and stress summary reports and spreadsheets prepared by site geotechnical engineers always include the magnitude, trend and plunge of the principal stresses. Remarkably few site-based summaries include the full stress tensor. This is a significant gap as the full stress tensor is vital for any further data manipulation. However, without the algebraic tools to undertake those manipulations, their value is diminished. This paper seeks to provide a checklist of ideas to be considered. It provides commentary on the options available to dissect the stress measurement report and ensure that the maximum possible value is derived from it. The manipulation and presentation of component stress data is also discussed. The various methods of stress measurement are not the focus of the paper but some of the strengths and weaknesses of them over which the site geotechnical engineer has some control, are highlighted.

Nov 29, 2022

In the course of an investigation of the influence of bismuth on copper carried out some years ago, (1) the author found that phosphorus exerted a beneficial effect on bismuth-copper alloys of low bismuth and oxygen content by neutralizing the embrittling effect of the bismuth. In the intervening years, a further examination of bismuth-phosphorus-copper alloys has been canied out and the influence of other elements and combinations of elements on copper containing bismuth has been studied.The results recorded in the present paper are part of this investigation.MATERIALSAll the alloys were made from high-grade copper (KS.A. wire-bar) of the following composition: copper 99·95%, oxygen 0,040'%, iron 0·0015%, sulphur less than 0-001%, bismuth less than (j>'OOl%, other elements each less than O· 0010/<-. The bar was hot rolled and cold drawn to strip which was cut into short lengths and cleaned in nitric acid ready for melting.A piece of this 'strip was drawn to wire 0·08 in. diam., annealed at 5000 C, and measured for electrical conductivity as a check on purity. The result was 101·5% of the I.E'.C. standard.In making the alloys, phosphorus was added as 14% phosphor-copper, bismuth as 17% bismuth-copper, and the other constituents either as copper alloys or as elements of a high degree of purity.PREPARATIQN OF STRIPSThe charges were melted in plumbago crucibles (Morgan salamander brand) in an oil-fired furnace, Le;, in the manner commonly adopted in industrial practice. The copper was first melted under charcoal, well stirred with a chaned stick, and the necessary alloying elements added and stirred in with the stick. The weight of a charge varied according to requirements but generally was about 4 lb. The charges were poured into slightly tapered brass moulds heated to about 1000 C and dressed with a mixture of mineral oil and tallow. They were not only poured under charcoal through the burning mould dressing but also- through a ring of flame produced by burning kerosene on asbestos cord wrapped round the top of the mould. Experiments carried out with plain copper proved that by this means oxygen could be excluded from the stream of metal. The billets were 7·5 in. long x O·83 in. diam. x 1·3 lb. weight.The billets were cropped about 1 in. from the top, cleaned in nitric acid, and measured for density by the usual method of weighing in air and -in water. As these measurements were required only as a check on casting, technique a high degree of accuracy was not essential (accuracy = -+ 0·2%).

Jan 1, 1942

By E Christodoulou, L Zoumpoulakis

The kinetics of the thermal decomposition of MgCO3 was investigated using isothermal experiments performed in a thermogravimetric analyzer under a nitrogen atmosphere at 380¦, 400¦, 450¦ and 480¦C. The weight loss data as a function of time were modified to give the fraction that reacted (ß) and the rate of reaction (dß/dt) vs. time (t). Kinetic analysis of the experimental results, using three different methods, showed that diffusion predominates the MgCO3 decomposition over the investigated temperature range, with the data being best fitted by JanderÆs equation ([1−(1−ß)1/3]2=kt). The activation energy was estimated by Arrhenius plots using both the initial reaction rates and rate constants from fitting the above equation. The values estimated were 27.1 and 171.4 kJ/mol respectively.

Jan 1, 2001