Search Documents

By Joseph Bloch

The hydriding of bulk metals and alloys is a gas-solid reaction in which a hydride product layer is initially nucleated adjacent to the gas-solid interface and continues to grow until a complete transformation of the parent (a) phase into the hydride phase. The combination of measurements of the overall hydriding kinetics of samples having defined shapes and dimensions, together with examinations of partially hydrided samples, enables the presentation of the reaction rate in terms of an appropriate reaction model. A common and important type of topochemical development of the hydride in bulk metals and alloys involves a hydride layer formed on the metallic surface. The continuity of the layer can affect the reaction rate. The rate of hydrogen absorption in a sample, in the presence of a hydride layer, is usually analyzed using a model combining several sequential steps in which the hydrogen is transferred from the gas phase into the reaction site. Coupling the flux equations across the layer under proper steady state conditions, results in a complex rate equation in which the steady state rate of hydrogen absorption (proportional to the hydride layer velocity) is expressed in terms of the pressure, temperature, the rate constants of the sequential steps and the critical concentrations of hydrogen in the hydride. Generally, the rate constants of the individual microscopic processes are comparable in magnitude, so that the overall rate is not controlled by any of the specific sequential steps. However, there are two limit cases related to the first stage, the adsorption, for which the general rate equation is much simpler, namely, the fast and the slow adsorption approximations. Using this limit cases, equations are derived for the steady state hydriding rate of a given system. These equations provide means to anticipate the pressure dependence of the steady state absorption rate under low pressures, close to Peq and under very high pressures. At the low pressure regime both the fast and slow absorption cases yield linear pressure dependence. For the very high pressure range, it is found that the rate become independent of the applied pressure. The rate is given then by a combination of the individual rate constants of the system and the critical hydrogen concentrations. The model is shown to apply in several real cases, such as ZrCo, LaNi5 and titanium.

Jan 1, 2002

By A. J. Jeffery

Heat transfer to a fluid flowing through a rough duct has been shown by many researchers to be a function of surface roughness. The effect of roughness asperities on the duct surface is to turbulate the fluid as it flows through the duct, increasing frictional pressure losses and convective heat transfer rates, and also increasing the surface area per unit length available for heat transfer. These factors combine to increase the total costs to the mine in terms of refrigeration and fan power requirements. A measurement system designed to automate the collection of tunnel roughness information and based on an infra-red timed pulse laser has been developed at the Royal School of Mines in London. The system allows accurate, high resolution digital recordings of tunnel surfaces to be made in two or three dimensions. Software for analysing the data has been written, and the description of a complex surface via single numerical term has been explored. A relationship between the numerically measured surface roughness and the pressure loss of the ventilating air is being investigated with a view to establishing an alternative method of describing tunnel roughness. The paper describes the roughness measuring technique developed and the analytical techniques explored so far.

Jan 1, 1993

By Yves C. Lizotte

Although blasting remains the most inexpensive method of fragmentation in hardrock mining, the significance of the costs of blast-induced rockmass damage in terms of mining efficiency and safety is becoming increasingly recognized. There is no straightforward and systematic method of adequately measuring blast damage in on-going mining operations. This paper considers various techniques available to measure blast damage, making particular reference to recent underground hardrock mine studies. It concludes by proposing a damage audit procedure for integration into routine mine production control.

Jan 1, 1996

By William R. Adamson, Carlos R. Scherpenisse

The successful development of surface mining operations depends, amongst other factors, on the successful creation of final pit walls which offer long term structural stability. The achievement of such walls will be much more feasible if the mechanisms of rock mass deterioration in the mine are well understood, permitting the control and reduction of this deterioration (or damage). The role of drilling and blasting in causing damage is widely accepted but rarely fully quantified. It is also true that the dependence of rock mass damage on vibration levels is only incompletely understood and little accurate field measurement is routinely conducted in the mining industry.

Jan 1, 1998

Dilution in underground coal operations can be underestimated by up to five times during feasibility studies, with disastrous economic consequences. Every one per cent of stone waste introduced can reduce an in situ specific energy of 25 MJ/kg by some 0.25 MJ/kg and increases the abrasiveness of the run-of-mine coal. Where a wash plant is not in place, penalties imposed for not meeting contractual specifications alone can amount to some $A 1 million per year. This paper presents a method for monitoring, reporting and ultimately controlling dilution in an underground coal mining operation and presents the dilution trends from a continuous miner/longwall mine over an eight year period. The overall dilution level for the mine can be back-calculated by comparing the run-of-mine coal quality to the predicted in situ, undiluted quality. However, this will not identify the actual contaminant types, areas of the mine responsible for the dilution and the reasons for the dilution. This additional information is essential for controlling dilution to acceptable levels. Quality and horizon control using existing sampling information is generally only adequate for longer-term control purposes, and is not suitable for monitoring mining-induced dilution. The cost of close-spaced surface drilling to collect the information necessary for short-term control is prohibitive, particularly for deeper mines. However, much of this data can be collected through underground channel sampling and horizon control measurements taken during continuous miner development and longwall extraction. The mine runs the risk of not meeting contractual quality specifications and of increased equipment wear if this additional information is not available and the sources of dilution cannot be controlled. The information can also be used to plan longwall extraction heights on a short-term scale with resulting improvements in productivity.

Jan 1, 2003

By M. Noppé

"Dilution in underground coal operations can be underestimated by up to five times during Feasibility Studies, with disastrous economic consequences. Every 1% of stone waste introduced can reduce an in situ specific energy of 11,000 BTU/lb (25 MJ/kg) by some 110 BTU/lb (0.25 MJ/kg) and increases the abrasiveness of the run-of-mine coal. Where a wash plant is not in place, penalties imposed for not meeting contractual specifications alone can amount to some AU$1 million per year.This paper presents a method for monitoring, reporting and ultimately controlling dilution in an underground coal mining operation. The dilution trends before and after introducing the recommended controls in a continuous miner/longwall mine are presented over an eight year period. The additional information from such a dilution monitoring program can also be used to control mining horizons and plan longwall extraction heights across the face proactively, on a short-term scale with resulting improvements in productivity. INTRODUCTION Grade control, as practiced on any mine, is concerned with predicting routine quality and tonnage values for short- to medium-term mining operations, and the reconciliation of these predictions against “actual” results. For a longwall mine supplying steam coal, such routine parameters may include the proximate analyses, specific energy (SE), abrasiveness and sulphur, as well as float and sink analyses if the coal is beneficiated. In addition, grade control is concerned with identifying the mineable horizon (or horizons) in a selective-mining operation, together with monitoring how well these horizons have been extracted or adhered to. Close-spaced surface drilling can be costly for any mining venture, particularly for longwall mines operating in the deeper seams. For this reason, much of the data for short-term grade control requirements are acquired during actual bord-and-pillar development. The underground data are derived from so-called “channel” samples. These samples are cut or chipped from the coal seam, perpendicular to the mining horizon, with dimensions suitable for obtaining sufficient “representative” sample for analyses. For a 2m thick mining horizon, a channel sample 300 mm wide and 50 mm deep over the thickness of the horizon would provide some 4.5 kg of sample, sufficient for most of the necessary tests. To allow the information to be computer recorded, additional information such as seam thickness, sample co-ordinates, and the elevation of the seam (or horizon) roof or floor, may be required."

Jan 1, 2015

By J. A. Finch

The use of pneumatic methods for measuring interface level in flotation columns is analysed. It is shown that errors can vary over a wide range (e.g. 40 cm. in one industrial application) depending on bubble size, particle size, bubble loading, liquid hold-up and bulk slurry density. Accurate measurements (+ 5 cm) can be obtained by measuring intensive properties of the froth near the interface. Methods based on the measurement of temperature and conductivity are described and analysed. Control of the interface level using these measurements subject to various disturbances is demonstrated.

Jan 1, 1988

By P. H. Strickland, F. Lawson

It is now well established that in the majority of cementation processes used industrially, the rate of reaction can be described in terms of the mass transport from the bulk of the solution to the deposition sites on the metallic surface. Thus it should be possible to design cementation equipment from a knowledge of the flow situation in the equipment, and of absolute kinetic data. One way of obtaining such absolute data is by the use of the rotating disc geometry; this geometry is particularly suitable for a detailed study of cementation reactions. In spite of the similar mass transfer mechanism, cementation processes differ from other ionic transport processes in at least two respects. The presence of an attached deposit generally has a significant enhancing effect on the reaction rate; and side reactions involving oxygen and/or hydrogen ions can completely change the course of a reaction. Investigation of these peculiarities is necessary for a complete understanding of the process; since they cannot be isolated from the basic mass transport mechanism, close control of experimental conditions is essential. It has been found that the enhancement in deposition rate persists even when the deposit reaches a thickness several times that of the transport boundary layer thickness on the smooth surface. An explanation of the enhancement in reaction rate is proposed.

Jan 1, 1973

By M. J. H. Ruscoe

"The circulation wear rates of pure nickel, cupronickel and nickel-plated-steel coins were measured and found to be in the ratio 1:3:1 . The relative wear rates of nickel and cupronickel coins were similar to those reported in earlier studies, and the circulation wear data for nickel were used as a reference in laboratory wear tests. A correlation between circulation wear rates and laboratory wear rates formed the basis for a prediction of service life using relief legibility as an 'end of life' criterion. This criterion was determined to be an average surface thickness loss of 12 um. The surf aces of nickel and Nickel-Banded-Steel (N-B-STM) coins were observed to harden both in circulation and in the laboratory tests at a rate of approximately I VHN/year of actual or simulated service life. It was also observed that the laboratory wear rate of N-B -S coins increased as nickel cladding thickness increased and this effect was attributed to differences in surface hardness.Wear test results are also reported for the new Canadian dollar coin material which shows a better wear resistance than pure nickel. IntroductionThe subject of coinage wear has a long history, and a number of studies have been published, concerned both with the measurement of circulation wear rates and with accelerated laboratory tests to simulate the behaviour of coinage materials in service. As early as 1803, wear tests were conducted by Hatchett on gold coinage using various types of vibratory and tumbling machines». These tests were commissioned by King George III of England who was concerned about the wear of gold coins in circulation.Early in this century, Adrian performed laboratory tests that showed that the wear rates of cupronickel 75/25 and nickel coins were in the ratio 3:1 and this ratio was later confirmed in laboratory tests reported by Daeppen and Zurrerw, The latter authors also weighed cupronickel and nickel coins that had been in circulation for various times and observed the same 3: I ratio. There was further support from Tylczak and Blickensderfer who reported significantly higher abrasive wear rates for cupronickel compared to nickel, when rubbed against sand paper."

Jan 1, 1988

By G C. Sen

All mining and quarrying operations that employ blasting to fragment and move broken ground have a price to pay for æby-productsÆ such as vibration and noise. These æby-productsÆ cannot be eliminated but they can be controlled and modern blasting techniques have improved to the point that excessive environmental restrictions can be adhered to whilst maintaining acceptable production rates and quality. Accurate measurement is the key to control, and as the environmental limits are becoming tighter, the proper way to measure vibrations from blasting operations becomes an integral part of the mining or quarrying operations. The basic vibration monitoring system consists of a primary sensor connected to a data logger and computer software for the analysis of the signal received and recorded. Currently, as with all fields of measurement, much improvement has occurred over the past decade, and electronic devices are much more accurate and reliable. Data analysis has also improved considerably with the computing power that is available to field operatives today. Mounting the primary sensor has been often overlooked in supposed æstandardsÆ with procedures such as double sided tape, resting on a flat surface provided the vibration level is less than a given amount. But if it is worth going to the expense of the monitoring equipment and manpower, surely it is worth a little extra effort to ensure the primary sensor is coupled to the ground effectively. The primary sensor must move with the ground and measure this movement; so if the primary sensor is allowed to move without respect to the ground (ie poor coupling to the ground) then a false record of the physical event will be measured. This scenario can easily be a practical reality if the primary sensor coupling method to the ground is not effective. In this study a number of mounting methods were fabricated and connected to similar data monitors and a series of ænormalÆ production blasts were used as the vibration source. These mounting devices were measured against an in-house procedure (the æstandardÆ) and the relative merits compared. A laboratory investigation was also carried out to look at the physical parameters of the æsoil and their effect on vibration attenuation of the in-house standard method.

Jan 1, 1999

By C De La Cruz

The use of a thin-film piezoelectric stress gauge to determine the pressure profile in a detonating explosive has been demonstrated. These PVDF gauges have measured, in the borehole, the Chapman-Jouget pressure and the release adiabat of the detonation products for several explosives including ANFO and ANFO/emulsion mixtures. The technique can provide: (1) a direct measure of the blasting stimulus, (2) a sensitive QA tool for the blaster, and (3) a means to examine the magnitude and effects of preshock from adjacent bore holes. The PVDF pressure gauge is self powered, can measure pressure from a few bars to 400 kbars, has high time resolution (0.05 µsec), and is easy and economical to use.

Jan 1, 1997

By D. B. Stewart

This paper reports on an investigation undertaken to determine the exhaust gas temperatures of operating underground mining equipment. The effectiveness of platinum catalytic purifiers is discussed. From exhaust temperatures, it is concluded that LHD engines are highly loaded, haulage truck engines are moderately loaded and utility vehicle engines are lightly loaded.

Jan 1, 1979

By Armstrong ME

The gas bubble energy generated by an explosive plays a major part. in the fragmentation, muckpile movement and damage produced. Previously, the interaction between gas pressure and the rock has been interpreted from a theoretical basis or a qualitative study of breakage mechanisms. A method to measure the fluctuations in gas pressure in rock adjacent to the blast has been developed. This peak pressure will vary with structure, as well as with distance and explosive type. The technique is simple to apply and can be used to observe the flow rate of gas at. varying distances. The apparent velocity of penetration is an indication of whether gas has travelled through pre-existing or blast induced cracks. The technique provides a ?n:eans of determining the suitability of an explosive for a given rock type, depending on the amount of displacement desired. The technique has application in optimir.irig throw blasting and predicting and controlling damage, particularly in highly structured rock masses.

Jan 1, 1986

By C. A. Jermy, B. J. Venter

Excessive build-up of methane and water pressures was identified as the leading cause of some Q/the roof falls in a coal mine in the eastern Transvaal. In order to characterize the migration of the methane and water into and around the mined coal seam, a laboratory investigation of the permeability of the roof strata was undertaken. The aim of the investigation was to correlate changes in the fades with changes in permeability to enable the prediction of possible zones of pressure buildup. The tests were carried out on samples from borehole core that had been obtained from the roof strata as part of the mine exploration programme. Permeability measurements were then conducted under atmospheric and triaxial-stress conditions. For the tests under atmospheric conditions, a modified Ohle cell was used and, for the tests under triaxial-stress conditions, a modified Hoek cell was used. The liquid equivalent permeability?s of the different samples were obtained by use of ASTM D4525- 85, and these were then used as a basis for comparison. Facies type, i.e. grain size, was found to have an influence on the permeability but, owing to the variable nature of the sediments, a range of permeability rather than a specific permeability value was associated with each type of Jades. The measured permeability was bound to decrease with an increase in gas pressure. The liquid equivalent permeability was bound to increase with an increase in grain size for the coarser-grained Jades, and to decrease with an increase in grain size for the finer-grained types. The application of an external stress regime to the sample was bound to reduce the permeability, but the amount of the reduction depended on the type of stress. The permeability was also found to depend on the recent stress history of the sample. The authors conclude that the methods described are useful for the correlation of facies type with permeability, but that the results are sensitive to changes in locality.

Jan 1, 1994

By F. W. H. Dean

A very sensitive sensor for the detection and measurement of hydrogen in solid steel is described. This technique is non-invasive and uses a collector to sweep the hydrogen emanating from a steel surface and feed to it sensor. This method is particularly sensitive, resolving fluxes to < 2 pI cm?2 S?I, with a linear measurement up to 1000 pI cm&apos;2 S?I, The collector is held on the steel substrate by magnets and it is shown that emanation of hydrogen from the steel is controlled by bulk diffusion of the hydrogen through the steel. The technique is demonstrated to have an excellent response time and reproducibility.

Jan 1, 2001

By Leigh G, Gottleb G, Wilkie G

The estimation of particle liberation is important in the study of mineral concentration. With simple systems, where the densities of the components are low, the liberation can be studied directly by density fractionation. For most practical systems, and particularly for the dense, complex sulphides, the only method known is by measurement in polished section. There are two major difficulties with such measurements. Firstly, the measurements themselves are difficult and considerable care is needed before reproducible results can be achieved. Secondly, a well known stereological problem arises which gives the estimates an inherent bias. The paper discusses both aspects of the problem. The practical features of measurement are treated in detail and a method described which has been developed and proven to give reproducible estimates of the liberation in the section. This discussion relates to automated measurements by QEM*SEM and presents a way of estimating the confidence limits within which measurements lie. Comparisons are shown between measurements made by the traditional manual optical technique and automated equipment. Stereological reconstruction is also discussed briefly. Several methods have been presented in the literature but all are complex and none is yet widely accepted. Area measurements are less biased than linear estimates so a practical approach is to use area measurements in uncorrected form. The topic is still being actively researched so it is expected that one method will soon emerge as the standard technique.

Jan 1, 1993

By J. W. M. Porritt, K. C. Cheng

Knowledge of radon emanation rates from uranium-bearing rocks is essential to the design of mine ventilation systems for uranium mines. Measurements of equilibrium ratio between radon and its daughters in mine air are important for a better control of mine radiation conditions. The concentrations of radon and daughters were monitored at cut-and-fill stopes in the Beaverlodge Mine of Eldorado Nuclear Ltd. during all phases of the mining cycle. The radon emanation rates of ore and rock samples were measured at the laboratory and the results were compared with in-situ emanation tests in an isolated ore drift. Samples of backfill solution, backfill drainage and ground seepage water were measured [or radon and analyzed for radium and uranium. The results showed that discharges of backfill solution and daily shift-end blasts were the two major sources for a rapid release of radon gas in the ventilation air. Other mining operations, such as drilling, mucking, etc., contributed little effect on radon release to the mining environment. Radon emanation rates of the Beaverlodge are samples ranged from 13 x 10-18 to 600 X 10-18 Ci/cm2/ sec and that of waste rock samples from 0.54 x 10-18 to 13.4 X 10-18 Ci/cm2/sec. The in-situ emanation rate of mine walls with ore-to-rock ratios of 1 to 7 was 60 x 10-18 Ci/cm2/sec. The average equilibrium ratio of radon and its daughters in stapes was 32.6%. Under a normal ventilation condition, the average background levels of radon concentration in cut-and-fill stopes ranged from 13 to 80 pCi/L. The discharges of backfill solution during backfill operations at 100 tons solids per hour released approximately 1.8 x 106 pCi/min of radon and elevated radon concentration in stapes 2 to 5 times above the background levels.

Jan 1, 1981

By A. Montini, M. H. Moys

A technique for the measurement of slurry consistency inside a grinding mil is described. The rate of slurry drainage from a sensing probe mounted through the mil shell is measured and correlated with the percentage solids of the slurry discharging from the mil. The response time of the measurement(obtained on a pilot bal mil) is compared with the response time of the viscosity of the mill discharge. It is shown that the new measurement should allow much tighter control of the mil behaviour, with concomitant savings in the consumption of power and steel.

Jan 1, 1988

By A. N. May

"This paper describes the present approach of the Mines Branch to the problem of measuring the stress condition in the interior of rocks surrounding underground openings. An instrument, which will be referred to as a stressmeter, has been developed at the Mines Branch to measure un-directional stress changes in absolute units. There are two modes of operation of this stressmeter. It can be regarded as a fixed instrument, in which case it is installed at the end of a diamond drill hole and left in position to record any subsequent stress changes taking place. Alternatively, three of the stressmeters can be used in conjunction with a trepanning opera-tion to allow the existing stress condition to be determined. The initial laboratory work and subsequent experiences in the field with the stressmeter are described. All the field development work on the stressmeter was made possible through the co-operation of Canadian Refractories Limited, Kilmar, Quebec."

Jan 1, 1960

A review is presented of techniques cur- rently in use, or being developed, to enable the determination of virgin rock stress at consid- erable depth (> 1000 m) from small diameter sur- face drill holes (

Jan 1, 1975