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By Lars Skogsberg

Work with hand-held power tools can be found in most industries all over the world. This type of work exposes the operators to different kind of loads like gripping-forces, feed-forces, exposure to vibration and noise, holding hot or cold surfaces and the exposure to dust. Designing a power tool with good ergonomics is a matter of finding the best compromise. As a simple example, increasing the mass is not acceptable because it will increase the forces needed to handle the tool. At the same time increased mass will in most cases reduce the vibrations. Vibration disorders related to the use of hand-held power tools has been known and reported since long. It is therefore essential that low vibrating tools are developed and used. The new vibration regulations in Europe, based on the Physical Agents (Vibration) Directive, have put increased focus on the vibration control in industry. Forces acting on the tool cause vibration Tools for industrial use must be of very robust design to withstand the very hard use they are exposed to. Industrial tools are therefore normally designed with the main parts made of metal. From a vibration point of view this means that most tools can be regarded as rigid bodies, especially because the dominating frequency normally is equal to the rotational frequency of the tool spindle or the blow frequency for a percussive tool. These frequencies are with few exceptions below 200 Hz. Handles however can not always be regarded as rigidly connected to the tool. There are several examples of weak suspensions designed to reduce vibration transmitted to the hands of the operator. There are also examples of designs where the handles just happened to be non-rigidly connected and in some cases even in resonance within the frequency region of interest. Oscillating forces act on the tool and the result is vibration. Design principals In all cases forces are the source of vibration. This leads to the three basic principles to control vibration: • Control the magnitude of the vibrating forces. Examples are the balancing unit on a grinder or the differential piston in a chipping hammer. • Make the tool less sensitive to the vibrating forces. Examples can be when the mass of the guard on a grinder is rigidly connected to the tool to increase the inertia of the tool. • Isolate the vibrations in the tool from the grip surfaces. Examples are vibration-dampening handles on grinders or pavement breakers, the air-spring behind the blow-mechanism in a riveting hammer or the mass spring system in a chipping hammer.

Jan 6, 2006

Jan 1, 1881

By J. Engelbrecht

South Africa?s re-entry into the fast moving and competitive global economy calls for some careful strategic planning and a good deal of co-operation between suppliers and end-users. The issues that need addressing are generally well known and include: ?South Africa was ranked 45th out of 46 i.r.o. productivity ?SMMEs contribute 1% to exports compared to 40-60% for the ?tigers? ?High unemployment ?Limited skills of the majority of workers ?Slow growth rate of the economy ?The vast majority of suppliers are not world-class ?The vast majority of suppliers are not export or marketing orientated. In order to survive, all parties, i.e. government, labour and business, will have to play their part.

Jan 1, 1999

By Gerald A. Muson, Fremont F. Clarke

"INTRODUCTION The use of scrap mica as an industrial raw material has grown rapidly during the past two decades. Demands by various industries for ground mica for use in the roofing, paint, rubber, plastics, and wallpaper trades as well as for less extensive uses in insulation, oil-well drilling, welding, pipeline enamel, decorative material, and for other purposes exceed present (1947) supplies.A small proportion of the raw material used comes from the Black Hills of South Dakota, where casual recovery has been practiced in the exploitation of pegnatite deposits for more valuable minerals. The annual production of scrap mica in the Black Hills for the years 1939 to 1946 is shown in figure 19. 4/Although small, this production of scrap mica materially augments the incomes of numerous operators.Volume production of mica would offer attractive opportunities for obtaining steady and more economical supplies of the rare minerals as byproducts. Appreciable supplies of beryl, lithia minerals, sheet mica, tantalite-columbite, and cassiterite could accrue. Furthermore, a stable scrap-mica production would complement the production of quality feldspar, for which the Black Hills pegmatites are noted, and would help balance the economy of pegmatite mineral production.Mechanical methods of separation are requisite to production of enough scrap mica to be generally profitable. Various phases of the characteristics end treatment of mica have been investigated by the Bureau of Mines. A bibliography of these reports is appended.In 1945 the Bureau of Mines conducted pilot-plant tests to recover scrap mica by selective screening of crushed pegmatite. More recently the problem has boon studied in the Pegmatite Research Laboratory to aid in developing technological methods by which scrap mica may be separated from crushed pegmatite."

Feb 1, 1949

By Paul Wellman

A computer program is presented that may be used to calculate the bare equipment cost of the major processing units for any hot potassium carbonate gas purification system. The program is designed such that, with only minor modifications, it could be used with a variety of computer systems.

Jan 1, 1968

By B. Simser

Noranda?s Brunswick mine is a 10 000 t/d producer of lead-zinc-copper-silver ore that has been in operation since 1964. Mining of this multiple lens deposit is primarily by blasthole stoping techniques between 400 m and 1200 m below surface. The combination of a high overall extraction ratio, an overall steeply dipping tabular shape, and high horizontal stresses (twice the vertical) have elevated the induced stress regime to levels comparable to much deeper operations. Improved mine design, and a better understanding of how the rock mass responds to mining in high-stress environments is essential to improve overall recoveries and maintain safety. Seismic monitoring has proven to be an essential tool at Brunswick, for both short-term safety of workers, and long-term strategic planning. Practical case studies illustrate how seismic data, particularly source parameter information, can be used to measure the rockmass response to mining and improve mining layouts in difficult regions. As the global trend continues toward mining in deeper, higher stress environments (e.g., South African Witswatersrand Basin, Sudbury Basin) and as local extraction and thus ground stresses continue to increase in existing deposits, seismic monitoring will play a critical role in mining safely and economically.

May 1, 2004

By B. Simser, V. Falmagne

"Noranda’s Brunswick mine is a 10 000 t/d producer of lead-zinc-copper-silver ore that has been in operation since 1964. Mining of this multiple lens deposit is primarily by blasthole stoping techniques between 400 m and 1200 m below surface. The combination of a high overall extraction ratio, an overall steeply dipping tabular shape, and high horizontal stresses (twice the vertical) have elevated the induced stress regime to levels comparable to much deeper operations. Improved mine design, and a better understanding of how the rock mass responds to mining in high-stress environments is essential to improve overall recoveries and maintain safety. Seismic monitoring has proven to be an essential tool at Brunswick, for both short-term safety of workers, and long-term strategic planning.Practical case studies illustrate how seismic data, particularly source parameter information, can be used to measure the rockmass response to mining and improve mining layouts in difficult regions. As the global trend continues toward mining in deeper, higher stress environments (e.g., South African Witswatersrand Basin, Sudbury Basin) and as local extraction and thus ground stresses continue to increase in existing deposits, seismic monitoring will play a critical role in mining safely and economically."

Jan 1, 2004

Traditional fine grinding mills in mineral processing relied on the use of steel medium for particle size reduction. The successful development of the Isa Mill(a horizontal stirred mill with 3000 litres of net chamber volume and 1120 kW rated motor power)adopted a novel product separator design that has led to a major revision of medium use in fine grinding. The Isa Mill separator has also successfully operated with a wide variety of medium types such as silica sands, river gravel, smelter slag, run-of-mine ore fractions and steel shots, with size ranges from 0.5 to 10 mm. A great flexibility of the Isa Mill operations has been achieved for processing a feed as coarse as 120 um to a product as fine as 5 µm. This paper discusses the performance of two inert grinding media used in the Isa Mills in Mount Isa Mines of Australia for processing galena and sphalerite bearing ores to below 10 microns. They are the copper reverberatory furnace slag (CRFS)and the heavy medium plant rejects (HMPR). A methodology was also demonstrated for comparing the medium performance and for scaling up the Isa Mills from a 1.5-litre laboratory batch mill to a full scale 3000-litre mill.

Jan 1, 2000

The selection of the mining fleet can have as much of an effect on the efficiency and effectiveness of an operation as the mining method. This is not to say that inefficiencies are only attributable to inappropriate equipment selections, these aspects have many factors but are not the subject of this paper.This paper will give an overview of equipment selection processes that have been utilised to date. It will also look at the increase in application of study programs/simulations from an aspect of accuracy, as well as the importance of enabling the analysis of multiple sensitivity scenario planning. An aspect that is increasingly important in project planning with commodity market movements.Another aspect that is increasing in popularity is that of automation, what effect does this have on equipment selection? What additional aspects need to be taken into consideration when assessing Automation of equipment from the beginning of a project as well as introduction into an operating mine?Once the selection process has been finalised and equipment implemented, how do we, as an industry, 'close the loop' through analysis of estimated versus actual equipment application?

Dec 6, 2010

By P. J. Foster

A common theme running through recently introduced mining health and safety legislation in many parts of the world is risk assessment. Most recently, risk assessment legislation has been introduced across the mining industry of South Africa and the view that the introduction of risk assessment based legislation provides an ideal opportunity to improve on past health and safety performance is presented. Risk assessment techniques range from highly complex safety system techniques that are used in high technology process industries, to subjective techniques based on simple judgements that are finding use in many other industries. The objective of this paper is to shed some light on risk assessment, not by detailing the risk assessment process but by identifying the crucial elements that need to be considered if risk assessments are to be successful in changing health and safety performance. A case study is presented illustrating the introduction of risk assessment into the Ingwe Coal Corporation, one of South Africa?s largest mining houses, to indicate how the system was developed and how it is being used.

Jan 1, 1998

By J. L. Gillson

The word "other" in paragraph 4, line 11, column 1, page 205, should read "over;" the correct version of reason 2, this paragraph, is: 'L. . . 2) to evaluate the usefulness of certain geo-chemical techniques, V. C. Kennedy and S. W. Hobbs of the USGS had already studied the distribution of copper, lead, and zinc in the soils (both in background areas and over veins) and in the water and plants, providing a criterion for measuring the magnitude and effect of soil contamination; ...9 On page 206, in the top left hand corner of Fig. 1 (in the area bounded by 47°35' and 116°10), the reference to Fig. 3 is incorrect. The area of Pine Creek, South Fork Coeur d'Alene River, and portion of Big Creek (the area which includes, from left to right, Kingston, Pinehurst, Smelterville, and Kellogg) should be identified as that of Fig. 2A. The headings for columns 1, 3, and 4, Tables I and 11, page 209, column 2, were reversed when the paper was printed. The corrected tables are:

Jan 1, 1961

By Susana Bolhão Muiños, José Hipólito Monteiro, Martin Frank, James R. Hein, Henrique Garcia Pereira, Fátima Abrantes, Tracey Conrad, Luís Gaspar

In spite of all the work that has already been done on ferromanganese deposits, studies on the Atlantic Ocean occurrences are still in their infancy and there is a clear need for investigations concerning the origin, distribution, and resource potential assessment of these deposits. Nevertheless, studies already carried out on northeast Atlantic seamounts indicate the general presence of ferromanganese deposits of hydrogenetic origin, i.e. deposits formed by direct precipitation of colloidal, hydrated metal oxides that are scavenged from the water column on hard-rock substrates. The hydrogenetic precipitation promotes the enrichment of ferromanganese crusts in many trace metals, most of which are of economic interest, such as Co, Ni, Te, rare earth elements, and platinum-group elements and thus ferromanganese crusts are considered an important metal resource.

Sep 1, 2014

By P E. H Gregg, R B. Stewart

Restoration trials established in 1985 included a treatment where pasture seed was sown directly into fertilised tailings. After seven years, accumulated soil data was used to compare physical and chemical changes in the plots with the original tailings control area nearby.   A known amount of annual fertiliser additions over the seven year period allowed nutrient balances to be calculated. Losses of S and P were relatively high at 72% of applied S and 28% of applied P. Calculations show that at least 240 kg N/ha/yr was fixed by clovers and this is likely to be under-estimated given that the calculation did not allow for leaching losses.

Jan 1, 1993

By R. S. Dean

"INTRODUCTION The metallurgical research program of the Bureau of Mines has been somewhat disorganized, but generally advanced by the increased activities of the war period. The present report is for the purpose of summarizing the work of the Bureau in this field for the past 15 years and indicating its future plan.Fifteen years ago the Bureau turned from its pioneer work on the physical chemistry of steelmaking to an emphasis on raking a pure steel synthetically, rather than by refining, that is, :producing each of the steel 'constituents in the pure state and combining them by simple melting. Such a procedure permits the use of less high-grade ores, not only of iron, but of the ferroalloy metals, such as manganese and chromium,This program has led to extensive work on iron-ore concentration, agglomeration, reducibility of ores and agglomerates, direct reduction of iron ores and concentrates by a wide variety of processes; special refining processes for iron, the production of pure mangenese, chromium, and cobalt from low-grade ores by electrolytic processes, the production of ferrochromium, ferronickel, and ferronickel-cobalt from low-grade domestic ores, and the development of many special alloys to effectively use the new products.The status of the work in each of these fields and the future program of work, together with a bibliography of papers and patents by the Bureau staff on each of these subjects, are given."

Jul 1, 1946

By T. Phiri, Antoine Floribert Mulaba-Bafubiandi

Microwave energy has been recently used in minerals processing to speed up the leaching process or to improve the liberation of targeted minerals (Al-Harahshed and Kingman, (2003); Bradshaw et al., (2001)). Applied to the roasting of sulphide minerals, microwaves allow the ?tunning? of calcine types and products quality in addition to the energy savings as opposed to the conventional roasting (Mulaba, 2006). As more than 85% of world zinc is produced through the ?roast-leach-electrowin? route, an attempt was made to optimize cost, energy and product quality for metal extraction process route. The use of microwaves was the alternative process route selected for the optimisation. Pyrite concentrate (0.17% Zn, 0.09% Cu, 35.71% Fe, 43.76% S) and sphalerite concentrate containing 43.81% Zn, 0.37% Cu, 3.86% Fe and 44.39% S were microwave roasted in a multimode cavity of 2.45 GHz with varying power levels and for different durations. The produced calcines were characterized using AAS, XRF, XRD and Mossbauer spectroscopy while the determination of residual Sulphur was used as products quality control tool to ascertain the degree of roasting achieved on the feed. The leachability of the produced calcines in HCl, HNO3, H2SO4 and HNO3 + HCl has been studied in terms of the best leaching yield, process kinetics economics and environmental aspect. With 800 W power for 30 minutes, ZnO and Fe2O3 were formed corresponding to a 70% sulfur removed from sphalerite and 80% from pyrite concentrates respectively. While the roasting of the above concentrates appeared to be a first degree processes, it was noticed that the microwave assisted roasting of sphalerite and pyrite concentrates yielded lower sample surface temperature for a shorter time (i.e.less than 30 minutes) microwave exposition. Longer time (more than 30 minutes) microwave exposure showed a linear increase in temperature in function of power level used. While optimum roasting conditions were found at 800W, 30 minutes, a 10% increase of sulfur removal was noticed while pyrite concentrate was microwave roasted. Sulfuric acid was seen to give higher leaching yield than nitric acid. Zinc dissolution was hindered by the presence of franklinite.

Jan 1, 2007

By J. G. Bruwer

Paper written on project work carried out in partial fulfilment of B Eng Met Surface coatings persisting on zircon particles, after being leached in an acidic solution, are believed to be the cause of zircon misplacement during the electrostatic separation of heavy mineral beach sands. Electrostatic separation is employed to separate non-conductive zircon particles from more conductive rutile particles. Surface coatings on zircon particles are believed to render the non-conductive zircon particles more conductive, resulting in the contamination of the more conductive rutile stream with zircon particles. Resistivity measurements, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) were performed to compare the surface characteristics of zircon particles found in the different product streams following electrostatic separation. XPS analysis showed that no significant difference exists in the outermost layer of the zircon particles found in the different streams. SEM analysis showed the existing surface coatings on zircon particles from different product streams to have similar chemical compositions. Resistivity measurements confirmed the results obtained from both the XPS and SEM analysis; no significant differences in the resitivities were observed. From the results obtained it suggests that surface coatings present on zircon particles are unlikely the primary cause of zircon misplacement. Zircon losses can possibly be a result of machine related aspects. Key words: XPS; SEM; resistivity measurements; electrostatic separation; heavy mineral sands.

Jan 1, 2007

Grey River Gold Mining Ltd commenced dredging alluvial flats in the Grey River Valley in 1989. Previous drilling indicated over 100 million cubic metres of gravels with some 90 per cent of the gold in the bottom seven metres. The dredge built by Rahco, Spokane, was innovative in a number of aspects but particularly in the fact that a separate ladder with a cutter and pump was used to strip the overburden and a bucketline to mine the gold bearing wash below. Metallurgical studies and exploration were initiated when the project commenced. Leasing and environmental considerations were investigated and action taken. While progress is being made, the operation at this stage is not meeting required production and performance. Main problems have been with the stripping system and wear.

Jan 1, 1990

By G. Major-Marothy

"INTRODUCTIONA beneficiation plant to upgrade earthy iron ores is being installed by the Iron Ore Company of Canada in Sept-Iles, Quebec.The crude ore for the plant will come from the Knob Lake area, located in Northern Quebec, where mining has been in progress since 1954.Some 170 million tons of ""direct 11 ores have been mined and shipped in the past eighteen years, with an overall silica content of 7 to 8 percent. No beneficiation - except the reduction of the top size to about 2 inches - took place during this period, but extensive research work has been carried out, in order to find a feasible process.Since “washing"", gravity separation, roasting and magnetic separation experiments did not indicate positive enough results, flotation was tried and found to be feasible.The beneficiation complex being installed will consist of grinding, flotation, dewatering - i.e.: thickening, filtering and drying - balling feed preparation, and agglomeration - i.e.: balling and induration.This process will result in a product superior to the ""direct shipping"" ores and will also expand the ore reserves by allowing material with a higher silica content to be utilized.THE OREThe Knob Lake ores are grouped by mineralogical composition and by grade.BLUE ORES, representing roughly two thirds of the reserves, carry their iron content mostly in the form of massive, blue hematite and martite.YELLOW ORES, about one sixth of the reserves, have predominantly hydrated iron oxides as the iron bearing minerals.RED ORES, the other sixth of the reserves, carry the iron mostly in the form of red hematite.The gangue in all ores is mainly quartz, but aluminum oxides and hydroxides are also present, particularly in the red ores."

Jan 1, 1972

By G. W. Jones, R. E. Kennedy

"INTRODUCTION In the manufacture, storage, transportation, and use of combustible gases and vapors, explosion hazards, which at times may be present when air becomes mixed with the gases and vapors, become of primary importance. Such conditions are especially dangerous where large volumes of gaseous atmosphere are involved, because an explosion under such circumstances is capable of doing tremendous damage to both property and personnel.Because of its interest in safety in the mining and allied industries, the Federal Bureau of Mines has investigated, and published results dealing with, the explosibility of various types of combutible atmospheres. The explosion hazards of natural gases have received attention, and results giving the limits of inflammability and ignition temperatures in air have been determined and published. 4/ Other investigations have shown how explosions of natural gas-air mixtures may be prevented by the addition of nitrogen and carbon dioxide. 5/Because of the increased demand for crude oil for war purposes, the application of secondary-recovery methods of stimulating oil production have received considerable attention during the last few years. The process consists in the injection of natural gas into partly depleted oil wells to cause the oil in the sands to flow into producing wells and so increase the amount of recoverable oil. 6/"

Feb 1, 1945

By Jon Sinnreich

Ensuring the accuracy of collected data during deep foundation static load tests is of paramount importance. Typically, pile head displacements are measured relative to a purpose-built reference system, which is assumed to be fixed. This study presents a simplified error analysis of this assumption, illustrates the potential magnitude of these errors, and proposes an improved method of pile head displacement monitoring.

Jan 1, 2009