Search Documents

By John Gamble

This paper summarizes the weight of epidemiological evidence to evaluate the hypothesis that asbestos exposure is causally associated with increased risk of gastrointestinal (GI) cancers as suggested by Selikoff in an early study of insulation workers. This review looks at populations that develop GI cancers, namely stomach, colorectal, colon and rectal. Guidelines for assessing causality are strength of association, biological gradient and consistency of the associations. Exposure?response (E?R) was evaluated using three methods to estimate exposure. Rate Ratios (RRs) for lung cancer and percent of mesothelioma are used as surrogate measures of asbestos exposure for all the cohorts of exposed workers. Quantitative or semi-quantitative estimates of cumulative exposure to asbestos were also used to assess E?R trends and were compared to E?R trends for lung cancer and mesothelioma in individual studies. Surrogate measures are important since there are few individual studies that have assessed E?R. None of the various methods to estimate asbestos exposure yielded consistent E?R trends and the strength of the associations were consistently weak or non-existent for the four types of GI cancers. The epidemiological evidence detracts from the hypothesis that occupational asbestos exposure increases the risk of stomach, colorectal, colon, and rectal cancer. Findings are briefly summarized below. © 2007 Elsevier Inc. All rights reserved. Keywords: Asbestos; Colon cancer; Colorectal cancer; Gastrointestinal cancers; Ingestion; Lung cancer; Mesothelioma; Rectal cancer; Review; Stomach cancer

Jan 1, 2007

By Soner Top

In this study, a process to separate manganese and iron from manganiferous iron ores by reductive acid leaching followed by magnetic separation was conceived and experimentally tested. In the leaching process, sulfuric acid was used as lixiviant and oxalic acid was used as reductant. The experimental results showed that the manganese and iron separation was optimum when the concentration of the sulfuric acid and oxalic acid were 0.75 M and 30 g/L, respectively, at a temperature of 80 °C, a solid/ liquid ratio of 67 g/L, stirring speed of 400 rpm, and leaching duration of 60 min. Under this condition, 90.49% and 6.78% of Mn and Fe were dissolved, respectively, from the ore sample with a size fraction of − 106 μm. It was determined that the leaching of manganese from the ores was a second-order reaction with an activation energy (Ea) of 53.38 kJ/mol. The leaching residues obtained under the optimum condition were subjected to high-intensity wet magnetic separation tests to recover the remaining iron content. This separation process produced a concentrate containing 56.20% Fe and 1.79% Mn with iron and manganese recoveries of 56.83% and 66.73%, respectively. A magnetic separation test from an unleached ore sample was also carried out as a benchmark. To the best of our knowledge, this is the first time that a magnetic separation process was used to a residue obtained from reductive acid leaching of manganiferous iron ores to recover iron.

By Soner Top

In this study, a process to separate manganese and iron from manganiferous iron ores by reductive acid leaching followed by magnetic separation was conceived and experimentally tested. In the leaching process, sulfuric acid was used as lixiviant and oxalic acid was used as reductant. The experimental results showed that the manganese and iron separation was optimum when the concentration of the sulfuric acid and oxalic acid were 0.75 M and 30 g/L, respectively, at a temperature of 80 °C, a solid/ liquid ratio of 67 g/L, stirring speed of 400 rpm, and leaching duration of 60 min. Under this condition, 90.49% and 6.78% of Mn and Fe were dissolved, respectively, from the ore sample with a size fraction of − 106 μm. It was determined that the leaching of manganese from the ores was a second-order reaction with an activation energy (Ea) of 53.38 kJ/mol. The leaching residues obtained under the optimum condition were subjected to high-intensity wet magnetic separation tests to recover the remaining iron content. This separation process produced a concentrate containing 56.20% Fe and 1.79% Mn with iron and manganese recoveries of 56.83% and 66.73%, respectively. A magnetic separation test from an unleached ore sample was also carried out as a benchmark. To the best of our knowledge, this is the first time that a magnetic separation process was used to a residue obtained from reductive acid leaching of manganiferous iron ores to recover iron.

By A. Sadik

The proliferations of media sources and non-profits organizations in Ghana have put the negative impacts of mining on the ?spot?; this has resulted in public outcry about mining. Although, the gold mining industry has responded by implementing several voluntary measures to ensure sustainable mineral development, these critics label such measures as ?green wash?. In this study, a content analysis of newspaper articles of the Ghana Web Database was carried out after the collection of a total of approximately 900 newspaper articles from it. The data were statistically analyzed to chronologically examine the main media view points and the changing perception of mining issues as reported by private and public media. The results showed government, mining industry (Gold), illegal miners and non-profit & community groups as the main media view points and total of twenty-eight related gold mining sustainability issues. The findings of this study could be used by the gold mining companies to improve upon the communications of their unknown sustainable mineral development measures and to design effective communications and education programs for the public.

Jan 1, 2009

By David L. Shearer

INTRODUCTON James Howden first secured an order for two Service Tunnel Boring machines in November 1986. These Tunnel Boring machines were 5.7 and 5.4 metres in diameter and the full length including back up was 215 metres. Manufacture commenced in December 1986 at the Glasgow factories of James Howden & Company with the deliveries to site of the machines in September 1987 and March 1988 respectively. In December 1987 two further orders were secured for the land running tunnels at 8.7 metres diameter. This paper presents some of the challenges in building tunnel boring machines for the Eurotunnel project between Britain and France. The general specifications of the Tunnel Boring machines and length of drives are shown in Appendix 1. DESIGN PARAMETERS The specification given by the Consortium TML on behalf of their client Eurotunnel cleary indicated that cutting of the face should be concurrent with the building of the precast concrete lining rings. In order to do this a telescopic machine was thought to be the best solution. Ground conditions were described as chalk marls of homogeneous nature with the possibility of friable areas and some revelling. A shielded type TBM with open cutter head was chosen together with a telescopic section and a rear

Jan 1, 1989

By G. E. Vaninetti

During its modem era, the southern Powder River Basin (PRB) in Wyoming has grown from meager origins in the early 1970s to become one of the most important coal-producing regions in the United States. In 1993, production and sales of southern Powder River Basin coal exceeded 190 Mt (209 million st), or about 20% of the US coal industry. Despite the remote location of the PRB relative to its potential markets, most coal industry observers anticipate continued strong growth to meet utility compliance plans for Phases I and II of the Clean Air Act Amendments (CAAA). This article is an overview of supply and demand issues concerning the marketing of southern PRB coal. It reviews the events leading up to the recent run on spot coal and offers a forecast of demand and prices.

Jan 1, 1994

In 2002 the authors updated the MFire model developed by the US Bureau of Mines. MineFire, developed by Mine Ventilation Services, Inc. (MVS), uses the MFire model to perform mine fire simulations on typical mine ventilation networks. The MineFire program is capable of producing visual schematics and other analysis tools for input and output of the MFire model. The MFire model, however, was limited to 500 branches and 10 fans. This paper discusses the newly modified MFire model that is now capable of modeling over 5000 branches and over 400 fans among other expansions and improvements. Given the long history and proven track record of MFire, the expansion did not modify the core calculation methods or results. This paper focuses on a general discussion of the MFire program and issues encountered in expansion of the algorithm. An example large network with simulation results is discussed.

Jan 1, 2011

The Department of Health and Human Services (HHS), National Institute for Occupational Safety and Health (NIOSH), Office of Mine Safety and Health Research (OMSHR), with the assistance of cooperating underground mining operations and state agencies, has conducted research exploring devices and technologies that could be used to assist miners navigating through smoke and dust resulting from a fire or explosion. Recent events in mines confirm that smoke and dust can enter and contaminate mine escapeways creating an atmosphere with severely reduced visibility. This reduced visibility results in substantially increased escape times, possible disorientation or confusion, and increased stress levels, and may prevent evacuation altogether. Tools or devices that assist miners in navigating through smoke-filled areas void of lifelines could make the difference in successful escape from the mine. This paper presents the results of OMSHR research to identify and evaluate tools and devices that could provide meaningful information to evacuating miners in areas with limited visibility and without the benefit of a lifeline.

Jan 1, 2011

By A. B. Hazar-Yoruç

Ferrochromium produced by smelting chromite ores is an important alloying component in the steel industry. Ore, coke and fluxes are mixed and reacted in an arc furnace for a smelting process of ferrochromium. In ad-dition to this process, pre-reduction of chromite ore with carbon is an important industrial process. In all these processes, the mechanism and kinetics of reduction of chromite with carbon play an important role. In this study, the reduction of Turkish chromite ore with carbon was investigated. Chromite and carbon were ground to three different particle size groups. Chromite was mixed with carbon in stoichiometric and excess ratios. The samples were reduced under argon atmosphere at temperatures between 1,200° and 1,350°C. The formed phases and alloy compositions of reduced chromite samples were analyzed by optical microscopy, scanning electron microscope (SEM) with EDAX and X-ray diffraction analysis (XRD). Experimental results showed that the degree of reduction and the reduction rate increased with increasing temperature and decreasing particle size. The highest degree of reduction, 61.4%, was obtained at 1,350°C. The reduction took place in three stages: Stage 1: transformation of Fe3+ to Fe2+ and formation of metallic nuclei, Stage 2: formation of metallic crust around the particles and Stage 3: growth of the metallic crust and coalescence of the metallic phase.

Jan 1, 2007

By H. Lyn Bourne

This is the fifth annual tabulation of mineral royalty information. This tabulation, like the previous editions, includes all of the earlier data. There are also 60 new entries. In addition to royalty information, some entries show the cost of purchased reserves. Two articles relative to the evaluation of minerals reserves appeared in December, 1986. R.H. Paschall (In the Aggregate, ME, p 1139) wrote a good article, although it lacked specific royalty data. However, this author takes exception to two ideas in Paschall's column. Paschall contends that the royalty rate does not affect the mineral appraisal. This present author could not disagree more. Paschall also claims the location of an industrial mineral deposit is the only serious or practical caveat in comparing royalties. Comments received here from readers helped make the list of caveats that are cited each year. The readers will decide which factors influence the mineral value for their commodities of interest. Paschall's point about the relationship of the parties who are negotiating a royalty agreement is important and very well taken. The other article, written by William Vernon (Pit and Quarry, December 1986), gives a step-by-step process on how to conduct a mineral appraisal. The article cites three reasons for an appraisal: transfer rights; collateral for a loan; and taxation. A fourth reason is to establish adequate compensation for reserves lost through condemnation. This author has appeared in several court cases where compensation for loss of mineral reserves through condemnation required a mineral appraisal. Royalty rate becomes an important factor in the appraisal process, although the Pit and Quarry article refers to that part of the valuation equation as "profitability." Both articles were well written and are recommended reading for those interested in mineral valuations. The same caveats that have appeared in previous columns relative to factors that influence the value of reserves are restated. The data in the table serve as a general reference and are not intended to present an absolute scale of reserves costs. Several factors influence the value of any mineral commodity. The factors include: • location/transportation - especially significant for most industrial minerals; • market conditions both for the commodity and the company acquiring the right to mine; • quality or grade of the deposit as it reflects the amount of processing/beneficiation necessary to produce the finished product; and • legislative restrictions and conditions for mining a given material at a given site. These and other factors will significantly influence the cost of reserves. The table shows the range of royalties and the variations in the basis of computing the fees. In a few instances, it gives the cost of acquired reserves based on purchase price and quantitative estimates of the material in place. The table lists the commodity in column 1, and the subsequent columns give: • the location by state, US geographic area, or Canadian province ; • the cost - R for royalty and P for purchased cost; • the year in which the lease or purchase agreement occurred; and • comments or footnotes for more information. The cost column requires more explanation. The units may refer to cubic yards (/cu yd), cubic feet (/cu ft), short tons (/T), or acres (/A). 1 cu yd = 0.76 M2 1cuft = 0.28m3 1 st = 0.9072 t 1 acre - 0.4047 ha or m2

Jan 7, 1987

By L. Bergkvist

"History can provide many answers with regard to what today’s mining industry looks like and how we got to where we are today. It has always been self-evident that safety has to be given the highest priority and, throughout history, many mine workers have been injured, become ill and have even sacrificed their lives due to the way in which attempts have been made to extract the ore, often due to ignorance of the dangers being faced. In more recent stages of history we have seen certain dangers being compensated by means of higher wages and bonus systems in order to have the work carried out: one example of this is when the rock heating method was employed and the men who first went underground to put out the fires that were burning, were paid extra. The working conditions, to which these people were exposed, with smoke-filled closed spaces, shortened their life expectancy considerably and today we can ask ourselves whether it is really possible to value these efforts just by higher wages. In all mines worldwide the working environment has been improved and many mining companies have a zero vision where work-related injuries and accidents are concerned. Despite this, incidents of varying severity still occur and a continuous improvement process and ongoing training is necessary in order to constantly minimise risks and improve the working environment. Atlas Copco takes this into account in all its development and we not only review our own production units but also the needs of our customers, with regard to the machinery that is produced in order to cater for customers’ safety and production objectives. Underground mining probably started at the beginning of the 11th century when people with modest tools tried to extract ores that were present in the bedrock. Methodology has developed enormously over the years with a strong focus on increased efficiency and higher production. In different parts of the world the development is driven forwards at different rates depending on which controlling factors are regarded as necessary. Political decisions, profit goals and productivity have partly controlled the development, but the greatest factor where improvement is concerned still remains with increased understanding of the totality. During more than 1000 years since underground mining has been conducted, all individuals at all levels have constantly improved their expertise and the human element has been of great importance with regard to the development that has been made, even though technology often occupies a leading role when we describe the improvements made."

Jan 1, 2011

By J. R. Parga

In mineral processing, poor froth-flotation performance translates into both an enormous loss of revenue and an unnecessary waste of the ore reserve. In this context, Bacís Mining Company developed a versatile new, high-performance flotation-cell design that can be incorporated into various flotation circuits. The main feature of this circular cell is that it is comprised of two separate sections, namely, a flotation cell that uses wash water to minimize the entrainment of fine gangue particles into the froth product and an external bubble generator that produces small bubbles of relatively uniform size at a specified aeration-rate. The air/water mixture is blended with the pulp by gentle agitation, so as to enhance particle-bubble aggregate-stability. Comparative metallurgical performance with conventional flotation cells show that the power requirements and operating costs for precious metal flotation are three times lower, while the concentrate grade is 7% higher and the recoveries of precious metals are 5% higher.

Jan 1, 2009

By George K. Schenck

INTRODUCTION Recent advances in high-pressure water jet technology can be effectively employed in mining and tunneling. The new equipment is based on available industrial hardware such as pumps, nozzles, and rotary swivels and seals, and is compatible with present mining and tunneling techniques. Principal advantages of water-jet assisted cutting relative to standard cutting are higher production rates, lower dust levels, and reduced fines. When used on rock and coal miners, water jets mean that relatively smaller and cheaper machines can be purchased. If properly applied, the combined effect is lower cost and significantly improved health and safety. While commercial use of high-pressure water blast cutting and extraction of rock (and concrete) already has a firm foothold in Europe, application of this new technique is just beginning in America. This paper begins with current American applications of high-pressure water jets for drills, for slotting and channeling machines, and then discusses the emerging technology for initiating rock failure in conjunction with drag bits on coal plows, continuous miners and boom-type miners (roadheaders). The focus of this paper is use of high-pressure water jets for cutting rock. High-pressure water jet cutting utilizes water above 70 MPa and currently reaches to 300 MPa and above. Some informatfon is included on low pressure "wethead" coal shearers and boom miners with water pressure to about 15 MPa.

Jan 1, 1983

By R. Hipsley, D. Arbonies, P. Dobak

South Arturo is a “Carlin-type”, breccia-hosted, oxide gold deposit located at the north end of the Carlin Trend. The discovery hole was drilled in July 2005 from mine dumps 1,000 feet south of the Dee open pit. Discovery hole (BD-72) encountered a cumulative 245 feet @ 0.056 opt Au beneath 850 feet of post mineral Tertiary Carlin Formation. Oxidation extends to depths greater than 2,000 feet in the deposit area. The deposit is presently in definition drilling stage with approximately 190,000 feet of drilling completed to date. A resource estimate is in progress. This paper will focus on the discovery and descriptive characteristics of the mineralization.

Jan 1, 2007

By R. J. Boyd

SUMMARY The productivity of drill and blast methods of mining in hard rock is limited by the cyclic nature of the operation, and a plateau of performance has been reached, even with the most advanced equipment developments. Higher mine operating costs and lower metal prices have more than ever generated the need for breaking through these productivity barriers. After initial field testing The Robbins Company has designed and manufactured, on a joint venture basis with Mount Isa Mines, Ltd., Australia, a prototype "Mobile Miner" for continuous cutting of hard rock. This paper describes the cutting concept, the initial application of a completed 1,156 m (3792 ft.) long 14% decline, actual performance and delay analysis, developmental modifications, anticipated performances of a fully developed machine, and possible future applications. Sincere appreciation is expressed to the management of Mount Isa Mines, Ltd., for allowing access to the data used in this paper. The views expressed here are those of the author and not necessarily those of Mount Isa Mines, Ltd. INTRODUCTION A paper titled, "Design and Development of a Mobile Mining Machine", was presented by J.P. Kindsvater at the RETC, New York, in 1985. This paper described the evaluation of a test fixture in an andesite quarry near Seattle, followed by design, construction and

Jan 1, 1987

PolyMet Mining is developing the NorthMet property near Duluth, Minnesota. Laboratory investigations had led to the development of the PLATSOL process to dissolve in one step the base metals (copper and nickel) as well as the gold and PGM’s. To complete the pre-feasibility study, a fully integrated ten-day pilot plant trial was undertaken, comprising of: high temperature (>220ºC) pressure oxidation in the presence of 5-10 g/L chloride (the PLATSOL process), followed by solid/liquid separation, gold plus PGM’s recovery from solution, conventional Cu SX/EW and recycling of the copper raffinate to the autoclave. The concentrate tested was a NorthMet bulk flotation concentrate assaying 14.7% Cu, 3.05% Ni, 0.14% Co, 26.7% S, 1.4 g/t Au, 2.2 g/t Pt and 9.9 g/t Pd. Laboratory results were fully confirmed and with minor adjustments of the laboratory PLATSOL® conditions, the following leach extractions were obtained during the pilot plant trial: Cu 99.6%, Ni 98.9%, Co 96%, Pd 94.6%, Pt 96% and Au 89.4%.

Jan 1, 2001

By Jacek B. Stypulkowski

This paper discusses the challenges faced by the design team of the under-river crossings of electric transmission feeders in New York City, a densely populated urban area. The under-river crossing of a 345 kV feeder was initially designed as Horizontal Directional Drilling (HDD), but was redesigned as a utility tunnel because of site con¬straints on both sides of the river. Multiple studies addressed location, available tech-nologies and costs. Multiple soil investigation phases addressed design aspects of HDD, as well as tunneling. Contractual issues varied from a design build alternative with Geotechnical Data Report (GDR) to design tender approach with GDR & Geotechnical Baseline Report (GBR).

The exploitation of the underground is currently undergoing a major transformation process. Besides mining, alternative ways of utilization are playing an increasingly important role. These alternative utilizations include the storage of gases, the disposal of radioactive wastes and the implementation of geothermal storage facilities. In addition, more and more mining operations are being shut down, like the German hard coal mining industry in 2018. But the integrity of closed mines must be ensured in the post-mining phase.

Jan 7, 2020

By J. Wagner, P. Eger

Although lifetime estimates for sulfate reduction based on total substrate carbon typically range from 20 to 30 years, field and laboratory experiments showed that rates of sulfate reduction decreased over time as readily available organic material was consumed. When the rate of acid input exceeded the rate of sulfate reduction, alkalinity was removed from the substrate, pH decreased and metals increased. Output pH increased from 4 to over 6 after the system was shut down for several weeks and the rate of acid input was reduced. Successful long term treatment requires a design based on the input pH and the long-term organic decomposition rate.

Jan 1, 2001

By Terry W. Mellors, Robert J. F. Goodfellow

The underground industry has been forced to reconsider risk management sincethe introduction and implementation of the “Joint Code of Practice for Risk Management of Underground Works in the UK” published in 2003 and the subsequent international version published by the ‘International Tunneling Insurance Group’ (ITIG) in January 2006.What does this mean for major tunnel projects in the US and elsewhere? The discussion will highlight the implementation of the Codes to date, risk management principles embodied in the Codes and the use of risk registers as a projectmanagement tool and the management of risk.

Jan 1, 2007