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By Geoffrey Berry

Exposure?response relationships between the relative risk of lung cancer and quantitative measures of exposure to asbestos are available from a number of epidemiological studies. Meta-analyses of these relationships have been published by Lash et al. (1997) [Lash, T.L., Crouch, E.A.C., Green, L.C., 1997. A meta-analysis of the relation between cumulative exposure to asbestos and relative risk of lung cancer. Occup. Environ. Med. 54, 254?263] and Hodgson and Darnton (2000) [Hodgson, J.T., Darnton, A., 2000. The quantitative risks of mesothelioma and lung cancer in relation to asbestos exposure. Ann. Occup. Hyg. 44, 565?601]. In this paper, the risks derived in these meta-analyses have been compared. Lash et al., concentrated on process and found that the risk of lung cancer increased as the asbestos is refined by processing. Hodgson and Darnton concentrated on fibre type and found that the risk was highest for exposure to amphibole asbestos (crocidolite and amosite), lowest for chrysotile and intermediate for mixed exposure. Some of the differences between the conclusions from the two meta-analyses are a consequence of the choice of studies included. The range of asbestos types included in the studies in the analysis of Hodgson and Darnton was wider than that in Lash et al., enabling differences between fibre types to be analyzed more readily. There are situations where occupational exposure to chrysotile asbestos has shown no detectable increase in risk of lung cancer. Taconite miners have shown no increased risk of mortality due to lung cancer. © 2007 Elsevier Inc. All rights reserved. Keywords: Mesothelioma; Amosite; Grunerite; Taconite; Crocidolite; Tremolite; Anthophyllite; Winchite; Risk assessment; Etiology

Jan 1, 2007

By M. Ahrens

Gearless mill drives (GMD) are a well established solution for grinding applications in the minerals and mining industries. The paper describes the functionality and technical features of such drive systems as well as the development and the progress of GMD systems over the years. With an increasing installed base and many drives operating for many years, there is an increasing need to modernize or revamp existing GMD installations. The first installations of GMD took place in the cement industry and have demonstrated that ringmotors can achieve a lifetime well above 40 years, if maintained properly. The life cycle time of many other components, especially electronic parts, is usually shorter. It is therefore necessary to replace aged or out-dated components early enough in a planned manner in order to reduce the risk of component failures and the related shutdown times. Modernization upgrades can range from minor software updates to a revamp of the cycloconverter. The paper describes typical examples of such upgrades and shows the most important aspects that need to be considered.

Jan 1, 2008

By R. R. Oder, R. E. Jamison, E. D. Brandner

This paper presents preliminary test results obtained with a 0.38 kg/s (3000 lb-hr) beta prototype MagMill™. In processing Upper Freeport coal the beta prototype recovered 82% of the weight of the feed and 91% of the heat content while reducing the potential emissions of sulfur, kgSO2/GJ(lbSO2/MBtu), by 61%. Pyritic sulfur in the MagMill™ product was reduced by 78% compared to that in the feed. For all runs, the mill product was controlled between 70 to 80% finer than 74 µ particle size. Recoveries of mercury, arsenic, and selenium ranged from 35 to 45% of that in the feed. Power draw was reduced by 26% and mill throughput was increased by 9% compared to the pulverizer operating with no magnetic separator attached.

Jan 1, 2000

By T. M. “Mike” Gurr

"U. S. marketable phosphate rock production for the 2018 crop year (July 1, 2017 to June 30, 2018) showed an increase to 27.7 Mt (30.5 million st) from the 2017 crop year production of 27.1 Mt (29.8 million st), as reported to the U. S. Department of the Interior by the mining companies operating in the United States during crop year 2018 (Table 1). Domestic consumption decreased in the 2018 crop year to 23.9 Mt (26.3 million st), as compared to the 27.2 Mt (30 million st) consumed in crop year 2017. U.S. imports of phosphate rock increased to 3 Mt (3.3 million st) for the 2018 crop year from the 1.81 Mt (1.9 million st) for crop year 2017. Imports of phosphate rock were from Peru and Morocco. There was an increase of 2.85 Mt (3.1 million st) in producers’ stocks from 7.45 Mt (8.2 million st) in crop year 2017 to 10.3 Mt (11.3 million st) in crop year 2018 (Table I).For calendar year 2018, Florida and North Carolina phosphate rock production accounted for 75 percent of the total U.S. production, with the balance being produced in Idaho and Utah. The Florida and North Carolina percent of U.S. production is declining. U.S. production of 25.7 Mt (28.3 million st) in calendar year 2018 was produced by five companies at 10 mines in four states and accounted for approximately 9.6 percent of the world production of 267.7 Mt (295 million st) for calendar year 2018 (Table 2).In calendar year 2018, U.S. phosphate production decreased by 2.2 Mt (2.4 million st), while companies increased stocks of phosphate rock by 1.7 Mt (1.9 million st). The domestic production for calendar year 2018 of 25.7 Mt (28.3 million st) represents 78.4 percent of the domestic production capacity of 32.8 Mt (36.1 million st).At present, China reportedly produces more than 50 percent of the world’s phosphate rock. As a result of planned expansions, Morocco production has increased from 27 Mt (30 million st) in 2017 to 33 Mt/a (36 million stpy), which is approximately 12.3 percent of the world’s production, moving ahead of the U.S. production. In calendar year 2018, the U.S. phosphate rock production was 25.7 Mt (28.3 million st), which is less than 10 percent of the world’s production of phosphate rock (Fig. 1)."

Aug 1, 2019

By E. B. Graves

I have been asked to talk to you this morning about phosphate marketing and distribution. In discussing this I will attempt to answer such questions as: What is phosphate? Where do we get it? What form is it and how do we sell it? How do we distribute it? How is it applied? And last, but not least, What about the future? To start with, phosphate is one of the three primary plant nutrients. It is the element essential for root structure of plants. Plants, like humans, need a balanced diet. Thus, the amount of phosphate required by individual plants is, in part, related to how much of the other nutrients are used. Virtually all soils contain a certain amount of available phosphates. Back at the turn of the century the most common source of additional plant nutrient, including phosphates, was from cattle manure. The use of chemical fertilizers is something that has grown significantly during the last half century, and in particular, the last 20 years.

Jan 1, 1977

By Adam Shang Robert Fu

The Yung-Chung-Tunnel in Taiwan, constructed for the Taiwan-East Railway Bureau, collapsed during construction when a water bearing, fractured marble zone was intersected. The inflow was approximately 4,000 liters/second. In spite of 30 relief holes the total inflow into the tunnel remained constant. The pre-excavation grouting through the re-aligned tunnel had to be conducted under extreme flow-conditions. A hot bitumen grouting program was selected for technical and economical reasons out of 13 international proposals. The technical challenges were: grouting under severe flow conditions high formation water pressures to be injected with hot bitumen at high temperatures and pressures The hot bitumen grouting program resulted in a dramatic reduction in the hydraulic conductivity and stabilization of the formation and facilitated a problem-free excavation.

Jan 1, 2007

By W. Burger

In underground mines worldwide, a large number of short and small diameter slot holes need to be excavated. Herrenknecht has developed and built a new boxholeboring machine based on the well-proven Microtunnellingpipe jacking technology. The innovative Boxhole Boring Machine significantly increases work safety and requires only minimal drift dimensions. The high and consistent production rates that can be achieved result in enormous time savings compared to conventional drill and blast excavations. GENERAL ASPECTS In gold, copper and ore mines ventilation shafts are required to prepare block caving operations, to discharge ore onto the transportation level and to provide evacuation shafts. A high level of occupational safety and efficiency is the main objective when drilling vertical or inclined shafts. The faster and more safely shafts can be constructed, the earlier the actual production in the mine can start or be continued. Mechanized or conventional methods (drill&blast) that have been used to date only partially meet the required safety standards and fail to provide the requested production rates.

Jan 1, 2012

By Xuchen Fan, Chenyang Zhou, Yuemin Zhao, Liang Dong, Chenlong Duan

A gas–solid fluidized bed using magnetite particles is an effective methodology for coal beneficiation in the field of dry coal cleaning. Broadening the size range of magnetite used in the bed decreases medium preparation cost. In this study, a tapered fluidized bed was used to investigate a magnetite particle size range of −0.5 + 0.074 mm. The results showed that a tapered fluidized bed effectively strengthens mixing of magnetite with a wide size range (−0.5 + 0.074 mm). The results of beneficiation experiments indicated that with increasing tapered angle, separation efficiency increased and then decreased. The highest separation efficiency was obtained at a tapered angle of 10°. The optimal results showed that the ash content of the concentrate decreased from 31.82% to 12.33% with a probable error of 0.11, which indicated that a tapered fluidized bed was efficient to improve fine coal beneficiation performance.

By Kenneth N. Han

The effect of anions such as sulfate, chloride, and nitrate on the solubility of rare earth element-bearing phosphates and fluorocarbonates has been examined using relevant thermodynamic data. The study has found that these anions have significant influences on the overall dissolution of rare earth elements (REEs) from various sources in the aqueous media. The thermodynamic calculations in this study have indicated that the speciation of REEs with the anions tends to increase the overall solubility of the REE-bearing minerals. However, in some cases, strong precipitation of REEs with some of these anions causes an adverse effect on the solubility of these elements. It has been found that sulfate ion has the most pronounced effect on the solubility compared to nitrate and chloride, in which the latter two acids exhibited almost identical results. The calculated results have indicated that REE-oxide (hydrated) is the easiest compound to dissolve, followed by carbonate, phosphate, fluoride, sulfate, fluoro-carbonate, and oxalate in that order.

By Matthew E. MacGregor, Hugh T. Kelly

I.H. 635 (LBJ Freeway) was constructed as a loop freeway around the city of Dallas in the late 1960s and early 1970s with a design capacity of 160,000 vehicles per day (vpd). Today’s facility is carrying over 270,000 vpd. To help mitigate community concerns with regard to right-of-way issues, noise, safety, and traffic disruption, the Texas Department of Transportation (TxDOT) is planning a number of significant improvements. The West Section improvements include the construction of managed HOV/Toll lanes. Within this 8-mile section, TxDOT is planning two mined tunnels(1.5 and 1.9 miles long) beneath the LBJ Freeway. The mined tunnels will connect to cut-and-cover box sections in both the east and west directions. This paper presents an overview of the project development from the design schematic, through the geotechnical investigations, into the current design stage. The project is being planned for implementation by use of a Comprehensive Development Agreement.

Jan 1, 2005

By Mingyang Li, Yan Lv, Xiaolong Ma, Xudong Gao, Jie Zhao, Yingyi Zhang

The reduction process of pre-oxidized ilmenite concentrate powder in 30%CO–70%N2 atmosphere was characterized by thermogravimetric and differential thermogravimetric (TG-DTG) analysis system at the temperature from 1073 to1223 K. The isothermal reduction results show that the reduction process is divided into three stages and the corresponding apparent activation energies are obtained by iso-conversional method and model-fitting method, respectively. For the first stage, the conversion degree increases sharply with increasing time, and the reduction process is controlled by the random nucleation and subsequent growth model (A2 model). For the second stage, the conversion degree increases slowly with increasing time, and the reduction process is controlled by the diffusion of carbon monoxide in the reduced layer (D1 model). For the third stage, the reduction processes at different temperatures are controlled by the diffusion of carbon monoxide in the reduced layer (1073 K and D1 model), phase boundary chemical reaction (1123 K and R2 model), random nucleation and subsequent growth (1173 to 1223 K, A2, and A3 models), respectively. For the whole reduction process, the apparent activation energies obtained by iso-conversional method and model-fitting method are 71.72 and 31.92 kJ mol−1 , respectively

By Mingyang Li, Yan Lv, Xiaolong Ma, Xudong Gao, Jie Zhao, Yingyi Zhang

The reduction process of pre-oxidized ilmenite concentrate powder in 30%CO–70%N2 atmosphere was characterized by thermogravimetric and differential thermogravimetric (TG-DTG) analysis system at the temperature from 1073 to1223 K. The isothermal reduction results show that the reduction process is divided into three stages and the corresponding apparent activation energies are obtained by iso-conversional method and model-fitting method, respectively. For the first stage, the conversion degree increases sharply with increasing time, and the reduction process is controlled by the random nucleation and subsequent growth model (A2 model). For the second stage, the conversion degree increases slowly with increasing time, and the reduction process is controlled by the diffusion of carbon monoxide in the reduced layer (D1 model). For the third stage, the reduction processes at different temperatures are controlled by the diffusion of carbon monoxide in the reduced layer (1073 K and D1 model), phase boundary chemical reaction (1123 K and R2 model), random nucleation and subsequent growth (1173 to 1223 K, A2, and A3 models), respectively. For the whole reduction process, the apparent activation energies obtained by iso-conversional method and model-fitting method are 71.72 and 31.92 kJ mol−1 , respectively

By Klaus Rieker

North of Antwerp central train station, two single-track tunnels for the high-speed train line between Brussels and Amsterdam were constructed. At the same time, the central train station was modified to a through station. Both 1.23 km tunnels are situated in the Antwerp sands and were constructed using a slurry shield machine. Due to the inner city location, the tunnels run over their entire length underneath structures, in some cases with only minimal clearance. The paper deals with these challenging situations. In addition, the tunnel boring machine, the tunnel lining and measures to limit settlements will be introduced.

Jan 1, 2007

By W. G. Brunner

The slurry wall technique has undergone an evolution from its invention to its today’s status. In the early stages slurry walls were built with cable grab, later on with much stronger hydraulic grab and last but not least with the use of the cutter technique. The cutter allows thick walls with high verticality to extreme depths through hard soil and rock formations. With the rising demand of the construction of watertight diaphragm walls different joint systems have been developed. In addition to the rapid development of excavation systems it was necessary to improve slurry treatment and desanding plants, especially in conjunction with high performance trench cutters. Deep mixing methods can be used economically for the construction of cut-off or excavation support walls where other systems such as traditional soldier beams and lagging walls would yield unsatisfactory performance, where the installation of vibrated or driven sheet piles could cause vibration induced settlements and where concrete diaphragm walls would be time consuming and expensive. The new CSM method can largely replace the more conventional single or multiple auger methods of soil mixing or jet grouting. The cutter tool is similar to a cutter used in diaphragm walls or cut-off walls and is operated with a Kelly mounted on a drilling rig or rope suspended on a crane jib or mast of a base carrier. With this system much deeper walls can be installed and even hard soil layers can be penetrated.

Jan 1, 2007

By Jill Murray

This study focuses on the amosite mining region in South Africa and associated health effects, compared to other mined asbestos fiber types. Historically, dust and fiber levels were high in the amosite mills and mines, and many miners and members of the surrounding communities were exposed to the fibers. Research has shown that amosite produces both benign and malignant disease. Nevertheless, the mesotheliomagenic potential of amosite is several fold lower than crocidolite. The risk of disease associated with amosite exposure is difficult to quantify. Reasons for this include the scarcity of available information, including fiber measurements, and case ascertainment, as well as the juxtaposition of the amosite and crocidolite asbestos seams in South Africa. © 2007 Elsevier Inc. All rights reserved. Keywords: Amosite; Mesothelioma; Crocidolite; South Africa; Asbestos

Jan 1, 2007

By Steve Stuart

Deep-sea mineral SMS deposits present some of the world’s most challenging conditions for drilling equipment. As robotic seabed drilling services mature so too the ways that clients engage with service providers to maximise their data requirements. This presentation reviews key considerations for planning and executing a successful seabeddrilling program in variable mineralised deposits. Some of the means of collaboration between robotic seabed drilling contractors and those hiring their services are explored; where improved efficiencies and recoveries over the period of a drilling programme could be achieved. Potentially new technology or methodology can be looked at to further improve these approaches.

Sep 1, 2014

By D. Kwietnewski

With all of the unknowns associated with tunnel construction, how does a contractor choose a roadheader? This paper presents a review of several models of roadheaders being used in today?s tunnel projects. The features of different models of roadheaders are presented and compared. Roadheader size and cutter power generally determine which roadheader is best for a particular job. We will also present a model for matching features of the roadheader to the anticipated ground conditions such that the most efficient machine is selected for the project.

Jan 1, 2011

By Klaus Stoss, Bernd Braun

The sinking and lining of a large mine shaft with 8.0 m i.d. and 1,133 m total depth is described in detail. The ground freezing method was applied to safely sink the shaft through unstable, waterbearing strata. Following a brief introduction to the geological and hydrological conditions and the owner's shaft requirements, is the general technical concept to sink and line the shaft. Particular emphasis is put on the lining system which has to provide stability and absolute watertightness for the lifetime of the shaft, even though mining takes place in its immediate proximity. Machinery and equipment used to execute the work are mentioned and commented. Furthermore, the excavation and lining of the large filling stations using rock anchors and shotcrete are described. Details on performance rates are given.

Jan 1, 1983

By Jamal Rostami, Richard Kastner, Ahmad Ramezanzadeh

Improving the accuracy of the performance prediction models for hard rock Tunnel Boring Machines (TBMs) is important in estimation of the schedule and cost of tunnelling in related projects. The effects of rock mass on performance of TBMs has been studied extensively, yet due to the complex nature of the process, impact of many parameters influencing machine advance rate are not very clear and there is still room for improvements. More accurate estimates can be obtained by better understanding of operating parameters in various geological conditions and can lead to matching machine specifications with job conditions, optimizing machine performance, and avoiding long delays and downtime for increased productivity. This paper will offer review of two case histories including Queens Water tunnel in New York and KCRC project in Hong Kong. The analysis of the available field data, including the geological back mapping and results of laboratory testing of rock mechanical properties, machine operational parameters and achieved rate of penetration will be presented. This includes statistical analysis of available field data to provide a better understanding of the influence of rock mass properties on performance of hard rock TBMs as well as related formulas to improve performance estimates.

Jan 1, 2005

By H. B. Miller

Contract Incentives have long been employed in the underground hardrock industry as a tool to influence employee performance, enhance productivity, and control labor costs. While traditionally structured to establish a direct correlation between performance and compensation, many contract programs have evolved into elaborate systems that promote strategies often viewed as independent of productivity. This paper presents the findings of research into these contract incentives and was conducted with the cooperation of 33 mines utilizing a spectrum of employee compensation and incentive programs. Emphasis of this analysis focuses on the types of production contracts observed and their role with respect to employee earnings.

Jan 1, 1994