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By Matthew S. Sanchez, Richard J. Lee, Matthew D. Zock, Drew R. Van Orden

"Current Environmental Protection Agency (EPA) risk models and asbestos fiber counting techniques for monitoring airborne exposures treat all fibers as being equivalent and ignore the effect of dimension on toxicity. While this may have been appropriate when modern analytical methods were not available, the measurement world is now fully capable of making the appropriate distinctions. The importance of width as a determinant of carcinogenicity has been recognized for nearly 30 years within the published literature. Stanton,1 in a landmark study of a suite of fibrous materials, found that durable mineral fibers with widths less than 0.25 mm and lengths longer than 8 mm were causally associated with the induction of tumors. Pott,2 in a later study, postulated a fiber toxicity model that agreed reasonably well with the Stanton findings, but extended the concept to include varying toxicity as a function of length and width. Wylie et al.3 reanalyzed samples used by Davis et al.4 and found that tumor generation was strongly and inversely correlated with fiber width. Crump5 testified increasing fiber length was correlated with disease occurrence. Lippman6 reviewed a number of studies and suggested that mesothelioma was closely associated with long, thin fibers. Berman et al.7 published a risk model, which found that disease was correlated almost exclusively with fibers longer than 40 mm and width less than 0.25 mm. Recently, Loomis et al.8 reanalyzed textile mill samples and found that aspect ratios greater than 40:1 were highly correlated with disease. Incorporation of width into risk models has been limited by the availability of data from operating asbestos plants and, in particular, the observation of an asbestos plant for which there is no observable mesothelioma. There have been only limited studies published on the dimensions of asbestos fibers, with a few serving as the primary references in other literature.9_13 A rare opportunity to collect detailed concentration and dimensional data of airborne crocidolite from an operating asbestos-cement plant using modern analytical procedures arose, providing a chance to supplement the existing literature on airborne fiber dimensions. The asbestos-cement plant is located in the eastern end of Cochabamba, Bolivia along Highway 4. Cochabamba is a relatively large city located in the Andes Mountains, approximately 250 km southeast of the capital La Paz. The city sits in a valley that runs east-west with mountains to the north and south. The crocidolite used in the products made at this facility is mined in central Bolivia, approximately 75 km northwest of Santa Cruz. The crocidolite is a fibrous magnesioriebeckite 14 (blue asbestos). Crocidolite fibers from Bolivia were the subject of prior reports suggesting the fibers are generally longer and thicker than crocidolite from Australia or South Africa.9 At the cement plant, the run-of-mine crocidolite was first pulverized using a hammer mill and then sieved on vibratory sieves to produce fibers of limited size ranges for use in the cement. The sieved crocidolite is mixed with other components, including recycled cement product, to produce a slurry that is vacuum filtered into sheet form. The sheets are then manually molded into a corrugated shape, air dried, and sawed (using circular saws) to accepted dimensions. The sawed sheets are cured in soaking pits for 28 days before being shipped to the consumer. Prior to shipping, the sheets are finished by a light hand sanding followed (at customer request) by applying one or more coats of paint. A detailed description of the cement plant and the industrial hygiene results can be found in Van Orden et al.15"

Jan 1, 2012

By William S. Alldredge

The Washington Metropolitan Area Transit Authority(WMATA) officially came into existence in February 1967 after the District of Columbia, Maryland, and Virginia joined in a com¬pact pursuant to Federal creative legislation signed the previous November to build a regional rapid rail transit system called METRO (1). The parent organization was the National Capital Transportation Agency (NCTA), a Federal agency, subject to Federal statutes and regulations. Soon after the completion of the transition from NCTA to the new "non-Federal" status of the Authority, the Board of Directors of the Authority formally adopted procurement policies and procedures (2). These are specific statements concerning competition by formal advertising for bids or by solicitation of proposals for negotiation, contracting authority, approval of awards, awards of contract modifications, and processing of claims and disputes. These policies and procedures are silent as to Federal procurement statutes and regulations. But because of the Authority's origin, the sensitive nature of the compact among the several sovereign jurisdictions, Federal financing of two-thirds of the costs, and the resultant surveillance by the General Accounting Office over staff operations, the Authority's procurement practices follow closely Federal regulations adapted to WMATA's needs. This is an important point and is the foundation of contractual relations between the Authority as the owner and its construction contractors. Various constraints and flexibilities of this arrangement with respect to excavation and tunneling contracts will be pointed out in the ensuing discussions.

Jan 1, 1974

By Guillermo P. Selas

Perhaps this is the first time that an analysis of the industrial minerals panorama has been made in Mexico for that type of commodities. Because the non-metallic minerals lack the glamour of the metallic minerals and are usually of less unit value than metallics, a comparative study of these commodities has seldom been attempted. Sulphur, fluorite, barite and few others are an exception. Consequently, the statistics on the lowest per unit value industrial minerals, such as limestone, dolomite, gravels, sands, etc., are usually scarce and not always accurate. The following, then, will be an attempt to show a general status of the industrial minerals in Mexico with due reservations regarding volumes and values. According to Kruger (1971), this group of minerals surprisingly very little known, and called non-metallics because the lack of metallic luster, is the largest group of the mineral kingdom. It constitutes perhaps 75% of all the mineral varieties. For the most part, these minerals are compounds of common acids, sulphides, hydroxides and two elements carbon and sulphur. The list of non-metallic minerals is therefore very long. It includes the borates, carbonates, chlorides, fluorides, nitrates, phosphates, silicates, sulphates and less commonly arsenates, chromates, molybdates, sulphides, tungstates and vanadates. The latter group and many of the oxides are sought usually for their metal content.

Jan 1, 1974

By Jerry C. Tien

Without a doubt, the scope of China?s coal boom has been nonstop. Despite the world economic slowdown, China?s year-on-year gross domestic product (GDP) jumped 10.3 percent year-on-year in 2010, boosted by a faster than expected 9.8 percent expansion in the fourth [ ] quarter. And, the first quarter of 2011 expanded another 9.7 percent. According to a frequently cited statistic, the country is building two mid-sized coal plants each week. This amounts to a yearly increase equivalent to the entire power grid in the United Kingdom. China?s coal production was doubled in the last 10 years, from 1.044 Gt (1.15 billion st) in 1999 to 3.2 Gt (3.52 billion st) in 2010. This is 3.2 times the U.S. production (986 Mt or 1.085 billion st) and nearly half (46.3 percent) of the world?s total coal production (6.91 Gt or 7.6 billion st). This rapid increase of demand for coal has made China the world?s largest coal importer in 2009. With the economic situation improving, this trend is expected to continue.

Jan 1, 2011

By J. C. Watts

Monitoring and control of conventional industrial wet grinding circuits is conceptually straightforward. However, since production objectives and operating constraints can vary widely from plant to plant, there is probably no single overall grinding circuit control strategy which is "best" in all cases; in-variably some compromise is necessary between performance desired under ideal conditions and performance achievable in practice. The recent advent of relatively low cost, reliable, high speed small computer systems is revolutionizing daily operations in increasing numbers of metallurgical processing plants. Of special power and capability is a hierarchical computer network like that currently in use at the Pinto Valley Operations of the Cities Service Company. Several satellite processors for key plant areas communicate with a master computer operating under a powerful multitasking real-time operating system. Hardware and software structure is such that downtime on one of the processors -including the master -does not have a major impact on overall system operation. Admittedly, the powerful, core efficient table driven satellite software, which handles process/computer communication, calculation of nonmeasured process variables, and basic Direct Digital Control functions, is difficult to modify. However, important high level process monitoring, report preparation, graphic display, and supervisory control functions -including economic optimization -can be implemented by project engineers at the plant site. Thus, for example, new control strategies can be quickly examined and rapidly evaluated. Such computer monitoring capability also permits use of short duration process pulse tests for approximate dynamic modeling and rapid calculation of controller tuning constants for single loop dominant systems. Following a brief back-ground discussion of the Pinto Valley Project, we present some of the more interesting results and conclusions of our work over the past year.

Jan 1, 1978

By J. B. Lott

The authors' company has recently undertaken a development programme aimed at exploring the relationships between the variables of greatest importance in the design of mixer-settlers for metallurgical solvent extraction applications. Such applications vary from relatively small scale plants treating copper mine waters, nickel containing effluents, etc., where the total flowrates may be of the order of a few hundreds of gallons per minute, to very large scale plants treating several thousands of gallons per minute of leach liquors containing copper, uranium or other metals. This paper outlines the physical and mechanical factors which must be taken into account when designing mixer-settler systems for large scam. solvent extraction plants. The performance of the equipment will also be dependent upon the chemistry of the system, including the kinetics and thermodynamics of the ion exchange reaction itself, the effect of impurities flocculants, surfactants, temperature, etc., but these will not be dealt with here. Much of the laboratory work has been carried out using copper containing solutions and either LIX 64* or LIX 64N* as the solvent dissolved in various grades of kerosene. For simplicity, all the graphs and tables of results which are presented and discussed here will refer to the LIX-copper system, although the conclusions will in many cases be generally applicable to other systems also. The LIX-copper process is now sufficiently well known to obviate the need for a full description, however, an outline flowsheet of the process is shown in Figure 1. The ultimate objective of a laboratory programme for a particular extraction application is to provide data upon which a mixer-settler system can be designed to handle a given throughput of leach liquor and extract from this liquor the maximum quantity of metal for the minimum cost. In other words, the objective is to determine the design and operating parameters which achieve the optimum balance between capital and operating costs. * Trade-marks for General Mills solvents.

Jan 1, 1971

By V. K. Gupta

The experimental results of some wet batch and continuous grinding experiments carried out in a 40 x 40 cm grate discharge ball mill have been analyzed for the variation of the grinding rate parameters, Si, with various operating conditions using a linearized population balance model. The wet grinding tests were carried out under conditions which were very similar to those encountered in the actual practice in plant operation. Well distributed -4 and -20 mesh feeds of two complex pyritic ores were used. The volume-percent solids in the pulp ranged from 30-40, the particle load from 5-8 kg, and the solids feed rate from 70-1 10 kg/hr.

Jan 1, 1981

The paper describes a practical methodology based on numerical modelling for the prediction of progressive failure of underground mine stopes with cable bolt support. A case study of the 40-761 stope at Kidd Creek Mine, Timmins, Ontario is presented. The stope was mined by blasthole open stoping in 1986 as a lead stope within a mining block between 36-1 and 38-2 levels. Initially designed to peak at 38-2 level, the stope back caved upwards approximately 40m towards 36-1 level. Cable bolts were installed above the stope from 36-1 level after caving had begun. The stope eventually stopped to cave when the falling rock mass encountered a sufficiently high cable density. The paper provides details of the geomechanical data and modelling results of the case study. Numerical modelling is carried out using a finite element package known as e-z tools which has, among other things, a special cable/rockbolt simulation capability.

Jan 1, 1994

By Joseph D. Drew

Oregon Resources Corp. (ORC) has developed and permitted a new mining operation that incorporates a process design that will allow the unique paleo-beach placer deposits of southwestern Oregon to be extracted efficiently and economically, creating the only domestically mined source of a unique foundry grade chromite and specialty de-veining sand for precision casting. The operation will also provide an additional domestic source of garnet and zircon. Engineering design has been guided by the variable geology and mineralogy of the paleo-beach placer deposits as well as the need for a dry tailing scheme that resolves a lack of water resources at the placer locations and at the same time eliminates the need for slurry settling ponds, typical of paleo-beach placer operations in North America.

Jan 1, 2010

By J. H. Daniel

The reduction of accidents will play an ever increasing role in the mining of coal and hardrock ores as mining operations become more mechanized, the equipment becomes more costly and sophisticated, and as mineral production exploits deeper and more marginal coal and ore deposits. The most effective means to reduce accidents is through the design of mining systems and equipment. Results of safety research by the U.S. Department of the Interior, Bureau of Mines, to design safer coal extraction and haulage systems and to reduce electrical accidents are presented.

Jan 1, 1991

A computer simulation of the automatic control of continuous mining machines has been prepared, similar to previous simulations of longwall mining systems and coal thickness sensors. The simulation allows for programmed variation of the horizon detection method, the azimuthal guidance system, the type and configuration of the miner, varying hardness in the unmined face material (leading to varying error in the machine heading), and the miner's cutting cycle. It simulates control of the miner in three axes. Use of the simulator makes it possible to anticipate problems arising from the complex character of underground mining, which include unpredictable multi-pass coupling and unpredictable variation in geological conditions.

Jan 1, 1993

By Nasser Madani, SULTAN ABULKHAIR

The abstract of the paper discusses the challenge of quantifying iron content in a coal deposit in Kazakhstan. The iron dataset is limited, coming from only three drill holes and some stope samples, while a large amount of geological information is available from legacy drill hole data. The paper proposes a workflow using multiple-point geostatistics to model geological domains and two-point geostatistics to model iron content within these domains. The results show that the direct sampling (DeeSse) algorithm effectively reproduces the complex seam layers, and sequential Gaussian simulation models the iron within each domain.

Mar 30, 2022

By Clarence O. Babcock

Model pillars of limestone, marble, sandstone, and granite, with length-to-diameter ratios of 3, 2, 1, 0.5, and 0.25 (0.286 for granite), were broken in axial compression to determine to what extent an increase in end constraint increased compressive strength. Radial end constraints of 13 to 23 percent of the average axial stress in the pillar, produced by solid steel rings bonded with epoxy to the ends of dogbone-shaped specimens, increased compressive strength somewhat above that of cylindrical pillars without ring constraint. However, when the results were compared with those obtained by other investigators for straight specimens of several rock types taken collectively, with L/D ratios greater than 0.5, the resulting strengths were not significantly different. Thus, the amount of end constraint produced by the solid steel rings was about the same as that produced by the friction from the steel end plates. In other tests a radial prestress of 3,000 psi or 5,000 psi was applied prior to axial loading by adjustable hardened steel rings to increase the constraint above that obtained for the solid rings. The average radial constraint stress, expressed as a percentage of the average axial pillar stress at failure for the 3,000 psi prestress, was 54.3 percent for limestone, 40.3 percent for marble, 44.7 percent for sandstone, and 23.4 percent for granite. The average radial constraint stress, expressed as a percentage of the average axial pillar stress at failure for the 5,000 psi prestress, was 74.2 percent for limestone, 51.2 percent for marble, 61.6 percent for sandstone, and 29.7 percent for granite. These constraints increased the compressive strength significantly above the strength of straight specimens and solid-ring constrained specimens. These results suggest that large horizontal stresses in orebodies mined by the room and pillar method should increase the strength of the pillars and allow an increase in ore recovery by a reduction of pillar size when major structural defects are absent.

Jan 1, 1969

By S. K. Ghosh

This paper discusses how the information on ash composition, ash-fusion temperatures, and ash-slag viscosity can be utilized to predict slagging and fouling potentials of a particular coal. A review of several empirical parameters which are commonly in use for determining such potentials is given. Also, some guideline values for interpreting the relative propensity of slagging and fouling of various types of coal are provided.

Jan 1, 1983

By A. Ghosh

Commonly used predictors of ground vibration from blasting, being linear in log-log plot, do not model the underlying physics of wave attenuation. Amplitude of the wave decays with distance due to geometrical spreading and inelastic attenuation producing a nonlinear carve in log-log scale. The nolinear decay of seismic waves has also been observed from non-explosive sources, such as, pile driving, drop hammer, traffic, etc. The improved predictors, by explicitly taking these two mechanisms into consideration, model the data trend extremely well at all distance ranges. Actual field data from different studies have been used to validate the improved models.

Jan 1, 1991

By C. Feng, W. Song, B. Moudgil, P. Zhang, W. Xiao

Separation of dolomite from phosphate is the most challenging problem in phosphate mineral processing. Over 50% of the future phosphate reserves in Florida contains too much dolomite to process using the current industry practice. The FIPR Institute has collaborated with worldwide experts in the field to address this issue. As a result, the industry is now offered with three feasible options. Optional 1 involves crushing and grinding of high-dolomite phosphate pebbles followed by dolomite flotation at slightly acidic pH using a new collector that does not require phosphoric acid as a phosphate depressant, achieving a final concentrate analyzing less than 0.9% MgO at about 87% P2O5 recovery. Option 2 offers three methods for reducing MgO content in the concentrate from the Crago process, including adding a dolomite depressant in the rougher flotation step, dolomite flotation of the cleaner concentrate, and scrubbing the cleaner concentrate in quartz sand. These methods could reduce MgO content in the final concentrate by 20-40%. Option 3 is a gravity separation technique using an innovative separation jig, and may well be the ultimate solution to the problem. INTRODUCTION Magnitude of the Dolomite Problem With the depletion of the higher grade, easy-to-process Bone Valley deposits, the central Florida phosphate industry has moved into the lower grade, more contaminated ore bodies from the Southern Extension. The phosphate deposits in the Southern Extension may be divided into two zones: an upper zone and a lower zone. The upper zone is readily processable using the current technology, but the lower zone is highly contaminated by dolomite. Geological and mineralogical statistics (Hassan and Bogan, 1994) show (Table 1) that more than 50% of the phosphate resource would be wasted if the lower zone is bypassed in mining, and about 13% of the resource would be wasted if the dolomitic pebbles in the lower zone were discarded.

Jan 1, 2019

By S. Agarwal

The mining industry collects a significant amount of operational data. However, gleaning useful information from the terabytes of data is difficult, and not just because of the sheer volume of the data. Therefore, an automated tool was developed at the University of Alaska Fairbanks to go through data and apply very sophisticated statistical and neural network techniques, to identify the data streams that are important to a process. This paper presents results from the tool as applied to SAG mill data from a gold mine. The results were benched against commercial tool. Results indicate that there was little or no loss in performance by automating the very complicated process of neural network modeling. Therefore, the intent of the exercise, to examine if complicated modeling tasks can be automated, was realized.

Jan 1, 2011

By Kai Koosmen, Mehdi Serati, Tengzhou Wang

Spalling and rockburst are unwanted brittle failures at the boundaries of underground excavations that are commonly observed in hard rock and high-stress environments at significant depths, although, spalling has also been observed in comparatively shallow soft rocks. The crack initiation (CI) stress threshold (representing the stress level at which new micro cracks begin to form in an intact rock) is widely used to establish the in-situ spalling strength, and is generally regarded as the lower limit of the long-term rock strength. This study analyses the evolution of CI and other mechanical properties for a high-porosity sandstone with an average UCS of 38 MPa under unconfined cyclic compressive loading. The results indicate that rock properties are variably affected by cyclic loading with; no significant effect on Youngs Modulus; a moderate increase in Poisson’s ratio and fracture angle; a moderate decrease in UCS; and a major reduction in the CI stress threshold. All of these changes were generally amplified by cyclic loading at higher stresses. From the results, it is concluded that rockburst and spalling limit in underground structures may reduce over time if the rock is subject to repetitive cyclic loading, and that the reductions will be greater for higher cyclic stresses. This may be a significant factor in the design and operation of some deep underground structures.

Apr 26, 2022

By Nicola Della Valle

The Singapore Land Transport Authority (LTA) is currently expanding capacity by extending their Metro system from South of the city to the North East end of the island. The scope of Contract 704 involved excavating a long reach of tunnel which had a complex rock/soil interface comprised of fresh granite overlaid by clayey sand. Two 6.5 m diameter Earth Pressure Balance (EPB) TBM’s were used to bore the tunnels. These machines were designed so that both hard and soft rock could be excavated. The cutter head was equipped with a combination of both rippers and disk cutters. Soil conditioning was achieved by delivering foam through a multiple port injection system. This very irregular profile of the interfaces posed many challenges to the equipment and the people.

Jan 1, 2001

By Zhiguo Chang, QINGXIANG CAI, Ebelia Manda, IZHAR MITHAL JISKANI, XIANG LU, Wei Zhou, Saleem Raza Chalgri

The concept of mine safety is highlighted in the literature of sustainable mining but not extensively discussed. This study analyzes various aspects of underground and surface mine safety and emphasizes its importance in the context of sustainable mining. More specifically, this research attempts to find the relationship between mine hazards and demographic characteristics, examine and compare the perceptual difference among miners, and determine the impact of mine hazards on workplace safety and safety climate. Descriptive analysis, chi-square test, independent samples t test, and linear regression modeling were conducted to achieve study objectives. Results confirmed that mine hazards were significantly associated with age and experience. Miners perceived lower levels of management safety practices, followed by supervisor safety, coworker safety, and job safety. The analysis showed that underground miners reported lower safety scores than surface miners. There was a statistically significant difference between miners’ perception of safety climate (p < 0.05). The results showed that the higher prevalence of mine hazards predicts poor workplace safety and a low safety climate. The regression models revealed that mine hazards have a significant effect on workplace safety (p < 0.05) and safety climate (p < 0.05). In conclusion, the distinctive model of mine safety presented here contributes to the monitoring and design of comprehensive safety interventions and helps to better understand how certain factors interact on multiple levels to influence the overall safety of the industry. In this study, some suggestions are put forward to provide directions to develop a sustainable mine safety system.

Mar 27, 2020