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By S. D. F. Rocha

The influence of surfactants on the crystallization of calcium sulfate was investigated in both hatch and continuous systems. The investigation was per formed at the following conditions. 343 °K, 28% P205 and with a sulfate level of 2.0%. At concentrations of 5 and 200 µgig, respectively, dodecylbenzene sulfonic acid (DBSH) and sodium diisooctil sulosuccinate (SSNa) promoted both an increase in the size and a reduction in the length/width (L/W) ratio of the calcium sulfate hydrates produced in the hatch and continuous crystallizers. Unique effects were observed in the batch system at higher DBSH concentrations. At 10 µg/g, the precipitation of hemihydrate crystals with a distinct morphology and texture occurred under conditions where dihydrate precipitation was expected. Above 50 µg/g, the precipitation of calcium sulfate hydrates was completely inhibited.

Jan 1, 1996

By R. A. Burns

The production of kaolin and calcium carbonate in North America exceeds 13 million tons sold into higher value market segments. With a few exceptions, the markets supplied exhibit mature growth rates. In some market sectors, technology changes have and continue to occur shifting pigment-type consumption and growth. New sources of supply will impact current businesses. New product and process developments for kaolin and calcium carbonates are continuing. Each of these issues is examined in developing a view of the future for kaolin and calcium carbonate in North America.

Jan 1, 1997

By A. Yehia, J. S. Hu, J. D. Miller, M. Misra

Fluoride activation has been evaluated by Hallimond tube flotation of collophanite in terms of fluoride concentration, conditioning time, pH, and temperature. The results reveal that efficient oleate flotation of collophanite can be achieved by fluoride activation. Experimental results of fluoride adsorption by collophanite suggest that, at low fluoride concentration, a fluoroapatite-type compound may form on the collophanite surface by chemisorption of fluoride ions at calcium sites. At high fluoride concentration, calcium fluoride appears to form at the collophanite surface involving a surface precipitation phenomenon. The formation of CaF2 on the surface of fluoride-treated collophanite is further substantiated by the FTIR spectroscopic measurements, which suggest a metathetic exchange with phosphate from the collophanite lattice during the surface precipitation process.

Jan 1, 1988

By Devan Naik, Matthew Stokes, Andy Nigro

This paper describes the surgical removal of a 24 ft dia. Slurry Shield TBM entombed beneath one of the country’s busiest commuter rail interlockings, the Harold Interlocking in Queens, NY, and the construction of the interface to a cut/cover tunnel which extended the mined tunnel section. A sophisticated SOE was built around the TBM to support active track loads within 8ft. of the excavation. Once the TBM head and guts were removed, a full round CIP lining was installed connecting the existing precast tunnel liner to the C/C tunnel under construction. All this construction was done on a narrow island of land without road access nestled between 7 mainline LIRR/Amtrak rail lines.

Jun 13, 2021

By Stephen B. Castor

The rare earth elements (REE) which include the 15 lanthanide elements (Z = 57 through 71) and yttrium (Z = 39) are so called because the elements were originally isolated in the late 18th and early 19th centuries as oxides from rare minerals. Most REE are not as uncommon in nature as the name implies. Cerium, the most abundant REE (Table 1), comprises more of the earth's crust than copper or lead. Many REE are more common than tin and molyb¬denum, and all but promethium are more common than silver or mercury (Taylor, 1964). Promethium (Z = 61) is best known as an artificial element, but has been reported in very minute quantities in natural materials. Lanthanide elements with low atomic numbers are generally more abundant in the earth's crust than those with high atomic numbers. In addition, lanthanide elements with even atomic numbers are two to seven times more abundant than adjacent lan¬thanides (Table 1) with odd atomic numbers. The lanthanide elements traditionally have been divided into two groups: the light rare earths (LREE), lanthanum through eu¬ropium (Z = 57 through 63); and the heavy rare earths (HREE), gadolinium through lutetium (Z = 64 through 71). Although yttrium is the lightest REE, it is usually grouped with the HREE to which it is chemically and physically similar. The REE are lithophile elements (elements enriched in the earth's crust) that invariably occur together naturally because all are trivalent (except for Ce+4 and Eu+2 in some environments) and have similar ionic radii. Increase in atomic number in the lanthanide group is accompanied by addition of electrons to an inner level rather than the outer shell. Consequently, there is no change in valence with change in atomic number, and the lanthanide elements all fall into the same cell of the periodic table. The chemical and physical differences that do exist within the REE group are caused by small differences in ionic radius, and generally result in segre¬gation of REE into deposits enriched in either light lanthanides or heavy lanthanides plus yttrium. The relative abundance of individual lanthanide elements has been found useful in the modelling of rock-forming processes. Comparisons are generally made using a logarithmic plot of lanthanide abundances normalized to abundances in chondritic (stony) meteorites. The use of this method eliminates the abundance vari¬ation between lanthanides of odd and even atomic number, and allows determination of the extent of fractionation between the lanthanides because such fractionation is not considered to have taken place during chondrite formation. The method is also useful because chondrites are thought to be compositionally similar to the original earth's mantle. Europium anomalies (positive or negative departures of europium from chondrite-normalized plots) have been found to be particularly effective for petrogenetic modelling. REE were originally produced in minor amounts from small deposits in granite pegmatite, the geologic environment in which they were discovered. During the second half of the 19th century and the first half of the 20th century, REE came mainly from placer deposits. With the exception of the most abundant lanthanide el¬ements (cerium, lanthanum, and neodymium), individual REE were not commercially available until the 1940s. Since 1965, most of the world's REE have come from two hard rock deposits: Mountain Pass, United States, and Bayan Obo, China. GEOGRAPHIC DISTRIBUTION OF REE DEPOSITS More than 70% of the world's REE raw materials come from three countries: China, the United States, and Australia. China emerged as a major producer of REE raw materials during the 1980s, while Australian and United States market share decreased dramatically (Fig. 1). Table 2 gives recent annual production figures along with estimated reserves by country, and Fig. 2 shows loca¬tions of significant REE mining. MINERALS THAT CONTAIN REE Although REE comprise significant amounts of many minerals, almost all production has come from less than ten minerals. Table 3 lists minerals that have yielded REE commercially or have po¬tential for production in the future. Extraction from a potentially economic REE resource is strongly dependant on its REE miner¬alogy. Minerals that are easily broken down, such as bastnasite, are more desirable than those that are difficult to dissociate, such as allanite. In general, producing deposits contain REE-bearing min¬erals that are relatively easy to concentrate because of coarse grain size or other attributes. For more thorough discussions of REE¬bearing minerals see Mariano (1989a) and Cesbron (1989).

Jan 1, 1994

By S. Behl, S. Mathur

It was previously reported that dolomite samples from different locations showed varying flocculation behavior with poly(ethylene oxide) (PEO). In this study, a Florida dolomite sample was examined, and it was determined that palygorskite associated with dolomite was responsible for its flocculation with PEO. A detailed characterization of dolomite samples from different locations was made by electrokinetic, XRD and FT-IR analyses, and the relevance of these characteristics to flocculation with PEO is discussed.

Jan 1, 1996

By J. R. Blair, D. P. Lindroth, W. R. Berglund, R. J. Morrell

The objective of this US Bureau of Mines (Bureau) research was to determine the technical feasibility, principles and effectiveness of a combination energy method for drilling and cutting hard rocks. Experimental test results of microwave heating and drilling in basalt and granodiorite are given. The experiments were performed with pilot-scale, commercially available equipment employing microwave energy at a standard industrial frequency of 2.45 GHz. The data indicate that penetration rates, well in excess of the state of the art, are possible.

Jan 1, 1993

By James A. Deane

Strip mine reclamation Fs the process of restoring the land affected by the mining process to its most productive use. This can be timber production, pasture, crop land, wildlife and/or recreational use. The mining companies must determine, through the advice of their technicians, what the most advantageous use of the land will be. If the Company does not own the surface, the owner or owners must be contacted to determine their desires as to how the land should be reclaimed. Many times, in making the plans to restore an area with vegetative cover, the watershed and the quality of the water in the area is overlooked. The water itself must be an integral part of the reclamation plan. Many lakes and/or pits can be created with proper planning. In areas in the Midwest, where lakes are a scarcity, these strip mine lakes can become storage reservoirs for large amounts of water, They can help control runoff and low flow augmentation. The strip mining operation will affect the watershed regardless of whether a reclamation plan in made or not. It is up to the reclamation technician to see that the plan benefits the watershed instead of affecting it adversely. This can be done during the operation by intercepting the water before Pt enters the active pit. Diversion ditches above the highwall will handle the runoff water from the watershed. Water that does gain entry into the pit should be removed as quickly as possible. If the rules and regulations adopted by the Ohio River Valley Sanitation Commission in Resolution 5-60 are followed, water encountered during the operation can be handled with little or no adverse effect to the receiving watershed.

Jan 1, 1965

By F. F. Aplan, C. E. Raleigh

Three run-of-mine bituminous coals, ranging in rank from low volatile to high volatile A, were floated at nominal -28 mesh (590 µm), -100 mesh (150 µm), and -400 mesh (37µm) feed particle sizes with selected pyrite depressants and a dispersant. For the three coals tested, pyrite and ash -forming minerals were usually rejected best at -100 mesh feed particle size. Depressant additions tended to improve flotation selectivity between pyrite and coal. When joint dispersant-depressant systems were used at -100 mesh (150 µm) feed particle sizes, the total sulfur content of the clean coal decreased further. For a comparable coal yield, less fuel oil collector was required for the flotation of -100 mesh coal than was required for the flotation of either -28 or -400 mesh feed.

Jan 1, 1992

By DeVerle P. Harris

The structure of an exploration model reflects a number of design considerations, one of which is the question or issue-to be investigated by the model. Thus, a model designed to evaluate the magnitude of risk and its economic implication to optimal decision making at each decision juncture of a multistage exploration architecture differs considerably from one designed to evaluate, say, the long run average cost of discovery, in which the architecture of exploration is suppressed and risk is simply an element of average cost. The perspective of the model examined in this paper is that exploration is investment in (purchase of) information and that the next stage of an exploration program is undertaken only when the expected value of information to be acquired in that stage exceeds its cost. The degree to which this perspective is honored influences considerably model design. Consider two design objectives:

Jan 1, 1989

By Eberhard Werner

Existing reports on the effects of mine subsidence on water wells and springs appear to be inconsistent. Some report quick and complete recoveries to pre-mining conditions while others indicate long-term or permanent effects. It is clear that topographic and geological factors as well as precise position with regard to the mine are important in determining probable effects of subsidence on aquifers. Ridgetop aquifers which are well above regional base-level are much more susceptible to disturbance by mining activities than those located topographically lower. Effects seen are attributed largely to increased permeability, both horizontal and vertical. of the aquifer rocks. The deeper aquifers usually show short term losses or water-table declines. but the effects on the ridge-top aquifers persist for longer periods or may be permanent. Subsidence enhances permeability. so that infiltrating water moves much faster to lower levels. causing pond and stream losses and declining levels in wells as well as declining flows of springs of the higher aquifers, while increasing levels and flows of the lower aquifers. Additional effects are shifts of spring locations caused by minor tilts due to differential subsidence and redirection of shallow flows by changes of horizontal fracture permeability. These effects are seen as mining of a panel progresses beneath the site. and are often repeated when adjacent panel mining fronts pass the site. Analysis of water well level and spring flow records indicates that the effects are greatest at the edges of longwall panels in the tensional regime. These effects are amplified for locations close to topographically steep terrain and in close proximity to fracture traces mapped from medium-to small-scale aerial images.

Jan 1, 1986

By Dion Weatherley, Raúl Castro, Pablo Cid, René Gómez

In underground mining, hang-ups due to coarse fragmentation are frequently observed in drawpoints, drawbells, and ore passes during ore draw. Hang-ups can often require operational interference and hang-up removal activities. Drawpoint and drawbell design has been shown in some studies to influence hang-ups; however, the full extent of this influence remains open to question. In this study, the discrete element method was used to analyze the effect of hang-ups on three distinct drawbell geometries: the Drawer type, Circular type, and El Teniente type. The drawer type was used as the base case given that data was available from a physical model in which hang-ups were studied. The drawer type base case data was then used to calibrate our numerical model. Results show that the El Teniente drawbell geometry sustained 13% more hang-up events as compared with the base case, while the circular drawbell geometry had 16% fewer hang-up events than the base case. From this study, it can be concluded that fewer hang-up events will occur with a rounded drawbell geometry.

Apr 11, 2023

By I. Stavrakas

This work studies the variations of the electric current caused by the application of an electric field on marble samples when they are subjected to continuously increasing mechanical stress at a constant rate up to fracture. The external electric field is applied in a direction perpendicular to the applied mechanical stress. An increase of the level of the electric current was observed when micro-damages started to occur in the samples. The increase of the electric current was approximately 14%. Consequently, the current started to decay abruptly and the sample failed. This electric current recording is compared with the corresponding electric recording without applying the external electric field (Pressure Stimulated Current technique). Both recordings show similar qualitative characteristics. The most obvious of these characteristics are that the electric current starts to develop when microcrack structures start to form due to the externally applied stress. Both recordings show a maximum in the vicinity of fracture.

Jan 1, 2008

By Richard Jr. Ray, Richard Druesedow

The Virginia Operations of Consolidation Coal Co. include a diversity of mine fan configurations which have been tested to quantify pressure losses through the inlet ductwork. Airflow and pressure measurements were taken at four shaft sites to calculate losses for the 90-degree bend at the top of the shaft and the self-closing dampers or closing doors located between the shaft and fan. Velocity contours were then developed from the test data to determine flow patterns in each fan system component. In addition, yaw and pitch angles of airflow through the fan annulus were measured to evaluate turbulence levels created by various inlet ductwork designs. The test results indicate that proper design of the shaft collar and ductwork arrangement for main mine fans can substantially reduce system pressure losses and air turbulence. BY minimizing the pressure drop experienced on the surface, these design improvements enable the bulk of the total pressure developed by the fan(s) to be utilized in the mine.

Jan 1, 1995

By Dougal R. McCreath

The storage of energy in one form or another is a well established practice, demonstrated by the familiar sight of large oil storage steel tanks. Today, however, the problems of energy storage are taking on a new complexion. Increased emphasis on large and sometimes untried forms of energy storage is being generated by: (1) The uncertainties we face concerning future oil and gas supplies. (2) The growing need for the storage of peak-shaving energy on large utility systems. (3) The growing volume of highly toxic and energy generating wastes resulting from nuclear power plants. Concurrent with the growth of these pressures, legitimate environmental concerns now demand that the methods of storage which are utilized meet adequate criteria of safety and preservation of surface land, as well as fulfilling technical and economic functions. From these elements, increasing awareness has grown of the potential role that can be played by underground space in providing a storage medium for energy related materials. The vessels which must be built for underground energy storage will be built by the tunnel engineer, and the design requirements of such vessels will go far beyond the classical tunneling requirement to drive a stable, reasonably dry tunnel between two points. Depending on the nature of the material to be stored, the manner in which the storage is to be operated, and the specific risks to the environment which are involved, rock chambers must be designed as special purpose storage vessels. The tunnel engineer may be required to demonstrate that unusual pressure and temperature conditions can be sustained by the rock, or that containment of a toxic material can be assured. In certain cases there will be emphasis on

Jan 1, 1976

By Alain GSELL

The aluminous nature of the laterites capping the Minim Martap plateaus - named after two neighbouring villages - and the small nearby upland of Ngaoundal, was discovered by the Cameroon Mines and Geology Division in 1958. These deposits of worldwide importance, are located in the Ngaoundere region, some 500 km (300 miles) north-east from the port of Douala (as the crow flies). They constitute the major part of the Cameroonese mining potential. The study of the deposits and their economic development has been entrusted to SEBACAM, Societe d'Etudes des Bauxites du Cameroun, a company in which the Cameroon government participates. The bauxites originate from the transformation into laterite of lavas which covered a Precambrian basement during the Upper Cretaceous period and the Lower Tertiary era. The entire Minim Martap deposit comprises bauxite plateaus ranging in area from a few acres to several square miles. The average thickness of the bauxite layer varies from 10 metres at Minim Martap to 17 metres at Ngaoundal. The mineral constituents of the bauxite are gibbsite trihydrate, kaolinite and the usual iron and titanium oxides. Treatment of the ore does not involve any particular technical problems. Proven exploitable reserves amount to 560 million tonnes of dry bauxite with a reactive silica content of 1.80% and an available alumina content of 43.70% at Minim Martap, and 120

Jan 1, 1984

By N. G. W. Cook

The conventional cyclic system of deep-level mining by drilling and blasting gives rise to an inadequate degree of stope sorting when mining thin reefs. This results in poor utilization of the capital facilities of a mine in the form of shafts, haulages, airways and associated equipment. Continuous and controlled removal of the thin gold-bearing portion of the reefs would permit better stope sorting and hence greater utilization of capital facilities. Results of experiments to develop hard rock cutting machines for mining are reported and the benefits which could be derived from their use are discussed.

Jan 1, 1969

By Kim A. Lapakko, William W. III White

The ASTM standard method D 5744-96 was developed to provide a well-defined kinetic test protocol, conducted under controlled reaction conditions, with the intent of generating reproducible results. A preliminary indication of the repeatability of a simplified alternative method (MN DNR method) was assessed and results from the MN DNR method were compared to those from the ASTM method. To provide an indication of repeatability, six samples from three different rock types were subjected to dissolution testing for periods of 20 to 68 weeks. Drainage pH values at the end of the tests were within 0.5 units in all cases and within 0.05 units in four cases. The percent difference from the mean for overall sulfate rates from paired cells ranged from 0.04 to 1756, with a median of 6.3%. Nine samples from four rock types were subjected to both MN DNR and ASTM tests for periods of 20 to 132 weeks. The difference in final drainage pH values forsix of the samples was less than 0.1 unit, and these values were less than pH 3.65 or greater than pH 8.0. The final drainage pH difference for the last three samples ranged from 0.15 to 0.4, and these values were ill the pH range of 6.2 to 7.2. The sulfate release rates for the periods of record for the MN DNR method were 70 to 150% of those for the ASTM method, with a median value of 110%. Sulfate and calcium release from the two methods was not substantially different. The MN DNR method typically produced higher magnesium release.

Jan 1, 2000

By Steven A. Tesdahl

Maintenance means keeping equipment running or restoring it to operating condition. However, the 21st century will usher in a broader need for equipment management, a cradle-to-grave strategy to preserve equipment functions, avoid the consequences of failure and ensure the productive capacity of equipment. Profitable future mining operations will have reduced the 35% of operating costs typically spent on maintenance and the unfavorable impact of downtime that often multiplied these costs by 300%. They will survive those operations that tried to carry outdated "maintenance" thinking beyond the year 2000. These surviving operations will have applied modern management techniques, technology and information to align the efforts of people with the needs of equipment. Future managers will use equipment management as an integral part of an overall production strategy. They will see it as a means of raising productivity, improving performance and minimizing downtime to maximize profitability. This global thinking will characterize all operations planning to survive in the competitive world of mining of the next century.

Jan 1, 1998

By J. Koinig, K. Mussger, St. Reischl

Jet grouting is a viable supplementary measure for NATM tunneling in special softground conditions. In particular it is used as a type of forepoling to maintain face stability and to provide initial support for large openings until the shotcrete lining reaches sufficient strength. For this purpose cement grout is injected under high pressure through horizontal pipes outside of the tunnel perimeter and thoroughly mixed with the soil producing 1 to 3-foot diameter cylindrical beams. Excavation of the tunnel then proceeds beneath this umbrella of 40 to 50 foot long beams. Design and construction experiences from recent projects are presented for tunnels diameters between 30 and 50 feet in fill and alluvial and colluvial deposits.

Jan 1, 1987