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By P. Delogne, L. Deryck, R. Liegeois

So far as the propagation of electromagnetic waves is concerned, an underground tunnel behaves like a pipe or hollowed waveguide. Waves propagate in this tunnel with a low attenuation only if their frequency is higher than a so-called critical frequency which depends on the shape and mostly on the cross -dimensions of the tunnel and which value is in the neighbourhood of several tenths of MHz. However, when a metallic conductor is stretched along the gallery the electromagnetic characteristics of the latter are considerably modified and the effect of the cut-off frequency disappears; this is due to the fact that the gallery equipped with such a conductor works like a coaxial cable where the conductor serves as the outward conductor and the wall of the gallery as the return conductor. This is the principle of the monofilar waveguide cable which has been perfectly studied by Gabillard. Two mean characteristics of the monofilar mode are as follows: first of all, when the cable is suspended in the middle of the cross section of the gallery, the electromagnetic field occupies all the space between the wire and the walls of the gallery. When the wire is close to the wall, the electromagnetic field tends to become concentrated between the wire and the wall, with the consequence that, with the given monofilar mode power, the aerial of a receiver standing somewhere in the tunnel will capture a weaker and weaker signal. Secondly, owing to the fact that the mode of monofilar propagation uses the ground as return conductor, its power of propagation is considerably diminished; the closer the wire is to the wall the higher the attenuation, for only a very small part of the wall is utilized as return conductor. To cover great distances, everything else being equal, two or more conductors must be placed in the gallery. If the distance between two conductors of a cable is much smaller than the distance between one or other of the conductors and the walls; or again if one of the conductors surrounds the others and forms a screening, two sorts of modes appear: on the one

Jan 1, 1973

By G. B. Atkinson

The Bureau of Mines, in cooperation with McDermitt Mine, investigated a method for recovering mercury metal from mercury sulfide flotation concentrate by a hydrometallurgical technique. This preliminary report shows the feasibility of leaching mercury with a cupric chloride solution and electrowinning mercury from the solution. Proposed chemical reactions are shown in equations 1 through 3: 2CuC12 + HgS + 2CuCl + HgC12 + S°; (1) electrolysis HgC12 ?Hg + C12; (2) 2CuC1 + C12 ? 2CuC12. (3) A bench-scale leaching-electrowinning apparatus capable of treating 2.36 kg of sulfide concentrate in 11 days was operated continuously. An acid chloride solution containing, in grams per liter, 70 Ca, 60 Cu, 30 Fe, and 80 Hg was used as both leachant and electrolyte; 99.5 pct of the mercury was solubilized from the sulfide concentrate. Electrolysis of the leaching solution recovered mercury metal at an average current efficiency of 32 pct and an average energy consumption of 1.2 kwhr/lb Hg. Results from a preliminary economic evaluation indicated that a plant producing 31,500 flasks of mercury per year would have a capital cost of $3.7 million and an operating cost of $62 per flask of mercury.

Jan 1, 1983

To more rapidly and economically prepare solutions for chemical analysis, of a wide range of ores, slags, minerals, and metals. Approach A Simple pressure-dissolution system was devised using an inexpensive, heavy wall plastic bottle containing a sample in an acid medium. Using the technique, a complex silicate sample can be dissolved in less than 1 hour. How It Works A weighed portion of a sample, ground to minus 100-mesh, is placed into a polycarbonate or polysulfone plastic bottle. A mixture of hydrochloric acid, nitric acid, and hydrofluoric acid then is added. The bottle threads are wrapped with a layer of Teflon tape to prevent leakage, and the bottle cap is screwed on tightly. The sealed bottle is placed in a balling water bath. In the hot water, the plastic bottle acts as a pressure vessel to contain the pressure generated inside it. This technique should only be used by trained experienced people who are familiar with the hazards of hot acids under pressure. After being cooled in cold water, the resulting solution is brought to the final volume by adding 1.5 weight-percent boric acid solution to the bottle. The cap is replaced, and the bottle and solution is reheated. Precipitated fluorides, as well as any residue, are dissolved by the fluoride-boric acid reaction. The resulting clear solution then is suitable for spectro-photometric examination or other analysis.

Jan 1, 1980

To reduce the possibility of injury to operators and damage to equipment caused by collision of mining vehicles during coal loading. Approach An energy-absorbing bumper was developed and tested underground on a continuous miner. How It Works The bumper, a long box-like weldment backed by five energy absorbers, is attached to a continuous mining machine by a hinge behind the cab. See Figure 1. When a shuttle car collides with the bumper, or when it is otherwise struck, the energy absorbers are compressed. This absorbs and dissipates part of the kinetic energy of the colliding vehicle, thereby reducing or eliminating its destructive effects. Each energy absorber consists of two chambers separated by a freely-moving piston. One chamber (Figure 2) contains hydraulic fluid. The second chamber contains a gas. When a collision causes the absorber to compress, the hydraulic fluid in the first chamber is forced past a metering pin and through an orifice. The hydraulic fluid then pushes against the piston, compressing the gas in the second chamber.

Jan 1, 1978

By Richard J. Mainiero, James Q. Wheeler, Lewis H. Kopera, Yael Miron

The research reported here was part of the effort to evaluate the safety of a process to recover TNT from MK-9 depth bombs by the autoclave melt out process. In this process the depth bombs are heated to 121°C so that the TNT will melt and run into a vat. Unfortunately, asphalt lining the inside surface of the bomb also melts and flows out with the TNT. It is not known what effect the asphalt contamination and the higher than normal process temperatures (12°C) would have on the sensitivity of the TNT. Testing was conducted on molten TNT and molten TNT contaminated with 2 pct asphalt at 90, 100, 110, 120, 125, and 130°C. In the liquid drop test apparatus with a 2 kg weight, the molten TNT yielded a 50 pct probability of initiation at a drop height of 6.5 cm at 110°C,decreasing to 4.5 cm at 130°C. Asphalt-contaminated TNT was somewhat less impact sensitive than pure TNT at temperatures of 110 to 125°C, but became more sensitive at 130°C; 50 pct probability of initiation at a drop height of 7.8 cm at 110°C, decreasing to 3.3cm at 130°C. In the card gap test, the molten TNT detonated at high velocity for a gap of 0.25 inches at 90 to 125°C and detonated at high velocity for a gap of 0.5 inches at 130°C. For gaps of 0.5 to 3 inches at 90 to 125°C and 0.75 inches to 3 inches at 130°C, the TNT did not detonate at high velocity but produced a violent explosion that caused significant damage to the test fixture. For gaps of 4 inches the TNT did not react. In the gap test there was no significant difference between the pure and asphalt-contaminated TNT. The thermal analysis test results showed that when asphalt is present in TNT, it greatly accelerates the exothermic decomposition of TNT, starting at temperatures near 200°C. The research demonstrated that asphalt-contamination of recovered TNT does not appear to have a significant effect on TNT shock sensitivity, but does adversely affect impact and thermal sensitivity. The results also showed that molten TNT seems to be more shock sensitive than previously suspected. It appears that at relatively low shock stimulus levels, the molten TNT may be undergoing a low velocity detonation, wherein the shock wave traveling through the gap test pipe cavitates the molten TNT, greatly increasing its sensitivity.

By Arthur M. Hartstein

The Bureau of Mines, through contract with Ultrasystems, Inc., obtained data on the oxidative degradative behavior of a number of materials used in coal mines. Tests were performed using a stagnation burner arrangement. Materials examined included those used in typical coal mining operations such as (1) polyvinyl chloride-containing materials. (2) neoprene compositions, (3) rigid foams (urethanes/isocyanates), (4) miscellaneous materials (including jute, fiber glass, and polyethylene), (5) coal, (6) fluids (phosphate esters, organic esters, oil-water emulsions), and (7) composites. The composite comprised a mixture of a phosphate ester fluid with (1) coal, (2) a representative polyvinyl chloride sample, or (3) a neoprene-type composition. A number of decomposition products are identified that could represent a potential health hazard to miners including HC1, CO, SO2 and H2S, if they were generated to exceed toxic levels.

Jan 1, 1974

By B. T. Brady

Results of a study are presented of the effect of low radial reinforcement pressure on the postfailure characteristics of two types of granite, a sandstone, and marble. The low radial reinforcement pressure is applied to the rock surface by a gooch rubber sleeve. The gooch rubber sleeve provides a radial pressure of less than 1 psi pressure to the rock surface. This method of support gives an average strength increase of approximately 8 percent to the fractured rock sample.

Jan 1, 1973

By E. H. Denny

"Reduction of mine accidents appears to depend upon essentially the same fundamentals, whether considered from the viewpoint of the mine operator, miner, State mine inspector, or safety engineer. Conditions of mine operation with respect to safety are governed in most States by a mining law, usually somewhat general in its provisions but more specific than laws dealing with other industries, Methods of mining development and practice evolved through experience have been handed down from generation to generation; many of these are intended to avoid injury to men and also loss of property. To carry out the intent of these bases of law and experience relating to safety supplemental measures and conditions are necessary. Among these may be: (1) Planned safety rules adapted to the mine and compliance by both officials and Miners with such of these rules as pertain to their work; (2) a supervisory force adequate and competent to ¬administer the mining laws and safety rules; (3) discipline adequate to secure compliance with safety measures; (4) safeguards against mechanical, electrical, falling, and other hazards; (5) mining operations planned with respect to safety of workers; (6) an active safety organization of officials and employees; (7) education of officials and employees in safety practices; and (8) an active sustained interest in safety by management and employees.This paper presents the viewpoint of the safety engineer, though a safety engineer connected with a specific mine or group of mines would be in a better position than the writer to present the industrial engineer's thought. The application of the mine safety fundamentals just outlined will be given consideration from observations of methods used by safety engineers and supervisors.The term ""safety engineer"" includes men of various duties, various degrees of experience, and various authority. Depending upon the size of the operation or the interest of the management in safety, the safety engineer may have accident prevention as his sole duty; he may be the head of a sizable safety organization; or he may be in part a claim agent; a statistician compiling figures for the enlightenment of the company, the public, or a mining institute meeting; a surveyor who must convince the miner that his scale of 10/10 equals 1 foot does not defraud the miner of 6 inches to every yard measured; or he may be by heaven¬ly gift an orator capable of assuring the employees that ""all's right with the world""; he may be a young engineer gaining, experience while checking the observance of company rules and investigating accidents; or he may have the physical ills frequently resulting from several decades of mining experience and instead of a pension, the position of safety engineer has fallen to his lot. He may have mine-operating authority to correct immediately a dangerous condition or practice or he may have his recommendations officially disregarded at the monthly meeting or when the bottom of the desk basket is reached. He is likely to find that his viewpoint on accident reduction is considered unsound today because of youth and inexperience and unsound later because of old age and senility. He is likely to find the easiest course to be that of attributing to Providence and the carelessness of the worker the mishaps that result in the removal of a man to the hospital or the morgue."

Dec 1, 1936

The REL of 1 mg/m3 for respirable coal mine dust does not assure a zero risk for the development of occupational respiratory diseases among all miners exposed during a full working lifetime. Consequently, a medical screening and surveillance program that includes initial and periodic chest X-rays and spirometric examinations is important for the early detection of disease and the prevention of "material impairment of health or functional capacity" [30 USC 8 11(a)(6)(A)]. The medical screening and surveillance program is also useful for disease surveillance, which includes the tracking trends, the setting of prevention and intervention priorities, and the assessment of prevention and intervention efforts. NIOSH encourages both underground and surface coal miners to participate in the medical screening and surveillance program.

Jan 1, 1997

By P. Bhakta

The U.S. Bureau of Mines developed an alkaline oxidative pretreatment leaching procedure to increase the recovery of gold from arsenopyrite (FeAsS) ores. The best solution compositions for arsenopyrite dissolution were determined using cyclic voltammetry and chronocoulometry. Initial arsenopyrite dissolution occurred at -0.20 V versus standard hydrogen electrode (SHE) in a sodium hydroxide (Na0H) solution. Leaching of a high-grade arsenopyritic ore containing, in percent, 28.2 As, 25.3 Fe, 19.9 total S, and 1.0 Sb and, in troy ounces per short ton, 1.6 Au and 5.5 Ag resulted in >90 pct As extraction at 1000 C, 40 psig O2,4 h, and 2M NaOH solution in a 2-L autoclave. Cyanidation of the leach residues resulted in 90 to 93 pct Au and 60 to 80 pct Ag extractions, compared with only 5 and 15 pct, respectively, without the pretreatment. The procedure was further tested by leaching a low-grade gold ore and a bulk sulfide flotation concentrate prepared from it. Cyanidation of the leach residues resulted in 70 pct Au and 31 pct Ag extraction. The NaOH leachate was partially regenerated by precipitating the arsenate as calcium arsenate [Ca3As04)2] and the sulfate as barium sulfate (BaS04).

Jan 1, 1989

Develop an environmentally feasible method of mining shallow oil sands without removing overburden. Approach Oil sands are extracted through a single borehole by cutting into the sands around the borehole with a high pressure water jet, and pumping the resulting slurry to the surface. Although oil can be extracted from shallow fields by open-pit mining methods, this type of mining may create significant environmental impacts, including; (1) disruption of the surface, (2) accumulation of waste rock piles, (3) accumulation of tailings, (4) damage to the ground water quality, and (5) surface water pollution. The borehole mining system developed and successfully field tested by the Bureau of Mines offers a method for extracting oil from oil sand with minimal disturbance to environmental quality. (For examples of other applications of borehole mining, see Technology News Nos. 95, 63 56, and 48.) How It Works Prior to the start of mining operations, baseline conditions for ground subsidence and ground water quality are established at the test site so that the degree of subsidence and changes in ground water quality can later be determined. Oil sands mining is conducted using the Bureau of Mines borehole mining system. The borehole mining tool consists of a 12-inch-diameter pipe string and accessories capped with a three passage swivel terminated with a mining section. The mining section has an auger at the bottom. Four slurry inlet holes and an eductor are located above the auger, and a single cutting nozzle is located near the top of the mining section. The tool generates a high velocity water jet that erodes and slurrifies ores. The slurry is drawn into the inlet of the eductor which lifts the slurry to the surface where it is deposited into a slurry discharge sump. To detect evidence of subsidence, surveys of the land surface are made at regular intervals during, and until 30 days after, the termination of the mining operations. Samples of ground water from the borehole and two adjacent monitor holes are taken on alternate days during the mining operations, and are later analyzed to determine if any ground water contamination has occurred.

Jan 1, 1981

By Richard Hammer

Various alternating current (ac) methods can localize faults in mining power cables. Several methods considered by the Bureau of Mines in this report are the Murray loop for short circuits, wherein a bridge provides proportional distance to the fault; capacitance measurements for open conductors; inductance measurements for shorted conductors; phase comparison, high speed recordings of voltage and current in the faulted state are compared with normal voltage and current with the difference being a function of impedance change and impedance change being a function of fault location; and standing wave measurements, detecting the resonance of the length of cable to a fault (either short or open). Portable capacitance bridges are presently available for the second method, and the fourth method is well developed for use on large power distribution systems. Because it utilizes pulses rather than ac, the time domain reflectometer (TDR) method of fault locating was not included in this investigation. However, a comparative evaluation between this versatile method and the Murray loop might prove advantageous in locating high resistance faults.

Jan 1, 1977

By Suzann C. Ambrosio

The mineral industry in Burundi continued to be a minor contributor to the 1980 gross domestic product (GDP) estimated at $293 million in constant 1970 prices.2 Mineral export revenues, primarily from cassiterite, increased by a factor of 15 between 1979-80, reaching approximately $434,000 by yearend 1980. Gold, bastnasite, colombite-tantalite, and wolfremite continued to be exploited on a small scale, using manual and semimechanical methods. Despite a sharp decline in mining activities during 1979, attributed to a lack o? profitability and shortage of construction materials, the mining sector exhibited signs of recovery during 1980. The mineral exploration budget grew 32% over 1979 levels and was equivalent to approximately $42,000 in 1980. In addition, the Burundi Geographical Institute (IGE BU) was created in September 1980 and given responsibilities to collect cartographic, topographic, hydrogeologic, and other geomorphological data., SONIBUROM, the Burundian and Romanian Government joint mineral corporation, conducted mineral deposit inventories during 1979-80 and has been charged with exploiting some of these as yet unspecified resource areas. Another Burundian-Romanian effort, called Mabaya-Butahana, was initiated to search for gold deposits. Meanwhile on the Ruzizi plain, alluvial gold prospecting, with an estimated grade between 0.2 to 1.0 gram per ton, was carried out on a small scale.

Jan 1, 1982

By Roy Greenfield

During the detection phase, several procedures can be used to improve the signal-to-noise ratio (SIN) . • Subarrays of up to 10 seismometers should be used. The apparent failure to obtain improvement in SIN in the Westinghouse subarrav work is probably due to excessive noise in the electronics. The spacings needed for sensors in the subarray must still be established. • The sensors should be buried. Even burial to a few feet will probably give appreciable reduction of noise. A deeper burial will probably further reduce the noise; and, if the seismometers can be put below the weathered layer, the signal level will probably be increased. The reduction in noise by burial will be especially effective during high noise periods due to wind or rain. • Before attempting detection, the waveforms should be bandpass filtered. The bandpass should go from 25 Hz to an upper frequency of 100 to 200 Hz. Further measurements with a low noise system must be done before the signal-to-noise ratio can be determined for the 100 to 200 Hz range. Any narrow band noise should be removed by notch filters. • If noise levels differ among seismometers of a subarray, weights inversely proportional to the noise power should be applied to the seismometers. • Automatic methods of screening data for possible signal arrivals should be developed, but the final determination that the signal on a subarray output appears to be from a miner should be made by an analyst. Detection of "signal" on several subarrays should be required for positive identification. In the location phase, after detection: • If repeated signals are received, they should be coherently added (stacked) to give as good a SIN as possible for use in determining signal arrival times, to be used in location computations. The miner should, if possible, repeat the signal 25 to 50 times.

Jan 1, 1974

Permit visual inspection of underground cavities dam the surface. Approach A closed circuit TV camera and a 35mm still camera are lowered down a borehole, and remotely operated. How It Works A platform holding the cameras, and other equipment is lowered on a graduated cable until the depth of interest is reached. Then a quartz lamp and the TV camera are turned on. The television picture is monitored at the surface and recorded on video tape. Areas of special interest are photographed with a 35mm still camera. These photographs contain more detail than TV images because photographic film is capable of higher resolution than a TV transmission.

Jan 1, 1979

By W. H. Engelmann

The electrokinetic (zeta) potentials of a charcoal granite in an aluminum chloride (AlCl3) solution and in an oleylanunonium acetate (C18H35NH3+ -OCOCH3) solution have been correlated with the specific damping values as measured by the pendulum sclerometer. This investigation shows that the pendulum specific damping attains a minimum at the isoelectric point for the charcoal granite-aluminum chloride and charcoal granite-oleylammonium acetate systems, and thus indicates that the penetration of the diamond points is a maximum at the isoelectric point.

Jan 1, 1967

By C. L. Karr

The U.S. Bureau of Mines is currently investigating the use of genetic algorithms (GA's) for solving optimization problems. This computer search technique, based on the mechanics of natural genetics, was used to perform simple least squares curve fitting. Three examples are presented in which a GA manipulates binary coded strings to produce near-optimal solutions to least squares curve-fitting problems after having viewed only a small portion of the search space. The examples include fitting data to the equation of a line, the equation of a parabola, and the Ree-Eyring equation.

Jan 1, 1991

By Robert M. Becker

A thick-wall cylinder solution applicable to the evaluation of anisotropic elastic parameters is derived for the interpretation of stress relief data. For a restricted class of problems, a special relationship among certain orthotropic moduli yields stress distributions for the plane orthotropic problem that are identical to the corresponding isotropic case. A ring or hollow cylinder with these specialized anisotropic properties subjected to uniform radial loads is one of the problems in this class. Consequently, known stress solutions are used to develop the strains and displacements for a specialized orthotropic thick-wall cylinder under uniform pressures. The results are consistent with anisotropic equations used in the evaluation of in situ rock stresses.

Jan 1, 1968

By D. Montagna

Large quantities of zinc-base die-cast scrap containing 3 to 4 percent aluminum are presently refined by mixing with other secondary zinc products such as galvanizer dross and distilling in a retort. The Bureau of Mines investigated alternate aluminum removal processes utilizing low-cost fluxes. Basing the investigation on the metallurgical principle that a reactive impurity can be removed from a less reactive matrix metal by melting under a flux consisting of a salt or oxide of a metal less reactive than the impurity, three separate flux mixtures were studied. In the first flux system, [FeCl3] + NaCI (the active component is underlined), part of the aluminum is' eliminated by the formation of volatile aluminum chloride and the rest by the creation of a high melting point iron-aluminum intermetallic compound that can be separated from the remaining molten zinc by filtration. Aluminum removal in the second system, [Fe203] + CaClz + NaCI, is effected by the formation of the iron-aluminum compound and possibly aluminum oxide. The third system, spent sal skimmings--essentially a mixture of [ZnCl2], NH4Cl, and ZnO, depends solely on aluminum chloride formation. Of the three flux systems investigated, the best results obtained were with system 3. Aluminum was reduced in the molten die-cast alloy from 4.10 percent to 0.01 percent when depleted sal skimmings were used.

Jan 1, 1969

To provide a means for rapidly evaluating proposed mine layouts in order to avoid potential hazards while minimizing loss of coal. The Approach: Development of a computer program that will compute many possible mine layouts by changing the mine plan until the arrangement giving minimal hazards with optimum extraction is found. How It Works: The Hazard Evasion Program for Mine Planning, developed by the Bureau's Denver (Colo.) Mining Research Center, tests hundreds of possible solutions to a mining layout, and by sorting out the 10 best (based on the criteria of maximum safety for workers with minimum abandoned coal), limits the number of choices that need to be considered and appraised for applicability to a given mine scheme. The program is applicable for room and pillar or longwall mining, for oil and gas well hazards, and for other hazards that can be described mathematically such as channel sands, potential bad roof areas, faulting, voids, or water pockets.

Jan 1, 1974