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By M. J. Ferrante

The Bureau of Mines determined the enthalpies of Ni3S2 relative to 298.15 K to provide new thermodynamic data for advancement of mineral science and technology. Enthalpies were measured with a copper-block calorimeter from 298.15 to 1,197 K. A solid-solid transition was found at 834±1 K, with an isothermal heat absorption of 13.32 kcal/mol. The temperature of this solid-solid transition was accurately measured by differential scanning calorimetry. Because Ni3S2 does not melt congruently, the heat of fusion of 4.70 kcal/mol was obtained by extrapolation of enthalpy measurements from the solid and liquid phases to approximately 1,064 K. Tabulated values are given for the relative standard enthalpy, heat capacity, entropy, and Gibbs energy function between 298.15 and 1,800 K. Enthalpies are also given in equation form and combined with data from the literature to derive values of standard enthalpies of formation and Gibbs energies of formation. Similar calculations were made for the reaction of crystalline and liquid nickel with gaseous diatomic sulfur for Ni3S-2(c, l).

Jan 1, 1982

By B. J. Scheiner

Silver ores from the Candelaria District, Nevada, and Round Mountain District, Colorado, were investigated mineralogically and metallurgically. Silver minerals of four distinct groups were identified: (1) silver sulfide; (2) argentojarosite; (3) silver contained in the iron oxide; and (4) manganese carbonate-oxide minerals, Electrooxidation and acid-chloride leaching techniques were investigated as means of altering silver minerals, and their effects on subsequent silver extraction were determined. Application of the knowledge obtained from mineral leaching studies resulted in development of a sulfur dioxide-sodium chloride leaching sequence for extracting silver from these types of ores. Silver extractions of 80 to 85 percent were obtained by leaching the ores with a sulfurous acid-sodium chloride system. This was an increase of 9 to 61 percent silver extraction over that obtained by conventional cyanidation techniques.

Jan 1, 1973

By Ralph B. Adair

The Bureau of Mines conducted laboratory and small-scale, continuous tests of weathered mica-pegmatite ores from Randolph County, Ala., to determine the feasibility of recovering commercial-grade mica concentrates by flotation. Two flotation methods were used in continuous tests for recovery of mica. One method utilized acid-cationic flotation for the recovery of coarse mica and alkaline-anionic-cationic flotation for recovering fine mica. This method yielded mica concentrates containing 98.6 percent mica with a recovery of 85.9 percent. The other method was based on the Bureau-developed alkaline-anionic-cationic method, and yielded concentrates containing 97.5 percent mica with a recovery of over 90 percent. In both methods, preconcentration of the ground ore on a Humphreys spiral was employed to reject over half of the feed in a product virtually free of mica.

Jan 1, 1968

By E. R. Cole

A lead smelting process that appears to present minimal pollution problems has been developed at the Bureau of Mines, Rolla Metallurgy Research Center. Ten and 100 g samples of PbS mill concentrates were vaporized at 1,000° to 1,100° C in a furnace with an inert gas atmosphere during a 2-hour period. The PbS vapor was transported by the inert carrier gas to the reduction zone of the furnace where it was reduced at the same temperature with excess hydrogen to metallic lead. Lead of 99.9 pct purity was produced. The H2S formed can be decomposed into elemental sulfur and water vapor by a modified Claus process. Approximately 90 pet of the Cu and 70 pct of the Ag and Zn remain in the residue and are potentially recoverable. More than 98 pct of the lead in the concentrates was extracted.

Jan 1, 1974

By Forrest T. Moyer

OVERALL data for 1963 on injury experience and the levels of employment, worktime, and operating activity of the mineral industries are shown in the statistical tables of this chapter. The general groupings of the industries are presented in greater detail in Volumes I and II of the Minerals Yearbook. A corresponding chapter in Volume I contains additional breakdowns of the data on metal, nonmetal, sand and gravel, slag, and stone mines and quarries together with separate information on the related processing mills and plants including primary nonferrous smelters. The more specific information on the anthracite and bituminous-coal, petroleum and natural gas, peat, and natural asphalt industries is given in the similar chapter of Volume II. Injury and employment data were collected from coal producers on the mandatory basis required by the Federal Coal Mine Safety Act (30 U.S.C., sec. 455). Producers of all other minerals (fuel and nonfuel) voluntarily reported the requested injury and employment data. The figures for 1963 are preliminary except for anthracite, coke, petroleum and natural gas, native asphalt, and slag which are final. Data for earlier years are final. The figures represent full coverage for all industries except the oil and gas industries for which coverage is not complete, particularly with respect to small companies.

Jan 1, 1964

By Foster Fraas

In this Bureau of Mines report, use of the photoemission of electrons to produce electric charges for the electrostatic separation of sonic dispersed minerals, which had previously been ground to pass a 43µ-opening sieve, is demonstrated. It appears that many of the oxides, carbonates, sulfides, and arsenides will respond to photoemission. Minerals least responsive are the oxides of silicon, the oxides of aluminum, and minerals that have a high concentration of these oxides. Although several synthetic ore mixtures did not yield to complete separation in a one-stage operation, it is probable that preliminary neutralization of the initial electric charges produced by powder dispersion will provide complete separation. That the separation can be carried out in air and without the use of reagents or heating, which are required in the present practice of electrostatically separating coarse granular feeds, is of special significance.

Jan 1, 1972

Reduce fire warning time and avoid activation of false alarms in underground mines. Approach A heat activated stench/tracer gas system was developed which automatically releases the gas mixture into the mine ventilation air. How It Works A canister approximately 12 inches long and 3 inches in diameter is charged with 50 grams of ethyl mercaptan or other appropriate stench gas and 500 grams of instrument detectable Freon. The canister is then pressurized to 100 psi with nitrogen. A disc is used to seal the contents of the canister. A low-temperature alloy designed to melt at a predetermined temperature is used to restrain a spring loaded plunger. Upon exposure to heat, the alloy melts and the plunger is released. The plunger ruptures the disc and the mixture of stench and tracer gas is released from the canister. Canisters are mounted in areas of a mine which are susceptible to fire such as near

Jan 1, 1983

By M. J. Ferrante

High-temperature enthalpy and X-ray powder diffraction studies were con-ducted on aluminum sulfide (Al2S3) as part of the Bureau of Mines effort to provide new data for the advancement of mineral technology consistent with environmental preservation and energy conservation. Relative enthalpies were measured with a copper-block calorimeter from 298.15 to 879 K. Tabulated values are listed for heat capacity, entropy, Gibbs energy functions, and relative enthalpies between 298.15 and 900 K. Enthalpies were also given in the form of an equation and combined with published data to calculate standard enthalpies of formation and Gibbs energies of formation for reactions of crystalline aluminum with crystalline, liquid, and gaseous diatomic sulfur. The hexagonal, rhombohedral, and cubic phases of Al2S3 were identified by X-ray powder diffraction studies, and the indexed powder diffraction patterns of these phases are given. The hexagonal phase was stable to about 852 K and was partially converted to the rhombohedral form at 879 K.

Jan 1, 1981

Develop methods of enhancing and measuring the high-temperature softening and melting properties of iron oxide pellets reduced under simulated blast furnace smelting conditions. Approach Add dolomite and Limestone flux and a low-cost organic binder, such as starch, carboxyl methylcellose (CMC), or waste papermill sludge, to the iron oxide concentrate to produce hematite (ferric oxide) pellets with superior high-temperature metallurgical properties. Simultaneous increases in softening temperature, gas permeability, and enhanced metallization rates are sought to improve blast furnace productivity and energy efficiency. Background In the past, bentonite, an inorganic binder, was the only additive (binder) used in the production of pellets made from iron ore concentrate. Research has shown that the reducibility of conventional (acid) pellets can be increased by the addition of flux or an organic binder. The increase in pellet reducibility results in less wustite in the center of the pellet at high temperatures, such as those obtained in the cohesive zone of the blast furnace.

Jan 1, 1990

Provide roof to floor closure rate measurements during underground mining, especially retreat mining of coal pillars, thereby helping the miners predict an imminent roof fall. Approach An electronic device and rugged potentiometric extensometer were developed to provide a means fur measuring total closure and the rate of closure. How It Works An intrinsically safe, battery operated instrument is enclosed in a rugged, hand carried field case. The unit is constructed using low-power, integrated circuits to provide minimal battery drain. Two digital Light Emitting Diode (LED) readouts are used; one displays the rate, the other displays the total closure. The unit will measure one extensometer continuously or two extensometers alternately. Two potentiometric extensometers with a closure measurement range of 6 inches are attached to the readout unit. As the roof to floor closure changes, the potentiometric resistance

Jan 1, 1982

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 Robert P. Vinson, Fred N. Kissell, Edward D. Thimons

The Bureau of Mines investigated the presence and extent of methane accumulations in mine roof cavities using a full-scale mine model. Methane was released at a constant rate into the roof of a cavity built onto a 700-ft wind tunnel. Two box-shaped roof cavities were used in the study: one had a volume of 114.7 cu ft; and the other had a volume of 57.3 cu ft. Methane concentration was measured at 28 sampling points in the cavities using 21 different combinations of gas emission rates and air velocities. Brattice hung in the cavity helped reduce methane concentrations without auxiliary ventilation. It was also found that the effective ventilation rate increased by a factor of 40 in the large cavity and by a factor of 20 in the small cavity when air velocity was increased from 100 to 600 fpm.

Jan 1, 1978

By Fred N. Kissell

In This Chapter [Early indicators of a gas problem How the methane hazard is reduced Ventilation principles for gassy tunnels Monitoring for gas Eliminating ignition sources and The all-important human factors component] This chapter gives guidelines for preventing methane gas explosions during tunnel construction. Emphasis is placed on assessing the hazard potential, on ventilation principles, and on monitoring for gas. The chapter also emphasizes the importance of human factors in reducing explosion risk. Ensuring safe conditions is much more than just good engineering design. It also involves the every-day vigilance of those working underground. This does not imply that the engineering design can be ignored, only that the job of providing safe conditions has just begun with design. EARLY INDICATORS OF A GAS PROBLEM For the engineer planning a tunnel project, reliable early indicators of methane are scarce. How-ever, the local geology can often provide some information.2 Carbonaceous rocks and tar sands are a likely methane source. Gas is also a distinct possibility if it is known to be present else-where in the same sequence of geologic formations. Swampy areas, sewerage systems, and landfills are also candidates because the decomposition of organic materials produces methane. The gas in a tunnel can originate in the strata being excavated, or it can migrate a considerable distance from adjacent strata. Test borings at the project site can also serve as initial indicators of gas. Methane has no odor, but may be emitted along with gases that do. If gas is emitted from the borehole, a sample may be collected by inserting a tube into the hole as far as possible and pumping the gas out. The gas sample should be collected in a sampling bag or canister for later analysis by a chemical laboratory.3

Jan 6, 2006

By Aarne Visnapuu

Pneumatic chipping, scaling, and grinding can expose the tool operator to noise levels in the range 90 to 120 dbA. In most chipping and scaling operations, casting resonance is the primary source of noise, followed by air exhaust, and machine and chisel resonance. In grinding, the air-exhaust noise predominates. The Bureau of Mines has shown that noise from these operations can be reduced by up to 15 dbA. Workpiece resonance was reduced by sand or other damping methods; tool resonance, by internal damping; and chisel resonance, by constrained-layer treatment. Mufflers reduced air-exhaust noise, and an acoustically treated booth was effective in containing noise around the work area without increasing operator exposure.

Jan 1, 1977

By J. E. Meacham

The U.S. Bureau of Mines investigated recovery of manganese from basic oxygen furnace (BOF) steelmaking slags because the slags represent a large potential resource of a metal for which there is no domestic production. BOF slags were leached using fluosilicic acid, a byproduct of the fertilizer industry. Manganese and iron were extracted as soluble manganous and ferrous fluosilicates while the calcium and magnesium remained in the tailings as insoluble fluorides. Treating the pregnant liquor with sodium chloride, precipitated sodium fluosilicate (Na2Sif6) which was recovered as a byproduct. Manganese and iron were precipitated as hydroxide-carbonate salts with the addition of sodium carbonate to the treated liquor. Recoveries for manganese and iron were 73 to 83 and 67 to 70 pet, respectively.

Jan 1, 1991

By M. J. Ferrante

Low-temperature heat capacities and high-temperature enthalpies were determined calorimetrically for Na2Cr04, A reversible transition was found at 700° K with an isothermal heat of transition of 2,263 cal/mole. High-temperature X-ray diffraction analysis showed that the transition was a crystal change from the low-temperature orthorhombic form to the high-temperature hexagonal form. At 795° K the hexagonal form had the parameters a, = 5.691 and co = 7.478 A. Powder diffraction data for the high-temperature form are given and possible structures discussed. The melting point was determined to be 1,065° K with a heat of fusion of 5,810 cal/mole. Enthalpy and entropy increments from this investigation were combined with other data from the literature to calculate enthalpies of formation, free energies of formation, and equilibrium constants of formation from 298° to 1,400° K. Equations that represent enthalpies above 298° K are given.

Jan 1, 1972

By G. M. Wilemon

The Bureau of Mines conducted preliminary investigations on the use of an acid-alcohol leaching technique for recovering phosphate values from phosphate matrices. H2S04 and methanol were used as the leaching agents. Starting-matrix particle size and acid-apatite ratio were found to significantly affect the efficiency of phosphate leaching. Phosphate extractions of more than 80 pct were obtained when minus 200-mesh ore was used and the acid-apatite ratio was 8:1 or more. The iron and aluminum oxide impurities (R203) present in the crude acid products were monitored, and R203-P205 ratios are reported. Phosphate extractions in excess of 80 pct also were obtained when phosphatic clay wastes were leached. Typically, leach slurries filtered using test leaf filters ex-hibited filtration rates of 100 lb/(h·ft2) or more.

Jan 1, 1987

By B. J. Scheiner

A ferrous chloride-oxygen leaching system was investigated by the Federal Bureau of Mines to determine its effectiveness for recovering copper and silver from a tetrahedrite concentrate that had been pretreated to remove a majority of the antimony. The pretreated concentrate contained coppers, silver, lead, zinc, antimony, and arsenic. Parameters affecting metal extraction (such as temperature, pressure, amount of ferrous chloride, and initial hydro-gen ion concentration) were studied. Copper extraction of 98 pct was achieved by leaching 4 hours at 40 pounds per square inch gage (psig) and 100° C. Copper was recovered from leach solutions by cementation with iron, and the resulting ferrous chloride was recycled. Leaching the residue with cyanide followed by electrowinning recovered 99.7 pct of the silver. Iron, antimony, arsenic, and sulfur reported to the tailings.

Jan 1, 1978

Provide an environmentally compatible means of producing lead from galena concentrates that replaces the current high-temperature pyrometallurgical primary lead smelting process and supplies pure lead metal within present and proposed Environmental Protection Agency (FPA) and Occupational Safety and Health Administration (OSHA) lead emission standards. Approach The U.S. Bureau of Mines developed an energy efficient and pollution-free leach-electrowinning method for use in recovering pure lead metal and byproducts from lead sulfide concentrates.

Jan 1, 1989

By James W. Vogh

The report covers initial findings in an experimental program to identify diesel exhaust odorants and determine their contributions to diesel odor. The approach was to isolate selected component groups from exhaust and to evaluate the contribution of each group to exhaust odor. Results were obtained for those carbonyls and phenols that could be isolated from exhaust through inter-mediate conversion to oxime derivatives. Unsaturated aliphatic aldehydes and sterically hindered carbonyls were not included. Hydrocarbons intermediate in the diesel range were "also evaluated and an odor contribution was found from those of the aromatic group. The evaluated carbonyls, phenols, and hydrocarbons were found to account for about 20 pct of the total odor in exhaust from an indirect-injection engine during idle. For exhaust from the indirect-injection engine operating under load and from a direct-injection engine at no load, these compounds were found to have no significant levels of odor.

Jan 1, 1972