U.S. Bureau Of Mines Research Articles

Effect of specimen thickness on the impact resistance of alumina

During the course of an ongoing study into the impact and erosion properties of alumina by the US Bureau of Mines, it was discovered that specimen thickness had a significant effect upon certain fractographic observations. To quantify this effect, impact studies were carried out on 1.9, 3.1 and 10.0 mm thick Al2O3 (alumina) discs. These discs were impacted at velocities from 15 to 65 m s−1 using 1.69 mm-diameter WC-Co spheres. In conjunction with this experimental approach, finite element models of the impact couples were constructed forthe 1.9 and 10.0 mm-thick alumina discs. An elastic/plastic analysis was performed of the impact event in each case. Experimental and numerical results indicate that the length, depth and geometry of radial cracks are strongly dependent upon specimen thickness.

Revegetation of coarse taconite iron ore tailing using municipal solid waste compost

On Minnesota's Mesabi Iron Range, coarse taconite iron ore tailing is often used as the principal material in the construction of dams for large tailing impoundments. Mineland reclamation rules in Minnesota require that tailing dams be vegetated to control erosion for dam stability and safety. Coarse taconite iron ore tailing is characterized chemically by an alkaline pH, low organic matter content, lack of plant-essential nutrients, and low cation-exchange capacity; physically by its coarse texture, lack of structure, low water-holding capacity, and dark color; and biologically by a lack of microorganisms. To investigate the potential of composted municipal solid waste to ameliorate these conditions and make the material more amenable to plant establishment and growth, the US Bureau of Mines implemented a series of factorial experiments at two active taconite mine sites in northeastern Minnesota. At each experimental site, vegetative cover has improved depending on the type of municipal solid waste compost used and rate of application. At site I, overall plant cover across all treatments has improved from zero prior to experimental manipulation to 72% after four years, with seven treatment combinations exceeding 90% cover. At site II, overall plant cover has improved from zero prior to experimental manipulation to 83% after four years, with 23 treatment combinations exceeding 90% cover. At both sites, total cover has progressively increased over four years and has not reached steady-state conditions. These results suggest a possible new strategy for reclaiming difficult sites through the use of municipal solid waste compost.

Using Alternative Chemicals in the Flotation of Heavy Metals from Lead Mill Tailings

Abstract The U.S. Bureau of Mines (USBM) investigated alternative chemicals for the flotation of heavy metal values from southeast Missouri lead mill tailings. The objectives of the study were to lower the Pb remaining in the reprocessed tailings to <500 ppm, concentrate the metal values, and lower the overall toxicity of the flotation reagent scheme. Due to the high toxicity of classic flotation chemicals, collectorless flotation, as well as nontoxic or less-toxic chemicals, was studied for use in the flotation process. The investigation centered on the National tailings pile in Flat River, MO. Advantages to using alternative chemicals for the flotation process are presented. Novel reagent schemes are discussed for the treatment of the tailings. Various nontoxic or less-toxic oils were tested, and a substitute for sodium sulfide was investigated. Using a food additive oil, soda ash, and a frother as the reagent scheme, froth flotation recovered 89% of the Pb values. Further scavenging lowered the Pb rema...

Methods of measuring wear-corrosion synergism

Wear and corrosion involve many mechanical and chemical mechanisms, and the combined action of these mechanisms often result in significant mutual reinforcement. Other researchers have studied the interactions of wear and corrosion in a qualitative way for specific wear-corrosion environments. The US Bureau of Mines is interested in presenting the results of wear, corrosion and wear-corrosion tests in a standard format, so that these data can be utilized to develop practical engineering criteria for any tribosystem. To reach this goal, penetration rate equations have been developed to quantify the wear and corrosion processes and wear-corrosion synergism.

Mechanical processing of iron powders in reactive and nonreactive gas atmospheres : J.C. Rawers, R.C. Doan (US Bureau of Mines, Albany, USA) Metall. Mater. Trans. A, vol 25, no 2, 1994, 381–388

A titanium-silicon diffusion couple was used to measure the interdiffusion coefficients for TiSi2, TiSi, Ti5Si4, Ti5Si3 and Ti3Si at 950–1150 °C. The activation energy for the TiSi2 interdiffusion coefficient agrees with the data reported in the literature for thin film interdiffusion at lower temperatures.Diffusion-controlled, multi-layered growth kinetics set a constant ratio for the thickness of the TiSi2 layer to the total sum of thicknesses for the TiSi, Ti5Si4, Ti5Si3 and Ti3Si layers at a fixed temperature. The thickness ratio predicted from the Arrhenius temperature dependence for layer growth was compared with that experimentally observed at 700–1150 °C. Comparison of this thickness ratio with data reported for Ti-Si thin film growth indicates that only TiSi2 should form at low temperatures. Competitive multi-layered kinetics decide that the low-temperature interdiffusion of Ti-Si thin films results in the exclusive growth of TiSi2, and consideration of nucleation or other constraints are not required to explain the absence of other Ti-silicide layers.

The role of micellar structures in shear flocculation Part 1: Flocculation of quartz with alkylamine surfactants

In a collaborative study between the US Bureau of Mines and the Department of Chemistry at the University of Alabama, research has been conducted to study the role surfactants play in shear flocculation. The shear flocculation of silica by amine surfactants was studied as a function of surfactant alkyl chain length. A six-carbon amine chloride did not produce shear flocculation. At twelve carbons and above, the average particle size increased steadily with chain length. Zeta potential measurements show that particle aggregation is due to shear flocculation and not electrostatic coagulation produced by charge neutralization by adsorbed surfactant. The presence of air bubbles was observed to alter the rate and degree of particle aggregation, and to cause floc flotation. The presence of surfactant aggregates in the shear flocculation process was confirmed by electron paramagnetic resonance (EPR) spectroscopy using a spin-labeled analog of cetyl-trimethylammonium bromide. Analysis of the EPR spectra clearly indicates that surfactant aggregation increases during shear flocculation. The EPR results were found to be consistent with both enhanced bilayer formation, and with displacement of the surfactant equilibrium due to inclusion of surfactant within the particle aggregates.

Yttrium recovery from Bokan Mountain, Alaska

The Bokan Mountain area on Prince of Wales Island, AK, contains vast quantities of heavy rare earth minerals. To lessen the US dependence on foreign sources, the US Bureau of Mines (USBM) investigated yttrium recovery from this ore. By sulfating the ore at 250° C for 1 hr at an H2SO4:ore ratio of 1:1 and then water leaching the sulfated material for 1 hr at 20% solids and 25° C, over 74% of the yttrium, cerium, and lanthanum were solubilized. Solvent extraction (SX), using a synergistic combination of OPAP and DEHPA, selectively loaded 100% of the yttrium. Yttrium was stripped directly as a solid using a 2M, 35° C NaOH liquor. When the OPAP/DEHPA mixture was tested in a continuous SX circuit, yttrium loading and stripping were 100% and 96%, respectively. The organic showed excellent recyclability properties with minimal solvent loss.

Microwave drying of flue gas desulfurized (by-product) gypsum

ABSTRACT The Clean Air Act of 1990 (USA) requires airborne sulfur-dioxide emissions removal from fossil-fueled, electric generating facilities. The result is production of commercial-quality, by-product gypsum that requires further drying for wallboard and calcining for cement. The objective of this research by the U.S. Bureau of Mines (USBM) was to determine the technical feasibility and associated pilot-scale data for drying powdered flue gas desulfurized (FGD) gypsum with microwave energy at a frequency of 2.45 GHz. The experimental data were obtained with the USBM's custom-designed, continuous-feed microwave system having a maximum power capability of 12 kW. Drying efficiencies ranging from 49 to 73 pct were achieved in removing feed moisture from 7 down to less than 1 pct. Microwave energy is a new technology application to this useful domestic resource and could shift the need for mined gypsum imports to an increase in domestic limestone production.

New USBM chief

Rhea L. Graham, a geologist with a background in environmental consulting and engineering geology, became the 19th director of the U.S. Bureau of Mines (USBM) last month. On taking the helm, Graham said, “I believe that the agency has a vital role to play in helping the nation solve its mineral‐related problems—problems that involve involve our environmental and economic goals, as well as basic human issues, such as worker health and safety.”

Abrasive wear behavior of MoSi 2-Nb composites

Previous research at the US Bureau of Mines has shown monolithic MoSi[sub 2] to be extremely wear resistant in a severe two-body abrasive environment. MoSi[sub 2] is attractive as a wear-resistant material because of its high hardness, high elastic modulus, low density, and excellent resistance to elevated temperature oxidation and hot corrosion. As with most intermetallic compounds, the low temperature fracture toughness is poor; however, reinforcing MoSi[sub 2] with SiC or Nb, for instance, has resulted in improved fracture toughness. It is also known that the wear rate of many materials can be reduced by a factor of up to ten by the introduction of a suitable reinforcement phase. While soft ductile phases have been effective in improving the fracture toughness of brittle matrices, it is intuitive that the addition of these phases should have a negative impact on wear resistance, i.e., the softer phase will wear at an accelerated rate. This study has been undertaken in order to make a preliminary assessment of the effect of adding a ductile reinforcement (Nb) on the abrasive wear resistance of MoSi[sub 2]. The wear behavior of the MoSi[sub 2]-Nb composites produced for this study are compared with the behavior of monolithic MoSi[submore » 2], Nb, aluminides, and ceramics.« less

Determining the effect of physico-chemical parameters on floc size using a population balance model

The US Bureau of Mines is investigating the fundamentals of the flocculation process. The objective of this study was to determine the effects of various physico-chemical parameters, namely, shear rate, polymer dosage, and polymer concentration, on floc growth and to determine the applicability of a model for predicting polymer-flocculation behavior. A rapid in-line particle size analyzer was used to follow the progress of both the floc growth and the breakage as a function of time. A genetic algorithm (GA) was used to determine the unknown parameters in the model and to fit a curve to the experimental data. The results showed that the model reproduces the experimental data with only reasonable accuracy and that it was relatively insensitive to the parameters. Results of the flocculation study showed that increases in the polymer dosage had a greater effect on the time required to reach the maximum floc size than on the floc size itself. It was also determined that, given all the above parameters, the degree of slurry mixing during the flocculation process had the greatest bearing on floc growth.

On-Line Radioisotope XRF Analysis of Copper, Arsenic, and Sulfur in Copper Electrolyte Purification Solutions

The U.S. Bureau of Mines (USBM) and Weber State University (WSU) have developed an on-line analysis system for copper electrolytic solutions in a laboratory-scale decopperization electrolytic cell using a portable energy-dispersive X-ray fluorescence (XRF) unit. The portable XRF unit utilizes Fe-55 and Cm-244 radioactive isotope sources for sample analysis. Copper, sulfur, and arsenic were successfully analyzed directly in electrolytic purification solutions without any dilution or sample alteration. Interelement deconvolution was conducted to compensate for interferences resulting from matrix absorption of copper fluorescence by sulfur. The ubiquitous presence of sulfur in copper refining operations necessitates sulfur correction in the analysis of copper by XRF. A unique flow-through sampling cell was engineered and constructed for the portable XRF unit which allowed real-time analysis of a continuously pumped sample stream from the electrolytic cell.

Ampacities of power cables wound on reels

This paper presents a mathematical model that is capable of calculating the ampacity of a wide variety of power cable designs consisting of an arbitrary number of layers on a cable reel. The model considers round cables with copper conductors. The validity and accuracy of the ampacity model were verified by comparing the predicted temperature distribution within the reel with measured temperatures collected during an extensive testing program conducted at the US Bureau of Mines (USBM). The mathematical model predicted a temperature distribution within the cable layers that was very close to the measured variation in temperature. The value of the program is illustrated by calculating ampacities for several copper conductor sizes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of Oxidation-Reduction Condition on Wettability Alteration

Summary This paper presents results of a laboratory study exploring the effect of the oxidation-reduction (redox) condition on crude-oil adsorption on rock mineral surfaces and consequent wettability alteration. Experiments were performed by aging Berea outcrop and Loudon reservoir sandstones with crude oil under various redox conditions and water saturations. Wettability alterations after aging were evaluated by the U.S. Bureau of Mines (USBM) method and by waterflood tests. The natural, oxidized Berea cores changed from strongly water-wet to mixed-wet conditions when aged at irreducible water saturation. Wettability alteration was greatly reduced when aging experiments were conducted under reduced conditions. The degree of wettability alteration depended on availability and redox state of iron on the mineral surfaces and also on aging time. We suggest two possible mechanisms to explain the role of iron in the wettability-alteration process. Wettability alteration in the water-wet Berea cores was insignificant when the cores were aged at residual oil saturation (ROS). Wettability alteration was also insignificant in the mixed-wettability Loudon reservoir cores, regardless of the water saturation or redox condition used in the aging experiments. We present the implications of these findings on core-handling procedures for wettability preservation.

Nitrogen in pressure-diffused powder iron alloys

In this study, high-pressure high-temperature diffusion at the US Bureau of Mines was used to increase the nitrogen concentration in both b.c.c.- and f.c.c.-iron alloy powders. Microstructures of the powders and precipitates were determined using microprobe, scanning electron microscopy (SEM)_and X-ray diffraction. Formation of Fe 4N was observed in Fe, Fe-1018, and Fe-2Al. For FeCr alloys, either b.c.c or f.c.c, the first precipitate to form was CrN. Experimental results compared favorably with computer generated phase diagrams and computer predictions from the Swedish Institute for Metals Research of nitrogen concentration and as a function oof diffusion pressures.

Study of shear-flocculation of silica

The US Bureau of Mines investigated the fundamental aspects of shear-flocculation using a rapid, in-situ particle size analyzer. Silica was stirred in the presence of an aliphatic amine to determine the effects of collector coverage, stirring speed and solids concentration on the kinetics of shear-flocculation. The results showed that shear-flocculation is a two-stage process. In the first stage, which occurs during the first 1–2 min. of the reaction, the mean particle size increases rapidly, and in the second stage, an equilibrium is set up between the rates of floc growth and floc decay. Collector dosage affected the position of the equilibrium by altering the number of surface sites for particle-particle attachment. A minimum stirring speed was necessary for shear-flocculation, which was dependent on solids concentration and collector dosage. This stirring speed was the minimum necessary for particles to overcome the electrostatic energy barrier, and that results in keeping the conditioned particles dispersed. Larger particles flocculated more rapidly. At very high stirring speeds, large flocs became unstable, resulting in a narrowed particle size distribution in the slurry.

Conditioning parameter effects on the recovery of coarse phosphate

A fundamental study of the mechanisms involved in the conditioning of coarse Florida phosphate has led to some interesting discoveries. Studies by the US Bureau of Mines have shown that conditioning time and mixing intensity greatly affect the grades and recoveries of the phosphate minerals and quartz in the rougher concentrate. In particular, as the conditioning time or mixing intensity increased, the phosphate recovery remained constant while the amount of quartz floated decreased. This phenomenon is contrary to conventional wisdom and could lead to a more efficient coarse flotation circuit.

New insights into the mechanism of shear-flocculation of silica with fatty acids

The US Bureau of Mines studied the mechanism of shear-flocculation of silica with stearic acid. At pH 6 and 12, shear-flocculation of silica was not observed with the addition of up to 4.5 x 10−4 M (5 lb/st) stearic acid. However, in the presence of 0.1 M NaCl at pH 6, shear-flocculation was observed at stearic acid concentrations ≥ 10−4 M (22.5 lb/st). Adsorption of stearic acid on silica was studied using stearic acids spin-labeled with a doxyl group. The presence of the spin-labeling group did not greatly affect the shear-flocculation properties of stearic acid. Adsorption of labeled stearic acid on silica was measured as a function of surfactant concentration with electron paramagnetic resonance (EPR) spectroscopy and gas chromatography (GC). The GC results indicated that the stearic acid was predominately adsorbed on the surface at concentrations above 10−4 M. From the EPR spectra, the formation of aggregates of stearic acid was apparent at concentrations of approximately 10−5 M (22.5 lb/st). The results are discussed in terms of a possible mechanism for shear-flocculation.

Direct-reading instruments for aerosols. A review.

Direct-reading instruments for aerosols have not had the popularity within the industrial hygiene community that similar instruments for gases and vapours have enjoyed. There are several reasons for this: aerosols have complex properties that are difficult to characterize with a single measurement, commercial instruments often do not provide an accurate measure of a useful aerosol property and aerosol instruments are relatively expensive for industrial hygiene use. A variety of instruments are commercially available and are briefly reviewed. Two general classes of instruments used for industrial hygiene measurements are covered: field instruments and research instruments. The International Symposium on Air Sampling Instrument Performance held in Research Triangle Park, NC, USA, in October, 1991 included a workshop on direct-reading aerosol instruments that produced several recommendations to advance the state of the art. The two primary recommendations approved by the symposium attendees were to develop voluntary consensus standards for aerosol mass measuring instruments and optical particle counters and to develop an accurate, portable, direct-reading aerosol mass monitor. Some progress is being made on the latter recommendation through a project supported by the US Bureau of Mines. Other instruments have found specific application in industrial hygiene measurements. A miniaturized condensation nucleus counter is being used to estimate fit factors for respirators. A fibre monitor is used for monitoring asbestos, especially in asbestos abatement operations. Optical particle counters are used for low-concentration aerosols, especially in clean rooms. Aerosol research instruments are being used to evaluate and improve field instrumentation, such as respirable, thoracic and inhalable samplers and cascade impactors.(ABSTRACT TRUNCATED AT 250 WORDS)

In-line static mixer rapid flotation system for improved flotation kinetics

The US Bureau of Mines investigated rapid froth flotation through more efficient bubble-particle collisions that improved the overall flotation kinetics. An in-line static mixer efficiently mixed the bubbles, water and ore, selectively attaching these bubbles to the hydrophobic mineral’s surface. As the mixture entered the flotation chamber, the hydrophobic mineral was already attached to the bubbles and was quickly floated away from the remaining ore pulp. The rapid flotation system was evaluated for beneficiation with a western porphyry copper ore containing 0.67% copper and with a phosphate-bearing amine flotation tailings sample containing 9.5% P2O5 in a quartz matrix. Over 88% of the copper was recovered from the ore in a rougher concentrate containing 5.9% copper at a rate seven times faster than conventional flotation. Sixty percent of the quartz in the phosphate-bearing sample was floated at a rate four times faster than conventional flotation. The unfloated product retained 80% of the phosphate in a 16.9% P2O5 concentrate.