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By Ralph Bernstein

The processing of earth observation sensor data by digital technology is almost two decades old. Only recently, however, has this technology become practical and economical. The reasons for this are interesting to analyze, and they provide some insight into what the future may bring. Some of the earlier activities and their limitations, current systems and their applications, and future technology direction are summarized.

Jan 1, 1979

By R. H. Grau

The National Institute for Occupational Safety and Health's Pittsburgh Research Laboratory is now involved in research to identify silica dust generation in underground metal/nonmetal mines. The ultimate goal of this research is to develop control technologies to reduce worker exposure to respirable silica dust. Commodities and job classifications with the highest silica dust exposure have been identified through analysis of the Mine Safety and Health Administration's compliance dust-sampling database. Dust surveys were conducted in an underground limestone and gold mine to investigate silica dust sources, generation levels and the controls being used. A summary of the mining operations, sampling procedures, resulting data and suggested methods to improve dust control are provided.

Jan 1, 2003

By Bob Gordon, Allen Furth, Dan Dobbels

A 4.8 m (16 ft) diameter hard rock tunnel was driven through granite bedrock to create the 1.7 kilometer (1.1 mile) long Hampton McCloy Retention Tunnel for the city of Richmond, Virginia. During the work the tunnel encountered narrow seams of partially decomposed granite that were not self supporting and could be dealt with using ribs and lagging. However, as the tunnel approached the receiving shaft, it encountered a large seam of highly decomposed rock, alluvial deposits and running sand which resulted in soil loss into the machine. As a result of this condition, a jet grouting program was quickly developed to allow the tunneling to continue. This paper will describe the manner in which jet grouting was used to solidify and stabilize the decomposed bedrock, alluvial soils, and running sand to allow the TBM to continue tunneling.

Jan 1, 2003

By P. V. R. Bhaskar Sarma, P. K. Sahoo, G. Roy Chaudhury

A process was developed to treat an ammoniacal leach liquor containing zinc using Di (2-ethyl hexyl) phosphoric acid (D2EHPA) as the extractant. The objective of this work was to develop a process package for the treatment of complex sulfide leach liquors. Zinc extraction could not be carried out directly from the ammoniacal solution in mixer-settler units because of crud formation and low extraction efficiency. After neutralizing the free ammonia with H2SO4, the extraction efficiency was only about 40%, due to the high concentration of (NH4)2SO4. To decrease the (NH4)2SO4 concentration, the free NH3 was steam stripped, and the resultant liquor was subjected to zinc solvent extraction. An extraction efficiency of 98% could be achieved by controlling the equilibrium pH. Stripping studies were also optimized after removing ammonia from the zinc-loaded organic. A continuous 100-hr operation that included extraction, scrubbing and stripping, was carried out successfully.

Jan 1, 1995

The objective of the fines flotation step in a coal preparation plant is to maximize coal recovery subject to a constraint on the allowable ash in the concentrate. The objective is achieved when the incremental ash is driven to a target value determined by an economic constraint. In this paper, a phenomenological flotation model and ash analyzer combination are identified that allow the development of a soft sensor for incremental ash and subsequently a model-based strategy which manipulates key flotation variables to achieve the control objective. A combination of plant tests and computer simulations are presented to evaluate control-system performance in one operation.

Jan 1, 1999

By D. T. Maiers, P. L. Wichlacz, P. A. Pryfogle, J. H. Wolfram

The effects of metal solution concentration, biomass density, length of exposure time, and pH were determined for biosorption of molybdenum (Mo) and chromium (Cr) by three organisms. Results indicate that it is possible to sorb Mo and Cr from dilute solutions. Differences were observed in the abilities of an organism to sorb Mo and Cr as well as among respective abilities of the three microorganisms. This suggests an inherent selectivity of the organism which may afford the means to control a sorption-based process. Results also indicate that the metal sorption abilities of these microorganisms depend on duration of exposure, biomass density, solution pH, and the metal concentration of the solution. Each of these parameters suggests an additional means of controlling the sorption process.

Jan 1, 1989

By Raymond F. Mikesell

This paper evaluates the contributions of "third parties" to surplus capacity in the world metals industries in the 1980s. Special attention is given to the role of international development agencies, such as the World Bank, that have made project loans to state mining enterprises. The paper also reviews the contributions to surplus capacity of the International Monetary Fund and evaluates the large volume of credits from commercial banks to developing countries. Although the credits to Third World countries during the 1970s facilitated the expansion of mining capacity in those countries, no one source of financing can be held responsible for a significant portion of the expansion.

Jan 1, 1989

By A. S. Malicsi, M. D. Baker, I. Iwasaki

Fine grinding may he required for- some coals to remove sulfur and ash or to prepare coal-water slurry. Fine grinding leads to increased hall wear and its effect on the surface properties of the ground coal becomes of concern. Marked hall wear - tests were performed to study the effects of oxygen, pH, the soluble species of coal, and the addition of pyrrhotite on hall wear. The synergistic action of coal and oxygen greatly enhanced the corrosion of mild steel halls during grinding. Elec.trochemica1 measurements on a mild steel electrode in coal slurries and SEM observations of grinding hall surfaces were carried out to explore the corrosive wear mechanism.

Jan 1, 1991

By K. A. Natarajan

This paper deals with the various electro- and biochemical mechanisms involved in the bioleaching of multisulfide minerals such as those containing copper-lead-zinc and copper-nickel-iron. Galvanic series for sulfide minerals consisting of pyrite, chalcopyrite, galena, sphalerite, pentlundite, and pyrrhotite in an acid bacterial leaching system is illustrated, and the role of relative electrochemical activity on selective dissolution is discussed. Typical leaching results are shown to illustrate the practical applicability of galvanic effects in bioleaching of multisulfides. Attachment of Thiobacillus fewooxidans onto chalcopyrite and sphalerite mineral substrates is illustrated through scanning electron micrographs. The role of high-metal-tolerant, specially adapted strains in the leaching of multimetal concentrates is also outlined.

Jan 1, 1987

There has been some confusion over the selection of discount rates when performing stochastic simulations of a project's net present value (NPV) using risk- adjusted discounting techniques. Some argue that lower discount rates should be used when performing stochastic valuation simulations. This creates higher NPV values and improves the attractiveness of a project. Others argue that the discount rate should not be lowered for these simulations. This paper exposes the source of this confusion. It demonstrates that stochastic simulations do not remove the risk inherent in a project and, therefore-do not improve a project's value to the risk-averse investor. Risk-adjusted discount rates should, therefore, not be adjusted downward when performing stochastic NPV simulations. Stochastic simulations are, however, shown to he useful in several aspects of project valuation.

Jan 1, 1996

By John T. Bartlett

With more stringent environmental and economic constraints being placed on mining operations, it has become necessary to optimize each process to minimize energy and raw material consumption and reduce waste discharge. In most cases, detailed process analysis is required to detect inefficiencies and provide alternative solutions for process improvement. HETSIM, a microcomputer process modeling and simulation system, is routinely used to analyze communition, hydrometallurgical, pyrometallurgical, and coal preparation processes. The process modeling techniques used in METSIM, including process control simulation, will be presented and illustrated using actual plant processes.

Jan 1, 1987

By J. Drelich, J. Pletka

Lost foam casting is a process in which a polymeric material is formed into the shape of the part to be cast. Parts that are more complex are fabricated by simply gluing several patterns together. The pattern is then coated with a refractory material consisting of a mineral mixture and binders. Finally, hot metal is poured into the pattern, evaporating the expanded polystyrene and taking the shape of the coating shell. Prior to casting, a significant number of the patterns are damaged and inevitably landfilled. In this study, a process was developed for the recovery of expanded polystyrene from the coating and glue contaminants. The process consists of shredding, impact comminution, size classification and pneumatic separation. It is successful in separating up to 97% of the contaminants, while recovering 95% of the polystyrene. Key words: Casting, Lost foam process, Expanded polystyrene recovery

Jan 1, 2003

By William E. Foreman

The results of the electrokinetic study of the activation of quartz by divalent cations showed that the charge reversal was related to the point at which the cation hydrolyzed. The reversal was not due to the presence of solid hydroxide at the surface of the quartz but due to the charged ions in the solutions. The charge reversal for beryllium at a log molar concentration of 1x10-4 was observed at pH 5 and 9. The quartz was positively charged between a pH reading of 5 to 10. Magnesium at the same log molar concentration did not show a charge reversal from pH 2 to 12. The probable cause of the charge reversal was due to the ionized Be3 (OH)3+3 or Mg (OH)+ . Variations in the electrokinetics of quartz were minimized by heating the sample to 300° C.

Jan 1, 1968

By V. E. Ross

A model has been developed that describes the behavior of mineral particles and water in the cleaning zone of flotation columns. The possible detachment of particles from their sites of attachment at the bubble surfaces is related to the flux of bubble surface area with increasing distance from the interface between the collection and cleaning zones and the late at which floated particles are transported into the cleaning zone. The drainage velocities of floated and entrained particles are calculated from the drainage velocity of water and the properties of the particles. The effects of wash water and inhibited drainage in the froth are also explicitly accounted for.

Jan 1, 1988

By F. M. Doyle, K. Osseo-Asare, E. Peters

With the aid of molecular orbital theory, a discussion is presented of the relationship between the electronic structures of ions and molecules, and the elementary steps involved in homogeneous electron transfer reactions. An electronic theory of the reactivity of oxidants and the mechanism of action of oxidation catalysts is then presented, with emphasis on the oxidative decomposition of metal sulfides. For model oxidants, two molecular reagents: O2 and Cl2, and two ionic reagents: Fe3+ and CU2+ were selected; silver (1) was chosen as the model catalyst. The reactivities of these reagents are rationalized in terms of constraints on orbital overlap, the availability of unoccupied d orbitals, and the rearrangement of electronic configurations.

Jan 1, 1993

By J. D. Miller, P. L. Sibrell

The nature of surface sites for the adsorption of gold from alkaline cyanide solutions has been investigated using samples of synthetic, highly-oriented pyrolytic graphite (HOPG). This HOPG material offers an idealized graphite structure enabling the independent study of the graphitic basal-plane sites and the edges, or defect sites, of the graphitic planes. Radiochemical and X-ray photoelectron spectroscopic experiments independently demonstrated that gold adsorption was much higher on the edges (defects) of the graphite planes than on the planes themselves. These results suggest that site-specific adsorption is prevalent in the adsorption of gold by graphitic carbons (including activated carbon, carbon black and graphite) and that most of the favored sites are at edge defects in the graphite crystal structure.

Jan 1, 1993

By Joyce A. Ober

Strontium occurs commonly in nature, averaging 0.034% of all igneous rock; however, only two minerals, celestite and strontianite, contain strontium in sufficient quantities to make its recovery practical, and these minerals are found in sedimentary rocks. Of the two, only celestite has been found to occur in deposits of sufficient size to make development of mining facilities currently attractive. Celestite, the most common strontium mineral, consists primarily of strontium sulfate (SrSO,). Strontianite, the second most common mineral, consists primarily of strontium carbonate (Sr CO3). Strontianite would be the more useful of the two common minerals because strontium is used most commonly in the carbonate form, but few deposits have been discovered that are suitable for development. The physical properties of strontium ores are listed in [Table 1].

Jan 1, 1994

By Hajime Miki, Michael J. Nicol

Relatively simple techniques have been developed which enable the electrochemistry of sulfide minerals to be studied with particles varying in size from above 100 pm to less than 1 pm. Both oxidative and reductive processes have been studied wing the minerals pyrite, arsenopyrite and chalcopyrite. It has been shown that it is possible to completely oxidise or reduce the minerals during a single voltammetic sweep. The resulting voltammogram produces peaks which are characteristic of each mineral and can be used to qualitatively identify the minerals. In the case of chalcopyrite, it has been demonstrated that the charge involved in the anodic oxidation can be quantitatively related to the amount of copper dissolved. Quantitative information can be obtained using peak fitting techniques. Interesting differences in the behaviour of the minerals in sulfuric and hydrochloric acids have been observed, particularly in the case of pyrite for which a second major peak is obtained which has been attributed to the oxidation of elemental sulfur in the presence of chloride ions. The technique offers the possibility of providing mineralogical information of individual particles based on an electrochemical voltammetic finger print.

Jan 1, 2005

By Kenneth N. Han, Yuhong Chen

The removal of carbonaceous material from Carlin gold ore has been investigated via froth flotation. The effect of type and concentration of various oils as flotation collectors and of sodium silicate as the dispersion agent on the overall recovery of carbonaceous material has been studied. Other variables affecting froth flotation efficiency were also examined closely. These included particle size, pH of the solution, and temperature. The effect of reduction and oxidation of carbonaceous material on froth flotation efficiency has also been investigated. This investigation showed that aromatic type oil was the most effective collector. Also found in this investigation was that oxidized carbonaceous material was difficult to float unless the oxidized portion was subject to reduction before flotation. More than fifty percent of the carbonaceous material was able to be removed via froth flotation. It can be concluded from this study that the effect of pH and temperature during the rougher flotation state is of little significance to the overall recovery of carbonaceous material. Since pyrite is responsible for the high consumption of chlorine, removal of pyrite is very important in order to reduce the overall consumption of chlorine.

Jan 1, 1990

By R. Lindsay Mundell

During the past 12 years, use of longwall methods to mine coal in the United States has continually in- creased. Although these methods offer several advantages, health hazards often exist because of unique and difficult problems in the control of respirable dust. This paper discusses the results of respirable dust studies conducted on United States longwall mining operations in 1972and 1978. Current engineering control methods (ventilation, water application and use of machine cutting parameters) and administrative controls for minimizing employees' respirable dust exposures are discussed.

Jan 1, 1980