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By M. K. Patel, K. C. Wade, M. Cross

In the past decade a good deal of effort has gone into the computer simulation of the heat distribution of pellet induration systems. The major uncertainty in the analysis of such systems is the gas flow distribution and, in particular, the role of leakage. Evaluation of the leakage into or out of a zone has proved to be very difficult, as has the cross-flow from one zone to another when adjoining zones have gas flows which change direction from up draft to down draft for example. This paper describes an initial model to calculate the gas flow distribution in a variety of practical situations of interest to those involved in pellet induration. The model is based upon a multiphase CFD code called CASCADE which is used in conjunction with the pellet induration simulation INDSYS.

Jan 1, 1990

By Donald A. Dahlstrom, Soumitro Nagpal, Timothy Oolman

Bacterial oxidation of a pyrite/ arsenopyritic gold-ore concentrate was carried out with continuous flow operation in 14 liter (1.4x10-2 m3) mechanically agitated reactors. 02 and C02 uptakes were determined at varying residence times. Bacterial concentrations were measured using a protein assay. A sharp optimum in biooxidation rates was observed with increasing steady-state residence times. Growth of the bacteria and biooxidation of the mineral were both shown to be strongly dependent on dissolved 02 levels in the liquor.

Jan 1, 1990

By Chris McKee

Quartz has been of interest in occupational health for years because it can cause silicosis after prolonged exposure. New OSHA regulations (Air Contaminant; Final Rule) list perlite as a nuisance dust. They conclude that perlite is nontoxic when air-borne total particulate concentrations are 15 mg/m3 or below and when quartz content is less than 1% crystalline silica. OSHA has established an 8-hour PEL of 15 mg/m TWA for total perlite dust containing less than 1% quartz. OSHA has established a 5 mg/m3 TWA PEL for respirable perlite. These limits will protect workers from significant risk of eye, skin, or other physical irritation. This regulation is based on a Group 2A classification as a probable carcinogen in humans, at the 0.1% crystalline silica level, by the International Agency for Research on Cancer (IARC 1987a, b). IARC found sufficient evidence for carcinogenicity of crystalline silica in animals and limited evidence in humans. Perlite is not listed as a carcinogen by OSHA or the National Toxicology Program.

Jan 1, 1990

By R. A. Pindred, M. P. Lam

Cyanide is a conventional lixiviant for gold extraction but its' toxicity is a major concern for the environmentalist. There are many alternative non-cyanide lixiviants, such as thiourea, thiosulphate, chlorine and hypochlorite etc., which may reduce environmental sensitivity. This paper will discuss the leaching characteristics of gold in hypochlorite leaching solutions. The dissolution of gold in a hypochlorite solution not only depends on the concentration of the hypochlorite but also on other variables, such as hydrochloric acid, sodium chloride and temperature. The dissolution rate of gold in hypochlorite solution is much faster than other lixiviants. Due to the interference of impurities, gold extraction from an ore under ambient conditions requires large quantities of reagents. However, refractory gold ores may be successfully pressure oxidized in an autoclave at reasonably low reagent levels. Gold extraction to the pressure oxidation leach solution is rapid and complete in one stage, thus eliminating the need for further cyanidation.

Jan 1, 1990

By H. Sevim

Three transportation systems in surface coal mines: 1-Truck Haulage, 2-Belt Conveying, and 3-Coarse-Coal Slurry Transportation are compared from the operations and cost point of Views. Computerized design and cost models were developed and cost data banks were compiled for each system. These models can be used to evaluate transportation systems and layouts that are practiced in most of the U.S. surface coal mines. A typical midwestern area strip mine was considered for illustration purposes. Sensitivity analysis on critical parameters such as production rate, transportation, distance, etc. was conducted and the outcomes are presented.

Jan 1, 1990

By A. J. Getz

The paper reviews the status of the major precious metals projects in Australia, Papua New Guinea, Indonesia, the Philippines, and New Zealand. The projects may be at the stage of exploration, development, operation, or expansion. The paper covers project location, reserves, method of resource exploitation, anticipated production, and other unique conditions.

Jan 1, 1990

By Jane Morrison

Permanent magnets are used in most electromechanical and electronic devices to convert electrical to mechanical energy and vice versa. More than fifty are commonly found in the average American home and car. A new species of permanent magnet composed of iron, neodymium, and boron has recently been developed which combines superior magnetic properties with compact size. The reduced size of the magnets has enabled significant new developments in such areas as robotics and consumer electronic, among others. The objective of the present work is to efficiently and economically separate valuable rare earth materials from the relatively worthless iron constituent in NdFeB magnet scrap. Several magnet producers have expressed interest in the development of such a process and have provided information and scrap samples to aid in research. Scrap is generated in a variety of forms from different stages in the processing stream. Pieces of magnetic and non-magnetic metal as well as sludge and ribbon from jet casting must all be treated. Beneficiation techniques have been studied and size distributions developed for the different scrap types. Slag from the casting process is resistant to crushing and may need to be embrittled first, but all other types are amenable to crushing and ball mill grinding using stainless steel balls and water. Tabling was found to be useful in classification of magnet sludge. Two major techniques for separation of rare earths have been studied:

Jan 1, 1990

The new generation of computer environment provides mineral processing plants with convenient tools to store and retrieve or to analyze on-line process variable values as given along time by the various sensors installed in the plant. The paper describes the application of classical tools, such as time series analysis, to retrieve the hidden information contained is such data. The concepts used in single signal processing (autocorrelogram, power spectrum, ARIMA descriptors) and multi-signal processing (cross-correlogram, cross-spectrum) are briefly reviewed. Some examples are given to illustrate their application (sampling, data filtering, process behaviour prediction, process evaluation, data synchronisation). Examples are taken from mixing, flotation and leaching processes.

Jan 1, 1990

By M. Sengupta, N. I. Johansen, A. K. Sinha

In Arctic surface mines, frozen ground adds to the complexity of slope stability analysis. The seasonal temperature change may thaw permafrost, and this thawed ground is often unstable. A computer program, GEODYNE, was used to simulate the movement of the thaw front in bare and insulated permafrost slopes. The simulation shows that the insulation can be used on mine slopes to prevent thawing.

Jan 1, 1990

By Z. F. Wang, W. K. Choi, A. E. Torma

The present study has investigated the bioleachability of low-grade and high-grade pyritic gold ores and the extraction of gold from the leach residues of bioleaching with thiourea solutions. Final gold extractions as high as 96% were obtained from the high-grade ore and above 93% from the low-grade ore. The gold extraction was found to follow the extent of pyrite biooxidation. Using a cyclic voltammetric technique and carbon-paste-FeS2 electrode it was found that the semiconductor pyrite oxidation involves many intermediate electrochemical reactions. Furthermore, the oxidation is solid-state diffusion controlled as suggested by chronoamperometric and chronopotentiometric measurements.Using Sand's approach, the activation energy of solid-state diffusion biooxidation of pyrite was determined to be AEa=22.4 kJ. A generalized model for the mechanisms of pyrite oxidation has been presented.

Jan 1, 1990

By T. Cienski

The paper presents and discusses the results of a detailed study conducted on the subject of energy consumption in the comminution of industrial minerals. The study was based on pilot circuit testing, plant operating data collection, detailed equipment data and literature research. The areas covered by investigations include: high efficiency classification; air classifiers for cement grinding circuits; grinding aids in dry grinding: dry grinding circuit, control based on particle size measurement. Results obtained indicate a large potential for the reduction of energy consumption, in particular in the traditionally high cement clinker grinding circuits. Better classification techniques and correct application of grinding additives can significantly reduce power used per ton of product and also substantially increase grinding circuit output.

Jan 1, 1990

By G. P. Larson

We define a specialized mineral market as follows: Specialized Markets are markets where a low volume of a given mineral is used to convey a large benefit to a specific product. Sales of these value added minerals to small markets generally require a different marketing approach compared to bulk or commodity markets for traditional minerals. Specialized and commodity markets are differentiated by several characteristics as listed in Table 1.

Jan 1, 1990

By Stanley C. Suboleski

1977 was the modern day low point for productivity in the coal industry. At that time, no one could have predicted that the industry was about to enter a productivity rise that would continue unabated through the 1980s. Thirteen years later, the cause of this phenomenon is still not well understood. While many government studies focused on the fall in productivity from 1969 to 1977, none have been undertaken to explain the rise. Some of the likely causes of the gain in productivity during this period will be discussed here. An attempt will also be made to quantify the value of some of the technical innovations that have taken place. The remainder of the gain is assumed to come from non-technical sources. The nature of these sources, although largely non-quantifiable, is also discussed. Since the number of mines that have adopted the technical innovations noted here is largely unknown, the actual contribu¬tion of technological changes to the overall productivity gain can only be estimated.

Jan 1, 1990

By Jeff W. Butwell

Mill flotation tailings impounded at the Gooseberry Mine site between 1976 and 1984 were determined to be an economic source of gold and silver recoverable by standard heap leach technology in conjunction with feed agglomeration. Metal recovery at 85 percent Au, 75 percent Ag is attained on properly agglomerated (pelletized) tailings which average 85 percent -75 micron. Because the impounded tailings averaged over 18 percent moisture (32 percent moisture maximum at depth) in place behind the storage dam, the mining method, mixing and agglomeration technique, and materials handling practice were major considerations in making this operation a financial success.

Jan 1, 1990

By R. C. Bunge

A magnetogravimetric separation is the consequence of two competing forces with opposing directions, i.e., magnetic buoyancy and gravitation (or centrifugal force). While magnetic buoyancy is a function of particle volume, gravitational force depends on particle mass, thus permitting a separation according to specific gravity. Since magnetic buoyancy is not a phenomenon of common knowledge, this chapter is meant to briefly introduce the theory of magnetogravimetric separations. A particle that is suspended in a magnetic fluid which is exposed to an inhomogeneous magnetic field experiences a repulsive force -the so called magnetic buoyancy. In order to illustrate this effect, an analogy with the more familiar hydrostatic buoyancy is drawn. Hydrostatic buoyancy occurs due to unsymmetrical pressure distribution 'above' and 'below' a suspended particle (fig. 1).

Jan 1, 1990

By J. Iannicelli

Kaolin, normally an inert filler when compounded with polymers, is converted into a strongly reinforcing pigment by prereaction with certain functional silanes. Modification of kaolin with amino and mercapto silanes allows it to form crosslinks and confers significant improvements in modulus, abrasion resistance, compression set and other physical properties of a broad range of polymers.

Jan 1, 1990

By Clark J. Gilbert

The mining method at the Cannon mine uses heading and bench stopes, which are subsequently backfilled with cemented high-strength fill before pillar removal. The dimensions of the pillars are 7.3 m wide by 19.8 to 28.9 m high (24 ft by 65 to 95 ft). They require careful blasting in order to not damage the rock, compromising pillar strength and complicating later removal. Additionally, the proximity of dwellings makes vibration control a must for good neighbor relations. A blast monitoring study was conducted in order to optimize bench blasting practices to maximize fragmentation, reduce costs, and to minimize wall damage and ground vibration. The Cannon mine is a joint venture between Asamera Minerals (US) Inc., a 92% owned subsidiary of Gulf Canada Ltd., and Breakwater Ltd. Asamera is the operator. The mine is located at the south end of Wenatchee, WA, a town of roughly 45,000 people on the eastern flanks of the Cascade Mountains. Gold is the primary product at the mine. The rock is extracted using a sublevel end-slicing method on 15 m (50 ft) lifts, with subsequent backfilling and pillar removal. The stope widths, dictated by rock conditions at 7.3 m (24 ft), are the same in the primaries as in the pillars, or secondaries.

Jan 1, 1990

By William H. Bird

Over the past 14 years, the efforts of 2 companies and several individuals have outlined a major solfataric gold ore body in the Summitville district in the southeast San Juan Mountains of Colorado. The hard work of these years could not have flowered without a dedication to modern exploration methods, an intense interest in new theories of ore genesis, and a relentless discontent with the accepted geology of the Summitville area. To set the stage for this discovery period, it must be noted that it began 100 years after gold was first found at Summitville. It was the height of the "porphyry copper" era and gold was still not a part of the explorationists' portfolio. It was also a time of great intellectual stimulation. Theories were rapidly developing to relate different types of ore deposition and to place ore genesis within the fabric of plate tectonics. Summitville itself had just been linked to the newly discovered Platoro caldera complex and the Platoro lineament. This in turn related Summitville to the other San Juan volcanic field caldera ore deposits.

Jan 1, 1990

By J. P. Allen

Cobalt, nickel, and manganese can be recovered quickly, cleanly, and selectively from cobalt-rich manganese crust by leaching in dilute acid solutions in the presence of hydrogen peroxide. Common selective precipitation methods can then be used to recover these metals from the leach liquor. The leaching reaction produces only oxygen as a byproduct, and the waste residue from leaching was tested and found to be non-hazardous under existing EPA specifications. The leaching process is effective in either fresh water or seawater. This research is a part of the Bureau of Mines program to identify the mineral resources of the Exclusive Economic Zone and devise methods for recovering their valuable components.

Jan 1, 1990

By W. A. Niepelt, F. A. Locher

Flow in steep cascades may lead to the occurrence of a nearly periodic train of waves known as slug flow. This, in turn, may result in overtopping of the channel walls and problems with energy dissipation in receiving sumps. Experimental data from an operating facility was used to extend clear water technology for predicting the occurrence of slug flow to conditions with slurry flows. A design methodology and a design chart to determine the region of steady flows is presented that will permit the design engineer to avoid slug flow in cascade systems for conveyance of slurries.

Jan 1, 1990