About David

Since 1993, when he obtained his Mining Engineering Degree from Queen’s University, David has acquired experience in operating roles including many years in post-commissioning operations troubleshooting. Mineral Processing and Metallurgy has become a core strength and passion for Mr. Michaud. Learn more at

Cyanide Leach in Cold Temperatures

In October of 1987, the U.S. Bureau of Mines (Bureau) initiated a study on the applicability of cyanide technology to the Alaska mineral industry. The study included the collection and analysis of cyanide literature and leaching costs, as well as the generation of several generic feasibility studies. Although other methods of cyanide use in the mining industry such as in situ and vat leaching have been examined, heap leaching is the main focus of the study.

This report discusses heap leaching methodology and evaluates the capital and operating costs of a “typical” Nevada heap leach operation of variable tonnage as it would exist in Interior Alaska. Cost data was generated by the Bureau’s Cost Estimation System (CES), Western Mine Engineering’s Mining Cost Service (MCS), and published case histories. The objective of these analyses is to compare the hypothetical costs of heap leach mining in Alaska to those of Nevada.

Heap leaching is a metal recovery method which typically uses a sodium cyanide solution to dissolve and remove precious metals from low-grade ore that is stacked into piles. In the last decade, the number of mines using this technology has mushroomed with the majority of this increase occurring in the Western United States.

Tin Tungsten Mineralization

Tin and tungsten are critical and strategic minerals to the United States. The basis for such a designation exists in the historic and current (1989) net import reliance of these metals by the United States as a percent of apparent consumption. Estimates by the U.S. Bureau of Mines for 1989 indicate a 73% net import reliance for both tin and tungsten with the balance derived largely from recycled scrap. Net import reliance is defined as imports minus exports plus adjustments for government and industry stock changes.

The identification of tin resources in the United States is critical due to the minimal tin reserves compared to the net import reliance. Most domestic tin resource potential lies in Alaska. Published estimates by Warner in 1985 of tin resources in Alaskan lode and placer deposits are 96.0 million lbs of measured plus indicated and 44.9 million lbs inferred. By comparison, the United States consumed an apparent 107.6 million lbs of tin in 1989.

The Sleitat Mountain tin-tungsten-silver deposit adds significantly to the tin resource base of the United States. This deposit was discovered, explored, and is owned by Cominco Alaska Exploration and an undisclosed joint venture partner. Cominco Alaska Exploration, at the reguest of the

Produce High-Purity Ultrafine Nonoxide Ceramic Powders by Turbomilling

The utilization of high-purity ultrafine SiC for high-temperature applications could reduce the Nation’s dependence on critical imported chromium, nickel and cobalt presently used in high-temperature alloys. Sinterable ultrafine SiC powders are presently required to meet high-temperature design criteria for conventional and advanced heat engines, heat exchangers, military applications, and many environments where conventional ceramic materials are known to fail. Pressureless sintering of SiC powders offers an alternative to hot-pressing or hot isostatic pressing for obtaining shapes that require little finishing. However, high-purity ultrafine α-SiC powders that can be pressureless sintered and have the required high-temperature properties have not been produced by conventional grinding techniques.

The use of turbomilling (also referred to as attrition grinding) to produce ultrafine particles is well documented. This technique, originated and patented by the Bureau of Mines, consists of intense milling and agitation of a slurry composed of a relatively coarse milling medium, the material to be milled, and the suspending liquid. Stanczyk and Feld, in a previous report, presented diagrams of the turbomill and turbomill process, summarized the Bureau’s research on turbomilling, and discussed commercial applications of the process.

In past studies, the turbomills used were of all-metal construction, which resulted in metal contamination of the materials

Platinum & Palladium Ore Flotation Pilot Plant

We have been conducting research on methods for beneficiating platinum-palladium ores from the Stillwater Complex, Montana. The Stillwater Complex contains the only known major deposits of platinum-palladium ores in the 48 contiguous States. Exploration by Johns-Manville Corp. (Manville Corp.) has resulted in the delineation of an approximately stratigraphic zone (J-M Reef) rich in platinum- and palladium-bearing sulfide minerals. The zone is 1 to 3 m thick, is composed of anorthositic rocks, and has been traced for 40 km. Anaconda Minerals Co. has been exploring a platinum-palladium deposit which is the strike extension of the J-M Reef developed farther to the west. The extension, called the Howland Reef, is sheared and serpentinized, and there are significant differences in primary stratigraphy between the Howland Reef and the J-M Reef.

The Bureau has conducted flotation studies on the anorthositic ore from the complex but not on serpentinized ores. This report presents the results of a pilot mill study using xanthate-normal dodecyl mercaptan suites in the flotation of serpentinized ore from Anaconda’s Minneapolis Adit on the Rowland Reef.

Sample Description

A 20-ton bulk sample of minus 2-in ore from the Minneapolis Adit was obtained for pilot mill testing. Analysis of the sample showed 0.10 oz/ton

Precipitation of Mercury in Cyanide Gold Leaching

Numerous low-grade gold-silver ore deposits are being mined and milled throughout the Western United States. In addition to gold and silver, many deposits contain as much as 15 ppm of mercury. During cyanidation, 10 to 30 pct of the mercury and 85 to 90 pct of the gold are typically solubilized. The reactions for gold and mercury extraction with cyanide are —

2 Au + 4 CN- + O2 + 2 H2O → 2 Au(CN)2- + 2 OH- + H2O2………………………………………….(1)

2 Au + 4 CN- + H2O2 → 2 Au(CN)2- + 2OH-………………………………………………………………..(2)

Hg²+ + 4 CN- → Hg(CN)²4-…………………………………………………………………………………………(3)

2 Hg + 8CN- + O2 + 2H2O → 2Hg(CN)²4- + 4 OH-……………………………………………………….(4)

Mercury builds up in the recycled leach solutions because only part of the mercury is adsorbed on carbon in the loading circuit. Mercury and gold are stripped from the carbon with caustic cyanide solution and electrowon on steel wool cathodes. Mercury must either be recovered or precipitated because of the health hazard during smelting of cathodes and regenerating of activated carbon. One gold mill recovers mercury by retorting the cathodes prior to smelting. Another mill autoclaves the ore to extract minimal mercury. Soluble mercury can be precipitated with sulfides, as

Potash Recovery by Solar Evaporation & Flotation

Over 80 pct of U.S. potash production comes from evaporite deposits near Carlsbad, NM. Most potash products are concentrated by flotation, selective dissolution of the gangue minerals, or precipitation of the mineral from hot brine. The majority of sylvinite ores, mixtures of KCl and NaCl, mined in New Mexico, are processed in grinding, desliming, sylvite flotation, and drying circuits to produce directly marketable KCl fertilizer. Some langbeinite (2MgSO4·K2SO4) is concentrated by dissolving the readily soluble halite and sylvite gangue minerals. A heavy-medium process is used to physically separate the minerals into sylvite and langbeinite concentrates. Langbeinite is directly marketable or can be chemically refined to recover K2SO4 fertilizer. Some carnallite and sylvinite ores, with abundant insoluble material in the sylvite grains, are processed by selectively dissolving the potassium minerals in a NaCl brine and desliming the brine. A pure sylvite product is precipitated by controlling brine composition and temperature.

Nearly all of the above methods generate potassium-rich brines. In addition, most potash operations bleed off brine to control magnesium and sulfate levels. Some potash producers operate gas- or oil-fired evaporators for crystallization of salts to recover potassium from these brines. Rising costs and limited availability of fossil fuels throughout the United

Oxygen Self Rescuers

Coal mine operators in the United States were required to make available to each underground coal miner a self-contained self-rescuer (SCSR). The regulations (30 CFR 75.1714) require that each person in an underground coal mine wear, carry, or have immediate access to a self-rescuer that provides an oxygen source. The oxygen self-rescuer will replace the filter self-rescuer (FSR) as primary escape equipment. FSR’s protect only against low levels of CO.

In an effort to compare performance of the six SCSR’s approved by the National Institute for Occupational Safety and Health (NIOSH), a breathing and metabolic simulator (BMS) was used to test the apparatus at a work rate equal to the average rate of a 50th percentile miner performing man-test 4 for 1 h as described in 30 CFR 11H. In addition to the six U.S. apparatus, six other oxygen self-rescuers from different countries and four prototypes developed for the Bureau over the past decade and stored since then were tested. All of the apparatus tested are listed in table 1, with their rated durations (service lives), country of origin, oxygen source, and weight.

It was not attempted to do an in-depth analysis of the design of each apparatus but merely to scrutinize

How to Recover Potash from Carnallite

The Bureau of Mines conducted research on techniques for recovering potash values from high-insoluble-slimes-bearing domestic carnallite ores. In the first phase of the study, two techniques were devised: (1) a method where the insoluble slimes were depressed during potash flotation and (2) a method where insoluble slimes were removed by flotation prior to potash flotation. Reports of the first phase of the research described batch- and locked-cycle, bench-scale testing of the two techniques. This report describes results of the second phase of the research: (1) operation of a continuous 100-lb/h flotation unit designed to technically evaluate the two methods and (2) an economic evaluation of the two methods.

Potassium is one of three basic chemical ingredients used for promoting plant growth. Refined potash salts, obtained from either ores or brines, are the only economically significant sources of potassium used in fertilizers. Current domestic demand for potash is 6.0 million tons of K2O. However, only approximately 1.8 million tons of K2O are produced in this country. The balance of the domestic demand is supplied by Canadian exports. About 84 pct of the domestic production is from bedded deposits in the Carlsbad, NM, area. This area has been a source of high-grade sylvinite

Electro-depositing PGM Platinum Group Metal Coatings

The Bureau of Mines has evaluated the substitution of platinum-group metal coatings for bulk platinum-group metal objects as a means of reducing the consumption of the platinum-group metals. The Bureau has conducted several studies of the electro-deposition of the platinum-group metals from molten alkali metal cyanide baths during the last two decades. The major incentive for this work has been the need to protect materials from increasingly hostile environments imposed by modern technology. To withstand high-temperature environments, structural materials must possess high-temperature strength as well as resistance to oxidation and corrosion. Refractory metals such as molybdenum, tungsten, and columbium, and alloys of these metals that have the required high-temperature strength, are readily oxidized. Protection of the refractory metals could be accomplished by coating them with a suitable platinum-group metal, and a composite material with highly desirable properties would result. Bureau research has focused on producing platinum-group metal coatings on refractory metals as well as on more common materials of construction. This research has shown that high-quality deposits which are thick, adherent, and coherent can be prepared of each of the platinum-group metals, as well as select binary alloys of these metals.

Historical Perspective

In 1937, Atkinson obtained a patent describing

How to Keep Bins Flowing – Safety & Material Handling

Over the past several years, a number of deaths have occurred in the minerals industry as a result of workers entering bins or silos to correct flow stoppages or to conduct maintenance. In almost all of the fatalities, the direct cause of the accident could be attributed to a failure on the part of the victim to obey one or more of several common-sense safety regulations. As a result, there is a temptation to prescribe preventative action based solely on such conclusions; namely, better safety training and closer supervision.

But there may have been underlying causes for the accident, causes not necessarily evident to an inspector trained primarily on the safety aspects of the problem. Why did the victim have to enter the bin? Is this action a routine part of his job, or just an occasional happening? If routine, is there a design or process change or equipment that would minimize the problem? If it is a material flow stoppage, could it have been avoided by better bin design or the use of flow-aid accessories, or was it an unavoidable result of the property of the material being stored, possibly because of weather conditions?

These are questions that are more properly

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