Search Documents

By C. -S. Jiang

In most copper refineries, addition agents are added at predetermined rates with no further monitoring of their activity or concentration in the electrolyte. Increasingly stringent cathode quality requirements, and a desire for better process control in tankhouse operations, have recently directed a number of refineries to search for a better addition agent control strategy. Extensive development work has been carried out at the Noranda Technology Centre for the monitor in of glue and thiourea in copper refinery electrolyte using cyclic voltammetry (cv~. Data from both synthetrc and commercial electrolytes are presented, showing the ability of CV to produce reliable and easily identifiable fingerprints of addition agent concentrations in copper refinery electrolyte.

Jan 1, 1991

By P. Massacci

The modelling of phenomena by nonlinear dynamic Systems Theory representations require the specification and identification of suitable models of the phenomenon and the availability of good optimization algorithms to determine the optimal controls. Stochastic disturbances and difficulties of monitoring the process lead invariably, otherwise, to suboptimal performance. It will be shown that an algorithm can be formulated which will simultaneously identify and optimize such a system. The properties of the algorithm will be derived and its convergence to an optimal control proved. Some results of actual applications will be presented and it will be shown how this approach generalizes easily to optimal control of the actual processing system. These results generalize those of optimal learning and input conditioning.

Jan 1, 1991

By John W. Kelse

What happens when the skull and crossbones goes on a product? In the case of cancer warnings, the consequences can be severe. If the label contains the term "lung carcinogen", you might expect to compensate a lot of smokers, meet a lot of expensive lawyers, be counseled by equally expensive consultants and pay sharply elevated insurance premiums, if you are able to obtain coverage at all. At the extreme, you may face plant shutdowns, job losses or even Chapter 11 bankruptcy. Regardless of how you fare, you are likely to learn some very disconcerting things about the risk evaluation and regulatory system which required you to label in the first place. If a particular material or product does pose a health risk, you are obliged both legally and morally to warn those potentially exposed. Once that warning appears on the label, however, the consequences are often beyond your control. You and your embattled product become part of a legal/regulatory system which has a life of its own. Therefore, the issue of health labeling is not so much whether one warns but rather whether the warning itself is justified and the reasonableness of what happens afterwards. It is this matter of justification and reasonableness, particularly of cancer warnings, which this paper addresses. Until, as they say, your ox has been gored, we tend to believe that risk is determined by the best available technology and expertise We expect that risk evaluators appreciate the ramifications of their work and place things in proper perspective; that risk has been appropriately demonstrated before it is publicized and regulated; that the time-honored concept of prudence, to err on the side of safety, has not been excessively stretched. Unfortunately, the risk evaluation process is rarely, if ever, this

Jan 1, 1991

By Donna M. Noel

Bacterial strains have been cultivated from solids previously exposed to cyanide that will tolerate 300 ppm sodium cyanide under anaerobic conditions. In selected solid samples, these bacteria have been shown to reduce the level of cyanide from approximately 300 ppm to essentially zero in about 50 days under anaerobic conditions. Various media were investigated, and the nutrients providing maximal growth were ?established .. Degradation of cyanide in sterilized solids was determined for comparison with degradation obtained in bioactive solids. All experiments were conducted at ambient temperature and initial pH of approximately 10.5.

Jan 1, 1991

By Gale F. Hoffnagle

INTRODUCTION On November 15, 1990, President Bush signed the Clean Air Act Amendments of 1990. These Amendments cover many aspects of air pollution control. The provisions which seek to control emissions of "air toxics" may, however, be the most far-reaching and will potentially have the greatest effect on American industry. The Administration has estimated that by the year 2005 industry will be spending $6.7 billion per year on air toxics control. Meanwhile, the Business Round Table has estimated that the price will be far higher, up to $62 billion per year, depending on how EPA and the States implement the program. BASIC REQUIREMENTS Any "major" source of emissions of 189 air toxics will be required to install "MACT." The translation of this statement requires some definitions: •MAJOR SOURCE - A facility (a contiguous property under single ownership and control) which has actual emissions of 10 tons or more per year of any single one of the air toxics or 25 tons per year of any combination of air toxics. •AIR TOXICS - Congress has provided a list of the 189 chemicals on this list. Those that may be important to the mining industry are shown on Table 1. This list can be changed by petition or by EPA. •MACT - Maximum Achievable Control Technology is to be defined by EPA for each industrial source category. EPA says there are about 400 categories. The Act defines MACT as: "the average emission limit achieved by the best performing 12% of the existing sources ... for categories with 30 sources or more" or, "the average emission limitation achieved by the best performing 5 sources in the category." TABLE 1 SELECTED AIR TOXICS FROM CLEAN AIR ACT LIST IMPORTANT TO MINING INDUSTRY Antimony Compounds Arsenic compounds (inorganic including arsenic)' Beryllium Compounds' Cadmium Compounds Chromium Compounds Colbalt Compounds Cyanide Compounds (dissociation compounds) Lead Compounds' Manganese Compounds Mercury Compounds' Fine Mineral Fibers Nickel Compounds Radionuclides (including radon)1 Selenium Compounds 1Previously listed under NESHAP 2The Administration may not list elemental lead as a hazardous air pollutant.

Jan 1, 1991

By Hayward P. G

Complex ores, characterised by intimate intergrowths between minerals, have previously been treated by flotation with limited success. The most common problem has been that the liberation size is often finer than the lower size limit for selection flotation. A technique has been developed in which the problem is overcome by the use of a selective agglomeration procedure in which the values are coalesced with oil to a size suitable for flotation prior to introduction into the flotation machine. A complex lead ore was characterised by QEM*SEM mineralogy as having a mean galena liberation size of 15 ¦m. The best recovery of lead at 50 per cent Pb grade by standard flotation was 53 per cent. After application of the procedure, 86 per cent recovery was obtained after a single cleaner step. The oil functions as a bridging liquid in the presence of conventional collectors which render the mineral oleophillic.

Jan 1, 1991

By Henry L. Ehrlich

This survey compares bioleaching and biobeneficiation by autotrophic bacteria with that by heterotrophic bacteria and fungi Some physiological principles are reviewed. Advantages and disadvantages of autotrophic and heterotrophic leaching are discussed. Principles of anaerobic leaching by autotrophs and heterotrophs are introduced. and the advantages? over aerobic heterotrophic leaching are discussed. Examples of useful organisms in the autotrophic and heterotrophic categories are cited.

Jan 1, 1991

By Raimo Vuolio

"Over the past 30 years, the Nordic countries have developed similar practices for estimating damage caused by rock blasting vibrations. However, over the last few years the risk of damage has sometimes been estimated by using international values, which have created unnecessary costs, since they are too conservative. This paper gives a proposal for Finnish blast vibration standards and a calculation model for the extent of the zones for building inspection, risk analysis, and vibration measurements. The international conclusion is that particle velocity is the best descriptor for limiting damage potential for structures. Over 900 000 vibration data recordings from 52971 blasts were collected for this paper during 1970-1989. They show that the most practical description is the vertical component of the peak particle velocity. As rock is a nonhomogeneous medium, it is hard to predict the need and scope of risk analyses, building inspection, and vibration measurements. As a large number of blasts were monitored for the recording of the peak particle velocity in several locations in Finland, and the data combined, it is possible to establish safe scaled distances for the calculation of the need and scope of risk analyses, building inspections, and vibration measurements."

Jan 1, 1991

By B. R. Eichbaum

To develop technology to assure an ample supply of zinc and to reduce environmental pollution, the U.S. Bureau of Mines investigated alternatives to the roast-leach process for treating complex sulfide concentrates. Previous studies proved that low-grade zinc sulfide (ZnS) concentrates could be leached using chlorine-oxygen to produce zinc chloride (ZnCI2). The process involves high energy requirements for evaporating the pregnant solution to produce anhydrous ZnCl2 needed for electrolytic cell feed. An efficient hydrometallurgical process would facilitate treatment of lower grade ores than can be used in conventional processing and would render roasting unnecessary. An alternative method was devised for recovering ZnCl2 from solution. Zinc diammine chloride [Zn(NH3)2CI2] was precipitated from solution by adding ammonium chloride (NH4CI) and sparging with ammonia (NH3) to a pH of 6 to 7.5. The spent solution was treated with calcium hydroxide [Ca(OH)21 at 60° to 80° C for 1 to 4 h to remove remaining zinc and NH3. The Zn(NH3)2CI2 was heated to 300° to 400° C to remove NH3 and produce anhydrous ZnCI2. A possible flowsheet was devised and is included.

Jan 1, 1991

The STATE MINERAL SUMMARIES publication provides estimated data and summaries of mineral activities at the State level for 1990. Most of the estimates are based on nine months data. These summaries have been prepared in cooperation with State geological surveys or related agencies. Individual State summaries are published separately as State Mineral Industry Surveys and copies can be obtained from the appropriate State Activities field office.

Jan 1, 1991

By Susan Brink

The U.S. Bureau of Mines is investigating the potential of in situ leach mining a variety of Cu, Mn, and Au-Ag ores. Geologic characterization of ore samples from laboratory leaching experiments is conducted both prior to and after leaching to assess the effects of leaching on the chemistry, mineralogy, and texture of the rocks. The identification and chemical compositions of ore, gangue, and reaction products are determined by a combination of techniques such as reflected and transmitted light microscopy, X-ray diffraction, electron diffraction, electron microprobe analysis, and backscattered electron imaging with scanning electron microscopy. The distribution of the desired metal in various mineral phases can be illustrated using elemental X-ray maps. The potential of reactive gangue minerals to rob Cu from leach solutions is investigated with the aid of transmission electron microscopy. Porosity and permeability are measured to determine how effectively the host rock can transmit leach solution. Textural relationships between ore, gangue, secondary reaction products, and fluid channelways are determined by petrographic examination and are documented by optical photomicrographs and secondary electron imaging. Representative sample selection is described, and several epoxy impregnation and sample mounting techniques are discussed.

Jan 1, 1991

By G. H. Babcock, D. A. Knight, V. G. Medina

"Production commenced at the Golden Sunlight Mine in 1983 and at Kidston Gold Mine in 1985. These projects were both constructed under the management of the Placer Dome Inc. (Technical Services) group of Vancouver, B.C.Golden Sunlight uses a conventional rod mill/ball mill grinding circuit while Kidston uses a SAG /ball mill, and later on, SABC circuit. Since the hardness of the ore and the fineness of the primary grind in both mines are about the same, a meaningful cost comparison can be made. The comparison is made on the basis of capital and operating costs.The result of this study indicates that a significant capital cost savings can be achieved in favour of the SAG /ball mill circuit when the ore is amenable to semi-autogenous grinding. With a good maintenance program, the operating cost for the SAG /ball mill circuit could also be lower that the conventional rod mill/ball mill circuit.HISTORYGolden Sunlight MineGolden Sunlight is a 5 530 t/d gold mine located near Whitehall, a small town 60 km east of Butte, Montana. Originally optioned by PDI U.S. in 1958, the development of the property waited until 1981 when economic conditions became favorable for the project to proceed.Semiautogenous grinding tests were conducted during the final stages of the feasibility study. The hard near surface ore was not quite amenable to semi-autogenous grinding. The best result produced from a series of tests using a 1.83 m diameter mill was a semiautogenous work index of 39. This is substantially higher than the 22 Bond work index of the sample used in the testwork. A conventional SAG/ball mill circuit for this ore will be extremely inefficient, and for this reason, this circuit was rejected in favour of a conventional rod mill/ball mill circuit."

Jan 1, 1991

The value of processed materials of mineral origin was estimated to have exceeded $310 billion in 1990. U.S. raw nonfuel minerals mine production in 1990 was estimated at $33 billion, a 3.1 % increase over that of 1989. The value of minerals production increased in all but 3 of the last 30 years. The metals component of production value has fluctuated much more than the industrial minerals component. This reflects the greater volatility of metal prices. In 1990, total employment in metal mining continued the increase that began in 1987. This growth was partially offset by a slight decline in employment in industrial mineral mining, resulting in an overall in-crease of 1.1 % to 179,100 in 1990. Continuing high (by historical standards) metal prices led to expansions at some mines, as well as opening or reopening of additional mines, resulting in increased employment.

Jan 1, 1991

By Edward L. McHugh

The appraisal of mineral resources of the Challis National Forest, Idaho, by the U.S. Bureau of Mines, was made so that the mineral resources of the forest could be appropiately considered in land use planning. Information from this study is intended to tip the U.S. Forest Service to incorporate mineral resource data into forest plans The study was done in conjunction with the U.S. Geological Survey, which released a companion report on the geology and mineral potential of the Challis National Forest in 1989. This summary report is derived from a more detailed USBM Open-File Report (MLA 6-91) that includes descriptions of mines and prospects, commodity profiles, and development cost models. Since the 1860's mines within the Challis National Forest have produced mineral commodities worth more than $590 million at current (1989) commodity prices. Identified mineral resources have a gross value of about $2 billion at current prices, including 8 strategic or critical minerals. The U.S. Bureau of Mines study identified and described 723 active and inactive mineral properties within the forest. Mineral properties with identified resources were evaluate to determine their economic significance, and an assessment was made of the feasibility of mineral development. Of the 2,516,191 acres in the Challis National Forest, about 390,000 acres were classified as having mining development interest. Commercially important mineral production, mainly of molybdenum, gold, and silver from the Challis National Forest is likely for the foreseeable future.

Jan 1, 1991

This Bureau of Mines publication summarizes the industrial minerals industry of Idaho. It contains information on 119 principal deposits of 21 commodities in the State and describes the institutional and infrastructural factors affecting mineral development.

Jan 1, 1991

By J. E. Hamak

This publication contains analyses and related source data for 920 natural gas samples from 26 States and 2 foreign countries. All samples were obtained and analyzed as part of U.S. Bureau of Mines investigations of the occurrences of helium in natural gases of countries with free market economies. This survey has been conducted since 1917. The analyses published herein were made by mass spectrometer and chromatograph.

Jan 1, 1991

By Michael R. Norland

This U.S. Bureau of Mines report on U.S. and Canadian 1iterature pertaining to soil characterization and the use of soil amendments as a part of the reclamation process of coal surface-mined lands contains 1,280 references. The references were published during the 1977 to 1988 period. Each reference is evaluated by keywords, providing the reader with a means of rapidly sorting through the references to locate those articles with the coal mining region and subjects of interest. All references are annotated.

Jan 1, 1991

By Edward L. McHugh

The appraisal of mineral resources of the Challis National Forest, Idaho, by the U.S. Bureau of Mines, was made so that the mineral resources of the forest could be appropriately considered in land use planning. Information from this study is intended to help the U.S. Forest Service to incorporate mineral resource data into forest plans. The study was done in conjunction with the U.S. Geological Survey, which released a companion report on the geology and mineral potential of the Challis National Forest in 1989. Mineral development activity in and under the Challis National Forest has been of great economic significance to Idaho and the United States. Since the 1960's, mines within the forest have produced mineral commodities worth more than $590 million A current (1989) commodity prices. Identified mineral resources have a gross value of about $2 billion at current prices, including 8 strategic or critical minerals. The U.S. Bureau of Mines study identified and described 723 active and inactive mineral properties within the forest. Mineral properties with identified resources were evaluated to determine their economic significance, and an assessment was made of the feasibility of mineral development. Of the 2,516,191 acres in the Challis National Forest, about 390,000 acres were classified as having mining development interest commercially important mineral production, mainly of molybdenum, gold, and silver from the Challis National Forest is likely for the foreseeable future.

Jan 1, 1991

By Gordon T. Austin

The combined value of production of natural abrasives, which includes tripoli, special silica stone, garnet, staurolite, and emery, increased about 21070 in 1989. The increase in the value of staurolite and tripoli production was the result of an increase in the quantity of materials produced and an increase in the unit value. Emery decreased due to the significant decline in the volume of the material produced. Special silica stone experienced both a decrease in unit value and quantity produced. Garnet showed a small increase in quantity, but a decrease in unit value. The silicon carbide industry saw a slight decrease in the quantity produced and a 12070 increase in the value of production. The fused aluminum oxide industry showed a 5070 decline in the quantity produced, but enjoyed a 15070 increase in the value of production. Combined production for both industries decreased 4070 in quantity but increased 13070 in value compared with those of 1988.

Jan 1, 1991

By W. Hopkin

INTRODUCTION Necessary science and technology are not well established for the design of responsible treatment and disposal of arsenical residues from refractory gold ores. Specifically, there is uncertainty about the precise composition and behaviour of oxidised arsenic species in these wastes, and an analysis of possible chemical behaviour suggests that potentially difficult control and disposal problems remain to be so 1 ved. In tackling these the undoubted toxicity of arsenic in excess and its bad press should not blind one to the realities of actual behaviour in the environment, and that some adverse behaviour inevitably has to be to 1 erated as a cost in return for the recovery of an operation's gold for society. The problem is to minimise any such cost. Each refractory ore will be different. Many will contain so little arsenic that it will cause only trivial problems in disposal, but there remain others with significant arsenic content, say in the order of 1% or more, to cause concern. As already implied, concern can be over emphasised but equally underestimated. The balance which must be struck in the design of responsible disposal in the widest sense requires objective and practical assessment of a complex range of chemical, biochemical, engineering and economic design factors, all of which should involve the process design team in constructive dialogue with the 1 oca l regulatory authorities. In British terms, the general objective should be the Best Practicable Environmental Option. Arsenic is ubiquitous in waters, rocks and soils and all living things. Its compounds undergo natural geochemical and bi ochemi cal cycles including powerful adsorption and precipitation processes which return to nature all leakage from the inevitable disturbance of mining and extraction operations. Within limits, all life is tolerant to its presence, and adaptation and detoxication processes occur to deal with local excesses.

Jan 1, 1991