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By Raymond W. Peterson

The practice of Countertrade and all of its variations has increased dramatically during the last five years in great part due to the worsening world economic situation and the Third World's increasing debt problems. Conventional wisdom has held that the goods finding their way into countertrade will tend to be manufactured goods of ever increasing value added. It is my contention that this has not been the case. The continued depression of most metals and minerals prices has conspired to keep a great number of metals and raw materials in the forefront of countertrade negotiations. The concept that if a country needs hard currency it will simply sell metals into world markets for cash has been significantly modified by countertrade which encourages subsidies for raw materials which are in turn funded by higher prices for the manufactured goods which the country must import. Countertrade is a term that is relatively new to most of us who have been involved in the international trade of metals and minerals, but it is one that we will continue to hear more of in the future. Countertrade as it is generally known today had its beginnings after the Second World War in Eastern Europe. As the shattered economies of Europe struggled to right themselves, a "cashless" system of trade developed. This system included such ancient concepts as barter as well as more modern ones like bilateral clearing agreements. For over 30 years countertrade was confined mainly to the COMECON nations and their various trade protocols with Third World nations. If metals and minerals were involved, there was little disruption of world markets by such examples as Cuba shipping ferronickel and sugar cane to the U.S.S.R. for a host of manufactured goods and oil. As the world's economy began to slow in the late 70's and the debt crisis began in earnest in the early 801s, this all began to change. As more and more nations which had previously been almost totally dependent upon their mineral wealth over-extended themselves in an attempt to industralize, they concurrently found their income from minerals falling, due to the decreased demand and subsequently lower prices available in the marketplace. At first these nations attempted to balance their payments by promoting the sales of their high value-added manufactured goods. We have all heard numerous examples of U.S. companies going to sell their high technology products in Rumania or Yugoslavia and being confronted with counterpurchase requirements for machine tools, shoes or drill bits. When faced with these demands, a number of companies chose not to sell into those markets while others merrily signed up the obligations without much intent to carry them out. The Performance Bonds required were generally minimal, especially when considered in light of the high margin inherent in high tech items; and the penalty clauses were equally small or nonexistent. A third group of companies actually tried to buy the machine tools or drill bits either for their own internal use or resale but found that due to poor quality and high prices, they were faced with a difficult if not impossible task. This is not to say that no one was able to fulfill a countertrade requirement, but the success ratio on these transactions was incredibly low. This was one of the major contributing factors to the reputation that countertrade has gained as a discipline ... "that it is mostly talk and very little action." As this situation slowly evolved, both the countries imposing the countertrade obligation and the exporters assuming the obligation began to realize that something

Jan 1, 1986

By R. S. C. Rogers

Semiautogenous milling was the subject of 18 papers presented at the SME Fall Meeting in Albuquerque, NM. The process design and scale-up of SAG mills was discussed in several papers. These included a review of testing methods for the sizing of SAG mills by Barrett and Allan. Austin et al. presented an improved simulation model for SAG mill grinding, with model validity demonstrated against pilot plant SAG mill test results. Rogovin et al. presented some pilot plant results relating to the charge motion, hold-up, and particle size segregation in SAG mills. A number of papers described improvements achieved in operating SAG mill circuits. These included presentations by Dailey concerning mills at the National Steel Pellet Co., by Brown and Pipke concerning the Island Copper grinding circuit, by Lovering of Afton Mines Ltd., and by Bartrum et al. of Kidston Gold Mines Ltd. Bush and Hegerle of Amax also discussed SAG mill operations at the company's Henderson mill. They addressed the topics of SAG mill grinding economics. Other papers addressed the topics of SAG mill control (Vanderbeek et al. and Pennington), grinding media (Meulendyke et al.), liners (Kjos), and fabrication (Carr and Utley). The 1985 AIME Annual Meeting in New York featured four technical sessions concerning size reduction technology and practice. Papers involving fundamentals included one by Hinde describing simulation model usage for quantifying the classification and concentration of heavy minerals in grinding circuits. Another, by Rogers et al., discussed simulation models that were used as a design aid in evaluating screens versus hydrocyclones for fine grinding circuits. Arbiter discussed dimensional considerations in grinding mill design, and Schwechten and Schonert proposed the use of a high pressure roll mill as a means for reducing energy requirements in fine grinding. Internal classification in tumbling mills was the subject of a paper by Hogg and Rogovin. The mechanism of internal classification were identified and their effects illustrated. Simulation for the process design of ball mills was exemplified in a paper by Rogers, Austin, and Brame concerning phosphate grinding in laboratory to large diameter mills. The incorporation of liberation into size reduction models was the subject of papers by Austin et al., Herbst et al., and Choi et al. Gupta used simulations models to further investigate zero order fines production in ball and rod mills. Of the published literature, many articles on size reduction were published in various publications in 1985. Articles concerning ball mill grinding included an analysis of interstitial gas effects in dry grinding by Cottaar et al., an analysis of mill grinding noise by Watson, studies of factors affecting breakage rates in dry milling by Gupta et al., and in wet milling by Tangsathitkuchai and Austin. Austin and Klimpel presented two papers concerning ball wear and ball size distribution effects. Koka et al., and Gotsis et al., described recent developments concerning the Szego mill. A model for hammer milling circuits was described in papers by Gotsis et al. and Gotsis and Austin. Heim et al. reported on wet grinding in Perl mills, and Kuga et al. presented findings concerning pulverizing in a screen mill. Studies of grinding effects on particle surfaces were published by Meloy and Hofmann et al., and Scieszka proposed a technique to investigate pulverizing properties of coals. Austin and Rogers discussed factors of powder technology of significance in industrial size reduction in mills and crushers. (Space limitations preclude listing of references. A complete list is available from author.)

Jan 5, 1986

By Joseph M. Hans

INTRODUCTION The decontamination of a uranium mill site is principally an earth moving task. The task can be completed effectively and efficiently by selecting the proper earth moving equipment and using that equipment within its particular constraints for decontamination work. A considerable backlog of experience concerning earth moving equipment selection and use was acquired during the decontamination work conducted at the former Shiprock, New Mexico, uranium mill site. This experience was acquired by trial and error while decontaminating over a wide range of depths and different types of terrain. Many different types of excavation equipment were available to the Shiprock decontamination project because the Navajo Engineering and Construction Authority (NECA) heavy equipment operator's school was doing the decontamination work and a variety of equipment was needed for training. The equipment is described and its general use for decontamination is discussed. Its on-the-job use for decontaminating the Shiprock millsite is presented. [EARTH MOVING/ANCILLARY EQUIPMENT DESCRIPTION AND DECONTAMINATION CONSTRAINTS] Tractor-Scrapers The most commonly used scraper is the bottom-dump type because it is highly mobile and can dig, carry, and spread loads. In this type a tractor is connected with a yoke to a scraper bowl (Figure 1). The bowl is essentially a rigid box that pivots around the rear axle, opening to the front. A hardened steel knife, or bit, is attached to the leading edge of the bowl. When scraping, the bit penetrates and forces the earth overlying the bit edge into the scraper bowl as the scraper moves forward. When the bowl is full, it is closed by lowering a closure or apron against the cutting bit. The load is dumped while moving, by raising the apron and forcing the load from the bowl with a crowd, or ejector. The height of the dumped load is controlled by adjusting the bit height when dumping. Scrapers of this type generally do not have enough power to scrape up loads unassisted. Loading assistance is generally provided by a crawler tractor that pushes from the rear against the scraper's push block. Some scrapers are made self-loading by adding an additional engine for the extra power needed for the load pick up. Another commonly used self-loading scraper uses a loading elevator (Figure 2). The elevator consists of two roller chains carrying crossbars. The elevator is rotated when scraping and the crossbars cut the earth above or in front of the bowl bit, forcing the load into the scraper bowl. No apron is used on elevating scrapers. The load is dumped by partially retracting the bowl floor and pushing with an ejector. Scrapers have some undesirable characteristics when used for decontamination work. One characteristic is that a clearance space exists around the apron when it is in its closed position. Part of the load (especially sandy soils) dribbles through the

Jan 1, 1981

By Maribeth Amyot, Y. J. Wang, S. S. Peng

Introduction The impact of computers on individuals and businesses increases each day. And the mining industry is no exception. The growing number of short courses, symposia, and feature articles in journals on the subject of computers is indicative of the developments and interest in their application to mining. Given this interest and the growing importance of computers, a legitimate concern is the computing background of graduating mining engineers. Based on a sample survey, this paper presents the current status of computer education in Accreditation Board for Engineering Technology (ABET)-accredited mining engineering programs in the US. Specific topics addressed include hardware and software available to students, integration of computers into curricula, concerns of mining educators, and historical and anticipated trends in computing education. Methodology Nine of the 19 ABET accredited mining engineering schools (as published in the SME-AIME Guide to Minerals Schools) were surveyed. Interviews consisting of open-ended questions were conducted with a knowledgeable faculty member from each of these schools. This was done to obtain an overall view of computing in mining engineering programs. The intent was not to evaluate nor compare individual schools, so a complete census was deemed unnecessary. The minimal deviations between the responses to the subjective questions reinforces the credibility of the sample as being representative. Results Hardware Most of the mining engineering schools polled had access to hardware on three scales - mainframe computers available university wide, minicomputers available in the college or department, and microcomputers available at all three levels. Without exception, each school had access to mainframe and microcomputers. Minicomputers, however, were not available at every school. The mainframe computers have been in place the longest. The predominant mainframe currently on campuses is the IBM model. Mainframes were once the essence of all applications. But the improved availability and capabilities of smaller machines have afforded users a viable alternative. The increasing practice in education of assessing charges for time used on the mainframe - as opposed to no charge for time on the mini- and microcomputers - makes use of the smaller machines attractive. Conversely, much of the mining engineering software is only operational on mainframes. Sometimes this restriction exists because the requisite speed or storage inherent in the software can only be met by the mainframe. More often, however, it is because the software was developed when mainframes were the only machines available, and it has not yet been adapted to run on a smaller machine. At the schools polled, many mining engineering problems that are well suited to microcomputers are being solved on mainframes simply because microcomputer software is not available. Minicomputers are available at the department or college level in many mining programs. DEC is the most popular make. Often, the minicomputers were installed to alleviate the inconveniences of attempting to access and use an overcrowded mainframe, to avoid being charged for time used on the mainframe, and to meet the needs of a specific research project. The minicomputers are currently used much more for research than for teaching applications. Therefore, minis are seldom used by undergraduate students. Microcomputers have become extremely popular at mining schools within the last five years. Generally, some form of computing policy or strategy was established near the time the first microcomputers were purchased. This was formulated in part to ensure consistency, or at least compatibility, in the type of machines acquired. Microcomputers were subsequently selected based on the established computing policies; ma-

Jan 7, 1985

By J. L. Schroder, William J. Halvorsen, Wiliam W. Lyons, Kent C. Ware, Sheridan A. Glen, Donald C. Simpsom

The prospects for near-term growth in coal demand are exceptional: the federal government recently targeted 141 oil- and gas-fired generating units for mandatory conversion to coal; coal-to-synfuel developments are proceeding at a steady clip, with construction of a $1.2 billion gasification plant to begin this year in Beulah, ND; uncertainty over nuclear power and stratospheric oil prices enhance the steam coal market; the export market is ripening; and an influential new political force (the Senate Coal Caucus and Congressional Coal Group) is flexing its muscles on Capitol Hill. But the rosy picture is muddled by signals, often conflicting, sent out by federal agencies. Although EPA can be credited with relaxing its grip on the Clean Air Act, its sulfur dioxide control strategy is still often at odds with the Administration's call for domestic energy (coal) development. B. R. Brown, president of Consolidation Coal Co., sums up the situation: "Every mule is pulling in a different direction." Often in the midst of the fray is the small operator who has been hardest hit by the stagnation of coal markets. Layoffs, shortened work weeks, and mine closures were rampant in the eastern and midwestern coal fields, even among large producers. The longstanding boom in western coal was tempered during 1979 by a noticeable slowdown in announcements of new mine construction. The prognosis: Eastern coal will remain in the doldrums for quite a while to come as it works off some 90 Mt of overcapacity. Midwestern coal will fare no better due to the regulatory-influenced appetite of midwestern utilities for low-sulfur western coal. This displacement should ease, though, as new power plants equipped to burn high-sulfur coal come on line in the years ahead. In the West, the National Coal Association projects production to increase a healthy- 10% this year, although mine-to-market transportation looms as the single largest stumbling block to marketing efforts. Fatalities Up 40% in 1979 The National Coal Association estimated total coal production in 1979 at 671 Mt, an increase of 13% over 1978. Of this total, the East and Mid-west accounted for 476 Mt (71%) and the West produced 195 Mt (29%). With the consistent rise in western production playing against flat outputs in the East and Midwest, underground mining's share of total production continues to slip and is expected to account for only 38-39% in 1980. Incidence of deaths and injuries at US coal mines soared in 1979 over 1978 rates. MSHA figures (still subject to final adjustments) reveal a death rate of 0.07 per 200 000 man-hours, up 40% over 1978's 0.05 figure. MSHA chief Bob Lagather attributed the death incidence to the large number of new coal mines put on line in 1978, which he estimated at between 350 and 400. Nonfatal injuries rose to 8.48 per 200 000 man-hours, up about 15% from a 1978 rate of 7.35. In absolute numbers, MSHA counted 144 fatalities and 18 111 lost-day injuries during the 1979 calendar year. The 144 coal mining deaths in 1979 is the highest number of coal fatalities at US mines since 1975.

Jan 5, 1980

By Thomas J. Neil, O&apos

Most analysts find that progress has been evolutionary in any technologic field. To be sure, a few discrete breakthroughs can usually be identified, but viewed in its entirety, the curve of technologic progress over time tends to be relatively smooth with few discontinuities. Even in those cases where a major scientific discovery is achieved, the rate of technologic progress is limited by the often surprisingly slow rate of commercializing the concept into usable products. Whereas discovery and invention tend to be discrete events, technical innovation is often a painfully slow process. In spite of overall gradual change, technologic progress in most fields, when viewed in retrospect, tends to reveal certain relatively homogeneous periods where little change is evident, separated by episodes of accelerated progress. Thus, open-pit mining over the past century has changed from predominately train haulage to truck haulage and is now experiencing a major increase in belt haulage. Ore reserve estimation is another field that fits the same pattern, and the history of mine evaluation lends itself to a similar analysis. Evaluating mine investment opportunities is a fascinating aspect of mining. The unique set of risks inherent to every mining project is particularly intriguing. Geologic risks are most obvious, since faulty ore grade and tonnage estimates are among the leading causes of mine failures. Wide swine's in mineral commodity prices are usually cited as another major risk in mining. Because any ore deposit is a finite resource and the miner has limited discretion in selecting a mining sequence, mines are generally at the mercy of notoriously fickle commodity markets. There is a tendency for many mine investment analysts to feel that mineral market uncertainties are unprecedented in severity. Of course, prices in other markets rise and fall also-in some cases as precipitously as with minerals. However, two other mining characteristics tend to compound this marketing risk. First, the preproduction development period for a new mine is characteristically long. Under extremely favorable conditions, a significant mine may be developed in as little as two years, but the norm is four to six years or more. Second, mining is among the most capital intensive industries, consistently ranking near the top among all industrial sectors in assets per employee, and near the bottom in annual sales dollars per dollar of assets. Thus, mine investors typically have large sums invested for a long time before the outcome of the venture is determined by notoriously unpredictable markets. This is not a business for the faint of heart, and the importance of sound investment decision making is obvious. The high risk and technical complexity of mining operations have combined to require greater attention to financial evaluation by mining engineers than by most engineers in other specialties. Nearly all early mining engineering textbooks dealt with problems in mine valuation in a detailed manner; and, today, the sophistication of capital investment analysis is high in the mineral industries. Traditional Mine Valuation Methods Although some evaluation process has no doubt accompanied nearly every mine development throughout history, a formalized quantitative approach first emerged in the last half of the 19th century with the establishment of academic programs in mining engineering. The philosophy and approach to mine valuation that evolved at this time were, with periodic minor refinements, considered the standard for nearly a century. Only after 1960 did major changes begin to occur. The traditional approach to mine valuation reflected the investment community's historic attitudes toward risk. Mines were generally considered too risky for debt financing, and virtually every new mine was financed from internally generated funds or new equity subscriptions. The investment evaluation methods that evolved focused on mining's higher risk relative to other

Jan 11, 1982

By Warren D. Stanford

The Alligator Ridge mine is a near-surface gold mine located in a remote area 113 km (70 miles) northwest of Ely, NV. The deposit was discovered in 1976 by a lone prospector working under a grubstake contract for Amselco Minerals Inc. Evaluation of mine potential proceeded quickly. Favorable drilling results led to feasibility and mine design studies by the end of 1978. Mine construction began in early 1980. By September of that year, the process plant was fully operational. The first gold was poured a few months later. Alligator Ridge is designed to produce 1.9 t (60,000 oz) of gold each year. The projected mine life, based on proven reserves, is to mid-1988. However, Amselco is actively conducting exploration nearby for additional reserves to extend the mine's life. Amselco, a subsidiary of the British Petroleum Co., is based in Denver, CO. The company is mine operator and jointly owns the project with Nerco Minerals Inc., a wholly-owned subsidiary of Pacific Power and Light. Alligator Ridge is Amselco's first US mining operation. Geology Alligator Ridge, so named because it appears in outline to be an alligator at rest, contains disseminated micron gold embedded in iron-streaked siltstones. Although definitive conclusions have not been drawn on age and origin, the gold ore bodies are probably young by geological standards. They were formed in a recent volcanic period still evidenced in parts of Nevada by geysers and hot springs. As these superheated solutions rose through the permeable siltstones, they deposited minerals in the rock and formed the present gold ore bodies. During 1977, an extensive soil geochemical sampling program with additional geologic mapping and outcrop sampling were conducted. The results generated several drill targets. Initial drilling was performed in November and December 1977, and ore grade mineralization was encountered in the first drill hole. The Alligator Ridge mine is unusual in relation to other and more recent western US mineral discoveries in that it occupies an area that had no previous mining history. The ore deposits are hosted in upper Paleozoic sedimentary rocks that consist predominantly of a thick carbonate sequence. The main ore host is the Devonian-Mississippian Pilot shale, which occurs locally as a sequence of thin bedded calcareous, carbonaceous siltstones and claystones. The maximum observed thickness of the Pilot section in the mine area is about 140 m (460 ft). Rocks in the Alligator Ridge area have been folded into a series of low amplitude anticlines and synclines that strike north-south and plunge to the south at about 20°, with limbs that dip nearly 20°. The folds have been truncated and deformed by later high-angle faults that generally strike northwest. Although multiple stages of movement are evident on the fault systems, the youngest period of activity is along the major northeast trend. The predominant structural pattern in the area is of the basin- and range-type high angle normal faults. Alligator Ridge is actually a horst block between two basin and range faults. Vantage Ore Deposits There are three principal ore deposits within the Vantage Basin and several smaller satellite mineralized areas. The three Vantage deposits are encompassed in a mineralized zone that covers an area 915 m (3,000 ft) long and 305 m (1,000 ft) wide. All mineralized zones have been outlined by more than 600 rotary drill holes, with an average depth of 150 m (500 ft). Mineralization occurs in both carbonaceous and oxidized rocks. The carbonaceous gold-bearing material is not amenable to current heap leaching practice. Therefore, only oxidized ores are now treated. The carbonaceous gold-bearing material is segregated and stockpiled as it is encountered during mining. The three ore bodies occur along a north-northeast strike, with mineralization becoming progressively deeper from north to south. The ore block dimen-

Jan 6, 1984

By Werner Hofmann

INTRODUCTION The attempt to interprete lung cancer incidence caused by inhaled radon decay products in items of radiation dose raises the question of the relevant dose. The various dosimetric approaches published by now are characterized by an increasing complexity in the structure of the models used. Ranging from organ doses to microdosimetric specific energy distributions in the cells at risk, a significant trend from the macroscopic to the microscopic scale can be observed. Since tumors originate preferentially in the basal cells of the lobar and segmental bronchial epithelium, these cells are regarded as the critical target for inhalation carcinogenesis. The evaluation of basal cell doses is, therefore, the main objective of lung dose assessments. Various dosimetric models have been published in the past (Altshuler, Nelson and Kuschner, 1964; Haque and Collinson, 1967; Harley and Pasternack, 1972; Hofmann, Steinhäusler and Pohl, 1979, 1980; Jacobi, 1964; Jacobi and Eisfeld, 1980; James , Greenhalge and Birchall, 1980). Due to incertainties of physical and biological parameters involved and the application of different anatomical and physiological models the claculated doses are varying up to one order of mangitude. Independent of the choice of these dosimetric models applied to the calculation of lung doses, deposition, clearance and resulting dose are affected essentially by the properties of the inhaled aerosol as well as by personal characteristics. Both the properties of the exposed individual as well as of the inhaled environmental atmosphere have to be considered in radiation protection. It is the main objective of this paper to illustrate the influence of both parameter sets on basal cell doses by varying the above parameters. PERSONAL CHARACTERISTICS Though it might be more convenient for radiation protection calculations, the biological "man" cannot be represented by a uniform standard man. In Tab. 1 these personal characteristics which cause the variability of man are listed together with the region of their effectiveness. In the following the influence of these parameters will be discussed with regard to lung dose assessments. Besides these factors the great biological variability of all anatomical and physiological parameters involved as well as pathological alterations due to lung diseases cause additional variations in lung dosimetry. [ ] Age Age can be considered as the most important personal factor influencing the anatomical structure of the lung between birth and about 15 years of life. This period is characterized not only by an enlargement of already existing respiratory units but also by structural changes. Besides these anatomical alterations deposition is strongly dependent also on respiration parameters, such as tidal volume (TV) and respiratory frequency (RF). Whereas RF decreases with progressing age in an exponential manner, TV increases significantly resulting finally in a growth of the respiratory minute volume (RMV). Also mucus clearance in the infant might be more effective than in the adult, though no reliable experimental data are available. Superposing all these age-dependent changes mean basal cell doses are higher for children by about a factor of 2 than for adults living in the same radioactive environment (Hofmann, 1981). In the adult the following alterations of respiration standards with age are reported: total lung capacity diminishes with age, functional residual capacity is unchanged or increases with age and the dead space rises slightly with age (ICRP, 1975). The influence of these lung capacities on deposition, however, can be regarded as insignificant. Due to the ageing process mucus velocities my be considerably smaller in older people. This effect can also be superposed by the simultaneous influence of ciliatoxic effects of cigarette smoke and air pollutants or other bronchial diseases. Since the lower age limit for occupational exposure is about 18 years, age can be disregarded in the uranium mining industry for the determination of radiation doses, though lung cancer induction is significantly dependent on age.

Jan 1, 1981

Brace yourself-what used to be a 1 billion ton deposit is now a 1 Gt deposit. And that 1520-hp ball mill is now a 1.134-MW ball mill. Beginning with this issue, all engineering units and statistics in MINING ENGINEERING will be reported in SI units. The exception to this is the Technical Papers section, where units may still be reported by dual notation. For the past four years, ME has reported all units of measurement first in SI, followed in parentheses by the equivalent English value. This metrication policy, adopted by the SME-AIME Board of Directors in September 1975, was designed to aid magazine readers through a transitional period from English unit reporting to SI unit reporting. In October 1979, the SME-AIME Publications Board completed the English-to-SI transition by requesting the editorial staff, beginning February 1980, to report exclusively in SI. The Publications Board also requested the editors to prepare a chart of SI conversions useful to ME readers; this information follows on pages 156-157. The What and Wherefore of SI In 1960 the General Conference on Weights and Measures met in Sevres, France, and recommended that a new metric system-one that could uniformly cross all international borders-be adopted to replace all other metric systems. The outcome of this recommendation was the SI system of units, an abbreviation for le Systeme International d'Unites (the International System of Units). It replaces the more familiar cgs (centimeter-gram-second) system and the m/ksA (meter-kilogram-second-Ampere) system. SI consists of seven base units, two supplementary units, and a number of derived units. Other units, called allowable units, may be used even though they are not part of SI. The seven base units are: meter (length); second (time); kilogram (mass); mole (amount of substance); kelvin (temperature); ampere (electric current); and candela (luminous intensity). The two supplementary units are radian, a measurement of plane angle, and steradian, a measurement of solid angle. Supplementary units can be used in combination with SI units, e.g., radiant intensity is expressed in W/sr, watts per steradian. Derived units are combinations of base and supplementary units. Velocity is expressed as meters per second (m/s), and acceleration as m/s'. Using the relation established by Newton's second law of motion, force is expressed as kg-m/s2, more commonly known as the newton (N). Energy (work) is force times distance, expressed as kg-m/s2 and known as the joule (J). Power is work per unit time, expressed as kg, m2/s3 and known as the watt (W). Allowable units are the exception to the rule-they are not taken from base or supplementary units but, nevertheless, are used in the SI system. Volume units are normally expressed as the cubic measure of a length, such as cm 3. But a fluid volume of a cubic decimeter (dm3) is called a liter (L); the "L" is capitalized in another special SI rule to keep the lowercase "1" from being confused with a numeric "1". Other allowable units are degrees Celsius (°C) for temperature; and the minute (min), hour (h), day (d), and year (a) for time measurements. The prefixes in the table on the following page are used with SI units to express the magnitude of a measured quantity. A mill that processes 1000 tons of ore per day would be designated a 1 kt/d mill; a mine producing 10 million tons of ore per year would be called a 10 Mt/a mine. The rule here is to use prefixes that keep the value in a convenient range from 0.1 to 1000. In other words, it would be incorrect to write 25 000 kg-the prefix should be changed to indicate 25 Mt. One of the distinct advantages of SI is that it retains the decimal relation between multiples and submultiples of the base units for each physical quantity except for time. One more rule of SI syntax-numbers are separated into groups of three with a space between each group rather than a comma, e.g., 3,839,174 becomes 3 839 174. By the same token, a decimal number is also broken by spaces, e.g. 0.738153 is written as 0.738 153.

Jan 2, 1980

By Richard R. Klimpel

INTRODUCTION The process of froth flotation as a means of upgrading the quality of coal by removing water and/or ash and/or pyrite has been receiving increasing attention since the 1960's by the world-wide coal industry. Historically, coal preparation practice has involved the use of primarily gravity based separation techniques, screening, and/or water washing in removing the larger fragments of inert material from coarse raw feed coal. The preparation, handling, and cleaning of raw coal finer than 500 micrometers was deliberately avoided. Most often the fine coal that was produced would be judiciously incorporated into the bulk of the larger sized cleaned coal product or simply discarded. Since the 1960's and accelerating in the 19701s, the desirability of performing some type of coal cleaning or upgrading on the finer raw coal feed materials has been increasing. There are several apparent industrial incentives for implementing fine coal ((500 urn) processing alternatives including the gradually increasing value of the normally lost fine coal product; the additional amounts of fine coal being produced due to changes in mining techniques; the need to appropriately dewater and upgrade fine coal streams in order to meet increasingly stringent environmental regulations on water quality. storage of fines, etc.; the increasing need to lower undesired sulfur and ash contents in some coal end-use applications; and the increasing development of speciality coal use processes that require inherently finer and cleaner coal particles such as in gasification, liquefaction, fuel injection, etc. Looking at the over 70 years of mineral oriented fine particle separation successes at the industrial level, the use of froth flotation in fine coal would also seem to be a natural process to utilize at the industrial level. In the world of strictly mineral processing technology and, more importantly in the world of mineral commodity economics, there are clearly a number of advantages to using froth flotation that are well documented and universally accepted. These include: the relatively low capital and space requirements required when compared to other process options available to upgrade minerals; the extreme flexibility inherent to the froth flotation process both with regard to throughput and differences in raw feed characteristics; the general availability of a wide range of equipment sizes and reliable suppliers of equipment; and the general availability of appropriate and relatively cheap chemicals that are the major driving forces behind mineral flotation. Just how has the implementation of froth flotation fared in coal upgrading over the last 20 years? It is towards answering this question that this paper will be oriented. As such, the discussion will be somewhat philosophical. The comments offered are based on the personal experiences of this author who has worked in the basic side of inventing new flotation chemistry and flotation analysis techniques with the major overriding goal of implementing this new technology successfully at the industrial level in both coal and mineral flotation throughout much of the world. This paper is not intended to be a complete reference to all published scientific work on the subject of industrial froth flotation of coal. As a brief background to what will be expanded upon in this paper, the author would like to offer the following summary comments: 1) the industrial practice of fine coal froth flotation is qualitatively similar but quantitatively different than industrial mineral froth flotation when viewed from either research considerations, operating viewpoints or economic evaluation criteria; 2) it is clearly possible to invent and/or develop new technology (such as new chemistry and/or equipment) that can do statistically better than current plant practice in well-controlled tests in either coal or mineral flotation circuits; 3) there is so much inherent variability to the raw feed coal streams and other operating parameters that even if there is a documented technical incentive to implement some new piece of technology, the people, instrumentation and control methodology required are often simply not available or not economic unless the potential payoff is quite large.

Jan 1, 1988

By J. A. Herbst

Introduction The ability to evaluate the improvement resulting from the implementation of an automatic control system is essential to the Justification of its cost. This evaluation may occur after anew control system has been commissioned. In other cases an existing plant which is operated manually may be automated only In part in order to determine In ether the met of it should be. Finally. in some instances dynamic isolation my be used prior to installation of the control system to determine the strategy to be used or to evaluate the improvements In process performance expected from automatic control. This paper describes the development of a methodology for making these evaluations. In order to obtain an accurate assessment of Improvements In a short time, statistical methods can be employed. Mineral processing plant, are subjected to many types of both random and deterministic disturbances of various duration. The statistical method, available for process control at analysis are designed to counter the obscuring effects that random disturbances have on such as evaluation. The basis for evaluation and comparison is some freely chosen measures of process performance termed the performance index or objective function. The experimental data used to calculate the performance index should, if possible, be collected by alternately running a circuit Or plant with the two or more type, or control being tested ("serial testing”) or more preferably, by running two circuits with the two type, of control side by side ("parallel testing") . The performance index is a random variable so that when comparing two types of control, statistical hypothesis testing must be used. By testing s hypothesis statistically one accept, or reject, a (null) hypothesis [ ] concerning the mean or variance of one or more performance indices. For example, a hypothesis Ho might be that the mean of a performance index with stabilizing control is larger than with manual control. Defining a Performance Index The performance index, denoted by [ ] , is a measure by which alternative strategies or situations my be cam peered on either s technical or an economic basis (see Table 1). Technical measures are concerned with the effects of control on process variables or outputs or on the deviations of controlled variable, from their setpoints. For commotion circuit, important technical measures of performance are throughput, product fineness and the consumption of liners, media and electrical energy. For flotation circuits important technical .satires are recovery, grade and reagent consumption. Economic measure such a, cost and profit n usually determined from a combination of technical measures and are usually the final factor upon which a decision may be made, although a control system my achieve higher values of technical measure , the control effort expended my be of such magnitude that the economic measures, such as cost, are poor. Running Comparisons Comparison, between automatic and manual control are normally done with data obtained before and after control system Installation, unless ore characteristics remain the same during the period of data collection the results will be biased. By running the test circuit with the control system alternately turned on and curled off until all possible ore type, have been run through the circuit, unbiased result, can be obtained. This mode of testing is termed “serial testing.” An alternative and potentially more powerful and quicker made of testing is "parallel testing" in which two circuits, one with the type of control being tested and one without, arm run aide by side. In this type of testing both circuits process the same ore so that valid results occur sooner than with aerial testing. The data may be averaged before testing or the differences in the performance indices may first be calculated before averaging. However, the two circuits must be nearly identical in their mechanical characteristics otherwise differences other than the degree of control will bias the results. It mechanical differences exist than it my be necessary to adjust one or the circuits prior to testing. Sometimes it is possible to correct far mechanical differences based on Inherent efficiency calculations made with a model. Hypothesis Testing Once the data is collected, hypothesis fencing can be carried out to determine if the automatic control system has resulted in a statistically significant improvement. One can construct a histogram of the distribution or performance indices with am without control such as Figure 1, or the

Jan 1, 1991

By A. H. Leuschner, P. J. Kruger, J. Kruger

INTRODUCTION This paper deals with some practical aspects of the use and interpretation of dosimetric methods for assessing the exposure of workers to natural uranium. Consideration must be given not only to the scientific value of the method of dosimetry, but also to the practicality of the method in the particular working environment. It is generally accepted (IAEA, 1976) that uranium does not present a hazard during the mining and extraction processes up to the final concentration stage, that is precipitation as ADU or calcining to the oxide. Further processing (e.g. conversion to oxides, fluorides, etc.) is generally associated with the nuclear industry. It is customary for uranium processing facilities to be managed according to industrial norms rather than according to those applied for the purpose of radiation protection. This is mainly because of the large quantity of material to be processed and the fact that uranium is considered to be of a low radiotoxicity. Although ventilation is used to some extent, provision is not made for the same level of protection as would be required in a radiochemical facility. It is typical in such a plant to find that the process itself may be enclosed and ventilated, but the ventilation is inadequate to cope with an accidental release of material. The working environment is poorly ventilated, sometimes only by natural ventilation, and one frequently finds areas with high airborne dust levels, designated as mandatory respirator areas. Protection of personnel is dependent on personal protective equipment. Radiation protection is not of prime concern and personnel are not specifically trained in this subject. It is in this type of environment that acceptable monitoring procedures and personnel dosimetry must be established. The effectiveness and practical application of the dosimetry must also be judged against this working environment. DOSIMETRIC TECHNIQUES The methods available for assessing personnel exposure, whether it be in terms of chemical or radiological hazard, include urinalysis, faecal analysis and [in vivo] monitoring. Faecal analysis does not present itself easily as a method for routine use. Techniques for [in vivo] monitoring have been developed recently and as expensive instrumentation is required, it is not generally available. That leaves urinalysis as a dosimetric technique for routine use, and it is probably for this reason that urinalysis is still widely used. Guidelines for the interpretation of urinalysis results, as originally provided by Neuman (Neuman, 1950), are still used in practice, even though it has become clear that this method has severe limitations as regards the assessment of the dose as a result of the intake of class W or class Y compounds (Alexander, 1974). Typically a level of 300 µg [U/C] urine can serve as an indicator of an acute exposure (above which chemical damage to the kidneys may occur) and a level of 100 µg [U/C ] urine can serve as an indicator for an investigation. Such levels are determined and are used in conjunction with several factors, such as mode of intake (ingestion or inhalation), solubility of compound (D, W or Y), means of intake (acute or chronic), environmental monitoring results and frequency of urine sampling. Since the ICRP concept for internal radiation limitation changed from that of the critical organ, i.e. the single organ of greatest significance under the circumstances, to that of effective dose equivalent, i.e. account being taken of the total risk due to the exposure of all tissue, the maximum permissible organ burden (MPOB) was replaced as secondary dose limit by the annual limit on intake (ALI) (ICRP, 1977). The ALI values are calculated from the committed dose equivalents of the various organs, and are used to determine organ burdens, which are then used to interpret the dosimetric results. Using the ICRP model (ICRP, 1979), a comprehensive calculation was made by Johnson (Johnson, 1980), giving organ burdens and excretion data in terms of intake for acute and chronic exposures for different categories of uranium compounds. The question arises as to what extent the direct measurement of intake can be utilised as a method of dosimetry. This will require a method of personal intake measurement for each individual worker, with both ingestion and inhalation being taken into account. A measurement of

Jan 1, 1981

By R. Poulin, R. Pakalnis, D. Peterson

Introduction A comprehensive project has been completed at the University of British Columbia that focused on the development of a commercially competitive composite cable bolt. Laboratory evaluation consisted of pull tests, preliminary shear tests, grout column testing and scanning electron microscope evaluation of the composite cable bolt. Field implementation at five underground mines throughout Canada were completed for technical and overall performance evaluation of the new product. The project began in 1989 under the sponsorship of HDRK Ltd., a consortium of mining companies including Inco, Noranda and Falconbridge Ltd. The objective was to develop a cuttable cable bolt that would serve as support for a continuous miner within a hardrock environment (Mah, 1994). The bolt was required to be cuttable by a continuous roadheader without adverse effects to equipment, personnel and the milling process. From the beginning, the focus was to employ existing cable bolt installation technology (Goris et al., 1994) whereby the cable bolts are grouted within a 4.8-cm-diam (1.08-in.diam) or larger employing a portland cement grout having a water: cement ratio between 0.35:1 to 0.4:1. The prototype, developed from Phase I, was technically comparable to that of conventional steel cable bolts. However, high cost and limited accessibility hindered its commercial acceptance. The second phase of the project was sponsored by the British Columbia Science Council and Pacific Pultrusions Ltd. of British Columbia to locally develop a glass fiber cable bolt. This phase of the project has resulted in the DAPPAM cable bolt (Pakalnis et al., 1994). DAPPAM Cable bolts are the second most used support method in Canadian underground mines after mechanical rock bolts. It is projected that 870,000 m (2.9 million ft) of cable bolts are installed annually in Canada (Poulin et al, 1994). The objective of the research program was to develop a glass fiber cable bolt with similar pullout strengths to the conventional steel cable bolts (267 kN - 60,000 lbf). More than 200 laboratory pull tests were conducted employing standard cable bolt test procedures, as outlined by the US Bureau of Mines (Goris, 1994), to assess optimum rod and surface composition, geometry, number required, pullout and shear characteristics, among others. This resulted in the DAPPAM cable bolt (Fig. 1). It consists of 10 individual 0.6cm-diam (0.25-in.-diam) rods enveloping a 2.2-cm (0.8-in.) outside diameter, high-density polyvinyl grout tube. The composite used in the construction of the rods is comprised of about 65% glass fiber within a 35% polyester resin matrix (by volume). Through pultrusion (a continuous fabrication technique), the fibers and resin are combined into a composite material. The strength of the overall composite is largely governed by the material properties, the alignment [ ] of the fibers relative to the applied load and the density and interaction of the overall components within the composite. A further modification to the composite was the addition of a sand grit to the surface of the individual rod. This increased the overall bond strength between the rod and the cement-based grout, used to solidify the cable bolt to the rock mass. The grout tube has an inside diameter of 1.9 cm (0.75 in.) and is rated at a pressure of 1.72 MPa (250 psi). During installation, the grout is pumped through the annulus of the grout tube thereby filling the hole from toe to collar. Laboratory and field trials concluded that a minimum drill hole diameter of 4.8 cm (1.08 in.) be used to ensure optimum grout coverage. Table 1 compares the design strengths (as tested) for DAPPAM vs. the ultimate strengths for a conventional 1.6cm (0.6-in.) steel cable bolt. The characteristics for the steel cable have been derived directly or indirectly by Goris et al. (1994). A design tensile strength of 289 kN (65,000 lbf) was proposed for the composite developed. However, recent tests have indicated maximum breaking strengths of more than 400 kN (90,000 lbf) (Fig. 2). Figure 2 shows the load vs. displacement pull out curves for steel and DAPPAM cable bolts. The methods of testing were standardized so as to be able to compare the results directly. The shear strength of the fiberglass cable is largely a function of the surface area sheared. Shear strengths of 89 kN (20,045 lbf) were obtained for the configuration shown in Fig. 1 when sheared normal to the axis of the cable. The testing procedure was similar to the shear tests performed on steel by Goris (1993). It is important to reinforce the implication that critical bond strength has on the success of an overall support system.

Jan 1, 1995

By Karl W. Mote, R. K. "Ivan" Urnovitz

One of the Northwest Mining Association's guide-lines is: "If you always do what you've always done, you'll always get what you've always gotten." Another way of saying this is, simply, "when the road curves, don't refuse to turn." Our industry has been roundly criticized for living in the old political world, and, I believe, justifiably so. Until about 20 years ago, members of both houses of Congress deferred to specialists among their members for mining legislation. This was true for all public lands and natural resource issues, and were referred to as the mining bloc, or the timber bloc, or the ranching bloc. We felt safe, and to a large degree, were safe in the sense that western members of the US House of Representatives and of the US Senate understood the need for multiple use of public lands, and the need for the natural resources they supply. They also knew what it takes to stay in business and how to create the economic atmosphere that encourages private industry to find and provide the natural resources. Almost daily, members of our industry bemoan the destructive effects that current regulations, let alone new proposals, are having on American industry. And, there are some intriguing aspects for us to ponder. First, the specific complaint about the government is not regulation per se, but rather that the rules or policies don't make sense. We recognize that few understand our industry, but we have assumed that the government will rely on people experienced and knowledgeable in the area being brought under government controls. There was a time that this assumption was valid, but it is no longer true since we have entered the era of the professional regulator. Much like the MBA who believes that a professional manager can manage anywhere, the new breed of regulator sincerely believes that process is the key to developing effective regulations or programs. They reason the process virtually assures that all the pertinent facts will inevitably come to light and, after receiving appropriate considerations, will result in the proper decision being reached and implemented. Unfortunately, following the process also allows politics to play a new and greater role than ever before, since information based on what can only be called weird-science can now be presented to the professional regulator and accepted as fact. Regulators do not have the background to question the basic tenets of the conclusion being presented to them. To add insult to injury, testimony from people in the industry involved, intended to set the record straight, is too easily discounted as being merely self-serving. A second aspect is that the question of why the associations aren't doing more to stop poorly conceived legislative and regulatory proposals, or to counter the ever-increasing influence of the selfappointed public interest groups is being increasingly discussed. This is occurring despite the fact that there is a higher level of involvement and closer cooperation between the various associations than ever before. This raises a most important question: where are we going wrong? In the last 20 years or so, major changes have taken place. A new philosophy, taking advantage of the public's recognition of need to protect our environment, has swept through the nation, resulting in a whole new body of law enacted to assure environmental protection. We all acknowledge the need to prevent undue degradation during the course of mineral development, and we all consider ourselves to be responsible stewards of the land, because we live and work in the outdoors and know the importance of environmental protection. The changes in the federal statutes apply now to every aspect of mineral discovery, development, and production, and assure adequate reclamation of lands when we are done. Along with the positive changes, are a constant barrage of attempts to stop public land use, or stop mining, or stop any new economic development, ostensibly to "protect the environment," but often reflecting a hidden agenda of social reform. These types of extreme, irrational, and just plain impossible proposals are everyday occurrences, but we have not geared up to challenge all the proposals which could end mining. Instead, we did what we always had done. The road turned, but we didn't. And we wondered why those who had always protected mining weren't doing their job, and why we were having such limited success in reining in the regulators. The Congress had changed, the public demands had changed, the recognition of importance of natural resources had

Jan 1, 1991

By William F. Riggs

The basic theme of this symposium and panel Is Rotation Pads: Are They Optimized? There Is a. reason for phrasing the title In the form of a question. There Is not only the technical competency which we must address; there Is the operating philosophy that must be evaluated on the part of both the customer and the supplier. Customers desire reagents which are trouble-free and capable of providing that extra amount of selectivity or recovery. When they receive ft, after the supplier has provided several years of Internal research, one of the first concerns/complaints Is the price of the product. This has a tendency to rapidly reduce a supplier's support level In the future. Suppliers are equally guilty from another perspective. When they approach a customer to Introduce a product, they often attempt to market by offering only a price Incentive. They then wonder why a customer doesn't respond Immediately to the incentive. They are often oblivious to the fact that the reagent cost is such a minor aspect of the operating budget, and the customer has many more pressing problems on a day-to-day basis In comparison to the reagent cost. We need to establish the understanding that reagent cost Is an Inconsequential cost of operation, and yet has such a disproportionately high Impact on the success of the entire operation. This understanding Is required by both the customer and the supplier. We say to each other,' why are we discussing this since this has been obvious for some time?' The reason is relatively simple in that we talk about it, acknowledge it, and yet we do not adhere to it. The supplier provides a product along with test data containing statistics, analysis, recovery, grade and cost calculations while most of the time ignoring the operating technique which must be applicable In the plant In order to optimize the product. He expects the reagent to be substituted In the plant for the existing reagent and ft works or does not work after trying several variables. The operating management Is equally guilty, In order to best explain this to both the customer and the supplier, ft becomes necessary to review the basic purpose of the major reagents utilized In flotation. A collector is basically to Impact selective, maximum water repellency on the surface of a particular mineral, The frother has the purpose of providing a chemically stabilized membrane on the surface of the bubble at the air-water interphase. This, then, provides a host environment for the attachment of the collector-coated mineral to a bubble. The depressant functions In the reverse of the collector and must demonstrate the same or greater degree of selectivity than expected of a collector. The key area which has been Ignored Is the rate by which these reactions occur and Interrelate. This has a very specific effect on the operating technique and the compatibility of the chemistry, equipment, and the operator himself. Researchers, suppliers, and customers provide reams of data to demonstrate how their products or design produce, for example, higher kinetics, more selectivity, or more recovery. The Information is often true. After all, we are all learned men and laboratory and actual plant data do not lie. However, we must remember the theme of this symposium and panel: Flotation Plants: Are They Optimized? and Optimizing of Flotation Reagents? The direct, honest comment to the two titles is very simple. OF COURSE THEY ARE NOT The plants, equipment, and reagents had better not be optimized or else we are in trouble. The Issue of this panel discussion is to approach this subject from a slightly different or perhaps mainly Ignored aspects of optimizing reagents in flotation. When we have reagents which provide higher kinetics, more selectivity, and better recovery, how do we use them? Since each reagent has a different physical characteristics of froth, rate of recovery, volume effect on the compatibility of equipment, and many more aspects too numerous to mention, the question which has been severely Ignored Is, 'What degree of study and cooperation by both the supplier and the operating management has been conducted In order to prepare the operator for maximizing the performance of a reagent In relation to the rest of the system?" Prior to testing a new reagent, how much time Is spent to bring the actual operator(s) Into the program to make them feel part of the program? How much time is spent explaining to the operator on the float floor how to possibly take advantage of a reagent with faster kinetics or one which Is Inherently more selective? What

Jan 1, 1993

By H. O. Seigel, John C. Robbins

Luminex is a new method of prospecting for mineral deposits based on time-resolved mineral luminescence created by an ultra-violet light source. Developed by Scintrex Ltd., Luminex detects and resolves a group of key minerals - either ore minerals themselves or, more often, accessory or pathfinder minerals for certain types of economic ore deposits. These minerals are commonly found on the earth's surface, even in areas of considerable weathering. The method extends the range of mineral deposits that are remotely detectable from the air. Tungsten, tin, molybdenum, gold, and bedded lead-zinc deposits are included. Therefore, Luminex is a natural supplement to the three classical methods of airborne geophysics. The luminescence of minerals has been known and used qualitatively in mineral exploration for many years. But there are more than 500 minerals known to be at least sometimes luminescent. Luminescence of most is unpredictable and the colors they emit may vary from locale to locale. It is, perhaps, this apparent complexity of the field that has discouraged its proper scientific scale until now. There are two basic types of luminescent minerals - intrinsic and impurity activated. In the first type, luminescence is an inherent property of the mineral in its purest form. In the latter, luminescence is due to the introduction of foreign trace elements, often in very modest amounts (ppm), into the crystal lattice. These trace elements are known as activators. There are very few intrinsic luminescent minerals commonly found in nature. Chief among these are the calcium tungstatemolybdate family, more commonly known as the scheelite-powellite family, and the uranyl minerals such as autunite and saleeite. The vast majority of other known fluorescent minerals such as fluorite, hydrozincite, and many calcites, are impurity activated - that is, they will not fluoresce in purest form. In addition to the many minerals likely to luminesce at the earth's surface under ultraviolet excitation, any prospector who has ventured out at night with a mercury lamp will know that much organic matter luminesces - for example lichens and even scorpions. Just as the eye finds difficulty in resolving the luminescence of minerals from that of organic materials, it also has its limitations at sorting out minerals from one another by their luminescent colors. Figure 1 shows, in part, the photoluminescent emission spectra of scheelite, hydrozincite, and autunite. It is clear that there is a considerable similarity in spectrum between scheelite and hydrozincite and a great deal of overlap. In fact, a small amount of molybdenum in the scheelite lattice can almost bring these two spectra into coincidence. On the other hand, the autunite emission spectrum is clearly resolved from the other two. Basis of the Method The right-hand side of Fig. 1 shows the time waveforms of decay of the photoluminescence of the same three minerals. It is apparent that the lifetimes of photoluminescence of scheelite and hydrozincite are radically different and that these two minerals, therefore, may be readily resolved through their emission lifetime characteristics. It is in the realm of time-resolved measurements (lifetime characteristics) that Scintrex has made its major advance in the Luminex method. With the exception of some work by Exxon confined to uranyl minerals, to the best of our knowledge, no systematic scientific investigation has been carried out in the field of time-resolved mineral luminescence studies other than the work of Scintrex. Scintrex's findings are that all organic materials and most commonly activated luminescent minerals have lifetimes shorter than one microsecond. In addition, only a relatively small number of minerals - among them those called key minerals, or certain ore and pathfinder minerals - have lifetimes greater than one micro-second. Scintrex is able to characterize these minerals primarily by their emission lifetimes and secondarily by their emission spectral characteristics. By a combination of these factors a mineral index is arrived at. From that, photoluminescent minerals can be resolved from one another with a high degree of probability. At least two spectral channels and two time channels - of which one can be common - are required to apply this mineral index. Ground System A portable hand-held Luminex analyzer based on a modulated mercury lamp has been used to date in Canada, the US, and Australia. The current production model of this device is the LG-2. It has two spectral channels and two time channels for each spectral channel. Figure 2 shows a ground Luminex traverse over the Texas-Arizona zinc prospect in Arizona. The instrument was set so the channel read was hydrozincite-specific insofar as possible. The mineralization in this prospect is known to be hydrozincite and other zinc secondary minerals in limestone. Figure 3 shows a ground Luminex traverse over the AAA uranium prospect in Nevada. The instrument was set to optimize the uranyl response. For comparative purposes, broadband scintillation counter readings were made on the same stations (also shown in Fig. 3). It is apparent that both the Luminex and the scintillation counter results reflect a near-surface distribution of uranyl minerals. It is interesting that no visible uranyl secondary minerals

Jan 7, 1983

Last year in the US alone, about 425 Mt (468 million st) of minerals and coal were beneficiated by froth flotation. This number indicates that from 1983 there was a 10% increase in tonnage of min¬erals and coal beneficiated by the indus¬try. A significant improvement was seen in the tonnage processed by the nonferrous minerals and coal industries. BP Minerals America installed 85 m; (3000 cu ft) flotation cells at the Bing¬ham Canyon mine and concentrator. The new flotation circuit has fewer than 100 cells compared to 2000 flotation cells used in the old plant (Mining Engi¬neering, November 1988). Column flotation use on a commer¬cial scale continues to expand as seen from the interest expressed at the Col¬umn Flotation Symposium (Column Flotation '88). The Magma Copper Co., San Manuel Division replaced all con¬ventional cells with 1.8 x 12 m (6 x 40 ft) column flotation cells for copper con¬centrate cleaning. Also, 1220 mm and 760 mm-diam (48 in. and 30 in.-diam) column cells are operating at the plant in the molybdenum circuit. A commercial Diester Flotaire col¬umn cell for fine coal recovery was installed at the United Coal Wellmore No. 20 plant. The 36.8 m3 (1300 cu ft) cell recovers 13.6 to 18 t/h (15 to 20 stph) of -590 gm (-28 mesh) coal. A similar unit has been installed at Tanoma Mining Co. in Pennsylvania. Various modifications of the column cells are being designed around the world. Jameson (Mining and Metal¬lurgy, 1988) described a new concept whereby the feed and air stream mixture is discharged into a cylindrical column of about 1.2 m (4 ft) height. Recovery and grade of nonferrous minerals have been reported to be better than that in a four-stage conventional flotation clean¬ing circuit. Flotation reagents American Cyanamid and Dow Chemical continued development of a new generation of sulfide collectors. A general feeling is development of new sulfide collectors has not kept up with flotation technology. Additionally, joint efforts between industry and chemical suppliers will likely be necessary to realize the economic benefits of the new technologies, since new chemistries respond differently compared to the conventional collectors. Flocculant development in recent years has been evolutionary rather than revolutionary. Rothenborg reported on development of a new flocculant family (a hydroxymated polyacrylamide desig¬nated S-6703) that has shown consider¬able promise in red mud clarification. Plant testing showed that this new floc¬culant could replace starch and poly¬acrylate and provide significantly higher overflow clarity. Barol Kami (Siirak) and Cleveland¬Cliffs (Hancock) reported development of an amphoteric apatite collector (ATRAC 873) that was used in Tilden's silica flotation process to increase apatite rejection. The collector was engineered for the particular flotation conditions in the complex Tilden process. Significant plant testing with ATRAC 873 showed that this reagent gave significantly in¬creased apatite rejection without any effect on silica flotation effectiveness or selectivity. Electrostatic separation Electrostatic separation is now em¬ployed in the precious metals mining industry to recover gold and silver grills from crushed slag. The installation at Paradise Peak has prompted other op¬erators to consider this application. In another development, attractive potentials for treating very fine minerals (-45 µm or -325 mesh) are being devel¬oped by Advanced Energy Dynamics and by the Department of Energy. Demonstration tests using triboelectric charging/electrostatic separation have been successful on a variety of minerals as well as coal. Magnetic separation Developments in magnetic separa¬tion have transpired on a production scale. Superconducting, high gradient magnetic separation has gained accep¬tance with the successful startup of a second unit treating kaolin at J.M. Huber Corp. This liquid-helium-cooled mag¬net generates 2.0 tesla in a 3-m-diam (120-in.-diam) bore with no power con¬sumption. Wet, high-intensity magnetic separation has been applied to sulfide mineral separations both domestically and abroad. These continuous type of separators are effective in removing residual chalcopyrite and sphalerite from other base metal sulfide concentrates. Separators using high energy rare earth permanent magnets are continu¬ally increasing. Now offered as both drum and roll type, these units are be¬coming a staple in the processing of industrial minerals. Tests using rare earth magnets strategically placed on a spiral concentrator have demonstrated the enhanced recovery of heavy miner¬als such as ilmenite. Classification Although no major technology break¬throughs in classification appear immi¬nent, there is an increasing need for more efficient and cost-effective meth¬ods to make size separations. It is be¬coming more apparent that mineral concentration methods will be more common at very fine sizes, say below 50

Jan 1, 1989

By M. J. Meulendyke

Within the mineral processing Industry. a range of grinding conditions exists which include semi-autogenous grinding (SAG), rod milling. and conventional ball milling. Each of these mill environments presents a unique environment for grinding media, requiring the application of specific physical and chemical properties for optimum grinding media performance. The environments are characterized by varying degrees and combinations of abrasive, corrosive, and impact wear. An extensive test program has been conducted to determine the extent wear rates vary between these different applications. Test results are related to production results, ball size, and mill operating conditions.

Jan 1, 1989

By M. Gershon

Four computerized approaches for coal blending are described and their strengths and weaknesses are explored. Spreadsheet analysis Other than word processing, spreadsheet software is the most commonly used software. Its wide availability and ease of use are two desirable features that have led many to try to adapt it to the purpose of coal blending. These are the two main advantages of this approach. To use a spreadsheet for coal blending, each row of data represents one source of coal. Each column represents a quality of the coal, with the last column specifying the tonnage of that coal in the blend. The calculated figures are the blended qualities, which can be programmed to appear in the bottom row. A trial-and-error approach is then used to develop the best blend. Inserting any blend in the last column provides the blend characteristics at the bottom of the page. If any specifications are not met, the blend can be changed, all calculations being immediately updated. This process is repeated until all specifications are satisfied. A third advantage of this method is that it is exactly the procedure that one would go through if doing this by hand. With a spreadsheet, many more blends can be evaluated in much less time, allowing the designer to try to improve over satisfactory blends to find the best of them. The resulting improved blends or cost savings are a fourth advantage of this approach. There is only one major disadvantage of using the spread-sheet. This is that most probably the best blend is not found. As an inexpensive introduction to computer-assisted blending, which can be easily understood and cost just a few hundred dollars, this is a recommended place to begin. Computerized search Computerized search approaches represent crude first attempts at letting the computer design the blend. Unfortunately, the blends found by these programs are very often less satisfactory than those developed manually. The way these techniques work is that they design, according to some predesigned pattern, a number of different blends and then quickly evaluate them. It is then straightforward to select the best from this sample set. The quality of the results depends on the number of blends designed, the way they differ from each other (the search procedure), the number of sources available, the number of quality specifications, and the severity of the specification limits. Good results are usually obtained for small, simple problems. At best, the results obtained are inconsistent from one blend to the next. Programs of this type are advertised in the mining literature. They usually mention how many different blends are evaluated, making it clear that this is more than can be tried manually. Expert systems Expert systems use a source of information known as a knowledge base. The knowledge base, usually a set of if-then rules, attempts to reconstruct the deductive reasoning process of an expert in some job capacity. For coal blending, the usual trial-and-error process has an easily recognized pattern of rules that are followed to try to find a better blend. By following these rules, it is possible to home in on the best blend without the exhaustive search required by the previous method and without the manual manipulation of the spreadsheet approach. The use of an expert system accomplishes this. One of the rules may say something like "if BTU is out of spec, then add more in the blend from a source having a high BTU and subtract some from a source having low BTU." In other words, it goes through the trial-and-error process. The process continues until all specifications are achieved and can continue further to try to optimize the cost. Of course, less simplistic rules are also needed. One set of rules would determine maximum changes in the tonnage added or deleted to the blend or from any one source. Other rules would be needed to determine which quality to improve if two or more are out of spec. At this level, the process of building the knowledge base provides the engineer with a deeper understanding of his or her own thought processes. The advantage of obtaining better blends is clear for this approach. Two more advantages should also be apparent. One is that it follows the same common sense logic that is used when doing the blends by hand or by spreadsheet, making it easy to understand. The other is that, like the search procedure, it designs the blend rather than just analyzing manually designed blends. Thus, it has all the good features of both approaches discussed thus far while providing improved results over each. A final advantage is the ease of use and ease of development. The expert system shells that are on the market are very easy to use and can be run on microcomputers. Linear programming Linear programming is an algebraic tool that solves a set of linear equations to yield an optimal solution to a problem. The optimal solution is based on the linear model so the results are only as good as the ability of the linear model to accurately portray the reality of the problem situation. It is fortunate for the coal blending problem that a linear model can be devel¬oped that reflects exactly the problem that is required. Unfortunately, the mining industry has been slow to use this tool. Coal blending applications available that use linear programming take one of three forms. The first, requiring exper-

Jan 12, 1988

By D. L. Kuck

Water ice pillars far underground mine roof support can be frozen and/or maintained and/or melted on demand. The system to do this consists of a refrigeration brine chiller, brine circulation system and disposable plastic containers. Fusion expansion, resilience to dynamic loads, plastic deformation under stress, and non-contamination of coal or ore are unique properties of ice. Lower labor and material costs are economic advantages of ice far mine structural support. Ice brattices can become ice pillars on retreat. For safety, ice pillars can be placed (by remote control, if necessary) in hazardous sites without human entry.

Jan 1, 1988