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By Frank H. Skelding

A new, large mine is about to be born. Many years and millions of dollars have been invested in exploration. An orebody has been found and proven. All necessary political and legal work to establish rights and conditions for development are complete. The feasibility studies are favorable. Financing has been arranged. Board approval has been given to proceed. The time has come to engage a contractor to design and build the new facilities in a location, as is the common case today, far re¬moved from the centers of advanced technologic development where the minerals will ultimately be used. A select list of Engineering and Construction (E&C) companies is asked to prepare proposals. At this point the common viewpoint among mining companies is that the company's sole remaining problem, a major one to be sure, is to select qualified contractors to design and build the project at the lowest cost and shortest time possible so that production can start generating a return on investment. The purpose of this discussion is to explore the viewpoint of the large E&C contractor toward such projects. It differs in important ways from that of the client mining company and it is these differences and the reasons for them that must be understood by the client if severe difficulties and misunderstandings with the contractor, starting at the beginning of contract negotiation and continuing through design and construction to final startup are to be avoided or minimized. Often enough, the difference is in degree, not kind, which only serves to obscure the fact that a difference exists.

Jan 1, 1975

By John H. Bassarear

How best to grind? This article compares conventional crushing and grinding circuits to semiautogenous circuits, reviews recent installations of each circuit, and describes seven methods of using autogenous or semiautogenous techniques. In addition, steel and power consumption data are reported and benefits of a dedicated digital computer are discussed. Size reduction is the most expensive operation in most mills. Crushing and grinding are usually the greatest part of capital costs. They often make up 60-70% of total mill operating costs. Picking the proper crushing and grinding method must, therefore, be done with great care, so the best circuit is chosen. In the past 10 years, there has been a strong trend toward using autogenous or semiautogenous grinding in mills throughout the world. Autogenous grinding is favored when the ore is quite competent and a fine grind is needed. Semiautogenous grinding is applied when fine crushing could cause severe problems or when ore varies in hardness or competency. The taconite iron ores of northern Minnesota fit the description for an autogenously ground ore and many are successfully ground that way. Most im¬pressive are the nine lines of 11 x 4.9 m (36 x 16 ft) mills powered by 9 MW (12,000 hp) motors at Hibbing Taconite. Porphyry copper and molybdenum ores fit the description for semiautogenous grinding. Recent installations include Highmont in British Columbia, Canada, and Quintana in New Mexico. Sampling Many mills have been built based on inadequate sampling data or insufficient tests. With the cost of many mills exceeding several hundred million dollars, it is mandatory that geologists, mining engineers, and metallurgists work together to prepare representative testing samples. Simple, repeatable work index tests are usually sufficient for rod and ball mill tests. However, pilot plant tests on 50-100 t (55-110 tons) of ore are frequently necessary for autogenous or semiautogenous mills. Preparation and selection of the test sample is of utmost importance. Procedures for autogenous and semiautogenous mill pilot plant tests are relatively simple for those experienced in running them. Reliable and repeatable results can be obtained if simple, fundamental procedures are followed. The accompanying figure shows a typical conventional crushing-grinding circuit with three stages of crushing followed by ball mills or a rod mill-ball mill combination. This flowsheet is typical of many mills that have been built throughout the world. Also shown is a typical semiautogenous (SAG) circuit with feed coming directly from a primary crusher, and the semiautogenous mill product going to the separation process. Many similar semiautogenous circuits are built today because they are simple and flexible, lend themselves readily to high tonnages, and usually cost less to build and operate. With some ores, it is possible to send mine-run ore directly to the semiautogenous mill, eliminating the need for a primary crusher, as at Benquet's Dizon mill in the Philippines. An autogenous or semiautogenous circuit, as the name implies, uses the ore itself to assist in the grinding process. Generally, for this type of circuit, the ore must be competent so large ore chunks can be used to grind smaller ones. If ore alone is used, then the circuit is autogenous; but if balls are added to supplement the charge, then the circuit is termed semiautogenous. Ore competency is not always a criterion, to break up large pieces and wash away cementing material. Autogenous and semiautogenous mills have been very successful on relatively soft uranium ores where the values are frequently found in the material that cements together the sandstone grains. Autogenous Circuits When an ore is hard and competent, it is always possible it might make good "pebbles" that could be used for fine grinding media. Seven methods have been tried using combinations of autoge-

Jan 6, 1982

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 E. F. C. Ferrett

The benefits derived from the use of main fan evasees or diffusers are well known. If a well designed evasee is fitted to a fan either more air will flow through it or the same air flow rate will be discharged at a lower fan speed. This latter possibility will reduce the air power requirement of the mine, the fan input power and the overall energy costs. Despite these apparent advantages, many reports have been received from the industry of poor evasee performance. After examination, it appears that these problems are often caused by installation difficulties or inaccurate design procedures. The performance of an evasee is affected by several independent factors. Some of these factors describe the evasee geometry whilst others are concerned with the behaviour of the air as it passes through the evasee. This paper shows that the divergence angle is by no means the only ;important parameter which affects evasee performance and that the size of the inlet boundary layer has a significant influence. The performance of evasees of differing geometric shape are compared and the criterion to be used for optimum performance is discussed. It is shown that the commonly used evasee efficiency is a poor indicator of good performance. Recent work by the author and others is evaluated and a simple design. guide discussed. For more sophisticated work, details of a. computer program are provided. Finally, a brief resume of the performance of truncated diffusers is given. Since compressibility effects can be ignored for most mining applications, incompressible flow has been assumed for most of this paper.

Jan 1, 1980

By Craig Ammar

JAMIE DAVIS: Our next speaker is Craig Ammar. He's director of equipment management for Cyprus Climax Metals Company. He has, prior to this assignment, been responsible for maintenance at Bagdad Copper, Cyprus' Miami smelter, and Thompson Creek. Like Jerry, he's very shy and retiring, and doesn't have any strong opinions about maintenance. INTRODUCTION CRAIG AMMAR: The ultimate goal behind implementing a proactive equipment management process is to provide capacity assurance and ultimately increase an organization's ability to generate revenue while reducing operating costs. Targeting such lofty objectives has brought many an organization to its knees, utilizing new maintenance techniques, concepts, and technology aimed at making our lives better and more organized. The root cause of such frustration generally stems from a lack of understanding or support for the fundamentals of implementing a proactive equipment management process. There are just two types of maintenance programs, reactive and proactive. It's an established fact that you need a little of both to run an effective equipment management process, obviously more of one (proactive) than the other. Here are some telltale signs that your equipment management process is in trouble: -Maintenance is performed as a knee jerk reaction when equipment fails. -Repeated and frequent equipment failures occur, with no focus on eliminating the root cause. -Sketchy, inconsistent, unclear preventive maintenance is performed or there is no support for the preventive maintenance process. -No predictive maintenance technology process is in place, or little support for predictive maintenance exists. -Less than 50 percent of your work is generated by the maintenance group resulting from inspections.

Jan 1, 1998

By H. T. McAdams

The logic of regression analysis as an operations research tool is critically examined, and a formal basis for its application to mining problems is developed. The traditional view of regression analysis as a statistical discipline does not provide an adequate basis for evaluating a regression model in a specific area such as ore reserve calculation or process control. In particular, the validity of the residual-sum-of-squares criterion is questioned, and the need for a criterion based on interpolative features of the model is emphasized. Strictly speaking, a regression model is statistically supported only at points at which observations are available, yet inferences are drawn with regard to a continuum. When considered as a mathematical function, therefore, the model is observationally defined only on a domain consisting of a finite number of points. Extension of this domain to an interval of the real line must be based on physical rather than statistical argument. Vector space and function theory concepts useful as a logical framework for a physically oriented problem analysis are discussed and their usefulness demonstrated in a practical problem.

Jan 1, 1966

By Lisa A. Banick, Robert A. Rubin

The lawyer's role in underground construction, certainly for the past 20 years, has been principally that of the advocate in disputes resolution. Disputes in underground construction have been steadily increasing, making the lawyer a more prominent participant in the underground construction process. It is widely believed, however, that this is not a salutory state of affairs. It is our thesis that lawyers ought not be eliminated from the process, but rather that their role should be changed. They should function as prophylactics rather than as swords, i.e., they should be used to prevent or reduce disputes rather than, after the fact, to champion their clients' causes. a. Mr. Rubin is a partner in the New York law firm of Postner & Rubin. He has litigated and arbitrated numerous complex construction disputes. He has also participated in efforts to improve contracting practices on committees of ASCE and the National Academy of Engineering. b. Ms. Banick holds a BS in Civil Engineering from the University of Virginia and is a law student at New York Law School. She is a law clerk at Postner & Rubin.

Jan 1, 1983

By Michael J. Howes

The nature of business in a free enterprise system is to maximise the return on an investment i.e. to maximise the wealth of the shareholders. This is normally achieved within constraints dictated by many agencies, one of which is the health and welfare of the employees. In the mining industry considerable effort has been expended in improvements in this field, however, the major problem still confronting the practicing ventilation or environmental engineer is the determination of what standards he should design for, which satisfy both the economic and health requirement s. Normally the basic health requirements are satisfied by the minimum standards defined in regulations and codes of practice. These are, however, based on an acceptance of a certain risk or lower production potential. A prime function of the ventilation engineer is therefore to financially justify and implement improvements to both standards and systems. The main purpose of this paper is to examine the basis and techniques of providing this financial justification. Changes in existing methods to achieve the same standards but at lower costs are also covered.

Jan 1, 1980

By C. Yao, T. M. Yegulalp

The scale effect on rock properties has been discussed and studied since the introduction of the weakest-link idea by Weibull (1939). In this study, the capabilities of a dynamic lattice network model to simulate failure of rock under uniaxial tension is utilized. A number of randomly distributed microcracks that contribute to the development of uneven stressfields are introduced. In addition, each unit element in the model is assigned a random value representing its strength properties. Each application creates a randomly created specimen that is subjected to uniaxial tension. The specimens are grouped into three sets according to their size. The results of the study show that the scale effect is present in a statistical sense, i.e., the observed statistical distributions of strength for each specimen group is distinctly separate, and they follow the expected inverse relationship between strength and size. The observed probability distribution for each group of specimens give rise to the estimation of a different set of parameters. In this paper, the potential relationships among these parameters as a function of specimen size is investigated.

Jan 1, 1999

By Howard M. Wells

The future is uncertain. In these circum- stances how can we rationally decide whether to commit funds to an investment that may or may not turn out to be successful? To date no certain answer to this problem has been found, nor is one likely to be found in the future. At best we can attempt to assess the possible outcome in terms of probability, taking into account all sources of information that may be available at the time the decision must be made. This subject is addressed with some trepidation and much humility. Any attempt to fore- tell the future is by its very nature controversial. The purpose of ' this .chapter is to present a proposed rationale for decision making under uncertainty which relates the probabilistic risk of the investment to the capacity of the firm to absorb possible unfavorable consequences if they should occur. It is not the intention to propose a cut-and-dried methodology but rather to examine the conceptual philosophy on which a methodology may be based.

Jan 1, 1979

The need for geological control in orebody estimation and modelling is self- evident to geologists and mining engineers engaged in practical day-to-day estimation. It is only fairly recently, however, that attempts have been made to incorporate explicitly such requirements into published accounts of geostatistical estimation; see, for example, Dowd and Scott (1982, 19841, Rendu and Readdy (1982), Dagbert et al. (1984), Dowd (1984), Benest and Winter (1984). In practice, many geological controls in automatic or semi-automatic estimation and modelling are essentially geometrical controls. The aim of this paper is to present two techniques for geological/geometrical control. Whilst the applications are new, neither technique is entirely original and both have been adapted from other fields and sources. Both techniques are, in some sense, types of estimators and/or interpolators of shapes. The first is a method for fitting spline surfaces to control orebody boundary estimation and to unroll orebodies. The second is an application of Minkowski addition to interpolate shapes such as orebody outlines or stope boundaries and to control estimations.

Jan 1, 1986

By Tim Neil, O&apos

The coming years should see moderate growth in the US coal industry. That growth may come at the expense of the oil and natural gas industries. Conoco pegs coal growth at 2% a year, until the year 2000. During that same period, Conoco projects only 0.5% annual oil growth and "a flat or negative trendline" for natural gas. This is compounded by the fact that coal has a delivered cost per Btu that is only half as much as it is for natural gas and only a third as much as it is for oil. So said Ralph Bailey to many of the 2600 attending the opening session of the American Mining Congress Coal Convention, May 12-15, in Pittsburgh, PA. Bailey is chairman of the AMC. He is also chairman of Conoco. While coal's projected growth is not spectacular, "it is in fact almost an assured growth," Bailey said. Weak oil and gas prices will likely prevent faster growth for US coal. Most of coal's increased demand will come from the electric utility industry and expanded steam coal exports. Conoco's study projects that domestic coal demand will be strengthened in the 1990s. By then, the present surge of nuclear power plant constuction will be over. And there will be a lack of acceptably priced, large-scale generation alternatives for utilities. "It is not likely that any electric utility is going to be ordering new nuclear reactors," Bailey said. "And as oil and gas supplies become scarcer and more costly, it is only logical that coal is going to fill the gap." At the same time, Bailey believes the US coal industry must find ways to lower its costs. He said cost excesses can be found in "regulatory overkill, labor, and simply bad habits" hidden by years of high inflation. "Those costs have now been laid bare, because we are going through a pe¬riod of disinflation. We have to put our house in order, particularly if we are going to compete in world markets." Bailey also touched on coal research. "The industry certainly accepts the fact that we must find a way to burn coal as cleanly as possible. A lot of work in that regard is going on. I expect there will be some significant break-throughs." Bailey said the coal industry is being squeezed this year. Last year, coal customers accumulated inventories in anticipation of a major coal strike that never materialized. Now, many utility customers are working down these inventories. So they are not taking deliveries on their coal contracts. But coal use is up in 1985, compared with 1984, Bailey said. So increased coal use, along with supply drawdown, should strengthen the coal market before the year is out, he said. After Bailey's presentation, some 100 speakers addressed policy and technical topics at 15 sessions during the four-day meeting. It was the first time since 1977 that the AMC Coal Convention has been held in Pittsburgh. And this year's attendance was up 40% from the last AMC Coal Convention held two years ago in St. Louis, MO. This year's registrants included 228 companies, 225 manufacturers, and 106 associated members. The only negative was the David Lawrence Convention Center. It was less than ideal. By turns, meeting rooms were too small, too cramped, or too far from one another. The session on longwall mining was so crowded that the doors were propped open so conference delegates could peer in. A concurrent manufacturers' forum session needed 50 more chairs to accommodate those wanting to attend. However, on to summaries of some of the presentations. Coal transportation and export Since Congress approved the 1980 Staggers Rail Act, railroad rates for hauling coal have not been excessive. In fact, rail rates for coal have increased less than 0.5% a year, in real terms, since 1980. Moreover, the market oriented principles written into Staggers are contributing to the improved financial and operational health of the nation's railroads. But no railroad is earning excessive profits. That is the gist of a coal transportation study being completed by the US Department of Energy. William Vaughan is DOE's assistant secretary for fossil energy. He affirmed the thrust of the upcoming report. Vaughan did allow that Interstate Commerce Commission (ICC) regulations on rate reasonableness could permit the railroads to exploit their monopoly power on captive shippers. Luncheon comments later made by Don Hodel confirmed Vaughan's comments on railroad rate justification. Hodel is Secretary of the

Jan 7, 1985

By J. M. Mutmansky

The usual method employed to determine the direction of flow in a connecting airway in advance is to conduct a survey between the two existing nodes being connected by means of the new airway. It is then assumed that airflow will take place from the node with higher pressure to the node with lower pressure. The purpose of this paper is to examine this direction-of-flow problem --using properties of the system characteristic curve for a two-terminal network --and specify some conditions that ensure that flow will take from the higher-pressure node to the lower-pressure node. It is concluded that the only requirement is that all characteristic curves of fans in the network should be strictly decreasing. Five numerical examples illustrate some important properties of the direction-of-flow problem.

Jan 1, 1999

By Andrew S. Prokopovitsh

The Bureau of Mines is concerned with all the approximately 60 industrial minerals, although its research program currently is focused on 10 of them--bauxite, chromite, clay, manganese, phosphate, potash, refractories, sulfur, titanium, and zirconium. To alleviate reliance on imported materials, particular attention is directed to those minerals having a potential for production from domestic resources. Another important consideration is environmental problems associated with the production of industrial minerals, principally in mining and mineral processing operations, The Bureau also is looking at the opportunities to substitute more abundant minerals for scarce raw materials such as rutile, fluorspar, and bauxite. In its overall minerals surveillance, the Bureau's mining and metallurgical research and development are coordinated with its minerals information activities from which reviews, projections, and forecasts identify the potential for critical disruptions and short supply situations.

Jan 1, 1975

By B. K. Mishra, S. P. Mehrotra, Anand Katti

Particle-size monitoring has become routine plant prac¬tice, and on-line measurement techniques have facilitated the proper control and monitoring of particle size. In this paper, the progress on an on-line size measurement technique using a y-ray source is discussed. The tray is emitted from a nucleonic density gauge (NDG) that serves as a slurry den¬sity-measurement device. This unit is calibrated and tested to predict the slurry density. Batch experiments were conducted to study the variation in slurry density of different types of ores, namely, quartz, bauxite and hematite. This data, in turn, is used to predict the size distribution of the solid particulate material making up the slurry. To calculate this size distribu¬tion from the slurry density, the theory of incremental sedi¬mentation is used. Experimental results show that the pre¬dicted size distribution compares well with the actual size distribution, as measured by the Andreasen pipette technique. Finally, a simplified scheme is proposed to monitor on-line size distribution using the nucleonic density gauge

Jan 1, 2000

By I. Nishkov, L. Alexandrova

The kinetics of froth flotation and the three-phase contact (TPC) parameters are studied at temperatures varying from 20°C to 40°C. The material floated consists of glass spheres and a quartz particles with various diameters. Dodecylamine hydrocloride (DDAHCI) is used as a collector. The equilibrium three-phase contact angle is measured with a microscope technique using the modified Mingins-Scheludko method. Using a Wilhelmy method, the temperature effect on the surface tension of the DDAHCI solution is determined. The formation of the thin film on a polished plate of vitreous silica and the expansion of TPC is monitored by means of a metallographic microscope and recorded on a attached camera at different temperatures. The experimental data show an intensification of the flotation kinetics at 30 and 40°C in the case of small particles. Such an intensification is not observed with the larger particles. The cause for intensification of the flotation kinetics is sought for in the dependence of the TPC rate of expansion and induction time on temperature.

Jan 1, 1995

By André Vervoort, Jef Caers

Compound lognormal distributions serve as new generalized distribution laws for analyzing and estimating ore value distributions or related properties such as the average ore grade. These models are an alternative to the well known lognormal distribution. They are the translation of general geological constraints on the genesis of the deposit cumulated in suitable statistical properties. In this paper a maximum likelihood framework is established for estimating the parameters of such laws or parameter functions thereof. It is shown that under certain conditions maximum likelihood estimation is accurate and efficient in estimating the mean value even when relatively few samples are available. The method is based on a numerical maximization of the likelihood function of these models given the data. Confidence limits on these estimates are set up using resampling techniques such as the bootstrap. By this a complete methodology is presented for inference on ore grade distributions such as is shown in an example of gold data from the Merriespruit mine (South Africa) and the diamond size distribution of the Bougban deposit (Guinea).

Jan 1, 1996

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 K. Bragg

During the last several years considerable discussion has taken place on the long term aspects of uranium tailings management. These discussions have centered around a variety of topics which in turn lead to a variety of opinions. In order to come to grips with the various differences of opinion and points of view, the Atomic Energy Control Board has decided to prepare, as an interim measure, a list of proposed close-out criteria for uranium tailings management facilities. It is important to keep in mind that the criteria set out in this paper are proposals and are intended to initiate a continuing dialogue between the uranium mining industry and the various regulatory and government agencies. It is envisaged that this dialogue would continue for a period of from six to twelve months after which some final form of these criteria would be issued and applied to the active uranium mining facilities. In attempting to understand the reasons why the Atomic Energy Control Board has decided to propose these criteria now instead of at some future point in time, it is necessary to look at a number of existing facts. One of the most important of these is that something in excess of one hundred million tonnes of tailings currently are placed in various tailings management facilities. Furthermore, the rate at which tailings are being deposited into such management facilities is on the increase and this increase is expected to continue over the next five to ten years. The management of these tailings is currently covered under the Mine Facility Operating Licences issued by the AECB. Implied within these licences and supporting documents leading to them, are requirements for the conceptual approach to be used at abandonment. There is however, no current requirement for a detailed study on the engineering or financial aspects of such abandonment procedures. This is a gap which the Board feels must be addressed. There are, at this time, various initiatives underway both in Canada and within the international community which are attempting to address the problems and concerns of the very long term management of tailings. For example, current research in Canada which is composed of two components, one by the AECB dealing with purely regulatory aspects and a second major coordinated program under the direction of the Department of Energy, Mines and Resources and in particular by CANMET is going to deal with the technical problems. On the international scene

Jan 1, 1980

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