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By G. Sánchez, S. Seiler, B. Klein, T. Cebeci, P. Bradshaw

The Decar Nickel District is a greenfield discovery by FPX Nickel Corp., of nickel mineralisation located in central British Columbia (BC), Canada. The Baptiste deposit is part of the Decar Nickel District and is a unique deposit containing a nickel-iron alloy mineral called awaruite, with over 2-billion tonnes of inferred resource grading 0.12% Davis Tube Recoverable (DTR) nickel. This deposit represents a significant nickel resource. Awaruite is a high density and ferromagnetic mineral, which could be recovered, along with magnetite that is also present in the samples, using magnetic separation. However, there is still a lack of understanding of the properties of the awaruite and its metallurgical response. This information is imperative for the set-up of the variables involved in its concentration. The aim of this paper is to show and discuss the effect of magnetic field strength for the recovery of nickel from Baptiste deposit samples. Magnetic separation at bench and pilot scale with different magnetic field strengths is evaluated as a concentration method for awaruite. Mineralogical information is provided to support the results and also to briefly assess the variability of DTR nickel within the deposit. The Baptiste deposit is unique and will benefit from a sound scientific understanding of the process solution as well as other ongoing work. If successful, the outcome will lead to the development of a mine. With greater than 2-billion tonnes of inferred resource, the mine would represent a significant new source of nickel globally. Keywords: Nickel ore processing, magnetic separation , awaruite, magnetite

Jan 1, 2020

By K. Narayana Swamy

Experimental results of 3-phase mixing in a physical model of a CCRL for metals refining, at high levels of bottom gas injection (up to a superfIcial gas velocity (Us) of 12.5 cm/min), are presented. A thermal tracer technique was used to elucidate both longitudinal mixing and interphase heat transfer. The results indicate that even under conditions of significant bottom gas injection, it should be possible to maintain acceptably low longitudinal mixing (D. < 20 cm2/s and D/uL < 0.1) in the CCRL. Interphase mass-transfer coefficients of the order of 0.02 cm/s and higher, are predicted from the measured interphase heat transfer coefficients using the mass and heat transfer analogy. Adequate performance is likely to be possible for an industrial CCRL, based on extrapolation of these results to full-scale conditions.

Jan 1, 1996

Application of Gy?s formula is appropriate for calculation of the Fundamental Error (FE) prior to samples being collected at any stage of the minerals process, provided that sampling parameters K and a (alpha) have been determined by calibration of the ores. Two types of calibration procedure are well established in the industry, the Hetrogeneity test and the 32-piece sampling tree experiment. The sampling tree experiment uses the variance and average grade of metal analyses from four series of samples at different nominal fragment size, as the basic input data. Pierre Gy suggested the cube as an appropriate exponent of the nominal fragment size for use in his equation. More recent work suggests that this exponent is variable and characteristic of specific ores and therefore requires calibration. The method described here explains the experimental procedure of the calibration. It is then possible to calculate a sampling nomogram using the sampling parameters K and a. This allows the sampler to determine a suitable protocol for the sampling event that will ensure that the FE does not exceed a predetermined precision at any point in the sampling procedure.

Jan 1, 2007

By C. H. P. Lupis, R. Hocine, G. Bernard

The necessary and sufficient conditions for the stability of a multicomponent phase with respect to infinitesinzal fluctuations are derived and transformed to be written in terms of activity coeffcients and mole fractions rather than in terms of the customary second deritlatives of the free energy. NECESSARY conditions for the stability of a multi-component system were derived by Gibbs as early as 1876.&apos; However, as the usefulness of these conditions is greatly enhanced by the simplicity of their translation in terms of functions of common usage, the present contribution establishes these conditions in terms of activities or activity coefficients-and mole fractions. It was shown in another article2 that not only may these conditions be used for the prediction of the appearance of new phases, but they may also provide a check on the orders of magnitude of the interaction coefficients involved. "Spinodal" decomposition is said to occur when, at constant temperature and pressure, the system is unstable with respect to infinitesimal fluctuations in composition. As a result, the "phases" which appear may be attained through continuous changes in the system rather than discontinuous ones, and, consequently, the free energy of these phases may be described by a unique continuous free-energy function. For a binary system, the familiar curve of Fig. 1 illustrates the case we wish to extend to a multicom-ponent system. The conditions to be written pertain to the decomposition of a system of n moles into moles of phase moles of phase v, ...hen moles of phase 9, where the phases a, ...v, ...9 are—at least initially-arbitrarily close in composition to that of the original phase. Each A, is positive and since the total number of moles n in the system remains constant: Each phase v contains hv(nl +dnY) moles of component (I), ...xV(ni +dny) of component + dnk) moles of component (m). The total number of moles ni in the system remaining also constant, it is clear that:

Jan 1, 1968

By G. Y. Chin, M. T. Dolan, W. L. Mammel

The least work analysis of constrained deformation, first proposed by Taylor and recently modified by Chin, Hosford, and Mendorf to include twinning, has been applied to the problem of axisynmetric flow. Calculations were made, for the case of (111}(110) slip and {111}(112) twinning applicable to fcc deformation. The solutions were obtained by linear programming techniques and with the aid of computer methods. The results show that in axisymnzetric tension the onset of twinning tends to decrease the plastic strength anisotropy as compared with the case of defortnation by slip alone. In compression, however, the strength anisotropy is increased as a result of twinning. The [100] and 11111 orientations and their vicinity are unfavorable for twinning in tension and compression, respecticely. With slight modifications, the present results may be applied to bcc metals deform ing by {110}(111j slip and (112} (111) twinning. Implications of present results to wire texture development of low stacking fault energy fcc materials arc discussed. PREVIOUSLY we&apos; have applied linear programming techniques to obtain solutions to Taylor&apos;s least work analysis2 of constrained deformation of single crystals undergoing axisymmetric flow, such as occurs in an axially loaded polycrystalline aggregate. These solutions yielded values of the parameter M = o/.r = Y/w which relates the external stress-strain (u-c) curve to the shear stress-shear strain (7-y) curve for the crystal. The value of M is dependent on crystal orientation and hence enters significantly in texture strengthening considerations.3&apos;4 Recently the Taylor hypothesis was modified by Chin, Hosford, and Mendorf&apos; to include mechanical twinning. The latter has now been applied to the problem of axisymmetric flow and the results are reported in this paper. Calculations have been made for {111 )( 110) slip and {111 )(112) twinning applicable to fcc crystals. With minor changes in the indices of the slip and twin systems, the present results are also applicable to bcc crystals which slip on (110) (111) and twin on {112)(111) systems.

Jan 1, 1970

By C. A. Fleming, R. G. Williamson

Process development for Eskay Creek began in early 1990 at Lakefield Research, and was initially focused on producing a high-grade/high-recovery concentrate for sale. Owing to the significant base metal sulphide (Cu, Zn, Pb) content of the ore, such a product would have made an attractive feed to a copper smelter, while a gravity and/or flotation flowsheet would have circumvented many of the environmental permitting problems that were anticipated. In the event, it was found that neither gravity nor flotation (nor even a combination of the two) was able to produce a discardable tailing and, in late 1990, attention shifted to the development of a hydrometallurgical flowsheet.

Jan 1, 1995

By C. Massola, E. E. M. N. de Guzmán, M. G. Bergermana

The abrasiveness of a mineral or rock is an extremely important topic in the mining industry and is generally measured by the Bond abrasion index (AI). However, to determine such an index by the Bond test requires 1,600 g of sample with particle sizes ranging from ½” to ¾”, which are not available in certain situations, such as ore prospecting, drilling, and geometallurgical studies. In order to investigate the abrasiveness of smaller-sized sample materials, a modified LCPC test was developed, which allows testing fine materials (i.e., 1.0 mm or smaller) to predict wear in ore processing circuits and anticipate possible failures resulting from changes in abrasive characteristics of the ore being processed. The results for 16 different materials indicated a good correlation with the AI and the modified LCPC, resulting in a reliable alternative for the AI. Keywords: Bond Abrasion Index (AI), LCPC, abrasiveness

Jan 1, 2020

By William D. Monaghan, Michael A. Trevits

Over the period 2000 to 2003, roof falls have accounted for 4 to 14% of the fatalities in underground mining operations. The National Institute for Occupational Safety and Health (NIOSH) is conducting research to reduce the frequency, exposure, and risk of these events through an ongoing program of field and laboratory studies. One area of research involves the evaluation of polyurethane grouting technology that is commonly used to stabilize fractured mine roof strata. Concurrently, NIOSH is conducting work to evaluate the application of ground penetrating radar for advanced delineation of problematic mining areas. In this study, NIOSH partnered with Sub-Technical, Inc. who injected a polyurethane grout (also known as glue) into a roof area of NIOSH’s Safety Research Coal Mine. The mine roof area was scanned using ground penetrating radar technology before and after grout injection in an attempt to determine the extent of grout infiltration. A comparison of the pre-and post-grouting radar records showed a significant change at a mine roof depth of about four to five feet. The interpreted radar records were then compared with drill core information, borescope evaluation of roof-bolt holes in the study area, and underground observations. At this site, the interpretations of the radar records correlated with data obtained from the core holes, borescope evaluations and underground observations. This study showed that ground penetrating radar technology can be a useful tool for detecting changes in mine roof due to the injection of the grout.

By L. E. Murr, P. J. Smith

A study has been made by transmission electron microscopy of thin foils of 304 stainless steel fatigued external to the electron microscope in reversed bending, and of thin foils fatigued directly within the microscope in alternating tension. The build-up of stacking faults in the thin foils during fatigue zoas correlated with the dislocatirm structures found in thin films prepared fror fatigued bulk specimens. The performance of the special devices designed for fatigue of thin foils so outlined and the importance of alternative methods of preparation of more uniform fatigue specimens bY vapor deposition are emphasized. INVESTIGATIONS on fatigued bulk aluminum1,&apos; and stainless stee13j4 have revealed the existence of dislocation substructure on examination by transmission electron microscopy of electrolytically thinned foils representative of these bulk specimens. While this technique has proved extremely valuable, it has several shortcomings. First, the method of fatiguing bulk specimens and then thinning to foil for electron-transmission observation allows only one observation of internal structure at any one portion of the fatigue life. Second, thinning the bulk fatigued specimens to foil results in the loss of at least one original surface. Thus, what one sees in the remaining electron-transparent sections is an internal dislocation or fault structure which in many cases cannot be correlated with the original surface markings. This is an undesirable feature, since it is well-known that metal surfaces play an important part in the fatigue process.5 An obvious third undesirable feature of the thinning-from-bulk technique is the fact that static observations have difficulty (in the case of fatigue) explaining the mechanism of a dynamic process. What is required then is a method whereby a selected thin area can be continuously observed either while undergoing cyclic deformation or at various fixed stages of fatigue deformation. While Murr and wilkov6 have reported some success with an apparatus designed to fatigue thin metal foils directly within the electron microscope, the nature of the specimen-mounting procedure and the mechanical features involved in the adaptation of the fatigue device to the electron microscope make this method difficult to operate. It was not possible, for example, to make frequent observations of a selected area because of difficulty in maintaining a chosen area in a stable viewing position inside the electron microscope. Except for the build-up of a dislocation substructure and what are commonly referred to as "slip striations", little else has been reported from observations on thin-foil sections prepared from bulk fatigue specimens. segal17 has found "slip striations" in stainless-steel fatigued specimens which were electropolished from both sides, but gave no explanation as to their origin or identity in terms of lattice imperfections. The research to be reported in this paper was undertaken with the following objectives in mind. First, an attempt was made to devise a technique or techniques whereby thin metal foils could be fatigued and repeatedly observed by transmission electron microscopy. Second, it was hoped that some correlation could be made between deformation striations found in fatigued thin transmission specimens and thin foils prepared from bulk fatigued specimens. These investigations illustrate quite convincingly that a feasible method is available for the direct study of the fatigue mechanism and similar dynamic phenomena in thin transmission specimens inside the electron microscope. I) EXPERIMENTAL METHODS Three modes of specimen fatigue and observation of fatigue damage were used. These involved fatigue of thin-foil specimens in a special arrangement external to the electron microscope and observation of a selected area at various stages in the fatigue life, the fatigue of thin-foil transmission specimens inside the electron microscope, and the fatigue of bulk specimens external to the electron microscope followed by thin-foil preparation for direct observation at predetermined stages. Design of the External Fatigue Clip and Specimen Holder for the Hitachi H.U.11 Electron Micro-scope. The purpose of the fatigue clip was to provide a reversed bending fatigue stress to a thin-foil transmission specimen outside the electron microscope. In order to accomplish this, a flat-bottomed, U-shaped brass clip was made as shown

Jan 1, 1965

By K. Kasas, J Kermeci, S. Vujic, S. Secei, P. Kermeci

On the ‘Majdan III’ open pit mine, supplying with brick clays the production plants of the industry of building material ‘Potisje-Kanjiza’ from Kanjiza, a modern ECS (excavator-conveyor-spreader) complex was built, integrating four bucket excavators, six conveyors and one spreader into a whole. This complex connects the mineral-exploitation unit with the final brick-products plant of the company. Monitoring and management of the ECS complex is carried out by modern computer-supported information-management system (IMS) implementing most modern measuring-regulation, computer and GPS equipment. It was concluded that, for safety reasons, the functions of the IMS should be developed by a component of active visual monitoring of the ECS complex. For this purpose, the task of making a project on intelligent system for visual monitoring of the ECS complex was entrusted to the Department of Computer Application at the Faculty of Mining and Geology, University of Belgrade. This paper gives a review of basic project solutions. Keywords: Automation, process management, information management technology, visual system, intelligent systems, TV monitoring, surface exploitation, clay, Majdan III, Potisje-Kanjiza.

Jan 1, 2003

Following a short review of selected literature, a back analysis of stress measurements of stress regeneration in a closed mini-longwall is shown. The agreement is good, lending confidence to the parameters used in the proposed numerical model. Foundation yielding was modelled in the absence of total stope closure. A ?Prandtl? wedge was formed, coinciding with the yield point of the pillar/foundation system. Some theoretical work is used as a starting point for the formulation of a new design methodology for strike or dip stabilizing pillar/foundation systems in deep level goldmines. The existing guideline for the stability of foundations (APS< 2.5UCS) is critically examined. Finally, the advantages of the new approach, and the work required to substantiate the proposed new design methodology, are outlined.

Jan 1, 1998

By Wing G. Agnew

[This report presents the results of tests made by the Mining Division, Bureau of Mines, on the relative durability of manganese-steel drill rods and carbon-steel drill rods for use with detachable bits.]

Jan 1, 1941

By J. L. Llanca

The New Level Mine project (NLMP), the planned underground expansion of the El Teniente mine in Rancagua, Chile, is expected to reach a daily extraction rate of 137 to 180 ktpd upon achieving full capacity. Production is planned to start in the year 2017 and the current plan is to meet that target through two development phases, from the year 2012 to 2014 and from the year 2015 to 2017. To achieve the 2012 to 2014 underground development schedule, the ventilation requirements have been estimated in the range of 189 m3/s (400 kcfm), and cannot be made available without significant modifications to the current system of El Teniente. As a result, a certain number of alternatives were explored to find a solution to this shortfall, for example, adding raises to generate parallel airways and installing fans to reinforce the current ventilation system. From the alternatives studied, the installation of a second main fan (system) in parallel to an existing one was identified as the best solution, and selected for implementation, however the location was not ideal and there were concerns as to the operation of both fans once the second fan was installed. This paper presents the study used to estimate the operational points of both the current and the new fan, and to justify the parallel installation of the additional main fan. An additional computational fluid dynamics study was undertaken to validate the operational point, given the particular geometry of the fan?s location and placement, to guarantee a stable operation of the fans. Finally, the protocols arising out of this work for starting the fans, and operating them in parallel to avoid generating a stall condition and damaging the investment are discussed.

Aug 1, 2013

By Katzer R. Klimpel, J. Sewell

Dr. Roussey Roussev The use of chemical additives on grinding is of significant importance considering the high energy consumption of grinding processes. My research indicates that the dispersant approach explains the effects, in this particular case of wet grinding. Further, the dispersant approach combined with torque measurements give the possibility of clarifying the mechanisms involved when using grinding aids. I find the conclusions derived from the data obtained to be correct and useful for grinding. In general, I agree with the explanations. However, I would like to discuss several additional points that I consider to be important, and in the same time to mention some of my own results from investigations similar to those presented in the study under discussion. The "bed volume concept" and the change of slurry viscosity explain adequately the data plotted on fig. 3, in conjunction with Figs. 1 and 2. However, the significant increase of the average torque in the case of 83% solid with XFS-4272 introduces the necessity of establishing the optimum of percent solid when dispersant is used. For example, the optimum percent of solid for different materials varies. One of the reasons is the material&apos;s mass density. On the other hand, it is necessary to determine the concentration of the chemical used. Because of this, it would be interesting to know how the cited concentration was selected. The supportive discussion and verification by Dr. Roussev, with results similar to that of the paper, is appreciated. I will try to answer the additional questions he has raised. To begin with, the mill was fitted with six lifters of approximately one-quarter inch height. There has been extensive lab and plant level work to understand downstream influences of using dispersants like XFS-4272*. In sulfide ore processing, which is the area in which most industrial scale testing has been performed with this approach, neutral to positive influences have been observed. For example, positive effects (e.g., increased recovery) have been noticed in flotation operations involving ores that have a tendency to produce excessive slimes upon grinding. (1) Also, the use of a dispersant has been shown to demonstrate a positive influence on classification by improving the sharpness of separation and preventing a decrease in d50 value that usually accompanies increasing flow rates to classifiers.(2) The biggest potential downstream problem is in thickening, which at the dosages involved, has not been a problem in plant scale usage. The commercial price of dispersants like XFS-4272 is quite variable depending on source, concentration, etc, but a typical cost of XFS-4272 to achieve a 10% increase in throughput in industrial mills has been between 20 and 35- US per ton of feed ore (1981).

Jan 12, 1982

By F. A. Forward

Introduction The main line of ascent in the development of the nickel industry may be traced back through the International Nickel Company of Canada, Limited, to its earliest antecedents, the Canadian Copper Company and the Orford Copper Company. Mining geology is but one aspect of the overall development of this organization, and the stress it has placed on geology grew according to the need. In the early days, intensive geology was not required because ore supply was not one of the main problems of this or any of the pioneer companies. The difficulty then was to find economic methods for reducing the ores to nickel and copper, and markets for absorbing nickel in the face of a limited demand from consumers heavily prejudiced in favour of the New Caledonia product. "Very early in the history of the region it was patent to everyone that to share in the full benefits of the industry the same individuals or company must control the whole of the operation necessary to manufacture the finished product&apos; (1, p. 45). These conditions were fulfilled for the International Nickel Company in 1902 when the Canadian Copper Company (incorporated 1886), with its ample ore supply, took the initiative to merge its interests with those of the Orford Copper (Refining) Company (incorporated 1887) to form the new company which, with reorganizational changes, emerged as the producer of the overwhelming bulk of the world&apos;s nickel. The Mond Nickel Company, Limited, entered the field in 1899 with a refining process, and over a period of years acquired ore through purchase of mining properties. This Company operated successfully and independently until 1929 when its assets were joined with those of the International Nickel Company in order to permit the most economic exploitation of the Frood-Stobie orebody in which both Companies were interested.

Jan 1, 1948

By C. T. Cox

The title of this short paper necessarily implies that friction articles comprise a distinct and unique field and are different from the other metal-powder articles, such as bearings, electrical contacts, and magnets. However, this distinction is rather hard to define in that it is really one of degree and not Of kind. It would appear that the main distinction is that friction are are articles of rather large pressing area. In other words, they are articles in which the area Of the mold in which the metal powder is pressed is relatively large. Other articles made from meta1 powders are generally of rather small area, usually a few square inches, while in friction articles the area ranges up to several hundred square inches. The satisfactory production of meta1-powder friction articles involves many production problems and a large number Of these are accentuated by the large area&apos; Since it is impossible in the short space of this Paper to describe adequately all the problems involved, I have thought it best to merely mention some Of them and to place particular emphasis upon a problem that is common to all metal-powder articles, although it is of greater importance in the making of friction articles. This problem has to do with the effect On the properties of a friction article of small variations in the composition. However, before discussing the problems, it is probably appropriate that some mention be made of the limitations on the use of friction articles. Most engineers are familiar with the general field that can be characterized as constituted by clutch facings and brake linings, and undoubtedly have heard many stories of how metal-powder friction articles have had a service life 10 times as long as nonmetallic friction materials, and of instances where metal-powder friction articles have operated satisfactorily where no other material could be used. These instances should not be regarded as criteria for the assumption that metal-powder friction articles are capable of universal use in the friction field and will always outperform other materials. On the contrary, metal-powder friction articles are unsuitable for numerous applications, either on a performance or on a cost basis. Metal-powder friction articles will not replace wooden block brakes for wagon wheels nor cast-iron brake shoes for railway car wheels, to mention just two obvious examples. Metallic friction articles cannot be used where they must act as heat insulatorsl for they have a relatively high thermal conductivity as compared with asbestos. This is a detriment in some uses, as in certain airplane brakes having hydraulic actuators provided with rubber seals. The metallic friction material readily transfers the heat developed at the braking surface back through the material to the rubber seal and destroys it. Within its limited field, metal-powder friction material has proved satisfactory, but many problems are involved in the Selection of the proper material to use in an application and in the commercial pro-

Jan 1, 1945

By R. Strydom, J. H. Selby

Published information is available on the radiological impacts of disposing of zircon sand in a landfill. Zircon flour by virtue of its finer particle size presents a different set of issues during disposal. This paper describes two options for disposal of such fine grained materials – namely incorporation into concrete aggregates and agglomeration by addition of cement. The study considers the radiological exposure of the public from such disposal methods and concludes that these options are viable alternatives for the safe disposal of waste zircon flour. The disposal of zircon into concrete aggregates at a rate of 10 per cent produces a sufficiently low effect to allow such aggregates to be used in building foundations or other such mass concrete applications. The use of cement agglomeration methods will also provide a safe method of landfill disposal provided at least 20 cm of soil cover is included.

Jan 1, 2003

By Leigh J. Wardle

This paper describes a numerical method for calculating the three¬-dimensional stresses and displacements induced by tabular excavations in a rock mass consisting of parallel layers of distinct material properties. The method is based on the superposition of numerical solutions for elementary displacement discontinuities in a parallel layered rock mass. The method can be used to analyse complicated excavation layouts such as those encountered in room-and-pillar or longwall mining. The method can automatically take into account the effect of the earth&apos;s surface. The method offers an economic and efficient solution to stress analysis problems which cannot be adequately modelled using two¬-dimensional methods and for which the expense of three-dimensional finite element or general boundary element analysis cannot be justified.

Jan 1, 1984

By Micheal Mitariten

The recovery of natural gas (primarily methane) from coalbed deposits is an established and growing source for the U.S and accounts for over 7% of its total production. The gas from on-purpose degassing is often pipeline quality and requires only compression and dehydration before being admitted to the pipeline grid. However, the raw gas is sometimes contaminated with nitrogen (N2) and/or carbon dioxide (CO2) that can make the gas inadmissible to the transportation pipeline. In general, the N2 must be 4% or less and the CO2 should be 2% or less. In treating gas produced from virgin coal bed or from degassing operations where CO2 is present, amine systems are traditionally used for its removal. Engelhard’s Molecular Gate® adsorption system offers an attractive alternative due to its skid-mounted equipment, low pressure and unattended operation, cost and high on-stream reliability. Natural gas can also be sourced from the residual coal, after the coal has been mined. This source can be the GOB or gas remaining in abandoned coal mines. This source is almost universally contaminated, often with a combination of CO2 and N2. If the source is from air intrusion, the source can also be contaminated with O2. In treating CO2 / N2 contaminated feeds, the Molecular Gate adsorption system removes both of the impurities along with a level of O2 within a single processing step. To date, ten Molecular Gate units are underway with three systems having been installed for upgrading gas from abandoned coal mines. The technology consists of specialty adsorbents and advanced PSA processes that are jointly offered as fabricated packaged equipment by Engelhard Corporation and Guild Associates, Inc. Upgrading requirements, project challenges and project arrangements are discussed in this paper.

Jan 1, 2005

By Ivanildo Hespanhol

"DALYs are a measure of the health of a population or burden of disease due to a specific disease or risk factor. It evaluates the time lost because of disability or death from diseases compared with a long life free of disability in the absence of disease. DALYs are calculated as the sum of years of life lost by premature mortality (YLL) and years of healthy life lost in states of less than fully health, i.e., years lived with a disability (YDL), which are standardized by means of severity weights, thus: DALY=YLL+YLD.WHO has established for wastewater use in irrigation (1) the same reference level of health protection as established for drinking water quality (2), i.e., the additional burden of disease from consuming water irrigated food should not exceed 10-6 DALY(Disability-Adjusted Life Years) loss per person per year (pppy). This level of risk means that a single additional case of disease may occur in a population of 1 million, during a life time (70 years). In a individual basis is equivalent to the occurrence of a mild disease during about 31,5 seconds.Such a restrictive risk is almost impossible to be attained in most developing countries which may not be able to afford the cost of wastewater treatment and of other protective measures, even for restrict irrigation.This paper presents proposals to adapt the reference level of risk to local technical, cultural, economical and social conditions of developing countries on the basis of a risk benefit approach."

Jan 1, 2008