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By Siegmund Babendererde

Introduction Lyon, with 1.1 million inhabitants, is the third largest city in France after Paris and Marseille. It is a lively industrial centre. Lyon lies at the intersection of many transport routes and at the fluence of Rhone and Saone. Like all large cities, Lyon is attempting to alleviate inner city traffic problems by constructing a metro. Metro construction in Lyon began with tunnels built by cut and cover methods along the streets. Deep diaphram walls, which were back anchored and toed into imperveous strata, formed the excavation walls. It is a very economic and simple method. However during the construction period, it has the disavantage of strangling urban life for several years. It is therefore increasingly being replaced by subsurface tunnelling methods. As it was decided to build the metro tunnel between the Guillotiere and St. Jean stations, and thus cross under the Rhone and Saone, the client, Semaly, put the contract out for a competitive tender in which the general parameters were defined. Line, level and construction method were left to the contractor. There was an extensive examination of the tenders, during which reference projects from competitors in Japan were visited, as well as in Germany. Finally the consortium of Dragages, Campenon Bernard, Colas and Hochtief was awarded the contract to drive this tunnel section with an hydro-shield and an extruded steel fibre concrete lining, a Hochtief design.

Jan 1, 1987

By Keith G. Wallace, K. M. (Chris) Chmura, Kirk H. McDaniel

The Waste Isolation Pilot Plant (WIPP) performed a feasibility analysis for the purpose of either modifying, supplementing, or replacing its two main mine fans. The WIPP, located near Carlsbad, New Mexico, is a U.S. Department of Energy (DOE) fa¬cility designed to demonstrate the permanent, safe disposal of U.S. defense-generated transuranic waste in a deep bedded salt deposit. Since the centrifugal fans were installed in 1988, multiple op¬erational and performance concerns have been identified. A com¬prehensive engineering study was conducted in 1995 to: 1) Qualify and quantify operational concerns, 2) Evaluate possible alternatives, and 3) Recommend an optimum solution. Multiple system modification and/or replacement scenarios were evaluated with associated cost estimates developed. The study considered replacement with either centrifugal or axial fans. Multiple fan duties are required at the WIPP. Therefore, Variable Frequency Drives and Inlet Vane Controls (IVC) were investigated for centrifugal fans. In-flight adjustable blades were investigated for axial fans. The study indicated that replacing the existing system with two double-width, double-inlet centrifugal fans equipped with IVCs was the best choice. This alternative provided the most desirable combination of: 1) ensuring the required operational readiness, and 2) improving system performance. The WIPP is currently planning to replace the first fan in 1997.

Jan 1, 1997

By Błażej Doroszuk, Robert Król

Mill drums are essential equipment in various industries for the comminution of materials. To optimize their design and operation for efficient and cost-effective processing, it is necessary to understand the behavior of the mill drum under various operating conditions. This study investigates the behavior of a mill drum using a combination of experimental and numerical methods. The factors that can influence the behavior of the mill drum, such as the size and shape of the mill, grinding media, rotational speed, filling level, and material properties, are discussed. Experimental methods can be limited in obtaining measurements of internal processes, so numerical methods such as the Discrete Element Method (DEM) are also used to simulate the behavior of the mill drum. In this study, the experimental measurements of the motion of the grinding media are obtained using computer vision methods, and the numerical simulations are calibrated using the experimental results. A designed experiment approach is used to evaluate the performance of the mill drum under various operating conditions. The results of this study can be useful for the design and optimization of mill drums to achieve better performance and energy efficiency.

Jun 25, 2023

By Milton E. Wadsworth, M. Ken Han

The kinetics of leaching of galena in hydrochloric acid solutions with sulfur dioxide gas have been investigated experimentally. The leaching method is then applied to complex sulfide concentrates to evaluate its selective leaching capability and to develop a new hydrometallurgical lead extraction process based upon the method. The leaching reaction follows a linear rate with an activation energy of 61.9,KJ/mole. The rate Is of first order with respect to the product [H+] [Cl-] . Excel lent selective leaching capability f s demonstrated and an attractive hydrometallurgical process flow sheet is proposed.

Jan 1, 1989

By P. T. Luckie

Analysis of classifier performance independently of a closed grinding circuit configuration may result in a poor match-up between the grinding device and the classifying device. This paper examines the relationship between classifier and grinding device in dry grinding circuits by employing a semi-empirical methodology.

Jan 1, 1980

By D. H. Desy

This research was undertaken to establish the lncendivity of aluminum alloys against rusty steel under frictional impact conditions at typical coal mine fan speeds, to determine any differences in incendivity among various aluminum alloys, and to Investigate less incendive materials as substitutes for aluminum alloys. With a specially designed apparatus, three aluminum casting alloys and three constructional steels were tested for incendivity in frictional impact against rusted steel in flammable methane-air mixtures. Although varying in degree, all aluminum alloys investigated exhibited a high ignition probability under the test conditions; none of the steel specimens tested caused any ignitions under the same conditions.

Jan 1, 1973

By Ivor Hawkes, Malcolm Mellor

INTRODUCTION There are currently around fifteen companies in the United States and Europe manufacturing hard rock tunneling machines. In recent years upwards of 200 hard rock tunnels of lengths up to 12 miles and diameters to the order of 30 ft have and are being successfully driven by over 100 different machines. It has been predicted that within the next decade over 2,000 miles of tunnels will be driven for transportation purposes in the United States alone (OECD Advisory Conference on Tunneling, Washington, 1970) and it is expected that eventually most tunnels including mine drivages will be excavated by machines. All tunneling machines have certain common basic functions; thrust is applied to drive or hold the rock cutting tools into the face, and torque is applied to rotate the cutting tools over the face so that they can continuously break out rock. The speed of head rotation, together with the torque requirement, determines the cutter head power. (The power required to push the head forward is usually negligible.) There are many factors which determine how successfully a given tunneling machine will perform in a given rock but one of the most important is effective utilization of cutter head power. This paper is a review of the specifications and performance of hard rock tunneling machines, obtained from manufacturers' catalogs, published literature, talks with manufacturers and visits to operating machines throughout the United States and Europe.

Jan 1, 1997

"From April 22 to 28, the eyes of the tunneling and underground construction world will be on San Francisco, CA, as the world’s most influential underground construction industry leaders gather at the Moscone Center for the 2016 World Tunnel Congress.Recognized as the most important international annual meeting for the industry, the 2016 version comes to the United States for the first time in 20 years and will be hosted by the Underground Construction Association of SME (UCA of SME). The conference will be held in lieu of the UCA’s biennial North American Tunneling Conference and will bring the strengths and resources of the UCA of SME and the International Tunnelling and Underground Space Association (ITA). The result will be a conference with unmatched technical programming and a showcase of more than 200 exhibiting companies.A program committee led by Randy Essex of Mott MacDonald, Lonnie Jacobs of Frontier Kemper Constructors, Michael Mooney, of the Colorado School of Mines, Priscilla Nelson, of the Colorado School of Mines and Amanda Elioff of Parsons Brinkerhoff formed the program committee and worked for more than two years to build the program. The result is four technical sessions with five tracks in each session and 185 oral presentations.“One challenge was the sheer size of the group that would be assembled, perhaps 2,500 attendees or more, and the large number of abstracts we were likely to receive,” said Essex. “ We investigated extending the conference a fourth day, but that was not workable with the Moscone Center. We settled on having five concurrent technical tracks – something that has not been attempted in past NAT or RETC conferences to my knowledge. The next step was to develop suggested session titles that would span the breadth of subjects that would interest conference attendees as well as serve the conference theme.”"

Apr 1, 2016

By J. C. Zelanko

The U. S. Bureau of Mines conducted a multi-faceted geomechanics research project at a bump-prone longwall coal mine in eastern Kentucky. This mine presented a unique opportunity to study coal mine bumps in that the problem appeared to be confined to areas beneath a sandstone channel of limited areal extent. The Bureau's research plan sought to exploit the uniqueness of the site by monitoring strata behavior and longwall support reactions as the longwall face approached and passed beneath a sandstone channel. The study incorporated static pillar stress and strata deformation measurements, shield support leg pressure measurements, and microseismic monitoring as well as geologic mapping and the collection of observational data. Data collection was underway when a major coal bump occurred on the longwall face at the mine. Pillar behavior (load and deformation), shield loading, and microseismic activity were monitored prior to, during, and after the bump. Observations in the tailgate indicated that these pillars were failing prior to and after the face bump. Shield load data which were evaluated in an effort to identify trends which could be used to forecast coal bumps appear to provide a measure of the effectiveness of destressing operations conducted on the face (e.g. shot firing). Analyses of microseismic data revealed anomalous values associated with microseismic "energy" prior to the face bump. In addition, microseismic source location data and underground observations provided some insight as to the sequence of pillar and face bumps.

Jan 1, 1991

By Kenneth J. Miller

A novel two-stage froth flotation process to remove pyritic sulfur from fine- size coal is described. The process consists of a first-stage, standard coal flotation step in which high-ash refuse and some of the pyrite are removed as tailings. The first-stage clean coal froth concentrate is then repulped in fresh water, and a coal depressant, a pyrite collector, and a frother are added to float the remaining pyritic material. Laboratory and pilot plant flotation results with coals from the Lower Freeport and Pittsburgh beds are given. The pilot plant test results show that up to 80 percent pyritic sulfur reduction was achieved with the Lower Freeport bed coal and up to 50 percent with the Pittsburgh bed coal. Laboratory and pilot plant results were in excellent agreement, indicating that the process is a viable means of removing much of the sulfur from some coals.

Jan 1, 1974

By Francis Martino

There are numerous techniques and predictive models used by geologists and mining engineers to define coal reserves and plan mines. The traditional reserve estimation methods commonly used include the isopach, triangular, polygonal, inverse-distance weighting, weighted-moving-average, and trend-surface methods. Geostatistically-based estimation techniques are now being examined by many geologists and mine planners as a superior alternative to these traditional methods. With today's coal mine development costs often exceeding $100 million, and power generation $1 billion, it is logical that a technique that can indicate the degree of confidence associated with a reserve estimate (fuel supply), and thus also the degree of risk, is highly desirable to the coal producer, the financiers, and those desiring to commit to coal utilization under short or long-term supply arrangements.

Jan 1, 1983

By N. P. Titkov

This paper presents the results of laboratory and pilot plant investigations for the development of efficient methods of beneficiating hematite ores from the Krivoi Rog, Kursk Magnetic Anomoly, Olenogorsk, and other localities. The tests included gravity, magnetic (in a high intensity field), flota¬tion, and magnetizing roasting methods. It was possible to develop efficient beneficiation methods depending on the mineral composition of the ore and degree of dissemination of ore and gangue minerals. The paper shows the relationship between the iron silicate and quartz content of the ore and the technologic indices of the various beneficiation methods. Some of the conclusions based on these investigations and the technical and economic computations related to the cost of one ton of pig iron produced from concentrates obtained by the various beneficiation methods are: 1. If the hematite ore is not disseminated uniformly, it is expedient to use a combined gravity and flotation process. Ore particles up to 50 am. in size are beneficiated by gravity (heavy suspension, jigging, and others) and yield a lump concentrate. The middlings from this process are recrushed and floated; 2. Finely disseminated hematite ores, containing small quantities (less than 5 percent) of iron silicates, are most effectively beneficiated by flotation. Anionic (sulphate soap, tall oil emulsion with various foam depressors) as well as cationic collectors may be used. Depending on the mineral and chemical composition of the ore, it is possible to obtain concentrates containing up to 65 percent iron with an extraction up to 94 percent; 3. Finely disseminated, mixed hematite-magnetite ores may be beneficiated by flotation or a magnetic separation-flotation process; 4. Finely disseminated hematite ores, containing large quantities of iron silicates and earthy hematite ores are most efficiently beneficiated by the magnetizing roasting method. This method will yield concentrates containing up to 68 percent iron with extractions up to 90 percent. Although beneficiation by the magnetizing roasting process is costly, it will nonetheless, when employed on this type of ore, yield the least expensive pig iron.

Jan 1, 1960

By Emily Muto

LiDAR technology has made it possible to map large areas of underground mines accurately and rapidly in three dimensions. MSHA Technical Support began implementing LiDAR technology in conjunction with the Agency’s Pillar Collapse Initiative, using scans to determine width-to-height ratios (w/h) of pillars adjacent to mass collapse areas and to conduct risk assessments for global pillar stability in U.S. stone mines. This work quickly expanded to include change detection, such as measuring many pillars to show which are deteriorating over time. Change detection has also been used in ground falls and squeeze areas to see if they have continued to propagate. LiDAR technology supports accurate data acquisition of unstable mining conditions from safe distances. For example, once the LiDAR scan has been processed, it can measure roof fall cavity heights and volumes with the user at a stable ground location. Some LiDAR scanners can collect geologic data, such as joint orientations.

Jun 25, 2024

By H. W. Hitzrot

Introduction Mechanical classifiers consist of a settling tank with parallel sides and a sloping bottom equipped with a mechanism which continuously agitates the pulp and removes the settled solids. The functions served by mechanical classifiers include the following: (1) allow the particles larger than the desired size to settle in the tank and provide an overflow product with a minimum of oversize particles, (2) produce an overflow product of sufficiently high solids content to meet the requirements of the subsequent processing steps, (3) agitate the pulp and permit separation of the entrapped undersize particles so they can report in the overflow product, and (4) drain and remove the underflow solids from the settling pool. Various types of mechanisms have been used to agitate the pulp and remove the settled solids, which include: (I) endless belt and chain drags, (2) reciprocating rakes, (3) helical flights mounted on a rotating shaft which extends through the settling pool, (4) helical flights inside of a rotating drum which contains the classifier pool, (5) troughed conveyor belts forming the settling pool in the concave curve of the belt closely following the tail pulley, and (6) low-speed impellers agitating the underflow settled in the apex of cone-type mechanical classifiers.23 The principal use of mechanical classifiers has been in closed¬-circuit wet grinding; however, this application has been widely displaced over the past few decades by the hydrocyclone. The hydrocyclone installation, including its feed pump, offers lower capital costs and requires less floor space. Nominally it produces an overflow prod¬uct of higher solids content, compared with a mechanical classifier, for comparable classification size up to 400µm (35 mesh). However, these advantages of the hydrocyclone are being gained at the sacrifice of some of the advantages of the mechanical classifier. The mechanical classifier requires less power and has lower maintenance costs than the hydrocyclone and its feed pump. The underflow product from the mechanical classifier can have a higher solids content and contain less entrapped undersize particles than the comparable product from the hydrocyclone. Consequently, it is capable of operating at a higher classification efficiency. A reduced circulating load24, 25 results under these conditions in a closed-circuit grinding application. Other applications for mechanical classifiers include desliming, dewatering, and washing operations. Sand-slime separation may be achieved using one or more stages of mechanical classifiers. Typical applications would include washing and deslimining of concrete aggre¬gate or sand; glass sand; abrasives; oyster shells; phosphate rock; iron, nickel, and chromium ores; alumina; zeolites; solar salt; and precipitates from chemical processing. As an example for the latter, Bitzer26 recommended the use of mechanical classifiers for countercur¬rent cementation-in-pulp of copper from the leach liquor. Similarly, mechanical classifiers are used in uranium processing27 for separation of the barren sands from the pregnant leach solution. Depending on the particle size and the effectiveness of the sand¬slime separation, the sand product from mechanical classifiers may be drained to solids content approaching 84%. Thus, mechanical classifiers are frequently used as dewatering equipment for various applications, such as: 1) Make a product having suitable solids content for subsequent transport by belt conveyor. 2) Provide a drained product to reduce cost of drying. 3) Provide a drained, washed, heavy sand product for return to the circuit. 4) Recover fine values from dilute plant effluents from coal, sand, phosphate-rock, and iron-ore washing plants and from steel-mill flue¬dust scrubbers. 5) Drain residual reagents of a preceding process stage prior to conditioning with reagents of different characteristics, e.g., cationic¬anionic flotation of phosphate rock, iron ore, etc. Design and Operating Features The proper selection of mechanical classification equipment re¬quires that the properties of the solids and liquid are adequately de¬fined. The following descriptive information regarding the solids is desired: feed rate, chemical and physical composition, density, tem¬perature, size analysis, and desired separation size. For the liquid used, the following data would be needed: feed rate, density, viscosity, pH, and temperature. Settling Area. The pool area required to permit a particle larger than the separation size to settle depends on the density and shape of the particle and on the density and viscosity of the pulp within the classifier pool. These criteria of the solids and pulp determine the settling rate which, in turn, determines the settling area required. Determination of the settling rate by long-tube batch tests can be used to calculate the settling area. A theoretical approach for estimat¬ing the settling area requirements is discussed in Chapter 1, Classifica¬tion Theory. This procedure can be used when neither test data nor empirical data from similar operations are available. Data on settling-area requirements and settling rates have been compiled by the manufacturers of mechanical classifiers. The approxi¬mate settling area required for a particular separation size can be estimated by using the curve shown in Fig. 65. This curve applies for closed-circuit grinding applications. For dilute velocity classification in open circuit, desliming, the length of the overflow weir, W, multiplied by the weir's mean distance from the feed opening, E, is used as the design criterion, instead of the settling area, in sizing the classifier. The area requirements, W X E, for dilute velocity classification can be expressed in terms of volumetric flow, Q, and settling rate, Rs, as follows: W x E = Q/(18.06 Rs) where W and E are feet, Q is gallons per minute, and Rs is inches per second. Overflow Weir. The hydraulic head, and thus the velocity at which the overflow crests the overflow weir, is one of the factors controlling the particle size of classification. Consequently, the length of the overflow weir must be designed to provide the overflow velocity which allows the particles larger than the desired size of classification to settle in the working area of the pool. Obtaining the necessary

Jan 1, 1985

By Byron R. Berger

Epithermal Ag-Au deposits form at low to moderate temperatures in near-surface environments. Historically, these deposits have been the source of high-grade ores. Increases in the market prices for gold and silver make lower-grade ores economically viable when available in large tonnages. Both the high-grade and bulk-tonnage ores are a consequence of the same processes, and general models of epithermal systems can be useful in the search for new precious-metal resources. A detailed study of deposits at Round Mountain, Nevada; Balei, Russia; Creede, Colorado; Guanajuato, Mexico; and Chanarcillo, Chile, indicates that the hydrodynamics of the fluid systems as determined by fracture geometries, the permeability, and composition of the host rocks are the key factors in the creation of both high-grade and bulk-tonnage epithermal deposits. End-member models that explain the range of observed deposit characteristics are: (1) the hot-springs deposition model; (2) the stacked-cell convection model (where mineral deposition occurs laterally along the interface of two partially separated fluid reservoirs); and, (3) the closed-cell convection model (where deposition occurs in vertical zones due to the relatively unimpeded vertical flow of hydrothermal fluids). Boiling and fluid mixing appear to be agents of precious-metal deposition with the self-sealing of the hydrothermal system being an important adjunct to boiling. Imaginative application of model concepts in exploration has led and can lead to the discovery of new high-grade and/or bulk-tonnage precious-metal deposits.

Jan 1, 1982

By W. Burger

For the development of deep, hard rock, mines fast access to the orebody is critical. In some cases the mineralized area is more than 1,500 m (5,000 ft) below surface. Excavation of shafts or declines is typically on the critical path of the project schedule. Saving time on those activities can significantly increase the net present value of the mining project. Mechanical excavation methods are a step-change in excavation performance and labor safety compared to drill-and-blast operations. In hard rock conditions, roadheaders cannot be used effectively, so disc cutting is the first choice. For excavation of declines, tunnel boring machines (TBM) can be used in many cases. These provide, in certain rock conditions, considerably higher production rates com-pared to drill-and-blast excavation. Herrenknecht AG has developed a vertical shaft sinking machine (VSM) that is able to excavate shallow shafts in soil and medium soft rock. The ground is excavated by a roadheader boom. The muck is removed by a slurry system or a pneumatic system in combination with hoisting of skips. These machines have been applied successfully on shafts down to 100 m (300 ft). A pre-sink for a deep mine shaft has been excavated by this technology. For deep, hard rock shafts, a new shaft boring system has been developed by Herrenknecht AG in collaboration with Rio Tinto. Based on proven technologies, the system uses a unique arrangement of existing proven technologies. The system integrates excavation, mucking, primary rock support, installation of the final lining and shaft infrastructure. This new system improves the health and safety of shaft construction. Detailed performance estimates indicate significantly higher shaft construction rates are possible compared to conventional shaft sinking methods.

Jun 1, 2010

By G. T. Adel, P. E. Richardson, R. Pazhianur

Cathodic protection using impressed current was employed to reduce mill wall wear during ball milling. Wear rates were determined from weight-loss measurements made on four 1-in.-diam mild steel coupons that were installed flush with the interior surface of the mill wall. Grinding tests were conducted on quartz, pyrite and quartz-pyrite mixtures at pH levels of 4.6, 7.1 and 9.2. Cathodic protection was shown to reduce mill wear by 30% to 60%. An examination of the coupon surfaces using scanning electron microscopy showed that cathodic protection greatly reduced pitting corrosion. The presence of a sulfide mineral, such as pyrite, was found to increase the wear rate significantly, possibly due to galvanic interactions. It was also found that the wear rate is significantly higher than the sum of abrasive wear and the corrosive wear, due to a synergistic effect.

Jan 1, 1998

"The Industrial Comminution Efficiency (ICE) working group, part of the Global Mining Standards and Guidelines Group (GMSG) has engaged a large number of industry professionals representing mining companies, equipment vendors, consultants and metallurgical laboratories with interests and capabilities in the comminution field. These participants have collaborated to develop three guidelines for the assessment of the efficiency of mineral comminution circuits. Two of these guidelines deal specifically with power based modelling techniques to quantify energy efficiency using widely practiced techniques, those developed by Bond (1961), Rowland and McIvor (2009), and Morrell (2009). The third guideline deals with the sampling and surveying of grinding circuits as is required to provide the necessary information, at appropriate quality, to furnish the efficiency analysis promoted by the first two guidelines. This preprint will focus on the Guideline on Methods to Survey and Sample Grinding Circuits, which is currently in the final stages of peer review and finalization by the GMSG. INTRODUCTION It is important to make a clear distinction on the scope of work of the GMSG guideline for sampling grinding circuits. Many mineral processing practitioners are familiar with the sampling and surveying of comminution circuits, in particular grinding circuits, for performance diagnosis and the identification of optimization potential. These surveys often provide information for population balance modelling of individual comminution and classification unit processes, and as a result require a large amount of information to calibrate and validate the unit models. As a result these surveys are labour intensive, somewhat expensive depending on internal capabilities of the mine site or company, and have a long time span from initial planning to final reporting. They also require a high level of expertise to process the survey data, simulate the circuit and make sensible recommendations on follow up actions. As a result of these factors full grinding circuit surveys are not a common occurrence at a large number of facilities, and several years may pass before follow up surveys are conducted. In the ensuing gap between surveys, the efficiency of the grinding circuit must often be taken on faith, and this is considered an unacceptable lapse in an environment of strained natural resources and low commodity prices. To support the rapid and productive energy efficiency analysis being promoted by the ICE working group, a much simplified survey and analysis process is required. The process reflected in the GMSG guideline is indeed more conducive to frequent analysis, at a skill level that is well within the capabilities of the average plant metallurgist. As a result it becomes feasible to conduct mini-surveys of plant performance, which can be used to quickly and precisely diagnose the high level impact of process changes. It can also be manipulated by experienced practitioner to provide sufficient information for modelling of the circuit to estimate the impact of process changes, supporting an initial rate and rank exercise to focus plant optimization efforts."

Jan 1, 2016

By Frank J. Skudrzyk, Vladimir F. Petrov

In compliance with the current Russian environmental legis­lation, possible impact of industrial activities on the environment is restricted by acceptable limiting values (maximal allowable concentrations - MAC) of individual chemical substances in the natural environment - water, atmospheric air and soils. These norms have federal status and are valid for the whole territory of Russia. Disposal of the substances, for which no MAC is estab­lished, is forbidden by the law. Many gold mining companies use cyanide in precious metal recovery. This paper overviews the Russian experience in pro­tection of natural water reservoirs from technogenic impact of cyanic technologies. Major toxic compounds, contained in liquid and solid rejects from hydrometallurgical treatment of gold ore using cyanidation, are cyanides (CN), thiocyanates (SCN) and cyanide metal com­plexes. Unlike western classification of various cyanide types, in Russia any inorganic cyanide compounds (simple and in com­plexes with metals), with the exception of iron cyanide com­plexes, are considered toxic and the acceptable limiting value is established for them. MAC is 0.05 mg/I for fish reservoirs and 0.1 mg/I for drinking water. For iron cyanide complexes MAC is 0.15 mg/I for fish reservoirs and 0.25 mg/I for drinking water. Russian norms for thiocyanates are practically as rigid - the acceptable limiting value for them in fish reservoirs is at the level of 0.07mg/l (0.15 mg/I for potassium thiocyanate) and for drinking water - O. lmg/1. Norms for metals are established on the basis of total content regardless of the form in which they are present in water - as cations or complex ions. It should be noted, that in case several toxic compounds of the same limiting value (for cyanides, thiocyanates and base metals the limiting value is toxicological) are present in water. Their allowable concentra­tion is calculated as the sum of actual concentration of each com­pound, divided by the corresponding acceptable limiting value, with the result not to exceed one (compounding effect). Differences in cyanide classification and the necessity to include thiocyanates dictate different analytical methods. This, in a number of cases, results in certain discrepancies in analytical results. Until recently chlorination was used as a basic process of detox­ification of wastewaters. Calcium hypochlorite powder or hypochlorite pulp, prepared of lime milk and chlorine shipped to the plant, were used as a reagent. Chlorination is an efficient method: it allows to completely destroy plain and complex cyanide, in addition to iron complexes, and thiocyanates. A good example of high efficiency chlorination can be found at the Mnogovershinniy mill near the Okhotsk Sea located in the salmon spawning area, for which we designed an automated chlorination plant for tailings dam. Since plant start-up ten years ago, the required concentrations of cyanides and thiocyanates have been kept at the MAC level required by environmental regulatory agen­cies and no harmful affects on ichthyofauna has been reported. One major drawback of chlorination is high cost of the major reagent, as well as secondary contamination of detoxified waters by chlorides. Secondary contamination by chlorides becomes obvious in the course of detoxification of wastewaters of com­plex composition, which require increased reagent consumption. Recent changes in economic conditions in Russia caused the necessity to direct efforts to reduce the costs of precious metals recovery, and in particular, wastewater treatment. We have con­ducted certain work in this direction and obtained positive results. We hope that our experience described below will be of interest to other specialists particularly taking into account the current low gold prices.

Jan 1, 1998

By J. R. Gaw

Recent events pertaining to U. S. energy needs and development of alternative energy fuel resources have made the American public more aware of past and present coal mining operations, and their impacts on the nation's economy and environment. This awareness has developed rapidly due to increased government involvement and consequent media coverage. This is true particularly in the Western states and in Texas. One of the consequences of this increased public awareness is public concern over the perceived and real consequences of mining operations. Emphasis has been placed on potential releases of toxic and hazardous substances, and possible carcinogens. The result of this public concern is a mounting effort at both state and Federal levels to promote stricter laws regulating the mining industry.

Jan 1, 1992