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By Somia Gurunathan, Harry Castrantas

Hydrogen peroxide and calcium peroxide are used to improve the extraction of gold/silver and reduce cyanide consumption in heap leaching and mill leaching operations. FMC's standard grade H2O2 and FMC's Permeox™ solid peroxygen, a formulated product containing cao2, was used for the experimental work. It was found that the rates of release and the longevity of these peroxygens in ore-cyanide mixtures are significantly different. When choosing a peroxygen, one of the key factors is extrac­tion time, with the longer extraction times of heap leaching primarily favoring calcium peroxide and the shorter extraction times of mill leaching primarily favoring hydrogen peroxide. A series of laboratory leach tests showed the choice between H2O2 and CaO2 to be ore and process specific. H2O2 and/or Permeox™ improved the gold extraction in four out of five ores tested. (2 sulfide and 2 oxide). Mixtures of H2o2 and Permeox™ were also found to significantly increase the gold extraction rate. A fifth ore (sulfide) did not respond to peroxygen treatment. In addition, savings in NaCN consumption was obtained with Permeox™. Both peroxygens offer economic incentives to gold processing.

Jan 1, 1992

By R. S. Mateer

Linear programming on desktop computers is commonly used to optimize coal blending proportions. The objective function is usually the cost of the blend. The constraints consist of materials and heat balances as expressed as linear functions of the blend. This is illustrated in Example 1. Inclusion of a sulfur compliance constraint in more complex because the maximum permitted sulfur percentage is not a pre-specified constant. Rather, it is a function of the calorific power of the blend itself. The current limit of 1.2 pounds of sulfur dioxide per million Btu may be expressed as: [Sulfur Max%= 0.6 . Hl10,OOO with H in Btu/lb.] A proper constraint equation may be formed by defining for each coal a function that is the difference between the actual sulfur percentage and the maximum sulfur percentage. This may be regarded us an excess sulfur percentage. For Coal A of Example 1. this would be: [ Sulfur Excess%=0.5-0.6 13,000/10,000=-0.28] This value would be used as the coefficient of the weight proportions of this coal in the blend. The complete constraint equation would then be the sum of such terms for each coal set less than or equal to zero. This is illustrated in Example II. [ ]

Jan 1, 1995

By A. Goulsbra, S. McAllister, R. Dunne

Since 1992, a tailings gravity re-treatment plant has been in operation at the New Celebration Gold Mine to recover aurifer­ous pyrite (Martins, Dunne and Gelfi 1991; Martins, Dunne and Delahey 1993). The gravity pyrite concentrate is ground in a Tower mill to liberate gold (average particle size around 25µm) prior to cyanide leaching. Although the re-treatment plant has met the predicted gold recovery, based on original laborat01y testwork, there is still room for improved gold recovery. This requires enhanced pyrite recovery, especially in the finer size ranges. The application of centrifugal gravity separators would seem to be an ideal means to achieve this criterion. In particular, the Falcon continuous centrifugal separator (Series C machines) would appear to be ideal for this particular duty. A testwork program to evaluate the application of the contin­uous Falcon to recover pyrite from New Celebration ores was unde1iaken over a six month period during the later part of 1997. The work involved laboratory batch testwork, followed by con­tinuous testing of the Falcon Cl0 (2tph to 3tph) and Falcon C40 (l00tph) units. A summary of the results from this evaluation program are provided in this paper.

Jan 1, 1998

By Stephen LaBrooy, David Muir

Gold ores in the geologically more recent rocks are often associated with copper minerals which pose problems of high reagent consumption with conventional cyanidation practice. Many examples exist in northern Australia, Indonesia, Papua­New Guinea, Chile, and Brazil where, despite various treatment options (LaBrooy, 1992), the processing of oxide and transition ores is uneconomic either for copper or gold recovery. Hence, there is a need for a reagent which is selective for gold without leaching copper minerals. The ammonia-cyanide system appears to meet this criterion (Muir et al, 1989; LaBrooy et al, 1991; Costello et al, 1992; Hayes and Corrans, 1992) but it has proven difficult to optimise and apply to a variety of ores due to differences in the mineralogy and reactivity of ores and a lack of understanding of how the system works. Recent work on the mechanism, however, (Muir et al, 1993) has thrown a new light on the problem which should allow better process control. Ammonia­cyanide mixtures behave neither like free cyanide nor free ammonia and too much of either reagent in the mixture is detrimental. The key to the process is understanding how ammonia enhances gold extraction yet inhibits copper extraction in an essentially cyanide environment.

Jan 1, 1993

By Robert Jedrzejczak

The Endako Mine is an open-pit molybdenum mine located in the north central region of British Columbia, Canada, about 960 km (600 road miles) north of Vancouver. Production for the latter part of 1992 was expected to averaged 63.5 kt/d (70,000 stpd). Of that amount, 27 kt/d (30,000 stpd) was the mill feed. This production is achieved with five 11.5 to 14.5 m3 (15 to 19 cu yd) electric shovels, six Euclid R190 and two Unit Rig M120 diesel-electric haul trucks, and three 320 mm (12.25 in.) electric rotary drills. There are three ore zones delineated into pit areas: the Endako, Denak East and Denak West. Present mill feed source is the southeast stage of the Endako Pit. Stripping is carried out in the south wall stage also of the Endako Pit. The mine high grade aggregate is reduced in the primary and secondary crushing circuits before processing in conventional RM-BM-flotation circuits. The majority of the molybdenum sulfide (MoS2) is roasted on site to produce technical grade molybdenum oxide (M003). A portion is further refined and treated to yield a 99.9% pure MoS2 product.

Jan 1, 1993

By Samantha Smith

Nautilus is completing the world's first environmental impact assessment (EIA) of seafloor mineral extraction and Nautilus has gained extensive experience conducting environmental studies in subsea environments. Nautilus is currently working on the Solwara 1 Project in the Bismarck Sea, Papua New Guinea, where high grade seafloor massive sulfide deposits lie at ~1600 m water depth. Conducting an EIA in the deep sea presents some interesting and exciting challenges. Seafloor studies commenced in December 2005 using a remotely operated vehicle (ROV) fitted out with highly specialized scientific equipment to conduct water quality, sediment, biological and oceanographic studies. During 2007 and 2008, Nautilus launched two two 30-day ROV programs dedicated to environmental baseline studies and during this campaign, over 550 biological, sediment and water samples were collected and over 20,000 seafloor observations were logged. On board specialists included an international team of experts in the field of deep sea marine science. Collaboration between industry and scientific research institutions allows data to be collected for the EIA but also provides an extraordinary opportunity for researchers to access sites that might otherwise remain unobtainable to science. This presentation will review the studies conducted as part of this exciting project. Keywords: Seafloor Massive Sulfides, Environmental Impact Assessment

Jan 1, 2008

By Jaye Pickarts, Bret Boster, Jack McPartland

Pegasus Minera de Chile, Ltda. is completing three phases of metallurgical evaluation on the Pullalli project to develop a preliminary process flowsheet. A project feasibility study is in progress. The feasibility study includes a proposed process flowsheet designed based on results from the multiple stages of metallurgical evaluation. Phases I and II of metallurgical evaluation included laboratory scale heap leach and milling cyanidation testwork on multiple drill core composites and bulk ore samples from the Pullalli Project. Phase Ill included pilot scale milling/cyanidation testwork on Pullalli drill core composites. The proposed flowsheet includes selective mining and separate processing of low grade and high grade ores. Low grade ore will be crushed and heap leached. High grade ore will be milled leached for 12 hours in an agitated cyanidation circuit. After 12 hours of leaching, sands and slimes will be separated and the sands will be washed using a counter current cyclone (CCC) circuit. Partially leached and washed sands will be added to the crushed low grade ore for heap leaching treatment and permanent placement. Partially leached slimes will be thickened in a high capacity thickener and will be processed in a CIP circuit. Leached slimes will be placed in a tailings impoundment.

Jan 1, 1996

By M. Di Tommaso

Acid Mine Drainage (AMD) is a quite diffuse environmental problem in dismissed sulphur mine districts. AMD is related to sulphur oxidation of abandoned tailings, generating heavy metal-bearing streams with high iron and sulphate contents and low pH. Treatments of AMD aim firstly to increase the pH to reduce its leaching power causing the further release and mobilization of heavy metals through soil solution and groundwaters. Increasing the pH also allows the precipitation of iron (III) (involved in sulphur oxidation and then in AMD generation) and the partial removal of other toxic components such as arsenic. pH adjustment and the reduction of the high concentration of iron are also necessary for the successive biological treatment in permeable reactive barriers (PRB) with sulphate reducing bacteria (SRB) (II step, biologically mediated precipitaton/biosorption) to avoid the rapid plugging of the barrier (for the large amounts of iron precipitates) and to ensure neutral pH conditions for SRB growth. In this work the first step (chemical precipitation) of a combined chemical and biological treatment of AMD is presented. Experimental data from column tests using carbonate stones to remove iron and increase pH were reported. Toxicity tests have been carried out on the treated wastewaters by Lepidium sativum.

Jan 1, 2006

By George A. Hoffman, Richard J. Proctor

INTRODUCTION We will discuss here only the subway construction phase; that is, two to five years at a given location--not the long-term analysis. We also will compare some tunnel construction methods used for BART and in Los Angeles. Typically, urban planners and engineers try to balance a new mass transit system to include tunneled subways, cut-and-cover construction in city streets, and elevated guideways. Their decisions are based on many factors, most of which can be quantified. But there are some socio-economic-environmental factors which are almost intangible, or nonquantifiable, and these are rarely included in the final report for a rapid transit system. There are two reasons for this: First, it is difficult to evaluate disruptions and psychological inconveniences to individuals and to the community during the construction period, and even more difficult to assign costs because the valuations are always subjective. Second, the rapid transit project capital costs are given in the final report and the public knows them; but the intangible social costs are borne by the affected neighborhood community, not the entire city, and as such they are "hidden costs," which in fact may add as much as 25 percent to the total system cost.

Jan 1, 1974

By Steve Karl, Rock Jenkins

Continuing its objective of sharing new ideas, methods, theory, and engineering developments, more than 550 members of the underground fraternity gathered in New York City for the 1985 Rapid Excavation and Tunneling Conference (RETC). Since the first meeting in 1972, RETC’S aim has been to lay a foundation of tunneling experience on which the industry could expand and develop over the years. The RETC is jointly sponsored by the American Institute of Mining, Metallurgical, and Petroleum Engineers (AIME), the American Society of Civil Engineers, in cooperation with the Canadian Institute of Mining and Metallurgy, and the Engineering Institute of Canada. The 17 sessions included 72 papers that explored up-to-date practices in the mining and civil engineering fields. Session topics ranged from geotechnical and seismic design, through design, construction, and support of underground openings, to ground water control in shafts and mine openings. Case histories of tunnel boring machines and large diameter tunnel and underground openings were also reviewed. All the papers presented at the three-day conference are valuable additions to improving the state of rapid excavation. A few sessions, however, are particularly noteworthy as they are geared to the mining industry. The two volume proceedings of the entire conference are available from SME. (See ad on page 1003).

Jan 7, 1985

By M. G. Ayat

Engineers in the field of coal preparation are continually striving to increase the efficiency of various circuits used in preparation plants. Undoubtedly, one of the important factors concerning the processing efficiency of a coal preparation plant is improved analyses and control of the processing equipment. The necessary link between the performance criteria of a circuit may be provided through on-line determination of various parameters. Currently, there are a certain number of on-line instruments developed for measurement of ash content of coal (Watt and Sowerby, 1983; Kawatra, 1976; Fauth et al., 1984; Lyman and Chester, 1980), moisture content (Hall et al., 1969), and sulfur content (Stewart et al., 1974). In the case of coal separatory units, these parameters are often directly related to the quality of the product. In other words, the extent of misplacement of refuse in the product, or vice versa, would indicate the performance characteristics of any particular coal washing equipment. Partition curves are therefore established to predict the performance of coal cleaning operations. Conventional sampling and testing is currently the major tool with which partition curves are produced and the performance efficiency of the operation is assessed. While conventional analysis techniques are accurate, they are slow and time-consuming.

Jan 1, 1987

By B. Govindarajan, T. C. Rao, M. Vanangamudi

The results obtained from hatch, flotation experiments on two coals were used to develop relationships between the recoveries of water and solids into the concentrate. When the recovery of non-ash material (RN) for any size fraction is plotted against a parameter X, defined as [x _ Amount of (W) recovered x Collector dosage (C)in the concentrate (cc)(kg/t)] a single "non-ash recovery curve" is obtained. Non-ash recovery curves thus obtained from different size fractions are used to get a unique "modified non-ash recovery curve" for a given coal, using the reduced efficiency curve concept. Similar observations have been noted in the case of recovery of ash material (RA) also. The amount of water recovered into the concentrate is plotted against a parameter "Water Recovery Factor (WRF)," defined as [WRF = T.F.(1+C)] where T is time (in sec) and F is frother dosage (in kg/t). Plotted in this form a characteristic water recovery curve, for a given coal is obtained that may be defined by the following equation: [W4=W_(1 pWRF-e] The above relationships have been verified against the experimental results obtained from three more coals and are found to give satisfactory predicted values.

Jan 1, 1992

By Thomas J. Regan

The first stage of the Massachusetts Bay Transportation Authority's Red Line Extension Northwest, is a two-track rapid transit extension from Harvard Square in Cambridge, through three stations, to the Alewife Station/Garage complex in North Cambridge. The extension, about 5.0 km. (3.1 miles) in length, is entirely in tunnel, with the Alewife Station/Garage complex and adjacent line sections of tunnel constructed by cut-and-cover methods. The Station/Garage complex, just west of Alewife Brook Parkway, is in an area underlain by deep deposits of very soft highly sensitive clays. It is proposed to construct the station and adjacent tunnel sections by the slurry trench method, using the slurry wall as the permanent structural wall of the station and tunnel. The unusual nature of the underlying clay and its very high sensitivity raised questions concerning the feasibility of the proposed construction. Since research failed to reveal any construction precedent for the specific conditions encountered, a test section was undertaken to determine construction problems, resolve uncertainties, and to establish acceptable parameters for the construction of the slurry walls. PROJECT ORGANIZATION Sverdrup & Parcel as tunnel and transit systems consultant for the Red Line Extension-Davis Square to Alewife had overall responsibility for determining program objectives, project management and test implementation.

Jan 1, 1979

By D. A. Dahlstrom

Energy costs have had a serious impact on all basic industries today. This is due to the significant amount of energy that is used to convert natural resources into usable products. Other factors such as transportation with its major energy requirement and materials employed in processing that have already required significant energy input for their manufacture accordingly influence delivered cost to the user. The farmer is a good example of this. While his large capital investment for land, machines, and buildings is highly impacted by today's interest rates, his chemical fertilizer, herbicides, and pesticides as well as those same machines and transportation costs for his products have also been seriously affected by energy costs. With the many unit operations involved in mining and mineral processing, several of which require significant inputs of energy, one can only conclude that this industry has experienced a great increase in percentage of total cost for energy alone. Fuerstenau (1975) indicated that the minerals industry used about 12.5% of the total energy produced in the US. McNulty (1983) listed the total energy requirements for the production of 0.9 t (1 st) of various metals including the energy consumed in the manufacture of supplies employed, such as tires, explosives, chemicals, grinding media, etc. (Table 1).

Jan 1, 1987

By Maurício L. Torem, Isabella A. Scorzelli

Taboca Mining is one of the largest producers of tin in the world. In its pilot plant, significant amounts of a middling of 90% xenotime (YPO4) and 10% zircon (ZrSi04) are produced. Until now, these minerals of this ore body could not be separated successfully. This paper presents some aspects of the fundamentals of xenotime and zircon flotation with anionic (fatty acids) and cationic (amine acetate) collector, as well as the influence of the superficial leaching of the minerals with cold HCI and HNO3 on the floatability. The mineralogical studies showed that both minerals are optically liberated in -212+106 µm size fraction. Surprisingly, SEM analysis indicated that both xenotime and zircon contain very small inclusions (1-5 µm) of thorite (ThSiO4). On the other hand, zircon is fairly metamictizated giving rise to malacon. Zeta potential tests showed that the isoelectric points of xenotime and zircon correspond to a pH value of 4.5 and 4.7, respectively.The pretreatment with HCI and HNO3 displaced the isoeletric point (IEP) of the minerals to the left. The microflotation tests indicated that the floatability of both untreated and treated minerals are quite similar in the presence of the collectors studied in this work. Adsorption mechanisms are also suggested.

Jan 1, 1995

By P. L. Stavenger

Principles of Operation and Mechanical Features General Mechanical Description Sieve-bend screens are high-capacity screening devices which utilize stationary, concave, wedge-bar screening surfaces. A complete sieve bend is comprised of a feed distribution chamber, a structure for holding the screen surface, and collection chambers or chutes for oversize and undersize materials. In devices used for metallurgical practice, provision is usually made for reversal of the direction of flow over the surface, either by rotating the surface or by changing the feed nozzle position. The size of the unit varies in height from 5 to 8 ft, and in width from 2 to 8 ft. The orientation of the wedge-bar surface is such that the slots between the wedge bars are perpendicular to the flow of feed material over the surface. The feed distribution means is arranged such that the flow of liquid suspension is distributed evenly and tangentially over the width of the screen surface. A variety of means are used including simple gravity weir feeds, long slotted nozzles, and a multiplicity of round nozzles. A typical gravity-fed weir type nozzle is shown in Fig. 18. Most sieve bends are fed with gravity feed in such

Jan 1, 1985

By V. Vesselinov, S. Orr

"Enhanced heap leaching - Part 1: Insights" (Orr, 2002), different flow and transport phenomena that could significantly reduce leaching recovery were investigated. The combination of such understanding with advanced flow and transport modeling establishes the link between cause and effect, thereby, directing operators to optimal design and construction of new heaps. Modeling of flow and transport in heaps could also point to a unique change in application method or rate that would maximize leaching enhancement of an existing heap under existing situation and leaching history. The use of such a model is cost effective in that it can simulate multiple scenarios of alternative leaching enhancement methods. By simulating a large number of irrigation scenarios, such a model can point to the optimal and/or the most promising alternatives for a particular heap. The authors' simulations concentrate on the effects of changes in application rates and heap design on changes in flow paths and enhanced leaching recovery. Based on such simulations, an intelligent control agent, such as Multiple Resolution Decision-Support System (MRDS) (Meystel and Albus, 2002), could build a new representation of the complex heap-leaching system. And, by learning from historical data and current information, it could provide optimal management of heap leaching and heap decommissioning.

Jan 1, 2003

By R. Fraher

The control of mine roof is of vital interest in underground coal mining not only for reasons of safety, but also to avoid the high costs of cleanup, resupport and production losses that can result from roof falls. The difficulty in determining roof stability mine-wide is due in large part to the broad variation of geologic and structural conditions that typically exist throughout a mining area. To ensure a stable roof over the entire mine, support systems must be selected to minimize the possibility of failure. The magnitude and cost of the support selected is a trade off against the cost of the number of falls that can still occur after it is installed. Because of the large number of variables involved in analyzing and optimizing roof stability versus support, a digital computer simulation was selected to find a cost effective solution to roof support design. A total cost approach is used which includes the actual cost of the roof support as well as the cost of the roof fall in terms of resupport and loss of production (Fraher 1990a). A Monte Carlo simulation program called ROCSIM (Roof control Optimization Cost SIMulation) has been developed for determining the optimum roof control system and design layout for underground room-and-pillar mining.

Jan 1, 1992

In the hierarchy of performing mine planning tasks, production scheduling is naturally at the bottom. Yet good production scheduling is probably the most demanding and difficult task to achieve for various reasons. Being the last task in the mine planning hierarchy, a proper production schedule must not only conform to both the long-range and the short- range mine plans but also satisfy many practical details that are unique to day-to-day operations. For example, the averages which were good enough for both long-range and short- range mine planning are no longer good enough for production scheduling. Instead, the variations become the overriding concern. The answer must also be obtained quickly and on time, thus adding another dimension to the overall problem. Because of these considerations, many production scheduling problems have been begging for solution during the past decade. Many attempts were made to solve the production scheduling problems in the past using computers and the available operations research (OR) techniques, particularly among academic groups. However, it is probably true that, compared with the current full-time computer usage in long-range and short-range mine planning, very little computer usage is being made in production scheduling to date.

Jan 1, 1979

By Bruce W. Cavender, Brian L. Granger

The leaching characteristics of non-homogeneous ores have traditionally been difficult to assess in laboratory tests. A result of the large sample size necessary to ensure representativity, this difficulty is most acute for ores containing nuggets or other irregular occurrences of precious minerals. Consequently, small-scale leaching tests are often regarded as indicative rather than conclusive. The predictive nature of leaching tests can be improved by applying the experimental design concepts of blocking and randomization. In the case of column leaching, experimental 'blocks" are constructed with the same number of columns as there are separate test conditions. These blocks are treated identically throughout the test, with differences between columns within each block being the variables of interest. To maximize the uniformity of the blocks, randomization procedures are employed in the preparation of the sample and conduct of the test. The initial ore sample is screened and individual column charges composited from randomly selected increments from each size fraction. The leaching order, daily solution analyses, and processing of leach residues are similarly randomized. The observed differences in leaching performance between the columns in each block are compared to determine the over-all outcome of the test. A statistical analysis using t distributions gives a quantitative measure of the reproducibility of the outcome.

Jan 1, 1995