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By Hans G. Machel

In low-temperature diagenetic environments (0 c T c 60 - 80°C), elemental sulfur forms by six common processes: via (1) inorganic oxidation of H2S by molecular oxygen, (2) inorganic oxidation of H2S by ferric iron compounds, (3) polysulfide disproportion- ation; and via the microbial metabolic actions of (4) colorless sulfur bacteria, (5) colored sulfur bacteria, and (6) some types of thiobacilli. Economically viable deposits of native sulfur usually are formed by only one process: inorganic oxidation of H2S by molecular oxygen. The amount of elemental sulfur is also limited by three common processes that destroy it in low- temperature diagenetic environments: bacterial reduction, bacterial oxidation, and inorganic oxidation. In high-temperature diagenetic environments (80 - 10o°C c T c 150 - 200°C), particularly in sour gas reservoirs, there are seven common processes forming elemental sulfur: (1) SOdH2S reaction, (2) H2S- hydrocarbon reaction, (3) polysulfide disproportionation, (4) catalytic H2S decomposition, (5) C02-H2S reaction, (6) chlorinification, and (7) exsolution of physically dissolved elemental sulfur. Natural processes that destroy or remove elemental sulfur in such settings are hydrocarbon sulfurization, polysulfide formation, and advection. In most sour gas reservoirs, relatively small quantities of elemental sulfur occur as a free phase (solid or liquid). However, elemental sulfur often precipitates in copious amounts from the reservoir fluids via exsolution and polysulfide disproportionation during production of sour gas reservoirs. By extension, elemental sulfur may precipitate from reservoir fluids in relatively large quantities upon uplift and erosion of deep sour gas reservoirs, or from advection of sulfurous fluids into shallower settings via faults or other high-permeability pathways.

Jan 1, 1992

By Lynn B. Hales, Randy A. Ynchausti

Because of the high economic value associated with small improvements in the operating performance of mineral processing plants, innovations in instrumentation, stabilization and expert control systems have been an ever-present part of the landscape in plants throughout the world since the I 960s. Expert control systems are computer programs that continuously monitor plant conditions; contain "expert knowledge" concerning the process, equipment and operational knowledge; and make timely recommendations for new process set points or even directly change the process set points to achieve desired management goals. Early rudimentary expert control systems first appeared in the early 1970s. They have grown from small, experimental but ambitious projects in which single unit operations were controlled to plant-wide systems that include technologies used in the U.S. space shuttle program. Experiences and results of applying these systems throughout the world will be explained discussed and analyzed. Typical results will be outlined and the use of expert control in the future will be projected.

Jan 1, 2000

By Sushil Bhandari

A computer model is developed for the problem of dispersal of dust (suspended particulate matter) resulting from blasting operations in surface mines. Undulated surface (lower boundary) simulation was carried through sixth order polynomial by least square approximation. Segmentwise terrain simulation was linearly added to build ground feature extending either side of the blast location. Assuming the initial dust concentration in the vertical column to. be uniform and treating the finite vertical line sources as a series of point sources to height, H varying from zero to top of the dust mushroom, integration was done of the concentration effects from H = 0 toL tan[0] (L = horizontal distance of the blast location and [0] is the angle of the top of dust cloud from the point of observation). Using frame of reference moving with the mean wind, the ground level 'concentration (GLC) has been computed over the undulated terrain. Standard deviation (s) of concentration has been parameterized based on mixed layer similarity theory in convective boundary layer.

Jan 1, 2002

By J. F. Abel, R. J. Spengler

Convergence measurement across the 17.4-m (57-ft) high shaft station/loading pocket at Mt. Taylor provided continuing verification of stability and safety. Three levels of instrumentation, consisting of three lines each, were installed and monitored. The instrumentation showed that the flexible lining restrained the adjacent rock. The flexible lining consisted of pea gravel with neat cement between rock and liner plate, wooden crush blocks between liner plate and steel ring beams. The loading pocket is elliptical, 11.6 x 9.6 m (38 x 31.5 ft) inside diameter. The crush blocks were designed to allow 15 cm (6 in.) of convergence. Maximum predicted convergence was 7.0 cm (2.75 in.), and 5.7 cm (2.25 in.) was measured. Convergence measurements also demonstrated decreasing deformation with respect to elapsed time and distance from the measurement station to the temporary bottom of the shaft excavation.

Jan 1, 1987

A Mark IV surface force apparatus (SFA) was used to conduct direct force measurements between mica surfaces in dodecylamine hydrogen chloride collector solutions at varying pH levels. It was found that long-range hydrophobic forces reach a maximum at pH 9.5, which also corresponds to the maxima attained by the contact angle and flotation recovery of quartz. The charge densities are comparable on both mica and quartz surfaces (0.40 to 0.48 nm2), making it possible to draw conclusions on the flotation of quartz from the direct force measurements conducted on mica. Therefore, it may be suggested that, in the pH range of 8.0 to 10.3, the maximum flotation recovery of quartz may be attributed to the appearance of a long-range hydrophobic force, which, in turn, can be related to the formation of a close-packed monolayer (or hemimicelle) in the presence of neutral amines formed as a result of hydrolysis.

Jan 1, 1998

By B. Anameric, S. K. Kawatra

Pig iron nuggets were produced in a laboratory scale furnace at Michigan Technological University. These nuggets are produced from pellets consisting of a mixture of iron oxide, coal, flux, and a binder, which are heated to 1450°C.These pellets then self-reduce to produce a solid, high-density, highly metallized (96.5% Fe) pig iron. During the nugget production process, a separate slag phase forms that cleanly separates from the metal. The physical and chemical properties of the pig iron nuggets are similar to pig iron produced by blast furnaces, which is distinct from Direct Reduced Iron (DRI).

Jan 1, 2004

By Kevin Sharman, Peri Mehling

A detailed assessment of acid rock drainage (ARD) potential was conducted at the Quintette Coal Mine site in northeastern British Columbia The site is unusual in that the coal seams contain low sulphur levels as compared to eastern coals (typically less than 0.5%), and the non-coal wastes generally do not to have the potential to generate acid on the basis of static ABA tests. The presence of small iron-stained seeps on the pit walls indicate localized sulphide oxidation, while the overall mine site drainage has remained of excellent quality with extremely low levels of metals after approximately 15 years of mining. Thus the site provides an excellent comparison to more problematic coal mine sites. For the Quintette assessment, static acid-base accounting (ABA) analyses of individual samples were compared to criteria for potentially acid generating materials developed for the U.S. Appalachian coal, as well as criteria developed in British Columbia for hard rock mines. Geologic units were characterized by the percentage of samples, or weighted thickness, that was deemed potentially acid generating (PAG). Links were then made to actual seepage and water quality emanating from geologic units around the site. Seeps at the site demonstrate a large range in pH (2.32 to 8.18). The few acidic seeps (pH < 4.0) were found to contain elevated levels of sulphates, dissolved iron, manganese and aluminum, consistent with the metals typically of concern in Appalachian coal mines. Other heavy metals that were detected in acidic seeps at Quintette included copper, zinc, nickel and cadmium. The use of simple ABA tests, and comparison of individual sample results with the Appalachian and British Columbia criteria, was found to be useful in predicting the probable sources of the small localized acidic seeps.

Jan 1, 2000

By Dipl. -Ing. H. -J. Sager

The ‘Westerschelde Tunnel’ underpasses the estuary of the Schelde in the Netherlands. The tunnel will consist of two tubes which are driven by two hydroshields (slurry shields). The tunnels will each have a length of approx. 6.6km and a bore-diameter of 11.33 m. Demanding ground conditions had to be considered during the design of the shield machines. Loose sands, extensive clay formations and high ground water pressures of up to 6.5 bar will be encountered during the tunnel drive. The tunnelling activities will start in the middle of 1999 and are scheduled to end by the end of 2001.

Jan 1, 1999

By O. Tsuge, G. Hoffman

ITmk3®(Iron Technology Mark III) is an innovative new ironmaking technology whereby high quality iron nuggets are produced directly from iron ore fines and coal in a rotary hearthfurnace1). The reaction mechanism has been investigated in detail through fundamental laboratory research2)3), and the ITmk3 process has progressed from the laboratory to commercialization by the success of the pilot plant tests initiated at Midrex’ Technical Center and at the Kakogawa Bench Plant (KBP) located at Kobe Steel Ltd. Kakogawa Steel Works4)5). Pilot operations have demonstrated rapid production of the iron nuggets with complete metal/slag separation at a relatively low operating temperature. The Kakogawa Bench Plant (KBP) in Japan has logged 21 days continuous operation during which high quality iron nuggets were produced directly from fine ore and coal. The operation technology and the engineering data obtained from these pilot tests were instrumental for the scale-up of the ITmk3 process for the Mesabi Nugget Corp. pilot demonstration plant, which is located at Cleveland Cliffs Inc. Northshore Mining iron ore pellet plant in Silver Bay, MN. The ITmk3 process is an ideally suited technology for siting at the iron ore mine, as it allows the economical production of a value-added merchant iron product.

Jan 1, 2003

By Frank F. Aplan, G. Rinelli

INTRODUCTION Coal is a solid, combustible mineral substance resulting from the degradation and alteration of vegetable matter largely in the absence of air. In this natural process of coalification, some non-combustible mineral matter is always associated with the combustible material. Coal preparation or cleaning is the process of removing this inert mineral matter from the coal. Preparation is highly successful in removing the large fragments of inert material, but is not very effective in removing the fine inorganic mineral matter intimately associated with the coal. Of the 600 million tons of coal produced in the United States every year, approximately one-half is produced by coal cleaning methods (1). The bulk of this tonnage is cleaned by coarse or intermediate gravity preparation methods (5 inches to 28 mesh, Tyler). Fine cleaning, say, -28 mesh, is done by shaking tables, washing cyclones, and flotation, or, until recently, the fines were either incorporated into the clean coal or simply discarded--not infrequently, the latter. In 1972, only 13 million tons of raw coal were cleaned by flotation in the United States, and from this 8.4 million tons of clean coal were produced (1). The percentage of clean coal produced by flotation in Europe (England, West Germany, Poland, U.S.S.R., etc.) is substantially higher. However, coal flotation has grown rapidly in the United States from only a few plants in 1950 to 31 in 1960 (2) and 66 in 1970 (1). Virtually all new preparation plants incorporate flotation into their basic flowsheet. The essential difference between ore and coal flotation is that for ores the entire tonnage is ground to flotation size, whereas for coal

Jan 1, 1976

By Sakir Selcuk, Brian Hamilton, Paul Zick

The 1.8 mi (2.9 km) Minneapolis-St. Paul International Airport Light Rail Transit Tunnels and Station project is comprised of the underground segments of the 11.8 mi(18.8 km) Hiawatha Light Rail Transit route in Minneapolis, Minnesota. The 21 ft 2 in(6.5 m) diameter twin tunnels were mined 65 ft beneath one of the busiest airports in the United States using an earth pressure balanced tunnel-boring machine. This paper will provide a project overview, review the major equipment selected, tunnel segment casting, and describe excavation and lining operations for the tunnels and station.

Jan 1, 2003

By Kalyan Saikia

An integrated statistical-geostatistical modelling of gold exploration data of Gurahar Pahar prospect of Mahakoshal greenstone belt in Central India has been attempted. Statistical modelling of gold accumulation and width reveal a positively skewed 2-parameter lognormal distribution fit with an estimate of mean gold as 0.84 gram/tonne. Geostatistical modelling provided a spherical semi-variogram function fit with mean kriged estimate and mean kriging variance of gold as 0.76 gram/tonne and 0.23 (gram/tonne)2 -respectively. Ore inventory and grade-tonnage relationships for a selected part provided an estimate of 3,36,000 tomes of ore with an average gold of 0.76 gram/tonne at 0.5 gram/tonne cutoff grade.

Jan 1, 2002

By Mark Cadzow, Rodney Lamb

CARBAD is a recently developed Australian process for the recovery of gold and platinum group metals (PGM). The process relies on the selective agglomeration phenomena of the gold and PGM to capture the mineral in a carbon-hydrocarbon media. The precious minerals are then extracted from the loaded media by a solvent gold room process producing a relatively pure concentrate. The media is then reformed and recycled. The process development from batch test work to a 5 t/h commercial scale CARBAD plant is discussed. The operation and results of processing a variety of ore types at several alluvial and hardrock gold mines is examined. The operating and capital costs for the CARBAD process shows that it is significantly less than that the conventional CIP/CIL. The environmental safety of the process is a major feature where precious metal deposits are located within urban environments or within wilderness areas.

Jan 1, 1989

By N. Economou

Temporary local seismic networks were installed in western Crete, in central Crete, and on Gavdos, an island south of western Crete, in order to image shallow seismically active zones of the Hellenic subduction zone. Data acquisition was divided in four campaigns through the years 1996 to 2001. More than 4000 events in the magnitude range between 0.5 and 4.8 were detected and localized. The resulting hypocenter distribution allows the localization of seismically active zones in the area of central Crete from the Mediterranean Ridge to the Cretan Sea. The comparison of the hypocenter distribution and the structure has allowed intraplate and interplate seismicity to be distinguished. A southwards dipping zone of high seismicity within the Aegean lithosphere is found south of central Crete in the region of the Ptolemy trench. Between 20 and 40 km depth beneath central Crete, the Aegean lithosphere appears to be seismically inactive. Especially for the year 2001, 1560 events were localized, by the seismic network installed on Messara, central Crete. Most of the seismic events were located, as expected, in the South region of central Crete. National Observatory of Athens (NOA) maintains a permanent seismic network in Greece. In this work a comparison of the earthquake epicenters obtained from both the NOA network and the BOCHUM-TUC network is presented.

Jan 1, 2006

By R. V. Ramani

Control is a vital management function by which operations are brought into compliance with predetermined standards to achieve the goals of an enterprise. Events that are characterized by a low degree of expectation, avoidability, and intent necessarily have a low degree of control. Such events are difficult not only to predict but to control as well. Fortunately, very few industrial situations fall into that category of events. It is an axiom of control technology that in order to control, one must first measure; further to measure, one must know the characteristics of the subject (or environment) upon which the measurement must be made. Finally, if measurements are to be made reliably, the influences that affect the measurement must be known and, if possible, understood. The complete control cycle therefore consists of the following: (1) defining the objective, (2) planning to achieve the objective, (3) putting the plan into practice with appropriate instructions, (4) measuring variables or parameters of interest, (5) transmitting and transforming the measurements to analyze the system&apos;s status and to predict the future outcome, (6) comparing these with the defined objective, and (7) determining and taking corrective actions to bring the actual results closer to the objective. The management principle underlying the control cycle is the principle of management by exception. The application of the principle and the frequency with which corrective actions are taken vary according to the purposes of the review and control. For example, the control of a machine operation (e.g., truck on a haul road) may require adjustments and therefore data, analysis, and decisions, in intervals of seconds whereas the review for ore-grade control may take several hours. Reviews, on the other hand, for cost control may be done in intervals of weeks or months. In any case, three specific purposes of the control cycle are: (1) to correct the operation so that it follows the accepted plan closely, (2) to evaluate the operation and predict future outcomes in light of changes in the environment or of more experience, and (3) to review the objectives and modify these to be reasonable and realistic.

Jan 1, 1979

By R. R. Fernández

Newmont Mining Corporation has been processing refractory gold ores by roasting since January 1995. The ores are refractory due to the association of the gold with iron sulfides, namely pyrite and marcasite, and the presence of carbonaceous components and is oxidized in an oxygen-enriched gaseous atmosphere. The structural characteristics of the calcine have a strong influence on the eventual recovery of gold by cyanidation. These characteristics are strongly dependent upon the roasting conditions, mainly the roasting temperature. Originally, the sulfides and carbonaceous matter were oxidized at a temperature that typically ranged between 535 and 560 °C. Controlling the roasting temperature within the lower and narrower range of 510 to 515 °C produced a calcine with a larger surface area(e.g. higher porosity), which resulted in a gold recovery increase of3.3 percent in 2001 equivalent to 5.1 million dollars of additional gross revenue. The new strategies of operating at temperatures never tested before are discussed. It constituted a great challenge to the control room operators for the lower operating temperature falls much closer to the ignition temperature of the sulfide ore and smaller and more frequent adjustments in operating parameters were needed to improve and maintain high gold recoveries. Based on the encouraging results that were achieved in 2001, a decision was made to install a “smart” process control system because the roaster temperature control was performed by manual inputs from the control room operators. The development and implementation of the control system to reduce or eliminate the temperature variability between the different control room operators commenced in June of 2002 and was fully operational by the end of October. Lower roaster temperatures were achieved (500 to 505 °C), which resulted in further increase of gold recovery by about two percent. The overall recovery increase equated to 8.0 million dollars of additional revenue for the first 10 months of 2002.

Jan 1, 2003

By J. Moreno, P. Sinton, R. Vogwill

Groundwater models are often used to estimate and optimize dewatering volumes, locations, and rates, as well as water supply production for mines. Projections of future dewatering rates are highly dependent on the conceptual model used as a basis for the numerical model. This paper presents an audit of modeled dewatering rates versus actual data and an examination of the reasons for discrepancies. The setting is a gold mine, in a collapsed volcanic crater breached by the ocean. Mining will occur to about 200m below sea level within a remnant geothermal system. A detailed hydrogeologic investigation was conducted to support dewatering and geothermal depressurization design for future mining operations. These studies included development of a three-dimensional model to simulate heat and density-coupled groundwater flow, using software developed by URS/Dames & Moore. In this paper, the groundwater modeling results prepared 5 years previously by others was audited using operational dewatering data. This model was then extended using the new mine schedule and actual locations for dewatering wells to predict future dewatering requirements. In addition, a comparison between “hot” and “cold” model results was used to assess the need to use a heat-coupled versus a standard groundwater model for dewatering predictions.

Jan 1, 2003

By Eugene F. Casey, William H. Hansmire, J. Ghaboussi, Randall L. Lentell, Harvey W. Parker

INTRODUCTION Construction of a major intercepting sewer in Brooklyn, New York involved tunneling in soil over several subway lines. In two instances the clearance between the subway and sewer was sufficiently close that concern was raised about the influence of the new construction. Prior to each critical crossing, analytical studies were performed which characterized the tunneling influence. It was demonstrated that with adjustments in construction procedures the crossings could be made without affecting the integrity of the subway linings. A comprehensive program of instrumentation and full-time monitoring was undertaken to ensure that any unforeseen adverse developments during crossing would be recognized. The successful crossings were subsequently made with minimal influence. Reported herein are the special construction conditions for the two crossings, the analytical simulation of behavior, and the results of monitoring on the subway linings. SEWER TUNNEL CONSTRUCTION AND EXISTING SUBWAYS The Red Hook Intercepting Sewer is a 2600 m (8600 ft) long tunnel which is part of a major water pollution control project in New York City. For clarity of nomenclature, the sewer is termed a &apos;tunnel&apos; while the rapid transit structures are termed &apos;subways&apos;. For routine construction, the tunnel was mined by hand with a 3.2 m (10 ft-5 in.)

Jan 1, 1981

By George S. Austin

Perlite is rhyolitic glass with 2 to 5 percent by weight (wt.%) bound water held within the silicic-glass structure. It is often distinguished by vitreous, pearly luster and concentric perlitic fractures ("onionskin"). Occurrences worldwide are associated with Tertiary to middle Quaternary volcanic rocks. Perlite is in silicic domes, plugs, laccoliths, flows, vitric tephra, chill margins of dikes and sills, and welded ash-flow tuffs. It is a hydrated volcanic glass formed through secondary alteration of obsidian by the incorporation of water into the glass/silica structure. Post-emplacement hydration (weathering) of cooled glasses by meteoric water is the principal alteration process, but some hydration by magmatic or meteoric water during or shortly after emplacement, or hydration by water exsolved during cooling may occur. Commercial "perlite" is any volcanic glass that expands or "pops" when heated quickly to plasticity while evolving steam and thus forming a lightweight, frothy material. The expansion temperature typically ranges from 1,100 to 1,500°F. An expanded volume increase of 10 to 40 times the original volume yields expanded densities of 1.5 to 11 pounds per cubic foot (lbs/ft3). Perlite is mined by eight companies at 10 operations in six western states. New Mexico accounts for more than 80% of the total tonnage mined. The rest comes from Arizona, California, Colorado, Idaho, and Nevada. In 1992, domestic production was 571,000 short tons (st), domestic apparent consumption was 591,000 st, and the value of crude perlite was $15.3 million. In 1991, with about the same production and price of crude perlite, the gross value for expanded perlite was $101.7 million. Perlite exports in 1992, primarily to Canada, are estimated an 30,000 st; and imports, from Greece, are an estimated 50,000 st. In 1992, 70 plants in 33 states expanded crude perlite. Construction uses of expanded perlite accounted for 66% of total domestic sales. Expanded perlite used as filter aid accounted for 15%. All other markets, including use as a filler and in agriculture, accounted for 19%. Leading states for expanding perlite, ranked by order of sales, were Mississippi, Pennsylvania, California, Illinois, and Georgia. Domestic perlite encounters transportation disadvantages in some areas of the eastern United States compared to perlite imported from Greece. However, western U.S. perlite exports to Canada offset this in large part, and net import reliance for perlite is about 3% of domestic consumption. Perlite grab samples were tested at the New Mexico Bureau of Mines and Minerals Resources (NMBMMR) for their basic suitability in horticulture, construction, filter aids, and fillers/extenders using Perlite Institute techniques modified by the NMBMMR. Most commercial perlite ranged from 2.5 to 3.0 wt.% bound water for all major types (classical, granular, and pumiceous). Expanded density varied widely, but the lowest density of 1.9 lbs/ft3 was for granular. Average brightness of expanded perlite was 47.6 to 69.3%. Nonexpansibles, commonly obsidian or "dead" perlite, ranged from 18 wt.% to less than 1 wt.%, with granular perlte generally the lowest. Compacted density was not related to either perlite type or nonexpansibles present. Sieve analyses of the -50+100 mesh product showed that, in general, pumiceous perlite produces more fines and classical and granular perlite average 60 to 80% -30+100 mesh after expansion. Samples were tested for crystalline silica that ranged from below the detection limit of 0.5 wt.% to nearly 0.2 wt.%, but most tested below 0.5 wt.%. Although quartz content can be lowered in the expanded product by the expansion process, producers can further lower crystalline silica in the product by mixing low-quartz crude with high-quartz perlite before expansion. Chemical analysis by x-ray fluorescence confirms the rhyolitic composition of perlite, but indicates that surface weathering may increase the concentration of some elements, such as potassium and calcium, by infilling cracks or fissures developed during or after perlite emplacement.

Jan 1, 1995

By Bernd Hagenah, Eric C. Wang

New tunnels of significant alignment lengths such as mountain tunnels, base tunnels, as well as beneath urban centers pose unique environmental challenges. This paper highlights key environmental considerations for planning, design, construction, and operations by sharing lessons-learned from the authors' extensive project experience on these types of tunnels. Discussion of unique constraints include limited right-of- way, ventilation and emergency egress during the construction phase and revenue service, safety and security, and protection of existing structures. Practical approaches and applied innovative state-of-the-art solutions addressing distinct sustainability challenges and unique requirements are shared from US and international project examples.

Jun 23, 2024