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By Leon Maday, Robert Robinson, Judy Cochran, Don Davis

Over the past 20 years, several soft-ground tunnels have been successfully completed in the Seattle area. These tunnels were built using design-bid-build contracting methods, and have benefited from advancing technologies in exploration, design and construction methods. Owners have utilized various contractual means to share some of the risks that are inherent to tunneling projects. This has helped to foster a competitive bidding environment and to resolve issues related to unanticipated underground conditions in a fair manner. This paper presents case histories of tunnels constructed by King County and the Washington Dept. of Transportation that illustrate a common approach to design and construction issues. The common thread is successful project completion with minor cost changes under the design-bid-build contracting method. Lessons learned from these projects are being applied to the upcoming King County Brightwater Project tunnels, Sound Transit’s Light “Link” Rail tunnels and other tunnel projects.

Jan 1, 2005

By Ramsey Hart

MiningWatch Canada is the only national independent civil society organization with an exclusive focus on mining in Canada and Canadian mining companies operations internationally. In 2005, MiningWatch Canada collaborated with other NGOs to develop the Framework for Responsible Mining: A Guide to Evolving Standards. The project was the result of a perceived need by NGOs and retailers, particularly from the jewellery sector, for a framework that would set out environmental, social, and governance standards for the minerals sector ?providing recommendations for retailers and others seeking to source or invest responsibly, as well as regulate and encourage responsible mining practices?. This paper is a reflection on the Framework that examines key areas of concern and notes where the industry norms and expectations of civil society have evolved. The paper focuses on developments in social issues related to the UN Guiding Principles on Business and Human Rights, new initiatives associated with financial transparency, the UN Declaration on the Rights of Indigenous Peoples. The environmental components of the Framework that are revisited are waste management, biodiversity, energy and climate change, environmental assessment, mine closure, mercury and seabed mining.

Aug 1, 2013

By Tom Michaud, Rob Albinger, Ian Turner, Michael Rispin

Data transmission, communication, tracking, and the connection of equipment such as gas detectors, cameras, and collision avoidance systems in today's tunnel industry are critical pieces of the constructor's infrastructure. Reliability, flexibility, redundancy, and cost-effectiveness are key in selecting and implementing inte- grated systems. Both wired and wireless components are used to deliver custom solutions and can involve interconnectivity between backbones. Systems integration is important as industry adopts proven technologies from other industries. Case stud- ies are given showing how tailor-made approaches deliver needed functionality, with varying degrees of com- plexity, in various classifications of environment, in order to meet a project need.

Jun 23, 2024

By Marco Castenetto

Some of the most significant Danieli innovations in the field of long products are the: i) The EWR® system, through automatic continuous head-to-tail flash welding of billets at reheating furnace exit side, enables uninterrupted production of the mill for endless rolling of straight bars, wire rod and bar in coils. The process is particularly beneficial to wire rod and bar-in-coil mills as it enables production of “customized-size coils” (any coil weight according to specific Customer request) and with extra-high final coil weight, even starting from low-weight billets; ii) The Spooler process is based on twistfree winding of hot-rolled rebars into highly-compact/ultra-heavy coils featuring a unique cobble-free un-coiling capability. This enables high-speed feeding of the downstream cold-processing lines with hot-rolled spooled coils coming directly from the rolling mill without the need of any traditional off-line operation (such as de-coiling, stretching & re-winding). The system results highly beneficial both to bar-in-coil producers and to the downstream lines operators. The latest step forward is the combined application of these two systems that has made it possible for endless rolling of spooled bar in coils, enabling to cumulate the benefits of the two processes, particularly as far as transformation costs are concerned.

Aug 16, 2017

By Saskia Duyvesteyn

Small ion-exchange resin particles provide faster mass transport than conventional-sized beads. Unfortunately, high pressures are needed to pump solutions through columns containing small resin particles. It is preferable to disperse fine resins in the solution being treated. Screens have been used to separate the resin from the solution, but screens do not retain fines created by attrition of the resin particles. We have developed a separation process based on flotation, which relies on the surface characteristics of the resin, instead of size. The resin is conditioned with a surfactant before dispersing it in the solution to be treated; this increases the hydrophobicity of the resin sufficiently for froth flotation, without introducing surfactant directly into the solution. The surfactant adsorbed on the resin surface does not appear to impair the kinetics of metal ion removal. A flowsheet for an effluent treatment process is proposed; other applications are clearly possible.

Jan 1, 1998

By D J. McLane, J T. Rathbun, B T. Lusk

The dynamics of explosive detonations are understood, however recreating a real-world, full scale scenario is costly. The use of a shock-tunnel allows testing to be done on a smaller scale, with the simulated effect of a large explosion. Analyzing explosive waveforms using this method can greatly reduce cost in testing blast resistant products, such as anti-terrorism devices, mine safety products, and military equipment. The purpose of this paper is to better the understanding of how the waveform characteristics resulting from an explosive detonated within a shock-tunnel differ from those in an open-air arena test. The variables of comparison between an open-air arena test and those conducted within a shock tunnel are peak pressure, impulse, shock wave velocity, and cross sectional shape of the shock front. Understanding how these variables differ, tests utilizing a shock tunnel can be conducted with a higher degree of accuracy and repeatability.

Jan 1, 2013

By Michael J. Messel

THE critical shortage of asbestos fiber in the world today brings to the foreground the question of locating and developing new deposits. The object of this paper is to discuss some of the more important factors which should be considered in the examination and valuation of a new asbestos enterprise. Some of the more important uses of asbestos fiber are for textiles, heat insulators, building materials, filters and a series of other uses. The properties of this mineral, such as fibrous structure, color, strength, silkiness and flexibility, coupled with resistance to fire, certain chemical action and decay make its application unique for certain industrial uses which consume over 500,000 tons annually. These same unique properties which make this mineral so valuable also make a deposit one of the most difficult to appraise accurately, because of the many undeterminable and varying factors which must be considered before a deposit can properly be termed commercial. The majority of the asbestos fiber today, having the above mentioned properties, is sold by grades which are based on fiber length. Present day fiber prices vary over a wide range from $800 to $225 for crude fibers and $300 to $20.00 per ton for milled grades. For valuation purposes a careful study should be made of existing fiber prices and markets. EXAMINATION OF DEPOSITS In carrying out prospecting and examination of a deposit, considerable caution is required to get the necessary information in the form that will have the most value for the final determination. There are two main classes of asbestos fibers, chrysotile and the amphiboles, the chrysotile being, by far, the most important both in abundance and uses. This paper will stress mainly chrysotile deposits, however, the amphiboles have many important uses, especially amosite and crocidalite. Their valuation presents special problems as other factors may be involved, especially as they are not graded according to any well defined and adopted standard but usually according to the use for which they are being supplied. Most chrysotile deposits occur in two main types of rock, (I) mainly in basic igneous, such as dunite and peridotite, (2) to a lesser extent in sedimentary rocks, such as dolomite and limestone. All of these require a certain degree of metamorphism to be favorable to asbestos formation. Approximately 90 pct of the asbestos deposits are derived from serpentinization of dunite or peridotite, whereby the magnesiumsilicate olivine was altered to hydrous magnesium-silicate serpentine. Under certain favorable geological conditions, this serpentine takes a fibrous form having a definite crystal structure, probably due to molecular rearrangement, and is known as chrysotile. The fiber veins are usually ir-

Jan 1, 1947

By J. Noll, D. Yantek, B. Kendall, J. A. Organiscak

"A self-tramming remotely controlled mobile Dry Scrubber (DS) was developed by J. H. Fletcher and Co. under a contract with the National Institute for Occupational Safety and Health’s Office of Mine Safety and Health Research (NIOSH OMSHR) to reduce exposure of miners to airborne dust. NIOSH OMSHR laboratory testing showed that the DS averaged greater than 95% dust removal efficiency with the disposable filters and averaged 88% and 90%, respectively, for the optional washable filters in their pre-washed and post-washed test conditions. Although the washable filters could be reused, washing them generated personal and downstream respirable dust concentrations of 1.2 and 8.3 mg/m3, respectively, for a 10-minute washing period. The DS’s velocity pressure regulated variable frequency drive (VFD) fan maintained a relatively consistent airflow near the targeted 1.43 and 4.25 m3/s (3000 and 9000 ft3/min) airflow rates during most of the laboratory dust testing until reaching its maximum 60 Hz fan motor frequency or horsepower rating at 2610 Pa (10.5 in. w.g.) of filter differential pressure and 3.97 m3/s (8420 ft3/min) of scrubber airflow quantity. Laboratory sound level measurements of the DS also showed that the outlet side of the scrubber was noisier and the loaded filters increased sound levels as compared to clean filters at the same airflow quantities. With loaded filters the scrubber reached a 90 dB(A) sound level at 2.83 m3/s (6000 ft3/min) of scrubber airflow, indicating that miners should not be overexposed in relation to MSHA’s permissible exposure level (PEL) of 90 dB(A) at or below this airflow quantity (1). The DS’s washable filters were not used during field testing because of their lower respirable dust removal efficiency and the airborne dust generated from filter washing. Field testing the DS with the disposable filters at two underground coal mine sections showed that it can clean a portion of the section return air and provide about a 50% dust reduction at the face area downstream of the continuous miner (CM) operation. INTRODUCTION Coal mine worker overexposure to coal and quartz dust continues to be a problem at underground coal mining operations in the U.S. The U.S. Mine Safety and Health Administration (MSHA) recently changed the standard for coal mine worker respirable dust exposure from 2.0 mg/m3 average during an eight-hour shift to 1.5 mg/m3 average over the actual working shift, effective as of August 1, 2016 (1). If more than 0.1 mg/m3 quartz mass is found in the coal mine worker dust sample, the applicable respirable dust standard is further reduced to the quotient of 10 divided by the percentage of the quartz in the sample (1). Over 90% of the mechanized mining units operating in U.S. underground coal mines are continuous mining machines (2). MSHA inspector dust samples from 2009 to 2012 showed that 3.7% of continuous miner operators exceeded the 2.0 mg/m3 dust standard, while 8.8% of these dust samples exceeded the new 1.5 mg/m3 dust standard and 9.7% of these samples exceeded the reduced quartz standard (3). Additionally, roof bolter dust samples at these mechanized mining units during this same period have exceeded the 2.0 mg/m3, 1.5 mg/m3, and reduced quartz levels at 1.1%, 3.7%, and 10.6%, respectively (3)."

Jan 1, 2016

By J. Noll, D. Yantek, J. Organiscak

The Office of Mine Safety and Health Research of the U.S. National Institute for Occupational Safety and Health (NIOSH OMSHR) conducted laboratory testing of a self-tramming, remotely controlled mobile Dry Scrubber (DS) that J.H. Fletcher and Co. developed under a contract with NIOSH OMSHR to reduce the exposure of miners to airborne dust. The scrubber was found to average greater than 95 percent dust removal efficiency with disposable filters, and 88 and 90 percent, respectively, with optional washable filters in their prewash and post-wash test conditions. Although the washable filters can be reused, washing them generated personal and downstream respirable dust concentrations of 1.2 and 8.3 mg/m3, respectively, for a 10-min washing period. The scrubber’s velocity-pressure-regulated variablefrequency- drive fan maintained relatively consistent airflow near the targeted 1.42 and 4.25 m3/s (3,000 and 9,000 ft3/min) airflow rates during most of the laboratory dust testing until reaching its maximum 60-Hz fan motor frequency or horsepower rating at 2,610 Pa (10.5 in. w.g.) of filter differential pressure and 3.97 m3/s (8,420 ft3/min) of scrubber airflow quantity. Laboratory sound level measurements of the scrubber showed that the outlet side of the scrubber was noisier, and the loaded filters increased sound levels compared with clean filters at the same airflow quantities. With loaded filters, the scrubber reached a 90 dB(A) sound level at 2.83 m3/s (6,000 ft3/min) of scrubber airflow, indicating that miners should not be overexposed in relation to MSHA’s permissible exposure level — under Title 30 Code of Federal Regulations Part 62.101— of 90 dB(A) at or below this airflow quantity. The scrubber’s washable filters were not used during field-testing because of their lower respirable dust removal efficiency and the airborne dust generated by filter washing. Field-testing the scrubber with disposable filters at two underground coal mine sections showed that it could clean a portion of the section return air and provide dust reduction of about 50 percent at the face area downstream of the continuous-miner operation.

Jan 1, 2016

Laboratory tests were conducted to study the effects of thrust or pull-down force and rotary speed on the vibration signatures of a particular drill in a known rock type, and to determine how the vibration signatures could be used to assess bit wear. The vibration signatures were analysed using a Wavelet Transform analysis technique, which decomposes the signals in multi-bands of frequency and presents the results simultaneously in time and frequency domain. Results show that as the bit wears, large fluctuations in amplitudes in the high frequency ranges occur, and prominent peaks in the low frequency ranges were observed for a worn bit. The Wavelet Transform technique provides an appropriate and effective metrics for monitoring and evaluating the state of wear as drilling progresses through the post-processing of wavelet coefficients. This study provides a basis for the development of an on-line detection technique of bit wear in rock drilling through Wavelet Transform technique or time-frequency analysis that can be used in real time.

Jan 1, 2000

By W. P. Diamond, A. C. Smith, J. A. Organiscak, T. P. Mucho

The U.S. Bureau of Mines examined bleederless ventilation practices to evaluate their use as a spontaneous combustion control measure in U. S. coal mines. Results indicate that restricting airflow into mined-out areas (bleederless ventilation) is recognized worldwide as a spontaneous combustion control measure. However, ventilation practices commonly used to limit airflow to mined-out areas are not easily applicable to United States mining conditions, systems, experience and regulations. The types of bleederless ventilation systems used throughout the world and the spontaneous combustion risks associated with these systems are discussed. Primary design considerations for bleederless ventilation consist of the interaction of ventilation practices, methane drainage, ground control, seal construction and mine monitoring. Technological improvements needed for U.S. application of bleededess ventilation are also discussed.

Jan 1, 1995

By Hamid Maleki

This paper reviews a study conducted for Australian Coal Research Limited (ACARP) to assist Anglo-American operations with better understanding of coal burst mechanics and control based on U.S. practical experience, investigations, and inspections in three major U.S. coalfields over the past 45 years. The study examined both nonviolent and burst-prone case studies to identify contributing risk factors and addressed failure mechanisms for major U.S. coalfields in Utah, Colorado, and Kentucky, which have diverse characteristics. To investigate the mechanics of coal burst, a multipronged approach is used. First, field measurements in three mines from East Mountain, Utah, are complemented with finite-difference stress analyses to address the importance of horizontal stress in coal pillar mechanics of violent failure. Second, the computational procedures for estimating seismicity resulting from slip along geological discontinuities are reviewed, as these measurements point to seismicity being the trigger mechanism for violent failure of marginally stable structures. This joint-slip seismicity mechanism is in agreement with the more recentimproved re-examination of mining-induced seismicity (MIS) data from the Crandall Canyon Mine, Utah by University of Utah (UOU). Third, a hybrid statistical-analytical methodology is applied for identifying significant factors affecting coal burst. It utilizes data from 30 case studies including those from Utah, Colorado, Kentucky, and other eastern U.S. mines. The statistical approach reinforces field measurements and points to strata rigidity, joint spacings, and horizontal stress field as significant factors affecting damage resulting from coal bursts. This provides practical capabilities for identifying operations of higher risk using a rigidity-cavability variable. Overall, the study provides valuable insights into the mechanics and risk factors associated with coal bursts in major U.S. coalfields. By utilizing a multipronged approach that incorporates both field measurements and statistical-analytical calculations, the study offers practical capabilities for identifying operations of higher risk and improving coal burst control.

Jul 1, 2023

By Walter Dake

THE mining engineer is being more generally called on to examine and report on properties where the introduction of mechanical loaders is proposed, and as the use of these labor-saving devices presents an entirely different problem from that of hand-loading, an outline of procedure is herewith pre¬sented based on five years of intensive field experience in making such studies. It is impossible to outline an examination which will cover every condition but the most important variables are noted and the re¬port may be amplified or abridged to suit individual mine requirements. There are, of course, exceptional cases in which a single minor variable will determine the final conclusion; the result of mechanical loader application can be, estimated within close limits by considering all variables listed and taking into account the sum of all those found to be applicable to the property under examination. It is necessary that a high degree of accuracy be exercised in the analysis of conditions, and that a relatively narrow margin be figured on all estimates of tonnage outputs and costs. In making an examination for this purpose the data as to company name, business address, name of mine, geographical location, rail or water connections, type of mine (whether shaft, slope, or drift), and the name of seam should, of course, be included, to be followed by the minimum, maximum, and average thickness of seam, a brief description of the charac¬teristics of the coal, the impurities contained, location of regular impurities or partings, together with nota¬tion as to quality, uses, and-markets for the coal. It is also necessary to make cross-sections of the seam so that face preparation may be studied in an effort to eliminate all regularly-occurring impurities at the working place. The possibilities for further cost re¬ductions by the removal and gobbling of partings under¬ground before mechanically ? loading out a face are sufficiently great to warrant careful study and analysis. The classification of the mine from the standpoint of gaseous or non-gaseous operation will determine the general type of electrical equipment needed. A notation regarding the power whether generated at the mine or purchased, together with the amount, voltage, and type of current available is necessary since these matters determine the exact type of elec¬trical equipment to be used. A brief description of the ventilating system, giving type of fan, amount. of air delivered, water gage, and whether force or ex¬haust type, will enable the engineer' to figure venti¬lating requirements per man under mechanical loading practices. The pitch of seam in degrees, the pitch of working faces, and a brief description of rolls or horsebacks should be included, as these affect the efficiency of mechanical loading and, therefore, the economic re¬sults obtainable. -Notations should be made as to the amount of water found in working faces, and whether pumping, sprinkling or rock-dusting methods should be considered. As the character of the floor affects the operation of the machine at the face if a cater¬pillar-tread type, its hardness should be determined, and also whether impurities consisting of floor ma¬terial are likely to be loaded with the coal. The char¬acter of the roof and overlying stratification determine the mining system and width of roof span at work¬ing faces. It therefore directly regulates the amount of tonnage to be loaded by machines without a move from one place to another.

Jan 12, 1927

By C. J. Pritchard

Controlled recirculation of ventilation air in underground metal and nonmetal mines has the potential to improve airflow and the health and safety of miners when implemented properly. Previous research by Robinson, Marks, Cecala and others concluded that the success of a district recirculation system is predicated upon an adequate supply of fresh air and the use of a reliable monitoring system for safe operation. This recent research also showed that contaminant levels will not exceed pre-recirculation levels, and that district recirculation can improve the dilution of face contaminants, especially methane gas. To illustrate the process of implementing controlled recirculation and also to promote and give guidance to mine operators in consideration of this tool to improve mine airflow, Office of Mine Safety and Health Research (OMSHR) researchers acquired baseline airflow and contaminant data from a multi-level room-and-pillar nonmetal mine and used commercial ventilation network software to simulate base case conditions and recirculation of mine air. Mine return air baseline contaminants of dust and diesel particulate matter were at lower levels than intake air, providing the potential for improved face air quality. A ventilation model implementing controlled recirculation was developed and analyzed, showing an increase in air quantity at the face, improved intake air quality, and contaminant exposure levels below those set by statutory requirements. These results, along with conclusions reached by previous researchers, provide the basis for examining the safe and effective implementation of controlled recirculation in metal and nonmetal underground mines using this mine as an example.

By M. S. Moats, A. Luyima, W. Cui

"Organic smoothing additives are used to produce dense, thick, high-quality cathodes in copper electrowinning. Glue had been used traditionally and is still used in operations that do not employ solvent extraction to produce the electrowinning electrolyte. With the advent of solvent extraction–electrowinning, guar started to be used and remained in use for many years as it does not affect the phase disengagement in solvent extraction. Recently, however, guar has been replaced by less-expensive saccharide- and polyacrylamide-based additives. This paper is the first of a series of four papers that examine saccharides and polyacrylamides as new additives for copper electrowinning. A review of previous research related to copper electrowinning additives is presented here, along with a selected review of additives in other copper electrodeposition systems.IntroductionThe recovery of copper from solution by electrowinning was first practiced in the early 1900s, but it was the combination of solvent extraction with electrowinning (SX-EW) in March 1968 at the Ranchers Bluebird Mine (Kordosky, 1992) that changed the landscape for the electrowinning process. Most copper electrowinning capacity is now associated with solvent extraction, though some copper is still won directly from leach solutions (Robinson et al., 2013). The ability to produce high-purity copper cathodes from SX-EW has taken the continued improvement of SX-EW technology over the past more than 40 years.One of the technologies that has seen improvement is that of the organic smoothing agents used during the electrodeposition of copper in the tankhouse. These organic additives are added to the acidic copper sulfate electrolyte during electrowinning to improve the smoothness, brightness and density of the copper cathodes. The organic additives that are presently in use are different from those used in 1999 (Jenkins et al., 1999). Over the past decade, many tankhouses have replaced the use of guar-based organic additives with those derived from other saccharides. Until now, there has been no comprehensive publication in the open literature on the behavior of these additives during copper electrowinning."

Jan 1, 2016

By C. Heckman, M. S. Moats, A. Luyima, W. Cui

"Cyclic voltammetry, electrochemical impedance spectroscopy (EIS), and galvanodynamic and chronopotentiometric techniques were used to characterize the effects of DXG-F7®, a commercial smoothing agent, on copper electrodeposition onto 316L stainless steel from a synthetic electrolyte containing 40 g/L copper (Cu2+), 160 g/L sulfuric acid (H2SO4) and 20 mg/L chloride (Cl-) at 40oC. The findings were compared against results using HydroStar® 4208, a modified polysaccharide. The nucleation overpotential and plating potential observed in cyclic voltammetry and galvanodynamic testing showed that neither DXG-F7 nor HydroStar significantly polarized acidic copper electrodeposition. Subtle differences between the additives were found during EIS testing and modeling, but more research will be needed to fully understand these differences. Surface-roughness measurements of two-hour deposits indicate that DXG-F7 and HydroStar produced smoother deposits as their concentrations in the electrolyte increased. No difference in the surface roughness of deposits was detected between the additives. Based on the experimental evidence resulting from the laboratory testing, no significant difference was found between DXG-F7 and HydroStar at 20 mg/L Cl- concentration, with the exception that DXG-F7 dissolves more easily in water than HydroStar. Introduction Cathode deposits obtained from acidified copper sulfate electrolyte(s) without organic additives are often soft, coarsely crystalline and nodular (Sun and O’Keefe, 1992). Therefore, small amounts of organic additives are added to the electrolyte to produce level and dense cathodes during copper electrowinning. The action of organic additives is thought to be due to their adsorption on the surfaces of the newly formed copper grains. Hence, any copper grain that grows excessively fast adsorbs a layer of organic additive, which inhibits growth. The result is a smoother and harder deposit of suitable purity (Sun and O’Keefe, 1992). In part I of our four-part series on the examining of copper electrowinning smoothing agents, a review of previously published work on organic additives used during copper electrowinning was presented (Moats, Luyima and Cui, 2016). In the review, it was noted that many tankhouses had switched from guar to other saccharide-based products such as HydroStar and DXG-F7."

Jan 1, 2016

By C. Heckman, M. S. Moats, A. Luyima, W. Cui

"Chloride ions and their interactions with two organic smoothing additives – Cyquest® N-900 and HydroStar® 4208 – during copper electrodeposition were explored using cyclic voltammetry and electrochemical impedance spectroscopy. The results revealed that chloride ions, up to a concentration of 40 mg/L, depolarized the copper deposition reaction. A combination of chloride ions and Cyquest N-900 inhibited the depolarization reaction during copper electrodeposition. It is proposed that the chloride ions acted as bridging ligands between copper and Cyquest N-900. Addition of HydroStar at a concentration of 2.5 mg/L depolarized the copper deposition reaction when no chloride ions were present. This behavior did not change with the addition of chloride ions at the concentrations tested, indicating that chloride ions and the polysaccharide do not interact.IntroductionElectrowinning is a major production method used to obtain high-purity copper. In modern tankhouses, copper is electrodeposited onto stainless steel blanks and then stripped, washed and bundled for delivery. Significant improvements in the quality of electrowon copper have been made over the last few decades. Additives, temperature, current density, electrolyte concentrations and agitation are known to influence the quality of copper electrodeposits (Jenkins and Eamon, 1990).The influence of chloride and organic additives on copper electrodeposition has been the subject of considerable research. The addition of small quantities of chloride and organic additives has been recognized to significantly improve the properties of copper electrodeposits. These additives are critical in the prevention of dendrite growth and the production of smooth, dense cathode deposits.Chloride ions have been reported to catalyze the copper reduction reaction and assist in the production of uniform deposits (Lakshmanan et al., 1977; Sun and O’Keefe, 1992). Moreover, it is generally agreed that chloride ions depolarize the copper deposition process at low (several millimolar) chloride concentrations. This is because chloride ions catalyze the reduction of copper (II) ions to copper (I) ions (Cu2+ ? Cu+ + e-) in the rate-limiting step of this process (O’Keefe and Hurst, 1978; Ilgar and O’Keefe, 1997; Hebert, 2005; Shao, Pattanaik and Zangari, 2007)."

Jan 1, 2016

By C. Heckman, M. S. Moats, A. Luyima, W. Cui

"Nucleation and growth of copper on 316L stainless steel from synthetic acidified copper sulfate was studied in the absence and presence of chloride ions and/or organic additives – HydroStar® 4208, DXG-F7® and Cyquest® N-900 – using a potentiostatic technique. The current–time data obtained at 0.16V versus the SHE were analyzed using nucleation and growth models. Scanning electron microscope (SEM) images of deposits produced at 300 A/m2 show that the addition of 20 mg/L chloride ions increased the size and reduced the number of copper nuclei. Potentiostatic current–time data from the electrolyte without organic additives, and confirmed by SEM images, indicate progressive nucleation with two-dimensional growth under diffusion control. None of the organic additives studied at a concentration of 2.5 mg/L with 20 mg/L chloride changed the nucleation and growth mechanism, but the additives increased the number and reduced the size of copper nuclei, leading to more uniform coverage of the stainless steel substrate.IntroductionElectrowinning of copper is an important process in the manufacture of high-purity copper metal. Approximately 20 percent of the world’s refined copper is produced from acidified copper sulfate solutions by electrowinning (Schlesinger, Sole and Davenport, 2011). In many plants, copper is electrodeposited on AISI 316L stainless steel substrates for a period of 6-7 days, after which the copper is stripped from the blanks. Even though the deposition time for a commercial copper electrowinning circuit is around one week, it is critically important to control the nucleation, growth and nature of the initial deposit (Sun and O’Keefe, 1992).Deposit morphology and structure are influenced by the real current density at the electrode surface. The real current density across the cathode surface is made uniform by proper design of the electrowinning cell and electrodes and careful operational practice. Even with good design and control, some current maldistribution occurs. The outcome of severe current maldistribution is poor deposits that affect product quality and/or increase energy consumption. To combat current maldistribution and create a larger operating window in terms of current density, temperature and copper concentration, small amounts of organic smoothing agents – traditionally, guar products – are added to copper electrowinning electrolytes. Moreover, these additives inhibit the growth of copper nodules and lead to improved deposit quality by producing bright, smooth and dense cathodes.Recently, the use of polysaccharides, such as HydroStar 4208 and DXG-F7, and polyacrylamides, such as Cyquest N-900, has been reported in commercial electrowinning tankhouses as replacements for guar (Ashford, Clayton and Sandoval, 2012; Robinson et al., 2013; Sandoval, Morales and Bernu, 2010). However, little information has been published on the effect of these new organic additives, especially regarding the nucleation and growth mechanisms of copper electrodeposits in their presence."

Jan 1, 2016

By Jon A. Hummer, Emanuele Cauda, George H. Schnakenberg, Aleksandar D. Bugarski, Samuel J. Janisko, Larry D. Patts

A series of engine/dynamometer tests was conducted to assess the effects of three types of uncatalyzed diesel particulate filters (DPFs), a diesel oxidation catalytic converter (DOC) and three types of high temperature disposable filter elements (HT DFEs) on the concentrations and size distribution of diesel aerosols and concentration of nitric oxides in underground mine air. Tests were conducted in the NIOSH Diesel Laboratory at the Lake Lynn Laboratory experimental mine, a facility developed to allow evaluation of these and other control technologies directly in an underground environment. The aforementioned technologies are evaluated by comparing the aerosol and gas measurements in the mine air 60 m downstream of the exhaust from a naturally aspirated, mechanically controlled engine fitted with the tested systems or muffler and operated at four steady-state engine speed and power modes. The tested DPF and HT DFE systems caused a 10-fold reduction in total mass concentrations of aerosols. The size distribution and number concentration measurements showed that all tested DPF systems and HT DFE elements effectively removed accumulation mode aerosols (D50>30 nm) for all test modes. An increase in peak number concentrations of nucleation mode (D50>30 nm) diesel aerosols is evident for some of tested DPF systems when engine was operated at high-load modes. The effects of uncatalyzed DPFs on nitric oxide (NO) and nitrogen dioxide (NO2) concentrations are found to be minor. A four-fold increase in percentages of NO2 in total nitrogen oxides (NOx) over baseline case was observed for the DOC when the engine was operated at high-load modes. The findings from this study should contribute to better understanding the potential for various control technologies to reduce exposure of underground miners to nano and ultrafine aerosols. In addition, detailed physical characterization of diesel aerosols made directly in occupational setting should foster a better understanding of the health risks associated with exposure to nano and ultrafine diesel aerosols.

By Francis J. Dennis

(San Francisco Meeting, October, 1911.) MANY factors govern the value of dredging-ground, and much capital can be wasted by the mistaken policy of contracting for the purchase of property and the installation of machinery before a thorough, examination has been made. To the uninitiated investor the presence of gold is generally the criterion,, and very superficial evidence is necessary to satisfy him as to this point. He considers the comprehensive report of a competent engineer as a wasteful extravagance and cannot understand why the engineer requires so much time and money to ascertain the information on which to base his conclusions, when the promoter can furnish him such pleasing and satisfactory data with but little expenditure of time and money. The uninitiated investor will often optimistically risk capital for purchase and equipment, and not until the venture comes to grief does he learn that the conditions are wholly unsuited for dredging. In many instances, a short preliminary examination by a competent engineer would have disclosed these facts. The mere presence of gold is by no means sufficient; some of the other factors necessary to be ascertained in determining the value of placer-ground for dredging-purposes are : (1) character and distribution of gold, and how much can economically be recovered; (2) character of bedding underlying the gravel, its contour, and whether its gold can be recovered by ordinary dredging-operations; (3) area and depths of gravel, surface contour, over-burden, water-level, proportion of fine material and boulders, and the presence of any material which might interfere with the dredging-operations and the recovery of the gold; (4) water-supply, power available, labor, transportation, and supplies, and cost of these ; (5) climatic condi-tions; (6) title to property, cost and royalties, and legal obstacles to carrying on dredging-operations. A brief reconnaissance may be sufficient to determine that some of the essential conditions for successful dredging are

Apr 1, 1912