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By D W. MacFadgen

THE operating advantages of the longwall retreating system of mining, as opposed to longwall advancing, have been well known for many years. Although retreat walls have been successfully worked in the past in some of the collieries of the Dominion Steel and Coal Corporation in the Sydney, Picton and Cumberland areas, the adoption of longwaIl retreating as the general sys-tem of mining has not been attractive in the Sydney field, due to the time and expenditures required to drive roadways to the boundary. In addition. difficulties in maintaining effective ventilation on the faces, especially under conditions of low barometer, have made the operators in the field hesitant to adopt this as the general system of mining. The development of a machine capable of rapid entry drivage has made possible the driving of the necessary road ways to the boundary at a moderate cost, completely changing the picture and making a retreat system more attractive.

Jan 1, 1961

By Brennan Lang

Why Seal Tunnels? ?Restore groundwater levels to pre-mining conditions. ?Saturate rock mass to reduce acid rock drainage. ?Reduce discharge flow to the environment. ?Reduce or regulate flows to a water treatment plant.

May 1, 2002

By C. J. Simensen, R. Østhus, H. J. Roven, K. G. Skorpen, H. Kalager

"This work encompasses co-extrusion of alloy Al4.5Mg at the core and rapidly solidified Al4.5Mg1Ag forming the surface layer. The goal is to produce a multi-material by co-extrusion having a relatively hard surface as compared to a softer core. At the same time, work hardening in both alloys is expected to be significant due to Mg in solid solution. Precipitation hardening at 160°C is studied by applying solution heat treatments at 560°C. The hardness increased from 80 to 130 VH in the surface material after 236 h. Surprisingly, the Al4.5Mg alloy also shows pronounced aging at this temperature, i.e. from 70 to 90 VH. The relatively high solution heat treatment temperature introduces grain growth in the core, but this is insignificant for the RS surface alloy. Blisters forms at the surface and cracks follows large portions of the interface. However, the tensile ductility is significant in all conditions due to very pronounced work hardening, i.e. for the as co-extruded, T6, under- and over-aged. The elongation at fracture ranges between 40–45% and the tensile strengths 240–275 MPa. The tensile properties increase linearly with the thickness of the RS alloy, i.e. following the rule of mixtures.INTRODUCTION Al-Mg alloys in 5xxx-series are classified as non-heat treatable wrought alloys (Polmear, StJohn, Nie, & Ma, 2017). The formation of the binary ß-Al8Mg5 does not give a substantial increase in the strength of the alloys (Mondolfo, 1976). When a third element like Ag, Cu or Zn are added, G.P.?zones are formed at low temperatures and intermediate, partial coherent phases are nucleated somewhat higher temperatures and finally a ternary, equilibrium phase is formed (Auld, 1968; Cousland & Tate, 1986; Mondolfo, 1976). Both the formation of G.P.?zones and intermediate phases increase the hardness and strength of the materials. An intermediate, hexagonal T´?phase is formed in Al-5 wt%Mg-1wt%Ag, and finally the equilibrium, cubic phase (Al,Ag)9Mg5 is nucleated (Cousland & Tate, 1986; Mondolfo, 1976)."

Jan 1, 2018

By K. Robertson, K. A. Scalise, K. C. Kocsis, M. B. Teixeira

"Many deep and highly mechanized underground metal mines require cooling. In many cases, appropriate working conditions might be fulfilled by ventilation alone, but some require the implementation of cooling systems. The most common cooling systems are bulk air cooling and localized cooling. These systems are effective, but they use considerable amounts of electricity. Ground source heat pumps (GSHP) can supplement existing cooling and heating systems, while geothermal systems can cool the mines in their entirety if there are significant sources of geothermal energy are present. A major advantage of geothermal and GSHP systems are their renewability, which reduces the carbon footprint of the mine.INTRODUCTIONThe western United States has abundant alternative energy sources including a high potential for geothermal energy. Geothermal utilization is a viable energy alternative that many areas throughout the world have access to because high geothermal potentials are located near areas of volcanic activity such as along plate boundaries, mid-oceanic ridges, rift valleys and hot spots (IRENA, 2017). There is significant potential to use geothermal energy for many applications. With constantly evolving and innovative technologies being developed, an increasing number of geothermal applications are becoming feasible. The western United States is an ideal candidate for alternative energy applications due to the geothermal availability and the emergence of modern technology. This paper investigates the incorporation of renewable methods and the alternative energy possibilities of Barrick Goldstrike, located in northern Eureka County, NV and Rio Tinto/BHP Billiton’s Resolution Copper mine located in Superior, AZ.RENEWABLE SYSTEMSGeothermal SystemsGeothermal temperatures are typically defined as either high or low temperature systems(Shengjun, Huaixian, & Tao, 2011). The high-temperature reservoirs (>220°C / 428°F) are feasible forlarge, commercial production of electricity with dry stream and flash stream systems (Shengjun, Huaixian, & Tao, 2011). Low temperature systems, below 220°C (428°F) (Shengjun, Huaixian, & Tao, 2011), aremuch more difficult to use for energy production. Low-temperature reservoir heat can be harnessedthrough the implementation of a binary cycle plant. The working fluid for a binary cycle plant is eitherorganic (Organic Rankine Cycle (ORC)) or an ammonia-water mixture (Kalina cycle). Organic fluids andammonia-water mixtures have low boiling points that allow for the recovery of heat from low-temperaturesources (Eymel Campos Rodriguez, et al., 2013). The efficiency of the binary cycle plant varies depending upon the fluid, thus the proper selection of the fluid is critical for maximum energy output"

Jan 1, 2019

By G. Q. Zhou, H. C. Liang, X. D. Zhao

"This study describes the strain behavior in vertical shaft lining (VSL) embedded in thick soil deposits and its application in assessment of concrete deterioration. The observed strain in VSL continuously decreased companied by a sinusoidal fluctuation due to the influences derived from negative skin friction (NSF) and temperature. The increase in strain increment between peak and trough at each year and compressive strain level as the servicing time continued and VSL depth increased implies that the concrete strength was attenuated, and this attenuation was significantly dependent on the existing compressive strain level in VSL. The reliability of the proposed approach was validated by Schmidt Hammer Technique (SHT) – based concrete strength, and is applicable in concrete assessment and then fracturing prediction of VLSs in thick soil deposits.Concrete strength, Field monitoring, Strain behavior, Vertical shaft liningINTRODUCTIONOver 100 VSLs in Southeastern China subjected to an unpredictable fracturing as shown in Figure1, and there are over 1,000 VSLs embedded in thick alluvium su?ering from challenges of damaging and potential fracturing (Cheng, Yang, Zhou, Li, & Hu, 1993; Zhou, Cui, Lv, Huang, & Chen, 1999; Li & Li,2005). Therefore, a reliable assessment of these VSLs is significant to the normal servicing of mine shafts and the recycle of underground space when these mine shafts were closed.The continuous increasing of NSF induced by the drainage of water–saturated deposits well interpreted such extensive fracturing phenomenon, and it is universally regarded as the governing indicator to determine the VSL stabilization (Cheng et al., 1993; Zhou et al., 1999). Based on this recognition, the fracturing prediction and VSL strengthening according to the field monitoring on hydrogeological characteristics, servicing environments, and mechanical behaviors of VSL were carried out (Zhao, Zhou, Zhong, Zhu, & Liang, 2009; Liang et al., 2009; Xie, Lv, & Wu, 2014). As known, the compressive strain level in VSL and the in–situ strength of VSL concrete were the main factors to perform such fracturing prediction. However, the existing studies in literatures were limited to the strain accumulating or releasing behaviors (Zhao, Zhou, Zhao, Kuang, & Hu, 2017), and lack of considering the VSL concrete strength and its attenuation. In this reported study, the in–situ monitoring data on the strain in typical VSLs and the VSL elevations between 2004 and 2014 were initially analyzed. Then, an observed strain behaviors–based approach was developed to quantitatively evaluate the VSL concrete deterioration."

Jan 1, 2019

By W. Schubert, N. Radoncic

"The term “squeezing” is frequently used, although it is ill defined. Definitions like “large and long lasting displacements” raise the questions about the threshold values for the magnitude and duration of displacements. Large displacements during tunnelling frequently are observed in fault zones with high overburden. Whether this causes problems very much depends on the design approach used. On the one hand, the magnitude of expected displacements has to be predicted prior to excavation to provide for enough allowance for the displacements without violating the clearance profile. On the other hand, the support characteristics must be compatible with the expected imposed strains. As the magnitude of the displacements and thus the strains in the support depend on the support capacity and its characteristic (yielding potential), only well engineered systems will be successful.Experience in Alpine tunnels over the last decades has shown that closed shotcrete linings can sustain a strain of approximately 0.8% to 1% without failure. Any strain above this value inevitably leads to failure of the lining, and thus a loss of resistance, causing additional displacements. Based on a large number of simulations, a criterion for a critical overburden depth up to which closed linings can be used has been developed. Traditionally open gaps in the shotcrete linings have been used to allow for larger strains. To enhance the efficiency of the linings, yielding elements have been developed, which are integrated in the shotcrete lining, allowing large strains and controlled development of support resistance (Figure 2). When designing such yielding support systems, the development of the displacements, as well as the rheological behaviour of the supports must be considered. As the development of displacements to a large extent depends on the face advance, also the advance rate has to be considered, to be able to compare the time-dependent strength of the lining to the stresses developing as a result of the imposed strains. Another issue is the compatibility of the rock bolts with the large strains. With standard grouted bolts, there is a potential that the “fresh” grout is sheared due to the initially large strain rates. Special rib designs of the bolts allow for a higher strain tolerance.For successful tunnelling through fault zones quality monitoring and up-to-date data evaluation is of crucial importance. With advanced evaluation tools, changes in the ground conditions ahead of the face can be reliably predicted. With the help of empirical relations, the development of the displacements for different advance rates and supports can be predicted, allowing for the determination of the required overexcavation.The paper presents a review of the development of ductile elements, methods of analysis, and monitoring data interpretation."

Jan 1, 2015

By Tao Cheng

Previous research and applications in construction resource optimization have focused on tracking the location of material and equipment. There is a lack of studies on automated monitoring of the interaction between workers and equipment for safety purposes. This paper presents a new approach for measuring the safety performance of construction personnel particularly when they work in very close proximity to moving equipment as well as static hazards such as chemical and flammable substances. A method of generating hazardous zones according to the geometric and kinematic characteristics of the considered hazard is introduced. The spatio-temporal relationships between the hazardous zones and workers? positioning data collected by real-time location sensing technology are automatically analyzed. This approach has been validated in a controlled test bed environment that simulates a construction site. Results indicate that worker?s safety performance of selected activities can be automatically and reliably measured using the developed approach. Furthermore, a heat map is generated for visualizing proximity related issues in the test bed using the computed results.

Aug 1, 2013

By G. K. Quainoo

Investigation by researchers on the application of various thermo-mechanical process histories on 6000 series aluminum alloys have found improvements in mechanical properties of these alloys. However, natural aging, which is unavoidable in the automotive processing line, has been found to have deleterious effect on subsequent artificial aging properties in these alloys. In this study, the evolution of yield strength during natural aging modeled by Lloyd and Gupta has been adapted to investigate the effect of cold deformation on the natural aging kinetics in AA61 11 by means of tensile testing, differential scanning calorimeter (DSC) and scanning electron microscopy (SEM). Also, intermetallic particles in the alloy were extracted from the matrix and XRD performed on them to ascertain their composition and their role on the kinetics in the alloy. The results show that cold work effect on the natural aging kinetics of AA6111 is in very good agreement with the model proposed by Lloyd and Gupta. The kinetics of natural aging in AA6111 aluminum also decreases with increasing level of cold work. This is attributed to dislocations serving as sinks which consume quenched-in vacancies formed during the early stages of clustering. The phases of the intermetallic particles identified in AA6111 are those of a-A15Mn12Si7 and a-A15MnSi.

Jan 1, 2007

By Vladislava A. Ignatkina, Victor D. Samyguin

"Within the limits of two-phase approach, considering mass transfer with pulp and air streams was shown that each bubble appears to be an elementary carrier, transporting particles from the collection zone into the froth. The kinetics of flotation was described by the exponential equation in which first order flotation speed constant has to be replaced with two-phased coefficient of a mass transfer. Criteria of selectivity of two ore fractions separation, based on determination of optimum time at which maximum difference between extractions and components content in separated fractions were offered. An interrelation between optimum time of pulp residence in a flowing chamber of a flotation machine, time of bubbles mineralization and an optimum airflow has been ascertained. Cumulative criterion of mass transfer efficiency of flotation process has been ascertained to be a form of the spectrum and its position on axis of three-phase coefficient of a mass transfer.INTRODUCTIONRegularities of a mass transfer of three bearing streams: pulp stream, air stream and froth stream underlie theory of mineral complexes flotation (Samygin, Filippov, & Shekhirev, 2003)However, only description of mass transfer in pulp stream by means of kinetic equations that were simple and convenient for practical use, has gained a full distribution (Tykhonov, 2009;Rubinstein&Filippov, 1980; Saleh, 2010).Within the limits of a single-phase approach, the role of gas stream in increase of speed and selectivity of flotation, was associated with an improvement of hydrodynamic mode. An influence of particles and bubbles sizes (Rubinstein&Filippov, 1980; Rubinstein&Samygin, 1998, Samygin et al., 2003; Dai, Fornasiero,& Ralston, 2000), of pulpflow and airflow (Finch& Dobby, 1990) and turbulent energy intensity (Shubert, 1979; Massinaei, 2007) on the flotation process has been studied. It was stated that flotation selectivity is increasing by means of gradual airflow increase from first to final cameras of the impeller flotation machine (Aslan&Boz,2010; Finch, 2011) and by means of using a multizone flotation machine (Samyguin, Filippov, Matinin, Lekhatinov, &Tertyshnikov, 2013)."

Jan 1, 2016

By M. Bozorgtabar

Metal Matrix Composites (MMC) have a ductile matrix containing ceramic particles, Due to their improved wear properties, Al?SiC composites have economical applications in many industrial uses where wear is a problem, One of the most serious difficulties in manufacturing Al-SiC composites is obtaining adequate 'wetting' of the particles by the melt. In this research work, a stir casting system was designed for the improved manufacturing Al-SiC composites, The effect of some production variables such as the addition of SiC particles to the aluminum melt on wettability, was also studied. The results showed that the manual addition of particles would not be successful in manufacturing and that a system of adding silicon carbide particles through controlled temperature, atmosphere and improved mixing was needed.

Jan 1, 2005

By Lloyd Buckingham

"The operating cost of a gold mine employing granular activated carbon to recover gold can be greatly affected by the condition of in-circuit carbon and its attrition losses. To accurately identify and quantify carbon losses requires careful study. Carbon attrition in the mill can be attributed mainly to physical or mechanical breakage due to the transfer of carbon in the circuit and to carbon oxidation and thermal fracture occurring in the carbon reactivation kiln. Of the equipment involved in carbon transfer, the water powered eductors are the major cause of abrasion and should be replaced with pumps or alternate methods that can serve the purpose. This paper also reviews the impact of carbon stripping and washing on overall operations.IntroductionHolt-McDermott Mine operates a 1360 tonnes per day Carbon-in-Leach (CIL) mill to recover gold. The relatively high carbon consumption and high remaining gold values on carbon after stripping were viewed as a challenging project for research. Extensive metallurgical testwork was initiated to reduce these values. Figure 1 below indicates the carbon flowchart prior to any significant changes in the carbon handling procedures.Carbon consumption after commissioning which was as high as 10""/o of carbon eluted, has been brought down to less than 5%. Changes that brought about this 50% reduction in carbon consumption are:1 ) Improvements in kiln operation2) Elimination or replacement of eductors3) Reduction in tonnes of carbon eluted"

Jan 1, 1994

By C. Lara-Valenzuela, R. Perez-Garibay, F. López-Saucedo, A. Uribe-Salas, L. Magallanes-Hernandez

A relationship between gas dispersion parameters, namely gas rate (Jg), gas holdup (Eg), average bubble size (db) and bubble surface area flux (Sb), with the metallurgical performance (e.g., grade and recovery) has been established.. Results of eleven columns operating at five concentrators of Grupo Pefioles (Mexico), ranging between 1.52 to 3.35 min diameter and performing in the cleaning stages of lead and zinc circuits, are presented and discussed. The results showed that the effect of gas dispersion parameters was consistent and that both, Sb and Eg, correlate well with recovery particularly when the influence of feed pulp density is also considered.

Jan 1, 2009

By K. Kawagishi, J. Ang, A. Sato, H. Harada

"We have recently proposed a new ""EQ Coating"" bond coat system to solve the problem of secondary reaction zone (SRZ) formation caused by bond coats applied on the hot section components of modem jet engines. A viable EQ coating alloy was previously found for a representative znd generation superalloy, TMS-82+. It would be ideal if the same could be done for a representative 5th generation superalloy, TMS-173. In this paper, we will show that the coating with the best oxidation resistance in the EQ system of TMS-173, although possessing considerably better resistance than TMS-173, did not have sufficient oxidation resistance. In order to improve the oxidation resistance of the EQ coating for TMS-173, we have ventured into ""Pseudo-EQ coatings"". A diffusion couple between the Pseudo-EQ coating and TMS-173, after 300hrs at 1100°C, had a 0-15µm IDZ, but no SRZ. A diffusion couple between a conventional coating and TMS-173 formed a 80-150 µm SRZ. After a 1 hr oxidation test at 1100°C, the PseudoEQ coating formed a thinner oxide layer than the EQ coating, but still contained NiO and spinel. Aerospace"

Jan 1, 2006

HIGH LAKE PROPERTY --HISTORYHISTORY -19501950??s ??Kennarctic Exploration discovers Exploration sulphides (A/B & (D Zones) at High Lake during helicopter reconnaissance exploration program.- -1991 93 Aber signs agreement to earn in to the High Lake Property from Kennecott. 63 holes drilled, primarily testing the known deposits. -2001 Wolfden purchases 100% interest in High Lake from Kennecott and Aber -2002 Wolfden performs helicopter borne TEM Survey over the High Lake Greenstone Belt. -2003 West Zone was discovered following UTEM & Gravity Surveys (performed by Teck Cominco ) over an airborne anomaly approx. 1km west of the known deposits. -2004 Wolfden awarded Bill Dennis Prospector of the Year

May 1, 2006

By G. M. Ritcey, V. M. McNamara

"In the processing of gold ores by the cyanidation route, effluents which are discharged to the tailings areas can contain up to several hundred parts per million of cyanide in complex combination with similar quantities of heavy metals. Complicating this obvious problem of waste control are concentrations of thiosalts and thiocyanates which are roughly equivalent to the amounts of cyanide species. Although most gold mills are located in thinly populated areas, such contaminants can represent a potential environmental problem due to the various limitations exhibited by on-property ponding.The former Extraction Metallurgy Division of CANMET recognized the problem and, in early 1974, invited representatives of the gold mills to Ottawa to discuss the situation. At that meeting members of the Division presented a ""state of the art"" literature survey of cyanide abatement technology for waste solutions, together with preliminary cost estimate data(1). Shortly thereafter, Environment Canada, together with Environment Ontario, decided upon a guideline of 0.1 ppm (0.1 mg/l) total cyanide content as tolerable for an effluent stream which is discharged, in any manner, to the watershed."

Jan 1, 1978

By David W. Mogk, Tamara Darsow, Macgregor L. Fogelsong, Robert M. Hunter, Frank M. Stewart, Edwin H. Abbott, Courtney A. Young

Abstract: Development of cost-effective techniques for recovering precious metals from their ores has been the goal of metallurgists for hundreds of years. Today, metallurgists are increasingly called upon to design processes for ores that are refractory to conventional recovery techniques. These challenges and the addition of environmental costs (including site remediation) to the total cost of mining have stimulated a search for alternatives to conventional processes, such as cyanidation. This paper describes the progress made to date in development of an innovative alternative to cyanidation, termed bisulfide leaching, for extracting gold, silver and platinum-group elements from refractory ores and concentrates. While bisulfide leaching can be implemented abiotically, significant benefits accrue from its practice as a bioprocess that integrates the steps of precious-metals liberation and extraction. In many applications, bisulfide leaching appears to offer significant advantages over the traditional cyanidation process. Dissolved bisulfide and hydrogen sulfide are much less toxic than dissolved cyanide and hydrogen cyanide. Recommended workspace exposure limits and harmful concentrations for hydrogen sulfide gas are higher than those for hydrogen cyanide gas. While the facilities required to practice the bioprocess on an industrial scale would be similar to that of cyanidation plants, chemical reagent costs could be 80 percent less. The bioprocess may also offer advantages in the leaching of ores and concentrates that are not amenable to cyanidation. For example, bisulfide leaching of ores containing carbonaceous material may produce higher gold recoveries if the "preg-robbing" characteristic of the material can be controlled biologically or with dissolved sulfide binding. Moreover, in that precious metals are much more soluble than base metals in bisulfide solutions, bisulfide leaching offers distinct advantages over cyanidation for selective dissolution of precious metals from base-metal concentrates. Thus, the bioprocess uses the natural sulfur cycle to mitigate pollutant production and to enhance precious-metals recovery.

Jan 1, 1998

By M. Rafieazad, P. Fathi, X. Duan, M. Mohammadi, A. M. Nasiri

"Direct metal laser sintering (DMLS) is a metal additive manufacturing technology that creates highly complex components by fusing metal powder into a solid part. In this study, the impact of surface roughness on corrosion resistivity of AlSi10Mg_200C alloy manufactured through DMLS was investigated. The as-printed DMLS-AlSi10Mg _200C alloy was subjected to various surface finishing processes including grinding and sandblasting. The corrosion performance of the surfaces was then evaluated using potentiodynamic polarization testing and electrochemical impedance spectroscopy (EIS) in a 3.5 wt.% NaCl solution to mimic seawater environment. Surface characterization and corrosion morphology of the samples were assessed by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) spectroscopy. The results of this study show that the surface finishing process and the resultant surface roughness has a significant impact on the corrosion resistivity of the DMLS-AlSi10Mg_200C alloy in the seawater environment.INTRODUCTION Direct Metal Laser Sintering (DMLS), also known as Selective Laser Melting (SLM) (Sames, List, Pannala, Dehoff, & Babu, 2016), Laser Beam Melting (LBM), or Laser Metal Fusion (LMF) (Herzog, Seyda, Wycisk, & Emmelmann, 2016), is an additive manufacturing process that utilizes a precise, high-power laser to micro-join powdered metals and alloys layer by layer to form almost fully dense and functional components in three dimensions from the 3D computer-aided design (CAD) data. Complex geometries not possible with conventional manufacturing processes can be readily manufactured with high accuracy using the DMLS process with no need to time-consuming tooling."

Jan 1, 2018

By R. G. L. McCready, Marco Zentilli

"Brogan coal containing mean averages of 6,93% w/w total sulphur (1.1% sulphate sulphur, 1.6% organic sulphur and 4.24% pyritic sulphur) and 16.34% mineral ash was used as the test coal in these studies.Shake-culture leaching studies on seven size fractions of the coal, ranging in size from 0.045 mm to 1.7 mm, showed that the rate of pyrite leaching was inversely proportional to the particle size. As the use of continuous stirred tank reactors would be uneconomical for the reclamation of waste coal, column leaching studies were initiated on coal sieved to >6.35 mm to < 12.7 mm, The leachate was monitored for all metal ions and the release of iron was used to monitor the rate of pyrite oxidation . Measurable amounts of Zn, Co, Ni, Mn, and V, all of which can replace iron in the pyrite crystal structure, were released during the initial stages of leaching. Further, high concentrations of AI, Ca and Sr and trace amounts of Sn, As. Se, B, Ca, Cr, Si, and Ti were detected in the column effluents.These studies suggest that bacterial leaching will remove the pyrite and qualitative amounts of environmentally undesirable trace metals from the coal if such a process is developed for waste coal reclamation.IntroductionIn 1947, Colmer and Hinkle showed that acid mine drainage was the result of an oxidative attack of the iron-mineral sulphides by Thiobacillus ferrooxidans to produce sulphuric acid . Ashmead (1955) proposed the use of these organisms to desulphurize coal , but the subsequent research effort was concentrated on the metabolism and physiology of these extreme acidophiles.A limited number of studies have been reported on the bacterial leaching of pyrite from coal (Silverman et al., 1963; Dugan, 1977). However, the bacterial oxidation of pyrite is a self-limiting first-order reaction, probably due to the precipitation of Fe(OH)J and elemental sulphur , which progressively inhibits intimate contact between the bacterial cells and the sulphide-mineral surface. Consequently, the best pyrite oxidation experiments with coal reported to date required five days to remove 97070 of the pyrite (Dugan &Apel , 1978) using mixed cultures of T. ferrooxidans and T. thiooxidans."

Jan 1, 1985

By K. G. Wheeland, K. G. Byberg

The occurrence of a secondary, dust-fuelled explosion following blasting of sulphide ores has been reported in mines in many countries, including canada, the USA, Australia and South Africa. However there has been little effort to document the events and develop effective control technology. Following a detailed investigation of an incident at the Geco Di vision of Noranda Minerals Inc. , the company held a conference of interested parties in October 1986 to review the state-of-the-art and to agree on action. '!his paper outlines the causes and effects of such explosions, the key conference points and conclusions, and subsequent information-exchange and teclmology-developrnent activities.

May 11, 1988

By F. F. Roberto

Sulfuric acid has been demonstrated to be an efficient lixiviant for in situ extraction of copper in the past. It has also been proposed that microbial production (by iron-oxidizing acidophilic bacteria) of acidic ferric solution either in situ or ex situ could provide an economic strategy to generate an effective lixiviant for secondary copper sulfides like chalcocite and covellite. Copper heap bioleaching also takes advantage of this approach. One of the major environmental challenges for in situ copper recovery projects is the containment of acidic solution within the ore deposit, and ultimate restoration of the depleted ore body to its original state. A perhaps overlooked aspect of projected site operations is the possibility that transient acidic conditions and pumping of solutions from surface reservoirs into the subsurface could stimulate the growth of iron- or sulfur-oxidizing species of acidophilic microbes in the ore body, leading to additional generation of sulfate, acid, and ferric iron. This outcome would benefit extraction of copper in mixed oxide/sulfide deposits in the near term, but could complicate restoration activities. Possible impacts of pumping acidic solutions into the subsurface on microbes resident in, or introduced into the extraction zone will be discussed in the context of our understanding of copper heap bioleaching and acid rock drainage. INTRODUCTION As high-grade deposits of metals such as copper continue to decline, conventional mining methods have evolved to mine and process larger and larger quantities of ore. What is currently defined as ore today often contains less metal than the tailings of past operations. The throughput of current-day mines also leads to tremendous amounts of waste rock and tailings that may threaten the environment and communities around the mines, as has recently been experienced by 3 major tailings disposal facility (TSF) dam failures in the past 5 years. Community acceptance of large mine operations thus becomes more difficult to achieve—loss of the social license to operate. In response, the mining industry urgently pursues innovations that can fundamentally change the way in which metals are mined. In situ recovery (ISR) of metals represents one approach to a more sustainable mining industry, by virtually eliminating the need for a pit or underground excavation, eliminating the excavation and transportation of ore to a process plant and the ensuing noise and dust that is generated, and any need for waste rock dumps or TSFs. An ISR mine could have very little visible footprint beyond a network of wells, pumps, and piping to transport pregnant solution to a recovery facility, such as a solvent extraction- electrowinning (SX-EW) plant for copper. Some solid waste streams and/or storage ponds may still be necessary to treat and store bleed streams, PLS and raffinate, or as part of groundwater restoration activities. Thus capital and operating investments would be potentially much lower than that required for a conventional mine. In theory production could also be controlled to adjust to subsurface ore grade and match market demand. A not insignificant challenge of in situ recovery is the requirement for an efficient, low-toxicity, and ideally selective lixiviant for the metal that is targeted.

Jan 1, 2019