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By D. J. Englund, R. A. Davis

"A three-dimensional CFD model of a straight grate furnace for indurating iron-oxide pellets was developed for exploring conditions of furnace operation for fluid flow, heat transfer and reactions. The model includes reactions for natural gas combustion in the gas phase and calcination and magnetite oxidation as well as drying in the pellet bed. The performance of the model was investigated with a series of pellet production rates that included adjustments to the fuel rates to achieve proper induration temperatures in the pellet bed. The model may be used to discover opportunities for process improvement.IntroductionIron oxide pellets are a feedstock to blast furnaces for iron making. Pellets require physical strength characteristics needed to maintain their integrity during storage, handling, transportation and smelting. Pellets are produced from iron ore in a series of mineral processing operations that form wet green balls from slurries of iron-ore concentrate with binders, such as bentonite, and possibly fluxing-agents such as limestone and dolomite. The green balls are dried, fired at high temperature, and then cooled in an induration furnace to achieve the strength and chemical composition required for efficient reduction and slag separation in blast furnaces. Induration furnaces are generally straight grates or grate-kilncooler configurations. These furnaces operate with pellet beds passing through a series of temperature zones to control drying and chemical reactions in the bed.Process air passes through the zones in an overall counter flow direction to the pellets for efficient heat transfer and energy recovery from the cooling stage. Consequently, the zone conditions and the overall furnace performance are highly coupled. Thus, it becomes challenging to predict how changes to any single zone may affect the rest of the furnace. To gain a better understanding of machine performance and coupling, a three-dimensional, steady-state model of a complete straight grate induration furnace was created using computational fluid dynamics (CFD)."

Jan 1, 2015

By M. Laliberte

"Gold-mine effluents are often characterized by high concentrations of copper, ammonia and cyanide derivatives (mostly cyanates and thiocyanates). While not acutely toxic to birds, this water can be acutely toxic to fishes and invertebrates. In many jurisdictions, the effluent requires further treatment in order to pass a mandatory requirement to be nonlethal to species like the rainbow trout (Oncorhynchus mykiss) or Daphnia magna. Using actual mine water, it has been demonstrated that aerated moving bed biofilm reactors will biodegrade the ammonia, cyanides, cyanates and thiocyanates, thereby removing the toxicity associated with these components. By removing copper by precipitation the water can be made to pass acute toxicity tests. Tests have demonstrated that the process is stable between 4 and 25°C, with no significant changes in the treated water composition. Once the biomass is acclimatized, the process is resistant to upsets and requires very little inputs except for phosphorus and air. Furthermore, it has been demonstrated that an anoxic reactor can be added downstream of the aerated reactors to remove nitrates if required.IntroductionThis paper will demonstrate that gold-mine effluents, which are toxic to fishes and invertebrates, can be made nontoxic by using a combination of chemical precipitation and biological oxidation.The typical composition of gold-mine effluents will first be described. The applicable legislation will then be introduced, with its requirement that the treated effluent be nontoxic. The toxicity of a typical untreated effluent will then be confirmed, and the sources of the toxicity identified. After that, a number of toxicity reduction treatment methods will be presented, and the selected method will be described.The lab tests that confirmed the efficiency of the treatment method will be presented, with three phases of testing as the understanding of the process gradually improved. Toxicity test results showing that the water is nontoxic after treatment through the temperature range will be presented."

Jan 1, 2015

By C. Pomeroy, J. Weyer, J. Brune

"Mining began in the Erzgebirge (“ore mountains”) region of Saxony, Germany more than 800 years ago, and extensive underground workings cut through the entire area. Some of these old workings are still used today: not for production, but for offering an underground venue for research, tourism and university teaching. One example is the Reiche Zeche mine at the Technische Universität Bergakadamie Freiberg which hosts one of the oldest mining engineering programs in the world. It is imperative to keep all active mine workings well ventilated to make the mine safe for students, visitors and researchers. Since the mine workings at Reiche Zeche are so vast, extensive and, to a large extent unexplored and unmapped, it has been difficult to provide a complete, functioning and adequate mine ventilation model for this mine that accounts for all known and unknown leakage air flows. Researchers at the Colorado School of Mines have cooperation with their colleagues at Freiberg to establish a mine ventilation network model based on a limited number of air readings in known and accessible drifts. In order to balance the measured air quantities, leakage flows were quantified and mapped by comparing input and output flows of mapped drifts, and modelled using Ventsim Visual, a powerful visualization software package. The resulting mine ventilation model is used to locate and quantify the leakage air flows and to examine how much air is lost in each area. With this model, ventilation changes and improvements underground can be documented reflected in the model. This enables the Bergakadamie Freiberg to project air changes required for scientific experiments and to set up mine ventilation in specific areas and for specific needs. The model also enables better ventilation control and monitoring than before. Finally, the model can be used to predict ventilation changes and escape way contamination in case of a fire, ground fall or inundation in the mine. The latter becomes important as the lower mine workings are often flooded during spring runoff, which has created uncertainty about mine ventilation in the past. HISTORICAL BACKGROUND The discovery of silver, lead, zinc, tin and other valuable metal ores in the Erzgebirge region of Saxony, Germany began in the12th century and started a mining boom than lasted for centuries. Surface mines quickly developed underground to access the higher grade veins. Explored by the early geologists and driven by the ingenuity of the miners, the underground works expanded vastly throughout Freiberg and the surrounding region. Development followed the highest grade veins, and engineers developed solutions to drain water and provide limited ventilation to the underground workings. Still, engineered and planned ventilation was usually not a priority in the development of a new drift, which today makes ventilation modeling a significant challenge."

Jan 1, 2015

By H. -S. Yoon, C. -J. Kim, K. W. Chung

"With the final goal of ultrasonic application to ion exchange in a resin-in-pulp (RIP) system, the feasibility of an indirect ultrasonic application with a submersed ultrasonic probe was investigated first for the enhancement of ion exchange in the following resin-in-solution (RIS) system: Lewatit MonoPlus MP 600XL in an artificial solution with 106 ppm uranium. Ultrasonic radiation enhanced the ion exchange efficiency without mechanical degradation of resin. For 3.6 g/L of resin, the enhancement was 79 percent after 10 min of ion exchange and it gradually decreased to 11 percent at 60 min. In addition, a preliminary test of the mechanical stability of the resin in the RIP system showed little mechanical fracture of the resin due to ultrasound, which indicates that indirect ultrasonic application by a submersed ultrasonic probe is applicable for RIP systems. IntroductionIn uranium ore processing, the ion exchange process has been used on a commercial scale for preconcentration and purification (Gonzalez-Luque and Streat, 1984). The ion exchange process is divided into two processes: (1) a resin-in-column process with the uranium-bearing solutions passed through columns containing resins and (2) a resin-in-pulp (RIP) process with the leached ore pulp exposed to resins. The latter does not require the separation process of leach liquor and ore solids, which reduces process costs. This process, which has been developed commercially since 1955, has a certain drawback. The adsorption rate and efficiency in the RIP process are relatively low, so numerous contacts between resins and leached ore pulp are needed, which adds to the cost (Merritt, 1971). It is necessary to study methods to reduce process costs.Ultrasound can intensify mass transfer, increase the rate of chemical reactions, and change reaction pathways (Thompson and Doraiswamy, 1999; Luque de Castro and Priego-Capotem, 2007; Adewuyi, 2001; Luque-Garcia and Luque de Castro, 2003). It has great potential in chemistry and is especially considered to be a promising method for enhancing mass-transfer-limited processes, such as ion exchange. Enterzari and Tahmasbi (2009) reported the effect of ultrasound on water softening by ion exchange. Band et al. (1997) proposed a modulated ultrasound application to water desalination with ion-exchange hollow fibers. These reports revealed that ion exchange kinetics could be enhanced by the application of ultrasound. As for hydrometallurgy, Feng and Aldrich (2000) reported that the elution of an ion exchange resin was enhanced by the use of ultrasonication."

Jan 1, 2015

By Erica Frederickson

"Millennials. Doesn’t the word just make your blood boil? You’ve probably encountered one of those kids who think they know best despite a lack of any real experience.Hi, my name is Erica, and I am a Millennial. We often get a bad rap, sometimes for good reason. But we do have qualities that are often overlooked. For example, I am happy to share with my generation a real desire to make a difference in the world and a commitment to innovation. Does this mean I think we always have good ideas? No – especially not right away. After all, few of us came anywhere near a piece of construction equipment until arriving for our first job, as was the case for me. We may have fancy degrees, but not many of us learned to run a jackleg drill in school.Two weeks after graduating college in 2011, I packed up my bags and moved to New York City to work as a field engineer for Traylor Bros. Inc. on the Queens Bored Tunnels project (Granite/Traylor /Frontier Kemper, JV), part of NYC MTA’s multi-billion dollar Long Island Railroad East Side Access project. It was here I became acquainted with the notorious New York City union workers. Perhaps the greatest challenge of my career thus far was earning the respect of the field supervision and craft workers on this first project.The first time I asked a maintenance mechanic to clean a piece of equipment in accordance with our maintenance protocol I got a flat-out “No.” It was the most powerless I had ever felt. But why should these experienced workers trust a 21-year-old girl with her civil engineering degree and no prior experience? I realized no employee on the job had any reason to listen to me — not until I proved my worth. Fortunately, I arrived on the job site just as we were commissioning the slurry plant for the first tunnel drive. I dove into learning as much about the slurry tunneling process as possible and was able to quickly pick up the ins and outs of running the slurry separation plant. As none of the other engineers or management had first-hand experience on a slurry tunneling job, I soon became the go-to engineer in the slurry plant. No one questioned me if I asked to have something done around the plant after that, or if they did, they quickly learned that I had a convincing answer as to the need for the task. I was even able to play a large role in shaping our slurry monitoring and control methodology."

Jan 1, 2015

By William Gleason

"The Colorado School of Mines has used the Edgar Mine in Idaho Springs as an experimental mine to teach students since 1921. Since the school acquired the former gold, silver, lead and zinc mine, countless students have received hands-on engineering lessons on their way to earning mining engineering degrees. On Dec. 14, the House Subcommittee on Energy and Mineral Resources held a historic field hearing about the future of mining education in the United States in a classroom about 300 m (1,000 ft) inside the Edgar Mine. Representatives Doug Lamborn (R-CO), Rob Bishop (R-UT), Cresent Hardy (R-NV) and Ed Perlmutter (D-CO) were on hand for the first ever congressional hearing held in a mine where they heard testimony supporting the Mining School Enhancement Act, which was introduced to Congress by Hardy and Perlmutter on Oct. 9, 2015. The act, which is part of a larger mining development and reclamation reform package, seeks to address the absence of a viable pipeline necessary to replenish current faculty vacancies in United States Mining Schools. “What better place to hold a hearing to discuss the need for future mining engineering experts,” Subcommittee Chair Lamborn said in his opening statement. “It is a need felt by industry, states, the federal government as well as nonprofits.” The Mining School Enhancement Act would redirect millions of dollars in fees that are being collected from active mining operations to fund the research and educational programs at engineering schools with mining programs. Those fees now are being used in the form of grants awarded by the Surface Mining Control and Reclamation Act of 1977 (SMRCA)."

Jan 1, 2015

By M. Xing, S. Usman, K. Awuah-Offei

"While mines generally focus on achieving operational efficiency, creating shared value for all stakeholders is also a management goal. This includes taking a holistic view of their supply chains and increasing local participation. This paper examines the role of supply chain management in mine management; in particular the effect of a strong local supply chain on regional economic impacts. Using input-output analysis, the impact of a local supply chain on a mining sector’s regional economic impact is examined by increasing local sourcing (increasing local purchase percentage -- LPP) for 10 key commodities. An approach, based on multipliers and excess local capacity is used to identify key commodities. The impacts examined are sales, employment, labor income, and value added. The work is illustrated with stone mining and quarrying in Missouri. Ten percent increases in LPP of the key commodities, in this example, result in $4.1 million additional impact on the Missouri economy. This work can provide insight on how to better create shared value for all stakeholders. INTRODUCTION Little research has been published on improving mine supply chain management (SCM) to enhance regional economic impacts. Although some extensive academic research has explored the importance of an industries’ supply chain, not much is known about how a locally-based supply chain increases shared value in the resource sector. Across industries, traditional SCM is getting more and more complex. This is true of the mining sector as well. However, this increased sophistication is not directed towards increasing shared value for all stakeholders, particularly, the local communities. Further research is required to develop new SCM strategies that enhance local participation. One major point of difference between this work and traditional supply chain management is the inclusion of stakeholders’ shared value as a goal in SCM. Creating shared value has become a business goal in recent years (Porter and Kramer, 2011). The authors use input-output analysis (Leeuw, 2012) to evaluate the regional economic impacts of supply chain decisions, which is not part of traditional SCM. Although input-output analysis has been applied to SCM for decades, most of the research uses input-output analysis as a tool to advance an industries’ own operational efficiency (Accenture, 2014)."

Jan 1, 2015

By K. A. Natarajan, M. R. Sabari Prakasan

"Biodegradation of sodium isopropyl xanthate using two types of bacterial strains, Paenibacillus polymyxa and Pseudomonas putida, is demonstrated. At concentrations higher than 50 mg/L, the presence of xanthate in the growth medium resulted in bacterial toxicity, retarding growth kinetics. Adaptation through serial subculturing in the presence of higher xanthate concentrations resulted in the development of xanthate-tolerant bacterial strains. Stress proteins secreted by bacterial cells grown in the presence of xanthate were isolated. Bacterial cells could utilize xanthate as a growth substrate, degrading xanthate species in the process. Acidic metabolic products generated by bacterial metabolism promoted efficient xanthate decomposition. Probable mechanisms for the biodegradation of isopropyl xanthate are illustrated.IntroductionDifferent types of alkyl xanthates (ethyl, isopropyl, amyl, etc.) have been used as flotation collectors in the concentration of sulfidic ores for several decades. Large quantities of waste water and xanthate-containing effluents are generated by ore flotation processes, posing considerable environmental challenges. Billions of cubic meters of such process waste waters are produced annually across the world, most of which are discharged to the environment, often without any treatment. Leakages and accidental release of xanthate reagents from manufacturing plants and during transportation and storage can also contaminate the environment. Residual concentrations of xanthate reagents are encountered in waste effluent, which are found to be toxic to aquatic life and unfit for human consumption (Harris, 1984; Okibe and Johnson, 2002). Further, direct recycling of such waste waters for plant operations can compromise water quality standards required for process operations. The presence of residual xanthate in recycled waters from flotation plants deleteriously influences flotation processes. Xanthate can be easily decomposed at low pH values; however, CS2, which is more toxic, will be produced by the acidification of neutral and mildly alkaline xanthate-containing solutions. Physico-chemical methods such as flocculation, chemical oxidation and decomposition and physical adsorption used to remove residual collector reagents from mill process waters are often expensive and not environment-friendly (Oliveira and Rubio, 2009; Cheng et al., 2012; Molina et al., 2013,)."

Jan 1, 2015

By S. K. Kawatra, H. J. Haselhuhn

"Fine-grained hematite ore can be concentrated by the process of selective flocculation and dispersion, which relies on proper reagent selection and control of water chemistry. While many previous studies have been performed analyzing the effects of different reagents on this process in a laboratory environment, this paper focuses on investigating the water chemistry within the process in a pilot-scale continuous deslime thickener.The pH, sodium concentration, calcium concentration and magnesium concentration were varied to determine their effects on the iron concentrate grade and recovery, and the phosphorus concentrate grade and rejection in the pilotscale selective deslime thickener. The ideal pH for the iron grade and recovery of the process using a starch selective flocculant was found to be 10.5. Phosphorus rejection, however, was increased at lower pH values. Minimization of sodium concentration was shown to improve iron grade, iron recovery and phosphorus rejection. Calcium acted as a nonselective flocculant showing higher iron recovery, lower iron grade and lower phosphorus rejection with increasing concentration. Conclusions could not be drawn from the experiments that varied magnesium concentration.The zeta potential of the solid-liquid interface of particles in each sample taken was also analyzed to show relationships between zeta potential and process performance. In all cases, a maximization of the magnitude of zeta potential correlated with increased iron grade and recovery. This supports the hypothesis that a higher level of dispersion enhances the selective flocculation and separation process.IntroductionThe United States produced 53.2 million metric tons out of the 3,000 million metric tons of concentrated iron ore produced worldwide in 2012 (Tuck, 2013). With this in mind, there has been a large increase in iron ore processing research (Bolen, 2014; Carlson and Kawatra, 2008, 2013; Halt and Kawatra, 2014; Halt et al., 2014; Haselhuhn et al., 2012a,b, 2013a,b; Liu et al., 2014; Manouchehri, 2014; Sandvik and Larsen, 2014; Semberg et al., 2014). Of the 53.2 million metric tons produced, roughly 8 million metric tons of hematite (Fe2O3) concentrate were produced using a process known as selective flocculation and dispersion (Cliffs Natural Resources, 2011). This process is the only economically viable method for concentrating low grade (< 40% Fe) fine grain (< 25µm liberation size) hematite ores. It is scarcely used due to difficulty in controlling the surface chemistry of the ore and high reagent costs (Department of Energy, 2001; Haselhuhn et al., 2013a). The process is highly dependent upon both reagent selection and precise control of the water chemistry during separation. This study shows the dependence of the process performance of a pilot-scale deslime thickener on the water chemistry in the feed slurry."

Jan 1, 2015

By C. L. Peng, F. F. Min, S. X. Song

"Using a parameter representing the degree of hydration of particles in a liquid called hydration index I, which we derived based on Einstein’s viscosity equation, we evaluated the degree of hydration of fine montmorillonite particles in different aqueous solutions by measuring the viscosities of the montmorillonite dispersions and plotting relative viscosity against volume fraction of dry montmorillonite particles in the dispersions. We investigated the effects on the hydration of montmorillonite in aqueous solutions of (1) the type and (2) the concentration of electrolytes in the solutions and (3) pH. For the same concentration of electrolytes, the hydration index I of montmorillonite was found to increase in the order of Na+ > K+ for monovalent cations and Mg2+ > Ca2+ for divalent cations, and to decrease with increasing valence of cations in the order of Na+ > Ca2+ > Al3+. For both Na+ and Ca2+, the hydration index I first increased with increasing concentration of electrolytes and then decreased after a certain concentration. The hydration index I increased with increasing pH. IntroductionClay minerals have the distinctive ability to adsorb water molecules and hydrated cations in aqueous solutions, resulting in hydration on their outer surfaces and in their interlayer spaces. Many investigators (Jurinak, 1963; Anderson and Tice, 1971; Costanzo et al., 1982; Israelachvili, 1992) had found evidence of ice-like structures of water on clay minerals.This phenomenon of hydration plays an important role in the dispersion and sedimentation of clay minerals in aqueous solutions. To understand clay hydration, numerous experimental and simulation studies have been carried out since 1933, including the recent ones of Hawkins and Egelstaff (1980), Skipper et al. (1995), Karaborni et al. (1996), Salles et al. (2013) and Morrow et al. (2013). Among the factors that can influence a clay mineral’s hydration characteristics are chemical composition, type and degree of isomorphous replacement in its structure, and number and nature of associated exchangeable cations."

Jan 1, 2015

By A. D. Hammond

"INTRODUCTION Vanadium deposits in Arizona are distributed all across the state, from the rim of the Grand Canyon to the Tombstone mining district in the southeast corner of the state (Figure 1). The combined past production of vanadium from Arizona and New Mexico ranks second nationwide, after deposits in the Colorado Plateau In the northeast corner of the state, in the Carrizo Mountains and Monument Valley of Apache and Navajo Counties, vanadium was produced as a by-product of uranium in deposits of the Salt Wash and Shinarump members of the Morrison and Chinle formations, respectively. The production took place between 1943 and 1970. Another source of vanadium in Arizona occurs in vanadate deposits associated with supergene enrichment of base-metal vein and replacement deposits. The most important vanadate mineral is vanadinite, a chloro-vanadate of lead. Presently, there are no primary mines of vanadium in the United States. In 2012, a small production of vanadium pentaoxide (V2O5) was reported as a by-product of uranium at the White Mesa uranium mine in Utah1. This paper describes vanadate deposits in Arizona with emphasis in three districts, namely, the Mammoth, Globe-Miami and Banner districts.VANADIUM EPIGENETIC DEPOSITS: VANADATES Almost all vanadium epigenetic deposits occur as vanadates in oxidized zones of lead, zinc and copper veins and replacement deposits. Vanadinite, descloizite and mottramite are the most common minerals in vanadate deposits. Descloizite is a vanadate of lead, zinc and copper. Wulfenite, a molybdate of lead is also present. These minerals replace supergene base-metal minerals, form crusts on faces of open cavities, or are inter-grown with residual clays in pockets. The vanadium content in vanadate deposits is believed to have been leached from the country rock by ground-water and transported through porous rocks until precipitating as a relatively insoluble vanadium compound or until the solution evaporated. Precipitation was brought about by local concentrations of cations of divalent lead, zinc or copper. Lead is a constituent part of almost all of vanadate deposits and the vanadium pentaoxide (V2O5) content in vanadate minerals seems to have a direct correlation with the content of lead in the hypogene mineral. Vanadate deposits are restricted almost entirely to the oxidized parts of vein or replacement deposits. It is rare that oxidized zones extend past 100 ft from the surface. Vanadate deposits are largely restricted to tropical and temperate zones and regions of dry climate. Arizona and New Mexico have the largest concentration of vanadate deposits in North America."

Jan 1, 2015

By A. J. Martin, M. J. Peoples, D. J. Adams, A. Opara

"The weathering of coal mine waste rock releases iron, calcium, sulfate and associated trace elements like selenium (Se). Nitrogen species are also found in association with coal-mining drainages mainly due to the leaching of residual blasting compounds. Elevated concentrations of Se are a ubiquitous occurrence in coal-mining environments in British Columbia. A major concern with waterborne Se in British Columbia is the potential for its bioaccumulation in aquatic food chains.Treatment to remove Se from coal-mining waste waters has proven to be challenging for conventional water-treatment technologies. Compounding this challenge, many streams are characterized by high flows and low selenium concentrations. Conventional membrane and ion exchange treatments produce concentrated brine streams that are difficult to treat or require disposal. Conventional biotreatment systems use excess nutrients to provide the required electrons to compensate for inefficient and variable electron availability, as well as to adjust reactor chemistry.This paper's electro-biochemical reactor (EBR) technology provides a controllable and consistent supply of useable electrons to the microbes directly at a low voltage potential (1-3 V) and low current. In this manner, the EBR technology overcomes the shortcomings found in conventional systems, as it reduces the required nutrient addition and provides a more controllable, efficient, economical and robust biotreatment system. Additionally, the EBR process does not produce excess solids or biomass; therefore, solids management post-treatment is not required.Laboratory EBR bench-scale and on-site pilot-scale systems were used to treat five British Columbia coal-mine waste waters; influent Se concentrations ranged from 35 µg/L to 531 µg/L. Se treatment targets for the tested waters ranged from 5 to 10 µg/L. Mean Se concentrations in EBR effluents ranged from 0.5 µg/L to 1.4 µg/L, while reducing sulfate concentrations. The test data demonstrate that the EBR technology is an effective Se removal option for British Columbia’s coal-mining waste waters.IntroductionSelenium in Mining. Selenium (Se) is a naturally occurring trace element, which is an essential nutrient in small amounts (Thompson and Robinson, 1980; Brown and Arthur, 2001). However, it is also toxic to aquatic life, birds, and humans at very low concentrations. A major concern with waterborne Se is the potential for its bioaccumulation in aquatic food chains, resulting in acute and/or chronic toxicity to fish, water birds and amphibians (Besser et al., 1996; Conley et al., 2009)."

Jan 1, 2015

By K. A. Natarajan, K. Karthiga Devi

"A biodegradable flocculant was produced during growth of Bacillus megaterium. The major component of the bioflocculant was found to be a polysaccharide composed of some proteins. Fourier transform infrared (FTIR) spectra analysis revealed the presence of carboxyl and hydroxyl groups in the bioflocculant, and thermal characterization by differential scanning calorimetry (DSC) showed the transition and crystalline melting point at 90-105°C. The effects of bioflocculant dosage and pH on the flocculation of mineral suspensions were evaluated. The bioflocculant exhibited good flocculating capability on mineral suspensions and achieved flocculating efficiencies of 90 percent for kaolinite and 85 percent for hematite suspensions at a dosage of only 5 mL/L. The maximum arsenite removal was found to be 90 percent at a bioflocculant dosage of 2 g/L, which is better than traditional chemical flocculants. This study demonstrates that microbial bioflocculants have potential for application in environmental cleanup, such as in the flocculation of mineral fines and in the remediation of solutions that contain toxic heavy metals.IntroductionBioflocculants are biopolymers produced by microorganisms during their growths. The predominant components of a bioflocculant are extracellular polymeric substances such as glycoprotein, protein, cellulose and nucleic acid (Salehizadeh and Shojaosadati, 2001). Bioflocculants have gained much wider attention due to their biodegradability and safety. In recent years, the study of bioflocculants has attracted wide attention. Bioflocculants can be nontoxic, harmless and eco-friendly. Normally, they exhibit different functional properties, serving as stabilizer, dispersant or thickener. Among these properties, flocculation is of major interest. For example, Phormidium sp. strain J-1, isolated from a drainage channel, exhibited excellent flocculation activity for bentonite particles in liquid suspension (Fattom and Shilo, 1984). A protein bioflocculant produced by Rhodococcus erythropolis could efficiently flocculate suspended solids while losing their flocculating activity by enzymatic digestion (Kurane et al., 1994, Takeda et al., 1991). Klebsiella sp. strain S11 screened from activated sludge was unable to flocculate without the addition of calcium chloride (Dermlim et al., 1999)."

Jan 1, 2015

By K. Huttu, A. van Wageningen

"The Kittila underground mine is extracting one of the largest known gold deposits in Europe and has an estimated mine life through 2034. The Kittila mine is located in the Lapland region of northern Finland, approximately 900 kilometres north of Helsinki and 150 kilometres north of the Arctic Circle. The ore at the Kittila mine is refractory, making gold extraction relatively difficult because the gold is generally locked inside the two main sulphide minerals – arsenopyrite and arsenic-rich pyrite. The orebody consists of a complex pinch-and-swell structure including up to 100 different gold mineralization lenses. Fluctuating gold prices and other economic considerations increase the need to maintain and update the mining plans more frequently. Over 3,000 stopes need to be designed and optimized once a year for the LOM-plan and more frequent updates are needed for mid- and short term plans as well as production studies. As a large part of ore body is very sensitive to cost and gold price changes, stope optimization is crucial to find the best possible production scenario for every moment. Kittilä has gone through several methods for stope design and optimization. Most recently the Deswik Stope Optimizer (Deswik.SO) has been successfully used. Dewsik.SO has helped Kittilä to design and optimize stopes in a timely and cost efficient manner. Together with the Deswik suite of planning tools, reliable and auditable plans are created. This paper describes the methods used for stope design and optimization at Kittilä. THE KITTILÄ MINE The Kittila underground mine in northern Finland is extracting one of the largest known gold deposits in Europe. Kittila achieved commercial production on May 1, 2009, becoming Agnico Eagle’s first mine to open outside of Canada. The Kittilä orebodies were initially mined from two open pits – Suuri and Roura – and underground operations were added in October 2010. The pits were mined out in November 2012, so mining is now entirely underground in the Suuri and Roura deposits. Additional, small open pits will mine any remaining near-surface reserves in the future. The Kittila mine is located in the Lapland region of northern Finland, approximately 900 kilometres north of Helsinki and 150 kilometres north of the Arctic Circle. With a mine life estimated through 2034, Kittila is Agnico’s longest-life mine. The mine’s proven and probable reserves contain 4.7 million ounces (32 million tonnes at 4.6 g/t gold). Ore has been mined from underground since 2010. The original 3,000-tonne-per-day operation underwent an expansion project to increase the throughput capacity of the mill by 1,000 tonnes/day, starting by the end of 2014. The region around the Kittila mine is underlain by mafic volcanic and sedimentary rocks of the Kittila Greenstone Belt oriented nearly vertical. This greenstone belt is similar to those hosting Agnico Eagle&apos;s Canadian deposits in Quebec’s Abitibi region and Nunavut. At the contact point between iron-rich and magnesium-rich rocks lies a 100- to 200-metre-thick structural zone known as the “Suurikuusikko Trend”. This trend hosts the Kittila deposit, where multiple mineralized zones have been traced over a strike length of more than 25 kilometres."

Jan 1, 2015

By H. Huang, R. N. Gow

"The reactivity of an enargite mineral electrode was investigated spectroelectrochemically under conditions typically found in alkaline sulfide leach solutions, with pH 11-13 and Na2S additions of 50 and 250 gL-1. A bulk enargite electrode was cycled between 0 and -1,000 mV for each set of solution conditions. Raman spectroscopy was used to determine and compare surface formations against species in mass-balanced EH-pH diagrams generated using STABCAL. Previously, it was determined that arsenic could be selectively leached under alkaline conditions at an average solution potential of -300mV, across the pH range 11-13. Operating under such conditions allowed for the selective leaching of arsenic with elemental sulfur formation. From several of the voltammograms obtained during this current testing, the formation of elemental sulfur appeared at increasingly reducing conditions with increasing sulfide concentration. At high concentrations, copper started to dissolve, possibly as a bisulfide complex, reducing the selectivity of the leach, unlike previous studies. However, the presence of the higher sulfide concentration is also anticipated to prevent passivation by consuming any surface formation of elemental sulfur. This study provides insight into the operating parameters of alkaline sulfide leaching in regards to the selectivity of arsenic leaching, as well as guidance for control of reagents and solution potential and, of course, the need for water treatment afterwards.IntroductionEnvironmental limitations on the pyrometallurgical processing of arsenic-bearing concentrates have forced operations to consider other solutions. Attempts to hydrometallurgically process enargite (Cu3AsS4) fall into two categories: the co-dissolution of arsenic and copper under acidic conditions, and the selective leaching of arsenic under basic conditions. The authors believe that the selective leaching of arsenic is more amenable because it produces a solid copper phase, preferably chalcocite (Cu2S) or covellite (CuS) that could then be processed using conventional methods already in place in the copper and gold industries. Potential leaching methods include alkaline sulfide leaching (Achimovicovica et al., 1999; Anderson and Twidwell, 2008a,b; Tongamp et al., 2009 and 2010), hypochlorite leaching (Vinals et al., 2003; Curreli et al., 2005; Mihaljovic et al., 2007), ammoniacal leaching (Gajam and Raghavan, 1983), and acid leaching (Gow et al., 2014b) with or without fine grinding to mechanically activate the enargite surface and increase normally slow leach reaction kinetics (Achimovicova et al., 1999; Balaz et al., 2000; Balaz and Achimovicova, 2006). In this study, the reactivity of enargite under alkaline sulfide leach conditions was examined."

Jan 1, 2015

By Howard J. Haselhuhn

"The effectiveness of reagent adsorption onto hematite ore particle surfaces is critical during beneficiation to promote effective selective flocculation and dispersion and increase iron oxide recovery. The relationship between aqueous calcium in the process water and the effectiveness of common iron ore dispersants has never before been studied. The nature of common dispersants was studied in the presence and absence of calcium in the process water. The settling behavior of hematite-rich iron ore at pH 11 was assessed in the presence of calcium and inorganic dispersants: sodium silicate, sodium tripolyphosphate (STPP), sodium hexametaphosphate (SHMP) and organic dispersant ethylenediamenetetraacetic acid (EDTA). It was found that inorganic dispersants are ineffective at a pH of 11 without activating the surface sites of the ore particles with calcium. Organic dispersants, however, were found to be effective with and without surface site activation.IntroductionThe United States produced 54 million metric tons of concentrated iron ore in 2011 (Jorgenson, 2013). Over 8 Mt were produced using a process known as selective flocculation and dispersion (CCI, 2011). The grade of this ore is slowly depleting, making it imperative that processing efficiency improves. To increase processing efficiency, a complete understanding of the effects of chemical reagents in the process must be acquired. This process relies heavily on dispersants to disperse iron oxides from gangue minerals in settling processes. The mechanism that these dispersants use to disperse the ore and its relationship to calcium in the process water has never been studied. The following extended abstract summarizes the relationship between aqueous calcium in process water and the effectiveness of common iron ore dispersants at dispersing hydrated hematite ore. These tests were carried out at a pH of 11, as this is a typical pH used to ensure dispersion in selective flocculation and dispersion processes."

Jan 1, 2015

By M. Scaggs

"Respirable dust in underground coal mines has long been associated with lung diseases, and regular dust sampling is required for assessing occupational exposures. At present, respirable dust concentration and crystalline silica content are commonly determined, but considering recent and yet unexplained increases in the incidence of lung disease amongst miners in specific geographic regions, more information about specific dust characteristics is urgently needed. While particle-level dust analysis is ideal, it is impractical for large numbers of dust samples because it is both time and cost intensive. Thermogravimetric analysis (TGA), however, is an alternative option, which offers the ability to determine the total coal to mineral mass ratio in a dust sample – analogous to proximate analysis of bulk coal samples for determining ash content. Here, preliminary development of a TGA method for this purpose is presented. The method is being developed to evaluate dust collected on mixed cellulose ester (MCE) filters using approved permissible sampling equipment. INTRODUCTION Based on the particle size, airborne mine dust can be classified in three categories: inhalable dust (< 100 µm in size), thoracic dust (< 25 µm in size), and respirable dust (< 5 µm in size) (Ramani et al., 2003). The World Health Organization (WHO, 1999) defines inhalable dust particles as those which can be breathed into the nose and mouth, and thoracic dust particles as those which can penetrate airways of the head and enter the airways of the lung. On the other hand, respirable dust particles can penetrate beyond the terminal bronchioles into the gas-exchange regions (alveoli) of the lungs (WHO, 1999). Hlavay (1992) reported that the seriousness of the damage in the lungs and respiratory tract is based on amount of dust remaining in these organs, and the amount of dust depends on the extent of dust exposure, the size distribution of the dust particles, and the capability of the body for dust elimination. Inhalation of respirable coal dust by miners can cause a disabling and potentially fatal lung disease which is called coal worker’s pneumoconiosis (CWP). Silicosis is another fatal lung disease caused by inhalation of respirable silica dust. In CWP and silicosis, dust particles deposit in the lungs, damage the lung tissue, and ultimately cause scarring which cannot be reversed (Colinet, 2010). While overall incidence occupation-related lung disease amongst coal miners in the US has been declining for over 40 years, it appears that there has been a recent increase in specific locations in Central Appalachia (CDC, 2006; Pollock et al. 2010; Suarthana et al., 2011). Although this trend is yet unexplained, one theory is that particular dust characteristics in these locations may be a factor (Hassan and Lau; Page & Oraniscak 2002). For example, several studies have indicated that different coals may generate different amounts of respirable dust (e.g., see Page, 1993 and Litton and Page, 1994), and the surrounding geology may also play a role in terms of the types of dust particles generated. Although respirable dust concentration and crystalline silica content are commonly determined as part of regulatory compliance sampling, more information about specific dust characteristics (e.g., size, shape and composition) is urgently needed."

Jan 1, 2015

By K. Heatwole, D. Shier, A. Davis, J. Kidder, S. Sunkavalli

"Acid rock drainage (ARD) is produced when sulfides are exposed to oxygen and water. Oxidation reactions typically result in a depression of pH and leaching of solutes and metals. Many oxidation models have been developed based on oxygen diffusion, but in environments with high permeability, other transport processes (i.e., convection and advection) can play an important role. Multiple sulfide mineral phases with differing oxidation rates should also be incorporated. WROC, a finite-difference model, was developed to account for these factors in predicting ARD. The program includes sulfide mineral oxidation using a shrinking core mechanism, heat transfer by conduction, heat of reaction and oxygen transport by diffusion and advection. The model was validated using data from the literature. After validation, the WROC model was used to simulate several different waste rock scenarios, including different forms of sulfide mineralization and the effect of implementing a waste rock cover. The results demonstrate that including specific sulfide mineral phases can have a significant effect on oxidation and that implementation of a cover can also aid in reducing waste rock oxidation.IntroductionAcid rock drainage (ARD) is a notable environmental concern in areas where rock or other material with acid generation potential is disturbed. ARD is defined as drainage that occurs as a result of sulfide oxidation in rock exposed to air and water. ARD is characterized by low pH, elevated metals concentration (especially aluminum, iron and manganese), sulfate and high total dissolved solids. The low-pH water that results from acid generation is capable of solubilizing heavy metals contained within the rock. The principal sulfide mineral in mine wastes is pyrite (FeS2). Pyrite oxidation is complex and can involve chemical and biological reactions. Oxidation of pyrite by atmospheric oxygen produces one mole of Fe2+, two moles of SO4 2- and two moles of H+ for every mole of pyrite oxidized, as described by Eq. (1)."

Jan 1, 2015

By H. Burton

"The selection of the ultimate pit shell has a major impact on the overall value of a mining project. The size and shape of this pit drives the selection of pushbacks, equipment, and project strategy, each of which are significant in their own right. Optimization of the ultimate pit shape is typically done using the Lerchs-Grossman algorithm with inputs of production costs, commodity prices, and pit slope constraints. This method ensures that every tonne mined is profitable but does not take into consideration the timing of material release. This timing is essential when calculating the Net Present Value (NPV) of the project, which is one of the most popular metrics for valuing deposits. Often, when the mining schedule and discounting are applied, material that was considered profitable before discounting becomes sterilized. The objective of this paper is to show the methodology for improving ultimate pit selection by considering the production schedule. Application of this technique will generally produce a smaller and higher-value pit than using the Lerchs-Grossman algorithm alone. INTRODUCTION The Lerchs-Grossman Algorithm was developed in the 1960s and exists to produce a mathematically optimum shape for open pit mines (1). This algorithm is now an industry leading technique for producing the theoretical optimum shape for open pits and is used in many popular pit optimization and strategic planning software packages, such as GEOVIA’s Whittle. The Lerchs-Grossman (LG) Algorithm is based on graph theory and optimizes on the assumption of non-discounted cash flows. This produces a mathematically optimum shape, but does not consider the timing with which the material will be removed from the ground. This is an important consideration, given that one of the most popular metrics for evaluating mining projects is Net Present Value (NPV) (2), which relies on the timing of cash flows as a major differentiator between options. This paper will discuss issues inherent in the use of ultimate pit selection based on undiscounted economic factors and illustrate a simple technique in Whittle, a leading software package, which can be used to improve the NPV of projects."

Jan 1, 2015

By R. H. Clarke

"INTRODUCTION Characterization of waste rock is frequently an oversight in mine planning which can contribute to significant delay in permitting and ultimately development. Thorough waste rock characterization is now a prerequisite to developing operating and closure plans acceptable to regulators and the public. BACKGROUND A long history of mine development has placed virtually all focus on the economic extraction and beneficiation of ore materials, while waste rock characterization and management received substantially less attention and consideration. Inadequate waste rock characterization has contributed to planning and management practices that are having unintended and unforeseen impacts to surface and groundwater, and in some cases lead to significant long term closure liability. In response, the regulatory community has developed guidelines for performing waste rock characterization during the pre- mine permitting process that in some cases seem onerous (BLM, 2013). Additionally, where a project proponent has not met these guidelines or results have been deemed “inadequate”, the Nevada Division of Environmental Protection and Bureau of Land Management (regulatory agencies) will only issue operating permits with rigid management practices to address the uncertainty, including requirements for lining waste rock facilities. WASTE ROCK CHARACTERIZATION FOR NEVADA PROJECTS Newmont Mining Corporation (Newmont) operations in Nevada approaches waste rock characterization like ore characterization, as it requires a similar investment of time, funding and attention to detail in order to pass public and regulatory scrutiny. Newmont follows a tiered approach to characterization that creates three over-lapping data sets representing an “escalation” in analysis at each tier, an approach that has thus far gained regulatory approval. “Tier 1” waste rock characterization for most Newmont projects begins with exploration drilling which follows internal standards and procedures. 20-foot composite samples are prepared from all drilling and analyzed for multiple trace elements using inductively coupled plasma mass spectrometry (ICP-MS) methods and for acid-base characterization using method ASTM-E1915. If the exploration program is successful and further resource or reserve development is recommended, the Tier 1 data are used to prepare a Waste Rock Characterization Plan (Plan) that will be presented to regulatory agencies as a part of baseline project characterization."

Jan 1, 2015