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By T. Wajima

"A novel carbonaceous adsorbent for recovery of nickel from nickel plating waste solution was prepared from rice straw using sulfur impregnation. The rice straws were cut to 1 cm pieces, and then immersed in 0.01 - 3 M K2S solution to prepare sulfur-immersed materials. The immersed-materials were heated at 100-700 ºC in nitrogen gas to produce the sulfur-impregnated carbonaceous adsorbent by pyrolysis. The contents of carbon and sulfur in the adsorbent and abilities of adsorbent to recovery nickel from aqueous solution were examined. The contents of carbon and sulfur in sulfur-immersed materials are almost same as those in raw material. In pyrolysis, with increasing the heating temperature to 200 ºC, the contents of carbon and sulfur are almost constant, and then above 300 ºC those increase. The recovery for nickel using raw material, sulfur-immersed material and the product pyrolyzed at 100 - 200 ºC are almost same, and with increasing the heating temperature to 400 ºC, that of the product increases, and above 500 ºC that of the product decreases. In immerse step, with increasing K2S concentration, the carbon content of the product at 400 ºC gradually decreases, the sulfur content of the product increases, and the recovery for nickel using the product gradually increases and then above 1 M K2S decrease. The product prepared from material immersed in 1 M K2S solution at 400 ºC indicates a maximum recovery for nickel ion. The product can adsorb nickel ion in nickel plating waste solution coexisting with phosphate ion, and adsorbed nickel ion in the product was deposited as nickel metal after heating at 1000 ºC under N2 atmosphere.INTRODUCTIONRice is the second world’s largest cereal crop after wheat, but produces large amount of straw residues, of about 330 million metric tonnes. Rice is a widely grown crop in Asia, and rice straw is produced as a by-product of rice production. In most parts of rice fields, open-field burning of rice straw is commonly practiced in the region when there is limited time to prepare a field for the next crop. However, open-field burning of crop residues is an uncontrolled combustion process during which air pollutants are emitted into atmosphere. These air pollutants have significant toxicological properties and are potential carcinogens (Gadede et al., 2009). Although wildfires are prohibited in cultivation fields of most countries, farmers usually keep on burning their crop by-products. Biomass burning is an important source of aerosol particles which may affect local and regional air quality (Gao et al., 2011), and also contribute to global climate changes."

Jan 1, 2016

By B. K. Mishra, Avijit Biswal, B. C. Tripathy, Abhijeet Singh, K. Sanjay, T. Subbaiah

We studied theeffect of anode substrates such as pure lead (Pb), lead antimony (Pb-Sb), and lead-silver (Pb-Ag) on the structural and electrochemical properties of electrolytic manganese dioxide (EMD). X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and chemical analyses were used to determine the structural and chemical characteristics of the EMD samples. The charge-discharge profile was studied in 9 M KOH using a galvanostatic charge-discharge unit. In all the substrates the current efficiencies were more than 99% except with Pb-Sb where it was 90%. Results revealed the nature of the substrate strongly affected the morphology of the deposited material which in turn affected the electrochemical properties of the EMD samples. XRD analyses revealed that the nature of the anode did not affect the crystal structure of the deposited EMD and all the samples were predominantly ?-MnO2, which is electrochemically active for energy storage applications. The EMD deposited on lead substrate showed superior discharge capacity of 245 mAhg-1 when compared with other substrates.

Jan 1, 2014

By T. E. Wakefield

"Final Galloway (stage) designs for vertical drill and blast shaft sinking projects evolve from complex thought patterns which integrate operational processes, systems and methods of communication, power supply, drilling, blasting, ventilating, mucking, supporting, surveying, dewatering, sealing, concrete lining and shaft furnishing. Attention to ergonomic design detail at the shaftsman / structure interface is at the heart of safe and successful multi-deck working platforms. For economy the end product must have a low mass to reduce suspension rope end loads to be able to use smaller suspension hoists and have lighter headframe structures, be robust to withstand concussion damage, be easily constructible on site, be maintainable in the shaft barrel, and comply with safety and legislated standards. This paper’s ambition is to describe a systematic design framework and sequenced thought process that delivers a product that is engineered with excellence, illustrated by making use of two designs that evolved during recent Galloway projects, one destined for a large diameter man/material shaft, the other for a ventilation shaft. The stage engineering iterative process starts with mapping permanent and sinking hoisting layouts, followed by laying out horizontal deck plans, mostly constrained by the permanent shaft purpose and configuration, whilst maximizing openings to enable muck to be removed rapidly for the best sinking cycles. Concurrently the designer needs to understand the chosen sinking methodologies in conjunction with crewing to determine the number of decks and fix their spacing. Insufficient access to move and line up formwork, set reinforcing rods and pour concrete in the confined spaces of the stage is an inherent major risk to be mitigated. An iterative and integrative process follows for the primary configuration which delves into increasing design detail, accommodating all other methodology influences, resulting in 3D layouts for further risk assessment, review and fine tuning by seasoned shaftsmen. INTRODUCTION Documented colliery shaft sinking practice from the late 1800’s makes reference to purpose built walling (bricked lining) cribs with floors suspended in sinking shafts, thereby allowing shaft lining to proceed concurrently with the excavation. Improvements were made by Sir William Galloway who introduced two decks supported at the corners by angle irons. The sinking stage, or Galloway, has developed substantially over time to be the in-barrel heart of the sinking operation, with overwhelming complexity for those who have to design one for the first time."

Jan 1, 2019

By A. Zorkovská, S. Castro, P. Baláž, Z. Bujnáková

Enargite (Cu3AsS4) belongs among refractory copper minerals with very low hydrometallurgical extractability of copper. An application of enargite leaching in acid solutions leads to simultaneous dissolution of copper and arsenic and the final leach solutions have to be treated for the separation of both elements. However, the alkaline leaching of enargite is selective. Arsenic passes into leach while produced copper sulphide represents the raw material suitable for pyrometallurgy. The hydrometallurgical processing of mineral can be influenced positively by mechanochemical route. We have shown that more than 80 % of arsenic can be extracted from enargite concentrate by atmospheric alkaline leaching at 95 °C when mechanical activation in an attritor is applied. The produced Cu2S can be further treated with elemental iron where mechanochemical intervention is applied in the second stage of enargite processing. The final product forms Cu/FeS nanocomposite from which copper nanoparticles can be easily separated. The illustrated concept of copper obtaining from copper sulphide is an example of so-called “dry” processing, as reactions in gas and liquid phases are excluded. This concept of environmentally friendly metallurgical processing can be classified as an impetus for novel technology to produce copper from enargite concentrates.

Jan 1, 2012

By R. M. Graves, C. B. McKenzie, D. Barbour, D. W. Desnoyers

"Abstract -The prospective Tulks volcanic belt hosts five significant massive sulfide deposits, Tulks Prospect, Tulks East, Jack's Pond, Daniel's Pond and Victoria Mine, as well as numerous showings and indications throughout its 70 km outcrop length. Regionally, the 498 Ma sequence consists dominantly of felsic pyroclastic rocks and flows with interbedded mafic volcanic units and fine­ grained sediments, commonly graphitic. Contemporaneous granitoid rocks occur in the south half of the belt. Rocks usually display a strong NE-SW, steeply dipping, penetrative foliation and other shear-related high-strain fabrics. Facing directions are normally northwest, although there is local evidence of folding. Sulfide bodies and their alteration systems are deformed and shape-modified in the style of ambient strain.The Tulks, Tulks East and Jack's Pond prospects appear to occupy a similar stratigraphic level, on or near the contact between a thick felsic pile and an overlying broad, conductive package of graphitic sedimentary rocks. AU are pyritic deposits with well-developed footwall alteration systems. The Tulks prospect comprises four polymetallic lenses totalling 750 000 t. Three lenses constituting more than 6 000 000 t of sulfide mineralization are indicated at Tulks East but only the 210 000 t ""B"" lens contains significant base metals. Jack's Pond consists of a very extensive, zoned alteration complex in which four lenses of massive to semi-rnassive pyrite + chalcopyrite are known.The central part of the system, characterized by Mg chlorite and carbonate, is enveloped by pervasive sericitization and capped by intensely silicified and pyritized volcanics. The sulfide lenses are interpreted as part of the footwall zone and are beneath that part of the system most likely to host polymetallic massive sulfides.Daniel's Pond differs from the other prospects in such fundamental ways as metal content, associated alteration and structural setting. The deposit comprises strongly tectonized, Ag-rich, Zn-Pb mineralization distinguished by a pronounced Ba-As-Sb signature. Mineralization is confined to a narrow, north-south high-strain zone which separates unstrained mafic volcanic rocks to the east from well-foliated felsic rocks. The deposit Jacks an extensive alteration halo and at its north end is associated with a lens of barren, undeformed massive pyrite.The Victoria Mine deposit, the most cupriferous of the five, is related to a moderately dipping structure that separates well-foliated Tulks volcanic rocks from an overlying, Jess deformed volcanic­ sedimentary sequence that may be as young as 462 Ma. The structure is also the locus of black chlorite, dolomite and quartz alteration. Structurally remobilized precursor sulfide mineralization is one possible source for the deposit."

Jan 1, 1993

By C. George Miller

"As the influence of governments has become more widely felt, the use of research techniques to analyze policy has increased. Mineral economics, as one of the foundations of mineral policy research, has grown accordingly. Policy research and analysis has been carried out within governments, university departments and the private sector. Each of these institutional environments has characteristics which influence the topics of study, the approach, the methodology and the output of the research. A brief survey of recent research activities provides illustrations of trends and developments occurring within this organizational framework.A radically different organization, the independent research institute, has begun to make an impact on policy research in recent years, and will have an increasing importance in the future. Combining certain features of the traditional research organizations, it nevertheless has important differences which are essential to its effective functioning. An overview of the formation, goals, organization and operation of one such institute is presented."

Jan 1, 1976

By Jan Kvinge, Aina Opsal Bakke, Yanjun Li, Jan-Ove Løland, Svein Jørgensen

"Compound casting is a very attractive approach to reduce the weight of components for some specific applications while keep both the functional and the mechanical property requirements. In this work, Al-7Si-Mg alloy /copper compound castings were produced through a low pressure die casting process. To reduce the oxide present in the interface, flux coating of the copper pipes was tested. The interface layer formed between the two alloys was investigated using Optical Microscopy (OM), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). Vickers Micro-hardness was also measured across the interface. Results showed that the flux coating prevented the formation of the metallic bond between copper and aluminum. Instead, high concentrations of potassium, magnesium and fluoride, coinciding with formation of KMgF3 and MgF2, were detected in the interface. In the castings without surface treatment, a continuous metallurgical bond was achieved. In the bond layer, various Al-Cu intermetallic phases have been detected. In addition, formation of primary silicon particles in the reaction layer was observed in all castings. The mechanism for the formation of the intermetallic phases and the strength of the interface layer have been discussed.INTRODUCTION Recent development in the automotive industry has focused on producing lightweight components, which can reduce CO2 emission and increase the efficiency. Often, one material alone is not able to meet the requirements for a specific use. The need for lightweight bimetallic components has therefore increased. Aluminum-copper bimetallic components can be used in wires and bus bars where conductivity is an important factor (Lee, Bang, & Jung, 2005). Compared to Al-Cu alloys, Al-Cu bimetallic components can reduce both weight and cost without reducing electrical and thermal conductivity (Sheng, Yang, Xi, Lai, & Ye, 2011). A challenge is, however, that aluminum and copper have high affinity to each other, especially at elevated temperatures. This causes formation of brittle intermetallic phases with high electric resistance (Liu, Wang, Sui, Wang, & Wenjiang, 2016). In addition, both metals are subjected to oxide formation on the surface. Copper is especially exposed to oxidation at elevated temperatures (Pinnel, Tompkins, & Heath, 1979), while a thermodynamically stable oxide layer will spontaneously form on the aluminum surface (Papis, Loeffler, & Uggowitzer, 2009). Oxides are known to be passive substrates, which will reduce wettability and will thus prevent the formation of metallic bonding between aluminum and copper (Papis, Hallstedt, Löffler, & Uggowitzer, 2008)."

Jan 1, 2018

By Zetti Gavelán

Globalization and the search for new ore deposits inevitably lead to investment in foreign markets. Investors need to be aware of the effect of their venture on regional, social and economic issues when they invest. Decades of detailed statistics from various sources can be integrated and analyzed to predict the social-economic impact of investment, thereby mitigating risk. To this end, the correlation among variables such as foreign direct investment into mining (FDIM), reserves, and socio-economic indexes is examined. The investigation focuses on South America from 1992 to 2000. Throughout the past decade, South America has benefited from capital investment from more developed countries. This huge investment by the mining industry has impacted the South American economies and can be measured directly using the FDIM. Other economic variables investigated include mining gross domestic product, direct employment, and human development indexes. The correlation is based on data compiled from the World Bank, international risk assessment agencies, the United States Geological Survey (USGS), and the information agencies of various South American countries. Initial analysis of the economic data suggests various expected outcomes. For example, foreign investors may disregard a measured, highly negative country risk in deference to the quality of its mineral resources. It is important to note that the standard measures of country risk published by investment analysts are not industry or investor-specific. In the case of the investor, the level of accepted risk is based on their managed investment portfolio. It is noted that arguments for level-playing fields may be the antithesis of globalization. The discovery and exploitation of ore bodies in a globalized environment necessitates the development of economic measures that standardize mining-specific risk variables and trends. The latest published information on the security of mineral investments in South America is investigated by integrating databases of economic, geologic, production, human indexes, and risk ranking.

May 1, 2003

By Min-Yuan Cheng

Heavy rainfall and typhoon oftentimes cause the collapse of hillslopes across mountain roads. Disastrous consequences of slope collapses necessitate the approach for predicting their occurrences. In practice, slope collapse prediction can be formulated as a deterministic classification problem with two class labels, namely ?collapse? and ?non-collapse?. Nevertheless, due to the criticality and the uncertainty of the problem, evaluating the collapse susceptibility of an area is a challenging task. This study proposes a novel Artificial Intelligence (AI) approach, named as K-Nearest Neighbor Based Bayesian Classifier (KNNBC), to deal with slope collapse assessment. In the proposed model, Bayesian inference is used as a framework to achieve probabilistic prediction of slope collapse. Meanwhile, K-Nearest Neighbor (K-NN) is employed as a density estimation technique. Equipped with probabilistic outputs, the K-NNBC is able to yield predictions with different levels of confidence and diminish misclassified cases. Experimental results point out that the proposed model is very helpful for decision-makers in slope collapse assessment and disaster prevention planning.

Aug 1, 2013

By E. Wolmarans

The selection of the main mineralised zone (MMZ) concentrator milling circuit has followed a comprehensive route over the preceding 10 years. Many knowledgeable parties have contributed and assisted in developing the milling circuit according to the best available information. The final selection of the flow sheet was completed after DRA conducted a techno-economic study on four possible comminution circuits ranging from conventional crushing and ball milling to fully autogenous (AG) milling. The results from all the above mentioned work indicated that it is possible to treat the MMZ ore at the desired throughputs to the desired grind sizes in a fully autogenous grinding circuit. The flow sheet was designed to treat the main mineralised zone (MMZ) arising?s from both underground and open cast operations and incorporates a fully autogenous grinding (AG) circuit. Commissioning of the 375ktpm concentrator at Nkomati Nickel began in August 2009 with the first ore reporting to the mill on the 15th of September 2009.

Jan 1, 2012

By A. M. Elmahdy, T. Hirajima, M. Farahat

"Separation of molybdenite from chalcopyrite is mainly achieved through flotation technique to raise their grades up to 25% to be extracted in smelters. However, molybdenite recovery and grade obtained from this process is not satisfactory in most cases due to the natural hydrophobicity of both minerals. The influence of conventional heat treatment on pure chalcopyrite and molybdenite minerals was investigated. X-ray diffraction, TG-DTA and XPS techniques were applied before and after heat treatment. The results showed phase changes for both minerals. Magnetic separation experiments of single and mixture of both minerals at several magnetic intensities were made. For single mineral experiments, 100% molybdenite recovery was obtained at all experimental conditions as non-magnetic fraction whereas ca. 100% chalcopyrite recovery was achieved under certain conditions. In case of 1:1 binary mixture, 87% and 83% molybdenum and copper recoveries, respectively, were obtained. The increase in chalcopyrite magnetic recovery is related to the formation of more magnetic phases as confirmed by characterization techniques.The objective of this study is to increase the magnetism of chalcopyrite to make its separation from molybdenite by magnetic separation possible and to understand the mechanism behind it. These results indicate that it may be possible to upgrade molybdenite ores using heat treatment followed by magnetic separation to the required grade by smelters which is difficult to attain by froth flotation and the other techniques."

Jan 1, 2016

The Beginning ! The status quo simply isn?t sustainable ! Our social license is at risk ! The bar keeps rising ? We must improve our performance, both operational and social ? We must improve stakeholder judgement of our industry by taking action collectively Implementing TSM " TSM Guiding Principles " Performance Indicators " Crisis communications " External Outreach " Tailings management " Energy management " Performance manuals, guides " Reporting " Communities of Interest Advisory Panel

May 1, 2004

By Ye Chen, Jianhua Chen, Xianhao Long, Qingxia Liu, Zhenghe Xu

"It is crucial to understand the mechanism of the collector interacting with the mineral surface in the presence of water molecules, which could influence the relaxation and electronic properties of sulphide mineral surface due to the proximity effect for narrow band gap of semiconductors. The adsorptions of three typical collector molecules (xanthate, dithiocarbamate and dithiophosphate) on the sulphide mineral surfaces in the absence and presence of water molecule have been simulated by density-functional theory (DFT). The calculated results show that the adsorptions of collectors on clean mineral surface in vacuum are not in agreement with the observed flotation behaviours. The presence of water molecules has a great influence on the adsorption of collectors. The analysis of density of states of the mineral surface atom suggests that the adsorption of water molecules could influence the electronic properties of mineral surface and consequently influence the adsorption between the surface and the collector molecule.INTRODUCTIONIn the separation of multi-metal sulphide ores, the selectivity of a collector is a key factor for the efficient recovery of the aimed mineral. Xanthate, dithiocarbamate (DTC) and dithiophosphate (DTP) are the most common collectors used in the flotation of sulfide minerals. Generally, xanthate exhibits powerful collecting property but lack of selectivity. While dithiophosphate and dithiocarbamate show the good selectivity in the lead and copper sulphide mineral flotation. The mechanisms of these collectors interacting with the sulphide mineral had been attracted many attentions and several mechanism based on experimental results had been reported (Chander & Fuerstenau, 1974; Fuerstenau, 1990; Raju & Forsling, 1991; Crozier, 1991; Bradshaw, Cruywagen & O’Connor, 1995; Guler, Hicyilmaz, Gokagac & Emekci, 2006). However, the micro-mechanisms of the selectivity of these three thiol collectors on different sulphide mineral surfaces are not fully understood."

Jan 1, 2016

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

This study examines the impact of low-temperature heat-treatment cycles on microstructure and corrosion performance of Direct Metal Laser Sintered (DMLS) AlSi10Mg_200C alloy. It is known that the morphology and the size of eutectic silicon are the two most critical factors affecting mechanical properties of the AlSi10Mg alloy. Although high-temperature heat-treatment cycles are common practice for the strengthening of the cast Al-Si-Mg alloys, in the case of DMLS fabricated AlSi10Mg alloy, high-temperature solutionizing and low temperature annealing cycles result in mechanical properties degradation primarily due to a dramatic decrease in the solubility of Si in the super-saturated a-Al matrix of the as-printed alloy. In this study, low-temperature heat-treatment cycles that only promote precipitation of Mg2Si accompanied by the interruption of the silicon network were investigated. SEM and XRD analysis were utilized to observe the evolution of microstructure after different annealing heat-treatments at 200, 250, 300, and 350°C for 3 h. Increasing the heat-treatment temperature contributed to the Si networks interruption and an increased precipitation of Mg2Si phase. Low-temperature annealing from 200 to 350°C was found to promote the homogeneity of the microstructure characterized by a uniform distribution of eutectic Si in ??-Al matrix. Additionally, in order to investigate the impact of different heat-treatment cycles on corrosion resistivity of DMLS-AlSi10Mg_200C, the potentiodynamic polarization testing and electrochemical impedance spectroscopy were performed in a 3.5 wt.% NaCl solution. The results revealed more uniformly distributed pitting attack on the corroded surface by further increase in the annealing temperature, which was attributed to the uniformity of Si dispersion. In comparison, low temperature annealing at 200°C led to a penetrating selective corrosion attack along the melt pool boundaries, resulting in a higher corrosion rate associated with the lower absolute value of impedance of the protective passive film on the surface.

Jan 1, 2018

By Jon A. Carlson, W. Scott Williams

The EKATI"" Diamond Mine commenced operation in October 1998. It is operated by BHP Diamonds Inc., which is a part of the Non-Ferrous and Industrial Materials Division of BHP Minerals, a business unit of BHP Company Ltd. of Melbourne, Australia. The EKATI"" Diamond Mine is a joint venture of BHP Diamonds Inc. (51%), Dia Met Minerals Ltd. (29%), Charles E. Fipke (10%) and Dr. Stewart L. Blusson (10%). In December 1993, an office was opened in Yellowknife, Northwest Territories specifically for the then Northwest Territories Diamonds Project (EKATI"" Diamond Mine) development. EKATI"" Diamond Mine is located 300 kilometres northeast of Yellowknife and 200 kilometres south of the Arctic Circle in the Northwest Territories of Canada (Figure 1 ). The site is located in a remote tundra area of continuous permafrost, north of the tree line, which is part of the Canadian Shield. Wekweti (Snare Lake), a Dogrib community approximately 180 kilometres southwest of the project, is the closest neighbour. The mining area and facilities lie within the 10 960 hectares land leases held by the joint venture. The total claim block (core zone and buffer zone joint ventures) covers 344 000 hectares. To date, more than one hundred kimberlite pipes have been identified within the claims. Five of these provide the basis for the present mine plan. Total capital investment in the project is over C$700 million. At full production employment will be about 600, including employees and long-term contractors, with over 33% being Aboriginal from the Northwest Territories.

Jan 1, 2001

By Sazol Das, Hany Ahmed, Ganesh Bhaskaran, Zhuoru Wu

"Friction stir welding (FSW) process in lap configuration for dissimilar materials has been developed and tested for steel to aluminum joining. A novel cylindrical tool was designed for improved material flow. The joining of steel to high strength 5xxx and 6xxx aluminum was carried out by FSW technique using optimized process parameters. The microstructure, micro-hardness, joint strength and corrosion properties at the weld interface have been investigated. Optical and scanning electron microscopy reveled a well layered structure at the interface and lap shear tests of the welds showed excellent fracture resistance. Neutral salt spray tests for up to 500 hours (ASTM B117) were carried out on the bare steel to aluminum FSW joints, which did not show neither evidence of corrosion at the weld interface, nor any degradation of the weld strength. The FSW lap configuration was applied to prototype commercial vehicle structural component whereby a steel stiffener insert was friction stir welded to high strength 6xxx aluminum alloy. The interface microstructure showed layered root without any steel shattering in aluminum side. A finite element study was carried out to quantify the benefits where it was found that the stiffness increases by 76% under bending loads and 36% in torsion loads.INTRODUCTION Energy preservation and environmental issues, namely carbon footprint and legislation around emission in transportation industries has led to a growing need to use of lightweight materials such as aluminum and magnesium alloys along with various grades of steel in structural application, while still maintaining their strength and crashworthiness. Assembling dissimilar materials within integrated structure is thus a stringent requirement related to optimum performance. In order to achieve an efficient technology of joining dissimilar materials such as aluminum to steel, it remains difficult to select an effective welding process for a given joint configuration. The use of aluminum in transportation industries for structural component is not exclusive in a design and is almost always used along with various steel grades for a mixed materials solution, thus dissimilar aluminum/steel lap joining is of great interest since this is widely used in the assembly of parts (e.g. pillar, frame rails, chassis, body in white (BIW), CAB, etc.)."

Jan 1, 2018

By P. Dinham, G. C. Summerton, N. McCulloch, S. Dowling, D. C. Craig

"Development of a process for the treatment of a nickel copper matte rich in the minerals heazlewoodite, chalcocite and bornite has demonstrated significant base metal recoveries and metal separation efficiencies. The determination of chemical and mineralogical changes occurring in the individual leaching stages in laboratory experiments has enabled a better understanding of the complex leaching chemistry. The chemistry and mineralogy of the piloting and laboratory processes are discussed.INTRODUCTIONThe nickel-copper sulfide ores of the South African Bushveld Complex are among the most important Platinum Group Metal (PGM) bearing ores, and contain the world’s largest reserves of platinum. The treatment used in the recovery of PGMs from these ores includes three types of processes, namely ore concentration using physical techniques such as flotation and gravity separation, concentration by pyrometallurgical means, hydrometallurgical extraction of the base metals followed by the PGMs. Following milling of the ore, flotation involves the separation of high value minerals from gangue by taking advantage of the differences in their hydrophobicity. These differences are generally maximized through the use of a surfactant or wetting agent. Concentrates are then thermally treated and melted which brings about physical and chemical changes that enable the recovery of base metals and PGMs. The main aim of the smelting and converting process is to separate and eliminate the valuable metals from the bulk of the unwanted gangue and essentially all of the iron and to concentrate the metal VALUES (into a high grade converter matte. The matte can be further enriched by magnetic separation, producing a PGM-rich magnetic fraction and a base metal-rich non-magnetic fraction. The magnetic fraction is treated by hydrometallurgical processes to produce a PGM concentrate which is further refined to separate and purify the individual metals. The non-magnetic fraction is treated to produce marketable metal VALUES (such as nickel, copper, cobalt and to a lesser extent PGMs. The principal objective of any hydrometallurgical extractive process is to leach the desired elements selectively into an aqueous phase so as to separate them from the bulk of the material. (Crundwell, Moats, Ramachandran, Robinson and Davenport, 2011; Hundermark, Mncwango, de Villiers and Nelson, 2011)."

Jan 1, 2012

By James J. Roettger, Robert J. Mitchell

"The results of a series of model stope pours designed to investigate working pressures on bulkheads during hydraulic pouring of classified tailings backfill are reported. Total bulkhead pressures and fill water pressures were monitored under the condition of a fully saturated backfill. Similitude of the model testing is discussed and equations are developed to estimate bulkhead pressures under prototype conditions. The model results show that good base drainage, combined with a bulkhead setback, can reduce the expected bulkhead pressures to values such that timber or concrete block structures should be capable of supporting a saturated backfill. Introduction Bulkheads are used in underground running operations to block drift openings in order that hydraulically placed sand backfill can be contained in stope pours. Whenever possible, the sand fill is designed to have sufficient percolation rate so that excess hydraulic transport water will gravity drain out through the bulk headed drifts. This avoids costly decanting systems. Early bulkhead design assumed that the bulkhead pressure could be as high as 0h = Hy where H is the fill height and ""y is the saturated unit weight of the fill (Thomas et al., 1979)(1). A typical design pressure for a 50 m fill height would be 1250 kPa giving a design force of 12,500 kN on a bulkhead located in a drift of 10m2 in area . Typical bulkheads were 1 m thick heavily reinforced concrete structures formed and poured into a notched drift. Not only were these expensive structures but the associated problems of inside drainage systems and curing time delays increased production costs. As experience with bulkheads for large bulk pours increased and fill pressure measurements became available [see, for examples, Libby et al., 1975(2), Askey et al., 1978(3)] , 'free drainage' timber and concrete block bulkheads were designed. Substantial savings have been realized using these types of bulkheads but greater engineering design and monitoring of backfill pours is necessary to ensure that backfill pressures do not exceed the bulkhead design pressures.The effective and total stress components of fill pressure, the engineering concepts associated with the 'free drainage' design and some detailed design considerations have been discussed by Smith and Mitchell (1982)(4) . It is important to the safe use of these designs, however, that the basic engineering concepts be demonstrated and communicated to those responsible for the day-to-day backfill operations. This paper describes and explains observations from a series of model studies designed to measure bulkhead pressures in a saturated fill."

Jan 1, 1984

By G. V. Theja, V. B. Maji

Large infrastructure projects like tunnel excavations, underground constructions face innumerable risks. For successful completion of these projects, it is essential that we foresee and understand risks that could occur during different phases of the project. One of the risks affecting underground excavation projects is the inaccurate performance prediction of TBMs. As this could severely affect the project, resulting in lower advance rates and could also result in changing the excavation machine or method, due to difficulties in excavation, thereby increasing the overall cost of tunnelling. This makes performance prediction of the TBMs as one of the crucial aspects in tunnelling, as a precise estimation of its performance is required for planning and estimation of time and cost of the tunnelling projects. This performance prediction of TBM is a challenging geotechnical problem that is intricate and complex in nature, this is possibly due to the fact that TBM performance prediction involves understanding the rock fragmentation process in wide range from micro-scale (i.e. the interaction of surface of rock material and cutter tip) to macro-scale (including the interaction of rock mass and TBM). Thus in order for the performance prediction model to be efficient, parameters of both TBM specifications and ground conditions have to be considered. Various models have been proposed by researchers since the early phases of TBM application, these studies resulted in the development and improvement of numerous penetration prediction models. Most of these models consider the geotechnical parameters that are input to the model to be consistent along the TBM drive and neglect the uncertainties in parameters that occur. And so to improve the predictive capability of these models and to incorporate the above uncertainties, the penetration rate is modeled as a stochastic variable depending on the geotechnical and TBM parameters, its statistical distribution is determined and is used to characterize the penetration rate instead.

Jan 1, 2015

By V. Vakiloroaya

The paper aims at developing a hybrid solar-assisted air conditioner system for performance enhancement and energy efficiency improvement. To increase sub-cooling of the refrigerant at partial loads, we propose a new discharge bypass line together with an inline solenoid valve, installed after the compressor to regulate the mass flow rate of the refrigerant vapour passing through a hot water storage tank. For control design, a lumped parameter model is first developed to describe the dynamics of the system in an explicit form of input-output relationship. The system has been fully-instrumented to examine its performance under different operation conditions. The system model is then validated by extensive experimental tests. The predictions from the models exhibit a good coincidence with experimental results, judging by an RMS error less than 15%. Based on the obtained dynamic model, a linear quadratic regulator (LQR) is applied to optimize a cost function of the output errors and control efforts. The key challenge is to regulate the refrigerant temperature entering the condenser by controlling the valve opening. The design approach is then tested in a transient simulation tool to predict the system performance in transient conditions. The experimental results obtained from implementation with PLC demonstrate that the proposed system delivers higher system efficiency owing to the higher refrigeration effect in the direct expansion evaporator. Thus, the novel development is promising for improvement of energy efficiency, enhancement of the system performance while fulfilling the cooling demand. Consequently, between 25 and 43% of monthly electricity can be saved on average.

Aug 1, 2013