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By Rachel De Lucas

In recent years, as the price of oil soars upward, scientists have started to focus on other energy sources, such as hydrogen. As magnesium can be used for hydrogen storage by forming MgH2, industry will see a growing demand for the hydride. In hydrogen storage and release cycles using magnesium, hydrogen is released from magnesium hydride through hydrolysis and magnesium hydroxide is produced. Therefore, recycling magnesium hydroxide back to magnesium becomes important. The solid oxide membrane (SOM) process is an emerging technology for this process. In the SOM process, MgF2-CaF2-MgO flux is contained in a stainless steel crucible, which works as the cathode. An ionic-conducting YSZ membrane, connected to a liquid metal anode, is partially immersed in the flux. During electrolysis, when the voltage between anode and cathode is higher than the dissociation potential of magnesium oxide, magnesium ions move toward the cathode and are reduced into magnesium vapor. The oxygen ions move toward the anode, passing through the YSZ membrane. They are then oxidized, forming pure oxygen, CO/CO2 or steam (by reaction with hydrogen). The magnesium vapor, generated at the cathode, is collected in the condenser as high purity magnesium. SOM experiments have been conducted with different liquid metal anodes and without reductants. The SOM technique is a highly energy efficient process and with by-products being oxygen or steam, it is also an environmentally friendly green process. A 2-D electrostatics mathematical model was developed as an initial step towards optimizing the design for a three-tube scale-up SOM electrolysis cell. Several possible geometries were examined to develop the scale-up model and convergence of the model was achieved.

Jan 1, 2006

By Tim Hurley

On Friday, May 27, 1983 at about 6 p.m., an avalanche occurred at the Revenue-Virginius Mine. Six mine personnel and two contract diamond drillers were trapped when the avalanche covered and blocked the portal, the only access into the mine. The San Juan Mountain Range in southwestern Colorado is an old volcanic caldera. It has dikes and other intrusions, many of which are mineralized with sulfide ores rich in silver, gold, lead, zinc and copper. Several peaks rise above 4,260 m (14,000 ft) and the district has been the location of avalanches dating back to prehistoric times. This is evidenced by the numerous snow-slide chutes that are infamous enough to be named on topographic maps.

Jan 1, 2006

By P. Talonen

Since the last Iron Control in Hydrometallurgy Symposium in Montreal in 1996, the Kokkola zinc plant has increased its capacity from 175,000 t/y to 280,000 t/y by installing an atmospheric concentrate leaching process, which has also affected iron control in the leaching circuit. Major changes have been made at the jarosite residue pond; a subterranean plastic wall reinforced with bentonite and cement has been built around the pond. A new water collecting system that is used for groundwater level control in the pond area was installed. With these two investments in the pond area, it is now possible to prevent any seepage flow from the pond into the surrounding environment. Water pumped from the residue pond is treated in the water treatment plant. This paper describes the behavior of iron in Kokkola's current leaching processes. The treatment of the jarosite, the improvements to the residue pond and the water treatment process are also described.

Jan 1, 2006

By K. Goshtasbi

The mechanical behaviour of schistose sedimentary rocks such as slate show a great amount of anisotropy. Hence, the schistocity plane is essential when investigating the mechanical behaviour of such rocks. The presence of such rocks in civil projects causes non-symmetric deformation and their behaviour is unpredictable. In this research, the anisotropic strength behaviour of slates is studied. Uniaxial and triaxial tests were conducted on specimens having orientation angles (ß) of 0, 30, 45, 60, 75 and 90 degrees. The triaxial tests were done at confining pressures of 3, 5 and 10 MPa. The effect of anisotropy on uniaxial and triaxial strength, cohesion, angle of internal friction and Hoek and Brown's m and s constants were investigated. The results indicate that the strength of slates in uniaxial and triaxial compression exhibit a U-shaped anisotropic behaviour. In-order to evaluate the most suitable criterion for predicting the anisotropic strength of rocks in uniaxial and triaxial compression, an investigation was carried out on various criteria. In uniaxial compression, the Liao and Huong and Ramamurthy criteria had good agreements with the test results. In triaxial compression the Hoek and Brown and Mc Lamore criteria had better agreements with the test results. It should be noted that in-order to utilize these criteria, a large number of tests must be carried out. However, as the Ramamurthy criterion needs fewer test results, it can be the most suitable for investigating the behaviour of anisotropic rocks in triaxial compression. Keywords: Slate, anisotropy, schistose, failure criteria

Jan 1, 2006

By C. Allen

In 2004, Boliden Odda underwent an extensive modernisation project targeting mainly the leaching section of the plant. Direct leach technology was introduced as part of this project. The Direct Leach process, developed by Outokumpu, is an atmospheric oxidative leach of zinc sulphide concentrate. The effects of this new processing operation on behaviour of iron in the plant are discussed. As well, the filterability of the new residue on belt filters prior to its deposition in mountain caverns is also discussed. The solids from the direct leach process have been analysed by scanning electron microscopy, and the results of these analyses are presented.

Jan 1, 2006

By S. J. Laskowski

In potash ore flotation, carried out in NaCI-KCI saturated brine (about 6-7 molar KC1 and NaCI solution), long-chain primary amines are used as flotation collectors. Long-chain primary amines are poorly soluble in water and their solubility further decreases at high electrolyte concentration. For ionic surfactants there is a characteristic temperature (Krafft Point, KP) below which their solubility is too low for micellization. In a previous study, the effect of pH on the KP of dodecylammonium chloride in water was determined [Q. Dai and J.S. Laskowski, Langmuir, 7, 1361-1365 (1991)]. This paper deals with the effect of electrolyte concentration on the KP of dodecylammonium chloride. The derived theoretical relationship between the KP and the critical micelle concentration (CMC) for dodecylamine can be used to calculate the KP for electrolyte concentrations of up to 0.5 mol/L (about 8% NaCI-KCI brine). A simple experimental procedure for the determination of the KP for higher electrolyte concentrations is also described. The results show that the Krafft point of dodecylamine increases from about 17-18°C (in distilled water) to about 80°C at 16% brine saturation.

Jan 1, 2006

By L. Rosato

In the past decade, as a result of increasing iron loads, Canadian Electrolytic Zinc (CEZinc) has become a pioneer in understanding the critical factors that affect the roasting of concentrates with high pyrite contents as well as those factors governing the effects of high iron loads on the leaching circuit. De-bottlenecking efforts in the roaster and acid plant section of CEZinc have given rise to a better appreciation of the impact of iron on roaster productivity. High standards for impure solution quality, zinc recoveries and residue disposal have all led to an increased comprehension of the limits of the leaching circuit and the optimization potentials with respect to iron and ferrites. In this paper, the impact of iron on the roasting and leaching circuits of CEZinc will be reviewed and special emphasis will be given to some of the more recent process optimization and improvement activities.

Jan 1, 2006

By A. Singh

Deformation structures after tensile and compression tests on Mg926Zn64Y alloy extruded at 250°C and 400°C are studied, in as-extruded and heat treated conditions. The icosahedral phase particles stimulate recrystallization during extrusion, resulting in fine grain size. Tensile and compression tests at room temperature show comparable yield strength, with a yield asymmetry ratio up to 0.98. c-type dislocations are observed in the grains near the submicron size icosahedral phase particles. The source of these dislocations is believed to be dissociation of <c+a> type non-basal dislocations. No dislocation pile-ups on icosahedral phase particles are found. {10 1 2} type twinning occurs in compression.

Jan 1, 2006

By J. Loredo

The Asturian Central Coal Basin, in northern Spain, has been from 18th century an important coal producing area in Spain. Previously to mining activity, aquifer systems were of multibed porous type but the secondary porosity induced by mining operations and constituted by mine voids and fracturing modified the aquifer systems to karstic-porous type. The pumping stop associated with mine closure processes results in the flooding of the mining works. This causes important modifications in the hydrogeology and the hydrology as well as in water flow and in water quality. As a consequence of mine flooding, water overflows through shafts and old galleries or through not controlled ways of water leak to surface. Water tends to recover the original piezometric level, but materials significantly modified by the mining activity behave differently in terms of hydrogeology, and thus, the recuperation of the water level can affect infrastructures and housing in the area of the mine. When pumping stops, the quality of water can also be seriously affected when water comes in contact in oxidant conditions with sulphides and sulphates present in the surface of the materials that are flooded, especially in the subsequent period immediately after pumping stop.

Jan 1, 2006

By M. Gous

Keywords: Pyrometallurgy, Namakwa Sands, ilmenite, DC arc furnace, titania slag, pig iron Namakwa Sands is a heavy minerals mining and beneficiation business in the Anglo Base Metals Division, and operates along the West Coast of South Africa. The business encompasses mining, mineral concentration, separation, and smelting operations. The smelting process comprises the carbonaceous reduction of ilmenite to produce titania slag with a TiO2 content of 86%, and iron with a carbon content of 2.5%. The Namakwa Sands smelter, situated near the Saldanha Bay harbour, commenced smelting operations in 1994, when a 25 MW DC arc furnace was commissioned. The smelting operations were expanded in 1999, with the commissioning of a second 35 MW DC arc furnace. Despite the fact that ilmenite smelting poses a technical challenge in terms of the high temperatures required, the physical characteristics of the slag, the constraints placed on the feedstock, and the tight product specifications, Namakwa Sands has continually increased slag production since 1995. High furnace feed-on utilisation and furnace stability, complemented by continuous improvement drives, will be the vehicle to drive performance in the short term, with longer-term performance enhancements due to strategic process development.

Jan 1, 2006

By Georgina De Micco

The National Commission of Atomic Energy is investigating a suitable physicochemical process for the conditioning of spent nuclear fuel and treatment of the scrap of research reactors of the Al-UxSiy type. A possible way of processing is through dry chlorination of the cladding with the purpose of selective separation of the aluminium from the remaining elements such as Fe, Ni, Zn, Cu, etc. transforming them into volatile chlorides. Some important advantages of this method are the thermal stability of the chlorides that allow the easy separation of the halides by physical methods and the low volume of radioactive waste generated. The interactions in the following systems were studied in the range of temperature between 150º-500°C: Al-Fe, Al-Ni, Al-Cu, Al-Zn, Cu-Zn and the pure metals. We found that the reactivity was different depending on if the elements were alloyed or separated. The separation factors of the systems under study were determined. Nickel is perfectly separated from aluminium for all temperatures, whereas good conditions for copper separation were achieved below 400ºC. In the case of iron, complete isolation was never attained. However, by decreasing temperature to 150ºC it is possible to obtain aluminium chloride with less iron content. The separation of zinc from the product was also difficult. It was detected that zinc chloride volatilization decreases when other chlorides were present, for example cooper chlorides. In the Cu-Zn alloy, zinc chlorides remained in the condensed product due to interactions with copper. The samples were characterized by scanning- electron microscopy (SEM), X ray diffraction (XRD) and atomic absorption.

Jan 1, 2006

By V. Songmene, A. Tahan, J. P. Michaud

The machining of thin wall parts, often used in the aeronautical industry still creates a number of problems, including panel deformation. Quality and productivity are often affected. This study seeks to determine the optimal conditions for cutting in order to guarantee a competitive fabrication of parts while still maintaining quality and delivery deadlines. The studied model (Spar) is a typical structural part used in the assembly of airplane wings. The main objective of this study was to improve two performance aspects: surface quality finish (quality criteria) and the rate of cutting by stock removal (economic criteria). To achieve this objective, we used an evaluation process of the geometrical error issuing from the machine-tool. We also determined the stability zones of the machine-tool&apos;s dynamic system. Finally, a series of high-speed machining tests (finishing cuts) were conducted using an experimental structured approach (16 000 - 24 000 rpm). Profile measures of surface roughness and cycle times registered during trials allowed us to establish optimal cutting conditions. Surface roughness improved as well as cutting by stock removal. Four parameters were taken into consideration: axial depth of cut, chip load, spindle speed, and cutting fluid. Finally, the influence of the type of cutting fluid was evaluated to show that it did not significantly affect machining results.

Jan 1, 2006

By L C. Pretorius

Pipe pigging is a technique for the in situ (field) coating application, to create a seamless internal anti-corrosive lining of long pipelines. The technology originated in the cleaning of pipes, and these proven cleaning methods continue to be used today. Firstly mechanical cleaning of the pipeline is performed, using wire brush, razor back, course stud and fine wire pigs, then foam pigs, or criss cross pigs, and urethane blade scrapers to remove loose debris, wax, residual hydrocarbons and corrosion products from the pipeline. Part of the proprietary techniques and expertise is to ensure that these cleaning pigs do not get stuck Next chemical cleaning of the pipeline is performed, using repeated pig runs with detergents, solvents, acid etching, corrosion inhibitors, consecutively batched between two pigs, to ensure a clean, dry metal finish to a visual cleanliness standard of ISO SA2½. These in situ techniques were developed, 40 years ago to apply internal corrosion protection to pipes using a thin layer of epoxy based paint (50 to 100 micron). Until recently these old techniques were never improved upon. Although many thousands of kilometres of pipes were successfully coated with these thin film epoxy based paints and old application techniques, these thin paint films had problems in weld coverage, and were also unable to fill pits caused by pitting corrosion, and unable to replace metal loss caused by channel erosion. New coating material developments, revised application methods and modified pigging equipment have now made it possible to apply thick film coatings as corrosion barriers to the internals of pipes in the field, using these pigging techniques. The thick coating films can be up to 1 mm (40 mils) thick in a single coating run over long distances. The new thick film coating materials and application techniques are similar to continuous screeding, creating a far more robust seamless internal pipe lining when compared to the old technology of thin film paints. With thick film polymers the option now exists to create a structural GRP pipe within a pipe, be it steel or cementicious. It has been preferable, even necessary, to move away from the traditional epoxy paints and coatings. It was found difficult or impossible to use epoxy materials for these pipe coating applications due to the requirement for achieving a suitable viscosity with adequate hold up. In order to reduce epoxy viscosity a solvent or reactive diluent is required. This inevitably lead to solvent entrapment and poor cure characteristics in cold climates. Further mud cracking in over thick areas, the inability to extend or reduce pot life, poor control of cure time and limited resistance to aggressive or chemical environments made solvent based epoxy resins a poor choice.

Jan 1, 2006

By J. G. La Fonta

The rapid development of real-time monitoring technology for the construction of large underground structures in urban areas can be attributed to: the zero-risk objective, the need for transparency between all parties involved and the control of real cost within the budget. Real-time monitoring can be an integral part of the construction contract (for example when compensation grouting is required) or independent, in particular when measurements of existing structures and buildings bordering the project are to be taken before construction starts. Three examples of extensive field instrumentation schemes are described: a large road tunnel in the Moscow suburbs, a new metro line in Amsterdam and major redevelopment works at a busy Central London rail interchange.

Jan 1, 2006

By Matthew Janes

The RC Harris Filtration Plant, which treats the majority of the fresh water for over 2.5 million Torontonians, is a Canadian Architectural Heritage site demonstrating a classic example of Art Deco Architecture. The facility is undergoing an expansion to install an underground sludge treatment capability. Perched atop a bluff on the North shore of Lake Ontario the structure enjoys a commanding presence on the Lake Ontario shoreline. A series of underground tanks were proposed for the hillside below the structure, which when covered would preserve the building?s architectural presence. However, the plan required two, stepped excavations 12 m and 10m deep into compact, wet sands over stiff clays and clayey silts. Concerns regarding the original structure influenced designers to set the lateral deflection limit for the front footing of the existing structure at 4 mm, (0.03% excavation depth). The design-build team indicated at the time of tender that the movement criteria was unattainable using the tender design. Analysis indicated installation effects and overall elastic movement of the soil mass beneath the building would result in movements of 7 to 9 mm at the structure. Through extensive FLAC analysis and a novel construction geometry the design-build team crafted an alternative that produced significant savings over the original concept. Based upon the analysis the design-build team negotiated a new deflection criteria dictating a maximum of 2.0 mm of movement across the critical expansion joint between the Filter Building front footing and the tank slab beyond. The contractor invested in additional pre tender soils investigation to support the refined design process. The FLAC analyses indicated the Filter Building movements would be elastic and distributed up to 50 m back beneath the front footing of the structure. An extensive precision monitoring program proved construction related movements of 6 to 10 mm horizontal at the front footing. Extensometers placed at two locations over the critical interior tank expansion joint showed no measurable movements. The overall monitoring program, including inclinometers, tilt meters, tie back extensometers (smart cables) and tie back load cells indicated a good match between recorded movements and loads and those predicted by FLAC Analysis.

Jan 1, 2006

By Victor Bredykhin

The report is devoted to the investigation and improvement of processes taking place at contact of large quantities of water insoluble liquid and particles of solid phase in a pulp. Theoretical analysis and simulation of acting conditions have allowed to determine that after attaching of oleophilic particles on the «water-reagent» separation surface the break of a formed complex is taking place according to the reagent volume and for oleophobic minerals along the «solid-reagent» separation surface. As a result particles are selectively treated if the magnitude of the reagent adhesion to the surface of solid phase in water is great. The results of dispersion are influenced significantly by availability of sharp edges on the surface of real particles. They keep tree phase perimeter of moistening. It is possible to fix reagent in the form of lens whose contact angle is significantly smaller in comparison to the thermodynamic angle. In adhesion dispersion the reduction of reagent volume, covering the equal area of particles surface is possible when the reagent is in a pulp in the form of thin films on the «water-gas» separation border. The process is tested in laboratory conditions as well as at pilot concentrating mills in flotation of sulfide ores, non-ferrous metals (copper-molybdenum ore), native sulfur and coal.

Jan 1, 2006

By T. Sakai

Present authors have succeeded in single pass large draught rolling of AZ31 and ZK60A magnesium alloy sheets below 200 °C without heating rolls by raising rolling speed above 1000 m/min. Heavy reduction larger than 60% can be applied by single pass high speed rolling even at room temperature. The rolled sheets showed fine recrystallized microstructure by dynamic recrystallization. The improvement of workability at lower rolling temperature is due to temperature rise by plastic working. In high speed rolling, almost all of the work done by plastic deformation is converted into the heat that raises the temperature of the sheet during rolling because the heat did not flow out of the sheet by conduction and radiation within very short time.

Jan 1, 2006

By M. Medraj, M. A. Arafin, D. P. Turner, P. Bocher

In this study, the kinetics of isothermal solidification during TLP bonding of Inconel 625 and 718 superalloys with nickel based multi-component filler alloy BNi-2 have been studied through a combination of direct experimentation and mathematical modeling in order to determine the effect of process variables and, thus, to optimize the process. The predicted isothermal solidification completion times from the boron diffusion model and migrating solid/liquid interface model were in good agreement with the experimentally determined values and, they were found to be significantly less than those of other nickel superalloys with different nickel based filler alloys. Further, significant reduction of holding time was observed with increasing bonding temperature and with decreasing joint gap. No significant grain growth in the base metals has been observed in the temperature range being investigated (1325 - 1394K).

Jan 1, 2006

By R. P. Kofluk

The nickel-cobalt sulphides produced from limonitic laterite ores by Moa Nickel S.A. in Cuba are refined at the Corefco nickel-cobalt refinery in Canada. Significant economic implications are associated with the refining of precipitated sulphides containing elevated iron contents. The Moa Nickel S.A. operations encompass laterite mining, high pressure acid leaching (H PAL), and ultimately, precipitation of a mixed sulphide product. These processes are reviewed as they pertain to the control of iron and the formation of a mixed sulphide containing nominally 55% Ni, 5% Co and 1% Fe. The contributors to the iron content of the mixed sulphide product are reviewed; the major contributors are the HPAL operation and sulphide precipitation. The precipitation of iron during sulphide precipitation is influenced by the solution acidity, the iron and copper concentrations in the feed solution, and the presence of laterite leach solids. The significance of the copper concentration of the sulphide precipitation solutions is manifested by both physical and chemical modifications of the sulphide precipitates, presumably through the formation of fine copper sulfide seed particles.

Jan 1, 2006

By H A. Myburgh

The beneficiation of heavy metal oxides, such as iron ore, is usually performed with heavy medium separation in cyclones, static baths and lately with Larcodems. Atomized ferrosilicon is most suitable as a heavy medium at densities above 3600 kg/m3 whereas a mixture of milled and atomized ferrosilicon is suitable at densities below 3600 kg/m3. When operating a beneficiation plant at densities higher than 3600 kg/m3 the quality of the ferrosilicon particles is an important factor that influences the control of the beneficiation process. Therefore, it is important to know how the rheology would be affected by the ferrosilicon quality as it also influences the control of the process at these elevated densities. Background The Kumba Resources Sishen Iron Ore Mine in South Africa produces 26.5 Mt iron ore per annum from its beneficiation plant. The ore body consists mainly of laminated and massive type hematite ore that is crushed down to ?90mm before being beneficiated by means of a combination of Wemco drums, Larcodem and dense medium cyclone separators. The need for higher densities When the percentage of high-density gangue2 is higher than normal in the run-of-mine (ROM), a higher separation density is necessary to produce a product to specification. Certain ore types of this quality in the Sishen reserves require a separating density higher than 4000 kg/m3, whereas densities would normally average 3600 kg/m3 when beneficiating ores of normal high-density gangue content. Sink and float tests conducted on the ROM material at Sishen revealed some interesting characteristics. In the waste fraction, (density < 3600 kg/m3) it was found that the %Fe was <21% (Fig. 1). Similarly, for the product fraction (density >3000 kg/m3), the percentage Fe varied between 35% and 67.2%. The bulk of the material (88%) actually had a density greater than 4000 kg/m3 and a Fe content that varied between 63% and 67.2%. At a density interval of 3600 to 4000 kg/m3, the Fe content varied from 37% to 60% with an average of 45%.

Jan 1, 2006