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By Wang Yun-yan

In order to examine the adaptability and the kinetics of leaching different gold ores in alkaline thiourea system, six kinds of gold concentrate and/or calcine with different physical and chemical properties were chosen as objects. The leaching behaviors in alkaline thiourea system with high stability, acidic thiourea system and alkaline cyanide system were compared. Changes of phase, surface appearance, particle distribution and specific surface area of six kinds of gold ores before and after leaching were studied in virtue of modern analytic techniques, e.g., XRD, SEM, and so on. The results indicate that alkaline thiourea solution can be used to leach gold ore, for oxidized gold concentrate removed arsenic by microbe pretreatment(4#) the leaching rate of gold is up to 82.68%, such conclusion overthrows the parlance reported that pH value must be less than 1.78, or gold can not dissolve in thiourea solution. Chemical components and phase are related to gold leaching rate, different gold ores are fit for different leaching system, and alkaline thiourea solution is suitable for the pretreated oxidized gold ores with low content of sulfur and in which the main phase was SiO2, phase almost does not change after leaching basically. Generally speaking, when leaching in alkaline thiourea solution, surfaces of gold ores with glaze change greatly to ones with coarseness, distinct trace and holes of corrosion. Particle size decrease and specific surface area increase of gold ores after leaching in alkaline thiourea solution with high stability except gold concentrate of Zhongyuan gold smelter(5#).

Jan 1, 2006

By Emma Arakelova

?2?2 (98 %) vapour passed through a reactor at 25Pa where a Zn? target was placed at 273K- 373?. Experiments were carried out on a flow- type vacuum device. ?2?2 decomposition on Zn? surface accompanied by formation of a Zn-containing volatile complex which transferred to the gas phase, and Zn? deposited on a substrate at condensation. As the substrate, five sequentially located quartz cylinders were used at 293K- 423 K (?n). Decomposition of the Zn-containing complex on quartz substrates carried out as a first- order reaction. ?The complex decomposition constant (??) increased with the substrate temperature (?n=293 K, ??=7.05 sec-1;?n = 373 K, ?? = 87 sec-1;?n = 423 K, ?? =158 sec-1). ?The complex decomposition constant did not practically vary when the target temperature increased; the complex formation rate increased slightly.

Jan 1, 2006

By M. Fafard, D. Picard, J. -F. Bilodeau, G. Soucy

To simulate adequately the behaviour of a Hall-Heroult electrolysis cell, a finite element model must take into account the properties of each material. However, it has some lacking knowledge on the mechanical behaviour of materials, like the long-term visco-elastic (creep/relaxation) behaviour of cathode. A three-dimensional model is then proposed in this paper and will be ready to be implemented in the finite element code FESh++. The model was developed using the three-dimensional model based on thermodynamic of irreversible processes where the choice of the internal variables is based on a phenomenological approach. All parameters of the model are represented by constant constitutive tensors and the temperature and chemical dependencies are taking into account through scalar functions multiplying the constant constitutive tensor. The goal of the first part of this project was to determine the parameters of the threedimensional visco-elastic model at the reference state (virgin material at ambient temperature) of three different cathode materials. This paper presents the theoretical model and the results of creep tests at ambient temperature for the semi-graphitic carbon cathode.

Jan 1, 2006

By W. F. Riggs

1 Flotation Analogy To explain flotation in simpler terms the following analogy will be used. A factory (the flotation cell) manufactures a product (collector coated mineral). The product (collector coated mineral) is transported to market (the launder). A truck (the frother) is used to transport the product (collector coated mineral) to the market (the launder). The truck (the frother) transports the product over a road (the froth bed). The truck (the frother) and product (collector coated mineral) are supported by tires (the air). 2 Assumptions This operating philosophy assumes that the correct collector dosage is present along with the correct particle size distribution, pH conditions, etc. and that the minimum required frother dosage is correct. 3 Collector Addition The collector addition as used at a flotation plant is based on dosage rate as determined by the amount of mineral value entering the concentrator. Collector is normally added at two points in the concentrator: The primary flotation circuit and staged addition in the rougher scavenger circuit. Surveys have shown that the staged collector addition provides an increase in the kinetics and increases the recovery of the valued mineral in the rougher scavenger circuit. 4 Frother 4.1 Frother Dosage As explained in the above analogy, frother can be likened to the truck that transports the product (collector coated mineral) to market (the launder). Just as you would not use a truck rated at 15 tonnes to transport a 20 tonne load, you cannot expect to transport coarse minerals to the launder when there is insufficient frother present. Frother dosage must always be at, or above the minimum target. If less frother than the required minimum is used, then coarse mineral particles will not be supported and transported to launder where the mineral is recovered. To the naked eye the froth characteristics, even when insufficient frother is used, will appear to be correct. You cannot see the coarse particles that are not being recovered in the froth. (See Section 4.2 below for an explanation of why this occurs.)

Jan 1, 2006

By C. Gaubert, G. Bourassa

"The construction or rebuild process in the anode baking furnaces has been modeled with the software Rockwell Arena, in order to minimize the process cost and risk. The case study was focused on the sectional rebuild (""on the fly"") that needs a high coordination of the material inventory, the on-site personnel and the construction/production schedule. Multiple entities and resources were allocated for the different part of the process (in-furnace process, prefabrication, materials transportation, etc.). Logic flow charts and VBA macros were used to simulate the space utilization (including cranes utilization) and interaction with production. MS-Excel output files can show user-friendly results."

Jan 1, 2006

By H. Westengen

The AE alloy family exhibits remarkable combinations of properties when utilized as high pressure die castings. This performance relies on the fact that the rapid cooling rate resulting from the direct contact between the molten alloy and the steel die walls effectively refines the structure through rapid solidification. Furthermore, the rare earth additions modify the solidification pattern, dramatically reducing the solidification interval. A solid shell forms at temperatures exceeding 500C, reducing the tendency for die sticking and inverse segregation. As a result, the die castability is excellent, giving parts with a smooth and shiny surface. Unlike other magnesium die casting alloys developed to improve elevated temperature creep properties, AE alloys do not suffer from the commonly observed tendency to introduce brittleness. This feature is attributed to the fact that the massive magnesium- aluminium intermetallic phase is substituted by a finely dispersed lamellar structure of Al-RE intermetallics. The resulting combination of excellent elevated temperature properties and good ductility, as well as excellent corrosion resistance, means superiority of these alloys for demanding automotive engine and chassis applications.

Jan 1, 2006

By F. Ajersch, A. R. Hekmat

Apparent viscosities of hypo-eutectic (Al-7% Al) and hyper-eutectic (Al-35% Si) binary alloys were measured in the semi-solid state using a Couette type viscometer at variable shear rates. Analysis of the microstructural evolution demonstrates the differences in the rate and degree of attrition of the primary phase particles which are characteristic of the thixotropic nature of the semi-solid alloy. It was observed that the Si primary phase in the hyper-eutectic alloy is much more difficult to fragment than the dendritic a-Al phase in the hypo-eutectic alloy. For the case of the a-Al, the dendritic structure is broken down by attrition and fracture of the dendrite arms whereas the fracture of the Si hexagonal crystals in the hypereutectic alloy occurs along the {100} and {110} cleavage planes. Results are presented for fixed solid fractions of the primary phase at isotherm condition for each type of alloy.

Jan 1, 2006

By S. Spigarelli

The creep response of the AE44 magnesium alloy was studied by means of constant load creep tests carried out at 125 and 150°C, obtaining that at the latter temperature the minimum creep rate observed under an applied stress of 100 MPa was two orders of magnitude lower in the investigated alloy than in AM50. The minimum creep rate dependence on applied stress was described by a conventional power-law, e = Aon , where A was a temperature dependent parameter and n was the stress exponent, resulting in a n value close to 30, i.e. by far larger than those observed in commercial alloys with similar Al content. This large difference in creep response was attributed to the precipitation of rare earths (RE) intermetallic phases distributed in the grain boundary zone in form of an almost continuous network of dispersoids that were observed by means of scanning electron microscopy.

Jan 1, 2006

By R. F. Baxter, C. M. Read, R. I. McCulloch

"Globalization of the aluminium industry continues to increase the pace of change and the intensity of competition, while simultaneously, society demands better products, cleaner technologies and sustainable industries. Bechtel, a global engineering, construction and project management company, is not immune to either the opportunities or the challenges created by globalization. However, and not withstanding the challenges, for aluminium industry ""players"" with a true global perspective, globalization presents very real opportunities that may be leveraged to deliver value creating goods and services. The following paper will focus on the exploitation of one of the opportunities created by globalization in the Knowledge Management domain - the application of high level tools and methodologies to improve global delivery of greenfield and brownfield aluminium smelter construction projects. Specific examples will be presented of value driven solutions that were delivered at the early stages of project engineering."

Jan 1, 2006

By André de Jager, Henk Ludik

Navachab Mine experiences difficulties with pit wall stability in certain areas of the mine. The main reason for the instability is the fact that the geology comprises many joints and faults. Blasting, without impacting negatively on the stability of the pit walls, poses a major challenge. The mine has installed a technologically advanced seismic monitoring system with monitoring sensors positioned at various locations and depths throughout the pit. The electronic data recording system records all relevant information on a continuous basis with early warning signals in cases of potential danger. From the information recorded by this micro-seismic system it was established that the energy release into the high-wall is predominantly influenced by the mining rate, water content and mining tempo and to a lesser extent by the blasting operations. To limit the negative effects of blast vibrations, the use of Electronic Delay Detonators (EDDs) was introduced. The optimal delays were determined through signature trace analysis. The vibrations obtained during blasts initiated by means of electronic delay detonators were monitored and compared to those traditionally obtained when standard pyrotechnic delay detonators had been used. The measured vibration data indicated an improvement of 25% to 100% drop in vibration amplitude compared. The accuracy and programmability of EDDs presented huge potential for blast optimization in terms of limiting the vibrations without compromising fragmentation. The whole project was conducted over a twelve week period with some 4000 EDDs. The average size of a blast was in the order of 350 holes using about 40kg explosives per hole, which equates to 14,000 kg explosives over 12 different blasts. The paper deals in detail with the blast optimization process with regard to: - determining the rock response time; - establishing the signature traces; - analyzing the wave interference patterns; - predicting the direction of constructive and destructive wave interferences; - optimizing of the inter-hole and inter-row delay periods; - measuring the ground vibrations. The results obtained during electronic blasting are compared to those obtained during pyrotechnic blasting. Comparisons are being made with regard to the following: - ground vibration measurements; - pit wall stability measurements; - blast safety.

Jan 1, 2006

The New Zealand Minerals Industry Association was incorporated as the NZ Mineral Exploration Association in 1982, with a membership that consisted of the gold exploration companies then active in New Zealand . As its membership broadened, it changed its name to the Mining and Exploration Association in 1994, and more recently the Minerals Industry Association. It is a non-profit-making incorporated society relying on voluntary membership, and is not funded by industry levies.   It has employed a full time executive director since 1988 when Robyn Ross was appointed, followed by John Pfahlert (1991 - 1996) and now with Doug Gordon managing the Association.   The Association is one of a number of organisations that represent the mining industry in New Zealand. Others include the Coal Association of NZ (CANZ), the Aggregate and Quarry Association (AQA), The West Coast Commercial Gold Miners Association and Minerals West Coast.   NZMIA membership comprises the main exploration and mining companies that account for over 80 per cent of New Zealand Æs mine output, and nearly all of its exploration investment. Its membership has expanded from gold exploration to encompass exploration and mining companies active in coal, gold, aggregates and industrial minerals.   The Association has developed a National Minerals Strategy that determines its priorities, implemented via a Minerals Industry Advisory Committee. This group was established six years ago to advise the Associate Minister of Energy on issues relating to the long term development of the minerals sector in New Zealand.

Jan 1, 2006

Good morning ladies and gentlemen, and may I thank you for inviting me once again to address your conference. I would first like to welcome you all, especially international delegates and conference speakers. ItÆs a pleasure to be with you all and I hope that you have the time to enjoy the many beautiful sights that the Coromandel and Bay of Plenty have to offer.   Holding your conference in Waihi is particularly apt, especially bearing in mind the conference theme û 'Mining in the Community'. There can be few venues in the world that can boast a world class gold deposit of the likes of Martha Hill located right here in the centre of a rural service town. ItÆs a deposit that has a mining history active now in its third century and that to date has yielded some 7.5 million ounces of gold and 50 million ounces of silver. I doubt that when John McCombie and Robert Lee discovered gold at Martha Hill in 1878 that they had any inkling that their endeavours would be the foundation for a mine that would become such an inseparable part of the economic and social fabric of Waihi for the next 130 years.   This is now my fifth appearance at a New Zealand minerals conference, I especially value such occasions as it allows me to comment on your industryÆs performance over the past year, share my thoughts on matters affecting your industry, and also to give you some feedback from central government.

Jan 1, 2006

By L. Veleva, Garcia. A., G. Perez

Aluminum is a metal used for the transmission of electricity of high voltage, in the construction industry and other areas. In atmospheric conditions aluminum forms an oxide layer (Alz03'H20) as a result of its corrosion, entering the passive state. The oxide layer can be destroyed by the presence of ions (Cr, SOx-n) developing localized (non uniform) corrosion attack by pitting, difficult for evaluation. The concepts of fractals and self-similarity were used in this study for the characterization of the development of localized corrosion. Images obtained with a scanning electron microscope (SEM) of samples of electrolytic aluminum wire that have been exposed during one year in ruralurban and marine-coastal environments of the humid tropical climate of Mexico, have been processed. The development of pitting has been studied as a function of time, making a statistics of the frequency of appearance of pits versus the area occupied by them. The data show that the distribution of the pits follows a power law. Therefore, the concept of self-similarity can be applied for the study of the phenomenon of localized corrosion, describing their development with time.

Jan 1, 2006

By A. M. A. Mohamed, F. H. Samuel, S. Valtierra, H. W. Doty, A. M. Samuel

"The influence of Fe, Mn, Cu and Mg alloying additions, Sr modification and grain refinement on the microstructure of as-cast and solution heat-treated Al-10.8% Si alloys was investigated using optical microscopy and EPMA techniques. The results showed that the modification effect of Sr diminished with increasing Cu and Mg additions, due to Sr-Cu-Mg interactions. Strontium caused segregation of AlzCu in areas away from eutectic Si regions, and altered the precipitation sequence of the a-Ah5(Fe,Mn)3Siz iron intermetallic from post-dendritic to pre-dendritic, with the phase observed within the a-Al dendrites. Depending upon the alloy Fe and Mn content, a coarser variation (""sludge"") of the a-Fe phase occurred, in the form of polyhedral shaped particles. The AhCu phase dissolved almost completely during solution heat treatment, while Al5Cu2Mg8Si6, sludge, and a-Aln(Fe,Mn)3Siz phases persisted in all alloys, particularly at high Mg and Fe levels. The f3-Al5(Fe,Mn)Si phase dissolved partially in Sr-modified alloys, the dissolution becoming more pronounced after solution heat treatment."

Jan 1, 2006

The Daly-Judge Tunnel, begun in 1887 to drain mine workings, is now a source of potable water for the Municipality of Park City. The water is exceptionally clean; however, when roof falls occur, suspended solids levels become too high and water from the tunnel cannot be used in the treatment plant. In 2001, the tunnel was inspected and rehabilitated to ensure that the water supply for the 2002 Winter Olympic Games would be uninterrupted. Twenty-five timber tunnel sets were removed, and 86 steel sets were installed. Timber lagging was installed or replaced over about 230 m (750 ft) of tunnel length.

Jan 1, 2006

By H. Somekawa

The fracture toughness and deformation structures an AZ31 magnesium alloy processed by equal-channel-angular extrusion (ECAE) were investigated. The average grain sizes of as-ECAE and annealed-ECAE alloys were 4.0 and 16.3 µm, respectively. The plane-strain fracture toughness, Kip, in as-ECAE and annealed-ECAE were estimated to be 27.3 and 23.5 MPam1/2, respectively, by stretched zone analysis. The fracture toughness indicated higher value with grain refinement. From optical microstructural observations in samples after fracture toughness tests, although deformation twins were observed in annealed-ECAE, no deformation twins were observed in as-ECAE. From TEM observations, the dislocations on basal and non-basal planes were activated in as-ECAE. With grain refinement, the activations of dislocations on both basal and non-basal planes were possibly related to the reduction in formation of deformation twins in as-ECAE. In addition, in comparison with direct extruded process, ECAE process was more effective method to improve the fracture toughness in magnesium alloys.

Jan 1, 2006

By P. M. Wiltcher

The construction of a deep structural slurry wall in a restricted city centre location is always a challenging prospect. However, when the city is London and the site is bounded on two sides by high level canals and a main traffic highway on the third, the challenges are greater than usual. The paper discusses the design considerations required by the principal contractor to accommodate a single high level lateral support, value-engineered, bottom-up construction technique and the impact this had on the design detailing and construction of the slurry wall panels. This paper discusses the logistical challenges successfully overcome during the construction of 65,000sq ft of 40inch thick, 80ft deep structural slurry wall in the City of London. The paper reviews the benefits gained from using the state-of-the-art hydraulic grab and rotator system. Technological advances in computer instrumentation and real time monitoring were utilised to assist the grab operators in consistently delivering deviational control during excavation better than 1:200. With working space always at a premium on construction sites, the need for high quality, pre-fabricated reinforcement cages has never been greater. This paper reviews the argument for off-site fabrication of reinforcement members.

Jan 1, 2006

By H Lehtonen, H Mansikkaviita

In primary copper smelters, the received copper concentrate and other materials contain a certain amount of moisture, ranging from six to 14 per cent. Moisture in wet concentrate has a negative effect on the performance of the smelting furnaces when it is fed directly to the furnaces, namely increasing the energy consumption and the off-gas flow. There are several drying technologies available for drying copper concentrate, varying from direct heated rotary dryers and flash dryers to indirect heated steam dryers. Application of steam dryers has changed the drying process for copper smelters. Produced from a waste heat boiler, steam as heating medium enables plant-wide heat utilisation. Fossil fuel used from outside sources to remove water is no longer required and the combustion chamber is not required. In addition special attention has been paid to overcome the known problems of pollution emissions, excessive wear, clogging and frequent maintenance. The Kumera steam dryer is featured with many advantages based on principal improvements in reducing tube element wear and increasing drying efficiency. Thus, it has been considered as the first choice for those smelters where steam is available.

Jan 1, 2006

By Zhou Jiahan Wang Feng

This paper introduces the mechanism and the operating process of dike building by silt squeezing blasting. DBSSB (dike building by silt squeezing blasting) has the following advantages: shorter construction period (the construction period is decided only by the speed of rock materials filling)greater consolidation of the body of the dike, more structural stability, smaller settlement. Therefore by conventional standards the same dike can be designed with a smaller cross section than other construction methods, and at a reduced cost when enough rock materials can be provided in site.

Jan 1, 2006

By Tateo Usui

In the course of carbonization of coal under a rising temperature condition, volatile matter (V.M.) is released. The kind and amount of V.M. released depend on the kind of coal. Components of V.M. are tar, hydrocarbons (CH4, C2H4, C2H6, C3H8), CO, CO2 and H2, which are released in this order as a function of carbonization temperature. When the carbonization of coal under a rising temperature condition is interrupted at a certain temperature, TC, max, semi-coal-char with residual V.M. is obtained. If some optimum interruption-temperature is chosen, small but most suitable amount of V.M., namely H2, is retained. When the semi-coal-char thus obtained is heated again under the same rising temperature conditions but up to more than TC, max (1), the residual V.M. is released from just around TC, max (1). We propose novel iron ore agglomerate bearing such semi-coal-char with some strength. While simple iron ore agglomerate bearing coal char will start the reduction reaction as solid-solid reaction at somewhat higher temperature, the proposed one will start the reduction reaction as gas-solid reaction at somewhat lower temperature but a little higher than TC, max. Samples of semi-coal-char and novel iron ore agglomerate bearing such semi-coal-char have been prepared and evaluated.

Jan 1, 2006