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By M G. Aylmore, L W. de Klerk

Roasting of refractory gold ores has been a commercial process for many years. Improvements in design of fluidised bed roasting technologies and low capital and operating costs compared with other refractory treatment processes can potentially make roasting a viable option.However, gold extraction from roasted ores carried out on laboratory scale equipment often invariably yields lower recoveries than other processes such as bio-oxidation or pressure oxidation. Non-optimal laboratory roasting conditions can incorrectly write roasting off as a process option.Low gold recoveries from the cyanidation of calcine products from roasting can often be attributed to roasting conditions not favouring gold liberation and agglomeration processes, particularly if lockups of elements such as arsenic are being pursued for environmental reasons.This paper reviews the conditions favoured for gold agglomeration and accessibility of gold to cyanide, test conditions to achieve gold liberation and agglomeration on laboratory scale and designs that incorporate staged decomposition and roasting to make roasting a more commercial option.CITATION:Aylmore, M G and de Klerk, L W, 2013. Conditions and design considerations for maximising recoverable gold in roasting of refractory gold ores, in Proceedings World Gold 2013 , pp 375-388 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By B. Anameric

The pig iron nugget process is gaining in importance as an alternative to the traditional blast furnace. Throughout the process, self-reducing?fluxing dried greenballs composed of iron ore concentrate, reducing-carburizing agent (coal), flux (limestone) and binder (bentonite) are heat-treated. During the heat treatment, dried greenballs are first transformed into direct reduced iron (DRI), then to transition direct reduced iron (TDRI) and finally to pig iron nuggets. The furnace temperature and/or residence time and the corresponding levels of carburization, reduction and metallization dictate these transformations. This study involved the determination of threshold furnace temperatures and residence times for completion of all of the transformation reactions and pig iron nugget production. The experiments involved the heat treatment of self-reducing?fluxing dried greenballs at various furnace temperatures and residence times. The products of these heat treatments were identified by utilizing optical microscopy, apparent density and microhardness measurements.

Jan 1, 2007

By R. D. van der Weijden, W. F. C. van Wageningen

"Copper(II) can be recovered or removed from acidic copper sulfate solutions as cuprite or metallic copper powder by reduction with carbohydrates (van der Weijden et al., 2001, 2002). In order to make this process suitable for a commercial scale pipe reactor, process conditions and reactor configuration need to guarantee proper throughput of the dilute suspension. This is where crystal engineering also comes into view. Copper powder characteristics, such as size and shape of particles, influence the tendency to adhere to reactor walls and to agglomerate, which in turn influence the throughput. Furthermore, separation, drying, packaging and product quality, are dependent on the powder characteristics.In this paper the effect of both chemical and physical parameters on the shape and size of particles were systematically studied in a number of autoclave experiments. These parameters include mixing, Cu(II) concentration, pH, temperature, seeding, use of additives and reactor materials. Additionally, Monte Carlo simulations of copper growth inside a Kenics static mixer were made. Results show that the use of additives, and the use of static mixers influence particle characteristics the most."

Jan 1, 2003

By L. Bratek, K. Jaworek, M. Czaplicka

Methods for arsenic compound removal from aqueous solutions include processes such as: coagulation, adsorption, membrane techniques, electrochemical and biotechnology techniques. Advanced oxidation using both UV radiation and strong oxidizing agents such as ozone and hydrogen peroxide may also decompose these compounds. It is known that effluents from metallurgical processes contain inorganic arsenic compounds in addition to the organic compounds such as: dimethylarsinic acid and phenylarsonic acid. This paper presents the conditions that lead to the formation of deposits containing mainly arsenic, such as pH, the wavelength of the radiation and the type of oxidant, for this type of effluent.

Jan 1, 2014

By C. Zener, J. H. Hollomon

IT Is commonly recognized that a given material may be described as ductile or brittle only with reference to the conditions of test. Thus under the usual test conditions quartz is brittle, but under high pressures it is ductile. Salts that are brittle at room temperature become ductile at elevated temperatures. Pitch, brittle with respect o rapid loads, flows at low rates of loading. Pearlitic steel, ductile under the usual conditions of test, may be embrittled under the proper conditions of combined stresses, temperature, and rate of loading. EARLIER INVESTIGATIONS A clear analysis of the conditions necessary for plastic flow and for fracture was first given by Ludwik,1 who introduced two types of stress, the "flow stress" and the "stress at fracture." These stresses may refer to tensile or to shear stresses, or, in fact, to any type of stress. Ludwik considered these two stresses to be independent of one another, functions of the conditions of test and of the prior history of the material. For the purpose of analysis, both a flow stress and a stress at fracture can be envisaged as functions of strain over the entire range from zero to infinite strain. Thus, the material is brittle if the stress at fracture is less than the flow stress and ductile if the reverse is true. According to Ludwik's analysis, the problem of determining the effects of combined stresses, of temperature and of strain rate upon the behavior of metals reduces to a problem of determining the effect of these variables upon the flow stress and upon the stress at fracture. In the present paper, methods are described for determining the effects of two of these variables, temperature and strain rate, and examples are given of the dependence or now stress and stress at fracture, upon these two variables. The effect of combined stresses will be discussed in a succeeding paper. The flow stress may be determined from a load-diameter curve. Load-diameter curves were obtained over a wide range of temperature and over the limited range of strain rates obtainable with the lever-type Riehle machine used. The. curves were then converted to an extremely wide range of strain rate by making use of the equivalence of the effects of changes in strain rate and changes in temperature, previously proposed2 and demonstrated' by the authors. According to this principle of equivalence, strain rate E and temperature T affect the flow stress only through a single parameter p of the form: p = EeQ/RT [I] In this equation, R is the gas constant (2 cal. per gram mol per deg. C.), and Q is a heat of activation, which varies from material to material, and may depend upon the strain, but not upon the strain rate or the temperature. There is associated with every value of p a flow-stress curve. Combinations of strain rate and of temperature that give the same p have the same flow-stress curve. Therefore, merely by changing the temperature of test, the effect of changing the strain rate may be obtained. Thus, under isothermal conditions, the material will behave the same at

Jan 1, 1944

By E. Barsky

"The aim of separation is to obtain two products that are as distinct as possible from each other. It is currently believed that the most objective criteria for the quality of a separation are the Hancock criterion and the entropy criterion.1. Hancock criterion:- for yield of fine product"

Jan 1, 2003

By I. O. Flores, A. Anani, H. Li

Current technological advancement has increased the exploitation of deeper ore bodies using underground methods. In certain cases, the mineral deposit starts near the surface and continues deep within the earth's crust. Such deposits are best mined with both underground and surface methods. Two main techniques are used to determine the optimal transition depth from surface to underground - a disintegrated approach and an integrated approach. Both methods have limitations in their use to determine the optimal transition depth. The objective of this research is to investigate the conditions in which an integrated approach to the transition depth problem is superior to a disintegrated approach. Three binary integer linear programming models are developed for this purpose: a surface and underground model for the disintegrated instance and an integrated model. A case study is performed to validate the models, with a comparative sensitivity analysis to obtain operational insights.

Sep 1, 2021

By P Holtham, K Duffy, B, W Valery, E Tabosa, rade

Pre-concentration has potential to significantly improve Mineral Resource efficiency by removing gangue early in the process, before energy intensive and expensive comminution and fine processing. However, there are numerous options for pre-concentration and the performance and benefits of these are very case specific. To determine the best option for a particular deposit and to successfully integrate it into the overall mining and processing operations requires comprehensive evaluation. This needs to consider orebody suitability, technology capability and economic viability. The in-situ variability of a deposit and how it is influenced by mining methods and the liberation size of gangue are key factors which are generally not well understood. Geostatistical methods provide an insight into orebody variability, and the overall selection of any pre-concentration solution must be an integrated approach between geology, mining and processing. Many pre-concentration evaluations investigate the potential of just one option. Technology selection should start wide and may include: selective mining, pre-screening (with or without selective blasting), sorting (bulk and or particle), coarse gravity separation (e.g. jigging, DMS), coarse particle flotation, magnetic separation, etc. The upgrade performance of these processes is very ore specific and should be determined from testing, with detailed multi-component modelling used to determine the overall process performance. Many of these pre-concentration processes require significant ancillary equipment, feed preparation and materials handling. It is important to realistically estimate all costs to understand overall economics and select the best option. Some examples showing evaluation and comparison of pre-concentration options are presented in this paper. These include assessments of in-situ variability using geostatistical tools, process modelling of pre-concentration options and overall performance, preliminary layouts and cost estimates, and economic evaluations.

Nov 10, 2020

By C J. Greet, J Kinal, C Hitchen

Following the successful completion of a marked ball test defining the potential wear benefits the high chrome alloys may offer against forged steel, as well as laboratory test work investigating changes in pulp chemistry and improvements to metallurgical performance, a plant trial was commissioned at NewcrestÆs Ridgeway concentrator. The paper briefly describes these results.Newcrest decided to convert their media charge by the top-up method. To monitor the trial a sampling protocol was put in place whereby the pulp chemistry was monitored before, during and after the purge. The metallurgical shift data was analysed using various statistical methods to determine if the metallurgical performance had improved with the change in grinding media. While the analysis indicated that the metallurgy had improved, not all of the benefits could be assigned to the change in grinding media alone. However, the combination of reduction in media wear and the increases in copper and gold recoveries suggested that it was economically viable to operate with high chrome grinding media.As with many trials of this nature the prevailing economic conditions are fluid and a decision was made to revert back to forged steel grinding media in an effort to reduce operating costs. It was further agreed that Magotteaux could monitor the pulp chemistry and metallurgical changes in this reverse trial to confirm the results observed in the earlier conversion to high chrome grinding media.CITATION:Greet, C J, Hitchen, C and Kinal, J, 2012. Conducting high chrome grinding media trials at NewcrestÆs Ridgeway Concentrator, in Proceedings 11th AusIMM Mill OperatorsÆ Conference, pp 56-64 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Oct 29, 2012

By Milton E. Wadsworth

The evolution of engineering education and research has been profoundly influenced by computer technology and has concomitantly followed changes in this technology. Today, virtually all faculty have access to at least two hierarchies of computers: desk personal computers and at least one echelon higher (workstations or a variety of mid-sized computers). Most faculty have access to three or even four hierarchies: the two listed, plus super-mini and super computers. The ready availability of computers at a low cost has increased dedicated and site-specific computer technology. This has permitted universities to move into the field of macro-engineering, to address increasingly complex problems in resource recovery, manufacturing and many other areas, including important societal problems, like the environment. The creation of university research centers indicates the growing importance of macro-engineering involving large systems of interactive components. Funding agencies have increasingly favored such centers since they cross disciplines, generate inter-university consortia and foster university-industry programs.

Jan 1, 1992

By V. L. Ketellapper

This paper discusses the technical issues and stakeholder collaborative processes which resulted in achieving a balance between the reclamation of abandoned mine sites, providing affordable housing, and preservation of open space at the French Gulch Site. Through this process, it was discovered that mine site reclamation would need to be conducted in conjunction with two priorities for community sustainable development: providing affordable housing for locals who work in the resort town of Breckenridge, and open space preservation. It was found that conducting these activities concurrently would result in providing resources necessary to complete mine site reclamation. The first phase of the affordable housing development is almost completed. This development resulted in redevelopment of mining impacted lands and was recognized by the U.S. Environmental Protection Agency (EPA) with a National Smart Growth Award in 2002.Negotiations are also underway to preserve the remaining 1,800 acres of land held by the mining company as open space. This transaction will in turn provide resources to address water quality issues associated with mine discharges.

Jan 1, 2004

By K. S. Raja, F. Battick, B. Pesic

"CeO2 doped with lower valence cations, such as Y3+, Sm3+, Gd3+ etc. is considered as electrolyte material for low temperature SOFC. Doping introduces additional oxygen vacancies and improves ionic conductivity. This work describes the preparation of yttria-calcia doped-ceria precursor material, its sintering in DC and AC field methods, and characterization of sintered electrolytes with respect to the ionic conductivity. Doped precursor materials were prepared by a controlled co-precipitation process. Sintering of prepared, pelletized particulates was carried out using three different methods such as: 1) conventional; 2) spark plasma sintering; and 3) an alternating current field at 1125°C (AC assisted sintering). The mechanism involved in the conductivity improvement as a function of defect density, grain boundary area and phase stability will be discussed. INTRODUCTIONThe performance of SOFCs depends highly on the properties of materials. Subtle variations in the composition, microstructure, or density of SOFC components can considerably alter the power output capabilities of fuel cells. Early SOFCs utilized zirconia based electrolytes but efforts in lowering the operating temperatures of SOFCs have prompted investigations into several other oxygen ion conductors – often modified with dopants to either promote the formation of oxygen vacancies or to stabilize a vacancy rich high temperature phase – such as bismuth oxide, lanthanum gallate, and ceria.The transport of oxygen ions through the electrolyte first begins with diffusion into the material. While this is generally a surface kinetics phenomenon, it is safe to say that it is highly dependent on oxygen pressure and vacancy gradients. The role of the cathode in SOFCs is to reduce oxygen at the electrolyte surface creating an O2– ion gradient which induces permeation into the material. Once inside and under the influence of a potential field, O2– ions migrate by a vacancy hopping mechanism, Catlow, C.R.A. (1990), effectively exchanging positions throughout the matrix until they reach the anode and react, thus leaving the matrix."

Jan 1, 2012

By Susumu Imashuku

A pseudoternary phase diagram of the BaO?ZrO2?ScO1.5 system is established and the conductivities of the scandium-doped barium zirconate are measured in wet conditions. According to the phase diagram, the molar fraction of scandia in the barium zirconate phase that equilibrates with the cubic zirconia (ZrO2) and scandia (Sc2O3) phase is 0.03. On the composition line, where the molar fraction of barium oxide (BaO) is 0.50, the solubility of scandia into barium zirconate is 0.27 as a molar fraction of scandia. At around 500 °C, the conductivities of scandium-doped barium zirconate are estimated to be almost same as that of yttrium-doped barium zirconateThe activation energies for bulk proton conduction in scandium-doped barium zirconate (0.57 eV for BaZr0.90Sc0.10O3-d) are higher than that of yttrium-doped barium zirconate (0.44 eV for BaZr0.90Y0.10O3-d). In addition, the bulk conductivity of scandium-doped barium zirconate in this study is 10 times higher than the reported conductivities in the temperature range of 75 °C to 300 °C.

Jan 1, 2006

By J. D. Miller, C. L. Lin

As the techniques and resolution for 3-D spatial analysis have advanced in the last decade, it is now possible to map in detail the microstructure of multiphase materials in three-dimensional digital space. In this regard, three-dimensional x-ray microtomography offers a unique imaging capability. Spatial resolution on the order of ten microns can be achieved with the use of microfocus x-ray generators. Recently, a state-of-the-art cone beam x-ray microtomography system has been installed at the University of Utah for the quantitative analysis of multiphase materials in three dimensions. This facility has been designed to obtain 2048 x 2048 pixel reconstruction over a 10-mm diameter, while also allowing for the imaging of somewhat larger (40-mm) objects. The system is capable of handling high-density materials, even materials having a density as high as 8.0 g/cm3. This unique, one-of-a-kind, instrument will be used to obtain three-dimensional spatial reconstruction for such applications as specific examples 3D liberation analysis, pore structure analysis of particle beds during filtration and air-void system of concrete structures. The utilization of x-ray microtomography not only will allow for quantitative analysis of multiphase systems but also allow for textural characterization and the determination of phase continuity. In this paper, we present information regarding the current use of this new facility and reviewed potential applications for the advanced analytical system.

Jan 1, 2001

By U. S. Sawant

During the last few years, Process Machinery Division, Rexnord, has conducted extensive research on the effects of cone crusher variables such as speed, throw and cavity design on the productivity of the crushers. Simultaneously, Rexnord's engineers have developed advanced design and testing techniques and criteria that assure efficient and reliable crusher designs. The combination of these two has resulted in a design of the 2390 Omnicone (1000 hp) crusher which fits on an existing 7 ft. Symons foundation and yet is capable of producing twice the tonnage compared to our 7 ft. super heavy duty (500 hp) crusher. Both speed and throw can be varied to give a wide application flexibility from making twice the tonnage to the finest product. The 2390 Omnicone also incorporates innovative features such as full balance, cavity clearing, adjusting under load with automation capability, maintenance-free seals, one head for all cavities, ease of maintenance and servicing, etc.

Jan 1, 1987

By A. J. Magerowski

Energy consumption is a main component of operational costs for the comminution of mineral bearing ores. Reduction of energy consumption has continually been addressed by mill operators and equipment manufacturers. Our testing over the last few years strongly indicates that the overall energy needed to comminute a mineral bearing ore can be brought down significantly, if more work is done in the crushing stages of the comminution circuit.This calls for uprating of the conventional crushing equipment into a new generation of crushing equipment to produce finer products. This will result in the emergence of new ideas in the design and application of equipment and corrnninution circuits.

Jan 1, 1986

By Ronald B. DeDiemar

This paper will present the intrinsic factors of a cone crusher that affect performance, develop and define an ideal feed gradation for a cone crusher and, finally, bring out an important new development in computer design of crushing chambers and show an ability to predict crusher performance without trial-and-error methods.

Jan 1, 1979

By D Reid, A Fourie, J Ayala

This paper discusses cone penetration test correlations for loose gold tailings that were developed within a critical state soil mechanics framework. The development of a new calibration chamber for cone penetration testing that consists of a modified triaxial cell is described. Some of the early development and commissioning issues that were encountered, as well as the solutions adopted are outlined, including the system to prepare the samples and to acquire high-quality data from the testing. Also, the triaxial laboratory testing required to achieve the critical state line is described, including some of the basic precautions considered necessary as good practice. Additionally, the system adopted for volume tracking of the calibration chamber sample is described, which is essential for ensuring a reliable state parameter comparison against the acquired cone penetration test data. Finally, some laboratory test data from the calibration chamber is plotted against the soil behaviour type charts currently available from various authors.

Jul 1, 2021

By Baltus Cornelius Bonse

Foi desenvolvido um composto de elastômeros termorrígido (ebonite) para a fabricação de um selo mecânico de vedação de hélices de barcos, para substituir os modelos comumente encontrados de cerâmico, que possuem alto custo e são fabricados no exterior, e de borracha com face em Teflon®, que apresentam problemas de adesão na linha de junção entre estes materiais, resultando em vazamentos. O composto de elastômeros deveria possuir dureza em torno de 90 Shore D, baixo coeficiente de atrito, resistência térmica, a abrasão e a intempéries marítimas, ao ataque de radiação UV e ser autolubrificante. A formulação que resultou no melhor produto consistia das borrachas natural, nitrílica, nitrílica carboxilada, e fluorada (Viton®), aditivadas com alto teor de enxofre (37,5 phr), cargas reforçantes, plastificantes e lubrificantes sólidos, entre outros aditivos. A aditivação e mistura das borrachas foram realizadas em misturador interno Banbury e misturador de cilindros aberto, enquanto a conformação e vulcanização dos corpos de prova e dos selos foram realizadas por prensagem a quente. Foram realizadas análises de curva reométrica, morfológicas por microscopia eletrônica de varredura, de resistência à tração, rasgo, dureza e de abrasão em torno mecânico simulando a pressão de vedação em atrito com o aço inox girando a 800 rpm. O êxito do selo ficou evidente, pois após a montagem em barcos, durante um ano tem realizado com sucesso a sua função.

Aug 8, 2018

Following the suggestion of Engineering Council and at the direction of, the President, representatives from each of the Federal Government bureaus interested in map-making were called into a conference for the purpose of coordinating all of the Government's map-making activities. This conference has now reported back to the President the results of its findings, which indicate that Engineering Council's recommendation in this matter was well founded. While the conference report states that its members were of the opinion that little duplication of effort existed, it recommends the formation of a permanent Board of Surveys and Maps. An extended review of the map-making activities, which is given as an appendix to the report, indicates that this recommendation is a logical step. The conference recommendations concerning this Board of Surveys and Maps are as follows: (1) the Board is to he com-posed of representatives of mapping bureaus to be assisted by outside engineering organizations, which have been named above; (2) the estab-lishment of an information office in one of the Government bureaus, preferably the Geological Survey, which is to be under the supervision of the Board and is to be a mapping information clearing house for the Government and outside engineering organizations; (3) copyright laws are to be so changed that copies of all. maps made in the United States and with Governmental authority, will go to the central information office; (4) the Government departments are to receive orders to cooperate, with the Board; (5) future topographic maps of all kinds are to conform with specifications for the standard topographic map; (6) the U. S. Coast and Geodetic Survey to have supervision of final adjustment of all important control data under specifications approved by Board of Surveys and Maps; (7) surveys in the form of maps and publications are to be issued as soon as possible after field work has been completed; (8) program of the Interdepartmental Committee on Aerial Surveying was approved. Outside technical and scientific organizations that are called in for consultation are to operate in an advisory capacity only, responsibility for action on Governmental work is. to rest solely with the Governmental agencies.

Jan 12, 1919