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By Chao Li, Hongxu Li, Yang. Xie, Meng Wang, Xiangxin Hao

"With the development and utilization of resources of gold, high quality gold mine resources gradually exhausted, and refractory gold ore has become the main raw material for gold smelting, while the smelting pollutants impacting on the ecological environment is growing, in recent years there have appeared several methods of green extraction of gold such as bio-oxidation. In this paper, the life cycle assessment models about three different gold extraction technologies have been put forward. Material consumption, energy consumption and emissions during each gold production process are analyzed by using GaBi 6 software, and the environmental impact of each process is also evaluated by means of CML2001 methodology. Calculation and analysis results show that the energy consumption and material consumption are the main factors causing the environmental load; and the environmental impacts of the production process mainly attribute to the category of greenhouse effect, resources consumption and environmental acidification. Based on the evaluation, some optimization tips are proposed.IntroductionOver the past decades, as the industry policy environment continues to improve as well as gold exploration and mining smelting capacity continues increasing, gold production shows a prospecting tendency. With the wide use of gold, the demand for gold is growing, while easy smelting gold mine resources become exhausted and refractory gold ore has become the main raw material for gold smelting. In addition, pollutants impact on the ecological environment is also growing year after year.LCA (Life Cycle Assessment) makes evaluation of product “from cradle to grave” as its whole process, up to finding the sources of environmental impacts and solutions, to comprehensively account the use of resources and lower emissions. In the industrial field, life cycle can compare different technologies from different aspects of resource use, energy consumption and environmental emissions [1]. In recent years, using LCA to evaluate metallurgical industry process also has more development. The paper mainly uses LCA and scenario analysis for the gold metallurgical process by GaBi 6, to investigate the environmental impact of three different technologies of gold extraction metallurgical process. The established three evaluation models include the hydrometallurgical, pyro-metallurgical processes and bio-oxidation pretreatment methods respectively. Several environmental indexes would be selected to evaluate the environmental impact in order to find which process has smallest environmental load and some suggestion of reasonable way gold resource utilization."

Jan 1, 2014

By Guo Chen, Jin Chen, Jinhui Peng

"In this paper, the methods of life cycle assessment for microwave hot air systems, and the concept of green degree were proposed. Greenness evaluation index, evaluation system and evaluation model of microwave hot air systems were established. Also, life cycle assessment processing based on these ideas was introduced. Analytic hierarchy process and fuzzy decision- making method were utilized to establish and solve the greenness evaluation of assessment model, while the scores of green degree in microwave hot air systems were obtained. The results show that Life cycle assessment can be applied effectively and efficiently to the microwave hot air systems.IntroductionHot air systems are an important industrial operation condition, which is used to provide high temperature air for materials processing. Nowadays, high temperature airs are manufactured by the conventional heating processes, in which some ceramic materials are used as heating materials. However, these processes pollute the environment. Therefore, to explore new method to produce high temperature air with low energy consumption and less environment pollution are necessary.Microwaves are now being used in various technological and scientific fields in order to heat dielectric materials [1]. Microwaves irradiation has been explored in materials processing in recent years [2-3]. The main advantage of using microwave heating is that the treatment time can be considerably reduced, which in many cases represents a reduction in the energy consumption as well. Since there is energy absorption but no heat conduction, the heating is very rapid and highly efficient, resulting in energy savings and the shortened processing time [2, 4]. Compared with conventional heating techniques, the additional advantage of using microwave irradiation is that microwave irradiation achieves both internal and uniform heating [5-7]. In addition, it is more convenient to control the microwave irradiation processing, because of no direct contact between the heating source and heated materials with less equipment size and waste [2, 8-9]. Life cycle assessment is used and accepted methods for the evaluation of the environmental impacts of products or systems [10]. Recently, many appropriate evaluation methods have been developed for life cycle assessment [11-12]. These proposed methods usually are employed for the evaluating product and analyzing results [13]. Among them, the analytic hierarchy process and the fuzzy comprehensive evaluation stand out as a popular method utilized in many fields [14-16]. Analytic hierarchy process and fuzzy comprehensive evaluation are a combination of mathematical and statistical technique that is useful for analyzing the effects of several independent assessment aspects on the system goal without the need of the predetermined relationship between the objective function and the assessment aspects [17-19]."

Jan 1, 2013

By Maria Rashidi, Maryam Ghodrat, Bijan Samali

Treatment of sharp medical waste (waste disposable syringes) produced in hospitals or health care facilities in an environmentally sound ways have raised concerns relating to public health and occupational safety. Life cycle assessment (LCA) is a decision-supporting tool in waste management practice; but relatively little research has been done on the evaluation of sharp medical waste treatment from a life cycle perspective. Our study assesses the environmental performances of medical waste incineration as a type of dominant technology for specific medical waste of average composition. Inventory models were used for waste incineration and residues land fill. Background data were derived from modelling performed in HSC Chemistry thermochemical package linked with GaBi environmental assessment tool. Two scenarios have been considered and compared: Waste disposable syringes partially replacing coke in Electric Arc Furnace (EAF) steelmaking (WSI) and conventional incineration with pure metallurgical coke without adding waste syringes (CI). The results of this study could support the medical waste hierarchy and indicate that from a life cycle perspective, replacing part of metallurgical coke with waste syringes in electric arc furnace steelmaking leads to fairly significant reduce in most of environmental impact categories.

Mar 1, 2017

By Stephen Northey, Nawshad Haque, Terry Norgate

"Life cycle assessment (LCA) is a recognized tool to evaluate various processing routes for metal production. Declining ore grades and higher specific energy requirements for primary metal production put greater emphasis on recycling. Greenhouse gas (GHG) emissions of steel and aluminium metal production were quantified with recycling scenarios using material recovery facility (MRF) data from the database of SimaPro LCA software. The GHG footprint of the MRF is relatively minor compared with that of associated transport during collection (i.e. 10 times more than MRF) of curbside recyclable material. Additionally, if the bulk recyclable material is sent overseas (i.e. Australia to China) from the MRF for further processing, the GHG footprint of shipping can significantly be larger compared with the sum of the collection and MRF (assuming electricity is from same source). Thus opportunities exist for reducing GHG emissions from secondary metal production if it is processed close to the MRF.IntroductionIt is a challenge to recycle metals significantly, although theoretically infinite recycling is possible due to their elemental nature. Leaks from the metal stocks in society occur through corrosion, wear and dispersive uses, or via land filling or similar activities that return metals to the earth. In order to provide a technically sound and transparent assessment of metal recycling, a methodology such as life cycle assessment (LCA) should be used. By taking a life cycle perspective, the beneficial recycling properties of metals can be evaluated in a manner that enables appropriate comparisons with other materials or product systems that do not have recycling loops. In practice, mixtures of primary and secondary metals are often used in new products, and also at the end-of-life various processing methods are used for recycling.The difficulty of introducing recycling into LCA is to set the right boundaries for the different flows ending in different product systems. It is a question of which observed material flow belongs to the first product system and which one to the second or subsequent systems. Recycling can be part of any product LCA. However, it is often a complex issue which requires specific considerations. As pointed out by Yellishetty et al. and Birat et al. [l, 2], LCA practitioners are left with much freedom in allocation of environmental burdens to account for recycling, thus making subjective judgments on recycling and allocation of credits to recycling. This often makes it difficult to compare the results of LCA studies conducted by two different practitioners even on the same processes. As LCA is often used to define policy in government, business and society circles, it should be based on a sound, objective and unbiased description of recycling."

Jan 1, 2014

By He De-wen

Based on the principle of life cycle assessment (LCA), municipal solid waste management (MSWM) was analyzed by life cycle inventory method. According to the system expansion and substitution method, the content and frame of life cycle analysis is summarized and applied to municipal solid waste. On the basic of feasibility research of life cycle analysis on MSWM, the paper put forwards complete and concrete ?three changes? measures under life cycle analysis on MSWM. Some aims of MSWM can be achieved under above conditions of LCA on MSWM: to improve the current system efficiency of MSWM; to enhance the serve quality of MSWM, to increase recycle garbage from MSW; to reduce waste amount and reach minimization and innocuity aim of MSWM; to help the departments of MSWM to get over all difficulties to realize their ideal goals.

Jan 1, 2009

By Robert Hanson, Mayur K. Patel

"Pneumatic conveying pipelines are used throughout a variety of industries, from food processing/packing to power generation plants, as an efficient means of transporting materials between storage and processing points. In general, different phases of pneumatic conveying exist when material is conveyed from point A to point B in a pipeline. This depends on the operating pressure and the material conveyed. Lean phase conveying exists when pipelines are operated at high airflow rates, relatively low pressures, inducing sufficient turbulence for particles to become entrained in the air stream. Thus, particles are conveyed along the pipelines at velocities in the range of IS-2Sm/s. Generally, the initial capital costs for lean phase system is low, however the running costs are high. The opposite is true for dense phase, high-pressure systems. In considering either conveying system, it is important that the rate of erosion of the pipeline be considered when designing such a system, since it is the rate of erosion that dictates the lifetime of components. In general, the high level of erosion occurs for lean phase flows, where high impact velocity contribute substantially to the rate of erosion as well as other processes such as particle breaking, if the particles are friable. This would lead to poor quality of material, not normally desirable. On a positive note, the process of erosion is used in other applications, which benefits from this process, e.g. abrasive guns.The failure, by puncture, of pneumatic conveyor bends in industry causes several major problems. Two of these are: (a) escape of the conveyed product causing health and dust hazard and (b) repairing and cleaning up after punctures necessitates shutting down conveyors, which will affect the operation ofthe plant, thus reducing profitability.The paper reports on modelling strategy used in the development of a modelling framework and the initial validation phases of the models incorporated within. The modelling framework encompasses Computational Fluid Dynamics (CFD) related engineering tools, based on Eulerian (gas) and Lagrangian (particle) approaches, to represent the two distinct conveyed phases, to represent the erosion process which is used to ascertain the lifetime of conveyor bends."

Jan 1, 2001

By Khandaker M. Anwar Hossain

This paper presents the development of lightweight concrete (LWC) incorporating pumice aggregate and volcanic ash (VA) based ASTM Type I blended cement (PVAC). Fresh and mechanical properties of LWC mixtures such as slump, air content, compressive strength, tensile strength, density and modulus of elasticity are described. The durability characteristics are investigated by drying shrinkage (DS) and water permeability. The investigation suggests the production of LWCs incorporating blended PVAC and VPA having satisfactory strength/durability characteristics for structural applications. The use of PVAC induces the beneficial effect of reducing drying shrinkage and water permeability. Development of such non- expensive and environmentally friendly LWCs with acceptable strength and durability characteristics is extremely helpful for the sustainable development and rehabilitation of volcanic disaster areas around the world.

Jan 1, 2010

By Karel Van Acker

The automotive is a sector where energy consumption during the use phase prevails over the production and the end-of-life phase. Therefore, a lot of research and innovations at replacing classical steel parts by lighter materials like light metals and polymer composites. While composites are very attractive for the use phase of cars, their introduction suffers from the limited end-of-life options for composite structures. An extensive life cycle analysis for a reference car design has been conducted to study the effects of replacement of conventional steel structures by lightweight carbon fibre composite alternatives. The study also takes second order effects in the design of the car into account. The opportunities and treats of the trend towards more intensive use of carbon-fibre composites in car design are identified. A discussion on the potential of other types of composites for the automotive in terms of sustainability considerations is added.

Jan 1, 2010

By P. R. Taylor

Laboratory experiments have been performed to evaluate the kinetics of roasting pyrite and arsenopyrite in air at elevated temperatures, in the presence of lime. The effects of temperature, time, air flow rate, particle size, lime type, and mineral/lime weight ratio on the rates of oxidation, lime sulfation, and lime arsenation were studied. The reaction products were identified using chemical analysis, x-ray diffraction, SEM analysis, and optical microscopy. The results are discussed in terms of the utilization of lime to capture sulfur and arsenic during the roasting of refractory precious metal concentrates. More than 99.9% of the arsenic and 98% of the sulfur are contained when roasting pyrite and arsenopyrite with hydrated lime under typical roasting conditions.

Jan 1, 1991

Lime-enhanced carbothermic reduction may provide an alternative process for treating low grade chalcopyrite concentrates. To date, most research on lime-enhanced reduction has been on pure, synthetic sulfides. In this study, preliminary experiments were carried out on natural chalcopyrite using a thermal analysis system to assess the rate and extent of reaction at several temperatures and identify the major solid and gaseous reaction products. Calculations were performed to establish the thermodynamic limits of the reactions in the temperature range of interest in order to identify the potential conditions for processing chalcopyrite concentrate. The study found that finely ground chalcopyrite can be reduced carbothermically in the presence of lime at moderate temperatures and in a reasonable time to form metallic copper, with the sulphur reporting virtually entirely to calcium sulfide. At temperatures below about 750?770ºC calcium ferrite is the stable form of iron whereas at higher temperatures metallic iron is stable. Further work is required to demonstrate the reaction on a scale to obtain sufficient sample for evaluation of subsequent processing steps to remove the gangue material and iron products from the copper.

Jan 1, 2009

By P. M. Prasad

The last two decades have witnessed the emergence of numerous hydrometallurgical and direct processing techniques for the extraction of some metals from pocketed/lean/complex sulfide ore deposits. A new approach with some inherent technological merits, investigated in recent years, is the lime-enhanced reduction of metal sulfides. Thermodynamic aspects relevant to the lime-enhanced reduction of metal sulfides by H2,C0 and C are discussed. A survey of the researches on the basic features of and factors influencing the lime-scavenged reduction of selected sulfides and sulfide concentrates reveals that lime tremendously enhances the sulfide reduction rates (up to 100 times) and drastically reduces the sulfur emission into off-gas to negligible levels. Further successful practice of lime-enhanced reduction requires only a moderate temperature of reduction (characteristic of each sul¬fide) and, in the case of gaseous reduction, relatively low gas flow rates. Relevant kinetic aspects of the concerned reactions that have a bearing on process development and its understanding are also briefly discussed. A conceptual scheme of general applicability for the processing of sulfide concentrates by the lime-enhanced reduction technique consists of three main steps: (0 lime-enhanced reduction by a suitable reagent (e,g., H,2, CO, gasified coal, water gas), (ii) separation of the product metal from the dry slag (CaS + unused CO) by mechanical separation, magnetic/gravity concentration or flotation and (iii) melting and refining by standard procedures. This novel approach, which is patently less complex, is expected to employ basically simpler flow sheets at comparatively lower operational temperatures and aid in pollution abatement. Potential for developing such a route for the small scale extraction of metals like copper, molybdenum and antimony is indicated. Possibility of utilizing this technique for the production of fibers/ filaments of some metals is also outlined.

Jan 1, 1983

By Lucio Fabio Cassiano Nascimento, Luis Henrique Leme Louro, Sérgio Neves Monteiro, Jheison Lopes dos Santos, Fernanda Santos da Luz, Fábio Oliveira Braga, Rubens Lincoln Santana Blazutti Marçal, Hugo Concolato de Oliveira Freitas, Édio Pereira Lima Júnior

Epoxy matrix composites reinforced with up to 10, 20 and 30 vol% of continuous and aligned natural mallow fibers and 30 vol% of mallow and jute hybrid fabric were for the first time ballistic tested as personal armor against class III 7.62 mm FMJ ammunition. The ballistic efficiency of these composites was assessed by measuring the dissipated energy and residual velocity after the bullet perforation. The results were compared with that in similar tests of aramid fabric (Kevlar™) commonly used in vests for personal protections. Visual inspection and scanning electron microscopy analysis of impact-fractured samples revealed failure mechanisms associated with fiber pullout, rupture and layers delamination. When compared to Kevlar™, the mallow fiber and hybrid fabric composite displayed practically the same ballistic efficiency. However, there is a reduction in both weight and cost, which makes both, mallow fiber and hybrid fabric composites, a promising material for personal ballistic protection.

Mar 1, 2018

By Jean-François Domgin

This paper aims at presenting numerical results showing the impact of different parameters on the limitation of entrained slag from ladle to tundish during the ladle drainage. These parameters are process parameters, slag properties or external actuator acting directly on ladle slag behaviour. Numerical simulations based on the use of the CFD Fluent software illustrate the vortexing and non-vortexing phenomena appearing during the ladle drainage. This numerical tool validated by experimental data acquired on water model has been applied to industrial configurations. It shows that the slag properties (viscosity, surface tension?) or some modifications of parameters (slide gate opening, geometry of the ladle bottom?) have a positive effect on the slag entrainment and also on the decrease of the ladle heel. Finally, the modelling of the behaviour of an external actuator injecting some gas in the region of the nozzle reveals interesting possibility for reducing slag entrainment from ladle to tundish during the final steps of the drainage.

Jan 1, 2006

By R. M. Luna-Sánchez

Electrochemical studies, particularly Evans? diagrams, have been employed in hydrometallurgy to simulate and explain the redox phenomena that take place at mineral and metal surfaces during operations such as leaching and cementation. However, despite their utility, in some cases, the combination of the cathodic and anodic branches, determined separately, does not reproduce the chemical environment present when both processes occur simultaneously on a specific surface. In the present paper, limitations of Evans? diagrams are analyzed through two examples: silver sulfide cyanidation and gold cementation on zinc. In both cases, the surface kinetics are sensitive to the local pH and cyanide levels. When the electrochemical oxidation of silver sulfide or the reduction of gold are performed in the absence of its corresponding redox reaction, the local pH obtained does not simulate the real situation and the combined reaction kinetics may be very different from those determined from the Evans? diagrams.

Jan 1, 2003

By R. P. King

The linear intercept distributions provide unambiguous and accurate characterizations of the texture of mineralogical materials. The relation between the measured linear intercept distributions and the spatial correlation function is shown to be given by: in the Laplace Transform domain. The linear intercept distributions of the two phases in a low- grade chromite-serpentinite ore were measured. and the spatial correlation functions for both phases were evaluated using the above relation. The correlation functions are the primary relations for integral geometric models of mineralogical texture and this work demonstrates the relation between the 10 stereological model and the 3D integral geometry model for mineral liberation.

Jan 1, 1991

By Andre Thess, Jurij Kolesnikov, Christian Karcher

"During the motion of molten metal under external non-homogeneous magnetic field the induced electric currents produce Lorentz body forces in the opposite direction to the flow, causing deformation of velocity profile, vortical structures, and adding a pressure drop across the magnetic field. The same Lorentz force acts on the magnet system. We analyse these phenomena in metallurgy, namely, at molten metal pumping, stirring, continuous casting, and in contactless Lorentz force flowmeter (LFF). Experiments with liquid metal alloy, including direct measurements of Lorentz forces, velocities, and flow structure visualization were conducted. Based on this study the industrial prototypes of LFF systems were designed, built, and tested in a secondary aluminium production. A molten metal flow at high temperature (700°C-850°C) can be effectively measured. The LFF technique method allows measuring precisely the volumetric and mass flow rates linked with Lorentz force, and the mass accumulated within production process.IntroductionThe present work demonstrates the development of a non-contact electromagnetic system for measurement of a liquid metal flow. Our approach embodies the Lorentz force velocimetry [1-6] technique which is physically based on a measurement of the force acting on an external magnet system the field of which interacts with the flow. This force is exactly equal to the braking Lorentz force induced in a flowing conducting fluid. In what follows a measurement system based on the Lorentz force velocimetry principle. For monitoring and controlling the production process it is desirable to measure continuously the mean velocity of the liquid metal in order to deduce the mass-flux and volume-flux from it. The form and dimensions of the magnet system are in agreement with geometry of the operating channel. We consider here a version of magnet systems in a composition of permanent magnets.The LFF possesses a number of advantages which make it attractive for the measurement of flows in hot and aggressive melts. The relation between the measured force and the desired volumetric flow rate is often linear (for closed channel or at a constant liquid metal level in open channel). For the converting of the measured force into volumetric and mass flow rate we should know the calibration factor. The calibration factor is independent of the viscosity and density of the liquid metal and depends only on the magnetic field magnitude, the electrical conductivity of the liquid metal and the geometry of the channel in which the liquid metal flows. In aluminium production, for instance, there exists a number of standard alloy compositions having welldefined conductivities for which the calibration factors can thus be tabulated. We consider below consistently effects in liquid metals arising under influencing magnetic field, construction principle of LFF and measurements of metal flows at industrial conditions."

Jan 1, 2011

By S. Eckert, G. Gerbeth, K. Timmel, B. Willers, T. Wondrak, N. Shevchenko, M. Röder

The quality of the produced steel in the continuous casting process is significantly governed by the melt flow in the mold. However, direct flow measurements in liquid metals are still rather scarce. In order to investigate these flow phenomena, three experimental facilities operating with low melting liquid metals were installed at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The melt flow in the models is measured by the Ultrasonic Doppler Velocimetry (UDV) or the Contactless Inductive Flow Tomography (CIFT), multi-phase flows can be visualized by X-ray imaging. The obtained measurement results are primarily used for validation of numerical models. In this paper we will investigate the fluid flow in the mold and the behavior of the surface of the liquid metal using flow measurements by UDV and surface profile measurement by a laser scanner, respectively. Strong fluctuations and deviations of the free surface were observed in case of a static magnetic field

Jan 1, 2016

By Rauf Hurman Eric

The high temperature liquid miscibility gap in the Ag-Ag2S pseudobinary portion of the Ag-S system has been redetermined by very carefully conducted equilibration-quenching experiments. Samples were contained in evacuated and sealed silica capsules. The stratified liquid phase compositions were obtained by chemical analysis. The miscibility gap extends from 14 to 32.3 atomic percent at the monotectic temperature of 906°C and closes at around 1320°C.Thermodynamic properties of the liquid solutions, including the limiting activity coefficient of sulfur in molten silver were expressed analytically by using the sub-regular solution model which proved to be in excellent agreement with the experimental findings.

Jan 1, 2006

By N. B. Gray, I. F. Taylor

"Gas injection to promote chemical reactions or mixing is a feature of many metallurgical processes. Often the aim of gas injection is to bring about a chemical reaction between the gas and liquid but most of the past physical and mathematical modelling work has ignored the influence of such reactions. In the work reported here, cold model studies have been conducted in which gas reacts with the liquid into which it was injected. The rate of liquid mixing has been measured as an indication of the mechanical energy transfer. It has been found that gas generated chemically within the liquid is significantly less effective at promoting mixing than the equivalent volume of inert gas. The relative ineffectiveness of chemically produced gas is thought to be due to smaller bubble sizes in comparison to the inert gas case. Small bubbles characteristic of chemically generated gas move with low slip velocities relative to the liquid and lead to different turbulence generation mechanisms.IntroductionIn processes such as steelmaking, copper conversion, bath smelting and ladle steel finishing gas is injected into liquid metal where it reacts chemically or simply serves as a source of agitation. An understanding of fluid flow phenomena in such situations is an essential pre-requisite to the calculation of process intensity and the optimisation of vessel productivity. Traditional physical cold modelling approaches to prediction of liquid flow in such situations are now often augmented by the techniques of computational fluid dynamics. Even with the availability of numerical modelling techniques cold physical models continue to have an important role for validation because it is generally difficult to obtain quantitative data from high temperature processes.Almost all previous cold modelling work has been based on the injection of an inert gas into water or some other non-reactive liquid. Such models do not include the significant increase in gas volume inherent in some processes. For example the oxidation of carbon in steelmaking leads to a twofold increase in molar gas flux through the reaction:"

Jan 1, 1996

By Shinya Hodoshima

A catalysis pair of tetralin dehydrogenation / naphthalene hydrogenation has been proposed in the present paper as a liquid organic hydride for operating stationary fuel cells. Catalytic naphthalene hydrogenation, having been commercialized since the 1940s, proceeds to generate decalin via tetralin as an intermediate. The storage capacities of tetralin (3.0 wt%, 28.2 kg-H2 / m3) are lower than decalin (7.3 wt%, 64.8 kg-H2 / m3) but both tetralin dehydrogenation and naphthalene hydrogenation are much faster than the decalin / naphthalene pair. Moreover, existing infrastructures such as gas stations, chemical tankers and tank lorries are available for storage, transportation and supply of hydrogen. With respect to the stationary fuel cells with large space for hydrogen storage, tetralin as a hydrogen carrier is superior to decalin in terms of fast hydrogen supply or power density. Rapid hydrogen supply from tetralin under mild conditions was only accomplished with the carbon-supported metal catalysts in the ?superheated liquid-film states? under reactive distillation conditions. In contrast to the ordinary suspended states, the catalyst layers superheated in the liquid-film state gave high catalytic performances at around 250OC. As a consequence, both serious coke formation over the catalyst surface and excessive consumption of exergy were prevented simultaneously.

Jan 1, 2006