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By M. Hashiuchi

In 1972, the tankhouse of the Tamano Smelter adopted a high current density electrolysis operation applying the PRC (Periodic Reverse Current) method. In 1994, the phase four production expansion project, which incorporated significant re-structuring of the organization, was completed and we have achieved an annual production capacity of 191,000 tons. The target of this project, the production capacity, was increased by 1'8% and labor productivity by 25%. After the expansion, some improvements in the starting sheet section and the verticality of the electrodes were carried out, and the efficiency of the operation was greatly enhanced, including the improvement of the quality of the electrolytic copper.

Jan 1, 1999

By C. Anderson

Most applications of copper metallurgy are geared towards primary production. However, as recycling of materials is a growing industry, one future facility will rely on copper metallurgy as a means of processing precious metals. This paper will discuss the derivation of the proposed copper pyrometallurgical and electrometallurgical unit operations to be utilized in industrial recycling of secondary precious metals.

Jan 1, 1999

By J. Tang

The major problem with the Nd-Fe-B magnet is its low operating temperature, i.e., the coercivity decreases so rapidly with increasing temperature that the practical maximum operating temperature-is only 100 °C. Meanwhile, it has been reported that nitrogen addition can drastically increase the Curie temperature of both R2Fe17 and RTiFe11 (R = rare earths). A reasonable question is, then, can one see a similar effect in Nd-Fe-B system? Experiments have been conducted to examine how magnetic properties of Nd-Fe-B magnet are affected by the nitrogen addition. Our results show that part of Nd2Fe14B maintains its original crystal structure and no substantial change in To, due to such N2 treatment is found. However, part of the sample decomposes into a-Fe and, possibly, Nd nitride as a result of nitrogen treatment.

Jan 1, 1992

By Yves Fautrelle, Kader Zaidat, Hervé Combeau, Miha Zaloznik, Mohammed M'Hamdi, Bachir Saadi, Xiaodong Wang, Knut Omdal Tveito

"Numerical simulations of macrosegregation formation during horizontal solidification of a hypoeutectic Sn-Pb alloy in a rectangular cavity is presented and compared to experimental results. The experiment involves a melting phase, a holding stage at constant temperature with/without application of electromagnetic stirring, and finally solidification. We simulate all stages of the experiment and study the segregation of Pb throughout the experiment. A twophase volume averaged model is used for the numerical simulations, accounting for thermosolutal convection and assuming perfect microscopic mixing (lever rule). The influence of the melting phase and the electromagnetic stirring is studied with different cases to illustrate the consequences on the flow pattern and Pb segregation. The numerical simulations are compared to the experimental data and the impact of chemical inhomogeneities prior to solidification on macrosegregation formation is discussed.IntroductionMany extensive investigations have been performed so far on the solidification of metallic alloys. However, the melting process of metallic alloy has not attracted attention in a same manner. Nevertheless, melting of alloy may put forth peculiar effects as described in the present paper. It has been observed from a benchmark experiment [1, 2] that significant stratification might arise during the melting process of Sn-Pb alloy. That effect was put forth thanks to the analysis of the experimental temperature distribution which indicated that the convective fluid flow was almost zero. The effect was enhanced when the lead composition was higher (above 6wt.%). The present paper is aimed at confirming that the melting of an alloy containing a heavier solute may be accompanied with a stratification of the solute which exerts a stabilizing effect on the convective fluid flow. Results obtained from numerical modeling are compared with experimental data obtained from the benchmark facility."

Jan 1, 2012

By José García-Antón, Valentín Pérez-Herranz, José Luís Guiñón, Henry Reyes

"The majority of chromium electroplating operations employ Cr(VI)-based baths. During these processes, Cr(VI) is reduced to Cr(III). Besides Cr(III) other undesirable impurities are present such as iron, copper and nickel. The build-up of the impurities limits the lifetime of the plating solutions. Since the disposal of spent chromic acid baths is expensive and can cause significant environmental degradation, there is increasing interest in finding ways to regenerate waste chromium liquors.In this work, an electrolytic cell separated by microporous ceramic diaphragms was used to regenerate chromium plating solutions. The effect of the ceramic diaphragm structure parameters, such as porosity and pore size, on the performance indicators of the electrochemical reactor (fractional conversion, current efficiency, product yield, specific energy consumption) was investigated.The fractional conversion, the product yield and the current efficiency increased and the specific energy consumption decreased with the decrease in porosity.IntroductionChromic acid is widely used in industrial applications such as steel manufacture, metal finishing industries, aluminium anodising, pasivation of cadmium, magnesium, and zinc, etching of plastics and another industrial operations related with processing ferrous and no ferrous metals [1]. These processes employ baths with high concentrations in chromic acid, about 180 and 350 g/L, where hexavalent chromium is reduced to Cr(III):"

Jan 1, 2008

By Q. Chen

The magnetic properties and phase evolution of Nd-lean and/or boron-rich melt- extracted ribbons of Nd98Fe90.2xBx, where x = 6 through 11, have been studied using XRD, DTA, TMA, and VSM. The off-stoichiometric Nd2Fe14B compositions cause additional phases to be present after crystallization and affect the magnetic properties obtained. The crystallization temperature of this alloy series rises with the increasing) boron content. In addition to Nd2Fe14B and a-Fe, Fe3B is detected. It is found that increasing the boron content reduces B, within this composition range. The magnetic properties are directly associated with the relative magnetic phase content in the samples.

Jan 1, 1997

By V. A. Bryukvin

A characteristic feature of the macrokinetics of the interaction process is the presence of two specifically defined areas of oxidation which had a linear time dependence. The effect of variables, such as residual sulphur content of the melt, temperature and the oxidation potential of the gas phase, on the macrokinetics of oxidation are investigated. Phase composition and structure of products of solidification of partially oxidised melts and thermodynamic properties pentaining to Cu-S-O melts are used to analyze the macrokinetic behaviour and mechanisms of the interaction. The process of interaction of sulfide copper melts with oxygen may be considered as a disproportional absorption process and its mechanism is based on localized interaction on the surface and inside the melt volume. Superficial processes include also the process of primary chemisorption of oxygen by melts at place of metal-metal donor bonds proceeding with formation of oxysulfide liquid solutions and volumetric decomposition of the latter accompanied by evolution of sulfur dioxide and metallization of sulfide melts. It is the degree of dynamic balance of such interaction processes that determines specific individual features of the macro-kinetics and mechanism of oxidation of sulfide copper solutions with oxygen in the gas phase.

Jan 1, 2006

By G. Achurra

The products of the smelting of copper concentrates in an El Teniente Converter (CT) are a high grade matte, analyzing 74-76% Cu; and a highly oxidized slag, typically containing 15-20% Fe3O4 and 4-10% Cu. The El Teniente Division of CODELCO¬CHILE has developed a slag reduction-cleaning process, that is practised in a tilting, horizontal furnace, to recover copper from these slags. The El Teniente slag cleaning process has been successfully implemented at the El Teniente Caletones smelter and various other smelters in Chile: Today, eight such slag cleaning furnaces, each with a capacity of 800-1000 tonnes/day, are in operation in Chile. This paper discusses basic laboratory research and industrial tests that led to substantial reductions in the slag cleaning cycle time and the specific consumption of fuel and reductants. Simultaneously, the slag cleaning off-gas quality was improved. Based on the experimental results, recommendations were made to improve the practice of the El Teniente slag cleaning process. The recommended modifications have been fully implemented at the Caletones smelter.

Jan 1, 1999

By Taner Kavas

In the present study the utilization of coal ashes that appear at the end of firing process of brick production in cement pastes was examined. Ashes with three different particle sizes of 75 µm, 106 µm and 150 µm were used to replace ordinary Portland cement (PC) as 5 % and 15 % by weight. Seven samples were prepared and physical, mechanical, chemical and microstructural analyses were carried out. The compressive and bending strength values of samples were determined at the ages of 2, 7 and 28 days. It was found that cementitious pastes with finer particle sizes possessed the highest compressive and bending strength values at all curing ages. Both values after 2 and 7 days cure increased with an increase in ash content, no matter what the particle sizes of ashes were. However, strength decreased after 28 days cure as a result of ash addition of 15 %, although it was still above that of the PC.

Jan 1, 2006

By Emilia Visileanu, Eftalea Carpus

"The strategy of developing the Romanian textile industry sub-sectors envisages the achieving of certain superior production indices, from a physical and value point of view, in 2010, a quantitative increase of textile wastes by 14% in 2010 as compared to 2000, implicitly. The percentage of the turned-to-profit wastes will have an increasing tendency, from 53.6% in 2000 to 74.7% in 2010. The article synthetically presents the innovative elements of the technology of processing the industry textile wastes.1. Introduction“People will need to re-adopt this sense of rarity that has been forgotten over the last two centuries. Humans need to collect, sort, recover, going back to the old ideal of alchemists: complete the material cycle, turn waste into resource, reduce all forms of predatory behaviour as much as possible”Irrespective of the historical period, geographical positioning, economic power or employed technologies, wastes resulted and will result in a bigger or smaller quantity as long as life and activity on Earth go on. The negative effects of these over the environment factors and implicitly over population health are well known all over the world and not approaching this matter enough may have catastrophic consequences over life. Having in view these aspects, finding solutions for diminishing the general waste quantity and limiting the negative effects of those products is important, by effecting the reusing of the recyclable ones in the production processes as secondary raw materials, and by ecologically treating and storing those than cannot be reused.2. Experiments and researchesThe textile industry affects the environment by the high water, energy and chemical consumption, as well as by the high quantity of wastes that are the result of using an impressive number of chemical substances and technological processes.The development strategy of the Romanian textile industry sub-sectors foresees, for 2010, the achieving of certain higher production indices as compared to 2000, both in terms of materials (as merchandise) and in terms of value, which implicitly leads to a quantitative increase of wastes.The flexible, economic and ecologic technologies which include systems of waste preliminary preparing (cutting, opening) and conventional or non-conventional system of processing the recovered fibres lay at the basis of substantiating the activity of implementing the notion of zero wastes."

Jan 1, 2008

By Yang Tian-zu

Sodium pyroantimonate which is widely used as the clarifier in the glass industry and as the synergist in anti-flaming industry respectively has a production history of about 30 years in China. At present there is the production capacity of about 20,000 tons per year in China and China is chief producer of sodium pyroantimonate. In this work the production processes adopted by the producers of China, the operation conditions and the product qualities of sodium pyroantimonate prepared by different preparation methods have been summarized, and on the basis of comparing the advantages and disadvantages for each process the most advanced method - the air-oxidation method was introduced in detail. The production processes of sodium pyroantimonate mainly include the method of oxidation by sodium nitrate, the oxidation method of hydrogen peroxide, the potash salt method, the chlorination method and the air-oxidation method etc. The method of oxidation by sodium nitrate in which the crude antimony oxide, sodium carbonate and sodium nitrate are separately used as the raw material, the flux agent and the oxidant, has the advantage of short and simple technological process, but low grade quality of sodium pyroantimonate and bringing about serious environmental pollution are the disadvantages and this method has been substituted by other methods. Sodium pyroantimonate can be directly prepared by the hydrogen peroxide oxidation method with the advantages of simple technological process, high grade quality of the product and little environmental pollution. High grade quality of sodium pyroantimonate can be also synthesized by the potash salt method, in which industrial antimony white, the hydrogen peroxide, potassium hydroxide and sodium hydroxide are applied as the starting material. The disadvantages of these two preparation methods are high production cost and high requirements on the raw materials. The chlorination method with the crude antimony oxide, hydrochloric acid and chlorine as the raw material has the advantages of low production cost and high grade quality of the product. However complex process, high requirement of anti-corrosion for the equipments and producing plenty of waste water limit its application. The air-oxidation method with stibnite/jamesonite concentrate, sodium sulfide, and sodium hydroxide as the raw material and atmosphere as the oxidant is a newly developed method and its advantages are low production cost and the complex raw material can be treated by this method and its disadvantage is that the quality of sodium pyroantimonate is lower than that prepared by the oxidation method of hydrogen peroxide and the potash salt method.

Jan 1, 2006

By Thomas Schuman, Jaan Kers, Lucas N. W. Damoah, Xiangjun Zuo, Lifeng Zhang

"Rapid technological innovation has propelled the use of electronic equipment leading to the generation of more and more waste electrical and electronic equipments (WEEE). Printed wiring board (PWB) is a component made of one or more layers of insulating material with electrical conductors. To investigate an environmentally friendly process to recycle PWBs, PWB samples with and without additives were pyrolyzed. Liquid, gas and solid products were achieved with different conversion fraction. Analysis of the exhaust gases from the experiments using GC-MS and MS showed that without CaCO3 additives poisonous gases such as C6H6 and HBr were produced which were adequately controlled if CaCO3 was added.IntroductionPyrolysis is one of the best methods for treating complex mixtures of waste polymers and to recover the material and energy content. The process consists of thermal decomposition at moderate temperatures in total absence or small amount of oxygen in which the structures of polymers break down into smaller intermediate products "". The decomposition temperature of a substance is the temperature at which the substance breaks up into smaller substances or into its constituent atoms 2). Thermal treatment of PWBs were reported using DC Arc Plasma furnace 3), and fixed bed reactor 4). One drawback in dealing with thermal treatment of PWB scraps is the likely production of super-toxic halogenated dibenzodioxins and dibenzofurans from the bromine containing structures. Pyrolysis of organic materials contained in waste PWBs leads to the formation of gases, oils, and chars which can be used as chemical feedstock or fuels ""'. Dehalogenation of the pyrolysis product of electronic scraps is essential to make it commercially acceptable. It would be obviously the most advantageous solution as pyrolysis and dehalogenation are carried out simultaneously. Reported pyrolysis investigations are at experimental stage and have been carried out in vacuum, molten salt, fluidized bed, rotary kiln, entrained, stationary, and moving bed reactors 7). Comparing to the incineration and combustion of PWBs, the pyrolysis process has several characteristics: 8'"">) 1). Converting the organic solid substance into fuel gas, fuel oil and carbon-black as storage energy; 2) Emitting toxic substances such as sulfur, bromine and heavy metals in wastes; and 3) Keeping metals from being oxidized. Although many researches into the pyrolysis of PWB wastes have been reported, most of the works have been carried out using analytical pyrolysis techniques or very small batch reactors ""~'5). Also, most of the works for the pyrolysis of PWBs haves concentrated on the composition of the organic products, particularly the brominated organics. The current study is to investigate the pyrolysis of PWB powders in a small TG-DTA scale and a 50-gram tube furnace scale."

Jan 1, 2011

By llya Perederiy, Vladimiros G. Papangelakis, Indje Mihaylov

"Nickel slags obtained from various smelting furnaces and converters differ in terms of their chemical composition and microstructure. The microstructure of the slag is largely affected by how fast the slag is cooled after being discharged from the furnace. Slow cooling is known to promote crystallization and growth of phases such as crystalline fayalite (Fe2Si04), magnetite (Fe3Ü4) and vitreous silica (S1O2). Slag granulation causes rapid solidification of the melt in the form of either an amorphous solid or highly intergrown crystalline silicate and oxide phases. Smelter slags contain entrapped Ni, Co and Cu in the form of dissolved oxides and matte inclusions. Extraction of the entrapped metals by high pressure oxidative acid leaching (250°C, 70 g/L initial H2SO4, up to 90 psi O2, 45 min) relies on the dissolution of the metal bearing minerals. The impact of the slag microstructure on the accessibility of these minerals to leaching, as well as the morphology of the produced residues is discussed in this paper.IntroductionIt was shown previously that entrapped base metals can be efficiently extracted from naturally cooled (as opposed to granulated) crystalline nickel smelter and converter slags using high pressure oxidative acid leaching operating at 250°C, ~40 g/L terminal acid and 60 to 90 psig oxygen overpressure [1, 2,3,4, 5, 6].Mineral characterization work performed on a naturally cooled crystalline nickel furnace slag from Vale's operations in Sudbury (ON, Canada) was previously reported [4]. Fayalite (Fe2Si04) and magnetite (Fe3U4) were detected using powder X-ray diffraction. These two minerals as well as silica (S1O2) and matte ([Fe,Ni,Cu]Sx) were also identified with the help of energy dispersive X-ray spectroscopy (EDX) on cross-sectional images obtained with a scanning electron microscope (SEM) operating in the backscattered mode. Nickel converter slags obtained from Vale's operations in Sudbury were found to be mineralogically similar to the furnace slag, but with higher contents of matte entrainment and magnetite based on the SEM-EDX observations [6]."

Jan 1, 2012

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 Sundarrajm Suresh, Hrushikesh G. Pimpalgaonkar, Thiyagarajan Paramadayalan

In this paper, a model of a fuel cell system has been proposed to account for the membrane physics at the micro level which is coupled with the macroscopic flow and mass transport phenomena occurring in a single channel of a Polymer Electrode Membrane Fuel Cell (PEMFC) system. We have developed a novel approach to model the catalyst layer electrochemical processes in a Membrane Electrode Assembly (MEA) and coupled it with mass transport and fluid flow calculations at the channel level using STAR-CD commercial software. The predicted values of the cell voltage from this micro-macro model are validated with experimental data available in the literature. A sensitivity analysis has been carried out to study the effect of the design and operating parameters such as catalyst loading and initial temperature on the overall performance of the PEMFC. The results indicate that the cell voltage increases at higher platinum catalyst loading and is also independent of the choice of initial cell temperature.

Jan 1, 2012

By K. Kashiwaya, N. Hiroyoshi, H. Furuya, N. Sumiya, M. Tsunekawa, M. Ito

"The number of hybrid vehicles is increasing and this is causeing an increase in waste nickelmetal hydride batteries. The cathode activating agent of batteries is made of nickel hydroxide and the anode activating agent is an alloy of nickel and rare earth elements. Conventional rotary kiln methods cannot recover the rare earth elements, and hydrometallurgical treatment of crushed product consumes large volumes of agent. The physical separation of the anode alloy from the cathode hydroxide would make it possible to reuse the alloy. The authors have reported separation of anode and cathode components in the large size fractions using a newly developed dry magnetic separation method. Wet magnetic separation has been applied to the powder fraction and about 90% anode purity was achieved. This paper reviews experimental results from previous publications and proposes an integrated treatment process for crushed nickel-metal hydride batteries.IntroductionEnvironmentally-conscious clean energy vehicles have attracted much attention in developed countries and particularly hybrid vehicles are increasingly mass-produced as low emission vehicles. Hybrid vehicles have both a gasoline engine and an electric motor to save on gasoline usage and a nickel-metal hydride battery is used to store electric energy. The battery contains Nihydroxide and Co as the cathode activating agent and an alloy of Ni and mischmetal (mM), a rare-earth element mixture consisting of La, Ce, and Nd, as the anode hydrogen adsorption component. In conventional recycling, the Ni and Fe are recovered with a rotary kiln-electric melting process and the Co and mM go to the slag component [1] and hydrometallurgical treatment of crushed product consumes large volumes of agent. Japan Oil, Gas and Metals National Corporation have proposed a low energy and low cost recycling treatment process combining the physical and chemical treatments and the authors are investigating the physical treatment process."

Jan 1, 2008

By Bradford C. Wesstrom, Omar Araujo

"Impurities from an electrolytic refinery are typically extracted from the electrolyte utilizing conventional electrowinning cells. These cells are arranged in series with cascading solution flow and are commonly referred to as liberator cells. The Freeport McMoRan Copper & Gold El Paso Refinery has optimized the removal of arsenic in cascading liberator cells by utilizing two separate feed solutions. The primary feed solution is recycled liberator electrolyte and the secondary feed solution is ""neat"" tank house electrolyte. The secondary feed solution is added based on the voltage response across the individual cells utilizing independent variable frequency drive (VFD) pumps. When the voltage across a cell changes, a signal is sent to the VFD pump to maintain a cell voltage of 1.98 volts. By maintaining this voltage the copper content in each cell exits at 2-4 grams per liter. This safely optimizes the arsenic removal as copper arsenides on the liberator cathodes.IntroductionDuring the electrolytic refining of copper, impurities from the copper anode report both to the bottom of the electrolytic refining cell as slimes and to the electrolyte. The impurities which enter the electrolyte are arsenic, antimony, bismuth and nickel. The impurities that report to the electrolyte during the electrolysis process gradually increase. As these impurities increase, they are incorporated into the refined copper cathode. There are many processes that have been used to remove these impurities from refinery electrolytes. Some of them are listed as follows: solvent extraction, ion exchange, hydrogen sulfide reduction, bioreactor, adsorption onto a low - solubility metal-oxide hydrate, adsorption onto activated carbon and EMEW cells. The conventional process used by the copper refining industry for controlling the level of impurities in electrolyte involves multistage electrolytic cascading liberator cells. In these cascading liberator cells copper, arsenic, antimony and bismuth are removed as various mixed deposits from the electrolyte. Removal of these impurities is achieved through an increase in voltage resulting from the depletion of copper in the electrolyte through electrowinning. With this higher voltage, the Group Vb elements, arsenic, antimony and bismuth are deposited on the copper cathode and report as slimes to the bottom of the cells. Nickel is removed in a subsequent process."

Jan 1, 2012

By Magdelinka Padenkova-Yaneva, Emilia Christova Kostakeva

"Environmental protection is becoming over the years an increasingly significant problem of mankind. Up to the last decade the only way to make the domestic waste harmless in Bulgaria was deposition on uncontrolled landfills without undertaking actions for protection of the soils. This also caused pollution to spread into the surface and underground waters and that is why actions are now undertaken for remediation of contaminated soils. This is achieved by developing projects for the closing down of polluted sites. In the present paper some projects for closing down of polluted areas are discussed. The actual conditions are examined and project decisions for preventing the surface waters from penetrating into the waste are presented. In this way the pollution of the soil is stopped and the soils are gradually remediate.IntroductionSoil is the topmost layer of the earth crust. It consists of mineral particles, organic substances, water, air and living organisms and is an extremely complex and changing living environment. Soil is a non-renewable natural resource which is of considerable importance in a number of crucial processes (production of foods, storing, filtrating and turnover of many substances, including water, carbon and nitrogen). It also serves as a basis for human activities, shaping the landscape, ground on which cultural heritage is built, and source of raw materials. These functions of soil must be protected both because of their social and economic significance and from the point of view of environmental protection.The processes of erosion, loss of organic substances, compaction, salination and contamination contribute to the degrading of soils accompanied by a negative impact on human health, natural ecosystems and changes in climate, as well as on the economy. All these make it necessary to protect soils from contamination. Over the last years intensive work started in Bulgaria for the construction of controlled sanitary landfills for rendering municipal solid waste harmless. Pursuant to Bulgarian legislation, in these controlled sanitary landfills measures are undertaken for protecting the soils from contamination through appropriate project decisions – the filtration of the products from the biological decomposition of waste into the adjacent sites (soils) and, therefore, the contamination of the surface and underground waters is prevented. At the same time the purity of air is maintained, human health is protected and conditions are created for including the controlled sanitary landfills into the surrounding landscape."

Jan 1, 2008

By Magdelinka Padenkova-Yaneva, Emilia Christova Kostakeva

"One of the methods for waste treatment is composting during which as a result of controlled biological decomposition of organic waste in aerobic conditions harmless materials are received. Composting takes place in suitably designed premises which ensure the optimal conditions for biochemical decomposition of the waste. A usual way to process composting is the spreading of the waste on a base made from reinforced concrete.In the paper the phases and basic technical features of the process of composting, the requirements and properties of the base and the ways of protection of concrete base against corrosion are revealed. Technical decisions for a specific construction site in Bulgaria are shown and the advantage of achieving durability of the concrete constructions in the plant while achieving simultaneous environment protection from pollution is discussed.IntroductionComposting is the process of controlled biochemical decomposition of vegetable and animal organic waste in aerobic conditions as a result of which harmless materials are obtained. The latter have better stability and are rich in humus substances which are useful for agricultural crops and can be used for restoring the soil fertility [1, 2, 3, 4].In modern waste treatment plants a composting technology is adopted in which the waste is spread on a concrete base as piles with certain dimensions [1, 3]. These piles are periodically stirred or air is blown through them in order to ensure the quantity of oxygen required for the process of aerobic decomposition of the organic matter. The fluids and gases formed in the course of the composting are take away in order not to pollute the environment – air, water, and soils. For this purpose the base on which the waste is spread must satisfy certain requirements, and the gases must be taken away and rendered harmless in order to protect the atmospheric air from pollution. This paper discusses the need for protecting the concrete base from corrosion and characterizes the stages and main parameters of the composting process and the possibilities for primary and secondary protection of the concrete base from corrosion. Specific technical decisions applied in a composting facility in the area of the town of Plovdiv are presented."

Jan 1, 2008

By Frank Field, Elsa Olivetti, Randolph Kirchain, Elisa Alonso, Gabrielle Gaustad

"The primary technological challenge to increased use of secondary raw materials is the presence of undesirable elemental species in scrap streams. Recent literature indicates that this may become exacerbated by accumulation of impurities over time. Devising strategies to mitigate this problem depends upon understanding the mechanisms of accumulation. This paper takes a first step at characterizing the extent of this issue by presenting a simple analytical model of recycling rate for materials experiencing exponential growth. Low potential recycling rates limit accumulation due to dilution. Empirical analysis of several major materials indicates that, even for current recovery rates, theoretical recycling rates can reach above 60%, making accumulation issues a possibility.IntroductionIt is well known that recycling of secondary materials can provide significant environmental and economic benefits. Energy savings, in particular, can be quite large when substituting secondary materials for primary. Nevertheless, over the past decade, the recycling rates within the U.S. of many materials appear to not be increasing as rapidly as one would predict or even at all (Figure 1). While many barriers exist to increasing materials recycling, one that is cited consistently by the literature and producers[1-3] is compositional limitations; that is the mismatch between the characteristics of secondary materials and those desired for the finished goods into which they would be transformed..One particular aspect of compositional limitations that is receiving increasing attention is the potential for progressive deterioration of the quality of secondary raw materials streams. For some materials, for example paper or polymers, this phenomenon is inherent and relatively rapid[4, 5]. As such, it is well documented and plays a significant role in recycling decision-making even for prompt or in-house material recycling. Conceptually, this issue can manifest in other secondary materials as well, albeit through a different mechanism.As materials are mixed, used, and reprocessed during recycling, they come into contact with and often pick up other elements. The presence of these, so-called, tramp elements alters the original known composition, possibly requiring additional measurement and processing and may even preclude economic, productive reuse; ultimately, this unintentional pick up is unwanted. A growing number of studies and literature would suggest that accumulation of unwanted elements is an emerging problem, in most recycled material streams. Table I provides a brief literature review of various recycled material streams and the accumulated elements noted as problematic by various authors"

Jan 1, 2008