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By M. J. Adam

As part of its research programs, the Bureau of Mines is investigating the partitioning of complex sulfide minerals to simpler sulfide phases by sulfidation reactions. Partitioning in this manner can afford opportunity to improve selective extraction of mineral constituents of value. This report describes research involving the sulfidation partitioning of the mineral pentlandite, which is an important source of Ni in primary production. For the laboratory studies, the pentlandite was synthesized in nominally equiatomic proportions of Ni and Fe. Elemental Ni, Fe, and S powders were blended, compacted, and sealed under reduced He pressure in vitreous silica tubes. The tubes were heated under controlled conditions at SOD? C for 24 h. The product was verified by X-ray diffraction and chemical analysis to consist essentially of (Ni,Fe)9S8. Small samples of the (Ni,Fe) S were encapsulated with sulfur in silica tubes at reduced He pressures and heated for 1 to 24 h at specific temperatures between 400? and 600? C, both below and above the boiling point of sulfur (_445° Cl. Reaction rate increased with temperature. Within this temperature range, partitioning to individual Ni and Fe disu1fides proceeded to essential completion according to the reaction

Jan 1, 1988

By M. S. Moats

The treatment of oxidized residues of zinc with high iron content continues to present a technical challenge in both the steel and zinc industries. Two main problems are commonly identified and include high treatment costs and environmental concerns about contaminated, iron-bearing residuals. A new approach to this problem is described in which selective separation of the iron and zinc into salable products may be potentially feasible. The waste material is first leached to give a solution having an approximate concentration of 110 g/l Zn, 15 g/1 Fe and 40 g/1 H2SO4 and other impurities such as Pb, Cd, Cu and Sb. A suitable organic, such as D2EHPA, is used to load the majority of the iron. The aqueous phase is then acceptable for zinc electrowinning after standard solution purification. The novel step in the flow sheet is the efficient recovery of the ferric iron from the organic solvent using a solid metal to reduce the iron to the ferrous state. The Fe+2 is easily stripped into an aqueous phase in a relatively pure form, suitable for use in water treatment. Process parameters and possible flow sheet designs are described and discussed.

Jan 1, 1995

By M. C. Ruiz

The conventional pyrometallurgical methods to treat copper sulfide concentrates include generally, one or more oxidizing steps where the formation of SO2 gas can not be prevented. From the economical point of view and the nature of some of the processes in which SO2 is produced, its complete capture is not feasible; therefore an important fraction is released to the atmosphere as fugitive emissions. In this research, the reduction of chalcocite was studied in the presence of lime as an alternative method, which overcomes the pollution problems related to SO2 emissions. The effect of temperature, time, concentration of carbon and CaO on the reduction rate were studied. Among these variables, temperature affects most the reduction rate. Conversions over 95 % can be obtained in less that 20 minutes at temperatures over 1000 ° C. The measured partial pressures of the gaseous components indicated that the chalcocite reduction proceeded through the gaseous intermediate species CO, C02, and the overall kinetics was controlled by the Boudouard reaction. The kinetic model In(1-X)= kt fits well the experimental data. Apparent activation energy of 3 14 kJ/mol was calculated for the temperature range of 900 0C-1050 °C.

Jan 1, 1999

By Robert M. Leary

The Kennecott Utah Copper smelter operates two Outokumpu flash furnaces: a smelting furnace for production of high-grade matte and a converting furnace for production of blister copper. Flash furnaces typically possess several characteristic features that must be considered in process control development such as long lag times associated with settler volume, non-linear input and output responses, large process gains, and unmeasured disturbances. Additionally, the Kennecott smelter possesses certain unique characteristics which must be considered such as single mine concentrate source, limited concentrate blending capacity, and feed preparation facilities that inevitably cause significant lags between furnace control parameters and manipulated set points. In order to improve furnace control and on-line time, a process control system was developed to address these issues. The feed forward control module provides predictive control and operates in response to furnace feed input changes. The feed back control module provides responsive control and is based on furnace output deviations. To provide regular feed back information to the control room supervisors, new sampling methods were developed which provide the operators with molten metal and bulk material samples at regular intervals to provide information for control. The control system was implemented on the Flash Converting Furnace in May 1999 and on the Flash Smelting Furnace in August 1999.

Jan 1, 2000

By S. Vukcocic

A long term research project is in progress to establish the parameters of an acid leach process to recover alumina 'froui' high-iron and/or low-iron white bauxites, kaolinite, coal. ash and copper mine tailing. In this paper the results of acid leaching of copper flotation tailing for the removal of alumina are presented. The tailing is very complex material which contains 25% Al203 in the -10 lim fraction. X-ray diffraction indicates presence of quartz, kaolinite and minor 'alunite. After classification and ,separation of the -10 lim fraction, the raw material is fired to 550GC and leached at 90GC. Filtration is applied for the separation of white silicate residue form leach liquid. After the purification step, aluminum salt is crystallized from the solution, and calcined to alumina. Kinetic correlation and regime, of the processes are defined and presented in the paper.

Jan 1, 1992

By Girley Ferreira Rodrigues, Crocce Denise Romano Espinosa, Victor Bridi Telles, Eduardo Junca, Jorge Alberto Soares Tenorio

"Steel sector is responsible for the generation of solid waste, liquid and gaseous effluents. The Solid waste are mainly composed of slag, dust, sludge and scrap. The industry generates approximately 650kg of solid waste per tonne of steel. Approximately 10% of this waste is in the form of dust and mud. The basic oxygen furnace dust is a waste generate by steel sector. Each tonne of produced steel generates 10 to 20 kg dust. Thus, the aim of this paper is study the reduction of pellets made with BOF dust using hydrogen and study kinetic during the reduction. The tests were performed in a netzsch thermobalance to obtain the data of lost mass. This loss mass is coming from iron oxides present in the BOF dust.IntroductionThe generation of solid waste is a problem for many companies in the steel sector. The main solid wastes generated are slag, dust, sludge and scrap [1]. Beyond solid waste liquid and gaseous effluents are also generated.The basic oxygen furnace is responsible for 60% of all steel produced. This sector is the second largest generator of solid waste from an integrated steel mill, contributing with 27% of solid waste generated in a plant ( 5-7 million tons of waste generated annually worldwide) [2,3,4]."

Jan 1, 2013

By David M. Beckwith

Increased globalization and outsource manufacturing complicate the procurement and enforcement of intellectual property rights on a worldwide basis. Recent legislative and case law developments in the United States highlight the importance of a multinational intellectual property strategy. IP lawyers David Beckwith and John Hankins will discuss planning and pitfalls in this rapidly changing trans-border environment. Topics to be discussed include harmonization with international patent laws, protecting your technology and market space with a comprehensive approach to IP, and patent enforcement issues relating to import/export of products and components in the United States.

Jan 1, 2006

By J. R. Addison

Commissioned in September 1987, the Phelps Dodge Morenci, Inc. (PDMI) Central Electrowinning (EW) Tankhouse bas undergone two major expansions in its eleven-year history. A third tankhouse renovation, which began in November 1998, entails complete conversion of the 548-cell facility from a copper starter sheet based operation to Mt. Isa Process stainless steel mother blank technology. This paper outlines the operating history of the Central EW Tankhouse and reviews the conversion process, the rationale that led PDMI to undertake this project, and describes various design optimizations which have been implemented during the conversion.

Jan 1, 1999

By J. M. Figueiredo, A. R. Silva, M. C. Coelho, R. M. Guedes

"With the continuous depletion of conventional sources of non ferrous metals, low grade complex sulphide deposits have been regarded as an alternative source of supply of zinc, copper, lead and also silver and gold. In spite of very important efforts in research in this domain it is still a long way to go in order to achieve reliable technological solutions both in ore dressing and metallurgical treatments which enable these complex materials to be regarded as commodities. The RLE process to treat bulk concentrates such as those obtained from portuguese ores, under development at LNETI and QUIMIGAL premises, combines experienced unit operations and innovative configurations and is an effective contribution for the future use of these materials. The results of three years of experimental work and main conclusions on the overall feasibility of the process are presented.IntroductionIn spite of the very well-known problems associated to the development of complex sulphide deposits, the economical importance of the enormous reserves of these materials, widespread all over the world, is so evident that its future use as source of supply of basic and precious metals and other minor elements is almost unavoidable.Critical steps in that direction are mainly concerned with favourable economical conditions and sound metallurgical practice for the treatment of nonferrous metals concentrates, which are nowadays still considered as non-conventional raw materials.Since Portugal is one of the countries where these orebodies occur more extensively, Portuguese authorities have dedicated since the beginning of the seventies, a big effort on finding economical and reliable processes for the recovery of copper, lead, zinc and also gold and silver, and for this purpose, several alternatives on ore dressing and metallurgical processing were studied, however without full sucess.Five years ago LNETI, a research laboratory, and QUIMIGAL, a chemical company, both state owned, decided to launch a research programme for the development of a metallurgical process for the treatment of NFM concentrates, which received financial support from NATO under its programme ""Science for Stability""."

Jan 1, 1988

By John J. Jonas, Sang-Hyun Cho, Ki-Bong Kang

"The recrystallization behavior of Nb micro alloyed steels containing Cr, Mo, Ni and Ti. was studied using hot torsion testing with the aim of modeling the recrystallization processes and the mean flow stress taking into account the microstructural behavior during hot rolling. The kinetics of static and metadynamic recrystallization were characterized and appropriate expressions were formulated for the recrystallization kinetics. These are shown that the recrystallization kinetics depend on steel composition and the processing conditions. The stress-strain curves were determined in order to derive new equations for the peak stress, peak strain, mean flow stress and softening kinetics. The peak strain is influenced by the presence of alloying elements; their addition, which has a solute drag effect, retards the rate of grain boundary motion, shifting the peak to the right. The addition of Nb to the steel results in a significant increment in the activation energy for hot deformation, and Mo has smaller effect than Nb, but Cr has the opposite effect. It was also found that the deformation activation energy in these steels was not altered by the addition of Ni. The rate of metadynamic recrystallization increases with strain rate and temperature and is observed to be independent of strain, in contrast to the observations for static recrystallization.The mean flow stress (MFS) calculations, based on the Sims analysis, are then compared with the predictions of a model based on an improved Misaka mean flow stress equation in which solute effects, strain accumulation, as well as the kinetics of static and metadynamic recrystallization are accounted for. Good agreement between the measured mean flow stresses, which is obtained from the mill logs of POSCO Kwangyang #3 HSM (hot strip mill), and 'predicted ones is obtained over the whole range of rolling temperatures. The results demonstrate that dynamic recrystallization followed by metadynamic recrystallization, supported by the unexpected load drops, sometimes occurs for the rolling schedules studied in the present analysis."

Jan 1, 2001

By Edward P. Hagarty

The Hazardous and Solid Waste Amendments (HSWA) of 1984 added Subtitle I to the Resource Conservation and Recovery Act (RCRA), authorizing the Environmental Protection Agency (EPA) to develop and implement a new regulatory program for Underground Storage Tanks (USTs) containing petroleum and other regulated substances. Technical standards required for release detection, prevention, and correction as necessary to protect human health and the environment were promulgated as described in 53 Federal Register 37082 (September 23, 1988). Virginia State Regulations (VR 680- 13-02) and U.S. Army Regulations require that a Corrective Action Plan and a Site Clearance Report be prepared to explain the details of remediation of any contaminated media. Construction of new buildings is proposed in two different areas at Fort Myer in Arlington, Virginia, where USTs containing gasoline, diesel and heating oil were located. Tightness testing performed on these USTs in September 1991 indicated that some of the tanks were leaking. Many of the tanks were removed for permanent closure. Initial Abatement (excavation of contaminated soil) was &ed out immediately. A detailed Site Characterization Study which included Hydropunch", field screening using immunoassay, and pilot test - dual phase (water and soil gas) extraction was conducted. Environmental media were analyzed for volatiles, semi-volatiles and metals. A detailed risk analysis (RA) was performed to determine risk-based clean up levels for benzene, toluene, ethylbenzene, xylenes (BTEX); polycyclic aromatic hydrocarbons (PAHs); and methyl-tertiary butyl ether (MTBE). The RA also discussed the presence of lead in the soil. Before constructing any buildings in these contaminated areas, remediation must be conducted in accordance with the State, Federal and other applicable regulations. The remedial alternatives evaluated included Vapor Enhanced Groundwater Extraction, Soil Vacuum Extraction, Soil Washing, Soil Steaming, Active and Passive Ventilation SolidificationlStabilization, Vapor Barrier Construction, and Excavation with Off-site Disposal. This paper discusses: (a) delineation of soil contamination @) risk analysis (c) evaluation of remedial alternatives and selection of the most appropriate technology and (d) consideration of various regulatory issues.

Jan 1, 1994

Many studies have been conducted over the past 3 decades on the leaching of gold in solutions containing thiosulfate, ammonia and copper. However, most of these studies have been carried out using ore samples, with very few fundamental studies of this system being attempted. The majority of the published studies have failed to acknowledge the undesirable side reaction between copper(H) and thiosulfate, let alone account for its effect. The fact that the solution chemistry is constantly changing makes it very difficult to perform a fundamental study of gold leaching. With the advent of the rotating electrochemical quartz crystal microbalance (REQCM), such fundamental studies are possible as this instrument measures mass in real time. This has allowed leach kinetics to be measured in a matter of minutes and hence at essentially constant solution conditions; The present paper highlights that a sufficient concentration of copper(II) and ammonia are required in order to achieve appreciable gold leach rates. However, the use of air (oxygen) to maintain the copper(Il) concentration catalyses the undesirable copper(II) reaction with thiosulfate. The presence of ammonium ions is shown to have an effect on this undesirable reaction as well as on the gold leaching ?reaction. Preliminary electrochemical studies into .gold electrowinning using the REQCM show that gold(I) thiosulfate cannot be readily reduced to metallic gold in the potential region at which cementation usually occurs. However, it is well known that gold cementation onto copper occurs rapidly. The current study addresses this discrepancy by studying the effect that copper and silver have on the reduction of gold thiosulfate. It has been found that the presence of both silver and copper enhance gold deposition, particularly at low over potentials. While this is beneficial in cementation, the presence of copper and silver in solution has been found to cause passivation of the cathode surface during electrowinning at 'higher overpotentials.

Jan 1, 1998

By Batric Pesic

A hydrometallurgical process for recovery of Zn and Mn from Bunker Hill Water Treatment Plant sludge was developed. The process is unique because it treats an unusual combination of metals, Zn and Mn. Another non-standard feature of the process is that leaching takes place with ~S04 in the presence of a reductant (SO2). Zn and Mn are recovered simultaneously by electrowinning, Zn on a cathode and Mn on an anode, as MnO2 The major purpose of the process is to detoxify the sludge by removing toxic heavy metals. The recovered metal values could be marketed to offset the overall costs of water and sludge processing. This work is presented in two separate parts, 1. Leaching and Solution Purification, and II. Electrowinning. This paper covers only the first part of the hydrometallurgical process: Leaching and Solution Purification. Initially, the paper briefly discusses the history of the pollution problem at the Bunker Hill Superfund Site, the origin of heavy metals in the mine waters, and the development and use of the water treatment plant. The leaching of sludge was examined as a function of the following parameters: constant vs. initial pH, initial vs. delayed addition of SO2, temperature, and pulp density. It was found that leaching with H2SO4 at pH 2.0 for 15 minutes (at 60°C), followed by S02 addition for another 15 minutes, could completely dissolve Zn and Mn. Solution purifIcation was done in three stages. In the first stage iron was removed by adjustment of pH (to pH 5.0) and oxidation offerrous to ferric iron (with H2O2). In the second stage, Cu and Cd were removed by Zn dust cementation. Finally, Co and Ni were precipitated with the organic reagents 1-2 nitroso-naphthol and nitroso, respectively. Electrowinning of Zn and Mn is discussed separately in Part II of this paper.

Jan 1, 1996

By S. S. Ryu, J. C. Kim, H. Lee, Y. D. Kim, I. H. Moon

"Recently, W-Cu alloy becomes one of the very important candidate materials for heat sink and packaging in the field of microelectronics due to its good thermal properties. The metal injection molding of W-Cu powder can satisfy the requirement for mass production of complex shaped parts in microelectronic devices. In the present study, the application of MIM process to the nanostructured W-Cu powder prepared by mechanical alloying was investigated. The multi-component binder system of 45PW+ l 5BW+ 30PE+ I OSA was proven to be suitable one for the MIM of the W-Cu composite powders by adopting the debinding cycles of multi-stage in N2 and H2 atmospheres. Other process conditions for the MIM of the nanostructured W-Cu composite powder were also studied. The MIM debinding part of W-30wt.%Cu was sintered to the relative density of more than 96% by sintering at 1200 °C for !hour in H2 atmosphere. Such an improvement of sinterability was attributed to the intrinsic homogenous and fine mixing state of W-Cu phases in nanostructured W-Cu composite powders, and also partly to the effect of the activated sintering by the presence of impurity introduced during the extensive milling.IntroductionW-Cu alloys have been widely used for heavy duty electrical contacts and arcing resistance electrode(1-2). Recently there has been a growing interest in this W-Cu alloy because of its superior thermal managing properties and its high micro wave absorption capacity(3). Such W-Cu alloy parts are conventionally fabricated either by the Cu infiltration sintering technique or by hot pressing of W-Cu powder mixtures. However, these conventional PM techniques are hardly applicable for mass production of small size parts with a complicated shape such as the parts required for microelectronic devices. The metal injection molding(MIM) technique is potentially applicable for the mass production of small and complicatedly shaped parts compared with other PIM forming techniques."

Jan 1, 1998

By Yan Beygelzimer, Alexander Spuskanyuk, Victor Varyukhin

"The main idea of the report is that the yield surface can be presented as thick, ""foamed surface"" with dimensionality exceeding two. By other words, perhaps, the yield surface is fractal, i.e. it belongs to the class of geometric objects with fractional dimensionality. Apparently, fractal structure of the yield surface is determined by the fractal structure of natural materials. ""Cloud of internal stresses"" term is introduced to describe the stress distribution in representative volume element. Its plastic flow is determined by the interaction of this cloud with the thick yield surface. Thick yield surface and internal stress cloud concepts allow to determine an additional correlation between micro mechanical models of polycrystals and phenomenological theory of plasticity.1. IntroductionClassical plastic flow models are not satisfying the modem requirements. There are two main directions in their development. The first, mathematical, is connected with the development of the general theory of rheological relationships; the second, physical, is connected with the development of the representative volume element (RVE) models which are based on specific ideas about deformation mechanisms. Within the framework of the first direction, the macroscopic experimental data is formalized; the second approach deals with the generalization of physical research results for the different scale levels that are involved in plastic deformation.These approaches have advantages and disadvantages. In phenomenological theories, the advantages are the mathematical simplicity and laconic formulation of constitutive relations, which allows using them in practical calculations. However, the mathematical models of this class can not be considered as general, they are useful only for the description of limited range of deforming processes. On the other hand, physical theories that are based on the description of real plastic deformation mechanisms are very explanatory and predictive, but they lack mathematical simplicity. The above circumstances lead us to the necessity of compromise that can be found in determining the constitutive relations for RVE, which structure and parameters would bear the information about rnicrolevel and mesolevel phenomena. In this synthesis direction, the fundamental role belongs to [1,2], etc."

Jan 1, 2001

By Kyle S. Brinkman, Kenneth L. Reifsnider, Fazle Rabbi

"Mixed ionic and electronic conducting (MIEC) ceramic membranes are HeteroFoaM's which play an essential role in a number of energy conversion related systems including the solid oxide fuel cell (SOFC), oxygen separation and permeation membranes, partial oxidization membrane reactors for natural gas processing, and high temperature electrolysis cells. Dual phase oxygen membranes consisting of an ionic conducting phase Ceo.sGdo.z02 (CGO) and an electronic conductive phase C0Fe204 (CFO) were fabricated and characterized by structural (XRD), microstructural (SEM-EDS) and broadband dielectric measurement techniques. In-situ measurements of the dielectric properties of working oxygen separation membranes are presented which indicate that the material's dielectric behavior can be an indicator for MIECperformance.IntroductionCeramic membranes which transport oxygen ions play an essential role in a number of energy conversion related systems including the solid oxide fuel cell (SOFC) [l ], oxygen separation and permeation membranes in the commercial and nuclear arena [2, 3], partial oxidization membrane reactors for natural gas processing [4], and high temperature electrolysis cells [5]. For the electrolyte functions, the membranes must transport oxygen ions only. On the other hand, permeation membranes, typically used in combustion devices to support oxy-fuel combustion or for partial oxidation reactions involving the production of synthesis gases, require mixed oxygen ion and electronic conduction (MIEC). Traditionally the tailoring of the ratio of ionic conductivity to the materials electronic conductivity, measured as the transference number, has been accomplished by the introduction of aliovalent doping elements creating point defects in the material facilitating the diffusion of charged species. However, several decades of research have not yet produced single phase materials which possess the concomitant ionic and electronic conductivity required for use in membrane separation applications. It is clear that novel ""dual phase"" heterogeneous materials will be required and that the surface reactions of these materials will be of particular importance as the industry moves toward thin films membranes [6]."

Jan 1, 2013

By Sang-Joon Kim, Hae-Geon Lee, Hyun-Jin Cho

"Decarburization phenomena on the surface of liquid iron have been simulated by numerical method and the results were compared to the experimental data. During the DeC process in a converter, a large amount of splashed droplets are generated from the top surface of the bath and consequently the reaction surface area is increasing tremendously. Since the decarburization mainly occurs at the interface, it is important to understand the reactions on the liquid iron droplets. The flow and species concentration fields around liquid droplets taking into account the reaction of carbon with oxygen at the interface were calculated by a commercial CFD code FLUENT which solving multiphase Navier-Stokes equation with Volume Of Fluid method, species transport equations and energy transport equation. The initial carbon concentration was fixed to 4 wt% and the concentrations of oxygen in the atmosphere were varied from 5 to 50 wt%. As comparing the numerical calculation with experimental data written in the reference, the results have a good agreement for decarburization rate.IntroductionIn a primary steelmaking process, one of the main functions is to decarburize from hot metal and the 4% of carbon is decreased to about 0.5% of carbon. Even though there are some possible reactions leading to the removal of carbon from hot metal, the main reaction occurs on the free surface by direct oxidation of carbon at the gas-liquid interface with producing the carbon monoxide gas. In many metallurgical processes involving a jet impinging onto a steel bath surface, especially in a Basic Oxygen Furnace (BOF) converter, it is important to understand the behavior of molten iron droplets splashing out of the steel. The iron droplets are generated by an oxygen or air jet blowing and it increases the total surface area of liquid iron tremendously. Since the decarburization reaction is mainly affected by the surface area, it is necessary to verify the decarburization phenomena around the splashed droplets from liquid iron in order to allow an analysis ofBOF process possible."

Jan 1, 2011

By K. E. Gonsalves, G. M. Chow

"Nanostructured powders (particle diameter of 1 - 100 nm) have uses in electronic, magnetic, structural, thermal applications as well as advanced processing of materials. Among many methods of making nanostructured powders, chemical routes offer many attractive features such as feasibility of cost-effective bulk quantity production, design of chemistry at the molecular scale, and chemical homogeneity of the powders. In this talk, two systems of chemically synthesized nanocomposite powders are presented, namely, granular magnetic materials of Fe-Cu and Co-Cu, and thermal-structural materials of AIN-BN. Synthesis and processing, characterization and properties of these materials are discussed.IntroductionNanostructured powders (particle diameter of 1 - 100 nm) are attractive materials because of many useful properties (e.g. catalytic, optical, magnetic etc.) and processing advantages (e.g. lower sintering temperature) [1]. There are many methods of making nanostructured powders, for example, physical and chemical vapor deposition, mechanical attrition, and solution chemistry [1, 2]. A common method of making composite powders involves the grinding, mixing and blending of constituents powders, but it has the limitation of inhomogeneous mixing. Chemical routes have many useful features. Using solution chemistry, precursors can be molecularly tailored and homogeneously mixed at the molecular level. The chemical approach may result in better properties of the final product. Compared to vapor-phase fabrication techniques, chemical routes are more cost-effective in producing large quantity of material. In addition, control of particle size, size distribution and stabilization of the nanoscale particles against agglomeration can be more effectively manipulated via solution chemistry.In this paper, we present an overview of some of our work in nanocomposite powders prepared by solution chemistry. Metallic systems of FeCu and Co-Cu, and ceramic system of AIN-BN are discussed. The powders were characterized using x-ray diffraction (XRD) , scanning electron microscopy (SEM), conventional and high resolution transmission electron microscopy (TEM, HRTEM), vibrating sample magnetometry (VSM), inductively coupled plasmaatomic emission spectroscopy (ICP-AES)."

Jan 1, 1994

By Melvin H. Miles

"Considerable research has been conducted on the anodic oxidation of methanol in fuel cells. The electrochemical reduction of carbon dioxide in aqueous solutions to form methanol is the same reaction in reverse, i.e. CO2 + 6 H+ + 6 e- ? CH3OH + H2O. The same catalysts and conditions may operate for both reaction directions. This carbon dioxide reduction reaction, however, must be able to compete with the electrochemical reduction of water to form hydrogen gas. Thermodynamically, the reduction of CO2 to form CH3OH is slightly more favorable than the reduction of water. The use of nearly neutral electrolytes rather than acidic electrolytes makes the reduction of CO2 kinetically more favorable. The thermodynamics of various reaction steps are presented. Similarities exist with the electrochemical reduction of CO2 and the green-plant photosynthesis process that converts CO2 to carbohydrates.IntroductionVirtually all of the oxygen in the earth’s atmosphere is of biological origin having been generated by green-plant photosynthesis from water and carbon dioxide [1]. The net reaction can be represented byCO2 + H2O ? O2 + [CH2O] (carbohydrates, etc.) (1)Chlorophyll and enzymes promote this reaction, and the energy required comes from sunlight. The actual photosynthesis process is a complex multistage reaction and requires 469 kJ mol-1 of energy supplied by the sun. Isotope tracer experiments using 18O have shown that both the oxygen atoms in the O2 molecule originate from H2O, whereas oxygen atoms in the carbohydrates come from CO2 [1]. The total amount of water on the earth is split by photosynthesis and reconstituted by respiration and combustion once every 2 million years or so. The photosynthetically generated oxygen gas temporarily enters the atmosphere and is recycled about once every 2000 years [1]. The carbon dioxide is partly recycled in the atmosphere and oceans after an average residence time of 300 years and is partly fixed by precipitation of CaCO3 and other carbonate minerals [1]."

Jan 1, 2008

By Hao Deng, Hongmin Zhu, Jichao Li, Kai Huang

"Silicon and silicon carbide mixing micropowders obtained from the saw cutting industry of polycrystalline silicon ingot is separated by a simple sequential sedimentation. The Zeta potentials of the powders in the aqueous suspension are adjusted by varying the pHs with dilute acid or alkaline reagents. The dispersion and aggregation content of the microparticles is significantly influenced by pHs, and so their settlement velocity in the same hydraulic conditions are quite different, and silicon powders tend to suspend in the upper section of the suspension for its finer size and smaller density under the stronger Zeta potential repulsion force. The original content of the cutting powders with 30%wt silicon are separated into the Si-rich and SiC-rich powder respectively, and 62%wt Si-rich powder can be obtained after 4 times of sedimentation under pH = 8.0, showing the great potential for Si and SiC powder separation and recovery in a cost-effective way.IntroductionWith the fast development of photovoltaic (PV) technology these years, the market demand for the solar-grade high pure silicon material significantly increased, making the silicon recycling and recovery from the wire sawing slurry profitable and attractive[1]. Waste silicon slurry was produced in the multi-wire sawing process of a silicon ingot by using an ethylene glycol-based solution and silicon carbide abrasives as the slicing system. During this slicing process, about 30% of the silicon ingot will become the waste as the fine particles suspended in the slurry, which mainly consists of silicon kerf-loss particles, SiC fragmental particles, tiny iron fragments from the worn sawing wire and ethylene glycol-based solution [2]. The separation of above individual component is usually easy except for Si and SiC fine particles for their quite similar properties. So the biggest challenge for the effective recovery and recycling of silicon particles from the wire sawing slurry actually lies in the mutual separation of silicon and silicon carbide particles."

Jan 1, 2012