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By K. S. Raja, M. Misra, S. K. Mohapatra

"Ordered arrays of TiO2 nanotubular photocatalysts were prepared by a simple anodization process. Band gap states of the TiO2 were altered by controlling the anodization electrolyte composition and thermal annealing conditions that resulted in enhanced photo activity. These nanotubes were used for reducing CO2 to methanol either by photochemical or photo electrochemical routes. Pd nano-particle loaded TiO2 nanotubes were employed for photochemical reduction of CO2 to methanol that showed a conversion rate of 12 x 10-3 mol m- 2h-1. Carbon modified TiO2-xCx type nanotubes were used as photo anode and Ti as cathode for photo electrochemical reduction of CO2. The potential of Ti cathode was maintained at -0.5 V SCE. The formation rate of methanol was determined as 13 x 10-3 mol.m-2h-1.1. IntroductionGlobal warming due to emission of carbon dioxide is a serious environmental concern. The atmospheric concentration of CO2 is about 384 ppm by volume and about 3 x 1012 tonnes by weight. Burning of fossil fuels and deforestation are the leading causes for increase in the anthropogenic CO2. More than 32 x 109 tonnes of CO2 are released per year (based on 2006 data) worldwide from the fossil fuel. Pumping CO2 from the fossil fuel power plants into deep ocean basin is one of the most discussed disposal options. The other potential option is converting this green house gas into valuable fuels.Carbon dioxide feed stock can be converted into fuels of solid, liquid or gas phase by chemical, electrolytic, photocatalytic and photo-electrocatalytic methods. Reduction of CO2 to fuel form of any phase requires energy. The reduction process should be energy efficient so that we do not spend more energy and emit more (indirect) CO2 in the process of converting CO2. From this point of view, conversion processes occurring at room temperature look attractive.Electrolytic conversion of CO2 into various forms such as methane1, ethane2, ethylene3, methanol4,5, ethanol6, n-propanol, formic acid7, and formaldehyde has been widely reported. The standard equilibrium potential (at pH: 0) for reduction of CO2 to methanol is 0.14 VSHE and to methane is 0.2 VSHE which is thermodynamically more favorable than hydrogen reduction. However, the gas phase reduction is kinetically complex requiring effective electrocatalyst. The major issues with electrolytic conversion of CO2 to useful products are:"

Jan 1, 2010

By J. Ipinza

The slime formation with several metallic impurities from acidic electrolytes of copper has been studied. On fresh Pb-Ca-Sn anode surface firstly the formation of PbSO4 takes place, then, it is transformed in the conducting PbO2, which covers the anode surface. It has been experimentally established the formation of a manganese dioxide double layer at the anode; this double layer was always composed of a thick external layer of non-adhering and easily removable scales, and of a thin internal layer, which adheres relatively well to the surface of the electrode. It was found that manganese dioxides present in the slime were of different nature: a non-adhering layer produced by electrolysis (-MnO2) on the PbO2 surface and a pure chemical precipitation in the solution (-MnO2). When iron is present in the electrolyte on this last layer of manganese, lead sulfate was found. In the case of arsenic and antimony in the electrolyte the slime generated was found to be lead sulfate and amorphous compounds of those ions. The lower slime generation in Chilean EW plants could be due to the lower contents of iron and manganese in the electrolytes. It was found that this slime formation rate not only is due to the electrolyte composition but also to the poor control of operational parameters at EW plants.

Jan 1, 2003

By Wang Shuchan, Zhang Zimu, Zhang Dianhua, Liu Yan, Zhang Ting-an, Zhao Qiuyue, Lv Chao

Rare earth extraction tank has many adverse effects like big floor space and high production accumulation during industrial production. Current researches usually focus on changing the device structure without making a breakthrough towards gravity clarification. This paper attempts to achieve this goal by using both the action of clarification by gravity and clarification by stirring. Because many physical parameters affect the clarification and separation rates, the density, viscosity and surface tension of the two phases were determined at different temperatures and different concentration of aqueous solution. The innovation of this research involves adopting the Karl-Fischer method to investigate water content in oil phase during the stirred separation process. In this paper, the separation effect of different physical parameters was studied and the dimensional equation between water content and the physical parameters was established by combining with the experimental data.

Jan 1, 2014

By Varadajan Seshadri

Kambara Reactor (KR) consists of a ladle where pig iron is stirred by an impeller during addition of a flux powder. The objective is to improve agitation leading to dispersion, of the flux powder, in the molten pig iron in order to improve desulfurization of the liquid melt by improving solid liquid interaction. The life of the impeller is limited as it is subjected to abrasion at high temperatures. The shape and design of the impeller also has an effect on the performance of this reactor. A 1:7 scale cold model of a KR unit of the Companhia Siderurgica de Tuberao ,one of the integrated steel plants in Brazil was constructed in order to evaluate the mixing and mass transfer conditions. Mixing efficiency was investigated by tracer additions and subsequent measurement of conductivity. Mass transfer in the reactor was assessed through iodine transfer between water and kerosene and employing a macroscopic model. Mixing depends on impeller shape and depth of immersion The role of dispersion is highlighted by faster kinetics when impeller velocity is increased. The results enable assessment of design aspects of the impeller on the process.

Jan 1, 2006

By I. U. Onyenanu, C. E. Ilochonwu, E. I. Nwonye, C. O. Nwajagu

This work shows how pure silica was derived directly from rice husks ash (RHA) in different temperatures for reduction to Silicon (Si). The processes to form Si materials are usually complex, costly and energy-intensive. The silica in the ash undergoes structural transformations depending on the conditions of combustion. A high purity silica was produced at 650oC after burning the rice husk (RH) for up to 7 hours. The purity of the silica was determined by dissolving the RHA with alkali solution to form sodium silicate solution of pH 11.0. This was added to hydrochloric acid of pH 1.5 which lowered the pH of the solution to 4.0 to form silica gels. The silica gels produced were washed and dried to powder and then characterized using XRD and EDX techniques. This study was done to reduce energy waste and environmental pollution in Nigeria as silica is used to develop many materials.

Jan 1, 2015

By Wantae Kim

In order to establish the optimized recovery process for heavy minerals from Korean beach sand, we investigated the several physical separation methods such as gravity and magnetic separation followed by mineralogical characterization. There was clear relationship between the particle size and heavy mineral content that heavy minerals were mostly concentrated in the particles below 100mesh. Gravity separation using the spiral and shaking table separators made it possible to concentrate heavy minerals by rejecting the light and coarse particles consist mainly of quartz and other non-valuable minerals. The high-intensity magnetic roll separator and subsequent induced magnetic separator were applied to fractionate magnetic particles according to their magnetic susceptibility. The content of TiO2 of high susceptible ilmenite-rich fraction was 43.98wt.% while those of ZrO2 of non-magnetic and magnetic residue were 6.78wt.% and 3.11wt.%, respectively.

Jan 1, 2006

By Cameron Hams

Noranda's Process Reactor and Codelco's Teniente Converter are physically similar vessels, which leads to the commonly held misconception that the two processes are the .same. However, notable differences in chemistry, operating philosophy, and construction make them quite dissimilar. This paper compares and contrasts the Noranda Reactor and the Teniente Converter, and attempts to explain some of the apparent differences in behaviour and performance. The results of a worldwide survey of most operating Noranda Reactors and Teniente Converters, along with those processes that have ceased operation or are planning to be started-up in the future, are presented.

Jan 1, 1999

By P. R. Khangaonkar

The variety of intermediates, middlings, complex materials and wastes produced in the conventional processing of tin ores as experienced in the tin industry in South East Asia is reviewed. The problems associated with the treatment of these materials so as to produce useful products by hydrometallurgical or pyro-cum-bydrometallurgical approaches are discussed. Results of treatment of amang middlings consisting of cassiterite, struverite, ilmenite, zircon, monazite etc by chlorination with carbon tetra chloride are presented. The efforts to leach tin without letting iron coming in, by alkali leaching of certain wastes of tin processing are also briefly indicated. It is felt that pyro-cum-hydrometallurgical approach can help a viable treatment of these materials so as to obtain usable or value added products.

Jan 1, 1994

By Deventer Johanna van

Ore bodies around the world are declining in grade, whilst increasing in complexity. The level of impurities relative to the valuable metal is steadily increasing, posing new challenges to existing operations. Ion exchange is widely used in the hydrometallurgical industry for both primary recovery of metals and the removal of impurities. The superior selectivity of ion exchange resins makes them exceptionally suitable for the removal of target impurities to very low levels, thereby saving operating costs, increasing the value of the final product and significantly improving revenue. The ion exchange process in these applications is very simple, using standard ion exchange equipment and acid regeneration. The process can be fully automated, requiring minimal operator interference and supervision Examples of impurities that are successfully removed via ion exchange include iron, antimony and bismuth from copper electrolyte. In the copper electrolysis process, antimony, bismuth and arsenic tend to form slimes which are dispersed in the electrolyte. These slimes contaminate the cathode and/or decrease the quality of the copper deposition. A special chelating resin was developed to remove antimony and bismuth, while at the same time ensuring minimal chloride leakage to the sulphate matrix. The work is described in more detail in this paper. Ion exchange is also used to remove copper, zinc and nickel from cobalt electrolyte. This paper addresses a few of these examples in more detail.

By Kejun Liu

Platinum and palladium are usually dissolved together and followed by separation. In this study, the selective leaching of platinum and palladium from a secondary resource, such as dental waste, by using chloride solution (hypochlorite and chlorate) has been developed. Results indicate that about 100% of palladium could be initially extracted by the combination of 0.3 mol/L sodium hypochlorite (NaClO) and 0.068 mol/L sodium chloride (NaCl) at pH 1.2 and 298K in 1.5 hours, or the combination of 0.005 mol/L sodium chlorate (NaClO3) and 6 mol/L hydrochloric acid (HCl) at 298K in 0.5 hour. About 100% of platinum could be extracted from the residue by the combination of 0.47 mol/L sodium chlorate (NaClO3) and 12 mol/L hydrochloric acid (HCl) at 298K in 2 hours.

Jan 1, 2003

By J. Alexandre

The use of bricks of soil-cement is proving to be an important constructive methodology due to low environmental impact in the production process of these blocks comparing with conventional bricks are burnt, besides being easy to produce. However during the process of production of bricks, which are compressed, knowledge of the properties of the soil used is critical to the quality and durability of the blocks. The objective of this work is to evaluate the feasibility of using soil from the municipality of Goytacazes for the production of soil-cement bricks. Assays were performed the compaction, liquid limit, plastic limit, particle size analysis, EDX and X-Ray diffraction for later pressed blocks and analyze their compressive strength and water absorption.

Jan 1, 2015

By Dinesh Agrawal

Microwave energy has been in use for variety of applications for over 50 years. These applications include communication, food processing, wood drying, rubber vulcanization, medical therapy, polymers, etc. In the last two decades microwave heating has been also applied very effectively and efficiently to heat and sinter ceramic materials. Microwave heating is recognized for its various advantages, such as: time and energy saving, very rapid heating rates, considerably reduced processing cycle time and temperature, fine microstructures and improved mechanical properties, better product performance, etc. The most recent application of microwaves has been in the field of metallic materials for sintering, brazing/joining and melting. Several common steel compositions, pure metals and refractory metals have been sintered in microwaves to nearly full density with improved mechanical properties. Many commercial powder-metal components of various alloy compositions including iron and steel, copper, aluminum, nickel, Mo, Co, Ti, W, Sn, etc., and their alloys have also been sintered in microwaves producing better properties than their conventional counterparts by using a 2.45 GHz multimode microwave system. This work has been further extended to join and braze bulk metal pieces, especially super alloy based turbine blades. Further, in a specially designed microwave cavity, even the bulk metals can be made to couple with the microwave field and melted. The implications of these findings are obvious in the field of powder metal technology.

Jan 1, 2006

By R. G. Haire

Studies of the f-elements under pressure provide important insights into their solid state chemistry and physics. From such studies, of the elements and their alloys, it has been established that the normally localized f- electrons of several of these elements can become, involved in bonding under pressure. The electronic behavior of f-element compounds under pressure tend to be more difficult to interpret, due to the variety and the nature of electronic orbitals that are present. The 4f-elements and some 60% of the 5f-elements have been studied under The systematic comparisons that have been established for these materials are discussed.

Jan 1, 1992

By R. J. Dippenaar, W. H. Van Niekerk

"An injectable lime-based desulphurization reagent for the treatment of liquid iron was developed. Firstly, selected lime based slags containing small quantities of CaF2 to increase fluidity, and Na20 to increase the basicity, have been evaluated on laboratory scale from a thermodynamic point of view. Subsequently, pilot plant and full scale industrial injection trials were conducted. It was found that lime-based slags, containing Na20 and CaF2, are able to desulphurize liquid iron efficiently. By the injection of a lime based reagent consisting of 60% lime, 25% soda ash and 15% fluorspar at a rate of 7 kg reagent/ton hot metal, the sulphur level in the metal (115kg) was reduced from 0,07% to 0,01 % within 5 minutes. The lime-based reagent developed in this study was successfully injected, both from a metallurgical and from a pneumatic point of view, on an industrial scale. The mathematical model utilised in this study, can be used successfully to predict the course and extent of desulphurization by lime-based slags. IntroductionMainly due to environmental difficulties encountered with pure soda ash, dry slag formation with CaC2 and high cost when Mg are used as desulphurizers, much incentive exists for the development of an inexpensive, environmentally friendlier desulphurization reagent. As a first step in the development of such a reagent, selected lime based slags containing small quantities of CaF2 to increase fluidity, and Na2O to increase the basicity, have been evaluated on laboratory scale from a thermodynamic point of view. This was followed by pilot plant injection experiments in which the kinetics of the relevant desulphurization reactions were evaluated. Finally, full scale industrial trials were conducted. All three phases of the investigation will be discussed with the major emphasis being placed on the kinetic study."

Jan 1, 1996

By Wenbo Luo, Jilai Xue, Tiepeng Li, Jun Zhu

Sodium silicate solutions for producing silica have been ultrasound treated to enhance the precipitation process in laboratory scale. Higher precipitation rate was found with ultrasound treated solutions than those without ultrasound. The obtained SiO2 powder products were characterized using XRD, SEM, BET and laser particle size analyzer. The particle size distribution and the specific surface area of the powder products varied with the power input level and the processing time of the ultrasonic treatment. The results indicate that the efficiency of the precipitation process can be improved optimally when the ultrasound is conducted into the solutions before the nucleation stage.

Jan 1, 2015

By J. P. Downey, T. Salisbury, M. Berlin, E. Rosenberg, G. Pinson, R. Christianson, K. Gleason, W. Gleason, S. Davis

"Direct digital manufacturing offers promise as a technique for fabricating complex hydrogen purification membrane support structures. Free form fabrication methods can produce parts with complex structures, and sintering parameters can be controlled to adjust the density, pore structure, pore pathways and strength in catalytic substrate constructs. Efforts are underway to define the influence of selected process variables on the chemical and mechanical properties.IntroductionThe Center for Advanced Mineral and Metallurgical Processes (CAMP), in collaboration with the Metallurgical and Materials Engineering Department at Montana Tech and the Chemistry Department at the University of Montana, is engaged in the development of new methods and materials for hydrogen purification membrane production. Because hydrogen readily passes through palladium, a structurally sound palladium-based membrane is capable of separating relatively pure hydrogen from other gases. In order for this technology to succeed, a suitable substrate material must be identified.High purity hydrogen is produced by various means. A common method involves a two-stage process for separating hydrogen from a hydrocarbon gas stream: 1) hydrogen-rich syngas is produced by the catalytic reaction of natural gas or another light hydrocarbon gas with steam, and 2) hydrogen is separated from the other syngas components by pressure swing adsorption (PSA) (US. Energy Information Agency, 2011). In PSA, gases enter a column that is packed with a material that absorbs gases as the chamber is filled and pressurized. As the pressure is slowly relieved, the absorbent material releases hydrogen at a higher pressure than the impurity gases. PSA processes produce 99.99% pure hydrogen at a high recovery rate. These systems typically demand a high capital investment due to the high pressure and multiple stages (columns) needed to attain high hydrogen production rates.Research geared toward reducing hydrogen production cost is focused on the development of improved catalysts and adsorbent materials as well as more effective single-stage separation processes. An interesting method combines hydrogen reduction catalysis and filtration. Nascent hydrogen is separated from other gases as it selectively permeates the filter. Catalyst filters may be made of gold, silver, platinum, palladium or precious metal alloys (Davis, 2009)."

Jan 1, 2012

By Emil H. Geus

A process has been developed to recover aluminum from dross which does not require the use of salt flux as commonly employed, This results in a salt-free residue which has potential industrial uses or alternatively can be safely land-filled. The dross is first heated by an air-fuel or oxy-fuel burner in a sealable rotary furnace. At a suitable temperature the burner is turned off and the temperature of the dross thereafter controlled by means of an atmosphere of oxidative and inert gases. When the free metal has agglomerated it is first discharged from the furnace, followed by the residues.

Jan 1, 1995

By Bingyi Bai, Wangjun Peng, Yanling Guo, Jieyu Zhang, Guoding Gao

The phase transformation of bayan obo ore with high concentration of iron and calcium was reduced at temperatures no more than 1000℃ were investigated in this study. The samples with insufficient carbon were treated at the temperature using a vertical furnace with a thermogravimetry (TG). The mineral phases and content were examined using Xray diffraction (XRD) and X-ray fluorescence spectroscopy (XRF) respectively. The complex phases of bayan obo ore transformed to some simple phases after treated with different content of carbon at the same temperature for 10 hours. The result of XRD、 XRF and TG showed that the reduction degree of Fe3O4 phase formation varied with the temperature and the carbon content of bayan obo ore.

Jan 1, 2015

By G. A. Brooks, R. W. Matusewicz, Nazmul Huda

"A computational fluid dynamic (CFD) model of a conventional tuyere blown slag fuming furnace has been developed in Eulerian multiphase flow approach. The model was developed by coupling CFD with kinetics equations developed by Richards et al. for zinc fuming furnaces. The model integrates submerged coal combustion and chemical reactions with the heat, mass and momentum interfacial interaction between the phases in the system. The model predicts the velocity, temperature field of the molten slag bath, generated turbulence, vortex and coal utilization behavior from the slag bath. The highest coal penetration distance was found to be at l/L = 0.2, where / is the distance from the tuyere tip and L is the total length (2.44m) of the modeled furnace. The model also predicts that 10% of the injected coal bypasses the tuyere gas stream un-combusted and carried to the free surface, which contributes to ZnO reduction near the free surface.IntroductionSignificant metal values are often discarded with slag in the form of metal oxide produced by the smelting industries. These metal values can be recovered from the slag by proper treatment. Zinc slag fuming is such a process, where a reductant source (usually coal) is injected in the molten slag bath to reduce dissolved ZnO from the bath into metallic zinc vapour. The process can be carried out in either conventional tuyere blown furnace or top submerged lance (TSL) smelting furnace. Conventional slag fuming processes are carried out on batch basis in a rectangular tuyere blown furnace. Approximately 50 tonnes of charge (either molten slag or solid slag) is fed to the furnace at the beginning of each fuming cycle. Two opposing sets of submerged tuyeres are employed to inject air and pulverized coal into the molten slag bath to carry out combustion and reducing reactions."

Jan 1, 2012

By M. Huang

A conductivity-based sensor for on-line measurement of free acid was recently built. This sensor is suitable for high ionic strength solutions and its corrosion-free operation is based on induction currents. It has been tested against literature data and measurements made using a previous developed contact-type conductivity cell, with an average difference within 1%. The electrical conductivities of H2SO4?H2O, H2SO4?MgSO4?H2O and NaCl?Laterite-H2Osolutions at temperatures up to 250 °C were discussed. It was found that the solution conductivity depends on various factors, such as the electrolyte concentrations, the type of electrolytes, temperature and the amount of dispersions. A semi-empirical model was developed to account for all the factors discussed. This model was further tested on actual process solutions from the hydrometallurgy of nickel where sulphuric acid solutions containing a variety of metal sulphates and solids. The average difference between the estimated acid concentration from this model and the one from titration was generally less than 5%, which is excellent for industrial applications.

Jan 1, 2006