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By Qian Li, Haiyan Leng, Kuo-Chih Chou, Haoyuan Xiao, Zhigang Yu

Magnesium borohydride and Magnesium alanate were synthesized by mechanochemical metathesis reaction. The thermal decomposition behaviors of Mg(BH4)2-nMg(AlH4)2(n=0.5,1) systems were investigated as potential hydrogen storage materials. The results showed that the systems started to desorb H2 at 120 ℃ and desorbed 3.9 wt. and 4.9 wt.% H2 below 300 ℃ when n equals 0.5 and 1, respectively, while individual Mg(BH4)2 started to desorb H2 at 250 ℃ and desorbed only 0.82 wt.% H2. Because of the exist of the Mg(AlH4)2, the isothermal desorption kinetics of Mg(BH4)2 in the Mg(BH4)2-0.5Mg(AlH4)2 systems was 50% faster than that of pristine Mg(BH4)2. In addition, the re-hydrogenation rates also increased 49.4% and 37.9%.

Jan 1, 2015

By S. G. Kumar, R. G. Reddy

"Niobium aluminides offer the advantage of higher high temperature capability compared to other intermetallic aluminides due to the refractory nature of niobium. However, the reaction sequence in Nb-Al system is sluggish and currently there is a great interest in the processing aspects of these materials. In the present study, a systematic investigation was undertaken to compare the effect of different powder metallurgy processing routes on the phase relations and microstructure of 66Nb-22AH2Ti (in atom percent) alloy. The three different process routes adopted were: (i) cold pressing followed by reaction sintering; (ii) cold pressing and hot pressing followed by sintering; and (iii) arc melting, hydride-dehydride process to make the alloy powder followed by cold pressing and then sintering. The samples are analyzed by XRD, Optical Microscopy, SEM-EDS and EPMA. The analysis showed that alloy pellets made from pre-alloyed powders i.e., arc melting followed by hydride-dehydride process, gave good densification and more Nb3Al formation.1. IntroductionTo improve the performance standards of turbine engines, materials scientists are challenged to develop materials that have· high thrust-to-weight ratio with high specific strength, high specific modulus and good environmental properties at elevated temperatures. The conventional high temperature materials like nickel based superalloys are high in density and hence many of the high temperature materials scientists have focussed their attention on intermetallic aluminides like Fe-AI, Nb-AI, Ni-AI and Ti-AI in recent years. The phase relations and properties of alloys based on Fe-AI, Ni-AI and Ti-AI are fairly well known whereas little is known about the alloys based on niobium aluminides."

Jan 1, 1996

By Katsuyasu Sugawara, Takuo Sugawara, Shin-ji Abe, Tadakazu Kagami

"In order to clarify the mechanism and to obtain the fundamental data for heavy metal recovery from an incinerator ash by chlorination, pure chemical reagents, zinc oxide and lead oxide or the fly ash blended with calcium chloride and silicon dioxide were heated up to 1000°C in a nitrogen stream. Thermogravimetric curves of the samples with the chlorinating reagents indicated that solid-liquid reactions accelerated the chlorination and release of metals from the solid phase. The formation of liquid phase of calcium chloride played an important role on effective recovery of zinc and lead at lower temperatures below 800 °C. Although zinc and lead could be decreased in the incinerator ash without chlorinating reagents, addition of chlorinating· reagents enables the removal of metals in high extent· at lower temperature.IntroductionFly ash is discharged about 3,000 tons/day (about 110 million tons/year) from incinerators of municipal solid waste in Japan and mostly fly ash is disposed in landfills. Fly ash includes heavy metals e.g. zinc and lead. Since untreated fly ash caused hazardous leaching problems, Waste Disposal and Public Cleaning Law was revised in 1992, fly ash being designated 'specially controlled' general waste. Fly ash must be disposed by the following suitable, intermediate four methods: [I] Cement- Solidified Method, [2] Immobilized Chemicals Method, [3] Melting Solidified Method, [4] Acid Leaching Method, permitted by the Ministry of Health and Welfare, Japan."

Jan 1, 2000

By R. W. Smith

The flotation response and electrokinetic behavior of Chlorella vulgaris and Chlamydomonas sp . when using dodecylamine hydrochloride as collector were studied in the absence and presence of Pb(I1). Also, an electron microscopy study was made of the algae after Pb accumulation. The flotation behavior of the organisms after Pb accumulation appears at least partially related to the location of the abstracted Pb onto or into the organisms.

Jan 1, 1991

By M. Jennings

In 1987, Echo Bay discovered a major silver/gold ore body at their McCoy property in Nevada, and quickly made a decision to build a 5000 tpd mill which was expanded during the design to 7500 tpd. Since the ore reserves consisted of cyanide leachable oxide as well as sulfide, the plant flow sheet involved an oxide leach, a gravity circuit, and lead sulfide and a pyrite sulfide recovery by flotation. The paper describes the process development, equipment selection, plant design and the startup of the oxide treatment.

Jan 1, 1990

By Toyohisa Fujita

The effect of variables on the gold extraction with ammonium thiosulfate was investigated on sponge gold and ore samples. The Effects of CUS04, (NH4hS203, NH40H, (N~hS04' pH, stirring speed and retention on gold leaching rate and thiosulfate oxidation (consumption) have been studied. Almost 100% of gold was leached from sponge gold and over 96% from ore sample at optimum conditions. Trioctylmethyl ammonium chloride was used to recover gold from thiosulfate pregnant solution. It was found that more than 99% of gold was recovered by the extractant diluted with n-octane at 01 A ratio of 1: 1 without the re-adjustment of pH or others. Also, the gold cementation was conducted without de-aeration by using zinc, copper and aluminum powders. The result indicated that the gold was effectively recovered from a solution of low ammonia and copper concentrations and higher thiosulfate concentration. The gold recovery process by using ammonium thiosulfate is an environmental friendly method comparing to conventional cyanidation process.

Jan 1, 2003

By P. M. Tyroler

At INCO's Copper Cliff Nickel Refinery, nickel is extracted by using the INCO Pressure Carbonyl (IPC) process. The resulting IPC residue containing copper, nickel, cobalt, iron, sulphur, precious metals, selenium and tellurium is further processed at a hydrometallurgical plant. This plant treats approximately fifty metric tons per day of IPC residue. The components of the feed are separated in a number of steps and a precious metals concentrate, nickel-cobalt carbonate, a selenium-tellurium intermediate and copper cathodes are produced. An iron-arsenic waste stream is also produced and discarded to tailings. The hydrometallurgical processes include pres- sure leaching, cementation, precipitation, thickening, filtration and electrowinning. This paper describes in detail the individual steps of the flowsheet.

Jan 1, 1988

By Jari Aromaa, Olof Forsen

"Oxygen evolution by decomposition of water is the main anodic· reaction in sulphuric acid solution. Traditional anode materials have been relatively low-cost lead alloys, though the active lead dioxide layer has a high oxygen evolution overpotential. This causes a significant increase of cell voltage. To lower total energy use in metal production, electrocatalytical properties or corrosion resistance to decrease replacement costs must be improved. Addition of an catalyzing ion will decrease oxygen evolution potential. The effective area of an anode increases by calcium additions and by producing anodes with fine microstructure. Remelting and rapid quenching is possibly a method that is economically feasible and technically simple enough to be adopted.IntroductionPermanent anodes are widely used in several electrochemical processes and cathodic protection applications. The permanent or ""inert"" anodes can be either massive or coated anodes. The massive anodes are metals, like lead alloys, or non-metals, like magnetite, graphite or ferrite. The coated anodes are made of a valve metal base (titanium, niobium or tantalum) coated with an electrochemically active coating. The purpose of anodes is to supply current to the electrochemical cell. A vast number of materials and their combinations are electrical conductors and may hence be used as anode materials. However, good anode materials must survive in aggressive environments and also be able to pass high current densities. These opposite requirements restrict the amount of possible materials. Generally, an useful anode material must meet three requirements, electrical conductivity, electro catalysis and stability. Good electrical conductivity is essential for energy efficiency. Good electrocatalytical properties are essential to improve product yield. Long term stability is also an important property, because electrode wear and corrosion may cause product contamination, increasing energy consumption and material and labor costs due to need of periodical maintenance. Electrical conductivity and electrocatalytical properties are more widely studied subjects than long term stability of anodes, and a good amount of information about these two subjects can be found in the open literature. Wear and corrosion mechanisms of the anodes vary depending on the operational conditions, i.e. concentration of different species, temperature and operating current density."

Jan 1, 1997

By Andrzej Warczok

Liquid slags produced in smelting of copper concentrates contain copper in a dissolved form as well as mechanically entrained inclusions of copper matte. Coalescence and sedimentation of inclusions during slag cleaning plays a key role in copper recovery. Liquid matte inclusion in a molten slag presents a system of metallic conductor in an ionic solution. Constant electric field induces migration of the matte droplet along the current lines. Additional phenomena occur in a system under crossed electric and magnetic fields. Electromagnetic buoyancy force acting on the inclusion affects its settling rate. Electromagnetic buoyancy force of insulating and metal spheres has been measured in a liquid synthetic slag. It was found that depolarisation of the metal sphere, related to the electrode reactions occurring in the surface, plays an important role in the determination of the direction and magnitude of the electromagnetic force. On the basis of the existing theories and results of measurements a mathematical model describing the behaviour of metallic inclusions in the liquid slag under the influence of crossed electric and magnetic fields was developed. Simulation of behaviour of copper matte inclusions under crossed fields showed trajectory of motion in a liquid slag as a function of the slag properties and the inclusion size.

Jan 1, 2003

By W. L. Cornell

Ore microscopy was used in support of both bench-and large-scale continuous beneficiation testing programs. Reflected light microscopy and Vickers hardness measurements were utilized to help identify problems relating to mineral identification, mineral association, mineral liberation, mineral distribution in product streams, and froth entrainment. Specimens studied were size fractions of concentrates and tailings resulting from Bureau of Mines research to recover a siegenite-enriched product by beneficiating chalcopyrite concentrates. Other specimens were size fractions of bulk sulfide concentrates recovered during the enhanced amine scavenging of final tailings by froth flotation. The findings from studies directly affected flowsheet development.

Jan 1, 1987

By S. C. Sharma

The aluminium matrix composites with ceramic dispersoids can be separated by density difference concept. In the proposed work composite scrap is recycled using an oil fired furnace. The scrap is melted in the furnace and temperature is maintained below 740 degree centigrade. Because of the density difference the lighter dispersoids will float and heavier dispersoids will settle down. The clean melt is separated be removing the floating and settled disperssoils, and then filtering using ceramic filters.

Jan 1, 1995

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 Jogre A. S Tenório

he aim of the present investigation was to investigate technological features of the Fe-NbC dissolution in liquid Fe-C alloys. Fe-NbC is a Ferro-niobium alloy with 7%C, has a particle size smaller than 150 pm and its micro constituents are polygonal niobium carbides and an iron matrix. The obtained dissolution time was less than one-minute and the yields were in the range of 80-90% at 1873 K. In the Fe-NbC dissolution process, the dissolution occurs at first, and as a consequence the niobium carbides become free to dissolve. These carbides will dissolve until the melt reaches a saturation point. The non-dissolved carbides remain trapped in the liquid or will form a dross. The addition yields decreases when the niobium concentration reaches this limit value, that depends on the carbon concentration. These define a saturation curve.

Jan 1, 1994

By J. W. Matousek

In the flash smelting of copper sulfide concentrates, the course of reactions from the burner tip, through flame "burn-out" (the point of oxygen depletion), to settled matte and slag is of particular interest in understanding the mechanisms of the process. Numerous reaction sets can be proposed to describe the chemical changes that might be taking place, but from outside the furnace no one set offers an obvious advantage in explaining the actual processes involved. Only a combination of mathematical modeling and flame and bath sampling can achieve this result. This paper shows that flash smelting, while still reasonably orderly, is a more complex process than suggested by the technical literature.

Jan 1, 1993

By Shunhong Huang

To improve understanding the effect of heavy metal chromium on soil biota, laboratory incubation experiment was carried out in the soils contaminated artificially with five concentrations of chromate (50, 250, 500, 1000 and 2000 mg kg_1 soil) over time (35 days). The population and diversity of bacteria, fungi and actinomycetes in soils were measured as indicators of soil microbial processes in the disturbances mentioned above. Incubation experiment results elucidated that the population and diversity of microorganisms decreased with increasing Cr (VI) concentration. Furthermore, various microorganisms showed different sensitivity to total Cr contamination. The sensitivity of microbial population to chromium contamination was in the order: actinomycetes >bacteria>fungi. The resulted implied that the microorganism can be used as an indicator of chromium contamination.

Jan 1, 2008

Novel techniques were developed to obtain samples from and make measurements in the shaft of the flash furnace at the Kalgoorlie Nickel Smelter. The data obtained was used to validate mathematical models of the burners and the reaction shaft. Particle, gas and wall temperatures were measured along with the oxygen potential of the molten particles. Collected particles were characterised by sizing, chemical analysis and optical microscopy. The region of the shaft immediately beneath the burner where the rate of change was most rapid received special attention.

Jan 1, 1993

By Satian Niltawach

Iron sulphate jarosite through which iron in zinc sulphide concentrate feed is removed from the production circuit of conventional roast-leach-electrowin process, is chemically unstable and environmentally hazardous even if it is mixed with lime. If zinc silicate ore is used at similar chemical conditions in place of calcine in the jarosite precipitation, the resultant silico-jarosite residue having been mixed with lime is chemically stable and environmentally friendly. The recovery of zinc from silicate ore is also higher than that from calcine.

Jan 1, 1994

By Ignacy A. Lipiec

The advantage of microorganisms used in bioleach systems to conventional chemical reaction systems is that these apply the available energy more precisely where it is needed, either directly onto the mineral of interest or by efficiently catalyzing the production of a reactant. The literature cover the range from empirical models used in describing macro heat balance in heaps to detailed studies relating the micro heat effects of bacteria adhesion energy to the surface of minerals. In this paper, the heat effects are reviewed in a general way describing bioleaching in two macro systems, heap leaching and slurry bioreactors. The micro scale heat effects is the reactions and conditions at the microorganism scale, including the mechanism of leaching and bacterial behavior.

Jan 1, 1998

By R. D. Osmanson

A series of batch roasting tests was performed on minus 1/2 inch gold bearing refractory samples from the Gold Acres deposit, and 67 select particles were polished and the sulfide alterations were examined microscopically. The suite of specimens represents two hour batch roast treatments at 600°C, 700°C, 725°C, 750°c, 800°C, and 900°C. Auriferous pyrites were found to alter sequencially to pyrrhotite, magnetite and finally to hematite. It was found that the decrease in cyanidation extraction with high temperature roasting is likely due to the increas ing stability of magnetite and more crystalline hematite, and the decrease in porosity with these phases which occlude the gold. Gold has been noted to occur very early in the mineralizing sequence, with gold being found in quartz and in clay/carbonate rock matrix. No gold was found in the two pyrite phases, but numerous gold grains were found in pyrrhotite after pyrite and in subsequent iron oxides. Gold mineralization had apparently ended by the time base metals were introduced into the deposit.

Jan 1, 1987

By T. Alboussiere, O. Paireau

"We have designed an experiment to simulate natural convection in a direct-chill aluminium ingot. In this experiment we induce natural convection within a hemisphere filled with liquid-metal (mercury). The device consists of a copper hemispherical bowl closed by a copper plate. The top is maintained at superheat temperature while the boundary is cooled. While the temperature measurements were found using thermocouples, the velocities were obtained using an original technical procedure that relies on MHD properties. By applying a steady local magnetic field, we measure the velocity. The distribution of temperature and velocity can be separated into a thermally stratified core bounded by thermal wall jets. These wall jets greatly influence the degree of macrosegregation in ingots.1. Natural Convection in Aluminium CastingIt is well known that the quality of the final product in aluminium casting depends on the movements within the liquid metal such as forced or thermogravitational convection. Strong buoyancy-driven flows are known to occur in the liquid metal pool of an aluminium ingot caster. These flows have a significant influence on the metallurgical structure of the ingot through the redistribution of heat, fragmented dendrites and segregated material within the pool. Macrosegregation mechanisms depend on favourable temperature and flow distributions in the sump, and these factors will determine the pattern and degree of macrosegregation. Moreover, for many years, the importance of thermally-driven natural convection in casting has been underlined (Cole & Bolling, 1965). In this way, a precise determination of the velocity and temperature fields is required in order to improve understanding of the macrosegregation mechanisms. That is precisely the aim of this paper, which provides experimental data of the flow and the temperature distributions in a natural convection experiment. We intend, with this laboratory experiment, to determine accurately the velocity field, particularly within the thermal boundary layer where the effects of the flows may have an important role in the transport of crystals."

Jan 1, 1999