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By Hongbo Zhao, Jun Wang, Wenqing Qin, Guanzhou Qiu

Jan 1, 2015

By V. E. Antonov

Hydrides of iron and iron-based alloys are thermodynamically stable only at hydrogen pressures in the gigapascal range and rapidly loose hydrogen under ambient conditions. At low temperatures, however, these hydrides can be retained in a metastable state at atmospheric pressure after being cooled under the high pressure to liquid nitrogen temperature. This review will discuss the current state of studies on phase transformations in the Fe-H and related systems and also on the composition, crystal structure and physical properties of the hydrides, both under high hydrogen pressures and in the "quenched" metastable state at ambient pressure. The studies at ambient pressure include magnetization measurements, X-ray and neutron diffraction, Mossbauer spectroscopy and inelastic neutron scattering. In the sections on Mossbauer and structural investigations of hydrides of Fe-Cr and Ni-Fe alloys new experimental results will be presented.

Jan 1, 2002

By Maria Salazar-Villalpando, Todd H. Gardner

"Efficient utilization of CO2 can help to decrease global warming. Methane reforming using carbon dioxide has been of interest for many years, but recently that interest has experienced a rapid increase for both environmental and commercial reasons. The use of CO2 provides a source of clean oxygen, which eliminates the need for costly oxygen separation plants. The product of dry reforming is useful syn-gas, which can be used to generate electrical power in a SOFC or in the production of synthetic fuels (hydrocarbons and alcohols). Hexaaluminate catalysts prepared at NETL may represent a product that can be utilized for the conversion of CO2 to syn-gas. In this work, transition metals dispersed in barium hexaaluminate have shown to be promising new catalysts for dry methane reforming. In this investigation, a series of BaNixAl12-yO19-d catalysts with varying Ni content were prepared by co-precipitation followed by calcination at 1400°C. CO2 reduction by dry methane reforming was carried out to determine catalyst performance as a function of temperature and carbon formation was also quantified after the reforming tests. Results of catalysts characterization, dispersion and surface area, were correlated to catalytic performance.IntroductionEfficient utilization of CO2 can help to decrease global warming. Methane reforming using carbon dioxide has been of interest for many years, but recently that interest has experienced a rapid increase for both environmental and commercial reasons. The use of CO2 provides a source of clean oxygen, which eliminates the need for costly oxygen separation plants. The product of dry reforming is useful syn-gas, which can be used to generate electrical power in a SOFC or in the production of synthetic fuels (hydrocarbons and alcohols). The dry reforming reaction has been known for a long time. Recent publications have reported studies over several catalysts. For example, the CO2 reforming of CH4 over mesoporous nanocrystalline zirconium powders (ZrO2–3%M2Ox; M: Ce, La and K) at 700ºC have shown methane conversion up to 60% (1). Similarly, the effect of Ni content (1–12 wt%) on the surface and catalytic behavior of bimetallic PtNi catalysts supported on ZSM-5 for reforming of methane with CO2 has been studied and report shows a maximum conversion of 16% and catalyst deactivation was observed during the first hour of time on stream (2). In another report, (3) Ni/a-Al2O3 catalyst was tested for syn-gas generation at 750ºC. The maximum methane conversion was 25%."

Jan 1, 2008

By E. V. Verhoej

The proposed EU directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment promotes the substitution of lead in consumer electronics to reduce emissions from lead in the end of life phase. In this paper, the consequences of substituting lead in solders is assessed using the Eco-Indicator-99 method for the examples. The base metal production system is considered as an interconnected network modeled dynamically in Simulink 4 and Matlab 6 (Mathworks Inc 2000), where the recovery and production of metal components of the assessed product partially overlap. This approach requires global modeling of metal production processes and mass balances and resulting allocation choices. It also reveals the susceptibility of LCA scores to different choices in the modeling and data availability and uncertainty. Besides the comparison between lead-free and lead-containing solders, other side effects are revealed. Lead is carrier material for the recycling and production of many co-elements in the interconnected production and recovery system. Substitution may have adverse effects such as temporary shortages of other connected metals that are often not considered in normal LCA assessments, thus leading to erroneous results. The suggested approach provides directions for including these extemal effects and for further assessment of the environmental effects of substituting lead. This paper shows that in order to assess the environmental aspects of metallurgy, dynamic modeling of the total system is required based on the fundamental thermodynamics in each metallurgical reactor, the basis of this dynamic model. With this the true environmental impact of metallurgy can be explained. In the case of lead free solder, it is shown that the mining of substitutes has a very much larger impact.

Jan 1, 2003

By C. Lupi

The electrorefining of primary copper is a well known technology: in this work copper scrap was directly processed in the same way. he copper and copper alloy scrap was previously pressed by means of a 20 tons apparatus in order to avoid pyrometallurgical operations. The samples obtained in this manner showed a good compactness so that they were used as anodes in the electrorefining tests. The tests were carried out on anodes made by copper scrap, copper alloy scrap and a mixture of the two. The electrorefining tests were performed at both 303 and 333 K, in a perspex cell having a volume of 500 ml using a current density of 250 A/m2. The cathode used was always a sheet of pure copper and the electrolyte composition was 40-50 g/l Cu as CuS04 and 150-200 g/l H2SO4. Current efficiency in the range of 92-97% and specific energy consumption ranging from 0.14- 0.20 kWg of copper were reached in all the tests. The refined copper deposits were analyzed by AAS to verify their purity and observed by SEM to highlight their morphology.

Jan 1, 1998

By E. V. Verhoef

The proposed EU directive on the restriction of the use of certain hazardous substances in electrical and electronic equipment promotes the substitution of lead in consumer electronics to reduce emissions from lead in the end of life phase. In this paper, the consequences of substituting lead in solders is assessed using the Eco-lndicator-99 method for the examples. The base metal production system is considered as an interconnected network modeled dynamically in Simulink 4 and Matlab 6 (Mathworks Inc 2000), where the recovery and production of metal components of the assessed product partially overlap. This approach requires global modeling of metal production processes and mass balances and resulting allocation choices. It also reveals the susceptibility of LeA scores to different choices in the modeling and data availability and uncertainty. Besides the comparison between lead-free and lead-containing solders, other side effects are revealed. Lead is carrier material for the recycling and production of many co-elements in the interconnected production and recovery system. Substitution may have adverse effects such as temporary shortages of other connected metals that are often not considered in normal LeA assessments, thus leading to erroneous results. The suggested approach provides directions for including these external effects and for further assessment of the environmental effects of substituting lead. This paper shows that in order to assess the environmental aspects of metallurgy, dynamic modeling of the total system is required based on the fundamental thermodynamics in each metallurgical reactor, the basis of this dynamic model. With this the true environmental impact of metallurgy can be explained. In the case of lead free solder, it is shown that the mining of substitutes has a very much larger impact.

Jan 1, 2003

By R. Padilla

The reaction of chalcopyrite with gaseous sulfur has been investigated in the range 350-450 °C in order to transform this mineral into a more acid soluble copper sulfide and insoluble iron sulfide. The results of thermodynamic analysis of this system as well as the X-ray diffraction analysis of the reaction products showed that in the temperature range 350 400°C the sulfidation reaction proceeded without formation of intermediate copper-iron sulfides according to: The effects of temperature and time on the conversion of chalcopyrite were studied. Conversion of chalcopyrite reached about 80% very rapidly with increase in temperature up to about 400°C. The recovery of copper from the sulfidized samples was determined by leaching in oxygenated 1.2M H2S04, 2M NaCI solution. Copper recoveries over 90 % were obtained from samples sulfidized for 30 min at temperatures lower than 400°C.

Jan 1, 2001

By K. J. Cathro

A hydrometallurgical process is described for the recovery of copper from chalcopyrite concentrates. The process is based on a cupric chloride leach, the concentrate having first been "activated" by heating it with sulphur at a temperature near 400°C. This activation process converts most of the iron of the chalcopyrite to pyrite, which is insoluble in the cupric chloride leachant. The copper is converted to the mineral idaite, which dissolves readily in hot cupric chloride: at 106°C, 98% of the copper is extracted in a three-stage countercurrent leach, the leaching tirqe being 1 hour per stage. The sulphur of the chalcopyrite appears as elemental sulphur, which is recycled for the activation of further concentrate, the final leach residue consisting of pyrite, plus the gangue present in the original concentrate. The copper extracted can be recovered by electrowinning, using a diaphragm cell. Current efficiency (one-electron basis) is about 70% but the cell voltage is only about 1 V, so that power consumption is three times lower than for the conventional sulphate electrowinning process. The leachant is simultaneously regenerated in the anode compartment. The behaviour of minor elements in the concentrate has also been studied.

Jan 1, 1976

By Tianzu Yang, Weifeng Liu, Lin Chen, Wei Chen, DUCHAO ZHANG, HUI XIAO

Carbonaceous refractory materials are widely accepted in many reducing smelting processes such as iron and ferroalloys. Oxidizing processes such as copper concentrate smelting traditionally use magnesia and/or alumina/silica refractory materials. The main objection to the use of carbon-based refractories as the exposed working lining in oxidizing applications is the potential for free oxygen to react with the carbon at high temperature, which could rapidly degrade the refractory lining. In 2013, Outotec and GrafTech conducted joint trials of a thermally conductive, carbonaceous lining for smelting copper concentrates in the Outotec® pilot-scale top-submerged-lance (TSL) furnace in Dandenong, Australia. This testwork had two equally important goals; to demonstrate the ability of carbon refractories to withstand oxidizing process conditions, while ensuring that neither furnace operating conditions nor process stability were negatively affected by the refractory material. The paper discusses the input parameters of the trials, key observations during the testwork program, and the results and conclusions from both process and refractory design standpoints.

Jan 1, 2016

By Craig A. Johnson

Cyanide speciation and behavior have been examined at three active heap leach operations, three heaps undergoing rinsing, and three sites with cyanide contaminated groundwater, all in the southwestern U.S. Data from these studies demonstrate that strong cyanometallic complexes of iron and cobalt can play ?an important role in cyanide behavior throughout the lifetimes of heap leach operations. In active circuits, we find evidence that significant amounts of cyanide combine with iron and cobalt to form strong cyanometallic complexes, and that these species can be adsorbed, probably onto iron hydroxides, or precipitated as insoluble cyanometallic compounds. When spent heaps are rinsed, the release of this cyanide is likely controlled by the slow kinetics of desorption from, or dissolution of, solids that have gone largely uncharacterized. We find evidence that strong cyanometallic complexes can give rise to transient free cyanide in some settings by rapid photo dissociation where heap rinse effluent is exposed to sunlight in open channels or translucent sample bottles. Thus, these species can complicate the ,preparation of spent heaps for decommissioning, even where regulatory standards ?are based on weak acid dissociable cyanide. There is a critical need for information on the form and stability of adsorbed and precipitated cyanide in spent ore heaps, on the concentrations of strong cyanometallic complexes in mineral processing effluents -particularly the complexes of cobalt, and on the natural attenuation of iron and cobalt cyanometallic complexes in both surface and subsurface waters.

Jan 1, 1998

By Zemin Ma

A novel chromate [Cr(VI)] reducing bacterium was isolated from chromite ore processing residue disposal site of China and identified as a Leucobacter sp. by 16S rRNA gene sequence homology. The minimum inhibitory concentration of strain CRB1 was 820 mg l-1 of Cr(VI). The reduction of Cr(VI) occurred only under aerobic conditions. With an initial concentration of 2.5×108 cells ml-1, 1800 mg l-1 of Cr(VI) was reduced entirely within 38 h under the optimum conditions, at 30 °C and pH 9.0. Increasing Cr(VI) concentrations prolonged reduction process and higher cell densities meant quicker reduction. A blue precipitate was produced during chromate reduction of strain CRB1, which was binding to the surface of bacterial cells and determined as trivalent chromium with electron paramagnetic resonance (EPR) spectrometry. The conspicuous chromate reduction ability of Leucobacter sp. CRB1 suggested a potential for bioremediation of Cr(VI) containing wastes.

Jan 1, 2008

By Francis C. Furman

Microscopic evidence indicates that the high sinterability of certain commercial dolomites is tied to specific dolomite textural characteristics. This study encompasses detailed characterization of the unprocessed dolomite and sintering doloma results. The chemical and mineralogical compositions, insoluble residue, chemistry homogeneity, crystal size, primary carbonate texture, secondary dolomite texture, deformation structure, porosity type, porosity, and density of the raw dolomite were observed. These characteristics are compared with sintering trials of <74um powder-compacts samples in which holding times were varied. The evolution of the dolomite characteristics are reviewed and related to the final sintered doloma characteristics. The critical characteristics of a single-stage sintering brick dolomite are the following: 1) primary oolitic texture, 2) dolomite purity, 3) dolomite stoichiometry 4) minimal impurities, less than 1 weight {%} Fe2O3 Al2O3 and SiO2, 5) chemical homogeneity, 6) high density, 7) very low porosity, S) very coarse homogeneous crystallinity, 9) nonplanar dolomite texture, 10) abundant strain related slip microdeformation structures, 11) minimal subsequent alteration. Even with grinding to <74um the nonplanar dolomite texture and slip deformation still have a major effect on doloma sintered density. The three newly identified characteristics of single-stage sintered refractory brick dolomite are their primary oolitic texture, secondary nonplanar texture and abundance of stress related microdeformation structures. The primary oolitic texture reflects a homogeneous pure carbonate with respect to chemistry and crystal size secondary nonplanar texture produces crystals with large surface area to volume ratio. Stress related slip deformation moves CO, groups in to the same site of another CO, group but different orientation which is very unstable. All of these characteristics may facilitate the formation of higher density dolorna sinters.

Jan 1, 1995

By Barry J. Welch

The production of primary aluminium can potentially lead to metal that, with minimum treatment, meets a high purity standard. Smelters that can achieve a significant proportion of their production in this manner have a competitive edge which is of growing importance as the use grows for such items as compact discs and the like. Superimposed on the desire to produce high quality metal are stringent environmental requirements that the industry must adhere to. The environmental &apos;legislation focuses on fluoride emissions and the approach adopted is towards a zero waste management philosophy. The fluoride recycling process does, however, result in volatile impurities being captured and recycled to the cell. Aluminium has an extremely high reduction potential and this results in a significant proportion of the recycled impurities being reduced at the electrolyte metal interface and thus contaminating the metal. This paper reviews sources of impurities and the impact of the operating procedures adopted on metal treatment.

Jan 1, 1996

By J. D. Miller

Low-level radioactive contaminated soils (10-500 pci/gm) created by defense-related activities at certain superfund sites, such as Nevada Test Site (NTS), is a current environmental concern. Many of these contaminated sites may require appropriate cleanup and restoration, which could cost billions of dollars and put tremendous pressure on our limited financial resources. Therefore, the development of a selective flotation process to separate such radionuclides from contaminated soils should be considered. In this study, both a pure depleted UO2 sample and three synthetic UO2/soil mixtures were used to evaluate surface chemistry features and to examine the possibility for the flotation of fine UO2 particles from selected soils. It was intended that this model system would be a reasonable representation of contaminated soils such as those found at the Nevada Test Site which are reported to be contaminated by PuO2 fallout. The effect of reagent schedule, particle size distribution, and surface charge are discussed with respect to the flotation separation of the UO2/soil mixtures. It was found that both commercial fatty acids and reagent grade sodium oleate are effective collectors for UO2 flotation provided the pH is adjusted to the range of pH 8-9. The bench-scale flotation results successfully demonstrated that froth flotation technology can be used to remove UO2 from such model contaminated soils with appropriate flotation chemistry conditions which depend on the soil characteristics and other pretreatment procedures. In the best case, 90.2% of the UO2 was removed from a UO2/NTS soil mixture (119 ppm UO2) and the soil reduced in UO2 contamination from 119 ppm to 17 ppm in a single stage bench flotation. The impact of clay slimes present in the soil is revealed by the results which show that, for example, for a deslimed soil (28x400 mesh and 100 mg UO2/kg soil) 85¬90% UO2 recovery can be obtained with a reduction in contamination to 4.6 mg U02/kg soil.

Jan 1, 1995

By Kiyoshi Takai

The Para-Eco Incinerator Ash Processing System for cleaning slag has been developed after a seven-year pilot plant study. The major part of the system is an electric furnace heated to 1773 K. The feed material consists of a municipal solid waste incinerator ash mixture containing a reducing agent of a coke and an inorganic flux of calcium and magnesium. With this furnace system, three kinds of products are produced. They are an inorganic molten salt that is slag, molten iron alloy absorbing non-ferrous metals, and fly ash. Due to the reducing atmosphere in the furnace, the slag does not contain any metal components as well as chlorine components just like natural rock and/or aggregate. A retreatment plant modifies this slag into a practically useful aggregate. The plant consists of a slow cooling step for crystallizing the slag as well as a water granulation step. The iron components in the ash are reduced to molten iron droplets, which concentrate at the furnace bottom. The non-ferrous metal components such as copper, chromium, and others are absorbed into the molten iron but not into the molten slag. Volatile metals such as lead, zinc, cadmium and others as well as sodium, potassium, and chlorine go back into the fly ash. A solvent extraction method and/or other appropriate procedures can be used to extract the metal components from this fly ash.

Jan 1, 2003

By David B. George

Kennecott recently completed an $880 million modernization and expansion of its smelter and refinery to process all concentrates from the Bingham Canyon mine. This is the first application of Kennecott-Outokumpu Flash Converting. Molten material movement by overhead cranes is eliminated and high levels of oxygen enrichment result in very low process gas volumes and exceptionally control of sulfur oxide emissions. All existing in-plant hygiene, safety, and environmental regulations will be met and the smelter is positioned for anticipated more stringent future regulations. Sulfur capture is 99.9 percent resulting in sulfur dioxide emissions less than the 112 kg/hr Air Permit limit, making the smelter the cleanest in the world.

Jan 1, 1996

By I. Gaballah

Decontamination of synthetic solutions of copper acetate, chloride, nitrate and sulfate containing 10, 100 and 1000 ppm of copper, using chemically treated barks has been studied. Metal percent removal from solutions depends on the pH and the initial concentration and to some extent on the salt used. It varies from 40 to 99 % of the solution initial metallic ion&apos;s content. The maximum retention capacity of the treated bark varies from 31 to 43 mg of Cu per gram of dry modified bark. Bark loaded with copper had been analysed by Scanning Electron Microscopy and lnfra Red spectroscopy. Cu is uniformally distributed in the bulk of the bark. No copper segregation is observed. It seems that copper is bound to the acidic sites of the bark. Anions are not detected on the copper loaded bark neither with the SEM or with the IR spectroscopy.

Jan 1, 1993

By P. N. Anyalebechi

"The effects of solidification rate, initial melt hydrogen concentration, and grain refining on porosity formation in aluminum alloy 2024 have been investigated with unidirectionally cooled laboratory-size ingots. The ingots were prepared from melts containing hydrogen concentration of 0.059-0.27 cm3/100 g and solidified at 0.2-37 °C/s. As expected, the amount of porosity, average pore size, and pore number density increased with increase in melt hydrogen concentration and decrease in solidification rate. However, the effect of solidification rate was greater at the very low melt hydrogen concentration (0.059 cm3/100 g). These results are consistent with reported effects of solidification rate and melt hydrogen content on porosity formation in other aluminum alloys. Interestingly, addition of grain refiner slightly increased the amount of porosity and the average pore size, especially at solidification rates above 1°C/s. IntroductionIn shaped castings and wrought products fabricated from ingots, billets, bars, or slabs of aluminum and its alloys porosity formation is a problem. This is because it compromises their tensile strength, fracture toughness, and fatigue properties [ 1-18]. The pores are usually the crack initiation and propagation sites [6,8,9] and the largest pores tend to dictate the fatigue life of the aluminum products [9,10,14]. Porous regions within an aluminum product probably yield first due to the reduced tensile load bearing capacity, causing the concentration of the strain near the voids which subsequently results in premature fracture. In aluminum alloy ingots, billets, bars and slabs porosity formation is particularly problematic because of its persistence through fabrication and potential for reappearance or exacerbation during subsequent thermal treatment processes before and/or after fabrication [19]. In fact, persistence of microporosity is a serious problem in large thick plates of wrought aluminum alloy products that must be rolled from correspondingly large direct-chill or electromagnetic cast ingots. Some of these thick plate products are machined into large aircraft components that are required in service to withstand multi-directional stresses and to possess high fatigue strength, fracture toughness, resistance to stress corrosion cracking, and strength in the short-transverse direction [1,20]."

Jan 1, 2011

By Honggang Zhong, Tan Yi, Qijie Zhai, Zhao Dan, Xinping Mao, Huigai Li

"The influence of superheat degree on the distribution and volume content of inclusions were studied in 65Mn thin slab produced by compact strip production(CSP) in Zhujiang Steel in China, The results showed that the diameters of inclusions are mainly less than 5µm. Most of the inclusions gathered at the 1/4 thickness direction for the thin slab of 27? superheat degree, compared with the center position for that of 37?. There are more inclusions larger than 50µm in the low superheat samples, which is caused by the short floating time. In addition, the inclusions were observed and analyzed by metallurgical microscope, SEM and EDS in order to ensure their composition, type and further find their source. It was find that the types of these inclusions mainly are Al2O3, SiO2,CaO and their composites, a few of them are TiN and MnS.IntroductionIt is well known that inclusions have a great impact on the strength, plasticity, fracture toughness, cutting performance, fatigue property and corrosion resistance of steels. Especially, with the demand for thinner slab, the cleanness is increasingly becoming more significant as a quality criterion[1]. High manganese and carbon steels not only demonstrate high strength but also proper plasticity. There are many problems unsolved for 65Mn steel as a result of the low solidification rate, bad thermal strength, crack sensitivity and low casting temperature[2,3].The superheat of the molten steel has a great impact on the erosion of refractory lining, molten steel fluidity and non-metallic inclusion behavior[4]. The serious erosion situation of ladle lining, nozzle and casting tundish will give rise to more inclusions at a high superheat. Meantime higher superheat will make second dendrite arm spacing coursing and element segregation which lead to inclusion, bubble formation and shrinkage cavity. On the contrary, it is hard for non-metallic inclusions to float up with a low superheat value. Inclusions of 65Mn steel, which produced in different superheat condition by CSP, were studied for the sake of higher slab properties including statistics and EDS analysis."

Jan 1, 2012

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