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By Matthew Jeffrey

Due to the increasing environmental and public concerns over cyanidation, there has been a large amount of research into viable alternative lixiviants. Despite these studies, there is little published data directly comparing the kinetics of gold leaching for each of these alternatives: most of the literature is concerned with gold extraction from ores. This paper presents a detailed kinetic study of gold leaching in cyanide, armmonia/thiosulfate and chloride/hypochlorite solutions. The gold leach rates were measured using a rotating electrochemical quartz crystal microbalance (REQCM). This instrument allows the mass of a gold sample to measured in?situ, with a sensitivity of less than 10 ng. From the results of these studies, it is possible to select experimental conditions where the leach rates of the alternative lixiviants are similar to that for the traditional cyanide system.

Jan 1, 1998

By Nobuhiro Oguma, Yuji Mizuta, Hideya Sato, Shigehiko Iwahori

"Recyclable materials containing copper and precious metals have been treated at the Mitsubishi Process in Naoshima. In 2003, a new incinerating and melting plant (pre-treatment plant) for waste materials, such as shredder residue of automobile and scrapped appliance, was constructed. All of produced slag/metal mixture is treated at the Mitsubishi Process, and which results in the significant increase of recyclable materials treatment. The combination of two processes has realized a highly efficient and environmentally friendly system for recycling valuable metals in the waste which used to be sent to a landfill. Naoshima continues to make efforts to achieve the highly efficient operations of the two processes, and plans to increase the treatment of recyclable materials further. This paper summarizes the recent operations and the various improvements implemented in the pre-treatment plant.IntroductionRecyclable materials containing valuable metals such as copper and precious metals have been treated at the Mitsubishi Continuous Copper Smelting and Converting Process (Mitsubishi Process) since the start-up in 1991. In the early stages, recyclable materials consisting mainly of metal scrap were charged into the process and the treatment had been increased steadily. In order to promote the recycling business, treatment of various kinds of materials including printed circuit boards was started. However, the treatment hit the ceiling due to a limitation of furnace boiler capacity, since they contained large amounts of combustible materials. In addition, severe corrosion of boiler tubes was caused by halogen contained in recyclable materials."

Jan 1, 2012

By R. L. Nyirenda

An investigation of the reducibility of a cassiterite concentrate with charcoal was made in the temperature range of 1123-1373 K. The course of the reaction was monitored by a combination of sample weight loss measurements, product gas analysis, and chemical analysis of the reaction product. It was found that the cassiterite could be best reduced by a combination? of high temperature, reasonably high charcoal proportions, high charge poroslty, and the addition of a small percentage of lime. Analysis of kinetic data obtained from isothermal experiments using theory from the oxidation of carbon by carbon dioxide gave an activation energy value of 255 lci/mole for the consumption of carbon by reaction with cassiterite.

Jan 1, 1990

By Zengjie Wang

Investigation on hydrochloric acid leaching of the ilmenite from Panzhihua, China was carried out to prepare synthetic rutile. The leaching parameters were optimized to obtain high content of TiO2 in the products. The experimental data suggest that an optimum leaching can be realized with 30% acid, a solid/liquid ratio of 1/4 at 95°C for 4h, and ore ground for -400 mesh size. After the acid leaching, an additional alkaline leaching process using hot NaOH solution was performed, and then the products was in grain form followed by heat treated at 900°C for 2h in order to extract Si and increase the particle size of synthetic rutile. The final product has a high content of TiO2 (about 95%), a low content of chlorine consuming elements (total CaO+MgO =0.07%) and a suitable particle size distribution for chlorination process.

Jan 1, 2008

By KNona C. Liddell

Goethite is an important naturally occurring sorbent for divalent heavy metals and has often been used as a model compound in studies of adsorption on oxide mineral surfaces. Surface complexation modeling, surface spectroscopy, and electrochemical techniques have all been applied to goethite adsorption. Modeling studies have shown that usually several different sets of fitted parameters are equally successful in representing surface charging and adsorption data. Surface spectroscopic data are proving valuable in determining the nature of the surface sites, and refined models now incorporate structural information on interatomic distances and coordination numbers. Multisite surface complexation models can give very good fits to surface charging and adsorption data, but further improvements are needed to better represent surface reactions involving exchange of protons and divalent cations. Recent experimental and modeling studies on adsorption of divalent transition metals on goethite are described and the present status of the field is assessed.

Jan 1, 1999

By Dieter Wanner

Off-gas cleaning from metallurgical? plants, requires in many cases very low dust contents which are, difficult to achieve with conventional scrubbers, even with high energy input. Lurgi has developed a scrubber which improves the separation of the fine dust by electrical charge prior to the scrubbing zone,, An Electrostatic Scrubber has been successfully installed for the off-gas cleaning from slag granulation after a waelz kiln achieving less than l mg/m3 in the clean gas.

Jan 1, 1992

By Francis Vanbellen

Umicore Precious Metals Refining operates an integrated precious metals smelting and refining plant in Hoboken, Belgium. Once a smelter and refiner of complex concentrates, the plant today?s feed consists exclusively of industrial and consumer recycled products, making it the world?s largest recycling facility for precious metals. Unlike the fairy tale of the Frog Prince, it took much more than a princess? kiss to successfully realize this makeover. A completely renewed plant has been built over the past decade. The most visible technological innovation was the commissioning of the Pb-Cu smelter. Its flexibility towards very different types of feed makes it perfectly suited as main entry to the Hoboken flow sheet. A new Cu-leaching & electro winning plant and precious metals refinery make up the Precious Metals Operations (PMO) whose targets are fast throughput and maximized yields for gold, silver and the platinum group metals. The Base Metals Operations (BMO), flexibly process the by-products from the PMO, valorizing ?impurities? like indium, tellurium, selenium and others. Off gas and waste water treatments ensure compliance with strict environmental standards. Precious metals recycling is an art that goes beyond mastering a unique flow sheet. Umicore Precious Metals Refining offers a complete recycling service, taking care of sampling and assaying, metals management and logistics. The quality of this integral service is recognized through the attribution of ISO certifications for our operational activities, sampling and the environmental care. And it?s an art that follows Michelangelo?s experience: ?Art is 5% of inspiration and 95% of transpiration.?

Jan 1, 2006

By Francis Vanbellen

Umicore Precious Metals Refining operates an integrated precious metals smelting and refining plant in Hoboken, Belgium. Once a smelter and refiner of complex concentrates, the plant today?s feed consists exclusively of industrial and consumer recycled products, making it the world?s largest recycling facility for precious metals. Unlike the fairy tale of the Frog Prince, it took much more than a princess? kiss to successfully realize this makeover. A completely renewed plant has been built over the past decade. The most visible technological innovation was the commissioning of the Pb-Cu smelter. Its flexibility towards very different types of feed makes it perfectly suited as main entry to the Hoboken flow sheet. A new Cu-leaching & electro winning plant and precious metals refinery make up the Precious Metals Operations (PMO) whose targets are fast throughput and maximized yields for gold, silver and the platinum group metals. The Base Metals Operations (BMO), flexibly process the by-products from the PMO, valorizing ?impurities? like indium, tellurium, selenium and others. Off gas and waste water treatments ensure compliance with strict environmental standards. Precious metals recycling is an art that goes beyond mastering a unique flow sheet. Umicore Precious Metals Refining offers a complete recycling service, taking care of sampling and assaying, metals management and logistics. The quality of this integral service is recognized through the attribution of ISO certifications for our operational activities, sampling and the environmental care. And it?s an art that follows Michelangelo?s experience: ?Art is 5% of inspiration and 95% of transpiration.?

Jan 1, 2006

By Shizhe Liu, Bing Li, Heng Wang, Zuxin Zhao

In this paper, cyclic voltammetry and chronoamperometry have been applied to investigate the effects of Nd2O3 concentration on the anode effects, critical potential for the anode effects and Nd2O3 reduction in LiF-NdF3-Nd2O3 melts at 950℃. The results show that the oxidation peaks in the potential of about 2.7V are attributed to the oxygen ions oxidation and the peak current density increases with Nd2O3 concentration increase from 0 to 0.5wt%. The critical potential caused the anode effects shifts to 0.3V more positive value as Nd2O3 content in the melts decreases from 0.01wt% to 0.5wt%. The cyclic votammograms on W electrodes in the LiF-NdF3-Nd2O3 melts present two pairs of reduction and oxidation peaks, indicating that the reduction of Nd ions in the LiF-NdF3-Nd2O3 melts in two steps rather than one step.

Jan 1, 2014

By M. Soltanieh

The liquidus surface? and tie-lines in the nickel-cobalt-sulphur ternary system have been determined between 1<273-1573 K. The experiments were conducted by equlibrating the liquid sulphide with the metallic alloy phase. The liquid sulphide phase was sampled and chemically analyzed. The alloy was analyzed by electrol} microprobe. Combining the present results with the.avai1abl~ literature data, the thermodynamic properties of this system were calculated.

Jan 1, 1998

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 Norbert Steiner

For the desulfurization of weak SO2 gas streams, Degussa developed a process using dilute H2SO4 solution containing H2O, instead of conventional gas scrubbing with all solid absorbent medium (limestone, MgO). The process is based on fast reaction of H2O, with SO2 yielding H2SO4 up to 70% strength, depending on off-gas temperature. Compared to the conventional systems with typically < 95% efficiency, independent on the raw gas SO2 concentration, residual SO2 concentrations of less than 20 mg/Nm3 can be easily achieved, corresponding to nearly 100% removal. These features render the H2O, process a very attractive, low capital cost technology to retrofit existing conventional desulfurization plants.

Jan 1, 1996

By Cesar Garban

The samples of the washings are characterized of the ore for physical, chemical and metalurgical properties for representivity. the optimum values are determined for the recuperation of gold of the washings of the gold ore from the zone El Callao, Venezuela by acidic solutions of thiourea of the following parameters: Ph , contact time, composition of the liquid mixture, ratio of solid to liquid, grade of liberation, in an apparatus designed for contacting solid powder of the mineral with liquid solution of thiourea mantained in suspension by bubles of compressed air. The experimental results showed that the velocity of lixivation in primier time of (20) minutes is rapid and practically 2/3 part of the reaction is completed. For experimental design of parameters, the optimum conditions of recuperation of gold determind in this experimental investigation are:

Jan 1, 1999

By Alwin Frei, Aldo Steinfeld, Peter G. Loutzenhiser, Enrico Guglielmini

"Using concentrated solar radiation as the energy source of high-temperature process heat, the carbothermal reductions of Al2O3 to Al and SiO2 to Si were examined thermodynamically and demonstrated experimentally at vacuum pressures. Reducing the system pressure favors Al(g) and Si(g) formation, enabling their vacuum distillation and avoiding contamination by carbides and/or oxycarbides. Exploratory experimentation in a solar reactor was performed with mixtures of charcoal with alumina and silica in the ranges of 1300-2000 K and 1997–2263 K, respectively, at 10-3 bar by direct exposure to concentrated thermal radiation. Distilled samples contained up to 19 wt% of Al in Al-Al2O3 mixtures and 79 wt% of Si in Si-SiO2 mixtures. When the reducing agent is derived from a biomass source, the solar-driven carbothermal processes are CO2 neutral.IntroductionMetallurgical extractive processes for producing Al1-2 from Al2O3 and Si3-6 from SiO2 are characterized by their high specific energy consumption and concomitant emissions. Alternatively, concentrated solar energy can be used as a high-temperature heat source to drive the carbothermal reductions and, thus, avoid greenhouse gas emissions and other pollutants derived from fossil-fuel-based processes7-12. When the reducing agent is biomass charcoal, the solar-driven carbothermal reduction is CO2 neutral. The carbothermal reductions of Al2O3 and SiO2 are represented by the simplified overall stoichiometric reactions:"

Jan 1, 2011

By Oscar J. Restrepo

Through reactions in solid form at high temperatures, using iron oxide (Fe3O4) and chromium oxide (Cr2O3) in fixed proportions as precursors, the compound was synthesized with spinel structure type FeCr2O4. For different temperatures synthesis was conducted the characterization of the material obtained through X-ray diffraction (XRD), spectroscopy UV-VIS-NIR, scanning electron microscopy (SEM), energy dispersion analysis of X-ray (EDX) thermal analysis (DTA / TGA) and magnetic susceptibility of alternating current. The changes in the spectra of reflectance changes are related to the phase identified, the degree of crystalline structure, the spatial order of cations and the magnetic behavior obtained.

Jan 1, 2009

By M. Z. Quadir, M. A. Islam, P. J. Hazell, G. J. Appleby-Thomas, J. P. Escobedo

The mechanical response of closed-cell aluminium metallic foams subjected to low and high strain-rate loading has been investigated. A set of quasi-static and dynamic (shock) compressive tests have been conducted on closed-cell aluminium foams (CYMAT) with densities of 0.50 and 0.30 g/cc. Post-mortem characterization via optical microscopy and electron backscatter diffraction (EBSD) was performed on pristine and deformed specimens to elucidate the dominant deformation mechanisms in these materials. The combination of these techniques allowed for the assessment of critical deformation parameters such as changes in cell geometry and morphology, as well as microstructural evolution and deformation of the aluminium cellular network. These findings aim to aid in the design and development of optimized material structures for impact and blast protection.

Jan 1, 2015

By V. V. Satya Prasad, A. Sambasiva Rao

Electroslag melting technologies have recently been developed for recycling light scrap of valuable metals and alloys such as superalloys and oxygen free high conductivity (OFHC) copper at Defence Metallurgical Research Laboratory (DMRL), Hyderabad. Conventionally, electroslag melting processes use consumable electrodes. Because of the difficulty in compaction of scrap into a consumable electrode of satisfactory quality, non-consumable electrodes such as graphite and water-cooled copper have been designed. Electroslag remelting using a water-cooled non-consumable electrode was developed to melt scrap of a nickel base superalloy. Sound ingots with smooth surface finish and properties comparable to vacuum melted superalloys could. be obtained from scrap using this process. A modified electroslag crucible melting process using graphite crucible and graphite electrode was developed for recycling OFHC copper scrap. Copper ingots with less than 10 ppm oxygen and electrical conductivity"" 100% IACS could be produced. The same process was also utilized to produce copper-based alloys such as copper-chromium and copper-titanium starting from copper scrap.

Jan 1, 2000

By R. P. King

The essential features of an image analysis system for the measurement of mineral liberation are described. Good procedures for image acquisition and image processing prior to image analysis are defined. The basic stereological methods for the measurement of volume fraction, surface area per unit volume, particle size distribution and liberation spectra are given. The appropriate methods for fractal correction when measuring perimeters of irregular features and for frame correction when measuring linear intercepts are developed. Practically useful and accurate procedures for the stereological correction of particle size and liberation distribution methods are given.

Jan 1, 1995

The direct removal of lead ions from D2EHPA-kerosene using metallic zinc as the reducing agent was evaluated. The electrochemical process, called galvanic stripping, is a potential alternative stripping technique when standard chemical methods are not adequate. Four parameters found to be important in the rate of lead removal were studied in a factorially designed experiment. The variable evaluated included D2EHPA concentration, temperature, zinc surface area and solution agitation. Temperature and surface area were found to be the most significant, while agitation and D2EHPA concentration had less influence on the reaction. An activation energy of 22.5 Kcal/mole was calculated indicating a chemically-controlled process. The reaction was also sensitive to the concentration of oxygen in the system. The zinc required was considerably in excess of stoichiometry, possibly due to the dissolution and redeposition of lead: In general, the results were encouraging and demonstrated that lead impurities could be removed from D2EHPA using cementation type reactions.

Jan 1, 1995

By Guoqiang Lv, Xi Yang, Wenhui Ma

Cast multicrystalline silicon ingots are widely used in photovoltaic manufacturing. A key issue to achieve high solar cell efficiencies is to attain an optimized temperature field during directional solidification (DS) process. This paper reports numerical investigation of multicrystalline silicon (mc-Si) ingot production using two major types of DS furnace. Specific examination is made on thermal distribution, interface shape and stress field. Evaluation is performed for the applicability of thermal system design to reduce thermal stress, improve crystal quality and enhance energy efficiency. The effects of procedure parameters and geometric configuration on temperature distribution are discussed as well to provide the viable solutions for systems optimization.

Jan 1, 2015