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By Ximeng Zhu

The electrochemical behavior of mineral and coal pyrites in stirred and quiescent alkaline boratelsulfate solutions @H 7.9-10.5) have been investigated using cyclic voltammetry. Significant differences in the electrochemical response of these pyrites were observed. At the mineral pyrite surface, three anodic peaks at about -0.8 V, -0.1 V and +0.5 V (SCE) have been detected along with their corresponding reduction peaks. The first two peaks correspond to FeIFeOI) and FeOI)lFe(III) oxidation. The third peak is present for quiescent conditions but disappears as a distinct peak when the electrolyte is stirred. In the upper voltage region +0.30V (SCE), the current increases markedly during stirring and the reactions correspond to the oxidation of pyrite with the formation FeOII) oxides plus elemental sulfur. Also there is evidence that Fe oxy-ions form. Coal pyrites, under rapid sweep conditions display only the first two anodic peaks, the associated reduction peaks and an additional reduction peak corresponding to one or more of the high voltage oxidation products. After prolonged exposure to high potentials, coal pyrite displays reactions similar to those of mineral pyrite but at much higher current densities demonstrating the much higher reactivity of the coal pyrite. The reactivity sequence was Upper Freeport coal pyrite > Pittsburgh coal pyrite > mineral pyrite.

Jan 1, 1991

By David T. Hobbs

Large quantities of highly alkaline, radioactive, liquid wastes are stored in underground tanks throughout the Department of Energy complex. These wastes will be pretreated to separate radionuclides and the remaining decontaminated liquid wastes incorporated into solid waste forms for permanent disposal. Significant savings in disposal costs could result by recovering .the sodium as sodium hydroxide for reuse or disposal as nonradioactive waste. Recent testing demonstrated an electrochemical separation process for the recovery of sodium hydroxide from alkaline waste solutions; The separation process uses ion-selective membranes to separate sodium from the bulk of the waste constituents under an applied electrical field. The sodium is recovered as a 10-15 wt % solution of sodium hydroxide. Results of bench-sc3Ie and pilot-scale tests with simulated and radioactive waste solutions are presented.

Jan 1, 1999

By Ann M. Hagni

Microscopic and sub-microscopic gold commonly occurs in the sulfides pyrite (FeS2) and arsenopyrite (FeAsS). To recover refractory gold from pyrite and arsenopyrite, these sulfides are roasted to create porosity and permeability prior to cyanide leaching. A new technique of adding Ca(OH)2 and roasting. lime roasting. is being tested for retention of contaminant sulfur and arsenic and effectiveness of gold extraction. The lime roasting of pyrite at 500°C contains anhydrite (CaS04). oldhamite (CaS). calcium sulfite (CaS03). hematite (Fe2O:J), magnetite (Fe304). and minor amounts of pyrrhotite (Fe1.xS) and pyrite. At 600°C. 650°C and 700°C. the main constituents are anhydrite. oldhamite. and hematite. At 750°C. 800°C. and 850°C. anhydrite and hematite are the predominant phases with minor oldhamite. The roasted arsenopyrite at 450°C contains arsenic sulfides. calcium sulfite. hematite. and minor oldhamite. magnetite. and pyrrhotite. At 650°C. 700°C, 750°C. and 800°C, anhydrite, oldhamite. arsenic sulfides, and hematite are present. At 850°C. the same minerals are present with only minor oldhamite. The textures indicate excellent porosity and permeability at high temperatures. At lower temperatures, rims of low porosity and permeability surround many of the pyrite and arsenopyrite particles, and the complete oxidation process from pyrite to pyrrhotite to magnetite to hematite can be observed in individual particles. Additional process mineralogy techniques employed in this study are electron spectroscopy for chemical analysis (ESCA) and cathodoluminescence microscopy (CIM) in the determination of the calcium-sulfur-oxygen phases. Automated scanning electron microscopy-energy dispersive spectroscopy was utilized to analyze particles for gold content. Reflected light microscopy (RIM) revealed arsenopyrite and pyrite encapsulated in quartz particles of the gold-bearing concentrate, gold roast calcine, and cyanide leach residue.

Jan 1, 1991

By Yufeng Guo, Tao Jiang, Jianjun Fan, Haizheng Hao

"Function of High Pressure Roll Grinding (HPRG) in production of oxidized pellets from magnetite concentrate as raw material was systematically studied. It was found that bentonite dosage decreased from 1.3% to 0.8% if specific surface area of magnetite concentrate pretreated by HPRG was up to 2553.41cm2.g-1. The green ball quality improved obviously due to the increase of specific surface area and fine particles content, and the improvements of size distribution and the ballability of pretreated materials. However, the decrease of pellet porosity accelerated the primary solid phase reaction and oxidation reaction, which made the pellets surface form compacted layer that handicapped the diffusion and migration of oxygen, promoting the formation of double layer structure of finished pellet. Consequently, the compression strength of preheated and roasted pellets was not markedly improved by HPRG.IntroductionWith the increase of proportion of pellets in the BF recently, the technical-economic index of BF has obviously been improved. Consequently, the production and the quality of BF pellet are given more attention [1]. However, with the decrease of the quality of iron ore concentrate, the problems such as poor ballability, high bentonite dosage, high preheating and roasting temperature are becoming the great challenges to not only the quality of finished pellets, but also the energy consumption [2, 3]. In order to overcome these problems, mechanical pretreating technologies such as the High Pressure Roll Grinding (HPRG) and Damp-grinding are widely applied. HPRG has a number of advantages such as low energy consumption, high productivity and easy-maintaining. It is more economic and environmentally friendly than the Damp-grinding technology [4, 5]. A great number of experiments have revealed that HPRG can improve the quality of hematite pellets. Although there are some studies of function of HPRG in the magnetite oxidized pellet production, they are not comprehensive and systematic, especially to the preheating and roasting system [1, 2, 6, 7]. Accordingly, the influence of HPRG on the pelletizing system and the preheating and roasting system are systematically studied in production of magnetite oxidized pellets in this article."

Jan 1, 2011

By Tetsuya Uda, Sakae Shirayama

"With the aim of producing nickel (Ni) metal directly from acidic aqueous solution containing cobalt (Co) and other impurities, selective reduction of Ni was examined. As a preliminary experiment, sodium hypophosphite monohydrate (NaH2PO2·H2O) was selected as a reductant, and reacted with aqueous solution containing 0.1 mol L-1 nickel sulfate (NiSO4·6H2O) and 0 ~ 0.05 mol L-1 cobalt sulfate (CoSO4·7H2O) for 3 hours at 90 °C. As a result, it was revealed that Ni was selectively reduced and separated from Co in the acidic region (pH= 4.8). In this study, differences of reduction behavior between Ni and Co were investigated, and the feasibility of Ni I Co separation by the selective reduction of Ni was discussed.IntroductionEfficient Ni condensation and separation from Co are essential in nickel hydrometallurgical processes. Currently, the hydrometallurgical production of Ni from oxide ore is mainly carried out by acid leaching at elevated temperature, followed by the removal of impurities using neutralization, and condensation of Ni and Co into intermediate products such as hydroxides and sulfides. Then, the intermediate product is dissolved in acid aqueous solutions, and Ni I Co separation is conducted by solvent extraction. Finally, Ni and Co are recovered by electro-winning. This complicated process consumes large amounts of alkali, hydrogen sulfide (H2S), and organic solution in a multiple-staged process'. To reduce the consumption of these chemicals, it is important to recover Ni more efficiently from acidic aqueous solution containing impurities."

Jan 1, 2014

By Xin Zhang, Xu Zhang, Hao Bai, Ning Li

Organic Rankine Cycle (ORC) is an effective technology for low-grade waste heat power generation. In this paper, the thermal-dynamic performance of ORC system, in which low-temperature waste heat (from 40-140oC) is used as heat source, was evaluated with software RefProp8.0. The result indicates that in the range of low temperature, the working fluids like R601, R601a, R600a, R141b, R245fa and R245ca have better thermal performance. Furthermore, pilot-scale experiment using R245fa as working fluid was conducted, which validated the operation of the system for low-grade waste heat recovery. Finally, the economic feasibility of ORC has been analyzed for an ORC system using the waste heat from quenching water of blast furnace slag (80oC). According to the analysis, the project is reasonable in economy because the recovery period of investment is less than 4.2 years and environment-friendly since the CO2 emissions can be reduced by almost 43650.68t annually.

Jan 1, 2016

By Larry G. Twidwell

The removal of dissolved arsenic from mine waste waters utilizing a lime/phosphate precipitation technique has been studied on a laboratory scale at Montana Tech of The University of Montana and on a pilot scale at MSE Technology Applications as a wastewater treatment process potentially capable of removing dissolved arsenic to <50 µg/L. Arsenic bearing lime and lime/phosphate slurries were subjected to laboratory extended-time air-sparged aging for over four years. The lime slurries released their arsenic back into solution in a relatively short period of time, whereas the lime/phosphate slurries showed limited release of arsenic. The developed process has been pilot scale tested by MSE-TA for the EPA Mine Waste Technology Program on three waters, ASARCO smelter blowdown water, ASARCO thickener overflow water, and Mineral Hill Mine groundwater. The laboratory study results will be presented and discussed in this presentation. The pilot scale results will be presented and discussed in a companion presentation. Stability, Aging, Apatite, Johnbaumite

Jan 1, 2005

By Ki Joo Sim, Sung Beom An, Joonho Lee, Minsoo Shin

Valorization of the electrical arc furnace oxidizing slag by coke was carried out by the reduction of iron oxide in the slag. Since the reduction of iron oxide by solid carbon is an endothermic reaction, supply of heat energy is required. In addition, slag has a low thermal conductivity; traditional fuel injection is not suitable for this reaction. Microwave can be used to supply heat energy to the system. Commercial oxidizing slag was reduced by coke under the microwave irradiation (1.7 kW, 2.45 GHz). The maximum recovery ratio of iron was 87%. In addition, slag composition modification was attempted to use the remaining slag for a mixture in cement clinker. Free-CaO in the slag was successfully suppressed, and the use of the remaining slag as a potential mixture was confirmed.

Jan 1, 2014

By E G. Prado

We have confirmed on bench scale the removal of chlorides and alkalies (+95%) and over 2/3 of the zinc, lead and cadmium from EAF dusts. This has been achieved with arrononium acetate solutions alone, or with combinations of water wash, amonia-ammonium carbonate and ammonium acetate solutions. Also confirmed are the process routes for the recovery of the aforementioned elements into marketable products. The technology involves the complete recycling of the reagents. The FAF residue is returned to the electric furnace without risk of impurities buildup. Commercial scale testing with the recycled dust was satisfactory, including quality of the slag and its behavior during the melting stage. A cursory feasibility evaluation is presented.

Jan 1, 1994

By Uchil Jayagopal, M. Krishna, P .. V. Krilpakara, S. Manjunath

"There have been a pioneering efforts over the last forty years in the development of metal matrix composites (MMCs) as a new engineering materials, having improved properties, light weight characteristics and competitive costs compared to traditional materials. Following recent advancements in casting technology and the use of melt stirring device by foundries, discontinuously reinforced MMCs where prominent alloys are reinforced with particulates or short fibres and the being employed ·in the production of castings targeted for automotive and aerospace application.The ZA-27 alloy has a high strength compared to zinc or alluminium alloys with a lower melting temperature. The main objective of the present research is to study the effect of quartz particles on the mechanical behaviour of ZA-27 alloy composites. The results showed that the ultimate tensile strength, hardness, Young's modulus of the composite gradually increased with increase in the weight percentage of the quartz reinforcement. However overall ductility decreased with an increase in quartz reinforcementIntroductionMetal matrix composite (MMCs) offer outstanding benefits as they combine metallic properties with ceramic properties there by yielding improved physical and mechanical properties.1Among the various type of MMCs particulate reinforced composite are the most versatile and economical2. By suitable choice of metal matrix and particulate system a wide range of properties combination can be obtained such as strength, modulus, fiiction.al resistance, tribological performance and machinability. These composites are capable of replacing conventional alloys in a considerable range of applications. They also offer significant saving in energy and resources"

Jan 1, 2000

By Marcos Aurélio S. Costa, Nilton F. Nagem, Andreia B. Henriques, Herman S. Mansur, Alexandra A. P. Mansur, Antonio E. C. Peres, Valeria G. Silva

The superfine material generated in the Bayer process was used in one innovatively way as a precursor to geopolymerization techniques because of the presence of Gibbsite. Gibbsite can play a role in system adjustment because of the SiO2/Al2O3 ratio. Furthermore in the geopolymeric system it was studied the influenceof the additives such as kaolin, metakaolin and sodium trisilicate in an alkaline media. Others conditions to form the geopolymer were also evaluated such as solid/liquid ratio, SiO2/Al2O3 ratio and total alkaline. The raw materials and geopolymeric products were characterized by several techniques e.g. XRD, DSC, FTIR and SEM. Through the FTIR technique it was observed an increase in intensity and bandwidth in the region centered at 1010 cm-1, which is related to the asymmetric vibration Si(Al)-O, this is an indicating of the possible geopolymer formation This broadening of the band promotes a relative disappearance (overlapping) peaks at 965 and 935 cm-1 associated with raw material (ESPDust).

Jan 1, 2015

By Renato G. Bautista

The chemistry of the separation of metals from each other and from the other undesirable components involve multiple simultaneous chemical reactions. In the case of leaching, the heterogeneous chemical reactions between the solid and the liquid phase may be limited to a few reactions. In the homogeneous liquid phase, the number of simultaneous chemical reactions could be double or triple that of the number of heterogeneous reactions:. The rate of dissolution becomes very dependent on the changing concentrations of the significant chemical species taking part in the multiple reactions in both the heterogenous and homogeneous phase. The rate expression developed for the process must take into account the mechanism of chemical reactions in order to best represent the actual process. This paper also examine the role of mass transfer with chemical reaction in the develpoment of the rate equations for dissolution, liquid-liquid extraction, membrane separation, precipitation, and electrodeposition.

Jan 1, 1996

By Gerhard Bayer

X-ray and thermoanalytical studies were carried out on the formation and stability of Ca-, Mg-and Mn-tungstate, and of the corresponding minerals scheelite and wolframite. The tungstates were synthesized by different methods: precipitation from solution, solid state reactions, displacement reactions with solutions and in the solid state. The reactivity of natural scheelite and wolframite with different salt solutions and in mixtures with other minerals was investigated.

Jan 1, 1989

By William Gregg

Recent environmental and workplace safety legislation has Imposed more stringent limits on the amount and type of particulate emitted Into the air. In the past, the mass of particles contained In a volume of air was the governing criteria. Now the size and precise chemical nature of the particulate must be known and controlled In addition to it&apos;s ?mass. Processors of metallic materials have to implement stricter control practices and more efficient control equipment to meet the new regulations. Pulse-Jet dust collector systems are being used to control particulate emissions from various process gas streams. Pulse-jets :are also being used for maintaining a healthy environment In the workplace. this paper will discuss the impact of these regulations, the control techniques used to comply with such regulations, and the equipment needed for compliance.

Jan 1, 1992

By V. M. Lsoitko

Statistical methods of technological mineralogy are used to model processing flowsheets in order to improve ore dressing efficiencies. The procedure involves determining geological and mineralogical characteristics of ores, classifying ore types and metallurgical procedures, and developing computer programs to interpret essential mineralogical parameters from on-stream analysis data. The on-stream analysis data include magnetism, radioactivity, luminescence and assays. The data are interpreted by computer and appropriate adjustments are made automatically in the plant.

Jan 1, 1989

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 Zhihao Yue, Honglie Shen, Yahui Teng, Ye Jiang

"In this paper, manganous nitrate [Mn(NO3)z] was used to assist the etching of silicon wafer in hydrofluoric acid (HF) for the antireflective application, and alumina (Al2O3) layer was deposited on the surface of the etched sample by atomic layer deposition method for further antireflection. The surface morphological and compositional studies of these samples were performed by scanning electron microscopy attached with an energy-dispersive X-ray spectrometer. The surface reflectance measurements were carried out using UV-Vis-NIR spectrophotometer. Binary structures of pyramids and nanopores were obtained by etching the alkaline textured monocrystalline silicon wafer in HF and Mn(NO3)z mixed solution for not more than 15 min. But excessive increase of etching time of up to 30 min resulted in the whole destruction of pyramids. The average reflectances of the 5-min-etched sample before and after being coated with 75-nm-thick Al2O3 layer are 4.62% and 3.47% in the range of 200-1000 nm, respectively.1. IntroductionAs we know, the reflectance of silicon wafer after being sliced is so high that the maximal photoelectric conversion efficiency of silicon based solar cells is limited. Therefore, alkaline texturization process was used for silicon solar cell in industrial production. But the reflectance of this alkaline textured wafer is still greater than 10% and this process can only be used for monocrystalline silicon solar cell."

Jan 1, 2013

By Fuming Wang, Xin Lu, Hao Bai, Hebin Zhu

"In this study, CO2 emissions and carbon footprint of a typical steel works with integrated process and iron and steel industry in China was calculated and analyzed by a carbon footprint method based on the model of process CO2 emissions in iron and steel making. The carbon footprint of iron and steel industry from 1991 to 2010 in China showed a rapid increasing tendency. In 2008, the CO2 emissions of iron and steel industry in China was 1.289 billion tons, 19.71% of the national total CO2 emissions, and the corresponding carbon footprint was 159.13 million hm2 of green area. Carbon deficit of iron and steel industry also go up gradually if considering the carbon storage by green vegetation. Thus, the internal carbon reduction strategy, such as energy structure optimization and energy saving technology, was mainly encouraged for the sustainable development of iron and steel industry in China.IntroductionThe Global Warming resulting from the increase of Greenhouse Gases (GHGs), in particularly CO2, in the atmosphere has become the main reason of global climate change, and large emission reductions are required for sustainable development [ 1]. The iron and steel industry is the largest energy consuming manufacturing [2] in the world and the largest emitter of CO2 emissions. In 2005, it accounted for about 20% of global industrial energy use and 30% of energy and process CO2 emissions from industry [3]. In China, the crude steel has firmly been ranking at first of the world recent years and kept growing tendency year by year. With the production growth, the CO2 emissions of iron and steel industry also increased significantly and hence the steel industry has become one of the most sources of CO2 emission in China [4], which has attracted more and more attention to seek the carbon reduction strategies.Carbon footprint is an important and useful concept originating from Ecological Footprint, which was used efficiently to quantitatively analyze the impact of the human activities on ecological system, in particularly impact of the human energy activities [5]. In the view of Life Cycle, the carbon footprint is efficient to analyze the direct and indirect CO2 emission in the whole life of various products used in human activities. As to the iron and steel, the important materials and products in the human life, the carbon footprint analysis is quite necessary to evaluate the CO2 emission impact on the corresponding ecological system and global environmental."

Jan 1, 2013

By Michael Altepeter

Big River Zinc Corporation, located in Sauget, Illinois, operates a neutral leach residue circuit. The residue produced in the circuit is sold to lead smelters for subsequent recovery of valuable metals. A research program was initiated several years ago to find a means of treating the residue at Big River Zinc to recover the valuable metals. The Ausmelt submerged lance reactor was selected as the best alternative for the first step of the process. Pilot scale tests were conducted at Ausmelt&apos;s facilities in Melbourne, Australia. Separations were excellent. 99%+ of the Zn, Pb, Cd, and Ag contained in the residue reported to the oxide fume. 99%+ of the SiO2,, Fe, Mg, and Ca in the residue reported to the slag which passed the EPA TCLP test. Subsequent leaching of the oxide fumes and purification of the leach solutions using conventional procedures produced solUtions suitable for zinc electrowinning and an upgraded lead sulfate cake for sale.

Jan 1, 1992

By O. Norman Lotter

The formulation and use of mixed collector suites in sulphide flotation can be traced back as far as 1957 with the work of Glembottskii and his co-workers in Moscow. The subject was reviewed by Lotter and Bradshaw in 2010, and proposed a synergy between ideally-selected different reagent types to deliver improved performance, in particular the in situ catalysis of a xanthate to dixanthogen by a dithiocarbamate. Correctly formulated for a particular application, an optimally arranged mixed collector suite delivers the following improvements to the flotation process: • An increase in the flotation kinetics • Improvement in coarse, or middling, particle recovery • Reduction in total dosage requirement • Best results are found from testing the ratios of the collectors. This is of critical importance. In all an optimally formulated mixed collector system usually delivers an increase in paymetals recovery of 1–4% absolute, with a gain in concentrate grade in the range 10–20% relative. In recent years, the addition of semi-conductor theory and associated electrochemistry has contributed significantly to this toolbox by way of identifying optimum domains of Eh and pH for the flotation of individual minerals. In the case of mixtures of minerals, this is where the mixed collector system delivers significant value by way of presenting a mixed set of collector radicals and dimers in a common Eh and pH domain for overall performance. This calls on a fundamental understanding of organic chemistry, mineralogy, semiconductor theory, and electrochemistry. Whereas the selection of grinding media type effectively influences the Eh, the pH can be easily controlled by pH modifiers. The theory of this system, and some industrial case studies, are discussed.