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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 KNona C. Liddell

The time and spatial dependence of component and species concentrations during in situ uraninite leaching have been modeled using a reactive transport model based on partial equilibrium between reactive minerals and the solution. The flow field is represented by mixing cells in series. The effects of the H2O2, (NH4)2CO3, and NH4HCO3 component concentrations have been simulated, and results are presented for a one-dimensional flow field.

Jan 1, 1995

By Sung Jin Han

Magnesia-based refractory is generally used in an electric arc furnace (EAF) due to its relatively high corrosion resistance and strength at high temperatures. However, the magnesia refractory is attacked by EAF slag and thus the lining life continuously decreases. Thus, it is significant to identify the interfacial reaction between magnesia refractory and FeO-rich EAF slags. In the present study, the influence of FeO-rich slag on the corrosion behavior of MgO refractory was evaluated. The (Fe,Mg)Oss layer was observed at the slag-refractory interface and its thickness increased with increasing content of FeO in the slag. The specific reaction phenomena and formation behavior of (Fe,Mg)Oss layer were evaluated by thermochemical computing program, FactsageTM7.0.

By John A. Gisby

Phase equilibria for multi-component systems can be calculated reliably from critically assessed thermodynamic data for sub-systems using software packages like MTDATA, developed by the National Physical Laboratory, UK (NPL). Models and data resulting from an ongoing Mineral Industry Research Organisation (MIRO) project make such calculations possible for the complex systems encountered during sulphide smelting, involving interactions between matte, slag, metal, and gas phases. Predictive calculations can be made that are directly relevant to industrial processes, covering composition and temperature ranges beyond the scope of hard- copy phase diagram compilations, allowing the feasibility of more economic and environmentally sound routes to be explored, better choice of materials to be made, and pilot plant studies to ,be directed more efficiently. Current applications include the selection of suitable fluxing practices in copper and nickel smelting, analysing the operation of the Kennecott copper smelter, optimising the recovery of precious metals and investigating refractory wear.

Jan 1, 2002

By Guozhu Ye

"One of the most essential problems associated with the treatment of EAF dust is its high content of halogens. For most thermal processes for zinc recovery, such as the plasma processes with a zinc condenser, the halides in the gas stream will form a dross phase that results in a low zinc yield. For those with zinc oxide as main product, such as Waelz oxides, the high halogen content in the product implies a great degradation of the product quality and the product can only be sold at a low price. Further processing of zinc oxide with high halogen content either by pyrometallurgical or hydrometallurgical processes will also result in process problems.This paper will review the pre- and post-treatment alternatives for halogen removal based on the comprehensive characterization work that has been carried out at MEFOS and the preliminary experimental results.The experimental results show that chlorine and fluorine content could be reduced to 450 ppm and 50 ppm respectively by selective sulfation, and to about 200 ppm by soda leaching. Selective sulfation of zinc oxide in the EAF dust will also be discussed."

Jan 1, 2000

By M. S. Moats

A considerable amount of research has been conducted to determine the causes of anode passivation. Chemical and electrochemical reactions that occur after passivation have received little attention. Chronopotentiometry, linear sweep voltammetry, cyclic voltammetry, and impedance spectroscopy have been used to elucidate three reactions that occur after passivation of commercial copper anodes. These involve the dissolution of silver and subsequent cementation and transformation of selenides, the oxidation of lead sulfate to lead oxide, and oxygen evolution. The amount of silver dissolution depends on the silver content of the anode, the time to passivation, and the molar ratio of Ag/(Se+Te). The oxidation of lead from PbSO4 to PbOx explains a potential plateau of oxygen evolution. Silver affects the duration of oxygen evolution on the PbOx. Anodes containing kupferglimmer display a characteristic oxygen evolution potential. It is believed that kupferglimmer provides a lower overpotential for oxygen evolution than the other slime phases or passivated surface.

Jan 1, 1999

By N. Solak

CrN, TiN and Ti-B-N coatings were deposited onto H13 hot-working tool steel and alumina substrates by arc-PVD. The coatings were characterized with respect to their mechanical and structural properties. Oxidation behavior of the coatings on alumina substrates was investigated by TG/DTA. Samples coated on H13 substrates were oxidized in a tube furnace under atmospheric conditions at specific temperatures determined from TG/DTA tests of the same coatings deposited on alumina substrates. The oxide scale morphology was characterized by scanning electron microscopy and X-ray diffraction. Oxide scale thickness change and TG data were used to calculate oxidation reaction activation energies. It was determined that boron addition into TiN coating improves not only mechanical properties but also oxidation resistance. Depending on the substrate material different oxidation activation energy values for the TiN and Ti-B-N coatings were determined revealing the importance of film morphology on oxidation resistance.

Jan 1, 2006

By A. Kapilashrami

Slag foaming proves to be both blessing and curse for the process productivity, depending on where in the process it occurs. In pyrometallurgical processes, slag foaming is often a result of chemical reactions taking place in the slag. As the slag composition and reaction rates are changing, foaming occurs under dynamic conditions. In the present work, slag foaming was studied with XRF. The foam displayed a fluctuating behaviour, unaccountable by existing models. The concept of foaming index was found not to be satisfactory in describing the foam, resulting in the need for alternative theories. The rate of fluctuations was seen to be related to the difference between rate of gas generation and rate of gas escape from the system (Ug-Ue) as well as the bubble sizes. Thus, model development of dynamic foaming phenomenon has to take the effective chemical reaction rate as well as the bubble sizes into consideration. The first step in obtaining foam is to form bubbles. In the present work, gas bubbles were generated through chemical reaction at interface between two immiscible liquids and the bubble formation was studied optically. The gas bubble size was seen to be uninfluenced by the reaction rate. However, bubble formation was seen to take place in one of the phases and since the bubbles consequently traversed the interface under the influence of buoyancy, the viscosity of the first phase was found to influence the final bubble size where increased viscosity would yield a larger bubble size.

Jan 1, 2006

By Vladimir Lobanov, Pritchinm Alexander, Nikifor Ageev

"Sulfuric anhydride is one of the most voluminous technological emissions. The possibility of high-temperature SO2 oxidations without catalyst in presence of calcium-bearing filling materials (CaO, Ca(OH)2 and CaCO3) with obtaining of binding material on the basis of waterless calcium sulfate is studied. Due to application package HSC-4 the thermodynamic analysis of the specified interactions is made and following conclusions are drawn: 1) Reactions are feasible in the all range of investigated temperatures (400 – 1000 °?); 2) The best results should be expected at use of ???; 3) The heat of reaction does possible autogenous behavior of process. The researches have shown: 1) Practical possibility of the process; 2) SO2 oxidation without the catalyst is feasible in presence of ???, Ca(OH)2 and CaCO3; 3) The optimum temperature range is 600-800 °?; 4) The content of waterless calcium sulfate in a product reaches 48% that makes it possible to use as the binding material; 5) At excess of ??? the degree of SO2 collection is nearer to 100%. Introduction At processing of sulfide raw materials in metallurgical furnaces the significant amount of sulfur, mainly in the form of sulfuric anhydride is escaped. Rich gases (SO2>3 %) are used for the sulfuric acid or element sulfur production. Chemism of sulfuric acid manufacturing is based on catalytic high-temperature oxidation of anhydride. Poor gases of metal works (SO2 =2,5 %) and power combustion units (SO2 =0,5 %) after clearing discharge into the atmosphere. Commonly, to recovery of weak sulfuric anhydride the chemical and physicochemical methods are applied. A few chemical ways of recycling sulfur dioxide are applied practically. In a number of methods for SO2 recovery a pulp of metals oxides (magnesium, zinc, etc.) with formation of sulfites is used. In other case sulfuric anhydride is catch by weak sulfuric acid in the presence of an oxidizer (pyrolusite ore). Methods of absorption SO2 by solid sorbents, (carbon fibers, silica gels, zeolites) are known and put into practice. Regeneration of the saturated sorbents is realized by thermal decomposition or extraction. Obtained as a result high-concentrated solutions are a commercial product."

Jan 1, 2008

By B. J. Beaudry

Intermetallic compounds are frequently required in the form of thin sheets for magnetic refrigeration and other applications. Progress has been made in the preparation of thin sheets of brittle gadolinium intermetallic compounds by hot rolling of sheathed billets. The effect of fabrication procedures on the Curie temperature of GdPd and its heat capacity at low temperatures has been studied.

Jan 1, 1989

By Zviad Kovziridze

The problems related to the production and research of SiC-Si3N4 composite are presented. The technology of producing the protective casings for tips and thermocouples is developed. Optimum composition charge and technological parameters are defined. The results of casing testing at production plants are presented.

Jan 1, 2006

By Morimasa Ichida

One of the key factors of stabilized blast furnace operation under the conditions of high productivity and high pulverized coal rate is to enlarge the raceway to reduce the dead man area. With a reduced dead man area, the descent area is enlarged and the central gas flow is maintained at the same time. In this study, raceway furnace experiments were conducted with tuyere velocity and coke strength changed both in hot and cold conditions to measure the coke degradation rate. Using the coke degradation rate measurements, we examined the equivalent relation between the coke strength and tuyere velocity for coke degradation in the raceway. In addition, in this paper, we discuss the increase in tuyere velocity in relation to an increase in coke strength.

Jan 1, 2006

By Ximena Massone

Chile is the most important copper producer in the world and the mining sector plays a key value in its economy. However, at present the country does not have a satisfactory set of regulations about closure and restoration of mining operations. In our country many mining operations will, in the near future, shut down their activities, therefore, it is of utmost importance to elaborate and enforce a set of regulations to prevent risks and to protect the environment. The present study is focused on reviewing and analyzing the existing national regulations about the closure of mining operations and preparing a comparative analysis with other international regulations of countries with mining experience. The final results of the study will be a legal proposal to regulate the closure of mining operations in Chile, aiming at minimizing the potential environmental adverse impact, internalizing the social costs by the relevant operators and defining all aspects of liability for the environmental damage.

Jan 1, 1999

By Xiyun Yang

Magnetite was prepared by hydrogen reduction method. For a conversion to cobalt-modified magnetite, magnetite particles were suspended into a solution containing Co2+ and Fe2+ to precipitate a cobalt ferrite layer on the surface. pH value influences the particle composition directly, the desirable CoFe2O4 is obtained when pH value is 12. The coercivity increases with the increase of cobalt content, cobalt efficiency reaches a maximum value at cobalt content of 2.71wt%. With cobalt modification, magnetite particles have similar lattice constant and squareness ratio to that without cobalt modification. TEM and XPS analyses indicate that acicular morphology is retained during the coating process, the epitaxial growth layer consists of CoFe2O4and 0.3Co2O3CoFe2O4 at cobalt content of 2.71wt% and 5.03wt%, respectively.

Jan 1, 2006

By Jae-Chun Lee

Di-2-ethylhexyl phosphoric acid (D2EHPA) is widely used for separating rare-earth elements. In commercial plants, rare-earths are usually stripped from loaded extractant streams using mineral acid, then precipitated as oxalates. Many rare-earth uses demand specific powder characteristics, which are obtained by secondary processing. This paper demonstrates the feasibility of combining the stripping, precipitation and powder processing stages, thereby achieving considerable savings. MEHPA solutions were loaded with yttrium, then emulsified with oxalic acid-HC1 solutions to precipitate yttrium oxalate, which was readily calcined to yttrium oxide. The precipitation kinetics and yield were sensitive to process conditions. The morphology and size of the yttrium oxalate powders varied with the concentrations of D2EHPA and oxalic acid, and the presence of SPAN 60, which affected nucleation, growth, and the emulsion characteristics.

Jan 1, 1992

Iron, chloride and manganese are the three major impurities transferred to copper electrowinning tankhouses via chemical and/or physical entrainment. The control of these impurities via bleeding of tankhouse electrolyte is costly. Recently, Eichrom Industries have developed an improved iron control process and tested this process in a pilot study at the Girilambone Copper Company (GCC). The patented process utilizes a fixed bed ion exchange reactor filled with Eichrom's Diphonix® resin. Iron is loaded on the resin and subsequently eluted by a cuprous sulfate eluant. The control of chloride and manganese has been studied using different chemical techniques. The removal of chloride from electrowinning electrolytes was tested using precipitation of chloride as cuprous chloride. Copper wire cuttings are used to produce cuprous ions. Chloride levels are reduced to around 30 ppm in electrolyte at 40°C. The removal of manganese using a precipitation process practiced in zinc electrowinning purification has been tested for implementation. The process involves reacting manganous ions in solution with permanganate ions. The reaction produces an insoluble manganese dioxide reaction product. The bench scale and pilot plant results from testing of these purification processes are reported.

Jan 1, 1999

By Rikiya Kamezawa, Rudiono, Manabu Takeuchi

"Schottky type solar cells based on phthalocyanine (Pc) thin films were fabricated, and their photovoltaic performance was investigated in various ambient atmospheres. Most of cells prepared in this study showed a good rectification and photovoltaic effects in the visible wavelength region. The introduction ofN02 gas into the measuring chamber was confirmed to increase the current both in dark and under light illumination. However, chemical reaction between the Al electrode and N02 formed some oxide and deteriorated the Schottky barrier, resulting in an increase in cell resistivity. SF 6 gas also showed similar effects on the cell performance.IntroductionPhthalocyanine is one of the typical organic semiconductors, which shows high photoconductive sensitivity in the visible to infrared region. Today, several kinds of metal phthalocyanines are used in electrophotographic photoreceptors. In addition, application of phthalocyanines to solar cells have also been trying by many workers [1, 2]. Many efforts have been made for improving performance of phthalocyanine solar cells by modification of device structure [3, 4], doping by dye or pigment [5, 6] and incorporation of metal clusters [7]. It is known that electrical conductivity in phthalocyanine is increased by adsorption ofNO2 [8, 9]. We tried to improve photovoltaic performance ofphthalocyanine solar cell by adsorption ofNO2. This paper describes the influence of N02 adsorption on the photovoltaic behavior of phthalocyanine solar cells."

Jan 1, 2000

By M. A. Llavona

The study of the formation and components of copper patina and its conservation has assumed great importance. The changing environment has accelerated the processes of patinas degradation; thus, the exhaustive study of factors capable of affecting the patina formation, growth and durability has assumed great importance for the industrial activity of copper. The main components of the patina, oxides, chlorides, nitrates and sulfates, have been determined; the effect of physical, chemical and microbiological factors on patina formation, particularly the influence of acid rain, natural organic matter, particles and microorganisms have been defined. The effect of different electrolytic solutions that accelerate the formation of copper patinas has been determined, and a review of the state of knowledge of the formation and evolution of metal patinas has been made.

Jan 1, 1999

By Matthew D. Andriese, Jiann-Yang Hwang, Zhiwei Peng

"It has been demonstrated that metallic-bearing minerals are physically liberated from host rock when exposed to microwave (MW) energy. The metallic minerals are iron sulfides and spinel oxide minerals contained in peridotite rock. Experimental evidence has shown ore particles readily couple with MW energy at 2.45 GHz, 1000 W resulting in rapid heating. Thermal stresses are generated by highly absorbing metallic-bearing minerals resulting in cracking and embrittlement of ore particles that assists in crushing and grinding processes. The liberated metallic-bearing minerals are shown to report to coarser size fractions as a result of MW exposure.IntroductionComminution of ore material during beneficiation is a large energy expenditure for the mineral processing industry. Crushing and grinding operations alone consume 50-70% amount of energy used in mineral processing [1]. Size reduction becomes increasingly difficult with decreasing particle size making grinding the most energy-intensive step of comminution. The aim of comminution is to maximize liberation of economically valuable minerals from the host rock [2]. Overall, the less material that needs to be handled, then grinded, to create a useful product for hydro/pyro metallurgical processes will achieve the greatest reduction of energy.Much of the scientific interest for use of microwave (MW) energy in mineral processing has been for improved hydro/pyro metallurgical techniques [3-6]. Early authors have employed MW energy for improved grinding of ore particles but most conclude the energy savings do not justify the energy input [7-9]. The effectiveness of MW assisted grinding is dependent on the ore mineralogy and the absorptive properties of minerals contained within it. Ore containing magnetic minerals should prove successful with MW assisted breakage from highly absorptive properties."

Jan 1, 2012

By Shaolong Chen

Feeding dry sulfide concentrate into smelting furnaces enhances process performance and reduces the energy consumption and exhaust gas flow. Direct heated rotary dryers and flash dryers have being replaced by rotary steam dryers featured by very low wear rate of the pipe heating elements and long maintenance interval. Impact of the drying processes on the environment receives more and more attention as the emission legislation tightens. In this regard, environmental factors such as SO2, CO2, dust and gas flow among rotary dryers, flash dryers and steam dryers were compared. Selection of a rotary steam dryer for copper and nickel concentrate drying would be an ideal solution to reduce the pollution of exhaust gas, as drying is achieved by indirect contact to the steam at relatively low drying temperature and as the off-gas contains almost only water vapor and air. The emissions can be significantly reduced and only small and simple off-gas handling units are needed.

Jan 1, 2006