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By N. Kanari

One of the criteria to define the market value of chromite concentrate is its chromium to iron ratio. Changing this ratio for a definite chromite mineral is impossible by physical processing. This study investigated the possibility of increasing this ratio through the carbochlorination and the oxychlorination of chromite concentrates. Experiments are carried out up to 1000 °C. The characteristics of samples and reaction products are determined by SEM, XRD and chemical analysis. The carbochlorination of a chromite concentrate at about 600 °C leads to the . selective partial elimination of iron allowing a higher Cr/Fe ratio of the treated concentrate. Selective extraction of iron could also be achieved at about 950 °C by oxychlorination. In this case, a part of chromium contained in the concentrate is recovered as chromium oxychloride. The obtained residue had high content of Cr, Mg and A1 oxides. Such material has probably better chemical and thermal properties that may. be useful for foundary and refractory applications. Two flow-sheets for the beneficiation of the chromite concentrates using carho- and oxychlorination are suggested.

Jan 1, 1997

By I. Gaballah

Spent hydrorefining catalysts may contain 4 to 6 % of COO and/or NiO, 8 to 16 % of Moo3 and up to 10 % V205 generally supported by alumina. Raw samples are roasted in order to eliminate carbon, sulfur and hydrocarbons contained in the spent catalysts. The roasting optimum temperature and time are 500 "C and 7 hours. Selective chlorination of roasted samples with Cl2 + air, Cl2 + N2 and Cl2 + CO is investigated in order to recover the valuable metals. Depending on the chlorination it is possible to recover more than 80 % of the Ni and Co about 95 % of the Mo and up to 80 % of vanadium compounds. Cobalt and nickel chlorides are obtained by leaching the chlorination residues' by acidified water. Molybdenum and vanadium chlorides and/or oxychlorides are obtained by selective condensation from the vapor phase. The chlorination of the catalyst support, Al2O3, can be limited to less than about 5 %. Besides the reaction temperature and time, the oxygen partial pressure of the chlorinating gas mixture appears to be the key factor for the reactions' selectivity.

Jan 1, 1993

By G. L. Hundley, D. N. Nilsen

The U.S. Department of Energy investigated the use of liquid-emulsion membranes (LEM) for the selective removal and recovery of metals such as copper and zinc from mine waste waters. This investigation included field tests of a mobile, pilot plant-scale, continuous-flow LEM system. The system was tested at copper mines with solutions containing from 100 to 1,400 ppm Cu, and at a zinc mine with a solution containing 115 ppm Zn. Typical results from the copper tests were >90% copper recovery, and zinc extraction from waste water also was typically>90%. Although all of these waste waters contained high impurity levels, pure products were produced. On several of these field tests, integrated systems were tested that resulted in recovery of metal by-products, selectiv~ precipitation of iron, and polishing to reach discharge targets for essentially all of the contained metals. In addition, some results are included from laboratory-scale tests.

Jan 1, 2000

By E. J. Peterson

Oil shale retorting induces mineral and chemical reactions to occur on the macroscopic and microscopic levels in the kerogen-bearing marlstone. The nature and extent of the reactions is dependent upon process variables such as maximum temperature, time at temperature, atmosphere, and raw shale composition. This report describes the investigation of the mineral, chemical, and trace element release properties of spent shales retrieved from an experimental in situ retort at Occidental Oil Shale, Inc. 's Logan Wash site in Garfield County, Colorado. Correlation between mineralogy of the spent materials and the mobility of major, minor, and trace elements are indicated, and relationships with important process parameters are discussed. The progress .of carbonate decomposition reactions and silicat ion reactions is indicative of the processing conditions experienced by the shale materials and influences the mobility of major, minor, and trace elements when the solids are contacted by water. Shale minerals that are exposed to the extreme conditions reached in underground retorting form high temperature product phases including akermanite-gehlenite and diopside-augite solid solutions, kalsilite, monticellite, and forsterite. The persistence of relatively thermally stable phases, such as quartz, orthoclase, and albite provide insight into the extremes of processing conditions experienced by the spent shales. Leachate compositions suggest that several trace elements, including vanadium, boron, fluoride, and arsenic are not rendered immobile by the formation of the high-temperature silicate produce phase akermanite-gehlenite.

Jan 1, 1981

By G. R. Palmer

The success of future electric vehicles will depend greatly upon the power supply choices made today. Research is presently being conducted by automotive engineers and electrochemists to determine what battery type may be the most promising. Not only are product production and application efficiencies being evaluated but also environmental concerns of reclamation and recycling. Rechargeable batteries using nickel-metal hydride electrodes are strong candidates for these electric vehicle applications. The U.S. Bureau of Mines is investigating hydrometallurgical technology that separates and recovers purified metallic components present in nickel-metal hydride battery scrap. Sulfuric, hydrochloric, and nitric acids are all capable of dissolving the battery electrode alloys given the proper operating conditions. Solvent extraction of the leach solutions using D2EHPA removes iron, and selective precipitation shows promise of recovering the other metals in the H2SO4 and HNO, systems.

Jan 1, 1994

By S. E. Khalafalla

A method for preparing ferrochromium alloys containing less than 2 pct carbon has been devised in a single vacuum furnace reactor. This method can conserve chromium and should reduce the capital and energy requirements relative to chromite electrothermal reduction. Reduced products containing less than 2 and as low as 0.01 wt pct carbon were obtained by reacting pellets of chromite and carbonaceous reductant mixtures at pressures of 0.1 to 1 ton and temperatures of 1,230° to 1,320° C. The extent of reduction increased with increased temperature and decreased pressure; however, operating conditions were limited due to the onset of significant chromium vaporization at higher temperatures and lower pressures. Foundry coke, anthracite, and carbon black were found to be superior to graphite as reductants. The reduction of chromite to metallics was found to proceed via the carbide intermediates Fe3C or Cr3C2. Lime accelerates the. rate of solid state reduction of chromite and can shorten the furnacin1r time at 1,3000 C under vacuum from 13 hours to less than three hours. Additional lime and silica are added to the hot reduced chromite after releasing the vacuum and raising the furnace. temperature to 1, 700° C. Soaking the charge for about 20 minutes gave a button of low carbon ferrochromium alloy beneath a well-defined slag layer.

Jan 1, 1985

By Jerold L. Johnson

Remediation of small-arms firing ranges is being investigated by the Naval Civil Engineering Laboratory and the U.S. Bureau of Mines. Scheduled closures of military installations, as well as the management of active ranges, require the development of methodologies for heavy metals removal to prevent their entering the surrounding environment. The impact berms contain high concentrations of metals, and the soil and vegetation surrounding the berms were found to have slightly elevated levels. The heavy metals characterized are in the form of whole bullets, a wide size distribution of free fragments, smeared lead on the surface of the soil grains, and very finely attached particles. Gravity beneficiation can remove liberated metal contamination effectively. Weak acetic acid leaching shows promise in lowering the final metal contamination to allow the ,soil to pass the Environmental Protection Agency's (EPA) Toxicity Characteristic Leaching Procedure (TCLP) criteria.

Jan 1, 1993

By N. A. Barcza

DC plasma-arc technology using a hollow graphite electrode (cathode) has been successfully implemented in the primary metallurgical industry in South Africa up to the 30 MW scale. Mintek has applied its expertise base, established over the past fifteen years, to testing the treatment of metallurgical wastes such as carbon- and stainless-steel plant dusts, lead- and zinc-containing slags, and residues from the base-metal industry. Favourable results have been achieved, and disposable products were produced. The evaluation of numerous wastes indicates that recovery of zinc as metal gives the best economic return from these sources. Direct recovery via a splash condenser or electrolytic zinc extraction from fume are the two preferred alternatives under review. In both instances dehalogenation is an important issue, but can be achieved by suitable treatment processes. The Enviroplas technology provides a flexible, commercially viable approach to the treatment of a wide variety of wastes. Mintek, together with its associate Pyromet CC, are installing a plasma- arc pilot-plant facility with both an ISP lead-splash condenser of about 5 t/d condensed zinc capacity and a combustion chamber to burn zinc vapour to zinc oxide. This will demonstrate the suitability of the Enviroplas technology for treating specific metallurgical wastes, so that customized industrial plants can be engineered based on large-scale testwork.

Jan 1, 1994

By H. Y. Sohn

The ignition and combustion of chalcopyrite particles under suspension-smelting conditions, in which the particle-particle interaction is neglected, has been analyzed by considering the intrinsic kinetics of oxidation and heat and mass transfer between the particle and its surroundings. Reasonable agreement has been obtained between the calculated results and experimental results from a laminar-flow furnace reported in the literature. This computation- al procedure has further been applied to flash-smelting conditions. Under suspension-smelting conditions (Sh = Nu = 2), chalcopyrite particles ignite at around 960 K. The effects of various parameters, such as oxygen concentration, particle size, and gas temperature, have also been evaluated. Comparison between calculated results in this work and experimental observations indicates that SO is the important gaseous product that forms at the surface of the particle.

Jan 1, 1993

By F. F. Aplan, G. Simkovich

"A review is given of the effects of solid state point imperfections upon a number of mineral benefication processes and a metal extraction process. It has been found in numerous flotation studies that small amounts of aliovalent impurities (dopants) in binary compounds may show major effects upon flotation behavior. Both semiconducting and ionic conducting compounds are affected. These effects are also seen in hydrometallurgical studies as well as in electrostatic operations. Additionally, de-copperization of lead melts appears to be strongly influenced by similar defects. It is hypothesized that the effects observed in these studies are present in actual operations and should be considered in designing processes. A few speculations concerning future efforts are advanced. IntroductionImperfections [point (e.g., vacancies, interstials, quasi-free electrons, electron holes, impurity ions), line (e.g., dislocations), two dimensional (e.g., grain boundaries) and three dimensional (e.g., 2nd phases) defects] are generally present in solid materials and these imperfections may, and often do, have important effects upon a variety of properties and processes. In general, one may, in most cases, attain elimination of three dimensional defects by a separation process of one type or another (e.g., gravity, electrostatic, magnetic, flotation, hydrometallurgical etc.,). Thus, this type of defect has rarely been investigated in a systematic fashion. Two dimensional defects are always present in non-single crystal materials but have also escaped systematic studies in processes primarily because the control of such defects is not easily attained. Line defects are non-equilibrium entities which are present in ill-defined quantities so that they present a variable that cannot be easily controlled although through careful systematic experiments one can attain some reproducible relations pertaining to this type of defect.Contrary to the lack of studies concerned with the effects of 1, 2 and 3 dimensional types of defects there has been some activity concerned with point defects and their effects upon a number of mineral/metallurgical processes, especially flotation processes. Thus, this article will present a review primarily of point defects in relation to their effects upon flotation although other processes and defects will also be mentioned."

Jan 1, 1988

By Mukesh K. Agarwala

Alloy composite parts were made from powders by Selective Laser Sintering (SLS). SLS is a rapid prototyping process that uses data from CADICAMICAE systems to guide a laser beam and rapidly form 3-D prototype parts from powders without any part specific tooling. In this study, Bronze-Nickel parts made by SLS were studied for their mechanical properties. To make the parts structurally sound, SLS parts were further processed by conventional isothermal sintering, without loss of shape. The resultant densification and mechanical properties were studied and related to microstructures and P/M densification models. These results were then correlated to the SLS processing parameters.

Jan 1, 1994

By P. M. Swash

The paper describes the use of mineralogical methods in the exploration and evaluation of primary diamond occurrences. The most common methods that are used include the systematic search for kimberlitic indicator minerals, surface textural study of the indicator minerals, (garnet, spinel, ilmenite and chrome diopside) and alluvial macrodiamond studies so as to understand their provenance and guide exploration towards diamondiferous targets. The mineral chemistry of the indicator is used to positively assess the origin of the mineral grains and is also pivotal in the determination of the diamond potential of a deposit. Petrography of the primary deposit is able to identify the body to be kimberlitic and is also a support to the mineral chemistry findings. Unambiguous proof of a prospects potential to contain macrodiamond is proven by the occurrence of microdiamonds in the residues from the rock. The presence of a sufficient number of microdiamonds in the rock is enough to determine a semiquantitative grade estimate and warrant further metallurgical evaluation so as to determine its actual macrodiamond content.

Jan 1, 1991

By C. P. Manning

This paper reports recent progress in the development of a unique metal extraction technology utilizing zirconia-based inert anodes for the electrolytic reduction of metals from their oxides. In this process, the target metal oxide is dissolved in an ionically conducting liquid solvent phase. An extended anode consisting of an oxygen-ion-conducting stabilized zirconia membrane in intimate contact with a catalytically active electronic phase and an inert electronically conducting cathode are inserted into the molten flux containing the oxide. When the appropriate electric potential is applied between the electrodes the target metal is reduced at the cathode and oxygen ions are selectively transported across the stabilized zirconia membrane and oxidized at the anode. When the process is conducted at temperatures between 1200-1400°C, the ohmic resistance drop across the stabilized zirconia membrane is low, and high current densities on the order of I A/cm2 or greater can be obtained. In addition, the process efficiency can be increased further by directly reforming hydrocarbon fuel over the anode. Laboratory experiments at Boston University have demonstrated the technical viability of employing zirconia-based inert anodes for environmentally sound production of metals such as magnesium, tantalum, aluminum, etc., directly from their oxides. Significant progress has been made in the application of this concept to the electrolytic reduction of magnesium at 1300°C. The research topics covered include stability of the zirconia membrane in the selected molten solvent (flux), volatility of the flux, electrochemical characterization of the electrolytic cell, and analysis of the metals produced.

Jan 1, 2003

By Suresh Sundarraj

A diffusion mass transport model for predicting the microsegregation in a solidifying and coarsening dendritic mushy region of a binary alloy is presented. Two versions of this model are tested; one based on expressing the solute concentration in terms of mole fraction and the other on expressing the solute concentration in terms of mass fraction. On comparing previous model data sets and conditions, used in the analysis of Aluminum-Copper systems, a number of inconsistencies emerge. These inconsistencies are resolved on identifying a single set of data and conditions which take account of compositional density changes, "non-linear" thermodynamics and dynamic coarsening. An additional investigation is carried out to study the effect of assumed cooling mechanisms.

Jan 1, 1992

By S. J. Thiele, T. Newton, W. Magalhäes, T. Takayama, J. Welsh

Companhia Paraibuna de Metais (CPM) is presently pursuing a zinc production expansion project. Besides increasing production, the goal of the project is to address existing problems while providing a platform for a proposed twofold increase in production in 2003/2004. Therefore, the current expansion strategy was formulated to address present and future requirements. Computer simulation modeling and full scale plant testing are being used to generate data to optimize the operating conditions and to perform a sensitivity analysis. The initial phase of the project, which will boost CPM's capacity to 86,000 t/y of marketable zinc, is to be completed in September 2000.

Jan 1, 2000

By S. Seetharaman

A mathematical model has been developed to evaluate the viscosities of melts at high temperatures. The viscous flow in liquid is described by the equation, {n = Aexp(AG*/RT)} based on the absolute reaction rate theory. The Gibbs energy of activation,{ AG* } is considered to be a function of the temperature as well as the composition of the melt. The model has been applied successfully to various metallic and slag systems from unary to quaternary. On the basis of this model, a relationship has been suggested to relate the Gibbs activation energy of viscosity to the Gibbs energy of mixing in binary metallic melts. The viscosities predicted from available thermodynamic data in the case of a number of binary metallic systems using this correlation show satisfactory agreement with the reported experimental values.

Jan 1, 1994

By James P. Bennett

The U.S. Bureau of Mines, Tuscaloosa Research Center, is conducting a review of the usage of different types of refractories, the current industrial practices to recycle/dispose of spent refractories, and the concerns associated with these practices. This information will serve as the technical basis for initiating a research program to recycle or find alternate uses for spent refractory materials. Approximately 1.6 million metric tons of clay based and 1.2 million metric tons of non-clay based refractory materials were manufactured in the United States in 1992 alone, representing a value of almost 2 billion dollars. Landfill has been and remains the disposal means of choice. Issues such as environmental regulations, concerns over landfill disposal, future liability, and product stewardship programs have brought about increased emphasis for recycling or alternate material use. Information on refractory consumption and the issues associated with recycling or disposing of used materials will be discussed, including current recycling practices.

Jan 1, 1995

By Stephen Gale, David Clarry, Edmund Smith, Jon Feldman

"In 2006, a Canadian steel maker embarked on an ambitious initiative to become “Best in Class in Energy Management”. This initiative provides the framework for this paper, with some augmentation from other energy management projects carried out by Hatch. The initiative focused on identifying energy/GHG management improvements leading to low-cost implementation of energy savings or GHG emission reduction. The key components of the approach were:• Review site energy management practices and benchmark internationally.• Review best technical practices and benchmark against public energy intensity data.• Conducted a site-wide Energy Assessment and physical review of operating areas.• Facilitation of on site-workshops with staff to prioritize savings opportunities, as well as identify and remove implementation barriers.• Development of an Energy Management Action Plan for implementation of improvements.Most organizations can produce, with relative ease, a list of ideas for saving energy, implementing them is the challenge. This paper addresses these issues as well as the profitability of the energy efficiency improvements and the consequences for GHG emissions.IntroductionWhen one of the authors was an undergraduate engineering student at the University of Cape Town in South Africa, the technical drawing instructor made a statement that was both humorous, and mildly profound. He claimed that the most successful engineer is one who is both lazy and diligent. Lazy, in the sense that the engineer is constantly on the lookout for an easier, more efficient, way to do something. Diligent, in the sense that the engineer will work tirelessly to come up with a good technical solution for the easier way. This paper, somewhat of an anomaly in a compilation of technical proceedings, hopes to break the mould a little, and to show a “lazy-diligent” way of reducing the carbon emissions from an industrial facility, using a steel plant as an example."

Jan 1, 2008

By Godwin J. Igwe

For soil remediation technology to be effective, a thorough understanding of the interactions between a targeted contaminant and the soil matrix is crucial. Proper selection of remediation technology, based on understanding the bonding/binding characteristics of the soil and contaminant, can often result in significant remediation cost savings. Contaminated soil cleanup is complicated by both the physical nature of the soil formation and the behavior of contaminants introduced into the formation. Contaminants can exist in the subsurface in different phase attached to the soil surfaces, dissolved in the ground water, or occupying pore spaces as a separate gaseous or liquid phase. Contaminants properties and how they exist in the subsurface influence their toxicity, mobility and treatability with different remediation technologies A soil characterization study was performed to provide information for remediation technology selection for an inorganic lead contaminated soil. The soil pH, TCLP analysis, thermogravimetric analysis, the soluble anions and cations present, equilibrium leaching tests, analysis by x-ray fluorescence, sequential extractions and speciation analysis using scanning electron microscopy, were all used. Results provided many insights into contaminant behavior in the soil, indicating ultimately whether soil washing or solidification/ stabilization remediation technologies were applicable.

Jan 1, 1994

By G. Belardi

The purpose of the study was to check on the level of environmental contamination and to design a project for cleaning up the Abetina Mine area at Piancastagnaio (Grosseto, Italy). Contamination of this area had occurred during the mining and treatment of cinnabar (HgS) over a prolonged period. The aim of the project is to remove the sources of contamination or render them harmless. Mining of the Piancastagnaio deposit started in 1840, mercury metal being extracted from the ore by thermal treatment. Together with Spain, Italy was the first country to produce this metal and was the world leader in this field between 1936 and 1943. Though mercury production in the Monte Amiata region of Tuscany ceased in 1974 the ensuing environmental impact is very evident, taking the form of rusty old mining and processing works, plus waste tips which still contain considerable amount of mercury even after the ore had been subject to thermal extraction treatment. The research which has been conducted included mapping the area to identify the main sources of mercury and arsenic pollution, as well as the level of environmental contamination. Mercury and arsenic values in excess of 16,000 and 150 ppm respectively are encountered in the most highly-contaminated places. The cleanup project has been drawn up on the basis of the field and laboratory investigations. This provides for a combination of remediation measures on the land concerned, as well as in situ inertization of contaminating elements by means of mixtures of chemical compounds such as cyclosiloxanes. Due account has been taken of Italian and EU environmental regulations when establishing the measures for rendering the various polluting element innocuous. 'The efficacy of the inertization techniques has been checked by yield tests in acetic acid and carbon dioxide, reducing the Hg and As contents of the material in the untreated and treated states from maximum values of 7 mgll to minima close to zero.

Jan 1, 1996