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By Harsh Deep Chopra, Jason N. Armstrong, Susan Z. Hua

"Existence of anisotropic Curie temperature materials [E. R. Callen, Phys. Rev. 124, 1373 (1961); J. Appl. Phys. 32 S221 (1961)] is a longstanding prediction - materials that become paramagnetic at a lower temperature along certain crystal directions while remaining magnetically ordered in other directions up to a higher temperature. Validating Callen's theory, we show that all directions within the basal plane of monoclinic F e1Ss (pyrrhotite) single crystal remain ordered up to 603 K while the c-axis becomes paramagnetic at 225 K. Results prompt a re-evaluation of existing magnetic materials with a focus on magnetic characteristics along different crystal orientations above instead of below the ordering temperatures. Theoretical guidelines for identifying new materials with large anisotropy of Curie temperature are also given, and analysis protocol to characterize them in a self-consistent manner is discussed. Materials with such a large directional dependence of Curie temperature open the possibility for uniquely new devices and phenomena, including energy storage and spintronics devices.IntroductionThis paper is an overview of our recently published work on anisotropic Curie temperature materials [l]. As a background, ferromagnetic and ferrimagnetic materials are characterized by a critical temperature below which magnetic interactions prevail over thermal agitation, leading to the appearance of a spontaneous magnetization. Above this critical point, called the Curie temperature, thermal energy eventually overcomes magnetic interactions and the material becomes paramagnetic.It is less well known that the Curie temperature varies with the orientation of the crystal. In ordinary ferromagnets this orientation dependence of Curie temperature is negligible because of the vanishingly small ratio of anisotropy to exchange energy, i.e., the spherical or isotropic exchange term dominates. Thus Curie temperature in ordinary ferromagnets appears to be an isotropic property, and assigning it a single characteristic ordering temperature suffices. However, a 'small' difference is not equivalent to being the 'same', and under appropriate set of conditions the anisotropy of Curie temperature is predicted to become appreciable, as discussed in the following.In formulating the theory of 'anisotropic magnetization' [2, 3] E. R. Callen and H. B. Callen first discussed the ""interesting possibility"" of anisotropic Curie temperature [2] or ACT; Callen and Callen noted that it was W. J. Carr, Jr. who initially raised this question, and they discussed it in detail at the Conference on Magnetism and Magnetic Materials (NY, November 1960), see footnote on page 320 of Ref. [2]. Soon thereafter, E. R. Callen developed the theory underlying the anisotropy of Curie temperature and conditions conducive to its observation [4, 5]."

Jan 1, 2013

By B. L. Chulu

In the carbothermic reduction of lead sulfate to produce lead, the inclusion of soda ash (Na,CO,) in the charge provides for the control of sulfur dioxide in the effluent gas. An important mechanism in the process appears to be the carbothermic reduction of the sodium carbonate whereby sodium gas and carbon monoxide are produced. These intermediates then participate in the reduction of the lead sulfate to produce lead metal and stable sulfur species in the molten slag phase. In addition, there is some evidence that the presence of lead metal in the charge may also serve to increase the lead recovery in the process. These aspects were investigated by conducting laboratory-scale smelting tests with small charges (;3g), at 1173°K(9000C). Recovery did not exceed 74w% and the role of incipient lead metal in the charge could not be clearly assessed.

Jan 1, 1993

By M. T. Thomas

Sufficient development of the X-Ray Photoelectron Spectroscopy (XPS), the Auger Electron Spectroscopy (AES), and the Secondary Ion Mass pectroscopy (SIMS) has made these instruments ideal for solving problems related to mineral processing -particularly gold ore processing. XPS can determine both the surface composition and chemistry of ores and tailings, and the various phases within either of them. AES can also determine surface composition with the further advantage of having greater spatial resolution so the surface chemistry associated with specific minerals in the ore can be identified. This identification helps to clarify why some minerals pass through a chemical process unaffected, while others can be successfully treated. SIMS has an elemental sensitivity from one to four orders of magnitude greater than XPS or AES which makes it useful for detecting the presence of some elements in very low concentration (parts per million).

Jan 1, 1981

By Robert D. Rogers

The demand for phosphate will continue into the future, because phosphate is currently irreplaceable as a plant nutrient and in many chemical applications. Phosphate is not recycled, so the supply must be replenished through a process of mining and purification. Numerous microbial isolates. obtained from the environment were screened find those which demonstrated the greatest promise of solubilizing PO4 from the ore of interest. Screening was accomplished in a step wise manner an agar plate bioassay, shake flask studies, and semi continuous growth conditions. It was found that with the proper conditions of nutrient supply and solution pH; the bacteria and. fungus used in the semicontinuous process were able to solubilize in excess of 80% of an Idaho rock phosphate ore (RP) within nine days. A significant amount of solubilization occurred within the first six days. There was a 'reasonable correlation between the occurrence of soluble Ca and PO.4 during the processing of the RP thus providing evidence that the RP was being disintegrated by the organisms. In all cases, HPLC analysis of the solutions in which PO4 had been. extracted from RP showed that organic acids, which have been implicated as the mechanism of solubilization, were present.

Jan 1, 1991

By Liming Wang

One of the steps in the extractive metallurgy of lead is a refining process called drossing. Hot dross is mixture of impurity compounds that form on the surface during the cooling of lead blast furnace bullion, and in Missouri, the main impurities are copper and sulfur. The slow cooling of bullion throws out of solution all other minor impurity elements (or their compounds) which are much less soluble at lower temperatures (mainly nickel, arsenic, iron, and zinc). The transfer of bullion from the blast furnace to the refinery and the subsequent hot drossing step cause fugitive emission of lead-containing fume and dust, which creates a plant hygiene problem. One cause of the emissions is the high vapor pressure of lead and its compounds during transmission of = 1000 °C bullion to the drossing kettle. Another cause is the lifting of dross dust during manual skimming of dross. The environmental problems associated with the traditional hot drossing process provided an incentive to investigate a new drossing process that avoids contact between plant air and hot bullion or dross. A key aspect of the process development was a detailed mineralogical examination of dross from two different bullions. The bullion samples were cooled at different rates, and the dross filtered out and examined. The morphology, phase identification, and composition of the dross was examined by optical and SEM microscopy. The principal dross phases were copper and cuprous sulfide, galena, a complex sulfide containing copper, nickel and lead, and speiss (containing nickel, cobalt, iron, copper, lead, and arsenic compounds). The copper was acicular, with nickel and arsenic in solid solution. The cuprous sulfide was largely digenite in a granular or dendritic form. A substantial part of the dross was solidified matte with a eutectic microstructure, consisting mainly of CU2S and PbS. Small particles (some of which had a eutectic microstructure) never floated to the surface of the lead during the slowest cooling rate, thus indicating that flotation of tiny matte droplets and dross crystals is exceedingly slow. The success in separating dross and lead by centrifugal filtration suggests its application in industry as a replacement for traditional hot drossing.

Jan 1, 1995

By Arthur E. Morris

Fifty years ago when Professor Yazawa began his career, the field of process simulation and modeling was in its infancy. Since then, tremendous progress has been made in our ability to model metal production flowsheets from mine to refined metal. This progress has come about by parallel developments in basic understanding of process chemistry and in computational techniques. This paper will review the progress made in process understanding and modeling in lead, zinc, and copper metallurgy from its inception to the present, and the role of Professor Yazawa's work in furthering this progress. Specific examples wi1\ be given for the sintering of lead concentrates, slag fuming, zinc concentrate roasting, flash smelting of copper, and pyro-extraction of zinc. Factors limiting further progress will be described.

Jan 1, 2003

By Walter E. Dean

Twenty six samples of carbonaceous gold ores and associated rocks from outcrop and mine localities in northcentral Nevada were analyzed for concentrations of major. minor, and trace elements, total sulfur, and organic carbon. Q-mode factor analysis was used to define six distinctive carbonate, organic, and detrital associations of elements, and to group samples based on these associations. The trace metals that have clearly enriched the organic-carbon-rich samples are V, Zn, Ni, Cu, Cr, and Mo, although few of the samples could be considered "metal-rich" when compared to other organic-carbon-rich black shales. Rock-Eval pyrolysis was used to evaluate thermal maturity and hydrocarbon yield of the samples. Unfortunately, most samples were too thermally altered to be suitable for routine organic geochemical characterization of organic matter. The 813C values of organic carbon in rocks from different deposits have a trimodal distribution, but there is no clear distinction between the three groups of deposits that can be related to age, thermal history, or depositional environment.

Jan 1, 1987

By G. B. Harris

Much has been written over the past decade concerning the disposal of arsenic from metallurgical processes. In Canada, there are proposed regulations which would classify arsenic in the Primary Group of twenty one persistent, toxic pollutants to be banned or phased out. Since many nickel and cobalt ores, not to mention those of copper, gold and uranium, contain significant amounts of arsenic, it is pertinent to assess the current state-of-the-art of its disposal. The literature is reviewed, and it is demonstrated that from a purely chemical point of view, the family of ferric arsenates largely immobilize arsenic. There is clear evidence from laboratory studies that both crystalline ferric arsenate (scorodite) and amorphous ferric arsenates in which the molar Fe/As ratio is at least three (Fe/As = 3) have very low arsenic solubility; plant data are given to support this. The debate over the long term stability of these compounds continues however; the evidence presented for long term stability and for compound breakdown is critically reviewed in the light? of the recent structural studies, and the role of base metals in these compounds evaluated. Finally, conclusions are drawn as to the viability of a purely chemical process for the long term disposal of arsenic from metallurgical processes.

Jan 1, 1993

By Jr. Langhans, J. S. McPartland

"The presence of zinc in cyanide solutions is generally thought to not have an adverse effect on precious metal recovery or recovery rate by heap leach processing. However, analytical interferences of zinc in solution can cause problems in accurately determining and controlling cyanide concentration in the leach solution, leading to increased cyanide consumption. Analytical methods and the chemistry of cyanide in the presence of zinc are reviewed. The effects of solution pH and zinc concentration on the free cyanide determination were evaluated in detail. Use of the standard silver nitrate titration and a modified titration method for controlling cyanide concentration during heap leaching were investigated experimentally. The practical implications of cyanide heap leaching in the presence of cyanide soluble zinc minerals are discussed.IntroductionThe presence of zinc in precious metal cyanidation circuits is not uncommon. Zinc can be introduced into cyanide leach solutions through dissolution of various zinc minerals1>, or through the use of a Merrill Crowe (zinc precipitation) circuit. Zinc minerals typically occur infrequently and in low concentration in gold ores, but are more abundant in silver ores. Merrill Crowe systems are most commonly employed for recovery of precious metals from solution for relatively high silver ores. It is desirable to control the amount of dissolved zinc in a cyanidation circuit for several reasons. Excessive zinc build-up in cyanide leach solution can, under certain circumstances, inhibit precious metal dissolution and adversely affect solution recovery systems. Additionally, high zinc concentrations can lead to excessive in-process cyanide inventories and potentially, to higher cyanide consumption"

Jan 1, 1999

By Arthur E. Morris

Fifty years ago when Professor Yazawa began his career, the field of process simulation and modeling was in its infancy. Since then, tremendous progress has been made in our ability to model metal production flowsheets from mine to refined metal. This progress has come about by parallel developments in basic understanding of process chemistry and in computational techniques, This paper will review the progress made in process understanding and modeling in lead, zinc, and copper metallurgy from its inception to the present, and the role of Professor Yazawa's work in furthering this progress. Specific examples will be given for the sintering of lead concentrates, slag fuming, zinc concentrate roasting, flash smelting of copper, and pyro-extraction of zinc. Factors limiting further progress will be described.

Jan 1, 2003

By S. W. Marcuson

Smelting of nickel-copper sulfide ores at Vale Inco’s Sudbury operations commenced in 1888 and the first converting plant went into operation in 1892. As the demand for nickel grew, the smelting operations expanded and by the 1960’s the Copper Cliff Smelter featured the longest converter aisle in the world with space for nineteen Peirce-Smith converters. During this long period, different converting techniques and vessels were employed. The evolution of converting is reviewed with special emphasis on the modifications made to the Peirce-Smith vessel to accommodate the metallurgical and process needs of the changing times.

Jan 1, 2009

By Kenneth N. Han

Thermodynamic and kinetic aspects of nickel and cobalt leaching from metals. minerals and ores in various media have been reviewed and discussed in this paper. A kinetic model developed to delineate the leaching mechanisms for these metals has been discussed in view of experimental observations. The current review also includes the dissolution behavior of nickel and cobalt from various minerals such as oxides, sulrides. ocean floor manganese nodules, and laterites. A particular emphasis has been extended to similarities and differences of the dissolution behavior of these two metals in various media. The leaching of nickel as well as cobalt metal in acidic solutions and arnmoniacal solutions exhibits in most part mass transfer controlling. although at some pH's, chemical controlling or mixed controlling mechanisms seem to prevail. The leaching of nickel and cobalt from oxides in acids and ammoniacal solutions. on the other hand, can be described best by chemical controlling mechanisms.

Jan 1, 1993

By George Oprea, Tom Troczynski, Joe A. Rigby, Waiman Lo

The refractory lining of the tuyere line in Peirce Smith converters have usually much shorter life in service than the rest of the lining, above or below it. There are already recognized chemical, thermal and mechanical factors which contribute to the wear of the lining. Our study presents the experimental results on microstructural changes occurring on these tuyere line bricks in a nickelcopper converter. The experimental bricks, after use at the tuyere line, were investigated using SEM/EDS and XRD techniques, to identify the mineralogical changes due to interactions with the nickel-copper matte or fayalite type slag at the process temperatures. The microstructural changes were correlated with physical and mechanical properties of the brick before and after use and a wear mechanism was suggested. Although the matte does not theoretically react with the mineralogical components of the brick, a partial oxidation of the Ni-Cu sulphides was identified using a line analysis by SEM/EDS in the densified layer at the hot face, which allows for mineralogical changes at the matte-refractory interfaces, with a high probability of microcrack formation due to the thermal cycling during use. These microcracks were also identified to open through inter-granular fractures parallel to the hot face, which appeared to be the main cause of lost lining during use. The reactions between the fayalite slag and refractory brick could eventually play a role in chemical dissolution of the brick only in the superficial layer at the hot face, as no slag components were identified deep into the brick.

Jan 1, 2009

By Tom W. Gonzales

Magma Metals Company commissioned a 3000 tpd Outokumpu flash smelting furnace in July 1988. Through September 1992 the PSP has smelted a first campaign record 4.1 million tons of concentrate. This paper discusses modifications made to the original process equipment to overcome design flaws as well as future design changes currently under consideration.

Jan 1, 1993

By Stephen K. Pave1

Over 1,100 tons per day of Fluid Catalytic Cracking Unit (FCCU) catalyst is used worldwide. During the cracking reaction, catalyst is contaminated by deposited metals including nickel, vanadium, potassium, copper, iron, sodium, etc. To compensate for contaminants, a portion of the circulating catalyst inventory is withdrawn for disposal and fresh catalyst is added. The DEMETR process takes spent FCCU catalyst and removes a portion of the metal contaminants, enabling the refiner to recycle demetallized catalyst, thus reducing the solid waste from the refinery. Through August, 1993, the operation of one unit for one refiner has resulted in the recycling of over 7,500 tons of spent catalyst.

Jan 1, 1994

By Batric Pesic

The interactions of mineral-pyrite with T. ferrooxidans were studied by using a cyclic voltametry technique. The interactions with bacteria were carefully examined during the entire growth stage of bacteria (fermentation). Several very important discoveries were made. For example, the pyrite surface invariably drastically changed its properties at the second day of fermentation. Beyond two days of fermentation, the cyclic voltamograms were insensitive to convective diffusion produced by stirring. The SEM study revealed that bacteria populated the pyrite surface at an extremely high density levels. The high density of bacteria, and the solid reaction products formed on the pyrite surface created conditions for pore diffusion which explained why the CVs became insensitive to convective diffusion in solution (stirring).

Jan 1, 1990

By A. H. Rhoades

The modern polarizing microscope with such accessories as cameras, infrared devices, reflectance and/or transmission photometers, indention hardness, and heating stage is used to characterize coal, coke, and other carbon forms. It allows characterization of coke by-products, such as tars and pitches and their insoluble residues. A useful product of the microscopic approach is the coal petrographic analysis which permits the prediction of coke strength carbonization pressure and volume change. Carbonization tests are expensive, time-consuming and require large amounts of coal. Tests on the coke show it to be strong or weak but give no indication of why. Petrographic analysis requires grams of coal and yields data that indicates why the coal produces coke of a given quality. Small samples from drill cores are sufficient for petrographic analysis. These data are also used to optimize blends for coke production. When coke-plant problems occur, ~he microscope can be used to check the coal blend proportions, as well as for weathered coal. Microscopy is useful in spore correlation work which may be a prerequisite to sound coal reserve estimates. Dispersed vitrinoid reflectance studies are used to determine the degree of organic metamorphism which serves to establish oil and gas deadlines. Tars and pitches are examined microscopically for the amount of normal solids as well as the size of undesirable carry-over solids resulting from pollution abatement practices in coke works. The microscope is also used to study coals for gasification and liquefaction.

Jan 1, 1981

By Courtney A. Young

Cyanide is a critically important chemical to the mining and metallurgical industry. It has a strong affinity for metals making it favorable as an agent for metal finishing and treatment as well as a lixiviant for metal leaching, particularly gold. These technologies are environmentally sound but, because cyanide is very toxic, safeguards are required to prevent accidental spills and treat effluents before being discharged. Various methods of cyanide remediation by separation and destruction for cyanide management purposes are therefore reviewed. The methods have been broadly categorized as physical, -adsorption. complexation and oxidation methods including photolysis and other advanced-oxidation processes. Reaction mechanisms for these methods are presented throughout this paper, Finally, the methods are compared in regards to their effectiveness in treating various cyanide species: free cyanide, thiocyanate, weak-acid dissociables, and strong-acid dissociables.

Jan 1, 1998

By Jinxing Ji

Several fundamental aspects related to the nickel electrowinning from chloride electrolytes have been addressed in this paper. The thermodynamic study includes the activity coefficient of the hydrogen ion and the speciation diagram of NiCI2 solutions. The activity coefficient of the hydrogen ion (YH+) was calculated and estimated experimentally using a combination glass pH electrode. It was found that YH+ was greater than one in concentrated NiCl2 solutions and increased significantly with increasing NiCl2 concentration. The speciation diagram for NiCl2 solutions was plotted with YH+ and the effect of the ionic strength on the equilibrium constants being taken into account. It was discovered that the predominant nickel species in the acidic region were Ni2+ and NiCI+ in 0.937 M NiCl2 solution at 25°C. Electrodeposition tests demonstrated that higher Nit' concentration in the electrolyte improved the current efficiency of nickel electrodeposition (CENi). The additions of H3BO3, and NH4Cl increased very little the current efficiency of nickel electrodeposition at pH 1.5 and temperature 60°C. However, the addition of sulfate decreased the current efficiency of nickel electrodeposition. Nickel electrodeposition was also found to be a steady-state process since the amount of acid added to the electrolyte at a constant pH increased linearly with time during galvanostatic electrodeposition. The cathode surface pH during nickel electrodeposition was measured using a flat-bottom combination glass pH electrode and a 500-mesh gold gauze as cathode. The cathode surface pH was found always to be higher than the pH in the bulk electrolyte, and if the current density was sufficiently large, it would eventually reach a level causing precipitation of insoluble Ni(OH)2(s) on the cathode surface. Rotating disc electrode studies revealed that the rate of nickel electrodeposition was first order with respect to the activity of nickel ion and zero order with respect to the activities of chloride and hydrogen ions. The rate of hydrogen evolution was found to be first order with respect to the activity of hydrogen ion and to be zero order with respect to the activities of nickel and chloride ions. These findings indicate that nickel deposition and hydrogen evolution proceed independently.

Jan 1, 1995

By P. N. Anyalebechi

"The as-cast microstructure of two commercial-size ingots of aluminum alloy 3004 produced by the electromagnetic casting process was quantitatively characterized. This involved the quantitative determination of through-thickness and across-width variations in dendrite cell size, grain size, macrosegregation of alloying elements, interparticle spacing, and the types, volume fractions, and sizes of the constituent or second phase particles. More than ninety-five percent of the constituent phases in the ingots consisted of the A16(Mn,Fe) phase; the desirable a-Al 12(Fe,Mn)3Si phase was not detected in any of the ingots by Guinier X-ray diffraction analyses or electron probe X-ray microanalyses. A significant microstructural heterogeneity through the thickness and across the width of both ingots was observed. For example, macrosegregation, and the sizes of the constituent phase particles, dendrite cells, and grains increased concomitantly from edge to mid-width and from surface to center of the ingots. There was a -20% depletion (negative macrosegregation) of Mg and a +54-87% enrichment (positive macrosegregation) of Ti in the center of the ingots. With the exception of grain size, there was no significant microstructural difference between the two ingots examined. The causes and practical implications of the observed microstructural heterogeneity in the ingots are discussed.IntroductionThe first step in the fabrication of majority of wrought products of aluminum and its alloys is the casting of large ingots or billets of simple shapes (round or rectangular). The sizes of the ingots vary from 10 mm to 450 mm diameter or 25 mm to 780 mm thick. The quality of the finished products is established at the ingot casting stage. This is because the microstructural characteristics, such as secondary dendrite cell size or arm spacing, amount of alloying elements retained in solid solution, macrosegregation, and the characteristics of second phases, produced during casting cannot be reversed by subsequent processing. Up until twenty-five years ago, the effect of as-cast microstructure of large ingots on the structure and behavior of thin sheets (0.34 mm thick) during drawing and ironing processes was incorrectly assumed to be minimal or nonexistent. This was based on the erroneous notion that the thermal treatments and large reduction (>99.94%) and strain that the ingot undergoes during production of the sheets completely destroys the original ingot structure and its inherent heterogeneity. However, the effects of ingot structure can, a priori, be deduced from the observed effects of constituent phase particle size, type and volume fraction on recrystallization, development of texture during annealing and deformation, and earing. In fact, careful examination of the behavior of products produced from different size ingots or castings have shown that the original microstructure of the ingot has a direct impact on the properties and performance of the end products."

Jan 1, 2011