Showing papers on "Magnetite published in 1988"

Formation of ultrafine-grained magnetite in soils

Abstract: The magnetic properties of certain soils indicate the widespread presence of ultrafine-grained magnetite, even where there is no detrital input of magnetite. This suggests that in situ formation of magnetite can occur under soil-forming conditions. Schwertmann and Taylor have stated, however, that magnetite has not been found as a newly formed mineral in soils. Here we report the recovery and identification of pure, ultrafine-grained magnetite from some UK soils that have no apparent external sources of magnetite. We consider this magnetite to be of inorganic, in situ origin. The identification of magnetite formation during soil development has significance for studies of iron in soils but also has wider environmental implications. Soil-derived magnetite may contribute to the natural remanent magnetism of sediments, and act as a specific indicator of erosional events.

Internally consistent solution models for Fe-Mg-Mn-Ti oxides; Fe-Ti oxides

Abstract: Developpement d'un modele pour la coexistence ilmenite ss -magnetite ss , fonde sur des donnees experimentales nouvelles et existant deja pour les oxydes Fe-Ti et utilisant une programmation lineaire qui est egalement coherente de facon interne avec les donnees disponibles sur l'echange Fe-Mg dans olivine ss -ilmenite ss et olivine ss -magnetite ss et sur l'echange Fe-Mn dans ilmenite ss -grenat ss

Anaerobic magnetite production by a marine, magnetotactic bacterium

Abstract: Bacterial production of magnetite represents a significant contribution to the natural remanent magnetism of deep-sea and other sediments1–5. Because cells of the freshwater magnetotactic bacterium Aquaspirillum magnetotacticum require molecular oxygen for growth and magnetite synthesis6, production of magnetite by magnetotactic bacteria has been considered to occur only in surficial aerobic sediments7. Moreover, it has been suggested that deposits of single-domain magnetite crystals are palaeooxygen indicators presumably having been formed under predominantly microaerobic conditions5–8. In contrast, some nonmagnetotactic, dissimilatory iron-reducing bacteria, such as the recently described strain GS-15 by Lovley et al.7, synthesize extracellular magnetite from hydrous ferric oxide under anaerobic conditions. We now report the first isolation and axenic culture of a marine, magnetotactic bacterium, designated MV-1, that can synthesize intracellular, single-domain magnetite crystals under strictly anaerobic conditions. We conclude that magnetotactic bacteria do not necessarily require molecular oxygen for magnetite synthesis and suggest that they, as well as dissimilatory iron-reducing bacteria, can contribute to the natural remanent magnetism of even long-term anaerobic sediments.

Saturation magnetisation, coercivity and lattice parameter changes in the system Fe3O4-γFe2O3, and their relationship to structure

Abstract: This study has characterised the oxidation products of a fine-grained single domain magnetite which was made synthetically by a colloidal method. Changes in the intrinsic magnetic properties (saturation magnetisation, saturation remanence, and coercive force) during progressive oxidation are correlated with lattice parameter changes and an oxidation mechanism. It is proposed that magnetite oxidises to hematite via at least two metastable maghemites. The first of these, formed on low temperature oxidation by the formation of a magnetite/maghemite solid solution, is a face centered maghemite with lattice parameter a= 8.3419±0.0006 A. A second maghemite, produced on oxidation at higher temperatures, has a primitive cubic structure and a lattice parameter a = 8.3505±0.0005 A. Maghemite cation distributions are derived to explain the reduced saturation magnetisations of between 56 and 74 Am2 kg-1 observed, and a maghemite structure containing an increase in tetrahedral Fe3+ ions and up to 3 octahedral vacancies per 32 oxygen unit cell is proposed.

Magnetite authigenesis and diagenetic paleotemperatures across the northern Appalachian basin

Abstract: The concentration of magnetite in the Lower and Middle Devonian Helderberg and Onondaga carbonate formations varies in a distinct pattern along an east-west profile across New York State. Magnetite concentrations are uniformly low in the western half of the profile, increase sharply eastward to a peak value near Syracuse, and decrease farther east. The pattern strongly resembles previously reported variations in the extent of clay mineral diagenesis that reflect differences in paleotemperatures along the profile. Previous paleomagnetic studies have documented that the magnetite carries a well- defined magnetization of Pennsylvanian-Permian age, and magnetite authigenesis is therefore no younger than late Paleozoic. We attribute the correlation between high magnetite concentration and high illite content to temperature-dependent diagenesis triggered by orogenic fluids. The large proportion of secondary magnetite indicates that over most of the area, the mechanism of late Paleozoic remagnetization was principally chemical. Thermal effects played a less direct role in the remagnetization of the strata by controlling the extent of the chemical processes that resulted in overprinting of the original remanence.

Note on temperature dependence of exchange constant in magnetite

Abstract: We calculated the temperature dependence of the exchange constant between 20°C and 573°C using three previously published data sets from inelastic neutron scattering by spin wave excitations in magnetite. The exchange constant in magnetite varies as a function of temperature approximately as the saturation magnetization to the power 1.7. Our synthesis of temperature dependent spin wave dispersion data provides an experimental foundation for the temperature variation of the exchange energy which is critical for micromagnetic domain structure calculations and for an understanding of the acquisition of thermoremanent magnetization in rocks.

Volcanogenic iron oxide deposits, Cerro de Mercado and vicinity, Durango

Abstract: The iron deposits of the Durango City, Mexico, area were formed by subaerial volcanic processes during a hiatus between two major eruptive cycles emanating from the 30-m.y.-old Chupaderos caldera. The first major eruption of the Chupaderos caldera produced the hematitic rhyolitic ash-flow tuffs of the Aguila Formation. During resurgent doming of the caldera floor, the Cacaria Formation filled the moat around the central dome of the Chupaderos caldera. The lower Cacaria, the Leona Member, consists of extensive rhyolite flow domes, flows, and volcanoclastic tuffs. The various facies of the Mercado Iron Member were deposited on the surface of the Leona Member as well as on the resurgently domed Aquila Formation. A minor amount of quartz latite extrusive activity was concurrent with the eruption of the Mercado Iron Member. Both units preceded the eruption of a second major welded tuff, the Santuario Formation, which incorporated fragments of iron oxides in its base.The Mercado Iron Member of the Cacaria Formation consists of seven facies variations. The Cerro de Mereado iron deposit consists of four facies: (1) a martitc facies--massive to layered coarsely crystalline porous martitc (hematite pseudomorphous after magnetite) at the base, with dike and pluglike extensions downward into the underlying rhyolite, (2) a sandy magnetite facies--unconsolidated, laminated fine-grained sandy magnetite above the martite, (3) a blocky facies--unlaminated sandy magnetite matrix, mixed with blocks of the overlying quartz latite flow, and (4) a mixed iron oxide facies--tabular and dikelike bodies of fine-grained magnetite-hematite intergrowths that cut and cap the system. A satellite deposit at Pena Morada consists of three facies: (5) a breccia facies--dense, fine-grained hematite at the base with included rhyolite porphyry fragments, (6) the layered facies--dense fine-grained hematite layers interlayered with laminated hematite powder, and (7) the powdery hematite facies--a very fine grained cyrstalline hematite powder at the top which is finely laminated. The dense layers of the middle facies (6) exhibit crackled, vesicular, and ropy textures on their upper surfaces. The powdery hematite facies (7) also forms an extensive blanket of laminated, hematite powder referred to as the peripheral deposits. These deposits discontinuously crop out over an area of 300 km 2 around the Cerro de Mercado and Pena Morada deposits, wherever the contact between the Leona Member and the Aguila Formation, and the younger units is exposed. The peripheral deposits vary from 1 m in thickness to little more than staining of the contact. Regionally they thin away from Pena Morada, while locally they are thinnest on palcotopographic slopes.Geologic relationships suggest that the iron deposits formed as a result of a variety of subaerial volcanic processes. The main deposit at Cerro de Mereado apparently resulted from the eruption of an iron magma rich in fluorine, chlorine, carbon dioxide, and water. Sheeted flows and flow breccias formed a volcanic dome above an intrusive feeder system. Iron oxides crystallized as magnetite, with abundant, clear, yellow-green apatite crystals forming concurrently in gas cavities and open breccias. Large volumes of halogen-rich gases streamed up through the iron oxide flows and oxidized the magnetite to hematite (martite) and redeposited the iron leached from the now-porous martite as laminated sandy magnetite in an extensive fumarolic blanket. During the later stages of the cooling process, a quartz latite dike intruded and flowed out over the deposit. Basal blocky flow breccias of the quartz latite mixed with and disrupted the finely laminated texture of much of the sandy magnetite, creating extensive quartz latite breccias with a sandy magnetite matrix. Late-stage hematite-magnetite dikes cut the entire system and fed flows which capped the mound. Lateral to Cerro de Mereado large volumes of iron-rich vapor explosively vented into the atmosphere and crystallized as fine-grained hematite dust which formed an ashlike blanket covering an area greater than 300 km 2 . Flow textures, interlayered with the ashlike hematite, at the base of the Pena Morada deposit, suggest actual flows or welded flows of this material. The occurrence of a maximum thickness of the ashlike hematite at Pena Morada indicates its proximity to a vent. At Cerro de Mercado the volatile-rich nature of the system resulted in extensive replacement of the underlying premineralization rhyolites by a mixture of magnetite and pyroxene. Postminer-alization tuffs overlying the iron ore contain iron oxide fragments at their bases with no alteration.An immiscible iron-rich volatile phase is believed to have evolved from the parent rhyolite magma by the introduction of CO 2 into the magma from carbonate wall rocks. This volatile-rich phase rose to the top of the magma chamber and up through the resurgent floor of the caldera. The fluid is believed to have boiled during its ascent, separating into vapor and liquid phases. At the magmatic temperatures envisioned, water would disassociate and the oxygen would combine with the iron in the liquid phase to form a volatile-rich iron oxide magma which was driven to the surface by a continuing stream of escaping gases. The hydrogen escaped in the vapor phase along with chlorine and fluorine, forming an intensely acid environment capable of carrying significant volumes of iron in the form of iron chloride vapors until reaching the atmosphere where the microcrystalline hematite powder was formed.Comparison of Cerro de Mercado with other apatite-bearing, low titanium iron deposits associated with silicic volcanic systems suggests that this volcanogenic model may be applicable to many of them. The volcanic environment produces a mixture of intrusive, replacement, and sedimentary textures which may explain the heated debates found in the literature over the origin of many of these deposits. These systems include the Kiruna deposits of Sweden, the central Missouri iron deposits, and the Olympic Dam deposit, all of Precambrian age; the Jurassic deposits of northeast Nevada; and the Tertiary deposits of Mexico and Chile.

Magnetic Properties of Iron in Soil Iron Oxides and Clay Minerals

Abstract: The pie chart in Fig. 14-1 indicates the abundance of Fe relative to other major elements in the earth’s crust. It is the only one of the nine to bear a magnetic moment in its compounds. The bar chart compares the abundance of Fe with that of other magnetic ions, on a logarithmic scale. Since Fe is approximately forty times more abundant than all the others put together, it follows that magnetic properties of soils and clay minerals derive essentially from the Fe they contain. Magnetic measurements are highly specific to Fe, but, as we shall see, they are much more sensitive to some mineral forms (e.g., magnetite, maghemite, pyrrhotite) than to others.

Temperature dependence of magnetic domains in magnetite crystals

Abstract: Synthetically grown and natural multidomain magnetite crystals (d ≥ 30 µm) have strongly temperature-dependent magnetic domain structures. The unblocking of domain walls at moderate temperatures (T < 120°C) makes these magnetite grains unsuitable as paleomagnetic recorders. Approximately 15% of the smaller hydrothermally grown magnetite crystals (d ≤ 10 µm) show stable domain patterns when heated to 350°C. These magnetites with temperature-independent domain structures can possibly account for paleo-magnetic remanences with high blocking temperatures.

Fe-oxide microcrystals in welded tuff from southern Nevada: origin of remanence carriers by precipitation in volcanic glass

Abstract: Although it is widely recognized that remanent magnetism in ash-flow tuffs is carried by fine-grained Fe oxides, the origin, mineralogy, and significance of such magnetic carriers are not well understood. The authors have obtained transmission electron microscope images of distinctive Fe-oxide microcrystals in rhyolitic samples located 3.8, 7.6, and 18.5 m above the base of a 110-m-thick section of the Miocene Tiva Canyon Member of the Paintbrush Tuff. The Fe-oxide microcrystals are lath shaped and increase in size from 20 x 140 nm in the lowermost sample (near base of the member) to 120 x 800 nm in the uppermost sample (within the flow interior). Microcrystals in this size range are within or close to the range of single-domain grain size for magnetite. Electron diffraction and analytical X-ray data indicate that the microcrystals in the lower two samples are cubic Fe-oxides (magnetite/maghemite), with less than 10 mol% Ti end member, and that those in the uppermost sample are manganiferous hematite. Systematic variations in magnetic properties are consistent with the observed variations in size and mineralogy of the microcrystals. These microcrystals are morphologically distinct from grains that the authors interpret to be fragments of phenocrysts. The morphology and spatial distribution ofmore » the microcrystals as well as their increase in grain size, from the rapidly cooled base of the ash-flow sheet into the flow interior, are consistent with an origin by nucleation and growth from volcanic glass at elevated temperature, subsequent to emplacement.« less

Sapphirine and spinel phase relationships in the system FeO-MgO-Al2O3-SiO2-TiO2-O2 in the presence of quartz and hypersthene

Abstract: Sapphirine and spinel can accommodate significant ferric iron and therefore the mineral equilibria involving these phases must be sensitive to a(O2). In this paper we examine the theoretical phase relationships involving sapphirine and spinel in addition to sillimanite, garnet, cordierite, rutile, hematite-ilmenite solid solution (henceforth ilmenite), and magnetite-ulvospinel solid solution (henceforth magnetite), in the presence of quartz and hypersthene in the system FeO-MgO-Al2O3-SiO2-TiO2-O2 (FMASTO), with particular reference to the topological inversion in P-T postulated by Hensen (Hensen 1986). Documented natural associations suggest that the appropriate topology for assemblages involving magnetite and ilmenite is Hensen's higher a(O2) one, while, in contrast, the topology for assemblages involving ilmenite and rutile is the lower a(O2) one. The exact configuration of the inversion between these two topologies remains uncertain because of uncertainties in the ferric/ferrous iron partitioning between sapphirine and spinel-cordierite at high temperatures. By comparison with experimental data and natural occurences, the sillimanite-sapphirine-cordierite-garnet-hypersthene-quartz assemblage is in equilibrium at about 1000°–1020° C and 7–8 kbars, while sapphirine-cordierite-spinel-garnet-hypersthene-quartz occurs at temperatures in excess of those attainable during crustal metamorphism, for ilmenite-rutile buffered assemblages. This implies that sapphirine-rutil-ehypersthene-quartz assemblages, as found in the Napier Complex, Antarctica, can only occur at > 1000° C. Also, spinel-rutile-hypersthene-quartz assemblages should not be found in rocks because temperatures in excess of 1100° C are expected to be involved in their formation. The temperatures of formation of spinel-sillimanite-sapphirine-garnethypersthene-quartz, sapphirine-spinel-cordierite-sillimanite-hypersthene-quartz, and sillimanite-spinel-cordieritegarnet-hypersthene-quartz in assemblages buffered by magnetite and ilmenite are less well constrained, but are likely to be in the range 900°–1000° C. These conclusions apply to rocks with compositions close to FMASTO; the perturbing effects of substantial concentrations of additional components, in particular Ca, mainly in garnet, and Zn and Cr, mainly in spinel, may invalidate these conclusions.

The magnetic properties of metaperidotitic rocks as a function of metamorphic grade: Implications for crustal magnetic anomalies

Abstract: Seventeen samples from the Malenco serpentinite in the Swiss Alps, representing systematic prograde metamorphic conditions from prehnite-pumpellyite to upper amphibolite, are moderately to strongly magnetic (average susceptibility of 6.61×10−2 SI units) due predominantly to the presence of a magnetite-rich spinel. Some greenschist facies samples contain the metal alloy awaruite (Ni3Fe); these contain in addition much greater amounts of magnetite. Small amounts of pyrrhotite in about half the samples complete the contributions to the total magnetization. Susceptibilities generally decrease with increasing metamorphic grade because of the production of increasing amounts of chromerich spinel which dilutes the magnetite component. These results indicate that significant magnetic anomalies should be generated in suture zones containing metamorphosed serpentinite and in areas where serpentinite is being actively subducted.

Crystal Symmetry of Magnetite in Low Temperature Phase Deduced from Magnetoelectric Measurements

Abstract: Electric polarization of magnetite, induced by rotating magnetic field in the triclinic b c plane, was measured along the triclinic a axis below 60 K where magnetite is ferrimagnetic as well as ferroelectric. The magnetoelectric polarization was influenced by the way of application of mechanical stress onto the single crystal. Mechanism of this phenomenon was discussed on the basis of the formation of twins including new types. Point group of the crystallographic symmetry of the magnetoelectric single phase was analyzed. It was shown that the present experiment was not inconsistent with the fact that among three crystalline angles, in addition to the a c , at least the b c is not right-angle. Thus magnetite in the temperature range, 4.2 K to 35 K, is of triclinic 1 , irrespective of the magnitude of the angle a b .

Effect of temperature on magnetizing reduction of agbaja iron ore

Abstract: Agbaja oolitic iron ore, which has not been responsive to such beneficiation processes as froth flotation, gravity concentration, magnetic separation, and electrostatic separation, has been concentrated to 60 pct Fe grade and 87.3 pet Fe recovery (starting from a crude assaying 45.6 pct Fe) by the magnetizing reduction technique. The main parameter investigated was the effect of temperature on the magnetizing reduction process, and 600 °C was established as the optimum temperature for the reduction step. X-ray diffraction studies of the reduction products showed that the iron oxides were converted to magnetite, to wustite, or to metallic iron, depending on the temperature of reduction. The results from the subsequent magnetic concentration step were, in the main, dependent on the observed reduction products.

Influence of Manganese Oxide Minerals on the Formation of Iron Oxides1

Abstract: The influence of manganese oxide minerals (cryptomelane, hausmannite, and pyrolusite) on the formation of iron oxides was studied in the FeC12-NH4OH system at different Mn/Fe molar ratios (0, 0.01, 0.1, and 1.0) and pHs (3.0, 4.0, 5.0, and 6.0) by X-ray powder diffraction, infrared absorption, transmission electron microscopic, and chemical analyses. In the absence of Mn minerals, lepidocrocite (3,-FeOOH) precipitated at pHs 5.0 and 6.0; however, no precipitate formed at lower pHs. AH the Mn minerals studied promoted the precipitation of iron oxides and oxyhydroxides. In the presence of Mn oxides, Fe 2§ was oxidized to Fe 3§ which hydrolyzed and precipitated as noncrystalline and/or different crystalline iron oxides and oxyhydroxides, depending on the nature of the Mn oxides present in the system. Simultaneously, Mn 2§ was detected in solution after the reaction by electro'n spin resonance spectroscopy. The presence of cryptomelane and hausmannite resulted in the formation of ~kaganeite (fl-FeOOH) and magnetite (Fe304), respectively. Thus, the effect of Mn oxides on the formation of Fe oxide minerals in the weathering zone merits attention.

Magnetic Behavior of Natural Goethite During Thermal Demagnetization

Abstract: Goethite maximum blocking temperatures (60–105°C) are governed by the amount of isomorphous substitution in the goethite lattice. The goethite dehydration reaction (250–350°C) is attended with a concurrent remanence decrease in finely intergrown hematite due to a change of the original hematite structure promoted by the liberated water vapor. This remanence decrease leads to a bending point in the thermal decay curve, which could be easily mistaken for the presence of another magnetic constituent. The magnetic properties of the minerals formed through goethite dehydration (hematite and traces magnetite) strongly depend on their growth history.

Complex unmixed spinels in layered intrusions within an obducted ophiolite in the Natal-Namaqua mobile belt

Abstract: Spinellids showing unmixed intergrowths of chromite or chromian spinel (sensu stricto) and magnetite or chromian magnetite are not known in mafic or ultramafic igneous rocks. They do occur within metamorphosed rocks that attained temperatures sufficiently high (upper amphibolite facies) for the formation of homogeneous Al-Cr-Fe3+-Ti spinel phases with compositions not matched in slowly cooled igneous rocks. In the Tugela Rand intrusion complex intergrowths of chromian spinel, chromian magnetite, ulvospinel, ilmenite and a transparent aluminous spinel are observed and interpreted in terms of the thermal history of the rocks. Compositional differences between the separate areas of chromian spinel and chromian magnetite in complex intergrowths exhibited by the metamorphosed Tugela Rand and Mambulu Complexes confirm the extension of the magnetite-hercynite solvus (Turnock and Eugster 1962) towards magnesium- and chromium-rich compositions. The Tugela Rand spinellids are compared with those from the Carr Boyd Complex (Purvis et al. 1972) and the ultramafic rocks of the Giant Nickel Mine (Muir and Naldrett 1973) and the Red Lodge district (Loferski and Lipin 1983). Significant differences between the spinels from the Red Lodge district compared to the other three occurrences may reflect the different metamorphic histories of these areas.

The mechanism of ferrite formation from iron sulfides during zinc roasting

Abstract: The formation of zinc ferrite (ZnFe2O4) during the fluidized-bed roasting of zinc concentrates presents subsequent processing difficulties both for zinc recovery and for iron separation and disposal. A major source of iron in these concentrates is from the iron sulfides — pyrite and pyrrhotite. This study examined the changes undergone by these iron minerals when roasted together with sphalerite at 1223 K in a fluidizing gas mixture of 3 pct oxygen and 97 pct nitrogen. Optical microscopy and electron microprobe analysis were employed to identify the three stages that lead to ferrite formation and to examine the processes that occur within each stage. The first stage is oxidation of the sulfides to highly vesicular, amorphous magnetite particles containing small amounts of zinc. The second stage involves both densification of these particles by sintering and counterdiffusion of iron and zinc cations to form a continuous phase of homogeneous zinc-rich spinel and a precipitate of hematite. In the third stage, continuation of cation diffusion and increasingPo 2 results in the formation of stoichiometric zinc ferrite. These observations have been interpreted by reference to the established phase relationships that occur in the Zn-Fe-O system, and a detailed, solid state reaction mechanism for the formation of zinc ferrite has been proposed.

The field dependence of the complex frequency-dependent susceptibility of magnetic fluids

Abstract: A technique for the measurement of the field dependence of the complex frequency-dependent susceptibility of magnetic fluids together with some results for a colloidal dispersion of magnetite are reported.

The effect of the low-oxidation-state metal ion reagent tris-picolinatovanadium(II) formate on the surface morphology and composition of crystalline iron oxides

Abstract: The LOMI (low-oxidation-state metal ion) process is used widely in the decontamination of water reactor systems. An attempt has been made to elucidate the mechanism of dissolution by reference to a number of single crystals of iron oxides polished on specific crystallographic planes, e.g. magnetite, Franklinite and haematite. These have been studied by a combination of electron-spectroscopic techniques such as X-ray photoelectron spectroscopy, Auger electron spectroscopy and Mossbauer spectroscopy. Electron microscopy and chemical kinetic measurements have also been undertaken.

Process for beneficiating particulate solids

Abstract: The present invention provides a method for selecting magnetite to form a dense media for beneficiation of fine particulate solids such that the particulate solids are as buoyant with respect to the dense media as if the solids were in a true liquid having a specific gravity equal to that of the dense media The method involves determining a magnetite particle diameter such that the diameter ratio of particulate solid to magnetite lies above a diameter ratio partition curve The invention is also directed toward using magnetite having a particle diameter less than about 0005 mm and a mean particle diameter of about 00025 mm Such magnetite is formed from a gas phase pyrohydrolysis reaction on an aqueous iron (ferrous) chloride solution The present invention is further directed towards a method for determining the efficiency of separation of a dense media separation process This method includes determining an apparent distance a particle must travel in a dense media cyclone to be correctly beneficiated From this apparent distance, an apparent velocity a particle must achieve to be correctly beneficiated is calculated This apparent velocity is used, along with cyclone geometry and operational parameters to calculate a divergence value which indicates the efficiency of separation The present invention also includes a method for selecting cyclone geometry and operating parameters which includes determining separation efficiency and adjusting geometry and parameters in a manner to obtain improved efficiency

Plate-like magnetite particles, plate-like maghemite particles and process for producing the same

Abstract: Poreless and non-sintered plate-like magnetite or maghemite particles having average plate surface diameters of from 0.03 to 0.50 µm and a specific surface area of from 7 to 30 m²/g.

Magnetoadsorption of NO on iron oxides

Abstract: The effects of magnetic field on NO adsorption on iron oxides were examined at 30/degrees/C by means of the volumetric method. When the magnetic field of 7.5 kG was applied to the magnetite-NO system in adsorption equilibrium, the amount of adsorbed NO increased by 0.5% of the total adsorbed amount. The magnetoadsorption occurred as soon as the magnetite field was applied to the magnetite sample and reached the adsorption equilibrium within 10 min. When the magnetic field was removed from the sample, the adsorption amount decreased reversibly. The magnetoadsorptivity and reversibility depended on the pretreated conditions of the magnetite sample and on the kind of magnetism of iron oxide.

The dissolution of magnetite by nitrilotriacetatoferrate(II)

Abstract: The dissolution of magnetite particles in solutions containing nitrilotriacetatoferrate(II) has been studied as a function of total nitrilotriacetic acid (NTA) and iron(II) concentrations, pH and temperature. Experimental results are interpreted in terms of adsorption equilibria involving the free ligand and its metal complexes, and inner- and outer-sphere interfacial electron transfer from the adsorbed electroactive FeII species to surface—FeIII sites, either free or complexed by NTA. Ion transfer-controlled dissolution was ruled out by the experimental evidence. FeY–ions [Y = N(CH2CO2)3–3] have been identified as the electroactive species, electron transfer being an outer-sphere process for the present experimental conditions: the precursor complex can be represented by—FeIII—NTA…FeY–. Dissolution rate deviates from first order in [FeY–]; the order decreases with increasing [FeY–] as a consequence of the relatively high affinity of the complex for —FeIII—NTA surface sites. Reaction order on proton concentration is 0.67, reflecting the requirement of H+ ions adjacent to the site where the reductant is adsorbed. The apparent activation energy is 73 kJ mol–1, which is a composite of equilibrium and kinetic parameters.

Saturation of copper-iron mattes with solid magnetite

Abstract: Conditions which lead to the saturation of simple copper-iron mattes with solid magnetite have been evaluated in this study. Diagrams have been developed which illustrate quantitatively the surface of saturation of matte with magnetite in the phase and stability diagrams for the Cu-Fe-S-0 system at 1468 K and 1 atm total pressure. Conditions fo. simultaneous saturation of matte with magnetite and gas (P so2 + P s2= 1 atm) have also been estimated by extrapolation of the data on magnetitesaturated mattes. Comparison of the results with compositions of mattes from oxygen-enriched smelters indicates that these smelters operate at magnetite saturation under conditions close to equilibrium. Conditions during oxygen-enriched smelting can be predicted from the diagrams given in this paper and correlation equations for the oxygen and sulfur concentrations in magnetitesaturated matte which were previously developed from the experimental data.

Magnetic Properties of Synthetic Analogues of the Altered Olivines of Igneous Rocks

Abstract: SUMMARY A laboratory simulation has been made of the high temperature deuteric alteration of olivine such as occurs in slowly cooled basic intrusions. Three compositions in the Forsterite/ Fayalite solid solution series were synthesized by a three-firing method using self buffering and controlled atmosphere to obtain material containing no detectable magnetite (Fe,O,) as a contaminant (<0.005 per cent). The prepared olivines were oxidized between 850 and 1280°C at oxygen fugacities of between lo-”.’ and lop5.’ atmospheres. The composition and concentration of the multiphase oxidation products were studied by magnetic, optical, electron optical and X-ray methods. The magnetic constituent of the intergrowth was magnetite. Below about 1150 “C the microstructure is similar to the ‘dendritic’ intergrowths found, for example, in the altered olivine of the Central Layered Intrusion of the Isle of Rhum. Above about 1150 “C the form may be similar to ‘symplectite’ intergrowths. The magnetization process parameters (coercive force, etc.) vary systematically with temperature of oxidation ( To,) which evidently controls the microstructure of the magnetite. The magnetite produced is magnetically ‘hard’, samples altered at 900 “C and 950 “C having higher coercive force (Hc) than any magnetite reported in the literature. The room temperature properties appear to bridge the published trends found in ‘grown crystal’ magnetites and ‘crushed grains’. Inferred effective grain sizes of the complex intergrowths range from 0.1 to 3 pm as To, increases from 900 to 1200 “C. The temperature dependence of magnetization process parameters (principally H,) measured between room temperature and the Curie point are modelled in terms of (i) monodomain grains subject to thermal fluctuations, (ii) monodomain grains not subject to thermal fluctuations, and (iii) as multidomain grains. Model (i) yields plausible values for effective grain dimensions and length/diameter ratios, higher To, producing larger, more equidimensional particles. Model (ii) suggests that the relative importance of cubic and uniaxial anisotropies may be influenced by a microstructure-dependent uniaxial particle-particle interaction term. Model (iii) implies that, if domain walls are pinned by both surface and volume defects, magnetostriction plays a greater role in volume pinning than in surface pinning. Plausible values of demagnetizing factors appropriate to grains with few domains are produced by model (iii).