Dissolution Of Magnetite Research Articles

Dissolution of metal ferrites and iron oxides by HCl under oxidising and reducing conditions

A study has been carried out on the relative rates of dissolution of copper, zinc, and nickel ferrites in HCl solutions and on the effect of various oxidant and reductant species in solution. The results are compared with the rates of dissolution of hematite, magnetite, and nickel oxide, and correlated with their electrochemical behaviour. Cyclic voltammograms of the metal ferrites and oxides show oxidation or reduction peaks corresponding to changes in the oxidation state of the metal in the lattice. It is shown that the relative reactivity in 1 M HCl at 25° is in the order Fe 3O 4 ⪢ ZnFe 2O 4 > CuFe 2O 4 > Fe 2O 3 > NiFe 2O 4. The leaching of the metal ferrites and iron oxides is enhanced by the presence of 0.01 M Cu(I) or Sn(II) but the leaching of NiO is enhanced by oxidants such as 0.01 M Cu(II) in chloride media.

ChemInform Abstract: Mechanism of Dissolution of Magnetite by Oxalic Acid‐Ferrous Ion Solutions.

L'etape determinant la vitesse serait le transfert d'electron dans la sphere externe de Fe II (C 2 O 4 ) 2 2− au complexe superficiel oxalate-fer (III)

The dissolution of magnetite by nitrilotriacetatoferrate(II)

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.

The occurrence of Greigite in sediments from Loch Lomond

AbstractGreigite has been identified in the sediments of Loch Lomond using X‐ray diffraction. Greigite is the dominant magnetic mineral in the oldest sediments recovered, while magnetite predominates in the younger sediments which had previously been used for palaeomagnetic secular variation studies. A layer of sediment in between these two magnetic mineral regimes has very low magnetic concentrations, probably as a consequence of magnetite dissolution associated with sulphide rich pore‐waters produced at the time of a marine incursion.The greigite largely oxidises once the sediment is exposed to air, but if freeze dried the greigite becomes surprisingly stable. Following freeze drying the greigite can be heated to 280°C in air before it alters and loses its strong ferrimagnetic properties.

Mechanism of dissolution of magnetite by oxalic acid-ferrous ion solutions

L'etape determinant la vitesse serait le transfert d'electron dans la sphere externe de Fe II (C 2 O 4 ) 2 2− au complexe superficiel oxalate-fer (III)

Dissolution and pyritization of magnetite in anoxie marine sediments

Concentrations of magnetite were determined, with depth, in sediments of varying H 2S content taken from Long Island Sound (FOAM, NWC, and Sachem sites) and from a site in the rapidly depositing subaqueous portion of the Mississippi Delta. For the three Long Island Sound sites, dissolution of magnetite during burial is clearly demonstrated, and for all four sites the rate of magnetite dissolution is proportional to the concentration of dissolved pore water sulfide. By combining magnetite depth distributions with sedimentation rate data and measurements of dissolved sulfide, we find that magnetite dissolution is well described by the following rate law: dC mag dt = -1.1× 10 −5C 0.5 BC magA mag where C mag is the concentration of magnetite (grams per gram of sediment), C s is the concentration of dissolved sulfide (mM), and A mag is the specific surface area of magnetite in the sediment (cm 2 per gram of magnetite.) This equation means that, for a typical range of magnetite surface areas and dissolved sulfide concentrations, the “half-life” of magnetite in anoxic marine sediments ranges from about 50 to 1000 years. SEM observations of magnetite grains from the different sediment sites reveal that magnetite dissolution may be accompanied by extensive replacement by pyrite. This only occurs if magnetite is in contact with high concentrations of H 2S (>1 mM) for relatively long periods of time (several hundred years). With low concentrations of H 2S (<1 mM) magnetite dissolution occurs without identifiable pyrite replacement. We suggest that this feature of magnetite diagenesis may prove to be a useful paleosulfide indicator.

Dissolution and pyritization of magnetite in anoxic marine sediments : Canfield, D.E. and R.A. Berner, 1987. Geochim. cosmochim. Acta, 51(3):645–659

Dissolution and pyritization of magnetite in anoxic marine sediments : Canfield, D.E. and R.A. Berner, 1987. Geochim. cosmochim. Acta, 51(3):645–659

Dissolution of solid magnetite in Fe-S-O melt

The dissolution rate of solid magnetite in binary Fe-S and ternary Fe-S-O melts was measured at 1493 K using a rotating magnetite rod of 5 mm in diameter. At rotating speed higher than 52 rpm, the flow of sulfide melt was turbulent, and the effect of natural convection on the dissolution rate was negligible. Magnetite dissolution took place without the evolution of SO2 gas at the rod surface immersed in the interior of the melt. On the other hand, SO2 gas was evolved from a portion of magnetite rod which was in contact with the melt surface. The overall rate of dissolution was controlled by mass transfer through liquid boundary layer on the rod surface, and the dissolution rate of magnetite decreased with increasing oxygen concentration of the sulfide melt. Mass transfer coefficient was between 1.8 × 10−3 and 4.6 × 10−3 cm · s−1 at the rotating speed of 156 rpm, and it decreased with increasing oxygen concentration of the melt.

A comparative study of the oxidative and reductive dissolution of magnetite in acidified CuSO4-acetonitrile-H2O and CuCl2?NaCl?H2O leach solutions

The oxidative and reductive dissolution of magnetite in acidified aqueous acetonitrile and acidified aqueous NaCl solutions have been investigated by electrochemical methods and correlated with the proton activity in these fundamentally different solution systems. The results are compared with the rates of magnetite dissolution in the presence of copper(II) and copper(I). Under anodic or oxidizing leach conditions magnetite forms a passive Fe2O3 film which inhibits reaction, but under cathodic or reducing leach conditions in the presence of copper(I), magnetite is believed to dissolve via (FeOH)+ intermediate and reacts up to 600 times faster. The rate of dissolution of magnetite depends on its potential and the activity of the proton. The rate follows a Butler-Volmer relationship with a Tafel slope of 120–130mV per decade and exhibits a proton reaction order between 0.85 and 1.0. After allowing for changes in proton activity there is no significant difference between the rate of dissolution of magnetite in the sulphate and chloride leach solutions and no discernable effect of the presence of acetonitrile in the mixed solvent system. Electrochemical studies and leaching studies in which the potential is controlled by the Cu(II)−Cu(I) couple are in good agreement and lead to a fundamental understanding of the optimum conditions required to leach copper selectively from a Cu−Fe3O4 calcine derived from the segregation roasting of chalcopyrite concentrates.

Characterisation of soils by mineral magnetic measurements

Processes of iron mineral authigenesis, diagenesis, and dissolution, in interaction with primary inputs of iron minerals, act to produce vertical differentiation of soil magnetic properties. Thus, magnetic iron oxides, in common with other iron forms, may both respond to and reflect soil forming processes. Investigation of the degree of detectable and persistent magnetic differentiation within different soil materials can provide insights into the nature and direction of distinct sets of soil processes. Evidence of clear association between magnetic variation and discrete types of soil environment also has applied significance, in several areas of environmental study: for example, the observed magnetic variation can be used to discriminate between individual soils and soil horizons, for the purposes of soil surveying, sediment ‘tagging’ and tracing, and empirical modelling of source-sediment linkages. This paper reports the use of mineral magnetic techniques to characterise the iron oxide assemblages within soils of varying type and provenance. The effect of different pedogenic regimes have been investigated through measurement of a range of magnetic parameters (including magnetic susceptibility, frequency dependent susceptibility, and anhysteretic and saturation remanences). Contrary to current pedological thought, but in accord with other, magnetically-based, studies (e.g., Mullins ), the presence of magnetite/maghemite (typically of superparamagnetic-single domain grain size) within soils has been found to be an extremely widespread phenomenon. Its contemporary neoformation within the soil environment is inferred. However, the input of artificially-generated ferrimagnetic material is indicated for one of the magnetically ‘enhanced’ soils examined here, and the possibility of extraneous sources of magnetite in topsoils should be considered before pedogenic, processes of magnetic enhancement are inferred. From the data presented, discrimination of industrially-derived magnetic particles appears possible, on the basis of their very low levels of frequency dependent susceptibility (χ fd ), low anhysteretic remanence ( ARM ), and dissociation from the finer, clay-sized (< 2 μ m) components of the soil. Not the formation but the active dissolution of ferrimagnetic minerals is indicated for soils affected by the processes of gleying and podsolisation. Eluvial horizons of podsolised profiles demonstrate almost total loss of detectable magnetic content; variations in the form of the iron reprecipitated in the underlying illuvial layers may reflect differences in the pedological characteristics of these horizons. Within gleyed (waterlogged) soils, processes of magnetite dissolution appear to be grain size-specific; preferential reduction of those grains of ultrafine (superparamagnetic) and fine (single domain) magnetic grain size is indicated. Where soil forms a major contributor to catchment sediment loads, this has significance in the area of source-sediment modelling. Soil derived from permanently wet or highly leached catchment areas is unlikely to contribute to peaks in the magnetic content of deposited sediments; further, only those erosional processes that operate at a faster rate than those of magnetic depletion will have the capacity to produce peaks in sediment ferrimagnetic concentrations such as have been observed within the historical magnetic record.

Acidic and reductive dissolution of magnetite in aqueous sulfuric acid: Site-binding model and experimental results

The open circuit dissolution of ionic metal oxides in mineral acids is modelled assuming that the rate is controlled by the transfer of metal ions in hydrolytic equilibrium with bulk metal ions, from the metal oxide surface to the Stern plane. The site-binding model of the double layer metal oxide/electrolyte solution is used to obtain the pH dependence of surface and Stern potentials. The nature of the active sites is discussed and their surface concentration is assumed to be proportional to suface charge σ 0. Again, the site-binding model is used to detemine the pH dependence of σ 0. It is thus shown that the rate order in c H + is essentially defined by the potential dependence of the charge transfer process, for oxides with points of zero charge near neutrality that dissolve in mildly or strongly acidic solutions. The role of surface complexation is also discussed in terms of the site-binding model and the difficulties in interpreting dissolution experiments under constant external applied potential are discussed in terms of the complexity of the semiconductor oxide/electrolyte solution interfacial region in magnetite. An experimental study of the open circuit dissolution of magnetite in sulfuric acid is presented and interpreted according to the proposed model. The reductive dissolution of magnetite is modelled by extension of the Valverde-Wagner model of oxide dissolution. Experimental results are presented to demonstrate that the reductive dissolution rate of magnetite in ferrous containing solutions is controlled by the rate of electron transfer from adsorbed Fe(II) to Fe(III) surface states of magnetite.

Adsorption of EDTA and iron—EDTA complexes on magnetite and the mechanism of dissolution of magnetite by EDTA

The adsorption of EDTA on magnetite has been measured as a function of pH and EDTA concentration. The number of anchorage sites of EDTA on magnetite changes from 2 to 4 with increasing pH, while the affinity goes through a maximum in the pH interval 3–4. Adsorption of Fe(II) on EDTA has also been measured, the behavior being similar to that of other hydrolizable ions. The more complex composite systems EDTAFe(II), Fe(III)Fe 3O 4 are also analyzed and it is concluded that surface and dissolved iron ions compete for EDTA; thus the adsorptivity of the complex ions is less than the adsorptivity of either EDTA or aqueous iron ions. The rates of dissolution of magnetite in EDTA solutions with and without added Fe(II) have been measured and the results interpreted through a much faster rate of phase transfer for Fe(II) as compared to Fe(III). Heterogeneous electron transfer is involved in the dissolution of magnetite by ferrous ions, either exogenous or autogenerated. EDTA is necessary for the reductive pathway, as the larger stability constant of the Fe(III) complex over the Fe(II) complex provides the driving force for the heterogeneous electron transfer.

The Mechanism of Magnetite Dissolution in Chelant Solutions

Abstract Chelating agents are used to remove fouling deposits and surface films from industrial equipment. This paper discusses the mechanisms by which magnetite (Fe3O4) dissolves in chelating solv...

Determination of interacting configurations

The replacement of magnetite by hematite was studied through a series of experiments under mild hydrothermal conditions (140–220 °C, vapour saturated pressures) to quantify the kinetics of the transformation and the relative effects of redox and non-redox processes on the transformation. The results indicate that oxygen is not an essential factor in the replacement reaction of magnetite by hematite, but the addition of excess oxidant does trigger the oxidation reaction, and increases the kinetics of the transformation. However, even under high O2(aq) environments, some of the replacement still occurred via Fe2+ leaching from magnetite. The kinetics of the replacement reaction depends upon temperature and solution parameters such as pH and the concentrations of ligands, all of which are factors that control the solubility of magnetite and affect the transport of Fe2+ (and the oxidant) to and from the reaction front. Reaction rates are fast at ∼200 °C, and in nature transport properties of Fe and, in the case of the redox-controlled replacement, the oxidant will be the rate-limiting control on the reaction progress. Using an Avrami treatment of the kinetic data and the Arrhenius equation, the activation energy for the transformation under non-redox conditions was calculated to be 26 ± 6 kJ mol−1. This value is in agreement with the reported activation energy for the dissolution of magnetite, which is the rate-limiting process for the transformation under non-redox conditions.

Adsorption of EDTA and iron-EDTA complexes on magnetite and the mechanism of dissolution of magnetite by EDTA

Adsorption of EDTA and iron-EDTA complexes on magnetite and the mechanism of dissolution of magnetite by EDTA

Heterogeneous electron transfer as a pathway in the dissolution of magnetite in oxalic acid solutions

The dissolution of metal oxides is a process of importance in several fields such as hydrometallurgy, passivity of metals, and cleaning of boilers and metal surfaces in general. Oxalic acid is one of the most effective reagents for dissolution of magnetite under mild acid conditions. Magnetite is the oxide that confers passivity to steel surfaces. In the present communication, the more salient features of the mechanism of dissolution of magnetite by oxalic acid solutions are discussed with special focus on the role played by ferrous ions in the process. Oxalate plays an unique role among complexing carboxylic ligands in the dissolution of magnetite; it not only facilitates the electron-transfer reaction but also mediates in a relatively fast dissolution during the initial induction period (the induction period is much shorter than in the case of the dissolution of magnetite by ethylenediaminetetraacetic or nitrilotriacetic acid). This unique role has been used in the development of a very efficient scale removal formulation used in the decontamination of nuclear power plants.

ChemInform Abstract: KINETICS OF THE DISSOLUTION OF MAGNETITE IN THIOGLYCOLIC ACID SOLUTIONS

AbstractUntersuchungen der Kinetik der Reaktion Abei unterschiedlichen Thioglykolsäure‐Konzentrationen und spezifischen Oberflächen sowie als Funktion von pH und Temp. zeigen, daß die Gesamtreaktionsgeschwindigkeit der Reaktion von der momentanen Oberfläche der Magnetitteilchen abhängt und daß der Reaktionsmechanismus wahrscheinlich in der Zers. ‐der durch Wechselwirkung des Thioglykolat‐Anions mit den protonierten OH‐Gruppen an der Magnetit‐Oberfläche gebildeten Spezies besteht.

Magnetite Dissolution and Crevice Studies with Chelant Solutions

Work is described in two related areas: (a) fundamental studies of the dissolution behavior of synthetic magnetite in aqueous chelant solutions as functions of solution pH, temperature, heating time, chelant structure, and the presence of additives, and (b) more applied investigations in which information from the basic studies was utilized in choosing solutions and experimental conditions for the removal of magnetite based corrosion products from simulated steam generator tube-tube support plate crevices. The magnetite dissolution work has employed a novel, convenient, and sensitive experimental technique based on the ferromagnetism characteristic of Fe/sub 3/O/sub 4/. Since chemical reaction of magnetite with chelants results in nonmagnetic iron chelates, monitoring the ferromagnetism of a reaction mixture, as a whole, provides an in situ and quantitative measure of unconsumed magnetite.

Effect of pyrrole, indole and their dimethyl derivatives on the dissolution of magnetite

The effect of organic corrosion inhibitors (pyrrole, indole and selected derivatives) upon the rate of dissolution of magnetite in hydrochloric acid solutions has been studied. They can enhance the rate of dissolution by a factor of five. The effect of these compounds in inhibiting the attack of the acid on steel has also been investigated.

Kinetics of the dissolution of magnetite in thioglycolic acid solutions

The kinetics of the dissolution of magnetite by thioglycolic acid (mercaptoacetic acid) have been studied at different acid concentrations and specific surface areas, and as a function of pH and temperature. The experimental evidence points to the overall rate of reaction depending on the instantaneous surface area of the magnetite particles and that the probable reaction mechanism is the decomposition of the species formed by the interaction of thioglycolate anion with the protonated OH groups located on the surface of the magnetite particles. This mechanism explains the sharp maximum in the dissolution rate constant obtained at pH ca, 4.5, as it takes into account two phenomena which are sensitive to pH in opposite directions, the increase in thioglycolate anion concentration as the pH is increased and the increase in the amount of protonated superficial OH groups as the pH is lowered. The activation enthalpy for this reaction was found to be 15.5 kJ mol–1.