Solubility Of Magnetite Research Articles

Dissolution of magnetite by etidronic acid: Dependence on diprotic and monoprotic conjugates

A mechanism of Fe3O4 dissolution by the tetraprotic etidronic acid (HEDP) proposed 40 years ago is revised here. We reproduce the previously observed activation energy and reaction order of phosphonate with a selective subset of experimental conditions, showing that diprotic HEDP- and not the previously reported triprotic HEDP- is the species ultimately limiting the mechanism by protonating magnetite oxos and desorbing Fe3+. This proposed step is consistent with a speciation diagram showing monoprotic HEDP as the spontaneous chelator of ferric iron below pH 3, in the form of a partially soluble precipitate. Hence, while the magnetite dissolution rate is increased using the tri or tetraprotic acids, lower pH promotes reprecipitation of ferric iron. This has likely resulted in at least one previously reported upper bound for magnetite solubility in HEDP (0.6Fe:1HEDP)- and any others reported under conditions of the fastest observed dissolution kinetics- to be underestimated. This restriction on yield is avoided at the cost of rate by dissolving Fe3O4 at pH 5.

Insights into the formation mechanism of hard sludge on the secondary side of PWR steam generators

• Mixtures of alumina, silica and magnetite have been aged in hydrothermal conditions. • Kaolinite has been identified as a cement binding the magnetite particles. • In presence of metallic iron, iron silicate precipitates. In the secondary circuit of nuclear Pressurized Water Reactors, corrosion products and impurities lead to the formation of undesirable hard deposits, called hard sludge, on the tube sheet of steam generators. Theses deposits are mainly composed of iron (magnetite), alumina and silica. The formation of hard sludge piles is investigated by reproducing the reaction of precursor oxides in the conditions of the steam generator (275 °C, 58 bar). Mixtures of magnetite, γ-alumina and amorphous silica in binary or ternary systems in an alkaline ethanolamine-ammonia solution at pH 25°C = 9.6 are studied. Carbon steel was tested as an alternative source of iron. The analysis of the evolution of the suspensions, completed by the industrial feedback, allows to explain the process of hard sludge formation in the steam generators. The following sequence is proposed: sedimentation of magnetite/confinement of the interstitial fluid/concentration of aqueous species such as aqueous silica and alumina/sorption of Al on magnetite and/or growth of boehmite/reaction with aqueous silica to form kaolinite as a resistant cement. Once formed, the kaolinite cement tends to densify over time while magnetite is passive. The absence of Fe-phyllosilicates predicted by thermodynamics is explained by the low solubility of magnetite making unfavorable the precipitation of Fe-silicate. By contrast, metallic iron is not stable at contact with water and the continual production of divalent iron, whose solubility is much higher than that of magnetite, allows to overpass a threshold concentration what makes possible the precipitation of a berthierine layer at the surface of corroded steel. This layer constitutes the nucleation site for the further precipitation of other aluminosilicates.

Effects of Advanced Amines on Magnetite Deposition of Steam Generator Tubes in Secondary System

Ethanolamine (ETA) is widely used to control the pH value in the secondary water of pressurized water reactors. However, it is necessary to consider other advanced amines which can replace ETA due to its serious human hazards and environmental treatment problems. The purpose of this study is to contemplate the effects of three advanced amines (ETA, 3-methoxypropylamine (MPA), and dimethylamine (DMA)) on the magnetite deposition behavior of a thermally treated (TT) Alloy 690 tubes by using a steam generator (SG) tube fouling loop in simulated secondary water. All particles were identified as a magnetite and were polyhedral or spherical in shape. When using ETA, MPA, and DMA, the average porosity of the deposits was about 34.7%, 33.0%, and 24.6%, respectively. The amount of deposits was largest when ETA was added, and it decreased by 41% when adding MPA and 55% when adding DMA. The mechanism of magnetite deposition was discussed in terms of zeta potentials of both the magnetite particles and the Alloy 690TT surface and magnetite solubility depending on the amines. To compare the potential for replacing ETA with other advanced amines, the various factors such as SG integrity, human hazards, and environmental treatment problems were discussed.

Carbon Dioxide Contamination of Aqueous Morpholine Solutions and Effects on Secondary Coolant Chemistry Under CANDU Conditions

Exposure to air can cause amine solutions in CANada Deuterium Uranium (CANDU) reactor secondary coolant circuit feed tanks to absorb carbon dioxide (CO2). Likewise, carbon dioxide can be absorbed directly into the amine-containing secondary coolant by air ingress during shutdown, lay-up, and startup. Sampling operations, including transferring the sample to the laboratory and subsequent analyses, can also provide opportunities for CO2 contamination. This paper reports the results of laboratory and chemical modeling studies to examine the effects of CO2 contamination on aqueous morpholine solutions. The chemistry of CO2 uptake by feed tanks containing up to 50 wt% (11.5 mol·kg−1) morpholine at 25°C was modeled using the OLI Studio 9.5.2 chemical equilibrium model, and the speciation was confirmed by 13C nuclear magnetic resonance spectroscopy (NMR) measurements. The effects of CO2 contamination on the pH of the secondary coolant containing 60 ppm (0.006 wt%, 7.00 × 10−4 mol·kg−1) morpholine and the resulting effects on the solubility of magnetite and nickel oxide from 25°C and 250°C at steam saturation were modeled as a function of CO2 loading using the Electrical Power Research Institute chemical modeling software MULTEQ v.8. The chemical modeling calculations show that concentrated alkaline morpholine solutions at room temperature and pressure would be expected to have a strong tendency to absorb CO2 and have additional uptake abilities due to the formation of morpholine carbamates. For dilute morpholine solutions at room temperature and pressure, the solutions are still sufficiently alkaline to absorb enough CO2 to cause a measurable change in the pH of the secondary coolant. This effect was shown to be negligible under reactor operating conditions. The absorption of CO2 would potentially have the most effect on either unprotected feed tanks or during lay-up conditions in the steam generators, as it could depress the pH of the lay-up solution and adversely affect the rate of corrosion in the internal components of the steam generators (e.g., carbon steel materials). The 13C NMR measurements on samples of 50 wt% aqueous morpholine solutions from feed tanks at the Ontario Power Generation’s Pickering Nuclear Generating Station found that CO2 was below the 0.02 wt% detection limit, and suggest that the procedures used to avoid CO2 contamination in feed tanks are effective. The 13C NMR was shown to be an effective tool for monitoring CO2 uptake by morpholine solution in the feed tanks under conditions in which they may have undergone abnormal exposure to air.

Effects of NaCl addition on magnetite deposition on the outer surfaces of steam generator tubes

During the operation of a steam generator (SG), NaCl can be introduced into the secondary system of a pressurized water reactor owing to the condenser inleakage. In this study, the effects of NaCl addition on magnetite deposition on SG tubes were investigated using a magnetite deposition test loop that can simulate the secondary side condition of SGs. The results showed that the deposited magnetite particles were polyhedral in shape regardless of NaCl, but the particles became smaller and more round with the addition of NaCl. The two-dimensional porosity of magnetite deposits decreased from 30.0% to 18.9% with the addition of NaCl. Furthermore, the amount of deposits was reduced by 46% with the addition of NaCl, which is discussed in terms of particle size, magnetite solubility, and zeta potential. The concentration factor of Na and Cl within the deposits were evaluated to be 6.2 × 105 and 1 × 104, respectively.

Effects of pH control agents on magnetite deposition on steam generator tubes

Magnetite deposition on the secondary side of steam generators is a major concern in nuclear power plants. Therefore, it is necessary to mitigate the deposition using optimized water chemistry control. The purpose of this study is to investigate the effects of three pH control agents, ammonia, morpholine, and ethanolamine, on the magnetite deposition onto an Alloy 690TT tube under conditions similar to operating steam generators. The deposited magnetite particles were polyhedral or spherical in shape and numerous micropores were clearly observed in the deposits regardless of pH agents. The amount of deposited magnetite was lowest when ammonia was used, and increased approximately 1.7 times and 2.6 times when using morpholine and ethanolamine, respectively. The effects of the pH agents were discussed based on the difference of zeta potentials between magnetite particles and the bare surface of the Alloy 690TT tube, particle size, and magnetite solubility.

CRUD deposition in accelerated high-temperature water: Investigation on the effect of substrate material and water chemistry

Deposition of corrosion products (CRUD) on micro-orifice specimens under accelerated flow conditions was investigated in high-temperature water on several substrate materials (SS 304L, Titanium, Alloy 690, Zirlo and magnesia stabilised Zirconia) and water chemistries (0–2 ppm of Li, 0–2.5 ppm of H2). Regardless of the substrate material, no significant differences in radial CRUD build-up were observed in high purity water (0 ppm of Li and either 0 or 2.5 ppm of H2). Conversely, in lithiated water (2 ppm of lithium and 2.5 ppm of H2), the CRUD surface build-up was dependent on the oxide electrical conductivity, which in turn depends on the substrate material. In fact, no build-up occurred on Zirconia and only a minor deposition on Zirlo. The deposition mechanism was ascribed to be dominated by particulate deposition at neutral pH where magnetite solubility is the highest. Conversely, crystalline build-up induced by electrokinetic activity played an important role at alkaline pH where oxide solubility was the lowest.

Mechanism and kinetics of hydrothermal replacement of magnetite by hematite

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.

LIQUIDUS THERMO-BAROMETER FOR THE MODELING OF MAGNETITE — MELT EQUILIBRIUM

A system of equations of thermobarometer for magnetite-silicate melt equilibrium was obtained by method of multidimensional statistics of 93 experimental data of a magnetite solubility in basaltic melts. Equations reproduce experimental data in a wide range of basalt compositions, temperatures and pressures with small errors. Verification of thermobarometers showed the maximum error in liquidus temperature reproducing does not exceed ±7 °C. The level of cumulative magnetite appearance in the vertical structure of Tsypringa, Kivakka, Burakovsky intrusions predicted with errors from ±10 to ±50 m.

Dissolved Cl, oxygen fugacity, and their effects on Fe behavior in a hydrous rhyodacitic melt

We have conducted a series of experiments to evaluate the intrinsic effects of dissolved chlorine on Fe3+/∑Fe and magnetite solubility in hydrous chloride-rich rhyodaciticliquids. The addition of Cl to the melt appears to have two prominent effects on iron in the melt: (1) dissolved Cl appears to perturb the magnetite-melt equilibrium, such that greater FeOtotal contents are required to support magnetite saturation in Cl-bearing melts than in Cl-free melts of equivalent bulk compositions; and (2) a systematic and progressive decrease of the measured Fe3+/∑Fe as fO₂ is increased. These two intimately related effects each have important implications for redox processes occurring in Cl-enriched arc magmas.

마그네타이트 (Fe3O4) 전극의 제조와 전기화학 특성

Flow Accelerated Corrosion (FAC) causes unexpected accidents in a secondary side of a nuclear power plant. The secondary side pipes are mainly carbon steel tubes that have a protective magnetite (Fe3O4) layer on the inner surface. The stability of the protective magnetite layer depends on the parameters related to the FAC phenomena such as pH, temperature, flow rate, surface roughness etc. The dissolution of magnetite is basically the electrochemical reaction, but the most of the experiments of magnetite dissolution were carried out thermodynamically to determine the solubility of magnetite. The knowledge of the electrochemical properties of magnetite is required to understand the dissolution process of magnetite. This paper reviews the manufacture of the magnetite (Fe3O4) electrode, and summaries the electrochemical properties of the magnetite.

Predicting and Preventing Flow Accelerated Corrosion in Nuclear Power Plant

Flow accelerated corrosion (FAC) of carbon steels in water has been a concern in nuclear power production for over 40 years. Many theoretical models or empirical approaches have been developed to predict the possible occurrence, position, and rate of FAC. There are a number of parameters, which need to be incorporated into any model. Firstly there is a measure defining the hydrodynamic severity of the flow; this is usually the mass transfer rate. The development of roughness due to FAC and its effect on mass transfer need to be considered. Then most critically there is the derived or assumed functional relationship between the chosen hydrodynamic parameter and the rate of FAC. Environmental parameters that are required, at the relevant temperature and pH, are the solubility of magnetite and the diffusion coefficient of the relevant iron species. The chromium content of the steel is the most important material factor.

유동가속부식에 영향을 미치는 수화학 인자 : pH, 용존산소, 하이드라진

Flow accelerated corrosion(FAC) of the carbon steel piping in pressurized water reactors(PWRs) has been major issue in nuclear industry. Severe accident at Surry Unit 2 in 1986 initiated the worldwide interest in this area. Major parameters influencing FAC are material composition, microstructure, water chemistry, and hydrodynamics. Qualitative behaviors of FAC have been well understood but quantitative data about FAC have not been published for proprietary reason. In order to minimize the FAC in PWRs, the optimal method is to control water chemistry factors. Chemistry factors influencing FAC such as pH, corrosion potential, and hydrazine contents were reviewed in this paper. FAC rate decreased with pH up to 10 because magnetite solubility decreased with pH. Corrosion potential is generally controlled dissolved oxygen (DO) and hydrazine in secondary water. DO increased corrosion potential. FAC rate decreased with DO by stabilizing magnetite at low DO concentration or by formation of hematite at high DO concentration. Even though hydrazine is generally used to remove DO, hydrazine itself thermally decomposed to ammonia, nitrogen, and hydrogen raising pH. Hydrazine could react with iron and increased FAC rate. Effect of hydrazine on FAC is rather complex and should be careful in FAC analysis. FAC could be managed by adequate combination of pH, corrosion potential, and hydrazine.

Deposit models for tube support plate flow blockage in Steam Generators

Corrosion product deposits in the secondary side of nuclear power plant Steam Generators may result in Tube Support Plate flow blockage, and tube fouling. In order to simulate those two phenomena in the whole Steam Generator, a solid deposit growth model has been developed by the EDF R&D Division. This model is implemented in the frame of THYC, which is the EDF's reference code for the modeling of two-phase thermal-hydraulic phenomena at the subchannel scale. A new deposit process, based on Tube Support Plate flow blockage studies, has been developed and implemented in the model, and is presented in this work. It can be defined by two main steps: particle deposition, and strengthening process called “flashing” due to soluble species precipitation in the pores of the particle deposit. The relevance of this process is tested by comparing the simulation results to the actual levels of flow blockage observed in some nuclear plants. Two dominant trends are showed in this work: the flow blockage is more important on the hot leg than on the cold leg and at the top than at the bottom of the Steam Generators. Moreover the flow blockages at the upper Tube Support Plate have the special feature to be more important at the periphery than at the center. The “flashing” phenomenon allows one to underline the magnetite solubility dependence, so the pH dependence, of flow blockage phenomenon. A pH elevation of the secondary circuit seems to be a interesting remedy which is currently considered on EDF fleet.

Biogeochemical role of magnetite in urban soils (Review of publications)

The surface horizons of urban soils are enriched in technogenic magnetite Fe3O4 accumulated from emissions. Its content there reaches 3–4% and more, whereas it does not exceed 0.1% in the back-ground soils. In urban soils, large spherical magnetite particles of pseudo-single-domain and multidomain fabric predominate; the cavities in magnetic spherules decrease their chemical stability and increase their reactivity. Magnetite is most often destroyed in urban soils due to complexing; its destruction may be initiated by mineral salts entering the soil with deicing mixtures and by organic acids excreted by roots (e.g., by oxalic acid). The high solubility of magnetite with ammonium oxalate should be taken into account when using Tamm’s reagent for the analysis of urban soils. Magnetite is a mineral carrier of some heavy metals. Therefore, its content (as determined from the magnetic susceptibility) serves as an indirect index of soil pollution. In addition, magnetite may affect many soil properties as a reducer and sorbent. It adsorbs phosphorus thus preventing the penetration of this nutrient into rivers and lakes. Magnetite also oxidizes Cl-containing aliphatic hydrocarbons and purifies the soil. Although magnetite enters urban soils as a pollutant, its influence on the soil properties cannot be unambiguously judged as only negative.

PWR 1 次冷却材模擬環境中のほう酸および水酸化リチウムがステンレス鋼の粒界型応力腐食割れに及ぼす影響

In order to understand systematically the influence of an environmental factor on the intergranular stress corrosion cracking (IGSCC) susceptibility of cold-worked 316 stainless steel, constant extension rate tensile tests were carried out under simulated pressurized water reactor (PWR) primary water conditions while varying the boric acid, lithium hydroxide, and dissolved hydrogen concentrations and temperature. It was found that IGSCC susceptibility increased for a low boric acid concentration and high lithium hydroxide and dissolved hydrogen concentrations, and a high temperature. The influences of the water chemistry changes were recognized as the changes in pH and magnetite solubility in a manner that IGSCC was promoted for higher pH and magnetite solubility. On the other hand, IGSCC crack growth rates measured using compact-tension-type specimens revealed that boric acid, lithium hydroxide, and dissolved hydrogen did not affect IGSCC crack growth rate significantly.

Studying the solubility of magnetite in conditions simulating the digestive processes of the gastrointestinal tract

The paperproposed to usemagnetiteas biologicallyactive substancesin food.The human bodyonlyto a small extentcan control theintake of ironfrom food andhas no control overits expenditure. With a negativebalanceof iron metabolisminitiallyconsumesiron,thenthere istissueiron deficiency, which is manifested inthe form of disruptionof enzymatic activity andrespiratory functionin tissues, and then iron deficiency anemia develops. The solubility ofultrafine powdersof magnetitehas been studiedunder conditions simulatingthe processesof the gastrointestinaltract. The model parametersof the experimentwere chosen in accordancewith the termsof the humangastro-intestinal digestion, temperature, pH, digestive juices, as well as the timewhen digestive juicesare in the digestivetract. It is shownthat the solubilityof magnetitedepends on the durationof the experiment andpHmedium. The results of spectrophotometricand atomic absorptionspectrometry analysis are shown

Iron minerals in urban soils

Technogenically contaminated urban soils contain a substantial amount of magnetite Fe3O4, whereas another ferrimagnetic, i.e., maghemite αFe2O3, more often prevails in unpolluted soils. The content of magnetite may exceed the content of another iron oxide, hematite, in contaminated soils. In the town of Chusovoi, where emissions from a single enterprise, a metallurgical plant, predominate among pollutants, the upper soil horizons are contaminated with magnetite of one type. In the much larger city of Perm, the polluting sources are diverse, which results in a wide variation of magnetic susceptibility of technogenic magnetite. The difference in magnetite properties may depend on the composition and the content of heavy metals associated with this mineral. A considerable amount of oxalate-soluble magnetite in technogenically contaminated soils produces two important consequences. Schwertmann’s criterion Feox: Fedit as a gleying index turns out to be overestimated and, therefore, does not work in technogenically contaminated soils. The second consequence is that Tamm’s reagent is inapplicable to extracting heavy metals bound to amorphous iron compounds from contaminated soils. On the other hand, a high solubility (30–60%) of technogenic magnetite by oxalate favors the use of Tamm’s reagent for the complete extraction of iron (hydr)oxides and heavy metals bound to them.

The role of volatile exsolution and sub-solidus fluid/rock interactions in producing high 56Fe/ 54Fe ratios in siliceous igneous rocks

Highly differentiated igneous rocks can, in some cases, have 56Fe/ 54Fe ratios that are significantly higher than those of mafic- to intermediate-composition igneous rocks. Iron isotope compositions were obtained for bulk rock, magnetite, and Fe silicates from well-characterized suites of granitic and volcanic rocks that span a wide range in major- and trace-element contents. Sample suites studied include granitoids from Questa, N.M. (Latir volcanic field) and the Tuolumne Intrusive Series (Sierra Nevada batholith), and volcanic rocks from Coso, Katmai, Bishop Tuff, Grizzly Peak Tuff, Seguam Island, and Puyehue volcano. The rocks range from granodiorite to high-silica granite and basalt to high-silica rhyolite. The highest δ 56Fe values (up to +0.31‰) are generally restricted to rocks that have high Rb (>100 ppm), Th (>∼15 ppm) and SiO 2 (>70 wt.%) but low Fe (<2 wt.% total Fe as Fe 2O 3) contents. Magnetite separated from these rocks has high δ 56Fe values, whereas Fe silicates have δ 56Fe values close to zero. Although in principle crystal fractionation might explain the high δ 56Fe values, trace-element ratios in high-δ 56Fe igneous rocks indicate that crystal fractionation is an unlikely explanation. The highest δ 56Fe values occur in volcanic and plutonic rocks that contain independent evidence for fluid exsolution, including sub-chondritic Zr/Hf ratios, suggesting that loss of a low-δ 56Fe ferrous chloride fluid is the most likely explanation for the high δ 56Fe values in the bulk rocks. Based on magnetite solubility in chloride solutions and predicted Fe isotope fractionations among Fe silicates, magnetite, and ferrous chloride fluids, the increase in δ 56Fe values of bulk rocks may be explained by isotopic exchange between magnetite and FeCl 2 0 , which predicts an increase in the δ 56Fe values of magnetite upon fluid exsolution. This model is consistent with the δ 56Fe values measured in this study for bulk rocks, as well as magnetite and Fe silicates. Our results suggest that fluid exsolution from siliceous hydrous magmas, which sometimes produce porphyry-style Cu, Mo, or Cu-Au mineralization, may be traced using Fe isotopes.

Solubility of andradite, Ca3Fe2Si3O12, in a 10 mol% NaCl solution at 800 C and 10 kbar: Implications for the metasomatic origin of grandite garnet in calc-silicate granulites

The solubility of andradite garnet was determined at 800 °C and 10 kbar in a solution of 10 mol% NaCl and 90 mol% H 2 O. Experiments were syntheses carried out with high-purity natural wollastonite, reagent hematite or natural specular hematite containing ~1 wt% TiO 2 , and fluid. All experiments were performed with Mn 2 O 3 -Mn 3 O 4 or Fe 2 O 3 -Fe 3 O 4 oxygen buffers in a piston-cylinder apparatus with NaCl pressure media for 1–3 days. Andradite saturation was determined by the presence or absence of garnet in quenched charges. Andradite dissolves incongruently to hematite and fluid with CaSiO 3 molality ( m CS ) of 0.0838 ± 0.0015 for the reagent hematite and both buffers. Slightly higher m CS of 0.0895 ± 0.0005 for the natural hematite and Mn-oxide f O 2 buffer is interpreted as due to incomplete equilibration and/or ~9 mol% Ti in the run-product andradite. Dissolved Fe molality could be determined only approximately, but must be at least ten times lower than m CS . Quenched fluids were very basic (pH 11–12). The solubility of Fe 2 O 3 in andradite-saturated H 2 O-NaCl fluids is lower than that of Al 2 O 3 at grossular saturation at the same pressure ( P ), temperature ( T ), and fluid composition. The results permit a test of a model of CaSiO 3 dissolution in NaCl solutions to three dominant aqueous species: CaCl + , OH , and H 3 NaSiO 4 . Combination of the CaSiO 3 molality at andradite saturation with wollastonite solubility at the same conditions (0.1253 ± 0.0047 molal; Newton and Manning 2006) leads to a Gibbs free energy change of the reaction 3 wollastonite + hematite = andradite at 800 °C and 10 kbar of −32.21 ± 2.45 kJ. The good agreement between this value and that derived from previous studies supports the dissolution model of CaSiO 3 in NaCl solutions. The low solubility of the Fe 2 O 3 component of andradite contrasts with the high solubility of magnetite and of Fe in pelitic and granitic mineral assemblages measured in acidic chloride solutions by previous workers at lower P and T . The results imply that Fe 2 O 3 is conserved during metasomatic processes affecting calc-silicates at high metamorphic grades.