Über die Hydrolyse von Eisen(III)Salzlösungen. I. Die Hydrolyse der Lösungen von Eisen(III)chlorid

When a very diluted iron(III)chloride solution is slowly alkalified by a weak base, the deprotonation of [Fe(H₂O)₆]³⁺ proceeds in a first stage to form mono- and dinuclear hydroxoaquo-complexes. In a second stage 4 dimers condense around a chloride ion to form an eight membered ring, an embryon, which grows fast to very small crystals of the composition Fe₄O₃(OH)₅Cl and the structure of the β-FeOOH. These crystalline micells remain colloidally dissolved. If the pH is raised above approximately 3.4 the Cl^?- are exchanged against OH^?-ions and flocculation occurs. This shows that Pauli, assuming the micells of such sols to be polynuclear complex ions, is basically correct, and it follows that micells can also be micro-crystals. When an iron(III)chloride solution is neutralized fast with a strong base, an ‘amorphous’ precipitation is obtained which gives with MoK_α-X-rays only two broad reflections, showing that the iron oxide hydroxide octahedra are condensed in a highly disordered way. The coherently scattering areas of this precipitate are probably tetramers. Small amounts of primarily formed amorphous iron(III)hydroxide are transformed into β-FeOOH.     

Eisen(II)-carbonat als Ausgangsmaterial zur Herstellung von röntgenamorphem Eisen(III)-hydroxid sowie von γ-FeOOH und α-FeOOH

X-ray amorphous iron(III) hydroxide is formed on treating FeCO₃ with H₂O₂. However, oxidation of freshly precipitated FeCO₃ by means of air yields — in the absence of foreign cations — γ-FeOOH and α-FeOOH. The latter is obtainable in the pure state provided that FeCO₃ is air-oxidised in alkaline medium (excess of Na₂CO₃).     

Mössbauer and infrared spectrometric studies of some iron(III) precipitates

The composition of iron(III) precipitates prepared by different methods was investigated by Mossbauer and infrared spectrometry. The principal constituents were identified as α-FeOOH, β-FeOOH, α-Fe₂O₃, and the van der Giessen precipitate, α-Fe₂O₃· nH₂O. Effects of chloride ion and formic acid on the products of precipitation were studied.     

Nano size crystals of goethite, α-FeOOH: Synthesis and thermal transformation

An aqueous suspension of amorphous iron(III) hydroxide was kept at room temperature (298 K) for 23 years. During this period of time the pH of the liquid phase changed from 4.3 to 2.85, and nano size crystals of goethite, α-FeOOH crystallised from the amorphous iron(III) hydroxide. Transmission electron microscopy (TEM) investigations, Mössbauer spectra, and powder X-ray diffraction using Co Kα radiation showed that the only iron containing crystalline phase present in the recovered product was α-FeOOH. The size of these nano particles range from 10 to 100 nm measured by TEM. The thermal decomposition of α-FeOOH was investigated by time-resolved in situ synchrotron radiation powder X-ray diffraction and the data showed that the sample of α-FeOOH transformed to α-Fe₂O₃ in the temperature range 444-584 K. A quantitative phase analysis shows the increase in scattered X-ray intensity from α-Fe₂O₃ to follow the decrease of intensity from α-FeOOH in agreement with the topotactic phase transition.     

葡聚糖分子对氢氧化铁矿化结晶的调制作用

通过对比五种不同葡聚糖浓度的Fe3＋/葡聚糖矿化作用体系中Fe(OH)3凝胶在早期矿化阶段的成核和相变过程来研究葡聚糖对铁矿物的结晶与转化的调控作用. 运用ICP-AES(等离子发射光谱仪)观察各个矿化体系中上清液的[Fe3＋]浓度及相应pH的变化, 矿化产物运用FTIR、XRD进行表征. 结果发现, 上清液中[Fe3＋]经历了两次下降过程, 在陈化的第三天突然回增. 与不含葡聚糖的矿化作用体系很快形成结晶良好的α-FeOOH不同, 在含有葡聚糖的矿化作用体系中最初形成的物相主要为β-FeOOH. 葡聚糖分子通过与Fe3＋配位吸附在铁氧化物颗粒的表面促进了β-FeOOH转化为α-Fe2O3. 相变是经过溶解-再结晶机制进行的. [Fe3＋]第二次下降正是由于β-FeOOH转化为α-Fe2O3引起的. 葡聚糖浓度适当增大, β-FeOOH溶解加快, 有利于相变的进行. 因此葡聚糖的存在能显著影响在氢氧化铁凝胶中形成晶核的结构类型及其相变历程.     

Biogenic iron compounds: XRD, Mossbauer and FTIR study

Materials based on biogenic iron oxides, which are a product of the metabolic activities of the neutrophilic iron-oxidizing bacteria (NIOB) from Sphaerotilus-Leptothrix group, were investigated. Natural microbial probes were collected from freshwater flow from Vitosha Mountain (Bulgaria) and cultivated under laboratory conditions in respect to select suitable cultures and conditions (nutrition media) for biomaterial accumulation of biogenic oxides. Samples were studied by physicochemical methods: X-ray diffraction, Mossbauer spectroscopy and IR spectroscopy. Their phase composition and physicochemical properties were obtained. Presence of both amorphous and crystal phase (ultra- and highly dispersed particles) was proved. Iron-containing compound in the natural biomass consists of α-FeOOH. The cultivated materials have more complex composition with iron-containing ingredients as α-FeOOH, Γ-FeOOH, Γ-Fe₂O₃ and Fe₃O₄. The sample of natural biomass was tested in reaction of CO oxidation and it showed potential to be used as catalyst support.      

Mössbauer study of corrosion of mild steel induced by acid rain

Room temperature corrosion studies have been made on the rust of commercially available mild steel in a simulated acid rain environment using the method of transmission Mössbauer spectroscopy. The main corrosion products identified are α-FeOOH, γ-FeOOH, and a product with unfamiliar parameters which seems to be amorphous in nature (being very large linewidth ?2.5 mm/s) and may be considered as an intermediate phase. A small amount of γ-Fe₂O₃ (6–8%) is also observed.     

弱磁场下低温中和法制备亚微米非晶态δ-FeOOH的研究

利用XRD和SEM分别对在弱磁场下通过低温中和法制备的羟基铁氧化物进行相成分和颗粒形貌分析. 试验结果表明: 无磁场下, 产物是由部分球形和部分针状的α-FeOOH组成. 0.1 T磁场下, 产物是纺锤形的γ-FeOOH, 但是, 其粒度分布很不均匀. 0.3 T磁场下, 产物是球形的Fe_1.833(OH)_0.5O_0.25. 0.5 T磁场下, 产物是100 nm左右的球形的非晶态δ-FeOOH. Fe_1.833(OH)_0.5O_0.25是无磁场下制备的α-FeOOH向弱磁场下制备的δ-FeOOH转变的中间产物. 并且, 亚微米球形Fe_1.833(OH)_0.5O_0.25和亚微米非晶态球形δ-FeOOH的粒度分布都很均匀. 此外, 弱磁场影响羟基铁氧化物的结晶度.     

Development of an <Emphasis Type="Italic">Agrobacterium</Emphasis>-Mediated Transformation Method and Evaluation of Two Exogenous Constitutive Promoters in Oleaginous Yeast <Emphasis Type="Italic">Lipomyces starkeyi</Emphasis>

The biogenic iron oxide/hydroxide materials possess useful combination of physicochemical properties and are considered for application in various areas. Their production does not require special investments because these compounds are formed during cultivation of neurophilic iron bacteria. Bacteria from genus Leptothrix develop intensively in the Sphaerotilus-Leptothrix group of bacteria isolation medium and feeding media of Fedorov and Lieske. These media are different in their composition which determined the present study as an attempt to clear up the reasons that define the differences in the composition of the laboratory-obtained biomasses and the natural biomass finds. FTIRS, Mössbauer spectroscopy, and XRD were used in the research. Comparative analysis showed that the biomass and control samples contain iron compounds (α-FeOOH, γ-FeOOH, β-FeOOH, γ-Fe₂O₃) in different ratios. The biomass samples were enriched in oxyhydroxides of higher dispersion. Organic residuals of bacterial origin, SO₄, CO₃, and PO₄ groups were registered in the biogenic materials.     

Die durch die Anwesenheit von Eisen(III)-ionen bedingten Phasengleichgewichte kristalliner Aluminiumhydroxide des Nordstrandits,Hydrargillits und Bayerits

The investigation of ageing processes of coprecipitated aluminium and iron hydroxides—Al_0,5Fe_0,5(OH)₃, initially amorphous, reveals the major influence of Fe³⁺-ions on the transformation steps among the aluminium hydroxides.By combined X-ray and IR examination it has been found that the ageing of amorphous aluminium hydroxide in the presence of iron ions leads to the surprising coexistence of all known, well defined crystalline trihydroxide species of aluminium, namely nordstrandite, gibbsite and bayerite. Iron ions for their part transform from amorphous stage of hydroxide at the beginning into hydrohematite.The change in temperature orpH conditions of the milieu, or the change of both the parameters results in only one or two modifications from those aluminium hydroxides mentioned above.

     

Zur Kenntnis der künstlichen Alterung aluminiumhaltiger Eisen(III)-hydroxide

Study of the ageing process of amorphous ferric hydroxide has shown that the presence of traces of Al³⁺ can drastically change the course of the reaction under certain conditions. Al³⁺ traces delay crystallization, an effect which is dependant on the pH of the solution in which the originally amorphous gel is boiled. With increasing pH they favour the formation of the α-F₂O₃-phase, whereby the α-FeOOH modification, the formation of which should otherwise be favoured by the dehydrative conditions employed, is not formed at all. Inhibition of the formation of the α-FeOOH phase is already crystallographically detectable at a molar ratio of Al₂O₃/Fe₂O₃=0.001. The complete disappearance of this phase at pH=10 of the ageing medium is found at the molar ratio Al₂O₃/Fe₂O₃=0.03. At higher Al³⁺ concentrations the amorphous gel is converted into α-Fe₂O₃. In the range 10–20 mol% Al₂O₃, crystallization is strongly inhibited. Further increase in the Al³⁺ content favours the formation of Bayerite-phase, which then at 50 mol% Al predominantes, alongside poorly crystalline α-Fe₂O₃. For Al₂O₃/Fe₂O₃=0.55, three phases are present, hydrohematite, bayerite and boehmite. With still greater amounts of Al³⁺ only the boehmite modification is found. By stepwise crystallographic study of the progressive dehydration the duration of reaction has been established for ferric hydroxide both in the pure state and when doped with Al³⁺.     

Mössbauer study of the corrosion products of iron

Investigations of the possible use of Mössbauer measurements for the analysis of the corrosion products of iron are reported. The Mössbauer spectrum was measured at room and liquid nitrogen temperatures on two samples produced by different corrosion procedures. The isomeric shift, quadrupole splitting and magnetic splitting observed in the spectra yield information on the chemical composition. In this way, the chemical forms of the compounds in the samples could be established. The magnetic properties, revealed by the spectra taken at different temperatures, permitted the identification of the polymorphous modifications. The rust produced in air saturated with water vapour was found to consist of 50% (w/w) Fe₂O₃,～40% γ-FeOOH, and ～10% β-FeOOH, while the rust produced by periodical immersion in saturated calcium chloride solution is composed of about equal amounts of β-FeOOH and γ-FeOOH. These findings have been confirmed by the thermoanalytical curves of the samples. The Mössbauer effect presents a convenient method for the investigation of the corrosion products of iron.     

Surface analysis of stearic acid modification for improving thermal resistant of calcium phosphate coated iron oxide yellow pigments

In order to widen the application of iron oxide yellow pigments (α-FeOOH) in high temperature industry, α-FeOOH coated with calcium phosphate (α-FeOOH/Ca) were modified with stearic acid (Sa) through dry process. Scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and thermogravimetry (TG) were employed to characterize the effect of surface modification. The effects of Sa dosage on the thermal resistance of α-FeOOH/Ca after modification were also discussed. The crystal structure of α-FeOOH/Ca does not change after modification with Sa, but the ratio of length to diameter about α-FeOOH/Ca is smaller. Sa can react with α-FeOOH/Ca in the form of –COOCa and HPO₄²⁻ based on FT-IR and XPS analyses. TG-DTG results suggest that calcium phosphate and Sa improve the thermal stability of α-FeOOH. The value of color difference of modified α-FeOOH/Ca first decrease and then increase with increasing of Sa dosage, which is studied by CIE ΔL, Δa, and Δb colorimetric analyses. The amount of Sa affects the thermal resistance and dispersion performance of α-FeOOH/Ca simultaneously; also the relationship between thermal resistance and dispersion is inversely proportional. Experimental characterizations reveal that introduction of the phosphates and Sa not only prevents the loss of water on the surface of α-FeOOH but improve its activation index and dispersibility in organic solvents.     

L'hydrolyse acide des diazocétones alcoylées: Formation d'ions α-acylcarbonium secondaires

Hydrolysis of secondary diazoketones CH₃? CO? CN₂? R (R ? Me, Et, isopropyl) by aqueous perchloric acid is characterized by rate-determining protonation demonstrated by solvent isotope effects kD₂O/kH₂O = 0,4–0,6 and by the intervention of general acid catalysis. The product determining step, yielding keto-alcohols and keto-olefines, is independent of added nucleophiles; this is interpreted as resulting from the intermediate formation of (more or less free) αhyphen;ketocarbonium is ions. The hydride shift observed wih III (R = isopropyl) supports this interpretation. The difference between hydrolysis of primary and of secondary diazoketones is discussed.     

Die Bildung von kristallinem Böhmit in gemeinsam gefällten AlFe(III)-Hydroxiden unter hydrothermalen Bedingungen

Under mild hydrothermal conditions originally amorphous aluminium hydroxide coprecipitated with iron(III)ions as Al_0,5Fe_0,5(OH)₃ transforms into aluminium hydroxide crystalline phases which are not observed in products of ageing of pure aluminium hydroxide.By X-ray diffraction analysis, IR spectroscopic studies and microscopic observations it has been found that due to the presence of iron(III) hydroxide it is possible to stabilize the trihydoxide of aluminium i.e. bayerite until 130–140°C. Moreover, with increasing temperature well crystallized boehmite is obtained instead of the usually formed pseudoboehmite.Experiments revealed that the formation of crystalline boehmite does not take place as a process of pseudoboehmit crystallites growth but only as a result of bayeriteboehmite transformation.

     

Regularities of formation of iron(III) nanocrystalline oxides and oxyhydroxides during oxidation of iron(II) compounds in an alkaline medium

Regularities of formation of nanocrystalline iron(III) oxides and oxyhydroxides via oxidation of iron(II) compounds in an alkaline pH range (pH ≥ 12) were studied using pH and E _h measurements, chemical analysis, electron microscopy, and X-ray diffraction. When the molar ratio [OH⁻]/[Fe^II] ∼ 2 (pH ∼ 12–12.5), the oxidation process yields cube-shaped magnetite Fe₃O₄ particles. An excess of an alkaline agent with an overstoichiometric concentration equal to or higher than 0.5 mol/L (pH ≥ 13.5) induces the formation of anisotropic particles of nanocrystalline goethite α-FeOOH over the entire range of the synthesis parameters studied. Reaction products (Fe₃O₄ and/or α-FeOOH) are formed immediately as the initial Fe(OH)₂ starts oxidizing by the dissolution-oxidation-precipitation mechanism near the surface of Fe(OH)₂ precursor particles. Carbonate ions considerably change the structure and shape of newly formed α-FeOOH particles.     

Characterization of iron(III) oxide and oxide-hydroxide as Sr-sorbent

Iron(III) hydroxide and oxide-hydroxide samples prepared by precipitation of 0.2M iron(III) nitrate solution by 5M NaOH and subsequently aged at pH 12 for times of up to 50 h have been characterized. The sorption properties towards Sr²⁺ were characterized by radiotracer method using⁸⁵Sr, morphology of the samples was characterized by Transmission Electron Microscopy and Emanation Thermal Analysis. X-ray diffraction patterns characterized the crystallinity of the samples aged for various times. The maximum (100%) sorption capacity for⁸⁵Sr corresponding to amorphous iron(III) hydroxide decreased to 75% with the time of precipitate ageing (up to 40 h). This finding corresponds to the development in crystallinity and morphology of the sorbent.     

Goethite as a more effective iron dosage source for mineralization of organic pollutants by electro-Fenton process

The electro-Fenton process is an electrochemical method for wastewater treatment based on the production of hydroxyl radicals via H₂O₂ generation in the presence of ferrous ions. The aim of this work is to show the use of a new mineral iron dosage source (goethite, α-FeOOH) for electro-Fenton process that achieves a more efficient mineralization treatment. Our new proposed Goethite catalyzed electro-Fenton (GEF) process yields 95% of mineralization for an organic model pollutant such as aniline under optimum standard electro-Fenton (SEF) conditions. For that, GEF process uses only 2 ppm of soluble iron, compared with the 55 ppm of soluble iron used by SEF process. In order to show the potential scope of GEF process, the effect of goethite concentration, solution conductivity, solution pH, temperature, and applied current density are studied in detail.     

Compleximetric titrations of iron(III) and iron(II) with triethylenetetraminehexaacetic acid

The stability constants of the iron(II) complexes of TTHA (triethylenetetraminehexaacetic acid) were calculated from measured pH and redox potentials. The values of the cumulative constants obtained were: log β_FeL= 15.37, log β_FeHL = 23.83, log β_FeH2L = 28.0, log β_Fe2L = 24.73. On the basis of these values and the previously determined constants ofiron(III) complexes, the possibilities of titrating iron(III) and iron(II) with TTHA were investigated. Depending on the experimental conditions, either FeL or Fe₂L formed. Actual titrations were in agreement with the developed theory. The influence of aluminium and titanium on titrations of iron(III) solutions was elucidated.     

Über Ternäre Chelate des Eisen(III)-Ions mit Nitrilotriessigsäure und Phenolderivaten

On Ternary Chelates of the Iron(III) Ion formed with Nitrilo-Triacetic Acid and Derivatives of Phenol Ternary chelates of iron(III) ions are produced with nitrilo-triacetic acid and some derivatives of phenol in aqueous solution. Their reactions of formation have been controlled by spectro-photometric methods. The ratio of components in the compounds Fe: X: L is 1: 1: 1 without any exception. The measured optical properties (λ_max, ε_max) of the ternary chelates are discussed and compared with the corresponding binary iron(III) phenol chelate.