Oxidation Of Ferrous Hydroxide Research Articles

Purity of Colloidal Magnetite Particles Used as a Model Corrosion Product

Abstract Synthesis of magnetite as a model corrosion product by oxidation of ferrous hydroxide precipitated from ferrous sulfate by nitrate is a classical protocol to obtain monodisperse pseudosphe...

Electrochemical studies of pyrite oxidation and reduction using freshly-fractured electrodes and rotating ring-disc electrodes

Oxidation and reduction processes on coal- and mineral-pyrite surfaces have been investigated to better understand the reactions that control the hydrophobicity and flotation behavior of pyrite. The incipient oxidation and reduction reactions were studied using fresh surfaces of pyrite that were created by in situ fracturing electrodes potentiostated at a predetermined potential. Chronoamperometry immediately after fracture and subsequent cyclic voltammetry have established that fresh fracture surfaces of pyrite instantaneously assume a unique potential (referred to as the “stable” potential) at which neither oxidation nor reduction takes place. For Peruvian and Chinese pyrites, the stable potential is −0.28 V (standard hydrogen electrode, SHE) at pH 9.2 and 0 V at pH 4.6. The initial oxidation of pyrite begins at potentials slightly positive of the stable potential and is believed to produce a hydrophobic sulfur-rich species, most likely a polysulfide or metal-deficient sulfide. A rotating ring-disc electrode (RRDE) was employed to study the kinetics and mechanisms of surface reactions on pyrite over moderate potential ranges. Two distinct soluble reduction products (ferrous hydroxide and HS −) and one distinct soluble oxidation product (ferrous hydroxide) were observed on pyrite in alkaline solutions. It is concluded that the initial oxidation of pyrite and the oxidation of ferrous to ferric hydroxide occur in a similar potential range. When the electrode is oxidized, e.g. by polishing, prior to experiments, the initial oxidation of pyrite is masked by the oxidation of ferrous hydroxide, making it difficult to study the oxidation of pyrite itself.

Synthesis of nanostructured goethite and magnetite particles from the oxidation of Fe(OH) 2 in a high-oxygen-flow-rate medium

Results on the oxidation of ferrous hydroxide under different oxygen flow rates are reported. Oxidation under air produced mainly magnetite (Fe 3O 4) with a small amount of goethite (α-FeOOH), but as the oxygen flow rate was increased, their relative content and their crystallite size varied; the higher the oxygen flow rate, the higher the superparamagnetic goethite content and the smaller the crystallite size (nanometric scale) of both oxidation products. Slight quantitative differences were found between the Mössbauerand the XRD analysis while estimating the goethite and magnetite contents. These differences were associated with the fitting procedures but may also be due to different Debye Waller factors between the goethite and magnetite. Additionally, HRTEM images showed that distorted nano-fibers were characteristic for the goethite, and nano-platelets for the magnetite.

The oxidation of Fe(OH)2 in the presence of carbonate ions: Structure of carbonate green rust one

Sodium carbonate Na2CO3 is added to a solution containing an Fe(OH)2 precipitate in order to study the influence of CO32− ions on the oxidation of ferrous hydroxide. The first stage of the reaction leads to a ferrous-ferric compound, the carbonate green rust one (GR1), identified by its X-ray diffraction pattern. The Mossbauer spectrum at 78 K of this GR1 displays two ferrous doublets and one ferric doublet in the 3∶1∶2 abundance ratio. The quadrupole splittingsQS are 2.91, 2.58 and 0.42 mm/s, respectively, and the isomer shifts 75 are 1.25, 1.25 and 0.47 mm/s respectively. These values are very close to those of the three doublets of the chloride GR1, 3Fe(OH)2Cl·Fe(OH)2Cl·nH2O. This fact confirms that the crystallographic structures of these two GR1s are similar, formed by the stacking of hydroxide layers and interlayers containing the considered anions (Cl− or CO32−) and water molecules. The chemical formula of carbonate GR1 is Fe4(II)Fe2(III)(OH)12CO3·nH2O, and its standard chemical potential -853 900 cal/mol ifn=0. The second stage of the reaction is the oxidation of GR1, which leads to α-FeOOH goethite.

The influence of temperature on the oxidation of ferrous hydroxide in sulphated aqueous medium: Activation energies of formation of the products and hyperfine structure of magnetite

Oxidation processes of the initial products at any value of the ratio R = {[FeSO 4]/[OH −]} initial is characterized by a reduction in the overall oxidation time as the temperature of the medium increases; this has been valuable in the determination of the various activation energies. Magnetite predominates as the oxidation end product at the characteristic point B, where R = 0.5, at all temperatures; this confirms the proposed mechanism of formation of magnetite from ferrous hydroxide.

The influence of concentration on the oxidation of ferrous hydroxide in basic sulphated medium: Particle size analysis of goethite and δ-FeOOH

The evolution of the oxidation end product of ferrous hydroxide in the basic sulphated aqueous medium at R = {[FeSO 4]/[NaOH]} initial = 0.2 is investigated at various initial concentrations. The end product is essentially well crystallized goethite at relatively high initial concentrations of the reacting chemicals. The crystal structure of goethite is modified as the initial concentration is decreased; at a critical low concentration, the orthorhombic structure is no longer observed. Inactive α′-FeOOH, which has a similar X-ray diffraction pattern to δ-FeOOH, is obtained. All these compounds are crystallographically related.

The influence of concentration on the oxidation of ferrous hydroxide in acidic sulphated aqueous medium: Particle size analysis of lepidocrocite

The evolution of the oxidation end products of ferrous hydroxide in the acidic sulphated aqueous medium at R = {[FeSO 4]/[NaOH]} initial = 0.5833 has been investigated at various initial concentrations of ferrous ions. The oxidation end products consist of lepidocrocite and goethite at relatively higher initial concentration and mainly of lepidocrocite at lower concentrations. The crystal structure of lepidocrocite is not modified as the initial concentration is decreased, contrary to what has been noticed for goethite in the basic medium.

Influence of temperature and initial ratio of the reactants on the formation of rusts in sulphated aqueous media

The investigation of the rusts obtained in sulphated aqueous media is done using the Mossbauer spectroscopy by simulating the corrosion process through the oxidation of ferrous hydroxide obtained by mixing FeSO4 and NaOH in different initial ratios R=[FeSO4]/[NaOH]. The influence of the temperature of oxidation is studied from 10°C to 60°C for various values of R scanning from 0.2 to 3. One notes strickingly that goethite is always present whereas magnetite and lepidocrocite are never observed together.

蛍石鉱山廃水の高勾配磁気ろ過

Recently the output of fluorite has been increasing in China and environmental problems have been proposed accordingly by the waste water containing fluorine in the flotation plants of Dong Feng and so on. This paper describes the purification of artificial fluorite mill waste and colloidal calcium fluoride by high gradient magnetic filtration (HGMF) with the combined addition of magnetic seed particles and inorganic flocculant. The results are as follows.1) As fluorite and calcite particles suspended in water released calcium ions, the capture of suspended solids by HGMF and the hetero coagulation of each mineral and magnetite were estimated from their zeta potentials in the existance of calcium ions.2) The addition of magnetite which was prepared by the oxidation of ferrous hydroxide was the most effective for the removal of suspended solids in comparison with the use of magnetite prepared by grinding or coprecipitation.3) 0.2-0.5 T of external applied magnetic field was enough to capture suspended solids coated with magnetite. Theemployment of permanent magnet instead of electromagnet is possible, so that the energy cost will be reduced.4) Aluminium sulfate solution was added into suspension and pH was adjusted at 7 to 8 after the addition of magnetite. Thi s conditioning was very effective to purify artificial fluorite mine waste water or colloidal calcium fluoride by HGMF.

25. The oxidation of ferrous hydroxide

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